Saturday, October 24, 2009

Drainage Ditch Contrast

I was walking along 80th today and happened upon an interesting contrast in drainage ditch designs, conveniently located on either side of a fence.

The one on the left side of the fence must have been part of the surface water management plan when this little cul de sac was built. Can you see the mounds of rock placed perpendicularly periodically along the ditch? I would imagine those are for slowing down the flow of the runoff a bit and helping silt to settle out behind the mounds. That ditch also appears to be gravel-lined.

The ditch on the right is an interesting contrast. Just a steep-walled dirt ditch leading out to the ditch in the street.

The differences between these ditches remind me a bit of the stretch of Little Swamp Creek going through our yard. For the most part it is contained in a fairly narrow, deep channel. Over time the base of some of the steep bank areas become eroded enough that chunks fall into the stream, sending more silt downstream. Here's a good example of a chunk of bank that fell after the heavy rains last week -

The bank is only a foot or so high, but still... Ideally, we would love to create a gradually sloping bank along this stretch of the stream (on the side away from our house). The Adopt-A-Stream Foundation came up with a plan and received a permit to do the work, but the grant funding ran out. Stay tuned - I won't give up hope yet. Meanwhile, we have the great large woody debris that was installed this summer with the help of The L.E.A.F. School, which will help stabilize the bank in a few places, slow down the flow a tad and help collect silt and small pebbles. We also have a bunch of live willow and red twig dogwood stakes stuck into the bank in the worst spots. As those grow roots, they will definitely help hold the bank together.

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