The greatest concentration of pans in southern Africa occurs in the western Free State province, South Africa. A feature of many Free State pans is their fringing lunettes, located on the southern and south-eastern margins. Lunette dunes associated with pans in the neighbouring and presently drier Kalahari region show depositional ages, determined by optically stimulated luminescence (OSL) dating, primarily in the Holocene. However, to date, the precise timing of Free State lunette accumulation has not been investigated. The morphology, sedimentology and age of lunettes at five pan sites in the western Free State panfield are reported here. The lunettes form distinct topographic features, with heights up to 5 m above the pan floor, and all have been dissected by gully erosion. Sediment in the sand size class dominates in the lunettes, often overlying clay-rich basal or pan floor sediments. The intra- and intersite data consistency of 46 OSL ages is interpreted as reflecting regional causal factors responsible for lunette accretion, with phases of lunette building at 12—10 ka, 5.5—3 ka, 2—1 ka and 0.3—0.07 ka ago. These are in good agreement with the findings from pan-fringing lunettes in the southwest Kalahari and consistent with established records of palaeocirculation and wind direction over central southern Africa during the late Pleistocene. Lunettes in the western Free State are currently not in a major accretion phase. They are subject to degradation by localized fluvial erosion, with sediment being recycled into the pans.

Methods developed to determine the amount of water required (EWR) to sustain ecosystem services in non-perennial rivers need a different approach to those used in perennial rivers. Current EWR methods were mostly developed for use in perennial rivers. Non-perennial rivers differ from perennial ones in terms of variability in flow, periods of no-flow and related habitat availability. A DRIFT-ARID method (an adaptation of the Downstream Response to Imposed Flow Transformation (DRIFT) method) was developed, tested and adjusted, using the semi-permanent Mokolo River. Field data from five study sites was collected from April to May 2010 by a multidisciplinary team. The results were used in a DRIFT-ARID Decision Support System (DSS) to determine the impact of five chosen development scenarios in the Mokolo River Catchment. An integrated groundwater-surface water MIKE-SHE hydrological model was used to simulate the hydrology of the chosen scenarios. Specific non-perennial river indicators such as onset of dry phase were identified and included in the DRIFT-ARID DSS. DRIFT-ARID has the potential to be used in non-perennial rivers and, once set up, can provide results for future scenarios. The method now needs to be tested on other non-perennial river types, especially episodic rivers where data are scarce or non-existent.

Environmental water requirement (EWR) assessment methods, for ascertaining how much water should be retained in rivers to sustain ecological functioning and desired levels of biodiversity, have mostly been developed for perennial rivers. Despite non-perennial rivers comprising about 30-50% of the world's freshwater systems, data on their hydrology, biota and ecological functioning are sparse. Current EWR assessments require hydrological and other data that may not be available for such rivers and some adaptation in the methods used seems necessary. DRIFT is an EWR method for perennial (or near-perennial) rivers that has been developed in South Africa over the past two decades and is now widely applied nationally and internationally. When applied to the semi-permanent Mokolo River, challenges particular to, or accentuated by, non-perennial rivers included the reliable simulation of hydrological data, the extent of acceptable extrapolation of data, difficulties in predicting surface-water connectivity along the river, and the location and resilience of pools, as well as whether it was possible to identify a reference (natural) condition. DRIFT-ARID, reported on here, is an adaptation of the DRIFT approach to begin addressing these and other issues. It consists of 11 phases containing 29 activities.

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