The study area (Kayadhu river basin) is located in the eastern part of Deccan Basaltic Province (DBP), Maharashtra, India. The basin is confined between N19° 22¢¢, E77° 40¢¢ in the South East and N 20° 00¢¢ E76° 40¢¢ North West and total area of the basin is 2158.38 km
2. Out of the total area, around 1639.57 km
2 is covered with agriculture, 435.57 km
2 with waste land, 38.52 km
2 with settlements, 38.79 km
2 with forest and 5.92km
2 with water bodies. The Kayadhu river is seventh order and the major water source of this area and it originates from the Angarwadi village in Risod tauka of Washim district in Ajanta hill ranges with an elevation of 580 m. The drainage pattern in the study area is mostly dendritic as well as semi-dendritic. Climatologically, this area experiences semi-arid, sub-tropical condition characteristically hot summer with an annual rainfall ranging from 750 to 1244 mm and the temperature ranges between 12.7 and 41.7°C. The southwest monsoon is a major source of rainfall in the study area and it occurs during June to September (CGWB 2013). The population in the study area is around 5,00,000 and are distributed over 270 Panchayat villages and 4 townships (Fig 1).
For the present study, the methodology used is shown in the flow chart (Fig 2). In this study the spatial data base has been created using the topographic maps obtained from the Survey of India (SOI) 1:50000 scale, IRS P6 LISS IV MX satellite data, ASTER GDEM and field verification. Various thematic maps such as geology, drainage density, lineament density, rainfall data, soil, land-use/land cover, slope and geomorphology are prepared by using GIS and remote sensing. All of the map themes were presented in UTM Projection Zone 43 N, Datum WGS84 with 30 m resolution and converted to raster format.
Preparation of thematic layers
Geology
The type of rock exposed on the surface significantly affects the groundwater recharge
(Shaban et al., 2006). According to El-Baz and Himida (1995) geology affects the groundwater recharge by controlling the percolation of water flow. While, some researches have ignored this factor by regarding the lineaments and drainage features as a function of primary and secondary porosity, this study includes lithology to minimize uncertainty in determining lineaments and drainage.
Land use/cover
Land use /cover is an important indicator of the extent of groundwater requirements and groundwater utilization as well as important for selection of groundwater recharge. Satellite data LISS IV, topographic maps and field evidences were used as reference data. The different classes of land use /cover are identified on the basis of different tone in the satellite image such as barren land, water bodies, settlements, agriculture land and forest area.
Slope map
The study related with groundwater flow and storage the slope is often neglected; mainly in the plain areas (Al Saud, 2010). The slope gradient is directly affecting the infiltration of surface runoff. High slope gradient produces small recharge and the area where slope is minimum it tends to water longer had a greater chance of infiltration and recharge during rainfall
(Jasrotia et al., 2007; Yeh et al., 2016). The slope map was prepared from the ASTER GDEM in the GIS by using slope analysis function to assess the variation of the slope in the Kayadhu basin.
Lineaments
The term
lineament is a commonly used in remote sensing studies in connection with fractures or weak zone. Lineaments are defined as mappable linear to slightly curvilinear subsurface features, which are differ distinctly from the adjacent feature and pattern, reflect subsurface information (O’
Leary et al., 1976). The structural features usually related with joints, faults and lineaments may produce essentially straight rivers with minimum meandering (Twidale 2004). Lineaments are extracted from drainage pattern and vegetation shows prominent trends of feature observation on IRS P6 LISS IV satellite image. Lineaments in Kayadhu basin area were extracted through manual lineament extraction techniques
(Weerasekara et al., 2014). Many non-geological structures, such as roads and channels, cause errors in the analysis of lineaments. These features are eliminated from the resultant layer.
Drainage density
The drainage density map of Kayadhu river (Fig 6) is the total length of all the streams in a drainage basin divided by the total area of the drainage basin. The structural analysis of a drainage network access the characteristics of a groundwater recharge zone. It is well known that the denser the denser the drainage network, the less recharge rate and vice versa. The percolation rate is also depending upon geology. According to Greenbaum (1985) is determined by an equation (1):
Where,
denotes the total length of the drainage
On the basis of topographic maps drainage network is digitised and using density function in GIS, drainage density is calculated.
Soil types
The soil map of study area obtained from the National Atlas and Thematic Mapping Organization (2005) and subsequently georeferenced and digitized. Thickness of soil cover is less towards NW part of the basin where ground elevations are higher. Soil in central, southern and eastern regions of the basin near the banks of rivers are thicker. Here soil, ranging in depth from 1 to 2 m, are black and rich in plant nutrients (CGWB 2013). When assigning weights to each soil class, permeability of each soil type has been considered in this study, since inûltration and percolation rates is directly related to permeability
Senanayak et al., (2016).
Geomorphology
Geomorphologically, the study area is identified by various landforms such as older alluvial plain, present flood plain, pediments, pediplains, highly dissected plateau and denudational hills. Among these landforms older alluvial plain, present flood plain and pediplains have more potential for groundwater recharge, but the highly dissected plateau and denudational hills are not suitable for water augmentation because of the steep slope.
Rainfall
Rainfall is main source for groundwater recharge
(Musa et al., 2000) and similarly for all hydrological process. The annual rainfall data collected from the Indian Meteorological Department (IMD) for annual rainfall measurements from rain gauge stations in the study region. The rainfall map has been categorized into three categories of rainfall zones each of 100 mm interval.
Subsequently, the thematic maps are used to analyse in overlay and ranks and weights are assigned for each thematic layer to evaluate the groundwater recharge potential zone as shown in Table 1 and Table 2. For identifying ground water recharge potential zones for an area following equation (2):
Pr=GLwGLr + DDwDDr + LCwLCr + LDwLDr + RFwRFr + GGwGGr + SGwSGr +SCwSCr (2)
Where,
Pr is the groundwater recharge potential index, GL is the geology index DD drainage density index, LC land use land cover index, LD is lineament density, RF is rainfall index, GG is geomorphology, SG is slope gradient and SC is soil cover index. The subscript w and r represent the weight of a theme and the ranking of individual class of the theme respectively.