County Board Approves Flood Resiliency, Stormwater Projects

Published on March 24, 2021

The Arlington County Board took action at its March meeting on several stormwater projects that will help reduce the risk of flooding, create a more Flood Resilient Arlington, better manage stormwater runoff and improve water quality.

"These projects are part of the County's broad, system-wide effort to increase our resilience to extreme weather in a time of changing climate," County Board Chair Matt de Ferranti said. "They will improve stream resilience, maintain existing infrastructure and increase our stormwater system's capacity."

View a rendering of the Reed School with athletic fields - Arlington will install a detention vault under the new Reed Elementary Schools athletic fields to reduce flood risk in the area.

Reed School detention vault

The Board approved joint use permits and an agreement with Arlington Public Schools to build a stormwater detention vault under the new Reed Elementary School's future athletic fields. The vault will alleviate flooding in the Westover area, which suffered devastating losses to businesses and homes in the July 2019 storm.

This is the first partnership between the County and APS to dual-purpose public land, and the first underground stormwater detention facility.

The two-phase project will not impact the opening of the school this fall. Phase 1 — installing new underground pipe and junction fixtures beneath the new playground area — is expected to finish this summer. Phase 2, the underground detention vault, is under design, with construction expected to begin in Fall 2021 and to be completed in Fall 2022.

The Board voted unanimously to approve the Use Permits and Memorandum of Agreement associated with Phase 2 of the project. To view the staff report, scroll to Item No. 8 on the agenda for the Saturday, March 20, 2021, County Board Meeting Agenda.

Four Mile Run flood channel maintenance agreement

The County Board approved an intergovernmental agreement with the City of Alexandria for the two jurisdictions to share maintenance costs and the dredging of the two-mile Four Mile Run flood channel, which extends from Shirlington to the Potomac River. The channel straddles the boundary between the County and the City of Alexandria.

Maintenance of the open channel includes clearing debris, sediment and vegetation, and re-stabilizing stream banks as required by the United States Army Corps of Engineers (USACE) annual inspection program. The two jurisdictions have agreed to a 50-50 split of the costs of the dredging, which will help preserve the flood channel's capacity and reduce flood risk in neighborhoods surrounding South Four Mile Run.

The work will begin in late summer or early Fall, 2021 and take approximately four months. The Four Mile Run Levee System, a USACE flood risk management project, was completed in 1984 in response to several devastating floods in South Arlington. The Board voted unanimously to approve the agreement. To view the staff report, scroll to Item No. 26 on the agenda for the Saturday, March 20, 2021, County Board Meeting agenda.

Previous Dredging of the Four Mile Run Channel

Donaldson Run Tributary B contract

The Board approved a $1.82 million construction contract to complete the Donaldson Run stream resiliency project, which will re-shape the stream channel and use natural stream processes to reduce the stream flow's energy.

The project will protect infrastructure from stream erosion and help reduce sediment and nutrient pollution to help the County meet regulatory requirements for water quality. The project extends from Zachary Taylor Park 1,400 feet from N. Upton St to the confluence of the stream with Tributary A. The Donaldson Run neighborhood applied for and received Neighborhood Conservation funding for the project in 2007.

About 83 trees will be removed during the project, including about 20 trees that have fallen along Tributary B since 2017 due to erosion and storm damage. They will be replaced with 332 native trees, 180 shrubs, 200 live stakes (cuttings that will grow into trees), and more than 4,000 herbaceous plants. Construction will last approximately six months.

The Board voted 4 to 1 to approve the contract, with Board Member Takis Karantonis voting no. To view the staff report, scroll to Item No. 36 on the agenda for the Tuesday, March 23, 2021, County Board Meeting agenda.

Neighborhood Conservation projects include biorenttion facilities, stormwater infrastructure

The Board approved construction contracts for three green street projects, adding stormwater management to locations lacking any stormwater treatment.

  • A Neighborhood Conservation project in the Ashton Heights neighborhood will narrow N. Oakland street, and add a curb, gutter, and a new sidewalk on the east side from 113 N. Oakland St. to its intersection with North Pershing Drive. The project includes replacing a portion of street pavement with a bioretention area that will capture runoff from the street. Biorentention is one of the County's tools to mitigate water quality impacts from existing development. The Board unanimously approved the contract. To view the staff report, scroll to Item No. 24 on the agenda for the Tuesday, March 23, 2021, County Board Recessed Meeting agenda. (For an explanation of bioretention, see page 47 of the Stormwater Master Plan).
  • In a separate action at its Saturday, March 20 Regular Meeting, the Board approved a $1.6 million contract to A & M Concrete Corp for two Neighborhood Conservation projects -- one in Glencarlyn and the other in Dominion Hills. The Glencarlyn project will add four-foot-wide sidewalks, ADA pedestrian ramps, and stormwater infrastructure along 4th Street South for two blocks from South Kensington Street to South Illinois Street, making it easier to walk to the Glencarlyn Branch Library, Carlin Hall, and Kenmore Middle School.
  • The second project, in the Dominion Hills neighborhood, will realign the intersection of North Larrimore Street and 9th Street North, improving access and safety for pedestrians. A bioretention facility will be built at the intersection. The Board voted unanimously to approve the contract. To view the staff report for this item, scroll to Item No. 25 on the Consent Agenda for the Saturday, March 24, 2021, Regular Meeting.