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(4A N SER LIT,J AN & ASSO(IIATES <br />Hvdrogeolog,ieal and Environmental Consultants <br />Pre -Mining Topography <br />In order to accurately conduct a flood plain analysis prior to the existence of the Everist <br />Mine, it was necessary to obtain topographic data from a period before mining activities <br />commenced in 2004. These data need to reflect an undisturbed topographic surface <br />before any construction or earthwork began. <br />Pre -mining topographic data for this model were obtained from the 7.5 -minute digital <br />elevation model (DEM) data files from the USGS national elevation dataset (NED). <br />These data are digital representations of cartographic information in a raster form. DEMs <br />consist of a sampled array of elevations for a number of ground positions at regularly <br />spaced intervals. These digital cartographic/geographic data files are produced by the <br />U.S. Geological Survey (USGS) as part of the National Mapping Program. DEM data for <br />7.5 -minute units correspond to the USGS 7.5 -minute topographic quadrangle map series <br />and is based on 30- by 30 -meter data spacing with the Universal Transverse Mercator <br />UTM projection. Each 7.5- by 7.5 -minute block provides the same coverage as the <br />standard USGS 7.5 -minute map series. <br />The NED is a seamless raster product primarily derived from USGS 10- and 30 -meter <br />(DEMs), and, increasingly, from higher resolution data sources such as light detection <br />and ranging (lidar), interferometric synthetic aperture radar (ifsar), and high-resolution <br />imagery. The 3-D raster data file is from the same period of time that the 7.5 minute Fort <br />Lupton quadrangle map was generated and was used to create a 2-D contour map with 2 - <br />foot contours by interpolation algorithms using Autocad® Civil 3-D. <br />The pre -mine topographic map and cross-sections used as input data in the model are <br />shown on Figures 2, 4 and 5. The cross-sections depict the pre -mining topography with a <br />dashed line and existing topography with a solid line. <br />Existing Topography <br />The 2008 aerial survey topographic map submitted in the Deere and Ault report (2008) <br />was used as the current topographic surface of the study area. The map is presented on <br />Figure 3. Ineffective flow areas were used to represent natural and man-made <br />depressions. <br />Manning's Roughness Coefficient <br />Manning's roughness coefficient "n" was calculated from USGS curve rating data <br />measured at the Fort Lupton (U.S.G.S., 2013) gaging station located 1/2 mile to the north. <br />The curve rating data were obtained over a 10 -year period from 2003 until 2013 and <br />contain nearly 100 measurements. These measurements include channel velocity and <br />mean depth. The average channel velocity and average mean depth were calculated from <br />these data. Manning's "n" was back calculated from Manning's equation given by: <br />2 1 <br />1.49R3S2 <br />'U <br />n <br />-5- <br />