FLOOD08971 - Laserfiche WebLink

Home Browse Search

2- ('i'l' TRI-LAKES REALLOCATION STUDY MEMORANDUM TO: RICK MINER, OMAHA DISTRICT USACE; LARRY LANG, eOLORADOWATER CONSERVATION BOARD GEORGE carrON, SIMONS & ASSOCIATES SOurnPIA1TE RIVER BRIDGE INFORMATION- TASK 3.06 03/23/01 GARY DRFNDEL, FOSTER WHEELER ENVIRONME."IT'AL FROM: SUBJECT: DATE: ce: DESCRIPTION OF THE WORK South Platte River Bridge Information. Obtain bridge plans on the South Platte River between the Adams-Weld County line and the Colorado-Nebraska State line. Organize the bridge plans and incorporate bridge geometry into the HEC-2 model between the Adams-Weld County line and the Colorado-Nebraska State line. The existing models will be field checked during the site visit for the existing HEC-2 models. The need foor additional cross section and bridge information will be determined and ~dded into the HEC,2 models. This task will require a site visit to view the channel and bridges in the ,tudy area. Model encroachments as described in Training Doctunent No. 30. Use of the encroachment options in HEC-2 removes the ineffective flow area from both conveyance and volume calculations. Using roughness values to model ineffective flaw areas is necessary for HEC-2 to compute the stage, volume date required for the Modified-Puis routing method in HEC-1. DESCRIPTION OF THE BRIDGE INFORMATION There are a total of 93 bridge crossing analysis-nodes within the various Study Reaches of the South Platte River. Of these 93 crossings, 42 are located between the Weldl Adams county line and the state line, and 51 are located in metropolitall Denver. Table 1 summarizes the bridge locations according to river mile. In general, there are more individual bridge ;-tructures than there are bridge analy;-is nodes. Typically, parallel bridges are analyzed as a single bridge. For example, the Colorado Depamnent of Transportation lists 78 bridges over the South Platte River in Weld, Morgan, Logan and Sedgwick Counties, which we coded as 42 bridge crossings in the HEC-RAS model. We obtained data on bridges located between the Weldl Adams COWIty line and the state line from the Colorado Depamnent of Transportation, the Burlington Northern Railroad, and tne Union Pacific Railroad. We made a field reconnaissance to check out missing or unclear informacion. We took additional measurements where needed using cloth tape to clarify information. Documentation of bridge geometly was vel)' sparse for Sedgwick COWIty and several railro,.d bridges.