Peter Schneider wrote: > > Dear all, > I often come across the problem to determine the approximate flow of a > river, just to give people an indication of whether their site is worth > thinking about hydro power. > Of course, the bucket-and-watch method is straightforward, but not really > possible above a certain flow. > I know the weir method, but building an accurate rectangular weir takes > some effort and time. Therefore I am wondering, how accurate is it to use a > natural 'weir' for measurement? Usually, you would not have a sharp edge, and > often not a vertical fall behind it. I know this affects the accuracy, but by > how much? Is it safe to assume e.g. a maximum minus 30% for this? Does anyone > have experience with this? > > Peter Schneider
We frequently use a natural weir to estimate the flow rate of a stream. We may walk up an down a stream for 200m or so above or below a proposed turbine intake site to try and find a place where an identifiable proportion of the stream flows through a notch (usually a rock crevice) that approximates one of the regular notch shapes. Almost always it is a triangular notch. When the stream is perpetually tumbling over rocks in a myriad if little waterfalls and cascades, estimating the flow is difficult. So finding a natural notch is often the only convenient method we have and thus there is no "benchmark" against which the accuracy can be assessed. Other times it is easier and your suggestion of +/- 30% seems reasonable. Remember that there are two modes of uncertainty. The first is in the estimate of the flow rate through the notch, the other is is the estimate of the proportion of the total flow going through the notch. Regards, Max Enfield Planetary Power ------------------------ Yahoo! Groups Sponsor --------------------~--> Has someone you know been affected by illness or disease? Network for Good is THE place to support health awareness efforts! http://us.click.yahoo.com/RzSHvD/UOnJAA/79vVAA/FGYolB/TM --------------------------------------------------------------------~-> Does your company feature in the microhydro business directory at http://microhydropower.net/directory ? If not, please register free of charge and be exposed to the microhydro community world wide! NOTE: The advertisements in this email are added by Yahoogroups who provides us with free email group services. The microhydro-group does not endorse products or support the advertisements in any way. More information on micro hydropower at http://microhydropower.net To unsubscribe: send empty message to [EMAIL PROTECTED] Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/microhydro/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
