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<br />, <br /> <br />-. <br /> <br />Quentin Bliss - URS <br />Pawnee Creek EA Information <br />Page 2 <br /> <br />latest version of the "CDOT Erosion Control and Stormwater Quality Guide" <br />which outlines the NPDES requirements and provides design guidelines for <br />erosion and sediment control systems. <br /> <br />. <br /> <br />4. The channel bottom width through the HWY 6 and railroad bridge opening will <br />be 110 feet wide. The channel side slope will be a 2: 1 (H: V) slope with rip-rap <br />used to protect the bridge abutments. All other locations .along the channel will <br />have 3:1 side slopes. The channel top width at the HWY 6 bridge location is 155 <br />feet at the downstream side and 170 feet at the upstream side of the bridge. These <br />distances are at the point where the existing ground line meets the proposed. The <br />conceptual design layout sheet shows the channel bottom widths and the locations <br />where the widths change. <br /> <br />5. A wetland delineation has been conducted and is provided in the enclosed <br />document titled "Wetland Delineation, Pawnee Creek Flood Control Project, <br />Logan County, Colorado". This document has been sent to the COE. The COE <br />has approved the delineation. A letter from the COE stating their approval of the <br />delineation is also included. <br /> <br />A meeting was held on site with the COE and EPA to discuss wetland impacts, <br />mitigation, and to review from project. The only impacts are at the South Platte <br />River. The COEIEP A would like to have the banks of the channel vegetated with <br />native willow stakes or clumps of native wetland plants taken from the existing <br />vegetation. Due to maintenance issues, no willow stake revegetation will be <br />allowed in the flood control channel bottom. A Wetland Mitigation Plan will be <br />required for the project. It did not appear that either the COE or EP A disapproved <br />of the project or it's impacts. URS should coordinate with Margaret Langworthy <br />with the COE at 303-979-4120. Enclosed is a copy of the meeting minutes. <br /> <br />. <br /> <br />6. Enclosed is a copy of the channel/South Platte confluence grading plan and a <br />profile of the flood control channel with a section through the South Platte branch <br />channel. The South Platte will be excavated 2 feet over a 470 ft long by 60 ft <br />width. A proposed drop structure is located at the upstream limits of the <br />excavation to isolate the movement of the channel bottom. This is the planned <br />action today that would produce the greatest impact the South Platte. During a <br />recent field visit, it was discovered that the 2 ft headcut in the South Platte branch <br />channel showing up in our survey from a year ago is actually a beaver dam. The <br />dam has been breached and rather than excavating 2 feet we may need to excavate <br />less than a foot or not at all. So, the final impact during construction may be a lot <br />less than currently planned. If this is the case, the drop structure may be <br />eliminated and the sediment issue you asked about is non-existent. If sediment is <br />a problem, it will be cleaned out on a regular basis (See Item 7). <br /> <br />. <br />