The climatic weather forecast

Transcription

1 The climatic weather forecast More mild winters with more and heavier rainfall. Warmer and drier summers with more intense thunderstorms.

2 The Netherlands: general policy on mitigation measures against soil impermeabilization in urban areas Namur, November 5th 2014 Presented by Harrie Winteraeken Staff member on Strategy and Policy Water Authority Roer en Overmaas (Sittard, NL)

3 Watermanagement in the Netherlands The Netherlands: lowest part of Europe 25% below sea level 50% inundates without dikes Water Authorities Democratic governing body since 12th century. From thousands to 24.

4 State government Main lines in water management (strategic) Management/maintenance of great surface waters like Rhine, Meuse, North Sea (operational) Province Works out the global national policy for the regional water system Groundwater management Municipalities Water Authorities Local / regional water management

5 Water Authority Roer and Overmaas Full governmental body We are responsible for: Water quantity and water quality and ecology of local / regional streams and rivers in Southern Limburg. The protection of urban areas and infrastructure against flooding of the river Maas and the local and regional water system. We raise our own taxes!

6 Management area ± 950 km², 90% bounded to Germany and Belgium 945 km of streams 74 km of dikes 11 sewage water treatment plants (part of a collaboration with Water Authority Peel and Maasvallei: Water Authority Company Limburg) ± inhabitants ± 135 employees (exclusive WACL)

7 Namur Catchment area of the River Maas

8 Urban water cycle (1) Main goal: integral sustainable water management in urban areas. Collection of wastewater and rainwater management in urban areas are the responsibility of the municipality. At the moment in general (± %) combined sewage system rainwater and wastewater.

9 Urban water cycle (2) Transportation of wastewater is the responsibility of the Water Authority. Nearly 100 % of the wastewater is cleared in a wastewater treatment plant. A few buildings in rural areas have a individual treatment of wastewater. No direct flow of waste water into surface waters.

10 Urban water cycle (3) Maximum capacity of the combined sewage system of rainwater storage is about 7 mm. ( basic effort ). Heavy rain: Overflow of diluted dirty water in the surface water system. Old policy: average of 6 times in a year. New policy for ecologically vulnerable streams: once in 2 5 years.

11 Urban water cycle (4) Urban areas on slopes: less storage capacity of the sewage system expensive sewage water storage (concrete) cellars. Overflow in open retention reservoirs green storage + flow back in the sewage system. Storage of rainwater in the sewage system is to expensive!

12 Urban water cycle (5) Very heavy rain: supply exceeds the transportation capacity of the sewage system: Acceptance of water on the street. Flat areas twice a year. Urban areas on slopes: rainwater is flowing causing flooding and nuisance.

13 Separation of rainwater and wastewater large contribution of the solution of problems above. Collection on roofs, use of the rainwater.

14 Infiltration of rainwater in gravel columns, small urban ponds in parks, new urban developments and reconstruction areas. (Problems with less permeable soils like löss)

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16 Storage of rainwater in green-blue structures with the advantage of more enjoying your live environment, nature in the urban environment, recreation possibilities (relations with sports and public health)

17 Separated sewage system for wastewater and system for rainwater. About % and growing. Mostly in new urban developments and done when the sewage system is renovated / renewed. Contra development: relining sewage pipes is cheaper.

18 Rainwater system: direct flow into the surface water system? Rainwater from streets and roofs is of better (less worse) quality than diluted wastewater. But accelerated draining of rainwater gives extra discharge of the surface water system, more rainwater retention basins are needed.

19 Flooding from rural area s

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21 Three layer security Protection of urban areas and infrastructure against flooding from the surface water system and rural environment above: responsibility of the Water Authority. Dutch concept of Three Layer Security against flooding.

22 First layer: protection. Protection urban areas against flooding to a certain protection level (small surface waters). Regional water system only inconvenience / nuisance: 1:25; norms and standards on the protection level by the province. For example the flash flood of Hombourg and Slenaken of July 28 th Change of the general norm from 1:25 into 1:100 event repeating period?

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24 Protection river Meuse Protection Level river Meuse in Limburg 1:250; Holland 1: and more; based on the risks on the loss of lives and expected economic damage. Norms and standards on the protection level by the National Government ( The Hague ). September 16 th 2014: for large rivers the national government made the Delta decision : Urban areas like Maastricht higher protection level of 1: Villages from 1:250 1:300.

25 Second Layer: urban developments Water management and urban development Intense collaboration of the Water Authority and the municipalities who are responsible for urban planning. Interaction of the sewage systems, the transport and treatment of waste water and the surface water system.

26 Rainwater structure maps of urban New instruments: areas Very detailed modelling of surface runoff in urban areas: the Water Annoyance Landscape Map (TAUW) based on very detailed terrain model / surface information when the sewage system is filled. Surface module of the model Infoworks, which is normally used for calculations on the sewage system.

27 Water test strong advise on urban developments. Enough space for surface waters peak discharges means no urban developments in risk areas. Reducing risks on damage from flooding by other way of building / urban planning. New urban developments: municipality demands on less contribution of rainwater to the public system.

28 The Ordinance of the Water Authority Regulations on (urban) developments near surface waters (also natural inundation areas). Permits of the Water Authority are needed for developments in these areas.

29 Third Layer of Security Preparation on calamities of occurring flooding Responsibility of the Security Region This is an organisation of collaborating municipalities with public services like police, fire brigade, ambulances).

30 Other instruments to achieve goals Building ordinance of municipalities: Separation of wastewater and rainwater is ordered (not in reconstruction situations / projects in densely built areas). New possibility?: no pavements in front gardens with extra rainwater contribution to the public system.

31 Subsidies Subsidies of the municipality for inhabitants for measures on buildings and their environment. Subsidies of the Water Authority for the separation of rain water.

32 Stimulation of taking measures by taxes? For example larger paved areas?: more taxes. No rainwater to the system, use or infiltration measures?: less taxes. Municipalities do not often use the instrument of their ordinance on taxes on the sewage and rainwater system. The Water Authority for buildings neither, but indeed for roads and other paved surfaces.

33 Reduction of the population Recent urban developments Pull down of houses, old factory areas Less dense rebuilding with more public open space / parks where rainwater is collected.

34 Climatic Change Heavy rainfall in short period of time Climate adaptation in urban areas: everything in an acceleration?

35 Last remark: collaboration is essential.

36 Merci pour votre attention