If you want accuracy, actually measuring flow is reasonable, considering the work to collect all the other measures, especially if the contributing Watershed is not too large and sediment loading not great. Water level vented transducers record water level data at just about any frequency, and I would suggest every 15 minutes, except for very small streams of catchment size, then every 5 minutes. Stage discharge relations can be developed or installing a designed weir or flume to pass flow through a structure with stage discharge relationship calculated for dimensions. I personally installed a transducer in the upper Chattooga River (roughly 100 km2 watershed with rainfall over 2 m average annually), and related its flow to a down river stream gauge with long record, to help estimate extent of boatable days for recreation uses. I hired the USGS to measure several storm high flows, and measured wadable flows myself during site visits for data downloads to develop stage discharge relationship. With about a day or two training, most researchers interested in doing this type work can learn enough to do an adequate job to obtain quality estimate. I think I uploaded a short report into researchgate on this Chattooga River effort.

Otherwise, you might try the WEPP (Water Erosion Prediction Model) as I think it also estimates runoff, if you have adequate site data for model to run. There is the SCS (NRCS) Curve Number CN model that estimates response based on soil grouping, I would not recommend it for accuracy unless validated for your conditions, and adjusted as appropriate. Modelling runoff has not been a major interest of mine without collecting data, or without reading site indicators as bankfull flow or flood indicators. Low flow indicators are sometimes evident, for example culvert sites or extent of aquatic insects. There may be other models available that others may recommend, but validating a model to fit conditions for accuracy adjustments may be just as time consuming as actually making the measurements.

field measurement is most accurate but you can use HEC-HMS too.

William F. Hansen Amirhossein Salimi I sincerely thank you for your responses.

I would like to explain the context of my question here.

We train villagers to manage water resources in the village. In the process, villagers prepare the water budget for their village. We are fortunate to be engaged with 4000 villages. Thus we need run-off and evapo-transpiration coefficients for 4000 villages. These coefficients should be accurate enough to represent their localities. But, the process has to be simple enough so that villagers are not discouraged. What should be the process to estimate run-off and evapo-transpiration coefficients?

I sincerely apologize for not explaining the context earlier.

Hi,

I think the method presented here is simple and straight forward for anybody to understand.

https://www.hunker.com/12001914/how-to-calculate-runoff-coefficient

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