INTERNATIONAL JOURNAL OF GEOMATICS AND GEOSCIENCES Volume 2, No 4, 2012

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1 INTERNATIONAL JOURNAL OF GEOMATICS AND GEOSCIENCES Volume 2, No 4, 2012 Copyright 2010 All rights reserved Integrated Publishing services Research article ISSN Analysis of drainage morphometry and watershed prioritization in Bandu Watershed, Purulia, West Bengal through Remote Sensing and GIS technology - A case study Ajoy Das 1, Milan Mondal 2, Bhaskar Das 3, Asim Ratan Ghosh 4 1- Junior Research Fellow, West Bengal State Council of Science and Technology (DST), Govt. of West Bengal 2- Senior Research Fellow, The University of Burdwan, Burdwan Senior Research Fellow, West Bengal State Council of Science and Technology (DST), Govt. of West Bengal 4- Senior Scientist, West Bengal State Council of Science and Technology (DST),Govt. of West Bengal milanmondal2055@gmail.com ABSTRACT The study area, Bandu watershed of Purulia District extends from 23 o 20 N to 23 o 47 N and 86 o 0 E to 86 o 30 E. The study area is under the upper catchment of Kasai river, Purulia district is a drought prone district of the West Bengal. Inspite of considerable amount of rainfall, due to heavy runoff the main problem of this area is scarcity of water as well as soil erosion. It has been accepted that for sustainable rural livelihood water and soil conservation is a must. The most suitable way to achieve this is micro-watershed development. But there is an acute shortage of technical manpower to handle such a huge volume of survey related work. For that reason, application of Remote Sensing and GIS has become a necessity. Moreover since fund is limited, watershed prioritization is highly required. Key words: Watershed prioritization, Morphometric analysis, Micro-watershed, RS, GIS 1. Introduction In the present study various thematic maps viz. Geomorphological Map, Drainage, Watershed and Surface Waterbody Map, Landuse/ landcover Map, Transport and Settlement Map, Soil Map, Slope Map have been prepared. These maps have been used for prioritization of miniwatersheds through morphometric analysis, generally the criteria for watershed prioritization are subjective in nature and difficult to implement in ground reality due to various reasons. Some objective criteria are also available for watershed prioritization viz. Sediment Yield Index. In the present study another objective approach has been attempted which is based on morphometric analysis of drainage system and shape-size of their micro-watersheds. The study area, Bandu watershed (geographical area: sq.km) is lying between 23 o 20'00"N to 23 o 47'00"N and 86 o 0'00"E to 86 o 30'00"E, Jhalda-II, Arsha and Baghmundi and Jaipur block of Purulia district. Purulia district is a drought prone district of West Bengal. The main problem of this area is scarcity of water as well as soil erosion (Figure 1). 1.1 Geomorphology The Puruliya district of West Bengal presents a thoroughly pene-planated surface. The study area is composed of slightly elevated nearly level to moderately sloping tracts of uplands and Submitted on March 2012 published on May

2 shallow valleys alternating in space throughout the area. In the western part of the study area structural highlands that is Ajodhya hills (above 600 mts.) and part of the Baghmundi hills as well as some residual hills (inselbergs) are found. Figure 1: Location of the study area (Bandu watershed, Purulia, W.B) These highlands and residual hills are a testimony to the high plateau of ancient times which has been eroded down to produce the present landform. It can be said that in some sectors soil erosion to be almost completed. It is evident from the occurrence of erosion pavement at the surface. Some gully erosion has been taken place in the south-central part of the study area which comprises with foothill zone. Along the upper Kasai (Left Bank and few parts of right Bank) and Bandu River banks badland topography is found. The residual material on the 996

3 slopes has undergone deep weathering at places giving rise to deep in-situ soils. Local alluvium deposits are also found in rest of the region due to low relief condition (IMSD, 1996) (Figure 2). 1.2 Drainage Figure 2: Geomorphological map All the rivers of the study area flowing within it have south or south-east to north-easterly courses for Bandu river and in the upper reaches of Kasai river north-west to easterly courses seen. The Kasai has its origin in the Jhalda-II block of Puruliya district. It is the most important river of the region draining more than 50 percent of the region. The Bandu is the another important river of this watershed which takes its origin in the Baghmundi block of Puruliya district. The important rivers are Puran Baruadih nala and Chunmatia nala. All these rivers are non-perennial and subject to flash floods. The most striking feature of surface drainage in the area is the presence of several dug out ponds and some water harvesting structures locally called bunds. These structures are suitable for considerable amount of water conservation. These structures provide life saving irrigation to crops and helps in ground water recharge. The croplands located below the water harvesting structures are most suitable for paddy cultivation and the area is known as Bahal fields. Numerous small irrigation reservoirs and tanks are also found in the area (Figure 3). 1.3 Climate The climate of the region is characterised by a hot summer and well distributed seasonal rainfall. The year may be divided into the following four seasons. The average rainfall of Puruliya district is mm. South-western monsoon is responsible for the occurrence of rainfall. During June to September near about 80% annual rainfall occurs. The month of August witnesses highest rainfall. May is the hottest month with a mean daily maximum temperature of o C and a mean daily temperature of o C. January is the coldest month of the region. Annual and diurnal range of temperature is quite high in this district. 997

4 1.4 Soil The soils of the area under study are residual soils developed in-situ mostly from granitic rocks. They are mostly loamy sand to sandy loam at the surface with a heavier sub-soil showing evidence of clay illuviation at places, coloured various shades of red and are low in inherent fertility (Figure 4). Figure 3: Drainage water and surface water body map As the region is a part of eastern fringe of Chhotonagpur plateau the soil is predominantly loamy which is not very fertile. The soil of the study area can be classified into four broad categories namely Fine Loamy, Coarse Loamy, Loamy skeletal and Fine. Fine loamy soil is deep, brown sandy clay loam surface and clay loam sub-surface, imperfectly drained on gently sloping infilled valley having high water table. This type of soil is found in Ayodhya hill area. Coarse loamy soil is characterized by moderately deep, reddish brown sandy loam surface to sandy clay loam sub-surface (gritty), well drained on moderately sloping lower slopes of upper undulating plain (buried pediment).loamy skeletal soil is characterized by 998

5 shallow, brown to reddish brown, gravelly sandy loam surface to sandy clay loam sub-surface, well drained on moderately sloping upper pediment, stones and gravel on surface.gravel loamy soil is found in some form of patches in the eastern part of the region (Figure 5). Figure 4: Soil texture map Figure 5: Landuse/ Landcover map 999

6 2. Objectives The main objectives of this study are (i) prioritization of mini-watersheds through morphometric analysis generation of relevant thematic maps for the aforesaid studies. It has been accepted that for sustainable rural livelihood water and soil conservation is a must. The most suitable way to achieve this is micro-watershed development. Since fund is limited, watershed prioritization is highly required. Common Guidelines for Watershed Development has identified some criteria for this purpose. Some of them are (a) not more than 30% of the area should get assured irrigation, (b) acute drinking water crisis, (c) high SC/ST population, Some objective criteria are also available for watershed prioritization viz. Sediment Yield Index (SYI). In the present study another objective approach has been attempted which is based on morphometric analysis of drainage system and shape-size of their micro-watersheds. 3. Methods Remote sensing technique with visual interpretation approach was adopted for generation of various thematic maps. Figure 6: Flow chart showing methodology of thematic map generation It involves interpretation of imagery by using image elements and correlating them with land features such as lithology, landforms, vegetation cover, soil and drainage. To prepare thematic map first of all base map has been generated. A base map is a map shows only essential geographic references (such as rail, road, main drainage (double line) on which 1000

7 additional information is plotted; e.g., a topographic map on which geologic information is recorded. A map designed for the presentation and analysis of data; it usually includes only the coordinate, geographical and major political outlines. To prepare base map identify permanent features from georeferenced FCC images and rectify all features from SOI toposheet with scale of 1:50000.After rectification digitization of permanent features (metalled road, rail line, canal, political boundaries and forest boundary) has been done. Main drainage (double line) also has been digitized. Then central point of major settlement has been pointed out. To generate various theme maps of study area information has been extracted from three seasons ( Kharif, Rabi, Zaid ) satellite images taken by IRS-P6, LISS-III and LISS-IV of These Satellite imageries had been georeferenced and merged using image processing software ERDAS IMAGINE 8.4. These remotely sensed data were geometrically rectified with respect to survey of India toposheets on 1:50,000 scale. These merged data were used in the present study. Image enhancement techniques were applied for better interpretation of the study area. In the beginning a personal geodatabase has been created to generate feature class. With the help of these feature classes different themes have been digitized on screen. In this way different layers like geology, geomorphology, drainage, soil, landuse/ landcover, transport and settlement have been generated for corresponding theme maps. To compare and interpret all these theme maps overlay analysis has been done. The entire procedure of theme map generation from georeferenced data have been done in ArcGIS 9.3 environment. After completion of map generation field verification or ground truth survey has been done for area estimation. After that final theme maps have been prepared of the present study (Figure 6). 4. Fluvial Morphometry Fluvial morphometry is the measurement and mathematical analysis of configuration of earth surface and of the dimension of its landforms originated due to fluvial processes. The morphometric analysis is carried out through measurement of linear, aerial and relief aspects of the basin and slope contribution (Nag and Chakraborty, 2003) to understand the run-off characteristics of the area and potentiality of watershed deterioration. The measurement of various morphometric parameters namely stream order, stream length (Lu), mean stream length, bifurcation ratio, mean bifurcation ratio, drainage density, stream frequency, form factor, circulatory ratio, elongation ratio, length of overland flow has been carried out and the data are presented in the following table. In the present study, the satellite remote sensing data has been used for updation of drainage network, obtained from SOI toposheets and the updated drainage network has been used for morphometric analysis. 4.1 Linear aspects Fluvial morphometry include the consideration of linear, aerial and relief aspect of fluvially developed drainage basin. The linear aspects include the stream order, stream length, mean stream length, stream length ratio and bifurcation ratio, which were determined and results have been presented in the following Table Stream ordering Stream ordering is a method of assigning a numeric order to links in a stream network. This order is a method for identifying and classifying types of streams based upon their number of tributaries. Some characteristics of streams can be inferred by simply knowing their order. 1001

8 The designated stream order is the first step in the drainage basin analysis. In the present study, ranking of streams has been carried out based on the method proposed by Strahler (1964). It is noticed from the table that the maximum frequency is in the case of first order streams. It is also observed that there is a decrease in stream frequency as the stream order increases Stream length Stream length is measured from mouth of a river to drainage divide Mean stream length Mean Stream Length of a stream channel system is a dimension less property revealing the characteristics of size of a component of drainage network and its contributing basin set. Lu= Lu/Nu Where, Lu= Total length of a order Nu= No of stream of that order. Mean stream length (Lsm) is a characteristic property related to the drainage network components and its associated basin surfaces (Strahler, 1964). This has been calculated by dividing the total stream length of order (u) by the number of streams of segments in the order Stream length ratio Stream length ratio (RL) is the ratio of the mean length of the one order to the next lower order of the stream segments Bifurcation ratio According to Schumn (1956), the term bifurcation ratio may be defined as the ratio of the number of the stream segments of given order to the number of segments of the next higher orders. Bifurcation ratio shows a small range of variation for different regions or for different environments except where the powerful geological control dominates (Strahler, 1957). Bifurcation Ratio (Rb): Gregory Bifurcation ratio is defined as the ratio of the number of stream of a given order to the number of stream to the next higher order which is expressed in terms of following equation- Rb = Nu/ Nu+1 Where, Rb = Bifurcation Ratio. Nu= Number of segments of a given order segment. Nu+1=Number of segments of the next higher order. It varies from 2 to 5. Rb is used to find out the degree of integration in drainage basin. Rb depends on the slope, physiography, and climate. Aerial aspects include different morphometric parameters, like drainage density, texture ratio, stream frequency, form factor, 1002

9 circularity ratio, elongation ratio and length of the overland flow. The values of these parameters are presented in the table and discussed and interpreted Drainage density Drainage density is defined as the total length of streams of all orders per drainage area. Density factor is related to climate, type of rocks, relief, infiltration capacity, vegetation cover, surface roughness has no significant correlation with drainage density. The drainage density indicates the closeness of spacing of channels (Horton, 1932). It may be considered as one of the methods of measurement of basin area. According to Horton, Drainage Density is defined ratio of total length of all stream segments in a given drainage basin to the total area of that basin. It is expressed by a formula Where, L = Total length A = Total area DD = L/A The amount and type of precipitation influences directly to the quantity and characters of surface run-off. An area with high precipitation such as thundershowers loses greater percentage of rainfall in run-off resulting in more surface drainage lines. Amount of vegetation and rainfall absorption capacity of soils, which influences the rate of surface runoff, affects the drainage texture of an area. The similar condition of lithology and geologic structures, semi-arid regions have finer drainage density texture than humid regions. Low drainage density generally results in the areas of highly resistant or permeable sub-soil material, sparse vegetation and mountainous relief. Low drainage density leads to coarse drainage texture while drainage density leads to fine drainage texture Stream frequency/channel frequency The total number of stream segments of all orders per unit area is known as stream frequency (Horton, 1932). Hopefully, it is possible to have basins of same drainage density differing stream frequency and basins of the same stream frequency differing in drainage density. Stream Frequency is defined as the ratio between the number of stream segment per unit area which expressed by a formula DF= N/A where, N= Total no of stream segment; A= Unit area in km2 or m2 It is a technique which is also used in planning and development to identify land quality for optimum utilization Drainage texture Drainage texture is the total number of stream segments of all orders per perimeter of that area (Horton, 1945). It is one of the important concepts of geomorphology which means that the relative spacing of drainage lines. Drainage lines are numerous over impermeable areas than permeable areas. According to Horton (1945), infiltration capacity as the single important factors which influences drainage texture and considered drainage texture which includes drainage density and stream frequency. 1003

10 4.2 Areal Aspects Form factor Form factor may be defined as the ratio of the area of the basin and square of basin length (Horton, 1932). The value of form factor would always be greater than 0.78 for a perfectly circular basin. Smaller the value of form factor, more elongated will be the basin Circularity ratio The circularity ratio is mainly concentrated with the length and frequency of streams, geological structures, land use/land cover, climate, relief and slope of the basin. It is the ratio of the area of the basins to the area of circle having the same circumstance as the perimeter of the basin Elongation ratio Elongation ratio is the ratio between the diameter of the circle of the same area as the drainage basin and the maximum length of the basin Compactness constant Compactness ratio is defined as the ratio between the area of the basin and the perimeter of the basin. Table 1: Formula adopted for computation of morphometric parameters Sl Morphometric Formula Reference No. Parameters 1 Stream Order Hierarchical rank Strahler (1964) 2 Stream Length (Lu) Length of the Stream Horton (1945) 3 Mean Stream Length (Lsm) Lsm=Lu/Nu Where, Lu=Total stream length of order u Nu=Total number of stream segments of order u Strahler (1964) 4 Stream Length Ratio (RL) RL=Lu/lu-1 Where, Lu= Total stream length of order u Lu-1= Total stream length of its next lower order Horton (1945) 5 Bifurcation Ratio (Rb) Rb=Nu/Nu+1 Where, Nu=Total number of stream segments of order u Nu+1= Total stream length of its next higher order 6 Mean Bifurcation Ratio Rbm=Average of bifurcation ratios of all (Rbm) orders 7 Drainage Density (D) D=Lu/A Where, Lu= Total stream length of all orders A=Area of the basin(km2) Schumn (1956) Strahler (1957) Schumn (1956) 1004

11 8 Basin Length (Lb) Lb=1.312*A0.568 Where, Lb=Length of the basin(km) A=Area of the basin(km2) 9 Stream Frequency (Fs) Fs=Nu/A Where, Nu=Total number of stream segments of all orders A=Area of the basin(km2) 10 Texture Ratio (Rt) Rt=Nu/P Where, Nu=Total number of stream segments of all orders P=Perimeter of the basin(km) 11 Form Factor (Rf) Rf=A/Lb2) Where, A=Area of the basin(km2) Lb2 =Sq of basin length 12 Circularity Ratio (Rc) Rc=4*Pi*A/P 2 Where, Pi= Pi value i.e.,3.14 A=Area of the basin(km2) P2 = Sq of the perimeter(km) 13 Elongation Ratio (Re) Re=(2/Lb)*(A/Pi) 0.5 Where, Lb=Basin length(km),a=area of the basin(km2) 14 Compactness Ratio (Cc) Source: Thakkar, A. K. and.dhiman, S.D (2007) Cc=0.2821*P/A 2 Where, P=Perimeter of the basin(km) A=Area of the basin(km2) Table 2: Morphometric Parameters of Bandu watershed Horton (1932) Horton (1932) Horton (1945) Horton (1932) Miller (1953) Schumn (1956) Horton (1945) Sl. No. Mini- Watershed Circular Ratio Bifurcation Ratio Form Factor Elongation Ratio Compactne ss Constant Stream Frequency Drainage Density Texture Ratio 1 2A2B5C A2B5B A2B5C A2B5C A2B5C A2B5C A2B5C A2B5C A2B5A A2B5B A2B5B A2B5B A2B5A A2B5B A2B5B A2B5B A2B5A A2B5A A2B5A

12 20 2A2B5A A2B5A A2B5A A2B5A A2B5A A2B5A Table 3: Suitable Sensor and their application in Watershed Management Acquired on: Image number: 106/55 21 st January, rd April, th October, 2006 Acquired on: Image number: 106/56 16 th January, th March, th October, 2006 To prepare theme maps satellite data of geocoded FCC of bands 2, 3, 4 on 1:50,000 scales along with corresponding SOI toposheet no.73i/3,73i/4,73i/7 and 73I/8. The generated theme maps are as follows: (1) Geomorphological Map (2) Drainage, Watershed and Surface Waterbody Map (3) Landuse/ landcover Map (4) Transport and Settlement Map (5) Soil Map 6) Slope Map (7) Map showing catchment area of selected check dam sites 4.3 Watershed Concept Watershed is a technical term used by the British to denote a common drainage point. It is a hydro geological unit. In American terminology, it is referred to as Catchment Area. Watershed is the line separating neighboring drainage basins (catchments). In hilly country, the divide lies along topographical peaks and ridges, but in flat country (especially where the ground is marshy) the divide may be invisible just a more or less notional line on the ground on either side of which falling raindrops will start a journey to different rivers, and even to different sides of a region or continent. Drainage divides are important geographical 1006

13 and often also political boundaries. Roads (such as ridge ways) and rail tracks often follow divides to minimize grades (gradients), and to avoid marshes and rivers. 4.4 Causes of watershed deterioration 1. Uncontrolled, unplanned, unscientific land use and interventions lead to deterioration of the watershed area. Some of the activities detrimental to watershed. 2. Cultivation on sloping land without adequate precautions, cultivation without agronomic measures to conserve soil and water, cultivation along susceptible nalla banks, cultivation of erosion-permitting crops, over-cropping without soil fertility replenishment, faulty agricultural techniques etc. 3. Grass land: Excessive and uncontrolled grazing, growth of weeds, development of cattle tracks causing damage and compaction of soil resulting in lower infiltration rates, fires, theft etc. 4. Forest: Excessive and uncontrolled grazing which inhibits regeneration from seed or stock, clear felling on steep slopes, destruction of forest land by fires and thefts, biotic pressure for fuel, fodder, NTFP and small timber, drastic thinning of plantation along slopes etc. 5. Shifting cultivation: Shifting cultivation or Jhum kheti practiced in certain areas of counties (like North East India etc.) has proved to be very damaging to protective and productive vegetation. This practice results in damage to the topsoil and inhibits the growth of grasses, shrubs and trees. 6. Unscientific mining and construction activities: These activities damage the vegetation and the landscape. The natural drainage lines are often blocked by debris. 7. Fire: Intentional / accidental fires result in loss of vegetation, organic matter and micro-organisms. 8. Non-cooperation of the community: Non-Cooperation of the community in conserving, protecting and enriching then ecosystem and CPR has also resulted in most of the ills. 4.5 Why Watershed Management? Watershed management is required for the following reasons: 1. To control damaging runoff. 2. To manage and utilize runoff for useful purposes. 3. To control erosion affecting reduction of sediment production. 4. To moderate floods in the downstream area. 5. To enhance groundwater storage wherever applicable, and 6. To appropriately use land resources in the watershed, thus developing forests and fodder resources. 5. Methods 1007

14 To delineate micro-watersheds, prioritization of mini-watersheds through morphometric analysis in Bandu watershed has been attempted through integrated use of remote sensing and GIS techniques. In the present study, the drainage map of the study area has been prepared from three season s satellite images of IRS-P6 (Resourcesat) LISS-III and LISS-IV of LISS-III (106/55) satellite data were acquired on 21st January, 3rd April, and 12th October of 2006 and LISS-III (106/56) 16th January, 29th March and 07th October of 2006.These satellite imageries had been georeferenced and merged using image processing software ERDAS IMAGINE 9.1. These remotely sensed data were geometrically rectified with respect to survey of India toposheet with 1: 50,000 scale. These merged data were used in the present study. Image enhancement techniques were applied for better interpretation of the study area. To delineate drainage map satellite data of geocoded FCC of bands 2, 3, 4 on 1: 50,000 scales along with corresponding toposheets have been used 73I/3, 73I/4, 73I/7, and 73I/8. The morphometric parameters for the delineated watershed area were calculated based on formula suggested by various authors viz. Horton, Strahler, Schumn and Miller, presented in Table.1. Digitization and computation of output value were done in ArcGIS 9.3 environment. On the basis of some selected morphometric parameters watershed prioritization of all microwatersheds was carried out (Figure 7). Figure 7: Flow chart showing methodology of micro-watershed prioritization map The step wise methodology is listed as below 1. Drainage has been digitized as separate segments for every stream order. 2. Delineation of subwatershed, mini-watershed and micro-watershed have been done. 3. Computation of number and length of streams of every order for every miniwatershed area have been done. 1008

15 4. Computation of eight morphometric parameters namely Mean Bifurcation Ratio, Drainage Density, Texture Ratio, Stream Frequency, Circularity Ratio, Form Factor, Compactness Constant, Elongation Ratio have been made 5. Since higher value of Mean Bifurcation Ratio, Drainage Density, Texture Ratio, Stream Frequency indicates higher potentiality of watershed deterioration these parameters are given rank in descending order. Since lower value of Circularity Ratio, Form Factor, Compactness Constant, Elongation Ratio indicates higher potentiality of watershed deterioration these parameters are given rank in ascending order. 6. All parameters are assumed to have equal weights. The average rank for all miniwatersheds are computed. Final rank has been assigned in ascending manner. (Table. 4) 5.1 Observation On the basis of above mentioned observation it can be concluded that Remote Sensing and GIS techniques are efficient tools in drainage delineation and their updation. These updated drainages are treated as input data for morphometric analysis. This analysis was carried out through measurement of linear, aerial and relief aspects of micro-watersheds. This morphometric analysis reveals dendritic to sub-dendritic, parallel, radial drainage patterns with moderate drainage textures of the entire sub-watershed. The variation in stream length ratio reflects the change in slope and topography. The bifurcation ratio of sub-watersheds indicates normal basin category and the area having moderate drainage density reflects that it has highly permeable sub-soil and coarse to moderate drainage texture. The values of stream frequency indicate that all the micro-watersheds show positive correlation with increasing stream population with respect to increasing drainage density. The values of form factor and circularity ratio evolve that almost all micro-watersheds are elongated in shape. Elongation ratio indicates that Bandu watershed is a region of very low relief whereas other microwatersheds are characterized by moderate to high relief and steep ground slopes relief and steep ground slopes. 5.2 Results and discussion Stream length has been computed based on the law proposed by Horton (1945) for all the micro watershed of the study area. Usually, the total length of stream segments is maximum in first order streams and decreases as the stream order increases in the present case. The mean stream length is presented in the table. The Bifurcation Ratio (Rb) values of study area indicates that there is a uniform decrease in Rb values of 2A2B5A3 to 2A2B5A7, from one order to the next order whereas in other micro watersheds, the Rb values are not same from one order to next order. These differences are depending upon the geological and lithological development of the drainage basin. In the study area, the higher values of Rb indicates a strong structural control in the drainage pattern whereas the lower values indicate that the sub-basins are less affected by structural disturbances (Nag, 1998; Vittala et al., 2004 and Chopra et al., 2005). The Rb values of the micro watersheds of the study area range from 1.00 to 8.00 indicating that all the micro watersheds are falling under normal watershed category The drainage density in the micro watersheds of the study area shows variation from 1.47 to 4.20 per km 2 suggesting moderate drainage density. This moderate drainage density of the study area suggests that it has moderately permeable sub-soil and fine drainage texture 1009

16 observed on hilly terrain. The Stream Frequency (Fs) values of the of the study area are presented in the following table. It is noted that the values of Fs vary from 1.20 to It is also seen that the drainage density values of the micro watersheds exhibits positive correlation with the stream frequency suggesting that there is an increase in stream population with respect to increasing drainage density. The values of drainage texture ratio of the study area vary from 1.04 to According to Smith (1950), five different drainage textures have been classified based on the drainage density. The drainage density less than 2 indicates very coarse, between 4 and 6 is moderate, between 6 and 8 is fine and greater than 8 is very fine drainage texture. The 2A2Bb7 micro watershed has high values of Rt indicating very fine drainage texture whereas the remaining micro watersheds show coarse to moderate drainage texture exhibited by the surrounding source rock while the lower values may indicate that the rocks exposed in the form of small ridges and mounds and plains with lower degree of slopes.the form factor (Rf) values of the study area are presented in the Table. It is noted that the Rf values vary from to micro watershed suggesting that it is almost circular in shape. In the study area, the Circularity Ratio (Rc) values are ranging from 0.30 to Those micro watersheds have the value of Rc is less than 0.5 indicating those are elongated, whereas the remaining micro watersheds have greater than 0.5 values suggesting that they are more or less circular in shape and are characterized by the high to moderate relief and the drainage system were structurally controlled.the elongation ratio values of the micro watersheds vary from to On the basis of elongation ratio it is also suggested that the Bandu watershed is elongated in shape. A circular basin is more efficient in the discharge of run-off than an elongated basin (Singh and Singh, 1997). In Bandu watershed compactness ratio varies from 2.03 to Table 4: Prioritization Results of Morphometric analysis Sl. No. Mini- Watershed Circularity Ratio Form Factor Elongation Ratio Compact-ness ratio Stream Frequency Drainage Density Texture Ratio Bifurcation ratio SUM RANK Final Rank 1 2A2B5C A2B5B A2B5C A2B5C A2B5C A2B5C A2B5C A2B5C A2B5A A2B5B A2B5B A2B5B A2B5A A2B5B A2B5B

17 16 2A2B5B A2B5A A2B5A A2B5A A2B5A A2B5A A2B5A A2B5A A2B5A A2B5A Figure 8: Map Showing Mini-Watersheds Figure 9: Prioritisation Map Mini Watersheds 1011

18 5.3 Discussion about prioritization of mini-watersheds On the basis of above mentioned 25 drainage morphometric parameters prioritization procedure of Bandu watershed has been done at mini-watershed level (Figure 8 & 9). Since the value of Bifurcation ratio is highest (4.13) in 2A2B5A4 mini-watershed possibility of maximum erosion is maximum here. The highest drainage density is observed in 2A2B5B7(3.24) mini-watershed and it indicates that as this unit is situated on structural hill, soil erosion is quite high in this area. The 2A2B5B4 has the lowestest elongation ratio (0.260) indicating possibility of high erosion. Form factor values are in range of 0.39 to 0.46 which indicates that the Bandu watershed has moderately high peak flow for shorter duration. The compounded parameter is computed simply adding the ranks, giving equal weight to every factor. The compound parameter values and prioritization rating of 25 mini-watersheds in Bandu watershed is carried out through the table 4. 2A2B5A1, 2A2B5A5, 2A2B5A7,2A2B5A8, 2A2B5A9, 2A2B5A11, 2A2B5B5 mini-watershed with a compound parameter value of receives the highest priority (1) followed by 2A2B5 having the compound parameter value of Lowest priority has been given to the mini-watershed number 2A2B5C2 which has compound parameter value of (11.38). Highest priority indicates the maximum soil erosion in the specific mini-watershed and it must be given maximum attention for soil conservation. The final priority map of the area under study is shown. On the basis of priority map it can be recommended that 2A2B5A1 mini-watershed should be given first priority for soil conservation measures and followed by other miniwatersheds according to their rank of priority. 6. References 1. Das, Ghanashyam., (2000), Hydrology and Soil Conservation Engineering, Prentice Hall of India, New Delhi. 2. IMSD Special Programme-Baghmundi Block, Puruliya District, West Bengal (1996), State Remote Sensing Centre, DST & NES, Govt. of West Bengal, unpublished report. 3. Integrated Mission for Sustainable Development, Technical Guidelines, National Remote Sensing Agency, Department of Space, Government of India, Balanagar, Hyderabad , December Jala Bibhajika Unnayan Karmasuchi Parikalpana o Rupayaner Paddhatigata Ruparekha, Paschimbanga Sarkar, Panchayat o Gramonnayon Daftar, Rajya Panchayat o Gramonnayon Sangstha, Kalyani, Nadia. 5. Kuldeep Pareta, Upasana Pareta, (2011), Quantitative Morphometric Analysis of a Watershed of Yamuna Basin, India using ASTER (DEM) Data and GIS, International Journal of Geomatics and Geosciences, 2(1), pp National Remote Sensing Centre: Landuse/Landcover-50k ( ), Department of Space, Government of India. 7. Natural (National) Resource, Information System Project, Puruliya District, West Bengal, Unpublished Report. 1012

19 8. NRIS Project, Project Report On Soil Mapping of Puruliya District, West Bengal, Indian Resources Information and Management Technologies LTD., Plot No. 1299K, Road No. 66, Jubilee Hills, Hyderabad Rudraiah, Govinaiah, Vittala., (2008), Morphometry Using Remote Sensing and GIS Techniques In The Sub-Basins of Kagna River Basin, Gulburga District, Karnataka, India, Journal of Indian society of Remote Sensing 36, Seethapathi P.V, Dutta D, and Siva Kumar R., (2008), Hydrology of Small Watersheds (eds), New Delhi: TERI (The Energy and Resources Institute). 11. Sethupathi. A.S, Lakshmi Narasimhan C, Vasanthamohan V, MohanS.P, (2011), Prioritization of mini watersheds based on Morphometric analysis using Remote Sensing and GIS techniques in a draught prone Bargur Mathur sub water sheds, Ponnaiyar river basin, India,, 2(2), pp Sandipan Gosh, (2011), Quantitative and Spatial Analysis of Fluvial Erosion in relation to Morphometric Attributes of Sarujharna Basin, East Singhbhum, Jharkhand,, 2(1), pp Thakkar, A.K. and Dhiman, S.D., (2007), Morphometric Analysis and Prioritization of miniwatersheds in Mohr Watershed, Gujarat Using Remote Sensing and GIS technique, Journal of the Indian society of Remote Sensing, 35(4),