DESCRIPTION
Forest Service road construction occurred in conjunction with timber harvest activities within the watershed, primarily during the 1960's to 1980's. Stream crossing culverts installed at that time were often undersized, and are now reaching the end of their functional life. Those conditions, combined with the naturally high instability of the slopes, have led to road related mass-wasting disturbances within the Sitkum drainage (USDA 1998). The Sitkum and South Fork Calawah Watershed Analysis (1998) documents that 36% of mass wasting events were natural, 15% the result of harvest activities, and 49% caused by roads. The mass-wasting events have resulted in large amounts of fine and course sediment being delivered to the mainstem fish-bearing habitats of the Sitkum and South Fork Calawah sub-watersheds (USDA 1998). The culvert present at MP 15.9 is undersized in proportion to the bankfull width of the streams, dooes not allow normal transport of wood and sediment, and lacks capacity at flood flows. The expected trends on the Olympic Peninsula due to climate change include increased winter precipitation and increased flood frequency and magnitude from intensified heavy rain events (Halofsky et al. 2011). In present condition, the site is vulernable to expected increases in flow associated with climate change.
Forest Service road construction occurred in conjunction with timber harvest activities within the watershed, primarily during the 1960's to 1980's. Stream crossing culverts installed at that time were often undersized, and are now reaching the end of their functional life. Those conditions, combined with the naturally high instability of the slopes, have led to road related mass-wasting disturbances within the Sitkum drainage (USDA 1998). The Sitkum and South Fork Calawah Watershed Analysis (1998) documents that 36% of mass wasting events were natural, 15% the result of harvest activities, and 49% caused by roads. The mass-wasting events have resulted in large amounts of fine and course sediment being delivered to the mainstem fish-bearing habitats of the Sitkum and South Fork Calawah sub-watersheds (USDA 1998).
This project replaced an undersized culvert at MP 15.9, with a larger more suitable 5' diameter culvert. This culvert is in proportion to the bankfull width of the streams, allows for normal transport of wood and sediment, and has sufficient capacity at flood flows. Although this stream is non-fish-bearing, the Sitkum River is directly downstream from the project site, and supports a diversity of fish populations. Replacement of this culvert will benefit winter and summer steelhead, fall coho, chinook, sockeye, and chum salmon.
