Green Cove Creek Watershed

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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. Tidal influence occurs in the estuary and at the mouth of the creek, allowing for a fresh and saltwater mixing despite the presence of some bulkheads. Green Cove has two fishways assessed by WDFW; one has retrofitted baffles which impact upstream adult and juvenile migration while the other is passing fish. (Thurston CD 2004

Map Resources

Planning

  • A Comprehensive drainage plan was adopted in 1998 by Thurston County - http://www.thurstoncountywa.gov/sw/Pages/basin-plan-greencove.aspx
  • Thurston CD 2004 describes salmon recovery strategies for the WRIA 13, including Green Cove Creek, and reports use by Chum and Coho Salmon, and Steelhead and Cutthroat trout with anadromous use over 3.4 miles of stream.
    • The plan proposes replacement of the culvert on Country Club Road, protection and enhancement of riparian forest, increasing large wood recruitment, and protection of hydrology form development impacts.
    • The plan proposes a riparian assessment, but that appears to have not occurred.
  • File:Olympia 1997 grass lakes master plan.pdf defines the City of Olympia plan for the Grass Lakes Nature Reserve, the largest protected parcel in the watershed.

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.

Biota and Conservation

Mud minnow distribution estimate based on WDFW funded survey

Development

bubble size indicates population of census block centroid, superimposed on land cover which suggests development pattern
  • Green Cove Park Subdivision has plans for 181 units on 50 acres at 2200 Cooper Point Road - http://m.olympiawa.gov/news-and-faq-s/construction-news/green-cove-park.aspx (September 2018)
  • Watershed development continues, contested by local advocates - http://janineslittlehollywood.blogspot.com/2016/05/housing-development-threatens-west.html
  • A new subdivision is being constructed immediately north of the Evergeen Pointe subdivision.
  • 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.
  • 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.

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