STORM
. 7
Simulation Tool for River Management
STORM - Rhine
Main Report
Design of the Roleplay
STORM - Rhine
Main report
Design of the Roleplay
Simulation Tool for River Management
March 2002
The STORM project is sponsored by:
IRMA-SPONGE: Roleplay for transboundary river management
(Project number: 3/NL/1/164/ 99 15 183 01)
Delft Cluster: Ontwikkeling rollenspelen integraal waterbeheer
(Project number: 06.01.06)
The STORM projects are carried out in partnership by:
International Institute for Infrastructure, Hydraulics and Environment
P.O.Box 3015; 2601 DA Delft; The Netherlands Contact: J.C.Heun, +31-15-2151835, jch@ihe.nl
Contact: T.D.Schotanus, +31-15-2151853, tds@ihe.nl
Resource Analysis
Zuiderstraat 110; 2611 SJ Delft; The Netherlands
Contact: M.M.de Groen, +31-15-2191526, marieke.de.groen@resource.nl
WL | Delft Hydraulics
P.O.Box 177; 2600 MH Delft; The Netherlands
1. STORM – BETUWE, Final Report, Design of the Roleplay Schmidt, A.L., October 1998
2. STORM – BETUWE, User Manual, Design of the Roleplay Schmidt, A.L., October 1998
3. STORM – DELTA, Definitiestudie: demonstratiemodel voor Rivierinrichting Schmidt, A.L., December 1998
4. STORM – DELTA, Main Report, Design of the Model De Graaff, B.J., December 1999
5. STORM – DELTA Main Report, User Manual De Graaff, B.J., December 1999
6. STORM – RHINE, Main Report, Executive Summary Heun, J.C., De Groen, M.M., Werner, M., March 2002 7. STORM – RHINE, Main Report, Design of the Roleplay
Heun, J.C., De Groen, M.M., Werner, M., Schotanus, T.D.; March 2002 7A. STORM – RHINE, Main Report, Annex A, Documentation on Models on Water
Werner, M., March 2002
8. STORM – RHINE, Main Report, User Manual Schotanus, T.D., Versteeg, A., July 2002
9. STORM – RHINE Supporting Document 1: Dutch-German Water Management of the River Rhine, MSc. thesis
Bijman, S., January 2002
10. STORM – RHINE Supporting Document 2: Deciding about Safety; Flood Protection & Decision-Making Processes in Germany at the local level; M.Sc.thesis
IRMA project number: 3/NL/1/164/ 99 15 183 01
The IRMA-SPONGE Umbrella Program
In recent years, several developments have contributed not only to an increased public interest in flood risk management issues, but also to a greater awareness of the need for improved knowledge
supporting flood risk management. Important factors are:
• Recent flooding events and the subsequently developed national action plans.
• Socio-economic developments such as the increasing urbanisation of flood-prone areas. • Increased awareness of ecological and socio-economic effects of measures along rivers. • Increased likelihood of future changes in flood risks due to land use and climate changes. The study leading to this report aimed to fill one of the identified knowledge gaps with respect to flood risk management, and was therefore incorporated in the IRMA-SPONGE Umbrella Program. This program is financed partly by the European INTERREG Rhine-Meuse Activities (IRMA), and managed by the Netherlands Centre for River Studies (NCR). It is the largest and most comprehensive effort of its kind in Europe, bringing together more than 30 European scientific and management organisations in 13 scientific projects researching a wide range of flood risk management issues along the Rivers Rhine and Meuse.
The main aim of IRMA-SPONGE is defined as: “The development of methodologies and tools to assess the impact of flood risk reduction measures and scenarios. This to support the spatial planning process in establishing alternative strategies for an optimal realisation of the hydraulic, economical and ecological functions of the Rhine and Meuse River Basins." A further important objective is to promote transboundary co-operation in flood risk management. Specific fields of interest are:
• Flood risk assessment.
• Efficiency of flood risk reduction measures. • Sustainable flood risk management.
• Public participation in flood management issues.
More detailed information on the IRMA-SPONGE Umbrella Program can be found on our website: www.irma-sponge.org.
We would like to thank the authors of this report for their contribution to the program, and sincerely hope that the information presented here will help the reader to contribute to further developments in sustainable flood risk management.
Ad van Os and Aljosja Hooijer
Report Title:
STORM-Rhine
Main Report – Design of the Roleplay
Contact person : J.C. Heun
Date : March 2002
Author(s) :
J.C. Heun (IHE)
M.M. de Groen (Resource Analysis) M. Werner (Delft Hydraulics) T.D. Schotanus (IHE)
DC Project name : Development of roleplays integrated water management DC Project number : 06.01.06
DC Working Group Theme : Integrated water management DC Theme leaders : E. van Beek, H.H.G. Savenije Report Number : STORM report series no. 7
Number of pages : 64 Number of tables : 32 Number of figures : 21 Keverling Buismanweg 4 Postbus 69 2600 AB Delft 015-2693793 015-2693799 info@delftcluster.nl www.delftcluster.nl
Table of Contents
1 THE STORM PROJECTS 1
1.1 Objectives of the Projects 1
1.2 Objectives of STORM 1
1.3 The STORM Products 1
1.4 Making Use of STORM 2
1.5 Roleplay Setting 2
1.6 STORM Projects Implementation 3
2 THE REPORT 5
3 SCOPE OF STORM-RHINE 7
3.1 The Concept 7
3.2 Scale of the Simulation 7
3.3 River and Floodplain Functions 8
3.4 River and Floodplain management 9
3.5 The Models 9
3.6 The Roles 10
3.7 The Interface 10
4 RIVER MANAGEMENT 11
4.1 Introduction 11
4.2 Interventions in the Main Channel 11
4.3 Interventions in the Floodplain 12
4.4 Summary 13
5 MODELS ON HYDROLOGY 15
5.1 Introduction 15
5.2 Hydrology of the Rhine basin 15
5.3 Extent of the Rhine Basin considered 16
5.4 Modelling Approach 18
5.5 Hydrological Computations 19
5.6 Hydraulic Computations 20
5.7 Morphological Computations 22
5.8 Measures 22
5.9 Hydrological Routing Computations 25
5.10 Hydraulic Computations Upstream 27
5.11 Scenarios 28 6 MODEL ON SHIPPING 31 6.1 Introduction 31 6.2 Objective 31 6.3 Assumptions 32 6.4 Input 33 6.5 Model 34
6.5.1 Relation between water depth and ship load 34 6.5.2 Frequency distribution of normative water depths 36 6.5.3 Frequency distribution of ship loads 38
6.6 Output 42
6.6.1 Introduction 42
6.6.2 Economic effects 42
6.6.3 Environmental effects 44
6.7 Discussion and synthesis 45
6.8 Information on Role 46
7 PRESENT and TARGET LAND COVER 47
7.1 Introduction 47
7.2 General 47
7.4 North Rhine Westphalia 48
7.5 Rhineland Palatinate and hessen 49
7.6 Germany Target Distribution 50
7.7 Recommendations 51
7.8 Test of matrix approach 52
8 FLOOD DAMAGE MODULE 55
9 INSTITUTIONS 57
9.1 Water Management in Germany 57
9.2 Water Management in The Netherlands 58
9.3 Institutional Complexity of Inter-departmental Interaction 59 9.4 Comparison between German and Dutch Water Management 59
9.5 Application in the Roleplay 60
REFERENCES 63
ANNEX A MODELS on WATER
LIST of TABLES
Table 3.1 River and floodplain functions 8
Table 3.2 River and floodplain management measures 9
Table 3.3 Modules of the STORM-Rhine system model 9
Table 5.1 Cumulative chainage and catchment area of the Rhine ... 16 Table 5.2 Physical maximum and highest measured discharge 17
Table 5.3 Tributaries explicitly modelled 18
Table 5.4 Overview of branches considered in the model 18 Table 5.5 Geometrical properties of schematised cross sections 21 Table 5.6 Measures acting on geometry and hydraulic roughness 22 Table 5.7 Projected retention areas between Maxau and Lobith 23 Table 5.8 Projected retention downstream of Lobith 24 Table 5.9 Retention basins considered in the STORM-Rhine 24 Table 5.10 Nodes and branches of the routing model 25 Table 5.11 Comparison of observed and routed maximum discharges 27 Table 5.12 Overview of branches and approximate locations 27 Table 5.13 Estimates of climate change for the Rhine basin 29 Table 5.14 Discharges at different tributaries for selected scenarios 30 Table 5.15 Peak discharges at different locations for selected scenarios 30
Table 6.1 Representative sizes of ship classes 33
Table 6.2 Input information for changes in fleet 33
Table 6.3 Ship masses 35
Table 6.4 Number of journeys from ships from different ship classes ... 43 Table 7.1 Translation of GIS map of NRW to ecotope distribution in STORM 48 Table 7.2 Translation of Gewässerstrukturgütekartiering of Rhineland Paptinate 50 Table 7.3 Matrix to transform current ecotope distribution to target ecotope 51
Table 8.1 Unit flood damages 55
Table 8.2 Areas and land use classes of damage 55
Table 9.1 Water resources management framework in Germany 57 Table 9.2 Water resources management framework in The Netherlands 58
Table 9.3 Water quantity management 59
Table 9.4 River, floodplains and facilities management 60
Table 9.5 Roles in STORM-Rhine 60
LIST of FIGURES
Figure 3.1 Elements of a simulation game 7
Figure 3.3 Reach covered by STORM-Rhine 7 Figure 3.4 Relation between modules and system models 9 Figure 3.5 Compilation of elements from STORM-Rhine interfaces 10 Figure 4.1 Structural measures in the river and floodplain 11
Figure 5.1 The Rhine basin 16
Figure 5.2 Relation between the computational modules 19
Figure 5.3 Example of effect on discharge peaks 20
Figure 5.4 Illustration of link between hydrologic and hydraulic computations 21 Figure 5.5 Schematic cross section used in hydraulic computations 22 Figure 5.6 Structure of the hydrological routing model 25 Figure 5.7 Comparison between Muskingum routing model end SOBEK 26 Figure 6.1 Model results (Eq. 5.2) for different ship classes and empirical
relation for 4 barges convoy sets, derived by AVV (2000) 35 Figure 6.2 Derivation of relation between water depth and cumulative
probability of this water depth, from the Qh-relation in Lobith and the cumulative probability of certain discharges in Lobith 36 Figure 6.3 Probability distribution of the existing normative water depth (Eq.
3.2) and of the normative water depth that is 0.5 m larger 37 Figure 6.4 The probability that different ship classes can transport maximum
loads, plotted as a function of these maximum loads 40 Figure 6.5 Probability density functions of non-maximum loads for different
ship classes and a simplified model that uses an estimate of the load which is exceeded with 99% of the time and an estimate of probability that the ship can be fully loaded 40 Figure 6.6 Comparison of analytical and discrete way to determine average
load 41 Figure 6.7 Average number of tons transported, under the assumptions that
(1) always the maximum possible load is transported and (2) the demand of transport is equally distributed over the year and (3) the
loads cannot be buffered 41
1 THE STORM PROJECTS 1.2 Objectives of the projects
The objective of the STORM (Simulation Tool for River Management).projects is to develop simulation games for river management. STORM-Rhine specifically focuses on trans-boundary river and floodplain management, with as case study the River Rhine.
1.3 Objectives of STORM
Considerations
Large river basins are complex management systems because of
− the highly interrelated hydraulic, morphological and biological processes − the interactions between human activities and the physical system
− the management measures may mutually reinforce or counteract each other
− the multitude of policy makers and stakeholders with potentially conflicting interests. Simulation games can educate on the issues, provide a uniform frame of reference, and be a catalyst in cross-sectoral and multi-disciplinary dialogues. Simulation games can also explore how stakeholders may react in case of new scenarios developing.
The River Rhine
The River Rhine is an interesting case in point, where within less than a decade a complete new approach to river and floodplain management has been introduced with concepts as Room for the River, Flood Retention Areas, Resurrection of former River Channels and Living with the Floods, while at the same time the importance of Nature is widely accepted. Although there is a fair level of consensus amongst experts and politicians, there is still a great deal of
understanding and awareness raising to be explored, while the implementation of policy measures will highlight the real conflicts still to come. Besides that there are the new scenarios with higher design floods, and hence flood risks, caused by climate change and changing land use.
Objectives of STORM
The simulation game STORM intends to provide a platform for improving insight in river and floodplain management. It sets out:
− provide insight in river and floodplain management, showing the links between natural processes, spatial planning, engineering interventions, river functions and stakeholder interests
− formulate and analyse alternative management strategies − facilitate debate between different levels of stakeholders − explore the international dimension of river management − highlight upstream – downstream effects on river basin scale − explore river basin scale scenarios affecting river management − create awareness for the Room for the River concepts
− raise understanding of river regulation measures; decision-making mechanisms; floodplain use affecting river functions; river regulation affects flood plain use; the functioning of retention areas
1.4 The STORM Products
In the course of the projects three simulation tools were developed, Betuwe, STORM-Delta and STORM-Rhine, each with its own purpose and characteristics.
The concept
STORM – BETUWE
The STORM-Betuwe simulation game describes a typical stretch of some 60 km length of the Dutch River Rhine. The stretch is divided in eight sections in which the players can define the measures, both for the left and right side of the river. The roles represent four municipalities, each responsible for part of the river stretch and each with its own focus on economic development, nature and agriculture. In addition, the provincial and national government are represented. Because of the limited stretch of the river simulated, upstream-downstream affects do not appear. STORM-Betuwe facilitates most of the simulation game objectives described above. it was especially developed to create awareness for the Integral Reconnaissance Rhine Branches and Room for the River Projects in The Netherlands. Most of the river management measures as given in this report do apply, except that retention areas and green rivers cannot be created.
STORM – DELTA
STORM-Delta describes the Dutch Rhine Delta of the rivers IJsel, Lek and Waal from the border with Germany to the boundary of the salt intrusion. All river management measures and criteria listed in the report are available, including the “Green River”, flood retention areas (calamity polders) and redistribution of flows over the three river branches. However, the institutional framework has not been modelled. Consequently, there is no role-playing facility: one user may enter all measures and has access to all output. STORM- Delta is an interactive tool to provide insight in river behaviour, to create awareness for the Room for the River concepts and to test policies to enhance river (floodplain) functions for diverse stakeholder interests.
STORM – RHINE
STORM – Rhine is a full-fledged simulation game, which describes the river from the
downstream boundary of the salt intrusion in The Netherlands to Maxau in Germany, which is the site of the first weir in the river. It covers a total length of about 650 km, which is divided in 17 sections in which all the typical modern river and floodplain management measures can be taken. A total of eight roles represent the national, regional and local government and specific interest groups. STORM-Rhine incorporates the functionality of both STORM-Betuwe and STORM-Delta. The scope of STORM-Rhine is briefly described in Chapter 3.
1.5 Making use of STORM
Experience shows that simulation games can be used in very different settings, focusing on one or more of the objectives above, depending upon the participants and the time available. STORM is considered particularly suitable for the following settings:
− education (particularly to gain insight in complicated multi-disciplinary issues)
− training middle and higher level staff of local and regional government, water boards and members of interest groups from across the basin, who deal with particular stretches or functions of the river, but who need (1) to be better aware of the integrated whole, (2) to understand the interests and considerations of others and (3) to experience the mutual benefits of co-operation
− the same target group as above + policy makers and experts to explore the consequences of for example (1) different visions on development and policy targets and (2) different natural conditions, such as due to climate change and catchment characteristics
− at miscellaneous meetings and conferences for providing a uniform frame of reference or simply “breaking the ice”.
A special challenge would be to use STORM in the following, be it quite different, purposes: − to discover and explore new ways of river management
− as a tool to support interactive policy formulation and participatory decision-making in actual plans.
1.6 Roleplay Setting
The simulation game can be ‘played’ with a computer network, whereby each role can directly enter the desired measures it is mandated to enact. However, the respective roles responsible for issuing permits or binding advice, need to have done so on their own computers, before the measure will be executed. Players may communicate via the network with e-mails. The model (on a central database server) provides feedback on the state of the river in the form of tables, graphs and maps showing the performance criteria and state of the river. Based on an
individual or communal evaluation, players may decide to take additional measures. It is also possible to engage in the roleplay with one stand-alone computer which runs the model. The role representatives are then provided with hardcopy input sheets, while a ‘game-leader’ looks after processing and feedback with printed output.
1.7 STORM Projects Implementation
The research project was carried out from 1997-2001 by the following partners:
− IHE; International Institute for Infrastructural, Hydraulic and Environmental Engineering; Delft, The Netherlands
− RA: Resource Analysis; Delft, The Netherlands
− WL | DHL; WL | Delft Hydraulics Laboratory; Delft, The Netherlands Different phases of the research project were financed by
− European Union under the IRMA-Sponge Programme, − Land Water Impuls (LWI) (ICES I),
− Delft Cluster (ICES II), − RIZA
2 THE REPORT
2.1 This report is technical in nature and its purpose is to describe the design of the main elements of the simulation tool for STORM-Rhine.
Chapter 3 briefly describes the scope of STORM-Rhine.
Chapters 4 to 9 and Annex A describe in detail the system models, which are used in the roleplay:
the model on hydrology
• • • • • •
the model on hydraulics and morphology the model on land use in the floodplain the model on shipping
the model on damages in case of floods the roles representing the institutions.
3 SCOPE OF STORM-RHINE 3.1 The Concept
The main elements of the simulation game are depicted in Figures 3.1 and 3.2 below. The players represent the institutions
and stakeholder interests. They have mandates to take measures to pursue their interest in specific river and floodplain functions. The measures may be river engineering oriented, but also land use, economic or
administrative interventions are possible. They may reinforce each other or may conflict with each other The measures are analysed by a system model and translated into effects, which describe the functioning of the river and floodplain with respect to the interests of the players. The game may be played in different rounds representing distinct time periods. Player Player Player Measure Measure System Model Effects Effects Institutions, Stakeholders Interests River Management Strategy River Rhine Model River Rhine Floodplain Functions Evaluation System model Scenarios Institutional Actions Objective Budget Objective Actions Budget Financial Criteria Criteria
Figure 3.1 – Elements of a Simulation Game
The players are linked by a regulatory framework of licensing and budgeting. Scenarios determine under which conditions the game is played for example an increased demand for navigation, a specific design flood or a predicted climate change.
3.2 Scale of the Simulation
Figure 3.2 – Linkages between Players
The simulation model of STORM-Rhine
is restricted to the area where floodplains are of importance, as depicted in Figure 3.3. The upstream boundary is at Maxau, just upstream of Mannheim and just downstream of the regulated Upper Rhine. The downstream boundary is the limit of the salt intrusion in the three Dutch river branches: Waal, Lek and IJsel. The model is restricted to the main river corridor, with the tributaries incorporated as scenario variables.
Figure 3.3 – Reach covered by STORM-Rhine
The reason for this choice is that it is this reach of the Rhine where the main issues of flood
protection, nature, agriculture and navigation are dominant. Directly competing interests exist, especially with respect to land use in the floodplains and between shipping and nature development. Different, interdependent management interventions are available to influence the river functions. These issues and interventions occur at a scale and level, which are recognisable by the intended players of the simulation (see also Box 1, next page)
Design Conditions for Simulation Games
The design of the simulation game should fulfil a number of conditions, in order to make it interesting to play, and achieve the objectives described above:
•
• •
Realistic and recognisable: players should be able to recognise their situation and their own decision level. The complexity of river management is that interactions affect different stakes at very different scales. A rather visionary policy game at river basin scale is often not interesting to decision makers at a regional or local scale playing a policy game at a river basin scale if they do not recognise their own decision level. On the other hand, a regional scale policy game raises the awareness of decision makers at a river basin scale of their role in regional decision-making, provided that their role is represented in the simulation. A policy game at a more regional scale with representation of the river basin scale will create a platform for cross-level discussions.
Credible: the system model should report effects, which in their order of magnitude are subscribed to by the “experts”.
Conflict and dependability: competing interests and river functions, which are served by alternative river management strategies have to exist.
Box 1
3.3 River and Floodplain Functions
The river and floodplain functions identify the interests of the stakeholders. Criteria indicate the performance of the function. Setting the functions and criteria determines the type of system models, which have to be made in order to be able to give feedback to the players of the roleplay. The functions and criteria represented in STORM-Rhine are listed in Table 3.1.
Table 3.1 River and floodplain functions and criteria represented in STORM-Rhine
Function Performance criteria Indicator
Flood protection
Discharge of Water − maximum water level increase − unsafe river stretch − estimated flood damage − cost of all related measures − cost of flood damages
m km €/y € €/y
Shipping − change in average turn over per ship/year
− additional benefits industrial sector − change in employment in shipping sector − change in employment road transport sector − energy use
− CO2 emission, acid rain (NOX + SO2 ) and smog
− investments in new ships − costs of depth increase
€/y €/y persons persons % % € €
Nature − surface area nature
− ecological chances
− fulfilling of stepping stone function − presence of indicator species
− costs of acquiring and developing nature area − cost of nature management
ha - % # € €/y
Agriculture − (acquired and total) area of agriculture
− yield
− cost of acquisition and development
ha ton/yr € Landscape and
culture − degree of openness − agricultural character landscape − managed natural character − spontaneous natural character
% % % % Construction
Materials − amount of mined clay, sand, gravel − amount of mined polluted soil − cost of cleaning polluted soil
m3
m3 €
Recreation − land related recreation, water related recreation ha
3.4 River and Floodplain Management
The typical river and floodplain management interventions are described in Chapter 4. Table 3.2 lists the measures presented. The mandates of the different roles to enact management are described in Chapter 9. Not all management interventions can take place in every stretch of the river. The restrictions are also listed in Chapter 9.
Table 3.2 River and floodplain management measures represented in STORM-Rhine
River Training Vegetation Management
− Construct stone or natural river bank − Change length or height of groynes − Change height of summer dike − Change height of winter dike
− Change distance of winter dike from river − Change depth of river, dredging
− Construct / remove side channel
− Spontaneous succession − Extensive natural grazing − Meadow land management − Wetland management − Forest development
− Agricultural pasture management − Agricultural crop management
Physical Planning Administrative
− Construct retention areas
− Lower high terrain, excavate sand, clay − Remove earthen bridge ramps
− Build in floodplain (residential, industrial) − Construct recreational harbour, camp sites − Construct “green river “(outside flood-plain)
− issue floodplain activity permit − issue local land use permit − issue excavation permit
− change composition shipping fleet
3.5 The Models
The models together forming the heart of the simulation tool are shown below in Figure 3.4 and listed in Table 3.3. The models are described in more detail in subsequent chapters.
River network
Land-use morphology hydraulics roughnes
excavation
shipping landscape recreation nature
Performance Criteria
Interventions: river training, vegetation management, physical planning SCENARIO: hydrology shipping nature landscape mining agriculture recreation cost agriculture floods Geometry costs ecotope predictor
Figure 3.4 – Relation between modules of the system models
Table 3.3 Modules of the STORM-Rhine system model
Type Water-related Land-use related Other
Modules Hydrological routing module
Hydraulic module Morphological module Shipping module
Hydraulic roughness module
3.6 The Roles
The institutions are represented in eight roles as follows: 1 The national government Upstream (Germany)
2 The regional government for the Left River Bank Upstream(Germany) 3 The regional government for the Right River Bank Upstream (Germany) 4 The local government Urban Municipalities Upstream (Germany) 5 The local government Rural Districts Upstream (Germany) 6 The national government Downstream (The Netherlands 7 The local government Rural & Urban (The Netherlands) 8 An international environmental lobby group
The mandates of the different roles are described in Chapter 9.
3.7 The Interface
The interface of the STORM-Rhine model facilitates the selection of interventions and scenarios and gives output in the form of tables and maps showing the performance criteria. The interface also provides the facilities for communication between players so as to account for licensing of interventions. An compilation of the elements of the interface is given in Figure 3.5.
4 RIVER MANAGEMENT 4.1 Introduction
River Management of the River Rhine is a complex process in which the diverse stakeholders must be considered. These stakeholders include clear economic users of the river such as navigation, drinking water, recreation, but also important issues such as environment and safety. The current situation of the river is by no means a given constant but changes constantly due to for example climatic change, changes in perception of society as well as autonomous changes such as morphological aggregation and degradation (Silva et al, 2001). Perhaps the most apparent change threatening the river is that of the projected climatic change, where it is foreseen that the regime will move away from the snow-melt fed regime to a rain-fed regime, with higher peaks and lower troughs in the discharges as a result (Middelkoop, 1999). One instrument that can be employed to counter these influences and maintain usability of the river is to intervene, either in the geometry, land use or discharge regime.
Any intervention in the river system will affect the river response in terms of water level, discharges, morphology and sediment transport characteristics, and can directly and indirectly change those characteristics, since water movement, sediment transport and river morphology is strongly interrelated. For example, the construction of groynes to ensure sufficient depth for navigation initially leads to higher water levels. This would intuitively lead to the need for dredging. The higher velocities derived from the restriction of the channel, by progressively eroding the riverbed, leads to the ultimate effect of a decrease of the water levels. As a consequence channel dredging may no longer be required. The construction of groynes changes also the channel roughness so that the prediction of water levels should take this into account too. Other examples of river engineering works are channel modifications, the
construction of embankments, new or modified infrastructure (flood storage, weirs, barriers, sluices, bridges etc.) and, recently, river restoration and flood plain reforestation. By increasing channel roughness and reducing the cross-section for the water flow, those interventions may have drastic consequences for the water levels during floods.
From these examples it is clear that the consequences of each intervention are very complex, and where the use of the river for one stakeholder may improve, others stakeholders may suffer. In this chapter some of the options available for intervening in the river are discussed. The interventions, or measures, are divided into three main categories, where only options for interventions in the river system itself are considered, as interventions in the catchment to change runoff to the river are beyond the scope of this project.
Figure 4.1 shows the typical river and floodplain management interventions.
Figure 4.1 – Structural measures in the river and flood-plain
4.2 Interventions in the main channel
typically felt for a limited reach upstream rather than downstream of the measure, due to the limited change in storage.
Dredging
Dredging in the main channel is typically employed to keep the river navigable throughout its entire length, but due to the natural degradation of the river channel in most of the reaches, this measure is generally not well received (Silva et al, 2001). It is clear that the impact on dredging on high flows is also positive, as main channel conveyance is increased. Although dredging is required in some reaches to maintain navigability, application of this approach across long reaches may have undesirable side effects on groundwater table levels along the river, salt intrusion in the delta and long term morphology.
Groynes
Construction of groynes along the main channel has been widely employed along the lower parts of the Rhine, most notably the Lower Rhine and the branches of the Rhine Delta. Groynes serve to concentrate the flow in the main channel, and through this help maintain the depth in the main channel and prevent the development of sandbanks that could hinder navigation. Groynes are of great importance to ensuring navigation, particularly during low flows.
Construction of groynes may again be considered if the projected climatic change does indeed cause lower flows in the river during the summer. During higher flows groynes have a negative effect, as the conveyance of the main channel is reduced. From the point of view of flood protection construction of groynes is therefore not desirable, and even removing or shortening existing groynes is considered. An alternative to removal of existing groynes, and the negative effects this will have on shipping and stability of the main channel is to lower existing groynes. This option does need to be considered carefully in terms of the impacts on morphology (Silva et al, 2001).
Main channel banks
Although the influence on the flow in the main channel may be limited, main channel banks may be either fixed as stone banks or left in a natural state. Stone riverbanks are found along various reaches of the river, particularly in the Upper and Middle Rhine. Obviously natural riverbanks are environmentally appealing, but these do cause the roughness to increase and thus levels during high flow will increase.
4.3 Interventions in the floodplain
A wide variety of interventions may be taken in the floodplain and the number of users and usage’s of the floodplain are much more diverse than the main channel. Clearly the floodplain has limited influence on water levels at low-flow conditions, but for high flows it is of significant importance. Floodplains are used in a variety of ways, with environmental and agricultural being dominant, but also for recreational and even industrial and urban purposes. Broadly speaking, interventions in the floodplain can be categorised into interventions that involve excavation of the floodplains, floodplain landscape planning or the removal of hydraulic bottlenecks.
Depending on to what degree the storage in the floodplain is affected, the measures described will predominantly influence flood levels upstream of the location of the intervention. If
significant extra storage is created, the levels downstream may also be influenced through increased attenuation of the flood wave.
Floodplain excavation
Flood plain excavation is a measure by which the gradual development of heightening by sedimentation on flood plains may be counteracted. This heightening is generally caused by the construction of dikes, ‘normalisation’ of the river and by the construction of submersible
embankments.
To influence the hydraulic characteristics of flow significantly, floodplain excavation
not be left as bare soil, and some form of land-use management should be considered in conjunction with the excavation. Development of nature areas is one example.
Construction or maintenance of side-channels, either those connected to the main channel or isolated side channel (e.g. isolated oxbow lakes), can be seen as a special form of floodplain excavation. This intervention is well suited to increasing conveyance of the river during high flows, while promoting the ecological diversity of the floodplain.
Floodplain land-use
Land use in the floodplain is an important issue. Encroachment of urban areas on floodplains has not only significantly reduced the extent of floodplains, but urban and industrial
development in the floodplain has led to significant damages from flooding. For a large part, particularly in the Rhine branches in the Netherlands, the floodplains are used as agricultural land, often for grazing. Changing perceptions with respect to the environment is leading more and more to a drive for more natural floodplains, with the development of forested floodplains and wetlands very much in public interest. Development of floodplains in this way goes well with interventions such as floodplain excavation, but the combined effect on for example water levels during flood must be studied carefully when these types of interventions are employed.
Removal of bottleneck and submersible (summer) embankments
The removal of a bottleneck is a very local intervention. Typical hydraulic bottlenecks are bridge abutments, ferry ramps or flood-free areas in the floodplain. Other examples are sharp bends in the river or very narrow floodplains. Removal of these may be very effective in lowering
upstream flood levels, while being economically attractive when compared to measures such as floodplain excavation. Depending on the type of bottleneck, the impacts on other floodplain users may, moreover, be limited.
Submersible embankments have been constructed along large reaches of the main channel of the Rhine, and keep the floodplains free from flooding for all except high floods. Removal of these will have significant effects on the frequency of floodplain inundation, as well as possible effects on low flow conditions in the main channel. Increasing the frequency of floodplain inundation may allow for a more natural development of floodplain vegetation, but for other users the effects may less desirable.
Retention basins
A very effective method for reducing flood levels downstream is to retard water in the upstream part of the river. Retarding water in the catchments before it reaches the main river may be effective but is not considered here. Large volumes of water may, however, be retarded in off-line retention basins. When used most effectively these can be employed to as it where “shave off” the peak of the flood, thus lowering the flood peak downstream. Retention basins can be constructed either in the floodplain through the construction of a ring dyke, or out of the floodplain (Lammersen et al, 1999). The first category is usually somewhat limited in size and thus capacity to reduce the flood peak. Larger retention areas may be created beyond the floodplain, but this does lay a significant claim on land, with the use of land adjacent to rivers already being under much pressure. Retention areas are controlled through inlet structures, either as a fixed crest weir or an inlet structure that is operated. The water stored in the retention area is allowed to flow back into the river once the peak has passed. Control of the retention area, or the level at which the retention area starts operation is an important factor in determining the effectiveness of the area. If the area is put to use to early then it may be full before the peak arrives, and the effect on the peak may then be negligible. If it is too late then there will be no effect on the peak. Another problem is the location of the basin with respect to the dominant area of flood genesis. Clearly a retention basin in the Upper Rhine will have no effect on a flood generated in the catchment areas of the major tributaries flowing into the Middle Rhine.
4.4 Summary
5 MODELS on HYDROLOGY 5.1 Introduction
The roleplay for transboundary river management considers the Rhine River basin both in Germany and in the Netherlands. Central to the game is the assessment of possible river related measures, where these measures are targeted at one or more of the uses of the river system. Examples of these uses are navigation, safety etc.
Assessment of the effects of measures is accomplished by evaluating these in a
hydrological/hydraulic module, where the impacts of measures on different flow conditions are determined. These changed flow conditions are then applied in determining impacts for different users such as the navigation authorities, flood protection authorities etc.
In this chapter the approach taken in modelling the hydrological and hydraulic processes is described. This brief description focuses on the approach, without going into mathematical detail of the concepts applied. These details are given in the applicable sections of Annex A. A general description of the hydrology of the Rhine River basin is given, with particular focus on that part of the basin downstream of Maxau, being the upper limit of the basin considered. The approach taken in modelling the hydrology, hydraulics and morphology of the basin is
introduced, as well as how measures are incorporated. In the last section, the structure of the models as applied in this project are discussed, with particular focus on the determining of boundary conditions for different scenarios.
5.2 Hydrology of the Rhine Basin
The River Rhine has its source in the Alps, and stretches some 1300 km to its mouth in the North Sea. The catchment area is about 185,000 km2. The hydrological regime of the basin is a combination of rainfall and snowmelt. Engel (1997) identifies six major stretches by considering the geo-morphological characteristics. The Alpine Rhine and the High Rhine in the Alps are characterised by high mountains and extensive glaciers. Downstream of Rheinfelden/Basel, the Upper Rhine starts. Here the Rhine flows through a lowland plain at a much smaller gradient. The natural river once was of a braided nature, but in recent centuries elaborate river training works have been undertaken to improve navigability. These river training works are
concentrated mainly in the upstream half of the Upper Rhine (above Maxau, Figure 5.1). Below Mainz the river cuts through the Rhenish Slate Mountains, meandering through a relatively narrow gorge. This section is known as the Middle Rhine. Downstream of Bonn, the river once again changes in nature to become the Lower Rhine, a typical lowland river with wide meanders and a relatively wide and flat floodplain. Just after the Dutch/German border the Rhine Delta starts as the river bifurcates into three main branches, Waal, IJsel and the Dutch Rhine (Nederrijn-Lek), before flowing into the North Sea. At the downstream end of these three branches, the tidal influence of the North Sea becomes noticeable. In a transition zone, flood hazard is influenced both by upstream hydrology and downstream tidal conditions. Beyond this transition zone flood hazard is dominated by the tidal influences.
The hydrology of the High and Alpine Rhine is governed by snow-melt, with maximum discharges occurring in the summer months. These may be amplified by intensive, local summer rainfall (Middelkoop, 1999). The major tributaries of the Rhine are the Aare, Neckar, Main and Mosel. While the first is distinctive of the High and Alpine Rhine, the other three are typical rainfall dominated rivers, flowing into the lower half of the Upper Rhine and the Middle Rhine. These rain-fed tributaries contribute significantly to the genesis of the large floods in the Rhine, and most major floods have been caused by extreme discharges in these three
tributaries, as well as other predominantly rain-fed tributaries in the Upper, Middle and Lower Rhine (Engel, 1997). These major floods occur predominantly in late autumn or early winter during extensive frontal storms, usually preceded by long spells of wet weather.
Mountains poses clear constraints on the scour of the river bed, and a lower limit must be taken into account. However, in these reaches sedimentation may occur if hydraulic conditions are favourable, and these layers may subsequently erode again.
Figure 5.1 The Rhine basin (from Silva and Dijkman, 2000)
5.3 Extent of Rhine Basin considered
The models for the Rhine basin considered here do not cover the entire Rhine basin. The upstream boundary of the area considered is the gauging station at Maxau (Figure 5.1). Moreover, only the main river is considered, with tributaries dealt with as hydrological inputs. Table 5.1 gives an overview of the river chainage of various stations on the Rhine between Maxau and Lobith, including the locations of major tributaries.
Table 5.1 Cumulative chainage and catchment area of the Rhine between Maxau and Lobtih (adapted from Diermanse et al, 2000
Station Tributary Section Chainage Trib-area Area
Station Tributary Section Chainage Trib-area Area
(km) (km2) (km2)
Nette&Wied 610.00 1,100 139,586
Andernach Middle 613.80 139,795
Ahr 629.00 850 140,837
Bad Honnef Middle/Lower 641.00 -
Bonn Lower 654.70 141,162 Sieg 660.00 2,900 144,217 Koln Lower 688.00 144,612 Wupper 702.00 800 145,618 Erft 738.00 1,800 147,948 Dusseldorf Lower 744.20 148,040 Ruhr 779.00 4,500 153,143 Ruhrort Lower 780.80 153,176 Wesel Lower 814.00 154,528 Lippe 815.00 4,900 159,428 Rees Lower 837.40 159,683 Emmerich Lower 851.90 159,784
Lobith Lower/Dutch Rhine 862.22 160,800
Pannerden Dutch Rhine/Waal 867.20 -
Tiel Waal 915.00 -
Gorinchem Waal 955.00 -
Arnhem Dutch Rhine/ IJssel 878.70 -
Amerongen Dutch Rhine 918.00 -
Nieuwegein Dutch Rhine 950.00 -
Deventer Ijssel 935.00 -
Ijselmeer Ijssel 993.00 -
For the sake of simplicity, not all the tributaries given in Table 5.1 are individually modelled. Obviously three of the four main contributors in the genesis of floods (Engel, 1997) that are downstream of Maxau are explicitly considered. Table 5.2 shows estimates of the maximum discharges measured for the various tributaries, and those with estimated maxima in the order of 1000 m3/s or higher are also considered explicitly here. Smaller tributaries are added to the closest larger one such that the volumetric balance is maintained while simplifying the geographic distributions somewhat.
Downstream of the Dutch/German border the river bifurcates into three main branches. These three branches are considered as they were in the original Role play model for the Delta of the Rhine. The downstream boundary of these branches is located such that it is upstream of any tidal influence, with flood hazard therefore being dominated by hydrological conditions upstream. Using the locations of the stations and tributary inflows given in Table 5.1, this led to the definition of 17 main section in the model of the Rhine. Division of the sections discerned by Engel (1999) was driven by the locations of tributary inflows, administrative boundaries (both national and international) as well as other important towns/locations.
Table 5.2 Physical maximum and highest measured discharge (period 1880 - 1995) at various gauging stations on the Rhine and its tributaries (Silva and Dijkman, 2000)
River Estimated Physical Max. (m3/s) Highest measured discharge (m3/s)
Gauging station Date
Oberrhein (Worms, incl. Neckar) 6300 5600 Worms 550117 Main 3000 1980 Frankfurt 950130 Nahe 1200 1150 Grolstein 931221 Lahn 950 840 Kalkofen 460210 Mosel 4800 4170 Cochem 931221
Nette und Wied 400 202 Nettegut, Friedrichshal 840207
Table 5.3 Tributaries explicitly modelled
Tributary Added Tributaries
Neckar Main Nahe Lahn
Mosel Nette & Wied
Sieg Ahr
Ruhr Wupper, Emscher and Erft
Lippe
Table 5.4 Overview of branches considered in the model
Branch Name Start End Start Km
(approx.)
End Km (approx,)
Length (km)
U1 Upper Rhine 1 Maxau Mannheim 360 425 65
U2 Upper Rhine 2 Mannheim Mainz 425 497 72
U3 Upper Rhine 3 Mainz Bingen 497 530 33
M1 Middle Rhine 1 Bingen Koblenz 530 592 62
M2 Middle Rhine 2 Koblenz Bad Honnef 592 642 50
M3 Middle Rhine 3 Bad Honnef Köln 642 688 46
L1 Lower Rhine 1 Köln Düsseldorf 688 744 56
L2 Lower Rhine 2 Düsseldorf Wesel 744 813 69
L3 Lower Rhine 3 Wesel Lobith 813 862 49
R1 Dutch Rhine 1 Lobith Pannerden 862 867 5
R2 Dutch Rhine 2 Pannerden Arnhem 867 878 11
R3 Dutch Rhine 3 Arnhem Amerongen 878 918 40
R4 Dutch Rhine 4 Amerongen Nieuwegein 918 950 32
W1 Waal 1 Pannerden Tiel 867 915 48
W2 Waal 2 Tiel Gorinchem 915 955 40
Y1 Ijssel 1 Arnhem Deventer 878 935 57
Y2 Ijssel 2 Deventer IJsselmeer 935 993 58
5.4 Modelling Approach
In the context of the role-play, an attempt is made to keep approach taken in modelling the hydrology, hydraulics and morphology of the river as simple as possible. This section is designed as a brief introduction to the approach, while more detail on the computational
methods and the underlying assumptions is given in Annex A. The modelling approach is one of three steps,
1. Hydrological computations for determining discharges in the river system, 2. Hydraulic computations for determining water levels, and,
3. Morphological computations for determining variations in river bed levels. The relation between these three steps is shown schematically in Figure 5.2. There is a feedback loop between the hydraulic and morphological computations, due to changes in geometry determined in the latter, while the former determines velocities used by the latter. Predicting morphological changes in a first step and subsequently determining the final hydraulic conditions in a second step, using the predicted morphological changes account for this feedback loop. Further iteration is not required under the assumption that differences in the predicted morphological change due to the revised hydraulic conditions of the second step are negligible.
Although full hydrodynamic models are available for integrated calculation of the three processes considered, it was decided that using these would unnecessarily complicate the modelling approach, and lay too much emphasis on these models within the gaming
Hydrological computations Morphological computations Hydraulic computations Discharges Velocities Water Levels Hydrological Scenarios River Geometry
Figure 5.2 Relation between the computational modules
5.5 Hydrological Computations
In the original role-play model on which the development of this extended model is based, hydrological conditions were relatively simple. The upstream boundary of the model was at Lobith on the Dutch/German border. From a hydrological perspective this single source of flow is easy to deal with. For the Rhine in Germany the hydrology is, however, geographically distributed. Particularly for major flood events, the tributaries of the Upper, Middle and Lower Rhine have a significant influence, and the impacts of floods will be geographically distributed. This entails also that effectiveness of measures designed to alleviate floods will depend very much on where these are taken in comparison to where the flood is generated. As floods may be generated in the geographically distributed tributaries, the occurrence of extreme floods in the main river can be significantly influenced by how well the peaks of these tributaries and in the main river coincide.
To allow for the distributed nature of the tributaries, as well as attenuation of flood peaks, a hydrological routing scheme is used. The well known Muskingum routing method is applied (Fread, 1993). Using this approach the flood wave from the uppermost catchment is routed to the confluence with the first tributary, there the flood wave from this tributary is added, and the combined wave is routed to the next confluence. This is repeated until the downstream end of the model is reached.
The method of routing flood waves through the river network and adding discharges at confluences is applicable as long as the river network is dentritic. Once the river bifurcates, hydraulic conditions at the bifurcation will determine how the flood waves will divide. This would introduce a feedback loop (Figure 5.2) between the hydrological and hydraulic computations. In the Rhine below the bifurcation there are no major tributaries and attenuation effects are limited. To keep the interaction between the hydrological and hydraulic computations simple, the lower boundary of the hydrological computations is thus set between the Lower Rhine and the Rhine Delta on the Dutch/German border at the Lobith gauging station.
explored the hydrological routine allows for matching peaks of flood waves at the nodes where these are summed.
In Figure 5.3 an example is shown on the effect on hydrographs of peaks coinciding. The first inflow is routed, and the routed hydrograph clearly shows attenuation and a shift of the peak. At this point a tributary inflow is added. A second summed hydrograph may be obtained by synchronising the peak of the routed hydrograph with the peak of the tributary hydrograph.
50 100 150 200 250 300 350 0 1000 2000 3000 4000 5000 6000 7000 Qinflow,1 Qrouted Qinflow,2 Qrouted,lagged Qrouted+Qinflow,2 Qrouted,lagged+Qinflow,2
Figure 5.3 Example of effect on discharge peaks due to peaks of contributing hydrographs coinciding
Generation of flood waves, through the runoff of rainfall or snow-melt is not considered explicitly in the hydrological computations. These deal solely with the routing of flood waves through the river network. As only the main river is considered, flood waves from the tributaries are imposed at the confluence in the main river.
5.6 Hydraulic computations
In the original role-play model, on which the development of this extended model is based, the hydraulic and morphological computations were made based on a steady state approach. It is assumed that the time derivatives of flow conditions are very small, as well as for the flow being sub-critical (low Froude numbers). This allows for significant simplification of the flow equations (Vreugdenhill, 1973). The approach computes the head difference over a reach based on the geometrical properties of that reach. As the method is steady state, no storage or attenuation of discharges is taken into account.
Starting from the downstream end of each branch, the head difference over the whole branch is determined as the sum of the head differences over the sub reaches. Bifurcation of the Rhine into the Waal, Dutch Rhine and IJssel does complicate the solution procedure, as the exact division of discharges over the branches is not known a-priori. This is dealt through the introduction of computational meshes across which the head differences are known (Vreugdenhill, 1973). See Annex A for a full description.
discharges are kept constant between each of the sections of the hydrological model. This will give some overestimation at the downstream end of the hydraulic reach due to attenuation, but given the limited length of the reaches in the hydrological model when compared to attenuation effects the overestimation is considered not to be too large. Figure 5.4 shows the principle of sampling the peak discharge of the hydrograph in the hydrological model and imposing these discharges on the hydraulic model. Discharges at intermediate nodes in the hydraulic model are allocated the same discharge as the closest upstream hydrological node. The lengths of the sub-sections in the hydraulic model are typically in the order of 10 km.
Tributary Tributary
Hydrological computation reach/node Hydraulic computation sub-section/node
Sample Qpeak Retention
Basin
Figure 5.4 Schematic illustration of link between hydrological and hydraulic computations.
The geometry of the cross section used in the hydraulic computations is a schematised representation when compared to the actual geometry. Figure 5.5 shows this schematic cross section, with the symbols explained in Table 5.5.
Table 5.5 Geometrical properties of schematised cross sections.
Description Symbol
Levels
Bottom level main channel: zm
Left floodplain level (horizontal section): zlfp1
Left floodplain level (end of inclined section): zlfp2
Right floodplain level (horizontal section): zrfp1
Right floodplain level (end of inclined section): zrfp2
Left winter-dyke level: zwdl
Right winter-dyke level: zwdr
Left summer-dyke level: zlsd
Right summer-dyke: zrsd
Left groin level: zgl
Right groin level: zgr
Widths
Width main channel: bm
Width left floodplain (horizontal section): blfp1
Width left floodplain (inclined section): blfp2
Width right floodplain (horizontal section): brfp1
Width right floodplain (inclined section): brfp2
Length left groin: Lgl
Lgl bm brfp1 blfp1 zlfp2 zlfp1 zlsd zrsd zrfp zwdr zm zgl zgr Lgr zwdl blfp2 brfp2 zwdr
Figure 5.5 Schematic cross section used in hydraulic computations
5.7 Morphological computations
Morphological computations are kept very simple. Sedimentation and erosion are determined using the average velocity in a cross section. This average velocity is compared to a threshold velocity. If the threshold is exceeded the bed level will decrease through erosion while if it is not exceeded the bed level rises through sedimentation. To take the hard rock base level of the Middle Rhine into account, a minimum scour level is assigned. Sedimentation on this hard-base level can occur, and these layers can again erode until this fixed level is again reached.
5.8 Measures
Measures that can be taken to change the flow properties of the river are broadly divided into four categories; retention measures, geometrical measures, measures that have impact on the hydraulic roughness and finally side channels and green rivers.
Geometrical measures and measures influencing hydraulic roughness
Two categories of geometrical measures can be given; measures acting on the main channel and measures acting on the floodplain. Measures acting on the geometry of the cross sections are applied to the schematised cross section (Figure 5.5). Measures influencing the vegetation result in a change in the distribution and type of floodplain vegetation, and based on this new distribution amended floodplain roughness coefficients are calculated. These measures may in principle be taken at any location along the entire river system, excepting locations where geometrical properties make application of a given measure irrelevant (e.g. removal of groynes will have no effect for river stretches where no groynes are present). Other restrictions may also apply for specific reaches. In the Middle Rhine, dredging of the main channel is limited to the layer of hard rock. An overview of the measures supported is given in Table 5.6.
Table 5.6 Measures acting on geometry and hydraulic roughness
Measure type Measure Acting on
construction of stone river bank main channel roughness
construction of natural river bank main channel roughness
increasing length of groins main channel geometry
dredging main channel geometry
deposition of sediment main channel geometry
removal of summer-dykes floodplain geometry
raising of summer-dykes floodplain geometry
construction of side-channel (see next paragraphs)
lowering of floodplain floodplain geometry
inland moving of winter-dyke floodplain geometry
raising of winter-dyke floodplain geometry
River training
Measure type Measure Acting on
spontaneous succession floodplain roughness
extensive natural grazing floodplain roughness
meadow land management floodplain roughness
swamp management floodplain roughness
forest development floodplain roughness
agriculture: pasture floodplain roughness
Vegetation management
agriculture: crops floodplain roughness
construction of retention area (see next paragraphs)
construction of recreational harbour floodplain roughness
construction of campsite floodplain roughness
lowering of high terrain lowering of high terrain
removal of earthen bridge ramps removal of earthen bridge ramps
Physical planning
building in floodplain floodplain roughness
Retention measures
Retention basins are off-line reservoirs that can be employed to “shave” off the peak of a flood wave. This is achieved by diverting a portion of discharges in excess of a threshold discharge at which the basin starts operation to a low-lying area adjacent to the river (Silva et al, 2000). The volume thus diverted is later returned to the river when conditions are more favourable.
Obviously the impact of these retention measures depends very much on where the measure is taken in relation to where the flood is generated. For this reason, the impact of retention basins on the reduction of flood peak is considered within the hydrological computations, rather than in the hydraulic module.
This approach is applicable only for those retention basins in the reaches considered by the hydrological model, i.e. those in the Upper, Middle and Lower Rhine. For Retention basins projected in the Rhine Delta, retention basins are dealt with by considering the effect these have on the peak flow. Based on the threshold discharge and the volume that can be stored, a weir with a fixed level above which the basin comes into operation is applied. Clearly this threshold is set at the equivalent level of the threshold discharge, which is only exceeded for the extreme flood events. Table 5.7 shows the retention basins that have been projected or completed in the Rhine between Maxau and Lobith (Lammersen et al, 1999, Silva and Dijkman, 2000)
Table 5.7 Projected retention areas between Maxau and Lobith (Lammersen et al, 1999, Silva and Dijkman, 2000)
Measure Constructio
n Area (Ha) (million mvolume 3) Location Approx
In the Rhine Delta, downstream of Lobith, further retention basins have been projected. The two main retention basins are shown in Table 5.8. Numerous other small basins have been
projected on each of the three river branches.
Table 5.8 Projected retention areas between Maxau and Lobith (Silva and Dijkman, 2001)
Measure Construction Area
(Ha) Volume (million m3) Location (approx.)
Rhine Delta
Rijnstrangen unknown 3100 150 865
Ooijpolder/Duffelt unknown 1400 65 Waal (875)
In the role-play model for the Rhine Delta, the retention basin projected at “Rijnstrangen” (Table 5.8) is considered as a green river, with the outlet of the basin on the IJssel river. Rather than take the distributed retention basins actually considered, the approach taken in the role-play is to define retention basins along each of the main sections. In the Rhine Delta, approximate volumes are estimated at 100m3/s on each of the three branches, where for the upper three reaches, an “average” retention basin is estimated for each of the four federal states. This approach is followed as it allows for a clear selection by the different role-players, without making the number of options unnecessarily large. This leads to the retention basins in Table 5.9 being considered. Threshold discharges for the retention basin are derived from Lammersen et al (1999) for the basins in the Upper Rhine. For the lower Rhine, the 100 year discharge for Lobith is applied in the same way as in the original STORM model for the Rhine Delta (de Graaf, 1999)
Table 5.9 Retention basins considered in the STORM model of the Rhine
Retention basin Section Area
(Ha) Million mVolume 3 Location (km) QmStart 3/s
Rheinland Pfalz Upper Rhine 1495 48.4 373 4500
Baden-Württenberg Upper Rhine 610 18.1 395 4500
Hessen Upper Rhine 2700 80.0 468 5200
Nordrhein-Westfalen Lower Rhine 2600 75.0 846 13500
Waal Waal 100 13500
Dutch Rhine Dutch Rhine 100 13500
IJsel IJsel 100 13500
The discharge flowing into the retention basin is determined during the computations. For the retention basins considered in the hydrological routing model (i.e. the first four in Table 5.9), the discharge is calculated through a balance of flows into the retention basin and in the river downstream of the basin. On the basis of a volume balance and the ratio of the stage discharge relationship of the river at the location of the retention basin and the stage discharge over the inlet weir of the basin, an estimate of the discharge into the basin can be established. The procedure considers the water level in the basin, and once this equals the level in the river, the flow into the basin is stopped. No return flow from the basin to the river is currently considered. For further details on this algorithm as well as the derivation of stage discharge curves
reference is made to Annex A.
Side channels and green rivers
Side channels are channels excavated in the floodplain, parallel to the main channel. Rather than change the geometry of the river, side channels are incorporated in the hydraulic computation by estimating the discharge through the channel and subtracting this from the discharge in the river. Side channels may be applied along any reach of the river, given adequate space in the floodplain.
Green rivers are similar to side channels, but are excavated outside the floodplain. Green rivers need not start and end within the same river branch as is the case with side channels, but may start on one branch and end in another. Excavation of green rivers in the Middle Rhine is obviously not feasible due to the Rhenish Slate Mountains nor in most of the Upper and Lower Rhine as the area outside the floodplains is heavily urbanised. Currently only one realistic option for the creation of a green river is considered, the Rijnstrangen area, starting
5.9 Hydrological computations
The schematisation of the hydrological routing model covers the sections of the Upper, Middle and Lower Rhine, with the downstream boundary at Lobith. Further extension of the approach is difficult to apply due to the bifurcation downstream of Lobith. At this point the steady state approach is again adopted, as attenuation effects are now much smaller, and the problem of distributed inflows found upstream of Lobith does not occur.
For the structure of the routing model, calculation nodes defined at locations where tributary inflows are to be accounted for, locations where retention basins are defined, as well as at a number of intermediate stations. These intermediate stations are either points of interest or are chosen such that the length of routing branches is not excessive. The nodes and branches of the routing model are given in Table 5.10 and a schematic diagram of the structure is given in Figure 5.6. Maxau > Neckar > Main Mosel > Sieg > Ruhr > Lippe > > Lobith > Retention Nordrhein-Westfalen Lahn > > > Nahe > Retention Rheinland-Pfalz > Retention Baden- Wurtenberg > Retention Hessen
Routing branch with nodes
> Input hydrograph
> Retention Basin
Figure 5.6 Structure of the hydrological routing model (not to scale)
Table 5.10 Nodes and branches of the routing model
Location Start Node End Node Extra condition at start node
Branch 1 Maxau Retention Rheinland Pfalz Upstream boundary
Branch 2 Retention Rheinland
Pfalz Retention Baden Wurttenberg Retention basin
Branch 3 Retention Baden
Wurttenberg Mannheim Retention basin
Branch 4 Mannheim Retention Hessen Inflow of Neckar
Location Start Node End Node Extra condition at start node
Branch 6 Mainz Bingen Inflow of Main
Branch 7 Bingen Koblenz Inflow of Nahe
Branch 8 Koblenz Bad Honnef Inflow of Mosel and Lahn
Branch 9 Bad Honnef Bonn
Branch 10 Bonn Koeln Inflow of Sieg
Branch 11 Koeln Duesseldorf
Branch 12 Duesseldorf Ruhrort
Branch 13 Ruhrort Wesel Inflow of Ruhr
Branch 14 Wesel Retention Nordrhein-Westfalen Inflow of Lippe
Branch 15 Retention Nordrhein-Westfalen
Lobith Retention basin
The two parameters of the Muskingum routing equation (Fread, 1992 and also Annex A) for each branch of the routing model were calibrated using the SOBEK model of the Rhine to generate hydrographs at each of the nodes. This allowed for an inflow and outflow hydrograph to be established for each branch. A gradient based optimisation method was applied to find optimal parameter values. Discharge data for the 1993 flood event were applied in the calibration, and the parameter values were verified using discharge data for the 1995 flood event.
Comparison of the hydrographs which were calculated with the hydrological routing module and SOBEK are given in Figure 5.7 and Table 5.11. The comparison shows a very good fit between the two hydrographs, particularly as this is data for the verification event, the calibration event giving even better results. Errors between the two models are indeed smaller than between the calibrated SOBEK model and observed events. Interesting to note is that using the option to synchronise the peaks of the contributing hydrographs results in a discharge at Lobith of some 5% higher than without the synchronisation. This indicates that these floods may indeed have been more severe had an even less favourable synchronisation of peaks of the contributing tributaries occurred.
Figure 5.7 Comparison between Muskingum routing model and SOBEK for the 1995 event (verification)
200 300 400 500 6000 7000 8000 9000 10000 11000 12000
(a) Bad Honnef
