Pondology
news from the waterfront by Tim Matson

HAY IS FOR HORSES (AND SOMETIMES, PONDS)

Erosion control is important in many pond projects,whether new construction or repairs. Whenever the topsoil is stripped it will eventually need to be reseeded, or flooded to fill the pond basin. Hay has
long been used for erosion control. It’s often spread on disturbed soil at the end of a project, after the ground has been seeded. This cover of hay can help keep rain from washing seeds away and prevent seeds from drying out and failing to sprout, and reduce general erosion. Because mulch hay from forgage feed usually has seeds in it, unwanted weeds may sprout along with your desired grasses. To avoid weeds, barley straw is sometimes used, or chopped straw or other mulch applied by spray.

But there’s another use of hay that turns out to be less helpful. During construction or repair projects
where soil is exposed, streams or runoff channels from the site are sometimes going to carry soil fines
whether affected by rain or not; and rain or snowmelt will trigger more erosion. To prevent erosion from leaving a pond work site and silting up downstream waters, hay bales have often been used as filters.

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Position a few hay bales across a runoff stream, the theory goes, and stop sediment discharge. Sometimes you see bales staked to the ground to hold them in position. The problem is, these hay bales can quickly plug up with sediment and create a flooded pool that discharges around the sides of the hay bales, or over the top, causing more erosion. Because hay bales are sometimes used at the end of a project after the contractor leaves, they may go unmonitored and be even more likely to cause trouble. (Silt fencing is another erosion control tool that can be misused when installed in runoff streams. It doesn’t take long for sediment to plug up the silt fencing, and water will find its way around or over. Silt fencing can work on eroding slopes, but not in a stream.)

One contractor I work with advised me he never uses silt fencing or hay bales for sediment control in
pond discharge streams. Instead he builds check dams using crushed stone to create a series of silt pools in the discharge stream. They catch substantial if not all sediment without plugging up.

I haven’t given up on hay and straw completely. Strewn on disturbed soil, hay helps protect and germinate grass seed, and it is also useful to protect an exposed pond basin against erosion before or during filling.

Ironically, when hay is suited to a project it can be difficult to find: easy-to-use square bales are now
being replaced by big plastic-wrapped round bales.

 

August 13, 2011

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