Integrated modelling for sustainable management of salinity in the lower Vaal and Riet river irrigation areas

[摘要] English: This thesis is the culmination of salinity economics research conducted for the South African Water ResearchCommission. The contribution of this thesis to science is not only in the field of Agricultural Economics. but alsoin other fields involved in irrigation salinisation research. It integrates the diverse mono-disciplinary spatial andtemporal dimensions of the various disciplines of hydrology, agronomy, soil science and agricultural- andmacro-economics, into an economic base model, to test scenarios and evaluate the economic, social andenvironmental sustainability of irrigated areas subject to salinisation.Problem Statement and the Study Area:Salinisation of irrigation schemes has become a problem in various schemes in South Africa. One such areathat experiences salinisation problems selected for this research is the Lower Vaal and Lower Riet irrigationareas, upstream from where these two rivers converge and flow into the Orange River.By understanding the dynamics and interactions between irrigation water quality and the soil salinity status oncrop yield over time, mistakes made in the past by choosing unsustainable irrigation sites and practices can beprevented in the future. Furthermore the impact of various natural or artificial (e.g. policy mechanism) scenarioson existing schemes can be more accurately modelled, leading to increased economic efficiency andsustainability of the irrigation industry, together with its primary and secondary linkages, as a whole.Aims:The overall aim of the WRC study on which this thesis is based was to develop and integrate multi-dimensionalmodels for sustainable management of water quantity and quality in the Orange-Vaal-Riet (OVR) convergencesystem.More specifically the following sub-objectives had to be addressed:1. To better understand the polluting chemical processes and interactions in and in-between the plant andsurface-, vadase zone- and ground- water, to achieve efficient and sustainable water quality management2. To develop new economic models at both,a. Micro level, namely dynamic long term simulation models, and atb. Macro level, using a regional dynamic Input / Output model'3. To integrate these new economic models with models from the other disciplines of:a. Hydroloqy (incorporating a salt mass balance and flow), andb. Agronomy (crop growth in the presence of salinity model)4. To determine and prioritise best management practices at:a. Micro level, (i.e. per hectare and irrigation block level) and atb. Regional level.5. Through a better understanding of the multi-dimensional interactions, to enhance water use efficiency as thequantity and quality of water available for agriculture inevitably decreases6. To develop policy guidelines to ensure social, environmental and economic sustainability7. To achieve all these aims based on using the complex OVR convergence system as a study area, butdeveloping a method and models that can be applied elsewhere with relative ease.This thesis however only covers the micro-economic aspect of the WRC project conducted by the author, andhow it is driven by the hydrological and bio-physical processes and how it links and translates to the macroeconomic(regional) impact.Model:The economic base model of the integrated model uses hydrology and biophysical data and algorithms as inputinto the monthly time-step, per hectare Crop Enterprise Budget based, MSExcel simulation model (SMsim) togenerate the base data. The resulting steehastic and spatially differentiated data set of per hectare total grossmargin above specified costs data is then converted to sub-WUA, WUA, combined WUA and regional area leveldata for comparison and interpretation at these various levels and for input into the macro-economic regionallevel model (ISIM) and the index for socio-economic welfare (ISEW) for sustainability evaluation betweenalternative scenarios.Results:The results of this thesis inter alia show that the installation of irrigation drainage to facilitate leaching is a farbetter option than planting more salt tolerant crops. In the WRC project on which this thesis is based the resultsof a macro-economic analysis based on the micro-economic results from this thesis show that although at sub-WUA level it may not be financially feasible to install drainage in some sub-WUA areas, the secondary andregional socio-economic and environmental impacts justify the spending of government grants for drainageinstallation as the secondary benefits on the regional economy exceed the costs of the drains.

[发布机构] University of the Free State