European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

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B4-3040/97/730/JNB/C4

by S. Dautrebande, J.G.B. Leenaars, J.S. Smitz & E. Vanthournout (eds.) May 2000

European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Authors contributing to the present report were:

M. Bourouag C. Casse K. Couderé S. Dautrebande D. Deglin J.F. Deliège E. Everbecq V. Hallet P. Hennebert M.C. Hoogvliet J.G.B. Leenaars J.C. Maréchal A. Monjoie C.J.J.H. Schouten J.S. Smitz F.M. Uithol F. v.d. Coevering R. Van Looveren E. Vanthournout

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 ,1752'8&7,21 1.1 PROBLEM DEFINITION...... 1

1.2 PROJECT DESCRIPTION...... 4

1.3 PROJECT ORGANISATION ...... 4

 3URMHFWWHDP  1.3.1.1 Funding organisations and stakeholders...... 4 1.3.1.2 Project management...... 5 1.3.1.3 Project partners ...... 6

 &RPPXQLFDWLRQZLWKLQWKHSURMHFW  1.3.2.1 Management team...... 8 1.3.2.2 Technical meetings ...... 9 1.3.2.3 Project team meetings ...... 9

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 0(7+2'2/2*<$1'$3352$&+   3.1 METHODOLOGICAL MODEL DEVELOPMENT ...... 13

3.2 METHOD DESCRIPTION PER STEP ...... 14

 7HUULWRULDOGDWDLQYHQWRU\   3.2.1.1 The GIS database structure ...... 15 3.2.1.2 Map presentation and CD-ROM ...... 15

 3UHOLPLQDU\ULVNDQDO\VLV    6FHQDULRGHYHORSPHQW   +\GURORJLFDOPRGHODQGDQDO\VLV   3.2.4.1 Data collection ...... 17 3.2.4.2 Hydrological assessment...... 17 3.2.4.3 Model development and simulations...... 18 3.2.4.4 Hydrological analysis...... 18

 +\GURG\QDPLFVWXG\   3.2.5.1 Data collection ...... 19 3.2.5.2 Model development and simulation of scenarios ...... 19 3.2.5.3 Analysis of results...... 19

i European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

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 7(55,725,$/'$7$,19(1725<  4.1 INTRODUCTION...... 21

4.2 OBJECTIVES...... 21

4.3 SPATIAL DATA INVENTORY AND GIS DEVELOPMENT ...... 22

 0HWKRGV  4.3.1.1 Technical challenges...... 23 4.3.1.2 Inter-disciplinary communication ...... 24 4.3.1.3 Software standard...... 24 4.3.1.4 Data Acquisition ...... 24

 2XWSXWV  4.3.2.1 Required GIS map layers ...... 25 4.3.2.2 Digital Elevation Model...... 25 4.3.2.3 Soil...... 26 4.3.2.4 Land use...... 27 4.3.2.5 Historical land use...... 28

 &RQFOXVLRQV   5HFRPPHQGDWLRQV  4.4 DESCRIPTION OF THE GEUL CATCHMENT...... 30

 3K\VLFDOHQYLURQPHQWRIWKH*HXOFDWFKPHQWDUHD   4.4.1.1 Climate...... 30 4.4.1.2 Hydrology...... 31 4.4.1.3 Topography...... 32 4.4.1.4 Lithology and Soils...... 33

 &XUUHQWODQGXVH   4.4.2.1 Land cover ...... 38 4.4.2.2 Land management / tillage...... 39

 +LVWRULFDOODQGXVHDQGKLVWRULFDOODQGXVHFKDQJHV   4.4.3.1 Review of historical land use and historical land use changes...... 40 4.4.3.2 Historical land use map...... 43 4.4.3.3 Inventory of historical land use changes ...... 46

4.5 RISK ANALYSIS...... 47

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 7KHVLPSOLILHG86/(PHWKRGSDUDPHWHULQYHQWRU\  4.5.4.1 Land ...... 49 4.5.4.2 Land use...... 49

 5HVXOWVRIWKHULVNDQDO\VLVZLWKWKHVLPSOLILHG86/(PHWKRG   4.6 CONCLUSIONS AND DISCUSSION ...... 54

iii European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

$11(;(6 Annexes A till F can be consulted in a separate folder added to this report, even as annexes G, H and I (maps).

A. Spatial data inventory and GIS development B. Area description C. Preliminary risk analysis D. Hydrological study: original text and figures E. Hydrodynamic modelling F. Scenario development and legal framework G. Maximum water levels along the longitudinal profile of the Geul river for different scenarios (large sized paper map) H. Current land use distribution; input for flash flood analysis (large sized paper map) I. The historical change of the risk of runoff since 1950; reference for flash flood analysis (large sized paper map)

iv European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

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2EMHFWLYHV This Geul project intends to propose an effective policy to tackle the current trans-boundary water management problems in the Geul river catchment, particularly concerning flash flood events. The present policy only solves or reduces flooding problems at local scale, while being inappropriate to avoid severe flooding problems at catchment scale. The project envisages an integrated policy, aimed to prevent or reduce accumulated peaks in water supply to flood-prone areas along the Geul river, by increasing the water retention in the upstream parts of the river system and/or in the surrounding uplands.

0HWKRGV All stakeholders and the project-team (Technum/CSO/Ulg/FSAGx) cooperated to define applicable sets of measures, so-called ‘scenarios’, to prevent or reduce peak discharges in the Geul catchment. The effectiveness of these measures was studied by simulating the spatial and temporal distribution of water flow through the catchment area, the Geul river and its tributaries. The current and historical land use situations were simulated as state of reference.

• CSO inventoried all data required in the study and produced a Geographical Information System (GIS). CSO also performed a preliminary hydrological risk analysis at catchment scale. The outcome was directive and has been used to identify a number of alternative scenarios for the simulations. • The University of Liège (ULg) and the Agricultural Faculty of Gembloux (FSAGx) simulated the hydrology of the catchment area, including groundwater transfer functions. The outcome included the location, timing and quantity of water flowing into the Geul river and its tributaries under the reference situations (current and historical) and as a function of the identified scenarios. • Technum, together with IMDC, simulated the water flow in the Geul river for each of the scenarios in order to analyse the impact of the water retention measures. Technum also co-ordinated the scenario development and the assessment of the current legal framework in all involved regions. The outcome of these studies included the water level and discharges in the Geul river for the different scenarios and an analysis of the applicability and appropriateness of the current legal framework and policy instruments.

5HVXOWV FRQFOXVLRQV The international data inventory and -standardisation proved to be very time-consuming, due to a lack of uniformity in the data or data formats and poor reliability of some data segments. The analysis of the hydrological- and hydrodynamic simulation results suggests the possibility to reduce Geul river water peak discharges and water levels, although only slightly. The most promising environment-friendly scenario proved to be a combination of constriction devices in the upstream riverbed and the introduction of land use related

vi European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas measures, like the transformation of farming land on the steepest slopes into forest and the planting of hedgerows or green belts in the upland areas surrounding the Geul river system.

5HFRPPHQGDWLRQV The present project has proposed management directives and proved their usefulness. It is thus recommended to use these directives to define an integrated flood risk management scheme at catchment scale as an explicit goal with its own specific instruments.

The simulation model, developed in this Geul project, is a recommended tool to analyse the effectiveness of possibly in-situ applicable measures to reduce the risk of flood events at catchment scale.

vii European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

 ,1752'8&7,21 Technum, CSO, and the University of Liège (the latter in partnership with the Agricultural Faculty of Gembloux) have completed an 18-month pilot project for defining environment-friendly measures to reduce the risk of flash floods in the Geul river catchment. This introductory chapter defines the problem and challenges and describes the project and the project organisation, including the project partners. The Geul catchment is a trans-boundary river catchment of about 380 km², located in Belgium, Germany and the Netherlands, in the triangle between Liège (BE), Maastricht (NL) and Aachen (GE). The Geul is a tributary of the Meuse river. Due to the texture of the soils developed in the loess covering most of the catchment, during intense precipitation, infiltration is limited; runoff is high and may easily result in flash flood events. Erosion and flooding are common in the area since the Middle Ages but seem to have aggravated during the second half of the 20th century. Beyond long-term climatic changes, the causes may be multiple and could be due to hydrological - (increasing urbanisation, modification of agricultural practices, crops alteration…) and hydraulic modifications (straightening of watercourses, disappearance of JUDIWHQ (cultured talus)…). The type of flood problems encountered in the Geul catchment is typical for many lower hill river catchments in Northern-Central Europe.

 3UREOHPGHILQLWLRQ Flash flood events are increasingly common phenomena in the Geul catchment area. Water and mud damage cause enormous expenses, costing local authorities between 5 to 40% of their annual budget simply to maintain local infrastructure. The floods of 1982 and 1987 in Valkenburg, for example, cost Dutch society millions of guilders. Eventually, the flood events of June 1998 led to requests from local governments and regional water management authorities (Waterboard) to adopt land use practices that would reduce the risk of runoff (GH /LPEXUJHU, 9-6-1998). Photo 1.1 illustrates the damage in the city of Valkenburg caused by high Geul river water discharge.

The Geul catchment has experienced an increase in the number of serious flash floods over the past 50 years. This increase has been directly associated with the increase in river water discharge levels. Leenaers and Schouten (1989) have observed some differences in the hydrology of the Geul river since 1950. Their findings are illustrated in Figure 1.1. According to their study, the characteristic maximum water discharge based on a four years return period is 23 m3/sec during the 1950’s and 39 m3/sec during the 1980’s1.

1 The original discharge data were measured in Valkenburg for the 1950’s and at the outlet of the watershed (in Meerssen) for the 1980’s. In order to be able to compare these measurements, the difference in basin

Introduction 1 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Besides the early 1980’s being rather wet, Leenaers and Schouten estimate that one of the most important variables explaining this considerable difference in discharge is the land use changes that have taken place since the 1950’s in – especially – the Dutch part of the catchment. Leenaers and Schouten also bring forward the effects of increased urbanisation (Figure 1.2). It is obvious however that these effects are rather slight, for instance in the case of an increased urbanisation rate of 10 to 20%, especially during the high precipitation events as considered in this Geul project (high precipitation periods cause saturation of the upper ground layers in the catchment). Other authors confirm this.

Photo 1.1 Damage in the city of Valkenburg caused by high Geul water discharge.

Still, referring to literature summarised in Chapter 4, land use seems to be an important variable partly explaining runoff and hence, flood events. The results of a preliminary risk analysis, performed in Chapter 4.3, confirm that the change of land use practices may account for an increased risk of surface water runoff and consequently for an increased risk of flooding.

surface area (larger in Meerssen than in Valkenburg) has already been taken into account (discounted) in the figures as represented in Figure 1.1. Anyhow, there seems to be little difference in discharge between the two stations (Heidemij, 1973).

Introduction 2 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Large flood event

Small flood event

Base flow (3,6 m³ /sec.)

Figure 1.1 Illustration of the changes in river discharge (1950’s and 1980’s) at a given return time. Large flood events, small flood events and the average base flow (3.6 m³ /sec; see section on hydrology) are indicated.

Figure 1.2 Discharge frequency curves of a 1 mi2 catchment (1 mi2 = 2.59 km2) under various states of urbanization.

Until now, the water management policy to prevent local flooding was designed to accelerate excess rainfall water directly into the Geul River and its tributaries. This,

Introduction 3 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas however, resulted in more severe flooding problems at the catchment scale, particularly in the downstream part of the catchment. The risk of flooding is not expected to decrease in the future if this policy does not change. Furthermore, the International Panel for Climate Change (IPCC) predicts a change in the weather conditions for Western Europe: rainfall will be more erratic, probably resulting in more frequent and severe flash floods.

 3URMHFWGHVFULSWLRQ In 1996, Belgian (Walloon Region) and Dutch authorities (Province of Limburg) decided to cooperate in the field of water management. The flash floods that occurred during the past years in the trans-boundary Geul river region, as well as the problems concerning water quality and ecological protection of this river, prompted Dutch and Belgian authorities to integrate their catchment management. In this particular context, the current project has been formulated and funded by a number of regional governmental organisations and by the European Commission (Directorate-General Environment). The present report presents the outcome of the project.

This pilot project, which includes a hydrological and hydraulic study of the Geul river catchment, investigated various alternatives for improving trans-boundary river management and for preventing flash flood events in the Geul catchment.

 3URMHFWRUJDQLVDWLRQ The project followed an integrated approach based on participation of all major stakeholders in the catchment. In this paragraph the organisational structure of the project is shown (Figure 1.3). Technum NV (Belgium), CSO Consultants (The Netherlands) and the University of Liège (Belgium), the latter in partnership with the Agricultural Faculty of Gembloux, performed the study.

1.3.1 Project team

1.3.1.1 Funding organisations and stakeholders The European Commission, DG Environment, funded part of the project (Article B4-3040 of the general budget of the European Communities) without having a direct interest or being a direct stakeholder. The major objectives of their financing were improving and promoting demonstrative and technical actions performed by local authorities and supporting community-based legislation and policy.

The responsible administrative stakeholders in the Geul river management are the Ministry of the Walloon Region and the Province of Liège (Belgium), the Province of

Introduction 4 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Limburg (The Netherlands), the Waterboard Roer & Overmaas (The Netherlands) and the Province of Limburg (Belgium). They were all involved in the project and, although not actively participating in the research itself, provided valuable data while ensuring the political acceptance of the study. Four donors financed the project: • European Commission (45 %); • Ministère de la Région wallonne, Belgium (25 %); • Waterboard Roer & Overmaas, The Netherlands (25 %); • The Province of Limburg, Belgium (5 %).

The German authorities and other stakeholders were not included in the project team because of the limited territorial influence.

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Funding organisations Stakeholders Project management

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3URMHFWÃZRUNLQJÃWHDP Univ. de Liege Univ. Technum CSO

Project partners Figure 1.3 Schematic representation of the project organisation

1.3.1.2 Project management Technum managed the project being the leading partner in the Geul project consortium. The management tasks included formulating the project schedule and planning, as well as supporting the communication process in the project, decision-making and financial budget management.

Introduction 5 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

1.3.1.3 Project partners Three project partners, from both Belgium and Dutch origin and being of academic as well as private nature, made up the so-called Geul project consortium.

Technum (Belgium) was project manager and took care of the communication with the European Commission. Technum was involved in the legal framework and responsible for the hydrodynamic aspects of this study (locating flood-prone zones, proposing structural measures for flood management…). IMDC (International Marine and Dredging Consultants) was involved as subcontractor for technical input in the hydraulic simulations.

CSO Consultancy for environmental management and research (The Netherlands) was responsible for the design, implementation, maintenance and analysis of the geographical database of the Geul river catchment area. CSO analysed the data stored in the Geographical Information System (GIS) to estimate the effect of land use changes on the hydrological responses of the Geul river system.

The Centre Environnement of the University of Liège (Belgium) was responsible for the hydrological study and was involved in the definition of environment-friendly measures against flooding. For the hydrological and agricultural aspects of this study, the Centre Environnement cooperated with other departments of the University of Liège and with the Agricultural Faculty of Gembloux (FSAGx).

Introduction 6 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

European Commission Directorate-General Environment Boulevard du Triomphe 174, B-1160 Brussels Contact person: Mr. E. Schulte Telephone: +32 2 296 02 24 Fax: +32 2 299 03 14 E-mail: [email protected]

Ministère de la Région wallonne Direction générale des Ressources naturelles et de l’Environnement Division de l’Eau, Direction des Cours d’Eau non navigables Avenue Prince de Liège 15, B-5101 Jambes (Namur) Contact persons: Mr Materne, Premier Directeur Mr. D. de Thysebaert

Telephone: +32 81 33 63 70 +32 81 33 63 18 Fax: +32 81 33 63 50 E-mail: [email protected] [email protected]

Provincie Limburg Hoofdgroep Milieu en Water Afdeling Water en Ontgrondingen Postbus 5700, 6202 MA Maastricht (The Netherlands) Contact person: Mr. G. Kater Telephone: +31 43 389 76 82 Fax: +31 43 389 76 43 E-mail: [email protected]

Waterschap Roer & Overmaas Postbus 185, 6130 AD Sittard (The Netherlands) Contact person: Mr. F. Heijens Telephone: +31 46 420 57 00 Fax: +31 46 420 57 01 E-mail: [email protected]

Provincie Limburg 3° Directie Universiteitslaan 1, B-3500 Hasselt Contact person: Mr. R. Awouters Telephone: +32 11 23 73 20 Fax: +32 11 23 81 11 E-mail: [email protected]

Introduction 7 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

TECHNUM NV Wilrijkstraat 37, B-2140 Antwerpen Contact persons: Ms. E. Vanthournout Mr. M. Sas Telephone: +32 3 270 00 30 Fax: +32 3 270 00 31 E-mail: [email protected] [email protected] [email protected]

CSO Consultancy for environmental management and research Regulierenring 20, 3981 LB Bunnik (The Netherlands) Contact persons: Mr C.J.J.H. Schouten Mr J. Leenaars Telephone: +31 30 659 43 21 Fax: +31 30 657 17 92 E-mail: [email protected] [email protected]

Centre Environnement – Université de Liège Sart Tilman B.5, B-4000 Liège Contact person: Mr. J.S. Smitz Telephone: +32 4 366 23 53 Fax: +32 4 366 23 55 E-mail: [email protected]

Faculté Universitaire des Sciences Agronomiques (FSAGx) Unité d’Hydraulique Agricole (Génie Rural) Address:Passage des Déportés 2, B-5030 Gembloux Contact person: Mrs. S. Dautrebande Telephone: +32 81 62 21 87 Fax: +32 81 62 21 81 E-mail: [email protected]

1.3.2 Communication within the project

1.3.2.1 Management team The representatives of the three consortium partners were member of the management team. Meetings were organised regularly, depending on the project’s state. The

Introduction 8 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas management team prepared the project planning and work schemes, which were always submitted for approval during project team meetings.

1.3.2.2 Technical meetings The three consultancy partners formed a technical working-group and met regularly. These meetings were for technical fine-tuning and data exchange among the partners.

1.3.2.3 Project team meetings A project team, formed by the members of the management team, by representatives of the technical working-group and representatives of the stakeholders, was established to stimulate communication within the project and to improve stakeholder participation. During these meetings, the following items were discussed: • the decisions made during management team meetings; • the project progress; • communication and active participation of the policy makers. The project team did function very well for the total period of the project. It served many functions from acting as a sounding board for the outcome of the technical teams, arranging the accessibility to sources of information for the data inventory and representing policy makers by developing alternative catchment management scenarios, which were to be used during the study.

It was not possible to include even more stakeholder groups in the project due to its typical technical aspects, the size of the project teams, the available time and the limited financial resources. The Geul Committee, which was initiated late 1997 and intended to act as a steering committee, has never been involved as such and is at present not actively functioning at all.

Introduction 9 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Introduction 10 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

 2%-(&7,9(6 The overall goal in this pilot study was to define environment-friendly measures for increasing water retention in the Geul catchment, thereby reducing the risk of flash floods in the Limburg region of Belgium and the Netherlands.

Within the scope of this overall goal, the following objectives were identified: • to inventory relevant information and develop a methodology to combine the data coming from many sources of information and under different formats; • to perform a preliminary hydrological and hydraulic risk analysis; • to develop different scenarios, which are sets of possibly applicable environment- friendly measures with emphasis on water retention in watershed or river, to reduce the risk of flash flood events; • to analyse the effectiveness of these different scenarios to reduce the risk of flash flood events; • to assess the legal framework and policy instruments of the different regions and countries and analyse the applicability and effectiveness of these instruments for the development of an environment-friendly flash floods reducing catchment management.

Objectives 11 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Objectives 12 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

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 0HWKRGRORJLFDOPRGHOGHYHORSPHQW This pilot study can be used as a model for other studies concerning the reduction of the risk of flash floods in other watersheds. The study of the Geul river has a demonstrative character for the Meuse catchment and other similar river catchments in Northern- Central Europe. The major innovation of this project is that the investigated improvement of water control management will not be realised through civil-technical water control devices only, but through an integrated approach including civil-technical water control devices in the river as well as changes in land use and agricultural practices in the uplands surrounding the river.

Six major steps were defined and to be performed in this project: 1. Inventory the data required for analysis; 2. Perform a preliminary hydrological risk analysis; 3. Develop and define five scenarios of possible measures to reduce the risk of flash flood events; 4. Model the hydrology of the catchment, including runoff, hypodermic flow and groundwater flow, to calculate the water runoff to the Geul river network as a function of the land use measures defined in the five scenarios; 5. Model the hydrodynamics of the Geul river network to analyse the impact of the five scenarios at river level, including both land use measures and civil-technical water control devices; 6. Assess the legal framework in the different countries and regions to analyse the available political instruments and possibilities to realise favourable scenarios to reduce the risk of flash flood events.

These six steps reflect the expertise of the different consultants involved and were followed to structure the research.

Figure 3.1 shows a schematic representation of how these steps were used to approach the project. The arrows between the different items represent the transmission of output data of one study item, which are to be applied as input data into a following study item. The approach used in each step is briefly described below.

Methodology and approach 13 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Schematic representation of the project methodology

Collection of data Literature study and assessment Topographic Soil Hydrological Land use of legal framework data type data and policy instrument

Development of scenarios Legal Framework

Hydrological study

Hydraulic study

Analysis of results

Recommendations

Figure 3.1 Project methodology

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3.2.1 Territorial data inventory CSO and FSAGx collected relevant territorial data and stored them into a Geographical Information System (GIS) database. A GIS is a computer-based system for the collection, storage, analysis and presentation of spatial information. A GIS also offers the possibility to exchange information with all sorts of models. The information from the GIS database has been used to:

Methodology and approach 14 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

• Make a territorial catchment inventory [develop the GIS database]; • Perform a preliminary risk analysis; • Study the change in land use and river morphology since the 1950’s; • Provide input for hydrological and hydrodynamic models; • Make map presentations.

3.2.1.1 The GIS database structure The project partners made the decision to use the ESRI GIS software, Arc/Info and ArcView. All data exchange between the partners in the project, and delivery of end products, was done in the ArcView format. Arc/Info and ArcView are the major software tools used for GIS construction and analysis in The Netherlands, Belgium and throughout the world. These packages also provide the tools needed to access, visualise and query geographical and tabular data for better analysis and decision-making.

Because the research area is located in three different countries, the GIS database was built based on different sources of information, in different digital formats and with different cartographic projections and legends. Conflation of maps and standardisation of map legends from different sources of information was performed with great accuracy. The methods that were used in this process are described in Chapter 4. The Belgian projection method was chosen in this Geul project. At the end of the study, all digital maps were transferred into the Dutch projection system as well, so that Dutch authorities are also allowed to use the obtained geographical database.

3.2.1.2 Map presentation and CD-ROM With the use of the GIS, maps were made to present the basic information that was collected in the Geul project, to provide input data for the hydrological and hydrodynamic modelling, and to visualise the end-results of the different scenarios and model runs. These maps are available on the CD-ROM attached to this report.

3.2.2 Preliminary risk analysis Both CSO and FSAGx carried out a preliminary risk analysis, using two different approaches, to estimate the current- and historical risk of flood events and to determine the location of zones, which are importantly contributing to this risk. In this study, parameters explaining the risk of runoff were quantified for land- and land use GIS mapping units and were analysed by combining the relevant GIS map layers. The results of this preliminary risk analysis gave a qualitative insight to strengthen the outcome of the detailed hydrological and hydrodynamic modelling studies.

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3.2.3 Scenario development Five scenarios, reflecting possible measures to be implemented to reduce the risk of flood events, were identified and their effectiveness was simulated in the hydrological and hydrodynamic studies. The scenarios include two reference situations (land use distribution in the 1950’s and 1990’s) and combinations of measures selected by the stakeholders. The measures either have an environmental nature (land use) or a civil-technical nature (water control devices). The following procedure was applied to select a limited number of five scenarios, to be used as input in the simulations: • Identify all possible measures (review of literature); • Classify the measures into different groups; • Rank the measures per group; • Select the most preferred measures; • Combine the selected measures into scenarios.

These scenarios were simulated to analyse the effectiveness of the measures involved.

3.2.4 Hydrological model and analysis The hydrological study was aimed at the definition of the characteristics of flash floods in the Geul, and to study the effects of possible land use interventions on the reduction of peaks in water inflow rates.

The University of Liège and the Agricultural Faculty of Gembloux studied the distribution, frequency and duration of precipitation events, causing flash floods. Measurements on flash floods were analysed and the occurrence frequency was determined. A hydrological model of the Geul catchment has been set up based on the MOHICAN model (ULg-FSAGx). The model was used to simulate the amounts and arrival times of water into the Geul river and its tributaries as a function of the five scenarios defined in Chapter 5. The MOHICAN programme is GIS based using grid-cells as basic units for water balance calculations. The programme is therefore capable to take the spatial and temporal distribution of rainfall intensities into account, as well as the physiography, the morphometry of the catchment, the land use, the crops growth and the agricultural practices. The programme uses the soil-water balance equation, which includes terms for rainfall, infiltration, real evapotranspiration, soil humidity and percolation towards the root zone, which enables it to simulate surface runoff, hypodermic flows and groundwater flow. It can simulate long time periods, permitting notably multi-year frequency analyses.

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There are four important steps in the hydrological study: 1. Collect data required for the model; 2. Assess the hydrological conditions; 3. Prepare and simulate the models representing the different scenarios; 4. Analyse the results.

3.2.4.1 Data collection The hydrological model uses data from three different databases: 1. Water level database (flow rates at gauging stations) 2. Weather database • precipitation • temperature 3. Cartographic database (GIS) • digital elevation model (DEM) • soil map • hydrographic network • land use map Part of this information was already available from the data inventory (CSO). The remaining missing data was obtained via the stakeholders.

3.2.4.2 Hydrological assessment A simulation model is a representation of the real situation and has to reflect the processes and behaviour of the studied system. In the project’s case, the whole hydrological cycle (the repartition of rainfall to local surface runoff, hypodermic fluxes, percolation to groundwater and finally base flow to the river) is modelled. Therefore a full assessment and analysis of the collected data was performed. This study covered several aspects: • Water balances; • Frequency analysis; • Hydrogeology; • Groundwater response. As a result good knowledge about the hydrological behaviour of the catchment was obtained.

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3.2.4.3 Model development and simulations Based on the GIS maps prepared during the inventory and the knowledge obtained during the hydrological assessment, it was possible to derive the GIS map layers that are required as input for the hydrological model: slope classes, hydrological soil groups, erodability factors, cultural coefficients, Manning coefficients and runoff parameters. Each map represents specific parameters in the model that are used in the algorithms describing the water flows and fluxes in the hydrological cycle. The results of simulations with this model consist of long time series at a large number of points in the catchment. These points, representing the inflow points of the surface runoff, hypodermic fluxes and groundwater base flow, are usually located at the confluences where smaller streams flow into the Geul river. By introducing a simple propagation routine representing the water flow through the river, the model was validated for the past and present situations, after which the simulation of the scenarios started.

This model was applied to calculate the water runoff to the Geul river and its tributaries as a function of the five defined scenarios. The weather conditions of the period 1993- 1998 were selected as input data. The results of the hydrological simulations were used as input for the hydrodynamic model.

3.2.4.4 Hydrological analysis The results of the simulations have been analysed at different locations along the Geul river for the average yearly runoff as well as for specific peak discharges. These results indicate the effectiveness of the measures related to land use and agricultural practices.

3.2.5 Hydrodynamic study Knowing the space and time distributions of water flowing into the Geul river and its tributaries, the water flow through the riverbed itself can be assessed. This flow is a function of the morphology of the riverbed and of possible ‘obstacles’ in the riverbed. Technum used the hydrodynamic model ISIS Flow to study, indicate, and estimate the magnitude of the flood waves (water levels as well as discharges) and to analyse flood events. In consultation with the Belgian and Dutch authorities, this model was chosen to be applied in the Geul project. ISIS Flow is a computer programme used to model open- channel and overbank flows in any kind of channel network. ISIS Flow is based on the Saint-Venant equations, and can be used to simulate both steady and unsteady flow conditions. In this study, unsteady flow conditions were assumed. The model calculates water levels and discharges as a function of time at a discrete number of points based on external and internal boundary conditions.

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For the hydrodynamic study the following steps can be distinguished: 1. Collect data required for the model; 2. Develop the model and simulate the different scenarios; 3. Analyse the results.

3.2.5.1 Data collection The most important inputs in the model are: • hydrographs from the hydrological model, indicating the volumes water per second flowing into the Geul river system at several points; • topographical data from field surveys (for instance cross-sections of the river (example in Figure 3.2), longitudinal sections); • hydraulic structures.

Figure 3.2 Cross-section of the Geul river at Plombières (Belgium)

3.2.5.2 Model development and simulation of scenarios All river and infrastructure data were introduced in the ISIS programme and verified with experts from the stakeholder groups. Based on the resistance of the riverbed and the constrictive infrastructure, the programme calculates the water flow through the river. The hydrodynamic model has been calibrated in order to give results corresponding to the measured data. The calibrated model has been used to simulate the water flow under the different scenarios. Selected high precipitation events during 1993 and 1998 were simulated to study the effect of the measures on the flood propagation. The simulations resulted in time series of water levels and discharges at a great number of points.

3.2.5.3 Analysis of results The results are presented in a number of ways to facilitate access to, and analysis of, the data. The data are presented in tabular and graphical format for a great number of

Methodology and approach 19 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas locations along the river, and a longitudinal profile showing the water level for the different scenarios is also included.

3.2.6 Study of the legal framework and instruments A summary of the legal instruments and framework within the environmental and water management policy and legislation was made for different regulatory levels in both The Netherlands and Belgium (e.g. state or federal, regional, provincial, local level, water- basin authorities). This inventory is used as a reference to all stakeholders to co-ordinate measures following this pilot project or to propose adaptations and additions to the current policy. Technum investigated whether compatibility or conflicts existed between proposed interventions and the current legal framework (e.g. land use plans). Suggestions to modify the legal framework were made. The study of the legal framework and instruments was based on a so-called “DSSOLFDELOLW\ PDWUL[” for both countries. In this applicability matrix, possible water retention enhancing measures and interventions were compared against the inventoried legal instruments.

The applicability matrix uses the following scale:

6FDOH $SSOLFDELOLW\ + applicable 0 possibly applicable pprotection2 i indirect effect

The main advantage of using the applicability matrix is that it clearly indicates which legal instrument can provide the best framework for the implementation of a proposed intervention or measure. The applicability matrix also provides the opportunity to detect for which interventions and measures the legal framework remains inadequate.

2 This symbol is only used in the applicability matrix of The Netherlands.

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 7(55,725,$/'$7$,19(1725<

 ,QWURGXFWLRQ A Geographical Information System (GIS) of the hydrology, lithology and land use in the Geul catchment area was developed as part of this hydrological and hydrodynamic modelling study. A GIS is a computer-based information system for the collection, storage, presentation, and analysis of spatial information. A GIS offers several advantages over using analogue (paper) maps, namely that it can be used to import, export and visualise data from the hydrological and hydraulic models and other electronic databases.

 2EMHFWLYHV The main objective of building the GIS was: 7R FROOHFW DQG FRPSLOH LQSXW LQIRUPDWLRQ WR PRGHO WKH VXUIDFH DQG JURXQGZDWHU K\GURORJ\DQGULYHUIORZZLWKLQWKHFDWFKPHQW.

In addition, the GIS was used to perform the following tasks: • 6SDWLDOGDWDLQYHQWRU\DQG*,6GHYHORSPHQW Data has been collected from a large number of sources and under different types of formats. The data collection, the methodology used for the standardisation of the data in a GIS structure and the results are described. • 'HVFULSWLRQRIWKH*HXOFDWFKPHQW The general description of the research area was complemented with the results from GIS analyses. This description includes features like the spatial variation of soil characteristics, areas of the different land use types, elevation differences and slope characteristics. • 3HUIRUPDQFHRIDSUHOLPLQDU\ULVNDQDO\VLVIRUVXUIDFHZDWHUUXQRII A preliminary risk analysis was carried out to determine the location of the existing critical zones. In this study relevant thematic map layers were combined and analysed with the help of the GIS. The results of this study set a reference to the hydrological study and gave insight in the spatial variation of runoff-sensitive areas.

Throughout this chapter the following terms will be used frequently: GIS map layer: (Geographical Information System map layer) digital map that can be used for analysis with a Geographic Information System or in a hydrological/hydraulic model.

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Thematic data/maps: maps containing data about a specific theme like land use, soil characteristics or topography. Meta-data: information about GIS map layers like data sources, scales, dates, accuracy, use restrictions etc. Map legend: the collection of classes differentiated within a map or GIS map layer.

 6SDWLDOGDWDLQYHQWRU\DQG*,6GHYHORSPHQW Relevant data collected and processed in the GIS are those that determine runoff, routing of inflow hydrograph and erosion rate. In the Geul area, the following data are of great importance in relation to runoff, erodibility and the corresponding sediment yield: • elevation and slope; • soil characteristics; • the hydrographic network; • land use (urban areas, agricultural areas, etc.); • topographical features (roads, railways, parcel barriers etc.); • morphometry characteristics; • hydrogeological characteristics.

The data mentioned above is the basic information that was collected or generated at the start of the project. Most of this data was already available in GIS-format at several local and regional governmental authorities in The Netherlands and Belgium. Some data could be derived from other data by the use of GIS-analyses or had to be generated with the use of GIS functionality. Besides the thematic GIS data, the meta-data to match was also carefully archived in the GIS database structure that was built. Being aware of the properties of spatial data, and making sure that everyone working with these data knows its properties is an important part of quality control in all GIS-projects. Because the research area is located in three different countries, the GIS data had to be collected from different sources, in different digital formats, and with different cartographic projections and legends. Conflation of maps and standardisation of map legends from different sources had to be performed with great care. The methods that were used in this process and the data sources that were processed are described in this chapter and the annexes belonging to this chapter.

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4.3.1 Methods

4.3.1.1 Technical challenges The research area extends over three European countries and hence raises a number of technical and logistical issues concerning the use of Geographical Information (GI). As with all the other European countries, Belgium, The Netherlands, and Germany each use different GI software, hardware, and cartographic standards. When building a GIS, all of this data must be merged into a single system. The most significant technical challenges to developing the GIS for the Geul project were: • /RFDWLQJLQIRUPDWLRQVRXUFHVDQGGHDOLQJZLWKLQIRUPDWLRQRZQHUVKLS In each country, different companies, institutes and authorities collect and manage data. It is very difficult to obtain information on types of data and the availability of data in a particular country if one is not familiar with the information sources in that country. This is because centralised national catalogues on data and data ownership are often non-existent or difficult to find. Also, when the data has been found, problems about user restrictions and costs often arise. • 'LIIHUHQFHVLQVRIWZDUHVWDQGDUGV In every project common software standards must be chosen. Once a standard is chosen, it will always be necessary to convert some data to this standard. This often means that GI technicians must carefully ensure that all data and data structures are preserved throughout the conversion process. Programmes that automatically convert data at the “click of a button” either do not exist or can cause data loss. • 'LIIHUHQFHVLQPDSSURMHFWLRQV Almost every European country uses a different map projection with a specific co- ordinate system for their GI. It is therefore necessary to choose one projection method and convert all GIS map layers to this projection. • 'LIIHUHQFHVLQGHILQLWLRQVQRPHQFODWXUHDQGPHWDGDWD Besides the logistical problems of merging GI from different countries, differences in sampling and analysis methods between countries form a larger problem. As mentioned in the introduction, sampling and analysis methods, along with other important auxiliary information to thematic data, are described in the meta-data of the GI. Meta-data is particularly difficult to merge because each country uses their own language and nomenclature in their meta-data files. Hence, all legends and meta- data must be translated into a common language with new standard definitions for terms and legend units.

The solutions to these obstacles and the justification for these choices made during the development and application of the Geul project GIS are described in the following sections.

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4.3.1.2 Inter-disciplinary communication Because the accuracy of the hydrological and hydraulic modelling results relies on the contents and quality of the GIS map layers, modelling experts were closely involved throughout the data acquisition and GIS map layer construction phases. Before commencing with data acquisition, the GIS team consulted the modelling experts on the specific data they needed. Basic questions that were answered in this stage included: • Which thematic information do you need? • What must be the (minimum) accuracy and reliability of this information? • In which periods should the information been collected? • If working with raster data, what should be the grid cell size? • Are there examples of GIS map layers from former projects? • In what way can the GIS map layers be delivered to minimise pre-processing before modelling? GIS technicians continued to consult modelling specialists on all critical decisions during the construction of the GIS map layers. Furthermore, to ensure the quality of the GIS map layers and optimise communication between research partners, technicians who were specifically educated on the subject of land degradation performed the GIS activities in this Geul-project.

4.3.1.3 Software standard For the Geul project, the ESRI (Environmental Systems Research Institute) formats of the Arc/Info and ArcView software were chosen as the standard GIS software. Reasons for this choice include: • Most institutes and authorities in Belgium and The Netherlands use ESRI software, hence information from these data sources would be delivered already in an ESRI software format and would not require data conversion. • ESRI software is very powerful and capable of handling most other major data exchange formats; therefore loss of data caused by conversions was less likely to occur. This was relevant in merging GI from different sources but also in preparing data for the use in hydrological and hydraulic models. • ESRI software is widely available to all research partners and principals on this project.

4.3.1.4 Data Acquisition Once the approach to technical challenges and project management issues was organised, GIS experts proceeded to systematically acquire data through the following steps: 1. consulted modelling experts on their input data needs;

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2. requested information about relevant data from research partners and principals of the project; 3. searched Belgium, The Netherlands and Germany for local sources of relevant data; 4. searched the Internet for relevant data; 5. obtained an overview of data availability; 6. considered costs, user rights, and user restrictions; 7. selected data sources; 8. ordered / acquired the data.

4.3.2 Outputs

4.3.2.1 Required GIS map layers The hydrological and hydraulic models that are used in the Geul project required input from four main GIS map layers: 1. Digital Elevation Model (DEM); 2. Land use map; 3. Simplified soil map; 4. Historical land use map. The following section describes in detail the construction of the three main GIS map layers.

4.3.2.2 Digital Elevation Model The first and most important step in building a Digital Elevation Model (DEM) consists of deciding on the kind of elevation data that is going to be processed and the kind of interpolation method that is going to be used for processing. In the Geul-project the choice of elevation data sources was based on the following criteria: • The DEM will be used in the hydrologic and hydraulic models. Hence, the accuracy and resolution of the elevation data must be high and fine-tuned to the requirements of the models; • The accuracy and resolution of the elevation data sources must be comparable between the three different countries; • Since the scope of the project does not allow the collection of new elevation data (e.g. based on laser altimetry or aerial photograph analyses), only existing and relatively easy-to-access elevation data were used.

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Based on these criteria, elevation data from a number of sources was gathered (Annexe A2.1). Combining all information sources into a single DEM involved a number of steps. In the first step, all data formats were converted to Arc/Info format and data was transformed to the standard map projection. In addition, the reference level from which elevation is measured had to be standardised for all elevation data from the three countries. Background information on the differences between reference levels in the three countries in given in Annexe A2.1. As with the projection system, the Belgian elevation reference level was chosen as standard. The next step consisted of searching for the best method to interpolate between the elevation contours and elevation points and to construct an elevation grid. This step was only relevant for the Dutch and German data because the Belgian data was already available as an interpolated grid. A number of interpolation methods were tested for their suitability. The main criteria were: 1. the level of accuracy of the hydrographic network that could be constructed based on a DEM; 2. the level of accuracy between the contour lines based on the new DEM.

The best method for constructing the elevation grid proved to be the TOPOGRID command in Arc/Info. For instance, the maximum spatial (XY co-ordinates) deviation of the contours was less than 5 metres in the Dutch part of the research area. Annexe A2.1 contains a description of the algorithms incorporated in this command. The DEM that was constructed has a grid cell size of 30x30 metres. This is the highest resolution still acceptable for the entire research area while using the available data. All interpolation methods demonstrate ‘side effects’. These side effects consist of wrongly interpolated values on the borders of the area for which elevation data are available. By making sure that the available elevation data cover a larger area than the actual research area, side effects can be clipped out after interpolation. So, in the final step of construction a GIS map layer with the borders of the research area was used to clip out only the relevant and correctly interpolated part of the DEM.

4.3.2.3 Soil The data sources used in the construction of the Soil GIS map layer are listed in Annexe A2.2. Merging soil maps from different countries is problematic because most countries use different soil classification systems. Unfortunately, the differences between the classification systems of The Netherlands, Belgium and Germany are rather large. To be able to construct a Soil GIS map layer of the entire research area, it was therefore necessary to design a new common classification system in which information from all three data sources could be incorporated. This new system has been based on the input information required by the hydrological model. All soil classes in all three maps were studied and interpreted carefully in relation to texture (loess, sand, clay), percentage of stones and rocks, soil depth and drainage

Territorial data inventory 26 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas characteristics. This was done instead of choosing the soil classification system from one of the three countries as the standard system. The re-classification of the soil maps does not solve all merging-problems. Although the spatial distribution of soil types does not change abruptly when passing a country border, national differences in classification methods cause situations in which the boundaries of a soil type in one country do not connect seamlessly with the same soil type across the border in another country.

4.3.2.4 Land use Based on the requirements of the hydrological model and the nature of land use in the research area, the following land use classes were chosen to be included in the land use GIS map layer: • Weeded crops (maize, potatoes, beets, vegetables); • Non weeded crops (mainly wheat); • Grassland; • Orchards; • Water; • Deciduous forest; • Resinous forest; • Mixed forest; • Main roads / railroads (highways); • Buildings in agricultural area (including greenhouses); • Buildings in rural area; • Urban area.

Data sources for the land use GIS map layer are described in Annexe A2.3. The standard legend was based on the Belgian data, thus land use in the Belgian section of the study area was already classified accordingly. The Dutch data (an Arc/Info grid file) contained several more land use classes. For example, vegetation types in the Dutch data source were mapped in high detail, especially within the agricultural areas. It was therefore necessary to generalise (re- class) the data in the Dutch data source according to the standard land use classes listed above. To be able to merge the Dutch data with the other grids, the cell size of the grid had to be converted as well. The 25-metre cell size of the original Dutch grid was resampled to a 30-metre cell size. The German data sources (topographical maps) were digitised and classified according to land use classes listed above. Unfortunately, it was impossible to distinguish weeded

Territorial data inventory 27 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas from non-weeded crops based on the topographical maps. Because the area covered by crops in the German part of the catchment is relatively small, and agricultural statistics were also not available, the GIS team decided to group weeded and non-weeded crops into the “mixed crops” class. In digitising the forests, a distinction between deciduous or resinous trees was made wherever possible. Where both tree types occurred and the distinction could not be made, forested areas were classified as “mixed forest”. After synchronising the legends and cell sizes of the three data sources, the grids of the Dutch and German parts of the research area were transformed to the Belgian Lambert projection system. Before merging the three grids, the accuracy of the country borders in the grids was evaluated using detailed 1:10.000 digital topographical maps. It was concluded that the Dutch grid contained the most accurate representation of the national borders, followed by that of the Belgian grid. Therefore, during the merge operation, in case of data overlap the Dutch data overruled the Belgian data that overruled the German data. In some areas, small gaps appeared in the merged grid along the border between The Netherlands and Belgium. These gaps were filled by extrapolating from the adjacent land use classes from the Belgian part of the grid.

4.3.2.5 Historical land use A part of the Geul project focuses on the land use changes that took place in the Geul Catchment between the 1950’s and the 1990’s. The changes that took place during this time interval are known to have been contributing significantly to the increase in erosion and frequency of flash flood events. To study these land use changes and their influence on the model results, it was necessary to construct a GIS map layer of the historical land use in the 1950’s. Historical topographical maps provided the only information source available for the entire catchment area covering this time period. The legends of these maps distinguish different kinds of global land cover types common in all countries. The maps that were used in the construction of the Historical Land Use GIS map layer are listed in Annexe A2.4. The topographical maps were scanned and the resulting images were geo- referenced in the Lambert projection system. Using on-screen digitisation, a vector GIS map layer was constructed. The historical land use maps contained less information than the current maps. Therefore a more general classification was used. This meant that only an analysis of the land use trends across more general land use classes was possible. The maps used for the comparison contained the following land use classes: • Arable land (crops); • Grassland; • Orchard; • Forest; • Buildings in agricultural area; • Urban area;

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• Water. For use in the hydrological model, an adjusted GIS map layer of the fifty’s land use was constructed. This layer contained a differentiation between weeded; non-weeded and mixed crops within the original land cover type ‘arable land’. This adjustment was based on an analysis of historical agricultural data (1950) obtained from the Central Bureau of Statistics of The Netherlands (CBS) (see Annexes A2.4 & B1).

4.3.3 Conclusions A geographic information system of the Geul Catchment study area was constructed to centralise and merge the relevant soil, elevation, and land use data for use in the hydrologic and hydrodynamic modelling studies. The GIS was developed using the ESRI GIS software, Arc/Info and contains three main GIS map layers: a Digital Elevation Model, a Land Use map and a Simplified Soil map. If the data is to be used for further studies the work should be executed in close cooperation with the technicians responsible for that study. Close cooperation with the local stakeholders (governments, institutes) has showed to be very profitable during the inventory. Most data was obtained through research partners and representatives working for regional governments located within the study area. The map projections and co-ordinate systems used in Belgium, The Netherlands, and Germany are different and classifications are non-uniform. To merge the thematic GIS map layers, the legends and classification systems (e.g. soil and land use classifications) used in each country also had to be converted to a set of common standards. The TOPOGRID option available within ArcView proved to be the best interpolation technique to construct a DEM of the catchment, the elevation reference levels used by each study country had to be reset to a common reference.

4.3.4 Recommendations The use of a more uniform classification and improved availability of data within Europe could save a lot of time and money on similar projects in the future. As part of this report, the GIS team offers these recommendations to local, national, and European Commission officials: • A central European databank with meta-data should be created. A lot of time and effort could be saved in the future on GIS projects if there would be a central European databank with meta-data about GI. In this databank information on the most important GIS map layers for each country should be listed. World Wide Web services that exist on a national level should be unified, and data producers should be encouraged to document their data in a standard way to facilitate this unification.

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• GIS data should be made more affordable in Europe. The existence of good data, whether or not as GIS map layers, is a prerequisite for the high quality of project results. When project principals cannot obtain the desired GIS data, the data has to be purchased. In Europe, where digital geographical data is relatively expensive, this often raises the consideration to collect and digitise the desired data within the project itself, limit the amount of data or use more general approaches to the problem, in contrast to purchasing existing high quality GIS data. • Finally, agreements concerning user-rights and user-restrictions between governmental authorities should be made on national and (if possible) international levels in order to speed up and clarify data exchange on government-funded research projects.

 'HVFULSWLRQRIWKH*HXOFDWFKPHQW This chapter describes the physiography of the Geul catchment area as well as the spatial variables relevant for the preliminary risk analysis. The latter includes maps, map legend classes and the acreage of map legend classes. Described are the physical environment, the current land use and the historical land use as well as a first analysis of the land use changes.

4.4.1 Physical environment of the Geul catchment area The location and topographic context of the Geul catchment area is given in Map 4.1. The Geul catchment is a trans-boundary river catchment of about 380 km², located in The Netherlands, Belgium and Germany. It is located between 50°35' and 50°55' longitude (south to north) and between 5°40' and 6°10' latitude (west to east). The altitude of the basin ranges from about 50 meters to 400 meters above sea level. The elevation of the area is given in Map 4.2. The GIS provides maps of the catchment area of 500 km². This is because the exact localisation of the subsoil catchment area was still unknown at the beginning of the project.

4.4.1.1 Climate The climatic conditions of the Geul catchment area are favourable against runoff. Its moderate character includes a rainfall pattern rather evenly distributed throughout the year, ranging from approximate 45 mm per month in March to 75 mm per month in August. Rainfall intensities are generally low. The average annual rainfall amount is about 800 mm. With an annual evapo-transpiration of about 500 mm, this means a water surplus of 300 mm per year, concentrated during wintertime.

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4.4.1.2 Hydrology The location of riverbeds in the catchment area is given in Map 4.2. Its pattern is very dendritic and characterised by the Geul valley deeply dissected into the surrounding plateaux, fed by small streams originating from small dry valleys and even smaller dry gullies. The total length of the main stream is 58 km; the first 22 km in Belgium and the last 36 km in the Netherlands. The Geul connects with the Meuse some km’s north of the city of Maastricht. Before connecting, the Geul is led under the Juliana channel. The rivers are fed by surface water, hypodermic and groundwater flows. During rainfall excess rainwater infiltrates into the soil, continues through geologic layers of sandstone, chalks and (karstic) limestone, and recharges the groundwater. Groundwater is typically encountered at depths of about 30 to 45 m below the plateaux, where it collects on top of a confining (impermeable) clay layer (geologic formation of Vaals). Groundwater flows horizontally along this impenetrable clay layer and water springs originate where this groundwater meets the surface of a slope. Eventually these springs join the Geul downstream contributing significantly to the base flow of the Geul River. These groundwater-fed streams have a high erosive force and are therefore deeply dissected into the terrain. With an annual rainwater surplus of 300 mm and a catchment area of 380 km², one concludes an average continuous water discharge in the catchment area of 3,6 m³/sec. This water is predominantly discharged by groundwater, also known as base flow. The most severe flash flood events occur when the maximum base flow and the peak of fast runoff are in conjunction. The hydrology of the catchment area changed drastically since the second half of the 20th century. Originally meandering minor and major river courses were straightened and, in some cases, channelled in concrete riverbanks. Consequently, the frequency of downstream-peak discharges increased. Some basic hydrologic data of the Geul River and its tributaries are listed in Table 4.1.

Table 4.1 Hydrologic base elements of the Geul and tributaries

$UHDFDWFKPHQW /HQJWK 6ORSH 0D[GLVFKDUJH (km2) (km) (m/km) (m3/s) Geul 387,75 58,0 2-9 651 Gulp 46,40 17,0 6 5-10 Eijserbeek 29,60 11,8 6 7 Selzerbeek 30,25 14,5 7-34 8 1at Meerssen

The GIS map layer of the catchment hydrologic network indicates the location of minor- and major riverbeds. Combined with the GIS map layer of the topography it can be used

Territorial data inventory 31 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas to assess the maximum slope length. Long slopes promote accumulation of surface water runoff.

Photo 4.1 The Geul River, meandering in its Holocene valley floor, surrounded by a sloping to hilly topography.

4.4.1.3 Topography The topography of the catchment, in the form of slope gradient classes, is presented in Map 4.3 and is summarised in Table 4.2.

Table 4.2 Relative acreage (%) of slope classes

6ORSHFODVV$FUHDJH   0 - 1 % 9 1 - 2 % 13 2 - 5 % 33 5 - 8 % 19 8 - 12 % 13 > 12 % 13

Territorial data inventory 32 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

100 %

The catchment area has a rolling topography with the steepest slopes between 8% and 16% (FAO, 1977). The upper part of the Belgian area varies from sloping to moderately steep while the middle part of the catchment area is gently sloping. The transition from the middle to the lower part of the catchment area varies from rolling to moderately steep.

4.4.1.4 Lithology and Soils The upper part of the catchment has erosive soils derived from sandstone, shale and limestone. An extensive limestone plateau forms the middle part of the catchment area and is covered by deposits of the weathering products from the upper part of the catchment, and then covered later by aeolian deposited loess. The majority of soils in the catchment area developed within these loess sediments. The Geul River dissects this plateau and the resulting valley forms the lower part of the catchment. The Geul valley is characterised by terraces built from alluvial deposits, and has soils developed in the loess as well as in stony materials. The distinguished soil legend classes are not presented here in the form of a map. Chapter 6 will show a map of the hydrological soil groups derived. The original map with soil types showed a very large diversity of soil types. This large diversity is caused by the reclassification exercise performed to combine three national soil classification systems, as described in Chapter 3. Based on pedologic and geomorphic data, these soil legend classes could be grouped into four main groups of soils (Staring Centrum, 1990): soils developed in Holocene sediments (1); soils developed in Pleistocene loess (2); soils developed in Pleistocene alluvium and Tertiary and Cretaceous marine sediments (3); and soils developed in sloping terrain (4). Note the relationship between soil group and slope gradient. Below is a detail description of each soil group; the relative percentage land area of each soil group is shown in parentheses.

1. Soils developed in Holocene alluvial sediments (11%) The river clay areas correspond with the valley floors of the Gulp, the Geul, and the Meuse. The soils of the valley floor of the Geul and the Gulp are predominantly imperfectly drained and are regularly inundated. Young soils are developed in so-called young river clay sediments, indicating alluvial deposits of loess, washed down out of the catchment area. The short time of soil development hardly led to soil layer diversification. The valley floors are sharply dissected by the meandering small rivers. The river valleys are asymmetrically shaped with steep eroded slopes on one side and less steep slopes covered with terraces on the other side. (Includes soil types labelled with R, AB & V.)

2. Soils developed in Pleistocene aeolian sediments (loess) (55%)

Territorial data inventory 33 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

By far, the loess areas occupy the biggest acreage. The loess sediment is deposited over a landscape of steeply dissected near-flat limestone plateaux. The sediment is very uniform over large distances and is hardly layered. The thickness varies from almost ten meters to one meter. On sloping areas it disappears locally due to erosion. Soil development in the youngest loess sediments implied the downward washing of calcium and clay particles. This led to the formation of soils with a so-called Bt-horizon of clay-illuviation (‘EULNJURQGHQ’ in the Dutch soil classification system). Different soil types are distinguished on the basis of the depth of the Bt horizon and the depth where hydromorphic features start. The hydromorphic features are nearly always due to water stagnation upon the Bt-horizon (pseudo groundwater levels). Erosion on the borders separating the plateaux from the sloping areas resulted in soils with the Bt horizon at the surface (‘%HUJEULNJURQGHQ’ in Dutch). Many small valleys originate on these plateau borders. These valleys become deeper incised descending the slopes and transport water occasionally. They are filled up with so-called secondary loess. Soils developed in secondary loess are relatively young and have no Bt horizon (‘YDDJJURQGHQ’ in Dutch). Secondary loess is also found on the foot slopes near the valleys of the Gulp and the Geul. These foot slopes have angles of 5 to 8% but erosive gullies hardly occur. (Includes soil types labelled L & BL.)

3. Soils developed in Pleistocene alluvial- and Tertiary and Cretaceous marine sediments (6%) The eldest materials are of marine origin and are of Carbonic (approximate 300 million years ago), Cretaceous and middle-Tertiary ages. They gave rise to the formation of limestone and sandstone. The oldest alluvial deposits originate in the late Tertiary (10 million years ago) and are recognisable as the highest terrace of the Meuse. The Meuse shifted in the early Quaternary from its valley in the east to its present valley in the west. The youngest and lowest Meuse and Geul terraces originate in the late Pleistocene. The soils are mainly developed in coarse sandy- and stony materials. (Includes soil types labelled with F, M & K.)

4. Soils developed in sloping terrain (28%) The sloping areas include slope complexes with slope angles of > 8% and show a large diversity of parent materials shown at the surface. The soils are erosive and stony and loess is mostly absent. (Includes soil types labelled with AH.)

%HFDXVH WKH DUHD LV GRPLQDWHG E\ ORHVVGHULYHG VRLOV VRLO JURXSV    RYHU   UXQRIILQWKH*HXOFDWFKPHQWFDQEHFRQVLGHUHGUHSUHVHQWDWLYHIRUWKHZKROHORHVV]RQH RI1RUWKHUQ&HQWUDO(XURSH

Territorial data inventory 34 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Map 4.1 Location and topographic context of the Geul catchment area

Territorial data inventory 35 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Map 4.2 Elevation of the Geul river catchment area

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Map 4.3 Topography of the Geul river catchment, in the form of slope gradient classes

Territorial data inventory 37 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

4.4.2 Current land use

4.4.2.1 Land cover The current land use map combines aspects of land cover and management. The current land cover types are summarised in Table 4.3.

Table 4.3 Relative acreage (%) of current land cover types

/DQGFRYHUW\SHV$FUHDJH   Arable land 21 Grassland 51 Orchard 2 Forest 15 Buildings 1 Urban area 7 Roads 3 100%

The different land-cover types have different effects on runoff. Grassland, (half-standard) orchards and forest create relatively low risk for runoff. They occupy approximately two- thirds of the total acreage of the catchment area. Arable land (agriculture) has moderately high risk for runoff and occupies some one-fifth while buildings, urban area and roads occupy one-tenth of the catchment area. These are land-cover types causing high risk for runoff. Concluding, almost one-third of the catchment area is occupied by land-cover types with moderately high to high risk for runoff.

Figure 4.1 indicates current proportions of acreage of grassland in the entire catchment area over 50% on all slope classes. The proportion of forested land is low in all slope classes except the steepest slope class where it is relatively important. Orchards are very rare and currently exist in the Dutch area only. The relative acreage of arable land is rather evenly distributed over all slope classes, except the steepest slope class where it is less important. The proportion of urban areas increases with fainter slope class. The percentage of arable land and urban area are highest in the Dutch part of the catchment area across all slope classes.

Territorial data inventory 38 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

V V Crops OD ÃF H >12% S Forest OR 6 Grassland

Orchard

8-12% Urban

5-8%

2-5%

1-2%

<1%

0% 20% 40% 60% 80% 100% &XUUHQWÃUHODWLYHÃDFUHDJHÃ È ÃRIÃODQGÃFRYHUÃW\SHVÃSHUÃVORSHÃFODVV

Figure 4.1 Current relative acreage (%) of land-cover types per slope class

4.4.2.2 Land management / tillage The land management aspects were combined within the land-cover map to produce a land use map. The results are shown in Map 4.4. Map legend classes of management practices relevant for runoff risk analysis were defined to diversify agricultural land uses. The definition and analysis of separate management variables explaining runoff was too detailed for this study. Only two types of management practices were distinguished for arable land: intensive and extensive management. The corresponding map legend classes were named weeded- and non-weeded crops. The current acreage of management types, relative to the current acreage of arable land is given in Table 4.4. The type of management (weeded or non-weeded) is directly associated with the type of crop and reflects differences in crop density and soil coverage. The susceptibility to runoff of weeded and non-weeded crop types is discussed in Annexe C2.2. By definition, cereals are non-weeded crops and all other crops are considered weeded. The latter include tuber crops, fodder crops, trade crops, and leguminous crops. The most important fodder crop cultivated in the region is maize (corn).

The acreage of weeded crops relative to the total area of arable land derived from the current land use map (GIS) corresponds well with the statistical records on agriculture provided by the Dutch Central Bureau of Statistics (CBS). The CBS records (see Annexe B1) were used to verify current land use areas derived from classifying satellite imagery.

Territorial data inventory 39 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Table 4.4 Relative acreage (%) of management types in agricultural land use

0DQDJHPHQWW\SH $FUHDJH  Non-weeded 41.3 Weeded 42.9 Mixed 15.7 100 % (= 106,06 km2 arable land)

4.4.3 Historical land use and historical land use changes

4.4.3.1 Review of historical land use and historical land use changes Land use in the catchment area has always been related to the type of land. The presence of water and good quality grasslands attracted people to settle in the valley areas (soil group 1, or soils developed in Holocene sediments). Near all settlements originating from the early Middle Ages are located in a valley and this may explain the currently smaller population density in the Belgian part of the catchment area where there are less valleys. The grasslands of the valley floors were used as pastures. The higher parts were used as arable land. Soils developed in loess of the plateaux (soil group 2) were known for their high fertility, workability, water availability and good drainage. Some agriculture has been practised here since 5000 years BC. Massive deforestation took place between the 11th and 13th centuries when the Dutch and German plateaux were brought into cultivation. Most of the soils of the plateaux were in cultivation by the 19th century, when the demand for agricultural products changed towards more of milk and fruits. Pastures and orchards were installed directly around the settlements. Arable land remained dominant only on the central parts of the plateaux. Small areas with forest and shrubs remained scattered around. The soils developed in the old marine sediments (soil group 3) are only marginally suitable for agriculture and are mostly covered with forest. The imperfectly drained soils around Vaals were originally used as arable land but transformed to pasture land in the 20th century. The slopes (soil group 4) were deforested and transformed to grassland before the Middle Ages. Erosion did not increase but started increasing in the Middle Ages when large sloping areas with grassland were brought into cultivation. Steep slopes (> 16%) however have always remained forested.

Agricultural development increased during the second half of the 20th century. After 1960, the Dutch Ministry of Agriculture implemented several initiatives to modify the land tenure and ownership. Grassland was opened as arable land for crops like maize and potatoes. Old fruit orchards were destroyed and new dwarf-tree orchards were created. Most farm roads were tar-sealed for the first time and road drainage was improved. This accelerated surface water runoff. Population pressure increased and many new suburbs

Territorial data inventory 40 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas appeared around the old villages. This had important consequences for the catchment hydrology. In Belgian, the development of agricultural lands and urban growth started later than in the Netherlands, The hydrology in the Belgian area may therefore be less impacted. Table 4.5 shows land cover changes in the Dutch part of the catchment area between 1955 and 1985. Urban areas and sealed roads increased significantly, while the arable land somewhat decreased during this same time period.

Table 4.5 Average relative acreage (%) of land cover in 11 Dutch municipalities within the Geul catchment (Leenaers, 1989).

According to the statistical records on agricultural land use in the Dutch part of the catchment area by the Dutch Central Bureau of Statistics (CBS), however, the opposite trend is observed with respect to the relative acreage (%) of arable land (see Annexes A2.4 & B1). Instead of a slight decrease, arable land shows an increase from some 8200 ha in 1950 to some 12000 ha in 1997. The relative acreage of weeded crops relative to the total arable land increased in the same period from 36% to 64%. This means an absolute increase in weeded area from 2925 ha to 7833 ha. Van der Helm et al. confirms the relative increase in the area of weeded crops (Table 4.6). Table 4.7 also shows a decrease of grassland. Grassland decreased from 25000 ha in 1960 to 15000 ha in 1986. The decrease in grassland is confirmed by Leenaers and Schouten (1989) and by Renes (1988). According to Renes, since 1980, the area of grassland has increased again at the cost of arable land. Orchards have disappeared rapidly since the 1970s while the acreage of forest have hardly changed.

Table 4.6 Relative agricultural land use occurrences (%) in South Limburg (Van der Helm et al., 1987 or 1989)

Territorial data inventory 41 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Map 4.4 Current land use map

Territorial data inventory 42 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

The developments in the second half of the 20th century include large-scale projects for agricultural rationalisation and intensification. These were executed in areas such as Ransdalerveld, Mergelland West en Oost, Beek, and Centraal Plateau. The relationship between slope and land use was modified during these agricultural reform projects. Small-sized parcels were combined to form large-sized parcels. The original parcelling was adapted to cope with excess rainwater supply. The direction of the parcel as well as the ploughing direction followed the slope direction to cause runoff and improve drainage on the lower and flatter parts of the slopes, and followed the contour line direction to prevent runoff and erosion on the upper and steeper parts of the slopes. Animal traction however was replaced by the use of heavy equipment during the agricultural rationalisation projects. The original parcel configuration changed completely to adapt to the introduction of heavy machinery and parcel- and ploughing direction became increasingly perpendicular to the contour lines. Heavy machinery was also leading to soil compaction and consequent reduction of the soil water infiltration capacity.

Border hedges and old cultivation terraces, locally called ‘JUDIWHQ’, were constructed in the Middle Ages to prevent runoff and erosion on slopes brought into cultivation; particularly on the upper and steeper parts of the slopes and in the dry valleys draining the plateaux. *UDIWHQ serve as barriers for runoff water and erosion load and reduce the length and gradient of slopes, increasing the surface water storage capacity at meso- scale. They were destroyed during the projects of re-allotment (land consolidation projects; transformation of arable land into grassland) and agricultural intensification (scale enlargement). Approximately 200 km of graften existed in 1910. This amount decreased to 120 km in 1950 and continued to decrease to 80 km in 1985. Between Gulpen and Vaals approximately 55 % of the graften disappeared between 1949 and 1975. Agricultural intensification during the second half of the 20th century also changed agricultural management practices.

4.4.3.2 Historical land use map The historical land use map was developed based on three sources of information: (1) the historical topographic maps, (2) the statistical records of the Central Bureau of Statistics of the Netherlands (CBS), and (3) the current land use map (GIS). The results are shown in Map 4.5 and Table 4.7. Table 4.7 shows historical as well as current relative acreage (%) of land use types, relative to the acreage of the entire catchment area. The increase of acreage of urban area, buildings and roads, as shown in Table 4.7, agrees with the review of historical land use changes presented here above (Leenaers, 1989, Renes, 1988, Van der Helm et. al., 1989, CBS, 1950 & 1997). The statistical records of the CBS are presented in Annexe B1. The decline of orchard acreage and the constant acreage of forest were as expected, as was the increase of acreage with weeded and mixed crops. It can be concluded that the historical and current land use maps confirm the data suggested by the literature review.

Territorial data inventory 43 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Table 4.7 Historical and current relative acreage (%) of land use types

/DQGFRYHU0DQDJHPHQW+LVWRULFDO&XUUHQW Arable land 21 21 non-weeded (14.9) (8.7) weeded (4.7) (9) mixed (1.4) (3.3) Grassland - 45 51 Orchard - 15 2 Forest - 13 15 Buildings - 0 1 Urban area - 4 7 Roads - 2 3 100% 100%

Photo 4.2 Accelerated soil erosion in the Geul catchment area, caused by tillage with heavy machinery, perpendicular to the contour lines.

Territorial data inventory 44 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Map 4.5 Historical land use map

Territorial data inventory 45 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

4.4.3.3 Inventory of historical land use changes According to Table 4.7, approximately 42% of the whole catchment area land cover changed since 1950. In 1950, grassland, forest and orchards occupied some 73% of the whole catchment area; at present these same land-cover types occupy approximately 68%. The decrease of 5% is due to the nearly total disappearance of orchards, partly compensated by an increase of grassland acreage and a very small increase in forested area. The arable land remained constant (21%) while at the same time, the urban area, buildings and infrastructure almost doubled from 6 to 11%. In other words, a net increase of 5% acreage with land cover sensitive to runoff can be explained by an increase in urban area, at the expense of orchards. The acreage of arable land in the entire catchment area remained unchanged from 1950 till present but the proportion of, weeded, and mixed crops doubled from 29 to 57 %. (Weeded crops from 24 to 43 % and mixed crops from 5 to 14 %.) In conclusion, the acreage of management types sensitive to runoff increased.

Photo 4.3 Gully erosion in a potato field, caused by ploughing direction. Note the potatoes in the foreground, collected by the runoff water, and the deposited erosion load in the background.

Territorial data inventory 46 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

 5LVNDQDO\VLV

4.5.1 Introduction In their preliminary risk inventory, CSO assumed that the observed increase in (flash) flood events could be predominantly explained by an increased risk of runoff due to changing land use in the Geul catchment. Groundwater movements were not considered here, nor were the suppression of meandering and the suppression of JUDIWHQ (cf. §4.4.1.2 and §4.4.3.1). Regarding the effects of land use changes, geographical information on land and land use was inventoried and analysed to obtain a first qualitative assessment of the current and historical risk of runoff in the Geul catchment area, and the corresponding spatial repartition.

4.5.2 Objectives This risk analysis has a preliminary or exploratory character and therefore provides a preliminary qualitative estimate of the current and historical risk of runoff. The results of the preliminary risk analysis are presented in a current and historical risk map. Results were also used to support the outcome of the quantitative and detailed risk analysis in this Geul project (hydrological and hydrodynamic modelling study), and to check the hypothesis that changes in land use practices in the Geul valley since the second half of the 20th century may be one of the causes of the increase in surface water runoff.

4.5.3 Methodology The analysis is based on the comparison between actual risks of runoff, historically and today. The risk of runoff is estimated on the basis of analysis of input information. The relevant input information is inventoried, including the area inventory described in §4.4. The area inventory explores land and land use GIS map layers on hydrology, topography, soils, and current and historical land uses and results in lists of map legend classes with their acreage. The actual risk of runoff is determined by the properties of ODQG as well as by the properties of ODQGXVH

Two methods are used. The first method, implemented by CSO, makes use of the parameter inventory described in the next paragraph (§4.5.4) by using a simplified version of the Universal Soil Loss Equation (USLE). The parameter inventory is based on literature review and quantifies the susceptibility of land - and land use map legend classes to hydric sheet erosion for agricultural land. The Universal Soil Loss Equation is an applicable, non-dynamic approach to calculate the risk of HURVLRQ on the basis of the analysis of land use systems. Land and land use together form a so-called land use system. The land use system concept is commonly applied in agricultural research and analysis, and it can be assumed that the analysis of erosion risk provides an applicable

Territorial data inventory 47 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas concept in the analysis of runoff risk. The susceptibility to erosion of a certain land use type is thus used as a measurement of the susceptibility to runoff, keeping in mind that there is no direct quantitative relation between the two phenomena, but only an indirect qualitative relation. Using this approach, the runoff risk of each land use system existing in the catchment area has been estimated, and the total risk of runoff in the entire catchment area was then estimated summing them together. The results are presented in a map. The second method, implemented by the FSAGx, makes use of the runoff risk indicator (CN) of the well-known "SCS method" of the US Soil Conservation Service. This method utilises the classical parameters such as topography, land use and agricultural practices, but also takes into account the type of soil (infiltration capacity) and the water content of the soil. The results are presented in Annexe D (see Figures 6.6.11 to 6.6.13). These results show in particular the effects of soil saturation on the risk of runoff. The maps presented in Annexe D provide the spatial repartition of risks of runoff in the Geul catchment. It must be noted that the relation between the CN coefficient values and the runoff rates (runoff coefficients) is known (for particular rainfall figurer) and can be translated in quantitative values (effective runoff risk). This approach is integrated in the hydrological model MOHICAN used in the hydrological modelling of the present study (see Chapter 6). A detailed comparison between the results of both methods has not been done extensively, due to the fact that both indicators provide only qualitative results and trends.

4.5.4 The simplified USLE method: parameter inventory Relevant input information for the preliminary risk analysis includes map legend classes with their acreage (assessed in § 4.4) and their attributed characteristics. The latter are quantified parameters, correlated to the erosion rate per hectare. Their values are summarised for land in Table 4.8 and for land use in Table 4.9. Table 4.9 clearly indicates that land use types differ significantly in their characterisation for the considered factors (factor C, factor P, factor CP). As indicated above (§4.5.3), relevant parameters were identified on the basis of the Universal Soil Loss Equation, which has been developed to estimate the risk of erosion. The equation was adapted to estimate the risk of runoff per hectare (the constant in the original equation is left out in order to avoid any confusion between erosion and runoff) instead of the risk of erosion, the relevance of each parameter reviewed and the value for each parameter quantified describing runoff instead of describing erosion. It may be clear however that erosion and runoff are very related, but not similar processes. Therefore, in a first approach, it can be assumed that the results obtained by this method have only TXDOLWDWLYH UHODWLYH VLJQLILFDQFH and no absolute significance.

5LVNRI (VKHHWDQGULOOQRWJXOO\) HURVLRQSHUKHFWDUH / /8 (the USLE equation with the calibration constant being left out), with:

Territorial data inventory 48 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

/ = land factor = (5 . /H 6) /8 = land use factor = (& 3) with 5 = rainfall erosivity . = soil erodibility /H = slope length 6 = slope gradient & = land cover 3 = management factor These six parameters were inventoried and their qualitative importance for runoff risk was reviewed based on a literature study. This review is described in Annexe C2.

4.5.4.1 Land The land factor L = R * K * Le * S includes the climatic factor R, the soil factor K, the slope length factor Le, and the slope gradient factor S. Only the slope gradient factor S is quantified to be applied in this preliminary risk analysis. All other land factors are considered to be irrelevant and/or correlated with the slope gradient factor S (see Annexe C).

Table 4.8 Land factor L applicable in the universal soil-loss equation and used for analysing the relative risk of runoff due to land systems.

6ORSHJUDGLHQWFODVV /DQGIDFWRU/ 0-1 % 0,1044 1-2 % 0,1726 2-5 % 0,3546 5-8 % 0,7416 8-12 % 1,3660 > 12 % 2,5810

4.5.4.2 Land use Land use factors to be applied in analysing the risk of runoff due to land use practices are proposed in Table 4.9. The factors for agricultural land are the erosion factors used

Territorial data inventory 49 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas in the USLE equation (EU Project "Floodaware", partim FSAGx, Dautrebande S. & Laime S., 1997). The land factors C for urban area, buildings and roads are not derived from literature review, as they are not relevant for erosion. These factors are defined as values near 1, assuming that these land-cover classes UHGXFH the risk of erosion but LQFUHDVH the risk of runoff.

Table 4.9 Land use factors applicable in the Universal Soil Loss Equation and used for analysing the relative risk of runoff due to land use practices.

/DQGXVHW\SHVIDFWRU&IDFWRU3IDFWRU/8 & 3  Grassland 0.008 0.700 0.006 Orchard 0.013 0.675 0.009 Forest 0.018 0.600 0.011 Non weeded crops 0.045 0.810 0.036 Mixed crops 0.120 0.850 0.102 Weeded crops 0.320 0.870 0.278 Urban area 0.700 0.900 0.630 Buildings 0.800 0.900 0.710 Roads 0.900 0.900 0.810

4.5.5 Results of the risk analysis with the simplified USLE method A total of 54 possible land use systems can be defined in the Geul catchment area, based on nine land use types and six land types. The land factor L ranges from 0,1044 to 2,5810 and the land use factor LU (= C*P) from 0 to 1. They were multiplied to assess the actual risk of runoff per hectare per land use system. These risks were multiplied with the relative acreage of each land use system. The resulting values indicate the risk relative to a reference risk (based on the similarity between risk of erosion and risk of runoff), defined as land with a slope gradient 10% (L=1) and a land use of bare soil (LU=1). The results of this preliminary risk analysis method are given in Annexe C3 and are summarised in the present paragraph. The results for the current-risk analysis are illustrated in Figure 4.2 and in Map 4.6. The change of risk is illustrated in Figure 4.3 and in Map 4.7 and summarised in Table 4.10.

Territorial data inventory 50 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Map 4.6 Results for the current-risk analysis

Territorial data inventory 51 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

V V OD Crops ÃF H S >12% Forest OR 6 Grassland

Orchard

8-12% Urban

5-8%

2-5%

1-2%

<1%

0 0,002 0,004 0,006 0,008 0,01 0,012 0,014 0,016 0,018 0,02 &XUUHQWÃJHRJUDSKLFÃDFWXDOÃULVNÃ  ÃGXHÃWRÃODQGÃXVHÃIDFWRUÃGLVWULEXWLRQÃVORSHÃJUDGLHQWÃDQGÃVORSHÃFODVVÃDFUHDJHÃ UHODWLYHÃWRÃJHRJUDSKLFÃUHIHUHQFHÃULVNÃ Ã KD

Figure 4.2 Current risk (0-1) per slope class, relative to reference risk (1) due to land use, land factors and acreage.

V V OD Crops ÃF H S >12% Forest OR 6 Grassland

Orchard

8-12% Urban

5-8%

2-5%

1-2%

<1%

-0,001 0 0,001 0,002 0,003 0,004 0,005 0,006 0,007 0,008 &KDQJHÃRIÃJHRJUDSKLFÃDFWXDOÃULVNÃ  ÃUHODWLYHÃWRÃJHRJUDSKLFÃUHIHUHQFHÃULVNÃ Ã KD

Figure 4.3 Historical change of the geographic total actual risk per slope class for the entire catchment area

Territorial data inventory 52 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Map 4.7 Results for the change of risk

Territorial data inventory 53 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Table 4.10 Historical and current actual risk for runoff (%), relative to reference risk (100%)

$UDEOH )RUHVW *UDVVODQG 2UFKDUG 8UEDQ 7RWDO ODQG Historical 1,516 0,188 0,211 0,101 1,904 3,919 Current 2,254 0,218 0,246 0,008 3,650 6,376 Change 0,739 0,030 0,035 -0,093 1,746 2,457

The major land use contributor to the change of risk and to the current risk is the XUEDQ DUHD(this result is obvious and was expected, as the C parameter value for urban areas is about 1), followed by the DUDEOH ODQG. Urban area includes all paved surfaces with consequent high runoff. The arable land contributes in second position to the current risk, due to the important proportion of unfavourably managed arable land (weeded crops like maize, potato etc.). Though its acreage did not change since 1950, its contribution to the risk increased because of the increased proportion of ZHHGHG crops. Grassland and forest areas do not significantly contribute to the change of risk and to the current risk in the Geul catchment area (ten times less than, for instance, arable land). The current risk and the change of risk since 1950, explained by the current and the changed geographical distribution of land use systems, are higher with steeper slopes. Contrary to this tendency is the effect of land use only, irrespective of the effect of slope gradient. The current land use and the change of land use show a tendency of increasing risk with fainter slopes. Steeper slopes have a relatively favourable land use distribution. Land use is apparently adapted to counteract the effect of steep slopes on the risk. Slopes fainter than 2% hardly contribute to the change of the risk and to the current risk. The current risk and the change of the risk of the steepest slope class are very low relative to its potential risk. The contribution of the slope class 2-8% to the risk of the entire catchment area is relatively important, due to its important acreage. The Dutch part of the catchment area contributes most importantly to the current risk in the Geul catchment area, compared with the Belgian- and German parts. The same holds for the risk change since 1950. The Dutch tendency of the different slope classes with their land use contributing to the total risk is nearly similar to the tendency observed for the entire catchment area.

 &RQFOXVLRQVDQGGLVFXVVLRQ The present chapter describes an inventory of input information relevant for the analysis of the possible risk of erosion and of (flash) flood events in the Geul catchment area, in relation with land and land use parameters. The inventory is based on the GIS map

Territorial data inventory 54 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas layers constructed in the paragraph on spatial data inventory and GIS development (§ 4.3). The results of the area description are presented in § 4.4 in the form of thematic maps. The present chapter also presents a risk analysis, though with preliminary character. Emphasis is put on the risk of runoff, assumed as one of the significant variables explaining the risk of flash flood events. Parameters explaining the risk of runoff following the USLE equation are identified and quantified in Annexe C2 (literature review) and the results of the preliminary risk analysis are described in § 4.5. The detailed deterministic analysis is performed and described in the chapters 6 and 7.

GIS A geographical information system (GIS) of the Geul catchment study area was constructed providing relevant soil, elevation and land use data for use in the hydrologic and hydrodynamic modelling studies. All GIS activities were assigned to one research partner, who was designated to receive and assemble all data files provided by the other research partners and by the Belgian and Dutch Authorities. This centralised data acquisition facilitated the communication between the research partners and maintained a quality control of the GIS throughout the project. Once the data was obtained, the GIS team merged the data into unified map layers. Because the study area overlapped three countries (Belgium, The Netherlands and Germany), the GIS team had to surmount several technical challenges during the construction phase. The most important technical challenges included: • The map projections and co-ordinate systems used in Belgium, The Netherlands, and Germany had to be transformed to one standard system. • To construct a DEM of the catchment, the elevation reference levels used by each study country had to be reset to a common reference. • To merge the thematic GIS map layers, the legends and classification systems (e.g. soil and land use classifications) used in each country also had to be converted to a set of common standards. Centralising GIS data and availability within Europe could save a lot of time and money on similar projects in the future. As part of this report, the GIS team recommends the following to local, national, and European Commission officials: • A central European databank of unified meta-data should be created. • GIS data should be made more affordable in Europe. • Agreements concerning user-rights and user-restrictions between government authorities should be made to clarify data exchange.

Catchment area description The physical properties of the catchment area seem, at first sight, more or less favourable for the development of flash flood events. River water originates from running off the undulating plateaux and from continuous groundwater fluxes.

Territorial data inventory 55 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

The hydrological analysis of observed values (see also Annexe D) shows that the origin of the flash floods in the Geul catchment is due rather to the conjunction of arrival times of runoff water than to the runoff rates, which remain in the range of usual values for loess derived soils with silt textures. This origin of flash floods is related to the geomorphology of the catchment, with slopes steeper than 10% occupying about one quarter of the entire area, and to the elongated shape of basin and sub-basins. Land use provides some degree of protection to the soil surface. Currently, some two- third of the entire catchment area is covered with land use types reducing the risk for runoff (grassland, forests and orchards). Their proportion was 5% higher in 1950. The decrease is due to a nearly disappearing of orchards. The remaining one-third of the catchment area includes urban area and arable land; unfavourable land use types against runoff. The soil surface of urban areas, including roads and buildings, is generally paved. Paved surfaces provide high protection against erosion but cause runoff due to the seriously reduced possibility for infiltration. Its acreage almost doubled since 1950, from 6% to 11%. The acreage arable land remained constant but the proportion of unfavourably managed arable land (ZHHGHG FURSV like maize, potatoes etc.) almost doubled. Weeding reflects soil tillage with heavy machinery, introduced since 1950 in agricultural rationalisation projects. The use of heavy machinery requires following the slope angle, and tillage direction is consequently up and down the slope. It also required aggregating originally numerous small sized parcels into relatively few large sized parcels (land consolidation projects), favouring an increase in runoff. Its current acreage is comparable to that for the urban areas.

Parameter inventory Parameters were identified and quantified as input information for the preliminary risk analysis, which was performed to estimate the historical and current risk of runoff of all land use systems in the Geul catchment area. A land use system combines both aspects of land and land use. The parameters explaining the risk of runoff were identified on the basis of two methods, one method being based on the simplified Universal Soil Loss Equation USLE), the other being the US Soil Conservation Service (SCS) method. “Land” considers slope gradient and "Land use" includes land cover and land management practices. In the USLE method, all parameters describing the aspects of land were defined constant in space and time, except the slope gradient class, which determines the potential risk per hectare. The actual risk per hectare of a land use system is function of the land factor (slope gradient) and the actually practised land use. The actual and the potential risk of runoff were referenced to a hypothetical runoff per hectare observed on a land use system of a slope of 10% with a bare soil (reference risk = 1). In the SCS method, effects of soil humidity and spatial variability of soil types are also included.

Preliminary risk analysis In the simplified USLE method, the risk of runoff of all distinguished land use systems was estimated and multiplied with their acreage to yield a total risk for the entire Geul

Territorial data inventory 56 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas catchment area. The USLE potential risk of runoff in the entire area is estimated at some eighty percent of the reference risk (for bare soil). The average slope in the Geul catchment area appears to be fainter than 10%. The current risk of the entire catchment area is estimated to be about one tenth of the potential risk, and one fifteenth of the reference risk of runoff. Apparently, the practised land use significantly reduces the risk of runoff, relative to the potentially attainable (USLE method) risk of runoff in the area. The current actual risk of runoff (USLE method) has been analysed by slope gradient, land use type and national area. The most visible tendency is that the Dutch contribution to the risk of runoff (estimated with the USLE method) clearly exceeds the Belgian and German contributions (see also maps in Annexe C). The urban area is the largest contributor on all slope classes, followed by the arable land. The other land use types hardly play any significant role in being an indicator of risk of runoff, except for the steepest slope class where forest and grassland are still relatively important. The contribution to the total actual risk of runoff (USLE method) in the catchment area increases with steeper slopes, even though the land use distribution on steeper slopes is more favourable against runoff. Slopes of 2-8% contribute importantly, due to their large acreage. The actual risk of runoff (estimated with the USLE method) increased since the second half of the 20th century. The most important tendencies equal the tendencies mentioned above for the current situation. Noteworthy is that the acreage of arable land did not change since 1950: it decreased in the Dutch part, but increased in the Belgian and German parts of the catchment area. The contribution of the arable land to the risk of runoff (USLE method) however increased in all countries. This is due to the changed composition of arable land and to the urbanisation. Unfavourable managed crops (ZHHGLQJ) occupied one-third of the arable land in 1950 and nearly two-third at present. Changes in land use system distribution since the second half of the 20th century were such that the risk of runoff has increased about two-third, relative to its value in 1950. It has to be noted however that this change of the indicator of risk of runoff (determined with the USLE method) provides no direct indication about the change of runoff rates due to land use modifications (this will be provided by the hydrological modelling, see Chapter 6). Not all variables relevant for explaining the risk of flash flood events could be considered in this preliminary risk analysis (the effects of the following variables are for instance not considered: river straightening, suppression of JUDIWHQ, modification of field area, shape of the watersheds). However, using a simplified form of the USLE method, gave a significant insight into the tendencies of the risk of runoff, by estimating the actual risk of runoff today and since 1950 in relation with land use (changes).

Territorial data inventory 57 European Commission - DG Environment Walloon Regional Government Province of Limburg - The Netherlands Province of Limburg - Belgium Waterboard Roer & Overmaas

Territorial data inventory 58