Laserfiche WebLink
<br />0025 7 <br /> <br />In order to meet all of the objectives for a BHBF, the scientific community recommended that <br />discharges from Glen Canyon Dam should be of higher magnitude (> 55,000 cfs), and of shorter <br />duration (2-4 days). Based on the information learned to date, it is probably not appropriate to <br />continue referring to a flow of 45,000 cfs, as a DBeachlHabitat Building Flow.D Rather, a <br />discharge of 45,000 cfs, while above power plant capacity, may simply be a further stage in <br />habitat maintenance flows (GCDEIS, 1996). This document will refer to the flow being <br />considered as a DSediment Conservation Flow.D <br /> <br />Because a springtime flow of 45,000 cfs primarily benefits one resource, sediment, with little <br />positive effect on other downstream resources, then the development of resource criteria for use <br />in considering doing 45,000 cfs sediment conservation flows at times other than the spring will <br />be directed at providing information related to whether such a flow might cause an adverse <br />impact to those resources. Flows of higher magnitude, such as the 55,000 cfs or greater <br />recommended by scientists for accomplishing the objectives of a BHBF, would require different <br />criteria, not necessarily developed herein. <br /> <br />Concern has now developed over potential downstream losses of sediment due to high sustained <br />releases from Glen Canyon Dam during high water conditions (i.e., 25,000 cfs - 27,000 cfs). <br />Sediment lost downstream due to such high sustained flows is unavailable for deposit during <br />subsequent HMF or BHBF events. That concern led to the formation of a Subgroup to the <br />Techil.ical Work Group (TWG) to develop some hydrological DtriggeringD criteria for conserving <br />sedinient when faced with sustained high flows. <br /> <br />Two hydrological triggers, or decision mechanisms, were developed for use as a basis for <br />consideration in doing a sediment conservation release from Glen Canyon Dam. The hydrologic <br />criteria are very straightforward, based on the Annual Operating Plan and Lake Powell inflow <br />forecasts, and apply only to the months of January - July. <br /> <br />The Adaptive Management Work Group (AMWG) agreed that a BHBF (for sediment <br />conservation) should be recommended when one of the triggers occurred, but only if the flow <br />was also appropriate from an environmental perspective (effects to other downstream resources <br />would be within acceptable limits). The AMWG has further charged the TWG to work with <br />scientific and resource management authorities to develop resource-based criteria, to be used in <br />addition to the hydrologic triggers, in deciding whether to recommend a BHBF directed at <br />~onserving sediment. The hydrologic triggers are dependent on water year estimates, the annual <br />operating plan and subsequent dam operations, and resource criteria are necessarily dependent on <br />dam operation scenarios. <br /> <br />Reclamation will use the information developed to do an environmental assessment, and related <br />formal consultations for endangered species and cultural resources, in making a decision about <br />scheduled releases for sediment conservation. <br /> <br />Downstream resources are categorized into the following elements: <br /> <br />1. Biological <br /> <br />2. Cultural <br /> <br />3. Physical <br />