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.
The NH Department of Environmental Services has written the Lamprey River Water Management Plan (Instream Flow Plan) that seeks to ensure survival of aquatic organisms based on statistically normal flows throughout the year. Active management is based largely on restricting water use by registered water takers (such as municpalities) and releasing water from key dams during times of low flow.