Dambos, seasonally, saturated wetlands, are widespread in headwater catchme
nts in southern Africa and play an important role in the regional hydrologi
cal cycle. Hoc-ever, the processes influencing runoff from these catchments
are poorly, understood. This paper reports an isotopic investigation of ru
noff-generating mechanisms within a Zimbabwean catchment containing a dambo
. Hydrograph separation using deuterium reveals that, once the dambo is sat
urated, up to 70% of total storm flow can be considered 'new' water (i.e. d
erived directly from rainfall generating the runoff el-ent). However, both
the total proportion and the instantaneous maximum amount of 'new' water in
hydrographs are sensitive to rainfall characteristics and antecedent condi
tions. These results are (1) compatible with observations made in catchment
s in temperate climates when wetlands are present, and contrast with result
s obtained when wetlands are absent and (2) consistent with saturation over
land flow, generated in saturated regions of the dambo, being the major sto
rm runoff mechanism. To reconcile these observations with past perceptions
that dambos attenuate flood flows, a dual role for dambos in storm flow pro
duction is postulated.