In Fall 2021, the IWMP hired Alba Watershed Consulting to map and evaluate the condition of riverside (riparian) vegetation along 39‐miles between Hayden and Craig. This mapping helped the IWMP identify locations where improving riparian vegetation may benefit both the landowner (through reducing erosion through natural means) and the river’s ecosystem.

Method:

Vegetation structure and complexity were evaluated by delineating a 100-meter buffer from each bank of the river using publicly available aerial photographs, defining the Riparian Zone. The Riparian Zone was cut into polygons, each holding relatively similar land cover and land use. The consultant visited many of the sites to verify the land cover and land use, and the polygons received scores based on a criteria “A” through “F”, with an “A” being indicative of native riparian vegetation with no obvious stressors, and an “F” being indicative of bare ground or impervious surfaces.

Results:

The consultants final report is available here.

Of the 858 riparian polygons herbaceous areas (hay and pasture) were the predominate land cover type with more than 1,000 acres. The land cover types with the best scores were those in closest association with the river, including vegetated bars and scrub‐shrub habitats, likely because these areas are continually disturbed by natural processes and recover from disturbance rapidly. Cottonwood and subcanopy forests are next in terms of condition, and excellent examples of both land cover types exist. Developed polygons were assigned the lowest scores, with an average score of 56 (F grade). Many excellent examples of riparian habitat exist on hay and pasture lands.

Riparian condition scores

Riparian condition scores for each polygon (see report for map) were averaged for an overall score for each of the seven riverscapes in the study area. Results are:

RiverScape (see report for map) Average Score

17 82.4 (B‐)

18 79.9 (C+)

19 80.3 (B‐)

20 81.3 (B‐)

22 80.4 (B‐)

23 78.9 (C+)

24 76.9 (C)