6 - Update on Fourmile Canyon Creek and Wonderland Creek Flood Mitigation Master PlanningCITY Or BOULDER
AGENDAITEM
WAT~R RESOURC~S ADVI50RY BOARD
MEETING DATE: Apri121, 2003
SUBJECT:
U date on Fourmile Can on Creek and Wonderland Creek Flood Miti ation Master Plannin
REQUESTING DEPARTMENT:
Public Works Department - Utilities Drvision
Ned Williams, Assistant Director of Pubhe Works for UtihUes
Bob Haiberg, UtiliYies Projects Coordmator
BOARD ACTION R~QUEST~ll:
None at this time. Staff will be returmng to the Board with the Wonderland Creek restudy and
the I'ourmile Can on Cieek alternative evaluat~on in the fall.
Puraose•
This item provides the WRAB with an update on the status of Flood Mitigation Master Planning
for Fourmile Canyon Creek and Wonderland Creek
Background•
On April 1Q 2002, the WRAB received an Informahon Item regardtng the Fourmile Canyon
Creek and Wonderland Creek Flood Mitigation Plamm~g status. At that time the city and the
Urban Dramage and Flood Control District (UDFCD), woiking wrth Love & Associates, Inc.,
were proceedmg with a prelimmary design for contamment of spill flows from Fourmile Canyon
Creek based on direchon from City Council received in October 2000. The Selected Plan and
excerpts from the Phase B Prelimmary Design report weie included as attachments to the April
10, 2002 memo At the followmg WRAB meeting on May 13, 2002, Ned Williams provided a
staff update regarding the pio~ect Based on comments fiom the IRP, staff decided to delay the
master plans foi the Fourmile Canyon Creek and Wonderland Crcek floodplams until the city
could determme and implement a floodplain management policy that addressed the issues m a
larger manner. Staff is currently investigating floodproofing as an alternative to contamment of
the spill ilows, contmumg to inveshgate downstieam impacts of spill contamment, and prep~ving
a revised floodplam map for Wonderland Cieek based on existmg (non-containment) conditions.
Analvsis•
Evalualion of the floodproofing alternaYive ~equires that ihe study area be expanded to include all
areas impacted by the spill flows from Fourmile Canyon Creek mto Wonderland Creek and
Goose Creek, as well as the shallow flood spill areas between these drainageways. This
alteinative considers the costs and benefits of floodpioofing mdividual strucCures within these
floodplam areas, assuming no drainageway improvements along Pourmile Canyon Creek are
consuucted. The city and the Urban Dramage and Flood Control DistncC (UDFCD) have
contracted Love & Associates to peiform the flood-proofing evaluation with an expected
completion of the sCudy in late summer 2003
In order to regulate the additional floodplam areas resulting from the spill flows from Fourmile
Canyon Cieek, the existing hydrologic condihons are bemg used to delineate a revised floodplain
for Wonderland Creek and othei aieas impactcd by the spill. This remapping study is expected
to be completed m the summer of 2003 and will be taken through the pubhc process for a L.etter
of Map Revision m the fall. The current regulatoiy mapping for Fourmile Canyon Creek is
conservative and will be retained as iegulatory until the completion of the Master Plan.
Mitigation alternatives for properties m the counry along Fourmile Canyon Cieek downstream of
Highway 119 are still bemg mvestigated to fully understand the impacts and opportunides
associated wrth containment of the spill flows Options bemg considered mclude regrading of
fields to improve flood storage and conveyance, floodproofing of mdividual structures, and
channel improvements.
Neighborhood meetmgs and newsletters have been used to keep citizens informed about the
project The next newsletter is currently bemg prepared and will be sent to all residents in the
Fourmile Canyon Creek and Wonderland Creek floodplams, as well as the newly identified
floodplain areas resulting from the spill flows The newsletter will include a map of the newly
identified floodplam areas in addition to the regulatory 100-year floodplam,llood hazard
mformahon to increase public education and awareness, and information on floodproofmg
techniqucs that individual property owners may choose to install prior to completion of the
current studies A copy of the potential 11ood hazard noCification map fiom the newsletter is
mcluded as Attachment A to this memo.
When the remapping and floodproofing studies are completed, a public open house will be held
to present the results and to request comments from crtizens. The remapping study and the
alYeinative evaluahon will be taken to Yhe WRAB, the Plamm~g Board, and the CiYy Council in
the fall of 2003.
For addiYional mformation, please contact Nancy Stemberger at 303-441-4111 or
SteinberQerN@ci.boulder co us
Attachment A• Potential 11ood hazard noYification map for Apri12003 newsleYter
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LEG~ND
~aPII.L FLOW G~NERAL G3(RECTI~N ~
FEDER/k~, EM~RG~NCY fv1ANA~EMENT AG~NCY
f~EGUI.ATORY 1b0 YEAR FLC7pqPLAINS
AREftS ROTENTIALLY AF~ECTED BY ~FILL
FLC)W5 BETWEEN; FC1UFtMILE CANYC?N GREEtf ~y'Y ~~
AND WONpERLANO GREEK, WqNqEF2LANL?
G{~E~K AND EI~MERS TW~MiI.E CREEK,
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