4 - Call Up: 1498 King St. (LUR2008-00113) Floodplain Development Permit MEMORANDUM
TO: Planning Board
FROM: Katie I~~app, Civil Engineer, Floodplain and Wetlands Permitting
DATE: February 23, 2009
SUB.TECT: Call Up Ttem: Power 1498 King St.
Floodplain Development Permit (LUR2008-00113)
. This decision nzay be called up before Plaiming Board on or before
March 9, 2009
A Floodplain Development Permit was approved by Planning and Development staff on
February 23, 2009. The project involves construction of a fence within the flood
conveyance zone.
Tlic proposed project involves the construction of a fence that was designed to
automatically open during a flood event, allowing flood waters and debris to pass
through. Thc; applicant has demonstrated that the project will not adversely impact the
floodplain or cause a rise in the floodwater elevation during the 100-year flood event.
The application was reviewed by staff and indepe~idently reviewed by Alan Taylor, P.E.,
who reconunended that the permit be approved. A copy of the floodplain development
permit, the application materials, and the technical review letter from Alan Taylor are
attached.
This floodplain development penmit was approved by Planning and Development
Services staff on February 23, 2Q09, and the decision array be called up before Platming
Board on or before March 9, 2009. There are two Planning Board meetings within the
required 14-day call-up period on February 26, 2009 and on March 5, 2009. Questions
regarding this floodplain development permit should be directed to Katie Knapp in
Planning and Development Services at 303-441-3273 or knap~k c(~,bouldercolorado.~ov.
Attachments .
A: Floodplain Development Permit
B: Technical review letter fion1 Alan Taylor, P.E.
C: Application Materials
CITY ~®UL.®~R
~ Planning and Development Services
~7 ~ 1739 Broadway, Third Floor P.O. Box 791, Boulder, CO 80306-0791
-441-3241 ° web boulderplandevelop.net
phone 303-441-1880 fax 303
sand Use Review floodplain ®evelopment Permit
Date Issued: February 23, 2009 I~xpiration Date: February 24, 2012
(Pursuant to Subsection 9-3-6(e), B.R.C. 1981)
Permit Number: LUR2008-00113
Contact Information
DC VENTURES LLC
1535 APPLE VALLEY RD
LYONS, CO 80540
303-823-5121
Project Information
Location: 1498 KING AV
Legal Description: LOT 1 BLK 4 BELLEVUE PARK REPL AT PROPERTY ADDRESS: 001498 KI
NG AV BOULDER
Description of Work: Proposed fence in conveyancelhigh hazard zone.
Type of Floodplain Permit: Floodplain Review W/O Analysis
Creek Name: King's Gulch
Flood Protection Elevation:
Conditions of Approval
° The proposed pr-oject/activity is approved on the basis that it satisfies applicable requirements of Chapter
9-3-3, "Floodplain Regulations," Boulder Revised Code 1981. Other floodplain requirements as set forth in
Chapter 9-3-3 which are not specifically outlined in the conditions of approval below remain applicable to this
project/activity.
Construction activities must not change existing grades.
° Improvements shall be constructed in accordance with the plans submitted as part of the floodplain
development permit application.
The fence shall be constructed as shown on the plans. No landscaping or other obstructions will be
° allowed that would impede the automatic opening of the fence pannels during a flood event.
° l'he fence shall be securely anchored to resist damage and washing away as debris during flooding
events.
The applicant shall obtain a site inspection and approval from the City of Boulder Floodplain and Wetlands
° Coordinator upon completion of the projects. Please call Katie Knapp at 303-441-3273 to schedule a final
inspection.
° Certification by a Colorado Registered Professional Engineer that the development has been completed in
compliance with the approved floodplain development permit application and that all conditions have been
fulfilled must be submitted to the city of Boulder prior to scheduling final inspections.
ii
9nspections
To schedule an inspection, call 303-441-3280 and refer to your permit number (LUR2008-00113).
o Final Floodplain Inspection
_7
`y~
/~,L,AN ~AIf~.Q~. ~QNSU~.TING~ L~~ -a
Alan Taylor, P.E., CFM r
-
1167 Purdue Drive
Longmont, Colorado 80503
Phone: 720-334-9260 FAX: 303.772.8805 email: taylor alan comcast.net wwvr.taylorconsult.com
Nebniary 20, 2009
M Ic atie Knapp
1'laruung and Development Services
] 739 Broadway, Suite 300
Boulder, Colorado 80302
R1~:: "Technical Review of Conveyance 7,one >Hence Desi;;n for 1498 King Street
Dear Katie:
I reviewed the design for a proposed fence locat~:d along Icing's Gulch within the conveyance
zone submitted in the floodplain development pf;i7nit application for 1498 I{ing Street, dated
December 18, 2008, and supplemented with the design memorandum dated January 29, 2009.
The application provided enough detailed information about the proposed fence to complete this
review and offer a recommendation that the permit be approved.
The proposed concept to constn~et the fence using independent panels that are designed on
hinged posts to swing open to a position paralle' to flood waters is innovative a~ld in line with the
conveyance zone standards that prohibit improvements that obstruct flows and create a rise in
flood elevations. The affected fence panels are to be located along the right overbai~k area of
King's Gulch outside the main incised, rock-lined channel section where depths are expected to
be shallow. The "pontoon fence" panels are each fitted with an 8-foot by 0.5-foot by 0.25-fool
aluminum sealed float along the base rail that when submerged offers 62.4 pounds of uplift to
raise the 40.1 pound aluminum "wrought-iron" styled section. Less than 0.5 feet of flooding
depth will raise each pontoon fence section, allowing it to hinge open like a door to pass flood
waters without obstruction.
A total of 14 well-anchored fence posts will be placed along the overbank area of King's Gulch
to support the pontoon fence panels. The posts run parallel to the creek flow and are to be spaced
8.5 feet apart to accommodate the 8-foot fence panels. Soine consideration was given as to
whether the posts alone could create a flood obstruction based on the proposed spacing. Because
flood flows along the fence will be shallow, with projected depths less than 1.5 feet, and
upstream conditions through reasonably maintained yards reflect limited debris, it does not
appear that the posts will cause any adverse conditions.
The existing dwelling at 1498 King Street was constructed in 2006, and replaced a 1951
dwelling. The new structure was designed for floodplain conditions with floors elevated above
flood protection levels and pass-through vents in the foundation to eq~ialize hydrostatic pressures
1
-tea-~n~~
during flooding. The proposed fence will provide ail enclosed yard for the new residence and
will not adversely affect the building, floodplain or neighboring properties.
I11 COnC1US101], the floodplain development permit application for the proposed pontoon fence
design at 1498 King Street appears to meet the conditions of Boulder's floodplain regulations for
the conveyance zone. I am satisfied with the fence design and the proposed project overall and
recommend approval of the floodplain development permit.
Sincerely
_ !
/ ,
Alan Taylor
nluZ Taylor Consulting, LLC -
Colorado Registered Professional Engineer I,icensc No. 27075
Alan Taylor Consulting, LLC ~ 2 of 2
ENG/N£~fR/NG Professional Engineers
Civil Engineering
CONSULTAMS
TW J
January 29, 20Q9 `~'d r~~
Design Memorandum . r
To: Tim K er Desi Com leaf ~
y ~ ~ p ~FJS/• • •
Lyons, Colorado OfJAt_ _
~:z~'
Project: 1498 King Street, Boulder, Colorado JLB Project No. 1321
Subject: Fence Design - Floodway
Objective: Provide a fence design that will not impact the flood way.
Parameters: Design a fence section that will remain closed during normal periods and then
open upon engagement of the flood waters in the conveyance zone of Kings
Creek. Create a fence panel design that once open, will be able to swing to clear
any potentially caught debris to not increase the elevation of the flood plain.
Conclusions: A lightweight pre-fabricated aluminum fence panel with attached extruded
aluminum tubing along the bottom will provide the required parameters. The
fence panel will have standard mechanical connections on the upstream side to
utilize a j-bolt connection to a sleeved connection to the end posts. The sleeved
connection allows for the j-bolt to move up and down with the panel, and to swing
as a hinge. The downstream connection will be a fabricated tab mechanically
attached to the panel which sits inside a c-channel welded to the fence post. The
c-channel depth is set to hold the fence panel in place during normal periods, then
to allow the fence to swing open when the required depth of buoyancy is
achieved. The extruded aluminum tubing is connected to the bottom member of
the fence panel to provide for greater surface area and depth displacement for
Buoyancy.
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1=loodplain Development Plans for Boundary Fencing ~=;~.~t!~-
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Floodplain Development Plans for Boundary Fencing
January 25, 2009
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Floodplain Development Plans far Boundary Fencing '
January 25, 2009 DETAIL PLAN- FENCED AREAS ON NORTHERN PORTION OF LOT
(scaled as noted) (AREA INCLUDES ENGINEERED SECTIONS OF FENCE IN FLOODYVAY
- SCALE=1"=10'
Retention pin; provide 1"
Bolt-on bracket; steel retent (panel is buoyant at
tube welded to plate approx 1-29!32" water
depth)
Std. J-bolt as hinge pin
Welded brace with drill
y hose to receive
retention pin
BUOYANCY CHAMBER:
TYPICAL ALL PANELS 6"w x 3"h extruded
Pre-fab aluminum fence aluminum tubing (b463 T-
panel; modifi~ as noted 52) with welded end caps.
(Design based upon Melds must provide water
Ameristar Classic 5hi 3 rail tight seal. Weld to bottom
or approved equal) of pre-fab aluminum panel
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ELEVATION
PLAN
Stagger panels to accomodate falling grade.
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NOTE: T~15 S~GTION TO B~ USED IN I^'LOODPL~IK ~R~~S ONLY;
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1=loodpiain Development Plans.for Boundan,~ Fencing
January 25, 2009
(scaled as noted) TYPICAL FENCE SECTION
112"=1-0"
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TYPICAL D1MEN5fON5
Contractor to ensure that no part of the fencing
in the floodway 'ss unprotected by the use of
buoyant, hinged sections as shown in the
plans. YVhere fence crosses boundary from
floodway into floodplain, make sure hinged
section protrudes into floodplain at least 2
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fence panel hinged aluminum
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1498 King Avenue F, _
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Floodplain Development Plans for Boundary Fencing
January 25, 2009
(scaled as noted) HINGED FENCE PANEL DETAILS
1 l2"=1'-0"