Taking the Rushan River Basin in Shandong Peninsula as an example, a conjunctive regulation model of surface and underground reservoirs with multiple time scales of hours, days, and months was constructed. A floodwater resources utilization scheme through conjunctive regulation of surface and underground reservoirs was proposed based on the optimization of regulation rules of surface reservoir discharge, river gate and dam water level controlling, and surface and underground reservoir water supply. The results show that, through conjunctive regulation of surface and underground reservoirs to raise the river control level, increase the proportion of underground reservoir water supply, and increase the infiltration of rivers before floods, the excess water from surface reservoirs can be transferred to underground reservoirs timely, which can empty the storage capacity of the surface reservoir and effectively increase the amount of floodwater resources utilization in the watershed. Under the conjunctive regulation scheme, the floodwater resources utilization in the Rushan River Basin increased by 8.4696 million, 7.2877 million, and 1.0635 million m³ , respectively, in 2007 (wet year), 1994 (normal year), and 1967 (dry year), verifying the practical application effect of the conjunctive regulation model of surface and underground reservoirs.

In response to the lack of joint regulation methodsof the complex engineering system of surface-underground reservoirs in coastal small and medium-sized river basins, which leading to difficulties in flood resources utilization, the structure and function of surface-groundwater reservoir system was analyzed, the surface reservoir regulation and dynamic processes of rivers and groundwater under gate dam regulation were quantitatively simulated, and the intelligent replacement models to improve the calculation speed of hydrodynamic processes were used.A multi-time scale model coupling nesting method of hour/day/month was developed to construct a joint regulation model of surface-underground reservoirs that takes into account calculation accuracy and optimization efficiency. This model realized the unified allocation of floods, surface groundwater interactions, and water supply, which can provide new ideas and technical support for the utilization of floodwater resources in coastal small and medium-sized river basins.