Agenda - 11-19-1985 - Laserfiche WebLink

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, e 2 . Fortunately, the 'resumption of rainfall avoided the . depletion of all water in storage. The thought of what could have happened, however, prompted an interest in studying the frequency and duration of water supply conditions on a multi- . year basis. To this end a Water Committee was formed by the Board of Commissioners of Orange County (consisting of the water utilities of Hillsborough, MASA and OA together with the County) and the Division of Water Resourses of NEED was called upon to provide stream data to support the effort. This work was interrupted pending the completion of the State's study of Virginia Beach's claim of water from Lake Gaston. In the Spring of 1985 work on the Upper Eno began .' again culminating in the development of data shown under - Section V of this report. , II. MAKE UP OF THE •!ER 2k, R ar For purposes of this study the term "Upper Eno River" is . meant to refer to that part of the Neuse Basin bounded by the `'.. drainage area of Hillsborough, and the upstream vicinity in ., Efland and Cedar Grove townships together with related , . ., . reservoirs. It is referred to as one of the "headwater ? . areas" of the Neuse Basin. The most northerly points are the ' east and west forks of the Eno. The southern measuring point tf .i. is the former U. S. Geological gaging station site (Lunber 2- 0850) just below Lake Ben Johnson at Hillsborough. . ,-i Three man-made reservoirs lie within this expanse of , river. The uppermost is Lake Orange which is owned by Orange County. Built in 1969, it has a steady state safe yield of 2.2 million gallons a day (with one failure in 40 years) from 1,403 acre feet of total storage (1,394 acre feet of usuable storage) and a drainage area of 9.12 square miles. L Next is Corporation Lake owned by the Orange Alamance Water ,,.. • Corporation. It was constructed in 1965. The independent safe yield without Lake Orange is unclear (though rated at .79 MGD) because the present facilites do not permit , operation of the lake at less than full pool volumns. In . order for water to pass downstream it must flow over the spillway. The yield without Lake Orange in place would be much less. Its total storage is 72 acre feet (61 of which is useable) stemming from a drainage area that is four times (41.16 square miles) the drainage area of Lake Orange. The third reservoir is Lake Ben Johnson, built by the Town of Hillsborough in 1955. It has an independent (i.e. indepen- dent of Lake Orange and Corporation Lake) yield of .44 Mu, . total storage of 73 acre feet, usable storage of 66 acre feet and a drainage area of 59.81 square miles. See attached Upper Eno River map. . ; . e , Several observations can be noted as to the functioning of the three resevoirs. First, they are interrelated in •, their operation during a drought. When the normal river flow • ceases water must be released from Lake Orange to meet the :.•' ,le supply needs of Corporation Lake and Lake Ben Johnson. Secondly, all three reservoirs capture runoff from a limited area. While ostensibly the conbined drainage area consists ze. of 59.81 square miles, the effective drainage area (i.e. the