2010-10-21_REVISION - C1982057 - Laserfiche WebLink

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length is approximately 1,578 feet. The channel design specifies a bottom width of 3 feet, an overall depth of 1.1 feet and a lining TRM. The observed channel bottom width was between 3 and 15 feet, its depth was between 1 and 3 feet and its lining was TRM. The as-built channel location deviates significantly from the design location, including its intercept location with channel PM-2 and the intercept locations of channels PM-2C and PM-213 at the upper end of channel PM-2B. The channel was well vegetated, with only minor erosional issues observed in the channel. There are two surge ponds in channel PM-2B. One surge pond is at station 8+06 and the other is at station 10+79. There was some erosion at the inlets and outfalls of each of the two surge ponds. The as-built channel profile for channel PM-2B is between 25 and 60 lower than the design profile due to changes in the post-mining topography and channel location. Based on the changes, the as-built channel is slightly steeper at station 10+79 and again from station 16+40 to station 21+49. The following chart shows the GPS data for post-mining channel PM-2B. GPS Height Northing Easting Z Corr. Correct Z Exh D Elev. Z Diff. Exh 20- 5.9 Station 7528.9 4470025.5 310002.8 40.620 7569.497 7570 0.503 7613 0+00 7581.5 4469946.6 310082.6 40.620 7622.112 7624 1.888 7651 3+68 7617.1 4469826.8 310141.3 40.620 7657.743 7662 4.257 7700 8+06 7627.6 4469749.7 310172.6 40.620 7668.251 7678 9.749 7729 10+79 7677.5 4469652.1 310196.6 40.620 7718.100 7728 9.900 7773 14+09 7732.7 4469597.2 310254.4 40.620 7773.314 7772 -1.314 7813 16+40 7791.3 4469522.0 310379.4 40.620 7831.945 7838 6.055 21+49 - Channel PM-2C was not walked during the inspection. Based on a comparison of the as-built channel and the designed channel it appears as though the as-built channel is much shorter and deviates significantly from the designed channel. As stated in the discussion of channel PM-2B above, channel PM-2C intercepts channel PM-2B approximately 250 feet farther east than the design shows. There is also an unnamed channel to the north of channel PM-2C that does not have an approved permanent, post- mining channel design. - Channel PM-2D runs from south to north and flows into the top end of channel PM-2B. The channel has an as-built length of approximately 1,680 feet and a designed length of approximately 1,513 feet. The channel design specifies a bottom width of 3 feet, an overall depth of 12 feet and a lining of either 6 inch riprap or TRM. The observed channel bottom width was between 6 and 15 feet, its depth was between 1 and 2 feet and its lining was 6-9 inch riprap and TRM, depending on the location. The as-built channel location deviates significantly from the designed location below stock tank T-26 and generally follows the designed location above the stock tank. There was some side- cutting on the east side of the channel below stock tank T-26 but the majority of the channel itself was stable and showed little erosion. The exception to this was the lower approximately 50 feet of the channel, where it intercepts channel PM-2B, where there was down-cutting in the channel of approximately five feet. The channel flows through a 24 inch culvert (under a remaining road) at approximately station 11+27. The culvert was clear at the time of the inspection. There were no erosional problems noted at the