The relationship between stream flow and water temperature in the waters affected by Pacific Gas and Electric Company’s (PG&E) DeSabla-Centerville Hydroelectric Project, FERC No. 803, (Project) was an important relicensing issue. The Project diverts cool water from the West Branch of the Feather River (WBFR) into Butte Creek, a stream that supports the largest population of spring-run Chinook salmon in California. Annually, PG&E and resource agencies develop a coordinated plan to maximize the cool water benefits in Butte Creek through changes in Project operations (e.g., timing and magnitude of releases from Project reservoirs). The development of a predictive stream temperature model, focusing on summer months (June through September) when high water temperatures can be a limiting factor, improved our ability to manage stream temperatures. The Army Corp of Engineers CE-QUAL-W2.v.3.2 (W2) was used for modeling the portion of the study area that is operationally adjusted to control temperatures in spring-run Chinook salmon summer holding habitat. W2 is a two-dimensional, laterally averaged, hydrodynamic, water temperature and water quality model. It was successfully used in this high gradient stream system by producing a hydro-dynamically equivalent model of the plunge-pool topographies typical of most of our study area. The model accommodated multiple waterbodies representing reservoirs and streams, multiple inflows and outflows, time-varying boundary conditions, and layer/segment addition and subtraction. W2 is a finite difference equation model that can compute water temperatures at sub-minute time intervals; as such it effectively modeled daily variations in water temperatures (i.e., daily minimums, means and maximums). We calibrated W2 with two years (2004, 2005) of summer water temperature data from stream, canal and reservoir locations, travel time (from dye studies) at four stream locations, and stream wetted width versus flow relationships from 22 instream flow transects. Error statistics indicated model calibration was successful in producing good to excellent performance across all metrics. Simulations were conducted using 2005 hydrology (above normal) and meteorology (hot) and 2001 hydrology (dry) combined with the hot 2005 meteorology. To investigate the effects of alternate operational scenarios on summer-time Butte Creek water temperatures a total of 32 simulations were conducted. Effectiveness of an alternative to manage water temperatures was determined by comparing a base case (reflecting current operations) with the alternative. Simulation results were then used by relicensing participants to develop instream flow recommendations.
We compared summer stream temperature patterns in 40 small forested watersheds in the Hoh and Clearwater basins in the western Olympic Peninsula, Washington, to examine correlations between previous riparian and basin-wide timber harvest activity and stream temperatures. Seven watersheds were unharvested, while the remaining 33 had between 25% and 100% of the total basin harvested, mostly within the last 40 years. Mean daily maximum temperatures were significantly different between the harvested and unharvested basins, averaging 14.5C and 12.1C, respectively. Diurnal fluctuations between harvested and unharvested basins were also significantly different, averaging 1.7C and 0.9C, respectively. Total basin harvest was correlated with average daily maximum temperature (r2 = 0.39), as was total riparian harvest (r2 = 0.32). The amount of recently clear-cut riparian forest (<20 year) within 600 m upstream of our monitoring sites ranged from 0% to 100% and was not correlated to increased stream temperatures. We used Akaike’s Information Criteria (AIC) analysis to assess whether other physical variables could explain some of the observed variation in stream temperature. We found that variables related to elevation, slope, aspect, and geology explain between 5% and 14% more of the variability relative to the variability explained by percent of basin harvested (BasHarv), and that the BasHarv was consistently a better predictor than the amount of riparian forest harvested. While the BasHarv is in all of the models that perform well, the AIC analysis shows that there are many models with two variables that perform about the same and therefore it would be difficult to choose one as the best model.We conclude that adding additional variables to the model does not change the basic findings that there is a relatively strong relationship between maximum daily stream temperatures and the total amount of harvest in a basin, and strong, but slightly weaker relationship between maximum daily stream temperatures and the total riparian harvest in a basin. Seventeen of the 40 streams exceeded the Washington State Department of Ecology’s (DOE) temperature criterion for waters defined as ‘‘core salmon and trout habitat’’ (class AA waters). The DOE temperature criterion for class AA waters is any seven-day average of daily maximum temperatures in excess of 16C. The probability of a stream exceeding the water quality standard increased with timber harvest activity. All unharvested sites and five of six sites that had 25-50% harvest met DOEs water quality standard.In contrast, only nine of eighteen sites with 50-75% harvest and two of nine sites with >75% harvest met DOEs water quality standard. Many streams with extensive canopy closure, as estimated by the age of riparian trees, still had higher temperatures and greater diurnal fluctuations than the unharvested basins. This suggests that the impact of past forest harvest activities on stream temperatures cannot be entirely mitigated through the reestablishment of riparian buffers.
Digital data loggers (thermographs) are among the most widespread instruments in use for monitoring physical conditions in aquatic ecosystems. The intent of this protocol is to provide guidelines for selecting and programming data loggers, sampling water temperatures in the field, data screening and analysis, and data archiving.
U.S. Forest Service