iribarren: his research activity

IRIBARREN: HIS RESEARCH ACTIVITY

ANTONIO LECHUGA ÁLVARO Dr. Ingeniero de Caminos, Canales y Puertos Jefe de Área de Costas del CEDEX

t is not an easy task to try to summarise in an article Ramón Iribarren’s contributions to research. The difficulty lies mainly in the fact that practically all of his work is impregnated with ideas, concepts, intuitions and developments that encompass the immense field of coastal and maritime engineering. If we were to have to define his work, we would have to say that he was a skilful and energetic creator of tools with which to tackle almost all of the problems a design engineer must face. A second characte-

I

ristic was that he combined in one and the same person a solid academic background in theory with an almost unstoppable impulse towards experimentation. A third crucial characteristic is found in his extraordinary powers of observation, which helped him to unravel physical phenomena by being able to separate the essential from the accessory. The combination of these three characteristics made him a solid bulwark that left its mark on all of the issues that passed through his hands.

Caracterización de las ondas en profundidades reducidas y planos de oleaje. Ramón Iribarren Cavanilles y Casto Nogales y Olano, comunicación presentada al XVII Congreso Internacional de Navegación Lisboa, 1949


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The methodology used for this article is as follows: In the first place, we will enumerate the fields in which Ramón Iribarren’s innovating activity was particularly relevant. Then, we will go on to deal individually with those that have passed the irrefutable test of time. On the occasion of this centenary of his birth and from an adequate perspective, we are in a position to be able to highlight his clearest achievements. Some of these are still current today, more than fifty years after they were initially proposed. It is interesting to observe how, in some cases, researchers of the stature of Ramón Iribarren do not seem to be aware of the real transcendence of their achievements at the time when they are actually being produced. This occurs, for example, in his treatment of the sediment transport by oblique waves. A small difficulty to be overcome is the degree of contribution on the part of his collaborator (as Iribarren himself called him) Casto Nogales, in some of the developments, as, after a certain point practically all of the contributions are signed by them together. However, it appears clear that the original ideas must have been Ramón Iribarren’s, as can be corroborated in articles and initial papers signed by him alone. We have grouped his research activity into the following sections: Wave Maps and Theory of Waves, Undertow Currents and Oscillations, the Calculation Formula for Rubble Mound Breakwaters, the Iribarren Parameter and Sediment Transport by Oblique Waves and “Super-elevation”. We feel that this approach will cover all of Iribarren’s principal research activity. Particular mention should be made of the so-called dynamic-static method for the calculation of vertical breakwaters proposed as the Lira-Iribarren method and which is an improvement of the method used by the engineer, Lira, although in the exposition many of Iribarren’s original ideas appear. We are not going to discuss a number of other investigations here, such as the batching of concrete or the study of the cause of tides. A few of the other ideas put forward by Iribarren will be mentioned in passing, under the relevant points, such as his ideas on submerged beach profiles and the effect of the continental platform on sediment dynamics. Some of the theories Iribarren used were not his own originally, but were rather a product of the technical culture of his time, for example, the trochoidal wave theory. However, in all instances, he was capable of discerning the most interesting aspects for the specific application that he needed. Finally, we wish to note that it has been a true pleasure to encounter extremely valuable gems hidden in his produc-

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ANTONIO LECHUGA ÁLVARO

tion, both published as well as unpublished, and this has more than compensated our efforts.

THE WAVE MAPS With respect to the wave map method, what better than to transcribe the definition given by Iribarren himself: “This method consists simply of determining how waves are propagated, with characteristics and an orientation known in the open sea, on advancing towards a specific coast, where the depths or bathymetric curves, and the shape and orientation of the natural coastline are known, together with any protective works built or that may be assumed to have been built. For this purpose, let us base ourselves on the trochoidal theory, now generally accepted and, which, when duly applied, satisfactorily explains the phenomena observed. Recalling this theory, we know that the orbits of the liquid molecules, agitated by the waves, are circles, provided that the waves are propagated at indefinite depths. Although, theoretically, it is necessary for this depth H to be infinite, in order to be able to consider it indefinite, it practically suffices for it to be equal to or greater than the semi-length of the individual wave, so that its conditions of propagation can be considered as analogous to those of a wave, with the same characteristics, being propagated at greater depths. “

Surface waves have been observed from the remotest antiquity. However, their systematic study was initiated slightly over 300 years ago. In effect, Isaac Newton, in his famous work Principia Mathematica, Book II, Proposition XVL, Theorem XXXVI (1687) established the first characteristics of surface waves, correctly considering their velocity and wave length. Later, many mathematicians studied waves in the first steps taken towards making Hydraulics a science: John and Daniel Bernoulli, Euler and Lagrange, among others. 150 years ago, in 1847 to be exact, Stokes established and solved the hydrodynamic equations of the surface waves, creating a doctrine that, with a few changes, has come down to us today. The so-called trochoidal or Gerstner’s theory used by Iribarren is similar to Stokes’s wave. In his article published in 1941, entitled “Obras de Abrigo en Puertos” Iribarren described in detail and applied the wave map method to a number of cases on the coast with and without diffraction on obstacles or, as he indicated, “lateral feeding or transfer of energy”. Following the laws of geome-

Perfil de playa e indicación del transporte por oblicuidad. «Informe acerca de la defensa de las costas y playas de la ciudad de Cartagena». Ramón Iribarren Cavanilles. Madrid. 1958. (Biblioteca del Centro de Estudios de Puertos y Costas del CEDEX.)

tric optics, Iribarren was capable of acceptably reproducing the configuration of the propagation of waves, in a plan as well as an elevated view, by using basically what we call today the linear dispersion ratio or its equivalent, wave celerity

C= With k =

g th (kh) k

2π and h being the depth of the point. L

The problem for Iribarren was the consideration of the adequate depth in each case on variable seafloors. As we know, the transcendental equation must be solved. L = Lo th

2π h L

With L being the wave length at the depth point h and Lo the wave length in deep water. Iribarren’s ingeniousness consisted in applying the dispersion ratio in what he called the advance quadrilateral (L/2 being the side of the quadrilateral) in both directions, the objective of which was to make the bathymetry of the seafloor gentler. The solving of the problem in its longitudinal time had to be obtained by trial and error Up to the large-scale introduction of computers with wave propagation criteria relatively similar to that used by Iribarren, the wave maps did not fall into disuse.

In a so-called second approximation to the wave maps, Iribarren took into account the following phenomena, which had not played an appreciable role in the first: 1) Evaluation of the loss of energy by friction in propagation, 2) Lateral expansion assuming group celerity in the transmission of energy and 3) Deformation and dissymmetry of the wave by a change in celerity according to the phase. All in all, the wave maps were an effective tool during a considerable period of time.

UNDERTOW CURRENTS AND OSCILLATIONS With his characteristic foresightedness, Iribarren described undertows in the following terms: “To avoid confusion, we shall understand exclusively as undertows in ports and harbours, and in contraposition to the agitations of the same period as the waves, the alternative long-period currents produced inside them by sea storms. Their violence, principally in a number of small fishing harbours, tends to be such that even strong moorings can be severed, with serious danger for the vessels anchored in their basins. Although generally less violent, undertows are also annoying and their effects can even become dangerous in some larger harbours, for which reason, their study, on a general basis, is of interest. ”


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As we can see, Iribarren assimilated the phenomenon of undertows with the oscillations in the level and the currents associated with periods much longer than the normal ones for waves. In his many observations of the ports and harbours of Guipuzcoa, he reached the conclusion that, for time maximums of 18 seconds, the undertow waves can exceed a threeminute period. With his proverbial sharpness, Iribarren found that, on beaches, the groups of maximum waves have a period (in the enveloping line) noticeably identical to that of the undertow waves. Continuing with his line of reasoning, Iribarren attributed the undertow oscillations inside harbours to a phenomenon of resonance when the period of the basin coincides with the variations in the mean water level that appear in the wave groups. It is extraordinary to find that his theory of undertows coincides in all of its terms with that currently accepted, demonstrating to us, once again, his powers of observation, analysis and synthesis. In the calculation of the undertow wave and its characteristics, Iribarren substituted the wave celerity according to Stokes with the celerity in shallow water.

reby the study of the geometry of the surrounding area and its observation is essential for the solution of the problems created. At the present time there are quite sophisticated resonance models of the behaviour of basins that help to solve the majority of cases, however, Iribarren’s proposal for the “auscultation of basins” by direct observation of their “bellies” is valid at the present time.

CALCULATION FORMULA FOR RUBBLE MOUND BREAKWATERS Iribarren’s formula for the calculation of rubble mound breakwaters is probably his internationally best known and most highly recognised contribution, particularly during his lifetime and immediately afterwards. In a study dated in 1938, Iribarren echoed the formula of Castro and Briones in the following terms: “The formula of Messrs. Castro and Briones is as follows:

P=

704 A3d (T + 1)2

T–

2 (d-1)3 d

in which the slope T is T = cot a.

c=

gh

where h is the depth. Assuming that the dangerous length is that corresponding to one-fourth of the wave length ( Lr 2 in his terminology) the conclusion arrived at is that the Lp (dangerous length) is

Lp =

Tr 2

g hp

with hp being the mean depth of the basin and Tr the semiperiod of the undertow wave. Iribarren used this simple formula in a number of Bay of Biscay basins, obtaining satisfactory results. At the same time, it served as a tool in order to improve the conditions for attempting to eliminate the effects of undertows by means of a variation in the depth (dredging, for example), or by changing the geometry of the basin. By using the Iribarren Parameter, which we will examine later, Iribarren arrived at the conclusion that the undertow wave can even be reflected on quite flat beaches, whe-

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The fact that, through two so different procedures, it is possible to arrive at formulas of a structure somewhat similar, is highly satisfactory and indicates that if we have not yet arrived at the final truth, we are indeed coming close to it. Of these two provisional truths, which is closer to the final answer? Waiving inopportune and perhaps prejudicial considerations of modesty, I must admit that the formula that I have determined satisfies me even more than that developed by Messrs. Castro and Briones, which I have used in several designs drafted to date. In the first place, the formula that we have just determined has not needed any adjustment whatsoever, either in its coefficients or its exponents, in order to conform to reality. With the structure and exponents theoretically deduced, it is more than satisfactorily consistent with all of the phenomena observed and verified.”

Iribarren, thus, acknowledged the due priority of this formula, although he feels that his own is better (particularly, more rationally grounded). Another quite different case is his recognition of the formula he called the “American formula”, which he discussed

in the following terms: “In effect: the American formula is:

Pt = Rt

The first part of the procedure is to establish the celerity of the wave in shallow waters. Starting from the exact for of the celerity of the wave, linear in theory,

S H3 (S–1)3 (µ–r)3

and ours:

g πH . L . th π L

c=

Iribarren applies the approximation, P=

N A3 d (cos α–sen α)3 (d–1)3

0in which:

πH H =π L L

In order to obtain,

Pt = P = weight of the stones. H = A = 2 h = height of the wave. S = d = relative density of the material. µ = natural slope of the armour 1 r = tg α gradient of the armour. The coefficients being Pt and N. Adapting the American formula to our nomenclature, it becomes:

P = Rt cos3 α

th

N A3 d (cos α-sen α)3 (d-1)3

which is ours, with the sole difference of including cos3 α in the coefficient. On establishing our formula, we already indicated, as has been recalled, that the coefficient could vary depending on the relevant data of the problem.”

C = gh Where L is the semi-wave length and H is the depth. We must note that Iribarren, in line with the usage of the era, called the height of the wave 2h, while the wave length was 2L and the period, 2T. In this section, we will apply the same criteria in order to avoid unnecessary complications. The theoretical ruling gradient when the wave is reflected on the beach (figure 19 in Iribarren’s original) is when the depth H is equal to the semi-wave height, that is, the distance between the crest and the level of the sea in motion (including the set-up as we would say today). The diagram, taking into account the “advance quadrilateral “ is that shown in Fig. 21, H=

It is clear that in this case, Iribarren was somewhat reluctant to consider the formula to be different. We are not going to dwell on this subject at this point, as it will be examined in detail within this same framework.

L .i 4

i being the gradient of the beach. Taking into account that L = T . c = T . gH Iribarren obtains

RESEARCH ON BEACHES. THE IRIBARREN PARAMETER H= The so-called Iribarren Parameter is his most long-lasting contribution to maritime engineering. Since 1974, when Battjes claimed the name for him, the parameter has been used profusely accompanied by Iribarren’s name. It was created originally in order to determine the limit between the breaking and the reflection of the waves on a beach, although its current application is broader, including a value for two different types of breakers and even extends to other kinds of waves: shore waves, group waves, undertows, etc. The line of reasoning used by Iribarren for his presentation at the PIANC Congress in Lisbon (1949) is set out below:

gT2 i 2 16

and, therefore, i=

16 . H g

1 T

but taking into account the hypothesis that H = h, we finally obtain, i=

4 T

h g

which is the Iribarren parameter.


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The text written by Iribarren for his Report on the Defence of the Shores and Beaches of the City of Cartagena (Colombia), 1958, is shown below: “Furthermore, also during the unit of time, for the transport of the sand in section I, with its constant length V, up to section II, the power will be required, P1 V with P1 being the power necessary in order to transport the flow corresponding to the beach length unit, thus

P1 VQ tsV ó P1 Q ts

Parámetro de Iribarren. Esquemas en las ondas aproximándose a una playa de fuerte pendiente (Fig. 19) y pendiente suave (Fig. 20). Ramón Iribarren Cavanilles y Casto Nogales y Olano, comunicación presentada al XVII Congreso Internacional de Navegación Lisboa, 1949

CONDITIONS

GRADIENT MEASURED

PENDIENTES

CALCULATED

OF THE TABLE

2 h cm

21 seg.

Total break

5.5 4.5 4.5

0.66 0.92 1.00

0.42 0.29 0.33

Total reflection

Mean

0.86 0.59 0.49

0.64 0.44 0.41

If we call the power supplied by the waves in the direction of the beach P1 and, as the unit of their length, a large part of that power P1, proportional to it, will be used in the transport of the solid flow Q1, also corresponding to the beach length unit, that is, P1P1Q tsV, and consequently, Q tsP1Q 1 which is what was intended to be verified. Furthermore, the power transmitted by unit of breaker width is indeed P. In the attached figure, its component in the direction of the beach or deflection P sen a. 1 This power refers to the length AB = cos α , thus the power, per unit of length, will be:

i= 4 T

h g 0.66 0.42 0.38

P1P sen α cos α =

P 2

sen 2α P sen 2α

and finally we will have Q ts sen 2α »

Table 1 includes a part of the many trials made by Iribarren as verification. As from 1974, Battjes wrote the parameter as Ir =

tg β H L0

and thus it is known today, as an international recognition of Ramón Iribarren.

RESEARCH ON BEACHES. CURRENT GENERATED BY WAVES. SEDIMENT TRANSPORT BY OBLIQUE WAVES AND “SUPER-ELEVATION” It was simply extraordinary to find that Iribarren had a clear idea of our current method of energy flow in order to calculate the transport of sediment by oblique waves, considering that Iribarren’s original text, which we are transcribing below, dates from 1958, that is, around 20 years earlier than the so-called CERC formula.

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Transporte de sedimentos por oblicuidad. «Informe acerca de la defensa de las costas y playas de la ciudad de Cartagena». Ramón Iribarren Cavanilles. Madrid. 1958. (Biblioteca del Centro de Estudios de Puertos y Costas del CEDEX.)

The result obtained by Iribarren is so familiar to us today that the vigour and clarity of this text from more than 40 years ago is quite surprising. With respect to the so-called “super-elevation”, Iribarren had as much foresight as was evidenced in the case of the current produced by oblique waves. In the article he published in the Revista de Obras Públicas, “Corrientes y transportes de arenas originadas por el oleaje” (1947), Iribarren highlighted the significant transport of sand that occurs from exposed areas to sheltered areas. The application of his calculation is general, although it refers to the coves and bays along the Bay of Biscay. His reasoning in his own words is as follows: “Given the orientation, between the north and the northwest, of the coves and bays of this coastline, the storms out of the northwest build up water in the more open areas exposed to that direction, that is, the eastern and south-eastern areas, raising their mean water level in a greater proportion than in the western and south-western areas, less exposed to the action of these storms from the northwest. This different elevation of the mean level, originated by the waves, gives rise to a significant current, which, advancing from the east towards the west, moving across the bottoms of these bays or coves, carrying the sand in that direction. As this interesting current is generated as a consequence of the much-feared storms of the Bay of Biscay, it is very difficult to study it directly. Therefore, rather than determining its values, which can hardly be expected to be exact, for the purpose of obtaining an approximate idea of the importance of the phenomenon, we are going to attempt to determine its velocity, or rather, its approximate upper limit.”

For this calculation, Iribarren considered what he called the “super-elevation” of the surface in the exposed areas and in the sheltered areas and divided the difference in these values by the distance between them, whereby he obtained an energy slope with which he applied the Chezy formula, obtaining the current velocity. The formula for the “super-elevation” of the surface is Sr =

πh2K 2L

which, written in the variables that we use today, would be

Sr =

kH 1 8 th kh

k being the wave number and h the depth. As we can see, the structure of the formula is identical to that used at the present time for the calculation of the setup using the radiation stress theory. Iribarren calculates the virtual “super-elevation” on the seafloor and for each point takes the mean between the bottom and the surface. That is, he is calculating the excess pressure caused by the waves over that of the hydrostatic pressure, which is exactly the definition of radiation stress. Once again, this consideration was years ahead of its time, like taking a step directly into the future.

CONCLUSIONS In this brief look at the currency of Iribarren’s research, what stands out particularly is his capacity to anticipate -in some cases as much as forty years earlier- coastal and maritime proposals, which are absolutely current today. His powers of observation, together with his analytical mind, led to the result that there is practically no territory where he failed to leave his mark, with simple tools and his powerful intuition. We have sought to highlight the contributions that have endured and have therefore won out over the erosion of time. In another series of investigations, Iribarren improved some aspects of earlier theories and, thus, we did not feel that they would be of equal interest. This is the case, for example, of the positions in parameters, the stresses of broken waves, etc, etc. Finally, in other cases, his contribution takes a course different from that of his observations, such as the case of longshore sediment transport, included and expressed correctly in a broken profile analysed as a support to this transport. To sum up, it could be said that his contributions to the dynamics of sediment on beaches are those that are most highly valued internationally at the present time, without this being construed to mean that any of his later developments are no longer today an example for all of us and for future generations.


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REFERENCES TO PIBLISED WORKS OF RAMON IRIBARREN CAVANILLES Una fórmula para el cálculo de los diques de escollera. 1938. Pasajes, Imp. M. Bermejillo. Cálculo de diques verticales. 1938. Pasajes. Imprenta M. Bermejillo. Obras de abrigo de los puertos. Planos de oleaje. Revista de Obras Públicas, January 1941. Corrientes y transporte de arena originados por el oleaje. Revista de Obras Públicas. May and June 1947. Corrientes y oscilaciones de resacas en el interior de los puertos, in collaboration with Castro Nogales y Olano. Revista de Obras Públicas. April 1948. Penetración de la agitación en el interior de los puertos. Medios de preverla y de combatirla, with Casto Nogales y Olano. Rapport of the fourth paper in Section II of the 17th International Navigation Congress. Lisbon, 1949. Planos de oleaje en segunda aproximación, with Casto Nogales y Olano. Revista de Obras Públicas. November and December, 1949. Talud límite entre la rotura y la reflexión de las olas, with Casto Nogales y Olano. Revista de Obras Públicas. February 1950.

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