Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

Impacts of channelization of River Bala, eastern Himalayan foothills, India

Impacts of channelization of River Bala, eastern Himalayan foothills, India GEOLOGY, ECOLOGY, AND LANDSCAPES INWASCON https://doi.org/10.1080/24749508.2022.2130857 RESEARCH ARTICLE a b c a a Biswajit Bera , Sumana Bhattacharjee , Nairita Sengupta , Meelan Chamling , Supriya Ghosh and Arijit Ghosh a b Department of Geography, Sidho-Kanho-Birsha University, Purulia, India; Jogesh Chandra Chaudhuri College (Calcutta University), c d Kolkata, India; Department of Geography, Diamond Harbour Women’s University, Sarisha, India; ICSSR Major Project, Sidho-Kanho- Birsha University, India ABSTRACT ARTICLE HISTORY Received 04 May 2019 Hard river engineering or channelization alters channel bathymetry and river morphology and Accepted 27 Sep 2022 invites multiple fluvio-hydrological hazards. The linear (72 m), concrete, low height (1.6 m), multipillars (20 pillars) bridge with concrete embankments and revetments has been con- KEYWORDS structed across and along the river Bala within the Himalayan foothill zone in the year 2017. As Siltation; channel avulsion; a result, the rate of siltation has been tremendously increased at the vicinity of the pillars of the embankment; revetment bridge. The principal objectives are (i) to establish wrongly designed hard river engineering techniques and (ii) to find out the adverse effect of Bala bridge. Results showed that the highest rate of siltation was 0.55 m at the end of the monsoon in 2017 whereas the average of rate of siltation was 0.37 m between 2010 and 2017. If the rate of siltation is greater in a particular year, there is a high probability to divert the channel course. The thalweg line has tremendously shifted towards the right bank side. If the same condition persists for a long time, in near future (during monsoon) the river will avulse nearly 200 m right side on low lying topographic depression within the rich Buxa Tiger Reserve. 1. Introduction hydraulic dredgers apply suction pumps to bring materials via pipe lines. The principal purpose behind “Channelization is the modification of natural river the works was to train the river to flow in a deeper channels for the purposes of navigation, flood control, channel and reducing the devastating incidents of land drainage and erosion control” (Brookes, 1988). flooding. Channelization consists of different hard and soft th In the beginning of 20 century, the various tech- engineering processes that alter the configuration of niques of channelization like hard engineering tech- natural river channels. Channelization involves (i) re- niques (dam construction, bridge, culvert, and sluice sectioning and realignment, (ii) dredging, (iii) snag- gates) have been introduced to improve the smooth ging and clearing, (iv) construction of levees and transport and communication system (Bera et al., embankments, (v) bank protection, (vi) bed protec- 2019a; Ghosh et al., 2022a, 2022b).The architecture tion, (vii) river training, (viii) dam construction, (ix) of natural river channels has been modified tens of emplacement of locks and weirs, and (x) construction thousands of kilometers through channelization pro- of bridge, culvert, and sluice gates. Depending on the grammes or river training techniques in different size of the channel and the purpose of the engineering sites of developed nations of the globe (Brookes, work, re-sectioning or realignment is carried out 1985). Human interference can accelerate natural through dredging or by means of various river training fluvial processes and tends to reduce the time scale processes. History of dredging can be traced thou- for the river channel stability and adjustments (Dang sands of years. Egyptians, Romans, Sumerians and et al., 2014; Darby et al., 2016; Mei et al., 2018; Rinaldi Chinese have practiced dredging since ancient time & Simon, 1998; Yang et al., 2018). These modifica - through manual skills involving mass labour tions often accelerate to instability within the engi- (Petersen, 1986). In case of small non-navigable chan- neered reach upstream or downstream channel in nels, dredging is generally done by the bulldozer. In different morphogenetic regions of the world. There the late sixteenth century, China introduced mechan- is no as such geomorphic time scale to recover the ical dredging technique in River Yellow and during engineered river channel into natural river channel. that time, various river training techniques were In general, it takes thousands of years to attain new already started (Blazejewski et al., 1995). Mechanical equilibrium stage (Brierley & Fryirs, 2005). Natural dredgers bring bed rock materials or sediments by river channel alteration or channel modification has lifting from the bed in a bucket or dipper, whereas CONTACT Biswajit Bera biswajitbera007@gmail.com Department of Geography, Sidho-Kanho-Birsha University, Ranchi Road, Sainik School, Purulia, West Bengal, 723104, India © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of the International Water, Air & Soil Conservation Society(INWASCON). This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 2 B. BERA ET AL. brought multi-dimensional fluvio-hydrological findings will definitely help to policy makers for sus- hazards or problems which include river bank failure tainable river and floodplain management. or bank erosion, flood, inundation, property destruc- tion, and destruction of aquatic floral and faunal 2. Historical background of River Bala and habitats (Daniels, 1960; Emerson, 1971; Ghosh & research objectives Bera, 2022; Ghosh et al., 2022a, 2022b; Rentier & Cammeraat, 2022; Ritter, 1979). Meanwhile, it is Non perennial, braided and high-energy River Bala not true that multi-dimensional process of river (50 km) originates from Buxa hills of Indo-Bhutan training or channelization invites only negative boundary and flows within the Buxa Tiger Reserve of impact or threat on environment (Ritter, 1979). Alipurduar district of West Bengal. Buxa Tiger Not only broad positive impact of channelization Reserve is located in the eastern Himalayan fragile has been demonstrated but also the biological, mor- biodiversity zone. These terrestrial ecosystems have phological, and ecological consequences and impacts been fragmented due to human intervention along have been reflected through this approach (Brookes & with execution of different developmental projects Shields, 1996; Hart et al., 2002; Lin, 2011; Marren et al., and there is an imprint of climate change (Beniston, 2014; Das, 2012; Lennox & Rasmussen, 2016; 2003). Before 1972, the large-scale mining and quarry- Marcinkowski & Grygoruk, 2017; Dutta et al., 2018; ing activities took place in different parts of Buxa Hills Semwal & Chauniyal, 2019; Zarfl et al., 2019; Habel along with channel bed of River Jayanti, Bala and et al., 2020; Yao et al., 2020; Słowik et al., 2021; Raimatang and subsequently depleting floral and fau- Charoenlerkthawin et al., 2021). In the recent years, nal species (Chamling & Bera, 2020; Chamling et al., hard river engineering is largely reflected in the river- 2022). ine environment of urban areas (Marsh, 1864; Dynamic River Bala (highly variable discharge with Thomas, 1956). In addition, morphology and struc- abundant bed loads) maintains braided as well as ture of channel planform along with ecological habitat meandering channel pattern (Sinuosity Index > 1.5) factors have been immensely changed more than ten at lower stretch and ultimately discharges into River times of its original form (Gregory, 2006). Moreover, Kaljani near Alipurduar town. The lower stretch of time-space specific soft and hard river engineering River Bala is also called as River Kalkut. The non- techniques or channelization are more suitable with perennial, wide, shallow, and rugged channel path of experienced field based practical knowledge which can Bala directly assists to form different sized bars within reduce the negative effect of channelization in the the channel. Formation of multi channels with bars proximity of the urban environment (Dutta et al., continues until there is insignificant stream energy to 2018; Keller, 1975; Keller & Melhorn, 1978; Lennox erode the channel banks (Beniston, 2003; Ghosh & & Rasmussen, 2016). When Himalayan Rivers Bera, 2022; Ghosh et al., 2022a, 2022b; Leopold & debouch on the piedmont zone and floodplain region, Wolman, 1957). they become wide, shallow, and multichannel bars. Before the year 2000, there was an old bridge across South flowing Himalayan Foothill Rivers suddenly River Bala to connect Jayanti and Mainabari (tiny impede due to east-west high elevated national high- hamlets) with Alipurduar town via Rajabhatkhawa way and railway lines and this situation creates drai- Forest Range. The bridge collapsed in the year 2000 nage congestion and interlacing drainage system due to devastating flood hazard and for a few days the particularly for the fast changing Himalayan foreland entire region was partially inundated. After 2000, vehi- basin (Chamling & Bera, 2020; Chamling et al., 2022). cles ply on the natural channel path throughout Moreover, High Energy Rivers compel to flow through the year except heavy rains during monsoon. As narrow sluice gate and culverts at the crossing between Jayanti, Mahakal and Bhutan Ghat areas are popular railway line or road and river. During monsoonal tourist destinations, huge tourists come throughout months, development of spill channels and river the year. But every year during monsoonal months bank failure happen frequently within the North both tourists and local residents are seriously facing Bengal piedmont and floodplain region. Not only the troubles. To keep alive the tourism industry and to culverts and sluice gate but also many vertical and improve the transport system in this particular pocket horizontal engineering structures have also been con- of Buxa Tiger Reserve, the PWD, Government of West structed across and along the natural flowing rivers. As Bengal finally constructed 72 m long concrete bridge a result, flood contour is rapidly elevating at the foot- in 2017. hill zone in the recent years (Bera et al., 2019a; Ghosh In 2017 after the monsoon, entire channel path et al., 2022a, 2022b). River channel morphology and across the bridge was completely blocked by bed floodplain geomorphology are being modified due to rocks and sediments. Before 1975, there were several large-scale anthropogenic interference. This is a big mining sites (dolomite, limestone, and conglomerate) research gap in this context because such type of situated (Figure 2a; Table 1) along the Bhutan Bengal research work has not yet been done. The research foothills. But after 1975 to protect vulnerable GEOLOGY, ECOLOGY, AND LANDSCAPES 3 Table 1. Location of mining sites in Buxa hills. extension of 26°26ʹ54”N to 26°45ʹ15”N and longitudi- GPS Waypoint Latitude (N) Longitude (E) Altitude in meter nal extension of 89° 32’ 52” E to 89° 35’ 59” 1 26°44ʹ43.22” 89°34ʹ32.72” 385 E. (Figure 1). The investigation site is situated at the 2 26°44ʹ44.38” 89°34ʹ34.06” 399 latitudinal and longitudinal extension of 26°41ʹ47.4” 3 26°44ʹ50.17” 89°34ʹ30.18” 443 4 26°44ʹ47.87” 89°34ʹ36.98” 440 N; 89°34’ 10.5”E with an elevation of 141 m. Except 5 26°44ʹ59.68” 89°34ʹ27.25” 480 few scattered tribal hamlets, most of the area is cov- 6 26°44ʹ51.85” 89°34ʹ42.26” 481 7 26°44ʹ56.37” 89°34ʹ16.59” 517 ered by dense tropical deciduous forest with dotted 8 26°45ʹ09.98” 89°34ʹ30.16” 533 tourist watch towers. biodiversity, Government of India completely stopped 3.2 Fluvio-hydrological methods and to extract minerals within the Bengal territory. On the instrumentations other hand, Bhutan Government is still extracting Various fluvio-hydrological parameters like wetted peri- valuable minerals and rocks in their side. River Bala meter, cross-sectional area, hydraulic radius, width, is non-perennial stream but during monsoon the depth, velocity, and discharge have been considered to braided (upstretch) high energy and variable discharge measure fluvial dynamics of River Bala. Figure 2b shows stream become energetic and inherits complicated schematic diagram of various hydraulic parameters. behavior. The source area of the river is still connected with old exposed abandoned mining sites. After run- 3.2.1 Hydraulic Radius (R ) ning few kilometers from Buxa hills, the two small Hydraulic radius is the ratio between cross-sectional area branches (Bala) ultimately join together (above the and wetted perimeter. It is essential to determine the bridge) to form single channel Bala. During monsoon, channel condition and efficiency. Greater value of it receives huge sediments and bed rocks due to large hydraulic radius denotes the higher water holding capa- catchment area as well as high sediment yielding from city as well as energy to move water and sediment. If the the source area. Every year after monsoon, many tall channel depth is greater than average, water will flow at trees within Buxa Tiger Reserve also get severely a rapid rate and it causes generation of high kinetic damaged due to sudden obstruction created on the energy. rugged channel path and clogs the vegetation root R ¼ A=P, system due to continuous percolation (siltation) of Where, R is the hydraulic radius, A is the cross dolomite dusts. sectional area of flow and P is the wetted perimeter. After monsoon of 2017, the Department of Forest started dredging and clearing sediments and bed rocks 3.2.2 Wetted perimeter (P) by bulldozers at both the side of the bridge and simul- It is widespread method among hydrology, geomor- taneously constructed concrete embankments and phology, civil engineering, and environmental engi- revetments (form of loose rocks and boulders with neering. Wetted perimeter is also greatly associated weirs) on either side of the bridge along the river. with hydraulic diameter or hydraulic radius. It is sim- During the monsoon of 2017, there was high possibi- ply described as the perimeter of the cross-sectional lity to divert the channel Bala at both side of the bridge area of a channel that is directly connected with water. due to rapid rate of siltation across the bridge and proximity of big diameter horizontal pillars installed inside the channel. Besides there was also the prob- P ¼ li ability of Bala to search new path within the Buxa i¼0 Tiger Reserve. Such situation is due to implementation Where, P is the wetted perimeter, l is the length of of wrongly designed hard river engineering structures each surface in contact with the aqueous body. In case of and also invites negative effect of river engineering or open channel flow, the wetted perimeter simply defines channelization. length of the channel bottom and sides in direct contact The main objective of the study is (i) to prove with water. There is a close relationship among channel wrongly designed hard river engineering technique depth, channel width and wetted perimeter. If the chan- like concrete multi pillars low height bridge across nel depth is much lower than the width, then the wetted the river and (ii) to find out the adverse effect Bala perimeter is considered almost similar to the width. bridge and probable sites of channel diversion. Greater value of wetted perimeter and lesser depth sig- nifies high sedimentation rate and low flow discharge. 3. Methods and materials 3.2.3 Velocity (V) and depth (d) 3.1 Area of study Stream velocity is the speed of fluid that passes The catchment area of River Bala is approximately through a given surface per unit of time. Digital cur- 193.75 km which is extended between the latitudinal rent meter was used to measure the average velocity of 4 B. BERA ET AL. Figure 1. Study area. Figure 2. (a) Location of old exposed abandoned mining sites; (b) Schematic diagram showing different hydraulic parameters. the river in m/sec. Depth of the channel is measured September). Velocity is mainly regulated by channel by dipping iron ball method from bridge. Velocity and gradient, channel bed roughness, shape of the basin, depth data are collected by extensive field survey dur- discharge, sinuosity, etc. Stream velocity is compara- ing monsoonal months (June, July, August, and tively higher along the thalweg line of the stream. GEOLOGY, ECOLOGY, AND LANDSCAPES 5 3.2.4 Discharge (Q) Imagery Base map is used to show the distribution of It is the passing of volume of water through a given the mining sites, location of bridge as well as flow path cross section of a channel per unit time. of the river. CorelCAD 2018 software is used to depict Q = AV 3D schematic diagram of bridge and it’s surrounding In case of open channel, Q is the discharge (m /s or (Figure 4a). Besides, to understand the engineering ft /s), A is the cross-sectional area (sq.m or sq.ft), V is technology of the bridge, meticulous measurement of the average flow velocity (m/s or ft/s). length, width, diameters of the pillars, and height from This significant hydraulic parameter depends on the channel bed has been done with the help of mea- characteristics of catchment area, shape and size of suring tape, GPS and distance meter. Moreover, the catchment area and depth of the channel. High dis- structure and composition of the embankments and charge stream has high competency and capacity. revetments were also inspected and measured during the construction. 3.2.5 Rate of siltation Before the monsoon, gauge scale was fixed on the 3.4 Channel bed configuration through Total pillar of the bridge to obtain data of water fluctuation Station Survey level as well as to determine the rate of siltation at the Leica Builder 405 Total Station from Leica Geosystems vicinity of pillars across the bridge. Monthly was used to detect precise readings of elevation, dis- Xi i¼1 Arithmetic mean ðx ¼ Þ of velocity (m/sec) tance, and gradient of the channel bed of River Bala. and discharge is also systematically computed. 12 stations are fixed on the channel bed within 200 m up and down stretch of Bala Bridge. Local bamboos (12 bamboos with 2 m length each) were installed 3.3 Use of Garmin GPS Etrex 30x, Arc GIS and within the channel bed to experiment the changing CorelCAD 2018 configuration of channel bed or elevation difference. To identify the old abandoned mining sites (Table 1) Three times (before and after monsoon and after of dolomite, limestone, and conglomeratein the source dredging) survey had been conducted in the year area of the river (on the Buxa Hills), Garmin GPS 2017 to collect channel elevation data as well as to Etrex 30x has been used. ArcGIS Online World evaluate rate of siltation, unscientific channel bed Figure 3. (a) 3D Surface and (b) Long profile of River Bala. 6 B. BERA ET AL. dredging and thalweg line shifting at the proximity of sandstones are associated with some silt and clayey Bala bridge within Buxa Tiger Reserve of Alipurduar bands. These rocks show well and cross laminations. district of West Bengal. Pebble beds and conglomerates are quite visible in the upper part of the Shiwalik. The basalt rock in this area is red clay stone. Due to continuous soil erosion and weathering in the source area, River Bala brings var- 4. Results and discussions ious sized particles and sediments during monsoonal 4.1 Geology of the source area and sediment months (June – September). yields Lithologically, Bengal Bhutan foothill is composed of 4.2 Field based fluvio-hydrological investigation Siwalik group (Mio-Pliocene), Gondwana Group (Permian), Buxa Series (Precambrian), and Daling Fluvio-hydrological study of River Bala from 2010 to Series (Archaean). The rocks of the Daling Series 2017 (June, July, August, and September) revealed that mainly consist of chlorite-sericite-schists interbedded the average monsoonal velocity was about 2.70 m/sec with a flaggy green quartzite. These rocks are generally whereas average discharge was 208.54 cumec found along the northern fringe of the area (Indo- (Table 3).But in the month of August (2017) the high- Bhutan border). Basically, the rocks of Daling Series est average discharge of 367.20 cumec with maximum are composed of muscovite, quartz, sericite, and bio- wetted perimeter of 76.50 m had been recorded tite (Chandra, 1947). Buxa Series comprises dolomite, (Table 2). In order to generate the continuous fluvio- quartzite, and phyllite which cover most of the area. hydological data, gauge scale was fixed on the old These rocks are well exposed along the section of river pillar of the broken bridge. But after the construction Jayanti and Balaof Buxa Tiger Reserve. Phyllite con- of new bridge, the new gauge scale was marked on the stitutes the basal unit of the Buxas. Along the River pillar of the newly constructed bridge. The average Bala section and adjacent hilly areas, the intercalated gauge height has been recorded 130.99 m but in the phyllite band is found. At the upper portion of hill, month of August (2017), the River Bala experienced 200 m thick dolomite layer is also confined. Dolomite 140 m gauge height which was equal to the road is the most important member of the Buxa series. In height. As the river is linked with old abandoned and around the River Jayanti and Bala, two important mining sites, during rainy season the two branches of dolomite bands are exposed. The lower band is about river bring various sized particles. Due to the obstruc- 30 m while the upper one is about 540 m thick. These tions made by the wrongly designed big diameter dolomites are light to dark grey in colour highly multi pillars, the sediments get accumulated at the jointed, massive and generally fine grained. They are up and down stretch of bridge. The highest rate of composed of dolomite grains with fractured outline siltation of 0.55 m is recorded at the end of the mon- whereas quartz is rather rare but sometimes present in soon in 2017 whereas the average of rate of siltation is the calcareous matrix. They often contain nests of 0.37 m between 2010 and 2017. The maximum depth calcite. The general trend of the dolomite beds is was 2.10 m in the year 2010 whereas across the Bala NW – SE with a north – easterly dip direction. The Bridge the average depth is 1.35 m. 3D elevation map rocks of the Gondwana Group overlie the Shiwalik to along with long profile of River Bala was prepared the south and are underlain by the Buxa to the north. from digital elevation data to understand the channel They are exposed in the River Jayanti and Bala but in bed elevation as well as the surface elevation at the the hilly section to the west (Buxa-Jayanti bridle path) proximity of Bala watershed (Figure 4). and they are absent and dissected by the Buxa thrust. After the completion of monsoon in the month of Vertically dipping, hard quartzitic sandstone, carbo- November and December, Department of Forest used naceous shale and flaky coal are found here (Ghosh, bulldozers to remove silted materials from both side of 1968). The Shiwalik Group is extending from the west the bridge to keep the healthy flow condition of the of River Jayanti upto the Turturinala (Small River) and river. It is very hard and difficult task to remove such further east exposed along the outer fringe of foothills. channel bed sediments every year during monsoon or These rocks comprise brown, grey to bluish grey sand- post monsoon. If the rate of siltation is greater in stone which are micaceous and feldspathic. These a particular year, there is a high probability to divert Table 2. Fluvio-hydrological parameters of river Bala measured during monsoon, 2017. Wetted Average Gauge Cross sectional perimeter Average monthly discharge Channel Max. channel height Average monsoonal Month area (sq. m) (m) velocity (m/sec) (cumec) width (m) depth (m) (mtr) siltation rate (m) June 29.83 56.30 2.60 77.55 51.23 0.53 127.50 0.55 July 73.92 67.20 3.10 229.15 63.19 1.10 138.40 August 114.75 76.50 3.20 367.20 71.42 1.50 140.00 Sept. 60.81 64.70 2.50 152.02 60.35 0.94 132.00 GEOLOGY, ECOLOGY, AND LANDSCAPES 7 Table 3. Annual monsoonal average fluvio-hydrological parameters of river Bala (2010–2017). Max. Crosssectionalarea Velocity channeldepth Gauge Year (km ) Wettedperimeter(m) (m/sec) Discharge(cumec) Channelwidth(m) (m) height(m) Siltationrate(m) 2010 63.97 64.26 1.95 215.52 57.89 2.10 128.99 0.25 2011 65.27 63.95 2.10 201.90 59.21 1.71 126.35 0.29 2012 64.54 66.78 3.54 199.79 60.78 1.57 130.43 0.30 2013 66.21 64.89 3.35 212.65 62.89 1.22 132.88 0.24 2014 68.33 67.65 2.39 208.89 59.01 1.15 129.06 0.39 2015 67.19 65.45 2.66 213.45 56.65 1.05 131.76 0.42 2016 68.94 66.32 2.79 209.65 63.90 1.03 133.40 0.47 2017 69.82 66.17 2.85 206.48 61.54 1.01 134.47 0.55 Average 66.78 65.68 2.70 208.54 60.23 1.35 130.91 2.91 the channel course. Such diversion may take through widely used in different parts of the world where comparatively low lying topographic depressions of bank erosion is a serious threat to urban areas and rich biodiversity pocket (Buxa Tiger Reserve) in where natural river channel runs close to roads or front of concrete embankments or revetments made railways (Downs & Gregory, 2014). However, in less on both the narrow passages of the river. critical situation, the soft river engineering gives a more environmentally sensitive alternative (Dixon et al., 2016). In high-energy perennial or non- 4.3 Architecture of river embankment and perennial braided channel, the revetment or stone revetment apron protects the toe erosion. In case of low stream power, geo-textile, natural plant materials, jute, coco- Concrete embankment or hard river engineering and revetment or soft river engineering techniques are nut fiber, reeds, and grasses also provide the certain Figure 4. (a) Sketch of Bala bridge and surrounding; (b) Newly constructed concrete bridge and huge sediments accumulated at the vicinity of the pillars; (c) Concrete embankments and revetments along the side of Bala; (d) Dredging of bed loads and sediments through bulldozers; (e) Elevated channel bed of river Bala in the lap of Bhutan Himalaya. 8 B. BERA ET AL. Table 4. Structure and composition of embankment and revetment of river Bala. Length and Height width of Length and width of Height of Structure of the of revetment revetment Structure and composition River Bank embankment (m) embankment (m) embankment (m) (m) of revetment Left side 42.00 & 1.50 0.80 Concrete 29.50 & 2.0 0.80 Boulder, gravel and pebble Right side 39.00 & 1.50 0.90 Concrete 27.30 & 2.0 0.90 with iron weir Boulder, gravel and pebble with iron weir degree of protection from the bank failure or bank engineering layout does not interrupt the natural erosion. flow regime (Dutta et al., 2018; Lennox & In case of River Bala, both “soft” and “hard” river Rasmussen, 2016).The Bala bridge constructed engineering techniques had been applied. During the (2017) to link the Alipurduar town and Jayanti tourist bridge construction (2017), 39 m and 42 m length with site. It has a total length of 72 m and width of 10 m. 1.5 m width elongated concrete embankment The engineering design of bridge (Figure 4b,c) shows (Figure 4c) was designed in the right and left side of linear concrete, multi pillars with iron rods inside. the bridge along the flowing channel course. At the Structurally, it has 20 pillars with 4 m gap between ending part of long embankment, 29.50 m and two pillars. The diameter of each pillar is about 0.70 m 27.30 m length and 2 m width revetments have also with horizontal length of the pillar is 10 m and the been built (Table 4). Structurally, it is also composed average height between the channel bed and bridge of boulders, gravels, and pebbles with iron weir to floor stands at 1.60 m. protect bank failure and erosion during flood situa- The study found that the engineering layout of the tion. The wide up-stretch of River Bala is almost bridge has not maintained good scientific design. As passing through narrow concrete embankments and the river having narrow width of 72 m, unscientifically revetments (Figure 4c) in this particular biodiversity installed 20 pillars of 0.70 m diameters with rich Buxa Tiger Reserve. As the soft and hard river a minimum gap of 4 m between two pillars which engineering structures indirectly reduce the channel obstruct the huge sediment loads at the proximity of bed stability at the proximity of bridge, there is high these pillars across the channels (Table 5). On the possibility of the river to avulse in such critical or other hand, linear low height (1.60 m gap between threshold point. channel bed and bridge floor) bridge structure cannot accommodate such huge amount of sediment loads (0.55 m monsoonal siltation rate) during monsoon. 4.4 Engineering design of Bala bridge As a result, bank failure and inundation have been experienced in different sites along the river and this In the last couple of decades, almost all developing wrongly designed bridge also directly disturbs natural countries of the world have constructed bridge, cul- fluvio-hydrological rhythm. vert, and sluice gates across the natural river course to improve the transport and communication network between different urban nodes or growth centers. 4.5 Channel bed configurations and Besides, it also protects the river bank erosion, river modifications migration, flood control, and irrigation facilities. Many scientific studies have also been conducted on Specific events of fluvial system like channel incision, impact of channelization in different parts of the world channel bed instability, bank scouring, and lateral which is already mentioned earlier. instability of the channel have been rapidly accelerated The different studies reflected that due to installa- due to small- or large-scale channel bed mining or tion of big sized concrete multi pillars on the natural quarrying activities (Bik et al., 2021; Hámor & channel bed, the rate of siltation has been tremen- Kovács, 2018; Islam et al., 2018; Kondolf, 1994, 1997; dously increased (Dutta et al., 2018; Lennox & Rentier & Cammeraat, 2022; Saad & Habib, 2021; Rasmussen, 2016). The global research study has Smith et al., 2019). Various processes of channel bed found that scientifically designed good river mining (removal of gravel, pebble, cobble and sand) Table 5. Engineering design of river Bala Bridge. Horizontal Width of the length Name of Length and width individual pillar Total no. of the pillars Distance between Height between channel Bridge of the bridge(m) (m) of pillars (m) two pillars (m) Structure bed and bridge floor (m) Bala 72.00 & 0.70 20.00 10.00 4.00 Linear concrete with 1.60 Bridge 10.00 pillars inside iron rods GEOLOGY, ECOLOGY, AND LANDSCAPES 9 directly interrupt hydraulic equilibrium along the (Figure 6). Highest rate of siltation was found 0.55 m channel and leading to erode shoals and riffles (Bik at the station 9 across the Bala bridge due to great et al., 2021; Pauley et al., 1989; Rentier & Cammeraat, obstruction of big sized diameter pillars whereas the 2022). Moreover, flood frequency and tendency are average rate of siltation was 0.39 m (Table 6). After the being greatly reduced due to the incision of channel monsoon (December 2017), Department of Forest bed (Ghosh & Bera, 2022; Ghosh et al., 2022a, 2022b). started to remove sediments and bed loads through Besides, it also increases the accommodative capacity bulldozer to recover the previous flow path as well as of water and adjusts higher discharges within the to protect Bala bridge from large scale damage and channel path (Biswas & Banerjee, 2018; Bravard channel diversion. After dredging the maximum ele- et al., 1999; Hámor & Kovács, 2018; Smith et al., vation difference was 1.92 m at station 9 whereas the 2019). This is the alternative method of flood preven- average difference was 1.28 m (Table 6). Due to tion through extraction of sediments from channel unskilled river training or unscientific channel bed bed (Bravard et al., 1999; Ghosh et al., 2022a). mining, the channel thalweg line has been shifted as Despite the various positive aspects, large-scale chan- well as channel bed stability has also been decreased at nel bed mining has been banned or strictly prohibited up and down stretch of this bridge. in different countries of Europe (Kondolf, 1997). Total 12 stations were marked on the channel bed of Bala (within 200 m distance) at the proximity of 5. Conclusion and recommendations Bala Bridge to find out the changing configuration of The comprehensive study of channelization and its channel bed. Three times (before monsoon, after effects shows systematic, fundamental theory building, monsoon and after dredging, 2017) intensive survey and policy making results such as - had been done through Total Station (Leica Builder (i) On an average the gauge height of the River Bala 405) to get changing channel bed configuration at the is 130.99 m. But in August 2017, the river experienced vicinity of Bala bridge and adjacent stretch (Figure 5). 140 m gauge height that was equal to the road height. Before monsoon (April,2017), the highest elevation Therefore, the linear concrete, multi-pillars (20 pillars) was found 147.50 m at the prism reflector station1 of 0.70 m diameters with minimum gap of 4 m which was located at the confluence point of Bala between 2 pillars) bridge acts a barrier and obstructs whereas 139.00 m was a lowest elevation of the station the flow of sediments resulting into accumulation at 10. After monsoon 2017, the survey was conducted at the proximity of the bridge. The highest siltation rate the same sites. There was a drastic change observed was 0.55 m at the end of the monsoon 2017. The along the stretch of above mentioned stations Figure 5. (a) Location of Total Station sites along the channel bed of River Bala; (b) Channel bed elevation before and after monsoon and after dredging; (c) Elevation differences between before and after monsoon and elevation differences after monsoon and after dredging. 10 B. BERA ET AL. Figure 6. Google Earth (Landsat/Copernicus) image of (a) 2010 and (b) 2018 showing changing river geometry and Bala bridge. Table 6. Channel bed elevation profile before and after monsoon and after dredging (2017). Location of Channel bed Channel bed Channel bed elevation Channel bed elevation Prism reflector elevation before elevation after Channel bed differences (after differences (before of Total Latitude Longitude the monsoon monsoon (2017) elevation after monsoon and dredging) monsoon and after Station (N) (E) (2017) in m in m dredging in m in m monsoon) in m 1 26.69759 89.57017 147.51 147.89 146.98 0.91 0.32 2 26.69751 89.570036 146.53 146.85 146.31 0.54 0.35 3 26.69723 89.569896 146.07 146.7 145.44 1.26 0.48 4 26.69707 89.56979 145.24 145.81 144.57 1.24 0.38 5 26.69686 89.569859 144.09 144.73 142.95 1.78 0.27 6 26.69669 89.569819 143.20 143.63 141.95 1.68 0.42 7 26.6965 89.569721 143.91 144.05 142.22 1.83 0.31 8 26.69638 89.569779 141.51 141.96 140.25 1.71 0.46 9 26.69619 89.569,707 140.23 141.46 139.54 1.92 0.55 10 26.69581 89.569676 139.68 140.07 138.92 1.15 0.41 11 26.69531 89.569656 139.51 139.49 138.38 1.11 0.34 12 26.69496 89.569586 139.21 139.4 139.16 0.24 0.39 Department of Forest used bulldozers to remove the and adjacent areas, the field-based study reveals that silted materials after monsoon to maintain the healthy Soft River Engineering technique is more suitable to protect river bank erosion and suited to improve flow of the river. But if the rate of siltation is greater in channel bed stability within the rich biodiversity of a particular year, there is a high probability of avulsion Buxa Tiger Reserve as well tourist spot of Jayanti and of the channel course of Bala. inhabitants of Mainabari areas. (ii) The wide upstretch of River Bala is passing Moreover, the construction of such type of wrongly through narrow concrete embankments (39 m and designed hard engineering structures along or across 42 m length with 1.5 m width) and revetments the rivers of Himalayan foothill over the decades has (29.50 m, 27.30 m length and 2 m width) within the caused enormous loss of natural as well as human rich biodiversity of Buxa Tiger Reserve. These hard resources every year. Therefore, at this junction of river engineering structures directly reduce the river environmental crisis, this scientific study will prove bed stability (due to narrow hard engineering struc- to be a relevant tools and techniques to combat such ture across the river) and accelerate bank erosion at contemporary human induced environmental hazards the up and down stretch of this structures. or disasters. Besides, this innovative research work (iii) Unskilled river engineering and unscientific also provides crucial testimony for both the govern- river channel mining have adversely influenced the mental and non-governmental organization to deal channel bed stability. Subsequently, the thalweg line with such large scale spatiotemporal fluvio- has tremendously shifted towards the right bank side environmental attributes. Finally, National and of the river. If the same condition persists for a long International River research organizations will also time, in near future (during monsoon) the river will get a new horizon (policy framing components) to avulse nearly 200 m right side on low lying topo- work towards the restoration of river health by addres- graphic depression within the rich Buxa Tiger Reserve. sing contemporary fluvio-hydrological or environ- There are widely used nonstructural soft traditional mental hazards. bio-engineering techniques like wooden piling, willow posts, geo-bag dumping and bank vegetation which can directly protect erosion by reducing the near bank Acknowledgments shear stresses. Therefore, it is concluded that field based site specific hard or soft river engineering tech- We express our sincere gratitude to the Directors of niques may be implemented. But in case of Bala Bridge Geological Survey of India and Bhutan for their constant GEOLOGY, ECOLOGY, AND LANDSCAPES 11 help and assistance during field. We also extend our heart- Work identifier https://trove.nla.gov.au/work/18397029, iest thank to PWD Executive Engineer, Alipurduar for pro- Edition identifier https://trove.nla.gov.au/version/ viding valuable information regarding the layout and 21591674 composition of Bala bridge, embankment and revetment. Brookes, A., & Shields, F. D., Jr (1996). River channel restoration: Guiding principles for sustainable projects. John Wiley & Sons. http://agris.fao.org/agris-search /search.do?recordID=XF2015011453 Disclosure statement Chamling, M., & Bera, B. (2020). Likelihood of elephant No potential conflict of interest was reported by the death risk applying kernel density estimation model author(s). along the railway track within biodiversity hotspot of Bhutan–Bengal Himalayan Foothill. Modeling Earth Systems and Environment, 6(4), 2565–2580. https://doi. ORCID org/10.1007/s40808-020-00849-z Chamling, M., Bera, B., & Sarkar, S. (2022). Large-scale Biswajit Bera http://orcid.org/0000-0002-0957-8023 human intervention and estimation of flood susceptibility applying frequency ratio model. In Biswajit Pradhan, Pravat Kumar Shit, & Gouri Sankar Bhunia (Eds.), Compliance with Ethical Standards Spatial modelling of flood risk and flood hazards (pp. 161–183). Springer. https://doi.org/10.1007/978-3-030- The authors abide by the ethical standards of the journal. 94544-2_10 Chandra, D. K. (1947). A report on the Dolomite and other minerals in BuxaDuars, District Jalpaiguri and partly in References Bhutan Territory. Progress Report G.S.I, Geological Survey of India. https://employee.gsi.gov.in/cs/groups/public/ Beniston, M. (2003). Climatic change in mountain regions: documents/document/b3zp/mtix/~edisp/dcport1gsi A review of possible impacts. Climate Variability and govi121717.pdf Change in High Elevation Regions: Past, Present & Future, Charoenlerkthawin, W., Namsai, M., Bidorn, K., 15, 5–31. https://doi.org/10.1007/978-94-015-1252-7_2 Rukvichai, C., Panneerselvam, B., & Bidorn, B. Bera, B., Bhattacharjee, S., Ghosh, A., Ghosh, S., & (2021). Effects of dam construction in the Wang Chamling, M. (2019b). Dynamic of channel potholes on River on sediment regimes in the Chao Phraya River Precambrian geological sites of Chhota Nagpur plateau, Basin. Water, 13(16), 2146. https://doi.org/10.3390/ Indian peninsula: Applying fluvio-hydrological and geos- w13162146 patial techniques. SN Applied Sciences, 1(5), 1–14. https:// Dang, M. H., Umeda, S., & Yuhi, M. (2014). Long-term doi.org/10.1007/s42452-019-0516-2 riverbed response of lower Tedori River, Japan, to sedi- Bera, B., Bhattacharjee, S., & Roy, C. (2019a). Estimating ment extraction and dam construction. Environmental stream piracy in the lower ganga plain of a quaternary Earth Sciences, 72(8), 2971–2983. https://doi.org/10. geological site in West Bengal, India applying sedimento- 1007/s12665-014-3202-0 logical bank facies, log and geospatial techniques. Current Daniels, R. B. (1960). Entrenchment of the Willow Drainage Science, 117(4), 662–671. https://doi.org/10.18520/cs/ Ditch, Harrison County, Iowa. American Journal of v117/i4/662-671 Science, 258(3), 161–176. https://doi.org/10.2475/ajs.258. Bik, Y. I., Buchelnikov, M. A., Kofeeva, V. N., & Epikhin, A. I. 3.161 (2021). Scientific substantiation of dredging volumes on Darby, S. E., Hackney, C. R., Leyland, J., Kummu, M., the Ob River-the most important source of water resources Lauri, H., Parsons, D. R., Aalto, R., Nicholas, A. P., & in Western Siberia. In IOP Conference Series:Earth and Aalto, R. (2016). Fluvial sediment supply to a mega-delta Environmental Science, IOP Publishing, 867(1), 012033. reduced by shifting tropical-cyclone activity. Nature, 539 https://doi.org/10.1088/1755-1315/867/1/012033 (7628), 276. https://doi.org/10.1038/nature19809 Biswas, M., & Banerjee, P. (2018). Bridge construction and Das, B. K. (2012). Losing biodiversity, impoverishing forest river channel morphology—A comprehensive study of villagers: Analysing Forest policies in the context of flood flow behavior and sediment size alteration of the River disaster in a national park of sub Himalayan Bengal, Chel, India. Arabian Journal of Geosciences, 11(16), 1–23. India. Institute of Development Studies. https://pdfs. https://doi.org/10.1007/s12517-018-3789-7 semanticscholar.org/898a/4fa20b5844238 Blazejewski, R., Pilarczyk, K. W., & Przedwojski, B. (1995). f1e4ef684fbd8338d86a8f7.pdf River training techniques: Fundamentals, design and Dixon, S. J., Sear, D. A., Odoni, N. A., Sykes, T., & applications. CRC Press. Lane, S. N. (2016). The effects of river restoration on Bravard, J. P., Kondolf, G. M., & Piégay, H. (1999). catchment scale flood risk and flood hydrology. Earth Environmental and societal effects of river incision and Surface Processes and Landforms, 41(7), 997–1008. remedial strategies (pp. 303–341). John Wiley & Sons https://doi.org/10.1002/esp.3919 Ltt. https://hal.archives-ouvertes.fr/hal-02042770/ Downs, P., & Gregory, K. (2014). River channel manage- Brierley, G. J., & Fryirs, K. A. (2005). Geomorphology and ment: Towards sustainable catchment hydrosystems. River Management: Applications of the River Styles Routledge. https://books.google.co.in/books?id= Framework (p. 398). Blackwell Publishing. https://doi. 7f7pAgAAQBAJ&printsec=frontcover&source org/10.1002/9780470751367 Dutta, V., Sharma, U., Iqbal, K., Pathak, A. K., Pathak, A. K., Brookes, A. (1985). Traditional engineering methods, phy- & Pathak, A. K. (2018). Impact of river channelization sical consequences and alternative practices. Progress in and riverfront development on fluvial habitat: Evidence Physical Geography, 9(1), 44–73. https://doi.org/10.1177/ from Gomti River, a tributary of Ganges, India. Environmental Sustainability, 1(2), 167–184. https://doi. Brookes, A. (1988). Channelized rivers: Perspectives for org/10.1007/s42398-018-0016-0 environmental management (p. 326). Chichester: Wiley. 12 B. BERA ET AL. Emerson, J. W. (1971). Channelization: A case study. Environmental Management, 21(4), 533–551. https://doi. Science, 173(3994), 325–326. https://doi.org/10.1126/ org/10.1007/s002679900048 science.173.3994.325 Lennox, P. A., III, & Rasmussen, J. B. (2016). Long-term effects of channelization on a cold-water stream Ghosh, P. K. (1968). An investigation of Dolomite in the community. Canadian Journal of Fisheries and Aquatic Mahakal Hill area, near Jainti, Jalpaiguri district, West Sciences, 73(10), 1530–1537. https://doi.org/10.1139/ Bengal. Progress Report for the field session, G.S.I., cjfas-2015-0561 Geological Survey of India. https://employee.gsi.gov.in/ Leopold, L. B., & Wolman, M. G. (1957). River channel cs/groups/public/documents/document/b3zp/mtix/~ patterns: Braided, meandering, and straight. US edisp/dcport1gsigovi121717.pdf Government Printing Office , 1–84. https://doi.org/10. Ghosh, S., & Bera, B. (2022). River Raidak-I migration 3133/pp282B dynamics within Himalayan foreland basin applying Lin, Q. (2011). Influence of dams on river ecosystem and its Quaternary sedimentological bank facies and Geospatial countermeasures. Journal of Water Resource and Protection, techniques. In Pravat Kumar Shit, Biswajit Bera, & 3(1), 7. https://doi.org/10.4236/jwarp.2011.31007 Aznarul Islam (Eds.), Drainage Basin Dynamics (pp. Marcinkowski, P., & Grygoruk, M. (2017). Long-term 153–177). Springer. https://doi.org/10.1007/978-3-030- downstream effects of a dam on a lowland river flow 79634-1_7 regime: Case study of the upper narew. Water, 9(10), Ghosh, S., Mandal, P., & Bera, B. (2022a). Geospatial and 783. https://doi.org/10.3390/w9100783 fluvio-geomorphological investigation of confluence Marren, P. M., Grove, J. R., Webb, J. A., & Stewardson, M. J. dynamics of river Raidak within Himalayan foreland (2014). The potential for dams to impact lowland mean- basin, India. Physical Geography, 1–35. https://doi.org/ dering river floodplain geomorphology. The Scientific World 10.1080/02723646.2022.2068405 Journal, 2014, 1–24. https://doi.org/10.1155/2014/309673 Ghosh, S., Saha, S., & Bera, B. (2022b). Flood susceptibility Marsh, G. P. (1864). Man and nature; or, physical geo- zonation using advanced ensemble machine learning mod- graphy, as modified by human action. London: els within Himalayan foreland basin. Natural Hazards Sampson Low, Son, and Marston. Geological Research. https://doi.org/10.1016/j.nhres.2022.06.003 Magazine, 1(5), 208–209. https://doi.org/10.1017/ Gregory, K. J. (2006). The human role in changing river s0016756800163708 channels. Geomorphology, 79(3–4), 172–191. https://doi. Mei, X., Dai, Z., Darby, S. E., Gao, S., Wang, J., & org/10.1016/j.geomorph.2006.06.018 Jiang, W. (2018). Modulation of extreme flood levels Habel, M., Mechkin, K., Podgorska, K., Saunes, M., by impoundment significantly offset by floodplain loss Babiński, Z., Chalov, S., Absalon, D., Podgórski, Z., & downstream of the Three Gorges Dam. Geophysical Obolewski, K. (2020). Dam and reservoir removal pro- Research Letters, 45(7), 3147–3155. https://doi.org/10. jects: A mix of social-ecological trends and cost-cutting 1002/2017GL076935 attitudes. Scientific Reports, 10(1), 1–16. https://doi.org/ Pauley, G. B., Thomas, G. L., Marino, D. A., & 10.1038/s41598-020-76158-3 Weigand, D. C. (1989). Evaluation of the effects of gravel Hámor, T., & Kovács, G. (2018). Riverbed aggregates bar scalping on juvenile salmonids in the Puyallup River dredging. European Geologist, 45, 15–16. https://www. drainage. University of Washington Cooperative Fishery researchgate.net/publication/328783006_Riverbed_aggre Research Unit Report. University of Washington. gates_dredging Petersen, M. S. 1986. River engineering. Prentice-Hall. Hart, D. D., Johnson, T. E., Bushaw-Newton, K. L., Rentier, E. E., & Cammeraat, L. E. (2022). The environmen- Horwitz, R. J., Bednarek, A. T., Charles, D. F., tal impacts of river sand mining. Science of the Total Velinsky, D. J. (2002). Dam removal: Challenges and Environment, 834(1), 155877. https://doi.org/10.1016/j. opportunities for ecological research and river restora- scitotenv.2022.155877 tion: We develop a risk assessment framework for under- Rinaldi, M., & Simon, A. (1998). Bed-level adjustments in standing how potential responses to dam removal vary the Arno River, central Italy. Geomorphology, 22(1), with dam and watershed characteristics, which can lead 57–71. https://doi.org/10.1016/S0169-555X(97)00054-8 to more effective use of this restoration method. Ritter, A. F. (1979). The effects of channelization on a BioScience, 52(8), 669–682. https://doi.org/10.1641/ high-energy river. Environmental Geology, 3(1), 29–38. 0006-3568(2002)052[0669:DRCAOF]2.0.CO;2 https://doi.org/10.1007/bf02423276 Islam, M. K., Al Kibriya, N., Dustegir, M. M., Saad, H. A., & Habib, E. H. (2021). Assessment of riverine Paquier, A., & Rivière, N. (2018). Impact analysis of dredging impact on flooding in low-gradient coastal rivers Sand dredging from alluvial tidal river. E3S Web of using a hybrid 1D/2D hydrodynamic model. Frontiers in Conferences, EDP Sciences, 40, 03036. https://doi.org/ Water, 3, 628829. https://doi.org/10.3389/frwa.2021.628829 10.1051/e3sconf/20184003036 Semwal, S., & Chauniyal, D. D. (2019). Impact of dam on Keller, E. A. (1975). Channelization: A search for a better channel morphology of alaknanda river in srinagar valley way. Geology, 3(5), 246–248. https://doi.org/10.1130/ (Garhwal Himalaya).Himalayan. Journal of Social Science 0091-7613(1975)3<246:CASFAB>2.0.CO;2 and Humanities, 14, 19–27. https://doi.org/10.51220/ Keller, E. A., & Melhorn, W. N. (1978). Rhythmic spacing hjssh.v14i1.3 and origin of pools and riffles. Geological Society of Słowik, M., Kiss, K., Czigány, S., Gradwohl-Valkay, A., America Bulletin, 89(5), 723–730. https://doi.org/10. Dezső, J., Halmai, Á., Marciniak, A., Tritt, R., & 1130/0016-7606(1978)89<723:RSAOOP>2.0.CO;2 Pirkhoffer, E. (2021). The influence of changes in flow Kondolf, G. M. (1994). Geomorphic and environmental regime caused by dam closure on channel planform evo- effects of instream gravel mining. Landscape and Urban lution: Insights from flume experiments. Environmental Planning, 28(2–3), 225–243. https://doi.org/10.1016/ Earth Sciences, 80(4), 1–18. https://doi.org/10.1007/ 0169-2046(94)90010-8 s12665-021-09437-5 Kondolf, G. M. (1997). PROFILE: Hungry water: Effects of Smith, W. S., Silva, F. L. D., & Biagioni, R. C. (2019). River dams and gravel mining on river channels. dredging: When the public power ignors the causes, GEOLOGY, ECOLOGY, AND LANDSCAPES 13 biodiversity and science. Ambiente&Sociedade, 22. Yao, Y., Cui, W., Wang, W., Ma, F. M., & Chen, B. Y. (2020). https://doi.org/10.1590/1809-4422asoc0057r1vu19L1AO Impacts of dam construction on river channel evolution: Thomas, W. L. (1956). Man’s role in changing the face of A case of Minjiang River in South-eastern China. the earth (pp. 10–13). The university of Chicago Press, Proceedings of the International Association of USA. https://books.google.co.in/books?hl=en&lr=&id= Hydrological Sciences, 383, 341–346. https://doi.org/10. rFm7S7MzedEC&oi=fnd&pg=PA147&dq= 5194/piahs-383-341-2020 Yang, Y., Zhang, M., Zhu, L., Zhang, H., Liu, W., & Wang, J. Zarfl, C., Berlekamp, J., He, F., Jähnig, S. C., (2018). Impact of the operation of a large-scale reservoir on Darwall, W., & Tockner, K. (2019). Future large downstream river channel geomorphic adjustments: A case hydropower dams impact global freshwater study of the three gorges. River Research and Applications, megafauna. Scientific Reports, 9(1), 1–10. https://doi. 34(10), 1315–1327. https://doi.org/10.1002/rra.3372 org/10.1038/s41598-019-54980-8 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geology Ecology and Landscapes Taylor & Francis

Impacts of channelization of River Bala, eastern Himalayan foothills, India

Download PDF
13 pages

Loading next page...
 
/lp/taylor-francis/impacts-of-channelization-of-river-bala-eastern-himalayan-foothills-XNq0NVJir6

References (32)

Publisher
Taylor & Francis
Copyright
© 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of the International Water, Air & Soil Conservation Society(INWASCON).
ISSN
2474-9508
DOI
10.1080/24749508.2022.2130857
Publisher site
See Article on Publisher Site

Abstract

GEOLOGY, ECOLOGY, AND LANDSCAPES INWASCON https://doi.org/10.1080/24749508.2022.2130857 RESEARCH ARTICLE a b c a a Biswajit Bera , Sumana Bhattacharjee , Nairita Sengupta , Meelan Chamling , Supriya Ghosh and Arijit Ghosh a b Department of Geography, Sidho-Kanho-Birsha University, Purulia, India; Jogesh Chandra Chaudhuri College (Calcutta University), c d Kolkata, India; Department of Geography, Diamond Harbour Women’s University, Sarisha, India; ICSSR Major Project, Sidho-Kanho- Birsha University, India ABSTRACT ARTICLE HISTORY Received 04 May 2019 Hard river engineering or channelization alters channel bathymetry and river morphology and Accepted 27 Sep 2022 invites multiple fluvio-hydrological hazards. The linear (72 m), concrete, low height (1.6 m), multipillars (20 pillars) bridge with concrete embankments and revetments has been con- KEYWORDS structed across and along the river Bala within the Himalayan foothill zone in the year 2017. As Siltation; channel avulsion; a result, the rate of siltation has been tremendously increased at the vicinity of the pillars of the embankment; revetment bridge. The principal objectives are (i) to establish wrongly designed hard river engineering techniques and (ii) to find out the adverse effect of Bala bridge. Results showed that the highest rate of siltation was 0.55 m at the end of the monsoon in 2017 whereas the average of rate of siltation was 0.37 m between 2010 and 2017. If the rate of siltation is greater in a particular year, there is a high probability to divert the channel course. The thalweg line has tremendously shifted towards the right bank side. If the same condition persists for a long time, in near future (during monsoon) the river will avulse nearly 200 m right side on low lying topographic depression within the rich Buxa Tiger Reserve. 1. Introduction hydraulic dredgers apply suction pumps to bring materials via pipe lines. The principal purpose behind “Channelization is the modification of natural river the works was to train the river to flow in a deeper channels for the purposes of navigation, flood control, channel and reducing the devastating incidents of land drainage and erosion control” (Brookes, 1988). flooding. Channelization consists of different hard and soft th In the beginning of 20 century, the various tech- engineering processes that alter the configuration of niques of channelization like hard engineering tech- natural river channels. Channelization involves (i) re- niques (dam construction, bridge, culvert, and sluice sectioning and realignment, (ii) dredging, (iii) snag- gates) have been introduced to improve the smooth ging and clearing, (iv) construction of levees and transport and communication system (Bera et al., embankments, (v) bank protection, (vi) bed protec- 2019a; Ghosh et al., 2022a, 2022b).The architecture tion, (vii) river training, (viii) dam construction, (ix) of natural river channels has been modified tens of emplacement of locks and weirs, and (x) construction thousands of kilometers through channelization pro- of bridge, culvert, and sluice gates. Depending on the grammes or river training techniques in different size of the channel and the purpose of the engineering sites of developed nations of the globe (Brookes, work, re-sectioning or realignment is carried out 1985). Human interference can accelerate natural through dredging or by means of various river training fluvial processes and tends to reduce the time scale processes. History of dredging can be traced thou- for the river channel stability and adjustments (Dang sands of years. Egyptians, Romans, Sumerians and et al., 2014; Darby et al., 2016; Mei et al., 2018; Rinaldi Chinese have practiced dredging since ancient time & Simon, 1998; Yang et al., 2018). These modifica - through manual skills involving mass labour tions often accelerate to instability within the engi- (Petersen, 1986). In case of small non-navigable chan- neered reach upstream or downstream channel in nels, dredging is generally done by the bulldozer. In different morphogenetic regions of the world. There the late sixteenth century, China introduced mechan- is no as such geomorphic time scale to recover the ical dredging technique in River Yellow and during engineered river channel into natural river channel. that time, various river training techniques were In general, it takes thousands of years to attain new already started (Blazejewski et al., 1995). Mechanical equilibrium stage (Brierley & Fryirs, 2005). Natural dredgers bring bed rock materials or sediments by river channel alteration or channel modification has lifting from the bed in a bucket or dipper, whereas CONTACT Biswajit Bera biswajitbera007@gmail.com Department of Geography, Sidho-Kanho-Birsha University, Ranchi Road, Sainik School, Purulia, West Bengal, 723104, India © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of the International Water, Air & Soil Conservation Society(INWASCON). This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 2 B. BERA ET AL. brought multi-dimensional fluvio-hydrological findings will definitely help to policy makers for sus- hazards or problems which include river bank failure tainable river and floodplain management. or bank erosion, flood, inundation, property destruc- tion, and destruction of aquatic floral and faunal 2. Historical background of River Bala and habitats (Daniels, 1960; Emerson, 1971; Ghosh & research objectives Bera, 2022; Ghosh et al., 2022a, 2022b; Rentier & Cammeraat, 2022; Ritter, 1979). Meanwhile, it is Non perennial, braided and high-energy River Bala not true that multi-dimensional process of river (50 km) originates from Buxa hills of Indo-Bhutan training or channelization invites only negative boundary and flows within the Buxa Tiger Reserve of impact or threat on environment (Ritter, 1979). Alipurduar district of West Bengal. Buxa Tiger Not only broad positive impact of channelization Reserve is located in the eastern Himalayan fragile has been demonstrated but also the biological, mor- biodiversity zone. These terrestrial ecosystems have phological, and ecological consequences and impacts been fragmented due to human intervention along have been reflected through this approach (Brookes & with execution of different developmental projects Shields, 1996; Hart et al., 2002; Lin, 2011; Marren et al., and there is an imprint of climate change (Beniston, 2014; Das, 2012; Lennox & Rasmussen, 2016; 2003). Before 1972, the large-scale mining and quarry- Marcinkowski & Grygoruk, 2017; Dutta et al., 2018; ing activities took place in different parts of Buxa Hills Semwal & Chauniyal, 2019; Zarfl et al., 2019; Habel along with channel bed of River Jayanti, Bala and et al., 2020; Yao et al., 2020; Słowik et al., 2021; Raimatang and subsequently depleting floral and fau- Charoenlerkthawin et al., 2021). In the recent years, nal species (Chamling & Bera, 2020; Chamling et al., hard river engineering is largely reflected in the river- 2022). ine environment of urban areas (Marsh, 1864; Dynamic River Bala (highly variable discharge with Thomas, 1956). In addition, morphology and struc- abundant bed loads) maintains braided as well as ture of channel planform along with ecological habitat meandering channel pattern (Sinuosity Index > 1.5) factors have been immensely changed more than ten at lower stretch and ultimately discharges into River times of its original form (Gregory, 2006). Moreover, Kaljani near Alipurduar town. The lower stretch of time-space specific soft and hard river engineering River Bala is also called as River Kalkut. The non- techniques or channelization are more suitable with perennial, wide, shallow, and rugged channel path of experienced field based practical knowledge which can Bala directly assists to form different sized bars within reduce the negative effect of channelization in the the channel. Formation of multi channels with bars proximity of the urban environment (Dutta et al., continues until there is insignificant stream energy to 2018; Keller, 1975; Keller & Melhorn, 1978; Lennox erode the channel banks (Beniston, 2003; Ghosh & & Rasmussen, 2016). When Himalayan Rivers Bera, 2022; Ghosh et al., 2022a, 2022b; Leopold & debouch on the piedmont zone and floodplain region, Wolman, 1957). they become wide, shallow, and multichannel bars. Before the year 2000, there was an old bridge across South flowing Himalayan Foothill Rivers suddenly River Bala to connect Jayanti and Mainabari (tiny impede due to east-west high elevated national high- hamlets) with Alipurduar town via Rajabhatkhawa way and railway lines and this situation creates drai- Forest Range. The bridge collapsed in the year 2000 nage congestion and interlacing drainage system due to devastating flood hazard and for a few days the particularly for the fast changing Himalayan foreland entire region was partially inundated. After 2000, vehi- basin (Chamling & Bera, 2020; Chamling et al., 2022). cles ply on the natural channel path throughout Moreover, High Energy Rivers compel to flow through the year except heavy rains during monsoon. As narrow sluice gate and culverts at the crossing between Jayanti, Mahakal and Bhutan Ghat areas are popular railway line or road and river. During monsoonal tourist destinations, huge tourists come throughout months, development of spill channels and river the year. But every year during monsoonal months bank failure happen frequently within the North both tourists and local residents are seriously facing Bengal piedmont and floodplain region. Not only the troubles. To keep alive the tourism industry and to culverts and sluice gate but also many vertical and improve the transport system in this particular pocket horizontal engineering structures have also been con- of Buxa Tiger Reserve, the PWD, Government of West structed across and along the natural flowing rivers. As Bengal finally constructed 72 m long concrete bridge a result, flood contour is rapidly elevating at the foot- in 2017. hill zone in the recent years (Bera et al., 2019a; Ghosh In 2017 after the monsoon, entire channel path et al., 2022a, 2022b). River channel morphology and across the bridge was completely blocked by bed floodplain geomorphology are being modified due to rocks and sediments. Before 1975, there were several large-scale anthropogenic interference. This is a big mining sites (dolomite, limestone, and conglomerate) research gap in this context because such type of situated (Figure 2a; Table 1) along the Bhutan Bengal research work has not yet been done. The research foothills. But after 1975 to protect vulnerable GEOLOGY, ECOLOGY, AND LANDSCAPES 3 Table 1. Location of mining sites in Buxa hills. extension of 26°26ʹ54”N to 26°45ʹ15”N and longitudi- GPS Waypoint Latitude (N) Longitude (E) Altitude in meter nal extension of 89° 32’ 52” E to 89° 35’ 59” 1 26°44ʹ43.22” 89°34ʹ32.72” 385 E. (Figure 1). The investigation site is situated at the 2 26°44ʹ44.38” 89°34ʹ34.06” 399 latitudinal and longitudinal extension of 26°41ʹ47.4” 3 26°44ʹ50.17” 89°34ʹ30.18” 443 4 26°44ʹ47.87” 89°34ʹ36.98” 440 N; 89°34’ 10.5”E with an elevation of 141 m. Except 5 26°44ʹ59.68” 89°34ʹ27.25” 480 few scattered tribal hamlets, most of the area is cov- 6 26°44ʹ51.85” 89°34ʹ42.26” 481 7 26°44ʹ56.37” 89°34ʹ16.59” 517 ered by dense tropical deciduous forest with dotted 8 26°45ʹ09.98” 89°34ʹ30.16” 533 tourist watch towers. biodiversity, Government of India completely stopped 3.2 Fluvio-hydrological methods and to extract minerals within the Bengal territory. On the instrumentations other hand, Bhutan Government is still extracting Various fluvio-hydrological parameters like wetted peri- valuable minerals and rocks in their side. River Bala meter, cross-sectional area, hydraulic radius, width, is non-perennial stream but during monsoon the depth, velocity, and discharge have been considered to braided (upstretch) high energy and variable discharge measure fluvial dynamics of River Bala. Figure 2b shows stream become energetic and inherits complicated schematic diagram of various hydraulic parameters. behavior. The source area of the river is still connected with old exposed abandoned mining sites. After run- 3.2.1 Hydraulic Radius (R ) ning few kilometers from Buxa hills, the two small Hydraulic radius is the ratio between cross-sectional area branches (Bala) ultimately join together (above the and wetted perimeter. It is essential to determine the bridge) to form single channel Bala. During monsoon, channel condition and efficiency. Greater value of it receives huge sediments and bed rocks due to large hydraulic radius denotes the higher water holding capa- catchment area as well as high sediment yielding from city as well as energy to move water and sediment. If the the source area. Every year after monsoon, many tall channel depth is greater than average, water will flow at trees within Buxa Tiger Reserve also get severely a rapid rate and it causes generation of high kinetic damaged due to sudden obstruction created on the energy. rugged channel path and clogs the vegetation root R ¼ A=P, system due to continuous percolation (siltation) of Where, R is the hydraulic radius, A is the cross dolomite dusts. sectional area of flow and P is the wetted perimeter. After monsoon of 2017, the Department of Forest started dredging and clearing sediments and bed rocks 3.2.2 Wetted perimeter (P) by bulldozers at both the side of the bridge and simul- It is widespread method among hydrology, geomor- taneously constructed concrete embankments and phology, civil engineering, and environmental engi- revetments (form of loose rocks and boulders with neering. Wetted perimeter is also greatly associated weirs) on either side of the bridge along the river. with hydraulic diameter or hydraulic radius. It is sim- During the monsoon of 2017, there was high possibi- ply described as the perimeter of the cross-sectional lity to divert the channel Bala at both side of the bridge area of a channel that is directly connected with water. due to rapid rate of siltation across the bridge and proximity of big diameter horizontal pillars installed inside the channel. Besides there was also the prob- P ¼ li ability of Bala to search new path within the Buxa i¼0 Tiger Reserve. Such situation is due to implementation Where, P is the wetted perimeter, l is the length of of wrongly designed hard river engineering structures each surface in contact with the aqueous body. In case of and also invites negative effect of river engineering or open channel flow, the wetted perimeter simply defines channelization. length of the channel bottom and sides in direct contact The main objective of the study is (i) to prove with water. There is a close relationship among channel wrongly designed hard river engineering technique depth, channel width and wetted perimeter. If the chan- like concrete multi pillars low height bridge across nel depth is much lower than the width, then the wetted the river and (ii) to find out the adverse effect Bala perimeter is considered almost similar to the width. bridge and probable sites of channel diversion. Greater value of wetted perimeter and lesser depth sig- nifies high sedimentation rate and low flow discharge. 3. Methods and materials 3.2.3 Velocity (V) and depth (d) 3.1 Area of study Stream velocity is the speed of fluid that passes The catchment area of River Bala is approximately through a given surface per unit of time. Digital cur- 193.75 km which is extended between the latitudinal rent meter was used to measure the average velocity of 4 B. BERA ET AL. Figure 1. Study area. Figure 2. (a) Location of old exposed abandoned mining sites; (b) Schematic diagram showing different hydraulic parameters. the river in m/sec. Depth of the channel is measured September). Velocity is mainly regulated by channel by dipping iron ball method from bridge. Velocity and gradient, channel bed roughness, shape of the basin, depth data are collected by extensive field survey dur- discharge, sinuosity, etc. Stream velocity is compara- ing monsoonal months (June, July, August, and tively higher along the thalweg line of the stream. GEOLOGY, ECOLOGY, AND LANDSCAPES 5 3.2.4 Discharge (Q) Imagery Base map is used to show the distribution of It is the passing of volume of water through a given the mining sites, location of bridge as well as flow path cross section of a channel per unit time. of the river. CorelCAD 2018 software is used to depict Q = AV 3D schematic diagram of bridge and it’s surrounding In case of open channel, Q is the discharge (m /s or (Figure 4a). Besides, to understand the engineering ft /s), A is the cross-sectional area (sq.m or sq.ft), V is technology of the bridge, meticulous measurement of the average flow velocity (m/s or ft/s). length, width, diameters of the pillars, and height from This significant hydraulic parameter depends on the channel bed has been done with the help of mea- characteristics of catchment area, shape and size of suring tape, GPS and distance meter. Moreover, the catchment area and depth of the channel. High dis- structure and composition of the embankments and charge stream has high competency and capacity. revetments were also inspected and measured during the construction. 3.2.5 Rate of siltation Before the monsoon, gauge scale was fixed on the 3.4 Channel bed configuration through Total pillar of the bridge to obtain data of water fluctuation Station Survey level as well as to determine the rate of siltation at the Leica Builder 405 Total Station from Leica Geosystems vicinity of pillars across the bridge. Monthly was used to detect precise readings of elevation, dis- Xi i¼1 Arithmetic mean ðx ¼ Þ of velocity (m/sec) tance, and gradient of the channel bed of River Bala. and discharge is also systematically computed. 12 stations are fixed on the channel bed within 200 m up and down stretch of Bala Bridge. Local bamboos (12 bamboos with 2 m length each) were installed 3.3 Use of Garmin GPS Etrex 30x, Arc GIS and within the channel bed to experiment the changing CorelCAD 2018 configuration of channel bed or elevation difference. To identify the old abandoned mining sites (Table 1) Three times (before and after monsoon and after of dolomite, limestone, and conglomeratein the source dredging) survey had been conducted in the year area of the river (on the Buxa Hills), Garmin GPS 2017 to collect channel elevation data as well as to Etrex 30x has been used. ArcGIS Online World evaluate rate of siltation, unscientific channel bed Figure 3. (a) 3D Surface and (b) Long profile of River Bala. 6 B. BERA ET AL. dredging and thalweg line shifting at the proximity of sandstones are associated with some silt and clayey Bala bridge within Buxa Tiger Reserve of Alipurduar bands. These rocks show well and cross laminations. district of West Bengal. Pebble beds and conglomerates are quite visible in the upper part of the Shiwalik. The basalt rock in this area is red clay stone. Due to continuous soil erosion and weathering in the source area, River Bala brings var- 4. Results and discussions ious sized particles and sediments during monsoonal 4.1 Geology of the source area and sediment months (June – September). yields Lithologically, Bengal Bhutan foothill is composed of 4.2 Field based fluvio-hydrological investigation Siwalik group (Mio-Pliocene), Gondwana Group (Permian), Buxa Series (Precambrian), and Daling Fluvio-hydrological study of River Bala from 2010 to Series (Archaean). The rocks of the Daling Series 2017 (June, July, August, and September) revealed that mainly consist of chlorite-sericite-schists interbedded the average monsoonal velocity was about 2.70 m/sec with a flaggy green quartzite. These rocks are generally whereas average discharge was 208.54 cumec found along the northern fringe of the area (Indo- (Table 3).But in the month of August (2017) the high- Bhutan border). Basically, the rocks of Daling Series est average discharge of 367.20 cumec with maximum are composed of muscovite, quartz, sericite, and bio- wetted perimeter of 76.50 m had been recorded tite (Chandra, 1947). Buxa Series comprises dolomite, (Table 2). In order to generate the continuous fluvio- quartzite, and phyllite which cover most of the area. hydological data, gauge scale was fixed on the old These rocks are well exposed along the section of river pillar of the broken bridge. But after the construction Jayanti and Balaof Buxa Tiger Reserve. Phyllite con- of new bridge, the new gauge scale was marked on the stitutes the basal unit of the Buxas. Along the River pillar of the newly constructed bridge. The average Bala section and adjacent hilly areas, the intercalated gauge height has been recorded 130.99 m but in the phyllite band is found. At the upper portion of hill, month of August (2017), the River Bala experienced 200 m thick dolomite layer is also confined. Dolomite 140 m gauge height which was equal to the road is the most important member of the Buxa series. In height. As the river is linked with old abandoned and around the River Jayanti and Bala, two important mining sites, during rainy season the two branches of dolomite bands are exposed. The lower band is about river bring various sized particles. Due to the obstruc- 30 m while the upper one is about 540 m thick. These tions made by the wrongly designed big diameter dolomites are light to dark grey in colour highly multi pillars, the sediments get accumulated at the jointed, massive and generally fine grained. They are up and down stretch of bridge. The highest rate of composed of dolomite grains with fractured outline siltation of 0.55 m is recorded at the end of the mon- whereas quartz is rather rare but sometimes present in soon in 2017 whereas the average of rate of siltation is the calcareous matrix. They often contain nests of 0.37 m between 2010 and 2017. The maximum depth calcite. The general trend of the dolomite beds is was 2.10 m in the year 2010 whereas across the Bala NW – SE with a north – easterly dip direction. The Bridge the average depth is 1.35 m. 3D elevation map rocks of the Gondwana Group overlie the Shiwalik to along with long profile of River Bala was prepared the south and are underlain by the Buxa to the north. from digital elevation data to understand the channel They are exposed in the River Jayanti and Bala but in bed elevation as well as the surface elevation at the the hilly section to the west (Buxa-Jayanti bridle path) proximity of Bala watershed (Figure 4). and they are absent and dissected by the Buxa thrust. After the completion of monsoon in the month of Vertically dipping, hard quartzitic sandstone, carbo- November and December, Department of Forest used naceous shale and flaky coal are found here (Ghosh, bulldozers to remove silted materials from both side of 1968). The Shiwalik Group is extending from the west the bridge to keep the healthy flow condition of the of River Jayanti upto the Turturinala (Small River) and river. It is very hard and difficult task to remove such further east exposed along the outer fringe of foothills. channel bed sediments every year during monsoon or These rocks comprise brown, grey to bluish grey sand- post monsoon. If the rate of siltation is greater in stone which are micaceous and feldspathic. These a particular year, there is a high probability to divert Table 2. Fluvio-hydrological parameters of river Bala measured during monsoon, 2017. Wetted Average Gauge Cross sectional perimeter Average monthly discharge Channel Max. channel height Average monsoonal Month area (sq. m) (m) velocity (m/sec) (cumec) width (m) depth (m) (mtr) siltation rate (m) June 29.83 56.30 2.60 77.55 51.23 0.53 127.50 0.55 July 73.92 67.20 3.10 229.15 63.19 1.10 138.40 August 114.75 76.50 3.20 367.20 71.42 1.50 140.00 Sept. 60.81 64.70 2.50 152.02 60.35 0.94 132.00 GEOLOGY, ECOLOGY, AND LANDSCAPES 7 Table 3. Annual monsoonal average fluvio-hydrological parameters of river Bala (2010–2017). Max. Crosssectionalarea Velocity channeldepth Gauge Year (km ) Wettedperimeter(m) (m/sec) Discharge(cumec) Channelwidth(m) (m) height(m) Siltationrate(m) 2010 63.97 64.26 1.95 215.52 57.89 2.10 128.99 0.25 2011 65.27 63.95 2.10 201.90 59.21 1.71 126.35 0.29 2012 64.54 66.78 3.54 199.79 60.78 1.57 130.43 0.30 2013 66.21 64.89 3.35 212.65 62.89 1.22 132.88 0.24 2014 68.33 67.65 2.39 208.89 59.01 1.15 129.06 0.39 2015 67.19 65.45 2.66 213.45 56.65 1.05 131.76 0.42 2016 68.94 66.32 2.79 209.65 63.90 1.03 133.40 0.47 2017 69.82 66.17 2.85 206.48 61.54 1.01 134.47 0.55 Average 66.78 65.68 2.70 208.54 60.23 1.35 130.91 2.91 the channel course. Such diversion may take through widely used in different parts of the world where comparatively low lying topographic depressions of bank erosion is a serious threat to urban areas and rich biodiversity pocket (Buxa Tiger Reserve) in where natural river channel runs close to roads or front of concrete embankments or revetments made railways (Downs & Gregory, 2014). However, in less on both the narrow passages of the river. critical situation, the soft river engineering gives a more environmentally sensitive alternative (Dixon et al., 2016). In high-energy perennial or non- 4.3 Architecture of river embankment and perennial braided channel, the revetment or stone revetment apron protects the toe erosion. In case of low stream power, geo-textile, natural plant materials, jute, coco- Concrete embankment or hard river engineering and revetment or soft river engineering techniques are nut fiber, reeds, and grasses also provide the certain Figure 4. (a) Sketch of Bala bridge and surrounding; (b) Newly constructed concrete bridge and huge sediments accumulated at the vicinity of the pillars; (c) Concrete embankments and revetments along the side of Bala; (d) Dredging of bed loads and sediments through bulldozers; (e) Elevated channel bed of river Bala in the lap of Bhutan Himalaya. 8 B. BERA ET AL. Table 4. Structure and composition of embankment and revetment of river Bala. Length and Height width of Length and width of Height of Structure of the of revetment revetment Structure and composition River Bank embankment (m) embankment (m) embankment (m) (m) of revetment Left side 42.00 & 1.50 0.80 Concrete 29.50 & 2.0 0.80 Boulder, gravel and pebble Right side 39.00 & 1.50 0.90 Concrete 27.30 & 2.0 0.90 with iron weir Boulder, gravel and pebble with iron weir degree of protection from the bank failure or bank engineering layout does not interrupt the natural erosion. flow regime (Dutta et al., 2018; Lennox & In case of River Bala, both “soft” and “hard” river Rasmussen, 2016).The Bala bridge constructed engineering techniques had been applied. During the (2017) to link the Alipurduar town and Jayanti tourist bridge construction (2017), 39 m and 42 m length with site. It has a total length of 72 m and width of 10 m. 1.5 m width elongated concrete embankment The engineering design of bridge (Figure 4b,c) shows (Figure 4c) was designed in the right and left side of linear concrete, multi pillars with iron rods inside. the bridge along the flowing channel course. At the Structurally, it has 20 pillars with 4 m gap between ending part of long embankment, 29.50 m and two pillars. The diameter of each pillar is about 0.70 m 27.30 m length and 2 m width revetments have also with horizontal length of the pillar is 10 m and the been built (Table 4). Structurally, it is also composed average height between the channel bed and bridge of boulders, gravels, and pebbles with iron weir to floor stands at 1.60 m. protect bank failure and erosion during flood situa- The study found that the engineering layout of the tion. The wide up-stretch of River Bala is almost bridge has not maintained good scientific design. As passing through narrow concrete embankments and the river having narrow width of 72 m, unscientifically revetments (Figure 4c) in this particular biodiversity installed 20 pillars of 0.70 m diameters with rich Buxa Tiger Reserve. As the soft and hard river a minimum gap of 4 m between two pillars which engineering structures indirectly reduce the channel obstruct the huge sediment loads at the proximity of bed stability at the proximity of bridge, there is high these pillars across the channels (Table 5). On the possibility of the river to avulse in such critical or other hand, linear low height (1.60 m gap between threshold point. channel bed and bridge floor) bridge structure cannot accommodate such huge amount of sediment loads (0.55 m monsoonal siltation rate) during monsoon. 4.4 Engineering design of Bala bridge As a result, bank failure and inundation have been experienced in different sites along the river and this In the last couple of decades, almost all developing wrongly designed bridge also directly disturbs natural countries of the world have constructed bridge, cul- fluvio-hydrological rhythm. vert, and sluice gates across the natural river course to improve the transport and communication network between different urban nodes or growth centers. 4.5 Channel bed configurations and Besides, it also protects the river bank erosion, river modifications migration, flood control, and irrigation facilities. Many scientific studies have also been conducted on Specific events of fluvial system like channel incision, impact of channelization in different parts of the world channel bed instability, bank scouring, and lateral which is already mentioned earlier. instability of the channel have been rapidly accelerated The different studies reflected that due to installa- due to small- or large-scale channel bed mining or tion of big sized concrete multi pillars on the natural quarrying activities (Bik et al., 2021; Hámor & channel bed, the rate of siltation has been tremen- Kovács, 2018; Islam et al., 2018; Kondolf, 1994, 1997; dously increased (Dutta et al., 2018; Lennox & Rentier & Cammeraat, 2022; Saad & Habib, 2021; Rasmussen, 2016). The global research study has Smith et al., 2019). Various processes of channel bed found that scientifically designed good river mining (removal of gravel, pebble, cobble and sand) Table 5. Engineering design of river Bala Bridge. Horizontal Width of the length Name of Length and width individual pillar Total no. of the pillars Distance between Height between channel Bridge of the bridge(m) (m) of pillars (m) two pillars (m) Structure bed and bridge floor (m) Bala 72.00 & 0.70 20.00 10.00 4.00 Linear concrete with 1.60 Bridge 10.00 pillars inside iron rods GEOLOGY, ECOLOGY, AND LANDSCAPES 9 directly interrupt hydraulic equilibrium along the (Figure 6). Highest rate of siltation was found 0.55 m channel and leading to erode shoals and riffles (Bik at the station 9 across the Bala bridge due to great et al., 2021; Pauley et al., 1989; Rentier & Cammeraat, obstruction of big sized diameter pillars whereas the 2022). Moreover, flood frequency and tendency are average rate of siltation was 0.39 m (Table 6). After the being greatly reduced due to the incision of channel monsoon (December 2017), Department of Forest bed (Ghosh & Bera, 2022; Ghosh et al., 2022a, 2022b). started to remove sediments and bed loads through Besides, it also increases the accommodative capacity bulldozer to recover the previous flow path as well as of water and adjusts higher discharges within the to protect Bala bridge from large scale damage and channel path (Biswas & Banerjee, 2018; Bravard channel diversion. After dredging the maximum ele- et al., 1999; Hámor & Kovács, 2018; Smith et al., vation difference was 1.92 m at station 9 whereas the 2019). This is the alternative method of flood preven- average difference was 1.28 m (Table 6). Due to tion through extraction of sediments from channel unskilled river training or unscientific channel bed bed (Bravard et al., 1999; Ghosh et al., 2022a). mining, the channel thalweg line has been shifted as Despite the various positive aspects, large-scale chan- well as channel bed stability has also been decreased at nel bed mining has been banned or strictly prohibited up and down stretch of this bridge. in different countries of Europe (Kondolf, 1997). Total 12 stations were marked on the channel bed of Bala (within 200 m distance) at the proximity of 5. Conclusion and recommendations Bala Bridge to find out the changing configuration of The comprehensive study of channelization and its channel bed. Three times (before monsoon, after effects shows systematic, fundamental theory building, monsoon and after dredging, 2017) intensive survey and policy making results such as - had been done through Total Station (Leica Builder (i) On an average the gauge height of the River Bala 405) to get changing channel bed configuration at the is 130.99 m. But in August 2017, the river experienced vicinity of Bala bridge and adjacent stretch (Figure 5). 140 m gauge height that was equal to the road height. Before monsoon (April,2017), the highest elevation Therefore, the linear concrete, multi-pillars (20 pillars) was found 147.50 m at the prism reflector station1 of 0.70 m diameters with minimum gap of 4 m which was located at the confluence point of Bala between 2 pillars) bridge acts a barrier and obstructs whereas 139.00 m was a lowest elevation of the station the flow of sediments resulting into accumulation at 10. After monsoon 2017, the survey was conducted at the proximity of the bridge. The highest siltation rate the same sites. There was a drastic change observed was 0.55 m at the end of the monsoon 2017. The along the stretch of above mentioned stations Figure 5. (a) Location of Total Station sites along the channel bed of River Bala; (b) Channel bed elevation before and after monsoon and after dredging; (c) Elevation differences between before and after monsoon and elevation differences after monsoon and after dredging. 10 B. BERA ET AL. Figure 6. Google Earth (Landsat/Copernicus) image of (a) 2010 and (b) 2018 showing changing river geometry and Bala bridge. Table 6. Channel bed elevation profile before and after monsoon and after dredging (2017). Location of Channel bed Channel bed Channel bed elevation Channel bed elevation Prism reflector elevation before elevation after Channel bed differences (after differences (before of Total Latitude Longitude the monsoon monsoon (2017) elevation after monsoon and dredging) monsoon and after Station (N) (E) (2017) in m in m dredging in m in m monsoon) in m 1 26.69759 89.57017 147.51 147.89 146.98 0.91 0.32 2 26.69751 89.570036 146.53 146.85 146.31 0.54 0.35 3 26.69723 89.569896 146.07 146.7 145.44 1.26 0.48 4 26.69707 89.56979 145.24 145.81 144.57 1.24 0.38 5 26.69686 89.569859 144.09 144.73 142.95 1.78 0.27 6 26.69669 89.569819 143.20 143.63 141.95 1.68 0.42 7 26.6965 89.569721 143.91 144.05 142.22 1.83 0.31 8 26.69638 89.569779 141.51 141.96 140.25 1.71 0.46 9 26.69619 89.569,707 140.23 141.46 139.54 1.92 0.55 10 26.69581 89.569676 139.68 140.07 138.92 1.15 0.41 11 26.69531 89.569656 139.51 139.49 138.38 1.11 0.34 12 26.69496 89.569586 139.21 139.4 139.16 0.24 0.39 Department of Forest used bulldozers to remove the and adjacent areas, the field-based study reveals that silted materials after monsoon to maintain the healthy Soft River Engineering technique is more suitable to protect river bank erosion and suited to improve flow of the river. But if the rate of siltation is greater in channel bed stability within the rich biodiversity of a particular year, there is a high probability of avulsion Buxa Tiger Reserve as well tourist spot of Jayanti and of the channel course of Bala. inhabitants of Mainabari areas. (ii) The wide upstretch of River Bala is passing Moreover, the construction of such type of wrongly through narrow concrete embankments (39 m and designed hard engineering structures along or across 42 m length with 1.5 m width) and revetments the rivers of Himalayan foothill over the decades has (29.50 m, 27.30 m length and 2 m width) within the caused enormous loss of natural as well as human rich biodiversity of Buxa Tiger Reserve. These hard resources every year. Therefore, at this junction of river engineering structures directly reduce the river environmental crisis, this scientific study will prove bed stability (due to narrow hard engineering struc- to be a relevant tools and techniques to combat such ture across the river) and accelerate bank erosion at contemporary human induced environmental hazards the up and down stretch of this structures. or disasters. Besides, this innovative research work (iii) Unskilled river engineering and unscientific also provides crucial testimony for both the govern- river channel mining have adversely influenced the mental and non-governmental organization to deal channel bed stability. Subsequently, the thalweg line with such large scale spatiotemporal fluvio- has tremendously shifted towards the right bank side environmental attributes. Finally, National and of the river. If the same condition persists for a long International River research organizations will also time, in near future (during monsoon) the river will get a new horizon (policy framing components) to avulse nearly 200 m right side on low lying topo- work towards the restoration of river health by addres- graphic depression within the rich Buxa Tiger Reserve. sing contemporary fluvio-hydrological or environ- There are widely used nonstructural soft traditional mental hazards. bio-engineering techniques like wooden piling, willow posts, geo-bag dumping and bank vegetation which can directly protect erosion by reducing the near bank Acknowledgments shear stresses. Therefore, it is concluded that field based site specific hard or soft river engineering tech- We express our sincere gratitude to the Directors of niques may be implemented. But in case of Bala Bridge Geological Survey of India and Bhutan for their constant GEOLOGY, ECOLOGY, AND LANDSCAPES 11 help and assistance during field. We also extend our heart- Work identifier https://trove.nla.gov.au/work/18397029, iest thank to PWD Executive Engineer, Alipurduar for pro- Edition identifier https://trove.nla.gov.au/version/ viding valuable information regarding the layout and 21591674 composition of Bala bridge, embankment and revetment. Brookes, A., & Shields, F. D., Jr (1996). River channel restoration: Guiding principles for sustainable projects. John Wiley & Sons. http://agris.fao.org/agris-search /search.do?recordID=XF2015011453 Disclosure statement Chamling, M., & Bera, B. (2020). Likelihood of elephant No potential conflict of interest was reported by the death risk applying kernel density estimation model author(s). along the railway track within biodiversity hotspot of Bhutan–Bengal Himalayan Foothill. Modeling Earth Systems and Environment, 6(4), 2565–2580. https://doi. ORCID org/10.1007/s40808-020-00849-z Chamling, M., Bera, B., & Sarkar, S. (2022). Large-scale Biswajit Bera http://orcid.org/0000-0002-0957-8023 human intervention and estimation of flood susceptibility applying frequency ratio model. In Biswajit Pradhan, Pravat Kumar Shit, & Gouri Sankar Bhunia (Eds.), Compliance with Ethical Standards Spatial modelling of flood risk and flood hazards (pp. 161–183). Springer. https://doi.org/10.1007/978-3-030- The authors abide by the ethical standards of the journal. 94544-2_10 Chandra, D. K. (1947). A report on the Dolomite and other minerals in BuxaDuars, District Jalpaiguri and partly in References Bhutan Territory. Progress Report G.S.I, Geological Survey of India. https://employee.gsi.gov.in/cs/groups/public/ Beniston, M. (2003). Climatic change in mountain regions: documents/document/b3zp/mtix/~edisp/dcport1gsi A review of possible impacts. Climate Variability and govi121717.pdf Change in High Elevation Regions: Past, Present & Future, Charoenlerkthawin, W., Namsai, M., Bidorn, K., 15, 5–31. https://doi.org/10.1007/978-94-015-1252-7_2 Rukvichai, C., Panneerselvam, B., & Bidorn, B. Bera, B., Bhattacharjee, S., Ghosh, A., Ghosh, S., & (2021). Effects of dam construction in the Wang Chamling, M. (2019b). Dynamic of channel potholes on River on sediment regimes in the Chao Phraya River Precambrian geological sites of Chhota Nagpur plateau, Basin. Water, 13(16), 2146. https://doi.org/10.3390/ Indian peninsula: Applying fluvio-hydrological and geos- w13162146 patial techniques. SN Applied Sciences, 1(5), 1–14. https:// Dang, M. H., Umeda, S., & Yuhi, M. (2014). Long-term doi.org/10.1007/s42452-019-0516-2 riverbed response of lower Tedori River, Japan, to sedi- Bera, B., Bhattacharjee, S., & Roy, C. (2019a). Estimating ment extraction and dam construction. Environmental stream piracy in the lower ganga plain of a quaternary Earth Sciences, 72(8), 2971–2983. https://doi.org/10. geological site in West Bengal, India applying sedimento- 1007/s12665-014-3202-0 logical bank facies, log and geospatial techniques. Current Daniels, R. B. (1960). Entrenchment of the Willow Drainage Science, 117(4), 662–671. https://doi.org/10.18520/cs/ Ditch, Harrison County, Iowa. American Journal of v117/i4/662-671 Science, 258(3), 161–176. https://doi.org/10.2475/ajs.258. Bik, Y. I., Buchelnikov, M. A., Kofeeva, V. N., & Epikhin, A. I. 3.161 (2021). Scientific substantiation of dredging volumes on Darby, S. E., Hackney, C. R., Leyland, J., Kummu, M., the Ob River-the most important source of water resources Lauri, H., Parsons, D. R., Aalto, R., Nicholas, A. P., & in Western Siberia. In IOP Conference Series:Earth and Aalto, R. (2016). Fluvial sediment supply to a mega-delta Environmental Science, IOP Publishing, 867(1), 012033. reduced by shifting tropical-cyclone activity. Nature, 539 https://doi.org/10.1088/1755-1315/867/1/012033 (7628), 276. https://doi.org/10.1038/nature19809 Biswas, M., & Banerjee, P. (2018). Bridge construction and Das, B. K. (2012). Losing biodiversity, impoverishing forest river channel morphology—A comprehensive study of villagers: Analysing Forest policies in the context of flood flow behavior and sediment size alteration of the River disaster in a national park of sub Himalayan Bengal, Chel, India. Arabian Journal of Geosciences, 11(16), 1–23. India. Institute of Development Studies. https://pdfs. https://doi.org/10.1007/s12517-018-3789-7 semanticscholar.org/898a/4fa20b5844238 Blazejewski, R., Pilarczyk, K. W., & Przedwojski, B. (1995). f1e4ef684fbd8338d86a8f7.pdf River training techniques: Fundamentals, design and Dixon, S. J., Sear, D. A., Odoni, N. A., Sykes, T., & applications. CRC Press. Lane, S. N. (2016). The effects of river restoration on Bravard, J. P., Kondolf, G. M., & Piégay, H. (1999). catchment scale flood risk and flood hydrology. Earth Environmental and societal effects of river incision and Surface Processes and Landforms, 41(7), 997–1008. remedial strategies (pp. 303–341). John Wiley & Sons https://doi.org/10.1002/esp.3919 Ltt. https://hal.archives-ouvertes.fr/hal-02042770/ Downs, P., & Gregory, K. (2014). River channel manage- Brierley, G. J., & Fryirs, K. A. (2005). Geomorphology and ment: Towards sustainable catchment hydrosystems. River Management: Applications of the River Styles Routledge. https://books.google.co.in/books?id= Framework (p. 398). Blackwell Publishing. https://doi. 7f7pAgAAQBAJ&printsec=frontcover&source org/10.1002/9780470751367 Dutta, V., Sharma, U., Iqbal, K., Pathak, A. K., Pathak, A. K., Brookes, A. (1985). Traditional engineering methods, phy- & Pathak, A. K. (2018). Impact of river channelization sical consequences and alternative practices. Progress in and riverfront development on fluvial habitat: Evidence Physical Geography, 9(1), 44–73. https://doi.org/10.1177/ from Gomti River, a tributary of Ganges, India. Environmental Sustainability, 1(2), 167–184. https://doi. Brookes, A. (1988). Channelized rivers: Perspectives for org/10.1007/s42398-018-0016-0 environmental management (p. 326). Chichester: Wiley. 12 B. BERA ET AL. Emerson, J. W. (1971). Channelization: A case study. Environmental Management, 21(4), 533–551. https://doi. Science, 173(3994), 325–326. https://doi.org/10.1126/ org/10.1007/s002679900048 science.173.3994.325 Lennox, P. A., III, & Rasmussen, J. B. (2016). Long-term effects of channelization on a cold-water stream Ghosh, P. K. (1968). An investigation of Dolomite in the community. Canadian Journal of Fisheries and Aquatic Mahakal Hill area, near Jainti, Jalpaiguri district, West Sciences, 73(10), 1530–1537. https://doi.org/10.1139/ Bengal. Progress Report for the field session, G.S.I., cjfas-2015-0561 Geological Survey of India. https://employee.gsi.gov.in/ Leopold, L. B., & Wolman, M. G. (1957). River channel cs/groups/public/documents/document/b3zp/mtix/~ patterns: Braided, meandering, and straight. US edisp/dcport1gsigovi121717.pdf Government Printing Office , 1–84. https://doi.org/10. Ghosh, S., & Bera, B. (2022). River Raidak-I migration 3133/pp282B dynamics within Himalayan foreland basin applying Lin, Q. (2011). Influence of dams on river ecosystem and its Quaternary sedimentological bank facies and Geospatial countermeasures. Journal of Water Resource and Protection, techniques. In Pravat Kumar Shit, Biswajit Bera, & 3(1), 7. https://doi.org/10.4236/jwarp.2011.31007 Aznarul Islam (Eds.), Drainage Basin Dynamics (pp. Marcinkowski, P., & Grygoruk, M. (2017). Long-term 153–177). Springer. https://doi.org/10.1007/978-3-030- downstream effects of a dam on a lowland river flow 79634-1_7 regime: Case study of the upper narew. Water, 9(10), Ghosh, S., Mandal, P., & Bera, B. (2022a). Geospatial and 783. https://doi.org/10.3390/w9100783 fluvio-geomorphological investigation of confluence Marren, P. M., Grove, J. R., Webb, J. A., & Stewardson, M. J. dynamics of river Raidak within Himalayan foreland (2014). The potential for dams to impact lowland mean- basin, India. Physical Geography, 1–35. https://doi.org/ dering river floodplain geomorphology. The Scientific World 10.1080/02723646.2022.2068405 Journal, 2014, 1–24. https://doi.org/10.1155/2014/309673 Ghosh, S., Saha, S., & Bera, B. (2022b). Flood susceptibility Marsh, G. P. (1864). Man and nature; or, physical geo- zonation using advanced ensemble machine learning mod- graphy, as modified by human action. London: els within Himalayan foreland basin. Natural Hazards Sampson Low, Son, and Marston. Geological Research. https://doi.org/10.1016/j.nhres.2022.06.003 Magazine, 1(5), 208–209. https://doi.org/10.1017/ Gregory, K. J. (2006). The human role in changing river s0016756800163708 channels. Geomorphology, 79(3–4), 172–191. https://doi. Mei, X., Dai, Z., Darby, S. E., Gao, S., Wang, J., & org/10.1016/j.geomorph.2006.06.018 Jiang, W. (2018). Modulation of extreme flood levels Habel, M., Mechkin, K., Podgorska, K., Saunes, M., by impoundment significantly offset by floodplain loss Babiński, Z., Chalov, S., Absalon, D., Podgórski, Z., & downstream of the Three Gorges Dam. Geophysical Obolewski, K. (2020). Dam and reservoir removal pro- Research Letters, 45(7), 3147–3155. https://doi.org/10. jects: A mix of social-ecological trends and cost-cutting 1002/2017GL076935 attitudes. Scientific Reports, 10(1), 1–16. https://doi.org/ Pauley, G. B., Thomas, G. L., Marino, D. A., & 10.1038/s41598-020-76158-3 Weigand, D. C. (1989). Evaluation of the effects of gravel Hámor, T., & Kovács, G. (2018). Riverbed aggregates bar scalping on juvenile salmonids in the Puyallup River dredging. European Geologist, 45, 15–16. https://www. drainage. University of Washington Cooperative Fishery researchgate.net/publication/328783006_Riverbed_aggre Research Unit Report. University of Washington. gates_dredging Petersen, M. S. 1986. River engineering. Prentice-Hall. Hart, D. D., Johnson, T. E., Bushaw-Newton, K. L., Rentier, E. E., & Cammeraat, L. E. (2022). The environmen- Horwitz, R. J., Bednarek, A. T., Charles, D. F., tal impacts of river sand mining. Science of the Total Velinsky, D. J. (2002). Dam removal: Challenges and Environment, 834(1), 155877. https://doi.org/10.1016/j. opportunities for ecological research and river restora- scitotenv.2022.155877 tion: We develop a risk assessment framework for under- Rinaldi, M., & Simon, A. (1998). Bed-level adjustments in standing how potential responses to dam removal vary the Arno River, central Italy. Geomorphology, 22(1), with dam and watershed characteristics, which can lead 57–71. https://doi.org/10.1016/S0169-555X(97)00054-8 to more effective use of this restoration method. Ritter, A. F. (1979). The effects of channelization on a BioScience, 52(8), 669–682. https://doi.org/10.1641/ high-energy river. Environmental Geology, 3(1), 29–38. 0006-3568(2002)052[0669:DRCAOF]2.0.CO;2 https://doi.org/10.1007/bf02423276 Islam, M. K., Al Kibriya, N., Dustegir, M. M., Saad, H. A., & Habib, E. H. (2021). Assessment of riverine Paquier, A., & Rivière, N. (2018). Impact analysis of dredging impact on flooding in low-gradient coastal rivers Sand dredging from alluvial tidal river. E3S Web of using a hybrid 1D/2D hydrodynamic model. Frontiers in Conferences, EDP Sciences, 40, 03036. https://doi.org/ Water, 3, 628829. https://doi.org/10.3389/frwa.2021.628829 10.1051/e3sconf/20184003036 Semwal, S., & Chauniyal, D. D. (2019). Impact of dam on Keller, E. A. (1975). Channelization: A search for a better channel morphology of alaknanda river in srinagar valley way. Geology, 3(5), 246–248. https://doi.org/10.1130/ (Garhwal Himalaya).Himalayan. Journal of Social Science 0091-7613(1975)3<246:CASFAB>2.0.CO;2 and Humanities, 14, 19–27. https://doi.org/10.51220/ Keller, E. A., & Melhorn, W. N. (1978). Rhythmic spacing hjssh.v14i1.3 and origin of pools and riffles. Geological Society of Słowik, M., Kiss, K., Czigány, S., Gradwohl-Valkay, A., America Bulletin, 89(5), 723–730. https://doi.org/10. Dezső, J., Halmai, Á., Marciniak, A., Tritt, R., & 1130/0016-7606(1978)89<723:RSAOOP>2.0.CO;2 Pirkhoffer, E. (2021). The influence of changes in flow Kondolf, G. M. (1994). Geomorphic and environmental regime caused by dam closure on channel planform evo- effects of instream gravel mining. Landscape and Urban lution: Insights from flume experiments. Environmental Planning, 28(2–3), 225–243. https://doi.org/10.1016/ Earth Sciences, 80(4), 1–18. https://doi.org/10.1007/ 0169-2046(94)90010-8 s12665-021-09437-5 Kondolf, G. M. (1997). PROFILE: Hungry water: Effects of Smith, W. S., Silva, F. L. D., & Biagioni, R. C. (2019). River dams and gravel mining on river channels. dredging: When the public power ignors the causes, GEOLOGY, ECOLOGY, AND LANDSCAPES 13 biodiversity and science. Ambiente&Sociedade, 22. Yao, Y., Cui, W., Wang, W., Ma, F. M., & Chen, B. Y. (2020). https://doi.org/10.1590/1809-4422asoc0057r1vu19L1AO Impacts of dam construction on river channel evolution: Thomas, W. L. (1956). Man’s role in changing the face of A case of Minjiang River in South-eastern China. the earth (pp. 10–13). The university of Chicago Press, Proceedings of the International Association of USA. https://books.google.co.in/books?hl=en&lr=&id= Hydrological Sciences, 383, 341–346. https://doi.org/10. rFm7S7MzedEC&oi=fnd&pg=PA147&dq= 5194/piahs-383-341-2020 Yang, Y., Zhang, M., Zhu, L., Zhang, H., Liu, W., & Wang, J. Zarfl, C., Berlekamp, J., He, F., Jähnig, S. C., (2018). Impact of the operation of a large-scale reservoir on Darwall, W., & Tockner, K. (2019). Future large downstream river channel geomorphic adjustments: A case hydropower dams impact global freshwater study of the three gorges. River Research and Applications, megafauna. Scientific Reports, 9(1), 1–10. https://doi. 34(10), 1315–1327. https://doi.org/10.1002/rra.3372 org/10.1038/s41598-019-54980-8

Journal

Geology Ecology and Landscapes – Taylor & Francis

Published: Oct 6, 2022

Keywords: Siltation; channel avulsion; embankment; revetment

There are no references for this article.