OCEANS LEVEL? ... Not Along Isthmus
The Panama Canal Review - January 4, 1963
NO, THE ATLANTIC and Pacific oceans are NOT level with each other.
Not along the coasts of the Isthmus.
If fact, it's possible that the level of the Pacific could be nearly 12 feet above the level of the Atlantic at the the same time.
The difference in level averages only 9.2 inches, however, records of Panama Canal Chief Hydrographer W. H. Esslinger show.
Many Isthmians find it important to keep track of the tides. Bathers want to know whether they'll find good swimming or mudflats at a certain point. Fishermen say they affect the catch.
Where marine ways are not available for hauling out small craft, the practice is to beach them at high tide, then work fast to slap on a coat of paint or make repairs before they're seaborne again on the next high tide.
Balboa has a regular tide with two highs and two lows every lunar day, with an average range from high to low tide of 12.758 feet and a maximum range of 22.7 feet.
Cristobal has an irregular tide varying from two highs and two lows to one high and one low each lunar day - with all possible intermediate variations. But the average range from high to low tide is only .858 feet and the maximum range is 3.05 feet.
Why big tides on the Pacific and small tides on the Atlantic?
The two entrances to the Panama Canal, by air, are only 40 miles apart. and aren't the tides caused by forces of the sun and moon?
Here are the reasons - oversimplified - as given by Hydrographer T. C. Henter:
A look at tides in general is needed to understand their local peculiarities.
At times of new and full moon, tidal forces of the moon and sun pull the seas in the same direction. At first and last quarters, they are approximately at right angles to each other. When moon and sun unite their forces, the tidal range is large. when they are at right angles, the tidal range is small.
The mass of the sun is far greater than the mass of the moon. But the sun is many times farther from the earth than the moon. Hence its tidal effect is less than half that of the moon.
Relative movement of the earth, moon and sun, together with the daily moon and sun, together with the daily rotation of the earth, cause two primary classes of tide-producing forces:
(1) Those with a period of about half a day, called semi-daily forces;
(2) Those having a period of a day, called daily forces. the semi-daily forces are the larger, and consequently, at most places there are two high and two low waters each day.
But rise and fall of the actual tide at any locality, and the times of high and low water, depend on conformation of the ocean shore and depth of the water, as well as on the tide-producing forces.
The rise and fall of the actual tide is divided into three types of tides known as semi-daily, daily, and mixed. the semi-daily has two high and two low waters each day, with little difference in morning and afternoon tides. The daily type has but one high and one low water in a day and the mixed type has two high and two low waters in the same period with considerable difference between morning and afternoon tides.
The mixed tide results from a combination of daily and semi-daily tides.
At Cristobal, the daily tide-producing force is predominant. The afternoon tide is considerably larger than the morning tide.
The daily tide-producing force has little effect on the actual rise and fall of tides in Balboa. There is very little difference in morning and afternoon tides. their rhythm is characteristic of the semi-daily tidal forces.
Here a look at the "stationary wave theory" of the tide is in order.
In a rectangular tank of water, a wave may be started by raising and then immediately lowering one end of the tank. this wave will not be in the form of an ordinary wave with crest and trough. Instead, it is an oscillation, or apparent swashing back and forth (but with little water movement except up and down). This type of wave is known as a stationary wave.
The stationary wave theory is that the dominant tides in the seven seas are stationary wave oscillations set up by the tidal forces of the sun and moon in parts of the oceans having periods of oscillations approximately the same as the period of the tide-producing forces.
According to H. A. Marmer, of the Coast and Geodetic Survey, a number of puzzling tidal features can be explained by the stationary wave theory.
At Panama, the Atlantic end of the Canal opens into the Caribbean Sea, which is cut off from the open Atlantic by the girdle of Antillean islands that mark the limits of the Caribbean. Too, the Gulf of Mexico and Caribbean are of such length and depth as to have a period of oscillation of approximately 24 hours. Hence, in this area the daily tide-producing force is predominant.
The basin comprising the Gulf and Caribbean is much smaller and much shallower than the basins of the Atlantic and Pacific oceans. therefore the actual tides are smaller.
The Pacific side of the Canal is situated at the end of an oscillating system of semi-daily tides and at a considerable distance from the center of the oscillation. thus the range of the semi-daily tide at Balboa is much greater than the daily tide at Cristobal.
Despite the possible 12-foot difference in level of the oceans at the same time, there is no prospect that one would drain into the other if the Canal were a sea-level waterway.
In fact, maximum tidal flow current even at the greatest difference in levels would be only about 4.5 knots, it is estimated. Enough to cause transiting problems for ships in parts of the channel, but not enough to reduce the water supply of either ocean.
There are two main reasons for this. One is the restrictive effect of channel entrances and channel capacity itself. The other is that there are tide "reversals" - particularly with non-standard tides on either side - as soon as highs or lows are reached. Thus tidal flow volume and direction, or both, would be changing almost constantly if the Canal were a sea-level canal.
Levels of the oceans also vary from month to month due to effects of wind, ocean currents, and the cyclic variations of the heavenly bodies.
Normal dry season prevailing winds are north to northwest on the Atlantic side. wind effect on tides is influenced by land masses and the number of miles air flow has to "push" on open water surfaces.
To further complicate things -
There has been an apparent steady but slight rise in the levels of both oceans in the last several years. The "apparent" is stressed because there is still inconclusive debate in scientific circles as to whether the ocean levels are rising or the land masses shrinking slightly, or a combination of both.
Presented by CZBrats
October 4, 1998