HomeMy WebLinkAbout17 Surface WaterThe Lakes at Valley West Subdivision – Phases 1 and 2
Preliminary Plat Application
Surface Water
Exhibit A is a delineation of the boundaries of surface waters and wetlands (Waters of the US)
that currently exist within the Lakes at Valley West parcel. The surface water and wetland
resources are described below according to the Cowardin system of classification (Cowardin et
al 1979).
• The historic Baxter Creek channel and riverine fringe encompasses approximately 1.69
acres of a perennial stream and adjacent saturated to seasonally flooded wetland fringe.
• The West and East Lakes total approximately 8.29 acres of constructed mitigation
lacustrine wetland that are permanently flooded.
• The constructed lacustrine fringe surrounding the lakes totals approximately 2.56 acres
that exhibit seasonally flooded to saturated soil conditions.
• The constructed palustrine, emergent wetland southeast of the east lobe encompasses
approximately 4.06 acres of wetland exhibiting saturated to permanently flooded soil
conditions.
Exhibit A shows the historic Baxter Creek corridor and post-construction mitigation wetlands on
the property. The Baxter Creek riverine fringe shown on Exhibit A reflects the surveyed
boundaries drawn on the original delineation map that were detailed in the 1998 Wetland
Delineation Report. There have been no impacts or changes to the channel or riverine fringe on
this reach of Baxter Creek since the original delineation as verified by Vaughn Environmental
Services every year from 2008 to 2015.
The post-construction mitigation wetlands are considered waters of the US as approved by the
US Army Corps. Two linear wetlands that historically existed on this parcel were impacted to
develop a gravel pit and later create the twin lakes. The boundaries of the open water of the twin
lakes, the lacustrine fringe around the lakes, and the large palustrine wetland were established on
the ground based on the design and an intricate grid drawn, surveyed and constructed in 2008.
Aajker Creek is located outside the west property boundary, although the 50-foot watercourse
setback extends across the west boundary into the Lakes parcel. Baxter Creek and Aajker Creek
and the adjacent wetland fringes will be protected from development by 50-foot watercourse
setbacks in accordance with Section 38.23.100 Watercourse setback (A) of the City of Bozeman
Unified Development Code (UDC).
The Lakes at Valley West Subdivision – Phases 1 and 2
Preliminary Plat Application
The mitigation wetlands and the Baxter Creek corridor are protected in perpetuity from
development according to the conditions of the USACE 404 permit. The parcel was laid out to
provide 50-foot watercourse setbacks on Baxter Creek and 35-to 50-foot upland buffers around
the lakes and palustrine wetland. The surface water resources will be protected within park
and/or open space. The East Lobe, palustrine wetland, and Baxter Creek corridor will be
dedicated to the City as park land. There will be no impacts to the mitigation wetlands or Baxter
Creek as a result of the development except for a pedestrian bridge crossing on Baxter Creek.
The bridge impacts were included in the original 404 permit. The permit expired before the
bridge was constructed. The surface water resources will be protected during road construction
with construction fencing and erosion control measures. The resource conditions associated with
Baxter Creek, the Lakes, and the wetland complex are detailed in the following sections
Baxter Creek
The Gallatin County Conservation District (GCD) classifies Baxter Creek as a perennial stream.
The creek channel within the property is approximately 7 to 10 feet wide and 1,373 feet long,
flowing from south to north between the Baxter Natural Area city park and the Lakes at Valley
West. Baxter Creek is diverted from the Farmer’s Canal approximately 1.2 miles south of the
Lakes property. The boundaries of the open water channel and adjacent riverine fringe were
originally delineated in 1994 in anticipation of the original Valley West Subdivision plat
submittal. Fifty-foot watercourse setbacks were established from the edge of the riverine
wetland fringe in the October 2003 Preliminary Plat Application (Figure A). The watercourse
setbacks have been maintained to the present in accordance with Section 38.23.100 Watercourse
setback (A) of the City of Bozeman UDC.
Base flows fed by high groundwater and irrigation water originating in the Farmer’s Canal in
summer provide the main sources of hydrology for Baxter Creek. High flow events are typically
related to stormwater runoff events and melting valley snowpack. The reach of Baxter Creek
within the project boundaries had been negatively impacted by livestock grazing and agricultural
practices resulting in an overly wide stream channel, bank erosion, lack of pool habitat, and lack
of woody riparian vegetation. Restoration of a segment of Baxter Creek extending 1,800 feet
south of Durston Road was completed in 2006. The work included narrowing the channel,
stabilizing eroding banks, and enhancing fish habitat by constructing pools throughout the stream
reach located on the Lakes property. The restored banks were revegetated with salvaged sod
mats and custom seed mixes. The east side of Baxter Creek was planted with trees and shrubs as
part of the Baxter Natural Area construction in 2007. Approximately 692 containerized woody
plant materials were installed within the riparian corridor of Baxter Creek and the Baxter Creek
Natural area. The west side of the corridor was planted with trees and shrubs in fall 2008
coincident with construction of The Lakes. Planting details are included in the Vegetation
Section. The Baxter Creek corridor, adjacent riverine wetland fringe, and 50-foot watercourse
The Lakes at Valley West Subdivision – Phases 1 and 2
Preliminary Plat Application
setback will be protected from development. A gravel fines trail was constructed in 2008 at the
outer edge of the watercourse setback in accordance
Wetlands: The Lakes and Palustrine Wetland Complex
The US Army Corps of Engineers (USACE) authorized an Individual 404 permit (Permit
No.1998-90014) for the 360 Ranch Corporation to implement Phase I of the Valley West
Subdivision project on May 4, 1998, and Phase II on July 23, 1998. Bozeman Lakes, LLC, the
subsequent owners of Valley West Subdivision, applied for an amendment to the original 404
permit in May 2001. Primary design changes included a reduction in the number of impacted
wetland acres and a change in the location of the constructed wetland complex from an upland
area west of Baxter Creek to an upland area east of Baxter Creek. The permit amendment was
approved by the USACE in a letter dated November 21, 2002. The USACE 404 amended permit
required the construction of 49.5 acres of mitigation wetlands across the entire Valley West site.
Mitigation wetlands located within the current Lakes at Valley West property boundaries include
approximately 8.0 acres of open water in the West and East Lakes and an additional 6.5 acres of
lacustrine fringe and palustrine, emergent wetlands constructed adjacent to the lakes and Baxter
Creek (Figure A). The lakes were constructed with west and east lobes separated by the future
Laurel Glen Parkway. The shoreline was contoured to maximize safety and the extent of the
lacustrine fringe. The lake depth was excavated to a minimum of 25 feet to ensure adequate
turnover, maximize oxygen levels, and to provide a refuge for fish. The lake will be stocked
under management of Montana Fish, Wildlife, and Parks once the area is open to the public.
Anticipated uses of the public space are recreational including fishing, bird watching, and hiking.
The lacustrine fringe of the east and west lobes of Wing Lake was planted with wetland sod mats
salvaged from an onsite, non-jurisdictional wetland. The mats were placed on approximately
half of the perimeter of both lakes and around the fishing access points in June 2008. Over five
thousand wetland tubelings were planted within the lacustrine fringe of both lobes on August 27,
2008. The water levels were raised with the control structure after planting to ensure sufficient
inundation levels. Approximately 458 containerized trees and shrubs and customized seed mixes
were planted around The Lakes and the west side of the Baxter Creek riparian corridor in
September and October 2008. The clusters of trees and shrubs were staked and caged to prevent
browsing. The woody plants were manually watered during the first growing season following
installation.
The USACE wrote a letter on August 12, 2013, closing the Valley West 404 permit file based on
the successful completion of the mitigation wetlands constructed site wide including the Lakes at
Valley West and the adjacent lacustrine and palustrine wetlands. Success of the mitigation
wetlands was based the establishment of an optimal percent cover of wetland and upland
vegetation, the survival of a majority (96 percent in 2012) of the woody species, and meeting the
The Lakes at Valley West Subdivision – Phases 1 and 2
Preliminary Plat Application
mitigation acreage requirement. The results of the vegetation monitoring were documented in
annual reports submitted to the US Army Corps from 2008 through 2012. The August 2013
closure letter from the USACE was included with the City Pre-application submittal. Copies of
the original and amended permit approval letters were also included with the City Pre-
Application submittal.
Aajker Creek
The GCD classifies Aajker Creek as a perennial stream, diverted from the Farmer’s Canal
approximately 1.48 miles south of the project boundaries. The creek channel north of Farmer’s
Canal has been straightened historically for agricultural purposes. The creek flows south to
north outside the Lakes property boundary. The 50-foot watercourse setback for the east side of
Aajker Creek extends across the west boundary of the Lakes parcel (Figure A). The watercourse
setback will be maintained within the strip of open space located at the west subdivision
boundary. A piped outlet from the bottom of the West Lake conveys overflow to the borrow
ditch located on the south side of Durston Road east of Westgate Avenue. Surface water in the
borrow ditch and the pipe outflow are diverted north through a culvert across Durston Road to a
restored tributary of Aajker Creek within the Laurel Glen Subdivision. The tributary to Aajker
Creek and Aajker Creek converge approximately 1,400 feet north of Durston Road.