Streamflow, or channel runoff, is the flow of water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 in stream

Stream

A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...

s, river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

s, and other channel

Channel (geography)

In physical geography, a channel is the physical confine of a river, slough or ocean strait consisting of a bed and banks.A channel is also the natural or human-made deeper course through a reef, sand bar, bay, or any shallow body of water...

s, and is a major element of the water cycle

Water cycle

The water cycle, also known as the hydrologic cycle or H2O cycle, describes the continuous movement of water on, above and below the surface of the Earth. Water can change states among liquid, vapor, and solid at various places in the water cycle...

. It is one component of the runoff of water from the land to waterbodies, the other component being surface runoff

Surface runoff

Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...

. Water flowing in channels comes from surface runoff from adjacent hillslopes, from groundwater

Groundwater

Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

 flow out of the ground, and from water discharged from pipes. The discharge

Discharge (hydrology)

In hydrology, discharge is the volume rate of water flow, including any suspended solids , dissolved chemical species and/or biologic material , which is transported through a given cross-sectional area...

 of water flowing in a channel is measured using stream gauge

Stream gauge

A stream gauge, stream gage or gauging station is a location used by hydrologists or environmental scientists to monitor and test terrestrial bodies of water. Hydrometric measurements of water surface elevation and/or volumetric discharge are generally taken and observations of biota may also be...

s or can be estimated by the Manning equation. The record of flow over time is called a hydrograph

Hydrograph

A hydrograph is a graph showing the rate of flow versus time past a specific point in a river, or other channel or conduit carrying flow...

. Flood

Flood

A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...

ing occurs when the volume of water exceeds the capacity of the channel.

Role in the water cycle

Streamflow is the main mechanism by which water moves from the land to the oceans or to basins of interior drainage.

Measurement

There are a variety of ways to measure the discharge of a stream or canal. A Stream gauge

Stream gauge

A stream gauge, stream gage or gauging station is a location used by hydrologists or environmental scientists to monitor and test terrestrial bodies of water. Hydrometric measurements of water surface elevation and/or volumetric discharge are generally taken and observations of biota may also be...

 provides continuous flow over time at one location for water resource and environmental management or other purposes. For purposes that do not require a continuous measurement of stream flow over time, current meters or acoustic Doppler velocity profilers can be used. For small streams — a few meters wide or smaller — weir

Weir

A weir is a small overflow dam used to alter the flow characteristics of a river or stream. In most cases weirs take the form of a barrier across the river that causes water to pool behind the structure , but allows water to flow over the top...

s may be installed. One informal method that provides an approximation of the stream flow termed the Orange Method or Float Method is:

1. Measure a length of stream, and mark the start and finish points. The longest length without changing stream conditions is desired to obtain the most accurate measurement.
2. Place an orange at the starting point and measure the time for it to reach the finish point with a stopwatch. Repeat this at least three times and average the measurement times.
3. Express velocity in meters per second. If the measurements were made at midstream (maximum velocity), the mean stream velocity is approximately 0.8 of the measured velocity for rough (rocky) bottom conditions and 0.9 of the measured velocity for smooth (mud, sand, smooth bedrock) bottom conditions.

Flow monitoring in the United States

In the United States, streamflow gauges are funded primarily from state and local government funds. In Fiscal Year 2008 the United States Geological Survey

United States Geological Survey

The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...

 (USGS) provided 35 percent of the funding for everyday operation and maintenance of gauges.

Relationship to the environment

Runoff of water in channels is responsible for transport of sediment

Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

, nutrient

Nutrient

A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

s, and pollution

Water pollution

Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....

 downstream.

Relationship to society

Streamflow confers on society both benefits and hazards. Runoff downstream is a means to collect water for storage in dams for power generation of water abstraction. The flow of water assists transport downstream. When the flow of water exceeds the capacity of the channel, flooding occurs.

See also

• Discharge (hydrology)
  Discharge (hydrology)
  In hydrology, discharge is the volume rate of water flow, including any suspended solids , dissolved chemical species and/or biologic material , which is transported through a given cross-sectional area...
  
  
• Drainage basin
  Drainage basin
  A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...
  
   or watershed
• Drainage network
• Erosion
  Erosion
  Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
  
  
• Hydrological modelling
  Hydrological modelling
  Hydrologic models are simplified, conceptual representations of a part of the hydrologic cycle. They are primarily used for hydrologic prediction and for understanding hydrologic processes. Two major types of hydrologic models can be distinguished:...
  
  
• Losing stream
  Losing stream
  A losing stream, or influent stream, is a stream or river that loses water as it flows downstream. The water infiltrates into the ground recharging the local groundwater, because the water table is below the bottom of the stream channel...
  
  
• Runoff model (reservoir)
  Runoff model (reservoir)
  A runoff model is a mathematical model describing the rainfall - runoff relations of a rainfall catchment area, drainage basin or watershed. More precisely, it produces the surface runoff hydrograph as a response to a rainfall hydrograph as input...
  
  
• Surface runoff
  Surface runoff
  Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...
  
  
• Stream bed
  Stream bed
  A stream bed is the channel bottom of a stream, river or creek; the physical confine of the normal water flow. The lateral confines or channel margins, during all but flood stage, are known as the stream banks or river banks. In fact, a flood occurs when a stream overflows its banks and flows onto...
  
  
• Water resources
  Water resources
  Water resources are sources of water that are useful or potentially useful. Uses of water include agricultural, industrial, household, recreational and environmental activities. Virtually all of these human uses require fresh water....