Laserfiche WebLink
<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />well graded sand and gravel or concrete sand, to ensure that it is <br />compatible with the embankment material and can meet permeability <br />requirements of approximately 5 feet per day. Because the material will <br />have to be imported, the quantities were minimized with the use of a 3-foot <br />wide chimney filter with a slope of .5 vertical to 1 horizontal (.5:1). In <br />addition to the chimney filter, perforated pipes encased in filter material <br />and laid horizontally at 30-foot intervals are recommended to intercept <br />foundation seepage and allow an escape path for internal flows. <br /> <br />With the limited amount of information available during the <br />reconnaissance study, it was assumed that a grouting program would be <br />required to reduce seepage through the underlying shale foundation. After <br />the drilling program was complete, this assumption changed~ The drill hole <br />information revealed the overburden above the shale was moderately <br />consolidated, had very low permeabilities, and would probably not require <br />any foundation treatment other than a partial cutoff into the overburden. <br />The shale core recovery, the quality of the core, and the permeability <br />tests indicate that the shale is tight and relatively impervious. <br />Additional drill holes and permeability tests will be required for the <br />final design. Based on the information obtained from the initial <br />geotechnical investigation, a cutoff into the overburden in combination <br />with a filter drain should be adequate. <br /> <br />Drawings showing typical embankment sections and the overall plan and <br />profile of the dam are included in Appendix B. <br /> <br />5.3 SPILLWAY DESIGN <br /> <br />The probable maximum flood (PMF) analysis used to determine the <br />spillway capacity is included in Appendix C. Three storms were considered <br />in sizing the spillway; the September general storm, the June general storm <br />with snowmelt, and the local thunderstorm. The local thunderstorm <br />controlled the spillway design, due to the high peak flow, short duration, <br />and the short length of the drainage basin. The local thunderstorm has a <br />peak inflow of 14,332 cfs and a runoff volume of 710 acre-feet. The peak <br />flow after routing the storm through the reservoir is 1562 cfs. The most <br /> <br />5-2 <br />