The fluctuating amount of water in a river

3.3 Distinctive landforms

3.5 Flooding

The fluctuating amount of water in a river

  1. Discharge

    1. The discharge of a river denotes the amount of water passing a particular point on the river in cubic metres per second, or cumecs

  2. Hydrological cycle

    Hydrological cycle diagram

    1. Precipitation is any source of moisture reaching the ground, such as rain, snow and frost
    2. Interception is water being prevented from reaching the surface by trees or grass
    3. Surface storage is water held on the ground surface, such as puddles
    4. Infiltration is water sinking into soil or rock
    5. Soil moisture is water held in the soil layer
    6. Percolation is water seeping deeper below the surface
    7. Groundwater is water stored in the rock
    8. Transpiration is water lost through pores in vegetation
    9. Evaporation is water lost from the ground or a vegetation surface
    10. Surface-runoff, or overland flow, is water flowing on top of the ground
    11. Throughflow is water flowing through the soil layer parallel to the surface
    12. Groundwater flow is water flowing through the rock layer parallel to the surface
    13. Water table is the current upper level of saturated rock or soil where no more water can be absorbed

  3. Storm hydrograph

    1. A storm hydrograph shows precipitation, in millimetres, against time as a bar chart and the discharge of a rive, in cumecs, against time as a line graph after the start of a storm
    2. The discharge of the river during normal conditions is called the base flow
    3. The highest rainfall and discharge are called the peak rainfall and peak discharge respectively, with the time between them called the lag time
    4. If the lag time is short, the hydrograph is called a flashy hydrograph
    5. If the lag time is long, the hydrograph is called a delayed hydrograph
    6. The part showing an increasing discharge to the peak is called the rising limb and the part showing a decreasing discharge after the peak is called the falling limb

  4. Factors affecting discharge

    1. Discharge goes up with a higher amount of rainfall since the water saturates quicker, causing more water to flow into the river
    2. Discharge goes down with a higher temperature since more water is lost by evaporation & transpiration
    3. Discharge goes up if previous conditions were wetter since the land is more saturated
    4. Discharge goes up with a steeper and less obstructed relief since more surface runoff occurs than infiltration
    5. Discharge goes down with more permeable rock since more surface runoff occurs than infiltration
    6. Discharge goes up with land use, generally in the form of deforestation or urbanisation, since deforestation means there is less interception and urbanisation makes the surface impermeable, causing more surface runoff and drainage