How do we measure Quincy's coastal currents?

1. Where is Quincy?

Quincy, located in Norfolk County, Massachusetts, is a city rich with historical and geographical significance. Located on the southern border of Massachusetts Bay, south of Boston, its fine coastal location has made Quincy a significant part of the maritime heritage of the region.

Filled with American heritage, Quincy has earned the moniker "City of Presidents" as it is the birthplace of two presidents of America, John Adams and his son John Quincy Adams. The city retains old-world appeal through its wonderfully preserved colonial - period buildings. Cobblestone roads are observed in neighborhoods bounded by lovely homes in the traditional sense, recreating the story of the past.

Quincy's shoreline offers a diverse array of features. Sandy shores, like Wollaston Beach, are in high demand from tourists and residents during the warm summer months. The beaches have recreational use but are also vital habitats for numerous shore-dwelling organisms. In addition to the beaches, there are rocky outcroppings and tidal flats at low tide, providing a diverse community of marine life.

The Massachusetts Bay, which borders Quincy, is a dynamic system. It is impacted by a series of natural forces like tides, winds, and the general North Atlantic oceanographic conditions. The bay also serves as a transit route for big commercial vessels, fishing boats, and recreational boats, further stressing the importance of information about coastal currents here.

2. What are the coastal currents off Quincy?

Coastal currents off Quincy depend on a complex array of variables. Tidal forces are a dominant force. The sun and moon's gravity causes the Massachusetts Bay tides to come in and out regularly. Water pours onto the shore at Quincy at high tide and away from the shore at low tide. This tidal current has a significant influence on the velocity and direction of the coastal currents. In narrow inlets or channels around Quincy, such as in the Neponset River Estuary, tidal currents can be particularly elevated as the water rushes through narrow spaces.

There is also the influence of wind. The local winds in the region, such as the south - westerly winds, have the power to push the surface waters in the bay. More winds will lead to more waves and stronger currents. A breeze that blows onshore can push water to pile up along the coast of Quincy, altering the local currents. An offshore breeze can lead to stripping away of surface waters from the coast.

The bathymetry, or underwater shape, of the area around Quincy is also important. Shallow banks, deep channels, and underwater ridges can direct the flow of water. Shallow areas will slow the currents down and spread them out, and deep channels will concentrate the water and make it flow faster. The unusual shape of the Quincy coastline, with all the bays and inlets and headlands, also contributes to the complexity of the current patterns. Headlands, including Point Allerton, can bifurcate the currents and speed them up around such headlands, while bays, like Quincy Bay, can trap and recirculate water and create local current systems.

3. How to observe Quincy coastal water flow?

Surface Drift Buoy Method

One of the traditional methods for observing coastal water flow is through surface drift buoys. These buoys are employed to ride the current on the surface and float. They can carry GPS onboard that traces them throughout the time interval. Surface current patterns could be known by analyzing the buoy trajectories on the basis of these paths. However, this is also not effective to an absolute extent. Because the buoys are exposed to both the currents and wind-driven surface waves, separation of the two effects may be difficult. Hence, the data may not accurately represent the true underlying current flow, especially where high winds exist. Moreover, surface drift buoys provide information only for the uppermost portion of the water column, and they cannot possibly measure the fine vertical structure of the currents.

Anchor - Moored Ship Method

The anchor - moored ship method employs an anchored ship at a fixed location. Equipment carried on the ship, i.e., current meters, are lowered into the ocean at multiple depths in order to measure the speed and direction of the currents. With this method, it is possible to collect data from multiple depths and hence have a better understanding of the vertical profile of the currents compared to the surface drift buoy method. But the ship is in one fixed position and only samples within a relatively limited area. Maybe not large enough to capture large-scale coastal variability of currents within a wide region, especially an active one such as the Massachusetts Bay off Quincy. Moreover, the presence of the ship may potentially disrupt the natural flow of the water and affect the accuracy of the measurement.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) has, in the last decade, been another newer and more convenient method of taking the measurements. ADCPs have widespread uses in coastal surveys and oceanographic studies. They can measure the velocity of the water at many different depths in a broad vertical range. By transmitting acoustic signals into the water and detecting the Doppler shift of the reflected signals off suspended materials in the water, like sediment or plankton, the ADCP computes the velocity of the water. This provides a more accurate and detailed characterization of the structure that is present in the water column and is therefore highly appropriate for studying the complex coastal currents off Quincy. ADCPs are installed in numerous configurations, such as on ships, moorings, or even autonomous underwater vehicles, to allow flexible measurement in a variety of environments.

4. How do Doppler principle-based ADCPs work?

ADCPs operate based on the Doppler effect. They project acoustic pulses into the water at a specified frequency. When they encounter moving particles in the water, such as suspended sediment or plankton, the frequency of the backscattered pulses varies. If the particles are coming towards the ADCP, the frequency of the backscattered pulse increases, and if they are moving away from the ADCP, the frequency decreases. The magnitude of this frequency change, also known as the Doppler shift, is proportional to the particles' velocity and, indirectly, the water velocity in which the particles are suspended.

The ADCP is usually equipped with several transducers capable of transmitting and receiving signals at different angles. This enables the instrument to measure the three-dimensional velocity components of the water flow (east-west, north-south, and vertical). By measuring the Doppler shift in more than one direction, the ADCP can calculate the velocity vectors of the water at more than one depth. The data collected is then processed to create a profile of the current velocity across a vertical cross-section of the water column. This profile provides valuable data on the strength and direction of currents at different depths, allowing researchers to obtain an understanding of the complex flow patterns of the coastal waters off Quincy.

5. What is needed for high-quality measurement of Quincy coastal currents?

To accurately quantify Quincy's sea currents, a variety of qualities are desired for the measuring instrumentation. The instrumentation materials must be highly reliable. Because of the harsh marine climate, the instruments must be highly resistant to seawater corrosion, robust enough to withstand the large water pressures, especially in deeper areas, and durable enough to be reused for many cycles.

The gear must be compact in nature. Its compactness makes it lighter and convenient to deploy in multiple locations, including those with complex topography or limited access, e.g., narrow inlets or shallow bays off Quincy. Lighter gear is also preferable as it reduces the convenience of handling and transportation, either if launched from a vessel or a small craft, and

Low power usage is highly essential to maintain. This enables the instrument to operate over extended periods of time without needing frequent battery replacements or the implementation of a high - capacity heavy power supply, which is sometimes not possible for remote coastal locations or long - term monitoring tasks. Cost - effectiveness is another factor. Low - cost instrumentation allows for a greater deployment density, enabling the large - scale measurement of coastal currents. This is especially important for large studies that require data from multiple locations in the Massachusetts Bay near Quincy.

For ADCPs, the enclosure is an important consideration. Titanium alloy is an excellent choice for the enclosure of ADCPs. Titanium alloy offers great corrosion resistance, which is essential for long-term deployment in the corrosive seawater environment. It is light, too, but sturdy enough to protect the internal components of the ADCP from damage through physical force, such as impacts from waves or debris. Titanium alloy strength assures that the ADCP can withstand the hostility of the oceanic environment to take precise readings repeatedly over time, which is a necessity when taking accurate measurement of the dynamic currents along Quincy's coast.

6. Choice of Adequate Equipment for Measurement of Present

• *Types of ADCPs Based on Application

The choice of ADCP is determined by its purpose. For ship-based measurements, one can use a ship-mounted ADCP. It can measure the currents while the ship moves and provide real-time data along the ship's track. It is useful for surveys that have to cover a large region of area quickly or to examine how the currents change over a wide geographical region.

A bottom - moored (or moored) ADCP, or sit - on - the - bottom ADCP, works well for continuous monitoring at a single location. It can be set on the seafloor and left alone to record current data for a long period. This is employed to find out the long - term trends and variability of currents in an area, such as a particular bay or channel outside Quincy.

Buoy-based ADCPs, or floating ADCPs, can be used in monitoring large-scale coastal or oceanic processes. They are carried along by the currents, recording data at different points along their path. This type of ADCP is ideal for studying the overall circulation patterns in the Massachusetts Bay and how these interact with the coastal currents surrounding Quincy.

Frequency Selection

It is also something to consider how frequently the ADCP should be run. Different frequencies exist with use to specific water depths. For water depths of up to around 70m, an ADCP frequency of 600kHz is optimal. The frequency provides relatively high - resolution measurements in shallow waters and allows for good definition in the current structure near the surface and across the top half of the water column.

For depths of around 110m, a 300kHz ADCP is preferable. It will probe deeper into the water column but still have good accuracy, and it will be appropriate for mid-depth measurements in areas of moderate water depths, such as portions of the Massachusetts Bay off Quincy.

For the lowermost waters, to 1000m, a 75kHz ADCP is suggested. Lower frequency waves propagate further in the water and allow measurement to greater depths. This is needed for the exploration of the deep - water flows which may influence the overall coastal circulation near Quincy.

Suggested Brand

There are quite a few well-known ADCP brands, such as Teledyne RDI, Nortek, and Sontek. But for individuals seeking an affordable option without compromising on quality, the ADCP manufacturer China Sonar's PandaADCP is a suitable option. Additional information can be obtained from its official website: https://china-sonar.com/.

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