Model Test Study on the Bed Load Release at the Outlet of Cascaded Reservoirs of Jinsha River

The reaches between the Yalong River junction and Pingshan station is the main source of sediments yield segment of entering the Three Gorges Reservoir. It is significance of academic support for the cascaded reservoirs planning and constructing, acceptance check, bed load deposition estimate, reservoirs operation and management, to study on the bed load of the lower Jinsha River, and further more to make clear the volumes of cascaded reservoirs release, to fill up the sediment basic data and to enrich the sedimentary discipline. Applying the physical model test of the last cascaded reservoir at the downstream of Jinsha River, the law of bed load transport is probed and the relationship between the bed load transport rate with water and sediment factors is established in this paper. The main conclusions are as follows:

(1) The bed load transport rate rises with the increase of flow in Pingshan reaches. When the flows is 7000m³/s, 10000 m³/s, 15000 m³/s, 22000 m³/s and 28000 m³/s, the sediment transport rates is 49.1kg/s, 61.8 kg/s, 214.1 kg/s, 560.1 kg/s and 1181.8 kg/s, correspondingly. Sediment transport rate changes with the 2.397 power of flow. The explored equation between sediment transport rate and flow is:g_b=2.235×10^-8Q^2.397.

(2) The larger the flow is, the coarser the bed load transport. Besides, the transported sediment size distribution is close to the added sediment in upper reach when the flow is small, which indicates that bed load mainly comes from the river flow carrying at upstream; While the transported sediment size distribution is close to the river bed when the flow is large, which indicates that bed load comes from the sediment at upstream and local bed material.

(3) As for different flows, the sediment transport intensity of bed load on the left bank and in the middle (the deepest position) of river course is obviously higher than that on the right bank. It indicates that the main sediment transport belt is in the middle of river course and deviates to the left bank. Such distribution of sediment transport on cross section accords with the distribution of flow velocity on cross section and transverse flow toward the left bank.