Groundwater is the world’s second most abundant fresh water source behind the ice caps and glaciers. It accounts for some 30.1% of the Earth’s freshwater reserves whilst surface water sources such as lakes, rivers and reservoirs only account for about 1.2%. Velocities of groundwater flow generally are low and are orders of magnitude less than velocities of streamflow.
A velocity of 1 meter per day or greater is a high rate of movement for groundwater, and groundwater velocities can be as low as 1 meter per year or 1 meter per decade. In contrast, velocities of streamflow generally are measured in meters per second. A velocity of 1 meter per second equals about 86 kilometres per day.
