Victoria University of Wellington, New Zealand, is studying patterns of water flow at Palmyra Atoll, south of Hawaii. The 4.6-sq-mile atoll is comprised of a coral reef, vegetation-covered sand, reef-rock islets and bars that, along with the lagoons, form an intricate circuit of complex and poorly-understood water flow patterns.
The constructed islands have no indigenous population, only a few runways, roads and causeways built during World War II, which are no longer maintained and are breaking down, causing researchers to ask:
• If the erosion can be understood, can the findings be applied to shoreline changes and mitigation of coastal erosion around the world?;
• Can we model water flow through a complex lagoon system?; and
• As the atoll reverts to a more natural state, what does it tell us about how atolls elsewhere respond to human modification?
Researchers devised a plan to model water flow before, during and after construction took place at the atoll and to predict what would happen in the future if the causeways were removed. Researchers intended to use level indicators to gain knowledge of what was transpiring at the reef and in the lagoons.
They are hoping to apply their knowledge about Palmyra to other atolls around the world.
Modeling water flow through the complex lagoon system was to be accomplished by measuring the water depths at various sites. Researchers needed to account for unique factors in choosing equipment. The study was in an extremely remote location accessible only by charter flight, making size and weight of the research components critical.
Level measurement devices needed to be reliable, easy to use, and perform independently for extended periods of time, as researchers anticipated a limited number of return trips. Extreme conditions, including high humidity, extended submersion in salt water with moving coral sand and potential shark and sea turtle attacks, required the construction to hold up under harsh conditions.
KPSI’s Model 551 waterMONITOR submersible datalogging transducers, which can hold up to 400,000 scans, and feature a total error band better than ±0.05% full scale--which includes a temperature accuracy of up to ±0.2°C--were chosen. These level transducers incorporate rugged, titanium construction and an embedded, power-saving, datalogging circuit to deliver precise level measurements under extreme circumstances over extended intervals. An internal battery configuration, providing years of life, proved beneficial for this study, since it would be left unsupervised for months.
The data collected at Palmyra Atoll has helped researchers understand past and present lagoon environments. The atoll offers an opportunity for scientists to study the natural processes that form and erode islands and modify lagoons when there is no human population or the area is protected as a wildlife reserve. By reconstructing how the atoll was pre-World War II and comparing it to present day, scientists are able to learn how ecosystems are being restored naturally.
Source: Pressure Systems, Inc.
