A couple of roughly 30-year-old bird-watching towers of Metsähallitus were inspected in North Karelia in August. An inspector of bridge and engineering structures from Sweco crossed stretches of mire and forested hills to ensure the continued safety of the bird-watching towers of Huuhkajavaara and Teretti for the thousands of hikers and bird watchers that visit the area.
The bird-watching towers of Huuhkajavaara and Teretti were completed in Lieksa at the beginning of the 1990s. The viewing platforms of both towers rise to a height of roughly 10 metres, and they are accessed by sturdy wooden stairs. The stability of the towers relies on 200-millimetre-thick columns made of impregnated wood and concrete footings.
‘Neither of the bird-watching towers is located near actual transport connections: the Huuhkajavaara tower is situated in the Ruunaa hiking area on top of Huuhkajavaara Hill, while the Teretti tower is situated in the middle of the vast mire areas of Patvinsuo National Park,’ Jani Perttunen from Sweco says. Carrying out the inspections required the expert in engineering structures to have an energetic outdoor spirit. ‘The greatest challenge was getting there! Fortunately, I survived the encounter with a viper resting on top of the boardwalk by stomping my feet.’
Inspection of bird-watching towers is rare in Finland, and experienced inspectors can mostly only be found in Metsähallitus. At the start of the project, Sweco carefully considered what type of expertise was required to inspect the bird-watching towers. ‘In terms of its structure, a bird-watching tower is similar to a wooden bridge, so an inspector of engineering structures has suitable skills to inspect both of them,’ Perttunen says.
The safety of thousands of hikers is the priority
Metsähallitus’ own inspection rounds ensure that various bird-watching towers and other service structures are inspected and maintained annually.
‘We want to have our bird-watching towers, as well as road bridges and suspension bridges, inspected regularly, also by external parties,’ Heikki Räsänen from Metsähallitus says. ‘We wanted to inspect the roughly 30-year-old bird-watching towers more thoroughly than usual to make sure that the structures are definitely safe and to address any problems on time.’
The safety of the bird-watching towers, which are in public use, affects thousands of visitors per year. ‘The hiking area in Ruunaa is visited by roughly 80,000 people annually and Patvinsuo by roughly 16,000 people,’ Räsänen says.
Only wear and tear caused by time was observed in the towers
In the general inspection, the inspector looked for possible material damage and also inspected the joints and foundations. Core samples were taken of the columns with an increment borer through spot checks to find any rot.
‘The inspection was systematic, and we set out to carry it out one part at a time,’ says Räsänen, who monitored the inspection on site. He thinks that the inspector focused on the right structures from the perspective of safety. ‘The comprehensive inspection also brought to light important details, such as the protruding nails in some stair boards.’
One of the towers was also coincidentally test loaded while the inspectors were present. ‘Right before the inspection, there was a group of more than 15 tourists at the Teretti tower, and the tower held up well!’ Perttunen laughs.
No great surprises were encountered during the inspection, and the structures were in good condition. Neither was any rot found. ‘The inspection only revealed wear and tear caused by time,’ Räsänen says, satisfied. ‘Based on the inspection report, we will carry out the necessary repair and maintenance measures, which will lengthen the service life of the structures.’