703-324-5500
TTY 711
Craig Carinci,
Director, Stormwater Planning
The Middle Potomac Watershed Management Plan identified a potential stream restoration project (PM9203) in the Dranesville Magisterial District. In December 2019, staff from the Stormwater Planning Division, Urban Forest Management Division, Wastewater Collection Division, Fairfax County Park Authority (FCPA), and consultants visited Little Pimmit Run from Franklin Park Road down to Kirby Road to assess restoration opportunities. County staff and consultants identified several areas along the stream channel with eroded, vertical banks, trees undermined by erosion, and multiple exposed sanitary sewer crossings. Evidence of a previous outfall pipe to an existing stormwater detention basin located along the stream bank has become disconnected due to erosion. The project includes an assessment and improvements of approximately 7,500 linear feet of degraded stream channel and connecting tributaries. The project is being done in collaboration with employees of Fairfax County’s Wastewater Collections Division who are working on a project to improve and protect existing sanitary sewer infrastructure along the stream corridor. Visit Pimmit Run Sanitary Sewer Realignment (WW-000028-016).
The concept (35% design) plan was received in August 2021. Prior to moving the project to final design, all land rights must be acquired from private properties impacted by the project.
The project assesses approximately 7,100 feet of Little Pimmit Run from Franklin Park Road to just upstream of Kirby Road in addition to an estimated 1,250 linear feet of intermittent tributaries that flow into the main channel. Restoration efforts of these tributaries will be limited to a necessary effort to tie them into the main channel of Little Pimmit Run. The initial scoping identified areas of excessive stream bank and stream bed erosion throughout the project limits contributing to undercut banks, compromised trees, exposed utilities and infrastructure and headcuts. A stormwater pond outfall pipe has collapsed into Little Pimmit Run due to active streambank erosion.
Given the extent of the project, the project will be designed at one time but divided into two phases for construction. Phase 1 extends approximately 2,200 linear feet from Franklin Park Road to Chesterbrook Road. Phase 2 continues downstream for an additional 4,100 linear feet from Chesterbrook Road to Kirby Road. The downstream portion of Phase 2 provides greater floodplain width compared to more narrow and restrictive stream segments upstream due to adjacent private property and infrastructure.
The primary goal of this restoration is to stabilize the channel, protect property and infrastructure, and prevent future erosion and degradation along the stream. The project will also improve the diversity and health of the riparian vegetation with native trees and other vegetation to increase the viability of this habitat, improve bank stability, filter overland runoff, and shade the stream. This project is part of Fairfax County’s larger efforts to restore many of the county’s degraded streams while also improving overall water quality and the condition of the Chesapeake Bay.
The stream restoration project (marked in green) is located between Franklin Road and Kirby Road. Phase 1 is from Franklin Park Road to Chesterbrook Road and Phase 2 is from Chesterbrook Road to Kirby Road.
