PINE BLUFF — The cornerstone of artificial ponds and reservoirs is the dam. This structure impounds water, manages discharge and can even be a signature aesthetic feature, according to Scott Jones, small impoundment Extension specialist at the University of Arkansas at Pine Bluff.
“Proper sizing and construction of the dam is obviously important, but so is maintenance to keep them functional, safe and strong,” Jones said. “One aspect of maintenance that is often overlooked is keeping shrubs and trees from growing within the footprint of the dam.”
A misconception of earthen pond dams is that they are waterproof. Even well-built dams with good clay soil still pass groundwater through them; they just slow and redirect the groundwater to move underneath the base of the dam, he said. Core trenches are designed to contain highly packed clay through the center of the dam extending at least 12 inches below its foundation.
“This core provides the least permeable barrier within the dam and encourages percolated groundwater to travel underneath the dam’s foundation,” Jones said. “This helps slow water loss, but also keeps water from moving along the seam between the original ground level and the foundation of the dam.”
One of the most important steps in prolonging the integrity of a new pond dam is establishing and maintaining a healthy growth of grass. Each plant pushes roots into the soil anchoring the plant to the slope and subsequently reinforcing the soil against runoff and other forms of erosion. Once the grass is established, it is important to mow the grass regularly to prevent woody plants like shrubs and trees from getting started.
“The biggest dangers posed by woody plants, especially trees, is that their roots dig deeper into the soil. This can introduce routes of water flow through the core, increasing water loss through the soil and the chance of developing leaks,” he said. “Especially if a tree dies, its roots decay leaving an even larger void for water to move.”
Shade produced by trees can also reduce grass growth on dam slopes, increasing erosion of exposed soil during rain events. The worst-case scenario with large trees on dams is a strong storm with high wind striking the dam after the ground is saturated from heavy rains.