'N EKONOMIESE EVALUERING VAN TEKORTBE-SPROEIING EN VERHOOGDE WATERTOEDIENINGS-DOELTREFFENDHEID OP LANDBOUWATERGEBRUIK / AN ECONOMIC ANALYSIS OF DEFICIT IRRIGATION AND INCREASING IRRIGATION APPLICATION EFFICIENCY ON AGRICULTURAL WATER UTILISATION

Abstract

Tekortbesproeiing en verhoogde watertoedieningsdoeltreffendheid is as watergebruik-strategieë met kans-beperkte lineêre programmering (KBLP) ontleed om te bepaal of die strategieë ekonomies voordelig en waterbesparend was. Tekortbesproeiing is deur skalingsfunksies in die KBLP-model gemodelleer en potensiële terugvloei is vanaf optimale watertoedieningsdoeltreffendhede bereken. Resultate toon dat verhoogde watertoedieningsoeltreffendheid ekonomies voordelig was, maar die illusie kan geskep word dat water bespaar word, terwyl potensiële terugvloei verminder. Tekortbesproeiing bespaar water deurdat waterverbruik deurgaans meer daal as potensiële terugvloei. Tekortbesproeiing was alleenlik ekonomies voordelig indien groter oppervlaktes met die bepaarde water besproei kon word. Albei strategieë het substansiële ekonomiese voordele indien groter oppervlaktes met bespaarde water besproei word, maar het meer druk op stroomvloeivlakke uitgeoefen. Alvorens beleid wat in sosiale belang is, saamgestel kan word, word meer inligting aangaande die wisselwerking tussen waterwetgewing, waterbeleidsadministrasie, tegnologie, hidrologie en menslike waardestelsels benodig.

Deficit irrigation and increasing irrigation application efficiency were analysed as water-utilisation strategies through chance-constrained linear programming (CCLP) to establish whether these strategies were economically advantageous and water conserving. Deficit irrigation was modelled through scaling functions in the CCLP model, and potential return flow was calculated from optimal water application efficiencies. Results showed that increasing water application efficiency may be economically beneficial; however, the illusion might be created that water was conserved, while potential return flow was reduced. Deficit irrigation conserves water because water consumption decreases more than potential return flow. Deficit irrigation was economically advantageous only if larger areas are irrigated with the conserved water. Both strategies had substantial economic advantages if larger areas were irrigated with conserved water, but they did exert more pressure on streamflow levels. Before policies can be formulated that are of social importance, more information is required with regard to the mutual interaction among water legislation, water policy administration, technology, hydrology and human value systems.