CHANNEL INFILLING PROCESSES ON THE HUANGHE (YELLOW RIVER) DELTAIC COASTAL PLAIN, CHINA

For the Huanghe (Yellow River) delta, China, high sediment loads and frequent flooding events contribute to rapid modification of the coastal deltaic system. For example, the reoccurrence interval for mainstem avulsions on the delta topset is 7-10 years, and so the coastal plain adjacent to the Bohai Sea is littered with abandoned distributary channels. The Huanghe delta is unique in regard to the fate of its abandoned channels: reworking of deltaic sediments, likely sourced from abandoned and eroding lobes, supplies sediment that rapidly infills abandoned channels. Hence, all but one of the five most recently abandoned channels has been filled, and currently only the active channel retains its self-formed geometry. This presentation focuses on research efforts that aim to use field data and numerical modeling efforts to evaluate the morphodynamic processes that produce distributary channel sediment filling. Specifically, the focus concerns the two most recently abandoned channels: one artificially produced via engineering practices (1996), and a second which occurred naturally when an avulsion relocated the final 6 km of the channel to the northwest (2006). During a recent field campaign, twenty-six cores up to 575 cm in length were collected from these two infilled channels in order to constrain grain size and stratigraphy of the sediment deposits. Initial results show that the sediment infilling the channels is predominantly fine sand, which represents the coarsest fraction of Huanghe sediment. We speculate that this material is sourced from the eroding delta lobe, whereby wave and tidal activity rework deposits and transport material landward to fill the abandoned channel. Unlike many channel networks on deltaic systems, there is minimal upstream water input into the Huanghe abandoned channels that could otherwise inhibit landward movement of sediment. For both channels, the coupling between the eroding delta lobe and infilling channels is supported by GIS observations that show how the period of channel infill coincides with shoreline retreat. These data are used to validate a first-order numerical model that constrains the dynamics of channel abandonment, delta reworking, and channel infill.