RAINWATER HARVESTING IN AN URBAN AREA CONSIDERING CLIMATE CHANGE A Case Study

Abstract

Sustainable management of natural water resources is the need of hour for the decision makers in the early 20th century consequent to the crisis faced by the society due to the unplanned developmental activity. The anthropogenic activities have affected the quality and quantity of the natural resources, which is evident from the disappearance of the natural water bodies, degraded catchments and increased pollutants in water bodies, which necessitated optimal water resource -planning, spatial and temporal tools such as Geographic Information System (GIS), are helpful in analyzing the spatial data. To meet the growing demand of water due to increasing population, planner's attention is diverted towards alternatives such as rainwater harvesting, treatment of waste water, recycling etc. Rainwater harvesting and artificial recharge of groundwater augments the existing water resources, ground water recharge and improves the condition of other water resources in the vicinity. So rainwater harvesting forms one of the most cost-effective methods for improving the water resources for domestic water requirements in the urban area. The urbanization has resulted in development of new housing societies and construction of multi storied housing complexes. The public water supply to these multi storied housing complexes is insufficient As a consequence; many of the housing complexes have drilled bore wells which are being used to supplement the water supply. With more development, industrialization and increase in population, the demand for water would increase in near future putting greater stress on the available surface water resources. Due to the increase in housing, industries, asphalting and cementing of roads the area of natural recharge to ground water has reduced considerably. The rainfall in the area is moderate and a large number of bore wells are available for augmenting the deeper aquifers. Therefore roof-top rainwater harvesting to recharge the ground water in the deep aquifers is a feasible method in the study area. This would help to supplement the domestic water supply round the year to a large extent. In addition the construction of recharge shafts and recharge wells would also increase the groundwater. Lack of proper infrastructure such as water supply system along with lack of public participation in the city has induced stress on groundwater both qualitatively and quantitatively. There will be scarcity of water in the areas that are purely dependant on groundwater. The recharge to groundwater is decreasing due to urbanization and concrete jungles. Also pollution of xii surface water, due to discharge of untreated waste water on open drains and natural unlined nallahs make groundwater more vulnerable to contamination. If the rainwater is harvested, the scarcity of water can be minimized. This is an ideal solution of the water scarcity problem where surface water sources are insufficient or insignificant and there is inadequate groundwater supply qualitatively and quantitatively. Rainwater is bacteriological pure, free from organic matter and soft in nature. In the urban areas rainwater available from roof-top of buildings, paved and unpaved areas go waste. In urban areas, adequate space for surface storage is not available and water levels are deep enough to accommodate additional rainwater to recharge the aquifers. To cope up with the adverse impact of climate change, sound adaption and mitigation measures are imperative. Thereby, ideal option to solve the water scarcity problem in an urban area and as an adaptation to climate change is the roof-top rainwater harvesting. This rainwater can be stored in the storage tank for future direct use and also excess water can be diverted to recharge the aquifers through existing ground water tapping arrangements or by constructing suitable artificial recharge structures such as recharge pit, recharge trench, recharge shaft, recharge well etc. The choice/selection of any particular method is governed by local hydrological, land use, soil characteristics, etc. In the present study, planning and designing of rainwater harvesting in an urban area (Bhubaneswar - the capital city of Odisha) has been analyzed and proposed for future implementation. Also in this dissertation, attempt has been made to analyze the impact of climate change on rainwater harvesting components viz, filter tank, storage tank, recharge shaft and recharge well etc. Then it has been recommended to consider the impact of climate change during construction of rainwater harvesting structures in the study area. The amount of rainwater harvested depends on the frequency and intensity of rainfall. Climate change affects the intensity of rainfall and increased temperature, putting increasing pressure on availability of water resources in an area and rainwater harvesting system. In the present study, only positive changes in climatic parameters will have utility value, as for RWH, the sizes of the system can only be increased considering the climate change impact. The reduction in size in future would not be possible, thus negative changes would be very difficult to implement.