Morphometry of Selected Watersheds, their Bed Sediment Load Characteristics and Reclamation Measures for Sediment Control in Outer Himalayas

摘要

The Himalayas cover an area of about 50 m ha and there has been a very rapid increase in the developmental activities. A near experimental population growth has placed a further heavy demand on already limited natural resources. Debris load production from stream banks, land slides and mine waste causes in-equilibrium in stream flow regimes and further cause extensive damage to life and property. The paper deals with-(a) determination of Characteristics of Watershed situated in Himalayas and Shiwaliks, (b) to establish relationships between channel morphological parameters with drainage area and channel length upstream, (c) to evaluate the performance of the management strategies in the reduction of runoff and debris load production rates. The studies conducted clearly established that - a) bed material size increased up to about one-fourth to one-third of the length of torrent and decreased thereafter. Such a behavior is due to both colluvial and gravitational forces. b) an inverse relationship exist between channel width and local bed slope, c) the reclamation measures reduced runoff from almost 55 % to 33 % and debris load from 550 tonnes/ha/year to 8.0 tonnes/ha. When conservation measures are well planned and implemented scientifically would not only reduce runoff and debris load but also improve dry weather flow and sustain for a longer period. The conservation measures when implemented in a watershed situated in Himalayas proved effective in attenuating the peak rates of runoff (9.5 mm/hr to 1.6 mm/hr) , volumes of runoff (55 per cent to 33 per cent of rainfall) and increasing the dry weather flow (9% to 25 % ) & watershed lag time. This is attributed to decreased bed slopes and improved flow channelization. The debris load from both W_1 & W_2 watersheds reduced from near 550 t/ha/yr to about 8 .0 t/ha/yr four years after implementation of interventions.