Mapping the rockfall source and deposit areas in the Alps

Authors: Barbara Žabota & Gregor Bilban

Rockfalls are one of the major treats to the viability and liveability in the Alps. To recognise areas that are at high risk due to rockfalls, it is important to study historical events and develop spatial models that provide accurate mapping of rockfall deposit areas. To study the rockfall it is necessary to validate the results of modelling on the field – here is where Leica Zeno 20 GIS Collector and Leica GG04 Smart Antenna come in handy.

Project RockTheAlps (RTA) is an Interreg Alpine Space project which will reinforce and strengthen the implementation of rockfall risk prevention policy and mitigation strategy support in line with a sustainable forest management approach. To achieve this objective, the first harmonised rockfall natural risk and protection forest mapping for the entire Alps will be provided. Project RTA involves 15 interdisciplinary partners from six Alpine countries: Austria, France, Germany, Italy, Slovenia, and Switzerland. 

University of Ljubljana, one of the project partners from Slovenia, is responsible for developing a historical rockfall database which will serve for the testing of rockfall model developed within RTA.

As the main goal of this historical database is to get the locations for past rockfalls, researchers from the Department for Forestry and Renewable Forest Resources of the Biotechnical Faculty decided to use Zeno 20 GIS Collector to gather attributes of rockfalls and GG04 Smart Antenna for collecting their accurate location.

Collecting rockfalls with Esri's Collector for ArcGIS & Leica Zeno 20

An example on how to correctly measure angle and azimuth for source area (standing point of measurement marked by red line) based on available information on rockfall detachment point (purple rectangle marking the actual detachment point, green rectangle marking the top-most point of rock cliff).

When gathering information about historical rockfall events, researchers from University of Ljubljana collected data on the location of rockfall source area and rockfall deposits. The web map within the collector was, therefore, designed in a way the user collects one location of rockfall source area as a point feature and later adds multiple locations as point features of rockfall deposits in relationship class one-to-many.

As the rockfall source area is usually inaccessible, the faculty researchers designed a method to extract the location for the source area from a standing point. The exact location was later calculated based on angle and azimuth measurements using a precise digital terrain model.

Besides the location, Esri Collector for ArcGIS users can also add different attributes to both source (e.g. source area type or forest cover) and deposit feature, such as dimensions, shape of the rock and, the reason that rock stopped. Both features, as seen in the image, allow to add notes, attachments and track editors. 

Esri Collector for ArcGIS can be used offline –  once the user restores Internet connection the collected data are synchronized to the web map and can be seen by other users. Moreover, distinct types of maps can be added to the application and uploaded to your device enabling offline use.

 Leica Zeno 20 delivers centimetre accuracy to ESRI Collector for ArcGIS used for rockfall mapping.

Combining Esri's Collector for ArcGIS with Leica Zeno and Leica GG04 Smart Antenna

Based on measurements of angle and azimuth from different standing points (blue dots) and digital terrain model the actual location of rockfall source area (red dot) is being calculated.

The decision for top-class combination of Zeno GG04 Smart Antenna and 20 GIS Collector was no coincidence.

“Before purchase we tested GG04 Smart Antenna in the most demanding conditions which we are facing in our daily work such as narrow valleys and tree canopies. Its GNSS measurement engine provided us with position availability and an accuracy we could not achieve with any other device. Zeno 20, on the other hand, is a rugged Android based controller with a screen big enough for convenient work while still fitting comfortable in one hand,” said Frédéric Berger, communication manager of the RockTheAlps project.

While using Esri's Collector for ArcGIS with Zeno 20 for collaborative work of several field crews and project partners on the same database, the University of Ljubljana faculty researchers also make use of Leica Zeno Mobile software for many other mapping projects.

“We like Leica Zeno Mobile intuitive user interface. While still packed with necessary GIS features, its automatic functionalities enable us to store accuracy values as attributes of a point feature. All this rises the quality of our maps,” said Milan Kobal, head of the RockTheAlps project at the University of Ljubljana.

Leica Geosystems GNSS equipment offered the Slovenian team of researchers even more. “Due to the openness of Zeno GG04 we can connect this Smart Antenna to nearly any device or software requiring highest accuracy. This opens us additional options for future projects and research,” concluded Kobal.