Älgån is a tributary to the Nissan River and springs at Komosse nature reserve, a large marsh area approximately 30 km southwest of Jönköping, Sweden. It runs for ~18 km before flowing into Nissan River. The area of the basin is approximately 50 km2, of which circa 20 km2 is upstream the project area (Figure 1).
Only the headwaters of Älgån River are under protection in the form of a nature reserve. Älgån River is characterized by dark, humic water and steep incline in the section around the project area, entailing a bottom substrate of larger rocks and stone blocks (Figure 2). A small trout (Salmo trutta) population is present in the river, showing that this regionally important species reproduces along a 10 km reach downstream of the project area. The water in Älgån can drop to pH levels as low as 5.5 during high flows, which limits the biodiversity in the river to species that are more tolerant to lower pH-levels.
The river has no economically important resources, and was fragmented only by two barriers, the one presented in this project and a dam 5 km further downstream. Both barriers have been used for different purposes throughout history, including water-driven mills and saws and a steam saw.
The age of the original dam in Älgån River is unknown. It was modernized with concrete during the 1940’s, when the steam saw was modernized. This appears to have been the main purpose for the dam in modern times before the closure of the steam saw a few decades later. However, for several decades now, the dam has had no function or activity connected to it, apart from serving as a road crossing. The old bridge’s spillway with a 0.7-m head was a definitive barrier for all aquatic species. The combined discharge capacity of the bridge and the culvert next to it (Figures 3-4) was too low, leading to flooding of the upstream area at very high flows.
The modification of the dam and bridge at Älgån River had been on the agenda of Jönköping Municipality for a long time. Jönköpings Fiskeribiologi (Jönköping’s Fishery Biology), a small consultancy firm with over 20 years of experience specializing in aquatic environments with a focus on fish, fish ways and more hydraulicly complex solutions, visited the site for the first time in 2012. Jönköping Municipality gave the green light for the project to commence in late 2024, when the site was measured and the planning was carried out by Jönköpings Fiskeribiologi. The assignment was to design a solution to enable fish migration and remedy the flooding problem at the site.
The choice ultimately fell on replacing the concrete bridge, the old stone dam and culvert with a 4-m wide and 2-m high steel vault bridge placed on concrete supports. The alternative solution would be to replace the bridge with a new beam bridge, but this would have increased the cost significantly, which was not justified for a river crossing on a private road. The removal works were executed by Jönköpings Fiskeribiologi in the fall of 2025, between early September and early October (Figures 5-6).
To increase the discharge capacity at the site, the old road culvert, which was located about 5 m to the left of the bridge, was replaced with two larger plastic culverts. The culverts were placed at different levels and higher than the arch so that water is channeled through them only in high flows. This way, the steel vault becomes passable for fish and other animals at all flow conditions. A migration furrow was also created in the bottom of the project area to ensure sufficient depth to allow connectivity during low flows. Several blocks of stone in the riverbed and a well-designed erosion protection will ensure that erosion won’t occur during high flows. Decreasing the water velocity will also promote fish migration, while the added stone blocks will provide well-suited habitat for small and large fish (Figures 7-8).
The total cost for the project was around 160000 Euro. 90% of the cost was covered by the municipality, with the five adjoining properties to the project area sharing the remaining 10%. The main concern of the residents was the high cost, a problem which was solved when the municipality took the risk of covering any excess costs. Other concerns that were raised were that the pool above the old bridge would disappear, which would affect the fish, and that the new road would occupy more land. However, after assuring the residents that the pool would practically move from above to under the bridge, and that the new road standard would mean that heavy vehicles with a weight of up to 64 tons could now pass the bridge, they were very satisfied. This meant that they could now transport heavier loads from their forestry properties out on the road.
The work went smoothly thanks to good cooperation between the contractor Ulf Thelander, Jönköpings Fiskeribiologi, the client Jönköping Municipality and Ponova Nordic, the supplier of the steel vault. The residents nearby Älgån River are happy with the outcome of the project and the first trout are now expected to soon pass by the restored site.
Before & After photo pairs
With many thanks to Elliot Franzén from Jönköpings Fiskeribiologi AB for providing the information and the visuals presented herein.
Prepared by Foivos A. Mouchlianitis