Conversely, a small drainage basin means that water has a shorter distance to travel and will result in a shorter lag time. Circular drainage basins mean that all points on the watershed are equidistant from the channel and this will lead to a shorter lag time and higher peak discharge. Elongated drainage basins are characterised by longer lag times and lower peak discharge as the water drains from the furthest reaches of the watershed to the channel.
A steeply-sided river valley means that gravity assists water in its descent towards the river channel, whereas gently sloping valleys tends to produce longer lag times and lower peak discharges. Both types of rock are characterised by a lack of surface drainage and have high rates of infiltration.
Impermeable rock granite, shale, clay impedes drainage by restricting percolation. These areas are characterised by high rates of overland flow or surface runoff. Sandy soils have high rates of infiltration due to relatively large air spaces or voids between soil particles, whereas clay soils and silts have small pore spaces which allow very little throughflow.
Drainage basins characterised by impermeable rock and soils tend to have higher drainage density due to the lack of infiltration and percolation. This means that water enters a channel quickly, leading to an increase in discharge. Conversely, drainage basins with permeable rock and soil types tend to have low drainage density. Long periods of rainfall often lead to soil reaching field capacity saturation capacity , which impedes infiltration and leads to high rates of surface runoff.
The amount of rainfall which reaches the drainage basin is also influenced by vegetation cover. A drainage basin covered in dense vegetation will experience high rates of interception, root uptake and evapotranspiration - this will reduce the amount of discharge within the basin.
Heavy rainfall may exceed the infiltration capacity of the soil, leading to surface runoff and a rapid increase in discharge. Several weeks of prolonged, heavy rainfall will mean that a drainage basin reaches saturation capacity very quickly after a storm event. This can also lead to a rise in the level of the water table, further increasing the likelihood of saturation capacity being exceeded.
Rates of evapotranspiration are not constant throughout the year in mid-latitude locations like the UK. Low temperatures in the winter reduce evapotranspiration vegetation also experiences reduced growth rates at this time, meaning that there is less root uptake and so less interception.
Urbanisation reduces infiltration to 0 through its use of impermeable surfaces tarmac, concrete , and drains and gutters transport water quickly to the river channel.
Rivers which flow through urban areas are characterised by "flashy" hydrographs and represent a high flood risk. This leads to an increase in rates of infiltration and can result in saturation capacity being reached quickly. Rainfall will travel by overland flow and can lead to high rates of soil erosion without the binding nature of root systems in place. Afforestation has the effect of increasing rates of interception and evapotranspiration.
Basins vary in size: some are small while others span across state or national borders. The Amazon, Congo and Mississippi River basins are the largest drainage basins in the world. According to the U. Army Corps of Engineers, the Mississippi Basin covers an area greater than 1,, square miles, spanning across 31 states and two Canadian provinces.
Catchment basins are vital elements of the ecosystem in which soil, plants, animals and water are all interdependent. Basins are vital to human existence, since they provide clean water for drinking; water for growing food; and water to nourish plant life, which provides the oxygen people breathe.
Historically, basins were also an important factor in determining geopolitical borders. In modern times, the responsible management of river basins is vital to commerce, transportation and agriculture as well as basic human survival. As the North Carolina Office of Environmental Education and Public Affairs correctly points out, "everyone lives in a basin" and therefore the water quality downstream is affected by the actions of all people living on the land that drains into a river, creek, aquifer or other type of water body.
Some of the water may infiltrate much deeper, recharging groundwater aquifers. Water may travel long distances or remain in storage for long periods before returning to the surface. The amount of water that will soak in over time depends on several characteristics of the watershed:.
Evaporation : Water from rainfall returns to the atmosphere largely through evaporation. The amount of evaporation depends on temperature, solar radiation, wind, atmospheric pressure, and other factors. Most of this water moves through the plant and escapes into the atmosphere through the leaves. Transpiration is controlled by the same factors as evaporation, and by the characteristics and density of the vegetation. Vegetation slows runoff and allows water to seep into the ground.
Storage : Reservoirs store water and increase the amount of water that evaporates and infiltrates. The storage and release of water in reservoirs can have a significant effect on the streamflow patterns of the river below the dam. Water use by people: Uses of a stream might range from a few homeowners and businesses pumping small amounts of water to irrigate their lawns to large amounts of water withdrawals for irrigation , industries , mining , and to supply populations with drinking water.
This pool cover is an example of a watershed. All of the rain that falls into this area flows inside of the cover, in this case towards the center. You're expecting to see a picture of a watershed — so why am I showing you a picture of a common swimming pool in winter with a pool cover? This covered pool is really a good example of a watershed.
The blue cover represents the watershed, the area in which precipitation that falls flows "down-gradient" towards the lowest part of the basin, the center of the pool cover in this case. Likewise, in nature, water flows towards a valley, river, or lake. The lake in the center of the pool forms for the same reason that a lake will form on the landscape — it is the lowest area around and the water comes in, through a river, seepage into the ground, or by evaporation, faster than it can get out.
In most valleys, the land slopes downhill somewhere, in which case, a river will form. Do you see why this pool cover is not exactly the same as a real drainage basin?
There is no outlet for water to exit the "watershed", as almost all watersheds have, such as a stream flowing out of the watershed. Thus, in our pool watershed, you can see how a large "lake" is forming. Rain and snow are key elements in the Earth's water cycle, which is vital to all life on Earth.
Rainfall is the main way that the water in the skies comes down to Earth, where it fills our lakes and rivers, recharges the underground aquifers, and provides drinks to plants and animals. The USGS follows four basic steps for collecting streamflow data. The following example uses a streamgage though more portable methods are also frequently used. Read on to learn more. Water is nature is never really totally clear, especially in surface water, such as rivers and lakes.
Water has color and some extent of dissolved and suspended material, usually dirt particles suspended sediment. Suspended sediment is an important factor in determining the quality of water.
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