Water quality sampling from an unmanned aerial vehicle
Source: Pattle Delamore Partners Ltd
Water quality sampling can be a hazardous activity. Field staff contend with weather, exposure to contaminants, use of various sampling platforms, and access that can be restrictive due to bank vegetation and heights. While Professional Scientific and Technical Services is not recognized as a high-risk industry by New Zealand legislation, Worksafe notified injuries occurred at a rate of twenty-five incidents per thousand employees in 2017. In the last ten years there has been one registered fatality. Finding sampling solutions that keep hazards to a minimum and reduce staff risk can mean eliminating sampling points that are deemed too hazardous to access.
This presentation will detail a new process for the collection of marine water samples. Samples were required for enterococci analysis from four popular swimming beaches along Auckland’s east coast: Takapuna, Narrow Neck, Kohimarama and Mission Bay. These beaches are popular not only for casual swimming and access by members of the public, but also support organized summer swimming events (Summer Swim Series), and tourist operations (kayaking and stand-up paddle boarding) where the ‘contact zone’ of human interaction with water extends much further off shore. Typical water quality sampling that consists of a grab sample at knee depth may not be accurately measuring enterococci counts at representative locations for such activities.
In order to measure enterococci at these locations (and provide validation of the current Safeswim model), surface water samples are required to be collected in varying depths along transects that extend from the beach out to deep water. Across each transect samples need to be collected from just below the surface at six locations where the depth of water is as follows: at knee, waist, 1.5 , 2 , 4 and 6 metres. In the past, this would have required the use of a powered vessel with a Maritime New Zealand certificate of survey, qualified crew, and the added expense that is associated with such a sampling platform. Alternatively, a non-powered vessel (such as a kayak) can be used, thereby increasing the risk of staff being exposed to water related health and safety hazards.
In this project example, a waterproof drone was fitted with a tether to fly to waypoints and dip a sampling vessel. The drone can lift up to a one kilogram weight, allowing for adequate sampling volume for a range of tests if required. For each sampling transect, a one kilometre profile was surveyed using an Acoustic Doppler Profiler (ADP), allowing for the measurement of depth at a known tide datum. As each sampling run is conducted at different tide levels, reference to this surveyed transect can be made when calculating sample depth locations and the required sampling locations can be pulled from the surveyed profile. The drone’s autopilot is then used to fly to these sampling locations and collect the required water samples.
This methodology eliminated two major Health and Safety hazards that were identified at the beginning of the project: Working around deep water and working from a mobile sampling platform.