II-4-Impact of Geology and Landuse on Sediment Yield in Micro-Watersheds of Himalayas.

Abstract

To monitor the impact of the geological set-up and landuse pattern on the delivery of total load (suspended, dissolved and bed load) were measured during 1991-1993 in six micro-watersheds of Khulgad watershed, a tributary of Kosi River. The two watersheds (i.e., W1 and W2) made up of Gneisses and covered with thick Oak and Pine forest discharged total load at the rate of 41 t/km2/y and 135 t/km2/y, respectively. The W3 micro-watershed consist of quartzite interbedded schist and granite (fractured due to fault) with agricultural land use delivered the total sediment at the 591 t/km2/y. The three watersheds (W4, W5 and W6) made up of quartzite interbedded schist and having agricultural (W4 and W5) and barren land use (W6) pattern discharged the sediment at the rate of 419 t/km2/y, 272 t/kmVy and 268 t/lcm2/y, respectively. The ratio of total load discharged comes out to be 1:3:14:10:7:7 for W I, W2, W3, W4, W5 and W6 watersheds. The highest sediment yield recorded from W3, which is tectonically disturbed (highly fractured and sheared rock condition). The W2 watershed made up of gneisses and having Pine forest cover discharged 3 times greater sediment load in comparison to Oak forested watershed i.e., WI . Thus results clearly indicate that Oak forest is more effective in controlling the erosion than the Pine. On the other hand, among all the six microwatersheds the maximum rate of sediment delivery from the W3 microwatershed clearly indicate that sediment yield is primarily controlled by geological setup of the watershed and landuse is the secondary factor in the Himalayas.