1. How does water move
through the drainage
basin system?

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

4. Flow / transfer:
 Interception
 Throughfall
 Stemflow
 Overland flow
 Infiltration
 Percolation
 Throughflow
 Groundwater flow / baseflow
 Channel flow

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

11. Overland flow

12. Rills

13. Sheetflow

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

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.

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

22.  Groundwater Storage
 Interception Storage
 Aeration Zone Storage
 Depression Storage
 Surface Storage

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

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

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