Introduction (and aim) – Through sustainable stormwater management, protection from flooding and damage to buildings can be achieved, while at the same time reducing the pollutants that comes with stormwater. The urbanization contributes to larger water flows that need to be stalled, which can be done in stormwater dams. When conducting stormwater investigations, as well as when dimensioning and placing stormwater dams, the actual soil percolation is not considered. The purpose of the report is therefore to investigate how site-specific data from a percolation test can be used to precise the dimensioning and placement of stormwater dams. 

Method – The study consists of a case study where the area of Östad in Tanum has been chosen as the study area. The study uses both qualitative and quantitative methods to capture an overall perspective so that the goal can be met. Using the collection techniques of direct and indirect observation, document study and measurements, raw data could be collected, structured and then analyzed. The study is based on real conditions by using industry-standard software, while discussions with experts from AFRY, Tanum Municipality and BAGA Water Technology AB have strengthened the credibility of the study. 

Results – In the case study area, the soil consists of clay-silt and sandy moraine. After exploitation, the stormwater flow increases, which is proposed to be stalled in a permeable stormwater dam. With the site-specific data, the stalled volume could be reduced by 6 m3, and therefore 708 SEK in construction costs could be saved, while 8.64 kg of carbon dioxide (CO2) could be avoided from being released into nature. The location of the stormwater dam with and without consideration of site-specific percolation became the same. 

Analysis – The study shows that the percolation test can be used as a less important complementary factor when it comes to the placement of stormwater dams. The study also shows an increased precision when sizing stormwater dams with knowledge of site-specific percolation. After implementing the percolation test, the costs in the investigation phase increase, but the costs and environmental impact decrease in the construction phase. In this way, there is an opportunity for the industry to reduce its climate impact through an investment in the investigation phase.  

Discussion – When placing the dam, soil percolation can only be an additional supplementary factor. Since the precision of the dimensioning is percentage, it means that it is more worthwhile implementing the percolation test in large projects or in projects where the client is more concerned with the climate footprint than the cost. For clients with larger economic resources, who therefore can solve the cleaning effect of the storm water in other ways, and who are concerned about the buildable area, the percolation test may be the most favorable. However, there is a risk in using sitespecific percolation, since a certain safety margin of the stalled volume is lost.