Further work

The use of the HSVR method as a proxy for water saturation estimation in unconsolidated soils is the subject of active research work at Northumbria University. We are also researching a complimentary measurement that involves recording the passive electroseismic signals using an electrode pair. The data loggers developed at Northumbria University are low cost and have four data channels available and so can be used to measure the signals from the 3-component geophone as well as the signal from one electroseismic detector.

The use of 3-component data and electroseismic data for near-surface condition monitoring will be explored further using the geophysical node systems that are planned to be installed on the slope at Rest and Be Thankful should additional funds and planned mitigation works allow.

Recommendations

1. Time-lapse camera analysis developed by the team has already proven to be a valuable and impactful tool, identifying previously undetected areas of movement that have later led to potentially damaging events where severe impacts have been mitigated. Making sure the timelapse system is effectively utilised and operated is key to its success and further setting of appropriate alert thresholds relative to the conditions will help refine the data achieved.
2. NIR imagery has been effectively tested with useable images achieved from slope side camera position and IR flood lights for key areas. Additional testing is required to see the resolution of change detectable in NIR images and the effectiveness of wider scale monitoring from the opposite slope with the NIR camera co-located with the daytime (visible) cameras. NIR floodlights are effective but can cause high contrast issues further and testing is needed to ascertain their optimum set up (sited on-slope or on the opposite side to illuminate specific areas of concern or the whole slope respectively).
3. NIR image consistency requires further work to optimise the image settings and processing. Additional testing will improve the fidelity of NIR surveying by being able to dynamically compensate for dynamic changes in incident near infra-red light on the slope being monitored. Time-lapse image comparison to detect movement on the monitored slope will then be enhanced.
4. If event detection is critical, passive seismic systems have clear potential, but reliable power and streaming signal needs to be improved at the site and dedicated time provided for a detailed study of the various noise sources and frequencies to reduce the detection of false positives.
5. A wider network of seismic monitoring should be considered for better event identification and location, but a more cost-effective solution may be to monitor the impacts against the catch nets on site for more reliable filtering of the most significant events.
6. The passive seismic ground condition monitoring is an exciting new technique that the logging systems now make effective as a potentially operational tool to support and refine the rainfall threshold alerts and improve understanding of how the ground responses are developing during high intensity events.

Passive electroseismic monitoring requires more testing but effectively provided a very low cost and low power monitoring system of the ground conditions that could cost-effectively be used at useful scales across the site. This remains cutting edge research however and would need further testing before operationally ready.