Hi Michael,
We migrated the SAM website to a new platform in early 2019 and managed to import the old forum content but were not able maintain links between topics, hence the broken links you found. If you send me links to posts that contain broken links, I should be able to manually fix them.
The physical trough's water use for cooling equations are described in the physical trough reference manual (Wagner, 2011) at the end of Section 3.3.3, see Equation 3.25.
sam.nrel.gov/concentrating-solar-power/csp-publications.html
Best regards,
Paul.