Editing Water wheel (section)

=== Measurements ===
[[File:HeadMeasurement.svg|thumb|Parameters for measuring the head and flow rate of a water wheel]]

The pressure head <math>h_p</math> is the difference in height between the head race and tail race water surfaces. The velocity head <math>h_v</math> is calculated from the velocity of the water in the head race at the same place as the pressure head is measured from. The velocity (speed) <math>v</math> can be measured by the pooh sticks method, timing a floating object over a measured distance. The water at the surface moves faster than water nearer to the bottom and sides so a correction factor should be applied as in the formula below.<ref name="USFS">{{cite web|title=Float Method for Estimating Discharge|url=https://www.fs.fed.us/ARMdata/PDFfiles/floatmethod.doc |publisher=United States Forest Service|access-date=24 February 2017}}</ref>

There are many ways to measure the [[Flow measurement|volume flow rate]]. Two of the simplest are:
*From the cross sectional area and the velocity. They must be measured at the same place but that can be anywhere in the head or tail races. It must have the same amount of water going through it as the wheel.<ref name="USFS"/>
*It is sometimes practicable to measure the volume flow rate by the bucket and stop watch method.<ref name="SoW">{{cite web|last1=Michaud|first1=Joy P.|last2=Wierenga|first2=Marlies |title=Estimating Discharge and Stream Flows|url=https://fortress.wa.gov/ecy/publications/documents/0510070.pdf |publisher=State of Washington|access-date=24 February 2017}}</ref>