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TLpq2522385278
انگلیسی
Strategies to Cope with Risks of Uncertain Water Supply in Spate Irrigation Systems
[Thesis]
Bashir, Eiman Mohamed Fadul
de Fraiture, C. M. S.
Wageningen University and Research
2020
157
Ph.D.
Wageningen University and Research
2020
Spate irrigation is a flood-based irrigation, a special type of irrigated agriculture that has been practiced in arid and semi-arid regions for centuries. The irrigation is based on diverting into the low lands the highly variable and unpredictable flash floods from valleys and ephemeral rivers using gravity force. Water supply in spate irrigation system is highly uncertain with likelihoods of receiving both extremely destructive flood and drought years. The uncertainty is inherent in the flooding time, volume of River flows, and in the annual irrigable area. Irrigation systems are frequently exposed to the impacts of climate variability and related extreme events such as floods and droughts which could result in large losses in agriculture productivity, assets and lives. Water supply risk and strategies to cope with climate variability in spate system needs to be addressed because spate irrigation contributes to the livelihoods and food security of marginalized populations in water scarce regions, where occasional floods are often one of the few sources of water for irrigated agriculture. Generally, studies on spate irrigation systems are limited. Particularly in Sudan, spate system have been neglected in national development plans and strategies. In addition, risk and coping strategies assessment in poor rural community systems, such as spate irrigation, has not been adequately addressed in the literature. In this context, this research aims to assess the main sources of risk and coping strategies due to uncertain water supply in spate-irrigated systems. The case study of this research is the Gash Agricultural Scheme (GAS) in eastern Sudan. The research was conducted through the development of few methodological frameworks for risk and coping strategies assessment. Several methods were employed for data collection using field survey; questionnaires; and secondary data, and data analysis employing statistics, optimisation and modelling. For water supply risk assessment, a novel attempt is made to apply the SPRC (Source-Pathway-Receptors-Consequence) model originally developed for the flood risk management context, to a spate irrigation system in an arid region in Africa. The SPRC model, build upon the primary and secondary data, profoundly assisted in clearly comprehending and describing the sources of risks, propagation pathways, risk perceptions and consequences for the farmers, water user associations and water managers in the GAS. For coping strategies assessment, the Driving force-Pressure-State-Impact-Response (DPSIR) framework was used to identify strategies to cope with different water supply risks in the study area. Additionally, the mDSS4 (The MULINO Decision Support System) tool was employed to evaluate the effectiveness of the coping strategies. Then surface irrigation modelling using WinSRFR model was used to evaluate performance of locally developed practice for on-farm improvements for field design and water application. Performance of alternative designs and application times were simulated for different flood risks. Irrigation performance of different combinations was then examined using application efficiency, distribution uniformity, and adequacy criteria to obtain the best performing scenario. Last, a conceptual framework for establishment of real options in spate irrigation characterized by flexibility was developed with application in traditional, improved traditional and modernized spate irrigation systems. The SPRC was a useful framework for analyzing risks at different spatial scales and for different stakeholders in the spate irrigation system. Based on limited knowledge and lack of flash flood forecasting systems, water flow to the irrigation system was unpredictable, uncertain with regard to volume, timing and duration. The stakeholders perceived flood risks as low flood, high flood, short flood, extended flood, early flood and late flood risks. Observations of flood events in the historical records of hydro-climatic data were categorized based on stakeholder's perceptions on threshold values for low flood, high flood, short flood, extended flood, early flood and late flood. Findings showed that farmers, WUAs and system managers perceived the risks from floods differently. The farmers were primarily concerned by low floods, while the WUAs were more disturbed by untimely floods. The system managers were most troubled by high and potentially destructive floods. The poor state of the infrastructure, lack of proper maintenance and suboptimal operation aggravated the consequences of unpredictable flows. Consequently, the resultant impacts were low crop yield, highly variable crop production and highly variable irrigated area. The assessment of the effectiveness of existing coping strategies practiced by farmers, WUAS, and water managers revealed the most effective measures were crop management in terms of variety and change crop choices for farmers; pre-flood preparedness, risk sharing measures through water and land management during and after flood for WUAs; and flexibility in system operation by water managers. Unfortunately, the most effective measures were not the most adopted ones. The level of adoption is primarily related to the capacity of the farmers, WUAs and water managers to implement the measures without outside support. Three strategies were investigated to evaluate performance of locally developed practice for on-farm improvements for field design and water application namely; time management strategy, improved field design with time management strategy and improved field design with flow management strategy. The second strategy resulted in the highest performance indicator values compared to other strategies. The adoption of improved field design with time management strategy resulted in the highest performance indicator values compared to other strategies, can save 40% of the current application time during large flood seasons, and 20% during medium flood seasons. A conceptual, framework for flexibility consideration in spate irrigation was developed and applied. The framework consisted of four principle questions, eight main flexibility features and five sub-features that were found to adequately represent flexibility in spate irrigation systems. The conceptual framework demonstrated its beneficial use for the evaluation of spate irrigation system through its application on traditional, improved traditional, and modern spate systems to cope with high peak flood, low peak flood and untimely flood events. A key contribution of this PhD thesis is the development of methodology frameworks for risk and coping strategies assessment in spate irrigation systems. This research developed approaches on how risks in spate irrigation systems could be assessed to enhance irrigation performance and equity to support farmers trapped in poverty and illiteracy. Additionally, water related risk management in low cost rural community system, such as spate irrigation system in arid and semi-arid zones, has been presented to the literature. Further, this research showed that spate irrigation performance could be optimized when proper set of coping strategies/real options are in place. Flexibility of spate irrigation systems are enhanced by adoption of real options to cope with variability and uncertainty of water supply.
Agriculture
Civil engineering
Poverty
Rural areas
Water shortages
Water supply
Bashir, Eiman Mohamed Fadul
de Fraiture, C. M. S.
مطالعه متن کتاب p
[Thesis]
276903
a
Y
