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This is about science produced by the California Institute of Technology and originally broadcast by station KPCC Pasadena California. The programs are made available to distaste by national educational radio. This program is about a man made island with host Dr. Peter less a man and his guest Dr. Frederick Reitman. Here now is Dr. Lester Mann. Since antiquity man has been fascinated by islands. The ancient poet Homer spoke about them as druids scattered by the capricious hand of Zeus into an alien sea. Both a haven and a menace for mariners. Perhaps the romance of violence which has appealed to poets is the thought of a little piece of earth where no land should be struggling for existence in a hostile ocean. But man's technology has developed immeasurably over the centuries. Now he whirls the valleys and makes
Lakes where none were before. Water in the midst of land and recently he has been thinking of doing the reverse of putting land in the middle of the ocean. Manmade islands to serve the ever increasing needs of humanity. We have with us today Dr. Frederick Wright clen assistant professor of civil engineering at the California Institute of Technology who will talk with us about manmade islands. Dr. Reichman did his undergraduate work at Johns Hopkins and obtained his Ph.D. from the Massachusetts Institute of Technology in civil engineering working especially in problems related to bird Harbor resonance. He has been teaching at Cal Tech since 1962 and has been considerably concerned with many problems involved with the ocean with harbors with
mooring with docks and jetties and all the numerous interactions of the sea with the works of man. I'm going to ask him to talk for a minute about this manmade island which is the subject of discussion friend. Thank you Peter. You know the island that Peter was mentioning is a proposed Island where the Metropolitan Water District in the Los Angeles area and it is an island located off shore to house a camp a combined nuclear power plant and the salting plant for the water district. This island was the concept was originally. Give in to the Metropolitan Water District by the Bechtel Corporation.
Why should they want to put this off Sure Fred why wouldn't the land itself be suitable for building a power and disappointing plant. Oh I believe the primary reason is one of economics that of a large number of sites on land and comparing the cost of building the plant on land to that of building an island off shore it was found that the island was just more economical. You mean to say that it is really cheaper to give and take you know dirt and build an island in the middle of the ocean then to buy a piece of land in southern California these days and this is what it seems to be. Actually the island is roughly twenty eight hundred feet off Sure and in a depth of water of about 30 feet or so. So it's it's not in extremely deep water. Nonetheless this Sun's like a vast project. The thought
of building a artificial island of that size in the sea. This must certainly rank among the works of men as. One of the largest earthmoving projects ever envisaged Is that true. Well there's a significant amount of material necessary and based on a preliminary design that has been submitted to and it's of the order of one tenth of the volume of the Oroville dam which is under construction now and the Feather River project in California. Fred what is MWD the abbreviation used. This is the Metropolitan Water District. Yes. Forgive me I should have remembered that that is the metropolitan Los Angeles is it right. It seems to me that if one is going to build an island sand
off the ocean that one must take very special precautions to make sure that the sense thing is there and one doesn't as recommended in the Bible. One doesn't build a house upon the sands. I suppose the waves are one of your major considerations in such a design. This is true Peter this is where Cal Tech became involved Doctor of a nominee who is professor of hydraulics at Cal Tech and myself were approached to supervise a study of the offshore island with the main objective being to look at the effect of waves effect of the wave environment on the proposed Island design. Oh how high of the water will the island be Fred. And in what depth of water will it be located.
The island is located in roughly 30 feet of water and the. Island itself is that elevation plus 20 which means that it's 20 feet above the mean low or low water which is the basis for sea level elevation. One really commits one would expect that something which was essentially 20 feet above the low water level would be impervious to the to anything except the most severe waves. Maybe you can tell me a little bit about the type of waves that we get in the Pacific and sort of heighten the forces involved in these waves. I think first before I before I say anything about that actually the island itself is 20 feet above the sea level but the the object of the study was to look at the Wave defense
which runs around the perimeter of the island and the defense itself is actually for the defense that evolved from the laboratory studies is 20 feet higher than the island itself. And the main reason for this is that the wave environment. This island is designed for is the maximum possible wave and that particular depth of water. And for a 30 foot depth there are actually a 30 foot depth. Plus the possibility of having an extreme high tide and additional depth increase due to wind. This brings the total depth to about thirty eight feet of water. Under this condition the maximum possible wave would be about 28
feet. So you have to design this island to be protected against the maximum possible waves that can occur in these parts. Do those sort of waves occur with great frequency. These don't occur with great frequency actually the design wave is based on the 1939 hurricane which lasted roughly five days and this 28 foot wave is predicted from. Certain observations that were made at the time. So this is not a wave of frequently occurring wave. However because of the importance of the structure as far as the nuclear power plants and desalinization facilities it's quite important that the island be designed such that there be no overtopping due to waves and so that there would be
adequate defense from the highest possible wave. This monstrous 28 foot wave that you were talking about was produced by by the hurrican. Is it true that most of the larger waves in the ocean are produced by the wind. What other means do waves produced in the Pacific. Well in the Pacific one wave it comes to mind is the bi seismic impulse production of the so-called tsunami wave and tsunami is taken from the Japanese and usually engineers refer to this wave as a tidal wave. But to. So that this isn't confused with the tide the Japanese word is use the Japanese word Toonami is used however I've been told that tsunami actually means title in Japanese so that one hasn't gained too much.
I said it really rare thing the same thing Fred that your remark about Waze being caused by seismic impulse gives to me the picture of some sort of underwater earthquake is is this what happens. Yes and do these do these underwater earthquakes occur in any particular spot in the Pacific and with any particular frequency. Well this I really can't comment on. Of course there have been a number of earthquakes around the rim of the Pacific which have caused the so-called tidal waves or tsunamis. The Alaskan earthquake produced a wave which created a quite a bit of damage in northern California and the. Earthquake in Chile a few years ago created quite a bit of
disturbance in the Hawaiian and Japanese area but these these waves are are quite different from the waves that we're concerned with these waves are really so-called shallow water waves where the wave length is very large even compared to the depth of the ocean at its deepest point. It waves that we're concerned with in this particular study as with most coastal engineering works our wind generated waves which are of a much smaller wave length and with a wave length that vary significantly as the wave moves from the generating area into the coastal region. And these waves I understand can be generated many hundreds of miles away from the ocean and travel for long distances. Could you talk about that. This is true.
A wave may be generated over a a rather large area that is the generating area maybe large as well as the distance from the from the sure Southern California is. It disturbed during the winter by waves which occasionally are generated in the in the South Pacific and these waves travel a great distance without losing very much energy and of course being in some respects regenerated as it travels through these large distances. By the way it's regenerated by the prevailing wind as as it travels along. One could say this yes. Does this mean that we on the Californian coast have a have a fairly regular wave structure and that the waves come from a general direction much of the generally fixed direction of much of the.
Well perhaps as an example one could take the island site which is somewhat south of the Los Angeles area but this is a site which is exposed to both rather long period waves by period I mean the the time if one stood in one position the time that it would take for a wave to travel past that point it's exposed to long period waves coming from the south which are of the order of perhaps 14 seconds and exposed to more storm waves coming from more of a northerly direction which are of the order of perhaps 10 seconds. So there's quite a variation and some protection to the coast is afforded by the offshore islands the natural islands off the coast of California.
When you talk about these long period waves in the waves traveling this of course means simply that the hump in the water is moving at that speed. This is right the actually the water particles are at least a distance off shore are traveling more in a circular or elliptical orbits. What we see and what we think of as the wave traveling is just the effect of this circular elliptical water particle motion and the shape traveling not the water particles themselves. You one can see this by or I'm sure that that you yourself have felt this when you swim out past the surf zone and just bob in the water as the waves comes come by and you certainly aren't washed or unsure. Now we know as an ordinary person the sort of
mind of problems that waves of course one when one is surfing as you point out. But I imagine that there are many problems caused by waves in harbor installations which one doesn't normally think of. What about enumerating some of those. Well yeah. Perhaps one could describe this best by an example. One example that comes to mind. Living in Southern California is a rather large marina which is has been built. It was built a number of years ago about actually about three years ago and when this was first built there was a great deal of wave agitation inside the harbor which prevented people from moring boats in already built facilities.
This is a problem in some respects similar to or akin to resonance where waves of certain periods excite certain moods similar to if one took a spring with a mass on the end of it and and jiggle this mass at a certain frequency it would move in a certain way and if you jiggle it at a particular frequency it would be excited at a much greater amplitude. And I imagine you could also construct a even custom model by taking a bowl of water and swinging it. To him backwards and forwards is that a similar type of wave resonance that you're talking about this this certainly is this is likely the problem of trying to carry a coffee cup back to the table and having it slide show over. You can very easily set up modes in closed bodies of water. The this problem first was looked at in the
19th century in Lake where in one case in lake. Lake Geneva I believe and in another case in a lake in Scotland where a pressure disturbance is set up oscillations in the lake which were difficult once they were set up it was very difficult to do anything about this. I imagine another aspect of the protection of a harbor is the fact that the currents are going to be carrying sand into different places of the harbor and because one is changed the natural shoreline one may find that the shoreline itself starts changing on top of you where you didn't intend to do it at all. This would seem to me to be a major problem as well. This is a problem and this is certainly a problem in the southern California area and where one is trying to
build a harbor and protect the vessels in the harbor and vessels entering the harbor from waves. Dan as you say you're disturbing the environment and in doing this interrupting the sand the natural sand transportation down the coast this this can cause quite serious problems. But to return to our discussion of waves the natural idea of the century is to avoid some of the dangers caused by waves is to build some break water which will tend to resist the wave motion and to dissipate its energy and thus to maintain the integrity of the land behind it. I suppose this was one of your major considerations in designing the. What a protection for you a man made island. Yes actually we were engaged to to study an existing design and to make any suggestions
for increasing the safety of the island site. Since the waves that we're talking about are so large as I mentioned the 28 foot wave in the energy and forces associated with this wave impinging upon the structure are so large it's quite necessary to armor the face of the island to protect against. The way forces and the method that was proposed in this particular design. The design by the Becta corporation and their consultants was to use an item called a tri bar which is a blown up version of essentially of a child's jacks. There are a little larger.
The original size was of the order of 18 times and these units are built such that they naturally interlock so that you form almost a blanket of these concrete units with very large rock to either side of this blanket of so-called tri bars and this forms a protective surface for the for the island to protect against it to protect against both run up and boat and stability to increase the stability of the structure. In the course of the design of this type of wave wave protection. Do you concentrate most of your work in theoretical calculations to work out exactly how these things should be placed. Or do you use experimental techniques. Pardon me this is the this is actually the type of study where.
One cannot go into a great dear detail and in a theoretical sense and where a model of the structure is really necessary in order to obtain adequate information adequate design information. And this is perhaps similar to many other fields in engineering where one knows what the basic equations are which govern the motion or the action or the forces but these equations are because of certain other conditions are at the present time impossible to solve so that one has to resort to to a model and to observe the actions that one is interested in in the model and to try to scale these up to the the so-called prototype to the actual island structure in this particular case.
When you are talking about a model have Fred I imagine that you're talking about what is really an extremely realistic model in other words he was real water and real sand on a real island and if you looked on the thing from above you might think that it was a miniature of the actual. Island which you are trying to build Is this the case. This is this is this quite true we we try to we use certain modeling laws so to speak in modeling the various components of the armor and we build this model to a particular scale and try to build it as it would be built by a construction firm. And in this particular study we built two models one was a so-called two dimensional model a model that was exposed to waves in a long wave tank. And this model was used to study the stability of the
structure and the so-called run up how high the water would rise when the face of the structure because of waves. And then we built a second model which was a three dimensional model by the way the first model was built to a scale of roughly between 1 to 40 and 1 to 50 that is one foot in the model corresponding to 40 to 50 or 50 feet in the prototype. Then we built a three dimensional model which represents a part of the ocean. It represents the a part of the coast and going out to a depth of approximately 60 feet. I'm modeling both the bottom contours of the ocean and also the island structure in a full full sense. And in this particular case it was quite interesting we took overhead
photographs of waves coming in against the model island and it was just as you said like a an airplane or aerial photographs taken flying over the island in this case flying over the island at roughly seventy five hundred feet. What was the results of your own model studies Fred. Well the the major results were that. We along with the engineers of the Becta corporation we decided upon a particular size of a concrete armory unit that we felt would be would result in a stable structure. We were able to decide upon an elevation of the wave defense this elevation of 20 feet above the island which would prevent overtopping of the structure by
waves and also some observations of the three dimensional model of just how the waves reacted as they came around the structure and perhaps how they would affect any transport of sand in the area so that we feel that. The model was quite fruitful as far as providing some ideas to the engineers in coming up with a a design for the final Island site. Fred do you have any idea I don't think this is your province about whether this island will actually be built and how long it will take when they start to build it before they complete it. Well I really don't know whether it will be built or not. I imagine that if it is if the island is decided
upon as being the site for a plan such as this that it would be a way to. Two perhaps or three year construction program I see. And thanks to your investigations we feel sure that it will be safe against the worst waves that the worst hurrican could produce. Thank you very much Fred. This evening we've heard about a proposal for a 40 acre manmade island as the site of a combination nuclear power and a sorting plant. And the studies that were made to show that this island could safely withstand the heaviest ocean waves ever recorded on the southern California coastline. Our guest was Dr. Frederick Reich klyn And with that we close our talk about a manmade island. This was about science with host Dr. Peter Lewis a man and his guest
Dr. Frederick Wright one of the California Institute of Technology. Join us again for our next program when two more members of the Cal Tech faculty will discuss a subject of interest about science is produced by the California Institute of Technology and is originally broadcast by station KPP C. Pasadena California. The programs are made available to this station by national educational radio. This is the national educational radio network.
About science
About a man-made island
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California Institute of Technology
KPCC-FM (Radio station : Pasadena, Calif.)
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University of Maryland (College Park, Maryland)
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Episode Description
This program focuses on the science of man-made islands. The guest for this program is Fredric Raichlen.
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Interview series on variety of science-related subjects, produced by the California Institute of Technology. Features three Cal Tech faculty members: Dr. Peter Lissaman, Dr. Albert R. Hibbs, and Dr. Robert Meghreblian.
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Guest: Raichlen, Fredric
Host: Hibbs, Albert R.
Producing Organization: California Institute of Technology
Producing Organization: KPCC-FM (Radio station : Pasadena, Calif.)
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University of Maryland
Identifier: 66-40-66 (National Association of Educational Broadcasters)
Format: 1/4 inch audio tape
Duration: 00:28:20
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