从历史看潼关高程变化

渭河在潼关流入黄河。历史上，潼关上、下河道受地质构造的控制，河槽沉降导致大量淤积。在三门峡建库前的一个短期内，由于水沙条件变化，潼关和渭河有较大的抬高。但渭河下游一直为地中河，说明迄今淤积还没有导致潼关高程长期大量抬高。小北干流的淤积和抬高与其河性有关，和潼关以下的黄河河道在河流动力学(河势及水沙条件等)方面有本质区别。根据小北干流长期淤积抬高而认为潼关高程也会同样淤积抬高、论据似嫌不足。三门峡水库建库后，潼关高程大量抬高主要是水库壅水的结果。所以降低三门峡水库的运行水位，可为潼关高程的降低创造必要的条件。

Change in datum of Tongguan in the light of historical data

The Wei River joins the Yellow River at Tongguan.In the past,geological conditio ns were such that the river channels meeting at the confluence were sinking and heavy depositions in these channels thereby resulted.In a short period prior to the construction of Sanmenxia Project,due to changes in runoffs and sediment loa ds in the rivers,both the beds at Tongguan and in the Wei River were aggradated. There is no evidence,however,that this short term deposition at Tongguan may be extrapolated to predict the long term trend of deposition.Before construction of the Sanmenxia Project,the lower reach of the Wei River was an in the groun d river.This also indicates that long term,large deposition had not taken place at Tongguan.The depositon in the main stem of Yellow River upstream of Tonggua n is due to other causes.There is a radical difference between this reach and th at downstream of Tongguan,including alignment,runoffs and sediment loads.It is q uestionable to infer that large depositions and hence large rises in stage would take place at Tongguan,because historically,there was a long term deposition i n the reach of the Yellow River upstream of the confluence.The large rise in sta ge at Tongguan following the commission of Sanmenxia Project was due to the imp ounding of the reservoir to undue levels.Lowering operational water level of the Sanmenxia Reservoir will provide the necessary condition for the lowering of th e stages at Tongguan.