Strategies for Flood Resilience: A Four Point Guide to Helping Local Jurisdictions with Watershed Approach Flood Risk Reduction
Iowa Dept. of Homeland Security and Emergency Management (HSEMD) has drafted a report on strategies learned through recent experience with the Iowa Watershed Approach, relating to using watershed approaches to reducing flood impacts. The report, Strategies for Flood Resilience: A Four Point Guide to Helping Locals with Watershed Approach Flood Reduction, discusses four strategies or ways in which state, federal and non-profit agencies can help locals with achieving flood reduction through a watershed approach. Before examining these four strategies, the report first discusses different kinds of practices and how they each provide varying degrees of peak flow reduction.
The first strategy, or phase, examines how to determine, in a relatively quick way, an area’s potential of using a watershed approach to reduce flood impacts. Many people assume that if they can reduce peak flow, which is possible most anywhere using nature-based or watershed approach solutions, that they have then reduced flooding. But, reducing peak flow is NOT the same as reducing flooding, at least not flood impacts. The report explains that in the first phase an analysis should be done to find out, in dollars, the prospective impact of flooding, whether it be due to damaged buildings, overtopped roads (and subsequent detours), or other impacts. After estimating the flood losses for an area, the cumulative sum of those losses can be divided by the acres of watershed above the flood impact area to determine the “POWAR Floods” number, which allows quick comparison of areas to see which have greater Potential Of using a Watershed Approach to Reduce Floods. Places with a high amount of likely flood damage AND a little watershed area above that flood damage area will have a higher POWAR Floods # and are more likely to be good candidates for using a watershed approach to reduce flooding.
HSEMD is partnering with U.S. Army Corps of Engineers (USACE) and other agencies to figure out the POWAR Floods numbers for areas throughout the state. That project will be completed in 2024. The idea is that where an area has a high POWAR Floods #, then more planning is warranted and flood mitigation and watershed approach champions for the area should move to the second phase or strategy. The second strategy is to figure out how much flow reduction will be needed to reduce flood water surface elevations where damages occur. This particular strategy is one that has and is being implemented through initiatives of different agencies. Iowa DNR, HSEMD and USACE have provided or are providing this kind of assistance to several communities, including Hartley, Mason City, Oelwein and Cherokee. With the last three communities, DNR’s contractor calculated how much flow reduction was needed for the community to realize flood reduction. They looked at various scenarios and how much flood elevations could be reduced under different possible mitigation actions. This kind of analysis helps a community understand their options and what might be feasible.
The third strategy or phase is to do further engineering and design of practices that will hold back or store water, whether that be through wetlands or other detention, oxbow restoration, diversion, or a series of terraces and/or WASCOBs, or other solutions. Like the second strategy, this third strategy is already being implemented for some communities. For instance, Cherokee has been granted a direct technical assistance award from FEMA to get this kind of engineering and design done. Dyersville, Hartley and Oelwein will be getting hazard mitigation assistance funds from FEMA to pay contractors to do the same.
Finally, the report discusses funding for construction and implementation. Many would think of such funding as the first thing to look for, but it is the last considered in the report. It is considered last because there is no point of pursuing funding to reduce flooding with a watershed approach if you have not determined if you have a good chance of being able to do it, which the first 3 strategies help determine.
Any questions about the strategies report may be directed to Jim Marwedel, Hazard Mitigation Planner with HSEMD, at email@example.com or 515-709-6857.
Our goal is to provide universal access to this document, but it is a work in progress. Please email HSEMDPIO@iowa.gov to request a fully accessible document.
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