Multi‐objective optimal allocation of water and sediment in the Yellow River Estuary: Balancing flood discharge capacity, landform equilibrium and ecological functions

The Yellow River Estuary is the primary depositional zone for sediments from the Yellow River Basin and supports a key wetland ecosystem in the warm temperate zone. However, pressures from river, marine and anthropogenic activities have led to challenges related to flood discharge, delta morphology and wetland ecological function. This study employed statistical analysis, remote sensing, numerical modelling and physical experiments to calculate the thresholds for water and sediment necessary to sustain channel discharge capacity, maintain delta equilibrium and meet wetland ecological water demands. A multi‐objective collaborative allocation model for water and sediment in the Yellow River Delta was developed and applied. Results indicate that lower incoming sediment coefficients during flood seasons enhance flood discharge capacity. Increased sediment load and coarser grain sizes accelerate the expansion of estuarine sand spits. The critical sediment load to maintain area balance is approximately 1.31 × 10 8 t for the Qingshuigou Nature Reserve (QSGNR) and 0.59 × 10 8 t for the Diaokouhe Nature Reserve (DKRNR). Delta imbalance continues to worsen due to erosion in the DKRNR and accretion in the QSGNR, with the imbalance coefficient reaching 0.1202 in 2020. Total annual ecological water demand for the delta wetlands is about 367.18 × 10 6 m 3 , with 288.8 × 10 6 m 3 allocated to QSGNR and 78.38 × 10 6 m 3 to DKRNR. The flood discharge capacity competes with both the delta landform equilibrium and the wetland ecological function, whereas the delta landform equilibrium and the wetland ecological function are synergistic. In low‐flow years, priority should be given to maintaining flood discharge capacity while meeting wetland water needs. In normal and high‐flow years, appropriately increasing water and sediment diversion to the Diaokou River can help mitigate delta imbalance trends and satisfy wetland ecological water needs. This research offers scientific guidance for the multi‐objective allocation of water and sediment in the Yellow River Estuary.