Under
a grant from EPA, a draft report "Summary of Existing Watershed
Conditions Big Dry Creek Watershed" was prepared by Wright Water
Engineers, Inc., and released in February 1998. This report summarizes key
characteristics of the Big Dry Creek watershed for the purpose of
establishing a common base of information for watershed stakeholders. This
information can be used to help identify and prioritize future measures to
improve watershed conditions. Key conclusions and recommendations
identified in the report include the following:
A significant number of studies pertinent to the Big Dry Creek
watershed have been conducted on a wide variety of topics such as wildlife
habitat, aquatic life, water quality, stormwater management, and open
space planning. As the Watershed Association plans future monitoring and
special watershed projects, care should be taken not to "reinvent the
wheel" or restudy issues that have already been addressed.
A variety of efforts to protect water quality are currently in place
in the watershed. The Watershed Association should seek to complement and
stay abreast of these efforts. Key efforts currently in place include
extensive water quality monitoring and protection programs at Rocky Flats
and Standley Lake. Large amounts of water quality data are available
through these efforts. The Association should continue to include water
quality data from these ongoing efforts in the Big Dry Creek Water
Quality Database.
The Big Dry Creek Monitoring Program conducted by the Cities of
Broomfield, Northglenn and Westminster should continue because it provides
useful data for stream characterization from Standley Lake to the South
Platte. The data set obtained from this program is the primary source of
water quality information in the watershed below Standley Lake.
Stormwater quality and quantity impacts to Big Dry Creek are not
well-characterized although a variety of stormwater impacts such as
streambank erosion can be reasonably inferred from field observations. As
the Clean Water Act Phase II stormwater regulations are promulgated and
implemented over the next few years, the cities will likely be impacted by
Phase II requirements. It will be important for the cities to develop an
understanding of stormwater impacts to receiving water quality and
implement best management practices (BMPs) to minimize these impacts.
Several master drainage plans have been completed in the watershed which
identify existing and proposed patterns of stormwater flows (i.e.,
outfalls, flow volumes, etc.). This information can be helpful in
designing stormwater quality monitoring programs and developing an overall
understanding of stormwater issues in the watershed.
Documented pollutant sources in the watershed include discharges
from municipal wastewater treatment plants and Rocky Flats and spills and
releases from facilities regulated by the Comprehensive Environmental
Response Compensation and Liability Act (CERCLA) and the Resource
Conservation and Recovery Act (RCRA). Stormwater runoff from urbanized
areas and overland flow from agricultural lands are also expected to be
relevant sources of pollution, although studies of these sources are not
known to have been conducted in the watershed.
Groundwater quality and groundwater-surface water interactions are not
well-characterized along the main stem of Big Dry Creek. These issues may
be worthy of study in the future, particularly with regard to
understanding the role that groundwater plays in the hydrology of Big Dry
Creek.
Although the main stem of Big Dry Creek has not been identified on
the 1998 303(d) list, which would trigger the total maximum daily load (TMDL)
process for the creek, Big Dry Creek will be affected by the ongoing TMDL
process in Segment 15 of the South Platte River. The Big Dry Creek
Association should monitor and participate in the activities of the South
Platte Urban Watershed TMDL Advisory Committee.
Ecological studies along Big Dry Creek suggest that aquatic life in
the stream is limited due to poor habitat conditions. Future projects in
the watershed could consider areas of potential habitat improvement. In
planning these efforts, hydrologic information in the various master
drainage plans and flood hazard delineation areas should be taken into
account.
In the area downstream of I-25, agriculture is the predominant land
use. Cattle grazing and watering in the stream and runoff from adjacent
croplands impact water quality and streambank conditions. Quantitative
studies are not known to have been conducted to correlate agricultural
activities with water quality in this area; however, the Natural Resource
Conservation Service (NRCS) indicates that these impacts are potentially
present. In the event that a waste load allocation (WLA) for nitrate is
developed for Big Dry Creek as a result of the TMDL process for Segment 15
of the South Platte, additional quantitative study of this issue may be
needed. Similarly, the Association should work with the NRCS and farmers
in the area to determine what measures should be taken to minimize water
quality impacts associated with agricultural practices through measures
such as streambank stabilization and riparian buffer area
preservation/restoration.
All of the cities in the Big Dry Creek watershed have stormwater
and construction ordinances in place for new development that address
water quality. The Association should work with the cities to encourage
enforcement of ordinances requiring the implementation of BMPs at
construction sites, since much of the watershed area is rapidly
developing. Similarly, as the population within the watershed grows, water
quality impacts associated with urbanized areas will increase. Public
education would be a worthy effort of the Association to promote proper
handling and disposal of household waste, application of fertilizers and
pesticides, and other practices that reduce pollutant loadings to the
stream.
The City of Westminster and Jefferson County Open Space are actively
pursuing preservation of open space, particularly along Big Dry Creek. The
Association should support these and other similar efforts because of the
value that preserved riparian corridors play in protecting water quality,
maintaining streambanks, enhancing aquatic habitat, etc.
Geographic Information Systems (GIS) mapping is available from
various entities in the watershed for a large portion of the watershed,
excluding Weld County. Although Broomfield and Northglenn do not have GIS
systems in place, the mapping is in electronic form that should interface
with a GIS system. With some coordination, a good GIS map could be
developed for the watershed as a tool for linking water quality and
quantity with various geographic features.