Evaluation of the Flow Regime in the Lower Yellow River Delta, China

Ms. Dong Wu

Abstract

The Yellow River Delta is a place where hydrodynamics play a prominent role. The decreased Yellow River flow and the altered flow regime during the last decades are supposed to be the most likely factors responsible for the problems in terms of ecosystem deterioration, habitat evanescence, siltation of the river channel, as well as groundwater depletion and soil salinity increase. The investigation on the ‘minimum water-demand for the ecosystem in the Yellow River Delta’ was conducted by the Yellow River Conservancy Commission in the past years. This MSc study intends to contribute to this investigation by exploring the flow variability and alteration of the flow regime in the Yellow River Delta, and attempts to suggest a possible approach by assuming a synthetic flow which resembles the flow variability of the natural river state.

To evaluate the alteration of the flow regime, firstly statistical techniques were applied to analyse the hydrological data at Lijin station in the Yellow River Delta. Then the Richter’s Method was used to investigate the eco-related hydrologic parameters. As a result it was found that the hydrological records at Lijin clearly exhibited non-stationary behaviour. The most significant split points were found to be 1968 and 1985 in terms of mean annual runoff, and thus three distinctive periods can be identified. This implies that three periods can be distinguished in terms of seasonal pattern,

frequency of hydrologic events change, timing of extreme flows, and flow dispersion profile, in addition to the already detected decrease in flow magnitude and flood frequency. Generally, these alterations are supposed to have negative influence on the ecosystem preservation and river harnessing in the Yellow River Delta region, although the exact influences are obviously not

known. It is supposed that (partially) restoring the flow variability is one of key issues for the Yellow River delta.

In this thesis the Flow Duration Curve is adjusted for temporal interpolation in order to generate a preferred flow, based on the assumption that the same site is likely to experience similar flow variability in different time stages given that not much disturbance is imposed on the flow regime. It is shown that this approach can be applied to generate a synthetic flow which has similar flow

variability as the reference flow, although more investigations are suggested.

Keywords: Yellow River Delta, alteration of flow regime, daily flow generation, temporal interpolation, Flow Duration Curve, flow variability restoration