GENERAL54540 - Laserfiche WebLink

Home Browse Search

inlet structure to reduce erosion in this area. The existing diversion structure shall remain undisturbed and be utilized for the new inlet. As proposed, the irrigation water shall be transported through the project area in a 15 inch diameter high density polyethylene pipe with corrugated exterior and smooth interior wall at a grade of about 1.1 8. The pipe shall be buried about three feet deep below the top of the regraded coal waste. With an additional one foot of overlying soil, the total depth of burial below the final ground sur ace will be about four feet. Vertical risers will be installed about every 160 feet along the pipeline to serve as inspection ports and cleanout tees. Regraded waste material within the project area shall be covered with a layer of soil material about one foot thick which will be obtained from the permitted mine refuse disposal area. The topaoiled area will be fertilized, mulched, and seeded. Erosion control netting or a chemical stabilizer may be utilized in certain areas. Willows shall be sprigged along the entire north bank of the creek to encourage their re-establishment, which will aid erosion control and improve aquatic habitats. Other tree and bush species may also be planted for these purposes. It should be recognized that our final design, ae described above, will not completely eliminate the possibility of future erosion of coal waste material immediately adjacent to the river. The proposed project will, however, achieve several very beneficial ennvironmental accomplishments, including the following: 1) the volume of coal waste material eroded from the site during any particular flood event should be reduced by at least one and perhaps as much as two orders of magnitude, 2) the sharp, nearly right-angle bends in the channel created by the placement of coal waste over the river's floodplain shall be eliminated, which not only minimizes the volume of coal waste subject to erosion, but also reduces the erosive effects of flood waters on the stability of the embankments for the mine's sediment ponds and railroad tracks, 3) the on-going problem of reduced flow capacity in the irrigation ditch and poor equipment access due to sloughage of coal waste into the irrigation ditch will be mitigated, 4) the potential for creation of a new river channel along the existing irrigation ditch alignment during a major flood event and concomitment extensive erosion of farmland and possible damage to dwellings ie precluded by the backfilling and topaoiling of this area, and 5) since the effect of installing riprap on a river's dynamic equilibrium cannot always be readily predicted, our proposed design, which simply involves widening the channel and flattening the channel bank slopes to more closely approximate the natural channel configuration, should reduce the likelihood of serious erosion affecting areas on the opposite side of the channel or immediately downstream of the project area.