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Geothermal 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, business 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. Federal Emergency Management Agency-Floodplain Management Requirements

Floodplains Impacts & Mitigation

Typical floodplain impacts and mitigation for the following categories may include:

Construction: Any type of development may affect the river’s natural flow. Filling in natural drainage ditches, digging gravel pits, ground depression, building access roads, and retention and holding ponds are examples that alter the ground’s surface. All of these activities lead to drainage obstruction and encourage flooding. To reduce the impacts on the river’s natural meander, limit surface grading and use the contour of the land to guide construction. If these mitigation measures are not possible, use runoff spreaders or construct terraces to divert water from the project area.

Erosion/drainage control: Low surface flows are achieved by using sediment-trapping mechanism like water bars, berms, drainage ditches, sediment ponds. These structures mitigate erosion in times of high precipitation.

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

Water sources: Areas topped with asphalt or concrete inhibit snowmelt and runoff from absorbing into the soil. Instead, the runoff is diverted to drainage ditches and levees. In high precipitation events, these structures reach capacity fast and cause flooding. 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.

Infrastructure: Levees and dikes divert water to protect communities from flooding rivers. However, sometimes levees and dikes fail and flooding occurs. Urban ditches and storm sewers are efficient at directing water away from the floodplain quickly. However, high volumes of water in a short period of time, overwhelms the next tributary and causes downstream flooding to occur at a faster rate.

Wildlife and plants: Floodplains have high biodiversity. Development contributes to habitat degradation and species displacement.

Stormwater Management/Impervious Surface Mitigation Standards

<metadesc> NEPA Resource Analysis related to Floodplains </metadesc>