Effect of Rainfall Intensity Distribution on Excess Precipitation

by Roy W. Koch, Portland State Univ, Portland, OR, USA,
M. F. Kekhia, Portland State Univ, Portland, OR, USA,

Document Type: Proceeding Paper

Part of: Engineering Hydrology


The effect of the time distribution of rainfall intensity on the prediction of the depth of excess precipitation is evaluated. A comparison is made of the excess precipitation produced by an observed storm, a 10 time increment, variable intensity storm and a constant intensity storm, all with the same depth of rainfall. Excess precipitation is calculated using a physically based model for variable rainfall infiltration for three soil types. Results indicate that the required complexity of the design storm is dependent on soil type if cumulative excess precipitation depth is used as the criterion. For soil with low infiltration rates, the constant intensity approximation is adequate while for more permeable soils, the variable intensity is required. A bias toward underprediction is noted with more permeable soils under the constant intensity approximation. The 10 increment rainfall model appears adequate for all soil types.

Subject Headings: Soil classification | Rainfall intensity | Approximation methods | Rainfall-runoff relationships | Permeability (soil) | Comparative studies | Professional societies | Runoff

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