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Page 2 <br />July 22, 2008 <br />3. A monitoring plan will be developed to monitor (1) the rate at which the gravel pit is filling in <br />with river sediment, (2) the potential occurrence of headcutting in the Colorado River upstream <br />of the inlet (measurements and photographic documentation), and (3) annual inspection of the <br />inlet structure. <br />Glen Miller Comments: <br />Mr. Miller cited several concerns with a flow-through pit design in a letter to the FWS in May of 1999. <br />Mr. Miller's concerns include the following: <br />1. Small floods may build-up sediment in the pit lake and later large floods may scour and re- <br />entrain this fine sediment. A given flood event could cause a "slug" of suspended sediment to <br />enter the downstream channel of the Colorado River. <br />2. Larger, high velocity flood events will create a "plunge" pool 100 ft wide and 10 to 15 ft deep <br />on the downstream side of the inlet structure. <br />3. A moderate-to-large flood would discharge several 1,000 cubic ft per second (cfs) over the <br />inlet into the pit. "Such flows would likely destroy the structure, allowing rapid down-cutting <br />to the level of the riverbed, or lower." Such flows would divert most of the river flow through <br />the pit, and result in very low flow or no-flow in the "island" area. <br />4. Head cutting in the main channel would progress upstream from inlet which could result in <br />drying-up of some sloughs or backwaters in the Walter Walker Wildlife Area. <br />5. Past experiments with similar inflow structures at the Walter Walker Wildlife Area and an old <br />pit near 30 Road failed, in ways similar to those described above. <br />6. Any diversion of flood waters would reduce the river stage at flood peaks and result in above <br />normal deposition of sediment in the downstream "island" area, thus altering the existing <br />channel/slough/backwater system. <br />7. The project itself would increase the risk of diverting the main river, regardless of the final <br />state of the pit because pit operations are removing the more resistant coarse materials in the <br />floodplain area. <br />ACE 404 Permit: <br />1. The permittee shall maintain a minimum of 150 ft buffer between the Colorado River and the <br />excavation boundary of the gravel pit at all times. <br />2. The permittee will maintain the gravel pit as deemed necessary by the Corps of Engineers to <br />prevent the pit from becoming the main channel of the Colorado River. <br />3. A written response from a certified hydrologist addressing the concerns of Mr. Glen A. <br />Miller's letter to Ms. Sue Moyer of the FWS dated May 20, 1999, shall accompany the final <br />design. <br />July 15 Meeting Summary <br />On July 15, 2008, a meeting was held by Grand Junction Pipe to discuss the conceptual design and to <br />resolve the intention of key permit elements. Meeting attendees included Mr. Ed Settle and Mr. Ron