Groundwater development using Remote Sensing and GIS Techniques

D. Das
Department of Environmental Science, University of Kalyani, India,
Email: ahadnejad@mail.znu.ac.ir


Abstract
Morphometric and hydrogeomorphic characteristics of a watershed provide important clues about the hydrogeology of the area. Information about the above characteristics derived from satellite imageries (IRS-IB) aided by field verifications and subsequently analysed in Geographical Information System (GIS) environment can provide a composite map and which can be used for adopting a suitable strategy for managing watersheds in a better way particularly in relation to the augmentation of the status of groundwater by artificial recharge methods.

On the basis of the above concept, drainage density, lineament and hydrogeomorphic studies of the upper catchment area of Sali river basin, Bankura district, West Bengal, eastern India have been performed for demarcating prospective sites for construction of artificial recharge structures. Granitic lithology and uneven topography indicate that the surface run-off is high and infiltration is low and therefore groundwater recharge is inadequate in the area. So, mainly to keep the irrigation practice and drinking water supply alive, groundwater condition has to be improved by artificial recharge method. Integrating different types of thematic map like drainage density, lineament, land-cover, hydrogeomorphology in a GIS environment, it has been possible to generate a composite map showing prospective sites for construction of artificial recharge structures.

Introduction
In India 75 percent or more of its population are relying on agricultural for their livelihood. Scientific and optimal utilization of water resources is a pre-condition for sustainable socio-economic development in a sound environment. In order to ensure sustainable development, it is very essential to prevent precious water resources from further deterioration through a better water resources (surface and subsurface) development practice against the vagaries of rainfall in drought prone areas. Special emphasize has to be given to store and conserve rain water. The natural recharge studies have indicated that only 5 to 10 percent of the rainfall volume is able to percolate deep enough to augment the groundwater in hard rock areas which reminds the emerging critical situations like drying up of shallow dug wells, poor yields from shallow bore-holes (Muralidharan, 1997).

In the wake of population explosion, the deteriorating surface water bodies and constraints of harnessing safe groundwater, it is the high time that all possible measures are taken to augment water resources. In the follow up studies it should be remembered that surface and groundwater system are interlinked. Due to convenience, low gestation period and smaller scale of investment, the demand for groundwater exceeds the demand for surface water. And, that has been more strengthened due to the availability of institutional finance for agricultural water supply. Lowering of water level in the pre-monsoon as well as in the post-monsoon will slowly lead to a large scale change in the vegetation pattern of an area. This will in turn cause ecological imbalance. Drying up of domestic tube wells during summer months causes health hazards among the rural peoples

The main aim of this article is to discuss how the water table condition can be improved mainly in the hard rock region through artificial recharge. Here the selected river basin is Sali of Bankura district, West Bengal, eastern India, where country rock is granite gneiss and a.a.r. is 1200 mm.

In India, more than 90 percent of rural and nearly 30 percent of urban population depends upon groundwater for meetings its drinking and domestic requirements. Groundwater also accounts for nearly 60 percent of the total irrigation potential of the country (Reddy, 1999). However, the demand for water is 3-4times higher than the availability of both surface and groundwater resources. Hence, the gap between the resource available and its requirement is widening with increasing developmental activities. In the recent years it has been observed that a sharp decline in water table condition has taken place due to over withdrawal of groundwater. Due to such mismanagement in groundwater exploitation sector, a scientific budgeting of groundwater is needed on its spatio temporal distribution, it's allocation for meeting competing demands like irrigation, industrial and domestic requirements.

A thorough local and regional hydrogeological understanding is necessary for an effective development of groundwater resource, especially in areas where bed rock has low primary porosity and where the intersections of secondary structural features is crucial for stressful exploration (Babu Rao et. al., 1997).

Groundwater resource and its development
The earth's fresh water resources have been now entered an era of scarcity. It is estimated that thirty years from now approximately one third of the world's population will suffer from chronic water shortages. The consequence of this scarcity will be felt in the arid and semiarid regions. It will also be experienced in the rapidly grown coastal region and mega cities in the developing countries with special reference to India. Indicators of water stress and scarcity are generally used to refresh the overall water availability in a country or a region. When the annual per capita availability of renewable fresh water in a country or a region falls below 1700 cubic meters, it is held to be situation of water stress. If the availability is below 1000 cubic meters, the situation is labeled as water scarcity. And, when the per capita availability falls below 500 cubic meters, this is said to be situation of absolute scarcity (Bandyopadhyay, 2001).

Groundwater resource availability depends upon the geological, geomorphological and climatic set up of a region. And, this set up is not uniform through out the country/region. Accordingly sub-surface water resource availability is also highly variable. One third of India is covered by alluvial and sedimentary formations having very good potential and the remaining two-third by hard rocks, with a limited to moderate groundwater potential. The replenishabe groundwater resources in India have been estimated as 43.3 million ham. Out of this, allocation for drinking water, industrial sector and system losses comes to 7.1 million ham. Utilisable resource potential is to the tune of 32.63 million ham. The utilisable irrigation potential from groundwater has been estimated as 66.05 million ha out of which the potential already created works out to be 35.37 million ha, leaving a balance irrigation potential of 30.99 million ha for development (Kittu, 2003).

Despite national average of an estimated 2464 cubic meters of water per capita per year, parts of India face water scarcity largely due to the uneven availability of water. It is observed that though the demands are much less as compared to the availability, shortages occur mainly due to lack of conservation and regeneration. The efforts for conservation being inadequate, a large proportion of water is lost as run-off to the sea.

Large area of India is comprised of hard crystalline rock having low porosity (less than 5 per cent) and very low permeability (10-5 m/d) (Sahu, 2001). This area is drought prone and generally classified as semiarid to arid. The region receives characteristically low to widely fluctuating rainfall, hence requires optimal management of groundwater resources for various needs. There should be periodic reassessment on a scientific basis of the groundwater potential, taking into consideration the quality of water available and economic viability. Exploitation of groundwater resources should be so regulated as not to exceed the recharging possibilities as also to ensure social factors.

In general, water harvesting is the activity of collection of rainwater directly. The principle of water harvesting is to conserve rainwater where it falls according to the local needs and hydrogeological conditions. In technical terms, water harvesting refer to collection and storage of rainwater and also other activities aimed at harvesting surface and groundwater, prevention of loss through evaporation and seepage.

Groundwater recharge projects should be developed and implemented for augmenting the available supplies. In an effort to maintain the water table condition in balance, artificial recharge in India was recognised about four decades ago (Anbazhagan and Ramaswamy, 2002). The artificial recharge studies in India have been mainly concentrated on the mechanism of recharge and their feasibility for percolation ponds, check dams, flooding recharge trenches, recharge wells and induced recharge. The selection of sites for artificial recharge is no less important, and that is why a proper scientific method is needed to be followed.

Spatial technologies and groundwater
During the last two decades, satellite based remote sensing has been proved to be efficient in mapping the suitable areas for groundwater prospecting in different scales. During the first developmental stage of hydrogeologic remote sensing application, Landsat and IRS-series of satellites were used mainly for carrying out regional level mapping on 1:2,50,000 scale. Under National Drinking Water Technology Mission, the Department of Space, G.O.I, with the active support of different organizations has prepared district-wise hydrogeomorphological maps indicating prospective groundwater zones on 1:2,50,000 scale covering all the 446 districts of India during 1987-92 period (Reddy, op. cit.). Again in the recent years under Rajib Gandhi National Drinking Water Mission, NRSA (D.O.S., Govt. of India) has been entrusted to develop groundwater prospective zones in l:50,000 scale. In India the IRS WiFS-based detailed monitoring of drought was operationalised for Andhra Pradesh in 1998, and subsequently extended to Or

issa and Karnataka. IRS WiFS data having 188 m. spatial resolution is useful providing information about surface water spread, sowing etc.

By using the LISS-I1I and PAN merged data of IRS-IC/1D satellite, it has become possible to prepare maps up to 1:15,000 scale showing the surface water bodies, groundwater irrigated areas, canal commands, etc. as small as 0.25 hectares (Reddy, op. cit.). Geomorphology, relief of the terrain, weathering status, fracture and joint pattern, lithology. Soil type and land use can be deciphered from the satellite data with limited field checks. All these features are directly or indirectly influence groundwater occurrence, movement and accumulation. The information integrating lithology, landform, structure, land cover/land use and aerial aspects of drainage basin provides very useful clue for groundwater targeting and siting artificial recharge structures. By combining the remotely sensed information in the form of various thematic layers in a GIS environment with adequate field data, particularly well inventory and yield data, it is possible to arrive at prognostic models to predict the ranges of depth, the yie

ld, the success rate and the types of the well suited to various terrain under different hydrogeological conditions. In order to assess the groundwater prospect by quantitative modeling, data on geomorphology, geological structures, lineaments would also be required in addition to weathered zone thickness, saturated zone thickness and yield in the wells. Lineaments being line data have to be converted into spatial data by filling the lineament density on grid map.

Objectives of the present study
In the present study an attempt has been made including the factors like lineament, geomorphic features related to groundwater accumulation and drainage texture (drainage density in particular) to select artificial recharge sites in the upper catchment area of Sali river basin (a sub-basin of Damodar river), Bankura district, West Bengal, eastern India.

The followings are the objectives of the present investigation:

1. a. To create a spatial data base of hydrogeomorphological information for the area under study.
2. b. To delineate areas suitable for artificial recharge.

Methodology
Preparation of thematic maps pertaining to geomorphology, lineaments, drainage basins having different drainage density values (figure-1) and land cover/land use of the area under study is done. And, this has been performed using IRS-IB LISS-II on 1:50,000 scale, November 1996 (P-19, R-51) data and Survey of India topographical sheets (no. 73 M/3, M/7) aided by field verifications. Preparation of maps using collateral data collected from field and laboratory processing have been done. The used data sets are: a. Hydrogeomorphic features, b. drainage density, c. lineament density.

Figure-1: The main basin has been divided into third order sub-basins according to the drainage density values

Digitization of all the themes using ARC/INFO GIS software has been performed. Overlaid and analysed output shows the area suitable for the construction of artificial recharge structures. All the segment files were polygonised and rasterised for analysis purpose. Crossed thematic product has been overlaid on segment maps for easy understanding and better visual interpretation. Drainage texture analysis has been performed on the basis of third order basins for the convenience of study.

Regional geologic setting
The area is having an undulating topography with highs and lows. The maximum relief is found to be 154 m (spot height) above mean sea level (msl). The elevation varies from 60 to 80 m above msl. Nearly forty per cent of the area under study is covered by alluvium and rest of the area is covered by fairly thick weathered profile of laterite and granite gneiss (Figure-2). The region has been traversed by a network of oriented fractures and often includes pegmatite dykes that are genetically related to preferred boundaries of Bengal basin (Dasgupta and Sikdar, 1992). The basement gneiss and schist are much weathered at the surface and are generally mantled by a soil cover, the thickness of which varies from place to place. At places granite gneiss and hornblende schist stand as moulds and ridges being resistant to weathering. The rocks are foliated and have well defined joints. The four sets of joints are ENE-WSW, ESE-WNW, SE-NW, SSW-NNE. The common spacing of joints is between 1-1.5 m. Vertical joints are widely spaced and are not common. Geomorphologically the area exhibits stepped sequence by three terraces of which the oldest is capped by laterite and/or yellowish brown sticky clay with kankar.

Figure-2: Hard and crystalline (granite gneiss) nature of the country rock

GIS analysis
When a wide range of mono-disciplinary resource maps are available, the users must seek ways in which the available information can be combined to give an integrated overview, or a reclassification or generation as needed (Burrough, 1990). The criteria for GIS analysis are dependent on the objective and also the data sets. In the present investigation, thematic maps have been prepared on the basis of geomophology, drainage and other surface geological expression of a potential aquifer. Overlay analysis has been performed between lineament density raster map with channel fill land cover raster map and the product reveals the sites suitable for artificial recharge (Figure-3). High drainage density raster map has been crossed with land cover map. The product shows the suitable sites for the construction of artificial recharge structure. Drainage has been overlaid on digital elevation model (DEM) of the Sali river basin (Figure-4) to get a qualitative idea about the influence of slope factor in recharge site selection process.

Figure-3: Composite map shows the proposed area of artificial recharge in the channel fill land cover and high lineament concentration Contour interval is 20 m.

Figure-4: Drainage network super imposed on the DEM of the study area. Lighter tones depict higher ground, whereas darker tone indicates lower ground Observation

Observation
The Sali, ephemeral tributary of the Damodar river basin originates from the western part of the study area and flows in WNW-ESE direction along its course length of 74 km. The area comprises mostly agricultural land of single cropping. The soil cover in the Sali river basin varies from 2-5 m. depth of weathered residuum varies from 20-25 m. Extensive lateritization has taken place mainly at the water divide. The south east part of the Sali river exhibits a gentle gradient and is covered with sands. The main channel Sali contributes more water in the basin due to structural control over drainage development. The flood plain shows a narrow width. Groundwater yields in this zone appears to be moderate. Existence of a number of perennial tanks nearby Sali river is predominant. Third order sub-basins have been studied in context of their large dimension, which facilitate recognition of lithology, structure and nature of sediments in such basins.

The channel fill sediments and pediments with considerable thickness (>20 m) and weathered materials are potentially good aquifers. Drainage density theme is an influential input in deriving the results in locating the artificial recharge sites. Intersections of channel fill and deep seated lineament make potential aquifer of groundwater accumulation. Coincidence of basins with high to moderate drainage density values and channel fill land cover reveals promising sites for artificial recharge as well.

Discussion In spatial distributions, attitude and depth of the fractures/joints varies from rock to rock. The fractures may be spaced closely or ten meters apart, they may trend in one or several directions with varying degree of inclination and intersections. Recharge of aquifer occurs mainly in weathered and fractured zones. Most of the drought affected districts are having these units, where groundwater is the only reliable water source. Fracture and shear zones are promising location of rechargeable aquifers, and are indicated by alignment of drainage courses and by other geological features.

Though not directly measuring the hydrological properties, remote sensing data can enable direct and indirect observation of hydrogeomorphological/geological features significant to groundwater development. The spatial techniques have been proved to be a powerful tool in sub-surface water related studies. The recent advancement in this field have generated a great sense of awareness through out the world. These methods are much faster and improve the quality than the conventional methods. Conclusion

In selecting the sites for artificial recharge, it is necessary to study the lineament, drainage, hydrogeological land use, hydrogeomorphology of an area and their overlay/cross analysis in a GIS environment. Since the area under study is having a gentle slope, the influence of slope factor is negligible here in recharge site selection process. Once the sites are located in a composite map, suitable artificial recharge structures are constructed.

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