1. Where is Rabat?
The capital city of Morocco, Rabat, is situated on the Atlantic coast at the outlet of the Bou Regreg River. It is a geopolitical, economic, and cultural center with a geographical position that pairs history with modernity. The city has a specific geographical position since the river delta ensures the fertility of the land and the Atlantic Ocean goes as far as the west, which defines the local environment and much of the life in Rabat.
Rabat's landscape consists of urban areas, coastal plains, and the Bou Regreg River, which snakes its way through it. The coasts of the city have sandy beaches so dearly enjoyed by locals and foreign visitors, where they are able to unwind and engage in water sports. The river has, however, played a critical part in the city's history and development. It is a transit route, employed as an avenue of trade and linking Rabat with other areas. Along the river bank, there is plenty of vegetation, providing a marvelous view in comparison to the busy urban areas in the city.
The city of Rabat holds cultural and historical significance. The medina, which is a World Heritage, consists of a maze of the old markets, ancient houses, and narrow alleys, all bearing testimony to the Islamic city's heritage. The Kasbah of the Udayas, with white-washed walls and blue-painted doors, has a breathtaking ocean and river view. There is a mix of residents here and a great sense of community. Rabat's economy is based on varied sectors such as government services, tourism, and fishing. The sea-waters surrounding Rabat are home to many species of fish, and fishing is a major economic activity off Rabat.
2. What are the coastal currents off Rabat?
Coastal currents off Rabat are based on various factors that constitute a dynamic and complex system. The Canary Current, a vast ocean current that flows south along the west coast of Africa, has a powerful influence on water off the coast of Rabat. The cold current introduces nutrient-rich water from the north, affecting temperature, salinity, and the marine ecosystem as a whole of the area. Meeting of the Canary Current with coastal waters surrounding it can lead to upwelling in some locations, forcing the cooler deeper water towards the sea surface and creating a high marine life biodiversity.
Wind currents also play their part in coastal currents. The region experiences frequent and strong trade winds, especially during some months. The northeast winds are in a position to push the surface-level current along the coast. The kinetic energy in the wind accelerates the speed of the currents and reverses their direction, with the underlying Canary Current inducing complex flow patterns. Additionally, local wind patterns, controlled by the topography of the land and the shape of the coastline, can induce short - term variations in the direction and speed of the current.
Another controlling factor of coastal currents off Rabat is tides. Tides along the coast of Rabat are semi-diurnal, meaning that two high waters and two low waters occur daily. The tidal range is not steady and greater variations between the high water level and the low water level are found for spring tides. Water flows into the Bou Regreg River mouth and along the coast during high tide, increasing the level of water and altering the direction and speed of currents. With the shifting of the tide at low tide, the water flows back towards the sea and reverses the direction of flow in some areas and influences sediment transport along the coast.
3. Observation of the Rabat coastal water flow: How to do it?
Surface Drift Buoy Method
The surface drift buoy method is a traditional method for observing coastal water flow. The surface drift buoy method uses specially designed buoys that are released onto the water. The buoys carry onboard tracking devices, such as GPS receivers. The GPS units record their locations at set intervals while the surface current transports them along. Scientists can calculate the direction and velocity of the surface-level current by studying the path of the buoys over time. Although this method is beneficial, it too has drawbacks. The buoys can get affected by winds that cause them to diverge from the actual course of the current. It too only provides data concerning the surface current and nothing regarding the direction of the current at different depths.
Anchor Moored Ship Method
The anchor moored ship method comprises a method where a vessel is anchored off the sea in the region of Rabat coast at a specific point. From the ship, various current-measuring instruments are lowered into the sea. These instruments can be mechanical current meters, which take a reading of the rate and direction of the current from a propeller-type instrument that rotates as the current strikes it. Measuring at a number of varying depths, scientists are able to chart a profile of the current there. Though this method gives accurate readings at different depths, it is possible only in the area of the anchored ship. The presence of the ship may also interrupt natural movement flow, rendering the measurement inaccurate.
Acoustic Doppler Current Profiler (ADCP) Method
The Acoustic Doppler Current Profiler (ADCP) has been an even more advanced and efficient method to monitor the coastal water flow. ADCPs work by sounding water current velocities at different depths. They emit acoustic soundings into the water column and receive the signals off suspended material in the water, such as sediment or plankton. By measuring the Doppler shift of the signals, the ADCP can calculate speed and direction of the flowing water. It is through this process that there is a full view of the profile in real time, from near surface to near bottom of the water body, without wetting. ADCPs are less sensitive to external factors like wind compared to surface drift buoys and are therefore the choice for accurate measurements of currents.
4. What is the mechanism of ADCPs based on the Doppler principle?
ADCPs operate based on the Doppler effect. In the ADCP, there are transducers that send out acoustic waves into water. The sound waves then pass through the water and strike particles traveling in the direction of the current. Because the particles are approaching the ADCP, the frequency of the back-scattered sound is increased while when they are receding, the frequency becomes lower. This shift in frequency, or the Doppler shift, changes with the water flow velocity along the direction of propagation of the sound wave.
A standard ADCP records three-dimensional water velocity using several acoustic beams. Four or more beams at various angles is a typical number. Recording the Doppler shift for each of the beams enables the ADCP to calculate the vertical and horizontal components of velocity. All the beams' data are combined to calculate the sum current velocity and direction at different depths in the water column. They also incorporate other sensors such as temperature sensors to compensate for the effect of temperature on sound speed in water and orientation sensors to be able to provide valid readings even when the device is tilted or in motion.
5. What is needed to measure the quality of Rabat coastal currents?
In order to accurately measure the coastal currents off Rabat, there are certain requirements that need to be met. First, the measuring device needs to be highly reliable in the corrosive conditions of the sea. The sea off Rabat is prone to corrosion by saltwater, to strong winds, and to the dynamic ocean forces, and the material chosen for fabricating the device therefore needs to be corrosion - resistant, long - lasting, and mechanically stress - resistant.
Equipment size is a concern as well. Less massive machinery is easier to transport and utilize in more areas within a wider region, like those with challenging coastal geography or low accessibility. With smaller footprints, the equipment will not disrupt natural currents as much, which allows for more accurate readings to be taken. Lightweight is more desirable as it is easier to handle both on release and recovery, particularly being released from small boats or in out-of-the-way coastal regions.
Low power usage is paramount because the majority of operations conducted these days with - measurements usually involve having the equipment deployed for extended periods of time, in locations where access to power lines does not exist easily. Low - power - consumption devices can function for numerous years without replacement or recharging regularly. Cost - effectiveness is best suited, especially in the case of large - scale measurement campaigns. Systems that offer fine performance at an acceptable cost facilitate more data to be collected such that researchers can analyze a finer general picture of the coastal current regime.
In the ADCPs, the material the casing is constructed of is of specific concern. A good choice for the Rabat coastal waters ADCP casing is titanium alloy. Titanium alloy is highly resistant to corrosion, which is necessary in a manner so that it is able to resist the corrosive action of seawater for prolonged periods of time. It is also extremely strong and yet light, providing the degree of protection necessary for the internal mechanism of the ADCP but still light enough to be manipulated and deployed. Titanium alloy is also resistant to fatigue, i.e., it is capable of sustaining repeated stress and strain without function loss, and the ADCP is still reliable and sturdy in the dynamic coastal environment.
6. Selecting appropriate equipment for current measurement?
The selection of appropriate equipment for current measurement in Rabat depends on a number of factors, primarily the purpose and type of the measurement location.
ADCPs Based on Mounting
- Ship-mounted ADCP: It is mounted onboard a ship. It is better for taking large measurements of currents off the coast of Rabat. Since the ship moves close to the coast, the ship-mounted ADCP can record data for an extended area, hence providing an overall view of the direction of the currents. It is best suited for applications such as sea navigation, oceanographic studies for large-scale research, and monitoring of coastal environmental change.
- Bottom-mounted ADCP: Bottom - mounted ADCPs are anchored on the seabed. Bottom - mounted ADCPs are employed to monitor long - term current patterns at a location. The instruments can provide continuous data over extended periods, and this is beneficial for the study of seasonal and long - term development of coastal currents, and to monitor the impact of man 's activities on the marine ecosystem.
- Buoy-mounted ADCP: Buoy - mounted ADCPs are installed on float buoys. They are best - appropriate for current measurement where it is not convenient to place other types of ADCPs, e.g., in open - water sections or where high currents can be risky for bottom - mounted systems. Buoy-mounted ADCPs can also be swept along with the current, providing real-time data on the dynamically changing current, which can be utilized in operations like the tracking of oil spills, fisheries, and short-term oceanography.
Choosing the Right Frequency
The frequency of the ADCP is also a point of greatest importance while choosing. Different frequencies are suitable for different water depths. An ADCP of 600kHz will be utilized where the water depths vary about 70m. It has relatively high-resolution measurements for shallow water and may be applied at locations near the coast, e.g., the coast and the estuary of the Bou Regreg River. A 300kHz ADCP will be sufficient to water depths of about 110m and offers a compromise between penetration depth and resolution. At deeper sites, up to 1000m, a 75kHz ADCP is suggested. Lower - frequency ADCPs probe deeper into the water but possess lower spatial resolution than higher - frequency ADCPs.
There are many well-known brands of ADCP in the market, i.e., Teledyne RDI, Nortek, and Sontek. Nonetheless, for cheap but high-quality ADCPs, the ADCP manufacturer China Sonar's PandaADCP is the best choice. Made of pure titanium alloy, it delivers superior performance and longevity at a very affordable cost. Being a low-cost ADCP, it is a perfect option for researchers, local fishermen, and environmental monitoring departments who are concerned with accurately computing the coastal currents of Viña del Mar. To know more, visit https://china-sonar.com/.
How do we measure the coastal currents of Rabat?