Rain and snow are also known as precipitation. All water in lakes, streams, and ponds, and the water we pump from wells for drinking and other uses, began by falling from the atmosphere as precipitation.
Other forms of precipitation include hail, fog, hoar frost and dew. These are generally not important for water supply in temperate regions such as New Brunswick, but can be important in very dry climates, for example deserts such as the Atacama desert in Chile or the Namib desert in southwest Africa.
The water we pump from a drilled or dug well is known as groundwater. Groundwater is water which exists usually some depth below the ground surface, and is stored in the cracks and fissures in bedrock, or in the spaces between stone particles such as sand and gravel. Zones in the ground where void spaces are filled with water are termed saturated.
The source of groundwater is precipitation, which has made its way into the ground under the influence of gravity. Groundwater often flows beneath the surface in similar patterns to above-ground flow in streams, except that groundwater flow is much slower. A zone of gravel, fractured rock or other water-bearing layers of the earth can be used as a supply of water and is often called an aquifer.
Stream flow is the quantity of water flowing in a river or stream, and is usually measured in units such as cubic metres or cubic feet per second. Stream flow may be measured in various ways. Routine monitoring is often done at specially constructed weirs or flumes, where the flow of the stream is related to the water level or height of the water surface (known as the stage). Alternatively, many flow measurements are made at points across the natural stream bed at the gauging location. The measured flow is then calculated from the stage.
Large rivers have flows of tens to hundreds of cubic metres per second, whereas stream flow in smaller streams in dry periods may be less than 1 cubic metre per second.
Stream flow on this web page is shown as a percentage of normal. The "normal" is a long-term average, usually based on the most recent 30 years of record. Percentages less than 100 indicate below-normal flow, whereas values over 100 indicate above-average flow.
Long term average, or normal
The long-term average, or normal, is the average against which monthly or daily river flows, precipitation amounts or groundwater levels are compared. A long term average is, wherever possible, based on 30 years worth of results, but shorter periods may be used if a sufficiently long record does not exist.