FLOOD-FREQUENCY DERIVATION FROM KINEMATIC WAVE

The use of derived distributions to predict flood frequency is relatively new and requires refinement and improvement. This paper reports another effort to obtain and test a derived flood-frequency distribution, applicable to small watersheds in which overland flow is considered an important runoff component. Watersheds are conceptualized as first-order streams with two symmetrical planes. The kinematic wave theory is used to obtain expressions to compute peak discharge and time to peak, as functions of effective precipitation variables and watershed parameters, for four different runoff cases. These cases are formulated according to whether or not there is concentration on the overland flow plane and in the stream. Some of these expressions are subsequently improved using regression analysis and kinematic wave simulated results. The probabilistic model for rainfall characteristics and the infiltration model are taken from results presented previously in the literature for other derived flood-frequency distributions. The usefulness of the derived distribution approach is tested and demonstrated through application to two real watersheds.