Richter, B.

Tränckner, J.

I-Revues

NOVATECH 2016 
1 
Determination of morphological input data for 
hydraulic 1-D models by using purposeful geodetic 
surveying 
Détermination des données d'entrée morphologiques 
pour les modèles hydrauliques 1-D en utilisant des levés 
géodésiques ciblés 
 
Boris Richter, Jens Tränckner 
 
Department of Water Management, Universität Rostock  
Satower Straße 48 18059 Rostock, Germany (boris.richter@uni-rostock.de) 
 
RÉSUMÉ 
Les modèles hydrauliques basés sur la physique sont devenus de plus en plus populaires en raison 
de leur haute résolution et de leur capacité à simuler l’évolution de la qualité de l’eau et des 
contraintes hydrauliques pour différents scénarios de structures d’ingénierie hydraulique sur les plans 
d’eau urbains. Ces modèles de haut niveau nécessitent néanmoins des données physiques 
éprouvées pour que les résultats fournis soient fiables. Par conséquent, la première difficulté de la 
modélisation est la collecte exhaustive des informations nécessaires. En particulier, la morphologie 
des canaux ouverts n’est pas bien documentée. La plupart du temps, les données fournies par les 
institutions publiques manque de précision et/ou ne sont pas très à jour. Si l’on se base sur des profils 
standards de substitution, cela peut entraîner des erreurs considérables pour les résultats 
hydrauliques (niveau, vitesse d’écoulement, contrainte de cisaillement) par conséquent, pour les états 
et processus des modèles de qualité (par exemple la surface mouillée, la ré-aération physique), cités 
en exemple dans cet article. Pour une modélisation fiable, sur les niveaux inférieurs, les conduits 
souterrains et les sections transversales des cours d’eau urbains, en particulier, devraient être définis 
avec suffisamment d’exactitude par une méthode pratique. Cet article présente un concept d’étude 
géodésique rentable et efficace permettant de déterminer les données structurelles manquantes. Ce 
concept combine la technologie de réception GPS cinématique en temps réel et la technologie de 
l’arpentage optique. Il est capable de produire toutes les données structurelles nécessaires pour le 
modèle hydraulique 1D sans trop de difficulté. 
 
ABSTRACT 
Physical based hydraulic models became more and more popular, because of their high resolution 
and ability to simulate the evolution of water quality and hydraulic stress for different scenarios of 
hydraulic-engineering structures at urban watercourses. Nevertheless, these high-level models need 
well-proofed physical data for reliable results. Therefor the first obstacle for modelling is the 
comprehensive collection of required information. Especially the morphology of open channels is not 
well documented. Data provided by public institutions are in most cases not precise and/or not up to 
date. The assumption of standard surrogate profiles can lead to enormous errors for hydraulic results 
(level, flow velocity, shear stress) and accordingly quality related model states and processes (e.g. 
wetted surface, physical re-aeration), as exemplarily shown in the paper. For reliable modelling, 
particularly, bottom levels, culverts and CS (cross-sections) of the urban watercourses should be 
defined sufficiently exact by a practical method. This paper presents a concept for a time (cost) 
effective geodetic survey to determine missing structural data. The concept combines real-time 
kinematic GPS with optical based surveying technology. It is capable to produce all necessary 
structural data for the 1D hydraulic model with reasonable effort. 
 
KEYWORDS 
Cross-section, GPS, MIKE11, modelling, stormwater 
SESSION 
2 
1 INTRODUCTION 
A flat relief characterizes the North German Plain. In consequence of an anthropogenic influence over 
centuries, there are a lot of diverse, highly cross-linked water forms and uses. Caused by their small 
size, the hydraulic situation is very complex. The main target is the development of essential tools that 
provide an impression of the current state, forecasts and an assessment of structural measures. In the 
running research project, the following working packages are defined: 
• The development of a coupled urban macro model (large-scale approach) which includes the 
catchment area, public sewer network and the system of watercourses to simulate the 
hydrological, hydraulic and material system behaviour 
• Detailed measurement campaign at a characteristic subsystem for model calibration and clustered 
parametrisation of a reference model (small-scale approach) 
• Transfer results and knowledge of the reference model into the macro model 
The reference and the macro model will be constructed by coupling of sewer network model (MIKE 
URBAN by DHI) and a 1D streamflow model (MIKE 11 by DHI). Especially for realistic modelling of the 
natural watercourses, a precise knowledge of their morphology is mandatory. 
2 METHODS 
2.1 Key significance of cross-section in the model calculation 
For a better understanding of the interaction between rainwater drainage and second order water 
bodies the one-dimensional model (MIKE 11 by DHI) was chosen to simulate flow, water level, water 
quality and sediment transport. It provides a fully dynamic solution based on the nonlinear 1-D Saint 
Venant equations. 
Saint Venant Eq. according to the notation in MIKE 11 (1) 


+
(∝

	
)

+ 	


+
||
²
= 0 (1)  
where Q is the discharge (in m³/s), A is the flow area (in m²), q is the lateral inflow (in m³/s), h is the 
stage above sea level (in m), C is the Chezy resistance coefficient, R is the hydraulic radius (in m) and 
α is the momentum distribution coefficient. 
The parameters A, R and h are essential key variables in the Saint Venant equation and are the 
outcome themselves of the definition of the specific cross-section. In contrast to other modelling tools 
(e.g. HEC-HMS), the editing of the cross sections also defines the bottom slope. This underlines the 
strong influence of the cross-sections according to streamflow and water level calculation. The shape 
of the cross-section has also effect on ecological structure and functioning. According to the equation 
(2) the bed shear stress is a function of hydraulic radius.The quantity of the water surface or riverbed 
are input parameters for the simulation of the dissolved oxygen or the adsorption of dissolved 
phosphorus to particles of river sediment. 
Bed shear stress Eq. according to the notation in MIKE 11 (2) 
 = 
²
²/
 (2)  
2.2 Cross-section determination for the reference model 
The 1-D modelling program MIKE 11 (by DHI) needs geo-referenced cross-sections as input 
parameters. They are necessary to generate the longitudinal profile and the wetted area of the stream. 
The determination of the cross-sections is in the field of geodetic surveying. The objective is to use 
workable measurement procedures, which provides sufficiently precise coordinates.  
Table 1: Comparison between surveying technology for small water streams 
Method Altitude 
Error  
Advantage Disadvantage Geo-
referenced 
Total station ± 0,01m From one position several 
cross-sections could be 
Needs a long training 
period and relative high 
NO 
NOVATECH 2016 
3 
determined acquisition costs 
Manual measurement 
with levelling staff 
± 0,05m In contrast to the other  
methods, this method is 
inexpensive and is able to 
react fast 
Time consuming and also 
error-prone 
NO 
RTK-GPS ± 0,015m RTK-GPS makes flexible, 
fast and reliable surveying 
possible 
Signal disturbance by 
foliage of bank vegetation 
YES 
Spirit levelling in 
combination with 
distance measurement 
± 0,001m Very precise measuring 
method 
Have to change the 
position to determine 
several cross sections 
NO 
Generally, the RTK-GPS is the best choice for surveying of small streams. However, often one bank 
side is nearly complete forested. Under these conditions, no high reception quality is available for the 
RTK-GPS. In these cases, an intelligent combination of RTK-GPS and traditional observation (total 
station) results a good compromise between spatial resolution and time efficiency. 
There are no official benchmarks in the range of the total station to reference the elevation and 
position of measured cross sections. Therefore, we have to set temporary, not official reference marks 
at each measuring place of the watercourse. These reference marks are designed to be set in 
concrete structures or on similar position stable constructions and geo-referenced by measurement 
with the RTK-GPS. The reference marks have to be position-stable along the period of investigation (3 
years).  
2.3 Cross-section determination for the macro model 
The research area extends across the rural and urban regions of the city of Rostock and comprises 
water streams with a total length of more than 100 km.  For the whole system, a terrestrial surveying is 
only feasible in a long term approach. Therefore, it is necessary to investigate a method, which blends 
existing data with information from remote measurement technique. The profile was elevated and 
provided by the water information system of the Agency for the Environment, Nature Conservation and 
Geology of Mecklenburg-Vorpommern. This trapezoidal rule profiles are not georeferenced. The 
missing position information was edited by using digital terrain model with a vertical resolution of two 
meters and orthophotos. 
2.4 Comparison of the discharge capacity at a case study 
For a case study, the hydraulic deviations between an exactly measured cross profile and a nearly 
similar, simplified profile, which was achieved by the GIS-based method, are compared. The channel's 
discharge capacity was calculated by using the Manning-Strickler approach, with a value of Manning’s 
n (ressitstence number) of 0,03 and bottom slope of 0,001. In addition, several simulitions with the 
hydrodynomic modul of MIKE 11 (by DHI) verifys the result shown in Figure 2. 
RESULTS AND DISCUSSION 
The Figure 1 shows the detailed surveyed cross-section of the reference model in comparison to the 
generated cross-section from the macro model. In addition, in order to aid comparison, width and 
height of the cross-section were set to the similar value.  
 
Figure 1. Generated and surveyed profile. Squares: generated CS; Triangles: surveyed CS 
 
SESSION 
4 
 
Figure 2. Comparison of discharge capacity of the generated and surveyed CS. Circle: relative error; 
Squares: generated CS; Triangles: surveyed CS 
 
Figure 3. Comparison of potential sources of errors. Circle: hydraulic radius; Squares: wetted area; 
Triangles: wetted perimeter 
The following issues can be highlighted: 
• The hydraulic radius is the quotient of the wetted cross-sectional area and the wetted perimeter. 
The wetted area of the generated cross-section is overestimated while the wetted perimeter is 
underestimated. Simplified estimation of cross-sections lend to inexact hydraulic radii and in 
consiquence to rather strong deviations for discharge, flow depth and derived modelling results.  
• It turned out that the maximum discharge capacity of the generated cross-section (macro model) 
according to the surveyed cross-section (reference model) is overestimated (30%). This has an 
considerable effect on the flood simulation. At full charge conditions (max water level is 2.11 m) 
the real discharge capacity is much lower (6,27 m³/s) instead of expected one (8,24 m³/s). 
• Even more serious are the relatively large flow rate errors of 200-800% at dry weather flow 
conditions. There would be a danger of wrong calibration of rainfall runoff models where only 
water level informations are availible. In this cases a continues flow stream measurement system 
is essential. 
CONCLUSION 
At first glance it surprise, that very similar looking cross sections, have large differences in discharge 
capacity – especially at dry weather conditions. Therefore, high-resolution models are very sensitive to 
the accuracy of cross sections. This effect is particularly distinctive, when relatively small rivers are 
model- linked to large catchment areas. In further studies, we want to investigate the hydraulic 
performance of structured and renatured watercourses second order. 
LIST OF REFERENCES 
Belinska, V., Kluga, A., Kluga, J. and Bricis, A. 2014 Accuracy Estimation of TOPCON GRS-1 GNSS Receiver 
Parameters in Static and Dynamic Mode. ElAEE, 20(2). 
Castellarin, A., Di Baldassarre, G., Bates, P. D. and Brath, A. 2009 Optimal Cross-Sectional Spacing in 
Preissmann Scheme 1D Hydrodynamic Models. J. Hydraul. Eng., 135(2), 96–105. 
DHI 2014 MIKE 11: A Modelling System for Rivers and Channels. Reference Manual, 536 pp. 
Md Ali, A., Solomatine, D. P. and Di Baldassarre, G. 2015 Assessing the impact of different sources of 
topographic data on 1-D hydraulic modelling of floods. Hydrol. Earth Syst. Sci., 19(1), 631–643. 
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Détermination des données d'entrée morphologiques pour les modèles hydrauliques 1-D en utilisant des levés géodésiques ciblés

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Détermination des données d'entrée morphologiques pour les modèles hydrauliques 1-D en utilisant des levés géodésiques ciblés

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