Marseille’s rainwater problem

Zayane writes*

The effects of climate change are already manifesting themselves in the dense and urbanized coastal city of Marseille. Due to its characteristic Mediterranean climate (hot and dry summers and cool and wet winters), Marseille is vulnerable to heatwaves, drought, fires, acute rains and storms [pdf]. Scientists forecast that with climate change, extreme weather events will increase in both frequency and intensity [pdf]. Marseille will have to grow into an adaptable and resilient city to preserve its water resources.

To most, water in the «Rhône-Méditerranée» appears abundant. The population of Marseille proudly claim they have the best water of France. The Durance and the Verdon rivers are the principal sources of the city’s water. The canals of Marseille and Provence transport water to Marseille.

Research reveals an absence of flood risk awareness in Marseille. This finding is surprising if we take into account the upsurge in flooding episodes due to increasing urban planning and soil impermeability (as pictured).

Marseille regularly experiences excess rainwater runoff after heavy rain due to its dense industrial and urban landscape. Concrete, tar and other impermeable surfaces prevent rainwater from infiltrating the soil. Fifty-five percent of rain collects as runoffs in urban areas, compared to 10% in natural areas.

Rainwater that cannot infiltrate to complete its natural cycle is captured and channeled through pipes. The consequences are worse air pollution and urban heat islands in the city.

Most rainwater is mixed into the wastewater system, which concentrates rainwater and overwhelms the system in heavy rains. The Géolide plant treats 60% of the city’s wastewater, but it rejects excess water into the environment when it is overwhelmed. A large retention basin was commissioned to collect excess water.

Excess runoffs threatens residents, increases maintenance costs and harms the environment. Municipalities regularly close beaches due to runoff.

Marseille’s drainage system is not suited for climate change. Urban planners and water managers are working to retain water in the city using floodable sports fields, permeable parking, and green roundabouts.

Bottom Line: Marseille’s drainage system is not suited for climate change and the extreme rains it brings. Instead of building expensive, inflexible retention basins, the city should work to increase infiltration everywhere.

* Please help my Water Scarcity students by commenting on unclear analysis, alternative perspectives, better data sources, or maybe just saying something nice 🙂

Author: David Zetland

I'm a political-economist from California who now lives in Amsterdam.

4 thoughts on “Marseille’s rainwater problem”

  1. Hi Zayane, I really enjoyed reading your blogpost. Even though you mainly focus on rainwater, you manage to address many different aspects. I especially like how you juxtapose how the population of Marseille feels that they have good water, with the reality of flood risks and excess rainwater runoffs. Has this discrepancy resulted in reduced actions from the municipality or is the population just not aware of all the work that needs to be done? The way you link the issues surrounding rainwater to consequences that are not immediately related to water such as air pollution or urban is also great. However, I am not sure that I understood this connection correctly: Are air pollution and urban heat the consequences of the water leaving the natural cycle? It would be great if you could elaborate on this process. I was also wondering, whether the Géolide plant struggles with excess water often and how this has developed over the years.

    1. Thank you Xenia for your comment and for your questions!

      The population has access to good quality drinking water but doesn’t seem aware of the risks associated with runoffs. Research carried out on residents of officially declared flood-prone areas reveals that about a third of participants said they did not live in a flood-prone area.

      In order for the temperature in the city to be comfortable and the air less polluted, the water must return back to the air by evaporation and back to the soil and to the vegetation by infiltration. This will lower the temperature and increase the humidity.

      The Géolide plant is saturated when there is a lot of rain, this represents an excess of 1 million m3 of untreated water per year for 60 days of rain.

  2. Hey Zayane, super interesting blog post! I had no idea that Marseille suffered so much from water related issues. I feel especially shocked as I am a resident of the country, and I do not live miles away from Marseille, yet I am still only really hearing about this for the first time. It’s crazy how climate change can have such an effect! As the city is quite well known and touristic, I’d always assumed that they had everything under control, but what you say about the “absence of flood risk awareness” shows that they might not… It also makes you think about what the city views as priorities… However, now that they have experienced multiple catastrophic flooding events, do you know if the city is working on a system that focuses on these occasional floods? I hope it is as flooding is likely to happen more often in the future. Additionally, the fact that it affects so many residents and that beaches sometimes must be closed might affect the attraction of the city; as in, people might decide to move to a less dangerous area and tourists may not visit due to closed beaches, all of which might not be advantages for the city.
    On another note, I find it interesting that the Géolide plant collects 60% of the city’s wastewater – it shows promise. However, I am struggling to decide whether 60% is a lot, whether it is sufficient, or whether more could be collected… If you feel like it, I’d love to know you’re view on this!
    Overall, it was a very interesting read and learning experience! Thank you.

    1. Hello Ruby and thank you for your comment!
      The city is working on ways to improve permeability; notably through better urban planning. The SDAGE (Master Plan of the Development and Management of Water) encourages urban planners to consider the risk of flooding in designing new urban surfaces.
      The Géolide plant is the largest underground treatment plant in the world. The problem is that rainwater and wastewater are usually evacuated through the same system of pipes. The solution is to improve the impermeability of urban surfaces so that rainwater can follow its natural cycle and infiltrate the soil where it reaches the ground.

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