The difference in level between the top of a bank and supply level in a canal, is called

In irrigation engineering, the difference in level between the top of a bank and the supply level in a canal is termed as the free board. This term refers to the vertical distance between the water level in the canal and the top of the embankment or bank. The free board provides a safety margin to prevent overflow or breach of the canal embankment during high water flow or flooding events.