Good (silt) fences make good neighbors

I was reminded of the old saying about good fences, as I visited the Mitchell Marsh in Union County, just downstream from the dam at Green Valley State Park. Unfortunately the lesson today is the opposite of the old saw: bad fences making a troublesome neighbor. In this case, the fences in question are silt fences made of fabric, designed to catch eroded soil.

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The fences are situated along the slope leading down to the wetland. Similar fences have been a bane of my existence for years, because they seem to be installed incorrectly more often than not. The idea is to wrap the bottom of the fabric into the slope, so it is weighted down by the soil it catches, anchoring the fabric. Unfortunately, they are often installed such that the fabric never even touches the soil surface, and the soil simply slides underneath, heading downslope unimpeded. But here, it appeared the fences had been installed correctly. Unfortunately, they had subsequently been obliterated.

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Whether through vandalism, or careless trampling by humans or deer (I saw footprints of both), the fences were no longer able to do the job. This ersatz trail, interrupted in three places by these silt fences, had a sign next to it warning of a buried water line.  That’s the cause of this disturbance of the soil: they dug a trench and put in the water pipe, then backfilled and installed the fences to catch any eroded soil. I called the telephone number on the sign, to inform them of the condition of the silt fences. Actually, I helpfully suggested that they might wish to rethink the approach entirely: a long stretch of loose, exposed ground on a steep incline is an excellent conveyor of eroded soil. Attempting to catch the eroded soil with fences after it starts sliding is a less effective than covering and anchoring the soil in place, so it doesn’t need to be caught at all.

In a phone conversation, Chad from the rural water company was in complete agreement with me. He explained that indeed, they would put down seeds first thing in the spring, so there would be plants (turf) to cover the soil and anchor it. They simply ran out of time on the project in late fall. (Well. OK, then!)

 

Erosion has serious consequences. The shoreline down at the water’s edge was also eroded (probably by water  coming out of the dam), and as I walked about I unexpectedly crashed through ground undermined by the erosion. Several times my foot sank till I was in a hole well above my boot. All this disturbance will be hard on aquatic species, it promotes weeds, and of course threatens the structural integrity of the shore itself. So the erosion down by the riverbank needs attention too.

Away from the slope, on the other side of the stream, I saw signs of muskrat activity, and nest boxes at the ready. I have no doubt waterfowl and birds of prey visit the site, and other wildlife too. And so I hope that a bit of attention paid to the engineering, construction, and maintenance of the site will get things squared away. If you visit the site, please leave a comment and update us on the conditions. Thanks!

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Author: Paul Weihe

Associate Professor of Biology at Central College, traditional author (Textbook of Limnology, Cole & Weihe, 5th ed.; Waveland Press), and now...blogger!

5 thoughts on “Good (silt) fences make good neighbors”

  1. I’d be very interested in learning what state-of-the-art approaches to this situation might exist. I do understand that state-of-the-art approaches aren’t always feasible, physically or financially.

    And I appreciate that the rural water staff in this case are being commendably nice and had already intended to address the problem. Many Iowa wetland owners and managers, especially when runoff and erosion are coming from adjacent private land, are not so fortunate.

    My question is whether options exist that might allow effective erosion control measures to be installed in late-fall situations. Very generally speaking, I’ve seen: (1) Straw-like biodegradable loose-weave erosion mats that can be left in place permanently and allow plants to grow through them. (2) Rolled out close-weave plastic netting that helps hold soil temporarily and can be later removed. (3) A green sprayed-on mixture that includes both (temporary) annual cover-crop seeds and (permanent) prairie seeds. But maybe erosion controls like this have to wait until excavated areas have settled over the winter?

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    1. Cindy, those sorts of measures are what I often see. And I think any of them would be an improvement over what was on-site. The photo might not do it justice—it’s a really long slope, and quite steep. So bare soil is really unstable, so getting it covered should happen “yesterday.” I would think some sort of netting would be the best bet, least likely to start moving in spring rains. But also, grading it so that water is dispersed—don’t want a groove to form, and later widen. Anyway, whatever measures, it’s important to also follow up, and repair when necessary. Sadly that is so seldom the case…

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