SUSTAINABLE DEVELOPMENT OF WATER RESOURCES IN AN INTERMONTANE SUB-HIMALAYAN WATERSHED

Abstract

Groundwater utilization has increased dramatically in developing cities of the world over last few decades. With the increasing urbanization, the need to protect water resources from different types of contamination has increased. Dehradun city, the capital of newly created Uttarakhand State, gets its major drinking water supplies from groundwater for use by the increasing population. Yet, indiscriminate construction of private tubewells by commercial enterprises and households has led to phenomenal increase in the density of tubewells in the city, over the last few years. The pressure is increasing due to large migration into the city from rural areas coupled with increased influx of visitors in the form of tourists and students. In view of these factors, water resources management in Dehradun city is believed to have become unsustainable. The present study was aimed at assessing the sustainability of water resources development in the Suswa Watershed which also includes Dehradun city. The specific objectives of the study were as under: 1. To review available literature on sustainability indicators in terms oftheir applicability in the field of water resources development and their status in India, 2. To assess groundwater resources of the study area and evaluate its surplus surface runoff. 3. To assess and analyze the quality ofavailable water resources in the study area, 4. To identify and evaluate available sustainability indicators vis-a-vis water resources development in the study area, and To recommend suitable options for sustainable water resources development. The Suswa Watershed is located in the eastern part ofthe Doon Valley, Dehradun District, Uttarakhand, India. It includes hills of Mussoorie to the north whereas Siwalik range forms the southern boundary. The watershed pertains to the Song river system which is a tributary of the Ganga river. The area, covering about 292 km2, is situated approximately between 77° 57' and 78° 10' East longitudes and 30° 08' and 30° 27' North latitudes. The ground altitude varies between 420 mand 2000 mAMSL. The average annual rainfall varies from 1600 to 2200 mm. most ofwhich falls in the monsoon (June to 5 August) months. Its land use is characterized by forest and agriculture besides urban area of Dehradun city. Main crops grown in the area are paddy, wheat, maize and sugarcane. As per 1991 and 2001 census reports, total population of Dehradun city is 2,70,000 and 4,47,808 respectively, showing a high decadal growth rate of about 66 %. Although, it is difficult to give the precise population figures of the Suswa Watershed, above figures of Dehradun city reveal the magnitude of stress posed by the population in the area. The analysis of land use-land cover changes was carried out by using satellite imageries in GIS environment for the years of 1972, 1990 and 2000. This analysis has indicated that the rate of urbanization has increased drastically in the recent decade, especially in Dehradun city where forest and agricultural land use has decreased. Surface runoff was estimated for the study area by employing the Natural Resources Conservation Services-Curve Number method. The estimates of annual storm runoff coefficient indicate that the annual runoff is around 22 % of annual rainfall in the study area. Thus, the minimum surface water resources availability is about 63 million-m . Hence, it appears that there is adequate scope for the development of surface water resources. Groundwater estimation for 2005-06 was carried out by using the mass balance based methodology of groundwater budgeting practiced in India. The necessary data was collected from the concerned agencies and also monitored during 2005-06 from a number of wells distributed in the watershed. The annual groundwater recharge for the year was 11915 ha-m whereas the total draft was 4175 ha-m. The stage of groundwater development in the command and non-command areas was found to be 19 % and 38 % respectively, thus indicating the Suswa Watershed under 'Safe' category. However, within the Dehradun city, declining trend of groundwater table was recorded in the hydrograph stations. Therefore, during any further development of groundwater, there is an urgent need to arrest the declining trend of groundwater levels in the Dehradun city possibly through artificial recharge measures. Accordingly, it is imperative to construct water conservation structures in the study area especially rooftop rain water harvesting schemes in the Dehradun city. Chemical analyses of 37 groundwater samples (including one river water sample) were carried out for determination of physico-chemical parameters (TDS, EC, pH, Ca" , Mg2+, Na+, K+, CI", HC03", C032\ and S042~), nutrients (N03"and P043) and heavy metals (Zn, Mn, Fe, Ni, Cu, Cd, and Cr) by using the standard methods with the objective of assessing the water quality for drinking purpose on the basis of standards laid down by regulatory agencies like Bureau of Indian Standards and World Health Organization. The major ionic composition of groundwater evaluated using the trilinear diagram showed the presence of non-carbonate hardness during pre-monsoon period whereas during postmonsoon period the water had dominant carbonate hardness. This change in nature of hardness can be probably explained due to the dilution caused by rainfall recharge. The overall groundwater quality in the study area was found to be suitable for drinking purpose. Although, groundwater from shallow aquifers was not fit for drinking at few places, it was found to be within the 'permissible' ranges of Indian standards and can thus be allowed for drinking in the absence of alternate drinking water sources. Asynoptic assessment of groundwater quality was also carried out by employing a groundwater quality index (GWQI). For estimating GWQI, seven water quality parameters were selected viz. cadmium, nickel, chromium, total hardness, sulfate, total dissolved solids and total alkalinity. The necessary weights ofthese parameters were computed by using an analytical hierarchy process. The cutoff value of GWQI for groundwater fit for drinking purposes was 2.0, with higher values indicating undesirable groundwater quality. The indicators identified for application in the Suswa Watershed to assess the sustainability of water resources are deforestation rate, water barrier index (WBI) and integrated water stress score (IWSS). Water quality index based synoptic groundwater quality evaluation was used to assess the sustainability vis-a-vis water quality. It was observed that, the deforestation rate in the recent period of 10 years (from 1990 to 2000) was faster than that during the preceding period of 18 years (from 1972 to 1990), although it was not alarming. The WBI computations have put the Suswa Watershed in 'absolute scarcity' category whereas as per IWSS approach, the watershed can be classified as 'moderately stressed' to 'highly stressed'. Considering seven relevant chemical parameters in the groundwater quality assessment. GWQI values ranged between 0.42 and 3.30. Mapping ofGWQI indicated that, barring few locations, the groundwater ofthe study area is fit for drinking purpose, and also showed the poor groundwater quality areas in the watershed. It is necessary to adopt adequate measures to remedy the groundwater in such problematic areas for which suitable steps should be taken by concerned agencies. in Based on the evaluation of sustainability indicators, this study has employed a viable approach which includes regular assessment of indicators in ensuring the sustainable management of water resources in the Suswa Watershed. It was found that the groundwater resources development, in the context of declining trend of groundwater levels, in the Suswa Watershed in general, and Dehradun city in particular, is becoming unsustainable. In this context, this study has resulted in formulation of guidelines for assessment of sustainability of water resources for the benefit of the planners, hydrologists and decision makers. For future studies, it is essential to augment the existing groundwater monitoring network through construction of additional deep piezometers for enabling sustainable water resources management in the Suswa Watershed. Keywords: sustainability indicators, groundwater resources, water quality, water quantity, safe yield, sustainability assessment, groundwater quality index, surface runoff, Dehradun, Suswa Watershed, India.