THE USE OF PHOTOGRAMMETRY AND LIDAR FOR LANDSCAPE ROUGHNESS 
ESTIMATION IN HYDRODYNAMIC STUDIES 
M. J. Smith * *, F. F. F. Asal ^, G. Priestnall © 
^^ Institute of Engineering Survey and Space Geodesy (IESSG), "School of Geography, The University of Nottingham, 
University Park, Nottingham, NG7 2RD UK — martin.smith@nottingham.ac.uk, gary.priestnall@nottingham.ac.uk 
Now at Menoufia University, Egypt 
Commission III, WG III/8 
KEY WORDS: Photogrammetry, Remote Sensing, Environment, Floods, LIDAR, Landscape, GIS, DEM/DTM 
ABSTRACT: 
Flooding is a major problem for many countries causing damage to the environment and pressures on human activity. Engineers use 
Manning’s coefficient of roughness to determine water flow over floodplains which is a vital parameter in hydrodynamic studies. 
The coefficient is mainly a property of the ground surface texture and the changes in water surface elevation. The traditional method 
of determining the coefficient requires experience and often demands field visits. Airborne remote sensing provides an opportunity 
to produce good representations of the ground surface and therefore an easier and more efficient method of determining the 
coefficient. 
Digital surface model's (DSM's) are standard products from aerial photography and photogrammetry. The introduction of LiDAR 
technology has provided an alternative method for producing high quality DSM's. One of the main aims of this research was to 
assess the potential of using LiDAR and aerial photography/photogrammetry in analysing the landscape for the estimation of the 
coefficient of roughness. 
A test site with an excellent variety of features has been established close to Nottingham, UK and DSM's have been created from 
LiDAR data and photogrammetry. Analysis of the DSM's for different types of landscapes has been undertaken. 'Automated' 
techniques for the estimation of the coefficient of roughness have been investigated. Maps of the estimated values of the coefficient 
for different landscapes have been generated and compared with traditionally derived values for the test site. 
The research shows that airborne remote sensing has the potential to provide new methods for estimating Manning's coefficient of 
roughness (‘n’). 
and is known as Manning’s coefficient of roughness or 
Manning’s ‘n’ (Chow, 1973). The hydraulic roughness 
develops resistance to the water flow through creating a 
retarding force. 
1. INTRODUCTION 
River flooding is a major problem which faces many countries. 
Heavy rainfall in river catchments can accumulate large 
amounts of water which flow through the river system 
producing a rapid rising in the river water level and causing 
strong currents and wave actions. When the flow rate exceeds 
the discharging capacity of the river, water overflows the banks 
To determine the coefficient of roughness is an important step 
in the hydrodynamic modelling process. To obtain reliable 
estimates of the roughness has always been a difficult task often 
relying on experience and subjective judgement. A number of 
  
of the river to the surrounding land causing damage to the 
embankments, property and hazards to the environment. It can 
be disastrous to human and animal lives as well as creating 
health problems when sewers overflow. The infrastructure 
including electric power-lines, telephone cables, water networks 
and sewerage systems can be extensively damaged. Generally 
speaking, the flood can affect the infrastructure, threaten the 
population and create social problems (Environment Agency, 
2001). 
Studying the hydraulic properties of the flood surges helps 
develop an understanding of the factors controlling the 
behaviour of the water. Many different factors control the flow 
of water: the flow rate, the topography of the area, the cross 
sectional area of the water boundary, the wetted perimeter of 
the boundary layer and the coefficient of roughness. The 
coefficient of roughness ‘n’ represents the hydraulic roughness 
  
* Corresponding author. 
techniques have been implemented for determining the 
coefficient of roughness with some being dependent on 
applying field measurements of the flow parameters, others 
being based on studying the coefficient on hydrodynamic scale 
models or comparison with landscapes of ‘known’ Manning’s 
n. Most of the methods require the collection of information 
from the site of interest regarding topography, texture (ground 
features) and vegetation cover (French, 1994, Chanson, 2001). 
This task is a critical part of determining the coefficient of 
roughness and collecting reliable information can take a long 
time. 
Airborne and space borne remote sensing techniques can 
provide reliable information about the Earth’s surface. This can 
be for planimetric interpretation and measurement as well as for 
height determination. So it can be considered as a potential tool 
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