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<br />JCr-ld ~t IJ1U U\j.Jt: Nil vIII vr lJlc.rU.ll'tu <br /> <br />rHII !'iV. ~IU OCt UO~" <br /> <br />I, .v~ <br /> <br />J <br /> <br />PIONEER DRAINAGE DITCH <br /> <br />I <br />I <br />I <br /> <br />In order to develop the proposed improvements, the U. S. Anny Corps of Engineers created a HEC-2 <br />model by combining cross-section data from several existing HEC-2 files created by LeafIReI in 1983, <br />The COE then removed the undersized bridges and culverts from the model, and replaced them with <br />recently surveyed cross-sections of the ditch. Based on this HEC-2 model the COE determined several <br />lo.;ations where the existing ditCh does not have!: sufficient c,!-pacity for the lO-year event. The channel <br />improvement option was then used to determine the required channel cross-section for the insufficient <br />reaches. Where channel improvements were not able to contain the 10-year flows, the channel banks <br />were artificially raised to estimate the height of the levees required. . <br /> <br />I <br /> <br />The COE utilized hydrology from the LeaURCI 1988 Report to develop a hydro graph and route it <br />through the proposed North Division Detention Pond. A spreadsheet created by the COE was used to <br />calculate inflow. outflow, and volume for the pond. Again. a detailed description of the COE <br />hydraulics for the pond is included in their 1995 Report. <br /> <br />I <br />. <br />I <br /> <br />Plan n~cription <br /> <br />\ <br />100-Year Residual Floodplaln: The 100-year residual floodplain was delineated to represent the <br />benefits of the proposed improvements on Pawnee 'Creek and the subsequent elimination of the Pawnee <br />Creek Overflow; the benefits of the proposed Sand Creek improvements; and the improvements to <br />Pioneer Ditch itself. The 100-year residual floodplain presented on Map Sheets 3 and 4 was prepared <br />assuming that the Pawnee Creek improvements and the Pioneer Park Dani have been constructed. The <br />proposed improvements along Pioneer Ditch have very little affect on thecxisting 100-year floodplain <br />since these improvements are intended for the I Q-year storm. <br /> <br />I <br />I <br />I <br />I <br />i <br />t <br />i <br />I <br />t <br />l <br />I <br /> <br />Proposed Improvements: The COE 1995 Report identified several bridge and culvert crossings that <br />were significantly under sized. According to the CaE, locations where bridges n<i!ed to be significantly <br />upgraded in size or require other major improveDlents are as follows: <br /> <br />. BNRR <br />· Phelps Street <br />. Joining parking lots about 1,000 feet upstreaDl ofHWY 14 <br />· HWY 14 <br /> <br />It should be noted that the bridge in the parking lot about 1,000 feet upstream of HWY 14 nearly has <br />the capacity to convey the 10-year peak discharges CWTently. The CaE recommended that the bridge <br />deck be recoDstrUcted at a higher elevation in ord~ to maintain 0,5 feet of freeboard during the 10-year <br />stOrm. For the purpose of this tepOrt, it has been assumed that the existing bridge deck at this location <br />will not be reconstructed because It is in fairly g!xxJ condition. Rather, minor channel grading is <br />proposed under the bridge to create a larger opening, This proposed grading would create 1; 1 <br />sideslopes under the bridge; therefore, soil cement erosion protection is proposed to protect the bridge <br />and channel. <br /> <br />As discussed earlier, the special culvert routine of the HEC-2 program was used to size the proposed <br />roadway crossings. Double 10' wide X 10' tall reinforced concrete box (ReB) culverts will be <br />required at HWY 14 and Phelps Street to convey the IO-year peak discharge of 1,200 cfs without <br />developing the roadways. A single 8' wide X 8' taU RCB will be required at the BNRR to pass the 10- <br />year peak discharge of 672 cfs. <br /> <br />64 <br />