JpGU-AGU Joint Meeting 2020

Presentation information

[J] Poster

A (Atmospheric and Hydrospheric Sciences ) » A-HW Hydrology & Water Environment

[A-HW35] Perspectives on Surface- and subsurface-water resources, society, and the environment

convener: Abhishek(Tokyo Institute of Technology), Tsuyoshi Kinouchi(Tokyo Institute of Technology), Brijesh K yadav(Indian Institute of Technology Roorkee)

[AHW35-P07] Hydrochemical characteristics and sources of brines in the Sua Pans, Botswana.

*Fiona Segolame Motswaiso1, Kengo Nakamura1, Noriaki Watanabe1, Takeshi Komai1 (1.Tohoku Univeristy Graduate School of Environmental Studies)

Keywords:hydrochemical characteristics, origin of brines, Sua pans

Sua Pan is a basin of internal drainage located in northern Botswana in the easternmost part of the greater Makgadigadi pans area and contains a substantial amount of brine in which sodium chloride/common salt is the main constituent. A brine production wellfield managed by Botswana Ash (Pty) Ltd lies to the north of the westerly trending sand spit between the Nata and Mosetse rivers, extracting brine at a rate of 2880m3/hour. However, the origin of the abundant salt and potash resources remains highly contested. The main objective of the current study is to investigate the processes of brine formation/present-day recharge mechanisms at Sua Pan if any, including possible interactions of the solar evaporation ponds and brine resources.

A total of 39 brine, well and river samples were collected. Physical parameters of the samples such as electrical conductivity, pH, Temperature and salinity were also studied. Water temperatures on sampling varied between 23.8 and 29oC across the pans. The TDS concentration is highest 118400 ppm (mxw028) at the northeastern and within the pan. The TDS concentration is decreased to 41.28ppm (mxw011) at the wells between Ntwetwe pan and Sua pans outside the main wellfield. The lowest EC value was from borehole Mxw011 located on the western side of the project area. The vegetation is also more prominent in this area, indicating the potential for a perennially sustained freshwater regime. To a greater or lesser extent, the boreholes outside the pan reveal relatively fresh (or less saline) water overlying stronger saline water as observed from salinity profiling of monitoring boreholes. Major and minor elements were analyzed using Inductively Coupled Plasma–Atomic Emission Spectrometry (ICP–OES) and ion chromatography.