Evaluation of Local Scour along Rönne Å at Ängelholm

Abstract: Riverbed scouring is an emerging problem aligned with higher frequent river discharges, experiences in a short period of time with shifting climate conditions. This problem brings a huge challenge to relevant authorities to safeguard river stability and hydraulic structures. This master thesis study is a preliminary investigation of the local scour problem along a Rönne å river stretch which falls under Ängelholm municipality, Skåne. The main objectives included a mapping of existing scour holes along the river reach with an evaluation of possible causes, building a hydraulic model for the river stretch, and estimating the potential scour risk of some existing bridges. HEC RAS one-dimensional model was selected to establish a hydrodynamic model for the downstream reach of about 12 km of the Rönne å river. Bathymetry and geometry analyses revealed that the existing deep sour holes may be developed mainly by general scour mechanisms, such as bend scour and presence of hard non-erodible river bottom. The HEC RAS bridge scour analyses for six bridges disclosed that the bridges have more threat from abutment scour than contraction scour. The bridge Tegelbruksbron has the highest prone to abutment scour and Kristian II Bridge has the highest threat from contraction scour among the bridges. The results are reasonably good for initial assessment stages in bridge scour evaluation and useful for future investigations. The study further suggested for Ängelholm municipality, to conduct a comprehensive sediment analysis along the riverbed to get more interpretations and potential evaluations.