Evaluation of the geomorphological scenario of Shimsha River Basin, Karnataka, India

Water is an important component of life that is becoming a sparse resource for various reasons (du Plessis 2023). Due to the population growth, expansion of agriculture, and industrialization, water demand is significantly increased (Bantider et al. 2023). Due to the uneven distribution of water resources and rainfall, few regions face acute water shortages, whereas few regions face water surpluses (Tu et al. 2022). Water is an important resource whose misuse endangers the existence of life on the earth; hence, it becomes necessary to manage it sustainably (Osei 2023). Sustainable development aims at safeguarding and improving natural resources (Radwan et al. 2020; Shivhare et al. 2022; Verma et al. 2022). Natural resource management can be achieved by implementing and monitoring proper management activities at the watershed level, with which the impacts of floods and droughts can be mitigated (Abdeta et al. 2020; Wolka et al. 2023). A watershed is an area where runoff from a rainfall event is accumulated and drained through a common outlet point (Abdeta et al. 2020; Rajasekhar et al. 2020; Endalew & Mulu 2023). Watershed development activities are influenced by various factors such as available water, drainage morphology, physiography, soil type, land use–landcover, etc. (David Raj et al. 2022; Shivhare et al. 2022; Verma et al. 2022; Li et al. 2023). To plan an effective watershed management activity, many parameters need to be considered and analysed, among which analysing drainage morphometry is crucial (Umrikar 2017; Jain et al. 2020; Anshumali et al. 2023; Bashir 2023). Drainage morphometry is necessary for analysing many hydrological processes within the watershed (Magesh & Chandrasekar 2014; Şener & Arslanoğlu 2023), such as stream flow characteristics and sediment transportation. Assessment of drainage morphometry involves evaluation of the geometry of the watershed (Kudnar 2020), i.e., measurement and quantitative study of the earth's surface configuration, shape, and dimensions of its landforms (Pande & Moharir 2017; Prakash et al. 2019; Benzougagh et al. 2022). Drainage morphometry provides a quantitative explanation that helps in the categorization of basins (Saha et al. 2022). Basin morphometry is an essential source for carrying out investigations like an assessment of surface runoff, flood events, soil erosion, surface water storage, groundwater recharge, slope instability, landslides, and other environmental issues (Mangan et al. 2019; Sarkar et al. 2020; Gonçalves et al. 2023). The watershed morphometric study should be performed as it delivers essential information about the various features of the drainage network and its natural hazards. This could be used for sustainable manage the natural resources in a basin (Abdeta et al. 2020; Krishnan & Ramasamy 2022; Mani et al. 2022).

Morphometric analysis is a quantitative method for understanding various aspects that control the drainage network of a basin, viz. linear, areal, and relief parameters (Sarkar et al. 2020; Dimple et al. 2022). The morphometric analysis involves delineating drainage boundary and stream network, ordering the streams, computing the catchment area and perimeter, stream length, and evaluating morphometric parameters (Mangan et al. 2019; Sarkar et al. 2022). This helps to identify the various geological processes, geomorphological changes, and drainage pattern modifications that occurred over time due to natural phenomena (Abdeta et al. 2020; Iacobucci et al. 2022).

In recent years, considerable changes have occurred in geomorphological concepts, and many sophisticated techniques have evolved in analysing the earth's dynamic nature. Delineation of stream networks and the watershed boundary can be accomplished by traditional methods using toposheets and onsite observations or by sophisticated approaches using remote sensed data and Geographic Information Systems (GIS) tools (Rajasekhar et al. 2020; Bharath et al. 2021; Kadam et al. 2022). The traditional method of delineating the streams and watershed boundary is very tedious and time consuming as field observations need to be taken for a vast area, which restricts its usage (Bharath et al. 2021). At the same time, extracting the watershed boundary and stream network from the digital elevation model (DEM) is relatively easy as it presumes water flows from higher to lower elevations (Barbedo et al. 2022). Remote sensing data are a dependable source for preparing many thematic layers required for the morphometric analysis (Aziz et al. 2020; Dongare et al. 2022).

Numerous studies employing GIS for morphological evaluation and watershed prioritization have previously been reported. Magesh & Chandrasekar (2014) have evaluated morphometric parameters for Tamiraparani sub-basin using GIS tools and suggested that the study results help in landscape management at the sub-basin level. Mangan et al. (2019) studied the morphological characteristics of the Nanganji River Basin, Tamil Nadu, India. The authors have suggested that the morphological study helps in understanding the vulnerability of the watershed towards soil erosion. Singh et al. (2020) have performed the morphometric analysis of the Ghaghara River at basin and sub-basin levels and suggested that the results are helpful in providing useful information for societal interests. Gautam et al. (2020) conducted morphometric and morphotectonic analyses in the Sai River Basin, Uttar Pradesh, India, and explained the basin characteristics with respect to the morphometric and morphotectonic parameters. Jain et al. (2020) have derived the stream network from Survey of India (SOI) toposheet and four different DEM data of 30 m resolution: AW3D30, SRTM-GL1, CartoDEM-V3.1, and GDEM-V2. According to their study, when compared to topographical features generated from SOI toposheets, SRTM-GL1 outperforms AW3D30, CartoDEM-V3.1, and GDEM-V2 in terms of drainage delineation and basin morphometry. Khurana et al. (2020) extracted morphological parameters from DEM in conjunction with SOI toposheets for the river Ravi. The authors have also obtained the morphological parameters for eight sub-watersheds and prioritized them by computing the compound index value. Sarkar et al. (2020) have analysed morphometric parameters of the Nagar River Basin and suggested that the study results can be used for determining flood magnitude and planning flood mitigation measures. Lakshminarayana et al. (2022) have determined morphometric parameters of the Tidi watershed, Rajasthan, India, using ASTER DEM and GIS tools and suggested that the results are helpful in effective watershed management. Dongare et al. (2022) have performed the morphometric analysis of the Khapri watershed, Gujarat, India, and highlighted the use of morphometric factors to infer the basin-wide distribution of infiltration and runoff.

GIS provides a versatile environment and a vital tool for assessing various basin parameters and interpreting spatial data. The remote sensed data and GIS yield various derivatives like slope, relief, aspect, and drainage density, which can be further used for the morphometric analysis. Many researchers have utilized remote sensing and GIS tools for evaluating morphometric parameters and supported their suitability in drainage morphometric analysis (Shivhare et al. 2022; Verma et al. 2022).

The Shimsha River basin is one of the prominent sub-basins of the Cauvery River basin for which no studies related to drainage morphometry is reported so far. For any kind of watershed management planning and development drainage morphometry plays an important role. Hence, this study aims to analyse the morphometric and morphotectonic parameters of the Shimsha River basin in Karnataka, India, using the remote sensed data and GIS tools. One dimensional (linear parameters), two dimensional (aerial parameters), and three dimensional (relief aspects) of the basin are assessed and analysed to comprehend the drainage and physiological features of the watershed.

This investigation aims to analyse the morphometric properties of the Shimsha basin to understand the drainage features and to develop adequate water and soil conservation measures. The stream network is extracted using Cartosat DEM and spatial analyst tool in ArcGIS. Then watershed boundary is delineated by defining the proper pour point extracted by the field survey with GPS equipment. SOI topographic maps of scale 1:50,000 are georeferenced and projected to WGS 1984 UTM zone 43 North datum, which is then used to verify the stream network extracted from the spatial analysis. The specifics of the data used in this research are mentioned in Table 1.

The study aimed to integrate the usage of remote sensed data and GIS tools in drainage morphometry extraction. Hydrology tools extract the stream network and watershed boundary of the Shimsha basin from Cartosat DEM. The results indicate that Shimsha is a sixth-order river with an area of about 8,694.61 km². The geometric aspects of the basin are calculated by GIS tools and are highlighted in Table 3, which depicts that the basin length is 143.13 km, the basin width is 80.37 km, and the perimeter is 638.77 km. The morphometric analysis is executed in three aspects: linear parameters, aerial parameters, and relief parameters. In addition to the morphometric analysis, morphotectonic aspects such as hypsometric integral (HI) and asymmetry factors (AFs) are also determined. The findings of the obtained morphometric and morphotectonic parameters are briefly described and discussed.

Table 3 highlights the geometric parameters of the Shimsha River basin. The catchment area of the Shimsha River basin is 8,694.61 km², basin length and mean basin width are 143.13 km and 80.37 km, respectively, and basin perimeter and relative perimeter are 638.77 km and 13.61 km, respectively.

The linear parameters of a basin are directly linked to the stream pattern and are impacted by topographic features.

The mean stream length is a metric for a basin's features that may be used to examine the different components of its drainage system. It may also be used to analyse runoff and soil erosion. It is the proportion of a stream's overall length to the number of segments that make up that stream. Table 4 shows the mean stream length information, which ranges from 1.9 to 149.04 km and has a total stream length of 209.14 km. The findings show that the mean stream lengths of all orders are greater than those of their lower orders and smaller than those of their next higher orders.

The stream length ratio measures the length of a stream divided by the length of the stream that is next lower in the order. The research area's stream length ratio values range from 0.49 to 1.47, with the mean stream length ratio being 0.66. The largest stream length ratio (1.47) is observed in the sixth-order stream, which shows that the land it drains is more permeable and has milder slopes than the area drained by lower-order streams.

It is the ratio of the total number of streams of one order to the total number of streams of the next higher order. This dimensionless number demonstrates the level of convergence among streams in a watershed. It provides information on the watershed's shape and runoff behaviour and is a helpful metric for identifying areas prone to floods. The basin's bifurcation ratio ranges from 3.76 to 4.61, with a mean value of 4.21. The bifurcation ratio ranges from 2 (in flat and rolling surfaces) to 4 or 5 (in hilly or highly dissected). The Shimsha basin has a flatter or rolling surface as the bifurcation ratio value is very low. The result demonstrates that the study region is regulated by lithology and structural factors (Table 4).

Rho coefficient (ρ) measures the relationship between a stream length and its bifurcation ratio. It is a vital parameter that affects the level of drainage development and the system's storage capacity (Potter 1957) by addressing the basin's physiography and drainage density. It also regulates the intensity and the frequency of the development of the network (Horton 1945). The Rho coefficient measures the geological structure and environmental conditions of a region. Numerous elements may impact it, including geomorphic processes, human-made activities, and climatic circumstances (Tribhuvan & Sonar 2016). The value of the Rho coefficient of the Shimsha River Basin varies between 0.07 and 0.37 (Table 4), and the mean value is 0.16.

The evaluation of aerial (two-dimensional) morphometric parameters is presented in Table 2, and the following subsections discuss the findings.

Stream frequency mentions the number of streams per unit area (Horton 1945). The capacity for infiltration, permeability, and basin relief all affect stream frequency. It offers details on the basin's reaction to the runoff process. S_f is affected by rainfall, basin relief, rock resistance, and drainage density of the basin (Thomas et al. 2010). While limited perviousness and less accessible surface flow reduce the value of S_f in a plateau environment, a high slope and more rainfall enhance S_f in mountain settings. The S_f is lithology dependent and closely correlated with the volume of infiltration. A steep slope, more runoff, and poor infiltration are indicated by higher S_f values (Horton 1932, 1945).

The S_f value of the Shimsha basin is 0.19 per km², implying that the basin has low topography, relatively porous surface, and subsurface materials, and low to moderate runoff. The lithology of the basin primarily influences S_f; frequent draining will result in the increased surface runoff. The low S_f value denotes increased infiltration and groundwater potential.

The drainage texture denotes the infiltration capacity of a drainage system (Horton 1945). It is affected by vegetation, relief, soil type, lithology, infiltration capacity, climate, and development phase (Smith 1950). The value of drainage texture for the Shimsha basin is 2.61. The drainage texture may be categorized into five groups (Smith 1950), the drainage texture may be divided into five categories: extremely coarse (2), coarse (2–4), moderate (4–6), fine (6–8), and very fine (>8). The Shimsha basin has a coarse texture, according to the measured drainage texture value.

In the watershed, the distances between each drainage line are represented by the texture ratio (R_t). In addition, it has a favourable relationship with the denudation procedures in that area. The research area's texture ratio is 2.04, which suggests less runoff and more permeability.

In order to calculate the slope of the watershed, Chorley (1957) expressed the lemniscates value. For the Shimsha basin, the lemniscate value is 0.59.

Shape characteristics that can be used to describe the nature of a hydrograph include form factor (Horton 1932), circulatory ratio (Miller 1953; Gardiner & Park 1978), and elongation ratio (Schumm 1956). Watershed area and length impact the form factor and elongation ratio, while basin area and the area of a circle whose diameter is equal to the basin perimeter are considered to calculate the circulation ratio. Form factors have values ranging from 0 to 1, with 0 denoting an elongated shape and 1 denoting a circular basin. In the basin, higher peak flows with shorter duration are indicated by form factors with higher values (close to 1), and vice versa. For the Shimsha basin, the form factor, circulation ratio, and elongation ratio values were 0.42, 0.27, and 0.735, respectively. These numbers suggest that the watershed has a slightly elongated shape, reflecting flat to mild flow peaks lasting longer. Due to the elongated nature of the Shimsha basin, the hydrograph would have flat and longer flow durations, increasing the potential for water to percolate and perhaps supplement the groundwater. Due to the elongated nature, the basin gets considerable runoff from lower-order streams.

The length of the development of the drainage basin affects the physiographic and hydrological conditions of the ground surface before it plunges into streams. L_of is the distance that the water travels on the earth's surface before it enters into streams. It is inversely linked to the average channel slope and approximately half of the reciprocal of drainage density (Horton 1945). L_of is divided into three classes: low (<0.2), moderate (0.2–0.3), and high (>0.3). L_of of the Shimsha basin is 0.89, which implies the existence of long flow paths and mild slopes, as well as more significant infiltration and less runoff in the watershed.

The constant of channel maintenance is a handy way to represent how much space is essential to support a unit length of a linear stream channel (Shreve 1967). It is also used to estimate the erodibility of a watershed. It is influenced by the slope, geological context, and vegetation cover of the basin and is inversely relative to the drainage density. Regions with resistant rock types, highly permeable surfaces, or good forest cover have a high value of C and a low D_d. For weak rock types, regions with low soil infiltration and minimal vegetation have high drainage densities and low channel maintenance. Typically, the impermeable nature of rocks is related to the lower values of C, and vice versa. The C for the Shimsha basin is 1.78, reflecting better material infiltration and permeability, a good vegetative cover, and reasonably resistant rock types.

C_c is the ratio among the area and perimeter of the basin. For a perfect circle, the compactness constant is unity and increases as the basin length increases. As a result, it clearly indicates how long the basin is. The value of C_c for the Shimsha basin is 1.93, which indicates that the study area is slightly elongated, which further indicates low runoff and high infiltration.

R_f measures the topographic fitness, which is the ratio of the main channel length to perimeter of the basin (Melton 1957). The R_f value of the Shimsha basin is 0.22.

The infiltration number measures the river basin's runoff potential and infiltration capacity. It is obtained by multiplying S_f and D_d (Schumm 1956). It shows the difference between the high and low infiltration capacity. For instance, the high value of I_f implies higher infiltration capacity, while the low value implies lower infiltration capacity in the area. I_f of the Shimsha basin is 0.108, indicating a strong infiltration capacity and reduced runoff in the study region.

The drainage intensity is determined by taking the ratio of drainage density to stream frequency (Faniran 1968). The drainage intensity of the Shimsha basin is low (0.3417). Since the drainage intensity is modest, it indicates that stream frequency and drainage density are not particularly substantial.

The shape index, which is dimensions, is the reciprocal of the form factor. The value of S_i of the Shimsha basin is 2.35. A higher shape index indicates a weak flood discharge period and elongated nature.

The relief parameters of a basin are related to three-dimensional characteristics, and it considers the altitude of landforms. Relief parameters are also used to analyse the relationship between the area and the altitude.

Basin relief is a vital variable that can help us understand a watershed's mass movement and erosion processes (Schumm 1956; Yadav et al. 2014). The highest and lowest elevations of the Shimsha basin are 1,194 m and 292 m above the mean sea level, respectively. Considering the difference between the lowest and highest elevation, the total basin relief is calculated; in this case, it is 902 m.

The relief ratio is a gauge for the basin's overall steepness. It shows the severity of erosion in the basin and is inversely linked to basin length (L_b) (Schumm 1956). The relief ratio of the Shimsha basin is 6.3 m/km, indicating flat to moderate slopes.

Relative relief is defined as the ratio of the highest relief to the circumference of the basin. It signifies that the steeper the slope, the greater the surface above its base. Shimsha basin's relative relief value of 186.92 m/km indicates lesser variation in the basin's topography.

The value of the dissection index is used to understand the nature and the extent to which terrain is dissected (Nir 1957; Dongare et al. 2022). The Shimsha basin has a dissection index value of 0.755, which specifies that the terrain has been significantly dissected.

The ruggedness number is determined by the basin relief and the drainage density. It measures the slope's length and steepness (Strahler 1958; Prakash et al. 2019). Higher values of R_n reflect higher relief and drainage density, as well as steeper and longer slopes of the basin (Strahler 1958). The value of R_n of the Shimsha basin of 0.51; this shows that the study region has intrinsic structural complexity regarding relief and drainage density and is less prone to soil erosion.

The MR_n is a slope index that shows the level of relief ruggedness in a basin (Melton 1965). For instance, in the Shimsha basin, the MR_n value is 0.0097, a low value that denotes a nominal mainstream flow free of additional debris flow.

The AF determines the tectonic orientation of the drainage about the mainstream (Cox 1994). This index also identifies the neo-tectonic activity directions and oversees the uplift and sinking of specific blocks instead of wide tilting (Keller & Pinter 1996). The AF is the ratio of area of the drainage basin facing the main stream's right to the basin's total area.

Significant tilting of the drainage basin is because of lithologic control or active tectonics. Moreover, the tilting is indicated by the AF; AF index values greater than 50 indicate left bank tilting, and a value less than 50 indicates right bank tilting (Cox 1994). AF of the Shimsha basin is 49.3, which indicates that the basin is slightly tilted towards the right (Gautam et al. 2020).

Despite having a decent annual rainfall of 800 mm, the study region struggles with a lack of surface and groundwater resources. The current work tries to comprehend the significance of morphometric characteristics in a hydrological setting to solve significant water issues. The geographical changes in drainage features across the basin may be quantified and analysed by the combined use of remote sensing, GIS, and statistical techniques. The findings help locate appropriate sites for water conservation and recharge structures and investigate prospective groundwater zones in the basin. The Shimsha basin is a sixth-order basin, with 98.74% of its streams being lower than the fourth order, which can be linked to the presence of complex, low-permeable rocks, and rough topography in the study region. Shimsha basin's bifurcation ratio values range from 3.76 to 4.61, resulting from homogeneous lithology and minimal structural control. The lower stream length ratios observed in lower-order streams indicate that they drain across less permeable rocks on steeper slopes. The sixth-order stream, which has a higher value of the stream length ratio than lower-order streams, runs over considerably more permeable rocks with a mild slope. The Shimsha basin's drainage texture is coarse, indicating moderate to high transmissibility of rock formation. The drainage density and stream frequency values also indicate the high transmissible nature of the surface and subsurface features, low relief, and low to moderate runoff in the basin. The shape of the watershed is slightly elongated, which manifests flat to moderate peak flow observed for a more extended period on the hydrograph and increased infiltration. The length of overland flow and the channel maintenance constant also specify that the study region has a gentle slope, long flow path, and permeable materials, indicating good infiltration and less runoff. The majority of the region in the watershed possesses a flat to gentle slope region. The relief ratio and relative relief imply a low degree of terrain variation and flat to moderate slope in the study area. The ruggedness and Melton ruggedness numbers indicate a low flow rate and soil erosion rate in the basin.

For a hydrological study, the morphometric analysis of a basin acts as a prerequisite. This study attempts to describe morphometric and morphotectonic parameters of the Shimsha basin using the remote sensed data and GIS tools. It is found that the remote sensed data and GIS tools are very competent in carrying out morphometric and morphotectonic analyses. The use of remote sensed data combined with ground survey data (SOI toposheets) provides a comprehensive view of the behaviour of a watershed. This approach allows hydrologists and geomorphologists to arrive at a holistic understanding of various characteristics of the basin. This study also supports that the GIS-based method is more suitable than traditional approaches for analysing drainage basins and the impact of different parameters on landforms, runoff, and soil erosion features. The analysis shows that the Shimsha basin has a sixth-order stream with a dominantly dendritic pattern. The study area has a more significant number of smaller-order streams, indicating permeable strata with flat to gentle slopes. The study area is noticed to have improved infiltration and low runoff due to more permeability. The results indicate that the flow in the study area is characterized by longer duration and less peak, which may enhance the possibility of infiltration and groundwater enrichment. The hypsometric analysis of the Shimsha basin specifies the mature stage of geomorphic evolution of the basin. The AF indicates that the basin is slightly tilted towards the right. Overall, the results imply that the study region is in the equilibrium stage, has a slightly elongated shape, and has moderate to low flow rates with less sensitivity toward erosion. The study results are highly beneficial for developing and planning soil and water conservation structures and watershed management strategies. The study can be further extended for sub-watershed prioritization, locating potential groundwater zones, and water harvesting sites.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.