The Palaeohydrology of the okavango delta some preliminary results

Geomorphological studies of Lake Ngami and the Mababe Depression, together with historical studies of the Okavango Delta, underline the instability of the Okavango Delta on different time scales, and under varying budgetary conditions. Shorelines at 945 m (Lake Palaeo-Makgadikgadi) and 936 m are found in both basins, the latter representing a continuous lake along the Ngami-Mababe axis, tentatively dated to 17 000-12 000 BP and to the late Holocene. Lower shorelines and associated fluvial landforms testify the final desiccation of the lake by a series of area: volume threshold controlled stages. Lake Ngami stood at c 930 m by the mid-nineteenth century diminishing rapidly thereafter to become an ephemeral lake with a maximum level of 923.5 m. A marked dry period occurred throughout the Delta from 1900-1950. Preliminary modelling suggests that the 936 m lake owed its existence to increased precipitation and possibly increased inflow, whilst the present erratic regime is the result of the interplay of several factors.