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  FORESTRY SYMPOSIUM 1996
RUNOFF GENERATION PROCESS UNDER DIFFERENT LAND USE AT HORTON PLAINS

J M N Chandrasiri and E R N Gunawardena
University of Peradeniya

Runoff, one of the major components of the hydrological cycle occurs when the rate of precipitation exceeds the rate of infiltration. However, for different land use types the soil properties that can affect the rate of runoff may vary significantly. At Horton Plains, there are two distinct vegetation types, the cloud forest and grassland (natural as well as that cultivated about two decades ago), which may impact upon the rate of runoff.

This study was conducted to explain the runoff generation process by determining soil physical characteristics. Soil texture, organic matter content, bulk density, infiltration and hydraulic conductivity were measured in all land use types. Rainfall intensity data from the Automatic Weather Station was used to estimate the runoff.

The bulk density values of soil up to 1 m is exceptionally low in all land use types due to high organic matter content. This results in higher infiltration rates. Comparison of rainfall intensities and infiltration rates indicated that rain water enters into soil without generating surface runoff for almost all the rainfall events experienced at Horton Plains during the first six month of 1996. However, the hydraulic conductivity values below 1.5 m are low compared to rainfall intensity and infiltration rate values indicating that water moves laterally to streams through the soil profile. It appears that land use has marginal effect on runoff process compared to soil and climatic parameters at Horton Plains.

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Department of Forestry and Environmental Science,
University of Sri Jayewardenepura,Sri Lanka. 1999. All rights reserved.