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. . . . <br /> . . • C 0 Py <br /> 4 <br /> INTEROFFICE MOggEggal, <br /> TO: John Link, County Manager <br /> FROM: Paul Thames, P.E. , County Enginele4c- <br /> D/t.TE: December 12, 1988 <br /> SUBJECT: Capacity Use Monitoring of Eno River <br /> - by Orange County <br /> I have visited the three existing impoundment sites on the <br /> Eno River upstream of the USGS flow monitoring station in <br /> Hillsborough. In general , I find the existing impoundments <br /> lacking the capacity for any degree of accuracy in . <br /> controlling flows or releases from the impoundments. <br /> The lack of control accuracy is particularly distressing in <br /> light of the requirements of conserving as much water as <br /> possible in the impoundments while maintaining the mandated <br /> minimum flow in the Eno at the existing flow monitoring <br /> station. The nature of the operation of the Eno system <br /> requires a precise knowledge of the exact flows—upstream and <br /> downstream of the Lake Ben aohnston Dam, upstream and <br /> downstream of the Corporation. Lake Dam, downstream of the <br /> , Lake Orange Dam and the daily totalized flow of the existing <br /> , flow monitoring station. In the following paragraphs, I <br /> have outlined my understanding of the existing control and <br /> monitoring system, my recommendations for improving the <br /> system and my conclusions regarding Orange County's <br /> participation in the monitoring program. <br /> In normal drought condition, operation of the Eno River <br /> system requires that a minimum flow be .maintained at the <br /> existing Eno River flow monitoring station in Hillsborough. <br /> Presently, this monitoring station consists of an electronic <br /> system with primitive telemetry giving up to the minute flow <br /> I . rate data that is instantaneously accessible to Orange <br /> County. The system also totalizes the daily flow, but that <br /> data is available to Orange County only on a bi-monthly <br /> basis. When flows are lower than target minimums at the <br /> monitoring station, a quantity of water sufficient to make up <br /> the difference between the actual flow and the target minimum <br /> flow must be released from the upstream impoundments. The <br /> first release must be made from Lake Ben Johnston. This <br /> release is replenished by a release from farther upstream at <br /> Corporation Lake which is, in turn replenished by a release <br /> • from Lake Orange. There are no metering systems at any of <br /> the impoundments to measure flows in or out. Releases are <br /> . . . <br />