Publication Summary

The Muck Creek watershed in southwestern Pierce County supports native runs of chum, coho, and steelhead salmon, as well as resident and sea-run cutthroat trout. Over time, human activities and land-use changes have reduced the quantity and quality of instream habitat within the watershed. Despite the initiation of several stream restoration projects, potentially valuable habitat in the upper watershed remains inaccessible to salmon due to intermittent stream conditions affecting the central watershed. This study was undertaken to evaluate the potential cause(s) of intermittent flow conditions within the watershed, and to provide a general overview of the hydrogeologic setting which gives rise to these conditions.

The Muck Creek watershed in southwestern Pierce County supports native runs of chum, coho, and steelhead salmon, as well as resident and sea-run cutthroat trout. Over time, human activities and land-use changes have reduced the quantity and quality of instream habitat within the watershed. Despite the initiation of several stream restoration projects, potentially valuable habitat in the upper watershed remains inaccessible to salmon due to intermittent stream conditions affecting the central watershed. This study was undertaken to evaluate the potential cause(s) of intermittent flow conditions within the watershed, and to provide a general overview of the hydrogeologic setting which gives rise to these conditions.

The study area hydrogeologic framework was subdivided into nine hydrogeologic units (five aquifers and four confining units) using data from 171 inventoried wells and springs. Groundwater recharge from precipitation was estimated using regression methods developed by Woodward et al. (1995). Water levels from inventoried wells were used to prepare a generalized water-level altitude map and to evaluate seasonal and long-term groundwater fluctuations. Mini-instream piezometers were used to define the vertical hydraulic gradient and direction of water flow between streams and groundwater at specific locations, while stream seepage evaluations were used to quantify gains and losses across larger stream reaches.

Results indicate that groundwater recharge from precipitation averages approximately 21 inches per year, or 108,000 acre feet, and ranges from 17 to 28 inches across the study area. Additional recharge through losing stream reaches was estimated at approximately 22,000 acre feet, and accounted for approximately 17 percent of total recharge. Groundwater movement is generally toward the west and northwest from upland recharge areas in the eastern watershed toward natural points of discharge along area streams and the Nisqually River.

Direct groundwater discharge to streams is largely restricted to the perennial reaches of upper and lower Muck Creek, central South Creek, and upper Lacamas Creek where measured streamflow gains ranged from approximately 0.1 to 1.3 ft3/sec per river mile. Seepage losses were greatest in central Muck Creek and lower South Creek where these streams are perched above the regional water table and naturally lose water as they traverse highly permeable deposits of coarse sand and gravel.

Link to EIM data for User Study ID KSIN0004