The Douglas Weir, the oldest weir, was originally constructed in 1890-91 by the Cape Government’s Department of Agriculture. It is located on the southern or left bank of the Vaal River, just upstream from its confluence with the Orange River. The initial weir, designed to irrigate around 364 hectares, was destroyed by a flood in 1892. Reconstruction, led by Mr. Litchfield, an engineer with the Public Works Department, involved building a new weir between 1894 and 1896. This new structure is a diversion scheme comprising a masonry wall about 399 meters long and 3.6 meters thick, built on a solid rock foundation. The weir links the Atherton farm on the north bank with St. Clair on the south bank, roughly 8 kilometers upstream from the village of Douglas.

The Douglas Weir has a significant historical background. In 1908, the masonry core wall of the weir was raised by 41 centimeters, and the downstream fill was adjusted with an ogee curve to allow floods to pass over the crest smoothly. Additional boulder fill was placed on the upstream side for support. By 1910, the original Douglas Canal had been extended to cover 80 hectares of prime land on the Bucklands farm, which was transferred to the Cape Government in 1889. In late 1911 or early 1912, the Turner Estate, including the farms Buccleugh, Bucklands, Nottingham, and Stratford, was purchased to expand the settlement, though only Bucklands and Buccleugh contained irrigable land; the rest were used for grazing.

The weir is protected on its downstream side by a hand-packed rubble slope. The lowest river flow typically occurs from October to December. The backwater created by the weir extends approximately 48 kilometers up the Vaal River and 14 kilometers up the Riet River, offering some storage capacity. However, this was found to be insufficient for the dry months.

The Douglas irrigation works began in 1882 when Gamble first suggested using the Vaal River’s water for irrigation. Initial construction included a weir made of loose stones, branches, and sods and a canal nearly 10 kilometers long. This early weir was damaged soon after completion and completely washed away by floods in February 1894. A new masonry weir was then started at a different site in August 1894. During the drought in the early 1980s, water use from the Vaal River for irrigation and domestic purposes became difficult. In response, the Nottingham Pump station was constructed, allowing water to be pumped from the Orange River via the Bosman Canal to the Douglas Weir in the Vaal River. On November 16, 1984, the Orange Vaal Irrigation Board was established to oversee water use and maintenance of the irrigation scheme. In 2002, it became the Orange Vaal Water Users Association. Currently, the scheme includes the Douglas Weir on the Vaal River with a capacity of 355,431 cubic meters, a 25-kilometer main canal connecting the Orange and Vaal rivers, a 24-kilometer smaller canal on the left bank of the Vaal River ending in the Orange River, and an 8-kilometer canal on the right bank ending in the Vaal River.

Douglas Weir was built in Year 1890 for providing water to the farming community, create employment for the local community, strategic source to relieve poverty and also stimulate local economy & Rural prosperity