FLOOD04286 - Laserfiche WebLink

Home Browse Search

11-3 With the exception of 1-25 and U. S. 36, the existing bridges are generally too narrow for the traffic and inappropriate for thei r projected use. Except for Isolated cases, the floodway and floodplain a,'e generally In- tact with lIttle encroachment from land development. In some Instances, "hydraulically small" bridges and high embankmen1:s combine to cause flooding to areas which will not normally be flooded by a given storm, such as that from the 100-year return design frequency storm determined to be approprIate for use in this Prel imlnary De,; Ign durin~1 Phase A. There are a variety of publ ic and private entl ties involved di rectly and indirectly with this study. Some of these include: Urban Drainage and Flood Control District Adams County City of Westminster Jefferson County Colorado and Southern Railroad Union Pacific Railroad City of Broomfield Colorado Department of Highways Sanitation Water Districts Water User's AssocIations Federal Aviation Administration (Jefferson ::ounty Airport) The Department of Defense, UnIted States of America Numerous private land owners, businesses, corporations, and Irrigation companies Historically, large damaging floods have not been cause for noticing Big Dry Creek as a hlstorl cal drainage problem. Due to the presently undeveloped nature of the basin, damage to structures has been confined to low-cost, not too greatly used bridges and to Irdgatlon diversion structures. As the basin develops, large damagi ng floods wi II become more frequent, since urbanization has Its most noticeable effect on runoff from storms of lesser return frequencies. Hand In hand with urbanization without olannlng Is the Increased Inconvenience due to mo,'e frequently occurring high rates of runoff; the more criticai importance of maintaining normal and emergency access ac"oss Big Dry Creek; i1nd the more frequent damage to structures which could be bui lt In the flood- plain. Two embankments are cause for concern" At the lower end of the basin Is the UnIon Pacific Railroad embankment, '"hich is 35 feet in height and Is of earthen construction. Near the upper end of the basin, Sheridan Boulevard rises 24 feet above the channel bottom. Under future urbanization, both embankments woul d be oV'Htopped, resul tl ng in greater flooding than would historically occur. I t is Important to note that both embankments, and especially the Union Pacific embankment, have a profound effect In reducing the dOwnstream floodplain. It Is also impor- tant to note that total elimination of the constrictions caused by these embankments would cause an IncreaSe in the floodplain area and would be most noticeable in Weld County.