Natural Currents Energy Services, LLC Potential Tidal Power for New Jersey 2010-15 Sponsored by NJDOT and UTRC Project Report 140-04 New Jersey Regional Tidal Data Resources Roger Bason March 6, 2011 Contact Information: 845-691-4008 (O), [email protected]
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Report #4- New Jersey Regional Tidal Data Resources
A review of available tide data, tables, graphics, interactive Internet services and software that provide both historical and real time tidal and water current data is presented in support of tasks required for NJDOT 2010-15 Potential Tidal Power for New Jersey. The purpose of this review is to provide both an understanding of tidal flow dynamics and to identify related information resources.
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Natural Currents Energy Services, LLC
Potential Tidal Power for New Jersey 2010-15Sponsored by NJDOT and UTRC
1. IntroductionA review of available tide data, tables, graphics, interactive Internet services and software that provide both
historical and real time tidal and water current data is presented in support of tasks required for NJDOT
2010-15 Potential Tidal Power for New Jersey. The purpose of this review is to provide both an
understanding of tidal flow dynamics and to identify related information resources. This task is completed (1)
to assist in the identification of the 20 best locations for tidal energy sites in New Jersey and (2) to support
the development of a high-resolution computer model of tidal flows in state river and shoreline areas.
The introduction presents an overview of each of the sections in the paper. Background on the nature and
terminology of tidal flow is then presented to provide a summary of the technical terms describing the various
tide states to enable an understanding of the dynamics of tidal flux and movement.
Next a description is made of the National Oceanic and Atmospheric Administration (NOAA)/ National Ocean
Service's (NOS) National Current Observation Program (NCOP) to collect, analyze, and distribute
observations and predictions of currents. The New Jersey sites included in the program are highlighted on
maps and then detailed with accompanying tables that present the information available using this resource.
Section 4 presents a web-based tidal prediction program called Mobile Geographic that provides tables and
maps of sites used for tidal flow predictions. The presentation is made for the applicable sites in New Jersey.
Almost all sites provide information on tidal height. A few of the sites in this resource include tidal currents
speeds. A map identifies the site locations in New Jersey. An example of the data table output is presented
along with a list of options for tidal data presentations by day, month, year. This is followed by a list of all New
Jersey sites for tidal height and current data.
Section 5 provides an example of one of many available tidal software programs. The program that is
detailed is called Mr Tides-3 that is available in both PC and Mac based applications. The Mr Tides-3
software presents data for many sites in New Jersey and also displays the information in four graphical
formats with optional time scales that may be useful in the overall analysis of tidal flows.
Section 6 presents the NOAA Physical Oceanographic Real-Time System (PORTS®) system. The objectives
of the PORTS® program are to promote navigation safety, improve the efficiency of U.S. ports and harbors,
and ensure the protection of coastal marine resources. This is a very robust and real time system that may
prove very useful to the 2010-15 Project.
Section 7 presents the NOAA 2011 Tidal Current Predictions. This system will allow you to obtain tidal
current predictions computed by CO-OPS for more than 2,700 tidal current locations along the U.S.
coastline. The publication of full daily predictions is limited to a select number of "reference stations." The
remaining stations are referred to as "subordinate stations." Tidal predictions for subordinate stations are be
obtained by applying specific differences to the times and speeds of the predicted tidal currents for the
specified reference stations. Section 8 presents a real time NOAA Now Coast application that provides both
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sea state and weather data. Section 9 presents the Coastal Digital data based on the Lidar data collection
housed and distributed by the NOAA Coastal Services Center. The data span more than a decade and were
collected using several different sensors. The collection includes data from topographic and bathymetric lidar
sensors.
2. Basic Terminology for Tidal Flow DynamicsThere are several different kinds of currents including oceanic, river, and wind-driven; all with their own driving
force. Tidal currents (a horizontal motion) are a result of the rise and fall of the water level due to tides (a
vertical motion). The effects of tidal currents on the movement of water in and out of bays and harbors can
be substantial. A fundamental understanding of tidal flow dynamics requires an understanding of basic terms
that describe the various aspects of the tidal cycle. These terms include:
Set - The set is the direction that current flows toward. This is the opposite of the way winds are reported.
Drift - This is the speed of a current. On ocean waters it is usually stated in knots; in rivers, mph.
Velocity - As the typical term in physics infers, this is an indication of both speed and direction (set and drift)
Speed - How fast the water is moving in relation to a stationary object (e.g. shore, light house).
Flood Flow - The tidal flood when flow is coming from the sea to the shore (tide is coming in).
Ebb Flow - The tidal ebb when it is coming from shore and returning to the sea (low tide ensuing).
Slack Water - The point between flood and ebb (or ebb and flood) is when there is no horizontal movement.
Stand - The point where vertical changes stop as the tide reverses. This is not the same as slack water; this
is a tidal (vertical) occurrence, not a tidal current (horizontal) occurrence.
Maximum Current - The normal maximum speeds of the ebb and flood currents. This does not include
effects of weather or run off from rain or melting snow, which can significantly effect tidal currents.
Water Characteristics and Related Tidal Flow Example
It has mass, therefore when it moves it has momentum, exerts force, and generates friction.
It's a fluid. Fluids are defined as any substance that has no rigidity. Liquids and gases are both fluids.
It is viscous. Viscosity is defined as a fluid's resistance to motion.
Water is a viscous fluid and exactly how water flows is a function of its viscosity. No matter how you move
water around, it will always take time to move any distance due to its own viscosity, or the interaction of its
viscosity with its surroundings.
As an illustration of the effects of the viscosity of water, consider this: No matter how fast you pour out a
bucket of water, it will always take some amount of time to empty the bucket. Always.
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Figure-1. A Schematic of Tidal Flow in a Bay.
Imagine a large, long, narrow bay on the coast. We position one person on the ship anchored at the opening
to the sea (lower right) and another at the distant white light, a point on the bay as far from the sea as he can
get. We assume the tide is low and there are no tidal currents in the bay.
The tide comes in and reaches high tide at 11 am so the person at the mouth of the bay reports high tide at
11 am. Meanwhile the person inland is still watching the water level rise until, at 1 pm, he announces high
tide where he is. That's a difference of two hours between high tide in the two locations.
Let's look at what actually happens throughout the cycle. As the tide comes in, the water entering the bay
has to overcome slow water to move forward into the bay (viscosity) so this change is not seen at the other
end of the bay immediately. The tidal currents in the bay are now in flood flow.
When the tide is highest at the entrance of the bay, the tide is at high stand in that location, but there is still a
flood flow into the bay because the high stand has not been reached further into the bay yet. A while later,
half way into the bay (the red light), the water also reaches its high stand, but there's still a flood flow
because the high stand has not yet been reached further in.
Finally the high stand is reached all the way inside the bay at the white light and the current stops. It doesn't
reverse; it stops. This is called slack water. Even though the tide may have started going out at the bay's
entrance, the current in the bay stops, like a ball that has been thrown up in the air stops at the apex of its
flight before falling back to earth.
As the tide starts going out, the same thing happens in reverse. The water level once again changes first at
the bay's entrance while the water further in the bay may still be at high stand. The current in the bay,
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though, is now in ebb flow.
When the ocean is at low tide at the entrance of the bay, the water is at its low stand. Further into the bay,
low stand has not yet been reached so the ebb flow continues. Finally low stand is reached all the way inside
the bay and once again slack water occurs in the bay.
To summarize, we can list the sequence of events at any point in the bay, but the time at which these events
occur will be different between any two points at different distances from the sea. The sequence is as follows
(starting at low tide):
Flood flow, when the tide starts to rise.
High stand, when highest water level is reached and flood flow continues.
High slack water, when high stand is reached throughout the bay and flood flow stops.
Ebb flow, when the tide starts to receed.
Low stand, when the lowest water level is reached and ebb flow continues.
Low slack water, when low stand is reached throughout the bay and ebb flow stops.
The same applies to rivers flowing into the sea, but with some important differences. The water flowing from
the river will tend to hinder the movement of water into the river, hence causing the flood current to be less
swift. On the other hand, the ebb flow currents can be extremely swift because water leaving the river at low
tide is augmented by water flowing from the river. Add to that the possibility of rain and/or snow runoff inland
that has caused the river to swell, and ebb currents can be even faster.
In some waters, even the maximum current is so swift that less powerful boats must wait for slack water to
navigate them effectively. In order to safely navigate inshore waters, it is important to be able to predict the
tides. This is accomplished with the use of tide tables. They can be found in various formats and contain
varying amounts of information. Some definitions that are useful in understanding the
Reference Station - Reference stations are points along the coast that are specified stationary points for
the measurement of tides.
Subordinate Station - A subordinate station is a point reporting information relative to it's assigned
reference station. One reference station can be assigned hundreds of subordinate stations. The National
Ocean Service (NOS) collects and publishes tidal data for various geographical areas. These publications
contain data for all reference stations and subordinate stations in a given area.
The data for all points in all areas is given as relative to a reference plane called Mean Lower Low Water
(MLLW).
To predict the tides at a point that is not a reference station, one uses a combination of data from a reference
station and data from a table of 'tidal differences' for that reference station. The table of tidal differences
actually tells the difference between a subordinate station's tides and that of it's 'parent' reference station.
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3. NOAA National Current Observation Program (NCOP)
Figure-2. NOAA National Current Observation (NCOP) Along US Eastern Seaboard
The National Oceanic and Atmospheric Administration (NOAA)/ National Ocean Service's (NOS) Center
for Operational Oceanographic Products and Services (CO-OPS) manages the National Current
Observation Program (NCOP) to collect, analyze, and distribute observations and predictions of
currents. The program's goals are to ensure safe, efficient and environmentally sound maritime
commerce, and to support environmental needs such as HAZMAT response. The principal product
generated by this program is information used to maintain and update the Tidal Current Tables.
Background
- NOAA and its predecessor agencies have collected information on currents in various ports and
harbors, and in the Gulf Stream, since the mid-1800s. The Coast and Geodetic Survey first published
tidal current predictions for the use by mariners on the East Coast in 1890 and for those on the West
Coast in 1898. By 2002, Tidal Current Tables contained predictions for over 2,700 locations throughout
the USA. Most of the data presently in use was collected between 1930 and 1980 when significant
resources were dedicated to the program. From the 1960s through the mid-1980s, two NOAA ships
(the McARTHUR on the West Coast and Alaska, and the FERREL on the East Coast) and numerous
staff oceanographers and technicians were dedicated full-time to the collection, processing, and
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analysis of tidal current data. These complete comprehensive physical oceanographic surveys measured
currents, water levels, water temperatures and salinity, and meteorological data. Many were the first
complete physical studies ever conducted on major U.S. estuaries.
Due to budget cuts and ship reassignments in the late 1980s, the program was reduced significantly.
Since the mid-1990s, the National Current Observation Program has been recognized as fulfilling a vital
mission of national interest to both the maritime industry and environmental stewardship. As a result,
many organizations strongly recommend that it is time for the program's data to be updated.
Future Directions -
Approximately 70 percent of the stations in the 2001 Tidal Current Tables are over 30 years old. Many of
these stations are based on analyses of less than 7 days of data (the data duration is known for 24% of
all stations). Channel dredging and changes in the configuration of ports and harbors over the years
have significantly altered the physical oceanography of many of the nation's estuaries. Reports from
local users indicate that many of the National Ocean Service’s tidal current predictions may be
inaccurate. NOS intends to address these deficiencies by rebuilding the program and re-sampling the
currents at every major port and estuary within the next 20 years. The majority of work to deploy,
recover, and maintain the program's sensors is likely to be conducted by contractors overseen by NOS
staff.
This system will allow the public to obtain tidal current predictions computed by CO-OPS for more than
2,700 tidal current locations along the U.S. coastline. The publication of full daily predictions is limited to
a select number of "reference stations." The remaining stations are referred to as "subordinate stations."
Tidal predictions for subordinate stations are be obtained by applying specific differences to the times
and speeds of the predicted tidal currents for the specified reference stations.
These pages provide a listing of the 2,700 plus reference stations and subordinate stations. Selecting
the "predictions" link beside a station listing will provide tidal current predictions for the location with the
differences already applied.
Unlike tide stations, which are normally located along the shoreline, most tidal current stations are
located offshore in channels, rivers, and bays. Tidal current stations are often named for the channel,
river, or bay in which they are located or for a nearby navigational reference point. A map or some
personal knowledge of the area may be necessary to help identify stations in the area you are interested
in.
The list of subordinate stations has been broken down into states and other areas where tidal current
stations are located. Each state is further broken down into regions. Each region presents a list of the
tidal current stations in the area. The stations are listed geographically; thus, stations that are near each
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other along the shoreline appear together in the listing. This assists the user in locating a station of
interest.
Depth of stations: Although current measurements may have been recorded at various depths in the
past, the data listed for many subordinate stations are mean values determined to have been
representative of the current at each location. For that reason, no specific current meter depths for those
stations are listed. Beginning with the Boston Harbor tidal current survey in 1971, data for individual
meter depths were published and subsequent data will be presented in a similar manner. Most historic
tidal current data is collected from meters suspended from survey vessels or anchored buoys, the listed
depths for these stations are those measured downward from the surface. More recent tidal current
data are collected from meters anchored at fixed depths from the bottom, the listed depths for these
stations are defined as depth below chart datum and will be accompanied by the small letter "d". All
depths listed are in units of feets.
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Figure-3. NOAA NCOP sites in New Jersey.
Data details of NOAA NCOP sites for New Jersey are presented below.
SANDY HOOK BAY Average Speed and Direction Min Before Min Before Flood Flood Ebb Ebb Station Depth Latitude Longitude Spd Dir Spd Dir Spd Dir Spd Dir