Not the Right Time

Currently Indonesia is experiencing a strange climate condition. It is already July now and in July usually we have dry season with very very little rain. Instead of being very hot and dry, there are still rains throughout Indonesia. The meteorological bureau says that the anomaly is caused by La Nina phenomenon which extend the rainy season in Indonesia.

With this in mind, measuring flow using grab method is not recommended in 2010. For the purpose of simplicity many MHP (micro isolated ones) planners are using grab method (either using current meter, salt dilution, or even the float method) to get the base flow of a stream. THe base flow is usually available at the driest moment in dry season (usually between July and August in many of Indonesian islands, although there is always local variation). Measuring the base flow in 2010 would need very conservative factor. I would say roughly the factor would be 0.5 (to be safe). So if one measures 500 liters per second in August 2010, he/she should multiply it with 0.5 to get a safe approximation of the base flow.

Things would be safer if there is rainfall data to collect. Using the data, one can determine whether 2010 is a wet year or very wet year. If it is very wet then the factor might be even smaller than 0.5 (say 0.4) to be on the safe side. 

I guess my recommendation for anyone who would like to measure flow in the wet dry season like now is to get the rainfall data from nearest station/s (I would say at least from 2 stations with at least 5 years rainfall data). Get the approximation for the factor and calculate with your field finding. I hope with this one can get a safe approximation of base flow for the design of isolated MHP. Or, do not measure this year and just postpone the development for next year.