Conjunctive management of surface water and groundwater resources under drought conditions using a fully coupled hydrological model

A conjunctive management model has been developed to obtain optimal allocation of surface water and groundwater under different constraints during a drought. Two simulation models-a fully distributed hydrologic model and a reservoir simulation model- were incorporated in an optimization formulation using a simulation-optimization approach with response functions. The model was tested for the Haw River Basin located in North Carolina. A fully distributed hydrologic model, penn state integrated hydrologic model (PIHM), was used to compute simultaneous depletions in streamflow and groundwater level under pumping. A reservoir simulation model was then incorporated within the optimization framework to determine the optimal allocation of surface water and groundwater resources by minimizing reservoir deficit. A new groundwater sustainability constraint, recovery time for groundwater levels, was introduced in the conjunctive management model. Incorporating the reservoir simulation model within the optimization model resulted in reduced reservoir deficits. Moreover, the recovery time constraint will allow decision makers to evaluate the trade-offbetween maximizing water availability and preserving groundwater sustainability during a drought. It is envisioned that the management model proposed in this study is a step toward sustainable groundwater withdrawal during a drought.