On the Trap Efficiency of Reservoirs and Sediment Budget in Japan

Abstract

Sediment of storage dams has long been and still is a most urgent problem to be solved. Thus, sediment trap efficiency is revaluated here by collecting and analysing data of storage dam sediment, mainly in relation to storage capacity index. Comprehensive studies on sediment budget throughout Japan, in relation to each sediment index, are also conducted. The main results are summarized as follows:
1) For the relation between C/I ratio and sediment trap efficiency E_T, more or less different distribution from the center curve by Brune and Dendy is indicated as is shown in Fig.4. The following equation is obtained as an experiential equation.C is storage capacity (m³), I is average annual inflow (m³), and E_T is sediment trap efficiency (%).E_T=100×0.96^0.25logC/I
Since close agreement between observed and calculated values by this equation is obtained, this equation can be considered applicable as an equation for estimating sediment trap efficiency for each storage capacity.
2) Comprehensive studies on sediment budget in Japan are made through rough estimations on production and run off sediment by relating specific sediment deposition of storage dams and sediment index of sediment trap efficiency E_T to drainage areas.
Consequently, it can be assumed that approximately 1/3 of sediment produced in mountainous regions is trapped in storage dams and the other approximately 2/3 is stored in mountainsides and riverbeds and then supplied to down basins resulting in environmental changes due to production and runoff of sediment with their concomitant merits and demerits.