Landslide area described as “high risk” in 2005 report – VG

In 2005, the Norwegian Geotechnical Institute (NGI) submitted a clay rapid landslide risk assessment in the municipality of Gjerdrum, on behalf of the Norwegian Directorate of Energy and Water Resources (NVE).

Two areas delimited by NVE are affected by the rapid clay landslide that affected the municipality on Wednesday morning. In the report from 15 years ago, both areas have the status of high risk areas.

TV 2 mentioned the report for the first time.

One of these zones is Hønsisletta, which includes the area where several houses collapsed on Wednesday. Risk is assessed based on a combination of the probability of a landslide and the severity of the consequences of a landslide in the given area.

GET AN OVERVIEW: We know this about the landslide

Development according to report

Hønsisletta is defined as having a low risk of landslides, the NVE overview shows. The other area, Fjelstad, has a medium risk of landslides. The affected housing area is in the Hønsisletta area, just across the border from Fjelstad.

“Development within fast clay zones is a major challenge as difficult stability issues must be addressed. First, the stability of the entire danger zone must be analyzed, ”the report states.

“This is done to assess whether landslides of such magnitude can occur that the development area may be threatened,” he further states. This means that areas must be “declared healthy with respect to landslides” before they can develop.

At the same time, land registry data from the Cartography Authority shows that much of the residential area was developed in 2008, just three years after the NGI risk assessment was submitted.

Gjerdrum Municipality Mayor Anders Østensen (Labor Party) says the municipality should be given time to assess planning and construction issues related to the landslide.

– It is clear that it has not been developed without having been authorized by the professional authorities of NVE or NGI. Where they have had objections, this has been observed. Østensen tells VG.

– There is a lot of clay in Romerike, but that does not necessarily impede development. I calculate that measures had to be taken, but they have also been done.

For the past 20 to 30 years, Odd Sæther has been the developer of more than 200 homes in the area by Ask. He tells VG that they have done all the landslide protection after the book and have followed the requirements for geotechnical investigations.

– I have not come close to believing that this was dangerous at all. If he had suspected something was not safe, he would never have built there, Sæther tells VG.

– It is very uncomfortable. We try to be careful and do things the way they should be. We have done the same. NGI has controlled in detail what we are going to do and we have followed what they have said. This included, among other things, the stabilization of rock massifs. I’m even more surprised that something like this could happen, he says.

He himself lives nearby and was one of the evacuees earlier today.

– I live right next door. Earlier today I heard the helicopter in the air, but I didn’t understand what it was. Shortly after, someone knocked on the door and I was evacuated. They said there had been a landslide, Sæther tells VG.

– It’s tragic all together. I sincerely hope that no life has passed, he says.

«Risk» also in previous report

Also in previous reports, NVE has described the area as dangerous. In 1984, the management wrote that “there are several recorded landslide wells in the area”, over the area around Fjelstad and Ask.

“Probe drilling indicates sensitive masses, probably fast clay, at different depths,” states the report from the 1980s.

Then fast clay was also found at a depth of 15 to 25 meters at the Fjellstad farm.