Chocolate fireguard
Active member
The second reference given by langcliffe in his 12.01 post today mentioned the Constant Injection Method as being easy to understand but difficult to do in the field.
If I were wanting to do a measurement on a typical smallish fast-flowing mountain stream I think it`s the one I would start with. Because you have to start somewhere.
If you introduce salt at a known rate into a stream then at points downstream the salt passes at the same rate (a bit like the electric current in a circuit being the same at all points I suppose). Obviously you have to allow time for this to happen, you have to sample far enough downstream for complete mixing to have occurred etc - no doubt these and other things will need thinking about.
But for a small fast turbulent stream with no big pools to delay things it should be possible to do a measurement when the introducing and sampling points are 100 metres or less apart, possibly taking much less than half an hour.
The sampling would need specialist equipment (to eventually come up with a concentration), but introduction could be done (accurately enough for trial purposes) with a big bag of salt, a teaspoon measure and a watch.
So if you introduce at 50g per minute and your titration/conductivity measurement says 10g/cubic metre you have 5 cubic metres of water per minute.
As always, repeatability will be a good guide to accuracy.
Feel free to scoff.
If I were wanting to do a measurement on a typical smallish fast-flowing mountain stream I think it`s the one I would start with. Because you have to start somewhere.
If you introduce salt at a known rate into a stream then at points downstream the salt passes at the same rate (a bit like the electric current in a circuit being the same at all points I suppose). Obviously you have to allow time for this to happen, you have to sample far enough downstream for complete mixing to have occurred etc - no doubt these and other things will need thinking about.
But for a small fast turbulent stream with no big pools to delay things it should be possible to do a measurement when the introducing and sampling points are 100 metres or less apart, possibly taking much less than half an hour.
The sampling would need specialist equipment (to eventually come up with a concentration), but introduction could be done (accurately enough for trial purposes) with a big bag of salt, a teaspoon measure and a watch.
So if you introduce at 50g per minute and your titration/conductivity measurement says 10g/cubic metre you have 5 cubic metres of water per minute.
As always, repeatability will be a good guide to accuracy.
Feel free to scoff.