Floodplain Storage Quantification

The loss of floodplain storage has been shown to alter the natural hydrograph of rivers, modifying the frequency, timing, and magnitude of floods. Developing incentives for creating or improving flood storage is important, especially where options to offset development impacts are limited.

Wolf Water Resources (W2r) is recognized for our engineering approach where floodplain function is integral to stream health. Because of this, we are helping the Willamette Partnership develop the Oregon Floodplain Attenuation Impact Mitigation tool (OFAIM) to assess floodplain storage and attenuation across spatial scales. It will be available to municipalities, drainage districts, developers, and others to help them compare the impacts and benefits of floodplain development and restoration.floodplain function is integral to stream health

The purpose of this tool is to provide a robust function-based framework for mitigating impacts to floodplain storage & attenuation that can be applied quickly and consistently. The specific impacts the tool intends to address are those identified in the NOAA Marine Fisheries Sciences (NMFS) Biological Opinion (BiOp) of the implementation of the Federal Emergency Management Agency’s (FEMA) National Flood Insurance Program (NFIP) in the State of Oregon (NMFS, 2016) under Reasonable and Prudent Alternative (RPA) element 4 section F (NMFS, 2016).

The architecture of OFAIM allows jurisdictions to tune weighted modifiers to achieve specific floodplain management objectives based on specific aversion to, or need for, particular actions and on the existing level of floodplain function in terms of three functional groups: In-Channel Complexity, Floodplain Connectivity, and Floodplain Complexity.