Thesis (DPhil)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Freshwater is the most fundamental of all life-supporting resources that determine our
social, economic and political wellbeing. It is, however, only a small percentage of
the world's water resources and is also unevenly distributed. Arid regions make-up
about forty percent of the world's land area and have a large proportion of the world
population, however, they only have a small fraction of the freshwater compared to
other areas.
Conventional freshwater sources in arid environments such as surface water in rivers,
lakes and dams are often seasonal, available mainly during the rainy season. Equally,
only a small part of the rain (0 - 5% of rainfall) infiltrates into groundwater reserves,
and even this groundwater displays high rates of salinisation such that the end-water
is too saline for human consumption.
The poor quality of groundwater in arid regions is generally understood, however, it is
always assumed that this is mainly a problem in areas where surface water does not
occur. The study investigates seasonal groundwater salinisation in ephemeral
(seasonal) river sources in some parts of Namibia and aims to derive a better
understanding of the nature of this problem and how it affects people in these areas.
It also looks at some possible solutions to the problem with the aim of informing
water managers and scientists who are responsible for formulating solutions for water
supply to areas in arid regions. These solutions are designed to take advantage of available opportunities in the study
areas namely; the abundant supply of solar energy, alternative sources of freshwater
such as fog and general atmospheric moisture, and adaptations for water collection in
animals that inhabit these regions.
The results show that groundwater in shallow ephemeral river sources of the Namib
Desert and the Cuvelai delta in North central Namibia display high seasonal variation
in Total Dissolved Solids (TDS) and chemical composition. The lowest TDS values
are recorded during the rainy season, mainly after the first rains in the high rainfall
areas and only after flood events in the lower rainfall regions. The groundwater
salinity increases during the remainder of the year and in most cases becomes too
saline for drinking purposes.
The investigations of possible solutions indicate that small-scale photovoltaic reverse
osmosis; solar distillation and fog collection could be used to address the seasonal
shortage of potable water in these areas. The low-pressure (6 bar) reverse osmosis
desalination experiments show that it is possible to operate the unit on a solar-driven
pump to produce enough water to cover the typical daily water demand of a village in
the Namib Desert. This unit would produce about 4600 litres per day (l/day) of 500-
mg/l TDS product water, which exceeds the water production of similar world-leading
small-scale RO units in Australia and The Canary Islands.
The results also show that the cost of solar distillation units (solar stills) can be
reduced sufficiently to make them a viable option for water supply to individual
households in these rural areas. The study also found that fog is a feasible alternative source of freshwater in some of
the study areas. The fog water is generally of 'A' quality drinking water according to
the WHO-derived Namibian Drinking Water Quality Guidelines (NDWQG) and can
be used directly or mixed with the saline groundwater to provide potable water.
Mixing of the above-mentioned waters is particularly suitable in the Central Namib
Desert because the period of high groundwater salinity coincides with that of peak fog
deposition.
The results also show that fog water can be collected with vanous polymeric
greenhouse shade netting that can be easily obtained, and provides guidelines on the
correct percentage shade coefficient and weave of possible fog collector mesh to
intending users of fog collection technology in areas where the polypropylene mesh
that is used in Standard Fog Collectors is not available.
The investigations of surface properties of fog-harvesting beetles and experiments
with various prototype collectors show that it is possible to increase water production
in fog collectors existing today. The hydrophobic surface conditions as were found
on the cuticles of fog-basking beetles (Onymaeris unguicularis and Onymacris
bieolor) would enhance formation and runoff of large fog droplets on the collector
surface. The prototype extractor-fan- and cooling system-based collectors show that
it is possible to increase fog collection on polymeric meshes about three times and
also that a comparable volume of atmospheric moisture can be collected even when
there is no fog, up to a relative humidity of about 40%. In conclusion the study emphasizes that groundwater salinity in arid regions is at
times a seasonal problem that should be considered in water supply strategies for
these regions. Also that atmospheric moisture is a feasible alternative source of
freshwater in some arid regions that often exceeds rainfall several times and should be
considered as an important aspect of the strategies to address water problems in these
areas. The study strongly recommends that scientists, engineers and water managers
in these regions should always investigate the available opportunities such as climatic
conditions (e.g. fog deposition) and adaptations for water collection/conservation that
are found in the endemic plants and animals in order to develop sustainable solutions
to this problem. They should also constantly update themselves on
developments/opportunities that arise in the larger water industry that could be of
benefit to water supply initiatives for remote areas in developing countries.
Lastly, the study serves to better the understanding of the nature of groundwater
salinity in arid environments that are dependent on seasonal surface flow for water
supply as well as to contribute to the formulation of solutions to this problem in these
areas, particularly in west coast hyper arid environments where conventional sources
of freshwater are most inadequate. It also emphasises the role of materials science
(polymers) and environmental engineering as well as that of UNESCO associated
scientific institutions in the formulation of sustainable solutions to some of the current
water problems in arid regions.
Keywords: Arid lands, hydrochemistry, sources of freshwater, desalination,
atmospheric moisture / AFRIKAANSE OPSOMMING: Vars water is die mees fundamentele van aIle lewensonderhoudende natuurlike
hulpbronne wat ons sosiale, ekonomiese, en politieke welstand bepaal. Dit is egter
slegs 'n klein gedeelte van die totale waterbronne van die wereld, en is boonop baie
oneweredig versprei. Natuurlike waterarm gebiede (woestyne en halfwoestyne)
beslaan ongeveer veertig persent van die landoppervlakte van die aarde en word
bewoon deur 'n relatief groot persentasie van die wereldbevolking, maar beskik oor
slegs 'n klein gedeelte van die varswater in vergelyking met ander gebiede.
Konvensionele bronne van varswater in waterarm gebiede, soos oppervlaktewater in
riviere, mere en darnme, is dikwels seisoenaal, en slegs beskikbaar gedurende die
reenseisoen. Verder beland slegs 'n klein gedeelte van die reenval (0 - 5%) in die
ondergrondse waterreserwes, en selfs hierdie grondwater vertoon 'n hoe mate van
versouting, sodat die eindproduk te brak is vir menslike gebruik. Die swak gehalte
van grondwater in waterarm gebiede word algemeen verstaan, maar daar is tot nog toe
aanvaar dat dit oor die algemeen slegs 'n probleem is in gebiede waar
oppervlaktewater me voorkom nie. Hierdie studie ondersoek seisoenale
grondwaterverbrakking in seisoenale rivierbronne in sekere dele van Namibie en
beoog om 'n beter begrip te formuleer van die aard van die probleem en hoe dit die
inwoners van hierdie gebiede raak. Daar word ook ondersoek ingestel na moontlike
oplossings vir die probleem, met die doel om 'n inligtingsbron vir waterbestuurders
en wetenskaplikes wat verantwoordelik is vir die formuleer van oplossings vir
watervoorsiening in waterarm gebiede daar te stel. Hierdie oplossings is ontwerp om voordeel te trek uit die beskikbare geleenthede in
die ondersoekgebiede, naamlik; die oorvloedige beskikbaarheid van sonenergie,
altematiewe bronne van varswater soos mis (Eng. "fog") en atmosferiese vog in die
algemeen en aanpassings (Eng. "adaptations") vir die opvang van water wat voorkom
by diere, veral insekte, in hierdie gebiede. Die resultate toon dat grondwater in die
vlak seisoenale rivierbronne van die Namibwoestyn en die Cuvelai-delta in noordsentraal
Namibie hoe seisoenale variasie in totale opgeloste stowwe (TVS) en
chemiese samestelling vertoon. Die laagste TVS-waardes word waargeneem tydens
die reenseisoen, hoofsaaklik na die eerste reen in die hoe-reenvalgebiede en eers na
vloede in die lae-reenvalgebiede, Die soutgehalte van die grondwater neem toe
gedurende die res van die jaar en in die meeste gevalle verbrak die water tot
ondrinkbare vlakke.
Die ondersoek na moontlike oplossings dui aan dat kleinskaalse fotovoltaiesgedrewe
tru-osmose, sondistillasie en die opvang van mis (Eng."fog collection") aangewend
kan word om die seisoenale tekort aan drinkwater in hierdie gebiede aan te spreek.
Die laedruk (6 bar) tru-osmose-ontsoutingseksperimente wys dat dit moontlik is om
die eenheid met behulp van 'n sonkraggedrewe pomp te bedryf en voldoende water te
lewer vir die tipiese daaglikse drinkwaterbehoeftes van 'n nedersetting in die
Namibwoestyn. Hierdie eenheid sal sowat 4600 liter per dag (l/d) water, met 'n TVSwaarde
van 500 mg/I, lewer. Dit is aansienlik meer as die lewering van soortgelyke
eenhede in Australie en die Kanariese Eilande.
Die resultate wys ook dat die koste van sondistillasie-eenhede genoegsaam verminder
kan word om dit 'n lewensvatbare opsie vir watervoorsiening aan enkelhuishoudings in die plattelandse gebiede te maak. Die studie het ook bevind dat die opvang van mis
'n toepaslike alternatiewe bron van varswater is in sekere van die studiegebiede. Die
miswater is oor die algemeen 'A' -gehalte drinkwater vol gens die Namibiese
gehalteriglyne Vir drinkwater (gebasseer op bepalings van die
Wereldgesondheidsorganisasie) en dat dit net so, of vermeng met brak grondwater,
gebruik kan word as drinkwater. Vermenging is besonder geskik in die sentrale
Namibwoestyn, aangesien die periode van hoe grondwaterverbrakking saamval met
die piek van benutbare misneerslag.
Die resultate toon ook aan dat miswater opgevang kan word met verskeie tipes
polimeriese skadunet, wat maklik verkrygbaar is, en verskaf riglyne vir die optimale
skadu-koeffisient en weefpatroon van moontlike misvangsnette vir voomemende
gebruikers van misvangstegnologie in gebiede waar die polipropileennet wat in die
standaard miskollekteerders gebruik word nie, beskikbaar is nie. Die ondersoek van
oppervlakeienskappe van mis-koesterkewers (Eng. "fog harvesting beetles") en
eksperimente met verskeie prototipe versamelaars toon dat dit moontlik is om die
waterproduksie van bestaande kollekteerders te verhoog. Die hidrofobe
oppervlaktetoestande soos gevind op die opperhuid van die mis-koesterkewers
(Onymacris unguicularis en Onymacris bicolor) bevorder die vorming en afloop van
groot misdruppels op die versameloppervlak.
Die prototipe suigwaaier- en verkoelerstelselgebasseerde versamelaars toon dat dit
moontlik is om die misvogversameling op polimeriese nette tot drie maal te verhoog
en dat 'n vergelykbare volume atmosferiese vog versamel kan word, selfs in die
afwesigheid van mis, tot by 'n relatiewe humiditeit van ongeveer 40%. Ten slotte benadruk die studie dat grondwatersoutgehalte in waterann gebiede soms
'n seisoenale probleem is, en dat dit in ag geneem moet word in
watervoorsieningstrategiee vir sulke gebiede. Dit benadruk ook dat atmosferiese vog
'n bruikbare alternatiewe bron van varswater kan wees in sekere areas, waar dit
dikwels verskeie male meer is as reenval, en gesien behoort te word as 'n belangrike
aspek in strategiee om waterprobleme in hierdie gebiede aan te spreek. Die studie
beveel sterk aan dat wetenskaplikes, ingenieurs en waterbestuurders in hierdie
gebiede altyd die beskikbare geleenthede soos klimaatstoestande (bv. misneerslag) en
aanpassings vir vogvangslbewaring wat voorkom by inheemse plante en diere sal
navors om sodoende onderhoudbare oplossings vir die probleem te vind. Hulle
behoort deurlopend op hoogte te bly met ontwikkelings/geleenthede wat ontstaan in
die wyer waterindustrie, wat van waarde kan wees in by waterverskaffmgsinisiatiewe
vir afgelee gebiede in ontwikkelende lande.
Laastens dien die studie om 'n beter begrip daar te stel van die aard van
grondwatersoutvlakke in waterarm gebiede wat afhanklik is van seisoenale
oppervlaktevloei vir watervoorsiening sowel as om 'n bydrae te lewer tot die
formuleer van oplossings tot die probleem in hierdie gebiede, veral in die hiperdroe
omgewings aan die Namibiese weskus, waar konvensionele waterbronne mees
onvoldoende is. Dit benadruk ook die rol van materiaalkundige wetenskappe
(polimere) en omgewingsingenieurswese sowel as die UNESCO-geassosieerde
wetenskaplike instellings in die formulering van volhoubare oplossings vir sommige
van die huidige waterprobleme in waterann gebiede.
Sleutelwoorde: Waterarm gebiede, hidrochemie, bronne van varswater, ontsouting,
atmosferiese vog
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52870 |
| Date | 03 1900 |
| Creators | Shanyengana, Shanyengana E. |
| Contributors | Sanderson, R. D., Seely, M. K., Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 186 p. : ill. |
| Rights | Stellenbosch University |
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