College of Forestry
Forest Hydrology
In Lieu of the Paired Catchment Approach: Hydrologic Model Change Detection at the Catchment Scale
Nov-23-2010
The paired catchment approach has been the predominant method for detecting the effects of disturbance on catchment-scale hydrology. Notwithstanding, the utility of this approach is limited by regression model sample size, variability between paired catchments, type II error, and the inability of locating a long-term suitable control. An increasingly common practice is to use rainfall-runoff models to discern the effect of disturbance on hydrology, but few hydrologic model studies (1) consider problems associated with model identification, (2) use formal statistical methods to evaluate the significance of hydrologic change relative to variations in rainfall and streamflow, and (3) apply change detection models to undisturbed catchments to test the approach. We present an alternative method to the paired catchment approach and improve on stand-alone hydrologic modeling to discern the effects of forest harvesting at the catchment scale. Our method combines rainfall-runoff modeling to account for natural fluctuations in daily streamflow, uncertainty analyses using the generalized likelihood uncertainty estimation method to identify and separate hydrologic model uncertainty from unexplained variation, and GLS regression change detection models to provide a formal experimental framework for detecting changes in daily streamflow relative to variations in daily hydrologic and climatic data.
The Effect of Timber Harvest on Summer Low Flows, Hinkle Creek, Oregon
Jun-26-2012
Changes to summer low flows from forest harvesting were measured for a gauged fourth-order stream in the Hinkle Creek Paired Watershed Study. At the gauged stream, August streamflow increased an average of 1.9 mm/year (45%) for the three summers following forest harvest of 13% of a 1,084 ha watershed. Following a second harvest of an additional 13% of the watershed the August streamflow increased by 4.5 mm (106%) the first summer and 2.0 mm (47%) the second summer. Master recession curves were fit to the gauged watersheds and the resulting recession coefficients were used to predict low flows from small watersheds nested within the gauged watersheds. The estimated low flows were used to evaluate changes in summer low flows associated with forest harvest for the small watersheds. Using recession curve analysis, the estimated range of the increase for average August streamflow for the four small watersheds in the Hinkle Creek Paired Watershed Study was 1.7 mm to 4.4 mm the first summer following forest harvest. August streamflow in the small watersheds was not distinguishable from preharvest levels within 5 years for all but one watershed, which had the highest proportion of watershed area harvested.
Effect of contemporary forest harvesting practices on headwater stream temperatures: Initial response of the Hinkle Creek catchment, Pacific Northwest
Oct-04-2013
We investigated the effect of contemporary forest harvesting practices on warm-season thermal regimes of headwater streams using a Before-After-Control-Intervention (BACI) design within a nested, paired watershed study. We applied harvesting treatments to four headwater tributaries of Hinkle Creek, designed in accordance with the Oregon Forest Practices Act. Therefore, fixed-width buffer strips containing overstory merchantable trees were not left adjacent to the four non-fish-bearing streams. The summer following harvesting, we observed a variable temperature response across the four harvested streams. Mean maximum daily stream temperatures ranged from 1.5 C cooler to 1.0 C warmer relative to pre-harvest years. We also observed significantly lower minimum and mean daily stream temperatures, and recorded particularly low temperatures in treatment streams on days that minimum stream temperatures in reference streams were high. At the watershed scale, we did not observe cumulative stream temperature effects related to harvesting 14% of the watershed area in multiple, spatially-distributed harvest units across four headwater catchments. At the watershed outlet, we observed no change to maximum, mean, or minimum daily stream temperatures. We attribute the lack of consistent temperature increases in headwater streams to shading provided by a layer of logging slash that deposited over the streams during harvesting, and to increased summer baseflows.
