| dc.description.abstract | During low Rhine discharges, saltwater intrusion can occur on the tidal Hollandse IJssel River (HIJ), resulting in heightened chloride concentrations at the freshwater intake location of the Hoogheemraadschap van Rijnland at Gouda (HydroLogic, 2015a). Future climate change is expected to increase the occurrence and duration of dry periods in Rijnland, while simultaneously increasing saltwater intrusion at Gouda (Van Beek et al., 2008). When saltwater intrusion on the HIJ coincides with freshwater demands in the Rijnland areas, this can jeopardize the freshwater demanding high-value agriculture within its borders (Stuyt et al., 2013).
To secure Rijnland’s future water demand an alternative freshwater supply has been realized: The “KWA” (small-scale water supply). To prevent intake of brackish water into Rijnland, this supply will commence when chloride concentrations on the HIJ exceed the threshold of 250mg/l. However, the quantity of this supply is insufficient for Rijnland’s theoretical water demand during dry periods (HydroLogic, 2015a). Therefore, efforts are underway to expand its capacity: The “KWA+”.
Current views on chloride acceptance levels of water systems in the Netherlands may be too pessimistic, and methods should be developed to increase shared understanding and commitment towards saltwater related policy (Stuyt, Kielen, & Ruijtenberg, 2015). This study aims to support this development by 1) developing a hydro-economic model to rationalize freshwater management cases, and 2) assessing the economic cost-effectiveness of implementing alternative water management investments and strategies.
An earlier study by Stuyt et al. (2013) to assess the effectiveness of water allocation strategies in Rijnland resulted in the €ureyeopener1.0 model. This rapid-assessment model uses single values for weather and chloride concentrations for a whole growing season and provides quick insights into the effects of changes to Rijnland’s water system towards water requirements and agriculture damage. The main research gap in this model lies within its lack of temporal variability within the growing season for weather and chloride concentration data, resulting in an omission of infrequent weather events and its effects on the system.
Therefore, in this study the hydro-economic WAOR (Water Allocation and Optimization Rijnland) model was created. With this model the cost-effectiveness of multiple alternative water management strategies, such as the “KWA+” investment, can be assessed. The WAOR uses a dynamic boezem-polder schematization of Rijnland in which polders demand (fresh)water from the boezem based on their requirements. It combines weather and chloride concentration data, agriculture damage functions, temporal variability, climate scenarios, and system constraints, in order to optimize the water intake of Rijnland based on agriculture damage reduction.
Furthermore, the WAOR can be used to determine the effects of a water allocation strategy on the agriculture crop yield losses in Rijnland for one or multiple growing seasons. The model was built 1) to be intuitive with regards to strategy and constraint selection and 2) to facilitate easy comparison of the different strategies.
It was found that the “KWA+” expansion results in noticeable agriculture damage reductions. However, for agriculture damage reduction alone the “KWA+” is not cost-effective with its investment costs, even for the most extreme climate scenarios. The results indicate that the consequences of delaying investments in freshwater infrastructure may not be as severe as anticipated. However, prevention of damage to nature and prevention of peat degradation, resulting from exposure to water with heightened chloride concentrations, are not modelled within this study and could provide additional (monetary) benefits. Additionally, sensitivity analysis with the WAOR has shown that lowering the chloride acceptance levels will reduce the agriculture damages, while requiring more frequent implementation of alternative freshwater allocation strategies.
The WAOR delivers a holistic approach to freshwater allocation questions and allows for the assessment of the cost-effectiveness of freshwater supply related investments within coastal areas. The inclusion of climate scenarios adds to understanding on how a changing climate may impact freshwater allocation strategies and investments in the future. Furthermore, the WAOR contributes to operational management by allowing for assessment of variations in strategies and chloride norms and helps to align hydro-economical concepts with contemporary water management practices. | |
