Beaver Dam Influences on Streamflow Hydraulic Properties and Thermal Regimes

Beaver dams alter channel hydraulics which in turn change the geomorphic templates of streams. Variability in geomorphic units, the building blocks of stream systems, and water temperature, critical to stream ecological function, define habitat heterogeneity and availability. While prior research has shown the impact of beaver dams on stream hydraulics, geomorphic template, or temperature, the connections or feedbacks between these habitat measures are not well understood. This has left questions regarding relationships between temperature variability at different spatial scales to hydraulic properties such as flow depth and velocity that are dependent on the geomorphology. We combine detailed predicted hydraulic properties, field-based maps with an additional classification scheme of geomorphic units, and detailed water temperature observations throughout a study reach to demonstrate the relationship between these factors at different spatial scales (reach, beaver dam complexes, and geomorphic units). Over a three-week, low flow period we found temperature to vary 2 °C between the upstream and downstream extents of the reach with a net warming of 1 °C during the day and a net cooling of 0.5 °C at night. At the beaver dam complex scale, net warming of 1.15 °C occurred during the day with variable cooling at night. Regardless of limited temperature changes at these larger scales, the temperature variability within a beaver dam complex reached up to 10.5 °C due to the diversity of geomorphic units. At the geomorphic unit scale, the highly altered flow velocity and depth distributions within primary geomorphic units provide an explanation of the temperature variability within the dam complex and insight regarding increases in habitat heterogeneity

Measuring Stream Flow and Sediment Transport to Evaluate the Cub River Basin, Idaho

The goal of this study is to examine the relations among stream flow diversions, inchannel processes, and the geomorphic framework of river basins. An essential component of this research program is a spatially distributed characterization of streamflow and sediment flux in a channel network affected by multiple diversions and tributary junctions. These data indicate that operation of diversions during the snowmelt runoff season affects the timing and spatial distribution of water and sediment flux. We measured stream flow and sediment transport and developed a geomorphic characterization of the study area. The study area extends from the confluence of Carter Creek to the mouth of the Cub River canyon, near Franklin, Idaho. It is 17 km long and drains approximately of 155 km2. Stream gradient varies from 0.001 to 0.033 and the average peak flow is 17 m3/s. Within the study area two major diversion structures are operated from May through mid-October for irrigation. A third diversion is operated nearly year-round for reservoir filling. We divided the study area into four segments, separated by the three diversions and established study sites in each segment. We measured streamflow at the first three sites and developed stage-discharge relations. We used an acoustic stage-measurement device at one site, which allowed us to construct a continuous record of stage and discharge for most of the runoff season at that location. We also obtained daily measurements of flow for each of the three diversions. We made periodic measurements of flow in the Upper and Lower Diversion to compare these records. We collected 212 bedload measurements during the 2006 runoff season in the Cub River and the diversion canals. Each of the measurements represents a set of three to six individual samples. Measurements were taken with bedload traps (0.3 m x 0.2 m nozzle) and hand-held Elwha sampler (0.2 m x 0.1 m nozzle). Bedload traps were mounted to the bed of the river for 60 minutes. Hand-held measurements were taken for 3 or 5 minutes depending on the flow. At each of the sites we collected at least 20 measurements with bedload traps and 10 measurements with hand-held sampler. We collected additional hand-held samples from nearby sites at road bridges during the peak flows. The measurements indicate a longitudinal variation in bedload similar to the longitudinal variation in discharge. The highest flow and highest sediment transport occurred in downstream reaches that were affected by tributaries earlier in the season, while natural snowmelt resulted in the greatest flow and sediment transport in the upper watershed later in the season. The grain size distribution of the bed load was much finer than the bed surface and similar or finer to that of depositional bars. The bed D50 decreases downstream, but the D50 of the gravel bars is similar throughout the study area. Thus, during a year of average peak runoff, depositional bars appeared to be fully mobilized while the bed was only partially mobilized

Repeat photography of the Colorado River Corridor in Grand Canyon National Park

There is an abundant record of sand bar change along the Colorado River in Grand Canyon National Park that is documented by repeat ground-level oblique photographs. We assembled photographs for 29 sites between Lees Ferry (River Mile 0) and Bright Angel Creek (River Mile 87) that were taken over a 30-year period. Despite a \u3e90% reduction in sand supply to this reach most sand bars have eroded to only a minor degree. The most significant change depicted in the photographs is a proliferation in riparian vegetation that has recovered from widespread scour caused by high flows in the mid-1980s. Increased bar size caused by recent controlled floods in 1996, 2004, and 2008 have caused short-term bar aggradation that does not typically persist for more than 1 year. We also compared recent photographs with those taken from the 1890 Robert Brewster Stanton collection. Changes in sand amounts were classified using three categories, each representing different flow elevation zone - 1) \u3c 25,000 ft3/s, 2) 25,000-50,000 ft3/s, and 3) \u3e 50,000 ft3/s. In addition, changes in vegetation were evaluated for the entire site/sand bar. The construction of Glen Canyon Dam in 1963 dramatically changed the hydrologic and geomorphic environment of the Colorado River corridor in the Grand Canyon (U.S. Department of Interior, 1995). Operation of the dam, driven by hydropower demand, resulted in major reductions in peak flows, elevated base flows, and daily fluctuations in stage up to 1.5 m. The supply of fine sediment was reduced approximately 99% immediately downstream from the dam in Marble Canyon and 81-85% further downstream at Bright Angel Creek

Predicting the effect of beaver dams on stream thermal heterogeneity

Restoration of the beaver population (Castor Canadensis) to streams and rivers is desirable because they are a sustainable and lower cost method of improving stream habitat when compared to human-engineered restoration efforts. Prior studies have shown that beaver colonization results in impoundments of water which increase channel width and surface area, increase sediment deposition, and slow flow velocities. While these changes can create a thermally heterogeneous environment promoting diverse aquatic communities and providing thermal refugia, there is a need to understand the spatial distribution of temperatures and to identify characteristics that produce this variability. To address these needs we developed a process-based temperature model for a beaver pond within Curtis Creek, UT. Using water temperature data distributed spatially within the pond, we delineated model segments into areas with similar temperature responses. This resulted in a main channel area and three surface transient storage (STS) zones– one of which was further segmented into two layers where thermal stratification was present. Onsite discharge, water temperature, sediment temperature, channel geometry, and meteorological data provided information for model inputs and calibration. The model formulation accounts for advection, heat fluxes at the air-water interface, lateral exchange between zones, vertical exchange between stratified layers, attenuation of shortwave radiation within the water column, and streambed conduction. The model captured each zone’s instream and sediment temperatures well and provided information regarding the dominant heat fluxes for each zone. These results can lead to insight regarding key processes and characteristics driving the thermal heterogeneity within beaver ponds over both space and time. Ultimately, this type of modeling approach can aid in future decisions regarding restoring beaver to certain stream systems and the associated ecological implications

Impacts of beaver dams on channel hydraulics and characteristics

Beaver dams have significant impacts on the hydrology, temperature, biogeochemical processes, and geomorphology of streams and riparian areas. They have also been used as a viable tool in restoring impaired riverine systems. Due to the dynamic nature of beaver dams, these impacts vary and are difficult to quantify. To begin understanding the impacts of beaver dams on riverine systems, we developed a 1-D hydraulic model for a beaver impacted reach that includes seven dams and a reach with no dams present to compare hydraulic responses. We also compared observations of substrate sizes, gradients, and geomorphic/habitat units for each reach. Results from the model indicated an alteration of the run-riffle-pool sequence, decreased flow velocities, and increased depths through the beaver impacted reach. These geomorphic and hydraulic adjustments are consistent with observed changes in the increased variability in sediment size distributions. Along with decreasing flow velocities and the storage and distribution of sediments, beaver impacted reaches showed the opportunity for greater channel and bank stability and increased habitat complexity. In general, these data and model results suggest that many common stream restoration goals could be met through the introduction of beavers