Next day, refill each hole with water to a depth of at least 300mm and observe the time in seconds for the water to seep away from 75% full to 25% full (i.e. a depth of 150mm).
Y diwrnod wedyn, ail-lenwch bob twll â dŵr i ddyfnder o 300mm o leiaf ac amserwch faint o amser (mewn eiliadau) fydd hi'n ei gymryd i'r dŵr dreiddio i ffwrdd, o 75% llawn i 25% llawn (h.y.