Dambos are shallow, seasonally waterlogged, tropical and subtropical African wetlands. Their importance, through their role in agriculture and water supply to downstream river networks, has been widely acknowledged. As a result, much research has been conducted on the hydrological functions of dambos and their hydrogeological structures, in an attempt to better understand, utilize and manage this regionally ubiquitous landform. However, these studies have resulted in little consensus regarding the geomorphology of dambos, their hydrological regimes and the hydrogeological model that drives those regimes. This review paper, focusing on dambo hydrology, hydrogeology and their primary determinants, highlights the key issues of the debate and draws some overriding conclusions from the divergent literature. Five hypotheses are proposed based on these conclusions, in an attempt to focus future dambo research efforts.

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Dambos are shallow, seasonally inundated wetlands and are a widespread landform in Central and Southern Africa. Owing to their importance in local agriculture and as a water resource, the hydrology of dambos is of considerable interest: varied, and sometimes contradictory, hydrological characteristics have been described in the literature. The issues in contention focus on the role of the dambo in (i) the catchment evapotranspiration (ET) budget, (ii) flood flow retardation and attenuation, and (iii) sustaining dry season flow to the river down-stream. In addition, both rainfall and groundwater have been identified as the dominant source of water to the dambo and various hydrogeological models have been proposed to describe the hydrological functions of the landform. In this paper, hydrological and geochemical data collected over a full hydrological year are used to investigate and describe the hydrological functions of a dambo in north-western Zambia. The Penman estimate of wetland ET was less than the ET from the miombo-wooded interfluve and the wetland has been shown to have little effect on flood flow retardation or attenuation. Discharge of water stored within the wetland contributed little to the dry season flow from the dambo, which was sustained primarily by groundwater discharge. Flow in a perched aquifer within the catchment soils contributed a large portion of baseflow during the rains and early dry season. This source ceased by the mid dry season, implying that the sustained middle to late dry season streamflow from the wetland is through discharge of a deeper aquifer within the underlying regolith or bedrock. This hypothesis is tested through an analysis of groundwater and wetland geochemistry. Various physical parameters, PHREEQC model results and end member mixing analysis (EMMA) suggest strongly that the deep Upper Roan dolomite aquifer is the source of sustained discharge from the wetland.

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