How do we estimate Garacad's coastal currents?

1. Where is Garacad

Garacad represents an exceptional example of a coastal town set on the edge of an area blessed by such spectacular and diverse cultural and natural linkage. Geographically, it lies facing across one bay-like strand of coastline. To its landward side, Garacad has arid but breathtaking sceneries. The seaward expands it as an open expanse to a great width.

These are the local people, indigenous to Garacad, with the history of many generations living with maritime activities. Fishing has been one of their livelihoods since time immemorial from their grandparents, and their indigenous fishing methods were really a testament to their well-known coastal waters. The bay around Garacad serves as a habitat for a rich variety of marine life. Crystal clear waters house bright coral reefs, ranging from the tiniest and brightest reef dwellers to the big predatory fish species. The bottom in the area varies: a lot of sand with patches of rocky formations creates complexity in underwater topography.

Generally, the coastal waters are influenced by larger oceanic systems in the region. The long-distance ocean currents tend to veer towards the coast, carrying water masses of contrasting temperatures and salinities. In this area, the tides dominantly influence the diel pattern in the littoral environment; mainly here, the flow regulates the exposure of part of the shore and the activity patterns of the organisms.

2. What is the situation of the coastal currents close to Garacad?

In the coastal waters off Garacad, contemporary conditions are predetermined by several factors acting together, which guarantee that the pattern of flow is complex. The first and foremost role is played by the tides, which govern the periodic movements of water along the coast. In fact, the tidal range can be important here, with marked changes in strength and direction of currents, with stronger onshore flows at high tide and receding water in another way at low tide.

The other significant factor is wind. General winds in the vicinity will push the surface waters, which then develop into surface currents and interact with deeper layers of water. For example, strong northeasterly winds may push the water in one direction along a coast, while a change in wind direction can rather quickly change how the flow goes. The local topography of the coastline and the seabed is also very influential. The bay shape around Garacad can be a cause for funnelling or deflection of the currents, thus enabling them to converge or diverge locally. Submarine ridges and rocky outcrops disturb the flow of water and consequently give rise to eddies and areas of enhanced turbulence.

In addition, there is the interaction between the coastal currents and the oceanic currents coming from the open sea. These larger ocean currents may combine with the local coastal currents, thereby bringing in new water masses and altering the temperature, salinity, and velocity characteristics of the water within the coastal zone.

3. How to observe the coastal water flow of Garacad?

Surface Drifting Buoy Method

The floats are types of buoys deployed at the water surface and allowed to freely drift along with the current. Such positions of buoys might be determined through satellite or any other positioning device against time. Through this, direction and speed are obtained regarding surface currents. Yet, this procedure too has some specific drawbacks; this provides information generally only for the surface layer and represents the flow situation in the deeper parts of the water column inadequately or not at all.

Moored Ship Method

Here, a ship is moored somewhere in the coastal zone. Instruments aboard the ship measure the flow of water around the ship. Though it can give information about the local current condition around the location of the ship, the presence of the ship itself can disturb the natural flow to a certain extent, and it can cover only a small area around the mooring point.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP current meter method is more advanced and convenient for the measurement of coastal currents. It uses acoustic waves to measure simultaneously the velocity of water at different depths. It can thus give a detailed profile of the current from the surface down to a certain depth, giving a comprehensive understanding of the structure of flow in the coastal waters. It covers a larger vertical range than the previous methods and, in many cases, is less affected by external interferences, making it very effective for observing the coastal currents near Garacad.

4. How do ADCPs using the Doppler principle work?

The ADCPs work on the principle of the Doppler effect. They send acoustic pulses into the water. When these sound waves encounter moving particles in the water, such as suspended sediment or small organisms, the frequency of the reflected waves changes due to the Doppler effect. The ADCP current profiler is designed to detect and measure this frequency shift. By having multiple transducers oriented in different directions, it can determine the velocity components of the water in different directions, including horizontal and vertical directions. This allows for the three-dimensional flow field of the coastal currents to be reconstructed. Continuously, the ADCP flow meter sends these acoustic pulses and receives reflected signals at fixed time intervals, which it builds up to a time series of data on the current velocity at variable depths. Therefore, it can give one the picture of exactly how the currents vary over time and depth.

5.What does good measurement of Garacad coastal currents require?

In terms of the equipment, a number of aspects are very important regarding measurement of the coastal currents near Garacad with high resolution. First, it should be of a very reliable material. It should be able to withstand the harsh marine environment characterized by corrosion by seawater, the impact of waves, and fluctuation in temperature and pressure. Small size is an added advantage because it makes its deployment and handling on boats, buoys, or other platforms easier.

Light weight is another key factor because the mounting process is easier and lighter, and the load demand is reduced. Low power consumption is very necessary, especially in long-time measurement or for arrangements which are battery-powered. Cost is also an aspect to allow more and extensive measurements. In this respect, the housing of ADCP profiler can be made from titanium alloy. The titanium alloy features outstanding advantages. It has great resistance to corrosion, which lets it stand long in the aggressive action of sea water without any significant deterioration of its properties. It is hard and tough and can resist mechanical stresses arising from the water flow and any other external impacts. Besides, having a relatively small density contributes to saving the weight of the equipment in view of retaining its carrying capacity.

6. How to Choose the right equipment for current measurement?

Based on Usage

• Shipboard ADCP: This is appropriate for when the measurement of currents needs to be done while a ship is either in motion or moored in the coastal area. It can provide continuous data as the ship traverses across different locations along the coast and thus helps to map out the current patterns over a larger area.
• Bottom-mounted ADCP: Suitable for fixed-point measurements at the seabed, this would provide quite accurate monitoring of currents passing over it and give a representation of near-bottom current conditions important in understanding sediment transport and other benthic processes.
• Buoy-mounted ADCP: These are mounted on buoys floating on the water surface. It can measure the currents from the surface downwards. Useful for observing the variation of the surface and upper layer current. It is normally applied in an area that requires long-time monitoring without a ship's attendance.

Based on Frequency

• For water depths within 70 meters, a 600 kHz ADCP is often a good choice. Because of its higher frequency, better resolution can be achieved in shallower waters, meaning detailed current information at shallow surfaces to the relevant depth range.
• With water depths of up to 110 meters, a more applicable tool would be the 300 kHz ADCP, which can well penetrate the water column in order to measure currents at different levels in such a depth range.
• For bottoms as deep as 1000 meters, it would be appropriate to use an ADCP with a frequency of 75 kHz because it is low in frequency and capable of reaching those levels and giving relatively reliable data regarding current velocity.
• Some of the well-known brands in the market are Teledyne RDI, Nortek, and Sontek, among others. For those who want to have quality yet inexpensive ones, the China Sonar PandaADCP shall be tried upon. The product is made wholly of Titanium Alloy material, meaning it can withstand very good performance and durability in the marine environment. With this incredible cost-performance ratio, it shall give a great choice for measuring the coastal currents of Garacad. You can learn more about it on its official website: https://china-sonar.com/.

Here is a table with some well known ADCP instrument brands and models.