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Application of GIS techniques to understand the geomorphometric characteristics of a tropical watershed in South India

Application of GIS techniques to understand the geomorphometric characteristics of a tropical... GEOLOGY, ECOLOGY, AND LANDSCAPES INWASCON https://doi.org/10.1080/24749508.2021.1952749 RESEARCH ARTICLE Application of GIS techniques to understand the geomorphometric characteristics of a tropical watershed in South India a b c Sreelakshmy M , Dhanusree M and Thangamani V a b Department of Geography, Nirmala College for Women, Coimbatore, India; Research Scholar, Centre for Water Resource Management, University of Madras, Chennai, India; Department of Geography, School of Earth and Atmospheric Sciences, Madurai Kamaraj University, Madurai, India ABSTRACT ARTICLE HISTORY Received 22 April 2021 Identifying and protecting natural resources is a meaningful way forward for achieving sustain- Accepted 4 July 2021 able development. Since water is a precious natural resource that is being depleted faster than it is recharged, there is an urgent need to evaluate and monitor this resource. Watershed-based KEYWORDS studies are gaining momentum, while studying about the natural resources. The purpose of Basin geometry; linear/ this study is to analyze the morphometric characteristics of a watershed. Numerous morpho- aerial/ relief aspects; SRTM metric parameters have been devised by various scholars to measure the drainage basin DEM; geo-spatial techniques; characteristics quantitatively. The methodology of this study is to make use of remote sensing Vannathangarai watershed and GIS techniques to analyze the drainage morphometry of Vannathangarai watershed in Tamil Nadu, India. The study has identified that the watershed has a low runoff and slow infiltration, thus pointing toward a probability of flooding. The study also revealed that the basin is well drained, basin where the surface is lowered by erosion. 1. Introduction in the preservation and management of natural Geomorphometry is the application of quantitative resources, especially water resources. Assessing the techniques to analyze the land surface characteristics. quantitative morphometric characteristics of the Geomorphometry is the science of quantitative land- drainage basin produces knowledge about the nat- surface analysis (Pike, 1961, 2000). It is an interdisci- ure of the rocks; this, consequently, renders the plinary field that makes use of the techniques in permeability index of the rocks and aids in under- Mathematics and Computer science into the broad standing the yield of the drainage basin (Singh field of Geography. It is widely applied to disciplines et al., 2013) like hydrology, climatology, meteorology, and drai- Generally, a morphometric study is carried out nage Morphometry. with the help of specific quantitative parameters, A drainage basin is an area that is drained by a river which are grouped into linear (uni-dimensional), and its tributaries. Drainage basins are considered as areal (two dimensional), and relief (three dimen- physical entities, which consist of many watersheds. sional) aspects (Melton, 1957; Horton, 1945; Miller, Every river consists of numerous watersheds, and all 1953; Strahler, 1964). The nature of a drainage these watersheds form a drainage basin. As drainage basin is characterized by its relief, lithology, and basins form discrete landforms capable of statistical the climatic factors that act upon the terrain. analyses, myriad means of quantitative and qualitative Earlier all these quantifications were done manually methodologies exist. Morphometric analysis is quan- with the help of topographical maps, but now with titative, which involves numerical variables recovered the advent of Satellite images, the extraction of from topographic maps or satellite images. quantitative parameters of morphometry is done The morphometric analysis provides insight into systematically, precisely and effortlessly (Aparna the geohydrological characteristics of that particular et al., 2015; Ayele et al., 2017; Javed et al., 2009; terrain and enables identification of surface runoff, Kabite & Gessesse, 2018; Kulkarni, 2013; Pande & infiltration, erosion, sediment movements etc. The Moharir, 2017; Prakash et al., 2016; Rai et al., 2017; relation between the drainage morphometric para- Singh et al., 2014). The characteristics of the basin meters and its underlying geological, hydrological are beneficial in determining the hydro- and geomorphological relationship has been estab- sedimentary flow regimes. The present study aims lished for a long time by eminent geologists and to characterize the geomorhometric properties of geomorphologists (Strahler, 1952) This in turn aids the Vannathangarai watershed. CONTACT Sreelakshmy M sreelumohan2010@gmail.com Department of Geography, Nirmala College for Women, Red Fields, Coimbatore 641018, India © 2021 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 S. M ET AL. shadow region of the Western Ghats above the 2. Study area Palakkad Gap(Figure 1) The current study was carried out in the The area of the Vanathangarai watershed accounts Vannathangarai watershed of River Noyyal basin. for 1512 square kilometers. This watershed is the most The Noyyal is a branch of river Cauveri and originates thickly populated area of the whole Noyyal basin. from the Velliangiri Hills in the Coimbatore district of A major metropolitan center in Tamil Nadu, Tamil Nadu. This watershed forms at the headwaters Coimbatore, which is the second-biggest urban center of River Noyyal and includes part of Coimbatore and in the state after the capital city, lies inside the Tiruppur districts. The river travels through the cities watershed. Many parts of Tirupur district, which is of Coimbatore and Tiruppur and meets the Cauveri in a major cotton-growing hub and possesses lots of Karur district. The “Noyyal” is a sacred river in Tamil cotton dyeing units and cotton textile mills, are history. included in this watershed. Coimbatore district occupies a significant share of The area is marked by the presence of shallow the region, while only marginal areas of Tirupur dis- weathered/buried pediplain, ridge type structural trict is confined to this watershed. It is bordered by hills, shallow and moderately buried pediment, shal- Palakkad district of Kerala to the west, Nilgiris district low floodplains, etc. Almost the whole eastern half of to the North, Tirupur to the north and east, and parts the area is filled by shallow weathered/buried pedi- of Coimbatore district to the south. This watershed is plain. Quartz vein, granitoid gneiss, conglomerate of paramount importance as the headwaters of the sandstone, granite, ultrabasic rocks, and carbonatites river Noyyal lies inside this. The western portion of are significant geological features seen in the region. the watershed embraces a small portion of the rain There are different varieties of soil seen in the study Figure 1. Location map of the study area. GEOLOGY, ECOLOGY, AND LANDSCAPES 3 area. Red clayey, red gravel loam, calcareous gravel Horton’s (1932) method, which is the quotient of loam and gravel clay are the dominant soil types seen area and basin length. To find out the basin slope, in the region. Chorley et al. (1957) has expressed the method of Lemniscate’s (K). The value ofK for this particular watershed is 4.65, and it shows that the watershed 3. Database covers the most significant share within the region of its origin with more streams of higher-order within The analysis was done with the help of SRTM (Shuttle the watershed (Table 2). Radar Topographic Mission) DEM (Digital Elevation Model) data with a 30 m spatial resolution satellite image obtained from the USGS earth explorer website. 5.3. Linear parameters Grohmann et al. (2007) have opined that the usage of Linear parameters consist of the one-dimensional SRTM data and GIS techniques enables fast, precise, characteristics, including all the linear features of the and cost-effective analysis of morphometric drainage basin, which are as follows: characteristics. 5.3.1.. Stream order 4. Methodology In a drainage basin or a watershed, stream network is the collection of stream segments (Horton, 1945; The watershed boundary is extracted automatically Strahler, 1957). The arrangement of stream in the from SRTM DEM data. The inputs needed for extrac- hierarchical order has been allotted a series of num- tion are DEM and pour point. The SRTM data was bers according to their position (Asfaw & Workineh, also used to generate the slope, terrain details, in 2019). Generally, the most significant, branched, chief, ArcGIS 10.3. The morphometric characters were cal- or stem stream is designated as order one and the culated using the spatial analysis tool and already smaller tributary streams of increasingly higher orders derived mathematical formula (Table 1). (Gravelius, 1914). According to Strahler (1964), there are no tributaries for first-order streams. All the tri- 5. Results and discussion butaries of the second-order streams belong to the first-order streams. The next higher-order streams 5.1. Drainage pattern possess the tributaries of all the succeeding lower- Drainage patterns are classified based on the form and order streams, continuing so on till any number of texture of the streams, in accordance with the slope higher-order streams. An area where erosion is still and structure of the surface. The local topography of prominent will have a larger number of stream seg- the terrain and its subsurface geology influences the ments in a particular order. In the present study, five shape and patterns of the river. The drainage pattern orders of streams are identified (Figure 2). of the current watershed is identified as dendritic, The total number of streams identified in the which has the tributaries joining the mainstream at watershed is 845, out of which 500 streams belong to acute angles. Dendritic pattern is the most commonly first order, 245-second order, 87 third order, 10-fourth occurring pattern, where the tributaries of the main -order, and 3-fifth-order. Generally, more water is river join together in shape, similar to the twigs of generated in a watershed, which has a maximum num- a tree (Guilbert & Zhang, 2012). ber of lower-order streams. There is an inverse rela- tionship between the stream number and stream order, which implies that the stream frequency 5.2. Basin geometry decreases with an increase in the stream order The Vannathangarai watershed constitute an area of (Figure 3). It is also noted that the highest frequency 1512.82 km with a perimeter of 194.63 km. According is noticeable among the streams of the first order. to Schumm (1956), the relative perimeter (P ) of the basin is the ratio between the area and the perimeter of 5.3.2.. Stream length the watershed, and here the value is 7.77. The length of According to Horton (1945), the entire lengths of the basin (L ) is 83.95 km. The length of the main a given order are the result of the quantity of streams channel (L ) is found to be 73. 45 km, which is the and lengths per stream. Where the bedrock is less most extended channel from the source point of the pervious, an enormous number of streams of minor watershed boundary. For many basins, the relation lengths are developed, while if the bedrock is porous, between the length of the stream and the area of the small quantities of comparatively larger streams are basin is associated to a function, known as the Length developed in a relatively well-drained watershed or area relation (L ), developed by Hack (1957), and its basin (Narasimhan & Vasanthamohan, 2011). ar value for the watershed is 113.24. The mean width of Typically, the lower order streams have the maximal the basin is 18.01 km and is computed based on stream length, and it declines with an increase in 4 S. M ET AL. Table 1. Morphometric characteristics of Vannathangarai watershed. Sl no Morphometric Parameters Formula/Definition/ method Reference Basin Geometry 1 Drainage basin area (A) Km GIS analysis - 2 Drainage basin perimeter(P) km GIS analysis - 3 Relative Perimeter(P ) Pr = A/P Schumm (1956) 4 Basin Length(L ) km GIS analysis Schumm (1956) 0.6 5 Length Area Relation (L ) Lar = 1.4*A Hack (1957) ar 6 Mean Basin Width(W ) km Wb = A/Lb Horton (1932) 7 Leminiscate’s (K) K = L /A Chorley et al. (1957) 0.5 8 Compactness Co-efficient( C ) Cc = 0.2821*P/A Gravelius (1914) 9 Length of main channel(L ) km GIS analysis - Linear Aspects 10 Stream Order Hierarchical order (GIS analysis) Strahler (1964) 11 Stream Length(L ) Length of the streams (GIS analysis) Horton (1945) 12 Mean Stream Length (L ) km Lsm = L */N *** Horton (1945) sm u u 13 Stream Length Ratio(R ) R = L /L -1, Horton (1945) l l u u 14 Bifurcation ratio(R ) R = N /N +1, Schumm (1956) b b u u 15 Mean Bifurcation ratio(R ) R = mean of bifurcation ratio of all orders Schumm (1956) bm bm Aerial Aspects 16 Stream Frequency(F ) Fs = N**/A Horton (1945) 17 Drainage density(D ) km/km Dd = L/A, Horton (1945) 18 Drainage Intensity(D ) Di = F /D Faniran (1968) i s d 19 Infiltration ratio /number(I ) If = F *D Faniran (1968) f s d 20 Texture Ratio(T) T = N/P Horton (1945) 21 Form Factor(R ) R = A/L Horton (1932) f f b 22 Circulatory Ratio(R ) R = 4πA/P Miller (1953) c c 23 Elongation Ratio(R ) Re = 2√(A/π)/L Schumm (1956) e b 24 Rho Coefficient (C ) C = R /R Horton (1945) rh rh l b 25 Shape Index(S ) S = 1/F Horton (1932) w w s 26 Shape factor(S ) S = L /A Horton (1932) f f b 27 Length of overland flow( L ) km L = 1/2D Horton (1945) of of d 28 Fitness ratio(R ) R = L /P Melton (1957) f f c 29 Wandering ratio (R ) R = L /L Smart & Surkan (1967) w w c b 30 Constant of channel maintenance(C) C = 1/D Horton (1945) Relief aspects 31 Maximum elevation (M ) m GIS analysis - 32 Minimum elevation (M )m GIS analysis - 33 Basin Relief(B ) M -M Schumm (1956) h a i 34 Relative relief(R ) B /P Horton (1945) r h 35 Relief Ratio(R ) R = B /L Schumm (1956) h h h b 36 Ruggedness Number(R ) R = B *D Strahler (1958) n n h d 37 Ruggedness Index(R ) R = D *(R /1000) Schumm (1956) i i d r 0.5 39 Melton’s Ruggedness Number (M ) (M -M )/A Melton (1965) rn a i 40 Watershed/ basin Slope(S ) S = H/L Miller (1953) b b b 41 Elevation at Source(E ) GIS analysis 42 Elevation at Mouth (E ) GIS analysis 43 Gradient Ratio(R ) R = (E -E )/L Sreedevi et al. (2005) g g s m b 44 Total Basin relief(H) m H = M -E Strahler (1952) a m 45 Total Contour length (C ) km GIS analysis - tl 46 Contour Interval (C ) m GIS analysis - 47 Average slope(S)% S = (M *(C /H)/(10*A) Wentworth (1930) a tl 48 Mean slope of the basin (S ) % S = (C *C )/A Chorley (1969) m m tl i 49 Coarse Ratio(C ) C = B *D Chorley (1966) r r h d Source: Compiled by the author) L * = Total length of stream, N** = Total number of streams, N *** = Total number of stream segments of order “U.” u u Table 2. Basin geometry parameters. Table 3. Linear parameters of the Vannathangarai watershed. Sl no Basin geometry Parameters Result Stream Number of Bifurcation Stream 1 Drainage basin area (A) Km 1512.82 order streams Length Ratio length 2 Drainage basin perimeter(P) km 194.63 Ratio Mean stream 3 Relative Perimeter(P ) 7.77 Length 4 Basin Length(L ) km 83.95 1 500 702.28 2.04 0.50 1.40 5 Length Area Relation (L ) 113.24 ar 2 245 351.18 2.82 0.29 1.43 6 Mean Basin Width(W ) km 18.01 3 87 101.73 8.7 1.14 1.16 7 Leminiscate’s (K) 4.65 4 10 116.03 3.33 0.31 11.6 8 Compactness Co-efficient( C ) 1.41 5 3 36.40 0 0 12.13 9 Length of main channel(L ) km 73.45 Source: Compiled by the author stream order. Fewer lengths of channels are more evident in areas with a steep slope, and longer streams is estimated to be 1307.62 km. Plotting the number of indicate plain regions where the slope is gentle. The streams and stream order on the logarithmic scale length of river channels in any watershed declines with reveals an inversely proportional relationship between arise in stream orders. The total length of the streams them (Figure 4) GEOLOGY, ECOLOGY, AND LANDSCAPES 5 Figure 2. Drainage map. (Source: SRTM-DEM) Figure 3. Interrelation of stream order with the number of streams. Figure 4. Interrelationship between stream order and stream length. 6 S. M ET AL. 5.3.3. Mean stream length(L ) ratio will be higher if the basin is elongated and is sm L is derived by dividing the entire length of the lower if the basin is circular. A higher ratio is also an sm channel by the total number of streams. There is indicator of the potentiality for flash floods. The a positive relationship between the L and the size first, second, and fourth-order streams show a lesser sm and surface features of the watershed. According to ratio, below 3.5, while the third-order streams possess Strahler (1964), the size of the stream networks and a higher bifurcation ratio, which is close to 8.7 (Table its related features has a significant relation with 3). The R for the watershed is estimated as 3.37. The bm the Lsm. There is a high association between the value indicates that the streams are well-formed on an mean stream length, runoff, and the erosional almost uniform topography, where its geologic struc- phase of the watershed. If the L is low, it shows ture least influences the pattern of drainage. (Asfaw & sm a higher surface flow and erosion (Gopinath Girish Workineh, 2019) . et al., 2016). The L of the watershed ranges sm between 1.4 and 12.13. It is shortest for the first- 5.4. Aerial parameters order streams and longest for the fifth-order stream (Figure 5). Aerial parameters or basin parameters indicate the whole area protruded upon a plane providing the 5.3.4. Stream length ratio (R ) overland flow to the stream network of a particular The proportion between the L of one order with the order and encompasses all the channel networks of its sm following lower-order stream is itsR . It changes with lower order. the variations in slope and terrain features, runoff, and erosional phase of the watershed (Sreedevi et al., 5.4.1. Drainage density(D ) 2005). In the watershed, the R value varies between 0 l D is the stream development level inside a basin and and 1.14 except for the third-order streams where it is is derived by finding out the mean length of streams slightly higher (Table 3). within the watershed per unit area (Horton, 1932). D provides a quantitative evaluation of the surface runoff 5.3.5. Bifurcation ratio(R ) capability and dissection of the landscape (Chorley, The ratio of the number of streams of a particular 1969). Horton (1945) explained D as a tool to esti- order to the number of streams of the succeeding mate the measured traveling time of water in the total higher order is called the R (Strahler, 1964). This drainage basin by evaluating the closeness of the describes the branching pattern of the drainage net- stream network. Areas that possess scanty vegetation work. If the value ranges from 0.6 to 2.9, it shows that generally show a higherD and have significant flood the watershed is included under the standard category. peaks. Areas with less pervious rocks and high relief For drainage basins where the geologic structure does show a higher D compared to places with highly not distort the drainage patterns, the Rb value ranges resistant and permeable surfaces, which show a low between 3.0 and 5.0. (Kale & Gupta, 2001; Strahler, profile of drainage density (Gopinath Girish et al., 1957). If the R value is greater than 10, it leads to the 2016). According to Langbein (1947), the D of b d formation of elongated narrow drainage basins, which humid regions ranges between 0.55 and 2.09 km . The are formed due to prolonged structural control and D of the current watershed is 1.72, which implies that erodible rocks of that basin (Chorley et al., 1984). The this is a relatively well-drained basin of a sub-humid R also indicates the pattern of the drainage basin. The region (Table 4) (Figure 6). Figure 5. Interrelationship between stream order and Lsm. GEOLOGY, ECOLOGY, AND LANDSCAPES 7 5.4.2. Drainage intensity(Di) Table 4. Aerial parameters. Sl no Aerial Parameters Result The proportion of the F to D is termed as drainage s d 1 Stream Frequency(F ) 0.55 intensity (Faniran, 1968). This study has identified 2 Drainage density(D ) km/km 1.72 a very low D of 0.32, which suggests that the D and i d 3 Drainage Intensity(D ) 0.32 4 Infiltration ratio /number(I ) 0.96 F have a meager impact, intending that denudation f 5 Texture Ratio(T) 4.34 agents have reduced the terrain. This is an indication 6 Form Factor(R ) 0.21 that the movement of the surface runoff is prolonged, 7 Circulatory Ratio(R ) 0.50 8 Elongation Ratio(R ) 0.52 making the area vulnerable to easy flooding.(Pareta & 9 Rho Coefficient (C ) 0.13 rh Pareta, 2011) (Table 4). 10 Shape Index(S ) 1.79 11 Shape factor(S ) 4.65 12 Length of overland flow( L ) km 0.86 of 5.4.3. Infiltration ratio(I ) 13 Fitness ratio(R ) 0.377 f f 14 Wandering ratio (R ) 0.874 Faniran (1968) has propounded another technique, 15 Constant of channel maintenance(C) 0.57 namely the infiltration ratio, which is the outcome of the D and F . Pareta and Pareta (2011) suggested that d s the infiltration number has an antagonistic relation- length of the streams and Rb (Horton, 1945). The ship with the infiltration capacity and a positive rela- C of the Vannathangarai watershed is calculated as rh tion with the runoff. The current study has identified 0.13, signaling that it has more extensive hydrologic that the infiltration number is 0.96, which implies storage during flood periods (Table 4). a lower surface runoff and lesser infiltration capacity making the area more susceptible to flooding (Table 4). 5.4.5. Stream frequency (F ) F is the number of streams per unit area. Higher Fs 5.4.4. Rho coefficient(C ) indicates more surface runoff, low infiltration capa- rh C is influenced by the climate, geology, geomorphol- city, sparse vegetation, high relief, and steep slope rh ogy of the terrain along with the biological and anthro- (Horton, 1945). The values of D and F of different d s pological factors. It is a significant parameter related to drainage basins with varying lengths cannot be asso- the D and geomorphic development of a watershed, ciated as they differ in their size. Since the origin of which enables the estimation of the storage potential a stream is based on the type of vegetation cover, of the rivers; thus it helps to determine the ultimate structure of rocks, amount of precipitation, and the stage of drainage development in a given watershed; in permeability of the soil, the F acts as an indicator of other words, it is defined as the ratio between the the evolution of the landscape of that region. The F of Figure 6. Drainage density map. (Source: SRTM-DEM) 8 S. M ET AL. Figure7. Slope map. (Source: SRTM-DEM) Figure 8. Aspect map. (Source: SRTM-DEM) the Vannathangarai watershed is 0.55. A positive cor- 5.4.6. Texture ratio(T) relation exists between the D and F ; with more The value of T is derived by estimating the ratio d s streams, the density also increases(Table 4). between the total number of stream segments and GEOLOGY, ECOLOGY, AND LANDSCAPES 9 Figure 9. Elevation map. (Source: SRTM-DEM) the perimeter of the watershed. Horton (1945) has 5.4.8. Circulatory ratio (R ) defined the texture ratio as the product of F and D The circulatory ratio is the proportion of the s d and opined that it is a crucial factor. Smith (1950) has watershed area and the area of the circle of perimeter done a detailed study about the texture ratio and of the watershed (Miller, 1953). The low, medium, and pointed out that it is dependent on numerous natural high R indicate the youth, middle, and old stages of characters like the amount of precipitation, types of the stream development (Narasimhan & soil, the density of vegetation, infiltration capacity, Vasanthamohan, 2011). The circulatory ratio of this relief, and the stage of geomorphic development. T is watershed is estimated to be 0.50, which, according to considered an essential parameter that shows the Miller (1953), symbolizes the basin’s elongated shape relative spacing of the drainage networks of any with highly permeable, analogous, geologic materials. watershed. If T’s value is below two, it indicates (Table 4). a very coarse texture; likely, a value between two to four is coarse, four to six is moderate, six to eight is 5.4.9. Elongation ratio(R ) fine, and above 8 is very fine drainage textures e The R value usually ranges from 0.6 to 1 over a broad (Smith, 1950). The T value of the Vannathangarai e climatic and geologic type; If R is near to 1, relief is watershed is 4.34, which denotes a moderate texture e generally very low. Areas with high relief and steep (Table 4). slope possess R values ranging between 0.6 and 0.8 (Strahler, 1964). These values can be arranged into 5.4.7. Form factor (R ) three classes; Circular (above 0.9), oval (0.9–0.8), and The R is defined as the flow intensity of a watershed less elongated (below 0.7) (Narasimhan & for a specific area (Horton, 1932). R indicates the Vasanthamohan, 2011). Efficiency in the runoff dis- maximum flow and duration; higher form factor sug- charge is more for a circulatory basin than for an gests maximum flow during a short span (Gopinath elongated one (CS Singh & Singh, 1973; Gajbhiye Girish et al., 2016). It is presumed that, R value of 0.78 et al., 2014). A watershed which has high runoff with is indicative of a perfectly circular basin. (Gopinath low infiltration capacity, will always have a higher R . Girish et al., 2016; Harinath & Raghu, 2013) The (Gopinath Girish et al., 2016). According to Chorley present study identifies the R of the basin as 0.21, et al. (1984), the areas with high relief possess R which suggests that the drainage basin is elongated around 0.6, and if it is near to 1, it implies a very low (Table 4). 10 S. M ET AL. relief. The R of the Vannathangarai is 0.52, thus 5.5. Relief parameters revealing a less elongated, low land region (Table 4). The relief parameters are connected with three- dimensional features like volume, altitude, etc., to 5.4.10. Shape index(S ) and shape factor(S ) w f investigate the various geo-hydrological characteris- The S is the reciprocal of the R and is w f tics. The maximum elevation of the watershed is a dimensionless property (Soni, 2016), and the shape 1928 m, and the lowest point is 301 m. The elevation index for the watershed is 1.79. Horton (1932) has at the river’s source is estimated at 1254 m, and its defined the S as the ratio of the square of L to the f b mouth is 304 m (Table 5). area of the basin. The S assists in interpreting the shape distortion of a watershed (Yadav et al., 2014). 5.5.1. Basin relief(B ) and total basin relief(H) The S for the Vannathangarai is 4.65(Table 4). Basin relief is expressed as the maximum upward distance between the lowest and highest point of the 5.4.11. Length of overland flow(L ) of area. Hadley and Schumm (1956) opined that basin Horton (1945) considered the L an essential tool to of relief is the causative factor for the stream gradient and analyze the development of physiography and the plays an influential role in determining the flood char- drainage basin and defined it as the measure of water acteristics and volume of materials that can be carried over the terrain before it gets collected into brooks. L of along. Sreedevi et al. (2009) identified this as an inte- is determined by the nature of rock, relief, and climatic gral factor in getting the basin’s denudation features. condition, vegetation cover, permeability, duration of Lower B is an indication of minimal surface runoff, erosion (Schumm, 1956). The current study reveals debris movement, and spreading of water basin while that the L of Vannathangarai is 0.86 km. A more of the higher values indicate enhanced flood peaks significant value of the L designates a more extended of (Gopinath Girish et al., 2016). The maximum eleva- flow path with gentle slopes (Narasimhan & tion in the watershed is noted as 1928 m, which is seen Vasanthamohan, 2011) (Table 4). at the western side of the watershed, while the lowest point is having an elevation of 301 m (Figure 9). Thus 5.4.12. Fitness ratio (R ) and wandering ratio(R ) f w the basin relief obtained for the watershed is 1627 m. The topographic fitness is measured using its fitness Thomas et al. (2010) presumed that river basins with ratio, which according to Melton (1957), is the ratio of mountain-plain front generally have higher basin the L to the perimeter of the watershed and is 0.37 for c relief than rivers with plateau-plain front. Strahler the Vannathangarai watershed. The proportion of the (1952) has defined the total basin relief as the differ - L to L is given by its wandering ratio (Smart & c b ence between the highest elevation of the watershed Surkan, 1967), and its value for the basin is 0.874 and the maximum elevation at the mouth. The (Table 4). Vannathangarai watershed has an H value of 1624 m (Table 5). 5.4.13. Compactness co-efficient(C ) Another crucial parameter is the C , which is the ratio 5.5.2. Relief ratio(R ) of the perimeter of the basin to the circumference of R is described as the ratio between the total reliefs to the circular area (Gravelius, 1914). The C value for the length of the principal drainage line. It is an a perfect circle is one and rises with the increase in L and hence it is independent of the size of the Table 5. Relief parameters. watershed. The value of the compactness coefficient Sl no Relief Parameters Result for this watershed is 1.41, which states that the shape is 1 Maximum elevation (M ) m 1928 more elongated (Table 4). 2 Minimum elevation (M )m 301 3 Basin Relief(B ) 1627 4 Relative relief(R ) 8.35 5 Relief Ratio(R ) 19.37 5.4.14. Constant of channel maintenance (C) 6 Ruggedness Number(R ) 2812.64 This concept was introduced by Schumm (1956) and 7 Ruggedness Index(R ) 2.81 is the reverse of D . C is defined as the area needed to 8 Melton’s Ruggedness Number (M ) 41.84 rn 9 Watershed/ basin Slope(S ) 19.37 sustain one vertical kilometer of stream (Dikpal et al., 10 Elevation at Source(E ) 1254 2017). C is highly dependent on the geology, porosity, 11 Elevation at Mouth (E ) 304 12 Gradient Ratio(R ) 19.34 climatic condition, type of vegetation, duration of 13 Total Basin relief(H) m 1624 erosion, and the terrain of the area. A higher C value 14 Total Contour length (C ) km 5393.453 tl 15 Contour Interval (C ) m 20 indicates rocks with more permeability (Narasimhan i 16 Average slope(S)% 0.42 & Vasanthamohan, 2011). The more the value of the 17 Mean slope of the basin (S ) % 0.71% 18 Coarse Ratio(C ) 2.81 channel maintenance, the more is its permeability. The constant for the current study is inferred to be 0.57, which indicates lower runoff (Table 4). GEOLOGY, ECOLOGY, AND LANDSCAPES 11 indication of runoff and severity of the erosion pro- 5.5.7. Coarse ratio(C ) cess, and it evaluates the steepness of a watershed Coarse ratio is described as the difference between the (Phani, 2014). There is a negative correlation with the maximum and minimum levels of the watershed R and drainage area and its size (Gottschalk, 1964) divided by its perimeter (Melton, 1957). C is an h r (Table 5). expression of the relationship between the B and D h d (Singh et al., 2014). The C for the Vannathangarai watershed is estimated at 2.81. Chorley (1966) stated 5.5.3. Relative relief(R ) that, coarse ratio, will be less at the youthful stage, R depicts the exact change of elevation in a unit area increases gradually, and will be the highest at the concerning its local base level. R can represent the mature stage and starts to decline, by the end of its terrain features without considering the sea level (S life cycle (Table 5). Singh & Dubey, 1994). It is termed as the amplitude of local relief. The relative relief of the Vannathangarai watershed is 8.35(Table 5). 6. Conclusion Morphometry is the science that studies the quantita- 5.5.4. Ruggedness number(R ), ruggedness tive examination of the drainage basin, which provides index(R ), Melton’s ruggedness number(M ) i rn an in-depth insight into the relief and topography of Strahler (1958) explained the Rn as the product of B the drainage surface. The Vannathangarai watershed and D . Selvan et al. (2011) considered it as a measure lies at the headwaters of river Noyyal. The watershed of the unevenness of the surface. The ruggedness has a generally low slope, with hills seen only along the number for the watershed is 2812.64. Ruggedness western fringes, and the remaining area is more or less index is a measure of the combined effect of the local an even plain. The streams of the watershed, which has terrain and the magnitude of D and other geographic 2 2 an area of 1512.82 km and perimeter of 194.63 km , parameters like rainfall, slope, denudation, nature of follow the dendritic pattern of drainage. The the soil, etc.(Chorley, 1969). The ruggedness index for watershed consists of five orders of stream, with this watershed is estimated at 2.81. Melton’s rugged- more than 800 streams, where more streams are seen ness number is an index of slope that gives in the lower order. The length of lower-order streams a specialized illustration of relief ruggedness within is higher than that of the next higher-order streams, the watershed (Melton, 1965). The M for the rn indicating less surface permeability. Analyzing the watershed is 41.84 (Table 5). bifurcation ratio makes it clear that the streams are developed over a homogeneous surface for almost the 5.5.5. Gradient ratio(R ) g entire watershed except for few areas at the western Sreedevi et al. (2009) devised the gradient ratio as hill reaches. a tool to evaluate the runoff volume. R is an expres- g The drainage density indicates that the watershed is sion of channel undulation that assists in assessing the well-drained and belongs to a sub-humid region. The runoff volume (Sreedevi et al., 2005). The gradient drainage intensity points out that the surface is low- ratio for the watershed is 19.34. A higher R indicates g ered considerably, and it takes a long time to remove a steep slope with high runoff, while lower runoff that runoff, indicating a probable chance of flooding. indicates lesser runoff and higher infiltration( Table 5). The Rho coefficient shows that the watershed has higher hydrologic storage during flood periods. Infiltration ratio indicates a low runoff and lesser 5.5.6. Slope analysis infiltration capacity making the area more susceptible Slope is an essential factor as it determines the infiltra - to flooding. The watershed is elongated in shape and tion and runoff; Infiltration capacity and slope are has a medium texture. A more significant value of the inversely related (Mahala, 2020). Most of the study L symbolizes a higher flow path with gentle slopes. area has a relatively low land without much undula- of Analysis of all these parameters enables the identifica - tion (Figure 7 & 8). Beside the left bank side of the tion of the potential groundwater zones as the source river channel, the slope is towards the south, and along of water is altered by the structural, lithological, and the right bank side, it is towards the north. Near the geomorphological set up of an area (Schumm, 1956). western fringes of the watershed, steep terrain is As the watershed is a densely populated region with observed, which is a part of the Western Ghats hill numerous industries and more number of agricultural ranges. Wentworth (1930) suggested that the erodibil- activities, it is essential to identify the prospects for ity can be estimated and can be compared with its groundwater and to safeguard the existing water slope. Higher the slope, higher is the erosion. The resources. The study is highly beneficial in this con- average slope of the area is 0.42%, and according to text, and for this, the geospatial technologies are path- Chorley (1969), the mean slope of the basin is 0.71% breakers providing easy and accurate information. (Table 5). 12 S. M ET AL. RS and GIS perspective. Applied Water Science, 4(1), Future scope of research 51–61. https://doi.org/10.1007/s13201-013-0129-7 There is a paradigm shift in geographical research over the Gopinath Girish, A. G., Nair, A. G. K., & Swetha, T. V. last few years; from political or administrative boundary- (2016). Watershed prioritization based on morphometric based studies now the emphasis is on natural boundary- analysis coupled with multi-criteria decision making. based studies; especially for natural resource assessment, Arabian Journal of Geosciences, 9(2), 129. https://doi. watershed boundaries are preferred. 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Geocarto International, 29(8), 895–914. https:// management using remote sensing and GIS techniques. doi.org/10.1080/10106049.2013.868043 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geology Ecology and Landscapes Taylor & Francis

Application of GIS techniques to understand the geomorphometric characteristics of a tropical watershed in South India

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GEOLOGY, ECOLOGY, AND LANDSCAPES INWASCON https://doi.org/10.1080/24749508.2021.1952749 RESEARCH ARTICLE Application of GIS techniques to understand the geomorphometric characteristics of a tropical watershed in South India a b c Sreelakshmy M , Dhanusree M and Thangamani V a b Department of Geography, Nirmala College for Women, Coimbatore, India; Research Scholar, Centre for Water Resource Management, University of Madras, Chennai, India; Department of Geography, School of Earth and Atmospheric Sciences, Madurai Kamaraj University, Madurai, India ABSTRACT ARTICLE HISTORY Received 22 April 2021 Identifying and protecting natural resources is a meaningful way forward for achieving sustain- Accepted 4 July 2021 able development. Since water is a precious natural resource that is being depleted faster than it is recharged, there is an urgent need to evaluate and monitor this resource. Watershed-based KEYWORDS studies are gaining momentum, while studying about the natural resources. The purpose of Basin geometry; linear/ this study is to analyze the morphometric characteristics of a watershed. Numerous morpho- aerial/ relief aspects; SRTM metric parameters have been devised by various scholars to measure the drainage basin DEM; geo-spatial techniques; characteristics quantitatively. The methodology of this study is to make use of remote sensing Vannathangarai watershed and GIS techniques to analyze the drainage morphometry of Vannathangarai watershed in Tamil Nadu, India. The study has identified that the watershed has a low runoff and slow infiltration, thus pointing toward a probability of flooding. The study also revealed that the basin is well drained, basin where the surface is lowered by erosion. 1. Introduction in the preservation and management of natural Geomorphometry is the application of quantitative resources, especially water resources. Assessing the techniques to analyze the land surface characteristics. quantitative morphometric characteristics of the Geomorphometry is the science of quantitative land- drainage basin produces knowledge about the nat- surface analysis (Pike, 1961, 2000). It is an interdisci- ure of the rocks; this, consequently, renders the plinary field that makes use of the techniques in permeability index of the rocks and aids in under- Mathematics and Computer science into the broad standing the yield of the drainage basin (Singh field of Geography. It is widely applied to disciplines et al., 2013) like hydrology, climatology, meteorology, and drai- Generally, a morphometric study is carried out nage Morphometry. with the help of specific quantitative parameters, A drainage basin is an area that is drained by a river which are grouped into linear (uni-dimensional), and its tributaries. Drainage basins are considered as areal (two dimensional), and relief (three dimen- physical entities, which consist of many watersheds. sional) aspects (Melton, 1957; Horton, 1945; Miller, Every river consists of numerous watersheds, and all 1953; Strahler, 1964). The nature of a drainage these watersheds form a drainage basin. As drainage basin is characterized by its relief, lithology, and basins form discrete landforms capable of statistical the climatic factors that act upon the terrain. analyses, myriad means of quantitative and qualitative Earlier all these quantifications were done manually methodologies exist. Morphometric analysis is quan- with the help of topographical maps, but now with titative, which involves numerical variables recovered the advent of Satellite images, the extraction of from topographic maps or satellite images. quantitative parameters of morphometry is done The morphometric analysis provides insight into systematically, precisely and effortlessly (Aparna the geohydrological characteristics of that particular et al., 2015; Ayele et al., 2017; Javed et al., 2009; terrain and enables identification of surface runoff, Kabite & Gessesse, 2018; Kulkarni, 2013; Pande & infiltration, erosion, sediment movements etc. The Moharir, 2017; Prakash et al., 2016; Rai et al., 2017; relation between the drainage morphometric para- Singh et al., 2014). The characteristics of the basin meters and its underlying geological, hydrological are beneficial in determining the hydro- and geomorphological relationship has been estab- sedimentary flow regimes. The present study aims lished for a long time by eminent geologists and to characterize the geomorhometric properties of geomorphologists (Strahler, 1952) This in turn aids the Vannathangarai watershed. CONTACT Sreelakshmy M sreelumohan2010@gmail.com Department of Geography, Nirmala College for Women, Red Fields, Coimbatore 641018, India © 2021 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 S. M ET AL. shadow region of the Western Ghats above the 2. Study area Palakkad Gap(Figure 1) The current study was carried out in the The area of the Vanathangarai watershed accounts Vannathangarai watershed of River Noyyal basin. for 1512 square kilometers. This watershed is the most The Noyyal is a branch of river Cauveri and originates thickly populated area of the whole Noyyal basin. from the Velliangiri Hills in the Coimbatore district of A major metropolitan center in Tamil Nadu, Tamil Nadu. This watershed forms at the headwaters Coimbatore, which is the second-biggest urban center of River Noyyal and includes part of Coimbatore and in the state after the capital city, lies inside the Tiruppur districts. The river travels through the cities watershed. Many parts of Tirupur district, which is of Coimbatore and Tiruppur and meets the Cauveri in a major cotton-growing hub and possesses lots of Karur district. The “Noyyal” is a sacred river in Tamil cotton dyeing units and cotton textile mills, are history. included in this watershed. Coimbatore district occupies a significant share of The area is marked by the presence of shallow the region, while only marginal areas of Tirupur dis- weathered/buried pediplain, ridge type structural trict is confined to this watershed. It is bordered by hills, shallow and moderately buried pediment, shal- Palakkad district of Kerala to the west, Nilgiris district low floodplains, etc. Almost the whole eastern half of to the North, Tirupur to the north and east, and parts the area is filled by shallow weathered/buried pedi- of Coimbatore district to the south. This watershed is plain. Quartz vein, granitoid gneiss, conglomerate of paramount importance as the headwaters of the sandstone, granite, ultrabasic rocks, and carbonatites river Noyyal lies inside this. The western portion of are significant geological features seen in the region. the watershed embraces a small portion of the rain There are different varieties of soil seen in the study Figure 1. Location map of the study area. GEOLOGY, ECOLOGY, AND LANDSCAPES 3 area. Red clayey, red gravel loam, calcareous gravel Horton’s (1932) method, which is the quotient of loam and gravel clay are the dominant soil types seen area and basin length. To find out the basin slope, in the region. Chorley et al. (1957) has expressed the method of Lemniscate’s (K). The value ofK for this particular watershed is 4.65, and it shows that the watershed 3. Database covers the most significant share within the region of its origin with more streams of higher-order within The analysis was done with the help of SRTM (Shuttle the watershed (Table 2). Radar Topographic Mission) DEM (Digital Elevation Model) data with a 30 m spatial resolution satellite image obtained from the USGS earth explorer website. 5.3. Linear parameters Grohmann et al. (2007) have opined that the usage of Linear parameters consist of the one-dimensional SRTM data and GIS techniques enables fast, precise, characteristics, including all the linear features of the and cost-effective analysis of morphometric drainage basin, which are as follows: characteristics. 5.3.1.. Stream order 4. Methodology In a drainage basin or a watershed, stream network is the collection of stream segments (Horton, 1945; The watershed boundary is extracted automatically Strahler, 1957). The arrangement of stream in the from SRTM DEM data. The inputs needed for extrac- hierarchical order has been allotted a series of num- tion are DEM and pour point. The SRTM data was bers according to their position (Asfaw & Workineh, also used to generate the slope, terrain details, in 2019). Generally, the most significant, branched, chief, ArcGIS 10.3. The morphometric characters were cal- or stem stream is designated as order one and the culated using the spatial analysis tool and already smaller tributary streams of increasingly higher orders derived mathematical formula (Table 1). (Gravelius, 1914). According to Strahler (1964), there are no tributaries for first-order streams. All the tri- 5. Results and discussion butaries of the second-order streams belong to the first-order streams. The next higher-order streams 5.1. Drainage pattern possess the tributaries of all the succeeding lower- Drainage patterns are classified based on the form and order streams, continuing so on till any number of texture of the streams, in accordance with the slope higher-order streams. An area where erosion is still and structure of the surface. The local topography of prominent will have a larger number of stream seg- the terrain and its subsurface geology influences the ments in a particular order. In the present study, five shape and patterns of the river. The drainage pattern orders of streams are identified (Figure 2). of the current watershed is identified as dendritic, The total number of streams identified in the which has the tributaries joining the mainstream at watershed is 845, out of which 500 streams belong to acute angles. Dendritic pattern is the most commonly first order, 245-second order, 87 third order, 10-fourth occurring pattern, where the tributaries of the main -order, and 3-fifth-order. Generally, more water is river join together in shape, similar to the twigs of generated in a watershed, which has a maximum num- a tree (Guilbert & Zhang, 2012). ber of lower-order streams. There is an inverse rela- tionship between the stream number and stream order, which implies that the stream frequency 5.2. Basin geometry decreases with an increase in the stream order The Vannathangarai watershed constitute an area of (Figure 3). It is also noted that the highest frequency 1512.82 km with a perimeter of 194.63 km. According is noticeable among the streams of the first order. to Schumm (1956), the relative perimeter (P ) of the basin is the ratio between the area and the perimeter of 5.3.2.. Stream length the watershed, and here the value is 7.77. The length of According to Horton (1945), the entire lengths of the basin (L ) is 83.95 km. The length of the main a given order are the result of the quantity of streams channel (L ) is found to be 73. 45 km, which is the and lengths per stream. Where the bedrock is less most extended channel from the source point of the pervious, an enormous number of streams of minor watershed boundary. For many basins, the relation lengths are developed, while if the bedrock is porous, between the length of the stream and the area of the small quantities of comparatively larger streams are basin is associated to a function, known as the Length developed in a relatively well-drained watershed or area relation (L ), developed by Hack (1957), and its basin (Narasimhan & Vasanthamohan, 2011). ar value for the watershed is 113.24. The mean width of Typically, the lower order streams have the maximal the basin is 18.01 km and is computed based on stream length, and it declines with an increase in 4 S. M ET AL. Table 1. Morphometric characteristics of Vannathangarai watershed. Sl no Morphometric Parameters Formula/Definition/ method Reference Basin Geometry 1 Drainage basin area (A) Km GIS analysis - 2 Drainage basin perimeter(P) km GIS analysis - 3 Relative Perimeter(P ) Pr = A/P Schumm (1956) 4 Basin Length(L ) km GIS analysis Schumm (1956) 0.6 5 Length Area Relation (L ) Lar = 1.4*A Hack (1957) ar 6 Mean Basin Width(W ) km Wb = A/Lb Horton (1932) 7 Leminiscate’s (K) K = L /A Chorley et al. (1957) 0.5 8 Compactness Co-efficient( C ) Cc = 0.2821*P/A Gravelius (1914) 9 Length of main channel(L ) km GIS analysis - Linear Aspects 10 Stream Order Hierarchical order (GIS analysis) Strahler (1964) 11 Stream Length(L ) Length of the streams (GIS analysis) Horton (1945) 12 Mean Stream Length (L ) km Lsm = L */N *** Horton (1945) sm u u 13 Stream Length Ratio(R ) R = L /L -1, Horton (1945) l l u u 14 Bifurcation ratio(R ) R = N /N +1, Schumm (1956) b b u u 15 Mean Bifurcation ratio(R ) R = mean of bifurcation ratio of all orders Schumm (1956) bm bm Aerial Aspects 16 Stream Frequency(F ) Fs = N**/A Horton (1945) 17 Drainage density(D ) km/km Dd = L/A, Horton (1945) 18 Drainage Intensity(D ) Di = F /D Faniran (1968) i s d 19 Infiltration ratio /number(I ) If = F *D Faniran (1968) f s d 20 Texture Ratio(T) T = N/P Horton (1945) 21 Form Factor(R ) R = A/L Horton (1932) f f b 22 Circulatory Ratio(R ) R = 4πA/P Miller (1953) c c 23 Elongation Ratio(R ) Re = 2√(A/π)/L Schumm (1956) e b 24 Rho Coefficient (C ) C = R /R Horton (1945) rh rh l b 25 Shape Index(S ) S = 1/F Horton (1932) w w s 26 Shape factor(S ) S = L /A Horton (1932) f f b 27 Length of overland flow( L ) km L = 1/2D Horton (1945) of of d 28 Fitness ratio(R ) R = L /P Melton (1957) f f c 29 Wandering ratio (R ) R = L /L Smart & Surkan (1967) w w c b 30 Constant of channel maintenance(C) C = 1/D Horton (1945) Relief aspects 31 Maximum elevation (M ) m GIS analysis - 32 Minimum elevation (M )m GIS analysis - 33 Basin Relief(B ) M -M Schumm (1956) h a i 34 Relative relief(R ) B /P Horton (1945) r h 35 Relief Ratio(R ) R = B /L Schumm (1956) h h h b 36 Ruggedness Number(R ) R = B *D Strahler (1958) n n h d 37 Ruggedness Index(R ) R = D *(R /1000) Schumm (1956) i i d r 0.5 39 Melton’s Ruggedness Number (M ) (M -M )/A Melton (1965) rn a i 40 Watershed/ basin Slope(S ) S = H/L Miller (1953) b b b 41 Elevation at Source(E ) GIS analysis 42 Elevation at Mouth (E ) GIS analysis 43 Gradient Ratio(R ) R = (E -E )/L Sreedevi et al. (2005) g g s m b 44 Total Basin relief(H) m H = M -E Strahler (1952) a m 45 Total Contour length (C ) km GIS analysis - tl 46 Contour Interval (C ) m GIS analysis - 47 Average slope(S)% S = (M *(C /H)/(10*A) Wentworth (1930) a tl 48 Mean slope of the basin (S ) % S = (C *C )/A Chorley (1969) m m tl i 49 Coarse Ratio(C ) C = B *D Chorley (1966) r r h d Source: Compiled by the author) L * = Total length of stream, N** = Total number of streams, N *** = Total number of stream segments of order “U.” u u Table 2. Basin geometry parameters. Table 3. Linear parameters of the Vannathangarai watershed. Sl no Basin geometry Parameters Result Stream Number of Bifurcation Stream 1 Drainage basin area (A) Km 1512.82 order streams Length Ratio length 2 Drainage basin perimeter(P) km 194.63 Ratio Mean stream 3 Relative Perimeter(P ) 7.77 Length 4 Basin Length(L ) km 83.95 1 500 702.28 2.04 0.50 1.40 5 Length Area Relation (L ) 113.24 ar 2 245 351.18 2.82 0.29 1.43 6 Mean Basin Width(W ) km 18.01 3 87 101.73 8.7 1.14 1.16 7 Leminiscate’s (K) 4.65 4 10 116.03 3.33 0.31 11.6 8 Compactness Co-efficient( C ) 1.41 5 3 36.40 0 0 12.13 9 Length of main channel(L ) km 73.45 Source: Compiled by the author stream order. Fewer lengths of channels are more evident in areas with a steep slope, and longer streams is estimated to be 1307.62 km. Plotting the number of indicate plain regions where the slope is gentle. The streams and stream order on the logarithmic scale length of river channels in any watershed declines with reveals an inversely proportional relationship between arise in stream orders. The total length of the streams them (Figure 4) GEOLOGY, ECOLOGY, AND LANDSCAPES 5 Figure 2. Drainage map. (Source: SRTM-DEM) Figure 3. Interrelation of stream order with the number of streams. Figure 4. Interrelationship between stream order and stream length. 6 S. M ET AL. 5.3.3. Mean stream length(L ) ratio will be higher if the basin is elongated and is sm L is derived by dividing the entire length of the lower if the basin is circular. A higher ratio is also an sm channel by the total number of streams. There is indicator of the potentiality for flash floods. The a positive relationship between the L and the size first, second, and fourth-order streams show a lesser sm and surface features of the watershed. According to ratio, below 3.5, while the third-order streams possess Strahler (1964), the size of the stream networks and a higher bifurcation ratio, which is close to 8.7 (Table its related features has a significant relation with 3). The R for the watershed is estimated as 3.37. The bm the Lsm. There is a high association between the value indicates that the streams are well-formed on an mean stream length, runoff, and the erosional almost uniform topography, where its geologic struc- phase of the watershed. If the L is low, it shows ture least influences the pattern of drainage. (Asfaw & sm a higher surface flow and erosion (Gopinath Girish Workineh, 2019) . et al., 2016). The L of the watershed ranges sm between 1.4 and 12.13. It is shortest for the first- 5.4. Aerial parameters order streams and longest for the fifth-order stream (Figure 5). Aerial parameters or basin parameters indicate the whole area protruded upon a plane providing the 5.3.4. Stream length ratio (R ) overland flow to the stream network of a particular The proportion between the L of one order with the order and encompasses all the channel networks of its sm following lower-order stream is itsR . It changes with lower order. the variations in slope and terrain features, runoff, and erosional phase of the watershed (Sreedevi et al., 5.4.1. Drainage density(D ) 2005). In the watershed, the R value varies between 0 l D is the stream development level inside a basin and and 1.14 except for the third-order streams where it is is derived by finding out the mean length of streams slightly higher (Table 3). within the watershed per unit area (Horton, 1932). D provides a quantitative evaluation of the surface runoff 5.3.5. Bifurcation ratio(R ) capability and dissection of the landscape (Chorley, The ratio of the number of streams of a particular 1969). Horton (1945) explained D as a tool to esti- order to the number of streams of the succeeding mate the measured traveling time of water in the total higher order is called the R (Strahler, 1964). This drainage basin by evaluating the closeness of the describes the branching pattern of the drainage net- stream network. Areas that possess scanty vegetation work. If the value ranges from 0.6 to 2.9, it shows that generally show a higherD and have significant flood the watershed is included under the standard category. peaks. Areas with less pervious rocks and high relief For drainage basins where the geologic structure does show a higher D compared to places with highly not distort the drainage patterns, the Rb value ranges resistant and permeable surfaces, which show a low between 3.0 and 5.0. (Kale & Gupta, 2001; Strahler, profile of drainage density (Gopinath Girish et al., 1957). If the R value is greater than 10, it leads to the 2016). According to Langbein (1947), the D of b d formation of elongated narrow drainage basins, which humid regions ranges between 0.55 and 2.09 km . The are formed due to prolonged structural control and D of the current watershed is 1.72, which implies that erodible rocks of that basin (Chorley et al., 1984). The this is a relatively well-drained basin of a sub-humid R also indicates the pattern of the drainage basin. The region (Table 4) (Figure 6). Figure 5. Interrelationship between stream order and Lsm. GEOLOGY, ECOLOGY, AND LANDSCAPES 7 5.4.2. Drainage intensity(Di) Table 4. Aerial parameters. Sl no Aerial Parameters Result The proportion of the F to D is termed as drainage s d 1 Stream Frequency(F ) 0.55 intensity (Faniran, 1968). This study has identified 2 Drainage density(D ) km/km 1.72 a very low D of 0.32, which suggests that the D and i d 3 Drainage Intensity(D ) 0.32 4 Infiltration ratio /number(I ) 0.96 F have a meager impact, intending that denudation f 5 Texture Ratio(T) 4.34 agents have reduced the terrain. This is an indication 6 Form Factor(R ) 0.21 that the movement of the surface runoff is prolonged, 7 Circulatory Ratio(R ) 0.50 8 Elongation Ratio(R ) 0.52 making the area vulnerable to easy flooding.(Pareta & 9 Rho Coefficient (C ) 0.13 rh Pareta, 2011) (Table 4). 10 Shape Index(S ) 1.79 11 Shape factor(S ) 4.65 12 Length of overland flow( L ) km 0.86 of 5.4.3. Infiltration ratio(I ) 13 Fitness ratio(R ) 0.377 f f 14 Wandering ratio (R ) 0.874 Faniran (1968) has propounded another technique, 15 Constant of channel maintenance(C) 0.57 namely the infiltration ratio, which is the outcome of the D and F . Pareta and Pareta (2011) suggested that d s the infiltration number has an antagonistic relation- length of the streams and Rb (Horton, 1945). The ship with the infiltration capacity and a positive rela- C of the Vannathangarai watershed is calculated as rh tion with the runoff. The current study has identified 0.13, signaling that it has more extensive hydrologic that the infiltration number is 0.96, which implies storage during flood periods (Table 4). a lower surface runoff and lesser infiltration capacity making the area more susceptible to flooding (Table 4). 5.4.5. Stream frequency (F ) F is the number of streams per unit area. Higher Fs 5.4.4. Rho coefficient(C ) indicates more surface runoff, low infiltration capa- rh C is influenced by the climate, geology, geomorphol- city, sparse vegetation, high relief, and steep slope rh ogy of the terrain along with the biological and anthro- (Horton, 1945). The values of D and F of different d s pological factors. It is a significant parameter related to drainage basins with varying lengths cannot be asso- the D and geomorphic development of a watershed, ciated as they differ in their size. Since the origin of which enables the estimation of the storage potential a stream is based on the type of vegetation cover, of the rivers; thus it helps to determine the ultimate structure of rocks, amount of precipitation, and the stage of drainage development in a given watershed; in permeability of the soil, the F acts as an indicator of other words, it is defined as the ratio between the the evolution of the landscape of that region. The F of Figure 6. Drainage density map. (Source: SRTM-DEM) 8 S. M ET AL. Figure7. Slope map. (Source: SRTM-DEM) Figure 8. Aspect map. (Source: SRTM-DEM) the Vannathangarai watershed is 0.55. A positive cor- 5.4.6. Texture ratio(T) relation exists between the D and F ; with more The value of T is derived by estimating the ratio d s streams, the density also increases(Table 4). between the total number of stream segments and GEOLOGY, ECOLOGY, AND LANDSCAPES 9 Figure 9. Elevation map. (Source: SRTM-DEM) the perimeter of the watershed. Horton (1945) has 5.4.8. Circulatory ratio (R ) defined the texture ratio as the product of F and D The circulatory ratio is the proportion of the s d and opined that it is a crucial factor. Smith (1950) has watershed area and the area of the circle of perimeter done a detailed study about the texture ratio and of the watershed (Miller, 1953). The low, medium, and pointed out that it is dependent on numerous natural high R indicate the youth, middle, and old stages of characters like the amount of precipitation, types of the stream development (Narasimhan & soil, the density of vegetation, infiltration capacity, Vasanthamohan, 2011). The circulatory ratio of this relief, and the stage of geomorphic development. T is watershed is estimated to be 0.50, which, according to considered an essential parameter that shows the Miller (1953), symbolizes the basin’s elongated shape relative spacing of the drainage networks of any with highly permeable, analogous, geologic materials. watershed. If T’s value is below two, it indicates (Table 4). a very coarse texture; likely, a value between two to four is coarse, four to six is moderate, six to eight is 5.4.9. Elongation ratio(R ) fine, and above 8 is very fine drainage textures e The R value usually ranges from 0.6 to 1 over a broad (Smith, 1950). The T value of the Vannathangarai e climatic and geologic type; If R is near to 1, relief is watershed is 4.34, which denotes a moderate texture e generally very low. Areas with high relief and steep (Table 4). slope possess R values ranging between 0.6 and 0.8 (Strahler, 1964). These values can be arranged into 5.4.7. Form factor (R ) three classes; Circular (above 0.9), oval (0.9–0.8), and The R is defined as the flow intensity of a watershed less elongated (below 0.7) (Narasimhan & for a specific area (Horton, 1932). R indicates the Vasanthamohan, 2011). Efficiency in the runoff dis- maximum flow and duration; higher form factor sug- charge is more for a circulatory basin than for an gests maximum flow during a short span (Gopinath elongated one (CS Singh & Singh, 1973; Gajbhiye Girish et al., 2016). It is presumed that, R value of 0.78 et al., 2014). A watershed which has high runoff with is indicative of a perfectly circular basin. (Gopinath low infiltration capacity, will always have a higher R . Girish et al., 2016; Harinath & Raghu, 2013) The (Gopinath Girish et al., 2016). According to Chorley present study identifies the R of the basin as 0.21, et al. (1984), the areas with high relief possess R which suggests that the drainage basin is elongated around 0.6, and if it is near to 1, it implies a very low (Table 4). 10 S. M ET AL. relief. The R of the Vannathangarai is 0.52, thus 5.5. Relief parameters revealing a less elongated, low land region (Table 4). The relief parameters are connected with three- dimensional features like volume, altitude, etc., to 5.4.10. Shape index(S ) and shape factor(S ) w f investigate the various geo-hydrological characteris- The S is the reciprocal of the R and is w f tics. The maximum elevation of the watershed is a dimensionless property (Soni, 2016), and the shape 1928 m, and the lowest point is 301 m. The elevation index for the watershed is 1.79. Horton (1932) has at the river’s source is estimated at 1254 m, and its defined the S as the ratio of the square of L to the f b mouth is 304 m (Table 5). area of the basin. The S assists in interpreting the shape distortion of a watershed (Yadav et al., 2014). 5.5.1. Basin relief(B ) and total basin relief(H) The S for the Vannathangarai is 4.65(Table 4). Basin relief is expressed as the maximum upward distance between the lowest and highest point of the 5.4.11. Length of overland flow(L ) of area. Hadley and Schumm (1956) opined that basin Horton (1945) considered the L an essential tool to of relief is the causative factor for the stream gradient and analyze the development of physiography and the plays an influential role in determining the flood char- drainage basin and defined it as the measure of water acteristics and volume of materials that can be carried over the terrain before it gets collected into brooks. L of along. Sreedevi et al. (2009) identified this as an inte- is determined by the nature of rock, relief, and climatic gral factor in getting the basin’s denudation features. condition, vegetation cover, permeability, duration of Lower B is an indication of minimal surface runoff, erosion (Schumm, 1956). The current study reveals debris movement, and spreading of water basin while that the L of Vannathangarai is 0.86 km. A more of the higher values indicate enhanced flood peaks significant value of the L designates a more extended of (Gopinath Girish et al., 2016). The maximum eleva- flow path with gentle slopes (Narasimhan & tion in the watershed is noted as 1928 m, which is seen Vasanthamohan, 2011) (Table 4). at the western side of the watershed, while the lowest point is having an elevation of 301 m (Figure 9). Thus 5.4.12. Fitness ratio (R ) and wandering ratio(R ) f w the basin relief obtained for the watershed is 1627 m. The topographic fitness is measured using its fitness Thomas et al. (2010) presumed that river basins with ratio, which according to Melton (1957), is the ratio of mountain-plain front generally have higher basin the L to the perimeter of the watershed and is 0.37 for c relief than rivers with plateau-plain front. Strahler the Vannathangarai watershed. The proportion of the (1952) has defined the total basin relief as the differ - L to L is given by its wandering ratio (Smart & c b ence between the highest elevation of the watershed Surkan, 1967), and its value for the basin is 0.874 and the maximum elevation at the mouth. The (Table 4). Vannathangarai watershed has an H value of 1624 m (Table 5). 5.4.13. Compactness co-efficient(C ) Another crucial parameter is the C , which is the ratio 5.5.2. Relief ratio(R ) of the perimeter of the basin to the circumference of R is described as the ratio between the total reliefs to the circular area (Gravelius, 1914). The C value for the length of the principal drainage line. It is an a perfect circle is one and rises with the increase in L and hence it is independent of the size of the Table 5. Relief parameters. watershed. The value of the compactness coefficient Sl no Relief Parameters Result for this watershed is 1.41, which states that the shape is 1 Maximum elevation (M ) m 1928 more elongated (Table 4). 2 Minimum elevation (M )m 301 3 Basin Relief(B ) 1627 4 Relative relief(R ) 8.35 5 Relief Ratio(R ) 19.37 5.4.14. Constant of channel maintenance (C) 6 Ruggedness Number(R ) 2812.64 This concept was introduced by Schumm (1956) and 7 Ruggedness Index(R ) 2.81 is the reverse of D . C is defined as the area needed to 8 Melton’s Ruggedness Number (M ) 41.84 rn 9 Watershed/ basin Slope(S ) 19.37 sustain one vertical kilometer of stream (Dikpal et al., 10 Elevation at Source(E ) 1254 2017). C is highly dependent on the geology, porosity, 11 Elevation at Mouth (E ) 304 12 Gradient Ratio(R ) 19.34 climatic condition, type of vegetation, duration of 13 Total Basin relief(H) m 1624 erosion, and the terrain of the area. A higher C value 14 Total Contour length (C ) km 5393.453 tl 15 Contour Interval (C ) m 20 indicates rocks with more permeability (Narasimhan i 16 Average slope(S)% 0.42 & Vasanthamohan, 2011). The more the value of the 17 Mean slope of the basin (S ) % 0.71% 18 Coarse Ratio(C ) 2.81 channel maintenance, the more is its permeability. The constant for the current study is inferred to be 0.57, which indicates lower runoff (Table 4). GEOLOGY, ECOLOGY, AND LANDSCAPES 11 indication of runoff and severity of the erosion pro- 5.5.7. Coarse ratio(C ) cess, and it evaluates the steepness of a watershed Coarse ratio is described as the difference between the (Phani, 2014). There is a negative correlation with the maximum and minimum levels of the watershed R and drainage area and its size (Gottschalk, 1964) divided by its perimeter (Melton, 1957). C is an h r (Table 5). expression of the relationship between the B and D h d (Singh et al., 2014). The C for the Vannathangarai watershed is estimated at 2.81. Chorley (1966) stated 5.5.3. Relative relief(R ) that, coarse ratio, will be less at the youthful stage, R depicts the exact change of elevation in a unit area increases gradually, and will be the highest at the concerning its local base level. R can represent the mature stage and starts to decline, by the end of its terrain features without considering the sea level (S life cycle (Table 5). Singh & Dubey, 1994). It is termed as the amplitude of local relief. The relative relief of the Vannathangarai watershed is 8.35(Table 5). 6. Conclusion Morphometry is the science that studies the quantita- 5.5.4. Ruggedness number(R ), ruggedness tive examination of the drainage basin, which provides index(R ), Melton’s ruggedness number(M ) i rn an in-depth insight into the relief and topography of Strahler (1958) explained the Rn as the product of B the drainage surface. The Vannathangarai watershed and D . Selvan et al. (2011) considered it as a measure lies at the headwaters of river Noyyal. The watershed of the unevenness of the surface. The ruggedness has a generally low slope, with hills seen only along the number for the watershed is 2812.64. Ruggedness western fringes, and the remaining area is more or less index is a measure of the combined effect of the local an even plain. The streams of the watershed, which has terrain and the magnitude of D and other geographic 2 2 an area of 1512.82 km and perimeter of 194.63 km , parameters like rainfall, slope, denudation, nature of follow the dendritic pattern of drainage. The the soil, etc.(Chorley, 1969). The ruggedness index for watershed consists of five orders of stream, with this watershed is estimated at 2.81. Melton’s rugged- more than 800 streams, where more streams are seen ness number is an index of slope that gives in the lower order. The length of lower-order streams a specialized illustration of relief ruggedness within is higher than that of the next higher-order streams, the watershed (Melton, 1965). The M for the rn indicating less surface permeability. Analyzing the watershed is 41.84 (Table 5). bifurcation ratio makes it clear that the streams are developed over a homogeneous surface for almost the 5.5.5. Gradient ratio(R ) g entire watershed except for few areas at the western Sreedevi et al. (2009) devised the gradient ratio as hill reaches. a tool to evaluate the runoff volume. R is an expres- g The drainage density indicates that the watershed is sion of channel undulation that assists in assessing the well-drained and belongs to a sub-humid region. The runoff volume (Sreedevi et al., 2005). The gradient drainage intensity points out that the surface is low- ratio for the watershed is 19.34. A higher R indicates g ered considerably, and it takes a long time to remove a steep slope with high runoff, while lower runoff that runoff, indicating a probable chance of flooding. indicates lesser runoff and higher infiltration( Table 5). The Rho coefficient shows that the watershed has higher hydrologic storage during flood periods. Infiltration ratio indicates a low runoff and lesser 5.5.6. Slope analysis infiltration capacity making the area more susceptible Slope is an essential factor as it determines the infiltra - to flooding. The watershed is elongated in shape and tion and runoff; Infiltration capacity and slope are has a medium texture. A more significant value of the inversely related (Mahala, 2020). Most of the study L symbolizes a higher flow path with gentle slopes. area has a relatively low land without much undula- of Analysis of all these parameters enables the identifica - tion (Figure 7 & 8). Beside the left bank side of the tion of the potential groundwater zones as the source river channel, the slope is towards the south, and along of water is altered by the structural, lithological, and the right bank side, it is towards the north. Near the geomorphological set up of an area (Schumm, 1956). western fringes of the watershed, steep terrain is As the watershed is a densely populated region with observed, which is a part of the Western Ghats hill numerous industries and more number of agricultural ranges. Wentworth (1930) suggested that the erodibil- activities, it is essential to identify the prospects for ity can be estimated and can be compared with its groundwater and to safeguard the existing water slope. Higher the slope, higher is the erosion. The resources. The study is highly beneficial in this con- average slope of the area is 0.42%, and according to text, and for this, the geospatial technologies are path- Chorley (1969), the mean slope of the basin is 0.71% breakers providing easy and accurate information. (Table 5). 12 S. M ET AL. RS and GIS perspective. Applied Water Science, 4(1), Future scope of research 51–61. https://doi.org/10.1007/s13201-013-0129-7 There is a paradigm shift in geographical research over the Gopinath Girish, A. G., Nair, A. G. K., & Swetha, T. V. last few years; from political or administrative boundary- (2016). Watershed prioritization based on morphometric based studies now the emphasis is on natural boundary- analysis coupled with multi-criteria decision making. based studies; especially for natural resource assessment, Arabian Journal of Geosciences, 9(2), 129. https://doi. watershed boundaries are preferred. 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Journal

Geology Ecology and Landscapes – Taylor & Francis

Published: Apr 3, 2023

Keywords: Basin geometry; linear/aerial/ relief aspects; SRTM DEM; geo-spatial techniques; Vannathangarai watershed

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