Laserfiche WebLink
<br />III-5 <br /> <br />t <br /> <br />1. Basin Characteristics <br />The entire study area was broken down into twenty-three sub-basins, ranging <br />in size from 14 acres to 311 acres (see Figure III-I). The separation of the <br />small sub-basin B-2 (14 acres) was necessary, as the runoff from the basin is <br />tributary to Bates Lake in a storm sewer for the 2 year storm only. The runoff <br />from a storm of greater magnitude is not tributary to the lake, since the water <br />surface in Bates. Lake would prevent even the low flows in the storm sewer from <br />entering the lake, <br />For each of the sub-basins, the area, length, centroid length, slope, <br />percent imperviousness, Cp and Ct values were determined for the existing and <br />future development. The parameters for the existing development were determined <br />from maps provided by Adams County and the City of Arvada. The existing develop- <br />ment areas were defined from the aerial photographs for the entire basin. The <br />future development parameters were defined by overlaying the existing zoning on <br />the undeveloped area, then recomputing the basin characteristics. A summary <br />of the existing and future condition parameters are presented in Table III-I. <br />The slopes of the sub-basins vary from 0.5% to 3.7%, with an average of <br />about 2%, The average imperviousness is about 41% for the existing development, <br />which will increase to about 55% for the future development. <br />2. Design Rainfall <br />A depth-duration-frequency graph for the Hidden Lake Major Drainageway <br />Planning Basin was obtained from the storm isohyetals presented in the Drainage <br />Criteria Manual(5), and plotted in Figure 111-2. A summary of the data plotted <br />on Figure 111-2 is presented on the following page: <br /> <br />" <br />