4 - Call Up: Thunderbird Lake Wetland Permit (LUR2009-00034)
MEMORANDUM
TO: Planning Board
FROM: Katie Knapp, Civil Engineer, Floodplain and Wetlands Permitting
DATE: May 11, 2009
SUBJECT: Call Up Item: Thunderbird Lake
Wetland Permit (LUR2009-00034)
This decision may be called up before Planning Board on or before
May 22, 2009
A Wetland Permit was approved by Planning and Development staff on May 8, 2009.
The project is a three-year trial management of Thunderbird Lake at Admiral Arleigh
Burke Park at 490 Mohawk Drive. The project includes the addition of dechlorinated
potable water to raise the water surface elevation and increase the surface area of the
lake. Also included in the project is the establishment of new emergent and shrub-scrub
wetland areas to mitigate impacts to existing wetland areas.
Project Background:
Admiral Arleigh Burke Park consists of 6.1 acres and includes Thunderbird Lake,
wetland vegetation areas around the periphery of the lake, a concrete walkway around the
lake/wetland complex, a gazebo and memorial, and irrigated and mowed bluegrass turf.
Thunderbird Lake has diminished in size over the past several years due to reduced water
inflows to the lake. Based on the city's wetland mapping effort in 2004, the lake and
adjacent wetland areas comprised 2.18 acres which corresponds to a lake surface
elevation of approximately 5315.0 ft. Currently, the lake elevation is at less than 5313 ft,
and the surface area is approximately 1.39 acres. As a result of lower lake levels,
wetland and riparian woody vegetation have become established in areas which were
formerly covered by water between the current water's edge and the maintained park
landscape.
Residents in the vicinity of Thunderbird Lake value the passive recreation opportunities
of Thunderbird Lake and have expressed their preference to restore the water level in
order to provide better views of the open water body and improve the water quality.
Many different management options were studied to address the residents concerns. The
different options were presented to the City Council on February 17, 2009 after being
presented to both the Parks and Recreation Advisory Board and the Water Resources
Advisory Board. City Council's decision was to proceed with a three-year trial during
which time the lake would be filled periodically with City tap (potable) water to increase
the lake's surface area.
i
Description of the Proposed Activity:
The City of Boulder Parks and Recreation Department has requested a City Wetland
Permit for management activities at Thunderbird Lake for a three-year period from May
2009 to May 2012. These activities would include addition of City tap water to increase
the lake surface area to approximately 2.3 acres. Water used for the initial fill would
come from one or more existing city water hydrants. The water would be directed into a
de-chlorination chamber equipped with Vitamin C tablets and then discharged through a
diffuser onto erosion control matting, to minimize disturbing nutrient-rich sediment on
the lake bottom. The lake water level would be monitored and additional water added as
needed to maintain the desired water surface elevation. Water quality would also be
monitored. Because much of the existing emergent and shrub-scrub wetland areas
around the lake would be converted to open water lake area, new emergent and shrub-
scrub wetland areas would be established to offset these losses.
The primary goals of the proposed activities are as follows:
1. Expand the lake surface area of Thunderbird Lake to a maximum of about 2.3 acres,
which is the surface area associated with an elevation of 5315.0 feet.
2. Improve the water quality of Thunderbird Lake.
3. Minimize the changes in wetland function by improving aquatic habitat and
mitigating changes in wetland types.
4. Improve lake conditions to provide opportunities for education and recreation in an
attractive, scenic, and safe setting.
This wetland permit was approved by Planning and Development Services staff on May
8, 2009, and the decision may be called up before Planning Board on or before May 22,
2009. There is one Planning Board meeting within the required 14-day call-up period on
May 21, 2009. Questions regarding this floodplain development permit should be
directed to Katie Knapp in Planning and Development Services at 303-441-3273 or
krlappk(r),bouldercolorado.gov.
Attachments:
A. Wetland Permit
B. Vicinity Map
ATTACHMENT A
CITY OF BOULDER
•r~~~' Planning and Development Services
7M r,
1739 Broadway, Third Floor P.O. Box 791, Boulder, CO 80306-0791
phone 303-441-1880 • fax 303-441-3241 • web boulderplandevelop.net
Wetland Permit
Date Issued: 5/8/2009 Expiration Date: May 7, 2012
(Pursuant to Subsection 9-3-9(k), B.R.C. 1981)
Permit Number: LUR2009-00034
Contact Information
CITY OF BOULDER PARKS AND REC
3198 BROADWAY
BOULDER, CO 80304
Project Information
Location: 490 MOHAWK DR
Legal Description: LOT 2 EXC SLY 54.76 W BLK 7 FR ASIER MEADOWS MOHAWK & PAWNEE
PARK PROPERTY ADDRESS: 000490 MOHAW K DR BOULDER
Description of Work: WETLAND PERMIT for addition of potable water to Thunderbird Lake.
Three-year trial period.
Conditions of Approval
The proposed project/activity is approved on the basis that it satisfies applicable requirements of Chapter
9-3-9, "Wetlands Protection," Boulder Revised Code 1981. Other wetland requirements as set forth in
Chapter 9-3-9 which are not specifically outlined in the conditions of approval below remain applicable to this
project/activity.
The wetland permit is for a three-year trial management of Thunderbird Lake with routine additions of
dechlorinated potable water. The permit also includes wetland mitigation and vegetation removal around
the edges of the lake.
The water shall be released in a manner to prevent erosion and minimize disturbance of sediment at the
bottom of the lake. If the water additions will flow through the wetland mitigation area prior to the
establishment of wetland vegetation, additional soil stabilization measures will be required in order to
protect newly seeded and planted areas.
Best management practices shall be applied to all phases of the project and shall conform to the
requirements of the "City of Boulder Wetlands Protection Program: Best Management Practices" adopted
July, 1995; and "City of Boulder Wetlands Protection Program: Best Management Practices -
Revegetation Rules" adopted July, 1998.
The wetland mitigation site shall be monitored annually during the three-year trial period. Monitoring
reports shall be submitted to the city of Boulder Planning and Development Services. If it is determined
that the restoration is not successful, then corrective measures will need to be established and
implemented to ensure a successful project. The following criteria shall be used to determine success:
At least 80% native vegetative cover
Invasive species on the Colorado Noxious Weed Inventory list-A shall be 100% eradicated.
Invasive species on the Colorado Noxious Weed Inventory list-B shall encompass no more than 10% of
the total cover of the restoration area.
Tree survival shall be 100%.
The water quality shall be monitored in accordance with the Thunderbird Lake Monitoring Plan. At a
minimum, the following parameters shall be tested monthly from April through October: dissolved oxygen,
water temperature, pH, phosphorus, nitrogen and water clarity (Secchi disk).
Lake levels shall be monitored weekly.during May through August and monthly from September through
April in accordance with the draft Thunderbird Lake Adaptive Management Plan. Water shall be added as
needed to maintain the established water surface elevation of 5314.0 - 5315.0 feet.
If during the three-year trial period it is determined that a different approach is needed for the
management of Thunderbird Lake, the wetland permit will need to be revised.
At the end of the three-year trial period, a revised wetland permit application shall be submitted to
Planning and Development Services for the long term management of Thunderbird Lake.
Prior to installation, details and proposed locations of interpretive signs shall be submitted to Planning and
Development Services.
The applicant shall obtain a site inspection and approval from the City of Boulder Floodplain and Wetlands
Administrator upon completion of the project.
Inspections
To schedule an inspection, call 303-441-3280 and refer to your permit number (LUR2009-00034).
Wetland Mitigation Inspection
Wetland Mitigation 2nd Year
Wetland Mitigation 3rd Year
Final Wetland Mitigation Insp
ATTACHMENT B
City of Boulder Vicinity Map
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Location: Thunderbird Lake
490 Mohawk Dr City of f
Review Type: Standard Wetland Permit Boulder
Review Number: LUR2009-00034 t_s t j The information depicted on this map is provided
as graphical representation only. The City of Boulder
Applicant: City of Boulder 1 inch = 400 feet provides no warranty, expressed or implied, as
the accuracy and/or completeness of the information
Parks & Recreation Dept contained hereon