Streamflow may be measured indirectly using hydraulic structures. Such hydraulic structures can be categorized into two main groups, namely weirs and flumes. Regardless of the group, these structures produce unique control section in flow, and subsequently enables us to express its discharge as a function of upstream head.
Other than using hydraulic structures, we can also use slope-area method. This method implements Bernoulli’s principle, considering the streamflow as uniform flow in an open channel. Based on this theorem, the head at the upstream equals to the sum of the head and head loss at downstream. Total head loss can then be further expressed as the sum of friction loss and eddy loss. The determination of streamflow is then performed with the aid of Manning’s equation.
Slope-area method is an iterative process. At first, we assume a head loss value. Then, we determine flow discharge through. Based on the continuity principle, discharge is constant for two different points in flow profile, and from here we can calculate the velocity and velocity head. Lastly, we will be able to calculate the friction loss and eddy loss. The sum of these losses is then compared to the assumed head loss value at the beginning of this iteration. The process can be concluded once convergence is achieved.
The following shows essential information for the indirect streamflow measurement. Watch the video above for full details.
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