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Engineers with the Stormwater Management Division inspect Holmes Run. During an inspection, engineers look for vegetation and debris that could reduce channel capacity, which could contribute to flooding.
What is stream and channel maintenance?
The City inspects 24.8 miles of streams and channels annually as part of the floodplain management program, which is certified by FEMA. City engineers note deficiencies and schedule maintenance to ensure the streams and channels can maintain capacity. Maintenance can include periodic vegetation removal along the banks and sediment removal from the channel bottom. Maintenance work is conducted every few years or as needed.
The City inspects:
• Holmes Run
• Backlick Run
• Cameron Run
• Strawberry Run
• Taylor Run
• Timber Branch
• Hooffs Run
• Lucky Run
The City performs maintenance to streams and channels throughout the city to preserve their capacity to carry 100-year floodwaters, and for repairs to erosion damage, stream corridor degradation, stabilization/restoration. The increasing frequency of intense storm events requires increasing funding for sediment and vegetation removal to ensure the conveyance capacity of these waterways as climate resiliency and adaption measures consistent with the City’s Climate Emergency Declaration.
Ongoing Maintenance
• Cameron Run: Vegetation Removal, Fall 2023
• Cameron Run: Sediment Removal, Fall/Winter 2023/2024
• Holmes Run: Vegetation Removal, Started Spring 2023 (April - May)
2023 Holmes Run Vegetation Removal Project
Holmes Run is due for regular vegetation clearing to maintain the 100-year floodwater capacity. The process will be as described in the Holmes Run Maintenance Plan approved by the Environmental Policy Commission in 2002. The work will be performed by the City’s on-call tree care contractor.
General practice is to divide the stream banks into three zones, top to bottom. Generally, the work will consist of removal of all woody vegetation from the bottom third of the stream banks and clearing of invasive species along the stream bank. Healthy trees at the middle third of the banks may be thinned and the top third of stream banks will not be removed.
The last time this maintenance was performed was in 2014.
Schedule of work: March 2023 – May 2023
2022 Four Mile Run Channel Dredging Project
The Four Mile Run Channel includes a federal flood control project. Periodic dredging of significant accumulated sediment in the channel that borders between the City of Alexandria and Arlington County is required to maintain conveyance capacity and free board for the channel. Evaluation for areas requiring dredging to re-establish the required freeboard was performed in Spring of 2018. The evaluation used the Re-Authorized flows which officially changed the “Authorized” design flow per the 2014 USACE Water Resource bill. Dredging is required to meet this requirement to mitigation against flooding loss for properties in the Four Mile Run watershed.
In an agreement entered on, and dated 26 March 1974 and 8 April 1974, respectfully, Arlington County and the City of Alexandria have a shared responsibility for maintenance of the Four Mile Run East and West Levee Systems to include the open channel of Four Mile Run - the north side being Arlington County’s responsibility and the south side being the City of Alexandria’s responsibility.
The Four Mile Run Sediment Removal Project will restore the required capacity to provide the free board set by USACE. Project work will be conducted in an environmentally sensitive area (in an RPA, FEMA Floodplain, Water of the U.S., and U.S. Army Corps of Engineers Flood Control Levee and Channel). Total Land Disturbance is 7.15 Acres. (311,517.5 SF). The shared maintenance of the open channel of Four Mile Run includes clearing of debris, vegetation growth, and shoaling as required by the USACE annual inspection program.
The project is in partnership with Arlington County, Virginia.
Timeline
Project Design: 2020-2021
Construction Procurement: Winter, 2022
Outreach: April-August 2022
Construction: September 2022 - February 2023
A virtual public meeting will be held in partnership with Arlington County on May 17, 2022, from 7:00 - 8:00 p.m. No registration is required. The Webinar ID is 960 3066, Password 123456. Everyone is welcome to attend.
Resources
VMRC #16-1420 Final Permit Extension, December 13, 2021
US Army Corps of Engineers Nationwide Permit 31 Authorization, October 23, 2020
Nationwide Permit (31) Maintenance of Existing Flood Control Facilities