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Better water management through GIS/Other strategies
Indian Water Management Scenario As compared to the other two nations (i. e., Israel and China) with ancient civilisations, India is neither as compact as Israel nor as big as China in terms of area [7th in the world with little under 3.3 million sq. km] as well as population [second in the world with little under 0.95 billions in 1996]. The lower and upper bound values of the annual rainfall range are exacly the same as that of China with the minimum rainfall occurring in the cold desert of Ladhak in Jammu & Kashmir as well as in the hot desert ‘Thar’ of Rajasthan while the maximum rainfall occurring in the Western Ghats as well as in Meghalaya. For the worst scenario of water management, one can cite the instance of drought at Cherraounji-the world’s wettiest place- in Meghalaya few years ago. On the other hand, we can cite many examples of success stories - like the artificial glaciers or ‘zings’ of Ladhak in Jammu & Kashmir, the narrow wells or ‘beris’ of Jaisalmer in Rajasthan, rainwater harvesting techniques adopted in thh Chennai Metropolis of Tamil Nadu, the 300-metre deep rock tunnels or ‘surangams’ of Kasargod, Kerala, the small covered tanks or ‘kundis’ for storing rainwater in Churu, Rajasthan. All these success stories not only testify our capability to achieve water conservation, but also hint us about the grim picture that we might face in the coming years if such attempts are not undertaken on a massive scale [Joshi,1998] In the following paragraphs, a brief outline is presented on the use of Geographical Information System (GIS) i. e., Geo-informatics and other strategies for improving water management. Other strategies for better water management are also mentioned in short. Geo-Informatics for Simplified Storage Computation and better Water Management Remote sensing (RS) and GIS has the potential to improve the water management, when it is adopted along with some field techniques such as constructing check dams for soil and water conservation. A simplified ‘Semi-Elliptical Cone (SEC) Model is described here.  Figure 1. Schematic of a Water Storage Created by a Check Dam Across a Stream/River If a simple check dam is created across a stream for soil and water conservation, it will result in storage which is shown by a triangle in the Reservoir Top View in Figure 1. If such series of check dams are constructed at appropriate locations, and remotely sensed images are taken at different values of suitable time intervals (e. g., at daily or weekly intervals), we can get the areas of water storage for all the sites at those time intervals. Once such a database is created, the next thing that is required to be done is the computation of the individual as well as collective water storage volumes( V i. e., ayz : Cross Sectional Coefficient (CSC) axz : Water Spread Coefficient (WSC). The main assumption in the SEC Model is that the water storage volume is considered to be of right elliptical half-conical shape. It means that the base of this cone is of semi-elliptical shape with half of the width (W) and depth (D) as its semi-major and semi-minor axes respectively. The vertex of this cone is the most upstream point in the Fetch direction. The coefficients CSC and WSC provide us with the representative variations in all the cross-sections considered parallel to the check dam and in all the water spread contour areas considered at all the depths respectively. Another important assumption in the SEC Model is that no tributary joins the stream or river at the reservoir area. One can notice that Equation (1) contains a constant term, two coefficient terms and three terms corresponding to the three dimensions of the reservoir. The two coefficient terms CSC and WSC broadly depend on the longitudinal and side slope characteristics and as well as the sedimentation and erosion characteristics of the reservoir area. Among the three dimensional terms of the reservoir, fetch and width can be obtained from the RS images while depth needs to be actually measured. By properly estimating and updating the two coefficients from time to time, the storage computation can be further simplified. On a short term as well as all-term basis such simplified storage computations can be used for modifying the elevation capacity curves as per the changed reservoir sedimentation/erosion characteristics. On a long term basis, these storage computations can also be used to complement other strategies for better water management as elaborated in the successive paragraphs. Other Strategies for better Water Management in Indian Conditions Uneven distribution of water resources is found almost everywhere in our country. This unevenness is spatial as well as temporal. As a result of this, it is very common to have flood as well as drought conditions existing in different parts of our country at any particular time. Nearly 75 to 80% of the annual rainfall in major portion of our country occurs during the south-west monsoon months of June to September. While the Himalayan and Sub-Himalayan regions receive water due to snow melting in summer, some regions in the north-east and the east coast receive rainfall due to north-east monsoon. Even the amount of annual average rainfall varies all the way from around 50 mm in the Ladakh region of Jammu & Kashmir to more than 11,000 mm in Meghalaya. Likewise the number of annual rainy days (with a minimum daily rainfall of 2.5 mm) varies all the way from less than 10 in Ladakh and Katch (Gujrat) to more than 150 in Meghalaya and the Western Ghat regions of Karnataka & Kerala [Rao, 1979]. Nearly a third of our country’s area is said to be either chronically drought prone area (with at least 40% probability of a maximum of 75% of the normal annual rainfall) or drought prone (with a 20-40% probability of a maximum of 75% the normal annual rainfall)[Subramanya, 1994]. It has been observed that these areas generally have an annual rainfall of less than 750 mm. In these areas scarcity of water is observed very frequently. It calls for effective water management mainly through techniques such as evaporation control and rainwater harvesting. |