Laserfiche WebLink
• INTRODUCTION <br />In a notice of violation (NOV) dated August 8, 1986 and subsequently <br />modified on August 15, 1986, the Colorado Yampa Coal Company (CYCC) was <br />cited for violations at isolated locations where drainageway or channel <br />gradients have been oversteepened relative to approved topography. To <br />stabilize the oversteepened channel gradients cited in the NOV, Water <br />Engineering and Technology, Inc. has developed proposed channel <br />stabilization measures (Sheets 1 through 7). Sheet 2 of the enclosed <br />set of drawings delineates the areas considered. Profiles and typical <br />section details are shown on Sheets 3 through 7. The following sections <br />describe some of the important factors considered in developing these <br />channel improvement plans. <br />HYDROLOGY <br />Hydrology for the channel analysis was calculated using criteria in <br />the 1984 SCS Publication, Peak Flows in Colorado. Runoff rates were <br />evaluated assuming an antecedent soil moisture condition classified as <br />AMC II with a curve number of 82. For design purposes, these conditions <br />provide a conservative estimate of flowrates. Sheet 2 indicates the <br />10-year, 24-hour peak flowrates at each of the design points. Hydrologic <br />information is also summarized in Table 1. <br />CHANNEL IMPROVEMENTS <br />Using information provided by CYCC (1985 topographic mapping, scale <br />1 inch = 200 feet, 5 ft. contour interval), proposed channel profiles <br />shown in Sheets 3 through 7 were established. Locations of channels <br />cited in the NOV were determined using survey coordinate information <br />which was also furnished by CYCC. The extent of protection and brief <br />discussions of significant features at each specific area follow: <br />Area 51E <br />The Area S1E channel drains an area of 255 acres. Sheet 3 shows the <br />proposed profile and typical details for riprap channel improvements. <br />Riprap protection over a length of 455 feet at a slope of 15.1 percent <br />is proposed for stabilization of this location. <br />Area 51 <br />The relatively large drainage area (495 acres) contributing to this <br />location (See Sheet 2) necessitates construction of a 20 foot wide <br />channel with riprap lining. A slope of 15.1 percent with riprap <br />protection extending over a length of 445 feet is shown on Sheet 3. It <br />will be important to ensure that the two drainageways which have their <br />confluence upstream of the proposed riprap channel are configured so <br />that a smooth transition of flow into the riprap channel is achieved. <br /> <br />