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Last modified
10/11/2023 4:58:17 PM
Creation date
10/5/2006 4:26:10 AM
Metadata
Fields
Template:
Floodplain Documents
County
Logan
Community
Sterling, Atwood
Basin
South Platte
Title
Pawnee Creek Flood Mitigation, City of Sterling, Town of Atwood and Logan County
Date
7/1/1999
Prepared For
Logan County
Prepared By
URS Greiner Woodward Clyde
Floodplain - Doc Type
Flood Mitigation/Flood Warning/Watershed Restoration
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<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 />SECTIONTHREE Affected Environments and Environmental Consequences <br /> <br />Utility Notification Center for Colorado and obtain the precise location of each of the utilities <br />identified prior to the start of construction. <br /> <br />A water well used by the cemetery is located immediately adjacent to the proposed floodway that <br />would be constructed adjacent to the cemetery. Special coordination would be required by the <br />contractor to assure the well is not damaged. Special construction safety procedures would be <br />employed at all construction locations to assure that overhead power lines are not accidentally. <br />encountered during construction. <br /> <br />3.8.3 Alternative 3 . Pawnee Creek Overflow Cutoff <br /> <br />With Alternative 3, construction activities would affect power, telephone, and fiber optic lines at <br />the Riverside Cemetery location. As previously stated, the contractor would call the Utility <br />Notification Center of Colorado and obtain the precise location of each of the utilities identified <br />prior to the start of construction. <br /> <br />A water well used by the cemetery is located immediately adjacent to the proposed floodway that <br />would be constructed adjacent to the cemetery. Special coordination would be required by the <br />contractor to assure the well is not damaged. Special construction safety procedures would be <br />employed to assure that overhead power lines are not accidentally encountered during <br />construction. <br /> <br />3.9 HYDROLOGY I WATER QUALITY <br /> <br />The Pawnee Creek Drainage Basin originates in Weld County, Colorado, flows in a southeasterly <br />direction and crosses a portion of Logan County before flowing into the South Platte River <br />approximately 1 mile downstream (northeast) of Atwood. Overall the drainage basin has an area <br />of 645 square miles. Upon entering the floodplain of the South Platte River, the gradient of <br />Pawnee Creek becomes quite low. This condition contributes to flooding on Pawnee Creek in <br />the vicinity of CR 3 I and CR 33, with a recurrence interval of once every 10 years. When this <br />occurs, overbank floodwater on the south side of the creek flows overland in the general <br />direction of Atwood. The overbank flow on the north side of the creek flows overland in the <br />general direction of Sterling (Exhibit 9). These overland flows, as they are transported lower in <br />the basin, are physically separated by topography features from the floodwater associated with <br />Pawnee Creek. Therefore, these two split flows contribute to separate flooding situations. <br />Factors that contribute to flooding at each location are outlined below. Generally, flooding is <br />attributed to conveyance constrictions created by road, highway, and/or railroad embankments. <br /> <br />Presently, the Highway 6 and UPRR bridges over Pawnee Creek have the capacity to convey <br />approximately 1,800 cfs. Water in excess of the three bridges' conveyance capacity is ponded <br />upstream of the bridges and/or pushed north along Highway 6 into Sterling. The water remains <br />pooled upstream of the bridges until the inflow of Pawnee Creek is reduced below 1,800 cfs. <br />Overland flow on the north side of Pawnee Creek enters the northwestern side of Sterling and <br />unites with water from the Sand Creek Drainage as it flows through the residential and business <br /> <br />3-12 <br />
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