Historical flows in the dry valleys of the Kalahari identified from missionary correspondence

Unpublished documentary materials written by missionaries working for the London Missionary Society in the Kalahari Desert of central southern Africa during the nineteenth century have been used to identify historical hydrological events in drainage systems of the region. Analysis and interpretation of missionary correspondence has identified previously unrecognized flood events in the Kuruman (1817/18) and Molopo (11871) rivers in South Africa, which represent the earliest recorded floods during the historical period In these systems. Documentary evidence also suggests that the 1894 Kuruman flood may have been the most extensive on record, with flow occurring along the entire length of the Kuruman and lower Molopo valley before linking with the Orange River. Floods or near-surface water are also recognized In a number of present-day 'fossil' Kalahari valleys. These include a flood event In the Letlhakane valley in 1851, only the second documented flood In an endoreic Kalahari drainage system. The presence of water is also identified In the fossil Xaudum and Ncamasere valleys in 1879. Documentary evidence has additionally been used to identify that the flow of water in the Thaoge River system, one of the key inflows to Lake Ngami, ceased in late 1879 to 1880, shortly before the desiccation of the lake in 1881. The possible causes of these hydrological events are discussed In the context of global and regional environmental changes.