Evaluation of the flow regime in the lower Yellow river delta, China

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 lastdecades are supposed to be the most likely factors responsible for the problemsin terms of ecosystem deterioration, habitat evanescence, siltation of the riverchannel, as well as groundwater depletion and soil salinity increase. Theinvestigation on the 'minimum water-demand for the ecosystem in the YellowRiver Delta' was conducted by the Yellow River Conservancy Commission inthe past years. This MSc study intends to contribute to this investigation byexploring the flow variability and alteration of the flow regime in the YellowRiver Delta, and attempts to suggest a possible approach by assuming asynthetic flow which resembles the flow variability of the natural river state.To evaluate the alteration of the flow regime, firstly statistical techniques wereapplied to analyse the hydrological data at Lijin station in the Yellow RiverDelta. Then the Richter's Method was used to investigate the eco-relatedhydrologic parameters. As a result it was found that the hydrological records atLijin clearly exhibited non-stationary behaviour. The most significant splitpoints were found to be 1968 and 1985 in terms of mean annual runoff, andthus 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 flowdispersion profile, in addition to the already detected decrease in flowmagnitude and flood frequency. Generally, these alterations are supposed tohave negative influence on the ecosystem preservation and river harnessing inthe Yellow River Delta region, although the exact influences are obviously notknown. It is supposed that (partially) restoring the flow variability is one of keyissues for the Yellow River delta.In this thesis the Flow Duration Curve is adjusted for temporal interpolation inorder to generate a preferred flow, based on the assumption that the same site islikely to experience similar flow variability in different time stages given thatnot much disturbance is imposed on the flow regime. It is shown that thisapproach can be applied to generate a synthetic flow which has similar flowvariability as the reference flow, although more investigations are suggested