Why Is Regular Mowing Important?

The largest enemy of any earthen dam is erosion; external or internal, both can have devastating consequences. The best protection is a healthy stand of shallow-rooted native grasses. Regular mowing promotes a dense cover of grassy vegetation that will help protect from surface erosion and does not allow brambles and trees to become established. Trees, brush, and vines can hide a dam embankment making inspections difficult, obscuring hazardous animal activity which can lead to internal erosion, and allow serious problems to be developing undetected. Often dam failure is thought of as a sudden event, when in reality the problem may have been occurring over a long period of time and gone unnoticed.

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                                                        Reference: https://www.fs.fed.us/eng/pubs/htmlpubs/htm12732805/longdesc/fig02ld.htm

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• Earthen dams that are not properly maintained can become a sheltered environment for burrowing animals such as Beaver, Groundhog, Muskrat, and Nutria. These burrows and dens often run deep in the dam causing voids that weaken the structural integrity of the dam. These voids within the dam can also lead to internal erosion (called piping) and go undetected until the dam’s integrity is severely jeopardized. Smaller burrowing animals such as Gophers, Moles, and Voles can have surprising consequences. Large colonies can excavate extensive burrow systems and produce significant integrity losses within the dam. A single Gopher may not cause a dam to fail, but larger predator animals such as Coyotes and Foxes digging several holes to get these rodents can produce devastating effects on the dam. Coyotes and Foxes may also enlarge old abandoned groundhog dens to use as their own den. Regular mowing will remove the habitat some of these animals prefer, and make inspections and corrective action easier.

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• Foraging animals across dam embankments can reduce or eliminate the vital vegetative cover that prevents surface erosion. Grazing livestock create paths on a dam’s crest or slope that will also lead to erosion, and precipitation often collects in these paths & hoof-tracks  keeping the soils wet which can lead to slumping. Regular mowing is a widely accepted alternative over grazing livestock on a dam’s slopes or spillways.

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• Trees have no place on dams. Roots can penetrate and clog chimney & toe drains, wedge into dam structures such as headwalls, spillways, valves, or gates, and have negative affects on the operation of these devices. When trees die, the decaying roots leave cavities within the dam and water leaking through these cavities can become a conduit for internal erosion and lead to piping failures. Another major hazard with trees are the large voids produced on the embankment surface when a tree is uprooted by severe wind and storms. Fallen trees can block emergency spillways and hinder flows at critical times. Brush and vines can hinder proper inspection of the embankment. A small seep or boil can severely impact the integrity of the dam if not corrected, and develop into a catastrophic event. Regular mowing will discourage trees and brush from becoming established, and improve the grassy vegetation that is  necessary to maintain a dam’s structural integrity.