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Appendix 14-5 <br />rock, and debris. With the upper set of culverts being 36 inches in diameter and encapsulated in <br />concrete, there is potential of debris plugging one or more of the culverts. The tendency of the <br />stream will be to both flow over the concrete (which also serves as the road surface) and to cut <br />around the concrete section. Water flowing over the concrete surface is preferable to the channel <br />moving laterally azound the culverts. Cutting azound would wash out a portion of road adjacent <br />and parallel to the drainage. To better assure that the channel is maintained in its present <br />location, wo propose construction of concrete'tivings" on the upstream side of the culvert ttnit.~z j <br />They would be tied into the existing concrete-with rebar, ezten~rerhaps 6 or 8.feet into the'~=• ", ~• <br />streambank;~be perhaps 8 or 10 inches thick, and be ai a similar height to the existing con <br />We believe construction of these wings would be less costly than removal of the culverts and <br />installation of a low water crossing. There is another issue with the alignment of_this set of <br />culverts, that being the water is being directed somewhat toward the right bank (looking <br />downstream). This is in the section of channel that had been relocated, rock check dams <br />installed, and is now viewed by the DIvIG as being out of equilibrium. Much work is proposed <br />for this section by the DMG, including removal of the rock check dams, removal of the detained <br />sediment, and reshaping the channel to uniform gradient for the reach between the culverts. <br />BLM believes that in'concert with that work, the channel could be aligned slightly to the ngh~ ql <br />it's`present location so that~the water is no longer directed toward the right bank. Doing this <br />would direct the water flowing through the culverts into the channel proper and avoid the bank <br />erosion. Another proposal to minimize future maintenance needs, is to place some of the rocks <br />from a rock check dam to the area immediately downstream of this culvert set. This would <br />• minimize the scour hole and undercutting associated with water pouring over the road surface or <br />flowing though the culverts. Another concern is when the section of channel between the <br />culverts is reconstructed, there will be the potential of increased energy within this portion of the <br />system, compared to the natural system above the realigned channel. A reduction in energy to <br />more closely approximate the natural channel conditions is desirable. This energy reduction <br />could be achieved by increasing the channel roughness, increasing the channel width and <br />creation of a floodplain, and/or by decreasing the slope within the reach. The only way to <br />effectively decrease slope is to lengthen the channel length which could be achieved by adding a <br />meander or two. Any decrease in energy in this reach would help assure that the arched culverts <br />could pass storm flow without washing out, again reducing future maintenance requirements. <br />BLM is interested in retaining the culverts to better facilitate administrative and public access. <br />Consideration of these suggestions to reduce future maintenance requirements would be <br />appreciated. If you have any questions related to these ideas, feel free to contact Jim Scheidt at <br />970-?-44-3075 or Bruce Fowler at 970-2=kf-3036. <br />Sincerely, <br />~ ~~ !~ <br />~ ~~~- ~~ <br />I !I <br />I ~~ % <br />iV[arian At n <br />associate ~ield Manager <br />• cc: J. E. Stover <br />2.~ <br />