What is BRAT?
Dam Building Capacity Model
The Beaver Restoration Assessment Tool (BRAT) is a tool for imaging what is possible with dam-building beaver. As (Goldfarb, 2018; page 237) elegantly states, “Although BRAT’s primary value is technical, it is, too, an achievement of the imagination, a method for visualizing the magnificently ponded world that predated European trapping — a time machine to the Castorocene”. The BRAT capacity model outputs ‘paint’ a vision of what watersheds once were, and what they could be if beaver were allowed to return. BRAT provides a vision
for what’s possible and how partnering with beaver can help increase the resilience of watersheds to drought, fire, and climate change. BRAT can be used for planning and outreach, expectation management, and conservation and restoration prioritization.
The four primary questions that the BRAT capacity model asks:
BRAT’s backbone is a capacity model developed to assess the upper limits of riverscapes to support beaver dam-building. Our estimates of beaver dam capacity come from seven lines of evidence: (1) a reliable water source; (2) stream bank vegetation conducive to foraging and dam building; (3) vegetation within 100 m of edge of stream to support expansion of dam complexes and maintain large beaver colonies; (4) likelihood that dams could be built across the channel during low flows; (5) the likelihood that a beaver dam on a river or stream is capable of withstanding typical floods; (6) evidence of suitable stream gradient; and (7) evidence that river is too large to allow dams to be built and to persist. This is estimated using the following five inputs:
The Beaver Restoration Assessment Tool (BRAT) is a tool for imaging what is possible with dam-building beaver. As (Goldfarb, 2018; page 237) elegantly states, “Although BRAT’s primary value is technical, it is, too, an achievement of the imagination, a method for visualizing the magnificently ponded world that predated European trapping — a time machine to the Castorocene”. The BRAT capacity model outputs ‘paint’ a vision of what watersheds once were, and what they could be if beaver were allowed to return. BRAT provides a vision
for what’s possible and how partnering with beaver can help increase the resilience of watersheds to drought, fire, and climate change. BRAT can be used for planning and outreach, expectation management, and conservation and restoration prioritization.
The four primary questions that the BRAT capacity model asks:
- Is there enough water present to maintain a pond?
- Are enough of the right types of woody resources present to support dam building?
- Can beaver build a dam at base flows?
- Can dams withstand typical floods?
BRAT’s backbone is a capacity model developed to assess the upper limits of riverscapes to support beaver dam-building. Our estimates of beaver dam capacity come from seven lines of evidence: (1) a reliable water source; (2) stream bank vegetation conducive to foraging and dam building; (3) vegetation within 100 m of edge of stream to support expansion of dam complexes and maintain large beaver colonies; (4) likelihood that dams could be built across the channel during low flows; (5) the likelihood that a beaver dam on a river or stream is capable of withstanding typical floods; (6) evidence of suitable stream gradient; and (7) evidence that river is too large to allow dams to be built and to persist. This is estimated using the following five inputs:
- a perennial water source
- availability of dam building materials
- ability to build a dam at baseflow
- likelihood of dams to withstand a typical flood
- likelihood that stream gradient would limit or completely eliminate dam building by beaver
Dam-building beaver management model
A beaver dam capacity model alone is not enough to effectively plan for large scale management and restoration of dam-building beaver. As such, the BRAT model assesses risk and opportunity for using beaver in conservation and restoration based on where streams with beaver dam capacity are relative to human infrastructure and high intensity land use.
Where have we used BRAT?
BRAT has been applied in the following areas:
significance of project
We believe the BRAT model helps build realistic expectations about what beaver dam-building may achieve locally on a given stream, and also helps scale-up those expectations at the watershed level, state level, regional level and US wide level. These applications of BRAT provide the information needed to understand actual and potential beaver dam capacities, where human infrastructure is present, where nuisance beaver can be relocated, where ‘living with beaver’ strategies may be needed and where beaver can be employed in watershed conservation and restoration efforts to recover degraded streams, meadows and wetlands.
How the data can be used
BRAT model outputs can be used to initialize restoration and conservation planning and can also support initial conceptual design and siting of specific restoration actions. BRAT model outputs can also aid with expectation management, and conservation and restoration prioritization.
Beaver dam building activities can cause conflict where valuable infrastructure and/or land is impacted. Many conflicts can be managed to minimize damage while ensuring animal welfare and delivering ecosystem benefits. Understanding the capacity of streams to support dam building and identifying areas of risk and opportunity is therefore critically important for the effective beaver management.
Beaver dam building activities can cause conflict where valuable infrastructure and/or land is impacted. Many conflicts can be managed to minimize damage while ensuring animal welfare and delivering ecosystem benefits. Understanding the capacity of streams to support dam building and identifying areas of risk and opportunity is therefore critically important for the effective beaver management.
