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Sosiale wetenskappe: aardrykskunde

Graad 7

Oorstromings/vloede

Module 1

1. Oorstromings/vloede

1.1 Die voorkoms en ontstaan van oorstromings

1.1.1 Wat is ‘n oorstroming?

Dit ontstaan wanneer daar ‘n oormaat water is. Grond wat nie normaalweg deur water bedek is nie, word tydens ‘n oorstroming deur water bedek.

Dit gebeur soms dat ‘n jarelange droogte skielik deur swaar, aanhoudende reën beëindig word. Sulke rampe lok dan vrae uit soos: Is die klimaat besig om te verander?

Aktiwiteit 1:

Om ‘n sekere opinie oor ‘n geografiese verskynsel te huldig

[lu 2.1]

  • Wat is jou opinie omtrent die stelling dat die klimaat van die aarde besig is om te verander? Skryf ‘n paragraaf daaroor.

1.1.2 Waar kom oorstromings voor?

Bestudeer figuur 3 (’n wêreldkaart van waar die meeste ernstige oorstromings al voorgekom het) op bl. 10.

Jy sal opmerk dat die meeste oorstromings in Indië, China, Noord- en Suid-Amerika voorkom. Tog kan oorstromings in feitlik enige omgewing voorkom waar water is. Selfs in woestyne kan ernstige oorstromings voorkom. Onthou dat daar verskillende oorsake vir vloede is en hierdie oorsake bepaal WAAR die oorstromings gaan voorkom.

1.1.3 Wat veroorsaak oorstromings?

Water wat dele van die aarde oorstroom, kan verskillende oorsake hê, soos die volgende:

  • Sneeu wat smelt, bring meer water in riviere mee.
  • Uitsonderlike hoe reënval in ‘n area laat riviere hulle walle oorstroom. Hierdie soort reënval kom gewoonlik voor in die vorm van storms, siklone en moesonreën (Indië). Voorbeelde hiervan in Suid-Afrika was die Laingsburg-oorstroming, asook sikloon Demoina, wat Natal getref het.
  • Damme en/of oewerwalle wat meegee of oorloop.
  • Grondverskuiwings, aardbewings en vulkane kan riviere en ander watermassas ontwrig en tot oorstromings lei.
  • Oorstromings langs kuste word veroorsaak deur reusagtige seegolwe (tsunami’s) wat deur aardbewings op die seebodem veroorsaak word. Meer hieroor as ons aardbewings bestudeer.

1.2 Die uitwerking (gevolge) van oorstromings op die lewens van mense en hulle sosio-ekonomiese aktiwiteite

Menslike bedrywighede kan nie oorstromings veroorsaak nie, maar mense kan op indirekte wyse die omvang en skade daarvan vererger, soos hieronder verduidelik word.

  1. Onnadenkende gebruik van die grond as gevolg van
  • ontbossing
  • oorbeweiding
  • gronderosie.

Natuurlike plantegroei en hulle wortels word dus vernietig en dit kan nie meer die bogrond vashou as daar swaar reën val nie. Die reënwater word ook nie maksimaal deur die grond absorbeer nie. Reënwater loop dus vinniger af en neem die bogrond saam. Riviere en damme slik as gevolg hiervan toe.

  1. Die bou van paaie, geboue en kanale veroorsaak ook die vernietiging van die natuurlike plantegroei.
  2. Huise word soms op minder geskikte en selfs gevaarlike terreine gebou, waar oorstromings kan voorkom.

‘n Voorbeeld van so ‘n oorstroming in Suid-Afrika.

Op 30 September 1987 het ‘n geweldige tropiese storm oor Natal gewoed. Minstens 180 mense is dood. Plakkershuise het in hulle duisende in die reën verkrummel. Ander se dakke is afgeruk en huise is ernstig beskadig. Seweduisend gesinne is in een dag koud, honger en dakloos gelaat. Die meeste brûe en paaie is weggespoel en reddingswerkers kon nie per vragmotor hulp aanbied nie. Daar was geen elektrisiteit beskikbaar nie, asook geen riool- en kraanwater nie. Alle pypstelsels is deur die vloedwater vernietig. Besighede het tot stilstand gekom en geweldige finansiële verliese is op ekonomiese gebied gely. Boere het ook hul oeste en diere verloor. Alle ryk bogrond het weggespoel en dit sal jare neem om weer te herstel. Plaasdamwalle het gebreek en alle heinings is meegevoer. Herstelwerk het natuurlik geweldige finansiële implikasies gehad.

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Source:  OpenStax, Aardrykskunde graad 7. OpenStax CNX. Sep 09, 2009 Download for free at http://cnx.org/content/col11020/1.1
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