Nemadji River Watershed Culvert Inventory for Fish Passage
In the summers of 2013 and 2014 Carlton County Soil and Water Conservation District and Carlton County Zoning and Environmental Services staff visited 86 stream/road and stream/trail crossings in the Nemadji River Watershed with the purpose to create an inventory for fish passage barriers.
The Nemadji River Watershed is an important fishery resource in Carlton County, containing self-sustaining populations of brook, brown and rainbow trout. All of these species must migrate between habitats during different seasons and life-stages, but improper culvert crossings can inhibit this movement. In addition, improper culverts in the Nemadji Watershed contribute to stream stability issues that increase erosion and degrade water quality. The Nemadji River and some if its tributaries are listed as impaired for turbidity by the Minnesota Pollution Control Agency.
86 crossings were inventoried through this project. Of those, 9 (10%) are Complete Barriers, 62 (72%) are Significant Barriers, and 15 (17%) are Passable. This graph shows the number of culverts inventoried that fell within the particular fish passage rankings. The largest number of culverts were in the ‘constricted’ category, which was a result of the culvert width being much less than the bankfull width ratio. Constriction of the stream increases the stream velocity and inhibits the ability of aquatic organisms to travel through the crossing.
|Ranking Priority||Criteria to meet ranking||# of sites|
|1. COMPLETE BARRIER TO NATIVE SPECIES: Infrastructure failing||Serious infrastructure damage, highest priority for restoration for either road safety concern or resource concern.||2|
|1. COMPLETE BARRIER TO NATIVE SPECIES: Perched > 2 Ft.||Perched +2 ft.||7|
|2. SIGNIFICANT BARRIER: Blockage||These sites were dammed at the inlet by beaver dams. This category was created so that future actions could consider beaver management as a possible solution.||6|
|2. SIGNIFICANT BARRIER: Perched 0.5-2.0 Ft.||Perched – 0.5-2.0 ft Most species and life stages cannot pass at most stream flows.||18|
|2. SIGNIFICANT BARRIER: <0.8 Culvert width to bankfull width ratio||<0.8 Culvert width to bankfull width ratio (constricted). These sites were not perched, but the culvert is likely undersized and the culvert width to bankfull width indicates the stream is constricted at the crossing.||38|
|4. Passable||These sites are passable for all aquatic life. Several are newer restoration projects, some have older infrastructure.||15|
High Priority Trout Streams
High quality trout streams were a high priority for this inventory to capture fish passage barriers. Below is a table and graph displaying the highest quality trout streams in the watershed, with the crossing ranking. It is beneficial to point out that there are very few Complete Barriers on these streams. Most of the Significant Barriers are from low culvert width to bankfull width ratios, meaning the stream is constricted at that crossing.
The Blackhoof River has the most crossings, followed by Clear Creek, then the Little Net River. Net River, Clear Creek, and Section 36 Creek all have one Complete Barrier crossing.
This project was funded primarily by a grant from the US Fish and Wildlife Service Fish Passage Program, with additional funding from the Minnesota Department of Natural Resources Stream Habitat Program.
The inventory will aid in prioritizing future culvert restoration efforts and will give the SWCD high-quality data to make the most effective use of future funding for culvert restoration projects.