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Introduction

Increasing population density in cities creates more demand for water. Among essential natural resources, available water has already become a COMMODITY due to its scarcity - Packaged drinking water industry is US$ 160 billion strong and growing which is really a worrisome trend.

The below image is Chennai, A metropolitan city in India

Chennai city

One was taken during Dec 2015 flood and another was on next summer tankers lining up for filling water from suburb lakes.

Poor water harvesting infrastructure combined with unpredictable weather due to climate change causing extreme events floods or droughts .

Groundwater is being exploited unsustainable way. It is critical to harvest rainwater to recharge groundwater for a sustainable usage.

To make life more comfortable, now we are turning cities into smart. We should to leverage the advances of spatial technology for sustainable use of natural resources like water.

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Methodology approach

Geographical Information System (GIS) helps to work with 2D information that means Spatial information.

We have tried a GIS-based approach for identifying the suitable sites for rainwater harvesting structures in Madurai, one among 100 cities in India selected by Government of India.


Data used

  • Digital Elevation Model data
  • Land use land cover map from NRSC, ISRO
  • Long term rainfall data from Global weather data, Texas A & M University.
  • Soil map

The above mentioned data are processed in GIS platform to obtain spatial thematic layers required for analysis.

Digital Elevation Model (DEM) data, reclassified Land use map, spatial rainfall layers were generated.

Detailed Methodology:


Generation of Runoff potential map

Runoff potential map is generated using Soil Conservative Service –Curve Number (CN) method - widely used methodology. Slope map is derived from the contour. These spatial data are processed with GIS software to obtain the required thematic layers.

(Runoff potential means the amount water flows above ground after a significant amount absorbed by the soil during a rainfall event)

Base data sets:

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Analysis

Thematic Data sets generated in GIS platform

Curve Number of a location is based on its Land use and Soil type - the parameters which decide the potential runoff of an area

Runoff Potential Map

Site selection for rain water harvesting structures is done using runoff potential of location, soil characteristics, slope details and land use pattern data.

  • An Analytical Hierarchy Process (A decision making methodology) – weighted overlay analysis is performed using GIS with priority values for different spatial layers.
  • The purpose of the weighted overlay analysis is to apply a common scale of values to diverse and dissimilar data input to create an integrated analysis.
  • The layers used for this work are LULC map, soil map, slope map and runoff potential map. Each layer has its own influence, based on its importance and necessity. So different weightages are assigned to each layers.
  • As a result of this process, the suitable macro level rain water harvesting sites such as farm pond, percolating tank and check dam are identified.

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Results

From the study area of Madurai district, the Madurai metropolitan area alone is extracted for validating the result. From the validation process, it is cleared inferred that the areas highlighted are highly suitable for setting up the rain water harvesting structures.

The Red area is 'Core built up of the City' so not suitable for macro harvesting structures.

Few Validated sites

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Conclusions and recommendation

Rain water harvesting structures are critical to conserve the scarce resource. It will be helpful to check floods during rainy season.

Most part of India is dependent on seasonal rivers where water flows only there is good monsoon.

Growing urban area and shrinking water bodies in the city makes the need for creation of more water storage structures to cater both agricultural need, domestic and drinking purpose.

With that view, Madurai is selected for identification suitable sites to create water harvesting structures utilizing remote sensing and GIS technologies and several suitable sites are identified for Macro level rain water harvesting structures.

The runoff potential map generated could be useful for

  • Flood risk zone analysis
  • Crop cultivation area analysis.
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