Abstract

The influence of nonlinearity in storage-discharge relationship on flood hydrograph prediction in three catchments in Zagros mountain region in south west of Iran is examined. An event based runoff routing model, watershed bounded network model (WBNM) is applied to assess the response of the selected catchments. Using all available hyetographs and corresponding flood hydrographs, the nonlinear parameter value of m = 0.61 is computed for the three study catchments. The obtained nonlinear parameter is applied to evaluate catchment response along with m = 0.77 (default nonlinear parameter value of WBNM) and m = 1.0  (complete linear response). It is found that there is no unique value of  that can be valid for prediction of all floods. The results showed that there is significant relationship between the antecedent wetness of soil and the response of catchment and hence less nonlinear response or maybe complete linear response can be expected in wet conditions of soil. The value of m = 0.61 is the most appropriate value for dry condition of soil. However, under wet and saturate conditions of soil, the values of m = 0.77 and m = 1.0 can be used accordingly.

Key words: Storage-discharge, runoff routing, hydrograph, watershed bounded network model (WBNM), linear-nonlinear response of catchment