| 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.
Keywords: dambo, hydrology, hydrogeology, stormflow, evapotranspiration, baseflow, sponge
effect, Zambia |