GIS BASED SITE AND STRUCTURE SELECTION MODEL FOR GROUNDWATER RECHARGE
(A HYDROGEOMORPHIC APPROACH)

CONTENTS

n INTRODUCTION

n LOCATION OF STUDY AREA

n RESULTS AND DISCUSSIONS

n CONCLUSION

INTRODUCTION

n  PRESENT SITUATION

     Groundwater is the most essential element for the existence of life and plays an important role in the socio-economic development of the country.  Presently 85% of the water requirement for domestic use in rural areas, 55% for irrigation and over 50% for industrial and urban uses is met from ground water.  Water resource in India are unevenly distributed both spatially and temporally with a greater paucity of water with varied physiographic and geographic conditions.  In light of climate change, where an unsustainable management of ground water resource may gain momentum by change in precipitation has led to depletion of aquifers. The consequences of unscientific exploitation of groundwater are moving towards water stress condition.  Despite being a very important part of the nations growth, groundwater resource analysis is a complex but not tedious. An integrated study covering the aspect of groundwater recharge is a crucial requirement of the present days.

 

n  GEOLOGICAL MEANING OF GROUND WATER

     Groundwater may be simply defined as the water contained by void space within rocks or rock material which are typically designated as the saturated zone of rocks and can be distinguished from an unsaturated or aeration zone wherein voids are filled with water and air. Groundwater occurs in an “aquifer”, a medium capable of storing and transmitting water in desirable quantities. So in nut shell aquifers are saturated portions of rocks or rock matter, the saturation usually a result of the water infiltrating the ground after rainfall. The mechanism of natural infiltration allows slow passage of water through the ground, thus ensuring good quality and consistent chemical composition of the groundwater in its natural state. Nature’s mechanism of replenishing aquifers makes it possible for aquifers to sustain its use by Man over prolonged periods of time. Groundwater emerges from aquifers, naturally, by way of springs, or it can be pumped from wells, tube well or bore wells, as a source of water supply. Springs and seepage emerging from aquifers provide the entire flow to streams and rivers during the dry season. Wetlands derive their “sustained feed” of water from aquifers discharging to the land surface through springs and/or seeps. Hence, groundwater clearly plays two roles, the first being in the form of a water supply source and the second as a mechanism in conserving the environment.

 

n  Ground Water Recharge Using GIS Tool

     Extensive work was carried out with the help of Arc GIS 9.3 to enable a faster and efficient data analysis, This exercise also aided in a better understanding of the Geographical Information Systems and its usages in earth science and engineering applications.  

     It requires huge amount of data because it depends on numerous factors as climatic, topographic, landcover, soil and rock formations. 

     Computer simulation models for ground water provide a solution especially in carrying out numerically initial estimations of recharge with readily available data. It requires data of hydraulic conductivity, water table and bedrock elevations.

     Ground water recharge studies reflect much on the nature and characteristics of the area especially on, elevation, geology, land surface slope, vegetation and climatic factors.

 

n Definitions

nA geographic information system (GIS) is a computer system for capturing, storing, querying, analyzing and displaying geospatial data.

nIt describe both the locations and the characteristics of the spatial features such as roads, land parcels, vegetation stands on the earth surface.

n Components of GIS

nComputer system:

nGIS software

nPeople

nData

MATERIALS AND METHODS

n  The study area is located due southwest of Solapur city at a distance of about 85 km. The area is accessible from Solapur by all weather tar road. 

n  Geographically Solapur is located between 17.10 to 18.32 degrees north latitude and 74.42 to 76.15 degrees east longitude. The district is situated on the south east fringe of Maharashtra State and lies entirely in the Bhima and Seena basins. Whole of the district is drain either by Bhima river or its tributories. 

n  The District covers geographical area of 14844.6 sq.kms. is 4.82% of the total area of Maharashtra  State. Out of the total area of the district 338.8 sq.kms (2.28%) is Urban area remaining 14505.8 sq.kms. (97.72%) is Rural area.

 

 

OUTLINE OF METHODOLOGY

n   Background data (supplied by GSDA).

n   Field studies with emphasis on monitoring of the wells in term of water table on selected sites.

n   Structures visa-a-vie type in the area

n   Use of GIS tools to create necessary maps and analysis

 

        Field studies focused on study of the drainage pattern, collection of hydrogeological data through a randomized well-inventory and collection of locational data of existing structures in the area. Intensive field investigations were conducted over a period of Six moths from Dec. 2010 to May 2011.

        The effective time frame for the project was slightly more than six months.

 

n  Regional Geology

nThe geological history of Maharashtra is largely confined by the Deccan Basaltic Province. The Deccan Volcanic Province is an important geological feature of Penisular India extending over an area of about 5,00,000 Km2 covering the states of Maharashtra, MP, Karnataka and Gujrat of western and central India.

 

n  Geology of Pachegaon(bk) watershed

nPachegaon(bk) watershed is underlain by basalts (also referred to as Deccan Trap or Traps) which were formed from the eruption of lavas some 65 million years ago. These lava ‘flows’ vary in thickness from a few meters up to 10s or even 100s of meters. Each lava flow can further be divided into sub-units. In general, the Deccan basalts can be grouped into two categories, ‘simple’ or ‘compound’ depending on the viscosity of the primary lava (Deshmukh, 1988) (Kale, 1992).

 

n Geomorphology

nWatershed in the Pachegaon(bk) region is much gentler in relief as compared to those forms in the Western Ghats in Maharashtra. The regional relief appears quite subtle, with the younger basalt outcrops standing out as ridges against a gently undulating and rolling landscape. The Pachegaon(bk) watershed gradually slopes towards the East,West and North but the regional slope being towards the North. With elevations in the range of 800 to 640 m above mean sea level, the average topographic gradient in the watershed works out to just under 160 m over a length of 3.07 km (i.e. 1: 25 or 4%). However, slopes are bound to be greater along the flanks of the low divides in the eastern, northeastern and southern portions of the watershed, where watershed slope treatment measures would be intensive. In fact, the divide itself is marked by an almost flat-topped, narrow plateau along the northern, eastern and southern margins. The central and eastern parts of the watershed occupy valley areas where slopes are much gentler.

  

n  Drainage Computation

nPresent day drainage has been shown on the hydrogeological map prepared from SOI toposheet (Figures 4.6). This drainage has been plotted followed by field inventories. From the field investigations it’s apparently observed that development of first-order streams along incipient fractures through "headward" erosion. Headward erosion implies erosion of a drainage channel in the upstream direction (towards the "head" regions of the watershed).

 

n  Data Collection Methodology

nInitial objective was to observe selected wells and structures from Pachegaon (bk) watershed. With the help of Vishwas Patil a resident of Pachegaon (bk) who was appointed to assist during the field visits; 07 wells were selected.

 

n Data Collection

nData collected from the wells was in form of:

nWater level in the well in meters.

nDepth of the well in meters.

nSurface elevation of each well.

nLocation of the well.

nLocation of existing structures

 

n  Instruments Used during the data collection

nMeasuring meter tape for taking the depth and water level for well inventory.

n  GPS for taking the location and surface elevation

 

     Other than these instruments, extensive work was carried out with the help of Arc GIS 9.3 to enable a faster and efficient data analysis. This exercise also aided in a better understanding of the Geographical Information Systems and its usage in earth science and engineering applications.

     The whole process was carried out in the following steps

n  Georeferencing of the Survey of India toposheet.

n  Digitisation of the contours and drainage network with wells.

n  Creation of various maps.

n  Spatial analysis of new possible structures on the basis of geology, recharge zones, and geomorphic characters.

 

n  Following is the detail flow chart and work methodology

 

n Use of GIS Tool

nArcGIS 9.3 evaluation version was used for the creation of a database, editing, analysis of the data and preparation of the required maps. Toolsets such as 3D analyst,Spatial analystwere used in the process. The entire digitisation process was also carried out in the same software. The layers were digitised at a constant scale of 1: 10000. A toposheet was used as the base map for the digitisation process. The geological map was created using survey readings taken in the study area during a field visit. The layers created were contours, geomorphological units, drainage, geology, settlements, roads, and recharge – discharge areas. After creating all the required layers, recharge and discharge areas were marked. This then enabled the suggestion of sites for new structures by taking into consideration the geology, drainage and recharge and discharge areas. The use of this software for digitisation increased accuracy and also helped in saving time. Drainage analysis, for example, was rendered a very straight forward process as the area of the watershed and the stream lengths were calculated by the software.

RESULTS AND DISCUSSION

n Drainage analysis

nDrainage analysis reveals the nature of contributing surfaces, both to surface drainage as wells as to the infiltration component. Pachegaon(bk) watershed was subjected to drainage analysis in order to index its length, number and area characteristics. These data are provided in Table 1 (a and b). The drainage analysis included Strahler’s method of stream ordering where first order drainage represents the streams originating in the head region; two first order streams form a second order stream, two second order streams form a third order stream and so on …(Strahler, 1952). Pachegaon(bk) watershed is a fourth order basin, with two third order sub-basins: a smaller sub-basin in the southern portion and the larger sub-basin making up all the area in the eastern and northeastern sectors of the watershed

 

(a): Bifurcation Ratio and Stream Lengths

 

 

 

 

 

(b): Area and Drainage Ratio Analyses

 

n  Modelling

     In general terms, a model is a representation of reality. Due to the inherent complexity of the world and the interactions in it, models are created as a simplified, manageable view of reality. Models help you understand, describe, or predict how things work in the real world.

There are two main types of models:

n  representation models—represent the objects in the landscape

n  process models—simulate processes in the landscape

 

Digital Elevation Model

n  Generating a continuous surface used to represent a particular attribute is a key capability required in most GIS applications. Perhaps the most commonly used surface type is a digital elevation model (DEM) of terrain. These data sets are readily available at small scales for various parts of the world. However, just about any measure taken at locations across a landscape, subsurface, or atmosphere can be used to generate a continuous surface.

 

 

n  Use of contour data

     Contours have historically been the most common method for storage and presentation of elevation information. Unfortunately, this method is also the most difficult to properly utilize with general interpolation techniques. The disadvantage lies in the undersampling of information between contours, especially in areas of low relief.

 

n Evaluating output

nAll created surfaces should be evaluated to ensure that the data and parameters supplied to the program resulted in realistic representations of the surface. There are many ways to evaluate the quality of an output surface depending on the type of input available to create the surface.

nThe most common evaluation is to create contours from the new surface and compare them to the input contour data. It is best to create these new contours at one-half the original contour interval to examine the results between contours. Drawing the original contours and the newly created contours on top of one another can help identify interpolation errors. Contours can be generated with the Contour function.

 

 

n   Selection of Structures

n   Structures for artificial recharge

       The suggested structures for the artificial recharge were obtained in a user friendly manner by clicking on the drainage or stream, for example, the point on the drainage shows the potential structures as per manual of groundwater recharge based on the climatic, topographic, hydrogreologic and landuse conditions of the area.

 

n   Structure Suggestion

n   The suitability of artificial recharge structures in a given area computed by the climatic, topographic, hydrogeologic and landuse conditions. 

n   Climatic conditions determine the availability of water resources.  Topography gives the extent of runoff and retention.  Soil and landuse works out the extent of infiltration.

CONCLUSION

     Groundwater is an important source of water supply for many small towns, villages and small scale farms, with in the country.  Development of GIS based model was an effort to reduce the overhead while dealing with site selection process for artificial recharge of ground water. Arc GIS 9.3 tool is found very useful in the selection of suitable zones and selected sites on drainage for recharge of groundwater. Model also provides information of artificial recharge structure at the site based on local geographic features and annual rainfall details available for the water shed. GIS based model demonstrated the recharge sites which are generally situated on a gentle slope and lower order steams provide more recharge. The developed GIS based model needs to be applied on real world situation which provides the usefulness as well as set of decision making tools for groundwater and watershed management.