BAGNOLD, RALPH ALGER

(b. Devon-port, England, 3 April 1896; d. probably in Blackheath, England, 28 May 1990), physics of transport of natural materials by wind and water.

Brigadier Ralph Bagnold is best known for his pioneering work on the wind-blown sands of deserts. He was also a professional soldier and desert explorer of considerable accomplishment. Bagnold authored many of the most fundamental and oft-cited papers on the physical nature of sediment transport in rivers, on beaches, and in the ocean.

Early Life. Bagnold was born at the Manor House, Stoke, Devonport, England, on 3 April 1896. His father, Colonel Arthur Henry Bagnold, was a contemporary officer with Hebert Kitchener, and he saw active service with the Royal Engineers in Cyprus, Egypt, South Africa, and the Sudan. His paternal grandfather, Major General Michael Edward Bagnold, served more than thirty years in India and its dependencies. Ralph Bagnold himself received a regular army commission in 1915, serving in France and Flanders during World War I. He subsequently took an honors degree in engineering from Cambridge University in 1921 and served thereafter in various military postings until retiring from the British army in 1935.

Ralph Bagnold’s lifelong scientific interest in the physical mechanisms for the natural transport of granular materials by wind and water was kindled at an early age. As a five-year-old, living in a converted coffee mill in the highlands of Jamaica in the Caribbean, he diverted part of the mill’s stream through a rock channel, built a working model of the household drainage system, and observed a flood event. These interests later overlapped with wide-ranging explorations, particularly when the army posted him to Egypt in 1926. There, Bagnold joined a small group of fellow officers who enjoyed traversing remote areas by cross-country expeditions in light cars. His many challenges included driving a Model-T the entire length of the Sinai Desert and driving a Ford truck from India to Egypt. However, it was in the sand seas of the Libyan Desert that science and adventure merged. A 10,000-kilometer (6,200-mile) trip, much of it in uninhabited northwestern Sudan, was organized in 1932 using Model-A Fords. These travels are described in Bagnold’s book Libyan Sands: Travel in a Dead World(1943), written in Hong Kong shortly before his first retirement from military service.

Research on Sand Dunes. During his expeditions Bagnold became fascinated with the geometrical order and regular spacing of the great desert dunes. He found that during violent sandstorms, the dense, moving clouds of sand, in contrast to the associated dust, extended no more than a meter or so (just over three feet) above the ground. This led to physical questions as to the forces that could lift relatively dense sand grains up into thin, moving air or how the mass rate of sand movement might be related to wind strength. With his retirement from military service at the rank of major in 1935, Bagnold was able to pursue the science that was necessary to answer these questions.

At the hydraulics laboratory of Imperial College, University of London, Bagnold constructed a wind tunnel

of his own design, much of it from salvaged materials. The resulting experiments and field measurements from return trips to Egypt were described in several papers and in his important book The Physics of Blown Sand and Desert Dunes, published in 1941. For his work on various projects, he conceived and produced instruments that were appropriate for measuring the parameters that he deemed to be of interest. These included the desert sun compass, the instant-reading, multi-tube manometer, and the piezometric pressure gauge. In 1938, he turned his attention to problems in the water transport of sediments, a theme to which he returned after World War II.

With the outbreak of war in 1939, Bagnold was recalled to military service. His return to Egypt was accidental, resulting from a convoy collision at sea that interrupted his posting to East Africa. Nevertheless, his unique knowledge of the remote areas of the Libyan Desert was eventually appreciated by the British command in Cairo. Bagnold was entrusted with the urgent raising and subsequent command of the Long Range Desert Group (LRDG). He assembled this special unit within a mere six weeks. Operating essentially as a private army, it was assigned missions of reconnaissance and raiding behind the Italian lines throughout the interior of Libya. Promoted to colonel, Bagnold led the LRDG on trips as far as eight hundred miles behind enemy lines. One daring trip to Chad resulted in that French province joining the Allied cause, becoming the only French overseas dependency to do so voluntarily. When Erwin Rommel’s Afrika Corps entered the war, the LRDG observation posts reported all movements along its supply routes to the front lines in northern Africa.

Sediment Transport. In 1944, Ralph Bagnold retired for a second time from the British army, having reached the ultimate rank of brigadier. He accepted the position of director of the Shell Research Laboratory near Chester, England. After two years, however, he resigned to continue his private studies of granular transport by water and air. His experiments were performed at Imperial College and also at his home office-workshop at Rickwoods in Kent. Around this time his sister, Enid Bagnold, reintroduced Bagnold to his future wife, Dorothy Plank, and the marriage took place in 1946. Enid was quite a famous author: Her novels include National Velvet (1935) and among her plays was The Chalk Garden (1956).

In 1958, Luna B. Leopold invited Bagnold to Washington, D.C., to be a consultant to the United States Geological Survey (USGS) on matters of sediment transport in rivers. He spent one month per year for the next several years in this capacity. This period generated several of the classical papers on sediment transport mechanics, many of which he published as professional papers of the USGS. One of these, a 1966 study titled An Approach to the Sediment Transport Problem from General Physics, treats the transport of grains by fluid as the work of a machine. As such, sediment movement depended on rates of energy supply and of transport work done against friction. The machine analogy led immediately to the concept of stream power, which controls the transport rate of the solids that are immersed in a fluid.

Bagnold’s approach to problems of sediment transport contrasted sharply with that of the hydraulic engineers of his day. The engineers followed a tradition of seeking to account for sediment movement in kinematic terms. Their approach derived from studies that simplified the complex dynamics of fluid flow by eliminating the fluid density. The result of this tradition was a lack of attention to the very important density differences between the moving grains and the transporting fluid. This density disparity is exactly what piqued Bagnold’s curiosity about wind transport of sand during his earliest desert explorations. Bagnold realized that the engineering approach was inevitably self-defeating. Thus, his most important contributions derive from looking at a very basic problem in a completely different way and in developing the insights, theory, and experiments to resolve the physical elements of that problem.

For his Libyan Desert explorations, Bagnold was awarded the 1933 Founder’s Gold Medal of the Royal Geographical Society. His scientific research accomplishments were recognized by a Fellowship in the Royal Society of London in 1944, the G. K. Warren Prize of the U.S. National Academy of Sciences in 1969, the Penrose Medal of the Geological Society of America in 1970, the Wollaston Medal of the Geological Society of London in 1971, the Sorby Medal of the International Association of Sedimentologists in 1978, and the David Linton Award of the British Geomorphological Research Group in 1981.

Brigadier Ralph Bagnold continued to work productively right up to his death in 1990, at age ninety-four. He disliked anything pompous or stuffy. He would often characterize himself as “a mere amateur” in science. Once he even registered for a major international symposium by listing his profession as “farmer” (in reference to his estate at Rickwoods). In commenting on his scientific research in 1988, he described his role in science to be “to stir the pool of complaisant tradition with the stick of fact.”

BIBLIOGRAPHY

A complete bibliography of Bagnold’s published works can be found in Thorne, MacArthur, and Bradley, 1988, cited below.

WORKS BY BAGNOLD

Libyan Sands: Travel in a Dead World. London: Hodder and Stoughton, 1935. A popular account of Bagnold’s desert expeditions of 1927, 1929, 1930, and 1932.

“The Movement of Desert Sand.” Proceedings of the Royal Society of London Series A, 157 (1936): 594–620.

“The Size-Grading of Sand by Wind.” Proceedings of the Royal Society ofLondon Series A, 163 (1937): 250–264.

The Physics of Blown Sand and Desert Dunes. London: Metheun, 1941. Reprint, London: Chapman and Hall, 1971.

“Early Days of the Long Range Desert Group.” Geographical Journal 105 (1945): 30–46. Bagnold’s account of his famous World War II military unit.

“Motion of Waves in Shallow Water. Interaction between Waves and Sand Bottoms.” Proceedings of the Royal Society of London Series A, 187 (1946): 1–18.

“Experiments on a Gravity-Free Dispersion of Large Solid Spheres in a Newtonian Fluid under Shear.” Proceedings of the Royal Society of London Series A, 225 (1954): 49–63.

“The Flow of Cohesionless Grains in Fluids.” Philosophical Transactions of the Royal Society of London Series A, 249 (1956): 235–297.

Some Aspects of the Shape of River Meanders. Washington, DC: U.S. Government Printing Office, 1960.

An Approach to the Sediment Transport Problem from General Physics. Washington, DC: U.S. Government Printing Office, 1966.

“The Nature of Saltation and of ‘Bed-Load’ Transport in Water.” Proceedings of the Royal Society of London Series A, 332 (1973): 473–504.

Sand, Wind, and War: Memoirs of a Desert Explorer. Tucson: University of Arizona Press, 1990. Bagnold’s autobiography.

OTHER SOURCES

Greene, Jay E., ed. “Bagnold, Ralph Alger.” In McGraw-Hill Modern Scientists and Engineers, vol. 1. New York: McGraw-Hill, 1980. Brigadier Bagnold himself contributed to this short biography.

Kenn, M. J. “Memorial to Ralph Alger Bagnold, 1896–1990.” Geological Society of America Memorials8 (1992): 91–93. A brief biography researched and written by the former head of hydraulics at Imperial College, University of London.

Thorne, Colin R., Robert C. MacArthur, and Jeffery B. Bradley, eds.The Physics of Sediment Transport by Wind and Water: A Collection of Papers by R. A. Bagnold. New York: American Society of Civil Engineers, 1988. Includes a brief biography, a bibliography, and reprints of many of the Bagnold’s published works.

Victor R. Baker