Few Parisians know that the River Bièvre joins the Seine right at the heart of the capital, even though its source lies 36 kilometers from Paris. It snakes through the outer suburbs for 20 kilometers, before disappearing under the streets of Paris. This river, which runs underground in its downstream section, is nonetheless clearly visible upstream in the Upper Bièvre Valley and comes under close and continuous surveillance. This is because, in “SIAVB’s territory,” the flows of this river and its tributaries – i.e. 38 kilometers of watercourses in total – are capricious and can cause considerable human and financial disasters in the event of heavy rainfall. In July 1982, in less than a day, 7.5 million m3 of water flooded the valley causing significant damage. With only two existing basins along the course of the Bièvre, the storage and outlet capacities were completely inadequate at the time to cope with the volume of water discharged.
Toward remote management of the hydrographic network
After this episode, 17 water-holding basins and dikes were built, creating the current storage capacity of 800,000 m3. SIAVB’s President, Thomas Joly, still remembers the 1982 flood, which was the trigger to putting in place an effective system to fight flooding: “Before these basins were created, our feet were in the water, and this could happen every 18 months. Floods are expensive for insurance companies and individuals who have to replace their furniture and repaint.” An initial phase of the work was launched with Veolia in 1991 to remotely manage these basins, which are able to store or release volumes of water depending on the pluviometry. “However, all these static reservoirs are not enough to entirely dam the runoff from the Bièvre river basin in the light of increasingly violent and often irregular rainfalls,” notes Bernard Willinger, in charge of managing the project at Veolia. The engineer continues, “We are in a valley that covers a great deal of land, with spatial constraints that no longer allow us to increase the storage capacities.” In 1993, SIAVB also entrusted Veolia with a maintenance and services contract to ensure monitoring and hydraulic management in real time under any circumstances. The Group then set up smart management of the entire hydrographic network: remotely managing the basins with “optimization of flow transfers from upstream to downstream.” In an initial stage, series of sensors were installed to remotely monitor and control the flow rates of the Bièvre and its tributaries, activating control gates at the exit of the storage basins. The runoff is modeled using satellite images, in order to plan response strategies to critical situations. SIAVB’s aim is to enable the Bièvre and its tributaries to swell if necessary in the expansion areas provided to this end, which are managed in concert with farmers and local authorities. This approach also guarantees the quality of the water and maintains biodiversity.
Protecting the valley of the Angkor temples and its population from flooding: a humanitarian mission
In the Cambodian jungle, the capital of the former Khmer Empire rests on a vast network of canals and basins that has stopped working over the centuries. Since 2012, this hydraulic system – weakened by the floods of the past decades and climate change and located at the heart of an environment jeopardized by demographic pressure and mass tourism — has benefited from assistance from a Franco-Cambodian project: “Paagera” (Project to improve sanitation and water management in the Angkor region).
Under the authority of Apsara (Authority for the protection of the site and development of the Angkor region) and supported by several partners*, Paagera relies on the expertise of water and sanitation players to harmonize the flows of water between the dry season and the rainy season. SIAVB and Veolia’s experience in the Bièvre Valley provided an initial technical solution: a telemetry device deployed in 2014 now makes it possible to regulate Angkor’s hydraulic network.
After an initial development phase, during which the hydraulic network flows were modeled and 20 first hydraulic measurement stations installed, a new phase began in 2018. It aims to set up the comprehensive remote management of water flows in three steps:
• creation of 22 real-time remote measurement sites;
• setting up of 10 gate automation sites;
• remote control and dynamic management of flows in the long term.
Disaster averted in 2016
As early as 1993, the whole system was managed thanks to a central computer, a world first at the time.
“Veolia’s teams provide the local authority with a complete range of solutions for optimized flow transfer management, continuously and in real time, heading downstream,” states Bernard Willinger. “In times of flood, we can therefore regulate these watercourses on the point of overflowing, without them ever overflowing!”
It has been an undisputed success: thanks to the combined action of the authority and Veolia, the floods of May 2016 – 80 mm of continuous precipitation recorded in two days – did not cause any damage for local residents. On the contrary, during this same rainy episode, those living near another river in a neighboring valley that does not enjoy the same infrastructure, suffered an estimated 35 million euros’ worth of damage.
An open, adaptable system
The Bièvre Valley optimal flood management and prediction system run by Veolia is enriched each year by data collected on the ground. “It’s an open system,” states Bernard Willinger, “which allows us to offer tools that are constantly evolving, such as computer and mathematical models that decipher the impact of the rainfall forecast regarding the river basin in real time using RADAR imagery. This helps us better predict the rivers’ behavior faced with precipitation, and take into consideration the saturation of soils, depending on whether they are located in an urbanized or rural area, obviously with different runoff percentages. We can consequently adapt our flow transfer management to lastingly protect residents, which is our priority.”
A model that has been exported… as far as Cambodia
The Bièvre’s automated flood management system has made a name for itself beyond the greater Paris region, both in France and abroad. Especially Cambodia, where we find a key World Heritage site: the valley of the Angkor temples, which are all located at the heart of an age-old network of canals, built in the 13th century at the height of the Khmer Empire, which had to be renovated to protect the site from flooding
The project was “entirely based on the experience gained in the Bièvre Valley,” underscores Thomas Joly. “We worked with the Veolia foundation to hold back the water around the temples to stabilize the land on which they are built.”
• 16 municipalities i.e. 200,000 inhabitants
• 3 departments
• 130 km2 (Bièvre river basin surface area concerned by the project)
• 20 km south-west of Paris + 18 km of tributaries under continuous surveillance
• 17 storage basins with a capacity of 800,000 m3
*Main partners: Veolia, the Veolia foundation, the Greater Paris public sanitation service SIAAP, SIAVB, the Friends of Angkor Association, APSARA.