Flood Prevention Starts at the Soil
How controlling sediment reduces flooding


Construction. It seems to be everywhere during the summer; along the highway on our drive to work, the neighboring plot of land that will become a single family home, or a new commercial facility that will bring jobs to the community. Part of our role here at Allegheny County Conservation District (ACCD) is to help ensure that these activities do not cause accelerated environmental issues that can result in stream pollution and flooding.

What it takes to control sediment in Allegheny County
ACCD’s Resource Conservationists review and regulate construction activities in Allegheny County through two courses of action: plan review and field inspection. A very important aspect in both of these areas is erosion and sediment best management practices, or E&S BMPs for short.

A few E&S BMPs that may be recognizable include compost filter sock, silt fence and erosion control blanketing. The main purpose of these controls is to keep sediment disturbed during earthmoving activities from leaving the site and polluting our rivers, streams, and tributaries as well as from entering roadways and neighboring properties.

Some BMPs keep sediment on site while allowing water to pass. Others are used to help stabilize disturbed soils from further erosion. During the review process, we evaluate the proposed placement of these, and other BMPs, to ensure suitable coverage with proper positioning and sizing. During field inspections, we make sure BMPs are installed and maintained per plan and, at times, make adjustments to provide proper control. This can be achieved with the installation of additional BMPs or adjusting placement and/or size.

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Sediment basins, a common E&S BMP, are designed to hold water long enough to allow sediment to drop to the bottom of the basin before water is released in waterways.

How Sediment Causes Flooding
We see a lot of flooding in our area, especially with recent rain storms. So why are we focusing so much on sediment rather than stormwater itself? Among other environmental issues, sediment pollution directly causes flooding.

When soil isn’t managed during construction, increased sediment can cause accelerated damage to the floor and banks of waterways. Vegetation buffers, that help control both sediment and water, are removed, which causes flow paths to continually widen and makes waterways more susceptible to flooding. Accumulation of sediment downstream can have an upstream effect when water is diverted to other nearby waterbodies, also causing additional flooding.

The Cost of Erosion
Removal of sediment in waterways can be difficult, costly and in some instances generates additional environmental issues. Erosion of soils is a naturally occurring activity, but construction can accelerate the process causing over $16 billion in environmental damage every year. Loss of land, flooded homes and streets, and irreparably damaged habitats are just some of the issues ACCD is trying to avoid through soil management.