North Fork Burnt River BRAT
Client: Powder Basin Watershed Council
This report presents an application of the Beaver Restoration Assessment Tool 3.0.20 (BRAT; http://brat.riverscapes.xyz/), a tool for building realistic expectations for partnering with beaver in conservation and restoration (Macfarlane et al., 2017). In this application, we analyzed all the perennial rivers and streams within the Burnt River watershed (8-digit USGS Hydrologic Unit Code (HUC 8)). The primary focus of this analysis as on the North Fork Burnt River watershed (HUC 10) which is the spatial extent of this project and contract.
The backbone to BRAT is a capacity model developed to assess the upper limits of riverscapes to support beaver dam-building activities. It outputs an estimated density of dams (i.e. dams per length of stream) and a rough count of an upper limit (i.e. capacity) of how many dams the conditions in and surrounding a reach could support. Both existing and historic capacity were estimated using readily available spatial datasets to evaluate 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. Fuzzy inference systems were used to combine these lines of evidence while accounting for categorical ambiguity and uncertainty in the continuous inputs driving the models. The existing model estimate of capacity was driven with LANDFIRE vegetation data from 2014, whereas the ‘historic’ estimate represents a pre-European settlement model of vegetation, also from LANDFIRE.
The estimated existing North Fork Burnt River watershed capacity is 7,019 dams or roughly 14 dams/km. By contrast, the same model driven with estimates of historic vegetation types estimated the North Fork Burnt River watershed-wide capacity at 11,036 dams or roughly 22 dams/km reflecting a 36% loss compared to historic capacity. Nearly all of this capacity loss can be explained in terms of vegetation loss and degradation associated with land use including, i) conversion of valley bottoms to agricultural land uses, ii) overgrazing, and iii) conifer encroachment of wet meadow areas. Despite the losses, North Fork Burnt River watershed’s waterways are still capable of supporting and sustaining a substantial amount of beaver dam-building activity.
Identifying these losses in beaver dam capacity incentivizes plans for restoration and conservation opportunities to be considered. To aid groups in their decisions and what possible risks may arise the BRAT model supplies the following management outputs: 1) conservation and restoration opportunities, 2) potential risk areas, and 3) unsuitable or limited dam building opportunities. As such, the BRAT model identifies where streams are relative to infrastructure and high intensity land use, and conservatively shows how that aligns with where beaver could build dams.
The performance of the existing capacity model was verified for the Burnt River watershed (HUC 8) using 58 existing dams throughout the full modeled drainage network extent representing 0.4% of the 2062 kilometers of perennial streams. We verified the existing capacity model for the North Fork Burnt River watershed (HUC 10) using 53 of those 58 existing dams representing 0.7% of the 495 kilometers of perennial streams. We found that model performance was spatially coherent and logical, with electivity indices that effectively segregated out amongst the capacity categories.
The spatially explicit outputs from this application of BRAT provides stakeholders with the information needed to understand potential risks, constraints and opportunities for using beaver in restoration and conservation. Not only does this information help with broad-scale planning efforts, but the resolution is sufficient to support design and on- the-ground implementation of conservation and restoration activities.
Scope and Extent of the Project
BRAT Deliverable Data Products include:
- KMZ files of the four primary BRAT outputs (existing dam capacity, historic dam capacity, human-beaver potential conflict and beaver conservation and restoration zones) here
Shapefiles and Geodatabases for the four primary outputs and standard inputs here
Layer packages that identify the inputs, intermediates, and outputs here
Inventory of existing beaver dams as KMZ here
- Atlas of BRAT outputs here
Macfarlane, W. W., J. M. Wheaton, N. Bouwes, M. L. Jensen, J. T. Gilbert, N. Hough-Snee, and J. A. Shivik. 2017. Modeling the capacity of riverscapes to support beaver dams. Geomorphology 277:72-99.