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’.

2.3 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

2.3 River functions Main components are: the stream channel, 2.3 .2 Stream corridors Main components are: the stream channel, the floodplain and the transitional upland fringe

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.

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.

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)

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

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

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

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.

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.

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

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

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

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.

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.

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

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

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.

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.

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.)

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.

2.3.7 Functions of the river system 2.3 River functions 2.3.7 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

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

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

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)

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

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

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

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

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

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

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