Laingsburg Flood

The 1981 Laingsburg Flood was a catastrophic event that occurred on 25 January 1981 in the town of Laingsburg, Western Cape, South Africa. The flood killed at least 104 residents, and the bodies of 72 people were never found. A total of 184 houses were destroyed.

Flood Waters
The town of Laingsburg is located near where the Buffels River converges with two of its tributaries: the Wilgehout and Baviaans (also known as Bobbejaans) rivers. The Buffels River catchment is usually dry, due to its location in the rain shadow of the Langeberg, Swartberg and Witteberg mountains. However, occasionally, a high-pressure system offshore of the Western Cape can push moist air from the coast over the mountains, resulting in increased rainfall in the Buffels River catchment, in turn leading to increased water flow in the three rivers that converge near Laingsburg. On 24 and 25 January 1981, a synoptic-scale weather event developed over the south-western parts of South Africa, causing heavy rainfall in the region.

On January 25, 1981, unprecedented rainfall in the Buffels catchment area caused the Buffels River to overflow its banks. The water level started to rise in town at about 12:00, and by 14:00, the town was almost fully covered. Flood waters and mud swept through Laingsburg, with some areas experiencing water levels reaching 10 metres above the usual flow level.

The river current, at its peak, was estimated to be 8000 cubic metres per second.

Damage
The flood destroyed two-thirds of Laingsburg's infrastructure, destroying 184 houses and 23 commercial buildings, including the town's old-age home. The flood killed 104 people, with 72 bodies never recovered.

A report published in January 1982 identified the geographical position of Laingsburg as making it particularly vulnerable to large floods. Laingsburg is situated on a natural flood plain on the inside bend of the Buffels River.

Another geographical factor contributing to the damage was the confluence of the Buffels, Wilgehout, and Baviaans rivers, and the east-west ridge directly downstream (south) of the confluence. The two large tributaries and the Buffels River converge immediately upstream of the poort (passage between mountains) through the ridge, and the ridge directed the flow in the tributaries northward into the southern part of town. The combined effects of all three rivers and the constriction of river by the poort accounted for much of the damage in the southern part of Laingsburg between Swartberg St and the river.

The deposition of sediment is a widespread form of flood damage in the drier regions of South Africa. Rivers in the Cape Midlands and the Karoo carry high sediment loads in high floods. The sediment-carrying capacity of flowing water depends on the velocity of the water. When the river overflows its banks, the velocity decreases as the water flows away from the river bed, particularly where it flows through a built-up area. The slower-moving water can no longer carry the sediment loads associated with the mid-stream velocities, and the sediment is deposited as the water slows down. Heavy sediment deposits result, especially in the vicinity of houses nearest to the enlarged river channel, where the flowing water's velocity is rapidly decreasing. Sediment deposits in Laingsburg were up to 3 m deep in many places and the total sediment volume deposited was about 200 000 cubic meters.

Another factor that caused much damage in Laingsburg was the large amount of floating debris. This consisted mainly of trees washed down the river from upstream, but it also included debris from buildings in the town itself. The debris caused physical damage to the buildings and aggravated sediment deposition. Many buildings in Laingsburg collapsed due to high water levels alone. Those that collapsed were mainly the older buildings. Newer, more soundly constructed buildings were not seriously damaged except those subjected to high scouring velocities.

First Reports
The first flood reports emerged after SADF Super Frelon helicopters flew over the town at 09:00 on Monday morning the 26th of January 1981.