Hydrology, water quality, and sediment transport rates in the Pipestone Creek watershed, Jefferson County, Montana

Berger, A.L., 2004, Hydrology, water quality, and sediment transport rates in the Pipestone Creek watershed, Jefferson County, Montana: Montana Tech of the University of Montana, M.S. thesis, 115 p., 69 figs,. 7 tables.

Abstract:
The long term environmental effects on the Pipestone Creek watershed caused by human activities such as widespread recreational all-terrain vehicle (ATV) use and the close proximity of the Interstate-90 corridor have a bearing on future decisions regarding land-use management. In this thesis, seasonal data on sediment transport rates (both suspended and bedload) and water chemistry were collected from Pipestone Creek and its main tributaries, including Homestake Creek and Halfway Creek. Sediment transport rates were found to be up to 5 times higher in Homestake Creek than the similarly-sized Halfway Creek. This is attributed to the proximity of Homestake Creek to I-90, a major source of sediment loading to the watershed. A significant proportion of the gravel in Homestake Creek was coated with asphalt, a clear indicator that the sediment was derived from I-90. In comparison, Pipestone Creek is sediment-depleted, because of the Delmoe Lake dam. All of the streams in the study area have similar water chemistry, with a pH of 7.5 to 8.5, low to moderate dissolved solids and alkalinity, and Ca-bicarbonate type water. Compared with the other streams, Homestake Creek has slightly higher levels of Na + and Cl -, which may be due to salt from I-90. In addition, total Cu concentrations at the mouth of Homestake Creek exceeded State standards for aquatic health during the Spring of 2003, based on 2 duplicate samples.

A sediment budget was performed for the entire watershed upstream of I-90 for the 2003-2004 water year. Approximately 1,146,000 kg of sediment was transported down the watershed, of which ~85% was bedload, and ~15% was suspended sediment. An average annual sediment yield of ~1,865,000 kg/year was estimated for Pipestone Creek during the period 1966 to 2003, based on the volume of sediment deposited in an ephemeral lake upstream of I-90. A comparison of these results suggests that the mass of sediment transported out of the study area in 2003-2004 was somewhat lower than the long-term average, consistent with the fact that this was a low-water year throughout southwest Montana. Overall erosion rates during the 2003-2004 water year within the upper Pipestone Creek drainage area were calculated to be 21,500 kg/mile 2 for Halfway Creek, 16,500 kg/mile 2 for Pipestone Creek, and 56,000 kg/mile 2 for Homestake Creek.

Based on the results of this study, the impacts of ATV use to water quality in the Pipestone Creek watershed are believed to be minor at the present time. Although ATVs cause rapid erosion of the thin soil of the Boulder Batholith, most of the sediment is in temporary storage within gullies and basins, and is not yet entering the creeks. By comparison, loading of sediment (and possibly heavy metals) from I-90 is a much greater threat to the water quality of Homestake Creek and lower Pipestone Creek.