[Paddlewise] Kayaks and River Entrances and Bars - the condensed version

Wherever separate bodies of water meet - and especially at a river bar - the
kayaker will encounter a complex system of currents that mostly depend upon
these factors:

1. The tide (whether slack, ebb or flood) and the tidal range;
2. The river current;
3. The wind (onshore, offshore or along-shore);
4. Any long-shore currents in the larger body of water;
5. The depth of the water at the confluence.

It already looks complicated, doesn't it? Boats have been navigating river
bars and river entrances for a long time and most of the time there is
little danger. But seamen like to refer to "local knowledge" and the first
thing I'm going to tell you is that you should find out where the people who
cross the bar in boats like yours hang out and seek them out. Their
knowledge of that particular piece of water will be invaluable. They will
know, for instance, which side of the jetty to hug (or whether to stay in
the middle); which tides to avoid; which winds to avoid; and other pertinent
bits of information.

So, having said that, there are some basics. I'm going to start with the
easiest set of conditions and then try to explain what factors complicate
them.

The easiest conditions in which to cross almost any river bar would be at
(or near) high-water slack tide (the part of the tide in which it's neither
rising or falling) on a small tidal range (the difference between low tide
and high tide is "tidal range"), no (or low) long-shore current, zero (or
almost zero) wind and low  - or no - river current.

Well heck. That's easy enough. Just hang around for all those conditions and
you'll be able to sneak across virtually any river bar in the world with
impunity.

Of course, in the real world those conditions are all met very seldom - and
almost always early in the morning if they are met at all. So let's take a
look at what complicates things.

1. High River Current. If there has been recent rain, or melt-off from the
mountains then the current in the river will be moving quickly and the
collision of the high velocity river current and the relatively low velocity
ocean currents can become violent.

2. High Onshore Wind. Wind blowing against the river current will create
"rips" of interesting (from a distance) triangular-shaped waves which vary
in height according to the depth of the water, the velocity of the current
and the strength of the wind.

3. Large Ocean Waves. Even in no-wind conditions a storm hundreds or
thousands of miles away can generate a large "swell" which can wreak havoc
with a bar crossing. Ocean waves inevitably get bigger when they get to a
river bar so if they're big to start with....  Of course, a well designed
and maintained entrance can mitigate this problem. But in general, be very
cautious when there are large swells.

4. Shallow Water at the Bar. Like a river flowing over obstructions creats
rapids, the same phonomenon exists at the river bar when the water is
shallow. In general, the wise paddler crossing a shallow bar or river
entrance wants to time the crossing so that there is higher water and
minimum current. A shallow bar also contributes to higher breaking ocean
waves.

5. Flood Tide. Depending upon the tidal range, the river current flow and
the wind, flood tide is the least hazardous period to cross next to no
current at all. This is because the rising tide tends to move up the river
(depending, of course, on the rate of elevation change in the river and the
tidal range) and give the river water less drop. The flood tide will also
tend to minimize the effects of an onshore wind.

6. Ebb Tide. A falling tide will tend to exacerbate the effects of the river
current because the water will have farther to drop. An ebb tide with an
onshore wind is NOT the time to cross a dangerous bar. Ocean waves meeting
both shallow water and the river current will steepen and often break
dangerously.

7. Long-shore Currents. Depending upon the location and the season, there
can often be currents of over 1kt moving up or down the beach. Since many
bar entrances have jetties extending seaward, the unwary kayaker can
encounter  some exciting water when the jetties no longer protect him from
these currents. Be prepared to deal with eddies.

8. Jetties in General. In most countries the jetties are dredged
periodically (or, sometimes, continuously). Check the entrance for the
presence of a dredge and carefully note which side of the entrance the
dredge is depositing its "spoils" (the name for dredged materials).

9. Ocean Waves in a Jetty Entrance. There is a tendency for waves to "break"
more on one side of the entrance (nearer one of the jetties) than the other.
A wise paddler figures this out before hand and hugs the side of the jetty
where these waves are not breaking.

What, in general, you want to avoid are:

1. Large current components against the wind;
2. Very shallow water;
3. Large breaking waves across the bar (well, duh!);
4. Large tidal range.

What, in general, you want:

1. Settled weather with little wind;
2. A period of lower tidal ranges;
3. A period of lower river currents;
4. A period of no (or minimal) swell;
5. A nice deep river bar (generally this means well-dredged).

This condensed version should serve as a basis for discussion. Paddlewise is
lucky to have a large contingent of expert paddlers experienced in crossing
river bars. Kruger, Gibbert, et. al. will certainly point out any follies
I've inadvertently written.

Craig Jungers
Royal City, WA
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