Applying DC resistivity imaging to investigating the relationship between water quality and transpiration beneath circular Islands in the Okavango Delta, Botswana

A case study of Thata Island

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

An electrical resistivity survey was carried out on Thata Island, one of the numerous circular islands in the Okavango Delta, to investigate the mechanism governing interactions between surface water, vegetation and groundwater. Seven data profiles were collected across the island and modelling results indicated that the centre of the island had low resistivity values (less than 10 ohm-m), while resistivity values increased laterally outside the island. Such lateral resistivity zoning responded to variation in shallow groundwater chemistry below the islands having a high concentration of solutes inside and the presence of fresh water outside the islands. Borehole to surface resistivity imaging results for the island indicated a plume of saline water sinking to depths of 60 m. Groundwater salinity below the island ranged from 11.7 g/l from the margin of the island to 122 g/l at the centre of the island. Beyond the 60m depth, groundwater salinity dropped to about 0.33 g/l at the centre of the island. Lateral and down-hole imaging results, as well as water salinity values, showed a migrating plume of high salinity groundwater from the surface of the island invading a relatively deeper low-density fresh groundwater environment. Combining geochemical, isotopic and electrical resistivity data indicated that capillary evaporation may have been the most important mechanism in creating high saline water under the centre of the island; however, high transpiration rates along the edges of the island may have been important in producing salts which could migrate toward the island's centre. The results of this study showed how high salinity levels may have formed in near surface aquifers in natural inland delta environments in semi-arid areas.

Original languageEnglish
Pages (from-to)25-32
Number of pages8
JournalEarth Sciences Research Journal
Volume17
Issue number1
Publication statusPublished - Dec 12 2013

Fingerprint

transpiration
electrical resistivity
water quality
groundwater
salinity
plume
water
zoning
solute
borehole
evaporation

All Science Journal Classification (ASJC) codes

  • Earth and Planetary Sciences(all)

Cite this

@article{f6b2580441974b3db417a3a877272efc,
title = "Applying DC resistivity imaging to investigating the relationship between water quality and transpiration beneath circular Islands in the Okavango Delta, Botswana: A case study of Thata Island",
abstract = "An electrical resistivity survey was carried out on Thata Island, one of the numerous circular islands in the Okavango Delta, to investigate the mechanism governing interactions between surface water, vegetation and groundwater. Seven data profiles were collected across the island and modelling results indicated that the centre of the island had low resistivity values (less than 10 ohm-m), while resistivity values increased laterally outside the island. Such lateral resistivity zoning responded to variation in shallow groundwater chemistry below the islands having a high concentration of solutes inside and the presence of fresh water outside the islands. Borehole to surface resistivity imaging results for the island indicated a plume of saline water sinking to depths of 60 m. Groundwater salinity below the island ranged from 11.7 g/l from the margin of the island to 122 g/l at the centre of the island. Beyond the 60m depth, groundwater salinity dropped to about 0.33 g/l at the centre of the island. Lateral and down-hole imaging results, as well as water salinity values, showed a migrating plume of high salinity groundwater from the surface of the island invading a relatively deeper low-density fresh groundwater environment. Combining geochemical, isotopic and electrical resistivity data indicated that capillary evaporation may have been the most important mechanism in creating high saline water under the centre of the island; however, high transpiration rates along the edges of the island may have been important in producing salts which could migrate toward the island's centre. The results of this study showed how high salinity levels may have formed in near surface aquifers in natural inland delta environments in semi-arid areas.",
author = "Shemang, {E. M.} and Molwalefhe, {L. N.} and K. Mickus",
year = "2013",
month = "12",
day = "12",
language = "English",
volume = "17",
pages = "25--32",
journal = "Earth Sciences Research Journal",
issn = "1794-6190",
publisher = "Universidad Nacional de Colombia",
number = "1",

}

TY - JOUR

T1 - Applying DC resistivity imaging to investigating the relationship between water quality and transpiration beneath circular Islands in the Okavango Delta, Botswana

T2 - A case study of Thata Island

AU - Shemang, E. M.

AU - Molwalefhe, L. N.

AU - Mickus, K.

PY - 2013/12/12

Y1 - 2013/12/12

N2 - An electrical resistivity survey was carried out on Thata Island, one of the numerous circular islands in the Okavango Delta, to investigate the mechanism governing interactions between surface water, vegetation and groundwater. Seven data profiles were collected across the island and modelling results indicated that the centre of the island had low resistivity values (less than 10 ohm-m), while resistivity values increased laterally outside the island. Such lateral resistivity zoning responded to variation in shallow groundwater chemistry below the islands having a high concentration of solutes inside and the presence of fresh water outside the islands. Borehole to surface resistivity imaging results for the island indicated a plume of saline water sinking to depths of 60 m. Groundwater salinity below the island ranged from 11.7 g/l from the margin of the island to 122 g/l at the centre of the island. Beyond the 60m depth, groundwater salinity dropped to about 0.33 g/l at the centre of the island. Lateral and down-hole imaging results, as well as water salinity values, showed a migrating plume of high salinity groundwater from the surface of the island invading a relatively deeper low-density fresh groundwater environment. Combining geochemical, isotopic and electrical resistivity data indicated that capillary evaporation may have been the most important mechanism in creating high saline water under the centre of the island; however, high transpiration rates along the edges of the island may have been important in producing salts which could migrate toward the island's centre. The results of this study showed how high salinity levels may have formed in near surface aquifers in natural inland delta environments in semi-arid areas.

AB - An electrical resistivity survey was carried out on Thata Island, one of the numerous circular islands in the Okavango Delta, to investigate the mechanism governing interactions between surface water, vegetation and groundwater. Seven data profiles were collected across the island and modelling results indicated that the centre of the island had low resistivity values (less than 10 ohm-m), while resistivity values increased laterally outside the island. Such lateral resistivity zoning responded to variation in shallow groundwater chemistry below the islands having a high concentration of solutes inside and the presence of fresh water outside the islands. Borehole to surface resistivity imaging results for the island indicated a plume of saline water sinking to depths of 60 m. Groundwater salinity below the island ranged from 11.7 g/l from the margin of the island to 122 g/l at the centre of the island. Beyond the 60m depth, groundwater salinity dropped to about 0.33 g/l at the centre of the island. Lateral and down-hole imaging results, as well as water salinity values, showed a migrating plume of high salinity groundwater from the surface of the island invading a relatively deeper low-density fresh groundwater environment. Combining geochemical, isotopic and electrical resistivity data indicated that capillary evaporation may have been the most important mechanism in creating high saline water under the centre of the island; however, high transpiration rates along the edges of the island may have been important in producing salts which could migrate toward the island's centre. The results of this study showed how high salinity levels may have formed in near surface aquifers in natural inland delta environments in semi-arid areas.

UR - http://www.scopus.com/inward/record.url?scp=84889690630&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84889690630&partnerID=8YFLogxK

M3 - Article

VL - 17

SP - 25

EP - 32

JO - Earth Sciences Research Journal

JF - Earth Sciences Research Journal

SN - 1794-6190

IS - 1

ER -