2007-01-31_REVISION - M1986015 (2)

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MINING PLAN again overtopped [he repair and the pi[ filled with water again. The dimensions of [he second breach were smaller than the firs[ one and some of the repairs [hat had been completed survived. Damages to other levees, no[ associated with this operation, also occurred downstream and threatened homes with flooding. Interestingly, bank strengthening at two locations further upstream which had been installed after the 1999 flood, were no[ damaged, even though both of those locations are where the force of the flooding river was greater than would have been the case at the breach location if the sand bar had no[ been [here to force the flow into [he bank. The technique used at those locations employed small jetties constructed of waste concrete patties that extended perhaps ten feet or so into the river and were keyed into the bank. The jetties were placed about 20 fee[ apart. Silt accumulated between the jetties which was then invaded by willows and small cottonwoods or other woody species as well as a dense growth of herbaceous vegetation. Once established, which takes two [o four years [o fully develop, this bank structure is very strong, and i[ produces a much smoother contour along the bank than that produced by rip rap. This creates a more laminar flow along the shore rather than the turbulent and therefore potentially erosive flow common with rip rap. These treated banks are clearly capable of resisting bank erosion in even the intense floods of 2006. In addition, [his approach produces a more attractive streambank than that produced with rip rap as well as providing excellent wildlife habitat beside the river. This technique was recommended by Anita Culp of the Pueblo office of the U.S. Army Corps of Engineers. Now that it has been thoroughly tested with the 2006 events and shown to work on two completely different, high intensity sites, this technique will be used to strengthen the bank on the Phase 2 area. Although, [his streambank does no[ have the high erosion potential of strong meander areas, as occurs adjacent to Phase I, the shoreline is definitely not straight. Amini-meander, so to speak, does exist in one location and [his now vegetated sandbar has a definite back channel and does present a moderate erosion hazard [o [he setback. Because a groundwater barrier wall will be installed in Phase 2 from near [he start, i[ is critical that [he streambank be strong enough to minimize the chances of a breach of the pit. At the time the groundwater barrier wall is installed, the existing condition of the streambank will be examined and any locations that show a potential for bank undercutting, especially in the vicinity of the mini-meander, will be treated with the jetty construction described above. Of course, it is impossible [o completely protect the pit from all possible events, but if the streambank is showing signs of weakness or erosion, a[ a minimum, those areas definitely need to be strengthened. r Pueblo East Pit Amendment 3 (2007) Exhibit D Page 23 of 34