Sedimentary response of the Huanghe (Yellow River) delta front to water-sediment regulation: insights from SedFlux simulations and interpretable machine learning

As sediment deficits increasingly threaten the sustainability of river deltas worldwide, artificial water-sediment regulation has emerged as an important strategy for enhancing downstream sediment delivery. However, how short-duration regulation events are translated into preserved delta-front deposits remains poorly quantified. Here, daily water-sediment inputs from hydrological observations during 2002–2014 were incorporated into the SedFlux model to simulate depositional responses across the modern Huanghe (Yellow River) delta front. Random Forest surrogate models, interpreted using SHapley Additive exPlanations (SHAP), were subsequently used to evaluate predictor importance and simulated response sensitivities associated with sediment supply, grain-size composition, hydrological forcing, and spatial setting. The SedFlux simulations showed that Water-Sediment Regulation Scheme (WSRS) events were associated with substantially enhanced simulated delta-front deposition. WSRS events occurred for 260 days, representing approximately 5.5% of the 4746-day simulation period, yet contributed 19.3%, 19.4%, and 25.4% of cumulative deposition in the 0–5 m, 5–10 m, and >10 m water-depth zones, respectively. Daily mean deposition during WSRS periods was 4.1–5.9 times that during non-WSRS periods. Total sediment supply was the leading SHAP predictor across all three water-depth zones. Adding sand and silt proportions increased the mean held-out-year R² from 0.8361 to 0.8417 and reduced RMSE from 114.5 to 112.2 m² and MAE from 43.6 to 42.7 m². However, the 95% confidence intervals for both the RMSE and MAE differences included zero, indicating that these improvements were not consistent across held-out years. Positive SHAP contributions became predominant at mean suspended sediment concentrations of approximately 5-6.4 kg/m³ in the 0–5 m zone and at monthly cumulative runoff of approximately 1.0-1.5 km³ in the 5–10 m and >10 m zones. These findings indicate that short-duration artificial water-sediment pulses can make disproportionately large contributions to simulated delta-front deposition and provide a framework integrating process-based modeling with interpretable surrogate analysis for application to other regulated deltaic systems.