TO: Mayor and Members of City Council
THRU: Adam Lindsay, Assistant City Manager
FROM: Sheila Thomas-Ambat, PE, CCM, CFM - Public Services Director
DATE: April 4, 2022
RE:
Title
Locks Creek Watershed Master Plan Recommendations and Letter of Map Revisions Update
end
COUNCIL DISTRICT(S):
Council District(s)
2
b
Relationship To Strategic Plan:
Goal 1. Safe and Secure Community
Goal 3. City Investment in Today and Tomorrow
Executive Summary:
Three options (Option 1 Phase I, Option 1 Phase II, and Option 2) have been developed to mitigate flooding impacts in the Locks Creek neighborhood.
Option 1 Phase 1 consists of drainage improvements, additional culverts on Locks Creek Road, and increased road height of Locks Creek Road. This option also includes secondary improvements to Pasture Lane, Windmill Rd., and Bridgeton Way. This option will mitigate flooding of approximately 3200 ft. of impacted lane length, and will provide emergency access for approximately 200 homes for up to the 50-year event. The improved emergency access is the primary benefit of this option. However, this option will not substantially mitigate flooding impacts of homes, mitigating flood impacts for only 1 home during the 2-year, 10-year, and 50-year storms. Total estimated cost is $8.8M. Given the improved access to about 200 homes, this option is recommended for further study, and detailed design and construction.
Option 1 Phase II will include the above and in addition increase the opening under NC53 and increase capacity of the downstream drainage channel, thereby eliminating the current bottleneck. This solution primarily mitigates road flooding, and additionally provides some mitigation of buildings in the neighborhood, along Turkey Run, Whisker Lake Drive, Pasture Lane, and some commercial property along Cedar Creek Road. While the LOS will increase for several properties along the south side of Bombay Drive, the highest level of service for many buildings does not exceed the 10-year event. Even with this solution in place, 6 homes along Bombay Drive and two at the southern end of Turkey Run will be impacted by flooding during the 5-year storm. The total additional estimated cost for Option 1 Phase II is $15.7M. This option is not stand-alone and would only be considered in conjunction with Option 1 Phase I. Flood impacts would be mitigated for a total of 5900 ft. of roadway and 32 homes for Option 1. While this option does not mitigate all flooding impacts, it does provide additional benefits, and this is recommended for submission as possible grant funding opportunities arise.
Option 2 includes a levee and pump station, in addition to making improvements on Locks Creek Road and drainage improvements on Pasture Ln, Windmill Rd, and Locks Creek Rd along Bridgeton Way. Option #2 mitigates flood impacts to approximately 5800 ft. roadway and 47 homes at an estimated cost of $45.4M. Property acquisition is included in this option. This option is not considered a viable option due to the high cost ($44.2M) compared to the benefits.
All options are planning stage only and detailed survey and Hydrologic and Hydraulic Analysis will be needed to verify if approved for design. None of the options meet the FEMA Benefit Cost Analysis of greater than 1 in order to be considered for FEMA Building Resilient Infrastructure and Communities grant funding
Background:
Flood Mitigation Options
The area that drains to the NC 53 culvert on Locks Creek is approximately 14 square miles, and mostly flat. Much of the Locks Creek neighborhood, bounded by Locks Creek Road to the north and Locks Creek to the south, experiences frequent flooding. The culvert underneath NC53 constricts flow, creating a backwater condition. Staff (and consultant teams) have evaluated potential viable solutions to mitigate the flooding, and have begun studies needed to support the application to expand the FEMA floodplain to more accurately reflect current conditions. Building on recent modeling results from the Watershed Master Plan program, several potential modifications/additions to both the primary system (Locks Creek, culverts under NC53) and secondary system (pipes and inlets within neighborhoods) were evaluated in various combinations to arrive at three potential options, or packages of solutions. While all three options have the ability to mitigate some flooding impacts for the 25-year storm, no solution has been found to mitigate flooding impacts 100%. The LOS ranges from lowest, primarily mitigating roadway flooding (Option 1 Phase I) to highest possible, that includes property acquisition (Option 2) with costs ranging from $8.8M to $45.4M. The three options are described below.
The highest priority option, Option 1 Phase I, includes elevating portions of the Locks Creek road, and upgrading selected drainage within the neighborhood on Pasture Lane, Windmill Road, and from Locks Creek Road along Bridgeton Way. The second highest priority (Option 1 Phase II) would be considered augmenting flood impact mitigations in Option 1 Phase I by also replacing the Locks Creek culvert under Cedar Creek Road (HY 53) with a 180 ft. long bridge and improving the drainage channel downstream of the bridge to I-95, which is about 5,300 LF. Option 2 includes the same drainage improvements as Option 1 with a shorter segment of Locks Creek Road elevated, and additionally includes a levee installed along Locks Creek and tributary up to Locks Creek Road. A pump station will be required for this option as well as property acquisition.
Parallel Effort: Letter of Map Revision (LOMR)
The City developed preliminary floodplain and floodway mapping for the Locks Creek drainage basin that identifies the 100-year floodplain and floodway. Structures and vacant parcels located within these boundaries were also identified. From a regulatory standpoint, the 100-year floodplain and floodway are known as the Special Flood Hazard Area (SFHA).
Inclusion in a regulated SFHA has significant impacts to property owners. This includes more stringent development standards be adhered to, mandatory purchase of flood insurance for government backed mortgages on all new home purchases and refinances, and the potential for lender required purchase of flood insurance for existing homeowners. Inclusion in the SFHA also provides property owners the opportunity to qualify for Hazard Mitigation Assistance funding to elevate existing structures or participate in a buyout program.
Staff presented the results of the flood study to City Council at the June 7, 2021 work session and again at the June 20, 2021 regular session and gained consensus to move forward with submitting the technical data and mapping of the study to the North Carolina Flood Mapping Program (NCFPM) as a request for a Letter of Map Revision (LOMR) or Physical Map Revision (PMR). A LOMR or PMR is FEMA’s modification to an effective Flood Insurance Rate Map (FIRM). A revision to the effective FIRM panel would bring the structures and parcels identified in the flood study into the regulated SFHA.
Issues/Analysis:
Flood Mitigation Options
Option 2 provides the highest LOS at the highest cost, and will require substantial property acquisition and ongoing operations costs of the pump station. Option 1 Phase 1 and Option 1 Phase II may require some property acquisition due to the raising of the Locks Creek road. None of the options will provide 100% LOS.
Parallel Effort: Letter of Map Revision (LOMR)
After Phase II of the project received City Council approval, staff began finalizing the study and preparing to submit the technical data and mapping to NCFMP as a request for a LOMR or PMR.
To date the LOMR package has not been submitted due to staff’s recommendation to complete the Cape Fear 2 East Watershed Study in hopes that there was a single (or phased) hydraulic and hydrologic solution to mitigate all of the flooding concerns for the area without bringing parcels into the SFHA. As the aforementioned efforts from the Watershed Study don’t support a feasible solution to mitigate all of the flooding concerns, staff will now move forward with the submittal of the LOMR to NCFMP.
The initial submittal package includes the following supporting data:
1. MT2 Forms (application)
2. Hydrologic and Hydraulic (H&H) Model
3. Work Map
4. Profiles of stream bottom and water surface elevations for the 10-, 50-, 100-, and 500-yr flood events
5. Proof of property owner notification
Follow up items for the initial submittal would require response to NCFMP comments regarding modeling, mapping, or supporting documentation. The schedule for a typical LOMR takes 6-9 month to review, but can extend longer based of the volume of submittals currently being reviewed by NCFMP. After approval of a LOMR it takes 120 days (4 months) to become the effective model and the identified areas to be included in a regulatory Special Flood Hazard Area on a FIRM panel.
To reaffirm what was previously presented to Council in June of 2021, the submittal and subsequent approval of LOMR will have significant impacts on property owners brought into the SPFA. Any new development, whether residential or commercial, would be held to a higher development standard and be required to meet the provisions of the City’s Flood Damage Prevention Ordinance to include provisions such as constructing finished floor elevations 2 feet above the newly established base flood elevation. If a home is purchased, refinanced, or built with a federally back mortgage, mandatory flood insurance will be required. If an existing homeowner has a federally backed mortgage, the lender can now require the mandatory purchase of flood insurance. If an existing homeowner currently has flood insurance, their insurance premiums could potentially increase as they would now be shown in the SFHA. A LOMR also opens up the ability for property owners to qualify for Hazard Mitigation Assistance funding. This can be achieved through Flood Mitigation Assistance (FMA) or after a declared disaster (i.e. hurricane) through HMGP. Such assistance can include elevation of existing structures or enrollment into a buyout program.
Budget Impact:
The estimated budget impact will be $8,778,700 for Option 1 Phase I. Should the City pursue grant funding options for the add-ons described in Option 1 Phase II, additional costs for developing grant applications and potential matching funds may be required.
Options:
Option 1 Phase I
1. Approve Option 1 Phase I to move forward with project development and design of the estimated $8,778,700 proposed solution and pursue funding options.
2. Remand the proposed solution back to staff for further consideration.
Option 1 Phase II
1. Direct staff to pursue funding options for the estimated $15,716,300 proposed solution improvements outlined in Option 1 Phase II.
2. Do not direct staff to pursue funding options for the estimated $15,716,300 proposed solution improvements outlined in Option 1 Phase II.
3. Remand the proposed solution back to staff for further consideration.
Recommended Action:
Option 1 Phase I
1. Approve Option 1 Phase I to move forward with project development and design of the estimated $8,778,700 proposed solution and pursue funding options.
Option 1 Phase II
1. Direct staff to pursue funding options for the estimated $15,716,300 proposed solution improvements outlined in Option 1 Phase II.
Attachments:
Locks Creek - Watershed Master Plan Recommendations