The document discusses factors that affect river discharge. It explains that river discharge is calculated based on the cross-sectional area of the river channel and flow velocity. Physical factors like rock type, drainage basin size and relief, and vegetation can impact discharge by affecting runoff and flow speed. Human activities such as urbanization and deforestation can also impact discharge by increasing runoff. Flood hydrographs illustrate how discharge changes during rain events, with peak discharge occurring after a lag time determined by drainage basin characteristics. Case studies can show how changes in discharge impact the drainage basin over time.

1. What is the River Discharge and
What Factors Affect it?
By Mischa

2. The Hydrological Cycle
This describes the process whereby water in its various forms
is continually cycled between the land, sea and atmosphere. It
also makes its way into the biosphere to influence animal and
plant ecosystems around the globe. It consist of
transfers, stores, and inputs of water, it is a closed system as
no gains or losses from outside are added to the system.

4. -It explains the distribution of water as it moves as either a
liquid, solid or vapour between the ocean, the atmosphere and the
land. It's a CLOSED cycle, no water added or lost.
-The hydrological cycle is powered by solar energy. The sun heats
the water from the ocean, lakes, rivers and the Earth's surface. The
water then evaporates into the atmosphere. Additional water is
drawn from the soil by plants, and it's evaporated into the
atmosphere from the leaves and stems= TRANSPIRATION
-The air rises & the temp. drops, the moist air condenses and form
clouds (eventually results in precipitation in the form of
rain, hail, sleet or snow). Water seeps into the soil (infiltration)
some into the rock (percolation).
-Water makes its way back to the ocean via surface runoff, through
flow and ground water flow.

5. Within the hydrological cycle, four
main processes operate:
Interception
• This is when plants prevent some rainfall from
directly reaching the ground, for example, water
on leaves or foliage. It may later reach the floor
via stem flow (water flows down the stem to the
ground) or through-fall, where water drips to the
ground. Secondary interception occurs at ground
level where water hits undergrowth. Some water
returns to the atmosphere via
evapotranspiration.

6. Evapotranspiration
• Water lost from vegetation via both
evaporation and transpiration.
Evaporation: A physical process where moisture is lost directly to the
atmosphere from the soil and water surfaces due to the suns heat
Transpiration: A biological process where water is lost from the
stomata pores in plant leaves

7. Infiltration
• Where water slowly soaks into the soil from
the ground. The maximum rate at which this
can occur is known as infiltration
capacity (mm/hour) and it is dependent on
the amount of water already present in soil
structure and vegetation.

8. Precipitation
• The most important input into the system
forms includes snow, hail, rain, and fog.

9. • Percolation:
• Water in the soil does not remain there but
moves down slowly into the lower layers of
soil and rock. It creates groundwater storage
found in rocks and this may later be moved
sideways through the rock via groundwater
flow.

10. Water flows through the hydrological cycle in
various ways:
• Throughflow: where water moves downwards
through layers of soil.
• Channel flow: downhill movement of water in
rivers.
• Groundwater flow: Lateral movement of
water from the water table.

12. The hydrologic cycle can be thought of as a series of
reservoirs, or storage areas, and a set of processes that
cause water to move between those reservoirs. The
largest reservoir by far is the oceans, which hold about
97% of the earth’s water. The remaining 3% is the
freshwater so important to our survival, but about 78%
of that is stored in ice in Antarctica and Greenland.
About 21% of freshwater on the earth
is groundwater, stored in sediments and rocks below
the surface of the earth. The freshwater that we see in
rivers, streams, lakes, and rain is less than 1% of the
freshwater on the earth and less than 0.1% of all the
water on the earth.

14. Drainage Basin
This is the area of land drained by a river system (a river and
its tributaries).

15. The drainage basin system is said to be open as
both inputs and outputs of energy and material
occur. All rivers receive a water from it. The
boundaries of the basin are known as
the watershed and will usually be marked by
areas of higher land. Drainage basins have many
different characteristics that influence how
quickly or slowly the main river within them
responds to a period of intense rainfall, these are
outlined in more detail in the section relating
to storm hydrographs.

16. Drainage patterns

17. The North East of England has 3 major drainage
basins, the Tyne, Tees and Wear, and several
other smaller drainage basins. These are tiny
compared to the worlds largest drainage
basins, such as the Nile, Amazon and
Mississippi, which covers 3,225,000km2

19. River Discharge
The discharge of a river is the volume of water which
flows through it in a given time. It is usually measured in
cubic meters per second.

20. Calculation:
Cross-sectional area of channel (m2) X Velocity of the river / water (m/s)
*This gives discharge as the volume (m3/s) or cumecs.

21. How is river discharge affected by
physical factors?
• Impermeable Rock (e.g. granite) – Water is unable to infiltrate
through, resulting in more surface runoff, increasing volume of the
channel and its speed.
• Permeable Rock – More infiltration, resulting in less surface runoff
and less volume in the river
• Size of drainage basin – Small  Water will enter the river quicker
and faster
• Relief of drainage basin – If the slope of the basin is more
steep, water in the river is likely to move down faster, increasing its
speed
• Percipitation – heavy rain can cause saturation in the soil and hence
cause more water to reach the river (runoff). This also means that
the speed of the river increases.
• Vegetation – allows more infiltration and interception, causing less
surface-runoff and slowing down the speed of the river

22. How is river discharge affected by
human factors?
• Impermeable man-made surfaces – Concrete and
tarmac can cause rivers in urban drainage basins to
have a higher discharge due to higher amounts of
surface runoff. Speed is also increased due to drainage
systems and ground.
• Destruction of vegetation (deforestation) – Less
infiltration + interception causes more surface run off
and increases speed of the water.
• River Management – Presence of dams allow river flow
to be controlled, which may cause more discharge
(before the dam) , or less (below the dam).

23. Hydrographs
Graphs which shows how the river discharge in a
drainage basin responds to a period of rain.

24. Base flow – the normal day to
day discharge of a river
The rising limb – the rapid increase
of discharge resulting from a
rainfall.
Peak flow – when the river reaches
the maximum capacity that it can
hold.
The recession limb – when the
discharge starts to decrease and
river levels fall.
Basin lag time – the time difference
between the peak of the rain event
to the peak flow.

25. What factors affect the shape of flood
hydrographs?
Drainage basin
- Type of rock (impermeable or permeable) –
Impermeable rock will not allow water to seep in, thus
causing larger amounts of surface runoff and a shorter
lag time.
- The gradient of the drainage basin – Steep gradients
will cause greater overland flow and a shorter lag time.
- Size of drainage basin – larger basins will take longer
to reach the river, hence a longer lag time
- Present conditions of the drainage basin – soil either
saturated, very dry or even frozen

26. Type and amount of Precipitation
- Rapid rain – soil will saturate at a very rapid
rate, excess water quickly transfers by surface runoff
thus causing a short lag time

27. Land Use and Human Impact
- Impermeable man-made surfaces – e.g. concrete
and tarmac roads, shorter lag times
- Vegetation area –infiltrates more and intercepts
water, a longer lag time, reducing discharge
- Area of deforestation – short lag time, increases
discharge

28. Time/season of the year
- Summer – evapotranspiration rates are
higher, reducing surface run off, longer lag
time
- Temperatures

29. Water Use
- Dams and reservoirs near area – slow down
the rate of discharge, a much longer lag time,
and may also cause a reduced amount of
discharge

32. How do flood hydrographs change as
river discharge changes?

33. • When it starts to precipitate, the level of discharge starts fairly low
at base flow level (1).
• As the rain starts to get heavy, the soil may be saturated, thus there
is an increase in surface run off. This causes water to start flowing
into the river channel, causing the level of discharge to
increase, making the line go up positively.
• A very steep rising limb (2) would indicate a fast increasing
discharge rate meaning water flowing into the river channel is a
faster rate, and thus a heavier rainfall.
• (3) When the amount of water in the river is at its maximum level
(peak discharge), the curve will reach its highest point on the graph.
• As river discharge starts to decrease (4), the curve will start to slop
gradually (gradient is normally less steep compared to the lag time).

34. Case study
changes in the river discharge an the
impact upon the drainage basin?

35. AFON GLASLYN, NORTH WALES.

36. • Afon Glaslyn= rises near the center of the
Snowdon massif and flows in a southerly
direction towards Tremadog bay.
•