HYDROLOGICAL PROCESSES
Hydrol. Process. 22, 4695– 4709 (2008)
Published online 16 June 2008 in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/hyp.7079
Comparison of hydrodynamic models of different
complexities to model floods with emergency
storage areas
Chandranath Chatterjee,1 * Saskia Förster2 and Axel Bronstert2
1
Agricultural & Food Engineering Department, Indian Institute of Technology Kharagpur, Kharagpur - 721302, West Bengal, India
2 University of Potsdam, Department of Geo-ecology, Karl-Liebknecht-Str. 24-25, 14476 Golm, Germany
Abstract:
A flood emergency storage area (polder) is used to reduce the flood peak in the main river and hence, protect downstream areas
from being inundated. In this study, the effectiveness of a proposed flood emergency storage area at the middle Elbe River,
Germany in reducing the flood peaks is investigated using hydrodynamic modelling. The flow to the polders is controlled
by adjustable gates. The extreme flood event of August 2002 is used for the study. A fully hydrodynamic 1D model and a
coupled 1D–2D model are applied to simulate the flooding and emptying processes in the polders and flow in the Elbe River.
The results obtained from the 1D and 1D–2D models are compared with respect to the peak water level reductions in the Elbe
River and flow processes in the polders during their filling and emptying. The computational time, storage space requirements
and modelling effort for the two models are also compared. It is concluded that a 1D model may be used to study the water
level and discharge reductions in the main river while a 1D-2D model may be used when the study of flow dynamics in the
polder is of particular interest. Further, a detailed sensitivity analysis of the 1D and 1D–2D models is carried out with respect
to Manning’s n values, DEMs of different resolutions, number of cross-sections used and the gate opening time as well as
gate opening/closing duration. Copyright 2008 John Wiley & Sons, Ltd.
KEY WORDS
flood; emergency storage area; hydrodynamic models; 1D-model; 1D-2D model
Received 25 September 2007; Accepted 23 April 2008
INTRODUCTION
Flood storage areas form part of the flood management
strategy at many lowland rivers. They are used to store
excess floodwater temporarily in order to reduce peak
flood flows downstream. In the last few years various
studies have been conducted to predict the flood peak
reduction in the main river and to simulate the inundation
process in the flood storage areas. These studies represent
a special case of hydrodynamic floodplain modelling
because of the controlled manner of detention and release
of flood water. Flow may be controlled by spillways,
adjustable inlet and outlet structures or engineered dike
breaches.
Various researchers have used the hydrodynamic modelling approach to simulate flood inundation in the
floodplains (Werner, 2004; Bates et al., 2005). The
hydrodynamic modelling approach of flood inundation
simulation essentially involves the solution of onedimensional and two-dimensional Saint Venant equations
using numerical methods. Various numerical models have
been developed for flood plain delineation/flood inundation and flow simulation. These numerical models
essentially involve solving the governing equations for
* Correspondence to: Chandranath Chatterjee, Agricultural & Food Engineering Department, Indian Institute of Technology Kharagpur, Kharagpur - 721302, West Bengal, India.
E-mail: cchatterjee@agfe.iitkgp.ernet.in
Copyright 2008 John Wiley & Sons, Ltd.
flow in rivers and floodplains using certain computational algorithms. Based on the approximations used,
the numerical models are categorized into (a) onedimensional (1D) models, (b) two-dimensional (2D)
models, and (c) one-dimensional river flow models coupled with two-dimensional floodplain flow (1D–2D)
models.
Software, such as HEC-RAS (HEC River Analysis System) from the US Army Corps of Engineer’s
Hydrologic Engineering Center (HEC, 2002), US
National Weather Service’s (NWS) DWOPER and FLDWAV (Fread et al., 1998), MIKE11 developed at the
Danish Hydraulic Institute, Denmark (DHI, 1997),
SOBEK-1D developed at Delft Hydraulics, Delft
(Werner, 2001), etc., has been used extensively for
dynamic 1D flow simulation in rivers. The 1D models, although simple to use and providing information
on bulk flow characteristics, fail to provide detailed
information regarding the flow field. Hence, attempts
have been made to model the 2D nature of floodplain flow. Some of the most widely used software
for 2D modelling are FLO 2D (O’Brien, 2006), RMA2
(King et al., 2001), MIKE-21 (DHI, 2000), DELFT-FLS
(Hesselink et al., 2003), DELFT-3D (Stelling and Duinmeijer, 2003) and TELEMAC-2D (Horritt and Bates,
2001).
The 1D models fail to provide information on the flow
field while the 2D models require substantial computer
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C. CHATTERJEE, S. FÖRSTER AND A. BRONSTERT
time; hence, attempts have been made to couple 1D
river flow models with 2D floodplain flow models. In
the coupled 1D–2D models, the flow in the main river
channel is simulated using the 1D equations, while the
2D equations are solved for the water spilling over the
banks to the floodplains. The link between the two kinds
of flow is usually made by a mass conservation equation.
Dhondia and Stelling (2002) describe the 1D–2D model
SOBEK (Rural/Urban) developed by the laboratory at
Delft Hydraulics. The MIKE-21 model has been dynamically linked to the MIKE-11 model, into a single package
called MIKE FLOOD developed at the Danish Hydraulic
Institute (Rungo and Olesen, 2003).
Hydrodynamic models of different complexity have
been used to simulate flow situations with flood storage
areas. 1D models for the river coupled with storage cells
that represent the polders have been used to simulate
the peak capping effect. The storage cells are usually
characterised by the relationship between volume or area
as a function of elevation or by a series of cross-sections
(Kúzniar et al., 2002; Minh Thu, 2002; Faganello and
Attewill, 2005). Also, there are a few studies applying
combined 1D–2D model, where the flow in the river
is solved in 1D whereas the flow in the storage area
is simulated using a 2D approach (Baptist et al., 2006).
Further, since full 2D or combined 1D–2D models
are generally computationally very extensive, quasi-2D
model approaches have been applied in order to give a
simplified 2D representation of the storage area combined
with a fast computation process (Aureli et al., 2005;
Huang et al., 2007).
As far as floodplain inundation is concerned, several
studies have been carried out to compare the predictive
performances of hydrodynamic models of different complexities (Horritt and Bates, 2002; Tayefi et al., 2007).
However, there has been no such detailed comparative
study for simulating floods with emergency storage areas.
In this study, a comparison of 1D MIKE11 and 1D–2D
MIKEFLOOD models to simulate flows for a proposed
flood emergency storage area at the middle Elbe River,
Germany is carried out.
STUDY AREA AND DATA USED
The proposed emergency storage area is located in
the lowland area at the Middle Elbe River, Germany
(Figure 1). It extends 7 km along the right bank of the
Elbe River. The overall area is 17 km2 with a maximum
storage capacity of approximately 40 ð 106 m3 .
The storage area is divided into a northern and a
southern polder basin by an already existing dike road
running through the area. The two basins are connected
by a sluice gate of 50 m width and 2 m depth. This
gate is termed the connecting gate. The filling and
emptying process of the storage area is controlled by
two adjustable overflow weirs, each of 25 m width. The
gate for the north polder is termed the north gate while
Figure 1. Map of the proposed flood emergency storage area at the Middle Elbe River, Germany
Copyright 2008 John Wiley & Sons, Ltd.
Hydrol. Process. 22, 4695– 4709 (2008)
DOI: 10.1002/hyp
HYDRODYNAMIC MODELS TO MODEL FLOODS WITH EMERGENCY STORAGE AREAS
the gate for the south polder is termed the south gate.
The emergency storage area is designed for reducing
flood peaks of not less than 100 years return period. It
has to be emphasized that the emergency storage area
is a potential retention site and hence, at present neither
the dikes surrounding the polder basins nor any control
structures exist. Topographic data, river flow data and
information on control structures and polder dikes were
provided by the local water authorities according to the
current planning stage.
In this study, the flood event for the period 5 August
to 17 September 2002, i.e. a duration of 44 days, is
considered to study the effectiveness of the proposed
polder. For this flood event, the peak discharge is
4420 m3 s1 , which occurred on 18 August 2002 at the
Torgau gauge. Four other flood events are used for model
calibration and validation as described later.
Currently about 90% of the area is under intensive
agricultural use. The rest is taken up by watercourses
and forests, most of which are under nature protection. It
is expected that the land will retain its original purpose
after designation as an emergency storage area.
METHODOLOGY
The 1D model MIKE 11 and the coupled 1D–2D model
MIKEFLOOD are applied to simulate the flooding and
emptying processes in the polders and flow in the
Elbe River. The governing flow equations of MIKE
11 are 1D and are of shallow water types, which
are modifications of the Saint Venant equations (DHI,
1997, 2000). MIKEFLOOD integrates topographic data
of the 1D MIKE 11 river network with the 2D MIKE
21 floodplain (bathymetry data) through four different
linkages: (i) standard link where one or more MIKE21
cells are linked to the end of a MIKE11 branch; (ii)
lateral link where a string of MIKE21 cells are laterally
linked to a specified reach of MIKE11; (iii) structure
link consisting of a three-point (upstream cross-section,
structure and downstream cross-section) MIKE11 branch
whose ends are linked to MIKE21 cells; and (iv) zero
flow link specified to a MIKE21 cell will have zero flow
passing across the cell (DHI, 2004). For this study, the
standard link is the only relevant link that can be used
and hence, it is selected.
One-dimensional model setup
The 1D model MIKE 11 is set up to represent
an18Ð6 km reach of the Elbe River (Figure 2), which is
described by a series of 34 cross-sections. These crosssection data are provided by the local water authority. The
cross-section data available downstream of Elbe 187 km
are not only very sparse but are available for the main
channel only. Hence, these cross-sections were extended
to the dikes using elevation data from airborne laser
altimetry.
The boundary condition at the upstream end of the
reach at 175Ð0 Elbe-km is a discharge hydrograph of
Copyright 2008 John Wiley & Sons, Ltd.
4697
the Torgau gauging station. Although this gauge is
located approximately 20 km upstream of the upper
model boundary, utilisation of these discharge data is
justified as there are only minor tributaries to the Elbe
River between Torgau and the modelled river stretch.
The downstream boundary condition at 193Ð6 Elbe-km
is provided as a rating curve.
The emergency storage area is schematized in the
model by two storage cells each representing one
polder basin. The storage cells are described by their
area–elevation curves (Figure 2). The curves are derived
from a high-resolution digital elevation model (DEM)
that was obtained from airborne LiDAR survey. The gates
are implemented as control structures that operate under
certain pre-set conditions as mentioned later.
Calibration and validation of model. Calibration of
the hydrodynamic models for emergency flood storage
areas is difficult as emergency storage areas are usually
designed to be used for flood peak capping during rare
flood events. The storage area may have never been
in operation before and hence, observation data for
calibration purpose may not be available. This is true for
the present study, which investigates a proposed flood
storage area that is not yet constructed. However, the
MIKE11 model is calibrated and validated for the flow in
the Elbe River and its floodplain within the embankments.
The MIKE11 model is calibrated and validated against
water levels recorded at the Mauken gauging station
at 184Ð4 Elbe-km. Because of the different nature of
bed materials two hydraulic roughness classes are distinguished, one for the main channel and one for the
adjacent floodplain. In order to identify the two roughness coefficients, a two-stage calibration and validation
procedure is adopted. In the first stage, the roughness
coefficient for the main channel is identified and in the
second stage the roughness coefficient for the floodplain
is identified. Four flood events during the period 1 October to 30 November 1999, 1 January to 31 March 2002,
1 August to 27 September 2004 and 1 March to 30
June, 2005 are selected for the process of calibration and
validation. Of these, water does not spill over to the floodplains for the first and third events and hence, these are
used for calibration and validation for the main channel.
Initially, the roughness information in the form of Manning’s n values is taken from the literature (Chow, 1959)
and similar studies (Horritt and Bates, 2002) which are
then modified during the calibration process.
Two goodness of fit criteria are used to compare the
simulated water levels with the observed values. These
are (i) the Nash–Sutcliffe coefficient (Ens ) and (ii) the
index of agreement (d), which are as follows:
⊲Qo Qs ⊳2
⊲1⊳
Ens D 1
⊲Qo Qav ⊳2
⊲Qo Qs ⊳2
dD1
⊲2⊳
⊲jQo Qav j C jQs Qav j⊳2
Hydrol. Process. 22, 4695– 4709 (2008)
DOI: 10.1002/hyp
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C. CHATTERJEE, S. FÖRSTER AND A. BRONSTERT
Figure 2. MIKE 11 model layout for the proposed flood emergency storage area
where, Ens D modelling efficiency, Qo D observed discharge (m3 s1 ), Qs D simulated discharge (m3 s1 ),
Qav D mean of the observed discharge (m3 s1 ) and d D
index of agreement.
One-/ two-dimensional model setup
In the MIKEFLOOD model layout, the Elbe River
and the three gates (inlet or south gate, connecting
gate and outlet gate) are represented in the 1D model
MIKE11. The polders are represented in the form of a
DEM in the 2D model MIKE21. Both the 1D MIKE11
and 2D MIKE21 models are dynamically coupled by
standard links. This coupled model is run with the same
boundary conditions, flood scenario (i.e. for the August
Copyright 2008 John Wiley & Sons, Ltd.
2002 flood event) and gate operation as the 1D model.
Thus, the essential difference between the 1D MIKE11
setup and MIKEFLOOD setup is in the representation of
the polders.
In this study, three different DEMs are used which
are obtained by resampling the LIDAR DEM to grid
sizes of 8 m, 25 m and 50 m. Initially, the LIDAR DEM
is processed to remove non-permanent objects, such as
dung hills or vehicles, and to correctly represent line
structures, such as dikes and ditches. While generating
a DEM by interpolation of point data obtained by laser
scanning, there is a risk that line structures are not
continuous in the DEM. Thus, the following procedure
is used to correct the representation of line structures:
Hydrol. Process. 22, 4695– 4709 (2008)
DOI: 10.1002/hyp
HYDRODYNAMIC MODELS TO MODEL FLOODS WITH EMERGENCY STORAGE AREAS
(i) line structures are digitised as line objects using
topographic maps; (ii) height information is attached to
the digitised line objects; (iii) a large number of points
are generated along the line objects; and (iv) the DEM is
generated by interpolating point data that were collected
by the laser scanner and generated from the line objects
using GIS. As the laser scanner only collects water
surface elevation, bottom height of ditches was obtained
by terrestrial measurements and included in the DEM
generation procedure. While aggregating LIDAR data to
other grid sizes, the DEM gets ‘smoother’, i.e. dikes have
lower elevation and ditches become shallower. In order
to preserve the flooding characteristics, post-processing
is done in the aggregated DEM by converting the line
objects (with correct height information) to grid objects of
the same grid size as the aggregated DEM. Subsequently,
the corresponding grid cells in the aggregated DEM
are replaced by grid cells of the line object. While
aggregating the DEM to grid sizes of 8 m, 25 m and
50 m, it is ensured that water does not spill over the
dikes (Elbe dike and polder dikes) by setting the dike
cells to their true elevations. However, the correct depths
of the ditches inside the polders are not included in the
aggregated DEMs as these ditches are very narrow (about
3 to 5 m wide) and hence, would be overrepresented
when converting them into grid sizes of 8 m, 25 m and
50 m.
Sensitivity analysis
A detailed sensitivity analysis is carried out for the
different hydrodynamic models with respect to a number of input parameters such as (i) Manning’s n values, (ii) DEM’s of different resolutions, (iii) number of
cross-sections used and (iv) gate opening time and opening/closing duration. The conditions under which the sensitivity analyses are carried out for each of these input
parameters is presented below.
Manning’s n. First, the sensitivity analysis of the
MIKE11 model setup for only the Elbe River (i.e. without
the polders) is carried out with respect to Manning’s
n values. For this purpose, two cases of Manning’s n
values are considered. In the first case, the n values are
decreased by 5% from the mean/calibrated values while
in the second case, the n values are increased by 5%
(Table I). Subsequently, the sensitivity analysis of the
MIKE11 model setup to the Manning’s n values is carried
out by including the polders. Again, the same two cases
of n values stated above are considered (Table I).
Table I. Range of Manning’s n values for different land-use
classes considered in sensitivity analysis
Class
River channel
River floodplain
Polder
Ł
Calibrated values are indicated in brackets.
Copyright 2008 John Wiley & Sons, Ltd.
Manning’s nŁ
0Ð0361–0Ð0399 (0Ð038)
0Ð0475–0Ð0525 (0Ð050)
0Ð0475–0Ð0525 (0Ð050)
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The sensitivity analysis of the MIKEFLOOD setup to
the Manning’s n values is also carried out. In this case
the n values for the river as well as the river floodplain
are kept at their calibrated values while the n values for
the polders are varied, i.e. increased and decreased by
5% (Table I).
DEMs of different resolutions. The sensitivity of the 1D
MIKE11 model to the use of different DEM resolutions
is studied. Two DEMs of horizontal resolution 8 m and
50 m are used to derive the area-elevation curves. The
MIKE11 model is simulated for the August 2002 flood
event with the area-elevation curves derived from the two
different DEMs.
The sensitivity of the MIKEFLOOD model to the
use of different DEM resolutions is also studied. The
sensitivity analysis is carried out considering three DEMs
of different horizontal resolutions for the polders, namely,
8 m, 25 m and 50 m. The sensitivity of the use of these
different DEMs to the water level and discharge reduction
in the Elbe River as well as the flow dynamics in the
polders is studied. The flood inundation extent and depth
in the polders at a particular instant of time for the
different DEM’s is also studied.
Number of cross-sections used. The sensitivity of the
1D MIKE11 model to different numbers of cross-sections
used is also studied. In this case also, only the Elbe River
is modeled and the polders are not considered. As stated
earlier, a total of 34 cross-sections are used to define
the Elbe River in the MIKE11 model (Figure 2). These
cross-sections are in general 400 m to 800 m apart but
the cross-section spacing is more in the downstream side
with a maximum spacing of 2Ð4 km between Elbe River
189Ð6 km and 192 km. In order to study the sensitivity
of the results to the number of cross-sections used, two
different cases are considered in which different numbers
of cross-sections are used:
(i) Case-I: Only 20 out of 34 cross-sections are used,
i.e. 14 cross-sections (nos. 3, 5, 7, 9, 11, 13, 15, 17,
19, 21, 23, 25, 27 and 29 (Figure 2)) are removed.
Here, the 14 cross-sections which are removed are in
the stretch of the Elbe River 175 km to 187Ð6 km.
In this stretch of the river, the cross-section spacing
varies from 400 to 800 m, i.e. they are closely spaced.
Thus, the results obtained from the removal of these
cross-sections would indicate the closeness at which
the cross-sections are to be provided.
(ii) Case-II: Again another set of 20 cross-sections are
used, i.e. a different set of 14 cross-sections are
removed (nos. 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22,
24, 26 and 28 (Figure 2)) in the same stretch of the
Elbe River 175 km to 187Ð6 km.
Gate opening time and opening/closing duration. The
sensitivity of the 1D MIKE11 model to the time of
opening of the south gate during the polder filling process
Hydrol. Process. 22, 4695– 4709 (2008)
DOI: 10.1002/hyp
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C. CHATTERJEE, S. FÖRSTER AND A. BRONSTERT
is studied. For this the following two gate opening times
are considered for the south gate:
(i) Case-I. 6 h ahead of the actual opening time.
(ii) Case-II. 6 h after the actual opening time.
The sensitivity of the 1D MIKE11 model to different gate
opening and closing duration during the polder filling
process is also studied. In this study all the gates (i.e. the
south and north as well as the connecting gates) open or
close over a time of 30 min (based on information from
local water authority). In order to study the sensitivity of
the gate opening and closing duration to the water level
and discharge reduction in the Elbe River, two different
gate opening and closing durations are considered:
gauging site during calibration and validation for the
floodplains.
Table III. Performance indices for MIKE11 simulated water levels at the Mauken gauging site during calibration and validation
(for the floodplains)
Events !
Manning’s n
For river
0.038
Calibration
Jan-Mar, 2002
For floodplain
0.035
0.040
0.045
0.050
Validation
Mar-Jun, 2005
Ens
d
Ens
d
0.976
0.980
0.981
0.979
0.724
0.728
0.732
0.736
—
—
0.979
0.982
—
—
0.584
0.594
(i) Case-I: All the gates take 5 min to open or close.
(ii) Case-II: All the gates take 60 min to open or close.
(a)
RESULTS AND DISCUSSIONS
Calibration and validation of the one-dimensional model
Table II shows the performance indices for different
trial values of Manning’s n for MIKE11 simulated water
levels at the Mauken gauging site during calibration and
validation for the main channel only. The Ens and d
values are found to be highest for n equal to 0Ð038
during calibration. Using this n the Ens and d values
are also found to be very high during validation. Hence,
a Manning’s n value of 0Ð038 is chosen for the main
channel.
Different trial values of Manning’s n for the floodplain
are chosen keeping the main channel n value equal to
0Ð038. Table III shows the performance indices for the
MIKE11 simulated water levels at the Mauken gauging
site during calibration and validation for the floodplain.
For the January–March, 2002 event, the Ens value is
found to be the highest for floodplain n value equal to
0Ð045 while the d value is found to be highest for a
floodplain n value equal to 0Ð050. But during validation
with the March–June, 2005 event, both the Ens and d
values are found to be highest for floodplain n value
equal to 0Ð050. Hence, a Manning’s n value of 0Ð050 is
chosen for the floodplains. Figure 3 shows a comparison
of the observed and simulated water levels at the Mauken
(b)
Table II. Performance indices for MIKE11 simulated water levels
at the Mauken gauging site during calibration and validation (for
the main channel only)
Events !
Manning’s n
(for river)
0.037
0.038
0.039
Calibration
Oct-Nov, 1999
Validation
Aug-Sep, 2004
Ens
d
Ens
d
0Ð662
0Ð925
0Ð844
0Ð931
0Ð984
0Ð967
—
0Ð920
—
—
0Ð983
—
Copyright 2008 John Wiley & Sons, Ltd.
Figure 3. Comparison of observed and simulated water levels at the
Mauken gauging site during (a) calibration for the flood event of 1
January to 31 March 2002; (b) validation for the flood event of 1 March
to 30 June, 2005
Hydrol. Process. 22, 4695– 4709 (2008)
DOI: 10.1002/hyp
HYDRODYNAMIC MODELS TO MODEL FLOODS WITH EMERGENCY STORAGE AREAS
(a)
(b)
(c)
Figure 4. MIKE11 simulation results for the proposed emergency storage
area for the August 2002 flood event (positive discharge in flow direction
from South to North): (a) simulated discharge and water levels; (b) gate
levels; (c) gate discharge
One-dimensional model results for flooding and
emptying processes in the polder
Figure 4a to c shows the results obtained from
MIKE11 simulation for the flooding and emptying processes in the polders and flow in the Elbe River for
the August 2002 flood event. The peak discharge for
this flood event is 4420 m3 s1 . Here, the area–elevation
Copyright 2008 John Wiley & Sons, Ltd.
4701
curves for the storage areas are derived from a 50 m grid
DEM. It is observed from these figures that the south gate
opens when the water level in the Elbe River reaches a
threshold value of 76Ð94 m corresponding to a discharge
of 4100 m3 s1 (Figure 4a and b). At this instant of time
a discharge of about 440 m3 s1 enters through the south
gate (Figure 4c) and this results in a sharp reduction in
the Elbe discharge and water level (Figure 4a). Subsequently, the connecting gate and the south gates close
when the water level reaches the design value in the north
and south polders, respectively. The entire filling process
takes about 30 h. After the gates close, the discharge and
water level in the Elbe River rise again. The water level
reduction at the Elbe River 184Ð4 km (i.e. at the Mauken
gauge) is 25 cm while the corresponding discharge reduction at this point is 310 m3 s1 (Figure 4a).
In order to achieve the maximum water level reduction
in the Elbe River for given polder volumes, the discharge
in the Elbe River should be as close as possible to
a straight line after the filling process starts in the
polder. The factors affecting the magnitude of water
level reduction in the Elbe River for given polder
volumes are (i) time of opening of the gates during the
polder filling process, (ii) gate opening/closing duration
(iii) gate width or partitioning of the gates and (iv) shape
of the flood hydrograph. A detailed investigation of the
effect of (i) sequential operation of the north and south
gates during the filling process (ii) partitioning of the
gates and (iii) shape of the flood hydrograph, on the
magnitude of water level reduction in the Elbe River
is reported in Förster et al. (2008). In this study, only
the south and the connecting gates (and not the north
gate) operate during the polder filling process. The gate
opening/closing durations are 30 min and the gate widths
are 25 m (based on information collected from local
water authority). Further, as stated earlier, the August
2002 flood hydrograph is considered here. Thus, in this
study, the time of opening of the south gate during the
start of the filling process of the polders is the only
crucial factor for obtaining the maximum possible water
level reduction in the Elbe River. The time of opening
of the south gate during the filling process of the polder
is decided manually based on a trial and error process
so as to maximize the water level reduction in the Elbe
River. Several trial runs are carried out with different
opening times for the south gate (specified in MIKE11
for each trial run) while the connecting and south gates
close when the design water level is reached in the north
and south polders, respectively. For each run the water
level reduction in the Elbe River is noted. It is observed
that when the south gate is opened corresponding to a
water level of 76Ð94 m at Elbe River chainage 184Ð4 km
(i.e. on 17 August 2002 at 15Ð40 hrs for the August 2002
flood event), a maximum water level reduction of 25 cm
occurs in the Elbe River.
The gate operation during the polder emptying process
is also decided manually. The objective is to empty
the polders as soon as possible. Thus, it is decided to
release the water from the polders into the Elbe River
Hydrol. Process. 22, 4695– 4709 (2008)
DOI: 10.1002/hyp
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C. CHATTERJEE, S. FÖRSTER AND A. BRONSTERT
as soon as the water level in the river falls below the
water level in the polders. Accordingly, it is decided
that the emptying process starts when the water level
in the Elbe River near the south gate falls to 75Ð64 m
(Figure 4a), i.e. 2 days after the filling process ends,
which allows for safe release of the flood water. The
south gate is opened first followed by the north gate
8 h later. The connecting gate is opened 7 h after the
north gate is opened (Figure 4b). Immediately after the
connecting gate is opened, the south gate is closed as
the flow direction reverses and water starts entering the
polders again. As per the MIKE11 simulation, the entire
emptying process takes about 24 days. The long duration
of the emptying process is because after a certain time
the water level of the polders become the same as the
water level in the Elbe and hence, the water levels in the
polder fall along with the river water level. It is to be
mentioned here that all gate operations are automatically
executed in the MIKE11 model simulations based on the
selected decision criteria.
As mentioned earlier the storage area under investigation is yet to be constructed and hence, only calibration
data for the river is available. Due to lack of calibration/validation data sets for the storage area the simulation results obtained herein are compared with a similar
study. In IWK (2003) the peak attenuation effect for several proposed flood storage areas along the Middle Elbe
River was simulated considering floods with peak discharges ranging between 4000 m3 s1 and 5000 m3 s1 .
For the same storage area as investigated in the present
study a peak reduction between 262 m3 s1 (14 cm) and
497 m3 s1 (23 cm) at the Wittenberg gauge was simulated. These results are very similar to the range of water
level reduction obtained in the present study.
Comparison of 1D and 1D–2D model results
The DEM grid size used for MIKEFLOOD is 50 m and
the area–elevation curves for MIKE11 are also extracted
from 50 m grid DEM. A comparison of the results
obtained from MIKE11 and MIKEFLOOD simulation
runs shows that there is absolutely no difference in the
water level and discharge reduction in the Elbe River.
This is because the discharge through the south gate
is the same for both models. The identical discharge is
because it is a case of free flow discharge controlled by
the upstream water level, and the upstream water level for
the south gate for both models is the same even though
the downstream water level differs.
The differences between MIKE11 and MIKEFLOOD
results are that for MIKE11 the water front reaches the
connecting gate at the instant at which the south gate
is opened while for MIKEFLOOD the water front takes
about an hour to reach the connecting gate. Further, due to
the different treatment of polder filling in the models, the
water levels upstream and downstream of the connecting
gate differ for the two models. As a result there is a slight
difference in the discharge through the connecting gate
for the two models.
Copyright 2008 John Wiley & Sons, Ltd.
In the polders emptying process there is a significant
difference between MIKE11 and MIKEFLOOD results.
For the MIKEFLOOD model, the emptying process
continues until the water level in the polders lowers to
about 73Ð25 m. The emptying process takes about 4 days
with most of the emptying taking place in the first day and
a half. The emptying process stops after the water level
reaches 73Ð25 m because the ground elevations near the
north gate are higher than its sill elevation (70Ð8 m) and
this does not permit further draining of the water to take
place. However, for the MIKE11 model, the emptying
process continues until the water level in the polders
lowers to the sill elevation of the north gate (70Ð8 m)
along with the river water level. The emptying process
takes about 24 days. This emptying result of MIKE11
is in fact incorrect since practically the draining process
cannot continue below the water level 73Ð5 m because of
the ground elevation conditions near the north gate, as
mentioned above. Such an error is expected to occur in
MIKE11 because the area–elevation curves that describe
the polders do not take care of the spatial variations of
ground elevations. However, a ‘work around’ is possible
in MIKE11 by raising the sill level of the north gate
to 73Ð5 m when the water level in the north polder
lowers to 73Ð5 m during the emptying process. However,
this would require the use of the MIKEFLOOD model
to ascertain the required water level (73Ð5 m in this
study) prior to using MIKE11. Such an approach was not
adopted as this paper aims at an independent comparison
of the 1D and 1D–2D models to model floods with
emergency storage areas.
MIKEFLOOD results for the polders show that large
tracts of agricultural land, particularly in the northern side
of the north polder (with depths of water as high as 1Ð5 to
2 m in some places) remain inundated after the emptying
process through the north and south gates. Because of
the topography, this water cannot drain using the gravity
process through the gates. Hence, some of the water may
be drained using a small gate in a stream on the northern
boundary (not considered here in the modelling process)
and the rest of it has to be pumped out or gradually
evaporate or seep away.
Additional information obtained from MIKEFLOOD
is the water velocities in the polders. It is observed that
at some places in the polder near the south gate, the
velocity is higher than the mean velocity of 1Ð5 m s1 (for
50 m grid size DEM). This type of information will be
of particular help in studying erosion and sedimentation
problems in the polder as well as in the subsequent risk
analysis.
Computation time, storage space requirements and
modelling effort
A comparison of the computation time requirements
for the two models was carried out. For this the models
were run in a personal computer having an AMD
Athlon(tm) 64 3500C processor with 2Ð2 GHz speed
and 2GB RAM. The models were run for the filling
and emptying processes in the polders as well as flow
Hydrol. Process. 22, 4695– 4709 (2008)
DOI: 10.1002/hyp
HYDRODYNAMIC MODELS TO MODEL FLOODS WITH EMERGENCY STORAGE AREAS
in the Elbe River for the same August 2002 flood
event. The MIKEFLOOD (with 8 m grid DEM for the
polders) model was run for shorter durations because
of the very high computation time and storage space
requirements. The simulation time step intervals and
result storing frequencies for the different runs are shown
in Table IV. The computation time as well as storage
space requirements for the model runs is shown in
Table V. It is observed that the computation time and
storage space requirements for the MIKE11 model are
very low while they are very high for the MIKEFLOOD
model. As expected, for MIKEFLOOD the computation
time and storage space requirements increase drastically
when finer resolution DEMs are used.
Table IV. Model run details for the August 2002 flood event
Model
MIKE11
MIKEFLOOD
Simulation time step
interval (s)
Result storing
frequency (min)
5 s
MIKE11–2 s
MIKE21–2 s
5
2
15
Table V. Computation time and storage space requirement for
different model runs
Model
MIKE11
MIKEFLOOD
DEM grid
size
Computation
time (h : min)
Storage
space
50 m DEM
25 m DEM
8 m DEMŁ
2 min
3 h 43 min
14 h 23 min
12 h 40 min
22 MB
1Ð1 GB
3Ð1 GB
1Ð3 GB
Ł
The MIKEFLOOD model with 8 m grid DEM is simulated only for the
polder filling process, i.e. from 5 August to 21 August 2002.
4703
As far as the modelling effort is concerned, considerable effort is required in setting up the MIKEFLOOD
model. For MIKEFLOOD, quite a few adjustments had
to be made in the DEM near its links with the MIKE11
structures to bring about model stability. The DEM is cut
and levelled near the structures and provided with an initial water level. In comparison, considerably less effort
is required in setting up the MIKE11model.
Sensitivity analysis
Manning’s n. Figure 5 shows the maximum water
levels along the longitudinal section of Elbe River as
obtained from MIKE11 (when only the Elbe River is
modelled and the polders are not considered) for different
‘n’ values for the August 2002 flood event. It is seen that
as the n values are decreased the water level decreases
and vice versa. When the n values are decreased by 5%,
maximum water level difference occurs at the upstream
end, at 16 cm, while the water level differences at the
points of interest, i.e. at the south gate is 15 cm and
at the Mauken gauging site is 13 cm. Similarly, when
the n values are increased by 5%, the maximum water
level difference still occurs at the upstream end, and is
15 cm, while the water level differences at the points
of interest, i.e. at the south gate is 14 cm and at the
Mauken gauging site is 12 cm. Considering the fact,
that the maximum water level reduction at the Mauken
gauging site is 25 cm (as stated earlier), these water level
differences of 12–15 cm due to a change of n values
seem to be significant.
Figure 6a and b shows the results of sensitivity analysis of the MIKE11 model to the Manning’s n values when
the polders are included. It is observed that when the n
values are decreased by 5%, the water level reduction
is only 12Ð3 cm and discharge reduction is 137 m3 s1
80
n (river) = 0.0361; n (floodplain) = 0.0475
n (river) = 0.038; n (floodplain) = 0.05
79
n (river) = 0.0399; n (floodplain) = 0.0525
Water level, m
78
77
South Gate
at 182.6 km
Mauken Gauge
at 184.4 km
76
75
74
174
177
180
183
186
189
192
195
River chainage, km
Figure 5. Maximum water levels along longitudinal section of Elbe River as obtained from M11 (polders are not considered) for different ‘n’ values
for the August 2002 flood event
Copyright 2008 John Wiley & Sons, Ltd.
Hydrol. Process. 22, 4695– 4709 (2008)
DOI: 10.1002/hyp
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C. CHATTERJEE, S. FÖRSTER AND A. BRONSTERT
(a)
(b)
Figure 6. Sensitivity of MIKE11 model to Manning’s n values when polders are considered (a) n D 0Ð0361 for river and 0Ð0475 for floodplain;
(b) n D 0Ð0399 for river and 0Ð0525 for floodplain
(Figure 6a). The water level reduction is only 17Ð0 cm
and discharge reduction is 218 m3 s1 when the n values
are increased by 5% (Figure 6b). This happens because
though the south gate is still opened at the same water
level value of 76Ð94 m, the river discharge corresponding
to this water level is different for the two cases due to different n values. As stated earlier, the water level reduction
is 25 cm and discharge reduction is 310 m3 s1 when the
calibrated values of n are used. Thus, the model is quite
sensitive to changes in n values.
In this study, as mentioned earlier, the Manning’s n
values obtained during the calibration and validation process are 0Ð038 and 0Ð05 for the main channel and adjacent
floodplain, respectively. The corresponding normal values
Copyright 2008 John Wiley & Sons, Ltd.
of Manning’s n for the prevailing land-use mentioned
in the literature (Chow, 1959) are 0Ð035 (for natural
streams—major rivers) and 0Ð05 (for floodplains—light
brush). As the calibrated values are very close to those
mentioned in the literature and the land-use in the study
area is quite uniform, a lower range (š5%) of Manning’s
n is used in the sensitivity analysis. The uncertainty associated with the roughness values in modelling floods has
been the subject of continuous research (Werner et al.,
2005). Horritt (2005) states the difficulty in specifying
the hydraulic roughness values in spite of having a reasonable idea of the land-use. The author further suggests
the use of a calibration approach to remove this difficulty.
Hence, it is proposed that a more detailed calibration
Hydrol. Process. 22, 4695– 4709 (2008)
DOI: 10.1002/hyp
HYDRODYNAMIC MODELS TO MODEL FLOODS WITH EMERGENCY STORAGE AREAS
and validation procedure be adopted considering a large
number of flood events in order to reduce the uncertainties associated with Manning’s n values. However,
it is also expected that the sensitivity to n values would
decrease when more than one polder is used and the consequent peak water level reduction in the Elbe River is
much higher.
The results of sensitivity analysis of the MIKEFLOOD
model show that it is insensitive to the variation of n
values in the polders. This is quite expected because
(i) the inflow to the polder remains the same as it
is not influenced by the polder water level and (ii)
n is proportional to the velocity which in the bulk
characteristic is low. This finding justifies using only one
roughness value for the polders rather than differentiating
into several roughness classes. Similar results are also
reported by Werner et al. (2005).
DEM’s of different resolutions. The results of sensitivity analysis of the MIKE11 model to area–elevation
curves derived from different grid size DEMs show that
the water level and discharge reduction in the Elbe River
remains unchanged. However, when the south gate is
closed after the filling process, the discharge in the Elbe
River for the 8 m DEM case increases to a lesser extent
than that of the 50 m DEM case. For both DEM cases
the polders are filled to their design levels, i.e. 76Ð14 m
for the south polder and 75Ð35 m for the north polder.
Although the discharge through the south and connecting
gates are the same for both cases, the gates close a little
earlier for the 50 m DEM case than the 8 m DEM case.
This minor difference in the result is due to the slightly
different volume–elevation curves derived from the two
DEMs. Because of averaging, the 50 m DEM has slightly
lesser volume for the design water level compared to the
8 m DEM. For the 50 m DEM, the volume of water corresponding to the design water levels are 20Ð24 Mm3 in
the north polder and 20Ð32 Mm3 in the south polder (i.e. a
total volume of 40Ð56 Mm3 ). Whereas for the 8 m DEM,
the volume of water corresponding to the design water
levels are 20Ð44 Mm3 in the north polder and 20Ð54 Mm3
in the south polder (i.e. a total volume of 40Ð98 Mm3 ).
Thus, the total difference in volume of the polders for
the two cases is 0Ð42 Mm3 . But this does not produce
significantly different results. Hence, a 50 m DEM can
be used to derive the area–elevation curves for the 1D
MIKE11 model and yet give accurate results.
The results of sensitivity analysis of the MIKEFLOOD
model to the use of different DEM resolutions for the
polders also show that the water level and discharge
reduction in the Elbe River remain the same. However,
when the south gate is closed after the filling process,
the discharge in the Elbe River for the 8 m DEM case
increases to a lesser extent than that of the 25 m DEM
case, which in turn increases to a lesser extent than that
of the 50 m DEM case. This is because, for the design
water level, the volume of the 8 m grid DEM is slightly
higher than that of the 25 m grid DEM, which in turn
is higher than that of the 50 m grid DEM. As a result,
Copyright 2008 John Wiley & Sons, Ltd.
4705
for the 50 m DEM case the south gate closes ahead of
the 25 m DEM case, which in turn closes ahead of the
8 m DEM case. The south gate discharge is the same
in all cases because of the same upstream water level.
So, even though the downstream water levels differ,
the discharge remains the same as it is a case of free
flow discharge governed by upstream water level. The
water front takes about an hour to reach the connecting
gate for all cases. However, the discharge through the
connecting gate is slightly different for the three grid
size DEMs because of varying upstream and downstream
water levels for the three cases. The upstream water level
for the 8 m case remains lower than for the other two
since the 8 m DEM has the same volume of water at
a lower elevation compared with that of the 25 m and
50 m DEM.
Figure 7a to c shows the flood inundation extent and
depth in the south polder for the three DEM cases (8 m,
25 m and 50 m) on 17 August 2002 at 16Ð30 hours, i.e.
40 min after the filling process starts through the south
gate. At this instant of time, the volume of water that
enters the south polder is the same for all three cases
as the discharge through the south gate is the same
for all cases. For the 50 m DEM, the inundation extent
is 1Ð35 km2 and the maximum water depth is 3Ð01 m
(Figure 7c). For the 25 m DEM, the inundation extent
is 1Ð23 km2 and the maximum water depth is 3Ð36 m
(Figure 7b). For the 8 m DEM, the inundation extent
is 1Ð23 km2 and the maximum water depth is 3Ð64 m
(Figure 7a). For the 50 m DEM, the surface elevations
are higher than the 25 m and 8 m DEM. Hence, the
maximum water depth is lowest for the 50 m DEM and
the resulting inundation extent is the greatest. Further,
although the total inundation extents for the 8 m and
25 m DEMs are the same, their spatial variation is
different, particularly at the fringes (Figure 7a and b).
Unlike floodplain inundation studies, for polder studies,
the analysis of the inundation extent and depth for
different DEMs is not of much significance since after
the initial phase where the water front progresses, the
polders begin to fill up and DEM resolution does not
play a major role.
Number of cross-sections used. Figure 8 shows the
maximum water levels along the longitudinal section of
the river as obtained from MIKE11 for the case when all
34 cross-sections are used and for the two different cases
of cross-sections used for the August 2002 flood event. It
is observed that for case I, the water levels are sometimes
a little higher and sometimes a little lower than the case
when all 34 cross-sections are used. The water levels for
case-II are, in general, a little lower than the case when
all 34 cross-sections are used. However, for the lower
reaches of the river, the water levels for both cases I and
II almost coincide with the water level for the case when
all 34 cross-sections are used.
The water level differences at the points of interest,
i.e. south gate and Mauken gauging site for the different
cases are shown in Table VI. It is seen that the water
Hydrol. Process. 22, 4695– 4709 (2008)
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C. CHATTERJEE, S. FÖRSTER AND A. BRONSTERT
(b)
(a)
Inundation area = 1.23 km2
Maximum water depth = 3.64 m
Inundation area = 1.23 km2
Maximum water depth = 3.36 m
(c)
Inundation area = 1.35 km2
Maximum water depth = 3.01 m
Figure 7. Flood inundation extent and depth on 17 August 2002 at 16Ð30 hours in south polder as obtained from MIKEFLOOD for DEM with grid
sizes (a) 8 m (b) 25 m and (c) 50 m
level differences are not that significant considering that
14 cross-sections are removed.
These results indicate that for the two cases when
14 cross-sections are removed, the shape of the river
including its depth and width are very well represented
by the remaining 20 cross-sections. Thus, in general it
can be seen that the number of cross-sections used in
this study to model the Elbe water level is reasonably
sufficient.
Copyright 2008 John Wiley & Sons, Ltd.
Gate opening time and opening/closing duration. As
mentioned earlier, during the polder filling process, the
south gate is opened at 15Ð40 hours on 17 August 2002
in order to obtain a maximum water level reduction of
25 cm in the Elbe River. When the south gate opens
6 h ahead of this opening time at 9Ð40 hours on 17
August 2002 (corresponding to the Elbe water level
of 76Ð71 m at the Mauken gauge instead of 76Ð94 m),
the water level reduction decreases to 14Ð8 cm (from
Hydrol. Process. 22, 4695– 4709 (2008)
DOI: 10.1002/hyp
HYDRODYNAMIC MODELS TO MODEL FLOODS WITH EMERGENCY STORAGE AREAS
25Ð0 cm), which corresponds to a discharge reduction
of 182 m3 s1 . Similarly, when the south gate opens
6 h after the actual opening time at 21Ð40 hours on 17
August 2002 (corresponding to the Elbe water level of
77Ð10 m at the Mauken gauge instead of 76Ð94 m), the
water level reduction decreases to 8Ð6 cm (25Ð0 cm),
which corresponds to a discharge reduction of 93 m3 s1 .
This shows the importance of a very good forecast
for effective reduction of water levels in the main
river.
The results of sensitivity analysis of the MIKE11
model to different gate opening/closing durations during
the polder filling process show that for case I, there is
a sudden fall in the Elbe River discharge (compared
with the 30 min duration case) when the south gate
opens. This is because the south gate opens faster and
hence, the initial discharge through the south gate is
higher. Also, the south gate closes earlier (than for the
30 min duration case). This is because both the south and
connecting gates are closed when the respective design
water levels are reached in the polders. As the gates
close very fast for case I, the water level (and hence, the
volume) in both polders after the gates are fully closed
are lower compared with the 30 min case. The final
volume of water in the north and south polders for case I
are 20Ð10 Mm3 and 20Ð08 Mm3 , respectively; while the
final volumes of water in the north and south polders
for the 30 min case are 20Ð32 Mm3 and 20Ð24 Mm3 ,
respectively. Thus, as the storage volume in the polders
Table VI. Water level differences (in m) in the Elbe River due to
use of different sets of cross-section data
Case
No. of cross-sections
removed
I
II
14
14
Water level difference (m)
at river chainage
182Ð6 km
184Ð4 km
0Ð05
0Ð09
0Ð02
0Ð08
80
All 34 c/s (Actual)
14 c/s removed (Case I)
14 c/s removed (Case II)
Water level, m
79
78
South Gate
at 182.6 km
77
Mauken Gauge
at 184.4 km
76
75
74
174
177
180
183
186
189
River chainage, km
192
195
Figure 8. Maximum water levels along longitudinal section of Elbe River
as obtained from M11 for different sets of cross-sections for the August
2002 flood event
Copyright 2008 John Wiley & Sons, Ltd.
4707
is a little less for case I, the discharge and water level
at Elbe River 184Ð4 km rise a little higher than for the
30 min case. However, the total discharge and water level
reduction in the Elbe River for case I is the same as
that for the 30 min case, because the total discharge
and water level reductions are still governed by the
threshold discharge and water levels at which the south
gate opens, and this threshold discharge and water level
are the same for both cases. Similarly, for case II, as
the gates open and close slowly the final volume of
water in the north and south polders are 20Ð58 Mm3 and
20Ð43 Mm3 , respectively. Thus, as the storage volume
in the polders is a little more, the discharge and water
levels at Elbe River 184Ð4 km rise a little less than the
30 min case. However, in this case also, the discharge
and water level reductions are the same as for the 30 min
case.
CONCLUSIONS
For the August 2002 flood event, the polder with the
proposed gate dimensions and gate control strategy is
capable of reducing the peak water levels near the
Mauken gauging site in the Elbe River by about 25 cm
while the corresponding discharge reduction is about
310 m3 s1 . The time of opening of the south gate during
the polder filling process is decided using a trial and error
process so as to maximize the water level reduction in
the Elbe River. The water level reduction can be further
improved through different gate control strategies. This
aspect, as well as the effectiveness of the polders in
reducing the water levels in the Elbe River for floods
of different magnitudes and duration, is discussed in a
separate paper by the same authors (Förster et al., 2008).
As far as the emptying of the polders are concerned,
there are no intricacies involved. The emptying process
starts when the discharge in the main river falls to a low
threshold value.
Both the 1D and coupled 1D–2D model simulations
for the polder yield the same water level and discharge
reductions in the Elbe River. However, due to difference
in treatment of the polders in the two models, the
results for the flow processes in the polders are slightly
different. For example, there are differences in the time
for the water front to reach the connecting gate as
well as the discharge through the connecting gate. Also,
the emptying process of the polders differs significantly
for the two models. While the 1D model drains the
polders completely in 24 days, the 1D–2D model drains
it only partially in 4 days. The 1D–2D model result
is practically correct as the polders cannot be drained
below a certain water level because of ground elevation
conditions near the gates. The 1D–2D model provides
additional information in terms of the areal extent as
well as depth of water in the polders after the emptying
process as well as the water velocities in the polders.
The information on velocities will be particularly useful
in studying erosion and sedimentation problems and
Hydrol. Process. 22, 4695– 4709 (2008)
DOI: 10.1002/hyp
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C. CHATTERJEE, S. FÖRSTER AND A. BRONSTERT
subsequent risk analysis in the polders. The computation
time and storage requirements for the 1D model are
very low, and are significantly higher for the 1D–2D
model and more so when finer resolution DEMs are
used. Further, unlike the 1D model, considerable effort is
required in setting up and simulating the 1D–2D model.
In view of this, it is recommended to use a 1D model for
studying the flooding processes of polders, particularly
the water level and discharge reductions in the main
river. The computation time requirement suggests that
a 1D model may be used in a near real time mode.
However, a 1D–2D approach may be used when the
study of flow dynamics in the polder is of particular
interest.
The 1D model is quite sensitive to changes in the
values of Manning’s n for the river and its floodplain
within the embankments. Thus, there is a need for
rigorous calibration and validation of the model before
it is put to use. The 1D–2D model is not so sensitive
to change in Manning’s n values for the polders. This is
because the ‘n’ values do not have a role to play once
the water front reaches the boundary of the polders and
the water level in the polders starts rising.
A coarse resolution DEM can be used to derive the
area–elevation relationship for the polders for use in
the 1D model and yet obtain accurate results. The same
holds true for a coupled 1D–2D model, wherein a
coarse resolution DEM for the polders can be effectively
used. This would result in significant reduction of the
computational time and storage space requirements. In
this study, the use of a 50 m grid DEM was found to
yield good results.
The number of cross-sections should be chosen such
that the shape of the river including its depth and width
are very well represented by them. In this study, it is seen
that the 34 cross-sections used to model the Elbe water
levels are quite sufficient.
A different gate opening time for the south gate causes
the water level reduction to decrease drastically. This
indicates that it is essential to have a good flood forecast
in order to effectively reduce the water levels in the
main river. The change in gate opening and closing
durations from 5 min to 60 min does not have an effect
on the water level reductions in the Elbe River. In this
study, a gate opening and closing duration of 30 min is
selected based on information provided by the local water
authorities.
ACKNOWLEDGEMENTS
The research was jointly funded by the Alexander-vonHumboldt Foundation Fellowship Programme and the
Sixth Framework Programme of the European Commission (FLOODsite project, EC Contract number: GOCECT-2004-505420). This paper reflects the authors’ views
and not those of the European Community. Neither the
European Community nor any member of the FLOODsite Consortium is liable for any use of the information
in this paper.
Copyright 2008 John Wiley & Sons, Ltd.
Data were kindly provided by the following authorities: Landesbetrieb für Hochwasserschutz und Wasserwirtschaft Sachsen-Anhalt, Wasser- und Schifffahrtsamt
Dresden and Landesvermessungsamt Sachsen-Anhalt.
The authors are also grateful to the Danish Hydraulic
Institute (DHI), Denmark for providing an evaluation
copy of the MIKE software.
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