The application of LS-PIV to a small irregular river for inbank and overbank flows

This paper examines the feasibility of applying a mobile, large scale particle image velocimetry (LS-PIV) system to a 300 m reach of a small river in order to estimate the discharge. Detailed velocity measurements at a number of locations were carried out using an acoustic Doppler current profiler (ADCP) and acoustic Doppler velocimetry (ADV) for inbank, bankfull and overbank flows. The lateral distributions of the velocity index kk (i.e., the ratio of the depth-averaged velocity to the surface velocity) were found to be influenced by the secondary currents, channel vegetation and flow conditions. An attempt is made to quantify the relationship between secondary flow and the velocity index. Appropriate conclusions and advice relating to the practical use of a LS-PIV system as applied to a small river are given.

► The ratio of the depth-averaged to surface velocity (k)(k) for a river has been examined.
► kk is highly influenced by the cross sectional shape, local vegetation and stage.
► The value of kk typically assumed for large rivers is not always appropriate.