Abstract: In view of the linear characteristic of Clark unit hydrograph, a distributed unit hydrograph representation was proposed in which the unit hydrograph for each derived isochrones of areas with Nash’s linear reservoir model can be established and then are overlaid in consideration of lag-routing time. Calculus parameter in the distributed unit hydrograph model can be computed by two methods: integral or gradually arithmetic average. In association with the proposed distributed unit hydrograph model, the unit hydrograph in Yandu river watershed was calculated and the result is consistent with that computed using Clark method by others. The result suggests that the improvement on Clark unit hydrograph by distributed representation in this article is reasonable, hence offering a foundation for further improvement in the application to hydrological response unit in the future.

Key words: Clark unit hydrograph, linear characteristic, isochronous cell, improvement by distributed representation, calculus parameter