Between heat waves, droughts, fires and floods, these last weeks Europe has been hit hard by these extreme weather events. While they are likely to intensify with climate change, what solutions are available to us to mitigate their effects?
From drought to flooding, there is only one step
Rivers turning into thin streams, land cracking and water shortages are just some of the consequences of the drought that hit European countries this summer. The latest work of the IPCC is clear:
“Human-induced climate change is already affecting many extreme weather and climate events in all regions of the world.”
Then the drought gives way to rain. Unfortunately, with dry soil, which is much less permeable and porous, water cannot infiltrate properly and causes flooding. A correlation between drought and flooding is emerging, one leading to the other, which plunges us into a spiral of extreme climatic events. This water runoff can have many impacts, since this water that does not penetrate the soil will be loaded with many pollutants, even more in urbanized areas. The treatment plants that receive stormwater and wastewater are then more easily saturated.
Rainwater alone accounts for about half of the water arriving at wastewater treatment plants in Europe: in 2021, out of 23 Mm3 of water arriving at the plant, 12 Mm3 was rainwater.
The problem is that if too much water flows in at the same time, it cannot be treated properly, which means that untreated water is discharged directly into the ocean and the aquatic environment.
It is therefore necessary to question our water management: to think about a more sustainable urban development, to give a more important place to the vegetation of the cities etc.
Urban gardens for a healthier environment
For a better water management, we decided at Surfrider to build an Ocean Friendly Garden also called a rain garden. The idea is to consider the plot of land as a small watershed and to capture water as close as possible to its point of fall in order to recover it, save it, infiltrate it or purify it. Thus, taking into consideration the constraints of the space, different landscaping techniques have been used:
Desealing
In normal circumstances, if the nature of the soil allows it, a large part of the rainwater infiltrates into the ground, thus not only feeding the underground water tables but also serving as a water reserve for the vegetation. Dewatering a soil contributes to a better regulated water cycle. The soil must be porous and permeable, in other words, it must allow liquids to pass through small holes invisible to the naked eye.
At Surfrider’s headquarters, 300 m3 were de-impregnated. A permeable porous floor covering replaced the thick layer of concrete. Drainage trenches called “noues” were dug at the edge of the garden as a reinforcement and as the first irrigation system.
Re-vegetation
It was important to plant a number of trees, shrubs and plants in the garden. This will help to infiltrate water into the soil. Plants also play an important role in filtering impurities from rainwater and improving air quality through photosynthesis, which transforms CO2 into breathable O2.
The presence of such gardens also helps to cool the space by forming real islands of coolness. A vegetated soil is also more resistant to water erosion during heavy rains as opposed to a bare soil.
Storage of rainwater
In order to reuse rainwater and save drinking water, an 18 m3 tank was installed in the garden. This tank is fed by 2 tanks connected to underground pipes where the water from the gutters installed on the roof circulates. This water network allows for the collection of water that can be used for tasks that do not require drinking water, while limiting the volume of water flowing into the ocean.
The benefits of such a project for SFE and the citizen
In 2020, 1721mm or 1.721 m3 of rain fell on Biarritz soil, compared to 1274mm or 1.274 m3 in 2021. We know that the price of m3 of wastewater in the Basque Country is 2.38€. With a roof catching water at Surfrider of 200 m2 and a desoiled plot of 250 m2, the savings for the two years would have been theoretically as follows
in 2020, a saving of : 450m² x 1,721 x 2,38 = 1842€.
in 2021, a saving of : 450m² x 1,274 x 2,38 = 1363€.
However, it should be kept in mind that such a system takes on average 1 year to stabilize. During the first year, the soils will not be sufficiently watered for the plants to draw on these reserves to hydrate themselves. It is therefore necessary to remain attentive to the needs of the garden and to water when necessary during the first year. To use a minimum of drinking water during this first year, an above ground pond was built at Surfrider. In addition to providing a home for aquatic plant life and colorful fish, the pond allows rainwater to be on hand to fill watering cans.
If you have a garden, it is possible to create your own Ocean Friendly Garden by following these three key principles to the fullest:
Desealing : make soil and surfaces permeable to allow rainwater to slow down and then infiltrate.
Capture : conserve water, energy and natural habitat.
Restore: prevent water shortages during droughts by using the collected water to care for your garden.
If you have a balcony or a surface too small for this kind of arrangement, it is possible to buy small cisterns that will allow you to collect rainwater to avoid watering your plants with drinking water and reduce once again the share of runoff. You can also approach your municipality to propose a desilting project near your home. It’s time to give back to green spaces to preserve our water resources.
