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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.