Item - Agenda w-Hillsborough 03-22-2004

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reduced to 1.36 mgd when the Lake Orange water level drops to two feet below full). Orange County's role in the agreement is to coordinate the overall operational activities related to water withdrawals; to release water from Lake Orange as necessary to meet the withdrawal demands; and to maintain a minimum rate of instream flow (1.7 cfs [1.1 mgd] specified to be an instantaneous minimum flow target) in the river as measured at the Hillsborough gage (a USGS operated stream flow gage located south of Town, below the last point of withdrawal but above the point where the Town discharges treated wastewater into the river). In the months and years since the agreement was first ratified, it has been modified in terms of operational requirements to allow for reasonable controls and to account for instream releases from Hillsborough's West Fork Reservoir. Specific operational changes include: 1) modifying the low instream flow trigger (requiring seven consecutive days of low instream flow) initiating withdrawal restrictions and the high instream flow trigger (requiring seven consecutive days of high instream flow) curtailing withdrawal restrictions; 2) allowing withdrawing entities to share unused portions of their allocations with sufficient notice; and 3) allowing essentially unlimited water withdrawals during periods of restriction when short -term (at least 24 hours) but high (above 10 cfs) instream flows exist as a consequence of intense and prolific thunderstorms; and 4) providing for higher instream flows by requiring and instream flow contribution from the west fork reservoir. Over the fifteen years that the Eno River Capacity Use Agreement has been in effect, the specified system of controlling withdrawals and releases has worked fairly well. In general, capacity use restrictions are in effect for a period ranging, on average, from early July to late December. Significant deviations to the usual low flow (dry) period include the summer /fall of 1989 and 2003 which were sufficiently wet that Capacity Use restrictions were not implemented at all and the drought of 2002 when the low flow period spanned from the beginning of April until the end of October. There have been occasions numerous occasions when operational difficulties have been encountered in the effort to limit withdrawals and maintain instream flow. Often the outcome of these difficulties has been a period of time when there was either too much or too little water was released for instream flow. Many of the problems have been related to equipment failure: the water release gates at Lake Orange and power outages and other failures at the USGS stream flow gage, for example. There have also been instances where excessive amounts of water were withdrawn for weeks at time. The processes of adjusting the release of water from Lake Orange (it is often 24 hours or more before such adjustments become evident as an increase or decrease in flow at the Hillsborough gage) and predicting when the users must reduce their Eno water withdrawals and supplement their water demand by other sources are often unwieldy and inaccurate. However, regardless of the various operational problems, stream -watch monitoring of macro - invertebrate populations and water quality parameters in the Eno River below Hillsborough has shown.the river to be more healthy during dry times than the upper reaches of the Little and Flat Rivers, which have much larger drainage areas and no water withdrawals upstream of the monitoring points. Addition indications of the efficacy of the Capacity Use Agreement may found by evaluating how the system worked during the 2002 drought in which this area, including the Eno basin, experienced the most severe r9 raft 4