Imagine the following scenario: You are driving in an area where there has been a lot of rain in the past, and this autumn evening it is raining a lot. You will then receive a text message saying that the water pressure in the ground on the mountainside above you is now so great that the road must be closed. After a few hours, you will receive another message saying that the water pressure has dropped again, and that it is now safe to drive again. This is not a wild fantasy. In a steep mountainside in Sogndalsdalen in Vestland, reeds have been seen that go several meters into the ground. It is equipped with a sensor that can record the water pressure in the soil, what is known in technical terms as the pore water pressure. Pore water Pore water is water that exists in the space between soil particles. Pore water exerts pressure on the soil and, if the soil is saturated with water, can set particles in motion due to the pore water pressure. In the area here, there have been several landslides and mudslides in the past, and it will happen again. When the autumn storms come with large amounts of precipitation, the painter will record how much water is standing on the ground – at any time. Landslide over county road on Kvamsøya in Møre and Romsdal. Photo: Arne Werkland Researchers from the University of Western Norway and professionals from NVE are working together on the project. The aim is to gain more knowledge about how much water is needed to trigger landslides. – We can probably cry wolf a little later. We can be more confident that it is now really critical, says Professor Stein Bondevik at the University of Western Norway. The meter is placed in a pipe, and records the water pressure from hour to hour. Photo: Arne Stubhaug / news Want better measurements Landslide events are complex, and the release depends, among other things, on the slope, the masses on the ground, snowmelt and rainfall. But the pore water pressure is absolutely central. Based on previous measurements of real landslide events, Bondevik found that the critical phase, where there is a risk of landslides, is shorter than is often thought. – In large parts of the time period we measured, 99.87 per cent, the groundwater was not critical. In a typical autumn storm in Western Norway, it is only critical for around four to five hours. Over time, NVE has built up a network of stations all over the country, which, among other things, measure groundwater, and which are a central part of the warning service varsom.no. Today there are stations all over the country that measure groundwater, but almost none of them are located in steep terrain. Photo: NVE But almost all the stations today are located on flatter terrain. Bondevik believes it is important to build more measuring stations in steep terrain. – Most of the data available today is based on how the groundwater is in the valley floor. It is not always representative of what happens up on the slope. Landslide earlier this summer in Rauma municipality in Møre og Romsdal. Photo: Arnt Olsen Local data The landslide warning has existed since 2013 and is based, among other things, on meteorological observations, model forecasts and analysis of historical landslide activity. This is how the landslide warning works The landslide warning is a collaboration between NVE, the Meteorological Institute and the National Road Administration. These models use weather forecasts from the Meteorological Institute as input data. The warning system is regional and, among other things, based on model calculations of water saturation in the ground and how much rain and snowmelt is expected for each square kilometer in Norway. When the model calculations indicate a danger of avalanches, a danger warning is sent out and published on varsom.no. The Norwegian Geotechnical Institute (NGI) has also taken a closer look at how local measurements of the water pressure in the ground have contributed to lower uncertainty in warning of potential landslides. The conclusion is that it is possible to significantly improve local warnings. – In the long term, one can imagine carrying out measurements in particularly exposed areas, something that will provide a real local warning of the risk of landslides and landslides, writes NGI in a summary. Landslide earlier this summer in Rauma municipality in Møre og Romsdal. Photo: Arnt Olsen NVE: – Will take time Norway’s Directorate of Water Resources and Energy (NVE) says the research field in Sogndalsdalen is particularly important to find out more about what triggers landslides and mudslides. Data from this station will be able to answer whether the models used in avalanche warning are precise enough. In addition, more surveyors can contribute to better local warning. The mountainside at Anestølen in Sogndalsdalen is steep. Several landslides have occurred here in the past. Photo: Arne Stubhaug / news Over time, NVE wants to put in place more stations and measuring points, which can measure the level of groundwater in steep terrain. – We want to establish more stations, but there are a number of challenges. We need several months, up to a year, to see if an area is suitable. In addition, it often takes many years of measurements to establish good enough statistics, says hydrogeologist and head of section Hervé Colleuille. He says it is also a matter of resources how many stations and meters are to be deployed, as there is a need for data control and maintenance.
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– We can call wolf a little less often – news Vestland
