Streamflow cannot be measured directly, it has to be calculated from variables that can be measured. In order to calculate the water discharge in an open channel it is necessary to have (1) depth of water, (2) the flow velocity and (3) the shape of the channel section. The depth of water and the stream velocity are dynamic in time and have to be measured every time the discharge wants to be known.
There are many different systems available for measuring the depth of water and the stream velocity, however most of them are intrusive (i.e. have to be located in the stream). There are some other systems that are non-intrusive, but they are constrained in their relative orientation with respect to the water surface (e.g. radar systems). Image based measurements possess some clear advantages since there is no need of expensive installations and they offer more flexibility than other non-intrusive measurements systems.
We have developed several solutions for measuring the discharge in rivers and furrows using images. The great advantage is that virtually no preparations prior to the recording need to be made. Among the key characteristics of the method is the fact that no tracer particles are needed. The only requirement is that the field of view contains two reference markers with known scale and with known position relative to the channel geometry, which makes it possible to take measurements in almost any place.
Discharge measurement via cameras provides a non-intrusive, accurate and cost-effective monitoring method.