Dynamic Representations of Hydrologic-Irrigator Interactions in Planning Models
In order to have Decision Support Systems that illuminate the effects of the various planning scenarios considered by Reclamation, it is necessary to incorporate irrigator decisions impacting on-farm recharge into water supply planning models. We define on-farm recharge as the utilization of transient surface water supplies for the purpose of recharging groundwater aquifers underlying agricultural fields. Effectively, this results in an increased storage capacity for a given water basin since flood conditions and other periods of excess precipitation are correlated with an inability for upstream reservoirs to store all the available water, but at least some of this excess water can be stored in aquifers and then withdrawn at a later date for beneficial use. Considering the increasingly constrained parameters governing the water supply projects managed by Reclamation, adapting to these constraints requires more flexibility in operations, including water storage options that augment existing reservoir infrastructure. Managed on-farm recharge is a key strategy to achieve this sort of flexibility.
To effectively pursue managed on-farm recharge as a strategy, decision makers need to know the constraints related to surface water availability, infrastructure, land use, operations, regulations, and contracts. A model that simulates on farm recharge needs to consider both the physical processes governing recharge from agricultural fields into the underlying aquifer, as well as the irrigator decisions that determine how much water is available for this recharge. Conventionally, planning models have not treated these two components of the overall process dynamically. Ideally, planning models will treat the two components of on-farm recharge in a rigorous and interactive way. This project addresses this need by considering three alternative methods of doing so.
The California Department of Water Resources (DWR) is in the initial phase of working on an improved detaile
Need and Benefit
Water resources are becoming increasingly constrained throughout all of Reclamation's five regions for a variety of reasons. While Reclamation's primary responsibility lies in operating its collection of large-scale surface water storage structures, groundwater supplies are an equivalently important component of the water supply systems throughout the West, and the interaction of surface and subsurface water supplies has been recognized as an important phenomenon to consider in the planned operation of water resource systems. Moreover, the subsurface provides an opportunity to have an additional storage component in the water resource system. This is a concept that has been recognized by the State of California (and is being pursued via the State's Flood-MAR program) and others. As such, it is critical that water operations and planning models account for management strategies that take advantage of this concept. This project will implement three different methods with varying levels of model complexity and analyze the results to identify the appropriate level of rigor for different planning questions of relevance to Reclamation.
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