This report describes a modified method of runoff analysis by the long and short terms runoff model (LST-II), which is proposed by Kadoya and Nagai. The modified method is atempted to introduce the effect of basin characteristics to the LST-II model.
The outline is as follows:
(1) The input sequence of areal mean rainfall in a basin is transformed to the delayed one as a method of modeling the delayed and progation process reflecting watershed characteristics in flood runoff. In modeling the formation process of a hydrograph of flood runoff, it is assumed that the topographical effects of a watershed is lumped by the distribution characteristics of concentration slope length which is approximated with gamma probability density function with two parameters.
(2) In the flood routine system, the delayed rainfall sequence is used as input condition to the LST-II model and is transformed to the caluculated discharge sequence by the LST-II model generating the effects of storage type process.
(3) As a case study, this method is applied to the flood in the Masuda reclamation basin of 0.29 km2. And it is shown that the reproducibility of observed hydrograph is improved about 10% by the modified method than the original one.
Key words: Runoff model; flood runoff; runoff analysis; hydrograph; watershed characteristics.