¹PARDYP Project, Pakistan Forest Institute, Peshawar, Pakistan
²Hydrologist, University of Bern, Switzerland
³Regional Coordinator, PARDYP/ICIMOD

^*Corresponding author: E-mail suhailzokaib@yahoo.com

Abstract

  The sediment loads of Himalayan Rivers are amongst the highest in the world, resulting in problems such as siltation of reservoirs, blockage of river channels, quality of water supplies etc. The major sources of sediment are considered to be glacial debris, landslides, over grazing and intensively cultivated hill slopes. The aim of the study is to develop total sediment calculation and distribution on different land uses and thus to provide an essential information source for the future planning which will aim to quantify the sediment load to river and reservoirs. For this purpose hydrological, meteorological and soil erosion data were collected during 1999-2002 from different land uses in the four watersheds. Runoff and sediment losses were monitored on erosion plots on different land uses i.e. degraded, pasture, forest and agriculture. Total annual rainfall in the region ranged between 972 mm to 2400 mm. Annual rainfall in different watersheds ranged between 2343 to 2469, 1110 to 1656, 972 to 1324, 1011 to 2048 and 1254 to 1706 mm in the Jhikhu Khola (JK), the Hilkot (HK), the Bhetagad (BG) and the Xizhuang (XI) watersheds, respectively. On the basis of quarterly distribution of rainfall, about 44 to 66% rainfall occurs in quarter 3, which prolongs from June to August, which is mostly Monsoon season in the region. In general about 60 % of the annual rainfall occurs in the Monsoon season. Results show that runoff and soil losses were higher in the months of May to September, when rainfall duration and intensity were higher in all the watersheds. There were some big events which contribute most of annual runoff and soil loss in the area. Highest annual runoff was generated in JK watersheds in all land uses while very low in BG and HK watersheds. Highest runoff was recorded from degraded land uses. Most of the runoff in all watersheds occurred in 2nd and 3rd quarter. In JK (92 to 96%), in HK (75 to 90 %), in BG (83 to 94%) and in Xi (87 to 90 %) runoff was recorded in 2nd and 3rd quarter. Annual soil loss from JK was recorded higher in degraded, forest, agriculture and pasture land-uses, while it was very low in HK and BG watersheds. Soil loss in April to September was higher in almost all watersheds. In JK watershed (95 to 99%), in HK (80 to 90%), in BG (83 to 96%), in Xi (90%) of soil loss occurred in 2^nd and 3^rd quarter of the year in all land uses.
Highest runoff and soil loss was found in degraded plots because of less vegetation and loose soil, susceptible to erosion. In agricultural plots runoff and soil erosion was higher during the periods when there was no crop canopy in it and soil was not compacted after the ploughing. During the months when crop cover was good there was less runoff and soil erosion. However in pasture and forest plots runoff and soil loss was minimum throughout because of good vegetation and well organic matter that increases the infiltration and reduces runoff and soil loss.