How do we measure Galveston's coastal currents?

1. Where is Galveston?

Galveston is a city located on the island of the Gulf Coast of Texas, USA. The city is situated in the Houston - The Woodlands - Sugar Land metropolitan region, and Houston city is some 50 miles northwest of this place. The island is around 30 miles long and in its widest points 3 miles and separated from the mainland by Galveston Bay.

The land of the island consists of sandy beaches, tidal mudflats, and salt marshes. The beaches are extremely popular, and visitors throng from all over the world. Climatic regimes of the area are humid subtropical, with warm summers and relatively moderate winters. Coupled with the oceanic character of the island, high diversity levels have been created. Salt marshes on the periphery of the island contain a rich species of fauna in the form of migratory birds, fish, and crabs.

Galveston has a very old and rich history. In the 19th century, it was a port town involved in the cotton trade. Its buildings reflect its history, as most of the Victorian-era structures are still standing. The place's culture is a blend of coastal and Texan tastes, evidenced in its celebrations, food, and music. The Galveston Bay, which is adjacent to the island, is a big estuary. It is nourished by a series of rivers, including the Trinity and San Jacinto rivers. The bay is a key component of the local ecosystem in that it supplies a nursery environment to a host of marine animals as well as a wide channel for shipping through the Port of Houston.

2. What are the coastal currents near Galveston?

The coastal currents off of Galveston are regulated by a variety of factors. The tidal forces are an important one. The Gulf of Mexico has a mixed - semidiurnal tide regime. That's what that is: There are two distinct highs and lows each day. When tides come in and go out, water flows into and out of Galveston Bay, producing normal flood and ebb currents. The shape and direction of the bay and channels connecting the bay to the open Gulf also determine the direction and force of the tidal currents. The channels get constricted and the area increases will speed up the flow of water and dilute the currents.

Wind currents have a contribution too. Predominant southeasterly summer winds force surface waters out into the seaward direction along the coast. These force long-shore currents carrying water in parallel directions to the coast. The long-shore currents also play a great role in transporting sediment, nutrients, and marine life. Additionally, large weather patterns like tropical storms and hurricanes also play an important role in current patterns. The intense storms have high-speed winds that can create storm surges. A storm surge is able to carry a huge quantity of water on to the island, inundate low-lying regions, and disrupt the natural regime of the currents.

The contribution of fresh water into Galveston Bay by the San Jacinto and Trinity rivers also affects the coastal currents. The fresh water, being lighter than seawater, floats on top and creates a stratifying layer. The intermixing of the fresh water with seawater produces complex circulation patterns in the bay. The patterns affect the distribution of the nutrients, and therefore, the growth and distribution of sea organisms.

3. How to track the coastal water drift along Galveston?

Surface Drift Buoy Technique

The surface drift buoy technique is a method by which buoys fitted with GPS tracking devices are dropped into the ocean near Galveston. While the surface currents carry the buoys along, their position is recorded at regular intervals. This method provides information on the drift of the uppermost layer of the water column. However, it is not without limitations. Wind - driven waves will cause the buoys to lose their way and give false readings. It only measures currents at the surface level and doesn't indicate what is happening in the deeper parts of the water.

Anchored Ship Method

In the anchored ship method, a ship is moored in one location off the coast of Galveston. Current meters are dropped from the ship at various depths. These meters measure the direction and speed of the water flow at each depth. While this method can give a vertical profile of the currents at a point, it is not without its constraints. The presence of the ship can disrupt the natural flow of water, and the measurements can only be made at one spot. This makes it difficult to gain a clear picture of the coastal current tendencies in a large region.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) is a more advanced and effective technique for measuring the coastal currents surrounding Galveston. ADCPs have the ability to produce real-time, high-resolution data over most of the vertical extent of the water column. They can also measure currents at multiple depths simultaneously, so that the entire three-dimensional picture of the coastal current system can be obtained. ADCPs use acoustic pulses to detect the movement of particles in the water, and this enables them to calculate the velocity and direction of the currents. They are therefore especially suited to examining the complex current patterns off the coast of Galveston.

4. Based on what is the operation of ADCPs named?

ADCPs operate under the Doppler principle. The ADCPs project acoustic signals in the water. When the projected signals encounter suspended particles in water, such as sediment or plankton, such signals are rebounded back into the ADCP. The signals rebounded at a different frequency compared to their emitted frequency. This Doppler shift, or variation, is proportional to the velocity of the particles and thus to the water flow velocity. The ADCP can measure the speed and direction of the water flow at various levels in the water column by measuring the Doppler shift at various depths. This enables an accurate and total measurement of the structure of the coastal current off Galveston.

5. What must be done in order to get high-quality measurements of Galveston coastal currents?

High-quality measurement of Galveston's coastal currents is dependent upon several key requirements the measurement device must meet. Material reliability is perhaps the most important of these due to the corrosive properties of seawater. The device will need to be constructed of material that can endure long-term exposure to the corrosive marine environment. Small size has the advantage that it minimizes interference with the natural flow of water. Lightweight is essential to enable easy deployment at many locations along the coasts. Minimum power consumption is also essential, especially for the long - duration, unattended operation in inaccessible coastal regions. Cost - effectiveness is also very important as it allows for measuring instruments to be deployed in multiplicity in the quest to scan the extensive coast line surrounding Galveston.

For textral materials of ADCPs, the choice of casing material is extremely critical. One excellent material for use in ADCP casings is titanium alloy. Titanium alloy offers outstanding corrosion resistance, which is critical for long-term use in Galveston's salty waters. Titanium alloy possesses high strength - to - weight ratio and therefore is not only strong but also light. This allows the ADCP to withstand the physical forces and pressure variations encountered in the ocean, to provide continuous and accurate measurement over a prolonged period.

6. How to Choose the proper equipment for measurement of currents?

According to Usage

• Ship-borne ADCP: This ADCP can be used effectively for wide-area surveys of the coastal waters outside Galveston. It is mounted on research vessels and has the capability to cover a great distance as the vessel moves, providing valuable information on the spatial variation of coastal currents. It can be utilized for mapping the overall current patterns along a long stretch of coastline.
• Bottom - mounted ADCP: It is placed on the seafloor and is well - adapted to long - term monitoring at a fixed point. It can record continuously long - term current data, which in turn is useful in monitoring long - term trends and patterns of coastal currents in the Galveston area.
• Buoy - mounted ADCP: Suspended below floating buoys, it is used for the measurement of surface and near - surface currents. It is simple to use in areas difficult to access by a ship or where there is a requirement of unattended long - term measurement of surface - level currents.

Depending on Frequency

The choice of frequency for ADCPs is important. A 600kHz ADCP is suitable for water depths up to approximately 70m. It provides high-resolution information, and so is suitable for the relatively shallow coastal areas off Galveston, where the depth of the water typically is in this range. A 300kHz ADCP will be suitable for depths up to 110m, providing a compromise between penetration depth and resolution. For deeper waters, up to 1000m, a 75kHz ADCP is more appropriate as it can penetrate to greater depths but with a lower resolution compared to the higher - frequency models.

Well-established firms manufacturing ADCP are Teledyne RDI, Nortek, and Sontek. But to those who seek a cheap alternative without compromising on quality, the ADCP manufacturer China Sonar's PandaADCP is a perfect choice. It is an economical ADCP utilizing all-titanium alloy material for maximum corrosion resistance and endurance. With its very favorable cost-performance ratio, it is the best choice for researchers and institutes that intend to carry out extensive coastal current surveys in the vicinity of Puerto Escondido. To know more, check their website at https://china-sonar.com/.

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