Jämtkraft AB is a Swedish energy company that provides electricity, district heating and electricity network, and produces only renewable energy. Östersund, Krokom and Åre are their main areas of business. Jämtkraft owns 17 hydropower plants in Sweden, and Hissmofors, which VRT inspected in summer 2018, is the biggest.
Hissmofors is in Krokom, in river Indalsälven. Jämtkraft wanted to get information about the riverbed’s topography, concrete structures in the dams, and pipelines that cross the river under water. The data was acquired with multibeam and laser scanning surveys, the former collecting data from under water and the latter from above water near the waterline.
During two days of inspections, VRT gathered data of 500 metres of vertical structures and 11 hectares of seabed. The data was then processed and analysed and delivered to Jämtkraft via GISGRO – VRT’s own online based service for survey reporting and data visualisation.
Earlier inspections in Hissmofors, like in most hydropower plants and underwater structures, have been done by divers. Lars Johnsson from Jämtkraft tells that diving inspections worked when the goal was to check a specific part of dam or there was a known problem in a certain location. But when in need of a larger picture of equally large structures, this method wasn’t enough.
That’s when VRT’s inspection services came into view. Multibeam sonar collects data from the riverbed from a survey boat. The method is faster and safer than other methods, and yet the data is detailed and comprehensive. The data provides a good overview, and the findings can be utilised easily.
For Jämtkraft the most interesting information from the scans was the accumulated material in front of the intake gates. Accumulated sediment can affect the way water streams, which affects how efficiently the plant produces energy.
Among the most important observations were also the several objects found in the river basin and the material left in the bottom from the earlier dam and the construction of the newest part. Large objects near pipelines, and especially on top of them, are a risk. They can move and in worst cases damage the pipe, causing leakage and thus economical loss. This is also why VRT recommends surveying all underwater structures after construction to ensure there aren’t anything left there that might cause problems.
Jämtkraft describes themselves as a very satisfied customer. The inspection results have exceeded their expectations. Findings and information they have gained, would have been very difficult to obtain using a diver alone.
“If we want, we can send a diver down to look at the details of your scans”, Johnsson describes the application possibilities of survey data. The benefits for asset management and maintenance planning are numerous in hydropower plants, where shutdowns are nothing short of undesirable.
The interest for the results have been much higher than I thought. When we discuss the findings in our company or with construction workers, they praise VRT for being very good.