Slides in this set
The drainage basin and hydrological cycle.
o Can be studied via a systems approach consisting of Inputs, Processes and Outputs:
INPUTS PROCESSES OUTPUTS
Precipitation Percolation Evapotranspiration
Infiltration Runoff channel
Throughflow River discharge
o Stores (where water is stored on the surface): puddles/lakes/glaciers
o Transfers and Flows (move water through the system): throughfall/stemflow/infiltration/through
flow/groundwater flow…read more
o EVAPORATION: the process by which liquid o PERCOLATION: downward movement of
vapour is turned into water vapour (gas) water within the rock under the soil surface.
Rate at which percolation occurs depends on
the type of rock.
o EVAPOTRANSPIRATION: total amount of
water removed by both evaporation and o PRECIPITAION: rain/snow/sleet/hail
o RUNOFF: Surface runoff is the water flow
o GROUNDWATER FLOW: slowest transfer of which occurs when soil is infiltrated to full
water, flows through bands of sediment rock. capacity and excess water, from rain,
It is the movement of groundwater beneath snowmelt, or other sources flows over the
the earths surface. land.
o STEMFLOW: water that runs down the stems
o INFILTRATION: passage of water into soil. of plants and trees, occurs after interception.
Occurs relatively quickly at the start of a
storm but once ground becomes saturated o THROUGHFALL: water that drips off leaves
takes time. Also depends on type of soil e.g. during rainfall. Occurs when full capacity of
sandy soil = quick, clay soil= long time interception has been reached.
o INTERCEPTION: process by which raindrops o THROUGHFLOW: the horizontal movement
are prevented from falling onto the ground. of water in the soil
Usually done by leaves/ plants /trees.…read more
FACTORS AFFECTING RIVER DISCHARGE
o River discharge is defined as the volume of water passing a measuring point in a river in a given
time. It is measured in cumecs.
o Can be illustrated via Storm Hydrographs
Use Sheet Jan Gave
THE STORM HYDROGRAPH Called: How The
o Shows variations over a short period of time, usually during a rainstorm. Drainage Basin
SHORT LAG TIME
LONG LAG TIME Continued...…read more
THE SHAPE OF THE HYDROGRAPH IS INFLUENCED BY A NUMBER OF FACTORS:-
1) INTENSITY AND DURATION OF THE STORM= if both are high they produce a steep rising limb
as the infiltration capacity is exceeded
2) ANTECEDENT RAINFALL= if the ground is already saturated from previous rainfall and it rains
again there will be a steep rising limb .
3) SNOW= heavy snowfall may not initially show up on a hydrograph as it has been `stored' but
when it melts massive amounts of water are released greatly increasing discharge. if the
ground is still frozen then it restricts infiltration resulting to increased surface runoff.
4) POROUS SOIL TYPES/PERMEABLE ROCKS= produce less steep/ flashy hydrographs as water is
regulated slowly through the natural system.
5) IMPERMEABLE ROCKS= have higher densities e.g. Clay+Granite. The higher the density the
faster the water reaches the river thus increasing discharge.
6) SIZE OF DRAINAGE BASIN= smaller drainage basin responds more quickly to a storm compared
to larger one meaning lag time is shorter.
7) SHAPE OF DRAINAGE BASIN= round basin = rainfall reaching river quicker/ elongated basin =
rainfall reaching slower.
8) TEMPERATURE= high temperaturehigh evapotranspirationless discharge
= low temperature frozen groundno infiltrationhigh overland
9) VEGETATION= varies with seasons, summermore interception
10) LANDUSE/URBANISATON= impermeable surfaceincreased surface runoff
= permeable surfaceless surface runoff…read more
o The work of a river consists of 3 main processes: EROSION,TRANSPORTATION,DEPOSITION.
EROSION----- NEEDS LOTS OF ENERGY ESP IN FLOODS
o Rivers erode because they possess energy. Their total energy depends on:
1) The weight of water: the greater the mass of water the more energy it has, (due to the force of
gravity on it).
2) Height of river above its base level: the higher above base level the more potential energy it has.
3) Steepness of channel: steepness of channel (gradient) determines velocity (speed of flow) which
then decides how much kinetic energy it has.
o Much of this energy is lost through friction either internally (through turbulence of flow or externally
(through contact with bed and banks).
4 MAIN PROCCESES OF RIVER EROSION.
1) ABRASION (CORRASION) sandpapering action (material being rubbed against river bank). Most
effective in short turbulent periods when the river is at bank full or during a flood. When river levels
are low it usually contains small particles such as sand grains which don't do much damage.
2) HYDRAULIC ACTION sheer force of water hitting the banks of the river
3) CORROSION most active on rocks that contain carbonates e.g. Limestone and chalk. Minerals in
the rock are dissolved by weak acids in the river and are carried away in solution.
4) ATTRITION rocks and boulders whack into each other and make them smaller. Consequently
larger more angular rocks are found upstream and smaller more rounded ones are found
o In the upper course of a river because the water is high above seal level VERTICAL EROSION is
dominant because the river is attempting to cut down to its base level (usually sea level).
o In the middle and lower course you get LATERAL EROSION where the valley floor lies close to the
seal level. Here the river possesses a great amount of energy, particularly close to bank full.…read more