Garwood Alston, land surveyor, was the eldest son of Edward John Alston and his wife, Mary Kenningvale. He came to the Colony of the Cape of Good Hope around 1856 and, in addition to surveying work, collected natural history specimens, published some meteorological investigations, and practiced agriculture at Vanwyksvlei. In 1860 he married Elizabeth de Witt, with whom he had eleven children, not all of which survived. His eldest son, Edward Garwood Alston*, also collected natural history specimens around the same time as his father, with the result that the contributions made by the two can easily be confused. Garwood and his wife initially lived in Woodstock, Cape Town, then for a time in Tulbagh, and then settled on the farm Boterleegte at Vanwyksvlei.
His career in surveying began with his admittance as a land surveyor in the Cape Colony in 1861. That same year he drew up a plan of a new postal route between Cogman's Kloof and Seven Weeks Poort. During the next four decades the high quality of his work led to frequent government contracts to carry out important surveys. For example, in 1871 and 1872 he was engaged to extend the survey performed years ago by Thomas Maclear* to measure an arc of meridian in the western parts of the Cape Colony, by connecting Maclear's Kliprug and Kebiscow stations to the village of Calvinia by a double series of primary triangles. During 1894 he surveyed the boundaries of a proposed Bushmanland Game Reserve just south of the Orange River and west of Pella mission station. Nothing came of this proposal, but his survey showed that the river was in places up to 14 km further north than indicated on existing maps, so that the Cape Colony was larger than had hitherto been assumed. That same year he produced a survey map of the Vanwyksvlei water supply, showing farms, dams and distribution furrows. During 1898 he was engaged to perform the primary triangulation connecting the eastern end of the geodetic chain in British Bechuanaland to the northern end of the Kimberley arc surveyed by Colonel W.G. Morris*, a 110 km chain of triangles along the Kimberley-Vryburg railway line. This was followed by a similar survey to connect the western end of the British Bechuanaland chain to the northern end of Maclear's arc of meridian. He completed the field work in October 1899 and recommended several improvements in the construction of beacons (then piles of loose stones) and in observational procedures. Even Alston's earliest work was so highly regarded that the Surveyor-General decided in 1901 to integrate a survey he had carried out in 1864 into the secondary triangulation of the Colony, which was then in its early stages.
Alston requested permission from the government of the Cape Colony to build an irrigation dam at Vanwyksvlei and submitted the necessary plans in 1880. With government support he built this dam - the first government dam in South Africa - during 1882-1884. Constructed of gravel and clay, it was over 300 meters long and almost ten meters high, indicating that he must have had some experience in civil engineering. From 1884 he and his sons managed the resulting agricultural settlement, though his work required him to move about the Colony and adjacent territories. In 1886 he reported that some 600 hectares of irrigated lands had been developed. Three years later he built a canal from Carnarvonleegte, some distance north of the settlement, to supply the dam with additional water.
Alston's interest in natural history is evidenced by a number of donations of specimens to the South African Museum in Cape Town. In 1891 he presented insects from British Bechuanaland (now part of the Northern Cape). These were followed by further donations of Coleoptera (beetles), many of them rare or new to the museum's collection, from Bushmanland and "the dry north-western parts of the Colony" in 1894, 1896 and 1899, and a few from Mashonaland (in present Zimbabwe) in 1897. His other donations included some snakes, scorpions, and solifugae from Vanwyksvlei in 1898 and 1899. The solifugae (1899) included several new species and were presented by G. and D.C. Alston (presumably Garwood and his son Daniel Constable, born in 1876). As a result of his donations he was named as one of only nine "correspondents" of the South African Museum in 1899 - a regular contributor of specimens who received the museum's publications free of charge.
Alston's botanical collecting was on a smaller scale. He sent some succulents from around Garies, in Namaqualand, to the Government Herbarium in Cape Town in 1897. The next year he donated plants collected during his survey in British Bechuanaland.
In 1886 the Colonial Botanist, P. MacOwan*, obtained seeds of the Australian salt bush, Atriplex nummularia and A. inflata, from Australia and sent them to Garwood Alston for test planting at Vanwyksvlei. He and his son Edward raised the plants successfully and in 1893 distributed seed to farmers in many parts of South Africa. Edward described the experiment in a pamphlet published by the Department of Lands, Mines and Agriculture in 1893. In some of the saline soils of the Karoo the first-named species has spread widely and is an important fodder plant. It is popularly known as Alston's Saltbush. Another of Garwood's contributions, this one to ostrich farming, was an article in the Cape Quarterly Review (July1882, Vol. 1(4), pp. 616-620) on the detection of break-outs by ostriches or other animals from their camps by incorporating the fence in an electric circuit - a very early application of electricity in South Africa.
Alston's first contribution to meteorology consisted of a short paper on meteorological data in the Cape Monthly Magazine (Series 2, Vol. 7, 1873, pp. 31-32, 383-384) in which he advocated that meteorological observations should be made systematically at selected stations. In 1882-1883 he published a description of the climate of the region between Calvinia-Carnarvon in the south and the Orange River in the north, in the Cape Quarterly Review (Vol. 1, pp. 544-554; Vol. 2, pp. 135-150, 312-320). Years later he made a comparison of the water supply (precipitation) and loss (evaporation, run-off, and percolation) at Brandvlei Dam in the Karoo to conditions in New South Wales, Australia. The study was published in the Transactions of the South African Philosophical Society (1895-1896, Vol. 9, pp. 8-19). He became a member of the society in 1895, but was no longer a member by 1906. His other publications included a paper on Vanwyksvlei (Transactions of the South African Philosophical Society, 1890-1895, Vol. 8, pp. 35-40), a response to the Report of the Commission on Van Wyk's Vley in 1892, and an open letter to the Commisioner for Public Works on Vanwyksvlei in 1906.