Making it easier to predict stream flows

Posted on July 25, 2012

To better understand patterns of sediment and pollution transport and predict the responses of stream animals and plants to water flow, it helps to be able to model stream velocities in two dimensions – that is, both vertically from the channel bed to the water surface and laterally across the full width of the stream.  In open channels velocities can be highly variable from bank to bank , and during high flow events the maximum velocity can occur well down in the water column – as low as 45% of the total distance from surface to bottom.  The most useful and powerful approach to velocity modelling is based on the concept of entropy (uncertainty).  In the context of hydraulics, entropy can be used as a measure of how far the expected distribution of velocities at different heights above a given point on the stream bed deviates from a uniform distribution.  This approach has been used to define a new entropy parameter (M) which expresses a range of flow characteristics and can be used to derive two-dimensional velocity distributions and estimate stream discharge.  M is easily determined from measured values of mean and maximum velocities.  The new method is straightforward and can be used with any velocity-measuring equipment, which drastically reduces the time and cost of measuring discharge.  It can be used with steady, unsteady and fast flow situations and in streams with or without suspended sediment. 

Reference:  Hao Luo & Vijay P. Singh.  2011.  Entropy theory for two-dimensional velocity distribution.  Journal of Hyrologic Engineering  16(4), 303-315.