/ Articles / Vilas Land and Water Committee takes a look at culvert study results

Vilas Land and Water Committee takes a look at culvert study results

February 21, 2020 by Beckie Gaskill


Last summer the Vilas County Conservation Department undertook the first phase of a study looking at culvert conditions at stream and road crossings. The team, headed by conservation specialist Quita Sheehan, looked at culverts in four watershed areas within the county. Those watersheds were the Mishonagon Creek, Eagle River, Plum Creek and Muskrat Creek HUC-12 watersheds. Sheehan presented the results to the land and water committee at their last meeting.

County conservationist Carolyn Scholl said the county had never had a culvert inventory. The grant that allowed the project to be completed was applied for from the state in 2018, and the work completed in 2019. The idea was to observe each culvert for effectiveness and identify the general condition of each culvert. Only road crossings were observed, she said, rather than a full culvert inventory. That, she said, would have entailed hundreds of sites being surveyed. Both flooding hazards and blockages for fish passage were of concern with the study. Road crossing culvert locations were also confirmed, with a few errors on maps provided. 

Forty-four culverts in all were observed and from there can be prioritized. Scholl said the study will allow the county to better understand which culverts could cause the biggest issues, and to hopefully direct funding in such as way as to be most effective. 

Soil erosion, quality of fish passage and water capacity were all concerns delineated in the original grant proposal sent to the Department of Natural Resources (DNR). The culverts studied were graded on all of those metrics. 

Scholl shared a comprehensive form used in the study with the committee. The protocol used, she said is a Great Lakes Stream Crossing Inventory. It has been around for a few years, she said, and the goal was to be consistent with the collection of data. 



What was studied

It was unsure how long the project would take, so four watersheds were chosen based on some selection criteria. One of the selection criteria was that each watershed has a Class I trout stream somewhere within it. Some, she said, were wild rice areas, which is important as well. If flooding did take place in those areas, she said, existing wild rice populations could go extinct. Another criteria would be an area of special resources interest to the DNR for one reason or another.

The culverts studied were split into four categories. Of those surveyed, 13 came back as being in new condition, 21 in good condition, six in fair condition and four in poor condition. 

In the Mishonagan Creek watershed, and the Tomahawk River, 17 locations were studied in the portion of the watershed in Vilas County only. Of those, seven came back in new condition and six in good condition. Only four of those culverts came back in the poor or fair categories. 

Next, Scholl said, they looked at constriction ratios. The calculation took the width of the culvert divided by the width of the stream at the culvert. If that ratio was more than 50%, she said, it was considered constricted. In that watershed, 67% were considered restricted, meaning there would be a bottleneck situation in periods of high water flow.

Fish passage was also studied, with each of the culverts getting a fish passability score. A score of zero, she said, would mean it was a barrier to most species in most life stages at most stream flows. A .5 score meant the culvert would be a barrier to some species or some life stages at most stream flows. A .9 or one would mean the culvert would only be a barrier at high stream flows. Six culverts were scored at a .5, and only three of those 17 at a .9.

Soil erosion was also studied at each culvert. Most in this watershed had a minor or trace amount, but there were still some in the heavy or severe category, showing there was still some severe erosion going on in some areas.

In the Eagle River Watershed, four sites were examined. Of those one was found in poor condition, but two in the good condition and one in the new condition. However, 100% of those culverts were considered constricted. In fish barrier scores, three received a zero score, which is the worst case scenario, showing they would be a barrier to most species or life stages at most flow levels. In the area of soil erosion, two sites received a minor or trace score, with the other two in the heavy or moderate categories.

Plum Creek in the St. Germain area has 13 sites surveys. The majority scored good or new, with seven in the good category and three in the new category. Only one site scored as poor, with the remaining two listed as fair. As for constriction ratios, 90% scored as constricted and only one as totally unconstricted. Nine of the 14 would be a fish passage barrier, the study found as well. Eight of the culverts scored as minor in the area of erosion, but the other five were either severe or minor in that area. 

In the Muskrat Creek area, 10 sites were examined. The majority of those were in either the new or good condition, with two in the first category and six in the second. Two were listed as fair. The constriction ratio was 50%. Four culverts were considered barriers, with one being a half-time barrier. The volume of soil erosion were in the trace and minor categories, meaning there was less of an erosion problem, which Scholl said was good to see.

In the next steps, she said, the department would continue to give presentations regarding the results. She also asked anyone seeing a presentation to report any issues they may see with culverts within the county. She said municipalities such as towns, who are largely responsible for the culverts being studied now, would also be receiving information on culvert scores within their boundaries. 

Scholl said the department would look to do more data collection as time goes on and would like to see a time when all road crossing culverts could be studied and scored. 

Beckie Gaskill may be reached via email at [email protected].

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