2. Elements of a drainage basin:
Inputs
Flow / Transfer
Storage
Output
3. Input:
major input - precipitation.
The type: rain or snow, hail, etc.
Factors affecting the amount of water in the
system:
the intensity,
the duration and
Frequency of the precipitation
5. Interception
defined as the capture of
precipitation by the plant
canopy and return to the
atmosphere through
evaporation or sublimation.
* Interception loss: water which is retained by plant
surfaces and which is later evaporated away &
absorbed by plant
6. leaf type – increase interception capacity if leaves &
twigs are dry
wind speed – the higher the wind speed the lower
the
interception capacity
- the more frequent the storm events
lesser
the interception loss
temperature, and the humidity of the atmosphere
7. Throughfall:
the process of
precipitation
passing through the
plant canopy (Yellow
lines)
Factors affecting:
plant leaf and stem
density,
type of the
precipitation,
intensity of the
precipitation,
and duration of the
precipitation event.
8. Stemflow:
is the process that directs
precipitation down plant
branches and stems (red
arrows ).
this process causes the
ground area around the
plant's stem to receive
additional moisture.
The amount of stemflow is
determined by
leaf shape and stem
branch architecture.
In general, deciduous
trees have more stemflow
than coniferous
vegetation.
9. Infiltration
Some of the precipitation
seeps into the ground and
stored in aquifers
then it is transported to
streams and lakes by
subsurface flow.
The amount of infiltration is
influenced by:
the permeability and moisture
content of the soil,
the presence of vegetation
and
the volume and intensity of
10. Overland Flow
Rills - Water moving over ground in small channels
Sheetflow - Water moving over ground across the whole
surface
Hortonian Overland Flow: Saturated Overland Flow:
infiltration excess overland Long period of steady
flow rain and water table
reach the surface
rainfall is greater than
infiltration capacity
No additional water can
E.g. If a soil surface can be infitrated so must
infiltrate 30mm/hr but remain on surface
precipitation is 40mm/hr,
therefore 10mm will be
overland flow Common in the
temperate
Very common in the tropics
14. A process where water enters the ground
vertically through pores
Factors affecting infiltration:
Intensity & duration of the precipitation
Type of soil
Vegetation & Land cover
Slope of the land
Evapotranspiration
Soil saturation
15. the slow movement of water through compact layers of soil
and rocks
Factors affecting percolation:
Precipitation
Relief – steeper the gradient the less water will be
percolated
Flora & fauna – animal tunnels & burrow
- root system of direct movement of
water in the soil
Rock structure / composition
Porous rock – sandstone
Permeable rock - limestone
16.
17. Water transfers laterally in the aquifers
If the water table reaches the surface it means ground is
saturated.
(a) infiltration to
deep
groundwater,
(e) overland flow
to (g)
(g) temporary
ponds
(f) deep
groundwater
flow.
18.
19. Channel flow
Water transfers to channel through 3
processes:
Surface run-off
Throughflow
Groundwater flow
/baseflow
20. Rainfall
Vegetation and land use
Climate
Shape
Conditions in drainage basin
Size and shape of the river basin
Soil type and depth
Bedrock
23. Process of percolation produces groundwater
storage
Water collected above the impermeable layer
Or it may fill all the pores spaces, creating a zone
of saturation
Above the impermeable layer, there are 3 zones:
An unsaturated zone
A saturated zone
An intermediate zone
24. Soil pores are mostly
filled with
microchannels so
water can move as
percolation and
throughflow
Biological activity with
plant roots, soil flora
and fauna create
microchannels
25.
26. Water accumulates
all the soil pores are full
of water
Baseflow / groundwater
occurs
No biological activity
27. Zone between the
unsaturated and
saturated zones
Changing patterns of
precipitation and EVT
throughout the year
gives a layer which is
alternatively saturated
and unsaturated
Interflow occurs
28.
29. 18
Infiltration rate
16 Rainwater which is not
infiltrated will become
14 surface run-off / overland
Infiltration Rate
flow
12
10
8
6
4
2
0
1 2 3 4 5 6
Hours from the start of rainfall
