Author(s):

M Nagarajan, G Thiyagarajan, Balaji Kannan and M Manikandan

Abstract: A study was conducted to compute the runoff in tank catchment using GIS databases. For the study 10 tank cascade system was selected in upper Noyyal river basin, Coimbatore region of Tamil Nadu. The tank catchment-wise map, soil and land use map were scanned, geo-referenced and digitized. The Thiessen polygons with rainfall data of three rain gauge stations were created. From the above, tank catchment-wise land use pattern, soil hydrological group with rainfall region were identified by superimposing the maps and the attributes were stored in dbf files, which can be opened by any database. These attribute values were directly taken in to Visual basic - 6.0 (used as a platform), Curve numbers and runoff of each tank catchments was calculated using Soil Conservation Service (SCS) curve number techniques. The actual part of runoff from streams of Noyyal River was also considered for the tank storage. The runoff was computed by Normal rainfall condition, deficit rainfall condition and surplus rainfall condition (based on IMD classification). The runoff calculated from GIS database was compared with observed runoff for each tank catchment. The number of fillings in each tanks was calculated based on the runoff generated from own catchment and found out none of the tanks was filled by its own catchment runoff for the entire season. Hence, there is a necessity to augment the storage position of all tanks from the external source of water supply i.e., from Noyyal river.

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