Put simply, trees weaken the structure of a dam. During significant or even moderate wind events, trees can fall and leave holes and voids in the dam that can potentially lead to a catastrophic failure of the dam.
Roots can also extend deeply into the dam, allowing water to travel along their path, a problem known as piping. This issue can occur even without inclement weather events and whether the roots are healthy or not.
Piping generally starts slowly and increases with time, with dead or diseased roots worsening the situation. Voids left by fallen trees then increase the rate at which water is able to escape. These situations can potentially cause the dam to fail and impact homes, roads, and other property downstream. Trees can also create shade on a dam, which hinders the ability to sustain grass cover. Bare areas are vulnerable to erosion during rain events and are especially dangerous if the dam over tops.
It is recommended that trees and brush be removed from the entire dam, including both slopes, the crest, 15 feet or half the height of the dam (whichever is greater) past the toe and the emergency/auxiliary spillway. Spillways should be kept clear at all times to prevent restrictions on the flow of water. South Carolina Department of Health and Environmental Control (SCDHEC) recommends removing tree saplings as soon as they appear. No permit is required to remove trees less than 4 inches in diameter. Generally, trees larger than 4 inches in diameter also require removal of the stump and roots. Because stump removal can affect the structural integrity of the dam, a permit to remove the trees and stumps through a tree management plan created by a South Carolina licensed professional engineer is needed.
Who owns the Duncan Park Lake and the dam?
The City of Spartanburg owns and maintains the Duncan Park Lake and Dam.
Who wants the trees removed from the dam?
Since the historic rainfall in our state in October 2015 and Hurricane Matthew in 2016, which caused multiple dam failures throughout South Carolina, SCDHEC has aggressively expanded its Dam Safety Program. The Duncan Park Lake Dam received an inspection by SCDHEC on May 12, 2015. The DHEC inspection revealed that the dam was “in overall fair condition” and “relatively well-maintained given its age” but also concluded that, because of large trees present on the dam structure, a tree removal plan was required.
What is going to be done to remove the trees?
The city has contracted with an engineer to develop the tree removal plan and design other improvements to the dam. The tree removal plan was developed based on guidelines published by the Federal Emergency Management Agency (FEMA) in their Technical Manual for Dam Owners. Those engineering plans will be used by a licensed and qualified contractor—selected by the city—to complete the project.
What will the dam look like when the work is completed?
When the project is completed, the dam will be predominately grass-covered. Along the shoreline, a stone “apron” will be put in place, which will extend approximately three feet above the surface of the lake. The current guardrail along both sides of Parkview Drive will be replaced with new guardrail.
When is the work going to take place?
Work will begin in April 2019. The contractor will be allowed only 45 days to complete the work.
How will traffic be affected during construction?
Parkview Drive will be closed during construction. Detour signs will be placed directing the flow of traffic around the construction area.
Please visit www.cityofspartanburg.org for additional information.
Photograph of Cagles Mill Lake in Indianapolis, IN.