reston/hunter mill stormwater facility repair and rehabilitation

Reston Section 24

Regional Stormwater Management

Facility Repair & Rehabilitation Project

Hunter Mill District

Project No. FX4000-DF006

Description and Overview:

This stormwater management facility (Facility ID 0067DP) is located on Reston Homeowner Association property within

the Difficult Run Watershed. The pond was originally built without adequate access to perform non-routine maintenance

such as sediment removal and structural repairs. This project was initiated because the existing facility was overtopped

during a storm event and severely eroded the emergency spillway and portions of the dam embankment. Also, the

upstream inundation area is wooded and the outfall structure tends to clog with debris and requires frequent

maintenance. To stabilize the emergency spillway and reduce the chance of dam failure, the capacity of the principle

spillway is increased by installing a larger size pipe and the emergency spillway is armored. To control the frequent

maintenance a larger size BMP trash rack is installed. A permanent maintenance road is installed to provide access for

all types of future maintenance work.

Project Scope of Work:

• The eroded emergency spillway was reconstructed and armored with CL-II rip-rap.

• The eroded dam embankment was reconstructed.

• The existing 48” corrugated principal spillway pipe was replaced with a larger 60” CL-III RCP.

• The existing riser structure was replaced by a large size (6’ x 6’ and 8’ high) structure.

• The pond was graded and sediments were removed to achieve the original storage capacity.

• Installed a 0.4 mile long permanent access road for future maintenance.

• Installed a Fair Weather Crossing capable for vehicular access.

• Restored the disturbed area using seeding and covering with coir fiber matting on all embankment slopes.

DPWES Project Team:

• Project Manager - Dipmani Kumar

• Construction Manager - Yousef Rayyan

• Project Inspectors - Yudhie Brownson & Jack Schambach

• Land Acquisition Agent - Carol L. Kresge

• Survey Analyst - Gregory Harper

Project Details

This stormwater management facility is located near Twin Branches and Snakeden Branch

in a low density residential area of Hunter Mill District and receives runoff from a 236 acre

drainage area. The access Road meanders through the woods along an existing pedestrian trail.

6’X6’ Riser

Location Fair Weather Crossing Site Entrance

Site Limits

Twin Branches Road - Tax Map No. 27-1

Stormwater Management Facility ID 0065DP

Pre-existing Condition: No adequate access

for maintenance

Post Construction: New permanent access

road for maintenance

Pre-existing Condition: Fair Weather Crossing

Post Construction: New Fair Weather Crossing

Dam Embankment

Pond Inflow

Pre-existing Condition: Sediment accumulation in pond and

blocked principal spillway pipe. Pond was originally

constructed with an outlet control structure (riser).

Pond Inflow

Debris Screen

Post Construction: New Control Outlet 6’X6’ Riser Structure,

disturbed areas were planted with native seed and

protected with Coir matting cover

Pre-Existing Condition: End Section of the Principal

Spillway 48” Corrugated Pipe

Post Construction: Endwall of the New 60”

Principal Spillway Pipe Culvert

Dissipater pool

Pre-Existing Condition: Severely Eroded

Emergency Spillway

Post Construction: Emergency Spillway

after Repairs

For additional Information, please call

Irene Haske, Public Information Officer

703-324-5821, TTY 711

SWPDmail@fairfaxcounty.gov

www.fairfaxcounty.gov/dpwes