4 - Call Up: Floodplain Development Permit (LUR2009-00043) - Pedestrian crossing at Alpine Ave. between Broadway and 13th St.
MEMORANDUM
TO: Planning Board
FROM: Katie Knapp, Civil Engineer, Floodplain and Wetlands Permitting
DATE: June 25, 2009
SUBJECT: Call Up Item: Floodplain Development Permit (LUR2009-00043)
Pedestrian crossing at Alpine Ave. between Broadway and 13th St.
This decision may be called up before Planning Board on or before
July 9, 2009
A Floodplain Development Permit was approved by Planning and Development staff on
June 18, 2009. The project involves roadway improvements to replace and improve a
pedestrian crossing at Alpine Ave. between Broadway and 13th St..
The proposed project includes roadway resurfacing, regarding, narrowing the roadway at
the pedestrian crossing, installation of an ADA compliant at-grade pedestrian crossing
and replacement of existing drive entrances along Alpine Ave.. The 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. A copy of the floodplain
development permit and the application materials is attached.
This floodplain development permit was approved by Planning and Development
Services staff on June 22, 2009, and the decision may be called up before Planning Board
on or before July 9, 2009. There are no Planning Board meetings within the required 14-
day call-up period, so the call-up period has been extended to the next Planning Board
meeting date on July 9, 2009. Questions regarding this floodplain development permit
should be directed to Katie Knapp in Planning and Development Services at 303-441-
3273 or knappWbouldercolorado. ov.
Attachments:
A. Floodplain Development Permit
B. Application Materials
ATTACHMENT A
CITY OF BOULDER
J:, Planning and Development Services
1739 Broadway, Third Floor - P.O. Box 791, Boulder, CO 80306-0791
phone 303-441-1880 - fax 303-441-3241 - web boulderplandevelop.net
Land Use Review Floodplain Development Permit
Date Issued: June 19, 2009 Expiration Date: June 19, 2012
(Pursuant to Subsection 9-3-6(e), B.R.C. 1981)
Permit Number: LUR2009-00043
Contact Information
CITY OF BOULDER, PW UTILITIES
PO BOX 791
BOULDER, CO 80306
303-441-3242 Annie Noble
Project Information
Location: ALPINE AV BTW 13TH ST & BROADWAY
Legal Description:
Description of Work: FLOODPLAIN DEVELOPMENT PERMIT for a pedestrian crossing of Alpine
between Broadway and 13th.
Type of Floodplain Permit: Floodplain Review W/O Analysis
Creek Name: Goose
Flood Protection Elevation: 5,372
Conditions of Approval
The proposed project/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.
The applicant shall obtain a site inspection and approval from the City of Boulder Floodplain and Wetlands
Administrator upon completion of the project.
Improvements shall be constructed in accordance with the plans submitted as part of the floodplain
development permit application.
Prior to final inspection, the applicant must submit to Planning and Development Services as-built
drawings of the new pedestrian crossing and street improvements prepared by a licensed engineer in
accordance with City Standards.
The floodplain development permit if not appealed, is final 14 days after notification of issuance.
Inspections
To schedule an inspection, call 303-441-3280 and refer to your permit number (LUR2009-00043).
Final Floodplain Inspection
AT'rAC11MENT B
•
is 5y. a•A .:-June 2, 2009
Katie Knapp
Development Review Coordinator
City of Boulder
P.O. Box 791
Boulder, Colorado 80306
RE: 0912A - FLOODPLAIN DEVELOPMENT PERMIT FOR ALPINE
AVENUE PEDESTRIAN CROSSING IMPROVEMENTS BETWEEN
BROADWAY AND 13TH STREET
Dear Katie:
The City of Boulder Transportation Department is submitting this Floodpiain
Development Permit Application for pedestrian crossing improvements on Alpine
Avenue between Broadway and 136' Street and adjacent to the Ideal Market and
Community Plaza shopping centers. The project is located entirely within the floodway
of Goose Creek and the majority of the project area is located within the High Hazard
Zone. The project location and flood zones are shown in Figure 1.
The project will replace and upgrade an at-grade existing pedestrian crossing spanning
Alpine Avenue. The existing asphalt road surface will be replaced with concrete
pavement within the limits of the crossing. The roadway width will be narrowed from
approximately 39.5-ft wide to 25-ft for a running distance of approximately 61-ft. The
portion of narrowed roadway includes shopping center drives on the north and south
sides of Alpine as well as the proposed pedestrian crossing. The top of roadway will be
lowered by approximately 0.2-ft and the double crown in the existing roadway will be
eliminated. This improvement will reduce roadway cross slopes through the project area
and allow the new crossing to be ADA compliant. The improved crossing will greatly
enhance pedestrian safety and the project will replace the existing, deteriorated asphalt
pavement.
Four representative cross sections were cut through the project site. These cross sections
are shown on the construction plan sheet included in the Appendix. The project will tie
into the existing grades at Cross Section 1 on the east and Cross Section 4 on the west.
Equivalent conveyance calculations were performed to compare the existing and
proposed conveyance capacities at Cross Sections 2 and 3. Cross Section 2 is located
3
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PLANNING CIVIL ENGINEERING Figure 1
LANDICAPE
ENVIRO VICINTY MAP
ENVIRONMMENTAL CONSULTING
Ball Conlne west (ermeAy Love a Associates. Im.) 0 10' 500' 1000'
NO Jeflernea Avenua. Smote B t , Alpine Roadway Improvements
1303--673--9 95 f. ~isi9s City of Boulder Transportation E9
nwveQGeltcdAesweslcom NORTH SCALE IN FEET 6111109
Katie Knapp
June 2, 2009
immediately east of the proposed pedestrian crossing. Cross Section 3 is located on the
west edge of the adjacent shopping center drives. Base flood elevations (BFEs) at Cross
Sections 2 and 3 were determined using interpolation between the bounding regulatory
cross sections, Cross Sections 391 and 401. A Manning's n of 0.015 (pavement) was
used for the existing and proposed roadway cross sections.
Detailed cross sectional survey was completed by City of Boulder Transportation staff on
May 18, 2009. Additional topographic mapping for the project area was supplied by
Boulder Land Consultants on September 20, 2005 and extended in this area on April 21,
2009. All elevations are in NAVD 88 vertical datum. The proposed cross sections are
based on the City's construction drawings.
Conveyance calculations and existing and proposed cross sectional profiles are included
in the Appendix. Flow area increases slightly at Cross Sections 2 and 3 for proposed
conditions.
The roadway at Cross Section 2 is not fully submerged under existing conditions. The
crown of the roadway is above the BFE which was computed by interpolation between
the regulatory 100-yr water surfaces at regulatory Cross Sections 391 and 401.
Topographic contours indicate the presence of islands in the 100-yr floodplain in the
parking lots at Ideal Market and Community Plaza and along the roadway crown for
segments of Alpine, Broadway, and North Street between regulatory Cross Sections 391
and 401. Relatively small islands such as these are typically not delineated in the 100-yr
floodplain and they are not delineated in this instance in the Goose Creek floodplain.
Because the roadway surface at Cross Section 2 is lowered by the project, Cross Section
2 will become completely submerged under proposed conditions. Consequently, the
wetted perimeter and conveyance capacity increase at Cross Section 2 for proposed
conditions.
Goose Creek is a steep-gradient stream (a defined channel does not exist through the
project reach as the flow path is defined through parking lots and across roadways)
through the project area with rapidly varying BFEs. At Cross Section 3, the Alpine
Avenue roadway is completely submerged for both existing and proposed conditions and
the wetted perimeter is approximately the same for both conditions. Conveyance will be
increased by the project at Cross Section 3.
DISCUSSION OF FLOODPLAIN CRITERIA. ITEMS
Section 9-3-6(c) of the Boulder Revised Code requires a discussion of several floodplain
criteria items for a Floodplain Development Permit. These items are discussed below.
The Floodplain Development Permit Application form can be found in the Appendix.
1. The effects on the efficiency or capacity Conveyance capacity is increased within the
of the conveyance zone and high hazard Alpine Avenue roadway within the project
zone. area.
Katie Knapp
June 2, 2009
2. The effects upon lands upstream, Lands upstream and downstream of the project
downstream, and in the immediate area will not be impacted. The roadway in the
vicinity. project area will be lowered by approximately
0.2-ft. Roadway drainage to downstream areas
is maintained, with average gutter flowline
slopes of 2.2% (north gutter) and 1.2% (south
gutter) from Cross Section 2 to the
downstream tie-in at Cross Section 1.
3. The effects upon the 100-year flood The 100-yr flood profile will not be adversely
profile. impacted because the conveyance capacity
within Alpine Avenue will be maintained and
slightly increased.
4. The effects upon any tributaries to the No impact to tributaries or other drainage
main stream, drainage ditches, and any facilities.
other drainage facilities ors stems.
S. Whether additional public expenditures No.
for flood protection or prevention will be
required.
6. Whether the proposed use is for human No.
occupancy.
7. The potential danger to persons No change.
downstream and in the immediate
vicinity.
8. Whether any proposed changes in a No. The project impacts only an existing
watercourse will have an adverse roadway. No streambanks or wetland areas
environmental effect on the watercourse, will be impacted.
including without limitation,
streambanks, and streamside trees and
vegetation.
9. Whether the proposed water supply and Not applicable.
sanitation system and other utility
systems can prevent disease,
contamination, and unsanitary or
hazardous conditions during a flood.
10. Whether the proposed facilities will be No change.
susceptible to flood damage and the
effects of periodic flooding.
11. The relationship of the proposed The project is consistent with the principles of
development to the Boulder Valley the Comprehensive Flood and Stormwater
Comprehensive Plan and any applicable Utility Master Plan. The project fulfills a key
floodplain management programs. goal of the Comprehensive Plan by bringing
the pedestrian crossing into compliance with
ADA standards and improving pedestrian
safety.
12. Whether safe access is available to the No change.
property in times of flood for ordinary
and emergency vehicles.
13. Whether the applicant will provide flood No.
warning systems to notify floodplain
occupants of impending floods.
Katie Knapp
June 2, 2009
14. Whether the cumulative effect of the No change in flood elevations resulting from
proposed development with other this project. See response to question 3.
existing and anticipated uses will
increase flood levels.
15. Whether the expected heights, velocities, No adverse impact to flood levels, velocities,
duration, rate of rise, and sediment duration, rate of rise, or sediment transport will
transport of the floodwaters expected at result from this project.
the site will adversely affect the
development or surrounding property.
We thank you for the opportunity to submit this Floodplain Development Permit
Application and look forward to the issuance of a Flood Permit for the proposed Alpine
roadway improvements. Please contact us if you have any comments or questions.
Sincerely,
LOVE & ASSOCIATES, INC.
Prepared By: Brianna L. Wallace, E.I.
Inc
Reviewed By: David I /Love, P.E.
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Computer File Information Sheet Revisions aF BOU Colorado Deportment As Constructed BROADWAY RECONSTRUCTION (PINE TO IRIS) Project No./Code
Cre6m Date: Nay 26, 2W9 IUaN IN of Transportation ALPINE PEDESTRIAN X-ING
Last "ricatioa Dale: Iu°s-d sn,r No Rerisims: (BROADWAY TO 13TH) STU M110-045
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