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Minimizing water shortages and operational costs of a water supply system by providing decision support on real-time control : a case study in La Paz, Bolivia

Kats, H. (2019) Minimizing water shortages and operational costs of a water supply system by providing decision support on real-time control : a case study in La Paz, Bolivia.

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Abstract:The citizens of the La Paz – El Alto metropolis in Bolivia depend on a natural system of catchments for their drinking water. The water supply consists of different source regions which are connected to multiple water treatment plants (WTPs). This natural system is subject to an annual meteorological pattern with a wet season usually occurring from December until April, while the remainder of the year is dry. To provide the citizens with drinking water during the entire year reservoirs are constructed to store water, which are connected to the WTPs by pipelines and open channels. In 2016 the La Paz – El Alto metropolis, experienced its worst drought in 25 years, which resulted in a water rationing period of two-months, affecting over 400.000 of its 1.6 million citizens. The drought problems are caused by a combination of climate variability and climate change, rapid urban expansion, extensive mining, agricultural and industrial activities, out-dated infrastructure and mediocre operational management. These different aspects have been studied, however the operational control of the infrastructure was not a subject of study. In 2018 some river intakes were built where water can be transported directly from a river to a WTP for additional supply. Using these intakes can mitigate or prevent water shortages but introduce additional operational costs. Furthermore, these intakes make the operational control of the water supply system more complex. Therefore, this thesis focuses on an optimal real-time control of the river intakes and provides decision support. Since the behaviour of the natural water system determines the amount of water available to the supply system, it is important to understand the hydrological behaviour. Rainfall-runoff models are built to estimate the runoff based on precipitation data. Uncertainty in future precipitation can be addressed by introducing precipitation scenarios. The combination of a limited intake capacity and a variable potential intake discharge makes it preferable to plan and execute the control on the intakes far ahead in the future. To make such a proactive control possible, the precipitation scenarios need a time horizon of at least one year. Besides the hydrological boundary conditions, an optimization approach is constructed that can determine the least costly operational control of the water supply system based on a given set of initial (hydrological) conditions and future discharges. The decision about which scenario to use depends on the desired trade-off between the water shortages and the operational costs. A conservative approach results in a guarantee of little water shortages but high operational costs, while a risky approach results in more probable water shortages but low operational costs. In the future water shortages and operational costs will both increase due to increasing population and consumption. Already in 2022 there will be shortages at the WTPs when using the intakes in full potential. By 2027 the water supply system will not suffice to reliably satisfy the increased demands of the WTPs, potentially leading to relative shortages between 2% and 10%. Besides the growing water shortages, this also results in an increase in operational costs, potentially leading to an increase of up to 0.04 €/m2 for the consumer by 2027. To use the decision support the decision maker should consider to what extent water shortages are acceptable and what budget is available for using the intakes. Ultimately the decisions regarding the operational control of the intakes is about the balance between the risk of having a water shortage in the future and the costs of lowering this risk. When the decision-maker has determined the preferred balance, the decision support on real-time control will provide advice on a strategic level of how much water to take in and how to distribute it over to the different WTPs.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
Link to this item:http://purl.utwente.nl/essays/78106
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