GG3021 Rivers

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GG3021 Rivers landscapeMonday 4.00pm G1

• Session 1 Introduction and course aims

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GG3021 Themes

• Human interventions in River systems
• Approaches to the management of rivers
• Relevant theoretical frameworks for management of
  river processes and change
• Modified Channels, Rivers in the Global South
• River Impoundment Dams their impacts
• Dry-land river systems Functioning hazards
• River floods
• Flood hazard estimation
• Flood warning
• Flood defence
• Flood Ranger game

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GG3021 Rivers and Landscape

• 20 lectures 1 revision session
• 4 tutorial/seminar sessions
• FloodRanger Game Computer Session
• Exam 2 questions from 6 67 marks
• Coursework 1 assignment per term of which the
  better counts 33 marks. Both MUST be attempted.
• Download of PowerPoint presentations
  http//www.gg.rhul.ac.uk/Thompson/teaching.html

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GG3021 Some key texts

• 1. Downs, P Gregory, K (2004) River Channel
  Management Towards sustainable catchment
  hydrosystems. Arnold. ISBN 0 340 75969 0 (pbk)
• 2. Newson, M (1997) Land, water and development.
  Second Edition. Routledge.
• 3. Thorne,C, Hey,R Newson,M (1997) Applied
  fluvial geomorphology for river engineering
  management. Wiley.
• 4. Smith, K Ward, R (1998) Floods Physical
  processes and human impacts. Wiley.

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History of river management.

• HYDRAULIC CIVILISATION Flow regulation,
  irrigation. Dams.
• PRE INDUSTRIAL REVOLUTION Flow regulation,
  weirs, water mills, navigation, land drainage.
• INDUSTRIAL REVOLUTION Industrial mills, cooling
  water, power generation, dams, channelization.
• LATE 19TH c- MID 20TH c Flow regulation,
  multiple use river projects, flood defence. Large
  Dam construction.
• gt1950 Flow regulation, flood control,
  conservation management. Large Dams.
• LATE 20th C-Early 21st C Conservation
  management, sustainable river use projects.
  River restoration.

Water mill- Cordoba
Pomme de Terre River dam lake, USA
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Perspectives and objectives of river management
River as Resource

• Aesthetics
• Conservation
• Ecology flora and fauna
• Navigation
• Recreation
• Rivers as boundaries
• Sand and gravel extraction
• Water source Irrigation, industrial/municipal
  supply

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Perspectives and objectives of river management
River as Hazard

• Bank Protection
• Bridge stability
• Flood control channelization, dams
• Floodplain zoning (avoidance strategies)
• Land drainage agricultural drains, road
  drainage, urban storm water systems
• Pollution of water and sediments
• Soil erosion and sediment transport

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Themes in 21st century river management in the UK

• Water Supply Reduction of total/seasonal yield
• Water Demand Increase mean peak needs
  pressure on distribution system pressure on
  treatment system
• Impact of catchment urbanisation on river flow,
  sediment loads flood response
• Flood management Increased flood risk Reduction
  in safety standards

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Themes in 21st Century River management

• Water Quality Lower quality in lowland rivers
  Abstraction- Ecosystem implications
• Navigation Lower summer flows and navigability
  in rivers and canals
• Aquatic ecosystem altered habitat potential
  (Arnell Reynard 2000)

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Catchment Ecosystem Exploitation Functions
(Source Newson )
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Impacts of Climate Change

• Change in mean monthly runoff by 2050s for six
  UK catchments Don, Greta, Harpers Brook,
  Medway, Tamar, Nith.
• Data based on climate models

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FLOOD HAZARD Tewkesbury July 2007
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RIVER IMPOUNDMENT The Three Gorges Dam-China
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RIVER IMPOUNDMENT - Glen Canyon Dam - Arizona

• Large dams gt15m high gt 3,000,000m3 reservoir
  storage
• Impacts Spatial temporal
• Upstream- base level
• Downstream Discharge sediment load changes
  Channel change.

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Impacts of Dams on flow regime (Petts 1984)
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HOW MUCH CHANGE? (Gregory 2006)

• River regulation dams, weirs etc
• Range of channel change ratios 0.09-3.0
• 73 studies show reduction of channel capacity
• Response depends on type of regulation, sediment
  transport post-impoundment, sediment
  availability, stream power. Reservoirs also may
  raise base levels of tributaries

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URBANISATION

• Flood hydrographs reflecting urbanisation of
  western Tokyo
• Source Yoshimoto Suetsugi (1990)_

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Possible impacts of urbanisation See Thorne, Hey
Newson
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HOW MUCH CHANGE? (Gregory 2006)

• Urban development
• Range of channel change ratios 0.15-gt10.0
• 72 studies show increase in channel capacity
• May get change in pool/riffle spacing, bed
  lowering may occur

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Modified rivers in the UK

• The map shows heavily (Black) Significantly
  (dark grey) and obviously (light grey) modified
  rivers in the UK

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Types of river modification

• Straightening
• Artificial meander cutoffs- steepen gradient and
  increase flow velocity
• Re-sectioning
• Widening/deepening of the channel to increase
  conveyance or capacity and reduce incidence of
  overbank flooding
• Levee Construction
• Channel banks artificially raised to confine
  flood flow
• Bank Protection
• Use of structures such as gabions steel piles
  to control bank erosion
• Clearing/Snagging
• Removal of obstructions from channel, reduces
  resistance and increases velocity.

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Common Forms of direct river modification (From
Acreman)
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Bank Stabilisation using gabions.Note- channel
bed armouring due to reduced bank erosion.
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Key issues in successful river management
(after Gregory Downs (2004))

• 1. Understanding river channel processes (eg
  flow-sediment transport interactions)
• 2. Interaction between channel form and channel
  process involves the ecology of the channel
  environment.
• 3. River channel management should take account
  of the drainage basin context. Multiple scales
  of response in space and time.
• 4. A channel should be managed within its dynamic
  temporal context. Understand that rivers respond
  to management over short and longer timescales.
• 5. River management should be sustainable.
  Adverse feedbacks should be avoided (eg in
  modification). This requires monitoring
  evaluation.

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The Rate Law of morphological changea) Gully
growth, b) Gully growth based on
dendrochronology, c) Channel width change after
Dam closure. Sources Graf(1977) Williams
Wolman (1984) Knighton (1998)
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Theoretical constructs for channel change
(Source Knighton 1998)
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Climate Change and catchment hydrology (Arnell
1996) See Acreman chapter 1
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Three Gorges Dam site - China