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PROJ00202
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Last modified
11/19/2009 11:43:11 AM
Creation date
10/5/2006 11:43:11 PM
Metadata
Fields
Template:
Loan Projects
Contract/PO #
C153474
Contractor Name
Oak Creek, Town of
Water District
0
County
Rio Blanco
Bill Number
XB 99-999
Loan Projects - Doc Type
Feasibility Study
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<br />I <br />I <br />I I <br /> <br />-18- <br /> <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 />IV.4 Incremental Damage Assessment (IDA) <br /> <br />Introduction - Rules and regulations of the SED will permit spillways of <br />lIhigh hazardll dams with capacities less than that required to safely pass a <br />PMF, provided that no significant incremental impacts occur downstream of the <br />dam in the event of dam failure during a flood. The process of evaluating <br />incremental impacts of dam failure for purposes of spillway design is a rela- <br />tively new concept. Colorado is one of only a few states in the nation that <br />will consider the design of spillways based upon an IDA. <br /> <br />The IDA is based on a comparison of the flood conditions for both base <br />flood conditions and for the base flood plus dam break flows. The incre- <br />mental difference between these two cases is evaluated according to two cri- <br />teria: <br /> <br />1. Incremental property damage potential. - In this case, if the incre- <br />mental increase in flow depth is less than 1 foot, the SED considers <br />the potential of incremental property damage to be negligible. <br /> <br />2. Incremental loss of life potential. - In this case, if the mathemati- <br />cal product of velocity times the flow depth in the incremental zone <br />is less than 7 (square feet per second), or if the incremental depth <br />of flow is less than 2 feet, the SED considers the potential for <br />additional loss of life to be negligible. <br /> <br />Base flood flows are generally those that pass through the spillway and <br />over the top of the dam to the point where dam failure begins. The base flood <br />also includes consideration of tributary flows from adjoining catchments <br />downstream of the dam but above the point in question, as per SED guidelines <br /> <br />In the case of Sheriff Reservoir, the first significant property develop- <br />ment is located approximately 6 miles downstream of the dam, off of the <br />National Forest property. Because the National Forest property provides a <br />buffer against any future property developments, the IDA analysis completed <br />for Sheriff Reservoir was aimed at meeting the above criteria at and below the <br />National Forest property boundary, where existing and possible future develop- <br />ments are, and would be, located. The paragraphs that follow describe the <br />results of the Sheriff Reservoir IDA and conclusions regarding required flood <br />routing protection. <br /> <br />Downstream Conditions - The study reach for the IDA was approximately 8 <br />miles in length, with an upstream boundary at the toe of the Sheriff Reservoir <br />Dam and a downstream boundary at the Knotts Ranch located just downstream from <br />the mouth of Trout Creek Canyon (see Fig. 4). Important features along Trout <br />Creek in the study reach, along with their distances downstream from Sheriff <br />Reservoir Dam, are as follows: <br /> <br />1. 2.4 miles downstream from the dam is the Dunkley Pass U.S. Forest <br />Service road. The road crosses Trout Creek via an earthen berm that <br />is approximately 4D feet high. A 13.5-foot-diameter eliptical <br />culvert conveys Trout Creek beneath this earthen embankment. The <br />characteristics of this embankment were incorporated into our routing <br />analysis. <br />
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