[3] He made notable contributions in the field of coastal engineering, including methods for the calculation of breakwater stability and research which led to the development of the Iribarren number.

[6] Iribarren recognised that many of the ports in the Bay of Biscay were insufficiently protected from severe wave and storm conditions, which had resulted in a number of shipwrecks and threatened the economic viability of the local fishing community, with whom he enjoyed a close relationship.

Iribarren was dissatisfied with such a wholly empirical approach, which he considered did not take into account the effects of location-specific issues such as wave and sediment behaviour, and having identified this as a problem, he spent a number of years developing scientific and mathematical approaches which could be applied to specific cases, based on extensive research and an understanding of wave behaviour and coastal dynamics, in which he made extensive use of observation and photography.

[3][4][21] Iribarren was transferred from Girona to his home province of Gipuzkoa in 1929, where he was appointed Chief Engineer of the Gipuzkoan Ports Group at the Ministry of Public Works, with an office in San Sebastián.

[2][4] The role provided Iribarren with the opportunity to make detailed observations of the Gipuzkoan coastline, which informed his theories and research output.

[21] He undertook research into several aspects of breakwater and wave behaviour at each of the ports under his control, as well as the general Gipuzkoan coastline and Bay of Biscay.

[23][24] Iribarren undertook extensive research at the Port of Mutriku, where he was responsible for the design and construction of a breakwater to the outer harbour in 1932.

Despite initial opposition from the local fishing community, he was successful in implementing a sloping breakwater at the inner harbour in 1936, which ended the problems caused by reflection and made safe berthing of ships possible.

In the author's opinion it is appropriate to call it the "Iribarren number" (denoted by "Ir"), in honor of the man who introduced it and who has made many other valuable contributions to our knowledge of water waves.In 1934, the City Council of Hondarribia approached Iribarren to investigate problems related to sediment transport and erosion at the Hondarribia Bar at the mouth of the Bidasoa River on the Spanish border with France, and proposed the construction of a breakwater.

He published his findings in 1941,[26] and although his plans were supported by the Ministry of Public Works, they were met with opposition from the City Council and the project was not approved.

[29][30] The project was a major success and in 1949, seeing the results of Iribarren's work in Hendaye, the City Council in Hondarribia approved the construction of a breakwater to his design.

The project was a success, solving the erosion problems, increasing navigation safety and creating a large recreational beach.

[7][28] Iribarren was appointed as professor at the ETSICCP in 1939, filling the vacancy left by the death of Eduardo de Castro Pascual during the Spanish Civil War in 1937.

[21][31][32] Iribarren promoted the idea of establishing a Spanish centre for the study of coastal engineering and harbour works, modelled on research facilities in universities such as Technische Universität Berlin and ETH Zurich.

[4] Between 1960 and 1961, he was commissioned by the Government of Spain to work alongside a French delegation in Paris to undertake studies for railway and port infrastructure at Villa Cisneros to transport iron ore mined in the Spanish Sahara.

[35] Iribarren noted that the orientation of the Port of Palma meant that it would only be exposed to storms whose direction varied from Southwest to Southeast.

Unlike existing approaches, his method was grounded in the principles of using the results of fundamental research to devise solutions to a practical problem.

[14] Iribarren's approach was not to design by intuition or simplified empirical comparisons with previous projects, as was the case in Spain up until the 1930s,[3][21] but rather to research and determine the nature of wave propagation towards a specific coastline and assess wave characteristics and bathymetry, along with detailed analysis of the shape and orientation of the coastline or harbour under consideration.

[38] Iribarren noted that detailed observation and the production of graphical records of wave and sediment behaviour were necessary to correlate, and if necessary modify, the theoretical approximations used in his method, as he had himself done at Palma de Mallorca.

[39] Iribarren had studied under Eduardo de Castro Pascal, who in 1933 proposed a formula for the design of breakwaters which he had developed based on earlier work by Briones.

has an imaginary value, indicating that for very steep slopes, a breakwater or dike cannot be successfully constructed no matter how large the armourstone is.

[42] However, the political situation in Spain and international attitudes to scientific co-operation with the Franco dictatorship restricted the dissemination of Iribarren's work, which led to more common international adoption of a similar method which had been developed by Robert Y. Hudson at the USACE Waterways Experiment Station (WES) in Vicksburg, Mississippi, known as Hudson's equation.

[17][43][44] Iribarren's 1938 paper included the following formula, which calculated the weight of the armourstone or wave-dissipating concrete block required:[41] Where: In this formula, the mass of the armourstone is proportional to the cube of the wave height, suggesting that a doubling of wave height necessitates an eightfold increase in stone weight.

This relationship, while seeming substantial, is logical as the linear dimension of the stone (with constant density and slope) is proportional to wave height.

becomes zero, logically indicating that if waves are negligible, a natural slope breakwater consisting of stones of any size is in perfect equilibrium.

A modified version of the Hudson formula is still commonly used for concrete breakwater elements, but for rock armour structures, it is valid only for situations with a permeable core and steep waves.

Beginning in the late 1940s, he was invited to the United States by the engineering schools of The University of California, Berkeley and Massachusetts Institute of Technology, where he delivered several lectures.

[21] He presented his research to the Beach Erosion Board of the United States Army Corps of Engineers, a body which subsequently organised the translation and publication of much of the research work Iribarren undertook with his long-term collaborator and fellow Spanish engineer Casto Nogales y Olano (1908-1985),[51][52] with whom Iribarren also collaborated on a two-volume engineering textbook entitled Maritime works: Waves and dikes (Spanish: Obras maritimas: Oleaje y diques) which was first published in 1954, with a second edition in 1964.

[6][54][55] In February 1967, Iribarren died as the result of a fire whilst driving in a Fiat 1500 on the main Valencia-Madrid motorway, near Vallecas.

[8] Iribarren had a highly theoretical approach grounded in detailed observation and assisted by experiment,[41] and his work continues to underpin several coastal engineering design methods.