the university of nottingham hervé p. morvan march 2006
TRANSCRIPT
The University of Nottingham
Hervé P. Morvan
March 2006
Joint SHSG-ICE One-Day Seminar:A New Challenge for Water Engineers –
CAR 2005
Hervé P. Morvan
March 2006
Modelling and Analysis of River Changes
linked to Ecological Considerations
Content The School of Civil Engineering CFD Group and
CFD@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.
Modelling of River Changes& Ecological Considerations
Hervé P. Morvan
2006
Introduction
Activities
NCI
CFD Group - 4 Staff
- 2 Post-Docs
- 10+ PhDs
- 6 MEng/M.Sc.Civil Engineering
CFD@Nottingham:
- Across Faculty
- Joint Course/Research
- Seminar/Conference
Wind Engineering and Atm. Models
FSIReactive Flows
Comfort, Fire and Safety
Hydraulics and Water
Engineering
Large Scale
Radial Basis Functions
Nottingham CFD@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:
[email protected] www.nottingham.ac.uk/cfd
Several ERCOFTAC SIGs are based in Nottingham: www.ercoftac.org
Modelling of River Changes& Ecological Considerations
Hervé P. Morvan
2005
Heard at a Recent NAFEMS-ERCOFTAC meeting…
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.
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.
Spatial Resolution Size of grid cells used to represent the
surface...
Comparative Work
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.
Modelling of River Changes& Ecological Considerations
Hervé P. Morvan
2006
Modelling of Ecological Systems
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).
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).
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.
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…
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.
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” .
Modelling of River Changes& Ecological Considerations
Hervé P. Morvan
2006
River Modelling
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.
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.
Modelling of River Changes& Ecological Considerations
Hervé P. Morvan
2006
Examples
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.
Swindale (1999) Implementation of the IFIM framework in
several models, including 2- and 3-D.
River restoration.
River Idle.
Swindale (1999)
Swindale (1999)
Swindale (1999)
Swindale (1999)
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).
Sanders (2005) Modelling the impact, transport, growth and
decay of bacteria in a stream.
Identifying the “dominant” processes and sources.
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)
Sanders (2005)
Sanders (2005)
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.
Modelling of River Changes& Ecological Considerations
Hervé P. Morvan
2006
Concluding Remarks
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”.
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.
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.
Thank you.
School of Civil Engineering, CFD Group,
Coates Building, University Park
NG7 2RD Nottingham