As part of the SITES Water Program, water balance, including stream water level and discharge as well as lake level, is measured. At Asa, water balance is monitored in the Feresjön catchment, which includes Feresjön lake as well as the lake inlets and outlet.
This summer at Asa the inlet weir design at the Main inlet sampling point in the Feresjön catchment has undergone a planned design change. The Feresjön catchment is part of the Mörrumsån catchment area. Within the Mörrumsån catchment area, the County Administrative Board is conducting extensive work to review hydropower and other water operations. The updated weir design is a requirement to improve the aquatic environment by creating free passage for fish and other aquatic organisms. As such, the inlet v-notch design at the Main inlet sampling point has been changed to a rectangular opening.
The new design allows for water to pass through a well-defined steel profile like the old v-notch construction and ensures that discharge can be calculated as exact as possible. A weir construction like this will never be as precise as a v-notch. However, to make sure that the data is still of acceptable quality, parallel measurements have been carried out further up-stream with a second sensor. It has been installed for one and a half years to make sure there is plenty of records representing all conditions from low to high water levels.
The Main inlet sampling point has been in operation since 2017, where water level, water discharge and water chemistry is monitored. All these measurements will continue, but the weir design for monitoring water level and determining discharge now has a slightly different configuration.
The new rectangular opening weir design at the Feresjön catchment main inlet. (photo: Niels Aagaard Jakobsen)