Down to the sea; 4; Erosion
Erosion at a beach is of course a natural process. It is rather amazing and much more severe. Than it actually is when you consider what a narrow ribbon or sandy beaches are and now the tremendous population growth of California and the tendency to live near the coastline has reached a point where we can no longer tolerate masterbate any. Thanks. This is another in a series of programs titled down to the sea a series concerned with various aspects of that vast world ocean that cover some two thirds of this blog. To many of us the open ocean is an unknown world. When we think of the sea we think in terms of the shoreline surfing sand one of waves crashing on rocks on against cliffs here on the shoreline. The ocean is a playground for millions. It is also a battleground for oceanographic engineers must fight to preserve
harbors and beaches from erosion. The topic of this edition of down to the sea. In many areas of the world we're pounding surf meets with. Sea caves have been formed as the result of eons of erosion and sometimes the sea caves are quite extensive and fascinating as the tide surges in and out. The sound you're listening to were recorded in the sea caves at La Jolla California. Thank you. Why would creation of sea caves over the centuries is interesting. The real problems of ocean
caused erosion are more often related to the movement of sand from one point to another. But let Dr. Robert Dill of the Navy's undersea research and development center in San Diego describe the overall problem starting early part of the century of course the development of a water need along our coastline and also power need. There are large dams made in the mountain areas and these have essentially cut off a great deal of the source saying and which would have been under normal conditions come down and formally made necessary material for our or our beaches. And this is a source of sediment which is essentially been cut off. However I think we still don't know enough about the dynamics of the movement of sediments. And this source to fully determine whether or not this is going to bring about a catastrophic reduction in the amount of beach material we have.
We know from continuing studies that sand once it arrives on the coastline is moved. Along by the prevailing currents in our particular region in a southerly direction and it will move until this sand encounters the head of a large submarine Canyon and the narrow shelf areas of Southern California we have several large canyons which come in to within six or seven hundred feet of the present shoreline. And some of this sand which is moving along the coastline is diverted out into deeper water by way of these canyons and as it moves away. Of course there is old but it's essentially a loss of sand to the coastline. There has been a great deal of concern and I think a little bit too much of alarm raised by that point that this will eventually bring about a depletion
of all sand resources along our coastline and that our beaches will gradually be cut back. I think a lot of this work has been based on theoretical examination of the coastline and really has neglected to look at some of the true physical properties of the sediments that we actually find going down canyons over a seven year period. The work that I've been doing in the head of Scripps in the Hoya Canyon indicates that much of the sand that goes down the canyon has actually been diluted a great deal by a tremendous amount of plant material. And that the indirect measurements made from surface ships passing back and forth using an echo sounder really aren't giving us the true values of the amount of material that is going down the canyon because they say that everything that goes out during a slump is all sand and then this
value then is used to apply to the sand budget the amount of sand that they know are coming down the rivers and lakes then begin to get to the feeling that. If you keep losing sand at the rate that these false figures give you you eventually will not have any beach in this would be true. However this lack of knowledge of what the true nature of the sediments are in the head of the canyons has led to us to lay a false belief and I think a little bit too much of alarm on this particular problem. A recent study by Dr Francis P. Shepard and Dr. Wanless out at Scripps Institution of Oceanography have indicated that our beaches have not been cutting being cut back. These are based on studies that started back in about one thousand ten into the extended all the way to the present time and a much more work needs to be done before we start a hue and cry and start damming up these natural the heads of these canyon in saying that theyre going to
destroy it. The beach is by cutting in and causing this loss of sand. One of the other things we must consider is that the canyons are really the essentially the garbage chutes of the continent and not only is the sand going out but a tremendous amount of organic material and this organic material is the food source for many of our pelagic fishes. For many of the bottom dwelling organisms in deeper water which are really the pelagic phase of many of our more important coastal fisheries and to cut off this source of organic nutrient would be much more disastrous than losing some of our sands on the beaches. Dr. Tiller went on to answer our question about forms of underwater erosion in the surf zone where Sandy material is washed back and forth across the coastal rocks. You have relatively high
velocities up to two and three knots as a wave breaks and washes back and forth in these form channels called surge channels. And this material moving back and forth is gradually eroding away our coastline. It's not a very rapid erosion in the formerly in the rocky areas. But if we go deeper and into the heads of some of the submarine canyons it's really amazing how fast the erosion is taking place in the head of La Jolla Canyon for instance. We have an old lagoon will be positive which is being the roaded headword or toward the beach at a rate of about two feet per year which is much faster rate of erosion and anything you find on land not only is this a row Asian moving toward the beach but it's also cutting down into the continental margin actually cutting down as well as toward the shoreline. And this is a course it's formed this spectacular underwater canyon which is
a important feature because we also have currents concentrated here we have organic material and this is a focal point for the breeding of many of our offshore fishes. I mean the squid for instance will come into the head of the canyon and breed in this area because the small squid when they're first come either egg cases that have an abundant food source within this particular area. It's also a region where internal waves seize or waves at the thermal boundary that below the the surface airfares the water surface will break and cause currents which will gradually move back and forth across these eggs and keeps them for a nation with a fresh supply of oxygen. It's it's a very dynamic region. And it wasn't until we were actually able to go down in scuba and in small submersible that we were fully aware of the tremendous changes that take place in the canyons and how fast
they're being cut and the large amounts of settlement and organic material that are building up in the heads of the canyons are have rather interesting physical properties in that they flow very much light. The glaciers in mountains do. And these this large a mass of sediment will gradually move into deep water and as it goes slowly down in the cross the continental margin it is causing erosion as well. And many of the features that we see underwater are very similar to those that we find up in the areas that have been glaciated in the past. And the study of the mass physical properties of this material is a very important new field as far as marine geologists are concerned. This is a practical importance because the as these large masses of sediment move out across the continental margins they're capable of breaking cables submarine
cables for engines they would carry any structure that was placed on the sea floor out into the sea. And there are something that certainly must be contended with any type of construction future construction short supply. To a. The earth is full of my riches soul is this great from wide sea where in our things creeping innumerable fold small. Right there go the ships. There is that leviathan Muslim doll has made to play there is a lay of the beams of his chambers in the waters who laid the foundations of the earth. But it should not be removed for ever. The cupboard stood with the beef was with a calm the waters above
the mountains. At by rebuke they fled at the voice of by funder the haste of the one little one by the mob. They go down by the valleys on to the place which thou hast on the fourth. Now has set a bomb. But they may not pass over but they turn up again helpers. To a. Wayward us. A US. Yes.
The old down to the sea reporter Ken Kramer took a recorder out to an offshore treasure operated by the Army Corps of Engineers and Simon was to investigate the problems of a specific erosion control project in a typical small boat harbor harbor at Oceanside.
The Corps of Engineers explained the project. The problem with Oceanside Harbor Harbor on the open shoreline and by that we mean moving along shore because of the breakers. It's particularly troublesome and greater than we normally have to deal with. This Harbor which was actually started by the Marine Corps in 1942 and expanded in 1963 harbor craft operated by that side. Has given us constant problems either within or adjacent to the harbor just in front of the city of Oceanside. So the program is presently.
Three hundred yards from the harbor the navigation taps back to Project depth and the sand is placed on the beach to maintain good bating beaches not only for recreational use but of course to prevent destruction of property also present. Medal of this operation what we call ironic pipeline hydraulic pump with a suction head to the bottom which stirs up the sand puts it in motion and is a mixture of sand and water down the beach and. Moving. Right in the entrance.
To not only. The wave. And the tape recorder happened to be running when this service both by the wake of a larger vessel but eventually the dredger was boarded. And one of my old Camry. OK bel air my good. Colleague and I go I get you mad. When you are not far.
There are a pain in anything that. You can manage to get a three hundred feet. And then we stay on the porch and I'm a sandwich coming through. And we have good evidence showing holding well here. Well listeners who have never had an opportunity to see or bored a working dredger the vessel is similar to a large rectangular barge with a simple square superstructure housing wenches cables pipes and engines. A crane lowers the suction tube of the dredger to the desired depth and location when a trail of heights carries the unwanted material to the dump site actually working. Oh my God. Oh. And a. Great.
Funny. Funny family but they damn bad. Find out some of it. Way back when. And when sort of level would it have been where you learned to read on air and had a nap of about 14 to think the unpaid of going out and reading at. All an attic fan time last year. And then began to carve a way out of a gap and create the matter in the way. I.
I. Project that 300000 You are not a large. Hydraulic. Pump and into the road. And into the French and it is simply where we began. And again thanks to the waters and it spills out onto the beach into the surf and then spread it up and down the beach
or were walking down the beach it seemed like it would take forever to accomplish the desired results. But we were assured that progress was not as slow as it might appear in the pipeline. Honestly theyll be a rather slow process but its extremely a fact that we can. All with this thread about 10000 cubic yards a day in this fashion. I know that's from the bottom of the harbor. We asked for a summary of the work of the Corps of Engineers in the Southern California location.
And not the faster type that we get appreciable quantity and position this material on the harbor and price points between the value. Property and how much it actually cost the Army Corps of Engineers to put it. Yes. Authority to work on public beaches is to protect public beaches or
to restore eroded and we do not have authority to develop new beach. This authority does lie with another local agency and in several areas where we have worked we have been able to supply or to build additional beachfront age for around a dollar or less per square foot where the ordinary real estate prices around the coastline now are in the order of two and a half dollars a square not a person I mean there is logic in carefully selecting areas where we can widen our beaches and increase public usage where it would be almost need doormen and cost you go in and acquire private property on the adjacent shoreline. Some beach erosion problems have been at least partially solved through the use of scale models. We asked about this process of testing and its real value. Our practice in recent years is that we make detailed models studies of barbers
before their belt course and our older IRAs we frequently have to make studies to determine how to either add to the harbor or correct existing conditions or adverse regards to beaches this is a much more difficult problem because. The coastal engineers have only had limited success on modeling beach sand is very fine and when you try to scale the model of sand them by a 1 to 40 scale you react to different public laws and it has not been too well accomplished. This study beach erosion to a considerable extent in an analytical study based on field observations detailed I do graphic surveys what we call literal dressed. And one of our best tools here is the fluorescent dye to determine the direction and the rate of movement of the sand in the water that is being and at present our Corps of Engineer office in cooperation with the coast and their research center
are making detail field studies on the use of radio isotopic tracers to improve our capability to determine just where this sand comes from and where it's going on and hopefully at what rate. These have been real tough questions for the coastal engineer to answer in the past. The work today that we've been doing on the air radioactive tracers as require quite sophisticated equipment we have borrowed the large end crash from the Army and in large 15s. We're cooperating with the technicians from the Oak Ridge Laboratories and we've had to develop new technician devices which we can roll along the bottom and detect these radioactive signals in measurable quantities. The actual application of the radioactive tracers has given us considerable concern because everybody wants this problem to be absolutely safe. So what we had to do is
develop a technique where we can take sand from the local area under study right now with a radioactive tracer of a short half life and then replace it in the water and then trace his progress from that point. And we've been quite successful in doing the material we're using you can actually handle in your hand and yet with sensitive instruments we're able to follow this far enough to determine its movement characteristics. And while of course work is efficiently carried on to preserve and build harbors and beaches and keep open waterways there is always at least one person who expresses his disagreement with any given project. I've had about 30 years now with a corps of engineers involved in harbor construction and protection of beaches and like all large organizations we have a very complex mail and record system. And a few weeks ago I got a letter very promptly delivered and the sole title was addressed to the engineer in charge of messing up the beaches.
I'm not sure how far we are progressing in this game. Thank you for listening to the voice of Dr. Robert Dill from the Navy's undersea research and development center in San Diego. And to Mr. Henning and Mr. McMahon. Coastal engineers with the Army Corps of Engineers Los Angeles office as recorded in Oceanside. They we discussed. Lucia. Another aspect of man's relationship to the ocean. Down to the sea is a production of public radio station KTVK s FM at San Diego State College San Diego California. Music for the series was arranged and performed by Sam Hinton political narrative passages are read by Cliff Kerr written and produced by your host Tom McManus with the assistance of Ken Kramer.
His programs were made possible in part by a grant from the Corporation for Public Broadcasting. This is the national educational radio network.
- Down to the sea
- Episode Number
- Contributing Organization
- University of Maryland (College Park, Maryland)
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- No description available
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University of Maryland
Identifier: 71-1-4 (National Association of Educational Broadcasters)
Format: 1/4 inch audio tape
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- Chicago: “Down to the sea; 4; Erosion,” 1971-00-00, University of Maryland, American Archive of Public Broadcasting (GBH and the Library of Congress), Boston, MA and Washington, DC, accessed February 23, 2024, http://americanarchive.org/catalog/cpb-aacip-500-08638h19.
- MLA: “Down to the sea; 4; Erosion.” 1971-00-00. University of Maryland, American Archive of Public Broadcasting (GBH and the Library of Congress), Boston, MA and Washington, DC. Web. February 23, 2024. <http://americanarchive.org/catalog/cpb-aacip-500-08638h19>.
- APA: Down to the sea; 4; Erosion. Boston, MA: University of Maryland, American Archive of Public Broadcasting (GBH and the Library of Congress), Boston, MA and Washington, DC. Retrieved from http://americanarchive.org/catalog/cpb-aacip-500-08638h19