Evaluation of Green Dam in a Forested Small Catchment with Long Term Hydrological Data and Tank Model

Abstract

 Although the importance of water conservation function of forest is widely recognized as "Green Dam" in Japan, its quantitative evaluation and clarification are insufficient. The authors evaluated the green dam's function by long term analysis of tank model parameter's variation with long term hydrological data in the forested catchment, Nakatsugawa city, Gifu, Japan. The side hole sizes of the first tank are on a decreasing trend along forest growth, and it is showed that the forest's flood mitigation function is improved. On the other hand, major changes of forest characteristics by forest growth are increase of surface soil layer thickness, big pore spaces and so on. Therefore characteristics about percolation such as cracks in bed rocks are not so much change. The authors showed the tank model, which has fixed bottom hole size and variable side hole size, can explain the improvement of Green Dam's function as a reduction of peak discharge and increasing of ground water recharge.