What is water quantity?

 flow gage in Newmarket

 photo by usgs.gov

Water quantity in a river is largely defined by the flow of the river. The flow of a river is usually measured in cubic feet per second (cfs). The flow is determined by gages in various locations along the river. During spring snow melt or following a strong rain storm, the river height and rate of flow increase. During droughts, the water level and flow decrease. A river in a natural state has a range of flows. A river with dams can sometimes be managed to keep water levels in the impoundment behind the dam higher than normal during a drought. The area behind a dam can also experience more severe flooding than normal during a severe rain event.