三门峡水库“拦粗排细”的分析

Analysis on “Trapping the coarse sand and discharging the fine sand” in the Sanmenxia Reservoir

三门峡水库自１９６０年至１９６６年为蓄水运用和滞洪排沙运用，受壅水作用，流速锐减，粗泥沙落淤而细泥沙排出库外，有“拦粗排细”作用。随着库区淤积发展，潼关以下库区形成高滩深槽，一般洪水不漫滩，较大洪水漫滩时，较细泥沙被水流带到滩地落淤。１９６７年以后，两条泄洪洞先后投入运用，泄流能力增加，河槽冲刷下切，洪水漫滩机会大减，泥沙都在河槽内运动。１９７４年以后改为蓄清排浑运用；非汛期蓄水，泥沙淤在河槽内，汛期降低库水位，借助洪水将前期淤在槽内泥沙冲刷出库，基本上保持库区冲淤平衡，亦起不到拦粗排细的作用。因此，拦粗排细作用只能在一定的条件下才能实现。

The Sanmenxia Reservoir was operated in the modes of “impounding water” and “flood detention sediment discharging” from 1960-1966. In this period, the velocity, because the water level in the reservoir was higher, was decreased sharply, the coarse sand was deposited and the fine sand was discharged out of the reservoir by the dammed water in flood season, which is characterized by trapping the coarse sand and discharging the fine sand. With the development of deposition in the reservoir, the high floodplain and deep channel were formed below Tongguan without overbank at normal floods. Once the overbank took place at large flood, the fine sand was deposited on the floodplain. However, after 1967, two sluice tunnels were put into operation, causing flow capacity enlarged and the water level lowered. The channel was cut down, the chance of flood overbank was decreased greatly and all the sediment moved in the channel. After 1974 the Sanmenxia Reservoir was operated by the mode “impounding clear water and discharging muddy water”. The amount of erosion and deposition was basically balanced in the reservoir area without trapping the coarse sand and discharging the fine sand. Therefore the socalled “trapping coarse sand and discharging fine sand” can by only realized under certain conditions.