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GG3021 Rivers

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Relevant theoretical frameworks for management of river processes and change ... Aquatic ecosystem: altered habitat potential (Arnell & Reynard 2000) 10 ... – PowerPoint PPT presentation

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Title: GG3021 Rivers


1
GG3021 Rivers landscapeMonday 4.00pm G1
  • Session 1 Introduction and course aims

2
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

3
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

4
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.

5
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
6
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

7
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

8
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

9
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)

10
Catchment Ecosystem Exploitation Functions
(Source Newson )
11
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

12
FLOOD HAZARD Tewkesbury July 2007
13
RIVER IMPOUNDMENT The Three Gorges Dam-China
14
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.

15
Impacts of Dams on flow regime (Petts 1984)
16
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

17
URBANISATION
  • Flood hydrographs reflecting urbanisation of
    western Tokyo
  • Source Yoshimoto Suetsugi (1990)_

18
Possible impacts of urbanisation See Thorne, Hey
Newson
19
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

20
Modified rivers in the UK
  • The map shows heavily (Black) Significantly
    (dark grey) and obviously (light grey) modified
    rivers in the UK

21
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.

22
Common Forms of direct river modification (From
Acreman)
23
Bank Stabilisation using gabions.Note- channel
bed armouring due to reduced bank erosion.
24
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.

25
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)
26
Theoretical constructs for channel change
(Source Knighton 1998)
27
Climate Change and catchment hydrology (Arnell
1996) See Acreman chapter 1
28
Three Gorges Dam site - China
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