AEX Group :: Ingeniería - Investigación

Oceanographic studies for submerged outlets

ZPL CALCULATION: The General Directorate of the Maritime Territory and Merchant Marine of Chile, defines ZPL as "a coastal protection zone including the water and seabed adjacent to the mainland or island, bounded by an imaginary line on the surface, measured from the maximum low tide line, oriented parallel to it and projected to the seafloor."

Discharges that are made inside or outside of it must meet different maximum allowable limits."However, in no case should the width of the ZPL be equivalent to the length a device will have if it is intended to discharge liquid waste (sewage outlets or other similar structures)", since the length in such systems requires other design factors.

DILUTION: To carry out a horizontal dilution calculation a rhodamine study is used, which seeks to estimate the natural pattern of the horizontal dilution. The rhodamine dye is injected instantaneously at the point of interest, and the time spent in different tidal phases (high and low) is controlled. The geometry of the stain generated is monitored aboard ship marking the outline of the pigmentation using GPS.

DISPERSION: Calculated by using software modeling of the mixing zone, this simulates pure or mixed plumes in arbitrarily stratified environments.

One of the objectives of Visual Plume is to provide a platform for mixing zone models, which are designed to predict the behavior of the plume in an initial dilution region. One way to strengthen the results of the modeling is to compare the predictions with field studies.

Bathymetry

Bathymetry is a technique associated with obtaining water depth values. AEX Group has a team which has been performing bathymetry work for more than nine years, giving us experience working in this field as well as the means necessary for its proper implementation.

Echo sounding equipment is used to complete bathymetric surveys. This equipment consists of a transducer that transmits two frequency bands and a video unit, in conjunction with GPS. The GPS position measurements and the echo to determine depth, are joined to create a bathymetric chart. This chart or map represents the shape of the bottom of a body of water, normally through the use of depth lines.

These depth lines are called contours, and are commonly seen on nautical charts. Bathymetric prospecting is performed in order to obtain a sampling of depths to provide support for work being carried out in the area, like an oceanographic study for example.

Characterization of coastline

Morphologic measurement and classification of rock quality depends on the type of rock (igneous, metamorphic, sedimentary), and the minerals with which they are composed. Rock quality will vary.

Spacing between joints: The rock's cohesive forces are lost along the joints (fractures).The more joints, the lower is the cohesion of the rock.

A classification table and morphological assessment is used to asses the quality of rocky bodies (Selby, 1980) and an on site estimation table of the rock's quality using a rock hammer (Hoek & Brown, 1997).

Eulerian Current Measurements

An ADCP (Acoustic Doppler Current Profiler) measures the profile of a water current using acoustic Doppler technology. It is designed for stationary applications and can be used on the seabed, on oceanographic moorings, on buoys or other fixed structures. AEX currently has 5 Nortek Aquadopp type profilers, of 600 and 400 Khz. These acoustic beam profilers use three beams tilted to 25 ° to accurately measure the current's profile in the number of layers or cells selected by the user. The tilt sensor and internal compass determine the direction of the current and the high resolution pressure sensor indicates the depth and the elevation of the tide if the equipment is mounted on a fixed structure.

The statistical analysis of the information provided by the device delivers maximum, minimum, average and standard deviations of the current's speed in each layer registered, and the directions, in order to develop distribution charts and polar graphs. This makes it possible to determine the behavior of the current in the water column in terms of its speed and direction.

The duration of current measurements using the Euler method varies depending on the objectives. Environmental legislation provides some guidelines for Environmental Impact Assessments and Declarations . But in the case of structure anchoring studies, there is no definite standard. So that the criterion should favor lunar periods associated with higher current speeds, for instance during maximum tidal flows.

Lagrangian current measurements

A technique for measuring near-surface ocean currents using "drifters", which are tracked by satellite, radar, radio, sound, etc. A drifter is a large plastic sleeve, which is exposed to the current. The sleeve is near 1m2 with a metal rod structure which holds it and gives it shape, the top is bonded to a buoy. Tracking is done from a boat using GPS. Each drifter is at a different depth, usually 0-7-15 meters deep for salmon farming cages, and in the case of mussels a depth of 0 and 8 meters due to the depth the hanging culture. This enables us to analyze the current's data, speed and tidal direction in a given sector so we can plot the displacement of a body of water in larger areas than with a current meter.

Each drifter is continuously tracked, performing position checks approximately every 10 minutes, depending on the displacement speed. The records are in UTM coordinates, the axes X and Y correspond to east and north, respectively. The reviewed and processed information is used to create drifter displacement charts and general flow tendences in both phases of the tide. The speed in knots of each drifter is shown according to its depth

Wind measurements

For each farming structure installation project and support, it is imperative to identify and consider the effect of the wind as an environmental burden on said structures. Data can be obtained from empirical formulas, however, it is recommended to supplement these studies with measurements of wind from the area of interest by installing weather stations; recording speed and direction over long periods of time.

On site wind data also helps to determine the environmental loads generated by the waves.

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