<p>Submerged groynes are applied in urban river systems for ecological purpose by creating varied flow zones to promote ecological diversity, even under spatial constraints. However, in addition to altering the flow field, they may raise water levels and cause flood-risks due to additional flow resistance. Although submerged groynes are relatively small in size, they are still classified as engineering structures which require a hydraulic design and an evaluation of their influence on the flood water levels. Until now, the hydraulic behaviour of submerged groynes has not been fully captured, the quantification of impacts on backwater effects still demands a significant effort through laboratories and computational models, both of which are costly and time-consuming, while existing calculation methods are lacking sufficient accuracy. A central component of this study is to quantify the impacts of submerged groynes across a wide range of parameters regarding geometric and hydraulic conditions using computational fluid dynamics (FLOW3D). After validating the 3-D numerical model against experimental data, systematic investigations on influencing parameters provided detailed insights into flow conditions and associated backwater effects. </p>