Agenda - 10-13-1999 - 2 - Laserfiche WebLink

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MEMORANDUM TO: David Stancil, AICP, Director, Environment & Resource Conservation Department Bob Jones, Director, Recreation & Parks Department FROM: Paul Thames, PE, County Enginee DATE: 9/30/99 SUBJECT: Evaluation of dam on "Red Hill Farm" property As per your request, I have visited the property I believe to be called "Red Hill Farm" for the purpose of evaluating the condition of the dam at the small pond (+/- 2 acres) located on the property. As a second phase of my evaluation (the site visit being the first phase) of the condition of the pond/dam, I have reviewed USGS topographical information for the area surrounding the pond. The USGS topographical data indicates to me that the drainage area supplying the pond is only about twice the size of the pond surface itself. This is not sufficient to support a pond (which needs a drainage area of approxf mately 5 or more acres for every acre of pond surface) in terms of maintaining it in a viable condition with water quality that would be categorized as neither stagnant or eutrophic. Although we have had sufficient rainfall over the last several weeks to potentially mask any normally poor water quality conditions, my working assumptions are that: a) this pond is primarily spring fed; and b) the water quality is generally acceptable. The condition of the dam is another matter. Trees and large bushes growing out of an earthen dam, as is the case at this dam, are generally considered to be unacceptable. The roots grow through the dam. toward the water. When the tree or bush eventually dies, the root decomposes and leaving apipe-like passage or opening through the dam. Water flows through the passage, enlarging it by erosion; the dam fails. One can try to remove the trees and repair the dam, .but the efFicacy of this process is questionable at best. It is generally better and safer to breach and abandon or rebuild the dam. Given the small area draining to the pond created by the dam, it is unlikely that the dam will be unusually stressed (structurally and hydraulically) by large quantities of surface water flow. The pond does not contain a sufficient quantity of water, nor is the dam .sufficiently high for the dam to fall under the regulations and guidelines of the dam safety act. The pond and dam probably do not represent a serious threat to property or life in the event of dam failure - at this time. Property development immediately adjacent to and downstream of the dam could change this assessment. If the County were to purchase this property, even given the current low level nature of the threat represented by a potential dam failure, I would recommend that the dam be breached or repaired. If I may provide additional information, please advise.