Geomorphic evolution of the Qingshuigou channel of the Yellow River Delta in response to changing water and sediment regimes and human interventions

Abstract

Delta channels are important landforms at the interface of sediment transfer from terrestrial to oceanic realms and affect large, and often vulnerable, human populations.Understanding these dynamics is pressing because delta processes are sensitive to climate change and human activity via adjustments in, for example, mean sea level, and water and sediment regime. Data collected over a 40-year period along a 110km distributary channel of the Yellow River Delta offers an ideal opportunity to investigate morphological responses to changing water and sediment regimes and intensive human activity. Complementary data from the delta front provide an opportunity to explore the interaction between delta channel geomorphology and delta-front erosionaccretion patterns. Cross-section dimensions and shape, longitudinal gradation and a sediment budget are used to quantify spatial and temporal morphological change along the Qingshuigou channel. Distinctive periods of channel change are identified, and analysis provides a detailed understanding of the temporal and spatial adjustments of the channel to specific human interventions, including two artificial channel diversions and changes in water and sediment supply driven by river management, and downstream delta-front development. Adjustments to the This article is protected by copyright. All rights reserved.diversions included a short-lived period of erosion upstream and significant erosion in the newly activated channel, which progressed downstream. Channel geomorphology widened and deepened during periods when management increased water yield and decreased sediment supply, and narrowed and shallowed during periods when management reduced water yield and the sediment load. Changes along the channel are driven by both upstream and downstream forcing. Finally, there is some evidence that changing delta-front erosion-accretion patterns played an important role to the geomorphic evolution of the deltaic channel; an area that requires further investigation.

Fluvial sediment source to sink transfer at the Yellow River Delta: Quantifications, causes, and environmental impacts

“…Substantial researches have been conducted on the channel geomorphic changes at the YRD Zheng et al, 2018;Han et al, 2020;Li et al, 2021). In view of this, this study focuses more on the quantification of sediment dynamics and flux at the deltaic channel since 1996.…”

“…The bankfull area (Abf) is calculated with the horizontal distance of the main channel (Wbf) enveloped with the channel geometry (Figure 2). The mean bed elevation (Zbe) is calculated as (Han et al, 2020): where u and v are velocities in x and y direction respectively, C is the depth-averaged SSC, h is the water depth. 𝜀 𝑠 is the turbulent diffusivity of the sediment.…”

“…Since the YRD is fluvial-dominated, the geomorphic evolution of the deltaic channel is closely related to the amount of upstream water and sediment delivery and their relationships (Han et al, 2020). In addition, the sediment dynamics behaviour is active at the main channel rather than over the floodplain even during hyperconcentrated floods, because of the restriction of farm dikes and artificial levees.…”

“…Distribution of sediment deposition at the deltaic channel, subaqueous delta and transport to the offshore, modified from Pang and Si (1980) and Dong (1997). The geomorphic transition of the active deltaic channel and river mouth is closely associated with the regime changes in water and sediment delivery Han et al, 2020). The basin-scale WSRS has shifted the imbalanced relationship between water and sediment discharge, with coarser sediment delivery and low suspended sediment concentrations delivered to the YRD (Ji et al, 2018).…”

“…After the Xiaolangdi Reservoir fully operated, the delta accretion rate significantly reduced at both the interannual and decadal scales, due to the dam-induced drastic decline of sediment delivery (Zhou et al, 2015;Jiang et al, 2017;Wu et al, 2017;Fu et al, 2021). The deltaic channel also experienced incision and deepening processes under changing water and sediment supply (Zheng et al, 2018;Han et al, 2020). Groundwater extraction and oil exploitation at the YRD accelerated the land subsidence and shoreline retreat (Higgins et al, 2013;Kuenzer et al, 2014).…”