I want to construct a device that can determine the rate at which water flows in a river at time interval. I need a circuit diagram for these device.

Originally Posted by Malvinelly

I want to construct a device that can determine the rate at which water flows in a river at time interval. I need a circuit diagram for these device.

There is no practical, accurate way to measure the flow rate of water in a river that doesn't involve multiple samplings across the width and depth of it, with the width and depth being variable conditions that also must be considered at different stages (i.e. flooding) The flow of a river is not laminar enough for accurate sampling in any one location.

a paddle/counter will not suffice on its own. River flow is typically measured with v-shaped wiers.

But if you wanted an electronic method, you might consider hollow tubes placed equidistantly across the river and fixed horizontal to the horizon and WITH the flow of the water so that the mouth of the tube does not restrict the flow. A slight connical shape to the tube would reduce eddies (think aerodynamics). An orriface of known dimensions would be located in the center of the tube, fixed with a flange, to cause a restriction and backpressure on the upstream side. Two ports located on opposing ends of the tube would be fixed with sealed (waterproof) pressure transducers. The differential pressure caused by the restriction would be a SQUARE ROOT FUNCTION of the flow rate, precluding of course that the orriface plate selected was of the appropriate dimensions.

With knowledge of the SURFACE AREA of the diameter of the tube, the pressure and thus flow of the water passing through the orriface, taken as an average across the river, and knowing the width and depth of that sampling area, a reasonable accurate flow calculation would be made.

Here is a tutorial on differential pressure flow measurement:
Differential Pressure Flowmeters

due to non linear and turbulant flow its not easy to measure it, but if you can make a spill way if its a small river, then when you bring it in steady flow in and out of the spill arrangement, it can be aproximated to be liner and you need to get velocity profile and cross sectional area of the flow to determine the exact rate....

It is possible to also check the amount of run of in the river after rain fall? If yes, with which device(s) and and how. If i can also get the circugt diagram and how i can construct it.

can you give some more explanation about your real project. if you want to measure the rain fall in cettain intervels then you may use different idea for that