PROJECT OVERVIEW
The Upper Willow Creek Watershed Flood Control and
Stream Stability Study was conducted by Agro Engineering, Inc. for the
Willow Creek Reclamation Committee in Creede, Colorado. Funding was
provided by the Colorado Water Conservation Board (CWCB) and the Federal
Emergency Management Agency’s (FEMA’s) Project Impact.
The primary purpose of the study was to analyze Upper
Willow Creek for flood control and debris/sediment problems, and develop a
plan to address these problems. The study reach was limited to the portion
of Upper Willow Creek and its associated watershed above the masonry flume
in downtown Creede. The goals of the study were to:
1)
Quantify the risk of flood damage from Upper Willow Creek
2)
Examine problems related to debris and sediment transport in Upper
Willow Creek
3)
Develop strategies to reduce the risk of property damage and
destabilization of potential pollution sources during flood events and
improve the aesthetic qualities, habitat conditions, and physical
functioning of Upper Willow Creek
A study report was presented to the Willow Creek
Reclamation Committee. The entire report is too large to download from the
internet. Please contact the Willow Creek Reclamation Committee
director
for a CD or paper copy of the report. However, the
executive summary and the
sections detailing potential mitigation strategies (chapters
3 and 4) can be downloaded here as adobe acrobat files.
Floodplain Analysis
55 stream cross-sections were surveyed in Upper Willow
Creek. These cross-sections were used in the U.S. Army Corps of
Engineers’ Hydraulic Engineering Center River Analysis System
model (HEC-RAS) to model the channel hydraulics of Upper Willow Creek.
Color aerial photos were taken of the floodplain and used with additional survey data
to map
high-resolution topography in the floodplain. Flood inundations at various flood return intervals were
mapped in GIS using water surface elevations from the HEC-RAS model and the
high-resolution topography. The GIS files for these flood plains can be
download here.
The floodplain analysis indicated several potential locations of flooding
that are described in the project
report. Potential flooding
problems of major concern include:
Commodore Mine
A flume and metal pipe carry West Willow Creek over and
through the large Commodore mine tailings pile. A 10-year flood will cause
flooding of the depressed area at the pipe entrance. A 25-year flood will
overtop the tailings pile, causing a high velocity flow down the very steep
face of the pile. This event could potentially erode tons of mine tailings
and mine debris into Willow Creek. Fine tailing sediments would probably be
carried by the flood into the Rio Grande potentially causing a major fish
kill.
Overtopping of Weir Above Mining Museum Area
The earthen and wood weir upstream of the mining museum
area will be overtopped starting at the 25-year flood return interval.
Flood flows will enter the depression west of the main channel and flow
downstream into the parking area east of the mining museum. However, these
flows should re-enter Willow Creek and be contained by the levees of the
masonry flume.
Windy Gulch Culvert
The roadway below Windy Gulch (just below the mining
museum) will be overtopped during flood events initiating at the 10-year
level. A portion of the overtopping flow will flow down the road and
potentially cause flooding in downtown Creede.
North Creede Culvert
The hydraulic analysis indicated that the culvert in
North Creede will be overtopped in nearly all flood events. Personal
accounts of flooding indicate that floods typically erode the roadway near
the culvert. A large flood will probably damage surrounding structures.
Timber Debris
Many areas of the Willow Creek channel were noted to
have significant amounts of timber debris. This timber debris will be
easily mobilized during small flood events and could easily plug culverts or
other structures.
Watershed Sediment Sources
Specific sediment sources in the Willow Creek
watershed that may be contributing sediments to the Willow Creek channel
were identified using aerial photography and delineated in GIS. Mapped
sediment sources included areas of mine tailings, mine related disturbance,
mobile talus/scree, and roadways.
ALTERNATE MITIGATION STRATEGIES
Mitigation strategies were developed to address
problems that were identified. Preliminary designs and approximate cost
estimates were developed for a number of projects. The following figure
shows the location of potential projects. These projects are in detail in
the Chapters 3 and 4 of the report.
Figure ES.1. Locations of Potential Mitigation Projects
|
