Estimating discharge in drainage channels through measurements of surface velocity alone: A case study

In the scientific literature it is possible to find at least two methods for estimating discharge in an open channel which represent a valid alternative to the Velocity-Area method; both offer a considerable advantage in that they are simple to apply and require knowledge solely of the channel bathymetry and maximum surface velocity. The first method is based on the entropy concept introduced into hydraulics by Chiu in the 1990s, whilst the second is focused on the reconstruction of dimensionless isovels in the channel cross-section. Both the methods have been extensively described in previous works and validated for medium/large-sized cross-sections where surface measurements are taken by current-meter or Acoustic Doppler Current Profiler (ADCP) sensor. In this technical paper, they are instead applied to a water drainage channel in a reclamation territory characterized by a very low velocity which required a particular measuring technique, called “total station”. This technique demonstrated to be reliable in situations where the velocity is very low and cannot be measured with other “no-contact” techniques, such as those based on the Doppler method, which are normally used when the use of current meters is not possible.