7.3.1

Waterlogging

Under the “Water Policy in the 21st century” memorandum, we have been working on reducing waterlogging for some fifteen years. During this period, the focus has been on the prevention of waterlogging caused by prolonged rainfall, in accordance with the “retention, storage, drainage” triad. Municipalities have expanded sewer systems, disconnected downpipes, and created more room for water in public greenery (wadis) and on streets (lowered street profiles). District water boards have created additional rainwater storage facilities in the water system, and improved the discharge efficiency. The provinces have set down function-specific waterlogging protection levels in provincial regulations, thus marking the boundaries of government responsibility. 

District water boards and municipalities have invested significant budgets in these measures. Over the period from 2003 up to and including 2015, the aggregate district water boards have spent some 1.5 billion euros on water system measures to combat waterlogging. In 2015 alone, municipalities spent a total of 1.56 billion euros on urban water management, of which 225 million euros to tackle pluvial flooding. Despite these efforts, waterlogging is occurring with growing frequency, due to climate change, and due to the increasing proportion of paved and built-up surfaces.

Climate change is visible: extreme precipitation is increasing

Recent analyses show that climate change is already manifest in the statistics on extreme downpours. The frequency of extreme precipitation has already increased by a factor of two to five compared to the 1950s, and it will increase even further in the future: by a factor of up to five by 2050, and by a factor of up to ten by 2085 vis-à-vis the current situation (based on the KNMI’14 climate scenarios). How this will affect the probability of waterlogging differs for each individual area, but by and large, the probability of waterlogging is increasing. Waterlogging can be caused by prolonged precipitation (usually in winter), but also by short, extremely severe precipitation (more often in summer). The impact of these two types of precipitation differs and also depends on the location hit by the precipitation: whether in rural areas or in a city.The impact may be so large that local residents or businesses sustain damage despite the preventative measures taken by the government authorities. The district water board and the municipality are not accountable for such damage. Although residents and businesses have a responsibility of their own, in many cases they are insufficiently aware of the risk and of measures to limit such risk. Consequently, not many of them are insured against damage caused by waterlogging. Furthermore, such damage is not fully covered by insurance companies, nor does the central government disaster fund provide a comprehensive safety net.

Figure 11

Situation involving more than 100 mm of precipitation in two days in August 2010 (left) and the transformation to a 2 degrees temperature rise in the climate (right); source: KNMI

Urban areas: short downpours are particularly problematic

In cities, short but extremely severe downpours have a disproportionally large impact. The densely built-up and largely paved urban areas need to drain most of the rainwater via sewers and public roads. The capacity of the sewer system is insufficient for draining so much water in such a short time. The excess water flows to lower-lying locations, where it can cause damage such as obstruction of roads or railroads, or can inundate houses and business premises. The impact differs strongly from one location to the next, and in addition to financial damage, repeated urban flooding can cause major emotional damage. Water storage on rooftops and in gardens, streets, and parks to combat waterlogging as a result of severe downpours is a more cost-effective strategy than the further expansion of the sewer system. In principle, local residents and businesses are themselves responsible for dealing with rainwater in their own premises.

Rural areas: the impact of downpours is increasing

In rural areas, prolonged precipitation poses more of a problem than do severe downpours. District water boards and provinces have developed a solution, in collaboration with municipalities and farmers, by creating water storage facilities in rural areas: during prolonged precipitation, farmlands are left wet, taken out of production, or converted to water storage areas. In recent years, short downpours have also caused occasional disruption in rural areas. Occasionally, rain volumes are such that even these areas cannot drain the water fast enough, despite the fact that rural areas have much more room for water than do urban areas, and water is more easily absorbed by the soil. For example, in such situations, sections of motorways may be inundated, or the banks of roads or railways may subside. Many such downpours occur in the summer season, which may cause entire crops to fail. 

  1. Cover letter and Delta Programme Commissioner’s recommendations
  2. Introductory summary
    1. Continuing the work on a sustainable and safe delta
  3. Part I National level
  4. Progress of the Delta Programme
    1. Progress based on Monitoring, Analysing, Acting
    2. General picture of the progress
      1. On schedule
      2. On track
      3. Integrated approach
      4. Participation
      5. Effectiveness of the regions
    3. Progress in flood risk management
    4. Progress in spatial adaptation
    5. Progress in freshwater supply
    6. Embedding, knowledge and innovation, international collaboration
      1. Embedding
      2. Knowledge
      3. Innovation
      4. International efforts
  5. Delta Fund
    1. Developments in the Delta Fund
    2. Resources from other partners
    3. The financial taskings of the Delta Programme
    4. Financial security of the Delta Programme
  6. Part II Regions
  7. Progress per region
    1. IJsselmeer Region/freshwater supply region IJsselmeer Region
    2. Rhine Estuary-Drechtsteden/West-Netherlands freshwater supply region
    3. Rhine/ Area around the major rivers freshwater supply region
    4. Meuse
    5. Southwest Delta/Southwest Delta freshwater supply region
    6. The Coast
    7. Wadden Region
    8. Elevated Sandy Soils South and East
  8. Part III Delta Plans
  9. Delta Plan on Flood Risk Management
    1. Implementation programmes
      1. Flood Protection Programme
      2. Second Flood Protection Programme
      3. Room for the River
      4. Meuse Projects
      5. WaalWeelde
      6. IJsselmeer Closure Dam
      7. Repair of Oosterschelde and Westerschelde stone claddings - Zeeland foreland deposits
    2. River widening in interconnection with dyke improvement
    3. Studies ensuing from knowledge agenda and in regions
  10. Map Flood risk management measures
  11. Delta Plan on Freshwater Supply
    1. Measures to ensure the availability of freshwater in the Netherlands
  12. Map Freshwater supply measures
  13. Delta Plan on Spatial Adaptation
    1. Introduction
      1. Justification
      2. Aim and state of affairs of the Delta Plan
      3. Collective realisation
    2. Context
    3. “Analysis, Ambition, Action” – state of affairs
      1. Waterlogging
      2. Heat stress
      3. Drought
      4. Consequences of urban flooding
      5. Current approach
    4. Our intentions: expediting and intensifying
      1. Vision: from the present to 2050
      2. Ambition and strategy
      3. Interim goals
      4. Nationwide governance framework regarding spatial adaptation
      5. Funding
    5. Appendix 1. Action programme
    6. Appendix 2. Outcomes of regional meetings and round table discussions
  14. List of Background Documents
    1. Background documents
  15. Colophon
    1. Colophon content Delta Programme 2018
  16. How to use Delta Programme 2018