INCORPORATING RESERVOIR MANAGEMENT INTO WATERSHED MODELS

Few river systems remain unaltered by engineered water management structures. Reservoir management in many river basins significantly changes streamflow, which subsequently changes the interactions between the streams and aquifers. Despite the importance of both engineered and natural components of the hydrologic system, the ability to simultaneously simulate both systems to capture the effects of their interdependence is limited. Recently, an object-oriented model of surface water operations (OASIS) was linked to a physically based, fully integrated surface/subsurface hydrologic model (HydroGeoSphere) to capture this interdependence. The new capabilities were demonstrated in the heavily managed Lower Republican River Basin (LRRB) in portions of Nebraska and Kansas. Water management and reservoir operations changed several times in the LRRB over the past few decades, often in response to disputes between the states. Implementation of water management policies from an inter-state agreement signed on August 24, 2016 has just begun, both on the ground and in the model. While integrating both reservoir management and groundwater/surface water flow into a model framework improves the representativeness of simulated results, it also greatly increases the level of complexity involved in simulating heavily managed basins, particularly when trying to predict future conditions.