TO: Mayor and Members of City Council
THRU: Adam Lindsay, Assistant City Manager
FROM: Sheila Thomas-Ambat, PE, Public Services Director
DATE: January 22, 2024
RE:
Title
Rose Lake Temporary Detention FEMA BRIC Grant Submittal
end
COUNCIL DISTRICT(S):
Council District(s)
1,2,3, and 4
b
Relationship To Strategic Plan:
Supports Goal 3. City Investment in Today and Tomorrow, through the Strategic Objective 3.1 Enhance City street connectivity, traffic flow, and stormwater systems
Executive Summary:
In FY 2019, City Council authorized a fee increase and directed staff to accelerate its watershed study program and related capital project program to help control stormwater runoff, reduce localized minor flooding, and improve our resiliency to major flooding. At the September 5, 2023, Council Work Session, staff presented an update on the Cross Creek Watershed Master Plan. This update focused on analysis of Cross Creek flooding through downtown Fayetteville and potential improvement concepts. Staff recommended Council provide approval to pursue funding sources for both the Channel Improvement and Rose Lake options, which Council approved.
Staff is now bringing an update on the Rose Lake temporary detention concept. Additional analyses have demonstrated that the temporary detention concept will reduce downstream structure flooding and reduce the depth and duration of Cross Creek overtopping downstream roadways. Further evaluation of the concept has also identified considerations related to property acquisition and long-term maintenance associated with the temporary detention concept. Staff recommends Council approval to submit a FEMA BRIC grant application to fund the detailed design and construction of the Rose Lake temporary detention concept.
Background:
Rose Lake is located along Cross Creek, generally between Country Club Drive and Shaw Mill Road, east of Murchison Road. The impoundment was originally constructed in the 1940s. Development around Rose Lake began in the 1970s and progressed over subsequent decades. The dam was partially breached in 1988 and further breached around the year 2000. The dam has remained in a breached state with volunteered vegetation and wetlands forming in much of the area previously inundated by the permanent pool.
Rose Lake was evaluated to examine whether improvements to the impoundment could help in alleviating downstream flooding concerns along Cross Creek. Three improvement concepts were identified and evaluated:
• Alternative 1: conventional permanent pool
• Alternative 2: permanent pool with an automated drawdown
• Alternative 3: temporary detention
Alternatives 1 and 2 were determined to be infeasible to implement as they would both involve significant wetland impacts and mitigation costs, along with substantially reduced public benefits downstream when compared with Alternative 3.
Alternative 3, the temporary detention concept, involves reconstructing the Rose Lake dam embankment and implementing a new spillway / outlet structure. During dry weather, the water level within Rose Lake would remain near its current level. During larger storms, runoff would be temporarily detained within Rose Lake, reaching water levels similar to those before the dam was breached in the 1980s, which are approximately 11-feet higher than current water levels. The temporarily detained runoff would drain over approximately 48-hours to return to typical dry weather conditions. The preliminary cost estimate for the Alternative 3 concept is $10M.
The effect of these impoundment alternatives were evaluated using hydrologic and hydraulic models developed in associated with the Cross Creek Watershed Master Plan.
Issues/Analysis:
Downstream flooding concerns along Cross Creek are significant, with flooding beyond the banks of Cross Creek during a 5-yr event and multiple road crossings having a level of service of 10-yrs or less. Rose Lake presents an opportunity to reduce flow rates and volumes downstream, helping to alleviate downstream flooding. In addition to downstream benefits, opportunities exist to improve conditions around Rose Lake in association with impoundment construction, such as improved landscaping or community access.
Benefits:
Hydrologic and hydraulic modeling efforts demonstrate that the Rose Lake temporary detention concept reduces storm flows downstream, resulting in reduced structure flooding and reduced roadway overtopping depths and durations. For example, under existing conditions, Blue Street is overtopped for 5 hours during a 10-yr 24-hr design storm. With the Rose Lake temporary detention concept in place, Blue Street is not overtopped during that 10-yr storm event. Similarly, flood depths are reduced by 1-2 feet along downstream reaches of Cross Creek. Flood reduction benefits diminish as Cross Creek reaches downtown such that Rose Lake by itself does not eliminate downstream flooding concerns; however, it does provide incremental benefits and could be combined with other future projects like the downtown channel improvement.
The benefits of the Rose Lake temporary detention concept, quantified in accordance with FEMA guidelines, combined with estimated project costs result in a benefit-cost ratio (BCR) greater than 1.0. A BCR greater than 1.0 is required to receive funding through the FEMA BRIC program.
Issues of concern:
Homeowners and residents surrounding Rose Lake may desire restoration of a permanent pool similar to conditions before the dam was breached in the 1980s. Analysis of concept alternatives for Rose Lake indicate such an improvement would have limited feasibility because it would provide substantially reduced downstream benefits compared to the temporary detention concept and would require significant wetland mitigation. Estimated wetland mitigation costs of restoring a permanent pool in Rose Lake are approximately $5M.
The City does not currently own property within or around Rose Lake. Property acquisition is expected to be necessary to provide access to the restored embankment for inspections, maintenance, and emergencies at a minimum. Additional property or easement acquisition may be required to encompass areas subject to temporary inundation.
The Rose Lake temporary detention concept will require some long-term maintenance. Inspections and routine maintenance, such as mowing, will be required for the new dam embankment. Routine maintenance of the outlet / riser structure would be required, with details of that maintenance depending upon details of design. Additionally, some maintenance around the periphery of the temporary inundation area may be required to address deposition of debris from large storms. Some deposition of debris is expected to occur under existing conditions during large storms.
Next Steps:
Staff will be reaching out in the next few weeks to set up at least two community engagement meetings with property owners abutting Rose Lake to discuss the impacts of the project and benefits to the community at large.
The current FEMA BRIC funding cycle has an application deadline of February 5, 2023. Rose Lake has progressed through the initial screening process with the North Carolina Department of Public Safety, which begins each fall, and is recommended by the NCDPS to be submitted to FEMA for consideration.
Following past FEMA BRIC schedules, the City will be notified of the grant award in July/August of 2024.
Budget Impact:
There is no impact to the General Fund.
The FEMA BRIC grant has a City match of 25%. With an estimated total project cost of $10M, a City match of approximately $2.5M would be required over the course of project implementation, originating from Stormwater Enterprise Fund. Specific costs are dependent upon detailed design, project bidding, and contractual agreements with FEMA to be determined following grant award.
Options:
1. Direct staff to submit the FEMA BRIC grant application to fund the detailed design and construction of the Rose Lake temporary detention concept.
2. Direct staff to withhold submitting the FEMA BRIC grant application from the current funding cycle and provide further direction.
Recommended Action:
Council direct staff to submit the FEMA BRIC grant application to fund the detailed design and construction of the Rose Lake temporary detention concept.
Attachments:
Rose Lake Temporary Detention Concept Update presentation