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Mitigating Dam Risks with Fox & Associates

Dam Safety Monitoring

Dam Safety in New Zealand: An Overview

In a time when severe rainfall and flooding events are in the news seemingly every week, one aspect of New Zealand’s waterways that gets less media attention is its many dams. There are thousands of dams throughout the country, from vast hydro-electric dams to the small stock water dams found on every hilly country farm, and while these create great benefits, they can also pose a big risk to property and human safety.

New Regulations for Dam Safety Assurance

In 2022 new regulations were introduced which for the first time creates a single nationwide safety framework for the approximately 900 dams that pose the greatest potential risk. Landowners with dams over a certain size or containing more than a specified amount of water are now obliged to implement a dam safety assurance program by May 2024.

As always, we are keen to solve our clients’ problems in innovative ways, so Fox & Associates has been working with a number of dam owners throughout the country to provide monitoring information to support their dam safety programs. A monitoring regime starts with a first visit to provide a baseline for the structure and subsequent visits thereafter provides a comparison showing the amount of change or movement (if any).

Like most survey work these projects generally start with a network of precisely coordinated reference stations surrounding the structure at a distance. From there the monitoring solution adopted depends on the type and risk profile of the individual dam and the final data/analysis needs which is resolved in collaboration with the client and their dam safety engineer.

Monitoring Methodology

The tried-and-true traditional methodology is still very much in use, establishing permanent monitoring points on the dam, which can be measured to from the reference stations at periodic intervals to monitor any small/discrete movement of the dam relative to the surrounding land or adjacent monitoring points. This work uses conventional surveying tools such as electronic total stations (for measuring angles and distances), precise levels and high precision GPS equipment.

Where the Fox and Associates’ difference arises is the innovative use of remote sensing technology such as laser scanners, drone mounted LiDAR or photogrammetry (where large numbers of photos from different angles can be used to generate a 3d surface). These methods are used to build up 3D models of the entire structure, which are then also re-measured at periodic intervals. The model is then compared to previous models to analyse and detect differences at any point on the dam (or the entire dam at a glance).

A further and important benefit of these tools is that the measurements are made remotely (not requiring physical access the dam structure), so that in the event of an earthquake, landslide, or other natural event a potentially compromised structure can be accurately checked from a safe vantage point.

Another often overlooked aspect is the not so easily seen part of the dam, that portion below the water line. Fox and Associates can also map what lies beneath the water to detect potential risks/changes including build-up of material against dam walls or scouring out of downstream areas.

Our next step in advancing monitoring strategies for our clients is the use of drone-mounted acoustic sonar sensors to remotely capture and facilitate analysis of the integrity of concrete structures, and the state of the art is now also moving to a point where AI is being harnessed to analyse photographic data for cracks and flaws as small as 1mm.

At Fox & Associates we are always looking for a better way to meet our clients’ needs, and with the rapid pace of technological advance, it is an exciting time to be working in this space.

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