The Drainage Basin

Components of the drainage basin - Soil storage, percolation and throughflow

-Clay has small pores and does not let water passs thorugh it easily. It is imperable and hold water well Sandy soil has lots of lkarge poors so wqater passes through it easily. It is porus and is very permeable A permeanble soil allows wate4r to pass through it in two wayts. Water that flows down into the bedrock which is percolation. Water that flows downhill through the soil, parallel to the surface which is throughflow

Influences on the shape of the storm hydrograph- Precipitation

-Prolonged rainfall leads to saturated ground and lots of overland flow Intense rainfall means that the infilitation capacity is exceeded - produces lots of overland flow -Snowfall - Cant flow into the river as frozen, cause lots of precipitation when it melts, ground is imperable so waer runs over it.

The drainage basin system and human activity

Actual evpotransipirtion is the amount of water that leaves the drainage basin in the form of water vapouir going back into the atmosphere. Potential is the amount of waterthat could go back if an unlimtuied amount of soil moisture was available.

Use of river water

Agriculture Indsutiral Domestic use

Types of hydrographs

Annual - showing river's discharge ove the course of one year Storm - How a rivers ducharge changes over a short period of time due to a single impit of rainfall

Key Words

Discharge - Amoutn of water in the river channel> It varies over tiem and is the reuslt of rainfwater flwoinmg into the channel through differnet methods of slowing Cimecs: Cublic metre of water per seconds Approach segement: The discharge before the rainstorm Rising limb: The dischjarge rises steeply after the storm; mostly due to overland flow Approach segement: Discharge risies steeppll after a storm Bankfull discharge - When the river channel is completely full Peak discharge - Highest level that a river reaches during a flood Lag time- The time between the maxiumum rainfall and the peak discharge . Drainfage basins with a lot of overland flow have a short lag time Falling limb - River level falls after peak discharge Stormflow- Stream discharge after a rain storm Baseflow - Stream discharge produced by water seeping from the edrock.

Where does deposition occur?

During a period of low discharge where there has been a dry spell with no rain On the inside of a meander bend When a river bursts its bank When the load is increased Whenthe river enters the still water of a lake or the sea

What is erosion?

Erosion is the wearing away of the surface of the Earth. It is an active process, involving movement. Rivers erode their channels as they flow downstream towards the sea. rivers have energy because the river water has mass and velocity and some of this energy is used to erode the river.

What are the outputs of the drainage basin?

Evapotrainspiration and channel flow.

Soft engineering flood strategies

Floodplain zoning Rely on washlands Plant trees in the upper part of the drainage basin Wetland and river bank conservation scheme River restoration scheme

Drainage Basin characteristics - Vegetation type and land use

Forestes reduce discahrge due to increase interception and greater evporation and transpiortion. Any land-use that creates imperable surfaces or reduces vegetation cover tends to icnrease overland flow and river dischatg. Pasture land allows rainfall to soak into the ground, but has less evpotransotion than foreseted increasing river discharge

Influences on the shape of the storm hydrograph- Vegetation

Forests encourage interception, evapotransipatrion and infiltration Forested areas have small flood peaks.

Factors that affect river discharge - Transpiration and evaportrainspiration

Forests in a river basin tend to reduces the discharge of the rive . INcreased interception and transpirtation means that evapotranspirtation coud be more of an output from the drainage basion than river discahrge Vegretation also encouragfes infiltiation and throughlow rather than overland flow. This reduces the speed at whicjh raomfa;; reacjes the rover, reducing river levels.

Factors that affect river discharge - Antecendent moisture

If the ground is already ssaturaed from pervious raifnalll, a new input of rain willl not be able to infialtre into the soiul, causing large amounts of overland flow and increasing discharge rapidly

Components of the drainage basin - Throughfall and stemflow

In a prolonged rainstorm, the leaves become saturated and water will begin to drip to the ground. Stemflow is another important way in which water moves from the tree to the ground, simply flowing down the outside of the tree trunk

Water storage

In agriculture water storage, water is stored for later use in natural water sources, such as groundwater aquifers, soil water, natural wetlands, and small artificial ponds, tanks and reservoirs behind major dams.

Influences on the shape of the storm hydrograph- Temperature

In summer it is warm so evaporation is high. In winter evaporation is low so more precipitation goes into the river. Frozen gorund leads to overland flow

Factors that affect river discharge - Seasonaility

In temperatre areasp f the world, such as Ireland the seasoson of the year has an importance imfluicne of river discharge.The cold the weather, redices the evaporation rates which reduces evpotranspoiration rates. Rainfall loccurs in the summer increasing river idshcarge in tropical monsson areas.

Causes of flooding

Intense rainfall, Rapid snowmelt, Imperable snow, Lack of vegetation Cold temperatures reduce evapotranspiration Deforestation, urbanisation, Mechanised farming, Acid rain Global climate change

What is a long profile of a river channel.

It is a line drawn from the source of the river to the mouth. It shows how the gradient of the river channel changes as it flows downhill. The typical long profile is concave. Steeper in hill and gentler in the lowlands.

Ground water

It is an important source of freshwater. Wells can be dug and boreholes cnas be drilled down to the water table and the groundwater can be extracted. Because it has been filitered through the rocks the water is usually very pure. This water is a renwable source but could dry up if extracted to quickly

What is the drainage basin as a system?

It is an open, dynamic system: Open because water and energy flow into, through and out of it. Dynamic because the system respsonds t o dchanges in its imputs e.g. river discharge varies in response to changing imputs of precipitation.

What is the sinuosity of a river?

It is measure of how bendy it is. It is calculated by dividing the lengrth of the river channel by the length of the valley in which is flows. This can be done for the whoel river or parts. A perfectly straight river will have a sinuosity of 1.0 but natural rivers are rarely this. Anything less than 1.5 is considered to be straight while a river over 1.5. is consdeired ot be meandering

What is abrasion?

It is sometimes called corrasion. A river uses it laod of sediment to wear away its bed and banks. In the uplands, pebbles get caught in hollows in the river bed. As they swirl around, the process abrasion produces a pothole.

What is the water budget?

It is the balance bwtween the precipation and potential evapotranspiration It is an accoutnign of the imputs and outputs of the water and can be calculated by the imputs, outputs and storage chainsees of water. Imput is allows precipation and outputs are evpotransiproiation and channel flow

What is hydraulic action?

It is the direct force of the flowing river water can break material from the bed and the banks. Even more powerful is the related process of cavitation, the force of exploding air. Powerful eddies in the flowing river compress and decompress water in cracks in the river which lead to formation of air bubbles in the water which weakening cracks and lead to rocks breaking off.

What is a floodplain?

It is the flat land next to the river which is liable to flood when the river rises after heavy rainfall. They are often badly dreained with marshes and ox-bow lakes. They unhealthy due to diseases found in them. Laterial erosion is common here. They are surrounded by natura enbankments of the river called levees.

Factors that affect river discharge - Precipitation

It is the major factor affecting 4river discharge because it is the only input into the system. Large amounts of rainfall will cause river levels to rise while a period of dry weather will lead to falling river levels. The type and intenstiy ofg rainfall are also important as heavy rainfall will excceed the infiltration capcity quickly.

What is sedimentation?

It occurs when river sediement is deposited from still water. Common on floodplains and on the seabed. On the sed bed it is aided by flocculation, the way that charged ions insea water allow clay particles to coagulate together and settle out of suspension. The bottomset, fforest and topset bed in a delta are produced by sedimentation.

The drainage basin as a system

Iti is the part of the hydrological cycle which operates once rain has fallen onto a drainage basin. It is known as the draige basin as it has imputs, stores, flows and outputs.

How to calculate bed roughness?

Manning's N (Roughness coeffeicent)= Hydraulic radius^0.67 x Channel Gradient^0.5 ------------------------------------------------ Mean velocity of the flow

What are meandering river channels.

Most rivers meader to some exrtent. Upland steams meander but the most pronounced meadewrs are found on lfoodplains where lateral erosion is facilitated by the soft nature of the river banks. Meanders are so common because spiralling is the normal behaviour of moving lfuods on the surface of a rotating plannel. Rivers are cofiend to channels to the tendency to spiral downwards produceds helicoidal flow.

What are the flwos in the drainage basin?

Overland, throughflow, baseflow.

What is the imput of the drainage basin?

PRecipitatio, Sunlight

What is attrition?

Particles of sediemtn in the load of the river bump into each other and wear each other away. As a result, river sediment becomes smaller and more rounded as it is carried downstream

how do people use water

People use freshwater which equates to less than 1 per cent of all the water on the planet.

Drainage Basin characteristics - Rock type

Permeable rocks allow water to pass throgujh them for different reasons. Granite and limestone contrain tiny crakcs, mostly vertically joints and horizontal bnedding planes. Water can percolate down through these rocks along the cracks and the rocks are called pervious as a reuslt.

Influences on the shape of the storm hydrograph- Soil and rock type

Permeable soil and rock reduce overland flow and enhance throughflow and baseflow Impermeable rock and soikl enhances surface run off

What are potholes?

Potholes are formed by turbances which swirls pebbles around in a depression on the river bed. The swirling pebbles enlarge the pothoels by the process of abrasion. They are usually quite small features and they are evidence that verticle erosion predominates in uplands rivers.

Components of the drainage basin - Precipitation and interception

Precipitation Water falling from the sky- rain is most important form Interception This is the rain which is intercepted before it reaches the ground. Usually by vegetation especially by leaves and trees. During a short summer shower it is possible to stay dry by standing under a tree because the tree's leaves intercept and store the raindrips before they reach the ground

How does a flood predition work?

Rainfall radar can plot the approach of depressions and other rain-bearing weather systems. These data are fed into the PC system Tipping rain gugages throughout the basin monintor amount of rainfall falling Automatic river discharge gauhaes monitor the risijng rivers levels and this added to the system data The systems database includes a model of the way the drainage basin behaves throughout the year

Components of the drainage basin - Channel Flow

Rainfall reaches the river via overland, throughflow and baseflow. Once it is in the river it flows downhill towards the sea as river discharge. This is another output

What are rapids?

Rapids are common along the upper course of the river. They form at palces where the gradient is steep and the river bed is rocky, resistant to erosion and irregular. They are usually caused by a band, or bands, or hard rock in the riverbed.

River Flow - Factors affecting energy of the river

Rivers have kinetic energy as they have a mass and velocity Discharge is affected by precipation and charactersitics of the basin. Velocity is affected by range of factors with friction and gradient the most important Rivers in lowland with a gentle gradient with smooth bed flow faster than rivers in upland with the opposite.

Drainage Basin characteristics - Size and shape of the drainage basin

Smaller drainage basin collect less rainfall therefore their discharge is wsmalle . They asl resposbily more rapidly to inputs of water. Basin shape affects floodomg. Circular basisn response more promptly to rainfalll inputs nad have qa higher discharge than long, narrow basins of a similar area

Equation for water budget

Soil Storage = Precipiation - Channel flow out of the basin - Evapotranspiration

What is solution?

Sometimes called corrosion. Natural river water is often slightly acidic and it can dissolve rocks such as chalk and limestone

Influences on the shape of the storm hydrograph- Basin Relief

Steep slopes and high relief in the drainage basin tend to get water to the river quickly and create high flood peaks

What are the three types of river channel?

Straigh Meandering Braided

What are pools and riffles

Straight rivers develop deeper sectiosn where erosion dominates (pools) ad shallower sections, sediment deposited (riffles). Process not fully understood by could be related to helicoidal flow and thalweg.

Influences on the shape of the storm hydrograph- Urbanisation

Tarmac and concrete increase overland flow, so water gets to the river faster. Gutters and drains speed up throughflow

River discharge

The amount of water flowing down a river at any one time is called the discahrge of the river. t is measured in cublic meters of water per seconds (CUmecs) Most large rivers shave several gauging stations along their lengh, where a continuous records is jept of the river;s discharge at that point. The discharge of a river changes over time.

Factors that affect river discharge - Cliamtic

The cliamte has a major impact on the operation of the drainage basin system. River dicharge responds to changes in the imput of precipitation and to changes in the outpuits of evaporation and transpiration.

Types of deposition that form a floodplain.

The deposition of fine silt and mud. As the floodwater spreads across the floodplain, the hydraucic readious decreases and friction becomes more important and depositon takes place. Mostly closest to the river menaing areas waway get a thinner layer. The deposition of point bars in the slow watyer on the insider of meanders. They spread across the floodplain as the meander moves. The deposition of sediemtn on the river bed at times of low water when the velocity of the river slows.

What is solution?

The dissolved laod is derived from soluable rock such as limestone and chalk. Chalk stereams are often clear because the dissolved load is not visable

Components of the drainage basin - Surface storage, infiltration and overland flow

The frist rain that reaches the gorund will soak into the soil. The speed depends on the surface nad the permability. During prolonmged and or heavy reain, the infiltration capacity is exceeded and water starts to build up on the surface. This is surface storage naad produces puddles. On a slow, surface flow will run towards the river; this is overland flow

What is a braided river channels?

These are river channels that contain a large number of islands and bars made of sediment. They are found in areas where discharge varies a lot during the year and where a large amount of fairly coardse sediement is being carried by the river. The braiding results from deposition of sediment on the riverbed during a time of falling discharge. The river splits as it follows around the deposits

What are arcauate deltas?

They are fan shaped and form when the tidal range is low and there is a stornge movement of sediment in one direction along the coast. This keeps the seaward edge of the delta to be smooth

What are straight river channels

They are rare because helicoidal flow domaitnes in most rivers and make sthem meander as well as the line of maxoum flow velocity moves from side to side.

What is cuspate delta?

They are saped like an arrowhead or a worn tooth. there is a low tidal range and two offshore currents shape this type of delta, opertating in opposite direcitons at different times of the year.

What are aquifers

They are underground stress of greoundwater

What are gorges?

They are when the waterfall is retreating. They can form in semi-arid areas, where there is a hsort wet season leading to verticle erosion of the river bed when the river is flowing but no water weathering for the resto f the year. Where a mountain range has bee formed across the path of a river but the verticle erosion of the river has been able to keep up with the growth of the mountain range.

What is suspension?

This accounts for most of the load, especially in a lowland river. Lowland rivers nearly always look muddy and brown becayuse of the large amounts of sand, silt and clay suspended in the water.

What is a delta?

This is a depositional feature which forms when the river meats a sea or lake. When the river meats still water it loses energy so sediemtn is displaces. Deposition of sediment blocks the river channel which splits into smaller channels. The delta grows otwards into the sea forming marshy land. They are attractive palces for human settlement due to fertile land.

What is a birds foot delta?

This is formed when the tidal range is low and the curretns are strong. there is no clear offshore current to shape the ddelta so each of the distributary builds the land out into the sea, acting like a series of thin conveyor belts.

!What is hortonian overland flow

This is overland flow which is shallow, laminar and fast moving, commom in cities

What is traction?

This is the larger particles of the bedload are rolled along the forcec of the flowing water. The bedload is the load that spends all or some of its time on the river bed

What is saltation?

This is the smaller particles of bedload tend to hop along the bed of the river. A faster eddy picks them up and they move along in the body of the water until the current slows and thehy fall back to the river

Drainage Basin characteristics - Drainage density

This is the total length of surface streams per square km. It is related to the infiltation rates. Basin with low infilktation have more overland flow and a higher draiange besintiy than those with a high infilitation. As a reuslt, drianage basins with a high drainage density respond more quickjly to inputs of rainfall so they haver rapid surface run-off and a rapidly rising, high discharge

What is the hydrological cycle?

This is the way that water moves from the sea, through the air, onto (and into) the land, and back into the sea. It is driven by the sun's heat and by gravity. It is often known simply as the water cycle.

What are ox-bow lakes?

This is when meanders become more bendy over time as erosion and depostiiob contubnes ti change their shape.. There is laterial erosion so the neck becomes narrower and is breached and the meander cuts itself off causing an oxbow lake.

Components of the drainage basin - Evpotranspiration

Water evaporates from leaves, puddles and streams. The rates depends opn the temeprpature of the water, the warmth and humidity ofd the aur and the speed of the winds. Plants draw water through their roots and allow it to evaporates through the leaves. The water leaves through the stomates in a process call transipirtion. Water loss from the bawsin as evportionions is the combinations of bvoth of them

What is turbulent flow?

Water in a channel is affect by friction which flows the water cloest to the bed and the banks and the water nearer the centre of the river overtakes the slow wayter whichrwesults in turbance. The water at the sides begin to eddy towards the banks.

What is helicoidal flow?

Water spiralling down a plughole. The line of the fastest flow follows a corkscrew or spiralling path as the river moves downstream. THis is closely related to the development of meanders. The spural movement of the line of fastest flow is constated by the river channel. Itmoves from the surface to the bed and back and also moves from one bank to the other which priduces pools and riffles in verticle movement and eorrosion on horizonal.

Components of the drainage basin - Groundwater and baseflow.

Water the percolates into the bedrock is groundwater This water flows down through the rocks until iut reaches the level of saturation or water table. Most groundwater eventually flows down through the rocks towards the nearest river. It is a slow process. the water table mvoes up and down depending on the amount of percolation.

What are waterfalls?

Waterfalls form where a horizontal layer of hard rock lies on top of a layer of softer rock in a river valley. The soft rock underneath is eroded quicker and forms a plunge pools. The splashing water and the eddy currents in the plunge pools undercut the har rock which then collapse into the plunge pool. The waterfall retreates and forms a gorges.

What is laminar flow?

Waterflowing downwards over a smooth surface can flow in a simple sheet, with no eddies or meanders. Laminar flow can be ovservced on a smooth road surface or paved area during heavy rainfall, but it is veryrare in nature fbecause most surfaces exert enough friction for turbulence to disrupt the flowing sheet

Factors that affect river discharge - Temerpature and evaporation

When temperatures drop below fdreezing points, thje soil becomes frozaen and imperable. Rain which falls on the frozen soil runs across the surface rapdily, iocnreasing discharge quickly. Temrpatures also effect evaporation rates. When temrpatures are high, evproation rates are high resulting in less water reaching the river

How is the Earth's Water distributed

87% in the sea 2.1% as frozen in snow and ice 0.8 per cent is fresh water 0.1 is in the atmosphere

Drainage Basin characteristics - Soil type

A draiange basin with imperable soil and bedrock will have more overland flow and less throughflow and baseflow. Because overland flow is a much faster process than the other two flowsm this basin will have a higher discharg . A draiage basin with permeable soil will have hgiher infiltration and percolations, so throughflow and baseflow woll be more inmportant than overland flow.

Drainage Basin characteristics - Slopes

A draianged basin with steep slopes will have more overland flow and a higher river levels than a basin with more gentle sdlopes where there is more time for water to infiltrate

What is a drainage basin?

A drainage basin is the area of land drained by a river. A drainage basin supplies a river withs its water. In the UK a drainage basin the the phrrease used to describe an area of land drained by a river and its tribuitatiers. Some also use the phrease river catchement and is also called watershed in the USA but in the UK watershed means the boundary of the drainage basin

Effects on indirect human modification of the drainage basin

Deforestation Changing the agricultural land use Urbaisation

Effects of direct human modification of the drainage basin

Changing the amount of precipation entering river Storing water Chaning channel caracteristics Transferring water Removing water

Features in Upland rivers and channels

Channel -Steep gradient, rough bed, narrow and shallow channel, high friction, high turbulence but low speed, vertical erosion predominates Landforms -V-shaped valley, itnerlockign spurs, waterfalls and gorges, rapids, potholes

Features of the channel and landforms in the lowland river

Channel Gentle Gradient, Smooth bed, wide and deep channel, low friction, low turbulence but high speed, lateral erosion Landforms -Wide floodplain, Levees, delta, estury, ox-bow lake

How to calculate hydraulic radius?

Channel cross- sectional area / Wetted perimeter CSA = Channel Depth x Channel Width WP = Length of the bed and banks in direct contact with the water in the river channel.

Precipiation

Cloud seeding involves adding artificial particles to clouds so water coneses and rain drops. Cities produce air pollutionwhich increases the amount of rainfall in the area Warmer seas lead to more evportation causing more rain

Hard engineering flood strategies

Dams and resviours Platforms build on floodplains Build embankemnts of river Drege the river Straighten the river Retention basins build Flood relief channel

Imapcts of river flooding

Death Damage to building, ingrasturucutre and farmland Distruption to peoples lives