Agenda - 04-06-1987 - Laserfiche WebLink

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165 O R A N G E C O U N T Y INTEROFFICE MEMORANDUM TO: Board of Commissioners FROM: County Manager SUBJECT: Background on the Question of Lake Orange Storage Capacity DATE: April 1, 1987 This project has been under consideration as one of several measures to increase the amount of stored water available in the Upper Eno River during a drought. Authori- zation was given by the Board in November, 1986 to develop engineering plans and specifications to raise the lake by one foot yet with the capability of being raised to two feet at a later time were such decision to be made; and to survey property owner title claims and sentiment as related to a one or two foot rise. Background facts concerning the decision are as follows: 1. Safe Yield. The Division of Water Resources, relying on drainage area and average rainfall calculations, has estimated a 51 million gallon increase or a 200, 000 gallon per day safe yield increase from a one foot rise and a 104 million or 400, 000 gallons per day safe yield from a two foot lake level change. 2 . Engineering. Either level is engineeringly feasi- ble while still meeting the requirements of the Dam Safety Laws of 1967. All clearances have been received for construction to commence for the one foot. Were a two foot rise to be pursued additional approval would be necessary for the design of the flashboard release mechanism. The system consists of a one foot fixed vertical addition to the spillway crest with provision for a further one foot addition. The timber flashboards are to be permanently bolted in eight foot long sections to vertical structural steel supports which are to be anchored to the spillway slab. They are designed to withstand hydrodynamic forces occurring during severe storm events without compromising the safety of the dam embankment.