Tides for Sea Kayaking

1. Tides for Sea Kayaking ACA IDW

2. Overview Tide types High and low tide Rule of twelfths Spring and neap tides Reading tide tables Tide races and overfalls Tidal flow direction

3. What is a tide? Tides are the repeated rise and fall of the sea due to gravitational forces exhibited by the sun and moon.

4. Tide Type There are usually two high tides, and two low tides daily. This is known as a semi-diurnal tide. A diurnal tide is a tide with one low and one high tide a day. Some irregularities do occur. For instance diurnal tides are also found on the gulf coast of Florida, but not the Atlantic side. The tidal range is less dramatic nearer the equator. Closer to the poles the tidal range can be quite dramatic. In some cases there are mixed tides. A diurnal and a semi-diurnal tide within the same geographic area. Important to Kayakers Knowing the tide type will aid in planning journeys. Being aware of how many tides a day prevents unexpected challenges when at sea. Knowledge of the tidal period aids in the ability to plan launching and landing in the event of emergency or a change in other weather conditions.

5. High and Low Tide Each tide has a low and a high point. High tide is when the water stops rising. This is called high water. The point when the water stops dropping is low water or low tide. The point in between when the water is neither rising nor falling is called slack water. Important to Kayakers Low tide: Exposes hazards and obstacles and in some cases may make landing difficult or impossible. Low tide may also increase the likelihood of breaking waves. What was once a tepid spilling beach break, might become a steep dumping beach. High tide: May cover certain land features and hide hazards. May make landing difficult or impossible by making a good landing spot inaccessible.

6. Rule of Twelfths Consider the general rule of twelfths: The flow of water between low and high tide is divided into a 6 hour period. The first hour will move 1/12 of the total volume of the tide. The second hour will move 2/12. The third hour will move 3/12. The fourth will move 3/12. The fifth hour will move 2/12. And the sixth hour will move 1/12. As a result the middle two hours move roughly half of the tidal volume. Important to kayakers Kayakers should be aware of when peak flow will occur to ensure they are either going with the flow, or off the water. Tidal periods are rarely exactly six hours. So peak flow may actually occur within a five hour period, or a six hour period.

7. Spring and Neap Tides Spring tides are caused by the alignment of the sun and the moon. The moon will either be full or new. The combined gravitational forces of the sun and the moon cause spring tides to have stronger than normal tidal flow. High water will be higher, low water will be lower, and the current will be stronger. Neap tides are caused when the moon is at quarter phase and is not aligned with the sun. The tide will be weakest at neaps. Important to Kayakers Spring tides will causea higher high water and therefore have a stronger flow during peak flood. What might normally be a 2 knot current could be a 6 knot current at spring tide. Making progress against this type of flow would be next to impossible. Neap tides could cause problems where features that normally are covered with water are uncovered and vice versa.

8. Reading tide tables If we were to attempt to leave from Moss Landing in Monterey Bay in the early afternoon when would peak flow be for the afternoon tide?

9. Reading tide tables If we were to attempt to leave from Moss Landing in Monterey Bay in the early afternoon when would peak flow be for the afternoon tide? Roughly between 12:00 and 2:00 pm.

10. Reading tide tables Based on the moon visible notation how close to Spring Tide is it?

11. Reading tide tables Based on the moon visible notation how close to Spring Tide is it? Full Moon was Oct 3rd, so the moon is waning, though still visible. It is not yet neap tides.

12. Tidal Races and Overfalls Tidal flow can be augmented by a number of factors: Shallow water-if a flood or ebb flow is forced over an obstruction this is known as an overflow. Overflows and races are often indistinguishable. Headlands-Often tidal races form around sharp headlands as they jut into a tidal stream. Picture putting your thumb over a garden hose that is turned on. The Penrhyn Mawr in Wales is a great example of an overfall and a headland type tidal race. Constrictions between landmasses-Where a mainland and an island constrict the sea in an area with a high tidal range, races can form as the water whips in-between at peak flow.Skookumchuk is a great example of a constriction. Standing waves are very common in this type of flow. Wind direction if the wind is with the tidal flow in a tidal race, the sea state will be calmer. If the wind is against tidal flow, the sea state will become very agitated. Important to Kayakers Tidal races and overfalls can be very hazardous to kayakers. Currents can be very strong, and if the wind is in the opposing direction of the tide this can create large standing waves. Currents could exceed 10 knots in extreme cases. Spring tides in an area with tidal races would be very … interesting.

13. Tidal Flow – Direction Tidal direction can vary based on the obstacles in its path. Note here that on the far side of Angel island in San Francisco bay it is headed at an almost 90 degree angle to the majority of the flow. Important to Kayakers If paddlers are unfamiliar with tidal flow and behavior, they could inadvertently be paddling against a strong tidal current, rather than choosing a less difficult route.

14. Tide Take-aways Know your tidal type (mixed, diurnal semi-diurnal) Know when high and low tide occur Know when neap and spring tides occur Know the rule of twelfths for peak flow Read up on tidal tables before getting on the water Be aware of tidal races and overfalls and where they are likely to occur Be aware of tidal directional flow and it’s variance around land masses