Improved Fitting for Three‐Parameter Muskingum Procedure

A method that allows better utilization of available data from a flood event is presented for the three‐parameter Muskingum floodrouting procedure. The procedure is based upon the three‐parameter Muskingum model, where the two conventional parameters (namely, the reach storage coefficient and the inflow/outflow weighting factor) are augmented by a third parameter to account for lateral inflow into the reach. Parameter estimation for the three‐parameter model is performed objectively by a matrix‐inversion method. The flood‐routing procedure consists of randomly splitting a group of flood events into two groups so that the three‐parameter model can be calibrated on one group and evaluated on the other, and vice versa. This procedure is improved by adjusting the previous parameter estimation scheme so that full advantage is taken of both the time interval at which the data is recorded and the lag time between the upstream and downstream hydrograph peaks. An application of the full, improved procedure is given using flood events from the Grey River on the West Coast of the South Island, New Zealand.