A performance investigation of stormwater accommodations in Stockholm : A multi-criteria decision analysis

Abstract: Stormwater management is a problematic area and has during the last 20 years been given an increased attention due to more pollution in the cities. The increased pollution and contaminants in stormwater implicates risks for animals, humans, the ecosystem and receiving recipients. Due to the increased attention, authorities, government and other stakeholders have developed measurements to deal with the problem. Stormwater accommodations and other type of stormwater detainment has been developed with increased modern technology and functionality to fit specific areas where different type of pollutants can vary. Stormwater treatment are necessary because it creates social, environmental and technical advantages combined with protection of ecosystem, increased multifunctionality when combining for example stormwater ponds in nature, parks or urban and rural environment. This report describes seven diverse types of stormwater accommodations systems; rain garden, stormwater ponds, wells, screen basins, infiltration trenches, pipe-/concrete magazine and swales in accordance from Structor Mark Stockholm. From these seven accommodations, three were chosen to be included in Multi Criteria Decision Analysis (MCDA). The purpose of the MCDA was to evaluate four different categories linked to stormwater, which are environment, social, technology and economical categories. These categories are broad concepts; therefore, parameters were developed to narrow down the areas within the concept, from which the area of investigation was founded within. The parameters created for each category are degree of purification for the environmental category, performance and maintenance for the technological category, aesthetical and social benefits for the social category and costs and risk for the economical category. The criteria developed from these parameters are specific topics that was scored from the scale between 0-5, where 0 = insignificant, 1= Low, 2= Moderate, 3= Major, 4=High, 5= Very high. A reference option was also created, considered as “no commercial treatment of stormwater”, only to transport stormwater. This reference option was also referred to as a zero-alternative and is drainage by piping. The scoring was conducted by stakeholders and citizens of Stockholm. The scoring of the three chosen stormwater accommodations and the reference alternative after calculating the mean value and summarize it resulted in that stormwater pond received the highest overall score of 11.9 followed by rain gardens 11.4, infiltration trench 11.3 and drainage by piping 7.3. The stakeholders are influential people that works either with stormwater, layout and planning or maintenance personnel. Citizens of Stockholm provided inputs only in regards of the social aspects. A total of 20 stakeholders were contacted and 5 stakeholders participated in the scoring procedure. Citizens were interviewed on the street; a total of 60 people was asked to participate and 13 people decided to participate in the scoring procedure of the social aspects. Although, the attendance of stakeholders was low, they are still considered important to this project since they provided the scoring of the criteria for each respective category (environment, technology, social and economic). In regards of the low attendance by stakeholders, this resulted in a way that it became hard to distinguish the result between the different stormwater accommodation. Therefore, it was hard to determine which stormwater accommodation that was the best out ofthe ranking provided by the MCDA. A benefit by using MCDA as a tool in this case, gave an indication that the MCDA can work as a framework to decision makers, even though the result in this case became difficult to manage and distinguish between the different stormwater accommodations. Finally, the method, layout and analysis itself can provide means of measurements for stormwater investigations when the purpose is to choose between the best stormwater systems included in the MCDA. Inputs from stakeholders concluded that depending on what type of existing circumstances, there must be a site-specific evaluation to treat every area as a unique area, before deciding what type of stormwater accommodation to apply to that specific location.