Impact of water harvesting structures on runoff and soil loss in Ayalur watershed , Erode district, Tamil Nadu India.

Abstract

The present investigation was carried out during the years 2015 and 2015 in Ayalur watershed located in Erode district of Tamil Nadu, India on the impact that the water harvesting structures constructed in a watershed have on impounding runoff and trapping sediment load from the watershed. This watershed which is located in semi- arid tropics has a series of 20 water harvesting structures in the form of perocolation ponds, dug out ponds and check dams with a total water storage capacity of 21868.8 m3. During the year 2014, when annual rainfall of 494.4 mm had been received , the 20 water harvesting structures had impounded 828.10 m3 of runoff and trapped 611.9 tonnes (t) of sediments in them. Similarly in the year 2015 which had received 610 mm annual rainfall , 26561.9 m3 of runoff had been impounded and 1643.5 t of sediment load had been trapped by the structures . When weighted with the annual rainfall, it was observed that the average runoff for Ayalur watershed in the study period was 18378.1 m3 and the average sediment load trapped by the structures was 1181.7 t . Taking into account 512.2 ha which is the catchment area of the last structure in the series, the soil loss was worked out as 2.3 t ha-1.