Development of a Watershed Management Model for the Chesapeake Using Multiple Model

Abstract:

Calibrated watershed models are widely used as tools for estimating the outcomes of management scenarios. Multiple models are often recommended for well-informed decision making to gain an estimate of uncertainty, to allow for multiple representations of the physical-chemical-biological system, and to provide confidence in the model predictions. Implementing and maintaining multiple watershed models, particularly of a large-scale watershed, poses significant financial and logistical challenges associated with model calibrations, computation requirements, and differences in data formats. Moreover, analysis of results from multiple models adds additional complexity in decision-making. We propose and demonstrate a framework to simulate management scenarios using a ‘sensitivity’ approach that incorporates the findings of multiple models into a single simulation framework. This simple and easily-understood modeling framework provides the ability to explicitly incorporate the best available science-based understanding of watershed responses to changes in nutrient balances. Generalized watershed nutrient response are derived from the synthesis of multiple lines of evidence, which include studies involving multiple physically-based models of watersheds at catchment to regional scales, along with experimental studies and watershed observatories. The framework provides simplified accounting for planning, implementation, and tracking of management scenarios while providing capabilities to incorporate complex watershed phenomenon such as lag-times in nutrient response. The framework is being developed by the Chesapeake Bay Partnership for an assessment of a Total Maximum Daily Load (TMDL) in 2017 and to develop management plans to meet water quality standards in the Bay waters.