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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 [he 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 around the culverts. Cutting around would wash out a portion of road adjacent <br />and parallel [o the drainage. To better assure that the channel is maintained in its present <br />location, we propose construction of concrete "wings" on the upstream side of the culvert unit. <br />They would be tied into the existing concrete with rebar, extend perhaps 6 or 8 feet into the <br />streambank, be perhaps 8 or 10 inches thick, and be at a similar height to the existing concrete. <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 [he section of channel that had been relocated, rock check dams <br />installed, and is now viewed by the DMG 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 [he culverts. <br />BLM believes that in concert with that work, the channel could be aligned slightly to the right of <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 [o lengthen the channel length which could be achieved by adding a <br />meander or two. Any decrease in energy in [his 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 />970-244-3075 or Bruce Fowler at 970-244-3036. <br />Sincerely, <br />arian At n <br />Associate field Manager <br />cc: J. E. Stover <br />