Flooding events have been some of the most widespread and costly natural disasters in the United States despite continued investment in structural flood controls and other non-structural measures. Flood events and impacts are anticipated to increase in the future as the frequency and severity of storms increases and development pressure increases in at-risk areas. As proof of this, six of the ten worst floods in Prairie Creek history have occurred since 2003. Limiting development in special flood hazard areas (SFHA) is absolutely necessary to reduce the future impacts and associated costs of flooding. Special flood hazard areas are those that would be under water during a 100-year flood. A 100-year flood does not mean a flood of that magnitude can only happen once every 100 years but rather, there is a 1 percent chance of a flood of that magnitude every year.
The City of Lebanon, in conjunction with Christopher B. Burke Engineering, LLC, recently created a Flood Resilience Plan (FRP) to identify measures to reduce the vulnerability of the community to damage from flooding and to support recovery after an extreme flood. Overall strategies to enhance resilience in Lebanon, as detailed in the plan, include:
- Integrate Flood Resilience Concepts into the Comprehensive Plan Update
- Update the Unified Development Ordinance to include Flood Resilience Strategies
- Integrate Flood Resilience Concepts into the Capital Improvement Plan
- Implement Flood-related Mitigation Strategies listed in the All-Hazard Mitigation Plan (2017 Boone County AHMP)
- Conduct Regular Audits of Plans, Programs, and Policies
A view of Prairie Creek and adjacent homes.
There are many structures within the Prairie Creek floodway and floodway fringe.
Additionally, the FRP defines five flood resilience planning areas within the City; they are the river corridor impact area, undeveloped high flood hazard/flood storage area, vulnerable developed areas, safer areas outside the SFHA, and the watershed.
- River Corridor Impact Area is defined as the floodway or fluvial erosion hazard, whichever is larger. The floodway is the river channel itself and the portion of the floodplain used to carry and discharge flood flows. Recommendations include:
- Adopt a River Corridor Impact Area Overlay Zone
- Protect Undeveloped Land in the River Corridor Impact Area
- Remove Non-Essential Bridge Crossings over Prairie Creek
- Restore Prairie Creek using an Open Corridor Channel Modification
Before and after renderings of proposed channel modifications to Prairie Creek. Credit: Christopher B. Burke Engineering, LLC
- Undeveloped High Flood Hazard/Flood Storage Area is made up of undeveloped land in the floodway fringe. The primary goal for this area is to keep future development out and preserve existing floodway and floodplain function. Specific recommendations include:
- Prohibit Development of New Critical Facilities in the Floodplain
- Protect Undeveloped Land in the Floodway Fringe
- Increase Compensatory Floodplain Storage Requirements
- Vulnerable Developed Areas are where existing development is already within the floodway and special flood hazard area. Here, it is important to protect people, buildings, and facilities and reduce future flood risk. Ideally, this would be accomplished with buyout of these properties and removal of structures. However, there are almost 1,500 structures in the SFHA in Lebanon and removing them all is unrealistic. Recommendations for this area include:
- Protect Existing Critical Facilities in the SFHA
- Impose a Post-Flood Building Moratorium
- Relocation and/or Buyouts of Structures
- Floodproof Structures
- Bring Nonconforming Uses into Compliance
- Promote Flood Insurance Coverage
- Create New Flood Storage through Redevelopment
- Require Building Expansions to Meet Additional Requirements
- Create a Flood Storage Facility Upstream of Lebanon
- Safer Areas are all of the lands in Lebanon outside of the SFHA. This is where new growth and development should be occurring. Specifically:
- Steer Public Policy and Investment into Safer Areas
- Promote Conservation Design and Development
- Promote Placement of Critical Facilities in Safer Areas
- The Watershed Area extends beyond Lebanon municipal limits to include all of the lands that drain into Prairie Creek and its tributaries. This area is identified to promote coordination and best practice implementation for the broader region. Recommendations include:
- Support USGS Stream Gages
- Adopt Natural Resource Overlay Zone
- Promote Use of Cover Crops and Soil Health Practices
- Reduce Impact from Tile and Surface Drains in the Watershed
For more details about these recommendations, please see the complete Flood Resilience Plan [LINK].
An example of what a regional detention basin may look like. Credit: Christopher B. Burke Engineering, LLC