Sea Technology

JUN 2018

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22 ST | June 2018 www.sea-technology.com "Our models aim to determine the environmental footprint the proposed operation might look like, what proportion of organic waste will fall to the seafloor and what kind of environmental management approaches are needed to develop a sustainable industry," said Shiell. "Most of the fecal matter is heavy and falls to the sea- floor. Provided there is sufficient water movement and oxygen, the waste material is broken down by bacterial activity." The danger, however, is that without sufficient water flow and oxygen, the waste builds up on the seafloor. The model balances the ability of the marine ecosystem to naturally assimilate the waste against the number of fish in the cages above. The modeling is complex because the water move- ment is influenced and constrained by various factors, including tide, wind and the topography and composi- tion of the seafloor. "The TCarta SDB data was critical in helping us build the hydrodynamic model, which allows us to understand how the water is moving through the system," said Shiell. "The accuracy and resolution of the data, combined with our own in-situ measurements, allowed us to build a ro- bust model." Once the flow modeling has been completed, BMT will pinpoint several potential fish farm zones, each sev- eral kilometers in diameter to accommodate periodic re- location of the cages within site. BMT will then overlay the results with the Marine Habitat layer on the GIS base- map to further evaluate environmental impact. "A key outcome of the modeling will be to make sure the footprint of the farm zone does not encroach on sensitive marine habitats like corals or sea grasses," said Shiell. Delivering Results BMT expects to deliver the modeling results to EAD by late 2018. Outputs are expected to include recommen- dations on the optimum siting of cage clusters and the maximum carrying capacity of the environment based on different finfish species. In addition, the model will provide key management recommendations including how often the cages should be moved under a process of fallowing. "The initial results with the SDB data in the Arabian Gulf, as well as other projects by our clients, tell us that aquaculture will be a huge emerging market for marine geospatial data," said Critchley. ST The two near-infrared (IR) bands collected by the WorldView satellites are vital to the seafloor extraction algorithms because these wavelengths penetrate the wa- ter column. Additionally, the WorldView satellites have what is called a coastal band, which sees through the haze often associated with optical image collection over shoreline environments. Optical imaging sensors, how- ever, are not capable of capturing data through clouds. In the SDB process, TCarta technicians use a heavily customized digital image processing workflow to isolate specific segments of the two near-IR bands and digitally combine them with other bands from the multispectral data to derive water depth and seafloor classification in- formation. "Quality of the derived data depends on the clarity and turbidity of the water. The Arabian Gulf has moder- ately clear water around Delma," said Critchley. "In that area, our SDB data provided depth measurements at a two-meter spacing with two-meter accuracy to a depth of about twelve meters." In addition, the extraction process differentiates sev- eral types of seafloor surfaces from the spectral bands of the satellite data. For the coastal area around Delma, TCarta delineated five seafloor classes: sand, seagrass, macro-algae, coral reef and hard rock, also to a depth of about 12 m. TCarta refers to this data set as a Marine Habitat Map, and it was included in the 2015 product delivery to EAD, which was subsequently built upon by BMT in the more recent aquaculture project. Modeling Water Flow Fish farm operations come in many shapes and sizes and are developed in both fresh and saltwater, explained BMT's Shiell. An offshore saltwater farm like the one be- ing assessed near Delma will likely comprise numerous individual cage clusters potentially containing tens of thousands of fish. The maximum number of fish, as well as the marine monitoring and management strategies re- quired to manage future operations, will be among the recommendations provided by BMT. BMT began running data through its models for Abu Dhabi in September 2017. For the relatively shallow coastal zones around Delma, BMT used the SDB and digital Marine Habitat Map from TCarta. In some of the deeper waters, Shiell's team acquired ship-borne bathy- metric data. A digital GIS layer containing seafloor depth data assembled from multiple sources was purchased from TCarta to serve as the project basemap. For a proposed aquaculture project of this type, the shallow-water data are an important model input, ac- cording to Shiell. "The bathymetry around the coastline is often some of the most complicated…and that is where we need reso- lution to predict the speed and direction of water move- ment around the island," said Shiell. He elaborated that the flow of water and the shape and depth of the seafloor are important variables in the aquaculture model because they influence flushing rates, one of the key factors for identifying which sites are most favorable for fish cages. Based in Bristol, U.K., Richard Flemmings is a partner in TCarta and responsible for compa- ny operations and management. He has been involved in the geospatial industry for more than 16 years. He has an M.S. in geographical information science and significant worldwide experience in offshore, airborne, land and satel- lite-based surveys and mapping. Flemmings is a qualified project manager and is experienced in project design, workflow development and lean management principles. He is a fellow of the Roy- al Geographical Society (FRGS) and a chartered geographer (CGeog GIS).

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