Thesis (MSc)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: A study was conducted between 2000 and 2002 in the lower Berg River catchment of
the semi-arid Western Cape Province to investigate the effect of irrigation
developments (wheat fields to table grapes) on the quality of the Berg River as well as
the sustainability of these developments. This study was necessitated by the
mineralisation of both the Breede and Berg River, probably due to irrigation together
with the higher pressure on these water resources from the growing demand for fresh
water from the Cape Town metropolitan area.
Water and Salt balances of two dominant soil patterns (Glenrosa/Swartland and
Oakleaf/Hutton soil forms) from the catchment area were monitored at two localities.
Vineyard blocks of different ages in the same soil forms were used to study the effect
of irrigation over time. The electrical conductivity of the soil water extracts (ECe) was
measured three times over depth at the selected sites and the quality of irrigation and
drainage return-flow were monitored. Soil water storing capacities of these stony
(high rough fragment' fractions) soils were also characterised for more efficient
drainage quantity prediction.
Glenrosa/Swartland soils showed the highest ECe's (200-400 mx.m") that decreased
significantly after four to five years of irrigation and distribution became more
uniform over depth. These high salt concentrations were explained due to natural
occurrence of salts, mineral weathering and salts from the irrigation water.
Oakleaf/Hutton soils showed lower ECe's « 200 nfS.m") but they are subject to the
quality of the irrigation water, which is not that constant over years. Localised salt
accumulation was observed due to the irrigation method and became more prominent
over years. Drainage quantities were under predicted because of the big/high rough
fragment fractions and the occurrence of preferential-flow. This prohibited the
accurate calculation of the soil water house holding characteristics. It also led to the
under calculation of salt return-flow, but it was very evident that the most salt retumflow
occurred from the Glenrosa/Swartland soils. Effective irrigation management to
achieve and maintain optimal soil water levels and to reduce the negative impact of
high ECe's is essential for the sustainability of these irrigation developments. At
present it does not seem that the irrigation return-flow is causing dramatic
mineralisation of the lower Berg River, but it is a situation that must be monitored as
the developments extent and become older (come into production). It seems that
irrigation return-flow only has an influence on the quality of the river at the beginning
of such a development, but after about three years the influence directly correlates
with the quality of irrigation water and mineral weathering. / AFRIKAANSE OPSOMMING: 'n Studie is gedurende die jare 2000 tot 2002 in die benede Bergrivier opvanggebied
van die semi-ariede Wes-Kaap Provinsie gedoen om die effek van
besproeiingsontwikkelings (koringlande na tafeldruiwe) op die kwaliteit van die
Bergrivier se water, asook die volhoubaarheid van besproeiingslandbou te ondersoek.
Hierdie studie was genoodsaak deur toenemende versouting van beide die Breede- en
Bergrivier, waarskynlik a.g.v. besproeiing, tesarne met groter druk op hierdie
waterbronne van wee die groeiende aanvraag na vars water deur die Kaapstadse
metropool.
Water- en soutbalanse van twee dominante grondpatrone (Glenrosa/Swartland en
Oakleaf/Hutton grondvorms) binne die opvanggebied was by twee lokaliteite
gemoniteer. Wingerdblokke van verskillende ouderdomme binne dieselfde
grondvorms is gebruik om die effek van besproeiing oor tyd te ondersoek. Die
elektriese geleiding van die grondwaterekstrak (EGe) was drie maal op verskillende
dieptes by geselekteerde persele gemeet en die kwaliteit van besproeiingswater en
dreineringsterugvloei was deurgaans gemoniteer. Grondwaterstoringskapasiteite van
hierdie klipryke ( hoe 'growwe fragment fraksie) gronde was ook gekarakteriseer vir
meer doeltreffende voorspellings van dreineringshoeveelhede.
Glenrosa/Swartland gronde het die hoogste EGe's getoon (200-400 mx.m') wat na
vier tot vyf jaar se besproeiing aansienlik afgeneem het en meer uniform met diepte
versprei was. Die hoe soutkonsentrasies is veroorsaak deur die natuurlike voorkoms
van sout in die grond, minerale verwering en sout vanuit die besproeiingswater.
Oakleaf/Hutton gronde het laer EGe's getoon « 200 mS.m-I
), maar hierdie gronde se
soutinhoud is ook onderhewig aan die kwaliteit van die besproeiingswater en
dreinering wat oor jare nie baie konstant was en nog is nie. Gelokaliseerde
soutaansarneling tussen wingerdrye is ook waargeneem a.g.v. die besproeiingsmetode
en dit word meer prominent oor jare. Dreineringshoeveelhede was onder-voorspel
a.g.v. die groot/hoe growwe fragment fraksies en voorkoms van voorkeurvloei, wat
die akkurate modellering van grondwaterhuishouding beperk het. Dit het ook daartoe
gelei dat soutterugvloei ondervoorspel was, maar dit was duidelik dat die meeste
soutterugvloei vanuit die Glenrosa/Swartland gronde plaasvind. Effektiewe
besproeiingsbestuur, om optimale grondwaterpeile te handhaaf en om negatiewe
effekte van hoe EGe te beperk, is noodsaaklik vir die volhoubaarheid van hierdie tipe
besproeiingsontwikkelings. Tans blyk dit nie of besproeiingsterugvloei drarnatiese
versouting van die benede Bergrivier veroorsaak nie, maar dit is egter 'n situasie wat
deeglik gemoniteer moet word soos wat ontwikkelings uitbrei en ouer word (in
produksie kom). Besproeiingsterugvloei het dus net aan die begin van so 'n
ontwikkelling 'n invloed op die EG van die rivier, maar na ongeveer drie jaar hou die
invloed direk verband met die kwaliteit van die besproeiingswater en minerale
verwenng.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/50227 |
| Date | 04 1900 |
| Creators | Engelbrecht, Hendrik Nicolaas |
| Contributors | De Clercq, W. P., Hoffman, E., Stellenbosch University. Faculty of AgriSciences. Dept. of Soil Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | af_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 143 p. : ill. |
| Rights | Stellenbosch University |
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