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SLIDES: One of the houses that collapsed in the Gjerdrum area on New Years Eve.
As early as 2008, hydrologist Steinar Myrabø warned of problems with increased water flow during floods and soil erosion in the landslide area in Gjerdrum. He believes the demands for measures were not heard.
– Here we are already facing significant erosion and contamination of the watercourse in a previously exposed area, hydrologist Steinar Myrabø told Romerikes Blad in 2008. He then mentioned problems with increased water flow during floods and erosion in the area by Nystulia, where Wednesday was a large landslide.
At that time he was the leader of the local teams of the nature conservation association in Nannestad and Gjerdrum. The union demanded action, but said it was not heard.
Myrabø now lives in Lillehammer, where he works, among other things, with vulnerability assessments and flood and surface water management at Norconsult. He also works with water-related landslide hazard assessments.
– The criticism at that time was mainly that the development did not take into account the delay of the water, he explains to VG on Thursday. Ten people are still missing after the landslide that affected Gjerdrum the day before.
Myrabø says that the Nature Conservation Association submitted several proposals for diversion measures, which were included in the municipality’s zoning plan.
– But they weren’t followed up later in the planning phase and during development, he says.
By delay we mean the measures that allow to delay the water runoff and limit the flood peak in a specific area, to avoid flood damage.
Romerikes Blad was the first to mention the case.
Washed clay
In his work as a hydrologist, Myrabø considers the best way to manage bodies of water and what it can lead to if not done correctly.
– May cause soil erosion and rapid clay leaching. At worst, it can lead to rapid landslides, he explains. In this landslide, he points out that there is a stream in the area where the landslide occurred, where large amounts of water in general can trigger the leaching of clay.
This leaching may have spread further up the ground. If the salts from the quick clay are removed, the dough becomes unstable and almost runny. Then the ground becomes unstable and large landslides can occur.
WARNING: Hydrologist Steinar Østensen. Photo: Private
– But this is just general. What is the triggering cause of this landslide ?, NVE should conclude. So the question of water dissipation is one of several that may be interesting, the hydrologist believes,
In 2008, Myrabø requested, among other things, diversion and clearing of dams and slopes with plantation. Vegetation can also help with water management, as plants attract a lot of precipitation.
Mayor: – Will turn over all the stones
VG has tried to contact Mayor Anders Østensen (Labor Party) for a comment on the matter, without getting a response on Thursday night. He has commented on the Romerikes Blad case, where he says he cannot take a position on the 2008 objections “on foot”.
Østensen himself entered local politics in 2011.
– We will turn over all the stones and review the case, possibly to find out if something in Nystulia should have been done differently. That said, the Gjerdrum municipality has always been concerned with following professional recommendations, he tells the newspaper.
“High risk”
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.
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.
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.
THE SEA: The landslide area described as “high risk” in a 2005 report.
