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<br />WWE
<br />
<br />Wright Water Engineers, Inc.
<br />
<br />DENVER OFFICE
<br />2490 West 26th Ave" Suite SSA
<br />Denver, Colorado 80211
<br />(3031480-1700
<br />
<br />TULSA OFFICE
<br />707 South Houston, Suite 302
<br />Tulsa, Oklahoma 74127
<br />(918) 584-7136
<br />
<br />GLENWOOD SPRINGS OFFICE
<br />818 Colorado Avenue
<br />P,O, Box 219
<br />Glenwood Springs, Colorado 81602
<br />(303) 945-7755
<br />Denver Direct Line: 893-1608
<br />
<br />Mr. Ben Urbonas
<br />February 27, 1986
<br />Page 2
<br />
<br />February 27, 1986
<br />
<br />A box culvert having a l5-year flood capacity is designed for Van Bibber
<br />Creek through the high value Arvada Plaza Shopping Center. With the pro-
<br />posed upstream detention facil ities, this box culvert will convey the
<br />100-year flood on Van Bibber Creek of 1,300 cfs. Without the detention
<br />storage, the 100-year flood would be 2,600 cfs at the Arvada Plaza Shopping
<br />Center. This would result in residual flooding.
<br />
<br />Mr, Ben Urbonas
<br />Urban Drainage & Flood Control District
<br />2480 W, 26th Avenue, Suite l56-B
<br />Denver, CO 80211
<br />
<br />Re: Agreement No, 83-1.6
<br />
<br />Dear Mr, Urbonas:
<br />
<br />The project as 1 aid out in this report
<br />be implemented without further delay,
<br />result in exposed flood hazard.
<br />
<br />The cost of constructing and implementing the project, in terms of 1985
<br />dollars, 1S approximately $33,000,000, This includes right-of-way,
<br />bridges, channel s, detention, dam rehabil itation and all other costs in-
<br />cluding an allowance of 30 percent for contingencies and engineering. The
<br />resulting benefits, measured in terms of reduced flood damages, exceed the
<br />project cost by a factor of two.
<br />
<br />is sound and practical. It should
<br />To wait a long period of time will
<br />
<br />The report entitled "Major Drainageway Planning Lower Ralston/Van Bibber/
<br />Leyden Creeks, Phase B Report" is attached, The engi neeri ng process i n-
<br />cluded regular meetings with the project sponsors and interested citizens.
<br />These meetings resulted in each portion of the streams receiving careful
<br />consideration during each step of the work from a variety of view points.
<br />
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<br />The flood control project presented in this report incl udes 12,7 miles of
<br />creek channel, 9 street bridges requiring improvements to pass the 100-year
<br />flood, 10 bridges to be improved to pass the 10-year flood, and 7 bridges
<br />which require no modification.
<br />
<br />The design call s for a major rehabil itation of the Leyden Lake embankment
<br />and spillway to reduce the risk to the downstream urban area from potential
<br />dam failure, The dam is classified as high hazard.
<br />
<br />Multi-use/multi-purpose detention storage facilities have been designed for
<br />Van Bibber Creek to store up to 187 acre-feet of flood waters during a 100-
<br />year fl ood. The mult i -use/mul t i-purpose rel ates to thei r use as soccer
<br />fields for recreational purposes,
<br />
<br />A structural European channel is planned for 2,3 mil es of the creek, most
<br />of which is in Ralston Creek, The European channel is designed for carry-
<br />ing the 10-year flood, however, because of normal freeboard and optimized
<br />depth of the channel bottom, the 10-year designed channel will carry most
<br />of the 100-year flood when running bank full. A low flow channel simil ar
<br />to the existing one will be included,
<br />
<br />An important aspect of the project is floodplain regulation and management.
<br />For instance, until the project is completed, construction in the flood-
<br />pl~'n must be subject to the floodplain regulation ordinances of Arvada or
<br />Jefferson County. An earl y warn i ng system is recommended. Moni tor i ng and
<br />inspection of Leyden Lake should be performed regularly.
<br />
<br />We have appreciated your cooperation and guidance.
<br />
<br />Very truly yours,
<br />
<br />
<br />WRIGHT WATER ENGINEERS, INC.
<br />
<br />By It." :>>-~..,~iJt-
<br />
<br />Kenneth R. Wr1gh~ P~--'
<br />Project Manager and Chief Engineer
<br />
<br />By ~ff~~~~
<br />
<br />Project Engineer
<br />
<br />MWG/KRW: ard
<br />
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