Morphometric analysis of Sonar sub-basin using SRTM data and geographical information system ( GIS )

The study focused mainly on the geometry, more emphasis on the morphometric characteristics of the drainage basin. An attempt has been made to study drainage morphometry and its influence on hydrology of Sonar Sub-basin, M.P. India. For detailed study we used Shuttle Radar Topographic Mission (SRTM) data for preparing Digital Elevation Model (DEM), and slope maps, Geographical Information System (GIS) was used in evaluation of linear, areal and relief aspects of morphometric parameters. A total number of 196 streams were identified of which 146 are 1 order streams, 38 are 2 order, 9 are 3 order, 2 in 4 order and 1 is indicating 5 order stream. 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 mean bifurcation ratio value is 3.65 for the study area falls within the standard range and shows that the basin conforms to the characteristics of a natural stream which indicates that the geological structures are less disturbing to the drainage pattern. The drainage density of the study area is 0.62 km/sq. km. This value indicates that for every square kilometer of the basin. This makes the study area fall into the group of low density basins which suggest that the low drainage density indicates that the basin is highly permeable subsoil and thick vegetative cover. These studies are very useful for planning rainwater harvesting and watershed management.


INTRODUCTION
Morphometric analysis will help to quantify and understand the hydrological characters and the results will be useful input for a comprehensive water resource management plan (Jawahar raj et al., 1998;Kumaraswami and Sivagnanam, 1998;Sreedevi et al., 2001).A drainage basin is the part of the earth's surface that is drained by main stream and its tributaries.The drainage basin is fundamental geomorphic unit of land and all flow of surface is governed by its properties.It is an open system into which and from which energy flows.Drainage basin is a fundamental, precise and usually ambiguous unit that is recognized as a reliable and useful Planning unit.It has now formed a framework for human activities like agriculture and has guided river navigation towards sustainable agriculture (Ofomata and Umeuduji, 2000).The scientific approach to the hierarchical classification of streams and basin area was initiated by Horton (1945) who defined several drainage basin characteristics that were measurable on topographic maps.Today, these characteristics can be measured not only on topographic maps but also on satellite imageries.These characteristics include stream order, stream length, bifurcation ratio, basin area and length, perimeter, drainage density, stream frequency, elongation ratio, circularity ratio, texture ratio and form factor ratio (Shreve, 1966).The drainage characteristics of Sonar sub-basins were studied to describe and evaluate their hydrological characteristics by analyzing topographical map and SRTM data.The main occupation of the people in this area is agriculture.They depend on groundwater, because surface water resources are scarce.Due to erratic rainfall pattern and uncontrolled abstraction, groundwater levels have declined to deeper levels.Therefore watershed development schemes become important for developing the surface and groundwater resources in these areas.To prepare a comprehensive watershed development plan, it becomes necessary to understand the topography, erosion status and drainage pattern of the region.For the purpose of detailed morphometric analysis we used SRTM data for preparing DEM map slope and aspect maps.GIS was used in evaluation of Linear, Areal and Relief morphometric parameters.Using SRTM data and GIS techniques (Map Maker) is a speed, precision, fast and inexpensive way for calculating morphometric analysis (Farr and Kobrick, 2000;Smith and Sandwell, 2003;Grohmann, 2004;Grohmann et al., 2007).An attempt has been made to utilize SRTM data and the interpretative techniques of GIS to find out the relationships between the morphometric parameters and hydrological parameters.

Study area
The Sonar sub-basin lies between 23°21′14″ to 23°50′05″ N and 78°35′48″ to 79°10′50″ E. The study area comes under the Sagar district of Madhya Pradesh, India (Figure 1).It is located in the north central part of the state of Madhya Pradesh or Bundelkhand and occupies an area of 1538 sq km (94% in Sagar and 6% in Raisen).The basin has a perimeter of 284 km and basin length of 72.12 km and an average width of about 40 km.Average annual rainfall of the region is about 1100 mm.The average numbers of rainy days are 45.The average annual potential evapotranspiration is 1852 mm.The mean annual temperature varies from 18 to 33°C.

Methodology
According to Clarke (1996), morphomerty is the measurement and mathematical analysis of the configuration of the earth surface, shape and dimensions of its landforms.The morphometric analysis carried out through measurement of linear areal and relief aspects of the basin and slop contribution (Nag and Chakraborty, 2003).SRTM has created an unparalleled data set of global elevations  that is freely available for modeling and environmental applications.The processed SRTM 90 m digital elevation model (DEM) for the entire globe was compiled by Consultative Group for International Agriculture Research Consortium for Spatial Information (CGIAR-CSI) and made available to the public at http://srtm.csi.cgiar.org.The SRTM DEM is a fast and inexpensive way for regional geomorphological analysis.Based on the data we prepared the digital elevation map, slope and drainage map (Figures 2, and 3) for the watershed.Stream network and micro watersheds were also prepared using ArcGIS.Based on the drainage order, the drainage channels were classified into different orders (Strahler, 1964).Basin parameters viz area, perimeter, length, stream length, stream order were also calculated which were later used to calculate other parameters like bifurcation ratio, stream length ratio, stream frequency, drainage density.Drainage texture, basin relief, relief ratio, elongation ratio, circularity ratio, and form factor were evaluated with the help of established mathematical equations (Strahler, 1964).The morphometric parameters were divided into three categories: linear, areal and relief aspects of the basin.

RESULTS AND DISCUSSION
The various morphometric parameters of the Sonar subbasin using ArcGis 9.3 and are summarized in Tables 1  and 2 Linear aspects of the drainage basin The linear aspects of drainage network such as stream order (N u ) bifurcation ratio (R b ), stream length (L u ) results have been, presented in Table 1.

Stream order (N u )
The streams of the Sonar sub-basin have been ranked according to the method described by Strahler (1964), when two first order streams join, a stream segment of second order is formed, when two second order streams join, a segment of third order is formed, and so on.In the drainage basin analysis the first step is to determine the stream orders.The channel segment of the drainage basin has been ranked according to stream ordering system using ArcGIS 9.3.The study area is 5 th order drainage basin (Figures 3).The total numbers of 196 streams were identified of which 146 are 1 st order streams, 38 are 2 nd orders, 9 are 3 rd order, 2 in 4 th order and 1 is indicating 5 th order streams.Figure 4 show the results of the queries that retrieved the total number of streams for each of the order as shown in Table 1.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.This pattern is characterized by a tree like or fernlike pattern with branches that intersect primarily at acute angles.The properties of the stream networks are very important to study the landform making process.The order wise total number of stream segment is known as the stream number.Laws of stream numbers states that the numbers of stream segments of each order form an inverse geometric sequence with plotted against order, most drainage networks show a linear relationship, with small deviation from a straight line.This means that the number of streams usually decreases in geometric progression as the stream order increases.

Bifurcation ratio (R b )
Bifurcation ratio is the ratio of the number of streams of an order to the number streams of the next higher order (Horton, 1945;Strahler, 1964).Bifurcation ratios characteristically range between 3.0 and 5.0 for basins in which the geologic structures do not distort the drainage pattern (Horton, 1945;Strahler, 1964).Higher R b indicates some sort of geological control (Agarwal et al., 2000).The mean bifurcation ratio value is 3.65 for the Where: ∑Lu = Total stream length of all orders, ∑Nu = Total number of all orders, ∑N 1 = Total number of 1 order streams 1 st , Π = 3.14.
study area (Table 1) falls within the standard range and shows that the basin conforms to the characteristics of a natural stream which indicates that the geological structures are less disturbing to the drainage pattern.

Stream length (L u )
Stream length is one of the most significant hydrological features of the basin as it reveals surface runoff characteristics streams of relatively smaller lengths are characteristics of areas with larger slopes and finer textures.Longer lengths of streams are generally indicative of flatter gradients.Generally, the total length of stream segments is maximum in first order streams and decreases as the stream order increases.The numbers of streams of various orders in the basin are counted and their lengths from mouth to drainage divide are measured with the help of GIS software.Plot of the logarithm of number of streams versus stream order, and logarithm of stream lengths versus stream order (Figure 4a and b) showed the linear pattern which indicates the homogenous rock material subjected to weathering erosion characteristics of the basin.Deviation from its general behavior indicates that the terrain is characterized by variation in lithology and topography.

Basin area (A u )
The area of Sonar sub-basin is 1538 km 2 .If the basin size is small, it is likely that rainwater will reach the main channel more rapidly than in a larger basin, where the water has much further to travel.Lag time will therefore be shorter in the smaller basin.The length of the Sonar sub-basin is 72.12 km.The shape of the basin is significant since it affects the stream discharge characteristics.It has long been accepted that a circular area is more likely to have a shorter lag time and a higher peak flow than an elongated basin.Three dimensionless ratios viz., form factor, circularity ratio and elongation ratio, reflect the basin shapes.

Form factor ratio (R f )
It is the ratio of a basin area A u (Horton, 1932) to the  (Nautiyal, 1994).

Circularity ratio (R c )
Circularity ratio is defined as the ratio of basin area (Au) to the area of circle (A c ) having the same perimeter (P r ) as the basin (Miller, 1953).He described the basin of the circularity ratios less than 0.5 which indicates strongly elongated and highly permeable homogenous geologic materials.The circularity ratio value 0.24 of the basin does not corroborates the Miller's range which indicated that the basin is elongated in shape, low discharge of runoff and highly permeability of the subsoil condition but rather the basin of the study area is pear in shape with high level of integration.

Elongation ratio (R e )
It is the ratio of the diameter of a circle of the same area as the basin to the maximum length of the basin (Schumm's, 1956).It is a very significant index in the analysis of basin shape which helps to give an idea about the hydrological character of a drainage basin.Values of elongation ratio ranging between 0 and 0.6 indicate rotundity and low degree of integration within a basin and values between 0.6 and 1.0 assumes pear shaped characteristics of a well integrated drainage basin (Strahler, 1964).The R e value of the study area is 0.62, the basin in the study area assumes a leaf shaped characteristics indicating high degree of integration.

Drainage density (D)
The drainage density (Dd) is defined as the length of streams per unit area.It is obtained by dividing the cumulative stream length by the basin area (Horton, 1932).The drainage density (D) of the study area is 0.62 km/sq.km.According to Strahler (1964) values of drainage density under 12 are low density, those with values of between 12 and 16 are medium density basins while basins with values above 16 are high density basins.From this classification, Sonar sub-basin falls into the group of low density basins.It is suggested that the low drainage density indicates the basin is highly permeable subsoil and thick vegetative cover (Nag and Chakraborty, 2003).The type of rock also affects the drainage density.Generally, lower values of drainage density tend to occur on granite, gneiss and schist regions.

Stream frequency (F s )
Stream frequency of the basin may be defined as the ratio of the total numbers of segments cumulated for all orders with a basin to the basin area (Horton, 1932).The stream frequency value of the basin is 0.13.The value of stream frequency (F s ) for the basin exhibit positive correlation with the drainage density value of the area indicating the increase in stream population with respect to increase in drainage density.

Texture ratio (T)
Texture ratio (T) is an important factor in the drainage morphometric analysis which is depending on the underlying lithology, infiltration capacity and relief aspect of the terrain.In the present study texture ratio of the basin is 0.52 and categorized as moderate in nature.

Figure 1 .
Figure 1.Location of the study area.

Figure 2 .
Figure 2. Digital elevation map of the Sonar sub-basin.

Figure 3 .
Figure 3. Drainage network of the study area.

Table 1 .
Linear aspect of the drainage network of the study area.

Table 2 .
Aerial aspects of the study area.