Tanwax Creek

   Basin Information

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Essentials
Tanwax Creek is just over 13 miles long, and the Basin drains an area of 26 square miles.  There are 9 recognized lakes, and the gradient is low.  The dominant land use is forestry, agriculture and rural residential.  Chinook, chum, coho, cutthroat, pink and steelhead salmon have been observed in Tanwax Creek. 
 
General

Tanwax Creek, located in Southern Pierce County, Washington, empties into the Nisqually River at its river mile 30.8.  The basin geology consists of continental glacial till and outwash and some sedimentary rock.  The headwaters are a series of lakes, with Tanwax Lake being the largest.  Click on the map for larger image.
   
Land Use
The lower 6.5 miles of Tanwax Creek, from its mouth to State Highway 7 is primarily commercial forestry land that is being converted into rural residences.  From above Highway 7 to Tanwax Lake, the land use is rural farmland that is gradually being converted into rural residences.  The creek and its tributaries have been used extensively for irrigation.  The Tanwax Lake area, including the small lakes and tributaries above Tanwax Lake is primarily residential use, with dense suburban and recreation homes along some of the lakes.  There are 2060 land  parcels and 1412 individual landowners within the Tanwax Creek Basin as of September 2005..
 
   
Stream Channel
The entire creek is low gradient, only losing 220 feet in elevation throughout its course.  This low gradient channel used to freely meander throughout the broad valley, which was carved during glacial times.  Due to land use practices, the channel now carves deeper and less sideways, which causes bank erosion rather than meandering.  Bank widths range from 25 to 40 feet. Wetlands are commonly associated with this valley segment type and beaver activity is prevalent, especially in the lower Tanwax (Highway 7 to the mouth).  Channels are dominated by plane bed run morphology, where deep glides intermittently separated by short riffles are common.  Channel bed material is typically a thin layer of small and large cobble setting on top of a dense layer of sediment or clay.
 
   
Hydrology
The creek has year-round flow although some tributaries exhibit intermittent flow.  Water quality can be degraded by the relatively high degree of development along lakes in the upper drainage, and ease of livestock access to stream banks.  Tanwax Creek is used for irrigation, but this has been reduced in recent years with the conversion of agricultural lands to rural residential.
 
   
Tributaries
Many of the small tributary streams of the lowlands experience intermittent flow problems and are likely to experience elevated stream temperatures due to lack of canopy closure.  These channels provide limited habitat capacity to anadromous (migrating from the sea to fresh water to spawn) salmonids due to their small size, intermittent flows and inaccessibility.  Habitat alterations similar to the mainstem have taken place in most tributaries.  Lack of wood, riparian vegetation, and substantial fine sediment input also limits this habitat.  The over-wintering refuge and migration pathway potential gives these tributaries unique importance, especially for coho, steelhead and cutthroat trout.
 
   
Barriers
The Pierce County Conservation District's barrier inventory identified a culvert at the Eatonville Cutoff Road crossing as a partial barrier.  This culvert impairs passage of juvenile and adult coho and steelhead.
 
   
Major habitat alterations include:
  • Decrease of large wood in the creek
  • Removal of streamside vegetation, including standing trees that would have provided a source of large wood and shade
  • Excess fine sediment input
  • Ditching and channelization of the creek and tributaries
  • Unrestricted grazing along streams and wetlands
  • Introduction of non-native fish species
  • Degradation of water quality
  • Water withdrawal in summer months
  • Changed run-off hydrology due to development in the basin
  • Introduction of invasive plants such as reed canary grass
  • Draining of wetlands
  
 
   
Agricultural and Rural Residential Development
Wetland ditching, stream channelization, wood removal, water diversion, and riparian forest pasture conversion are results of earliest agriculture endeavors, and have continued to influence channel and habitat forming processes.  Numerous wetlands were ditched and drained for agriculture, many of them associated with the inlets and outlets of the many lowland lakes.  Many of these grazing and ditch maintenance practices are still active.  Unrestricted grazing along stream banks have led to reduced riparian habitat effectiveness throughout much of the lowland streams.  Many farms have ceased operations in the recent years, many converting to rural residential development.

The lakes that have outlets that flow into Tanwax Creek are popular recreation lakes, and in some areas are densely lined with suburban and recreation homes.  Cranberry and Rapjohn lakes are the only two lakes without residential development along their shorelines.  Screening of the Tanwax Lake outlet used to eliminate access of anadromous fish to the lake and upstream tributaries.  Water quality is being degraded by the relatively high degree of development along lakes in the upper drainage, and by livestock access to stream banks.

Over-allocation of water and consequent low summer flows was once considered a major limiting factor (Walters, 1986), but the actual water use as compared to allocated rights remains largely unknown.  Irrigation has been reduced over the past with the conversion of agriculture lands to rural residential.  Many of the small tributary streams of the lowlands experience intermittent flow problems are are likely to experience elevated stream temperatures due to lack of canopy closure.  How all of these impacts have affected fish distribution and abundance remains largely unknown, since no information regarding fish use is available prior to settlement of the area.