APPLICATION OF GIS AND MCE TECHNIQUES FOR OPTIMUM SITE SELECTION FOR WATER HARVESTING STRUCTURES

Water is a primary necessity for the sustainable survival of all forms of life and enormously scarce in arid parts of the world including India. The basic unit of water resources assessment and planning is a watershed. Water resources management at a watershed scale requires both water supply and demand management which includes water conservation through rainwater harvesting, groundwater recharge, and recycling. The present study is aimed to assess the potential of water harvesting and to identify suitable sites for water harvesting structures in Kolayat watershed of Bikaner district in Rajasthan by using Geographic Information System (GIS) and Multi-Criteria Evaluation (MCE). Proposed methodology of water harvesting site selection has compared with traditional methods of site selection. In traditional practices, the location of the structure is selected by visiting the geographical areas and looking at the various drainage patterns, soil erosion, land use land cover, water storage areas, availability of insects/ animals, native population feedback and past experiences. These practices are entirely dependent on instincts and results of the selected zones are uncertain. However, geospatial analysis techniques like RS, GIS, and MCE are the innovative tools which can be used to determine suitable sites for rainwater harvesting structures based on the watershed characteristics. The soil conservation service model (NRCS curve number) has been used to estimate the runoff. Further, spatial analysis in GIS has been carried out considering MCE along with the Analytical Hierarchy Processes (AHP) to assess the water harvesting potential and to identify the optimum locations of rainwater harvesting structures.


Introduction
India is a developing nation with overall 2.4 per cent world geographical area, but irrespective of that it contributes 16.5 per cent of overall world population, has only 4 per cent of its renewable water resources (Nelson et al., 2009).Such a limited resource in the scenario of increased water demands from the everincreasing population is a big reason for concern especially in arid and semi-arid areas like Rajasthan in India. Rajasthan holds the most extensive geographical area which is around 10.5 per cent of whole nation area, however, contains only 1.15 per cent (Kumar et al., 2013;Narain et al., 2006) of the total available water resources. Water plays a vital role not only in satisfying the basic human need for life and health but in socio-economic development also.
Meanwhile, as the modernisation expanding its wings with the face of industrialisation, urbanisation and the importance of this finite natural resources is undervalued which results into over-exploitation of the water resource. To compete with the ever-increasing population, food production has to increase simultaneously with effective irrigation techniques. Optimum and efficient use of ground and surface water is the best way of water management practice to cope up with the water stress in the field of irrigation.
Its production, as well as demand underground water level, is sinking is the typical scenario of Rajasthan nowadays due to over-exploitation and improper natural recharge, and due to this irregularity in the groundwater recharge natural hazardous situation is prevailing in the areas of annual rainfall below 50-60 cm.
Over the years water management practices in India and most of the developing countries includes supply management where supply is augmented with an increase in demands, which is not feasible in water scarce areas. From many studies, it is well established that for sustainable water resources demand management practices should be adopted along with supply management. Demand management can be categorised into (1) wastewater recycling; (2) altering the nature of the work so it can be accomplished with fewer water use (3) reducing losses in drive from sources through use of disposal; (4) shifting time of use to off-peak periods; and (5) increasing the productivity of the system to work (Brooks, 2006;Pingale et al., 2014;Singh et al., 2009). Different water demand management techniques are water conservation through rainwater harvesting and groundwater recharge, grey water recycling, increasing awareness, differential water tariff system, etc.
From past several years human being is developing various methods to conserve water which is somehow not serving the problem as that technique is traditional, judged and adopted from past skills of precipitation movement, drainage patterns, soil erosion, forest/crop cover, water storage areas, availability of insects/ animals, native population feedback in watershed area. In recent past, new technologies have been developed to overcome shortcoming of traditional methods of water conservation like remote sensing, GIS and MCDM which is used to for accurate estimation of runoff produced from catchments, incorporating the spatial and temporal variations of catchment characteristics in resources estimation and making more informed decisions about selection of appropriate water conservation measures and sites of their implementation.Geospatial technologies like RS and Geographical Information System (GIS) are very efficient in capturing of watershed characteristics, bringing diverse data from different sources to a universal standard and analysing hydrological processing for making optimum decisions related to water conservation. Now a selection of water conservation structures, determination of their capacities and location are being assessed on the ground based on technical parameters like the slope of the land, contour lines, surface characteristics, surface & sub-surface drainage pattern, infiltration rate.
In recent years, new technologies have been proposed such as integration of MCE & GIS technology. This modern technique made work easy and accurate for best site selection of watershed intervention works (Tsiko and Haile, 2011). But still, efforts are needed to get the broader insight of such methods which were introduced in 1960 for supporting in decisionmaking. This method is dominantly accepted in the watershed development field. The spatial decision support system (SDSS) is the integral part of GIS and MCE for assessing the suitable site for a variety of facilities and works (Tsiko and Haile, 2011). The analytic hierarchy process (AHP) is based on multiple criteria decision-making theory which combines spatial analysis functions of the GIS (Yalcin, 2008) in the selection of WHS producing suitability maps. AHP is an organised method which gives proper decisions for site selection.

Study Area and Data Used
In the present study, Kolayat watershed in Bikaner district in Rajasthan State has been chosen as the study area. As per GIS, total catchment area of the Watershed is 793546 ha. To achieve the study objectives, a variety of data/information are required to be collected from various, sources.

Figure 1: Study Area
Methodology determine the runoff to be generated from the catchment to assess the available runoff for harvesting. Then all maps are categorised in the range of 1 to 9 by the technical parameter of water harvesting structure using AHP technique.
After this process, multi-criteria evaluation method has been used to determine the best suitable site for water harvesting structure. The detailed methodology has been presented in  The land use land cover pattern gives a significant effect on peak rate of runoff volume.
An area with dense forest cover, acts as a barrier to the water flowing velocity which results into a little surface runoff and gives enough time for water to settle down a bit, due to the fact that more rainwater is absorbed by the soil.  (1) Where n is the number of items being compared.
Consistency Ratio (CR): (2) Where RI is the random index, which is the consistency index of a randomly generated pair-wise comparison matrix. It can be shown that RI depends on the number of elements being compared and takes on the following values.

Results
To   To make rural areas water sustainable, efficient use of available water and their