what causes changes in stream course

What causes stream flow patterns to change over time?

A long-term trend toward an earlier date could be caused by earlier spring snowmelt, more precipitation falling as rain instead of snow, or other changes in precipitation patterns. Figure 5 shows trends in the number of days each year with very low flow, which indicates whether streams are becoming drier or wetter during the period.

How do human activities affect stream flow patterns?

Human actions that can change streamflow patterns include dam building, stream diversion, pumping of shallow groundwater, and covering the landscape with impervious surfaces such as pavement and roofs. Changes in climate also can alter flow by altering timing and amount of precipitation.

What are the factors that affect stream discharge?

There are several factors that affect stream discharge. The velocity of the water affects it; faster water means more passes per second so more discharge. The width and depth of the river also affects it; a larger river at the same speed will have higher discharge.

Why are streams so narrow and shallow?

Vegetation along the streambanks provides resistance to erosion so our streams are often narrower than streams in more arid regions. The mean depth of a stream varies greatly from reach to reach depending on channel slope and riffle/pool or step/pool spacing.

Why do streams change course?

Initially, when a slight curve is already present in the river, water travels around the outer edge of the curve faster than the inner edge, because it's covering a greater distance in the same amount of time. As water moves faster, more of the sediment in it stays suspended, instead of settling to the bottom.

How does the stream change?

The speed of the water in a stream depends on its slope. The steeper the slope, the faster the water moves. Fast-moving or large streams can carry more sediment than slow-moving or small streams. Abrasion occurs as sediment in a stream collides with rock in and along the stream.

What can affect stream discharge?

There are several factors that affect stream discharge. The velocity of the water affects it; faster water means more passes per second so more discharge. The width and depth of the river also affects it; a larger river at the same speed will have higher discharge.

What factors affect stream speed?

The velocity of a river is determined by many factors, including the shape of its channel, the gradient of the slope that the river moves along, the volume of water that the river carries and the amount of friction caused by rough edges within the riverbed.

What factors affect stream flow?

Mechanisms that cause changes in streamflowRunoff from rainfall and snowmelt.Evaporation from soil and surface-water bodies.Transpiration by vegetation.Ground-water discharge from aquifers.Ground-water recharge from surface-water bodies.Sedimentation of lakes and wetlands.More items...

What causes stream discharge to change over time?

Discharge increases as more water is added through rainfall, tributary streams, or from groundwater seeping into the stream. As discharge increases, generally width, depth, and velocity of the stream also increase.

What causes variation in river discharge?

Destruction of vegetation (deforestation) – Less infiltration + interception causes more surface run off and increases speed of the water. River Management – Presence of dams allow river flow to be controlled, which may cause more discharge (before the dam) , or less (below the dam).

What are the factors affecting the rivers?

Factors affecting river regimes: precipitation including storm hydrographs, temperature, vegetation, land-use, water abstraction, dams.

How does human activities change the river discharge?

The most significant impacts of human activity on WD occurred in the 1980s, where the contribution of human activities to WD increase was 56%. Deforestation in the watershed will lead to soil erosion and water loss, which will increase water discharge.

Which two factors will increase the rate of a streams flow?

Flood Erosion and Deposition: As flood waters rise, the slope of the stream as it flows to its base level (e.g., the ocean or a lake) increases. Also, as stream depth increases, the hydraulic radius increases thereby making the stream more free flowing. Both of these factors lead to an increase in stream velocity.

What three variables influence the speed of stream flow?

What three variables influence the speed of stream flow? Stream gradient, stream discharge, and channel growth.

What affects stream health?

Urban development is strongly associated with stream degradation, and much of that impact is due to storm water runoff from impervious surfaces (basically roads, parking lots, sidewalks, buildings, and other hard surfaces). Salt and other minerals applied to roads are also bad for many aquatic organisms.

Streamflow and the Water Cycle

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Importance of rivers

Rivers are invaluable to not only people, but to life everywhere. Not only are rivers a great place for people (and their dogs) to play, but people use river water for drinking-water supplies and irrigation water, to produce electricity, to flush away wastes (hopefully, but not always, treated wastes), to transport merchandise, and to obtain food.

Streamflow is always changing

Streamflow is always changing, from day to day and even minute to minute. Of course, the main influence on streamflow is precipitation runoff in the watershed.

Hydrologists study streamflows with hydrographs

USGS uses a hydrograph to study streamflow in rivers. A hydrograph is a chart showing, most often, river stage (height of the water above an arbitrary altitude) and streamflow (amount of water, usually in cubic feet per second). Other properties, such as rainfall and water-quality parameters can also be plotted.

Precipitation influences streamflow

On Dec. 24, 2002, about two inches of rainfall fell in the Peachtree Creek watershed. This provides a good example to describe streamflow characteristics during a storm since the rain fell for only a few hours on that day and Peachtree Creek was at base-flow conditions before the rain started.

Mechanisms that cause changes in streamflow

Rivers are always moving, which is good for everything, as stagnant water doesn't stay fresh and inviting very long. There are many factors, both natural and human-induced, that cause rivers to continuously change:

Streamflow and global water distribution

Even though the water flowing in rivers is tremendously valuable to not only people but also to much of life on Earth, it makes up just a miniscule amount of Earth's water.

How does the discharge of a river change?

But there are still ways that the discharge of a river can change. Discharge changes whenever you add or take away water. In a hot area, some discharge will be lost through evaporation. When it rains, the river's discharge will increase, too.

What happens when the discharge of a river increases?

When discharge increases, usually all the parts of the equation increase together. The velocity of the river increases, the width of the river increases, and the depth of the river increases. The latter two happen due to increased erosion. Let's go through an example of how to use the discharge equation.

How to calculate stream discharge?

You can calculate stream discharge using this equation: the discharge equals the velocity in meters per second multiplied by the width of the stream in meters multiplied by the depth of the stream in meters.

What is stream discharge?

Stream discharge is the amount (volume) of water carried by a stream past a point per second. It is measured in meters cubed per second or cubic feet per second. There are several factors that affect stream discharge. The velocity of the water affects it; faster water means more passes per second so more discharge.

Does stream discharge change from one part of the river to the next?

Generally, stream discharge doesn't change from one part of the river to the next. The same amount of water has to flow all the way down the river, otherwise you would get gaps in the river flow at one location and have the water build up at another location.

Does stream discharge change?

Generally, stream discharge doesn't change from one part of the river to the next. The same amount of water has to flow all the way down the river. The water all has to go somewhere, so it needs to keep flowing at the same rate.

What are the factors that affect the size of a stream?

Other factors which affect channel size and stream flow are land use, soil types, topography, and climate. The morphology, or size and shape, of the channel reflect all of these factors.

Why is channel slope irregular?

The profile of the streambed can be irregular because of variations in bed material size and shape, riffle/pool spacing, and other variables.

What is the most important process in defining channel form?

The most important stream process in defining channel form is the bankfull discharge, which is sometimes referred to as the effective discharge, or dominant discharge. Bankfull discharge is the flow that transports the majority of a stream’s sediment load over time and thereby forms the channel.

What is the function of riffles in a stream?

At low flows, water moves faster over riffles, which provides oxygen to the stream. Riffles are found entering and exiting meanders and control the streambed elevation. Pools are located on the outside bends of meanders between riffles. The pool has a flat slope and is much deeper than the average depth.

What is an entrenchment stream?

Entrenchment – A vertical description of the stream. Flood flows in an entrenched stream are contained within the streambanks or adjacent terraces. Flood flows in a stream that is not entrenched are spread out over a floodplain. For the purpose of this fact sheet, entrenchment and incision are synonymous.

How are perennial streams formed?

These streams are partially supplied by groundwater rising to the surface as stream baseflow. They dry up when groundwater levels drop. Further downstream where baseflow is large enough to sustain stream flow throughout the year, perennial streams are formed.

What is stream pattern?

Stream pattern describes the “plan view” of a channel as seen from above. Streams are rarely straight. They tend to follow a sinuous path across a floodplain. The sinuosity of a stream is defined as the channel length following the deepest point in the channel (the thalweg) divided by the valley length.

How does streamflow affect the environment?

Streamflow is a measure of the rate at which water is carried by rivers and streams, and it represents a critical resource for people and the environment. Changes in streamflow can directly influence the supply of drinking water and the amount of water available for irrigating crops, generating electricity, and other needs. In addition, many plants and animals depend on streamflow for habitat and survival.

Where are low flows decreasing?

Low flows have generally decreased in parts of the Southeast and the Pacific Northwest (that is, streams are carrying less water than before). Overall, more sites have experienced increases than decreases (see Figure 1). Three-day high-flow trends vary from region to region across the country.

What is the trend of three day high flows?

Three-day high-flow trends vary from region to region across the country. For example, high flows have generally increased or changed little in the Northeast since 1940, whereas high flows have increased in some West Coast streams and decreased in others.

Does precipitation increase streamflow?

More precipitation is expected to cause higher average streamflow in some places, while heavier storms (see the Heavy Precipitation indicator) could lead to larger peak flows. More frequent or severe droughts, however, could reduce streamflow in certain areas.