Report Lesson 3.1 #  MIKE 11
Team
1  HydroEurope
Deadline: December 16^{th}
2016
Benoît BESSEAS^{(1)}, Océane CALMELS^{(1)}, Laura DAUL^{(1)},
Guillaume HAZEMANN^{(1)}, Quentin MOLIERES^{(1)}, Blazej
SMOLINSKI^{(2)}, Arianna VARRANI^{(3)}, Robin WARNER^{(4)},
Taline ZGHEIB^{(5)}, Zhengmin LEI^{(1)}
Supervisors : Philippe GOUBERSVILLE^{(1)}, Olivier
DELESTRE^{(1)}
^{(1)} University
of Nice SophiaAntipolis, France
^{(2)} Warsaw University of Technology, Poland
^{(3)} Brandenburg
University of Technology CottbusSenftenberg, Germany
^{(4)} Newcastle University, United Kingdom
^{(5)} Vrije
Universiteit Brussel, Belgium
I.
Introduction
The project
of this lesson is to simulate the 1994 Var flood event and to compare different
result of different bed resistance and different weir value. Target of this
lesson is the introduction of Mike11 as software tool for 1D river modelling
within the context of the HydroEurope project.
In this
lesson, there are two exercises which are designed to get familiar with the
Mike11 software tool. The 1st exercise is to create a simple academic model to
understand the interface of Mike 11. The 2nd exercise is to compare the results
of different bed resistance and different weir value on the base of a given
simplified river mode.
II.
Methodology
The general
steps to create a project in MIKE 11 will be described as bellows:
Figure 1: Main Steps of the Mike 11 process
The
geometry data of river bank is set up in Network and crosssection file. In HD
parameters file, we can set up the bed resistance value.
III.
Results
and discussion
1. Exercise 1
In this
exercise, we set up a simple MIKE 11 model. The model contains a straight
channel of about 5000 m with a regular rectangle crosssection of about 50 m
width and 10 m depth. The boundaries conditions are given by the discharge
q(t)=0 (closed channel) at one side and by the water level h(t) at the other
side. The target is to compare two different water level conditions. The first
one is that h(t) equals to 4 m for time steps and that 6 m for second time step
to generate a kind of water wave in the system.
The second is that h(t) equals to 6 m for time steps and that 8 m for
second time step.
Figure 2 : Water level of longitude profile with simulation of wave (left: h(0) = 4m; right: h(0) = 6m) 
In brief,
the dissipation of the wave is longer with a higher water level. Bigger the
wave is, higher the water level is at the downstream.
2. Exercise 2
The second exercise
is based on a prepared data set for the lower part of the river Var with
simplified topography and without human infrastructure. Point remark: this
model did not consider the reality in the river.
Four tasks
are requested to complete. The Task 1 consist of observing the water level for
a steady flow condition. In the task 2, we need to setup of a basic unsteady
model for the flood event 1994. In task
3, we will study the results of two different bed resistance by changing the
Manning parameter. In task 4, we will analyze the impact of different weir
geometry values.
2.1.
Task 1
The outcome
for this task is a Mike11 model for the simplified river Var for about 5 days
with steady flow condition (Q = 300 m³/s).
Figure 3 : Water level of longitude
profile of simplified river Var with a constant flow condition 
In figure
3, we can observe that there isn’t any flood risk location with the constant
discharge of 300 m³/s.
In
addition, we can check the water level and discharge result of each cross
section in the table that can be analyzed more precisely.
2.2.
Task 2
The peak
discharges of the 1994 Var flood event was 3600 m³/s and two weirs were
destroyed which generated large flooding area and important damages. We
simulate the flood discharge in terms of the discharge measured on the Napoléon
III bridge in Nissa.
Figure 4 : Water level of longitude profile (right) with the simulated flood condition (left)
The red
dash line in figure 4 right represents the maximum water level. We observed
that the most dangerous cross section is at 7500 m. With the simulated flood
boundary condition, there is a flood risk at this cross section on the left
river bank.
2.3.
Task 3
The object
of task 3 is to study the impact of the bed resistance. The basic data set has
a Strickler value of 30. The impact of this value was studied by a sensitive
analysis with four different Strickler values which are 15, 45, 60 and 80.
Figure 5 : Different water level of longitude profiles for different bed resistance
The maximum
water level occurs at about 19:25 on the 5th November 1994. The figure 5 represents different maximum
water level profiles with four varied Manning values. It illustrates that the bigger
the resistance is or the rougher
the river bed is, the higher
the water level is. Besides, the
most dangerous cross section who have the biggest flood risk is still at 7500m.
Table 1: Discharge maximum ant its
occurrence time at cross section 7200m for different bed resistance

At cross section 7200m


Strickler value

Discharge maximum (m³/s)

Max. time

15

2782.617

05/11/1994 19:52:04

45

2791.600

05/11/1994 19:40:35

60

2794.733

05/11/1994 19:38:00

80

2796.729

05/11/1994 19:38:00

The higher
Strickler value indicates the lower bed resistance which means that the river
bed is smoother. According
to table 1, we can find
that the discharge maximum reduces with the increase of bed resistance. Also,
the occurrence time of discharge maximum become earlier.
2.4.
Task 4
In this
part, impact of different weirs ’geometry to the river flow will be analyzed. Three
different broad crested weirs (broad crested weir) were constructed
respectively at 15200m cross section. All the weirs have a simple geometry with
two levels: a lower level of and a constant width. The higher level is 45 m
which is set as constant. We change only one variable which is the lower level
or the width each time to analyze the impact of unique value.
Table 2 : Geometry
of different weirs

higher level

lower level

width

Weir 1

45

35

50

Weir 2
(shorten
width)

45

35

40

Weir 3
(shorten
height)

45

32

50








Figure 6 : Water level of longitude profile for three different weirs
Comparing
weir 1 et weir 2 in figure 6, we observed that the restrain capacity of the
weir becomes bigger when we shorten the width. Then it becomes smaller when weir’s
width is shortened by comparing weir1 et weir 2.
Table 3: Discharge maximum
ant its occurrence time at cross section 15200m for three different weirs
At downstream cross section 23726.88m


Discharge maximum (m³/s)

Max. time

Without weir

2773.909

05/11/1994 20:21:47

Weir 1

2728.565

05/11/1994 20:29:30

Weir 2

2705.905

05/11/1994 20:38:31

Weir 3

2747.756

05/11/1994 20:30:48

From table
3, the construction of weir can control the downstream flood flow efficiently. It
decreases the downstream discharge and postpone its occurrence time. That’s why
weirs are commonly used to control the flow rates of rivers and protects
villages and habitants downstream during periods of high discharge.
In
addition, the weir 2 with higher height and short width reduced the most the
downstream discharge.
IV.
Conclusions
In
conclusion, the analysis of bed resistance proves that the peak flood flow may
be considerably reduced by increasing the bed sediments. Flood risk especially
on downstream can be reduced by constructing weirs across river.
With the
help of MIKE 11, we can model and analyze a set of various parameters by
creating a 1D hydraulic river model. It’s an useful and efficient software.