The Impact of Timber Harvest on Stream Temperature at a Watershed Scale; Case Study from Hinkle Creek

One of the objectives of the Hinkle Creek Paired Watershed Study was to investigate the impact of contemporary forest practices on stream temperature at the scale of individual stream reaches and for a third-order watershed. The individual stream reaches were in non-fish-bearing and main stem, fish-bearing streams. Stream temperature was measured at 28 locations over 10 years in the Hinkle Creek study watersheds. During that time, two harvest entries were made into the South Fork Hinkle Creek Watershed, a 1,080 ha watershed. The first entry was made during the winter of 2005-06, consisted of five clearcuts that covered 152 ha of forest land. The harvest operations took place adjacent to non-fish-bearing streams. The second entry was made during the winter of 2008-09, consisted of four clear cuts that covered 131 ha of forest land. The harvest operations occurred adjacent to small and medium fish-bearing streams; 51 percent of the length of the fish-bearing streams in the South Fork had timber harvest activities adjacent to them. The impacts of timber harvest on stream temperature were detected at the scale of individual stream reaches. These results were highly variable and, at times, counterintuitive. The impacts included increases and decreases in maximum and minimum daily stream temperature. However, no impact was detected in the maximum or minimum daily stream temperatures at the mouth of the South Fork. In addition, for the reach of the main stem directly upstream of the first fish-bearing tributary in the South Fork, the maximum and minimum daily stream temperatures decreased as a consequence of timber harvest. Neither of these results at the watershed scale were hypothesized or expected. The flux of groundwater into the streams and the impact of timber harvest on the groundwater flux are hypothesized as the reason for the counterintuitive results.