“How do we use terrestrial laser scanning in hydraulic models?”
“The Hepple Lecture Theatre”
School of Geographical Sciences, University Rd., Bristol BS8 1SS
Wednesday 21 October 2009
Attendees:
Environment Agency
Geomatics Group, Co-Hosts
Academic Community
Al Duncan (Speaker)
Patrick Hogarth
Andrew Richman
Paul Smith
Adam Tobin
Albert Cheng, Exeter
David Mason, Reading
Pauline Miller, Newcastle (Speaker)
Adrian Saul, Sheffield (Speaker)
Nigel Wright, UNESCO IHE/Leeds
Environment Agency
University of Bristol, Co-Hosts
Chris Clarke, FRM&DM – Midlands Central
Richard Groom, FRM&DM - Thames West
Niall Hall, FRM&DM - Midlands West
Helen James, FCRM Mapping & Modelling
Sam Jamieson, FRM&DM - Thames SE
Claire Jarman, FRM&DM - SW Wessex
Julian Pillans, FRM&DM - Thames SE
Rupert Spark, FRM&DM - SW Wessex
Paul Bates (Chairman)
Guy Schumann
Jeff Neal
Tim Fewtrell
Mark Trigg
Liz Stephens
Amanda Hall
Miguel Rico
Dawei Han
Consultants
Local Authorities
Mike Panzeri, HR Wallingford
Neil Hunter, JBA Consulting
Matt Horrit, Halcrow
Ian Anderson, Halcrow
Sun Yan Evans, Mott MacDonald
Richard Allitt, RA Associates
Bruce Kerridge, Capita Symonds
Michael Lake, Capita Symonds
Nathan Muggeridge, Mouchel
Tony Donaldson, Derby Council
Syd Simpson, City of Bradford
Dave Stewart, Torbay Council (Speaker)
Nick Tolley, Derby Council
Mike Wood, Torbay Council
UKWIR
Barry Luck, Southern Water
Apologies:
Environment Agency
Academic Community
Mel Andrews, FCRM Inland Overview
Mike Coward, FRM&DM – NW North
Jim Walker, Flood Risk Science
Slobodan Djordjevic, Exeter
Garry Pender, Heriot Watt
Martin Smith, Nottingham
Consultants
David Hetherington, Arup
David Martin, Ambiental
Geomatics Group
www.geomatics-group.co.uk
School of Geographical Sciences
www.ggy.bris.ac.uk
Introduction to Mobile Terrestrial LIDAR
Al Duncan – Geomatics Group
 The Environment Agency Geomatics Group is synonymous with delivering the
highest quality, most accurate height data in the UK. Once considered
prohibitively expensive, LIDAR height data is now widely available at an
affordable price and has become a vital component for effective modelling,
planning and asset management for many organisations.
 Geomatics Group have invested in a Mobile Terrestrial LIDAR (an Optech
LYNXTM). This vehicle mounted laser scanner captures very high resolution data
and provides exceptional levels of accuracy. This system allows for the collection
of thousands of heighted co-ordinates per square metre within view of the sensor,
with a 360o field-of-view, mobile terrestrial LIDAR is ideally suited for surveying
roads, bridges, buildings, assets such as street furniture, and power lines.
 Description of sample data (previously supplied). This included the DSM with all
surface objects, DSM including objects of wall and vehicle height, DSM of kerb
height objects and the DTM of ground classified only points.
 Manual editing is then required to produce an enhanced DTM with kerb lines and
examples of this were shown at various resolution (10, 25, 50 and 100 cm) with a
view ot lowering file sizes versus requirements for modelling.
 The intensity image may also be useful in identifying drains and manholes. The
data can be combined with other mapping sources such as OS MasterMap. 3d
vectors can be derived from digitising features in the intensity image and the
DEM data.
 Examples were presented of the Point cloud data product, rendered in 3D with
colour to represent relative height and the brightness of shading intensity.
Questions & Answers
Do you have problems with backscatter?
The main technical issue comes from shadows / data gaps behind
vehicles and walls. This then requires interpolation in order to
generate a continuous terrain model.
Can you take the vehicle off-road?
Yes – the instrument can also be mounted on the most appropriate
vehicle for specific surveys.
Is the accuracy different from airborne LIDAR?
Yes, absolute accuracy of mobile terrestrial Lynx data is 3 – 5 cm x, y
and 3 – 5 cm z (relative accuracy 1 – 3 cm) RMSE.
Absolute accuracy of airborne LIDAR 40cm x, y and 5 - 15 cm z
RMSE.
Geomatics Group
www.geomatics-group.co.uk
School of Geographical Sciences
www.ggy.bris.ac.uk
Does the type of vehicle affect quality?
The instrument can be mounted on any vehicle. However, increased
height will not reduce shadowing significantly. Our operational height
of 2.5m was chosen to take account of bridges and overhanging trees.
Have you tried to remove vehicles from the streets prior to survey?
Not as yet but if this were possible, it would reduce the level of
shadowing / reflecting and resultant interpolation in the terrain model.
Do you have any idea of error sources?
We would only survey in dry conditions so there should be no
problems with signal response.
The vehicle’s position is monitored 200 times per second so pot holes
etc are accounted for. (Post workshop comment: error sources include
the GPS/IMU/Range/ temperature and surface reflectance.)
Why use vehicle LIDAR – can you quantify detail / accuracy / costs?
Deployment of Mobile Terrestrial LIDAR is cheaper than that of
airborne LIDAR. Precise costs will be dependant on the products /
outputs required by the customer. (Cost estimate to be provided with
Glasgow test site data.)
Urban Flood Modelling
Adrian Saul - University of Sheffield
 An integrated approach to urban drainage is vital to urban flood modelling within
integrated catchments.
 The research challenge is to develop a generalised tool to deal with the
interactions of any above ground flows and their interaction with the below ground
drainage system
 The foundation for successful modelling is an extremely accurate urban surface
DEM/DTM - sophisticated data is needed to understand complex flows.
 Street models are vital - without the precise positions of gulleys and manholes,
kerbs, walls, fences, permeable structures and other infrastructure affecting the
flow of water, the accuracy of a model is compromised.
 The Flood Risk Management Research Consortium (FRMRC) has developed new
urban interactive model which has been trialled in three UKWIR funded case
studies – including Torbay. These have highlighted the need for a joint 1D/1D
and 1D/2D approaches. The detail of the catchment surface is the critical factor
and enhanced DEM’s are the way forward.
 Mobile terrestrial LIDAR data has greatest potential in the intra-urban zone where
fluvial flows are just a minor consideration.
Geomatics Group
www.geomatics-group.co.uk
School of Geographical Sciences
www.ggy.bris.ac.uk
 Mobile terrestrial LIDAR data needs to be supported by topographical / historical
data to in order to validate the models produced.
Questions & Answers
Why not throw all the data into a 1D/2D model?
Whilst it is easy to collect the data required for 1D/2D modelling, it
very time-consuming to process. For this reason the combined
approach, which also employs faster 1D/1D models, has been
adopted.
What resolution of data do you/should we use?
As high as feasibly possible. Don’t confuse the resolution of models
with that of the data! High resolution data can be used to identify
features for input into models which use a coarser grid resolution.
Models will only be as good as the information used to create them.
You highlighted the importance of DTM’s for overland processes – how much
do we know about our underground drainage systems which also play an
important role in modelling?
Our understanding of drainage systems has improved over the last ten
years, particularly in those areas at risk. Models are often held by
water companies, although they are closely protected for legislative
reasons.
Further general discussion comments:
DTM’s need to be considered as an asset which is continually improved over
time.
Ground data (site walk by engineer) is and will always remain vital to
determine the success of a model and for verification.
Data and Models:
University of Bristol have run models for Tewkesbury at 1m
resolution in five to six days.
Environment Agency models of Tewkesbury at 10m resolution
took ten days to run.
Consultants tend to restrict the resolution of data to 4m when
working with the Environment Agency.
CCTV can be used to verify the overland flow model
Model application in Torquay with 1D & 2D surface flow modelling
Dave Stewart – Torbay Council

Presentation of work using the FRMRC urban interactive model (UKWIR funded)
showing the application of the data and modelling provided by the team. – see
slides.
Geomatics Group
www.geomatics-group.co.uk
School of Geographical Sciences
www.ggy.bris.ac.uk

CCTV was presented showing how it could possibly be used to verify the
overland flow model.
Terrestrial Laser Scanning: Applications in Civil Engineering
Pauline Miller – Newcastle University

Highlighted that we are looking at a technique, that can be applied using data
from a variety of terrestrial laser scanners.
Plenary Session
Paul Bates – University of Bristol
Four short presentations from members of the audience on experience with surface
water modelling:
Nathan Muggeridge with Mouchel software. Chris Clark (Environment
Agency) highlighted the importance of site survey walking for verification with an
example of introducing garden fences as break lines to improve the model output
against the event outlines. Matt Horrit with Halcrow ISIS-Fast software using the
10cm sample Lynx data. Tim Fewtrell Bristol University LISFLOOD-FP software also
using 10cm sample Lynx data.
General comments:
10cm sample data independently used by different people for the modelling
examples, probably a good resolution for the hydraulic modelling.
Elevation data is now widely available and the right resolutions. There is a need for
other model input data to improve, e.g. rainfall predictions, river flow monitoring
calibration and validation data, drainage knowledge and to a lesser extent surface
roughness.
Mobile terrestrial LIDAR should prove useful in providing the break lines (curbs etc)
that are vital in hydraulic street models and for adding such features to airborne
elevation data.
The issues of merging mobile terrestrial and airborne LIDAR data were discussed.
The costs of mobile terrestrial data vs. airborne data and airborne data at 25cm vs.
50cm need to be explored with the test site data capture.
Post workshop notes:
 Airborne data resolution for flood modelling:
50cm for urban areas, 1m for floodplain, 2m for rural areas outside of the flood plain.

Comments noted during the lunch time session on the RGB colour coding of the
airborne LIDAR with digital photography was that this provided an excellent
visualisation of the data and area of interest.
Geomatics Group
www.geomatics-group.co.uk
School of Geographical Sciences
www.ggy.bris.ac.uk