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<br />, <br /> <br />requires sustained dam releases at the lower discharges currently permitted undel the ROD (8,000 _ <br />10,000 cfs)_ <br /> <br />Recommendations for Future Mana~ement Actions <br /> <br />Even if rules for releases above peak power-plant discharge are revised to allow scheduling <br />during or shortly after periods of sand inputs, the objectives of improving or sustaining the desired <br />abundance, form, and function of sand bars may still not be possible because the long-term sand <br />supply from tributaries in critical reaches may be too small. The 76-mile reach downstream from <br />Glen Canyon Dam has but one large sand source: the Paria River. The supply of sand from the <br />Paria River is only about 6% of the sand that was supplied to this reach prior to the construction of <br />Glen Canyon Dam_ Natural floods from the Paria River may be too infrequent and too small to <br />restore sand resources in this critical upstream reach, which includes the 60-mile length of Marble <br />Canyon within Grand Canyon National Park, <br /> <br />Altering the timing of releases above peak power-plant discharge (or drastically reducing the <br />darn's discharge until such flows can be released) may be insufficient to rebuild sand resources <br />above existing levels or to achieve sustainability at present levels; additional monitoring will be <br />required to see if these options are successful. If alternative timing of releases above peak power- <br />plant discharge proves to be insufficient for sand-bar management goals, then other more effective <br />alternatives should be evaluated. <br /> <br />One approach would be to selectively add sand downstream of the dam, This alternative <br />("sediment augmentation") was considered and eliminated during the Operations of Glen Canyon <br />Dam EIS process, We are unaware of engineering feasibility studies of such a program, but <br />sediment by-pass is an attribute of some recently built dams, as well as harbors and estuaries, A <br />review of sediment pipeline technology is included on the EP A web site, <br />http://www.epa.gov/glnpolarcslEPA-90S-B94-OO31B94-OO3.ch5.h1ml. Addition of enough <br />sediment (continuously, seasonally, or perhaps only during releases above peak power-plant <br />discharge) would offer greater flexibility in dam operations, and it is conceivable that such an <br />approach might cost less than imposing new constraints on dam operations, It is possible that <br />sediment augmentation, substantial seasonal modification of flows released from Glen Canyon <br />Dam, or both, might be able to restore the sand resources in the Colorado River ecosystem in Grand <br />Canyon National Park without more extreme actions. <br /> <br />Conclusions <br /> <br />The post-dam Colorado River is depleted in sand resources relative to the pre-dam river. The <br />existing management strategy permitted under the ROD is failing to restore sand resources in the <br />ecosystem in Grand Canyon National Park, The bars are continuing to decrease in surface area, and <br />no long-term retention of tributary sand has been detected, <br /> <br />Our opinion, based on the infonnation presented in this swnrnary, is that any of the following <br />approaches will have a significantly greater likelihood of success in restoring or retaining sand <br />resources in the Grand Canyon ecosystem: <br />(1) Implement releases above peak power-plant discharge immediately after substantial inputs of <br />sand from tributaries, <br />(2) Maintain low flows following sand inputs until releases above peak power-plant discharge <br />can be implemented, <br />(3) Add sediment downstream from the dam_ <br /> <br />4 <br />