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Where sand is heavily deposited, either as a natural condition or as a consequence of <br />erosion, the sand resource becomes attractive as aggregate. In the far eastern plains of <br />Colorado, these streambeds are often the only source of any kind of course aggregate and if <br />these sands are not extracted the aggregate must be shipped in at considerable expense. Thus <br />sand and sometimes gravel mining is done in these ephemeral streams. This mining often <br />removes sufficient material that the water table adjacent to the stream declines and that can <br />induce the destruction of the adjacent cottonwood forest. However, it is also important to <br />recognize that if a cottonwood forest next to some sand mining dies it does not necessarily <br />mean the mining caused it. Large areas of these groves tend to die out more or less all at once <br />simply because most of the trees are practically of the same age. Also, intense grazing pressure <br />can cause the destruction of these groves. In other words, mining the sand in these drainages <br />is not necessarily harmful to the adjacent forests; it largely depends on the specific situation. <br />Philosophically, the simple correlation of two events does not necessarily indicate that the two <br />events form a causational sequence. <br />On this site, all three of these factors are at work. Land development upstream has <br />undoubtedly increased sedimentation in the stream, but, as will be seen, this does not seem to <br />be a factor immediately upstream from this site where the wetlands in the channel appear to <br />be in excellent condition. The surrounding prairie, especially in the drainages that feed into <br />the mining areas, are overgrazed and in some instances very severely overgrazed (this will <br />also be discussed in more detail later). Cattle utilization of the riparian forest is also intense <br />and probably intense enough to affect the porosity of the soils through compaction. The <br />understory has also been severely affected by grazing and in some places the understory is <br />completely absent -weeds barely even grow there. And mining of the sands in the stream <br />channel has been occurring for a very long time and this has definitely lowered the stream bed <br />and very likely the water table. Unfortunately, trying to decide whether the decline of the <br />forests is due to old age, cattle grazing, or water table decline as a result of mining is virtually <br />impossible to determine with complete confidence. It is probably a blend of all those influences, <br />but which is most important is difficult to determine because the impacts from both mining <br />and grazing can be intense. However, as will be shown later, it appears that cattle grazing <br />may have more to do with determining the future of the riparian forest and the streambed <br />vegetation than anything else. <br />The stream channel itself exhibits moderate to strong meandering and a fairly strong <br />dynamic profile. In many places along the unmined channel there are high cutbanks on the <br />outside of meanders. It is interesting that at or upstream from these large cutbanks the <br />channel vegetation is very often rich and has close to 100°/a cover. But just downstream from <br />these cutbanks the vegetation declines rapidly as the bed forms a nearly unvegetated <br />substrate. Further down the channel, the vegetation may start to increase again and <br />Coal Creek Wetlands and Wetland Mitigation DA Permit 198811488 August 2003 Page 4 of 23 <br />