Mapping rockfall sources and deposit areas

March 16th, 2018, Published in Articles: PositionIT, Featured: PositionIT

Rockfalls are one of the major threats to the viability and liveability in the Alps. To identify areas that are at high risk due to rockfalls, it is important to study historical events and develop spatial models that provide accurate maps of rockfall deposit areas. To study rockfalls it is necessary to validate the results of modelling in the field – something RockTheAlp (RTA) sets out to do.

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

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

Fig. 1: Collecting rockfall deposits locations for rockfall on Mangart Pass.

Fig. 1: Collecting rockfall deposit locations on Mangart Pass.

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 the Leica Zeno 20 GIS Collector to gather attributes of rockfalls, and the Leica GG04 Smart Antenna for gathering their accurate location.

Collecting historical rockfall data

Fig. 2: The GIS collector provides centimetre accuracy input to Esri Collector.

Fig. 2: The GIS collector provides centimetre accuracy input to Esri Collector.

To collect information about historical rockfall events, researchers from the University of Ljubljana needed to collect data on the locations of rockfall source areas and rockfall deposits. For this reason, the web map within the collector was designed in a way that allowed users to collect one location of rockfall source area as a point feature, and later add multiple locations, also as point features, of rockfall deposits.

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

Besides the location, Esri Collector users were able to add different attributes to both source (e.g. source area type or forest cover) and deposit features, such as dimensions, shape of the rock and how the rock likely came to a stop. Users were also able to add notes to both sets of features, as well as attachments and track changes. The app can be used offline, and once the internet connection is restored the collected data is synchronised to the web map and can be seen by other users. Different types of maps can also be added to the application and uploaded to a device for offline use.

Combining technologies

Before purchasing it, the researchers tested the Leica GG04 Smart Antenna in the demanding conditions they face in their daily work, such as in narrow valleys and under tree canopies. The GNSS measurement engine provided them with position availability and accuracy they felt they could not achieve with most other devices. They combined it with the Zeno 20, a rugged Android-based controller with a screen big enough for convenient work while still fitting comfortable in one hand.

The researchers used the Esri Collector app on the GIS collector to enable a collaborative workflow between several field crews and project partners and to record the data on the same database. The University of Ljubljana researchers also made use of Leica Zeno Mobile software for other mapping projects. This software’s automatic functionalities enable them to store accuracy values as attributes of a point feature. Due to the compatibility of the smart antenna, the researchers were also able to connect it to nearly any device or software for high accuracy.

Contact Crystal Richardson, Aciel Geomatics, Tel 011 312-7450, info@aciel-geomatics.com