Assessment of morphometric characteristics of Shetrunji River basin using remote sensing and geographical information system (GIS)

The study area, that is, Shetrunji basin falling in the district of Bhavanagar, Amreli and Junagadh, is a major one among 71 river basins of Saurashtra region of the Gujarat State, India. Using the remotely sensed images of the Indian Remote Sensing SatelliteP6 (IRS P6), Linear Imaging Self Scanner III (LISS III) and Carosat satellites, the maps for the theme of land use/land cover, soil, drainage, slope and contour were prepared adopting the PCI Geomatica 10.1 software. The geographical information system (GIS) analysis was made for the said themes using the ArcMap V9.2. The Shetrunji basin was found as 7 th order basin. The mean bifurcation ratio was found as 4.51 for the basin and it varied from 1.8 to 4 for the 17 watersheds which indicated that the geological structures did not amply disturbed the drainage pattern. The present study aims to assess the morphometric characteristics of Shetrunji basin and the sub-watersheds for its planning and development. Various morphometric characteristics of the Shetrunji basin have been assessed by applying GIS techniques. Strahler’s, method have been employed to assess the fluvial characteristics of the study region. Each morphometric characteristic is considered as a single parameter and knowledge based weight age has been assigned by considering its role in soil erosion. The morphometric properties determined for this basin as a whole and for each watershed will be useful for the efficient planning of water harvesting and groundwater recharge projects on watershed base.


INTRODUCTION
Shetrunji is a major river basin among 71 river basins of Saurashtra region of Gujarat encompassing districts of Bhavanagar, Amreli and Junagadh with 53.44, 45.21 and 1.35% of total area, respectively.The Khodiyar and Shetrunji Dams are located on Shetrunji River having catchment area of 384 and 4317 km 2 , respectively.A watershed is an ideal unit for management of natural resources like land and water and for mitigation of the impact of natural disasters for achieving sustainable development.Soil conservation is the most important measure taken to check the ravages of soil erosion in India.Land is a precious resource as it is the physical base of biomass on the earth.Conservation of such type of natural resources is important to mitigate the increasing demand of land and water resources.Morphometry is the measurement and mathematical analysis of the configuration of the earth's surface, shape and dimension of its landforms (Agarwal, 1998;Obi Reddy et al., 2002).The relationship between various drainage parameters and the aforesaid factors are well recognized by many workers.Recently, many researchers have used remote sensing (RS) data and analyzed them on geographical information system (GIS) platform for understanding the morphometric properties of the catchment.Analysis of various drainage parameters namely ordering of the various streams and measurement of area of basin, perimeter of basin, length of drainage channels, drainage density (Dd), drainage frequency, bifurcation ratio (Rb), texture ratio (T) and circulatory ratio (Rc) (Kumar et al., 2000).The close relationship between hydrology and geomorphology play an important role in the drainage morphometric analysis (Horton, 1932).River basins comprise a distinct morphologic region and have special relevance to drainage pattern and geomorphology (Doornkamp and King, 1971;Strahler, 1964).In a particular basin sprawl, a drainage type is developed when a drainage network of channel lines have adjusted together with the subsurface structure.Morphometric analysis of a watershed provides a quantitative description of the drainage system which is an important aspect of the characterization of watersheds (Strahler, 1964).Various scholars have carried out morphometric analysis of river basins by using RS and GIS techniques.Shrimali et al. (2001) have worked on Sukhana lake catchment in the Shiwalik hills for the delineation and prioritization of soil erosion areas by GIS and RS.

Study area
The study area is Shetrunji river basin in Saurashtra region of Gujarat (Figure 1).It is located between 21° 00' to 21° 47' N latitude The RS and GIS software used for the study is PCI Geomatica V10.1 and ArcGIS-ArcMap 9.2.The satellite images of Indian Remote Sensing SatelliteP6 (IRS P6), Linear Imaging Self Scanner III (LISS III) captured in October, 2005 and February, 2008 having resolution of 23.5 × 23.5 m and images from Google Earth Pro of study area were used.Map of India with scale 1:15, 00,000, Gujarat with scale 1:37,50,000 and Watershed map of Gujarat (scale 1:37, 50,000) and soil maps of India were used for the experimental study.The thematic maps like drainage map, land use and land cover map, soil map and contour map were prepared using ArcGIS-ArcMap 9.2.Based on visual interpretation of geo-coded IRS P6-LISS III and watershed atlas of All India Land Use Survey (AILUS) the demarcation of watershed area was done in Shetrunji river basin.A total of 17 sub-watersheds were identified within this basin.Digitization work has been carried out for entire analysis of basin morphometry using GIS software (ArcGIS ver: 9.0).The order was given to each stream by following Strahler (1964) stream ordering technique.The attributes were assigned to create the digital data base for drainage layer of the river basin.The map showing drainage pattern in the study area (Figure 3) was prepared.The linear parameters like stream order, stream length, bifurcation ratio, stream length ratio and length of overland flow stream frequency, areal parameters like stream frequency, drainage density, texture ratio, elongation ratio, circularity ratio, form factor and compactness coefficient and relief parameters relief, relative relief ,relief ratio, channel slope and ground slope or watershed average slope were determined using GIS.

RESULTS AND DISCUSSION
The GIS analysis of the land use showed that area of 17.48, 17.82, 12.49, 33.32, and 19.59% were under water body, wasteland, built up, agriculture and forest, respectively.The GIS analysis showed that 25.92, 5.19, 37.80, 5.27 and 36.27%area is having soil type of clayey, skeletal clayey, fine montmorillonitic, fine loamy and loamy, respectively.It was seen that the fine soil exist in major part of the basin.It could be seen that the major land area of the basin is having the slope less than 1%.The land slope of the basin in different watershed varied from 0 to 50%.The contour values in the basin varied from 0 to 605 m.The large difference in the contour value is due to the Shetrunjay Mountain at Palitana existing in the basin.The close spacing of the contour of the basin indicated hilly ranges, while wider spacing indicates flat topography.Drainage patterns of stream network from the basin have been observed as mainly dendritic type which indicates the homogeneity in texture and lack of structural control.The basin is divided into 17 watersheds with codes viz.5G2B2a, 5G2B2b, 5G2B2c, 5G2B3a, 5G2B3b, 5G2B3c, 5G2B4a, 5G2B4b, 5G2B4c, 5G2B5a, 5G2B5b, 5G2B5c, 5G2B5d, 5G2B6a, 5G2B6b, 5G2B6c and 5G2B6d shown in Figure 2.

Linear aspects of the watershed
Linear aspects of the 17 watersheds, related to the channel patterns of drainage network where in the topological characteristics of the stream segments in terms of open links of the stream network system are analyzed.The parameters such as stream order, number of streams, stream length, bifurcation ratio, length of overland flow and stream length ratio are taken into account for the present study and the results have been tabulated in the Table 1 as a whole and Table 2 as watersheds.
The study area is a 7 th order drainage basin covering an area of 5646.54 km 2 .The total number of 8284 streams were identified of which 6285, 1512, 351, 100, 27, 8 and 1 numbers were 1 st , 2 nd , 3 rd , 4 th , 5 th , 6 th and 7 th order streams, respectively.The higher amount of stream order indicates lesser permeability and infiltration in these sub-watersheds.The total length of the 1 st order streams is highest, that is, 4861.80 km, and that of 2 nd order is 1961.02km, 3 rd order is 1113.67 km, 4 th order is 552.47 km, 5 th order is 266.12 km, 6 th order is 135.89 km and the lowest is of 7 th order of 123.90 km, respectively.Generally, the higher the order, the longer the length of stream is noticed in the nature.Longer length of stream is advantageous over the shorter length, in that the former collects water from wider area and greater option for construction of a bund along the length.Lower stream lengths are likely to have lower runoff (Chitra et al., 2011).Horton (1940) and Strahler (1964) defined bifurcation ratio as the ratio of the number of streams of one order to the number of streams of the next higher order.The analysis of bifurcation value shows that the basin and its watersheds possesses well developed drainage network as the bifurcation ratio ranges between 2.8 to 4.7, that is, low value.

Stream length ratio
The value of stream length ratio ranges widely between 1.35 to 176 which shows the early stage of maturity of the watershed.

Horton's law of stream numbers
The number order relationship can be best explained by Horton's law of stream numbers which states "that the number of stream segments of successively lower orders in a given basin tend to form a geometric series beginning with the single segment of the highest order and increasing according to constant bifurcation ratio".

Horton's law of stream length
The cumulative mean lengths of stream segments of successive higher orders increase in geometrical progression starting with the mean length of the 1 st order segments with constant length ratio.

Length of overland flow
Length of overland flow is defined as the length of flow path, projected to the horizontal, non-channel flow from point on the drainage divide to a point on the adjacent stream channel.The length of overland flow for basin 0.3132 km and for watersheds ranges from 0.2026 to 0.4419 km.The watersheds 5G2B4b, 5G2B4c, 5G2B5d, 5G2B6c and 5G2B6d are having lower values of length of overland flow that comes under the influence of high structural disturbance, low permeability, steep to very steep slopes and high surface runoff.Other remaining watersheds having length of overland flow greater than 0.25 are under very less structural disturbance, less runoff conditions and having higher overland flow.For basin, it is greater than 0.25; it comes under very less structural disturbance, less runoff conditions and having higher overland flow.

Aerial aspects of the watershed
The parameters which are governed by the area of the drainage basin are classed as area aspects of the basin.
The aerial parameters include drainage density, stream frequency, elongation ratio, form factor, circularity ratio, compactness coefficient and drainage texture have been identified and results have been given in Table 2.

Drainage density
Horton has introduced drainage density (Dd) as an expression to indicate the closeness of spacing of channels.The drainage density of the basin is 1.5965 km/km 2 which comes under low drainage density.Low drainage density is more likely to occur in regions of highly permeable subsoil material under dense vegetative cover and where relief is low.The drainage density for watersheds varies from 0.1314 to 3.0857.The watersheds 5G2B4a, 5G2B4b, 5G2B5a, 5G2B5d, 5G2B6c and 5G2B6d show high drainage density (> 2 km/km 2 ) due to the presence of impermeable sub-surface material, sparse vegetation and high relief.Whereas remaining watersheds which fall under low drainage density indicate that the region has highly permeable     subsoil and dense vegetation cover (Sethupathi et al., 2011).

Stream frequency
The stream frequency is defined as the total number of stream segment of all order per unit area.The stream frequency for basin is 1.4671 and for watersheds varies from 0.9393 to 3.50931.It is low due to permeable rocks, the surface runoff is low and infiltration capacity is high within in the study area (Chitra et al., 2011).The stream frequency for all 17 watersheds of the study area shows direct relation with the drainage density which indicates that the stream population increases with the increase of drainage density (Rao et al., 2011).

Elongation ratio
It is the ratio of diameter of the circle of the same area in the basin to the maximum basin length.The elongation ratio for the basin is 0.6206 indicating less elongated in nature and for the watersheds, it varies from 0.45 to 0.85.The watersheds 5G2B2b, 5G2B2c, 5G2B4a, 5G2B4b, 5G2B4c, 5G2B5b, 5G2B5c, 5G2B6a and 5G2B2d are elongated in nature, while remaining are less elongated in nature.

Form factor
The ratio of the basin area to the square of basin length is called the form factor.The form factor for basin is 0.3023 and for basin watersheds varying from 0.16 to 0.56.These low values indicate that watersheds have flatter peak flow for longer duration.The watershed 5G2B5a, 5G2B5d and 5G2B6c are circular in shape showing less side flow for shorter duration and high main flow for longer duration (Chitra et al., 2011).The remaining watersheds are elongated watershed, indicating that they will have a flatter peak flow for longer duration.Flood flows of such elongated basins are easier to manage than from the circular basin.

Circularity ratio
Circularity ratio is the ratio of the basin area to the area of a circle having the same circumference perimeter as the basin.The circularity ratio for watersheds varies from 0.37 to 0.77 and for basin it is 0.3853 indicating elongated in shape, low discharge of runoff and highly permeability of the subsoil condition (Miller, 1953).

Compactness coefficient (C c )
The C c is independent of size of watershed and dependent only on the shape.The compactness coefficient for watersheds ranges from 1.14 to 1.79 and for basin is 1.6106.They have elongated shape so they have enough time for discharge.

Drainage texture
It is the total number of stream segments of all orders per perimeter of the area.The texture ratio for watersheds varies from 3.3 to 10.7.For watershed 5G2B4a, 5G2B4b 5G2B4c and 5G2B6c, it is greater than 8 indicating very fine texture that is, higher runoff potential, while 5G2B5d, 5G2B5c, 5G2B6a and 5G2B6d is moderate in nature.The rest watersheds are coarser in nature that is, having less runoff potential.For basin, it is 19.3095 showing very fine nature (Smith, 1950).

Relief aspects of the watershed
The relief aspects of drainage basin are also important in water resources studies.The character of the distribution of slope, angles sampled over the whole basin depends on the height distribution within it.Relief aspects like relief, relative relief, relief ratio, channel slope and ground slope were measured.

Relief
It is defined as the elevation difference between the reference points located in the drainage basin.The relief of basin is 0.605 km.The study area is of high relief region as it is greater than 0.3 km.The high relief value indicates low gravity of water flow as well as infiltration and high runoff conditions.The relief for watersheds varies from 0.095 to 0.445 km.The watersheds 5G2B5b and 5G2B6d are of low relief region, 5G2B2c, 5G2B3a, 5G2B5d and 5G2B6a are of high relief region and remaining are of moderate relief region.The high relief value indicates low gravity of water flow as well as infiltration into the ground and high runoff conditions .

Relief ratio
It is the ratio of relief to the horizontal distance on which relief was measured.The relief ratio for basin is 0.004427 and for watersheds, it varies from 0.00273 to 0.019.It was noticed that the higher values of relief ratio indicated steep slope and high relief (5G2B6d watershed), while the lower values in case of watershed 5G2B5a indicated the presence of basement rocks that are exposed in the form of small ridges and mounds with lower degree of slope (GSI, 1981).

Relative relief
It is the ratio of relief to the perimeter of basin.It is an important morphometric variable used for the overall assessment of morphological characteristics of terrain (Suresh, 2002).The relative relief for watersheds varies from 0.0915 to 0.5399 and for basin, it is obtained as 0.1410.The watersheds having higher relative relief have higher runoff potential than others.Therefore, the watershed 5G2B5a and 5G2B5d are having the lowest and highest runoff potential.

Channel slope
For watersheds, it varies between 0.001549 to 0.01224 km/km and for basin it is 0.002820 km/km.The higher channel slopes in 5G2B6d watershed indicated less time of concentration that is, peak flow occurs in short time, while lower slope in 5G2B5a watershed indicated less peaked flow for longer duration.Therefore, while constructing the water harvesting structures on channel of watershed 5G2B6d, the outlet should be designed of higher discharge capacity and the rest components like headwall, sidewall and wing wall should also be of higher height for the designed storage capacity (Suresh, 2002).The drop structures in series in the channels of this watershed are recommended.

Ground slope
It is the product of drainage density and relief of the basin (Suresh, 2002).For watersheds, it is obtained as 0.00307 to 0.0192 km/km and for basin 0.004427 km/km.The higher ground slopes in case of 5G2B6d lying in upper reach of the basin indicates lower time of concentration of overland flow.Also, the possibilities of soil erosion will be higher in this 5G2B6d watershed among all watersheds of this basin.

Conclusion
One of the purposes of fluvial morphometry is to derive information in quantitative form about the geometry of the fluvial system that can be correlated with hydrologic information.Usually, morphometric analysis of drainage system is a prerequisite to any hydrological study.The watersheds 5G2B4a, 5G2B4b, 5G2B5a, 5G2B5d, 5G2B6c and 5G2B6d show high drainage density due to the presence of impermeable sub-surface material, sparse vegetation and high relief, while remaining watersheds fall under low drainage density which indicate that the region has highly permeable subsoil and dense vegetation cover.The development of stream segments in the basin area is more or less affected by rainfall.The present study demonstrates the usefulness of GIS for morphometric analysis of the watersheds of Shetrunji river basin, Gujarat.Thus, the morphometric properties determined for this basin as whole and for each watershed will be useful for the sound planning of water harvesting and groundwater recharge projects on watershed base.

Figure 3 .
Figure 3. Drainage order map of Shetrunji river basin.

Table 2 .
Morphometric parameters of watersheds of Shetrunji River basin.