Turbulence is a flow condition characterized by irregular, chaotic, and fluctuating movement of water, in which velocity and direction vary rapidly over time and space. In stormwater management and hydraulic systems, turbulence contrasts with laminar flow, where water moves in smooth, parallel layers with minimal mixing.
In turbulent flow, water forms eddies, swirls, and vortices of varying sizes that continuously interact and dissipate energy. This mixing action increases the transfer of momentum, heat, and suspended materials throughout the flow. Turbulence typically occurs at higher flow velocities, in rough or irregular channels, around obstructions such as culverts or structures, and wherever there are abrupt changes in flow direction, slope, or cross-sectional area.
Turbulence plays a significant role in sediment transport and water quality. It helps keep fine particles in suspension, contributing to suspended load, and increases the ability of flowing water to erode and mobilize sediment from the bed and banks. At the same time, turbulence enhances mixing and oxygen transfer, which can influence biological and chemical processes in stormwater systems and receiving waters.
In stormwater design, turbulence is both beneficial and potentially problematic. It is desirable in certain contexts, such as energy dissipation at outlets, where turbulent conditions help reduce flow velocity and prevent downstream erosion. However, excessive turbulence can increase erosion potential, resuspend previously settled sediments, and reduce the effectiveness of treatment practices that rely on quiescent conditions for sedimentation. Managing turbulence is therefore an important consideration in the design of conveyance systems, outlets, and treatment facilities.