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Investigating groundwater and surface water interactions using stable isotopes and hydrochemistry in the Notwane River Catchment, South East Botswana.
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 molecule 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 characteristics. 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 concentrations 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 formations 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.
Investigating groundwater and surface water interactions using stable isotopes and hydrochemistry in the Notwane River Catchment, South East Botswana.
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 molecule 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 characteristics. 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 concentrations 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 formations 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.
Investigating groundwater and surface water interactions using stable isotopes and hydrochemistry in the Notwane River Catchment, South East Botswana.
L.T. Modie (author) / P.K. Kenabatho (author) / M. Stephens (author) / T. Mosekiemang (author)
2022
Article (Journal)
Electronic Resource
Unknown
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| Elsevier | 2022
| Elsevier | 2025