Alfred Dale Lewis was the son of Charles E. Lewis, professor of Classics at the South African College, Cape Town, and his wife Elizabeth Tryphena Lewis. He studied at the college from 1896 and passed the matriculation examination of the University of the Cape of Good Hope in 1898. Continuing his studies he passed the university's Survey Certificate examination in 1900, and in 1901 was awarded the degree Bachelor of Arts (BA) with honours in science. He then proceeded to England for further study, was awarded the degree Master of Arts (MA) by the University of Cambridge, and became an associate member (later a full member) of the (British) Institution of Civil Engineers. Subsequently he worked for some time on the Manchester ship canal, and then spent two years in the Public Works Department in India. In 1907 he returned to South Africa and in December that year was appointed as an engineer in the Irrigation Department of the Cape Colony.
In 1910 Lewis became the circle engineer for the lower Orange River region. Two years later, during November and December 1912, he undertook a journey along the Orange River by cart from Kenhardt to Pella, and from there on foot for a further 400 km to the river mouth. He prepared a detailed report on his observations and had already written an excellent description of the Augrabies Falls for the journal The State (1911). In 1913 he undertook a tour of the United States during which he inspected 17 irrigation schemes. His findings were published in Irrigation and settlement in America (Pretoria, 1915, 258 p.)
Lewis succeeded F.A. Kanthack* as Director of Irrigation of the Union of South Africa in 1921 and held this post until 1941. Not long after his appointment the government of Kenya asked him to comment on the draft Kenyan water ordinance of 1922, which he did in his Report on irrigation, water supplies for stock, water law, etc (London, 1925, 99 p.) Other publications by him included 'Sand dunes of the Kalahari within the borders of the Union', 'Fulgurites from Witsands on the south-eastern borders of the Kalahari' and 'Roaring sands of the Kalahari Desert' (all three in the South African Geographical Journal, 1936), a map showing the average annual rainfall over southern Africa (1926), Water law: Its development in the Union of South Africa (1933), and a topographical map of the Union of South Africa, on two sheets, showing aerodromes and other aeronautical information (1938).
In 1933 Lewis canvassed support for the compilation of a topographic map of South Africa, for which there was an urgent need at the time. The next year funds were made available to the Department of Irrigation by the government for this purpose. Plane table mapping commenced in June 1934 and continued to the early part of 1937, using the existing primary and secondary triangulation of the country as basis. Existing maps were also used where possible. The resulting map series consisted of ten sheets, on a scale of 1:500 000, with 500 foot contours, published from December 1935 to December 1937. These were the first reliable medium scale maps of South Africa, contained much detail, and were particularly useful to the Irrigation Department and the military. Lewis described the mapping project in 'Topographical mapping in the Union of South Africa' (South African Geographical Journal, 1938). During the field work measurements were also made of magnetic declination, which Lewis described in Magnetic declination in South Africa (Department of Irrigation, 1936, 19 p.), including a map on a scale of 1:5 000 000.
Lewis was a member of the South African Society of Civil Engineers by 1913 and served as its president for 1925. He played a leading role in the South African Geographical Society, serving as joint vice-president during 1934-1935 and as president for 1936. By 1917 he was a member also of the Royal Society of South Africa. In 1943 the University of Cape Town awarded him an honorary Doctor of Science (DSc) degree in engineering.
In 1921 Lewis married Laura Joyce Saunders, with whom he had three children. His recreational activities included racehorse breeding, on which he wrote a book.