Floods are complex events, difficult to predict and even more difficult to protect against. Typically, a watershed’s hydrology is poorly understood; weather is notoriously difficult to forecast. Using every tool of modern science, we cannot predict the next big flood. Human land use and development, as well as climate change, are transforming the “playing field” of flood protection. Decisions on flood protection have generally been based on hydrological modeling which provides a best guess at decade, 100, or 500 year flood levels. The topography, vegetation, soils, hydrology, flood creating rain events, impermeable surfaces, levees, dams, locations of farms, residents, businesses, and public infrastructure are all important factors in flooding, safety, and flood protection.
Flood regulation and its beneficiaries: ARIES maps sources of floodwater as precipitation or snowmelt, “sinks” of floodwater as areas that promote infiltration or detention of floodwater, and beneficiaries of flood regulation as homeowners, farmers, or users of public infrastructure within floodplains. Flood mitigation can occur via natural “green infrastructure” designed to promote natural infiltration and dispersal of floodwater, or engineered “gray infrastructure” such as dams, detention basins, and levees. Flow models show the areas that contribute floodwater to a specific area at risk of flooding. By comparing baseline conditions with scenarios to manage green infrastructure (e.g., forest management, levee setbacks) or gray infrastructure (constructing new flood control works), we can compare alternative levels of ecosystem service provision against life cycle costs of such investments.
Event-based modeling: ARIES currently models flood vulnerability based on coarse-scale data (e.g., annual or monthly average precipitation and snowmelt). Collecting data to support event-based modeling is difficult, as it requires fine-scale estimation of soil, streamflow, and weather conditions. We will seek to include existing flood models and their outputs in next generation ARIES models, increasing the accuracy and policy relevance of model outputs. Even in their current form, however, ARIES flood model outputs are useful in comparing vulnerability and exploring tradeoffs between multiple ecosystem services in alternative scenarios for flood management.
In May 2010, Earth Economics completed a comprehensive Ecosystem Service and Flood Protection Analysis for the Chehalis Basin in Washington State. Ecosystem services, such as flood protection are concerned with the way natural systems affect people. With this in mind, ARIES produces four types of models, based on GIS and other data: 1) Beneficiary models; 2) Provisioning models; 3) Sink models and 4) Flow models.
ARIES was used to quantify flood protection throughout the San Gabriel River/Coyote Creek watershed in northwestern Orange County, California. A higher-resolution analysis of flood regulation provided by an undeveloped 600-acre site being considered for development was also conducted. Southern California is characterized by its flash flood system due to the runoff-prone topography, climate, and highly urbanized land cover, where floods can reach full peak in a matter of minutes. These factors make the identification and protection of natural flood regulating regions vital to sustainable urban development.