Stream ecosystems can be dramatically altered by dam‐building activities of North American beaver (Castor canadensis). The extent to which beavers’ ecosystem engineering alters riverscapes is driven by the density, longevity, and size (i.e. height and length) of the dams constructed. In comparison to the relative ubiquity of beaver dams on the landscape, there is a scarcity of data describing dam heights. We collected data describing dam height and dam condition (i.e. damaged or intact) of 500 beaver dams via rapid field survey, differentiating between primary and secondary dams and associating each dam with a beaver dam complex. With these data, we examined the influence of beaver dam type (primary/secondary), drainage area, streamflow, stream power, valley bottom width, and HUC12 watershed on beaver dam height with linear regression and the probability that a beaver dam was damaged with logistic regression. On average, primary dams were 0.46 m taller than secondary dams; 15% of observed dams were primary and 85% secondary. Dam type accounted for 21% of dam height variation (p<0.0001). Slope (p=0.0107), discharge (p=0.0029), and drainage area (p=0.0399) also affected dam height, but each accounted for less than 3% of dam height variation. The average number of dams in a dam complex was 6.1 (SD±4.5) and ranged from 1 to 21. The watershed a beaver dam was located in accounted for the most variability (17.8%) in the probability that a beaver dam was damaged, which was greater than the variability explained by any multiple logistic regression model. These results indicate that temporally dynamic variables are important influencers of dam longevity and that beaver dam ecology is a primary factor influencing beaver dam height.
Damming of streams by North American Beaver (Castor canadensis) has been shown to provide a host of potentially desirable hydraulic, hydrologic, geomorphic and ecological impacts. Notably, substantial increases in surface water storage and ground water storage alter the timing and delivery of water, and anecdotal evidence suggests these changes may be important for elevating late season base flows and even switching some small intermittent streams to perennial flow. The degree to which the dam building of ecosystem engineers (beaver) can transform the degree of aquatic connectivity is difficult to overstate. In the arid west, these impacts could be particularly salient in the face of increasing drought severity and diminishing snow packs. While much is known about these impacts at the local scale of individual beaver dams and dam complexes, very little is known about how these changes might culminate at larger scales and whether these impacts may be detectable further downstream on larger mainstem rivers. More fundamentally, could increasing the number of beaver dams in headwaters be enough to potentially compete with declines in snowpack? Until recently, understanding or modeling these impacts at large spatial scales had been precluded by uncertainty concerning the number of beaver dams a drainage network can support. We can easily inventory how many beaver dams are on the landscape now. However, with new approaches for modeling beaver dam capacity across entire regions (Beaver Restoration Assessment Tool -BRAT), we can now produce realistic scenarios of how many additional beaver dams these riverscapes can support. Here we present the next steps towards addressing the question of if beaver dams might be able to provide enough increase in surface and groundwater storage to hold on to water later in the season (i.e. substituting a function historically provided by larger snowpacks). We present a model that simulates the, spatially-explicit water storage volume estimates associated with beaver dams. This lays the foundation for how we can modify hydrologic modeling frameworks to represent the hydrologic impact of these dams. Specifically, how do changes in surface storage, groundwater storage, potential evapotranspirative losses, losses and gains to groundwater, and routing of surface water flows combine to change hydrographs? Will these changes be enough to knock the peaks off spring snowmelt floods and return those flows later in the season, or do they represent losses for downstream water users? This information is critical to exploring the impacts on water resources of using beaver as a restoration tool and whether beaver may be a useful water resources management and drought resilience tool.
Damming of streams by North American Beaver (Castor canadensis) has been shown to provide a host of potentially desirable hydraulic and hydrologic impacts. Notably, increases in surface water storage and groundwater storage may alter the timing and delivery of water around individual dams and dam complexes. Anecdotal evidence suggests these changes may be important for increasing and maintaining baseflow and even helping some intermittent streams flow perennially. In the arid west, these impacts could be particularly salient in the face of climate change. However, few studies have examined the hydrologic impacts of beaver dams at scales large enough to provide insight for water management, in part because understanding or modeling these impacts at large spatial scales has been precluded by uncertainty concerning the number of beaver dams a drainage network can support. Using the recently developed Beaver Restoration Assessment Tool (BRAT) to identify possible densities and spatial configurations of beaver dams, we developed a model that predicts the area and volume of surface water storage associated with dams of various sizes, and applied this model at different dam densities across multiple watersheds (HUC12) in northern Utah. We then used model results as inputs to the MODFLOW groundwater model to identify the subsequent changes to shallow groundwater storage. The spatially explicit water storage estimates produced by our approach will be useful in evaluating potential beaver restoration and conservation, and will also provide necessary information for developing hydrologic models to specifically identify the effects beaver dams may have on water delivery and timing.