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The Boulder Creek Corridor Projects:
Riparian Ecosystem Management in an Urban Setting 1
David W. Crumpacker
2
Abstract.--Protection of the riparian corridor of
Boulder Creek is a major priority of the citizens of Boulder,
Colorado. A description of how this is being accomplished
and how the corridor will be managed for the benefit of the
community is presented.
INTRODUCTION
Frederick Law Olmsted, Jr., Harvard professor and
nationally known landscape architect, presented a
plan for preservation of Boulder's mountain
backdrop and streams as open space (Walker 1977).
Nothing-was done for many years. Then the City's
population grew from 20,000 in 1950 to 38,000 in
1960, causing concern about loss of open space.
Citizen action came in 1958 with an amendment to
the City charter that established an elevation
line of approximately 5600 feet above which the
City would not supply water. This was intended to
stop development of the mountain backdrop. However, the City had grown to 67,000 by 1970 and
development pressures were increasing rather than
abating. In 1967 the citizens voted a 0.4 percent
sales tax to be used for acquisition, protection,
and maintenance of open space lands (the "greenbelt" program). The City grew to 80,000 in 1975
during a period that coincided with the passage of
NEPA and other landmark federal environmental
legislation. The citizens responded again with
passage of a charter amendment in 1971 authorizing
the City to issue bonds that would allow more
rapid acquisition of open space and which could be
paid off with future sales tax revenues. A
citizens' Open Space Board of Trustees was formed
in 1973 to recommend additional acquisitions to
the City Council and a Boulder Valley Comprehensive Plan that united the City and Boulder County
efforts to preserve open space was adopted in
1978.
Boulder Creek is formed by the union of
Middle and North Boulder Creeks 5 miles west of
the City of Boulder, Colorado which lies at the
base of the first Rocky Mountain uplift from the
Great Plains. The Creek leaves Boulder Canyon at
the western edge of the City where its mean
annual flow approximates 100 to 200 cfs and it is
classified as a 5th order stream. From this point
it flows east northeast for 3.5 miles through the
City with a mean annual flow near 50 to 100 cfs
as a result of diversions, and thence northwest
18 miles through farms and rangeland to its
confluence with St. Vrain Creek (pers. commun.,
Gary Lacy, Boulder Creek Project Coordinator,
1985).
Boulder Creek is the major natural feature
of the Boulder Valley and has been since the City
was founded on its banks in 1859. Its rocky
substrate extends to a point well below the City
.of Boulder and it is classified by the State as a
coldwater fishery throughout the City. It has
very good water quality for aquatic life (Lewis
and Saunders 1984). The physical habitat is less
satisfactory because various sections through the
City have been channelized or otherwise stabilized
and only parts o~ the original riparian vegetation
remain.
CONTEXT FOR PRESERVATION
Formal recognition of the need to preserve
Boulder Creek occurred as early as 1910 when
1
Paper presented at the First North American
Riparian Conference, "Riparian Ecosystems and their
Management: Reconciling Conflicting Uses,"
Tucson, Ariz., April 16-18, 1985.
2
David W. Crumpacker is a Professor ofEnvironmental, Population and Organismic Biology, University
of Colorado, Boulder, CO, and Ecological Consultant to the City of Boulder, CO.
389
The City now owns approximately 14,000 acres
of open space, mostly on the mesas and plains, in
addition to its 5,600 acres of mountain parks and
reservoirs. The open space purchases have totaled
$36,600,000, not including interest on notes and
bonds. The land has been acquired by immediate
purchase, rolling options (seller agrees to sell
property at a fixed price in pieces over time),
notes and deeds of trust and, as a last resort,
condemnation. The flexibility obtained from
borrowing money through bonds, backed by the
steady income from the sales tax, is a powerful
approach. Important parts of the open space lands
are left in agricultural use under City super-
vision in order to provide income for maintenance
of the properties.
The City has now embarked on an exciting
series of riparian projects. Four will be
discussed, beginning upstream near the mouth of
Boulder Canyon and continuing downstream 9 miles
into the plains.
UPPER BOULDER CREEK CORRIDOR
This project involves 3.5 miles of the
riparian corridor from near the canyon mouth to
55th Street. This reach of Boulder Creek passes
through some of the City's busiest commercial
areas and 5 urban parks before it reaches the
vicinity of the Boulder Creek Cottonwood-Willow
Grove. The project goals are to enhance the value
of the riparian corridor as a place for both
active and passive recreation, provide a major
link to ~xisting and proposed bike and foot trail~
and simultaneously enhance the fish and wildlife
habitats (City of Boulder, Department of Planning
and Community Development 1984). Relatively
undisturbed parts of the corridor will be
preserved, while undeveloped but disturbed areas
will be restored and improved. The stream channel
including banks will be rehabilitated for aquatic
life and a diversity of native vegetation will be
planted as needed. Developed areas will continue
to provide formal parks and recreational
opportunities. Trout populations will be established and a fish management plan put into effect.
Consideration will be given in the stream design
to improvements for rafting and kayaking during
high flows. Trails and bridges will be designed
to direct traffic away from ecologically sensitive
areas.
The City and cooperating public agencies such
as the Boulder Valley School District and the
University of Colorado currently control more than
95% of the land required for a continuous trail
system in this part of the Boulder Creek Corridor.
Selective acquisitions will be made over time to
add unique or sensitive ecological areas, trail
system entries and linkages, scenic amenities,
and properties that will contribute to flood
management.
of "protecting the environment to a reasonable
degree.'' As a result of this legislation and
subsequent action, the State now owns a junior
water right for 15 cfs in Boulder Creek through
the City. In addition, the State recently purchased
a fairly senior water right in the same reach for
1 cfs during summer, with financial and legal aid
from the Nature Conservancy, a national, private,
non-profit organization dedicated to the preservation of ecologically significant lands and waters
(pers. commun., David Harrison, president of the
Colorado State Chapter of the Nature Conservancy).
The deal was complex, involved initial purchase
from a private party by the Conservancy followed
immediately by sale to the State, and took several
years to accomplish. This transaction is very
significant because it represents the first
transfer in Colorado of an agricultural water right
to an instream flow water right. The City's
Utility Department owns numerous senior water
rights and a senior exchange water right that
provide supplies in excess of its municipal needs
in most years. Development of a strategy to
manage the excess can provide some degree of
minimum flow in Boulder Creek throughout the City
in all but the driest years. Deep pools in the
rehabilitated stream channel can also help to
protect fish during extreme low flow periods.
Nearly $2,000,000 has been included in the
City's capital improvements budget over the 5-year
period of 1984-1989 to support Phase I of the
Boulder Creek Corridor Plan, i.e., the upper part
of the corridor. This includes maintenance and
management as well as improvements and limited
acquisitions. Potential sources of additional
support include the Urban Drainage District, state
lottery funds, federal grants, and private fund
raising.
BOULDER CREEK COTTONWOOD-WILLml GROVE
On the City's northeast edge near the downstream end of the upper corridor, Boulder Creek
flows through a 29-acre riparian woodland called
the Boulder Creek Cottonwood-Willow Grove.
Although the dominant tree in the Grove is the
peach-leavedwillow (Salix amygdaloides), numerous
plains cottonwoods (Populus sargentii) of various
ages and some narrowleaf cottonwoods (f.
angustifolia) also occur. This is probably the
largest riparian forest isolate left in the Boulder
Creek flood plain and is especially unusual because
of its rectangular rather than linear shape. The
City is currently obtaining ownership of the Grove
by one of its rare condemnation proceedings and has
been managing the Grove under court order since 1983.
Because the Grove is considered to be fragile open
space, public access is not allowed and the area
is used primarily by biologists from the University
as a riparian field station only 10 minutes from
the campus. It is hoped that some of the research
results will be applicable to long-term management
and preservation of the Grove and other riparian
properties in the City and in Boulder County.
In order to assure preservation of fish,
vegetation, and wildlife, the City will devise a
minimum flow strategy for the Creek based on the
amount and seasonality of water rights that need
to be acquired and dedicated to instream use.
Exchanges, purchases, and trades will be considered
and costs estimated. Low flows of 1-3 cfs have
been measured in careful studies of the Creek near
the upper and lower boundaries of the Upper
Corridor (Pennak 1943, Lewis and Saunders 1984)
and sections of this reach of the Creek have been
observed to dry up temporarily during certain
seasons and years at points below diversion
ditches.
Under Colorado Senate Bill 97 passed in 1973,
the State Water Conservation Board, upon advice
from the Colorado Division of Wildlife, can
appropriate water for instream flow for the purpose
The Cottonwood-Willow Grove has been one of
the most diverse sites in the entire Boulder Creek
390
Corridor. Observations over the last 15-20 years
have identified the following species:
approximately 150 birds, 14 mammals, and 6 fish
(Cruz and Bock 1975) • One hundred and seventy
native and introduced species of vascular plants,
including 16 tree species, were recently identified
(unpubl. data, Jane H. Bock, 1983). University of
Colorado biologists are just completing a major
year-long inventory of the birds, small mammals,
vegetation, water quality, and air quality in the
Grove.
riparian open space lands 3 miles to the northeast
in the vicinity of Sawhill Ponds and with City
conservation easements 2 miles farther east in
the White Rocks riparian area.
2. Improvement of the visual quality of the
Boulder Creek Corridor by reclaiming the Creek
and adjacent mined lands.
3. Enhancement of fish and wildlife riparian
habitat in this generally arid region.
4. Preservation under controlled livestock
grazing of the terrestrial uplands adjoining the
riparian corridor to provide feeding habitats for
raptors and mammalian carn~vores that reside in
the riparian habitat.
LOWER BOULDER CREEK
In early 1983 the City, in cooperation with
Colorado Open Lands (COL), a non-profit,publicpurpose foundation dedicated to preservation of
open space, began a project to reclaim and
preserve approximately 3 miles of the Boulder
Creek Corridor downstream from the CottonwoodWillow Grove and outside the City limits (Design
Studios West undated). The land was owned by the
Flatiron Company of Boulder and used in their
extensive gravel mining operations. This
remarkable project, which will benefit all 3
organizations, is now well underway. COL acted
as the facilitator and hundreds of hours of
negotiation were required over a 2-year period.
5. Completion of the extension of Pearl
Street that has been an element of the Boulder
Comprehensive Plan for nearly 15 years, while
simultaneously preventing the commercial .and
residential sprawl that would normally accompany
a new transportation link through a riparian
corridor.
Although current Boulder County zoning would
allow residential and commercial development of
the riparian lands involved in this project, the
Flatiron Company made a $15,000 cash grant to
COL to develop a preservation plan and also agreed
to implement a reclamation plan developed by COL
and give them the properties! The fair marketvalue
o.f the fir:st gift was determined to be $1,849,000,
of which approximately half could be used as a tax
deduction by Flatiron, based on their administra~
tive structure. This provided less benefit to
Flatiron than the company would have realized
from an open market sale. However, Flatiron will
receive a sizable tax deduction from the
reclamation work and will realize considerable
public relations benefits in the City and County.
The City has agreed to buy the properties
from COL at a bargain sale price which is less
than 20% of the appraised fair market value. In
the first phase of this project, the City
purchased $1,849,000 of riparian corridor lands at
$350,000. COL plans to use this payment in its
future land preservation operations that will
include establishing a revolving fund to provide
support for other state projects. The second and
third phases of the project, which a.re scheduled
for 1985 and 1986, will be structured similarly
but the purchase prices have not been finalized.
6. Construction of flood protection
improvements in this part of the Boulder Creek
Corridor that are compatible with the use of
certain open space lands to accept excess water
during years of exceptional flooding.
7. Linkage of the Upper Boulder Creek
Corridor pedestrian and bike trails with the
South Boulder Creek Trail and with other trails
in the vicinity of Sawhill Ponds and White Rocks,
plus provision of a new equestrian trail.
8. Construction of an open space buffer on
the north side of the Boulder Creek CottonwoodWillow Grove in the form of an 8-acre lake with
an adjacent reclaimed prairie and small stand of
large plains cottonwoods. This will greatly
enhance the biological diversity in the vicinity
of the Grove which is already bounded on the east
by a cattail pond and marsh that is owned and
protected by the Syntex Corporation. The new
lake will provide a limnological research
facility of medium depth for the University's
aquatic biologists in addition to an open space
amenity for the City.
9. Provision of a deep water limnological
research facility for the University and another
open space amenity by acquiring a 60-foot deep,
10-acre lake 1/2 mile northeast of the Cotton-.
wood-Willow Grove that was formed a number of
years ago by gravel mining.
With the exception of the 2 lakes in the
vicinity of the Cottonwood-Willow Grove, the
numerous remaining lakes and ponds in the Boulder
Creek Corridor are relatively shallow and more
suited for shore and wading birds and for aquatic
birds and mammals. In return for use of the 2
limnological facilities, the University has agreed
to use some of its water rights to keep the new
lake just north of the Grove filled and has
provided funds to the City for use with the legal
The Lower Boulder Creek Project will balance
the needs for flood control and transportation in
that area, while taking advantage of environmental
opportunities that are consistent with the City's
open space philosophy. Major benefits of the
project will be as follows:
1. Connection of open space lands in the
Upper Boulder Creek Corridor with City and County
391
CONCLUSION
and engineering work needed prior to d;lversion
of its water for this purpose. The City will
construct the diversion.
The riparian ecosystem preservation and
management activities described in this report
demonstrate how effective an informed and active
citizenry can be if it wants to preserve ecological
values. Skilled public and private organizations
are ready to help. Various tools are available
for accomplishing this goal. The Boulder Creek
projects have depended heavily on land purchases
funded by a reliable source of tax revenue and on
a willingness to use the acquired lands for
various purposes that benefit the local community.
WHITE ROCKS
Afrer Boulder Creek passes through the
Sawhill Ponds Area 3 miles northeast o~ the
Cottonwood-Willow Grove, it flows along the base
of the White Rocks geological formation at the
extreme northeast end of the Boulder Creek
Corridor planning area. This is a 300-acre sitE
of exceptional beauty and fragility that contains
a number of rare plant and animal species. The
massive white sandstone cliffs extend for a mile
along the north side of the Creek. This outcrop
supports a rather luxurious vegetation because
of seepage from the lower face of the formation.•
Here in the shade from the ledge are found
Asplenium andrewsii,one of the rarest ferns in
North America, and the only known Colorado
specimens of Aristida basiramea (Harvard three-awn~
a grass) and Apios americana (groqnd-nut, a legume
with red-purple flowers). The White Rocks area
also contains 4 rare species of ants, a rare mining
bee (Perdita opuntia) and a rare fairy shrimp
(Branchinecta packardi). Great horned owls and
the only barn owls in the Boulder Valley nest on
the cliffs. In general, the site contains a
diverse collection of mammals, birds, amphibians,
and reptiles (Stoecker 1972).
LITERATURE CITED
Cruz, Alexander, and Jane Bock. 1975. The
Boulder Creek cottonwood grove. Preliminary
report. 24 pp. Department of Environmental,
Population and Organismic Biology. University
of Colorado, Boulder, Coio.
City of Boulder, Department of Planning and
Community Development. 1984. A plan for
Boulder Creek. City of Boulder, Boulder,
Colo.
Design Studios West. Undated. An open space plan
for lower Boulder Creek. Concept plan. 12
pp. and 7 fig. Design Studios West,
Denver, Colo.
The City purchased a conservation easement in
1982 on 200 acres of the White Rocks area that
contain the rare plants and animals mentioned above,
with the aid of a low interest loan from the
Colorado Chapter of the Nature Conservancy. The
funds involved in this loan had been raised by
the Conservancy from various private sources.
When the City paid off the loan in 1984, the
Colorado Chapter of the Conservancy was then able
to use the City's payment to initiate its own
Colorado Land Preservation Fund.
Because of its exceptional flora and fauna,
White Rocks has been ranked by the Colorado
Natural Areas Program as one of the most important
natural areas in the state. It has also been
nominated as a national natural landmark by the
National Park Service. The remaining 100 acres of
White Rocks to the west of the City's conservation
easement have been officially designated as a
State Natural Area by permission of the owner.
Thus the entire 300 acres of this highly valued
part of the Boulder Creek Corridor is now protected.
392
Lewis, William M., Jr., and J. F. Saunders, III.
1984. Stream chemistry and precipitation
chemistry at the Boulder Creek Cottonwood
Grove. Report to the City of Boulder,
Department of Plannlng and Community Development. 15 pp. plus 12 pp. of data. Department
of Environmental, Population and Organismic
Biology, University of Colorado, Boulder, CO.
Pennak, Robert W. 1943. Limnological variables
in a Colorado mountain stream. The American
Midland Naturalist 29: 186-199.
Stoecker, Robert E. 1972. Fauna of the White
Rocks vicinity. In Application for mining and
reclamation permit for the White Rocks pit.
Flatiron Paving Co., Boulder, Colo.
Walker, Donald V.H. 1977. Boulder preserves
open space. Urban Land 36(9): 4-10.