The trash screen installed in the headwaters of Sligo Creek has been functioning for half a year now. The creek downstream of the trash catcher has significantly less trash as a result of the trash catcher. The trash level in the creek only starts to increase once trash from stormwater outfalls downstream of the trash screen enters the creek.
Observations:
The trash screen requires modest amounts of maintenance. During the flood on July 27th, the poles and fence were pulled out of one side of the creek. Fortunate, it only took about 20 minutes to hammer the poles back in place with a mallet. I had hoped that the gaps in the chain link fence would be large enough to pass through most of the leaves, sticks, and seed pods. Instead, the leaves and woody debris need to be cleared away periodically. In fact the screen ends up catching a lot of cigarette butts, small foam pieces and other small floating debris due to the leaves blocking the chain link fence openings.
I have also been finding that the force of the water flow during rainstorms is enough to stretch the fence linkages. This causes the fence to sag in the middle. Because the metal gauge is light, it is fairly easy to stretch the fence back into shape. This problem could be addressed with a heavier gauge fence links. I also noticed that there has been some minor scouring under the screen. About 6 inches of sediment under the screen has been scoured away. I assume that water velocity increases when the water flow through the chain link fence becomes obstructed with the leaves/debris mentioned above.
I was recently talking to one of the engineers with the Stormwater Facility Maintenance Program at Montgomery County Department of Environmental Protection (DEP). He mentioned that he was by the University Blvd Stormwater management ponds (about 3/4 mile downstream of the trash screen) recently, and he was surprised by how they were relatively trash-free. That confirmed to me my observation that the trash screen and our twice a year clean up workdays have made a difference in Upper Sligo Creek.
A photo of the trash screen taken Oct. 17, 2004.
The screen collects a lot of trash, leaves and woody debris.
Cleaning out the leaves and trash takes about 10 minutes.
Click here to see most recent update on this topic