tides and currents

Tides and CurrentsTides and Currents

ByBy

Andree HurleyAndree Hurley

ACA Instructor Trainer Coastal ACA Instructor Trainer Coastal

and Whitewater Kayakingand Whitewater Kayaking

Onwatersports.com!Onwatersports.com!

Planning a kayak trip Planning a kayak trip in Japan?in Japan?

A definitionA definition

TidesTides

Vertical Movement Vertical Movement of waterof water

Mostly affected by Mostly affected by the rotation of the the rotation of the earth and earth and gravitational pull gravitational pull of the moonof the moon

CurrentsCurrents

The resulting The resulting horizontal horizontal movement of the movement of the water.water.

Phases of the Moon Phases of the Moon Affect the TideAffect the Tide

New Moon and Full Moon have a lot of gravitational pull resulting in higher and lower tidesNew Moon and Full Moon have a lot of gravitational pull resulting in higher and lower tides The moon takes 24 hours and 52 minutes to travel around the Earth. This mostly produces two high

and two low tides each day. These are called semi-diurnal tides. Each tide is “about” six hours. The tides change by about an hour each day. If high tide is at noon today, it will be at “about” one o’clock tomorrow.

When the sun and moon and Earth are in a straight line, during the times of a full moon and new moon, the gravitational pull on the Earth is the greatest. It creates high tides that are very high and low tides that are very low. These are called spring tides.

When the sun and moon are at right angles to each other they pull in opposition to one another, and the difference between high and low tides is not very great. These tides are called neap tides.

Department of Fisheries and Oceans Canada http://www.glf.dfo-mpo.gc.ca/sci-sci/bysea-enmer/about-ausujet-e.html

Tide ChartsTide Charts

The publication of full daily predictions is limited to locations referred to as "reference stations".

The remaining stations are referred to as "subordinate stations".

Tidal predictions for the subordinate stations can be obtained by applying specific differences to the times and heights of tides at the specified reference stations.

http://tbone.biol.sc.edu/tide/sites_uswest.html

How Tide How Tide Affects KayakersAffects Kayakers Long (muddy) carries!Long (muddy) carries! No beach at allNo beach at all Secure your kayaks!Secure your kayaks!

Vertical Movement Vertical Movement in Tide Creates in Tide Creates

Horizontal Movement in Horizontal Movement in CurrentCurrent

During the New and Full moons, During the New and Full moons, the current is fastest as more the current is fastest as more water has to move through the water has to move through the same spacesame space

The rest of the time, currents The rest of the time, currents tend to be slower moving.tend to be slower moving.

Figure 1: Tidal current transports (current velocity times ocean depth) for the principal lunar tide in the Indian Ocean, at the instant when the mean moon passes the Greenwich meridian.

Within the central Indian Ocean, high tide occurred several hours earlier, and the water is now rushing away from that point.

Flood tides are occurring in the Timor Sea and in the Bay of Bengal.

These data were determined from TOPEX/POSEIDON altimetry.

Primary Primary StationsStations

http://www.dairiki.org/

Current ChartsCurrent Charts

http://co-ops.nos.noaa.gov/currents06refcurrents.html

Some TermsSome Terms

SlackSlack Flood - maximum floodFlood - maximum flood Ebb - maximum ebbEbb - maximum ebb Rule of thirdsRule of thirds

For example - kayaking into Deception Pass. I like to paddle into the pass on the tail end of a flood, wait for slack, play in the eddies

During the beginning of ebb, and get the free ride back!

9:00 am- slack before flood

10:00 am- 50% max flood 11:00 am- 90% max flood

12:00 pm 100% max flood (six knots)

1:00 pm 90% max flood2:00 pm 50% max flood (enter pass)

3:00 pm slack before ebb (hang out, watch pigeon gillemots)

4:00 pm 50% max ebb (work currents)5:00 pm 90% max ebb (think about leaving, free ride)

6:00 pm max ebb (six knots)

Bathtub Effect - Like the Sea of Cortez (Mar de Vermillon)

In 1940, Steinbeck and his biologist friend Edward Ricketts took a sardine boat out of Monterey on a 4,000 mile trip around the Baja peninsula into the

Sea of Cortez.

Water has momentum.Like a ball on a pool table, it moves

in a straight line until it hits something and is deflected.

The earth continues moving under the mass of water - so we can can

still have current going in one direction even though the tide has

changed.

How Does This Affect USHow Does This Affect US

We could be paddling against current and We could be paddling against current and going nowhere!going nowhere!

We want to look for the “free ride”We want to look for the “free ride” We might get stuck in an “eddy”We might get stuck in an “eddy” We need to enter and exit eddies - some We need to enter and exit eddies - some

as long as an islandas long as an island

Interactive Portion of Presentation

Now You Do It! Now You Do It!

We are going on the last We are going on the last leg of our trip - from leg of our trip - from Cypress Island to San Cypress Island to San Juan Harbor. We will cross Juan Harbor. We will cross a shipping channel a shipping channel (dangerous) and two (dangerous) and two bodies of water with two bodies of water with two different current stations, different current stations, Rosario Straits and San Rosario Straits and San Juan Channel. You choose Juan Channel. You choose the route and the times the route and the times you will leave, eat lunch you will leave, eat lunch and arrive!and arrive!