Green Cove Creek Watershed

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Lowland watersheds occur in the glacial plateau, draining to floodplains or Puget Sound

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Greencovecreek.jpg

Green Cove Watershed is the largest watershed on Cooper Point, and straddles the western Boundary of the City of Olympia. The headwaters of Green Cove Creek are a large relatively intact wetland complex with areas protected by conservation easements, acquisitions, and a City of Olympia nature area at Grass Lakes. The riparian corridor is comprised of mixed conifer and deciduous forest with only a few sites warranting improvement. Because it is relatively intact, Green Cove Creek is among Olympia’s priority for salmon habitat protection measures. The Green Cove Creek Comprehensive Drainage Basin Plan (1998) recommended minimum canopy cover of 60% within the watershed to prevent excessive stormwater impacts. The City of Olympia has down-zoned the upper Basin and instituted more stringent development standards to maintain the forest cover and protect the creek. Although the City has instituted these standards, significant residential development pressures exist in this desirable area, especially new home construction. (from Thurston CD 2004)

Map Resources

Planning

Hydrology

  • Cooke Environmental Services provided wetland assessments following hydrologic modelling in support of the 1998 Plan. The following observations are from the hydrologic summary which combines the hydrologic analysis with the wetland assessment.
    • Kaiser road serves as a weir separating Lake Lousie from the main stem creek and regulating lake discharge.
    • Some of the uppermost portions of Green Cove Creek, downstream of the Kaiser Road wetlands have been ditched.
    • Cooke speculates that increased runoff from development may increase flooding in some modified wetlands dominated by reed canarygrass.
    • Forested wetlands are most vulnerable to modified hydrology. Frog eggs are most vulnerable to modified hydrology in Grass Lakes.
    • The estimated surface storage (ESS) of the Lake Louise/Grass Lake complex is 509 acre feet. ESS of Kaiser Road wetlands are 294 acre feet. ESS of Evergreen Parkway wetlands are 185 acre feet.
    • The Lake Lousie basin is dominated by till soils, so soil saturation strongly affects discharge to the lake.
    • The storage of the Kaiser wetlands strongly mitigates stormwater flows, moreso than the Evergreen Parkway wetlands.
    • Roads discharge to the stream at Evergreen Parkway, 36th Street, and Green Cove Street. Several drains discharge to the creek from residential development west of the creek on Green Cove Street.
    • The lack of wetlands storage, steeper slopes, lower soil infiltration among compacted tills, and other landscape attributes results in flashier flow in the creek, north of Evergreen Parkway. In addition the seasonal stream that joins Green Cove Creek immediately before Evergreen Parkway (associated with the Olneys Garden Subdivision Proposal) has lower storage and may contribute flow.
    • Based on well logs, the actual extent of outwash soils may be less than mapped, reducing basin infiltration.
    • Hydrologic modelling of build-out indicate that peak flow at 36th Ave would increase by 30% resulting in stream instability.
    • The 1998 study does not model increased winter precipitation predicted by climate change.
  • Green Cove Creek has a water quality monitoring station identified by USGS but no time series data. https://www.waterqualitydata.us/provider/NWIS/USGS-WA/USGS-12078660/

Biota

The watershed is characterized by exceptional wetland habitats that provide headwaters for a summer chum stream.

Mud minnow distribution estimate based on WDFW funded survey

Conservation Landscape

  • Capitol Land Trust' has acquired 150 acres over 8 sights in the watershed focused on wetlands - https://capitollandtrust.org/conserved-lands/conservation-areas/green-cove-creek-wetlands/
  • City of Olympia has acquired lands to establish the 171 acre Grass Lake Nature Park which has a 1997 Master Plan. There appears to be some limited reforestation near the entrance. City Environmental Services has completed some habitat surveys and are discussing ecological management with parks staff (as of September 2018).
  • Grass Lakes Nature Reserve is the largest protected habitat area, managed by City of Olympia. Active restoration is underway with support to Parks from Public Works Environmental Services.
    • There is no safe pedestrian access between the Marshall-Hansen Campus and restoration areas of Grass Lakes, increasing cost of student participation. Both City of Olympia parks and road staff are aware of the issue and potential short term solutions, but no action has been taken (as of 2022).
  • File:Olympia 2015 gold crest HOA greenbelt assessment.pdf describes the ecological conditions and threats to extensive greenbelt areas owned and managed by the Gold Crest Homeowners Association.
  • 2022 - Olympia Coalition for Ecosystems Preservation has acquired two clear cut parcels at the headwaters in an attempt to reduce further hydrologic degradation of the watershed.
  • Cooper Crest subdivision was designed with Soil & Vegetation Protection Areas (SVPA) that were to be planted by the developer under a bond to the city. The developer, Tri Vo, did not complete the work and went bankrupt.

Social Landscape

bubble size indicates population of census block centroid, superimposed on land cover which suggests development pattern
  • Population - A quick population analysis based on 2010 census blocks suggests there are approximately 6,100 people living in a watershed of 2,750 acres with over 4,800 within the City of Olympia. Around 1,500 people are clustered in Evergreen Park Drive developments, around 500 people are in the western county landscape centered on Overhulse Road, with another 600 or so clustered around the South and West Side of Grass Lakes around Kaiser and 14th. Approximately 1,200 people are in subdivisions in the highlands east of the Kaiser Wetlands west of Cooper Point Road. Approximately 1,600 in the Green Cove portion of Westside Olympia, and another 600 or so are centered around the South and West side of Grass Lakes. Perhaps 500 people live along the mainstem of the creek, Around 36th and northward.
  • While a majority of the watershed lives in subdivisions, the City of Olympia recognizes only two as neighborhood associations in the watershed Cooper Crest and Gold Crest.

Hot Issues

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This page was last edited on 15 March 2024, at 21:43.
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