Resolution No. 4814 - Laserfiche WebLink

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6.8 Common Flood Mitigation Projects Potential mitigation projects to reduce the potential for future flood losses cover a wide range of possibilities. For either major rivers or the creeks, it would be theoretically possible to reduce future flood losses by building levees or flood walls. In practice, however, such projects are often very expensive and have a host of environmental and other regulatory hurdles. For the smaller creeks, channel improvements to improve water conveyance capacity and removal of flow-restriction obstructions may be desirable. Another possibility for some of the smaller creeks would be to construct detention ponds upstream (perhaps outside of the Eugene/Springfield Metro Area planning area) to temporarily store water during high rainfall periods. Detention ponds are basically leaky dams, designed to be dry during normal conditions. Detention ponds typically have restricted outlets with controlled flow rates. Thus, during periods of high inflow into the pond, water is stored temporarily and then gradually released. The effect of detention ponds is to lower peak discharge values and thus to lower peak flood elevations. For portions of the Eugene/Springfield Metro Area subject to flooding from storm water drainage, various storm water drainage system improvements may be desirable. Typical improvements include upgrades to the size of drainage ditches or storm water drainage pipes and upgrades to pumping capacity (for pumped portions of drainage systems). Another possibility for some areas may be construction of local detention ponds. For critical facilities at Iow elevations with high flood risk, such as the water and wastewater treatment plants, construction of berms or floodwalls to protect the facilities may be desirable. For residential, commercial or public facilities at high flood risk, elevation of structures or, for structures at very high flood risk, acquisition and demolition are potential mitigation options. Elevation and acquisition (especially), are expensive mitigation options that are generally not cost-effective unless the levels of flood hazard and flood risk are rather high. That is, these mitigation options are most attractive for structures deep in the flood plain (i.e., with first floors below the 10-, or 20-, or 30-year flood elevations). For structures outside of mapped floodplains, elevation or acquisition would likely be cost-effective only for structures with a strong history of major, repetitive flood losses. For structures near the fringe of the 100-year flood plain, near the 100-year flood level, or with some history of repetitive flood losses, various small scale flood loss reduction measures such as elevation of furnaces and utilities may be desirable. The following table contains flood mitigation action items from the master Action Items table in Chapter 4. Public Review Draft: August 6, 2004 6-15