Kostnadseffektiv och hållbar sedimenthantering i dagvatten- och fosfordammar

Sammanfattning

Stormwater ponds in urban areas and phosphorus ponds in agricultural landscapes are important treatment facilities for reducing the transport of pollutants and nutrients to receiving waters, but many facilities require sediment removal to maintain treatment efficiency. Existing guidance often treats dredging, dewatering, and sediment handling separately, despite their strong practical interdependence. This thesis analyses how technical, logistical, and regulatory factors influence the selection of methods for dredging, dewatering, and sediment handling in stormwater and phosphorus ponds. The study also evaluates the cost-effectiveness of different management strategies through five Swedish case studies in Haninge, Tyresö and Uppsala. The study combined literature review, interviews with industry stakeholders, field observations, and cost analysis. The results show that facility design, accessibility, and opportunities for local sediment handling are key factors influencing method selection. The possibility of bypass and drawdown was identified as particularly important, as drained facilities enable efficient mechanical dredging with lower water content in the excavated sediment. Where drawdown is not feasible, hydraulic dredging was generally found to be more suitable due to reduced environmental disturbance and the ability to pump sediment to remote dewatering areas. The findings further show that dewatering is a major cost-driving factor, since transport and disposal costs are highly dependent on sediment water content. Rural phosphorus ponds often allow local reuse of sediment, resulting in lower project costs, while contaminated sediments in stormwater ponds frequently require costly external disposal solutions. The study concludes that cost-effective sediment management depends on optimizing the entire handling chain rather than minimizing dredging costs alone. The results highlight the importance of integrating maintenance considerations into the design of new facilities, including bypass systems and accessible dewatering areas.