Rainfall energy loss model in soil erosion process

by Madhu S. Pudasaini

Institution: University of Western Sydney
Year: 2008
Keywords: Doctor of Philosopy (PhD); soil erosion; models; rain and rainfall; rainfall simulators; energy dissipation
Record ID: 1073750
Full text PDF: http://handle.uws.edu.au:8081/1959.7/42514


Soil erosion is recognized as a global threat against the sustainability of the natural ecosystem and the environment because of its severe effects in agricultural productivity, damage to infrastructure and pollution of water bodies. Adverse impacts due to human activities resulting in accelerated soil erosion process have been well documented. Much more attention has been given to study the mechanisms associated with the process of soil erosion in the second half of the 20th century. Different mathematical models have been developed to simulate soil erosion processes and incorporate the result in different options of erosion controls. Modelling soil erosion is a complex process that involves numerous parameters. It is for this reason that even highly sophisticated and advanced erosion prediction models like Water Erosion Prediction Project (WEPP) do not incorporate all mechanisms of the soil erosion process. An obvious gap is the satisfactory explanation and incorporation of soil erosion mechanism associated with the initial portion of microchannels where both inter-rill and rill erosion exist. This study attempts to fill this gap through extension of knowledge in the area of soil erosion mechanism, specifically within the initial portions of rill where both splash erosion and erosion due to shear stress exist. Detachment of soil particles from the soil surface depends on the kinetic energy imparted by raindrops. Therefore, it is essential to estimate kinetic energy as accurately as possible to enable study of soil erosion and infiltration mechanisms. Rainfall simulation is widely used to generate rainfall of desired intensities and durations to study soil erosion, infiltration and other dynamic behaviours of soil. Kinetic energy of a rainfall event is often estimated from its intensity. The actual kinetic energy imparted on a soil surface is generally less than the total value of kinetic energy of a rainfall event. This is because of the cushioning effect of the overland flow. Therefore, there is a potential risk of over prediction of splash erosion by an erosion prediction model that does not account for this cushioning effect. In this study, experiments were carried out to estimate the kinetic energy of three different simulated rainfall events produced by three different combinations of pressures and nozzle sizes. The equipment consisted of a multipurpose hydraulic flume, 2m long and 1.4m wide. Five highly sensitive force transducers were mounted on the surface of the flume to measure the impact of raindrops. Different slopes were represented in the experiment by tilting the flume in four different angles from 0 to 15 degrees. Two tipping bucket rain gauges were used to measure rainfall intensity. The nozzles were placed at a height sufficient to produce terminal velocity by the falling rain drops before they hit the flume surface. Overland flow was generated by continuously supplying water to the inlet tank constructed at the upstream of the hydraulic flume. Responses received from the transducers (in the form…