Morphometric assessment and prioritization of the South India Moyar river basin sub-watersheds using a geo-computational approach

ABSTRACT The present study analyzed the river morphometric characteristics of the Moyar river basin, which consists of seven sub-watersheds (SWS), located in the upper Bhavani River basin in South India. The morphometric appraisal was carried out based upon the digital elevation model using the geographical information system (GIS). The study area comprises the seven SWS. River morphometric parameters have been classified based upon the characteristics i.e., linear, areal, and relief aspects. The drainage patterns clearly exposed effective regional tectonics, and the stream orders of the basin are primarily controlled by physiographic and tectonic structure in the study area. The bifurcation ratio was recorded from 3.8 to 6.2, and the higher values of the mean bifurcation of the all stream orders revealed that the geological and tectonic control of the river basin i.e., SW1, SW2, and SW3. Likewise, the result exhibited that the priorities level of each and every SWS will assist the priority rank such as highest priority was given to SW3 (with a compound value of 2.40), and SW4 (compound value of 5.60) is the lowest priority in the Moyar river basin. Furthermore, the novelty of the study revealed that the three SWS (SWS3, SWS7, and SWS6) are highly susceptible and it requires appropriate sustainable soil and water conservation.


Introduction
Watershed is defined as part of river basin which is runoff from the rainfall, and its collected and drained by streams it analogous a watershed area.Watershed areas that act as a reserve for natural resources are water, soil, and biodiversity and amongst the ecologically richest place in the world.Furthermore, there are multiple human interactions with watersheds for socioeconomic and other livelihood activities.The watershed contains both natural and community aspects; therefore, as a result of the human interventions in these areas, it is necessary to consider watersheds for more sustainable resource management.Additionally, the watershed management is critical for achieving goal of food security (German et al., 2007;Meena et al., 2015).Morphometric analysis can help to provide improved knowledge and vital data for water resource management, and it led to the development activities (German et al., 2007;Javed et al., 2009;Meshram & Sharma, 2017).An appraisal of morphometric study is based upon the mathematical measurement approach of the earth's surface i.e., surface, shape, and dimension of landforms (Annaidasan, 2019;Verma et al., 2022).It calculates based upon the linear, areal, and relief aspects of the sub-watershed (SWS) and its numerical or geographical landscape characteristics.Direct or converse relationships for runoff, soil erosion, and sedimentation risks are based on morphometric assessment (Fenta et al., 2017;Meshram & Sharma, 2017;Singh, 2014;Verma et al., 2022) and can be categorized to prioritize SWS.Sustainable watershed development and planning are very crucial for natural resource management system based on the prioritization of SWS (Shrimalil, 2001).Geocomputational approach is an important technique of morphometric assessment, which provide the widespread information regarding the essential parameters, and it has extracted digital elevation model (DEM) from the remotely sensed data with respective sensor of shuttle radar topography mission (SRTM).
Watershed prioritization ranks different watersheds in a given catchment area in relation to the order in which they might require treatment or conservation measures.Numerous existing studies have undertaken watershed prioritization using morphometric analyses of linear, areal, and relief based on morphometric parameters that have been used with GIS and remotesensing (RS) techniques in the India, including (Agarwal, 1998;Jaganathan et al., 2015;Javed et al., 2009;Meshram & Sharma, 2017;NAG, 1998;Shrimalil, 2001;Singh, 2014;Verma et al., 2022) While the morphometric characteristics of the Karso watershed recommend the suitable SWS for soil and water conservation (Chopra et al., 2005).Remote Sensing and Geographical Information System (GIS) played an important role to assess the SWS measurements location of check dam priority which was estimated by sediment yield index and morphometric characteristics based on using geospatial technology (Srinivasa et al., 2004) Morphometric assessment of the SWS priority is based on the RS and GIS at Tumkur regions.Quantitative approach for morphometric analysis was carried out as linear and areal parameters of two watersheds, (Agarwal, 1998) based on the morphometric parameters.SWS prioritization was evaluated using the geospatial technology.Similarly, remotely sensed data and GIS technique were adopted for watershed prioritization that was undertaken by (Khan et al., 2001).A quantitative study of morphometric characteristics using a geospatial and geo-computational approach for the examination of morphometric characteristics and SWS prioritization was produced (Meshram & Sharma, 2017).RS and GIS techniques have been utilized for investigating morphometric characteristics; research investigations give new and timely data for researchers' examination.This research adds to watershed-based knowledge that will be better to enable the future planning and sustainable management of watershed areas.The research also provides additional information for researchers undertaking similar studies.Furthermore, drainage network and characteristics are formed based upon the regional tectonics (Verma et al., 2022).The present study is an extensive measurement of the Moyar river basin regardingg all the aspects of the basin i.e., areal, linear, and relief; it would be helping to emerge shortages such as ground water level and surface soil erosion of the basin.

Study area
The Moyar river basin is located in the Western Ghats near to the Erode and Nilgiris district of Tamil Nadu in Southern India; it is geographically located at 11° 34′ 0″ N and 76° 56′ 0″ E. The Moyar river basin is one of the tributaries of Bhavani river in South India which originating from a small town called Mayar near to Masinagudi.The environment of river basin is situated on subtropical region in India.The yearly average temperature is 30°C and minimum average temperature is 18°C.Furthermore, the elevations of the river basin from 300 m above mean sea level (mamsl) and 2600 mamsl at the upper levels.700 mm precipitation can be received at the lowlands, and almost 3000 mm in the upper land.The lower level topography is undulating whereas uplands are hilly in the western regions.The vegetation includes meadow, deciduous, and coniferous hilly forests estate and rural crop yields.Majority of the basin has been occupying the tropical climate, and from January to May dry climate can be found while substantial downpours during the Southwest (SW) monsoon (June-September), and Northeast (NE) monsoon (October-December).The Southwest monsoon predominantly playing a major role in the Western part of the basin.Furthermore, the Northeast monsoon mostly influences the eastern part of the basin.This formation of the slopes running North-South way acts to dissect the two monsoons.Furthermore, Moyer River is one of the crucial rivers for Bhavani river basin, and it is an ecologically potential area with Mudumalai tiger reserve forest, and politically it is very sensitive region, since sharing the boundary among the three Indian states i.e., Tamilnadu, Karnataka, and Kerala.Consequently, the study revealed the present circumstance status of the Moyar river basin by geo-computation approach.Moyar river's original drainage has been superposed by subsequent pattern as a latter development, and high hill slopes can be found subden trict, drainage density and texture is low, where soil can be found porous, since infiltration is more.Therefore, soil slips on the slopes have been transport of silts to the reservoir.Thus, these slopes of fail occur on steep slopes.There are two types of landforms i.e., Doddabetta and Udhagamandalam landforms, where Doddabetta land form consists of many high peaks, which have steep rocky without soil cover around which radial drainage pattern.Udhagamandalam landscape has gentle mounts with thick soil development, meandering stream, and general smoothening of hills and is also an important aspect.Hence, these areas are classified as Udhagamandalam land forms.

Morphometric parameters and methodology
The present study created the Moyar river basin's base map using the Survey of India (SOI) toposheet (1:50,000 scale).In addition, the Shuttle Radar Topography Mission (SRTM) (Figure 1) is produced the Digital Elevation Model (DEM) with 90 -meter spatial resolution and comparatively it has an adequate resolution.Consequently, SRTM radar has been penetrating into canopy, whereas ASTER radar recorded the reflections from the tree canopy.Therefore, the present study has adopted that the SRTM image was chosen as extracting the morphometric parameters (downloaded from https://earthex plorer.usgs.gov).Furthermore, it delineates into seven SWS for SWS-based assessment, and boundaries and streams are derived using (Figure 2) the hydrology tool in ArcGIS 10.6 software.
The present study area is divided into the seven SWS which have been numbered SW1 to SW7.The study area consists of a predominantly dendritic pattern.These types of dendritic pattern indicate homogenous rocks and uniform soil types in hilly areas (Girma et al., 2020).Morphometric analysis formula and methods have been defined.Refer Table 1, and the calculated final results show that the status of morphometric characteristics (Table 2) and parameter implication was discussed (Figure 3).

Morphometric parameters
Watershed area (A) is total area of a watershed and is basic watershed characteristics, indicating the storing capacity of water in the study area (watershed).Moreover, a higher number of intercepts indicate a greater capacity of rainwater, higher runoff, and peak discharge.Occasionally, the lower regions of the watershed area often record maximum flooding and sedimentation rates.For the reason that other watershed morphometric features such as shape, length, and stream network parameters also a play a vital role.The present study revealed that the watershed area varies from the minimum of 139.3 km 2 at SW6 with the maximum of 375.4 km 2 at SW1. Watershed perimeter (P) signifies the boundary size of watersheds, with the perimeter ranging from the smallest being 68.92 km in SW6 up to the largest of 137.21 km at SW1, followed by next largest SWS SW2, SW7, SW4, SW5, and SW3 (Figure 4).

Watershed length (Lb)
is the dimension of the basin calculated along the main water resources from the basin outlet to divide (Schumm, 1956).The huge volume of water travels to the main channel of the watershed; with the longest length of SWS is 31.18km in SW1, whereas the shortest length of SWS was 16.86 km in SW6; the next largest SWS being: SW4, SW2, SW5, SW3, and SW7.
Watershed relief (Bh) is calculated to define the grade of the river as the difference between upper and lower river elevation.The maximum elevation was 2633 m in SW3, and the lowest was in SW4 at 1196 m from the mean sea level.The highest perimeter of SWS SW1 was 137.21 and lowest perimeter was 68.92 in SW6.
Stream order (U) indicates the stream branching in the SWS river system which depends on the number and the kinds of tributary intersections.The streams are assigned according to the (Strahler, 1957) strategy.The outermost stream types are designated as first stream orders; where two first-order streams are connected and where second-order stream has been classified.Where the subsequent stream orders connect with each others, these are classified as third-order stream etc.It is categorized in increments from upstream to downstream in relation to the geomorphology of a watershed, and the most noteworthy stream order is a major channel of the river basin which create a discharges, runoff, and sediment (Kumar et al., 2017) In this study, the highest elevated order (fifth request) appeared at SW1 and SW7.
Stream number (Nu) is a numerical measure of a watershed's stream branching complexity (Horton, 1945).It reveals a various runoff feature of the basin; for instance, a huge number of firstorder streams demonstrate higher porosity and penetration rates, and it is highly possible to erosion-based topography.Higher number of stream orders is characterised by delicate slate and shale rocks (Biswas, 2016).In current investigation, highest first order can be found at SW1 (659), whereas the lowest first-order streams can be found at SW6 (242).
A stream length (Lu) measure is normal length of streams that differ from other order streams of the basin.Furthermore, it is the mathematical arrangement of initial term in which normal length of streams is of the first order.Generally highest stream order has shortest length (Horton, 1945).Generally, shorter stream lengths are located on upper, steeper slopes, and longer stream lengths located in the lower inclines (Strahler, 1957).Stream length indicates hydrological qualities and bedrock arrangement of the area.In general, porous bedrocks and depleted watershed are associated with a more modest stream number and longer stream length.The current study reveals the longest stream length of 601.75 km at SW1 and shortest of 215.174 km at SW6 (Section −4.2-Table 3).

Derived parameters
The bifurcation ratio (Rb) is an important derived parameter to find the ratio of streams; each order (Nu) deals about streams in the next higher stream order (NU+1; Schumm, 1956).The bifurcation ratio is measured which is of stream network branches (Horton, 1945).Lower RB values indicate a greater degree of branching in the watershed (Suji et al., 2015).In the current study, Rb values are highest at 31.4 in SW1 and lowest at 19.4 in SW6, respectively.
Stream length ratio (Rl): Is the mean stream length of each stream orders (Lu) to be considered the mean length of the next lower order (Lu-1; Horton, 1945).The mean length of the stream order is always higher than the length of the subsequently lower order.Furthermore, Rl indicates sequential improvements of the stream order and it shows the porousness of the rock (Table 1).
As indicated by (Horton, 1945), two basic laws are identified which is number of streams and total length of the stream orders in the basin.The basic law of streams is the relationship between streams number given order, and it is considered as an inverse geometric mathematical series, for example, bifurcation ratio (Table 2).According to Horton's law, stream numbers and stream length generate progressive geometric order in relation which is applicable to all the stream orders.Furthermore, this law appears as a direct mathematical arrangement.The laws can be chequered for every single SWS and the effect of digressed from that of Horton's law which is stream length, and the distinctions can be perform on the SWS.The results may be differing; it depends upon the lithology and presents land control and other natural variables.
Stream frequency (Fs) deals about the total number of streams per area (Horton, 1945).Densities of drainage and stream frequency are lower and higher drainage basins are not directly equivalent.This is based upon the size of the drainage.However, relationship between stream frequency and drainage density shows positively; it indicates the expansion of stream populace with drainage density which is equivalent (Suji et al., 2015).In this study, stream frequency is higher at SW3, SW1, SW4, and SW6, and lesser at SW2, SW5, and SW7.
Drainage density (Dd) shows the total length of stream orders per area (Horton, 1945).It describes the distribution and spacing of stream orders in the watershed.The study area consists of higher drainage at SW7, SW1, SW2, and SW3; and lesser at SW4, SW5, and SW6.
Drainage texture (Dt) considers the total number of stream orders within the perimeter of the watershed (Horton, 1945).This indicates the stream orders occupied in the study area.In the current examination, SW3, SW1, SW6, and SW7 are higher drainage textures, whereas SW2, SW4, and SW5 are lesser drainage textures in the study area.
Length of overland flow (Lo) is normally equivalent to 50% of the corresponding of drainage density of the study area (Horton, 1945).It indicates the total length of the flow of water over the surface concentration into the main streams of the channel.The study area examined the SW7 SW6, SW4, SW3, SW2, and SW1 as higher and SW5 is lowest length of overland flow, respectively.
infiltration number (If) is the overall production of stream frequency and drainage density which indicates the potential infiltration of a SWS area (Schumm, 1963).The results show that SW3, SW1, SW7, and SW6 have higher and SW5, SW4, and SW2 have lower values of infiltration number.
Areal aspects circularity ratio (Rc) shows that the overall ratio of basin to space of the circle boundary is equal to the perimeter of the respective basin area (Miller, 1953).However, it is an appraisal of low, medium, and high values considered as (Rc), which shows the youthful and older stages of basin area in advancement.In this study, SW1, SW4, SW5, and SW7 have lower, while SW2, SW3, and SW6 show higher qualities in circulatory ratio.Illimitable (Strahler, 1957) Estimated Areal/shape aspects Circulatory Rc = 4πA/P 2 ; π = 3.14 Illimitable (Miller, 1953) Elongation ratio Re = (2/Lb) x (A/ π) 0.5 Illimitable (Schumm, 1956) Form factor Ff = A/Lb 2 Illimitable (Horton, 1945) Compactness Coefficient Cc = P/2 (πA) 0.5  Illimitable (Horton, 1945) Elongation ratio (Re) is the measurement of circle shape of the watershed of a similar region as the watershed in relation to the greatest measurement lengthwise of the watershed (Schumm, 1956).As a rule, the ratio varies from 0.65 to 0.35, and if the value is equivalent to one, a watershed is equivalent from all sides.Re is lower at SW1, SW4, SW2, SW3, and SW5, whereas SW6 and SW7 have higher values of elongation ratio, and it is represented as highly elongated.
Form factor (Ff) indicates a watershed with a higher form factor associated with a small height flow (Horton, 1945).The study reveals that the Ff value is lower in SW4, SW2, SW5, and SW3, whereas SW6, SW7, and SW1 are highest form factor documented.
Compactness coefficient (Cc) is a proportion linking the perimeter of the watershed and the circumference of a sphere with an equal surface area to the watershed area (Horton, 1945).It is free of watershed shape and size; however, it relies based upon the slope.The present study reveals that the value for Cc is lower at SW7, SW2, SW3, and SW1 though SW4, SW5, and SW6 are generally higher in compactness coefficient; CC is not principally correlated with watershed size but it is determined through slope.
Ruggedness number (Rn) is the product of the maximum of the watershed basin height and drainage density of the watershed (Strahler, 1958).Rn consolidates inclination of sharpness and basin length.Highest Rn values occur when the slopes are sharp and long.The Rn values were higher at SW5, SW4, SW3, and SW, it is lower at SW7, SW2, and SW6 in the investigation of the watershed area.

Sub-watersheds prioritization
The morphometric assessment is a linear and elevation of their respective parameters with soil erodibility, (Balasubramanian et al., 2017;Meena et al., 2015;Nooka Ratnam et al., 2005;Sangma & Guru, 2020); in general, the most elevated values directly indicate the most erodible soil of the watershed.Accordingly, a SWS exposes the highest values in the linear and relief parameters as the highest ranking, second higher worth was appraised as second position, etc.Similarly, the lowest morphometric values of the watershed were evaluated as the last rank.Areal or shape of the watershed parameters indicates the inverse relationship with high soil erodibility (Farhan, 2017;Javed et al., 2009).The least values indicate the higher erodible of the soil in the respective watershed.In the way, an SWS exposes that the lowest value in the watershed area or shape parameters was appraised as first rank, the following lower value evaluated at second ranking, etc., at that point the highest values evaluated as ranked last.A compound method for averaging values was utilized in this investigation, as it was expected that all morphometric parameters had equivalent significance for each conclusive rank (Jaganathan et al., 2015;Prieto-ampar et al., 2019;Singh, 2014).The ranking of SWS is based upon the consolidate appraisal of adopted morphometric parameters, and the value of the SWS was considered as the quantity of all the parameters.In addition to the least compound values that indicated the highest priority, and it exposed  the immediate attention to sustainable management.These computational results show the highest priority that indicated the least value about 1, likewise second highest values indicated as a number 2, etc (Table 4 & Figure 5).The highest compound values are considered as a lowest priority of the respective watershed (Aher et al., 2014;Balasubramanian et al., 2017;Jaganathan et al., 2015;Javed et al., 2009;Khan et al., 2001;Kumar et al., 2017;Manzoor & Malik, 2017;Meshram & Sharma, 2017;Shrimalil, 2001;Suji et al., 2015;Verma et al., 2022).The results stated that the highest priority demonstrates the best level of runoff, top soil, and soil disintegration risk in that SWS.It is essential to consider an appropriate land and water practices for each SWS according to their rank.Additionally, 10 morphometric parameters were selected and utilized for ranking and prioritization of SWS dependent on their values acquired from the estimation (Table 4) Figure 5 exposes the final priority of the SWS.SW3, SW7, and SW6 are generally most vulnerable to land degradation and prone to soil disintegration.This is related to their intrinsic geomorphometric attributes.Consequently, each watershed needs appropriate consideration for soil and water preservation measures in relation to their priority ranking.

Hydro-geomorphologic characteristics
The morphometric parameters are strongly associated with river hydrologic processes (Diksha et al., 2019;S. Singh et al., 2018;Verma et al., 2022); it reveals an important hydrologic behaviour of a basin i.e., ground water recharge, and soil erosion of the river basin from the quantitative technique based morphometric assessment.

Potential of groundwater recharge
The groundwater recharge potential is defined by stream frequency, drainage density, drainage texture, and length of over land flow (Diksha et al., 2019;Kanhaiya et al., 2019;S. Singh et al., 2019).These are the morphometric parameters that clearly exhibit information regarding the infiltration capacity of the surface and surface runoff, and lower drainage densities of the sub-basins are SW4, SW5, and SW6 favoured of highly permeable subsoil materials, somewhere resistant lithology, under the dense vegetation (Strahler, 1957).The study revealed that these SWS (SW1, SW2, SW3, SW4, SW5 SW6, and SW7) show the potential of ground water recharge.

Characteristics of soil erosion of the basin
The following morphometric parameters, namely, stream frequency, drainage density, drainage texture, and length of overland flow are indicating the surface water runoff and sediments transportation.Furthermore, the surface runoff water could be the occurrence of permeable materials.An average drainage density of the Moyar river basin indicates that the sub-surface material is very hard and permeable cause of drainage density is 1.5 (Figure 6 & 7).The moderate  drainage and drainage texture characteristics show the slightly hard to constriction to artificial recharge structure in the study area.The mean bifurcation ratios were documented between 3.8 and 6.2, and it has been demonstrating the stream network formed in the least structural disturbances (Prieto-ampar et al., 2019;Strahler, 1958;Verma et al., 2022).Additionally, theories are designate that the landscape evolution intrinsically accounts interaction between climatic, tectonic, and surface processes.Subsequently, geological and topographic information can help to understand the soil erosion and topographic evolution.

Conclusion
The study revealed that the geospatial technology is an important tool to substantiate the different phases of the morphometric i.e., linear, areal, and relief, and  various stages of hydro-geomorphologic of the river basin.Morphometric analysis helps to understand the basin structure and pattern.In addition, high values of ruggedness (Rn) and relief (Bh) revealed that the Moyar basin is prone area for soil erosion with the higher of slopes will leadto high surface runoff.These morphometric analyses are supported by further moment of water resource planning and their better management in the water sacristy place of the basin.The various attributes of drainage of the basin play a crucial role in locating the ground water recharge sites.Among the seven SWS, SW4, SW5, and SW6 are secured as the low drainage density; these are the SWS suitable for the construction of ground water recharge structure.However, the study area encompasses the streams upto fifth order, whereas fourth-order and fifth-order streams are flowing on the comparatively plain area and this will be a suitable area for making a small dam (check dam) to recharge the groundwater and further planning to increase the water table in the Moyar basin.

Figure 1 .
Figure 1.Location of study area.

Figure 6 .
Figure 6.Nick point of the stream in Moyar river.

Figure 7 .
Figure 7. Geological structure and topography of the streams in upper Moyar river.

Table 1 .
Morphometric parameters in Moyer river basin.

Table 3 .
Linear aspects of sub-watersheds.