Debris Flow at Buffalora

In July 2022, there was a debris flow near the Ofenpass at Buffalora. Because there has not been much erosion yet, we saw the opportunity to investigate its "untouched" levées. So we decided to search for a correlation between the slope and the height of the levées. The levées mark the edges of the debris flow and are made of left-behind material of the flow.

How does the slope of the debris flow at the Buffalora influence the height of its levées? We assumed that a steeper slope would result in lower levées at the sides of the debris flow, since the debris flow is faster in steeper areas and thus less material is left behind.

Our methods were quite simple and needed little and accessible material. In order to measure the slope, we took a solid, straight stick, which used to be the stick of a mop. We placed it on the ground and put our smartphone on it to measure the slope. Then we converted the measured slope from degree into percentage. To get accurate results, we had to respect the following two aspects: The stick had to lie on a flat surface and had to be placed approximately one meter next to the highest point of the levée. In order to get a more representative result, we measured the height of the levée one meter away from the top on either side of it. We used the stick again for this task as a extension to the top. With this technique we managed to collect the data of 28 individual locations on the debris flow.

We confirmed our hypothesis and managed to find a correlation between the slope and the height of a levée. However, there were certain factors influencing the height of the levées regardless of the steepness of the slope. On factor is the tree density: If the tree density is higher, the debris flow gets decelerated. Another factor is the junction of two or more independent arms of a debris flow. When arms cross their ways the levées are junked together and it gets really confusing and complicated to measure them. A third big factor is the phenomenon of curves: If a debris wall rushes towards a slope, it gets deflected and material is pressed against the slope resulting in a higher levée on the outside of the curve. This is why we tried to avoid locations with different levels of tree density, junctions of arms and curves in order to get more precise measurements. We conclude that the steepness of the slope does influence the height of the levées. This happens due to the speed of the debris flow which is higher in steeper terrain and thus leaving less material behind.

One measurement shows, how the curve influences the height of a levée. The by far highest recorded levée was measured in a curve and is therefore a measurement which is very strongly influenced by a different factor than the slope. This point is visible on the 3D map as well as on the scatter diagram.