DAMAST - Dams and Seismicity

Regional Deformation Monitoring

WP A.4, B.1, B.7

A combination of geodetic and remote sensing methods is used to record the response of the dam to load changes and compare it with vertical and horizontal displacement patterns in its surroundings. We expect to observe vertical ground deformation of cm-magnitude in response to the annually varying water level, and we aim to estimate fault shearing and regional strain built-up in the tectonically active region. The integrated observation system for regional deformation detection is divided into three components:

1 Permanent GNSS stations for the acquisition of transient deformation signals with high temporal resolution. GNSS stands for Global Navigation Satellite Systems like the US-American system GPS and the Russian system GLONASS which are currently used in the project. The installation of two multi-frequency receivers is planned, which serve as reference stations to realize a geodetic datum for the project-wide survey points and as base stations for the campaign measurements as well as permanent single-frequency stations. The stations will be installed in the centre of the measuring network close to the dam. The GNSS network will be completed by four single frequency stations which will be used to detect localized (shear) movements along the Ingirishi Fault, which runs from the dam in a southwestern direction. Test measurements at potential places have been done during a field campaign in October 2019. Due to logistical and environmental issues finding a location at the northern side of the Ingirishi Fault turned out to be very difficult.

2 GNSS campaign measurements to record regional shear and compressive tectonic movements. A network of 10 fixed survey points was established in October 2019 along the eastern shore of the lake and in the southern foreland. The aim is to geodetically record regional shortening tendencies and shear movements over the area of the reservoir and to merge them with the results of radar interferometry. Two campaigns per year in static mode are planned, carried out during periods of yearly high and low water levels of the reservoir (August and March, respectively).

3 Persistent scatterer SAR interferometry (PSI) to capture the regional displacement field with high spatial resolution. In the last decade, the methods of multitemporal SAR interferometry (PSI, SBAS) have established themselves as a recognized method for the spatially dense detection of deformation phenomena on the earth's surface. However, the results are strongly dependent on the temporal stability of the backscattering conditions at the surface, which is not guaranteed in overgrown and forested areas. Interesting for SAR interferometry are, besides the dam and its foreland, especially the rocky shores of the reservoir. Hence, methods for the use of partially time-stable backscatterers and distributed scatterers must be further developed. It is planned to use three different SAR frequencies (L-, C-, X-band). While the X-band data will be used primarily for the precise observation of the dam structure, its abutments in the host rocks as well as exposed slopes along the reservoir, a significant contribution to the determination of the regional deformation field is expected from the evaluation of the L-band data. For the free of charge available C-band data the suitability for monitoring ground movements in the predominantly forested and mountainous terrain will be assessed and recommendations for similar monitoring projects will be developed. Corner reflectors will be installed as ground reference points and repeatedly measured by GNSS. These absolutely measured points are used as common points for regional and local PSI measurements to integrate all differential observations into a single geodetic datum.

 

 

 

Fig. 1: (left) Points on solid ground (concrete, rock) were selected for the GNSS campaigns. (middle) Massive ground bolts should allow a precise repeated installation of GNSS antennas. (right) Setup of a 24-hour GNSS-test-measurement near the dam.