Flow refers to the volume of water in the river flowing past a point in one second and is given in cubic metres of water per second. A cubic meter per second can be written as m3/s, or cumecs, and equals 1000 litres per second. To give you an idea about how much water that is, 0.7 m3/s would fill an Olympic swimming pool in an hour. A flow of 42 m3/s would fill the same pool in a minute.