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ueiu~ituol sun ua:sz rns <br />Y " <br />• Page 2 May 14, 2001 <br />23 March 2001, provides modeled water table drawdown amounts at varying distances from <br />a pit. At all three of the modeled transmissivities (gpd/ft), the water table drawdown at all <br />modeled distances (to 2000 feet from the pit center} were equal to or greater than three feet, <br />aftem 365 days of pumping. Thus, any dewatered pit within 2000 feet, and possibly a <br />greater distance, of cottonwoods along the river corridor could lead to critical drawdowns and <br />tree damage or death. <br />This subject is important for several reasons. Most trees are mature, and little cottonwood <br />reproduction occurs. Thus, maintaining the health and condition of these trees is critical for <br />maintaining the riparian ecosystem, and few replacement trees are maturing. Mature trees <br />are extremely susceptible to drawdown-induced cavitation. The trees, and stream channel, <br />in the stream reach in question are of historical signifignce, having been described in detail <br />by John C. Fremont on July 10, 1842. Likely many of the trees that Fremont saw and <br />discussed in his journals, are still alive today, and are threatened by this project. <br />The work initiated by Leonard Rice must be carefully applied in the analysis of pit location, <br />and the potential effects of drawdown caused by pit dewatering. In addition, their analysis <br />should be extended to include distances of 3,000 and 4,000 feet from the pit center. <br />The second issue that must be address is whether dikes will be erected t0 maintain the <br />South Platte River in its current alignment. This is typical practice to keep streams from <br />migrating into gravel pits. However, cottonwood tree seedlings establish only on the bare <br />wet mineral soils produced as rivers meander. Meandering streams erode banks on the <br />outside of stream bends, and point bars form on the inside of meanders. Trees establish on <br />point bars. The South Platte River riparian ecosystem can be sustained only by a stream <br />with room to meander. If the stream is confined by one or more dikes, then cottonwood <br />reproduction is likely to be curtailed. <br />These issues must be carefully considered before determining the potential impacts of the <br />proposed gravel mine on riparian ecosystems of the adjacent South Platte River. <br />Sincerely, <br />C// <br />David J. Cooper <br />~J UUJ/UUJ <br />