Study region: The ephemeral Notwane River Catchment (NRC) is situated in semi-arid Southeast
(SE) Botswana. It is part of the Ramotswa Transboundary Dolomitic Aquifer (RTBDA) in the
Limpopo basin, shared by Botswana and South Africa.
Study focus: Stable isotopic composition of deuterium (2H) and oxygen (18O) of the water mole-
cule and water chemistry of groundwater and surface water (GW and SW) including rainfall
samples were used to assess GW-SW interactions in the NRC. In addition, the seasonal effects on
GW-SW interactions were also evaluated. As such, sample collection excursions were timed to
coincide with the wet- and dry seasons, respectively.
New hydrological insights for the region: GW and SW were found to have similar chemical char-
acteristics. The major ions in both water types were Ca2+ and HCO-3 in both the dry- and wet
season. There was a clear inverse relationship between ground relief and/or elevation and the
concentration of chloride ions (mg/L) and electrical conductivity (μS/cm). That is, higher con-
centrations of chlorine were measured downstream compared to upstream and vice versa. The
same trend was manifested for EC levels. Overall, the data indicated the existence of some highly
active groundwater recharge sites along the Notwane River, that may be responsible for the
aquifer recharge during above-normal rainfall events. In addition, the data revealed albeit
inconclusively that GW-SW interactions in the NRC are likely to be influenced by an interplay of
several factors such as: (a) the difference in water levels between the river and the adjacent
groundwater table (b) the hydrogeology and location of the river channel because geologic for-
mations such as faults and karsts play a critical role in GW-SW interactions. Karsts are known to
support groundwater recharge which is different from the nearby semi-arid Kalahari region where
recharge is driven by soil profile.

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