Sediment Transport In The Huanghe River Mouth And The Recent Deltaic Evolution

This paper addresses the sediment transport in the Huanghe River mouth and the recent deltaic evolution, including the changes in water and sediment discharge, sediment transport in the river mouth, river mouth bar formation, subaqueous deltaic evolution, coastline changes and tidal flats' evolution, in light of hydrological records, field measurements, station-based monitoring, remote sensing interpretation, bathymetric charts and so on. Due to increasing human activities along the Huanghe River drainage basin, the runoff and sediment loads reduced greatly so that seasonal channel dry-ups in the lower reach frequently occurred since 1970s. A semi-analytic spectral reflectance model was presented on basis of previous studies, and some empirical relationships are established between remote-sensing reflectance in Landsat TM bands and suspended sediment concentration (SSC) through in situ spectroradiometric measurements. The best correlation was obtained for the reflectance ratio of Landsat TM3 and TM2, i.e. RT M3 /RTM2= 0.1683ln(SSC) + 0.2454, which was further used to determine SSC in the river mouth. Synchronous hydrological measurement data show that sediment exchanges between the water column and seabed occur down stream from the limit of tidal current in the Huanghe River mouth. The highest SSC value of turbidity maximum appears at the time of maximum or slack ebb tide. Turbidity maximum moves within a range of 10km. In addition, turbidity maximum can be interpreted from sea surface temperature map retrieved from Landsat TM6 via the mono-window algorithm. River mouth bar formation is a consequence of sediment entrapment in the low current velocity zone of the river mouth. Strong riverbed aggradation in the mouth channel is highly related to the river mouth bar progradation. From 1985 to 1996, the water level (at a river discharge of 3000 m3/s) rose at a rate of 0.164 m/a and 0.170 m/a, recorded at Lijin and Xihekou Hydrological Stations, respectively. Through calculating seabed change in the subaqueous delta using GIS software, the results show that more than 70% of sediment loads from the Huanghe River were sequestrated in the river mouth area. The subaqueous deltaic evolution is dominated by SE directed tidal current and tidal shear front in the river mouth. Because of the dramatic reduction in water and sediment discharge since 1986, the progadation rate of the delta, including subaqueous and subaerial, slows down. Natural coast accretion is observed around the active river mouth. Total length of eroded coast is about twice as that of prograded one. In the recent years, land reclamation was prevailed along the delta coast and thus large portion of coasts are changed into artificial coast. As a consequence, fractal dimension value of tidal creeks reduced and the retrogressive succession of tidal flats occurred.