Forecasting Multiple Watershed-Level Benefits of Alternative Storm Water Management Approaches in the Semi-Arid Southwest: Required Tools for Investing Strategically

The menu of alternative storm water management approaches and best practices has grown considerably over the last few years — even for densely urbanized areas. At the same time, watersheds have gained recognition as planning templates. Municipalities, counties, special districts, and private developers are now required to mitigate unavoidable impacts on aquatic resources of new and re-development projects in a watershed context. However, public agencies currently have few tools available, are faced with sometimes conflicting public policies, and often have insufficient expertise to translate the overwhelming choices on the LID menu into implementation guidance, let alone determine how to predict the off-site impacts of a project on watershed functions and processes. The role of watershed position in determining the effects small-scale, site-specific LID practices remains largely unexamined and unknown. Nor are the cumulative beneficial outcomes and cost-effectiveness of LID applications across a watershed sufficiently understood. As a result, scarce resources directed at alternative storm water management approaches are rarely maximized, although local government can ill-afford non-strategic approaches to LID. California has unique public financing constraints for storm water management and other public benefit expenditures. Therefore, any public investments using non-traditional management approaches have to pass a fairly high documentation threshold of anticipated environmental and public health and safety benefits, regardless of whether new expenditure requests are placed in front of the voters, or existing funds are re-prioritized. For these reasons, we propose that initial investments in forecasting tools capable of predicting the cumulative benefits of site-specific applications of appropriate bioengineering and design solutions are needed to guide implementation of appropriate mixes of runoff reduction, harvesting, re-use, and infiltration options in a climate with distinct dry and wet seasons. These up-front investments should include development and application of standardized monitoring infrastructure and protocols that are built into pilot LID designs to document environmental benefits and generate data for model calibration. Ultimately, the systematic application of forecasting tools, supported by performance monitoring data, will enable resource economists to compare the benefits of individual LID projects and their implementation and maintenance costs at a watershed scale with more traditional, centralized, and capital-intensive public infrastructure investments. We present examples that include interactive maps of existing natural and man-made runoff conveyance infrastructure, land use, land cover, and ownership, as well as other critical landscape characteristics at the appropriate resolution to model environmental outcomes prior to large-scale implementation.