+++ Robert Staven [2013-06-26 15:15 +0200]:
Short answer (from cave diving experience): Not much (if the water flow and passage size allows divers to swim thru)
Bit longer (scientific): Assume a 10cm/sec flow, 1 meter diameter tunnel, 10cm wall roughness, 1500 meter length -> http://www.pressure-drop.com/Online-Calculator/ Gives a pressure drop: 7.56 mbar / 0.01 bar
OK, which presumably amounts to a 10cm drop, and each bend, enlargement, and corner adds a few more millibars. That might add another 5-10 mbar total (100 features of 0.1-0.05 mbar each) which is another 5-10cm. Changing the pipe roughness to 500mm gets us 0.03bar, which is 30cm So roughness matters at least as much as corners, but whatever it looks like it seems unlikely (assuming thsese sums are a reasonable model), to have a difference of any more than half a metre. Wookey -- Principal hats: Linaro, Emdebian, Wookware, Balloonboard, ARM http://wookware.org/