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Transmission Floodplains

Floodplains
Present, Potentially Affected

  • DOI-BLM-NV-C010-2010-0010-EA (EA at Coyote Canyon and Dixie Meadows for Geothermal/Exploration Drilling and Well Testing)
  • DOI-BLM-NV-C010-2010-0016-EA (EA for Airborne Electromagnetic Survey at Patua Geothermal Project for Geothermal/Well Field, Geothermal/Power Plant)
  • DOI-BLM-NV-C010-2011-0516-EA (EA for Thermal Gradient Holes at Dixie Meadows Geothermal Exploration Project for Geothermal/Exploration, Geothermal/Well Field)

Floodplains are flat, low laying areas adjacent to rivers that are susceptible to flooding when dams and levees fail. Executive Order 11988 mandates that all federal agencies take preventative actions “to minimize the impact of floods on human safety, health, and welfare, and to restore and preserve…floodplains” Executive Order 11988 §1. These preventative measures reduce flood costs and the risk of flood loss.

Federal Emergency Management Agency (FEMA) prepares and supports communities before and after natural disasters. Floodplain management is handled through Federal Insurance and Mitigation (FIRM). FIRM provides risk analysis, risk insurance and risk reduction to homeowners, businesses and agencies. FEMA created the Risk Mapping, Assessment and Planning (Risk MAP) program for communities to see which areas will be impacted the most and what mitigation measures to take to reduce that impact.

https://www.fema.gov/floodplain-management-requirements

Floodplains Impacts & Mitigation

Few transmission projects interfere with floodplain areas; however, projects that do, impact these areas the most during construction phases. Runoff collection causes swampy conditions in the floodplain, which decreases the tower pad’s effectiveness. Runoff can also adversely affect erosion stability structures such as vegetation buffers or runoff spreaders, as runoff can loosen natural barriers and create soft soil. Floodplains insurance rates are typically higher than areas with lower risk.

Use the following mitigation measures to decrease floodplain impacts:

Construction

  • Avoid construction and pole structure placement within floodplain areas to mitigate impervious surfaces and facility damage.
  • Simulate floodwater pathways to site the best transmission line corridor. These plans can mitigate debris obstruction and sedimentation against transmission line structures such as fences and poles in flood events.
  • To mitigate unstable poles, mount poles on conventionally drilled pier foundations to be higher than runoff or 100-year floodwater events.

Runoff and Erosion

  • To mitigate runoff, use the natural contour of the landscape, runoff spreaders, grass or rock-lined swales, create vegetation buffers, minimize asphalt or concrete surfaces, and construct terraces.
  • To mitigate erosion in high precipitation events, use methods to achieve low surface flows. Use sediment-trapping mechanism like water bars, berms, drainage ditches, and sediment ponds.

http://tdworld.com/transmission/constructing-transmission-over-floodplain-minnesota-river-valley

Emergency plans

  • FEMA develops emergency plans that are area specific.
  • Typical emergency plans advise moving to higher ground and staying there until the storm has subsided and flooding has diminished.