Simulation Model for Collaborative Decision Making on Sediment Source Reduction in an Intensively Managed Watershed

Abstract

We developed a watershed sediment source and delivery model for use in evaluating conservation trade-offs in southern Minnesota, where sediment loading has been identified as a priority and there is substantial public investment in cleaner water. The model was developed in a stakeholder process and links user-specified management options to reductions in sediment loading at the outlet of a 2,880-km 2 intensively farmed watershed. The simulation model was formulated to allocate total sediment load among sources, which provides robustness to the model by constraining the relative magnitude of sediment loads and their reduction. A novel topographic filtering approach was used to develop spatially distributed maps of sediment delivery ratio, addressing the problem of storage between source and outlet. The dominant sediment source in the watershed is erosion of steep streamside bluffs in response to increases in river discharge. Rates of bluff erosion as a function of river discharge were determined from sediment loads measured at pairs of gages on individual streams. Using this analysis, upland water storage to reduce peak river flow was included as an option in the model. The model development process was designed to promote transparency and develop stakeholder trust through multiple meetings in which an underlying sediment budget was developed and refined. The model runs rapidly, providing real-time response to user choice and supporting Monte Carlo simulation of the influence of uncertainty on the calculated sediment load. The stakeholder group used the model to identify a priority strategy for investing public funds to improve water quality.Plain Language Summary Water pollution from excess sediment poses serious threats to the livelihood of aquatic ecosystem as well as recreation. We present a watershed model, developed through a collaboration with local stakeholders, that evaluates different conservation scenarios to reduce sediment source and delivery. The model is used to bring consensus among stakeholders in identifying a priority strategy for investing public funds to improve water quality.

Integrated assessment modeling reveals near-channel management as cost-effective to improve water quality in agricultural watersheds

“…We overcame this barrier by integrating three biophysical models into one agricultural field-to-river integrated model, hereafter referred to as the AgRiver model. The framework integrates two models of near-channel processes: the Nitrate Network Model (NNM) (39) and the Management Option Simulation Model (MOSM) (40), with the Soil and Water Assessment Tool (SWAT), a watershed model that is widely used to assess field management effectiveness (41). Using the AgRiver model and an evolutionary optimization approach, we compared performance of watershed management portfolios based on their ability to simultaneously reduce nitrate loads (N), sediment loads (S), and cost across a broad range in reduction targets.…”

The Power of Environmental Observatories for Advancing Multidisciplinary Research, Outreach, and Decision Support: The Case of the Minnesota River Basin

“…Many of our research findings have immediate and direct implications on federal and state policies, planning, and restoration strategies. For example, our approach has demonstrated the enormous potential for wetlands to abate nitrogen and sediment transport at watershed scales (Cho et al, ; Hansen et al, ; Mitchell et al, ), with wetland installation shown to be 5 times more effective at reducing nitrate than field‐based approaches (i.e., cover crops) under high to moderate flows (Hansen et al, ). At the same time, stakeholder‐driven modeling of management options to reduce sediment loading enabled consensus agreement among our stakeholder group for hydrology management to be included as an integral part of management portfolios focused on sediment reduction (Cho et al, ).…”

“…Sediment fingerprinting (described below) provided an independent constraint on sediment partitioning. The integrated sediment budget formed the foundation for investigations into landscape evolution in incising basins (Belmont, ; Gran et al, ); reduced complexity sediment routing and delivery models (Cho et al, ; Cho, ; Czuba et al, ; Gran & Czuba, ; Viparelli et al, ); investigation of the contribution of sediment sources to a watershed‐scale phosphorus budget (Baker, ); and participatory modeling efforts with stakeholders to determine optimal combinations of hydrology, field, and near‐channel management options to cost‐effectively reduce sediment loading in the GBERB (Cho et al, ; Cho, ; Cho et al, ; Lang & Rabotyagov, ).…”

“…However, participatory modeling efforts require nimble models that run quickly, allowing for real‐time feedback in stakeholder meetings. To accomplish this, the Management Option Simulation Model (MOSM) was developed with extensive stakeholder input and feedback in the GBERB to identify the most cost‐effective suite of management options to reduce fine sediment loading to the Minnesota River (Cho et al, ; Cho et al, ). MOSM simulates water and sediment routing across the watershed and incorporates different styles of management options that either reduce erosion of field and near‐channel sediment sources or reduce sediment delivery to streams.…”

“…Collectively, these data sets allow for the exploration of interactions and feedbacks between hydrologic and land use change and the geomorphic, geochemical, and biophysical responses in a large intensively managed agricultural basin. Much of this work was done in collaboration with local stakeholders including local, state, and federal resource managers, agricultural interest groups, land owners, scientists, and nonprofits and reflects an intentional, iterative, and participatory process in data collection and model building (Cho et al, ; Cho, ). In addition, our data collection and modeling efforts were explicitly integrated with the development of educational materials for teachers and high school students in the region, to broaden student participation in scientific inquiry motivated by challenges facing the natural world in their home landscapes.…”