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ABSTRACT
Groundwater mapping is essential for meeting the water requirement of people. Identification of groundwater potential zone was attempted for a watershed located in Mandal & Becharaji district, Gujarat, India. The Bhukosh data was used for land use/land cover analysis. For delineating groundwater potential zone, a total six thematic layers namely drainage density, slope, geology, soil, geomorphology, rainfall and land use land cover were considered during the analysis. Afterwards thematic layers were converted into raster using the GIS platform. Further, after assigning weights and ratings to each thematic layer, overlay analysis was applied and a total five zones were delineated as very good, good, moderate, poor, and very poor. The majority of the area has moderate groundwater potential zone.
Introduction
Groundwater is an important natural resource used in different sectors, namely, domestic, agriculture and industrial. In India, the majority of population depends on and also in the world because groundwater acts as an alternative source to surface water. Therefore, mapping and monitoring of ground- water resources are very important in semi-arid and arid areas.
Literature outlined the role of remote-sensing and geographical information system (GIS)- based multi- criteria decision-making (MCDM) analysis, analytic hierarchy method, fuzzy logic technique, influencing factors analysis, and Dempster-Shafer model for delineation of ground- water potential zones (GWPZs). The remote-sensing and GIS have many advantages over the conventional methods such as time and cost-effectiveness and provide synoptical coverage.
Studies reported that for delineation GWPZ mainly required input data such as on land use land cover (LULC), slope, drainage density, geological structures, soil, geomorphology, water level, rainfall, and others. The GWPZ’s can be assisted by surveys, namely, geophysical, hydrogeological, geo- logical, drilling and satellite data, global positioning system data and GIS. However, direct methods are time-consuming, cost intensive and require skilled manpower. The combination of earth observation satellite data and GIS gives information about the different effective components of groundwater existence and its movement corresponding to the geology, soils, geomorphology, LULC, drainage density and geology. These factors can play an important role in identification and evaluation of GWPZs. Overlay analysis of thematic layers in the GIS environment helps to identify the occurrence of groundwater. Therefore, the objective of the present study was to delineate the GWPZs using integrated methods for Mandal Becharaji Special Investment Region, Gujarat.
Study Area
Mandal Becharaji Special Investment Region (MBSIR) is spread over more than 425 Sq.km, MBSIR is a new industrial hub being planned about 90 km from Ahmedabad and 85 km from Gandhinagar near Becharaji town. Envisaged by the government of Gujarat, MBSIR is one of its kind industrial hubs and will comprise automobile, manufacturing and auxiliary industries. The SIR is strategically located, well connected with trade gateways and falls in the influence zone of the proposed Delhi – Mumbai Industrial Corridor project (DMIC), a joint initiative by the Government of India and Japan.
The dedicated freight corridor (DFC) passes through six different states. Distribution of its length in these states is mentioned below:
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Delhi NCR – 1.5%
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Haryana – 10%
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Uttar Pradesh – 1.5%
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Rajasthan – 39%
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Gujarat – 38%
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Maharashtra – 10%
Study Area
Total six types of datasets were collected and processed. Landsat 8 (1 January 2022, 31- December 2022) data sets have been downloaded from web portal: https://earthexplorer.usgs.gov/ and pre-processed before further analysis. Rainfall data in grid format were downloaded from (https://crudata.uea.ac.uk/cru/data/hrg/) CRU TS 2.1 Global Climate Database (The CRU TS2.1 Climatic Research Unit (CRU) of University of East Anglia has produced climate dataset). The SRTM 30 m digital elevation model data were downloaded from a web portal: https://earthexplorer.usgs.gov/ and used for slope and relief analysis. Geology and geomorphology of the study area was collected from Bukhoosh portal of Geological Survey of India (https://bhukosh.gsi.gov.in/Bhukosh/Public).
Methodology
Land use land cover (LULC) was prepared using Bhukosh data. Geomorphology and geology maps were prepared from the Bukhoosh portal of Geological Survey of India (https://bhukosh.gsi.gov. in/Bhukosh/Public). The drainage network and slope map were prepared from SRTM 30 m DEM and with the help of drainage map, and drainage density map was generated in the GIS platform using density analysis tool.
The total annual rainfall distribution map was prepared from the Climatic Research Unit platform. Rank and weights were assigned to each layer. Further, these layers were integrated using weighted overlay analysis (WOA). The weight for the selected thematic layer was calculated. The particular layer and their class have assigned a weightage and a rank ranging from 1 (low GWPZ) to 5 (high GWPZ), respectively.
The GWPZ map was prepared and categorized into five classes namely very good, good, moderate, poor and very poor. The Cumulative Score Index (CSI) method was used for this classification.
The CSI expression is as follows:
CSI = Σ (Geomorphology rank x weight + Slope rank x weight + Geology rank x weight + Drainage density rank x weight + Rainfall rank x weight + LULC rank x weight + Drainage Density x weight)
Result and discussion
The detail of different factors mentioned in following section given below:
Drainage density
Majority of drainage is found all over the area. In the rainy season, all drains have maximum water and almost flood condition because the watershed is located in a low lying area. In the case of GWPZ, natural drainage systems have importance to govern the water directly on the surface because more drainage is a sign of more possibility of water to drain out. While poor drainage networks in any region will have low possibility of good GWPZ. The study area comes under the 6th order drainage system. Drainage network has been derived from the DEM file from GIS and then Drainage Density Map has been prepared on GIS.
Geology
The flow and existence of groundwater depend on porosity and permeability of rocks. Geological areas fall under Undiff. Fluvial/ Aeolian/Coastal & Glacial Sediments (UF/CGS). For each geological unit, separate weights were supposed to be assigned according to their groundwater pro- spects. But in the study area only one soil type is available. High weight was assigned to Undiff. Fluvial/ Aeolian/Coastal & Glacial Sediments (UF/CGS) according to the groundwater prospects. The study area comes under the 3rd order in the weightage system.
Geomorphology
Geomorphologic features give a direct possibility about groundwater existence, flow and evolution. The hydro-geo-morphological features of the area were updated from Bhukosh data. Based on the Geological Survey of India (GSI) digital data for study area, a total of seven geomorphological features have been identified, such as: Dune Complex (23.85%), FluOri - Younger Alluvial plain (1.57%), FluOri - Older Alluvial Plain (71.32%), Dam and Reservoir (0.12%), Water Body – Lake (1.89%), Water Body – pond (0.8%) and Water Body – River (0.52%). Among these morphological features, Coastal Plain, Water body–Lake, Pond, River and are under very good condition hence assigned a very high rank of 5. The study area comes under the 1st order in the weightage system.
Land use land cover (LULC)
LULC governed the infiltration or percolation and permeability process. The major LULC class was agri- culture (91.77%), followed by Built up (4.38%), range land (3.03%), water body (0.68%) and trees (0.1%). Based on type of land use, the distribution map has been categorized into five categories (score is also 1 to 5). Score has been allotted as 1, 2, 3, 4 and 5. The LULC criteria comes under the 5th order in the weightage system.
Rainfall
Rainfall is a vital component to assess potential zones of groundwater. Rainfall, infiltration and percolation are three factors which directly control groundwater table of an aquifer. It has been found a good co-relationship between rainfall and groundwater table fluctuation. Based on average annual rainfall a distribution map has been categorized into five categories i.e. score 1, 2, 3, 4 and 5. The rainfall criteria comes under the 4th order in the weightage system.
Slope
Slope gradient directly impacts the infiltration and percolation process of rainfall. Therefore, slope information can be used as one of the vital keys for identification of GWPZs.
Therefore, slopes help to identify the infiltration and per- collation rate of rainfall into ground, however, higher degree of slopes means a rapid runoff and negatively correlated with infiltration and percolation rate. Whereas, at level and gently sloping area, rainwater always flows on the surface with lower velocities and positively correlates with infiltration and percolation rate. Flat slope area gives more possibility of infiltration and percolation process in comparison to the steep slope. This fact was considered while assigning the weightage or score for various slope classes. Score has been allotted as 1, 2, 3, 4 and 5. The LULC criteria comes under the 2nd order in the weightage system.
Weighted overlay analysis (WOA)
The WOA is a pixel based analysis technique. Different layers have different measurement units like rainfall layer in mm, DEM in meter, slope layer in degree, drainage density in per kilometer and others. For WOA these all layers must be in the same scale hence a score 1 to 5 was assigned to each layer. After assigning a score, all layers are at the same index and integrated into one. Following table shows the weightage given to each class and calculation of overall weightage for preparation of Groundwater Potential Zone in MBSIR area.
Conclusion
-The GWPZ delineation was carried out using six criteria i.e. Geomorphology, Slope, Geology, Rainfall, LULC Drainage Density and in GIS platform. The GWPZ map was categorized into different classes from Very High to Very poor.
-The areas under poor-GWPZs are required for appropriate planning and management because a moderate area of watershed area comes under poor GWPZs class. Total area under poor class is 13%. In such an area a small check dam and artificial recharge structure or bore well can be developed for improving groundwater resources.
-The medium GWPZ category covers a large part of the watershed around 70% of total area of watershed. This category has a large area of watershed because some part of agriculture land and barren land are contributed in this category. The medium-GWPZ, has vast scope for implementation of groundwater resource improvements programs because barren land gives the opportunity for it and for improving this category requires less efforts in comparison to the poor-GWPZs category.
-Around 19% watershed area falls in the good category. Moreover, present research work has a good possibility to improve the irrigation facilities as well as agricultural productivity.
-The result reveals that the study’s potential zones are high in the East and North portion, while the low to medium groundwater potential is located in the central and west portion of the area.
-The groundwater potential zones mapping using remote sensing and GIS techniques is a rapid, inexpensive, accurate and large area coverage. Thus, it provides a range by which the most potable zones within an area in which groundwater occurrence is expected.