Mobile Flood Protection Walls

Abstract

Flooding is a burning issue in Hungary because of its geographical conditions. The topic of this article is to describe the mobile flood protection methods, which are able to accomplish the criteria of environment and sustainability. Mobile flood wall is a new solution in flood protection which is used in populated area. The design of mobile flood walls must focus on surveying water levels, determination of loads and limitation of leaking water. The main types of loads on the structure are hydrostatic, hydrodynamic and impact loads. The DIN 1055 German standard is used to determine the loads.

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POLLACK PERIODICA
An International Journal for Engineering and Information Sciences
DOI: 10.1556/Pollack.10.2015.1.13
Vol. 10, No. 1, pp. 133–142 (2015)
www.akademiai.com
HU ISSN 1788–1994 © 2015 Akadémiai Kiadó, Budapest
MOBILE FLOOD PROTECTION WALLS
István KÁDÁR
Department of Geotechnics, Budapest University of Technology and Economics
Műegyetem rkp. 1, H-1111 Budapest, Hungary, e-mail: kadar.istvan@mail.bme.hu
Received 27 December 2013; accepted 23 June 2014
Abstract: Flooding is a burning issue in Hungary because of its geographical conditions. The
topic of this article is to describe the mobile flood protection methods, which are able to
accomplish the criteria of environment and sustainability. Mobile flood wall is a new solution in
flood protection which is used in populated area. The design of mobile flood walls must focus on
surveying water levels, determination of loads and limitation of leaking water. The main types of
loads on the structure are hydrostatic, hydrodynamic and impact loads. The DIN 1055 German
standard is used to determine the loads.
Keywords: Mobile flood protection, Flood, Environment, Mobile flood wall, Hydrostatic
loads, Hydrodynamic loads, Standard
1. Introduction
Hungary’s biggest natural hazard is flooding [1], [2]. 23% of the country’s territory
is situated in the floodplain. 97% of this area is protected by flood control dams and the
remaining 3% is generally low-value zone [3], [4]. Different ways of coexistence with
water were formed in the floodplain. In most parts of Europe where the flood exempted
area ratio is not as high as in Hungary, the population often refuses those new flood
protection improvements and investments, which disrupt the relationship between
people and river, whether it be fishing, canoeing, lakeside walk or simply the view of
the river. So, in many places the structural methods are refused and the closer way of
the river coexistence methods are chosen not forgetting the disadvantages related to

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their decision. Elsewhere people choose the higher security level and aspects like the
increasing transport path of boats are undervalued [5].
2. Mobile flood protection structures
Since the ‘90s several types of equipment have been introduced to the flood control
market with manufacturers claiming they were suitable for adding height rapidly to
protect against overtopping. These are the mobile flood protection dikes and mobile
flood protection walls. In Hungary we started to design and use these types of elements
with a 10-15-year delay.
The application of mobile flood protection dikes is a typical solution for emergency
heightening. Engineering development has produced several varieties of mobile flood
protection dikes like tube dikes, triangular dikes (Fig. 1) with watertight sheeting etc.
Fig. 1. Triangular mobile flood protection dike
Although they are only applied in high water conditions, mobile flood protection
walls are not designed for emergency operations. They are used first of all in locations
where the disadvantage of a flood protection dike (or a concrete wall) is intolerable (e.g.
due to traffic) or unwanted (e.g. a settlement does not wish to be separated from a river)
during periods of low and medium water level. Mobile walls are suitable in locations
lacking the space needed for building embankments. In Hungary the first mobile flood
protection wall was installed in 2006 in Baja (Fig. 2).
Similar solutions have been installed instead of a traditional flood protection dike in
several major European cities (e.g. Cologne, Paris, Prague. In June 2013 the Hungarian
Szentendre was also defended by a mobile flood protection wall (Fig. 3). In periods

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without high water, the elements of the mobile flood protection walls rest in a storage
room.
Fig. 2. First application of mobile flood protection wall in Hungary
Fig. 3. Mobile flood protection wall in Szentendre (Photo: Swietelsky Hungary)
Mobile flood protection walls have advantages and disadvantages. The pros help to
make the structure environmentally friendly, and to fulfill the criteria of sustainable
development. The elements are easy to carry so the installation is fast (8 people can
build a 300 m long section in 1 day).
The facts against the mobile walls are partial mobility and relatively high installation
costs. There are places where the earth dikes are the only reasonable option, e.g.
peripheral low cost areas where there is no need to keep in touch with the riverbank. But

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in crowded urban areas the mobile walls have far more advantages to satisfy the
inhabitant’s needs. A summarized list of advantages and disadvantages is shown in
Table I.
Table I
Advantages and disadvantages of mobile flood protection walls [6], [7]
Advantages Disadvantages
Small installation space required Partial mobility (specified place)
After flood the structure is unbuilt - the
landscape is not disturbed
Storing area needed
Reusable structural elements Subject of vandalism (permanent elements)
Light structural elements Higher installation cost
Rapid installation
3. Loads of mobile flood protection walls
The loads of the structure can be determined based on the German standard DIN
1055 [8]. This basically corresponds with the current Eurocode standards but in
Hungary there is no operative standard for mobile flood protection walls.
3.1. Dead load
The dead load is calculated based on the specific gravity of the used materials
according to the DIN 1055-1 standard.
3.2. Live loads
Hydrostatic pressure
By calculating hydrostatic pressure the whole structure and all the individual structural
elements must be examined for the biggest physically possible water height (Fig. 4a)
but with reduced safety factors. If the walls are not vertical, the vertical component of
the water pressure should be also considered and the water pressure is always
perpendicular to the surface.
Hydrodynamic pressure
• Flow pressure
Considering that the water flow direction and the longitudinal axis of the walls are not
parallel a pressure load should be calculated from the water flow (Fig. 4b). The pressure
depends on the velocity of the water flow, which is usually given by the client or
measurements can be observed. The relationship between pressure and flow velocity
can be given with the momentum conservation law. The effect of the flow pressure
depends on the angle of flow and the angle of the wall panels with the direction of flow.

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When the mobile flood wall on the water side does not interfere with the water flow it
means that the angle of the flow is parallel to the longitudinal axis of the wall. In this
case the flow pressure is negligible. The flow pressure is independent of the height of
the water level, only depends on the size of the loaded surface.
• Water elevation on outer bank;
When the mobile wall is situated on the outer bank of a river compared with the water
level of the centerline an extra water elevation can be calculated (Fig. 4c) as
g
v
R
B
H2
5.1∆
2
=, (1)
where ∆H is the water elevation on outer arc; B is the width of the river; R is the radius
of the river bend; v is the water flow velocity; g is the acceleration of gravity.
a) b) c)
Fig. 4. Hydrostatic pressure, flow pressure and water elevation on outer bank
• Wave pressure;
Further load can be determined caused by the water waves. The primary question is
whether the wall is situated in a protected area where only standing or breaking waves
reach the wall or overtopping is possible with ‘crashing’ (Sturzbrecher) waves (Fig. 5).
If there is no data about the waves of the area the wave load should be calculated based
on Table II. It gives the pressure wave load depending on the wave type and height.
Fig. 5. The position of the substitutional load, low waves case, high wave case

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Table II
Determination of the substitutional load
Wave height Substitutional load Point of contact under the
water level (H1 [m])
Type of wave
Hds[m] P1 [kN/m] Water height
(H) > 2.0 m
Water height
(H) < 2.0 m
≤0.40 20 1.00 0.4×H
Standing/ breaking wave >0.40 30 1.00 0.4×H
≤0.40 40×Φ (Φ=1.2) 0.80 0.3×H
Crash wave >0.40 60×Φ (Φ=1.2) 0.80 0.3×H
The calculated amount of the wave pressure load can be reduced when waves
overtop the wall,
,f if,0.1
, if,
3
η
η
η
>
<= f
f
k (2)
where k is the reduction factor; f is the height of the edge;
η
is the height between the
top of the wave and water level, its value is ds
H 78.0
=
η
(standing/breaking waves),
ds
H 3.1=
η
(crashing waves), and Hds is the wave height.
• Impact load
The mobile flood protection walls are not designed to bear the load of a much bigger
object (e.g. ship). In this case the buckling of the structure is unavoidable but usually at
the time of the flood the boat traffic is stopped. The water-borne sediments or ice floe
collision are realistic loads. For this kind of impact mobile flood protection walls must
fulfil the criteria of Ultimate Limit States (ULS). The impact load (F) in the calculation
is a distributed load (on 0.5 m x 0.5 m) (Fig. 6). The impact load depends on the water
flow velocity, the weight of the buffering object and the stiffness of the mobile flood
protection wall. The minimal weight of the buffering object is 0.4 t, which is
approximately a 5 m long wood log with 40 cm in diameter,
f
cmvF ⋅⋅⋅=
δ
sin , (3)
where v is the velocity of water flow; δ is the angle of water flow; m is the weight of the
buffering object, cf is the stiffness of the wall.
Based on the water flow velocity and the flow angle the impact load can be
determined easily from Table III. Among the rows of the table interpolation is
permitted.

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Fig. 6. Impact and wind load
Table III
Impact load (m = 0.4 t , cf = 497.78 kN/m, L = 3.0m, E = 70.000 MN/m2)
Water flow velocity Angle of water flow [°]
v [m/s] 15 30 45 60 75 90
1.0 4 7 10 12 14 14
2.0 7 14 20 24 27 28
3.0 11 21 30 37 41 42
4.0 15 28 40 49 55 56
The impact load component parallel to the wall stability is important for the wall
longitudinal stability of this flow and the pressure component parallel walls should be
checked.
• Wind load
During the flood defense when the walls are installed the wind pressure works above
the flood water level. Before high water conditions the stability of the wall should be
examined on both sides (Fig. 6).
The value of wind load is
qw ⋅= 2.1 , (4)
where q is the value of wind gust (Table IV).
Table IV
Wind gust coefficients
q [kN/m2] Height above sea level
Area 0-8m 8-20 m 20-25 m
Seashore / North-Germany. 0,95 1,25 1,45
Close-to-shore / North-Germany 0,80 1,05 1,20
Plain 0,65 0,85 1,00

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• Other live loads
• Live load (people);
A horizontal load on the top edge should be taken into account because of tourists or
workers. It can act in both directions (tension / compression). Its value is 0.5 kN/m.
• Live load (vehicle);
It is not a requirement to bear the load of an intentionally collisioning vehicle. The
vehicle load takes a slow, e.g. reversing car into consideration. The load is a
concentrated 5 kN/m force and the point of contact is at 1.2 m height (Fig. 7).
Fig. 7. Vehicle load and dry-side water pressure
3.3. Extra loads
• Dry-side water pressure;
It is important to ensure the stability of the walls against a dry-side water pressure
(Fig. 7) in areas with relatively slow runoff. The water level should be determined based
on local conditions taking into account that the flood went down.
• Screw loss;
It must be proved that with the loss of one bolt the ultimate and serviceability limit
states are feasible. It refers to the anchors, which can be moved (as they can fall out
accidentally by installation or due to deliberate vandalism).
• Overtopping;
By the design of the walls the physically possible maximum water level should be
taken into account, which can be determined by model tests.
In general, the mobile flood protection walls are not protected from overtopping that
threatens the protected area, so an immediate evacuation plan should be drawn to the
area (Fig. 7).
Considering possible future high water levels the anchorage structure of the mobile
flood protection wall can be designed for bearing larger loads. In this case the
replacement of the substructure is not necessary, only higher columns are needed (e.g.

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in Szentendre (Fig. 8) the design water level was 1,80m but the strength of the
substructure is enough to bear the load of 2.40 m high water).
Fig. 8. Mobile flood protection wall in Szentendre (Photo: Swietelsky Hungary)
4. Conclusion
The design and installation of mobile flood protection walls is still a recent topic in
Hungary. The available literature in this field is insufficient. This article aimed to give
an overview about mobile flood protection structures especially focused on the loads of
a mobile flood protection wall.
Acknowledgement
The work reported in the paper has been developed in the framework of the project
‘Talent care and cultivation in the scientific workshops of BME’ project. This project is
supported by the grant TÁMOP-4.2.2.B-10/1--2010-0009. Special thanks to László
Nagy who supervised the research.
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