Compounding morphometric parameters for prioritization of vulnerable watersheds for land restoration planning in Beas sub basin, India using geospatial techniques

Drainage catchments, basins and watersheds, at different levels, are the basic units for natural resource management including soil and water. Globally, integrated watershed management strategies have been recognized as the most efficient way of reclaiming degraded lands (Jain & Ramsankaran 2019; Garg et al. 2020; Kaur et al. 2022). Watershed management helps to systematically handle problems such as sediment reduction, flood control, drought and soil water conservation (Mehta et al. 2022; Sarkar et al. 2022). Soil supports life on Earth by supporting food production, biomass production and linkage between different spheres of Earth (Ferreira et al. 2022); therefore, soil is an integral part of the global ecosystem continuously affecting both environment and economy (Pandey et al. 2021). Combating soil degradation needs improved understanding over time of its causes, impact, degree and acquaintance with climate, soil, water, land cover and socioeconomic factors (Sur & Chauhan 2019a). Therefore, concerted efforts are required to prioritize the vulnerable areas to optimally conserve soil and water resources for a better tomorrow.

The watershed is regarded as an important entity because it is an integration of three major units, namely hydrological, biophysical, and socioeconomic units; therefore its importance is unarguable (Shivhare et al. 2022; Mehta et al. 2023). Prioritization of watersheds at micro level can help to judiciously rank environmentally degraded lands and treat them with soil and water conservation measures on a priority basis (Verma et al. 2023a). Studying morphometric characteristics of a watershed helps to identify effectively critical watersheds by quantitative assessment of their form, feature and size without much understanding of soil or land characteristics (Pourghasemi et al. 2021). It can directly and indirectly capture geomorphological, geological and hydrodynamic characteristics of a watershed by assessing the maturity of the fluvial system and the drainage patterns (Nikolova et al. 2021).

Development of space technology over the last four decades has significantly helped to replace conventional surveying techniques. Satellite images coupled with Geographic Information System (GIS) make complex spatial assessment and large dataset handling very easy for planning and management (Kadam et al. 2019; Verma et al. 2023b). Further, availability of open access high resolution digital elevation models (DEM) and high resolution satellite images has helped to calculate morphometric dimensions using different customized software and statistical tools in a robust way (Arefin et al. 2020; Tesema 2022).

The present study involves use of morphometry and land use change information coupled with the weighted sum analysis technique to prioritize critical watersheds in GIS environment. The results highlight morphometric characteristics for prioritization of the Beas sub basin, which is a perfect representative of high, medium and low relief regions from the Indus Basin in India. Beas River is susceptible to numerous catastrophic events due to its geo-climatic and socioeconomic conditions (Singh et al. 2021); therefore planning and management of this area is crucial. As land degradation is multilayered and complex (Sur & Chauhan 2019b), soil degradation should be prioritized to avoid vulnerable situations in this region. The literature review clearly demonstrates that many studies across the globe and in India have laid out successful planning of soil water conservation by dividing river catchments into smaller hydrological units (Ahirwar et al. 2019; Abdeta et al. 2020; Das et al. 2021; Manjare & Singh 2021; Kadam et al. 2022). This popular method of management was therefore integrated with morphometric analysis at different scales using multicriteria decision analysis (MCDA), weighted sum analysis (WSA), principal component analysis (PCA), and compound factor analysis (Rahmati et al. 2019; Shaikh et al. 2022) in several studies. The main objective of this study is to assimilate 49 morphometric parameters under three classes, (a) linear, (b) areal and (c) relief aspects, and land use land cover (LULC) change to model and identify critical watersheds using remote sensing-based geospatial techniques. This technique helps in quick assessment of the morphometric parameters and LULC to integrate all parameters in one platform for better understanding. Each of the parameters was computed for 28 watersheds delineated from the Beas sub basin and finally compound factor analysis was carried out. This study is unique because for the first time detailed morphometric analysis has been carried out in this area to identify the most vulnerable sub watershed in the Beas sub basin. This region supports a major portion of the agricultural base of the country and is socio-economically important. This study would help in laying down a holistic management plan which will enable the stakeholders to build soil erosion structures in upstream hills and downstream plains. In conjunction, this study would also help in establishing a methodology to integrate important parameters to aid in the identification of vulnerability to land degradation in a region.

The study is mainly based on the DEM. Advanced Land Observing Satellite (ALOS) Phase array type L-band Synthetic Aperture Radar (PALSAR) DEM data of 12.5 meters were downloaded from the Alaska satellite facility geo portal (http://asf.alaska.edu/) for analysis. Out of several open source DEMs, ALOS PALSAR DEM was preferred because of its high spatial resolution over other DEMs such as SRTM, MERIT, ASTER and GEOTOPO (Agarwal et al. 2020; Shaikh et al. 2021; Gangani et al. 2023). The 12.5 meter DEM can help to capture minute details of the terrain which is crucial for computation of the morphometric parameters. These datasets were further subjected to rigorous morphometric analysis for identifying critical watersheds. Ancillary datasets like Survey of India toposheets and hydrogeological maps were also used for validation purposes.

Using ALOS PALSAR DEM, Beas sub basin was divided into 28 watersheds (Figure 4(a)), in accordance with stream network which ranged from first to seventh order (Figure 4(b)). An outlet point was marked in each watershed, indicating that all streams within the watershed flowed finally into this point. Further, the final outlet point of the entire 28 watersheds comes out to be Harike wetlands located in the south of the Beas sub basin. The size of the watersheds range from the largest, number 28, at 2,748 km² (14.20%) to the smallest, number 19, covering 41 km² (0.21%). Detailed description of the 28 watersheds is provided in Table 2. The altitude range of the sub basin varies from 6,546 m in the northern part to 156 m in the southwestern part (Figure 4(c) and 4(d)).

Linear aspects consider only one-dimensional characteristics of morphometric analysis over any basin (Asfaw & Workineh 2019). This study accounted for linear parameters which consist of stream order characterization, stream length calculation, stream number identification, mean stream length calculation, stream length ratio, mean stream length ratio, weighted mean stream length ratio, bifurcation ratio, mean bifurcation ratio, weighted mean bifurcation ratio, mean basin width, mean channel length, channel index, minimum area distance, center of gravity of watershed, wandering ratio, fitness ratio, and length area relation.

Stream order, the very first step of drainage analysis was based on hierarchical ranking, following the stream ordering technique of Strahler (1964) because of its simplicity and fast computation processing (Dubey et al. 2015). The smallest tributaries were numbered as 1st order and so on. This stream order depends on basin shape, size and relief characteristics of the basin (Haghipour & Burg 2014). The result revealed that the Beas catchment has 4,126 streams connected with seven stream orders (Table 3). 1st order, 2nd order, 3rd order, 4th order, 5th order, 6th order and 7th order streams comprised 3,120, 769, 185, 41, 8, 2 and 1 streams, respectively. Lower order streams were found to be higher in number and in higher reaches, indicating young topography. The sudden fall in the number of 3rd and 4th order of streams indicates major morphological change in the basin.

The stream ordering always changed as per the change in the geological and geomorphological structure (Shekar & Mathew 2022) of the region; the same was perceived in the Beas catchment. Since the highest stream order existing in the watershed is regarded as the order of the watershed, Beas sub basin can be described as a seventh-order watershed system. Scientifically stream ordering has a negative relationship between number of stream and order of stream (Doke et al. 2020); the same relationship is also observed in this region where the 1st order stream is the maximum followed by the 2nd stream order and then the 3rd, 4th, 5th, 6th, and 7th stream order in decreasing pattern as shown in Table 3. As the order of stream increases, discharge also increases (Hajam et al. 2013) therefore the region with 7th stream order discharges the maximum amount of water in the Beas catchment.

The mean stream length value (Lsm) of Beas catchment ranged from 1.92 to 404.27 km (Table 3) with a mean value of 101.06 km. Lsm values are directly proportional to the size and topography of the basin (Rai et al. 2017), indicating characteristics property of the basin. The inference of detailed characteristics of the drainage pattern in the Beas catchment was identified to be a braided pattern because the streams flow along a slope which ranged from steep mountainous rugged terrains to gentle plains. The stream length ratio (Lur) between the streams of different orders did not show any particular pattern of increment or decrement. Therefore it clearly signifies that variation in slope and topography is observed in the region and the river in this region crosses youth, mature and old stages of geomorphic development. The weighted mean stream length (Luwm) is 2.15 indicating a longer mature stage in the region.

Bifurcation ratio (Rb) indicates the ratio of number of streams of a given order ‘u’ to its next higher order ‘u + 1’ (Horton 1945). It is an important parameter, expressing the water carrying capacity of any basin. Rb is a morphometric technique which helps to understand the degree of integration prevailing between streams of various orders in a sub basin; therefore it helps to interpret shape of the basin and runoff behavior in the region (Joy et al. 2023). Very high bifurcation ratio indicates time duration of runoff concentration in an area and vice versa. Rb for the Beas sub basin varies from 4.06 to 2 and the mean bifurcation ratio (Rbm) is around 3.98 and weighted mean bifurcation ratio (Rbwm) is around 4.11 which clearly indicate that in this region flow of water is at a medium rate and the region is semi-prone to floods.

Stream length was calculated according to law proposed by Horton (1945). Most of the time, the total length of streams is maximum in the 1st order, and decreases as stream order increases. In the study area main channel length is 203 km, mean basin width is 67.35 km and minimum areal distance is 256.85 km² of the Beas sub basin, which indicates that run off has a shorter distance to travel and therefore shorter lag time of discharge will be observed. The channel index (CI) was calculated to indicate sinuosity value. CI 1.27 indicates that the Beas River has a braided pattern and is highly dynamic in nature as per Mueller (1968). The center of gravity of the 28 watersheds in the entire Beas sub basin is 76°24′43.622″E 31°56′8.604″N; this point is extremely important because it forms the nodal point of load sharing sediments and water discharge from the upper catchment of the study area. The rho coefficient ranged between 0.40 and 0.80. The higher value of rho coefficient indicates higher water storage capacity during the flood time and as such attenuates erosion effect during the discharge. Rho coefficient indicates impact of climatic, geological, geomorphological and human-induced factors (Rai et al. 2018). According to Table 3 the rho coefficient value indicated moderate erosion effect whereas the few with higher coefficient indicated high erosion effect in the region. Wandering ratio (Rw) is the ratio of the mainstream length to the valley length (Smart & Surkan 1967); in this region wandering ratio is around 0.71 indicating the sinuous nature of the streams in the region. Fitness ratio is an indicator of topographical index (Kant et al. 2023); over the Beas sub basin it has been calculated to be 0.16. Finally length area relation (Lar) of the region was computed to be 522.38 which is an important factor to express the relationship between streams and areal dimension.

The areal aspects of a drainage catchment give inference about lithology, geological structure, climatic conditions, and denudation history of any river catchment. It comprises morphometric parameters such as drainage density (Dd), drainage texture (Dt), stream frequency (Fs), drainage intensity (Di), circulatory ratio (Rc), elongation ratio (Re), form factor (Rf), infiltration number (If), length of overland flow (LoF), constant of channel maintenance (C), circularity ratio (Rcn), lemniscates (k), compactness co-efficient (Cc), and texture ratio (T).

The drainage texture (Dt) for the sub basin was calculated to be 3.21 indicating that the texture of the watershed is very coarse. Low Dt results in a rough surface while high Dt leads to a smooth texture, therefore this region has comparatively course texture. The Dt for 28 sub-watersheds ranges from 0.28 to 1.47. The Dt is very high in sub-watersheds 28 and 9. It is very low in sub-watersheds 3, 7, 12, 13, 24, and 26 (Table 4). Texture ratio (Rt) is another factor which depends on the lithology, infiltration ability and relief aspect of the topography. The Rt value of 2.46 is comparatively low, indicating moderate influence of soil structure in the region.

Stream frequency (Fs) is the total number of stream segments per unit area, in other terms the ratio between the total number of stream segments cumulative of all orders and the basin area. Stream frequency is affected by infiltration capacity, permeability and relief. It depends on the drainage density, rainfall, relief, and resistivity of rocks in the basin. The lower value of Sf indicates a poor drainage network (Thomas et al. 2010). Stream frequency increases with high slopes and higher rainfall. The Fs of the area was calculated to be 0.21 per km², which is low. The Fs of the watersheds ranges from 0.14 to 0.34 per km² as shown in Figure 5(c). The stream frequency is very low in watersheds 2, 3, 7, 8, 13, 14, 24, and 25. Low Fs results in low water infiltration thereby reducing surface runoff. It is very high in watersheds 2, 6, 15 and 19 (Table 4). High Fs in these watersheds implies that they have more rocky outcrops and are devoid of vegetation.

Drainage intensity (Di) is ratio of stream frequency and drainage density. The Di in Beas sub basin was found to be 0.33, which is low, and it implies that the stream frequency and drainage density have slight importance to the extent to which agents of erosion work in this region. The Di varies from 0.14 to 0.34 with low Di values in watersheds 23, 24, and 25. The high Di values were found in watersheds 2, 9, 15, and 21 as shown in Figure 5(d) and Table 4.

Circularity ratio is expressed as the ratio between the areas of the basin to the area of a circle having the same perimeter (Strahler 1964). Its value varies from 0 (minimum circularity) to 1 (maximum circularity) and is affected by stream frequency, drainage density, climate, geological structure, slope, and relief of the basin, among other factors. The high, medium and low value of circulatory ratio indicates old, mature and young stages of the basin. The circulatory ratio of Beas sub basin is widely influenced by variety of factors like stream length and frequency, geological structures, land use/land cover, and climate (Vishwas 2021). Circulatory ratio of Beas sub basin is 0.15, which infers that it is a sub basin which is elongated in nature and with semi-permeable rock structures. Further elongated ratio of the Beas sub basin is 0.27 indicating a tectonically inactive setting which may make the region more vulnerable to disasters like floods (Sharma & Sarma 2013). In conjunction to this, the form factor was calculated for the Beas sub basin which was around 0.23, indicating no rapid discharge at the main outlets of the sub basin.

Infiltration number (If) helps to reflect the water transmission potential of any watershed (Prabhakaran & Jawahar 2018). Infiltration number in the Beas sub basin is 0.13 and in the watersheds it ranged from 0.07 to 0.25 as shown in Figure 5(e). Watersheds with low If values include 3, 7, 13 and 14 indicating that the amount of water entering the soil is high and by implication runoff is low, but this condition applies only when precipitation rate does not exceed infiltration rate. Whereas watershed 19 has high If value because it is a rocky outcrop region which means that the water infiltration rate is low and surface runoff is high over this watershed.

Length of overland flow (LoF) helps to understand the length at which rainfall runs over the land surface before it drains into a channel. The LoF for Beas sub basin was calculated to be 0.78 km, which implies that the watershed has a long flow path with reduced runoff. The LoF ranges from 0.58 to 1.06 (Figure 5(f)). The values of the LoF are lower in watersheds 23, 24, 25, 27 which means that surface runoff will enter stream channels very rapidly signifying steep slopes that lead to high runoff in the region. The areas with low LoF value are highly vulnerable to flooding due to reduced water percolation. Areas with high LoF values have high infiltration and less direct surface runoff especially in watershed 9.

Constant of channel maintenance (C) is defined as the reciprocal of drainage density as a property to define overland flow. Indirectly, it can be expressed as a required minimum area for the maintenance and development of a channel (Dutta & Roy 2012). Hilly areas generally have low C values due to lower infiltration of bare soil and high overland flow. Across the entire watersheds, the C varies from 1.16 to 2.11 (Figure 5(g) and Table 4). Watersheds 23, 24, 25 and 27 have very low C values indicating that they are highly erodible due to poor vegetation cover and low infiltration rate. Higher C value is observed in watershed 7 signifying that the area is least erodible which also reflects that it has dense vegetation cover and high infiltration rate in the soil.

Lemniscate (k) factor is used to determine the slope of the watershed. The k value of the Beas sub basin was found to be 2.46. The k value being moderately low indicated that Beas Basin is comparatively less erodible due to high vegetation cover and soil structure in the region.

Compactness coefficient (Cc) of the entire sub basin was calculated to be 2.62, which is low, and it indicates high infiltration and low erosion risk over the region. The Cc of the watersheds ranges from 1.38 to 2.59 (Figure 5(h)). Watersheds 1, 3, 5, 7, 8, 24, 26 have high Cc values and watershed 25 has low Cc value.

Relief aspect represents three dimensional characteristics of any watershed; it deals with topographic dimensions (Shekar et al. 2023). This study comprises morphometric study of relief aspects using the following parameters basin relief, relief ratio, absolute relief, relative relief, gradient ratio, ruggedness number, Melton ruggedness number, watershed slope, shape factor ratio, dissection index, height of basin mouth, maximum height of basin, hypsometric integral, and topographic wetness index.

Relief ratio (Rh) denotes the ratio between total reliefs to the length of the principal drainage line (Lindsay & Seibert 2013). This indicator measures overall steepness of the drainage basin and is an indicator of the intensity of erosion processes (Babu et al. 2016). The relief ratio of the river sub basin is 0.02. The high basin relief, circular basin shape, and small basin area increase the Rh. The Rh values generally are higher in the mountain environment than the plateau river basin (Thomas et al. 2010).

Relative relief (Rhp) is a morphometric parameter which signifies variance in height with respect to area. This parameter is a key factor to explain the intensity of erosion processes. The Rhp of Beas River sub basin varied from 0.38 to 34.14 (Figure 6(b)). Watersheds with high Rhp values are 2, 11 and 16. Watersheds with low Rhp values are 7, 8, 13, 14, 23, 24, 25, 26, 27. Gradient ratio (Gr) is an important factor which helps to indicate runoff assessment and slope channel. The gradient ratio of the Beas sub basin is 22.25 indicating steep sloping and high runoff intensity.

Ruggedness number (Rn) is a morphometric parameter which helps to determine slope steepness and length indicating the extent of the instability of land surface. The Rn values range from 0.08 to 3.16 (Figure 6(c)). The higher Rn values were observed in sub-watersheds 2, 4, 6, 9, 10, 12, 15 and lower values in watersheds 7, 8, 13, 14, 23, 24, 25, 26, 27, and 28. High Rn value indicates structural complexity in the area, which is therefore prone to erosion.

Melton ruggedness number (Mnr) helps to understand flow accumulation of a river in a watershed. The Mnr value of Beas sub basin ranges between 3.03 and 217.87 (Figure 6(d)). The higher Mnr values were observed in sub-watersheds 2, 3, 10, 11, 12, 15, 16 and lower Mnr values in watersheds 7, 8, 13, 14, 23, 24, 25, 27, 28. This indicated that risk prevailed more in high Mnr values because of high rate of water accumulation.

Slope is an important morphometric parameter controlled by morpho-climatic processes of any area. It is basically a function of gradient. It determines the infiltration vs runoff relation, so is important to understand the nature of slope (Sreelakshmy et al. 2023). The very high slope (>40°) dominating the upper reaches of Beas sub basin indicates low infiltration related high drainage density and frequency. Figure 6(e) clearly shows that the values of slope of Beas sub basin range from northeast to west. The values of slope in the region ranged from greater than 30° to less than 2°. Shape factor ratio (Sf) is the square of the basin length (Lb) to the area of the basin (A). The Beas River sub basin shape factor ratio is 4.26 which indicated that the sub basin is neither too elongated nor too circular so the sub basin takes a moderate time for concentration of flow of water.

Dissection index (Dis) is the ratio between relative reliefs to its absolute relief. It indicates the vertical erosion and dissected characteristics of a basin (Haghipour & Burg 2014). The value of Di ranges between 0 (absence of vertical dissection) to 1 (vertical areas) indicating maximum and minimum denudation stages, respectively. The dissection index was further used to estimate roughness in the region due to numbers of valleys and ravines formed by the stream. The dissection index ranged from 0.36 to 0.93 over the Beas sub basin (Figure 6(f)). High values of Dis were observed in watershed numbers 1, 3, 4, 9, 10, 11, 12, 15, 17, 18, and 21. And a low value of Dis was observed in watershed 27. High Dis indicates therefore high vulnerability in that watershed.

Morphometric parameters are true indicators of underlying geology, geomorphology, relief, slope, and climate as well as hydrological dynamics. The present study aimed to unearth the morphological and hydrological characteristics as well as changes of morphometric parameters in different morpho-climatic settings. This study integrates ALOS PALSAR DEM with GIS enabled quantitative and qualitative morphometric assessment of each linear, areal and relief parameter in 28 sub-watersheds. The Beas sub basin located in the northern part of India is drained by seven stream orders. The finding of this study showed that the potential for surface runoff, accumulation of water and erosion varied across the sub-watersheds as shown from stream frequency, infiltration number, drainage density, drainage texture and relief ratio analysis. The low elongation ratio and form factor values indicate that the watershed is elongated. The study also highlights that the hypsometric integral of the watershed indicates three stages of the Beas sub basin, old, mature and youth, and how the erosion process is affecting each stage. Out of the 28 sub-watersheds, sub-watersheds 2, 6, 12 and 16 are classified as a very high priority; hence, they are susceptible to erosion. The very high priority areas were suggested for watershed management measures to mitigate the risk of flood and erosion. The Beas sub basin holds much potential for resources exploration especially in agriculture, electricity generation, water resources management, and flood mitigation. Parts of the watershed with 4th, 5th, 6th, and 7th order streams are suitable for dam construction for irrigation farming, power generation, and supply of water for domestic use. This study can be used by policy makers for holistic management of the region.

The authors are thankful to NASA and JAXA for providing open source datasets. The authors are also thankful to Punjab Remote Sensing Centre for providing software facilities in the Geomatics laboratory.

All relevant data are available from an online repository or repositories: https://asf.alaska.edu/data-sets/derived-data-sets/alos-palsar-rtc/alos-palsar-radiometric-terrain-correction.

The authors declare there is no conflict.