Hydrological impacts of irrigated agriculture in theManuherikia catchment, Otago, New Zealand

摘要

Water for irrigation is becoming an in-creasingly critical component of NewZealand's rural economy. Projections ofexpanding agricultural sectors indicateincreased demands for water and a reliablewater supply. Hence, it is pertinent to assessthe impacts of water demand for currentand future irrigated agriculture on catch-ment hydrology. This case study focuseson estimating the hydrological impacts ofirrigated agriculture in the Manuherikiacatchment upstream of Alexandra, CentralOtago, New Zealand. In order to assessthe impacts of irrigation on streamflow,five land-use scenarios, including threeirrigation scenarios with varying efficiencies,are investigated with the ACRU agro-hydrological modeling system (AgriculturalCatchments Research Unit (ACRU),Department of Agricultural Engineering,University of KwaZulu-Natal, Republic ofSouth Africa, http://www.beeh.unp.ac.za/acru/). The results show a 37% loss of meanannual water yield under current conditionsdue to inefficient irrigation practices. Evenwith the most water-efficient irrigationinfrastructure, this loss could be reduced byonly 20% – meaning a 30% loss of meanannual water yield. These results emphasizethe significant and inevitable water demandsand catchment water yield losses associatedwith irrigated agriculture, which are due to losses in the conveyance system, on-farm application losses, increased actualevapotranspiration, and the development ofa deeper rooting system compared to naturalvegetation.