PERMFILE128204 - Laserfiche WebLink

Home Browse Search

The "maxir..um probable flood" is ar. essential part of the engineering studies for a mining project of wide scope and comp]exity. In the case of the ongoing ;!estmorelar.d operation, an estimate of the magnitude of this flood is a must not only fur the reasons stated above, but also from the standpoint of compliance with Federal and State la~•rs. Again, as pointed out by the USi;P, (1973), it is the unusual • event or series of events that produce the great .floods." Fecent exper- ience during the past 11 years (1905, 1969, 1973, and 1976) should be proof enough that large floods can and do happen in Colorado. Often, a misconception prevails that the absence of flooding in a particular area during the past 1C, 25, or perhaps SO years somehow ma4:es that area im-rune frog. high water. To ignore the Dossibility of flash floodir,c in the cesign construction, and opera?ion of major engineering works, simply on the strength of recent experience is to court disaster. In this report, the flood potential that exists in kestmoreland Canyon is evaluated, and a drainage plan for coping with extreme runoff is proposed. Flood Potential in Upper 4.'estmoreland Canvon kestmoreland Canyon, a tributar}• of Stevens finch (Figure 1) drains only ]67 acres; hence runoff resulting from a short intense burst of rain- fall r,i11 produce the highest peaks. The Ph1TS suggested for design by the USGR (1973) is a point rainfall of approximately 7.5 inches in one hour as sho~•+n in Figure 2. Prior to estimating the runoff that might be produced from this design • storm, an assessment was made of: (1) property ownership, (2) the areas impacted by Wining operations to date, and (3) the relationship of this watershed to (1) and (Z). Figure 3 sho~:~s that the tract owned by 41est:r.ore= land Coal is completely surrounded by land owned by the Eureau of Land "'.un~,~ement (6Lh1). Secondly, as seen in Figure 1, the watershed of ldestmore- land Canyon occupies both public and private land.