Hydraulic and Hydrodynamic Stormwater Model for the Västanfors Area of the Municipality of Fagersta, Sweden: Climate Change Impacts and Future Stormwater Management

Abstract: Global temperatures and frequency of extreme weather events have increased over the last decade, with 2015 globally the warmest year on record. Future climate models are consistent with this trend, predicting larger year-to-year variations in precipitation, more precipitation in larger single events, and more frequent extreme events. Changes in weather phenomena due to climate change will impact the infrastructure in cities and therefore the vulnerability of society. Today’s urban stormwater systems are closely related to local hydrological characteristics, with systems designed to accommodate specific ranges of rainfall based on historical data. An increase in rainfall or extreme weather events may result in capacity problems for these systems and in turn, negative impacts to people and the environment. Stormwater management in Sweden is guided by municipal plans and country-wide design standards. Within these documents there is information on who is responsible and what standards must be met, but there is a lack of specific requirements on how to undertake these tasks. Recently, Svenskt Vatten has started to recognize the need for a more defined stormwater management methodology, and commissioned a study titled ‘Guidelines for the modelling of wastewater carrying systems and stormwater systems’. While larger municipalities have the resources to develop hydraulic models, smaller municipalities are often left out of this drive for proactive management. Often, there is no requirement for master planning initiatives, and more realistically, no budget to implement such initiatives. Thus, stormwater management is left to conventional methods and often undertaken on an as-needed basis, with minimal long-term planning. This thesis shows how a hydraulic computer model can serve as a simple, low-cost tool to assist municipalities – especially those of smaller size - in the sustainable planning and management of their stormwater systems. A case study was used to exemplify the objective, by demonstrating a proposed methodology that can be used to assess the impacts of climate change on urban infrastructure. This study was undertaken in collaboration with ÅF Infrastructure AB in Stockholm and the municipality of Fagersta, Sweden.