1. 2.3 River functions
Good morning/afternoon. I would like, before I begin, to thank the search committee for giving me this opportunity. I have been enjoying my visit so far very well. My presentation is titled ‘observations, modeling and scaling: the three pillars of hydrology’.

2. 2.3 River functions 2.3 .1 River basins and catchments: Factors are:
physical, climatic, chemical and biological conditions determine how river works
River basin serves:
as the most appropriate unit for:
maintaining the health of its functioning and
the conservation of freshwater systems
Catchment defines :
dynamic hydrological-ecological processes, such as flood events, occur over areas
A useful method to “scale-up” from sub-basin levels to what is referred to as river basins-level

3. 2.3 River functions Main components are: the stream channel,
Stream corridors
Main components are:
the stream channel,
the floodplain and
the transitional upland fringe

4. 2.3 River functions the stream channel: 2.3.2 Stream corridors
contains flowing water for at least a portion of the year.
flowing water and the sediment it carries form, maintain and modifies the stream channel.
There are two key attributes (stream flow system —and channel size) cross sectional for scientists.

5. 2.3 River functions the stream channel: 2.3.2 Stream corridors
The two basic flow pathways are storm flow and base flow.
Channel size is determined by stream flow and sediment load.
A stream balance equation formally describes the dynamic relationship between channel size and sediment load and stream flow.

6. A stream balance equation
2.3 River functions
2.3.2 Stream corridors
A stream balance equation
Channel equilibrium involves the interplay of four basic factors:
Sediment discharge (Qs)
Sediment particle size (D50)
Streamflow (Qw)
Stream slope (S)

7. 2.3 River functions 2.3.2 Stream corridors
streams based on the balance and timing of the storm flow and base flow components
Ephemeral streams
Intermittent streams flow
Perennial streams flow

8. 2.3 River functions 2.3.2 Stream corridors Discharge Regime
There are three types of characteristic discharge
Channel-forming (or dominant) discharge
Effective discharge
Bankfull discharge

9. 2.3 River functions
2.3.3 Structural Changes in the Stream Corridor from its Headwaters to Outlet
The physical structure of the channel and floodplain changes as a river travels from its headwaters to its outlet.
Channel width and depth increase downstream as the drainage area and discharge increase.
A simplified longitudinal model captures these observed changes by disaggregating the river into three zones
Headwaters zone
Transfer zone
Depositional zone

10. 2.3 River functions 2.3.4 Stream Order Models
small headwater streams are designated Order I.
Streams formed by the confluence of two Order I streams are referred to as Order II, and so on,
with larger numbers indicating larger rivers with multiple tributary streams
Stream order is used primarily by hydrologists to construct models of stream flow.
Stream order correlates generally with gradient, drainage area, channel width, and discharge;
permits comparison of the behaviour of a river with others similarly situated.
useful for developing and testing generalizations and predictions about river processes.

11. 2.3 River functions 2.3.5 Longitudinal Changes in Stream Ecosystems
there are observable changes also in stream ecosystems from the headwaters to the mouth
Biological communities vary in different reaches of a river system
River Continuum Concept generalize and explain observed longitudinal changes in stream ecosystems
a ‘Flood Pulse’ model that describes habitat characteristics and biotic communities along a temporal continuum.
applies only to perennial streams
disturbances and their impacts on the river continuum are not addressed by the model.

12. 2.3 River functions 2.3.5 Longitudinal Changes in Stream Ecosystems
Commonly Observed Changes Associated with River Continuum Concept
patch dynamics model
stream habitat and species distribution exhibit patchiness
reflects relatively short-term observations on a stream-reach scale

13. 2.3 River functions
2.3.6 Key Stream Processes And Other Important System Characteristics
The observed structure in stream corridor is a result of
hydrologic
Geomorphic
physical and
chemical processes
operating within the river corridor as well as the influence of biological functions and overall system equilibrium

14. sediment flow through the watershed
2.3 River functions
2.3.6 Key Stream Processes And Other Important System Characteristics
Hydrologic processes
sediment flow through the watershed
If sediment supplied to the river stream’s power to transport the sediment
Provide mechanisms for geomorphic process
Shapes the terrain through
Erosion
Sediment transport
Sediment deposition
Land use
topography
geology
Climate
Intense precipitation
easily erodible rock and soil, and
land clearing
the channel characteristics will change over time to bring the river system into equilibrium

15. 2.3 River functions
2.3.6 Key Stream Processes And Other Important System Characteristics
Beds of headwater streams usually contain large particles such as gravel and boulders that are too heavy for the stream to move.

16. 2.3 River functions
2.3.6 Key Stream Processes And Other Important System Characteristics
Downstream, the size of particles decreases, as large rocks are broken and worn down, and smaller particles such as finer sands and silts are sorted out, carried off and eventually deposited in the river’s delta.
Natural and artificial obstructions in a stream cause localized changes in the stream’s ability to transport particles.

17. 2.3.6 Key Stream Processes And Other Important System Characteristics
Braided Channels
Straight Channels
Meandering Channels

18. 2.3.6 Key Stream Processes And Other Important System Characteristics
The amount of sediment a river can transport depends on stream energy or power.
Stream energy is a function of the velocity of its flow, the gradient of the channel , the channel depth and surface roughness also influence sediment transport
the figure gives better understanding of the relationship between flow rate, sediment particle size, erosion and transportation

19. 2.3 River functions
2.3.6 Key Stream Processes And Other Important System Characteristics
Physical and Chemical Processes
The physical characteristics and chemistry of water change as water comes in contact with air, soil, rocks, bacteria, vegetation and biological communities
As water moves along pathways in a watershed, eroded soil and plant materials enter the flowing water.

20. 2.3 River functions
2.3.6 Key Stream Processes And Other Important System Characteristics
Physical and Chemical Processes
Addition of these materials, in conjunction with chemical and biological processes operating within the river, influences the physical and chemical properties of the flowing water.
Stream water chemistry can vary both daily and seasonally.
Much of this variability results from changes in the proportions of storm flow and base flow, which often have very different chemical properties.

21. 2.3 River functions
2.3.6 Key Stream Processes And Other Important System Characteristics
Biological Community
Interactions among aquatic organisms and their sources of energy.(Dashed lines reflect weaker interactions.)

22. 2.3 River functions 2.3.7 Functions of the river system
River basins are very important systems. They fulfil many important functions,
water supply for households, industry and agriculture,
navigation, fishing, recreation, and "living space".
water has shaped and continues to shape the environment in which we live.
erodes mountain areas, transports sediment and creates delta areas.
cause floods and is essential for nature.

23. 2.3.7 Functions of the river system
2.3 River functions
Functions of the river system
Ecosystem services provided by RIVERS
Provisioning Services-food
Regulating Services: flood control
Cultural Services: Recreation & ecotourism
Supporting Services: Habitat / biodiversity

24. 2.3 River functions 2.3.7 Functions of the river system Food
Provisioning Services
Products obtained from ecosystems
Regulating Services
Benefits obtained from regulation of ecosystem processes
Cultural Services
Nonmaterial benefits obtained from ecosystems
Supporting Services
Services necessary for the production of all other ecosystem services
Food
Spiritual & religious
Soil formation
Fresh water
Recreation & ecotourism
Nutrient cycling
Energy
Aesthetic
Primary Production
Fibre
Educational
Habitat / biodiversity
Biochemicals
Bio-chemicals
Sense of place
Genetic resources
Cultural heritage

25. 2.3 River functions Low (base) flows:
2.3.7 Functions of the river system
Low (base) flows:
Normal level: 
Provide adequate habitat space for aquatic organisms
Maintain suitable water temperatures, dissolved oxygen, and water chemistry
Maintain water table levels in the floodplain and soil moisture for plants

26. 2.3 River functions Low (base) flows:
2.3.7 Functions of the river system
Low (base) flows:
Normal level: 
Provide drinking water for terrestrial animals
Keep fish and amphibian eggs suspended
Enable fish to move to feeding and spawning areas
Support hyporheic organisms (those living in saturated sediments)

27. 2.3 River functions Low (base) flows:
2.3.7 Functions of the river system
Low (base) flows:
Drought level:
Enable recruitment of certain floodplain plants
Purge invasive introduced species from aquatic and riparian communities
Concentrate prey into limited areas to benefit predators

28. 2.3 River functions
2.3.7 Functions of the river system
High pulse flows
Shape physical character of river channel, including pools and riffles:
Determine size of stream bed substrates (sand, gravel, and cobble)
Prevent riparian vegetation from encroaching into channel

29. 2.3 River functions 2.3.7 Functions of the river system
High pulse flows
Shape physical character of river channel, including pools and riffles:
Restore normal water quality conditions after prolonged low flows, flushing away
waste products and pollutants
Aerate eggs in spawning gravels and prevent siltation
Maintain suitable salinity conditions in estuaries

30. 2.3 River functions 2.3.7 Functions of the river system Large floods
Provide migration and spawning cues for fish:
Trigger new phase in life cycle (e.g., in insects)
Enable fish to spawn on floodplain, provide nursery area for juvenile fish
Provide new feeding opportunities for fish and waterfowl
Recharge floodplain water table

31. 2.3 River functions 2.3.7 Functions of the river system Large floods
Provide migration and spawning cues for fish:
Maintain diversity in floodplain forest types through prolonged inundation
Control distribution and abundance of plants on floodplain
Deposit nutrients on floodplain
Maintain balance of species in aquatic and riparian communities
Create sites for recruitment of colonizing plants

32. 2.3 River functions 2.3.7 Functions of the river system Large floods
Provide migration and spawning cues for fish:
Shape physical habitats of floodplain
Deposit gravel and cobbles in spawning areas
Flush organic materials and woody debris into channel
Purge invasive introduced species from aquatic and riparian communities
Disburse seeds and fruits of riparian plants
Drive lateral movement of river channel, forming new habitats
Provide plant seedlings with prolonged access to soil moisture

33. 2.3 River functions 2.3.7 Functions of the river system
Despite the important provisioning, regulating, supporting and cultural services provided by free-flowing rivers, in many places they are still seen as a threat, particularly in terms of flooding.
It is thus not surprising that throughout history people have sought to tame and control rivers by constructing dykes, diversions and dams