Water infrastructures like pipes, sewers and treatment plants provide water for many purposes, ensure safe wastewater disposal, and protect from floodings. However, they are long-lived, ageing and expensive: Swiss public water infrastructures need investments of more than 80 billion CHF in the next 40 years.
Climate change effects and socio-economic developments are uncertain, but strongly impact infrastructures. Current Swiss planning does not systematically integrate future uncertainty, past experiences, and different actors. Main goal of SWIP is an improved water infrastructure planning procedure that balances economic, ecological, and social aspects.
SWIP integrates engineering modelling with Multi-Criteria Decision Analysis (MCDA) as framework. The transdisciplinary approach included active stakeholder participation in a case study near Zürich. The engineering models predict deterioration and performance of water supply and sewer pipes and quantify impacts of climate change on urban drainage.
SWIP explicitly considers different sources of uncertainty: scarce data sets, models, climate, socioeconomic development, and stakeholder preferences. MCDA synthesizes all model outcomes and structures stakeholder participation. As a result, recommendations about robust infrastructure options can be made, which perform well for most actors in different future scenarios.
To forecast the condition of pipes with scarce data availability, probabilistic models were developed. By considering previous rehabilitation, overestimating the lifespan is minimized. For model calibration, knowledge from experts or other networks was combined with the limited data.
On the basis of historical data and ten climate predictions we developed a rainfall model. The results show that even under the present climate, extreme precipitation is highly variable, but not included in current planning. The case study didn’t clearly indicate that climate change increases this uncertainty; but the results need to be solidified for other regions.
In order to decide which actors will be included in the MCDA, we conducted a stakeholder and social network analysis. We found a very strong fragmentation between some stakeholders. The fragmentation was especially visible between the water supply and wastewater sector, or communal, cantonal, and national levels. For longer term sustainability and strategic objectives, better integration of all actors into planning processes is needed.
The project identified different objectives of the stakeholders and ranked them. A generic objectives hierarchy was developed that is transferable to other settings. The objectives hierarchy contains six fundamental objectives and 40 attributes (indicators). Most stakeholders had similar preferences: "good water supply", "safe wastewater disposal", "protect water and other resources", and “intergenerational equity" were their main interests, while "low costs" and "high social acceptance" were less important.
The project developed eleven possible strategic decision alternatives (infrastructure options). They concern different technical configurations (e.g. central vs. decentral treatment), rehabilitation strategies (e.g. continuous vs. no replacement), or management aspects (e.g. public vs. privatized utilities). MCDA predicted their performance was predicted for four future scenarios. Therefore predictions were combined with elicited stakeholder preferences. Result was a rank of alternatives from best to worst. This did not result in a single best-performing alternative for all actors and scenarios. Reasons are different preferences and the large uncertainties. Especially the "Boom" scenario with massive population growth was very sensitive. Potential compromise solutions are based on the current system. However the rehabilitation management and collaboration of municipalities and sectors should be improved. Interestingly, a decentralized high-tech wastewater alternative with nutrient recovery and micropollutant removal performed very well. For water supply, decentralized firefighting water tanks are interesting, because they allow reducing pipe diameters.
SWIP provides important contributions to quantitative water infrastructure management in Switzerland:
deterioration modelling of network infrastructure with limited, biased datasets
evaluation of the effect of climate change on drainage system performance
systematic inclusion of uncertainty
quantification of future infrastructure performance with respect to sustainability.
The MCDA links predictions of engineering models with social science data and provides a new framework for water infrastructure planning. The model can be adapted to various settings. It helps local actors to understand different perspectives and supports engineers and municipalities to change from problem-based repairs to a proactive and long-term rehabilitation concept. The readiness of major Swiss stakeholders to participate in SWIP indicates a strong interest in transferring the decision making through MCDA- into practice.
Sustainable water infrastructure planning (SWIP)