METHODOLOGY

Spatial- Temporal, drainage network and interconnectivity analyses:

Integrated approach involving remote sensing data, spatial and temporal analyses tools [Geographical Information System (GIS)], collateral data and conventional field survey were adopted for this purpose.  The base maps and the drainage maps were prepared using 1:50,000 scale Survey of India (SOI, 1973) toposheets. The thematic maps were prepared based on the visual interpretation of IRS-1C satellite imagery, using the visual interpretation keys such as tone, colour, texture, pattern, association, size shape, topography and drainage.

The 1:50,000 Survey of India (SOI, 1973) toposheets were used for the preparation of base maps and drainage maps giving a detailed drainage information of the area, showing the streams and the drainage channels. Ground verification and field validation of the thematic maps were done by selecting the training sites consisting of prominent features like water bodies, road and railway network and major settlements as ground control points, and field visits were made to check the interpretation accuracy.

Wetland Map

Wetland map of 1973 was prepared using 1:50,000 Survey of India (SOI) toposheets. IRS-1C imagery of 1996 was used for 1996 wetlands map. This was done by visually interpreting tools as tone, colour, texture, pattern, association, size, shape, topography, drainage and analysed using Image processing software (IDRISI) and GIS. The temporal changes in the number of water bodies over two decades was detected by overlaying maps of 1973 and 1996.

Water Quality Assessment

Exploratory field surveys and extensive literature review were carried out to find the present status of wetlands in Bangalore and the associated problems. This has helped in selecting the waterbodies (sample) for further study. [Detailed investigations were carried out in seven water bodies selected based on the type of pollution load and its location in order to get an overall picture. Water quality of these water bodies was assessed on monthly basis, by monitoring the physico-chemical and biological parameters following APHA [American Public Health Association, Standard Methods for Water and Wastewater Analysis, 1995], for about twelve months.

Tanks studied: Table 1