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Crow’s Nest: Culvert replacement on French Creek

September 1, 2011

We are just getting started on a major project at Crow’s Nest: replacing the failing culvert on French Creek located in the north central part of the preserve. The old culvert (left side of photo below) is called the “oil-tank culvert” and we don’t know how long it has been there, but it started to cave in a couple years ago and so we began the process of getting a permit to replace it.

The old culvert severely restricts the flow of French Creek. The reduced flow volume speeds up the flow rate which causes increased erosion. In heavy rains the small (less than 4′ diameter) culvert causes the stream to flood more than it otherwise would, and much of that water ends up on the creek trail.

The ends of the tank were apparently cut open to make it into a culvert; the line at the uncut section was horizontal until a couple years ago when the tank began to cave in. Right now the road over the culvert is open only to foot and horse traffic; farm equipment must reach the fields to the west of the creek through State Game Lands (with permission) from Bethesda Road.

The farm lane is also a key east-west trail for hikers and equestrians that connects Piersol and Bethesda Roads but gets these preserve users off of the busy roads to which it runs parallel.

Since French Creek is an Exceptional Value (EV) stream it is a big deal to replace a culvert on it, and particularly one in the middle of a Natural Lands Trust preserve. Buildings Supervisor Bob Johnson had engineering plans prepared for an application for a Pennsylvania Department of Environmental Protection/Army Corps of Engineers General Permit. After careful review the permit was granted and the work is about to begin. (Bob also oversaw the replacement of culverts along the farm entrance road at our Stroud Preserve.)

Silt fencing has been erected at Crow’s Nest in the work zone and along a stretch of farm lane leading to it—not only to keep silt out of the stream but to keep small wildlife out of the work area (openings the fences are kept closed when the work is not active). A biologist oversaw this step to make sure no wildlife was impacted, and he will return at critical stages throughout the project. (This is a standard requirement for these permits.)

There will be two culverts, five feet in diameter, to accommodate French Creek, which drains about five square miles of (nearly all permanently protected) watershed upstream. They will be installed below the grade of the existing stream bed so that their bottoms will fill with natural stream sediment and there will be continuous habitat through them.

They will be installed in a frame of concrete wing walls for stability, but these will not protrude above the existing grade of the land. The creek will still have the ability to flood when it needs to without damaging the culverts or the farm lane. During construction we will lose some native vegetation in the work site but after the soil is stabilized we will replant native shrubs and wildflowers for this riparian area.

The bad news is that the creek trail and farm lane are closed, effective immediately, for a few weeks while the work is going on. The good news is that long term this will be a real improvement to the stream quality and habitat at the preserve. Please bear with us and thank you for your support of Crow’s Nest Preserve.

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