Existing beaver dam density for the state of Utah. Our model estimates capacity by approximating the maximum number of dams that local riverscapes can support on average, based on vegetation resources and typical stream flows. Model outputs are calibrated to typical dam densities found in nature and reported in the literature, which can be as high as 40 dams per km, or roughly one dam every 25 m. These high densities are only found where multiple colonies maintain large dam complexes, which vary from 3 to 15 dams each (Gurnell 1998). We chose to model dams per kilometer because a) it is directly comparable to densities that can be calculated in GIS from field GPS measurements, b) densities can also be approximated with aerial imagery and/or overflights, and c) linear dam density is commonly reported in the literature so there are valid estimates for direct comparison. For more information: http://brat.joewheaton.org/
The Utah statewide Beaver Restoration Assessment Tool (BRAT) is a decision support and planning tool for beaver management. The backbone to BRAT is a capacity model developed to assess the upper limits of riverscapes to support beaver dam-building activities. Both existing and potential capacity were estimated with readily available spatial datasets to evaluate five key lines of evidence: 1) a perennial water source, 2) availability of dam building materials, 3) ability to build a dam at baseflow, 4) likelihood of dams to withstand a typical flood, and 5) likelihood that stream gradient would limit or completely eliminate dam building by beaver. Fuzzy inference systems were used to combine these lines of evidence while accounting for uncertainty.