Effect of rainfall interval on loss rates

• Main Author: Heng, Pei Kiat.
• Other Authors: Wong Sai Wai, Tommy
• Format: Final Year Project
• Language: English
• Published: 2010
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/39640
• Institution: Nanyang Technological University

Computer models based on kinematic wave theory can be developed to simulate the rainfall-runoff process on a catchment. In this study, computer models have been developed for a natural catchment (Upper Bukit Timah Drainage Basin) and two artificial catchments (Concrete and Asphalt Planes) to evaluate their respective optimum loss rates for the two loss models when catchments are subjected to natural rainfall. The loss models used are the upperbound loss model and the proportional loss model. Computer models for the respective catchments will be used to simulate flow on overland plane and in channel using the hydrograph fitting method. Using this method, rainfall data has to be input to generate simulated hydrographs; this implies that simulated hydrographs are dependent on rainfall data and thus the rainfall interval. In this study, rainfall data of five rainfall intervals will be applied to the computer models for the respective catchments to determine the effect of rainfall interval on loss rates. Results show that for both natural and artificial catchments, loss rates for the two loss models generally decreases with increasing rainfall interval, this shows that loss rate is not a constant rather it varies with rainfall intervals. A comparison of the observed and simulated hydrographs depicts that the optimum mean R2 values are significantly lower for longer rainfall intervals for both natural and artificial catchments. This may be due to the smoothing effect of the rainfall pattern as rainfall interval increases or/and rainfall interval being equal to or longer than the time of concentration for the respective catchment, thus resulting in simulated hydrographs tend towards equilibrium. In addition, upperbound loss model is found to be more suitable and accurate in modeling the three catchments as it produces simulated hydrographs which better fit the observed hydrographs than those produce by the proportional loss model. Lastly, recommended rainfall interval to be used for the Bukit Timah Drainage Basin is 0.50 hour interval and for the Concrete and Asphalt Planes is 1.00 minute interval. These intervals are considered optimum as they minimizes the space required for storing rainfall data and reduces the frequency of downloading without compromising on the goodness of the fit between the simulated hydrographs and observed hydrographs.