Description Of Study Area
The study area is located in the Lake Tana Basin, upper Blue Nile, Ethiopia . It is one of the largest contributing basins of the Lake Tana. The study watershed is located between latitude 10.56° to 11.22° N and longitude 36.44° to 37.03° E. The contributing area of the watershed is 3786 km2 with the longest path of the flow of 141 km. The higher elevation ranges are located at the southeast corner, while the remaining area is relatively uniform. The Shuttle Radar Topography Mission digital elevation model shows that the elevation of the Upper Gilgel Abay varies from 1695 m to3543 m a.m.s.l. The main rainy season of the watershed is from June to September, while the remaining months are dry. It receives annual rainfall between 1200 and 2400 mm. The average minimum and maximum annual temperatures vary between 3.4 and 33 °C from different meteorological stations located in the watershed. Generally speaking, the months of March through May are the hottest month, whereas the lowest temperatures occur during December and January. The upper part of the watershed is steeper slope which is about 70°, while the bottom part of the watershed toward the outlet is gentle slope and about 0°. The main land covers in the Gilgel Abay catchment are grassland, marshland, cultivated land, forest and grassland with frequent patches of shrubs, woods, trees, and cultivated lands. Cultivated land is the most dominated one.
Study area, Lake Tana and Blue Nile Basin and Ethiopia map (
A Watershed Is A Precipitation Collector
Most of the precipitation that falls within the drainage area of a stream’s USGS monitoring site collects in the stream and eventually flows by the monitoring site. Many factors, some listed below, determine how much of the streamflow will flow by the monitoring site. Imagine that the whole basin is covered with a big plastic sheet. Then if it rained one inch, all of that rain would fall on the plastic, run downslope into gulleys and small creeks and then drain into main stream. Ignoring evaporation and any other losses, and using a 1-square mile example watershed, then all of the approximately 17,378,560 gallons of water that fell as rainfall would eventually flow by the watershed-outflow point.
What Is The Largest Ocean Basin On Earth
The Pacific Ocean is the largest and deepest of the world ocean basins. Covering approximately 63 million square miles and containing more than half of the free water on Earth, the Pacific is by far the largest of the worlds ocean basins. All of the worlds continents could fit into the Pacific basin.
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A What Is A System And How Can This Be Applied To Drainage Basins
|Read and make notes on the slides and your textbook
Not All Precipitation That Falls In A Watershed Flows Out
To picture a watershed as a plastic-covered area of land that collects precipitation is overly simplistic and not at all like a real-world watershed. A career could be built on trying to model a watershed water budget . There are many factors that determine how much water flows in a stream :
Precipitation: The greatest factor controlling streamflow, by far, is the amount of precipitation that falls in the watershed as rain or snow. However, not all precipitation that falls in a watershed flows out, and a stream will often continue to flow where there is no direct runoff from recent precipitation.
Infiltration: When rain falls on dry ground, some of the water soaks in, or infiltrates the soil. Some water that infiltrates will remain in the shallow soil layer, where it will gradually move downhill, through the soil, and eventually enters the stream by seepage into the stream bank. 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.
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Storage Water Stored In The System
Interception this is when precipitation lands on buildings, vegetation and concrete before it reaches the soil. Interception storage is only temporary as it is often quickly evaporated.
Vegetation storage this is water taken up by vegetation. It is all the moisture in vegetation at any one time.
Surface storage the total volume of water held on the Earths surface in lakes, ponds and puddles.
Groundwater storage the storage of water underground in permeable rock strata.
Channel storage -the water held in a river or stream channel.
What Phrase Defines Basin
1a : an open usually circular vessel with sloping or curving sides used typically for holding water for washing a new washstand and basin. b chiefly British : a bowl used especially in cooking. c : the quantity contained in a basin spilled a basin of water on the floor.
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Flows And Processes Water Moving From One Place To Another
Baseflow water that reaches the channel largely through slow throughflow and from permeable rock below the water table.
Channel flow the movement of water within the river channel. This is also called a rivers discharge.
Groundwater flow the deeper movement of water through underlying permeable rock strata below the water table. Limestone is highly permeable with lots of joints and can lead to faster groundwater flow.
Infiltration the downward movement of water into the soil surface.
Interflow water flowing downhill through permeable rock above the water table.
Percolation the gravity flow of water within the soil.
Stemflow water running down a plant stem or tree trunk.
Surface Runoff the movement of water over the surface of the land, usually when the ground is saturated or frozen or when precipitation is too intense from infiltration to occur.
Throughflow- the movement of water downslope within the soil layer. Throughflow is fast through pipes .
Stores: When Water Is Stationary And Not Moving In A Drainage Basin
Interception: When water is caught and held by vegetation or man-made structures like buildings.
Surface store: When water is held in the surface of the earth. This may be a puddle, a lake or a garden pond.
Soil moisture store: When water is held in unsaturated soil.
Groundwater store: When water is held in saturated ground.
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Drainage Basin Facts For Kids
It is an area of land. All water that falls on that land flows into one river. It can flow directly into the river or go through tributaries first.
One river can drain a large area. For example, more than half of the United States is drained by the Mississippi and its tributaries. The is similarly large.
Outputs Water Leaving The System
Evaporation the transformation of water droplets into water vapour by heating.
Evapotranspiration the loss of water from a drainage basin into the atmosphere from the leaves of plants + loss from evaporation.
Transpiration evaporation from plant leaves.
River discharge the amount of water that passes a given point, in a given amount of time.
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What Does River Basin Mean
A river basin is the area of land over which surface run-off flows via streams, rivers, and lakes into the sea. A river basin sends all the water that falls within it to a central river, and from there to the ocean. A river basin drains all of the land around a major river. Basins are divided into watersheds, or land areas that surround a small, river or lake.
What Is A River Basin And Why Is It Important
Drainage basins are important in ecology. As water flows over the ground and along rivers it can pick up nutrients, sediment, and pollutants. With the water, they are transported towards the outlet of the basin, and can affect the ecological processes along the way as well as in the receiving water source.
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The Usgs National Water Information System Contains Extensive Real
When looking at the location of rivers and the amount of streamflow in rivers, the key concept is the river’s “watershed”. What is a watershed? Easy, if you are standing on ground right now, just look down. You’re standing, and everyone is standing, in a watershed.
A watershed is an area of land that drains all the streams and rainfall to a common outlet such as the outflow of a reservoir, mouth of a bay, or any point along a stream channel. Watersheds can be as small as a footprint or large enough to encompass all the land that drains water into rivers that drain into Chesapeake Bay, where it enters the Atlantic Ocean. This map shows one set of watershed boundaries in the continental United States these are known as National hydrologic units .
The word “watershed” is sometimes used interchangeably with drainage basin or catchment. Ridges and hills that separate two watersheds are called the drainage divide. The watershed consists of surface water–lakes, streams, reservoirs, and wetlands–and all the underlying groundwater. Larger watersheds contain many smaller watersheds. It all depends on the outflow point all of the land that drains water to the outflow point is the watershed for that outflow location. Watersheds are important because the streamflow and the water quality of a river are affected by things, human-induced or not, happening in the land area “above” the river-outflow point.
Great Lakesst Lawrence Drainage
This basin is dominated by the Great Lakes, covering 245,000 km2. About one half the basin is Canadian, Lake Michigan is wholly within the US and the international boundary passes through Lakes Superior, Huron, Erie, Ontario and St Clair. Most of the land drainage from the Canadian portion is from the Canadian Shield the St Lawrence Lowlands make a small contribution. The lowlands include peninsular Ontario, bounded by Georgian Bay, Lake Huron, St Clair, Erie and Ontario as well as the fringes of the St Lawrence River. The Great LakesSt Lawrence system provides an important navigable waterway of nearly 4,000 km from Ile d’Anticosti to the head of Lake Superior .
Most streams in the lowlands are less than 300 km long. They are important for industry, agriculture and urban water supply, and provide recreational opportunities for the region’s urban population. The intensive land use in the southern parts of the basin results in high variability of seasonal flows, localized flooding, periodic low summer flows and impaired water quality.
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Transfers : When Water Is Moving Within A Drainage Basin
Stem flow: When intercepted water runs down the trunks and stems of vegetation.
Canopy drip: When intercepted water drips off the leaves of vegetation .
Throughfall: Precipitation that falls directly through vegetation.
Infiltration: Water that moves from the surface of the earth into the soil below.
Throughflow: Water that travels through unsaturated ground.
Pipeflow: Water that travels through holes left by root systems and animals burrows.
Percolation: Water that travels from unsaturated into saturated ground.
Groundwater flow : Water that travels through saturated ground.
Capillary action : Water that may move upwards towards the surface.
Channel flow: Water that travels in a river.
Surface run-off : When water travels across the surface of the earth e.g. down a hill.
What Is An Example Of A River Basin
A couple of specific examples of river basins include the Amazon, Mississippi, and Congo River basins. The Amazon River basin is the largest in the world, is found in South America, and flows into the Atlantic Ocean. The Mississippi River basin covers nearly 40% of the lower 48 states and flows into the Gulf of Mexico.
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Why Are Watersheds Important
What are watersheds? How to find them? Why are they important? Watch permaculture instructor Andrew Millison’s highly informative video if you want to know more.
Another good knowledge booster video on watersheds can be found here, made by Time for Geography.
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The Water Budget Equation
Eep! Equations. Dont worry, these equations are easy , although there is a bit of Greek in them. The water budget equation relate precipitation \, evapotranspiration \, run off \ & soil water storage \. If you have a value for three of those variables, you can find the other one using simple addition. To find precipitation, for example:
That triangle is the Greek letter delta, it means change in, so that equation reads as precipitation = evapotranspiration + run off + change in soil water storage. Youve already met precipitation, evapotranspiration and soil water storage but whats run off? Run off is the volume of water passing the watershed that is, flowing out of the drainage basin and into another one.
Typically, we use the water budget equations to calculate the amount of water stored in the soil rather than the precipitation in the drainage basin because its a lot easier to measure all the other variables than it is to measure the volume of water stored in the soil. From this point on, when I talk about the water budget, Im referring to the amount of water stored in the soil with respect to precipitation, evapotranspiration & run off.
You can graph the water budget if you want. If you plot evapotranspiration and precipitation on one axis and the month on another, youll get two curves. Heres an example for a drainage basin in the UK or some other temperate climate:
Yet still not particularly fast. At top speed were talking less than 0.5mh-1.
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Western Hudson Bay And Mississippi Drainage
This region of 2.64 million km2 includes all of Manitoba, most of Saskatchewan, the southern third of Alberta, most of the District of Keewatin, a part of Ontario west of Lake Superior and about 150,000 km2 immediately south of the CanadianUS border. A 27,500 km2 zone of southern Saskatchewan and southeastern Alberta drains into the Mississippi Basin and then to the Gulf of Mexico.
The most important section of the drainage basin is the 1 million km2 drained by the SaskatchewanNelson river system. The Bow, Oldman and North and South Saskatchewan rivers rise on the eastern slopes of the Rockies and flow east for 1,900 km through the central plains. Extensive tracts in the plains region drain into interior depressions . Many of these sloughs have no outlet, and many others have outlets only in the wetter years to the principal streams which enter a chain of lakes in south-central Manitoba. Here the flow is joined with that of the Red River flowing in from the south and the Winnipeg River from the east. The latter carries drainage from southeastern Manitoba, the Lake of the Woods region of Ontario and Minnesota. The flow discharges from Lake Winnipeg into Hudson Bay via the Nelson River.
Outputs: When Water Leaves A Drainage System
Evaporation: The process of water turning from a liquid into a vapour. Evaporation only takes place from a body of water e.g. a lake, puddle or the sea.
Transpiration: The evaporation of water from vegetation.
Evapotranspiration: The combined action of evaporation and transpiration
Interbasin transfer: Water that either naturally or with human involvement moves from one drainage basin to another.
River discharge via channel flow: Water entering the sea and leaving a drainage basin. A very small amount of water also enters the sea via throughflow and groundwater flow .
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|May 7, 2015
A drainage basin is an area of land that contributes the water it receives as precipitation to a river or network of rivers. Drainage basins are defined by topographical features, called drainage divides, which determine the direction the water flows. Canada has six major drainage basins: the Arctic, Pacific, Western Hudson Bay and Mississippi, South and East Hudson Bay, Great LakesSt Lawrence and Atlantic.