Author(s): Ceyda Polatel
Linked Author(s):
Keywords: Discharge measurement; Indexing; Free surface velocity; Large Scale Particle Image Velocimetry (LSPIV); Laser Doppler Velocimetry (LDV)
Abstract: Discharge estimation is the essential part of any hydraulics problem related with rivers. A non-contact method, with lower cost, better accuracy and less hazards than those of traditional stream-gaging method, is currently being investigated. The indexing technique aims to relate remotely obtained pointwise velocity measurement to depth-averaged velocity for known bed characteristics. Taking the free surface velocity as indexing velocity has advantages in the aspect of appropriateness to non-contact measurement techniques. However, the free surface velocity and its relationship with depth-averaged velocity are sensitive to many factors. In this paper, the effect of channel bedforms on the free surface velocity is discussed. For a range of flow depth and surface velocity, the velocity fields at the free surface and in the water column were measured for flow over two-dimensional dunes, square cavities, and smooth bed. It is found that the roughness shows its effect on the free surface velocity, and hence channel bathymetry must also be considered to relate free surface velocity to depth-averaged velocity. The results of the experiments show that discharge can be appropriately estimated by free surface velocity indexing.
Year: 2005