This need is for areas of the earth within which we stand without our mechanisms that make us immediate masters over our environment...

Howard Zahniser, on Wilderness

Friday, May 1, 2009

Tidal Factors for Lost Coast Hikers


One of the most common questions I get over the telephone or by email is “What do I do about the tides?” Well the answer is easy: you keep an eye on them and never turn your back on the ocean!

The Lost Coast is a unique backpacking trip because all along it there is a large objective hazard that doesn’t exist along most hikes—the ocean. The ocean can hurt you in a variety of ways. It can knock you down with a wave and cause trauma. It can drench you so that you get cold and later hypothermic. It can sweep you off your feet and drown you at sea. It can steal your gear, leaving you cold and hungry. It can also trap you for hours if you get caught in the tide zone on a rising tide.

All of these mishaps are avoidable by following a few simple rules:

1. Never turn your back on the ocean and don’t trust the ocean to behave.

2. Carry a tide chart, know how to read it, and heed its warnings.

3. Know your limitations and don’t be afraid to wait.

There are two large segments of the Lost Coast Trail that show on many maps as “Impassable at high tide” or something similar. The fact is, these segments may be quite passable at a very low high tide with calm seas or somewhat impassable at a high low tide with big waves. It’s all a matter of what the situation is and how good you are at reading the conditions. I generally tell people to always travel in these zones on a receding tide. Based on the tide chart we distribute, I recommend not traveling in these zones at a tide greater than five feet.

Travel in these zones on a receding tide.

That’s the most important advice I can offer. On a receding tide, should you come to an impasse, it is quite safe to wait and the conditions will get better until low tide. If you are hiking along and you get to a rock that is awash, you just take a break and eat a snack.

If you are travelling on a rising tide, on the other hand, and have already passed two difficult sections when you reach this rock that is awash… you may be stuck and you may be in danger. The difficult sections you passed may now be quite impassable and the rock in front of you is only going to get worse. In this situation, seek out the highest, driest ground you can find and hunker down. At this point, you are at the mercy of the ocean and should pray that it does not produce any rogue waves or tsunamis.

The “tide zones” are not generally inundated by high tide. At any level short of seven or eight feet, there are likely sections within these zones where limited travel is possible. I have travelled from Cooskie to Randall Creek on a six-foot tide with small waves and stayed dry. I had to time my run around a couple of headlands to not get my feet wet but it is possible. Generally, the headlands that become impassable do this at between four and five feet on the tide chart. This assumes minimal wave activity. With larger waves, travel is more restricted or at least more risky.

The ocean may also move gravel and sand on the beach from day to day, so the exact heights at which some points are passable can change frequently.

Low tides on the Lost Coast tend to be between minus one and two feet. High tides are usually between five and seven feet. Anything greater than seven or less than zero is extreme. A high tide of less than five feet is not unheard of and some “low” tides may be greater than three feet. These are also extremes in the opposite direction. Look at your tide chart because any of these may affect travel. A three foot low tide with ten foot waves may make it impossible to get from Big Flat to Shipman Creek, for example, whereas a four-and-a-half-foot high tide with calm seas may allow unfettered travel along the entire Lost Coast.

Before you come to do your LCT through-hike, look at the forecasted tides. A good resource for visual learners can be found at http://129.252.79.73/tide/tideshow.cgi?site=Shelter+Cove,+California&type=graph

This is a graphical representation of the tidal activity forecast for Shelter Cove, near Black Sands Beach. The exact times of high and low tide may vary by up to fifteen minutes from Mattole, but on the beach it will be difficult to see these differences without burying a yardstick in the sand.

Don’t sweat the numbers in the tide book. Just ask these questions with reference to the time you plan to travel:

1. When is the low and how low is it?

2. When is the high and how high is it?

With this information you will know if you need to be in a hurry or not. Our tide cycle is always about six and a half hours so if the fluctuations are extreme, the tide will rise or fall rapidly. If the change between high and low tide is only a few feet, the change will be slow and subtle. The tide cycle forms a fairly regular, wave-like pattern over the course of a day and the rates of rising and ebbing tides will also be quite regular.

Take this example. High tide is forecast to be six feet at 9am. Low tide is forecast to be zero feet at about 4pm. What will the tide be at around 12:30pm? The math is fairly simple. About halfway through the tide cycle, the tide will have receded about half-way. The tide should be around three feet and receding—a great time to travel.

In either case, look at the tidal information with a recent marine forecast in mind. Waves of under five feet tend to be no problem. Waves of greater than ten feet can get quite intimidating or dangerous as the tide rises. Waves approaching twenty feet should be a big warning sign—don’t travel on the beach when sea conditions are extreme.

Remember also that forecasted wave and swell heights are forecast averages. If the forecast is for ten footers, most of the waves you see will be in the ten-foot range. Never turn your back on the ocean, though. Statistically, one in ten waves is likely to be greater than eleven feet. One in one hundred waves will exceed sixteen feet. One in a thousand waves will be greater than nineteen feet. Waves of even greater ratio are what are known as “rogue” waves. These can be more than twice the forecasted wave height and can occur at any time.

Remember also that if the forecasted wave period is eight seconds—meaning a period of eight seconds between waves—that the nineteen-footer could come ashore every eight thousand seconds. That’s less than two and a half hours. Never turn your back on the ocean.

Always watch the ocean and be prepared to respond to changing or unusual conditions. Most often, you will not see or notice these huge waves—travelling with seas forecast at two feet, a four-footer qualifies as “huge”. If you are reading ahead in your tide chart, you will not find yourself stuck in the tide zone at a rising eight-foot-tide. Take the time to plan out your day. Don’t hesitate to dawdle in camp for an hour and wait for more favorable tidal conditions.

Travel the Lost Coast on receding tides that are less than four-and-a-half feet.

1 comment:

Bill T said...

how do you know how far you have traveled---are there markers along the way --names of creeeks etc
Bill T