The University of Nottingham

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• The University of Nottingham
• Hervé P. Morvan
• March 2006

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Joint SHSG-ICE One-Day SeminarA New Challenge
for Water Engineers CAR 2005

• Hervé P. Morvan
• March 2006

Modelling and Analysis of River Changes linked to
Ecological Considerations
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Content

• The School of Civil Engineering CFD Group and
  CFD_at_Nottingham.
• Recent NAFEMS-ERCOFTAC Meeting on Quality and
  Reliability of CFD Simulations.
• Ecological Systems (Modelling of)
• River Modelling
• Applications of CFD to the Analysis of River
  Changes and Associated Ecological Impacts.

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Modelling of River Changes Ecological
Considerations

• Hervé P. Morvan
• 2006

Introduction
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Whoami?

• Dr Hervé MORVAN.
• Did my PhD in Glasgow, then worked for CFX (AEA
  Technology).
• Lecturer in Fluid Mechanics since 2003
• Member of the University Strategy Group on CFD
• Member of the ASCE EMD Fluids Committee
• Coordinator for ERCOFTAC SIG5 on Environmental
  CFD and member of ERCOFTAC UK an European SPC.
• Research
• CFD Environmental Applications
• Supervise 6 PhD students on channel flow, water
  engineering, aerodynamics and FSI.

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Activities
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Nottingham

• CFD_at_Nottingham is a joint effort project with
  Mechanical and Chemical Engineering, and Applied
  Mathematics
• run seminars and evening lectures
•  Geophysical Turbulence  on April 26th
•  SHP An Overview  on May 17th
• run CFD courses and the EPSRC  Summer School in
  Industrial CFD , June 19th-23rd
• CFD_at_Nottingham.ac.uk
• www.nottingham.ac.uk/cfd
• Several ERCOFTAC SIGs are based in Nottingham
• www.ercoftac.org

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Modelling of River Changes Ecological
Considerations

• Hervé P. Morvan
• 2005

Heard at a Recent NAFEMS-ERCOFTAC meeting
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Environmental CFD

• Verification and Validation in Uncertain
  Worlds, Joint NAFEMS-ERCOFTAC Seminar,
  Nottingham, Sept. 2005.
• Modelling natural features such as river channels
  is not easy.
• Issues with feasibility, choice of protocole etc.

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Geometries

• They are not always simple to acquire for river
  channels, countryside topographies, urban
  environments.
• Looking at river channels for example, these are
  irregular, dynamic systems with multiple
  boundaries and sources.
• Mapping the ground is difficult, costly
  vegetation, buildings, ponds.

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Spatial Resolution

• Size of grid cells used to represent the
  surface...

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Comparative Work
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Scales...

• Domain size is usually large and complex.
• Catchment to structure scale.
• Physical scales are multiple Which physical
  scales do we, or can we, model?
• Grain and form roughness, vegetation, buildings
  Momentum and energy losses.
• Turbulence scales.

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Modelling of River Changes Ecological
Considerations

• Hervé P. Morvan
• 2006

Modelling of Ecological Systems
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More Uncertainty

• We can explain observed phenomenon but not
  necessarily predict how species will react to
  imposed changes (Clifford, 1998).
• Who decides if you design a river specifically
  to improve habitat for salmonids? The answer is
  God decides (Hey, 1998).

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When there is a will

• Too many restorations in the past have been
  carried out with no quantitative prediction of
  the impact on the flow or on the environmental
  enhancements that will be achieved. Increasingly
  suitable quantitative methods are becoming
  available and it is a challenge for the research
  community to provide methods, in collaboration
  with the ecologists, which will predict the true
  impact of restoration. It is time that we
  replaced the guess work with accurate prediction
• (1997, ICE Meeting on Eco-Hydraulics).

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Methodologies

• Various methodologies exist
• IFIM flow model, depth, suitability curves
• CASIMIR more elaborate
• RCHARC similarity principle and variability
• SERCON survey and score (potential)
• RIVPACS and HABSCORE similar (predictive)
• IFIM, CASIMIR and RCHARC involve some hydraulics
  (dominantly 1-D) Combined approach.
• IFIM is the most commonly used. Quite sensitive
  however.

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Ecological Modelling

• Clifford et al (2005) indicate that the data form
  invites modelling, however difficult.
• Issues of scales are important here as well. So
  is resolution Fish habitat could be at the scale
  of a large boulder
• Clifford et al (2005) also indicate that we may
  want to forget a rigid, numerical use of
  modelling

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Nottingham

• It is a challenge to the habitat modelling
  community to decide what is the required level of
  accuracy (1D, 2D or 3D) for assessing habitat
  improvements (Swindale, 1999).
• PhD work to implement and compare various methods.

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General Env. Hydraulics

• Beyond ecological models, there are other
  applications linking river hydraulics and the
  environment.
• Uncertainty is found in many other aspects, as
  underlined in the examples chosen here, e.g. in
  Sanders et al. (2005) on urban pollution in a
  channel
• In cases involving FIB concentrations,
  uncertainties may be 200-500. By comparison,
  uncertainty associated with the mathematical
  model and numerical method are relatively small,
  roughly 20 and 1 respectively .

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Modelling of River Changes Ecological
Considerations

• Hervé P. Morvan
• 2006

River Modelling
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River Modelling

• Common in 1-D well established.
• Growing in 2- and 3-D for specific applications,
  e.g. flood propagation and detailed flow past
  man-made structures respectively.
• Validation is still needed and difficult, but
  better definitions for roughness and systematic
  methods are emerging together the use of with 2-
  and 3-D.
• Of course, it all depends on how we use the
  modelling outcome.

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Nottingham

• In spite of the aforementioned difficulties,
  modelling is improving rapidly and is proving
  very good at capturing trends.
• There is a lot of on-going work
• FRMRC work CFD Group, Geography and IESSG.
• Combining 1-, 2- and 3-D horse for courses.
• Using aerial/satellite data to look at roughness.
• Using 3-D to inform 1-D models, e.g. SKM.

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Modelling of River Changes Ecological
Considerations

• Hervé P. Morvan
• 2006

Examples
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Examples

• Swindale (1999) fish habitat
• Sanders et al. (2005) pollution
• Neary et al. (2005) man made structures
• There are many more in River Research and
  Applications, Hydrological Processes, Water
  Research, ASCE J. Hydraulic Engineering.

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Swindale (1999)

• Implementation of the IFIM framework in several
  models, including 2- and 3-D.
• River restoration.
• River Idle.

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Swindale (1999)


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Swindale (1999)

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Swindale (1999)

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Swindale (1999)


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Swindale (1999)

• 2- and 3-D modelling most useful to look at
  detailed/localised effects, e.g. due to work on
  the channel, and spatial variability.
• This is also picked on by Clifford et al. (2005).

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Sanders (2005)

• Modelling the impact, transport, growth and decay
  of bacteria in a stream.
• Identifying the dominant processes and sources.

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Sanders (2005)

• Use of Faecal Indicator Bacteria (FIB).
• Model predicts the advection, dispersion and
  die-off of TC, EC, ENT using a depth integrated
  formulations.
• In Talbert Marsh, it is not clear whether FIB
  concentration are predominantly controlled by
  urban runoff, erosion of contaminated sediments,
  birds faeces, or some combination of these
  factors. (Sanders et al., 2005)

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Sanders (2005)
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Sanders (2005)
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Sanders (2005)

• Sanders is able to conclude that
• Surface concentrations of total coliform,
  Escherichia coli and enterococci in the wetland
  are driven by urban runoff loads and resuspended
  sediments.
• Sediment, Sanders concludes, act as a reservoir
  of FIB and adds that this finding is important to
  temper the expectation that hydrodynamically
  active wetland serve to process FIB from runoff
  and other sources.

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Neary (1999)

• A parametric study to investigate the design of
  lateral intakes.

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Neary (2005)
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Neary (2005)

• We therefore have a qualitative idea of the
  phenomena involved based on observations and
  experiments.

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Neary (2005)
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Neary (2005)
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Neary (2005)

• Generally the results Neary and his colleagues
  obtain suggest that effective mitigation
  strategies for reducing sediment deposition at
  the intake should be based on
• counteracting or reducing the strength of the
  secondary circulation
• limiting the extent of the dividing stream
  surface at the bed,
• reducing the size of the separation zone
• promoting acceleration of main channel
  longitudinal velocities in the vicinity of the
  saddle point off the downstream corner of the
  intake.

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Modelling of River Changes Ecological
Considerations

• Hervé P. Morvan
• 2006

Concluding Remarks
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Concluding Remarks

• The scope for the regulations is considered under
  5 main headers in the Act
• controls over pollution
• abstraction
• impoundments
• building, engineering and other works
• duty to use water efficiently.
• Impact assessment
• One particular statement is worth noting as an
  excerpt of the overall section, p. 15 the
  site-specific assessment will typically involve
  the use of models or defined rules for
  decision-making.

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Concluding Remarks

• River modelling is very good at picking up
  trends.
• River modelling alone or combined with some
  ecological models can assist in evaluating the
  impact of a solution, e.g.
• Fish habitat (river restoration/management)
• Pollutant transport
• Hydraulic design.

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Concluding Remarks

• Naturally more validation work and guidelines are
  necessary.
• At Nottingham we are
• Building up validation libraries
• Preparing and distributing Best Practise
  Guidelines (Nottingham, ASCE EMD Fluids Cmmttee,
  NAFEMS)
• Using validated CFD to learn more about specific
  mechanical processes AND feeding the information
  back into application specific codes.

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• Thank you.
• Herve.morvan_at_nottingham.ac.uk
• School of Civil Engineering, CFD Group,
• Coates Building, University Park
• NG7 2RD Nottingham