Geosynthetics have provided a wide range of flood defense solutions around the world. They are used to halt erosion, strength coast lines and riverbanks. They support dunes and prevent sand wash out in the face of hurricanes. They provide alternatives to sand bags. For many projects, they provide essential levee reinforcement to provide long-term defense against flood threats.
Here, we summarize and link to some of Geosynthetica’s exemplary stories regarding geosynthetic strategies in flood defense.
Flood Protection with High-Strength Reinforcement
The summer 1997 flooding along the Oder River was part of what was called the Millennium Flood. It was the largest known flood along this major waterway border between Germany and Poland. The event lasted several weeks. On the German side, numerous dikes broke and around 5,500ha of agricultural land and settlements with around 400 residential buildings were flooded. Several thousand people were evacuated.
This disaster and subsequent weaker floods damaged the dike system in many places. Weak points in the dike geometry and subsoil problems were identified as causes of many of the breaks.
Since the events of 1997, dikes in this region have been rehabilitated or rebuilt entirely. Another phase of work was instituted in 2018 and 2019, within which one can find exemplary uses of geosynthetics.
Geogrid reinforcement was used along a 3km-long section of a new flood protection dike. The high-strength reinforcement geogrid (NAUE Secugrid® HS 1000/100 R6 geogrid) enabled the construction of the dike over relatively thick, soft layers of peat, mud, and clay.
The entire dike section required approximately 63,000m² of geogrid. A geosynthetic clay liner (GCL) was installed as a water-side sealing element.
RELATED: Revisiting LPV 111 and Geosynthetics in NOLA Levees
Controlling Coastal Flooding Impact with Geocontainers
For more than a decade, communities along the Sunshine Coast in Australia have utilized geosynthetics to mitigate the impact of storms on shorelines and to guard against future sea level rise.
One of these flood defense strategies previously profiled on Geosynthetica involved ELCOROCK® geocontainers for revetment on a highly erodible beach. The revetment provided 200 lineal meters of erosion protection to Mooloolaba Beach. The success of a 2010 installation led to an extension of the system in 2015.
The project came at a perfect time. A cyclonic storm washed away a significant amount of sand from in front of the revetment; behind the revetment, the beach was preserved and the geocontainer system remained intact.
Around the same time on a New South Wales coastal erosion hot spot, storm surges had stripped 1m of seafront per year. Homes had been lost. One property owner lost 40m of foreshore over 12 years!
The landowner’s installation of geotextile sand containers halted beachfront loss. Flood waters from a strong storm greatly affected the surrounding beach area but not the property protection by the geocontainers.
Geosynthetic Flood Defense Walls
The small town of Smithland, Kentucky is situated at the confluence of the Ohio and Cumberland Rivers. As a record flood began to develop in 2011, with very little notice, the US Army Corps of Engineers responded with one of the more unique approaches we’ve published on Geosynthetica: geosynthetic flood walls made of geotextile cells.
Within 24 hours of receiving a call from USACE, three miles worth of units of a system called Defencell Flood Wall were delivered. These stackable elements would provide almost four feet of additional flood protection height to a key stretch of the levee in Smithland.
The solution enabled placement, connection, and filling to begin quickly with conventional skid steers enabling much of the work. In just the first three hours, the Corps’ site crew achieved an installation rate of 20+ units per hour. It provided an equivalent protection 22,000+ sandbags!
Over the next 34 workable hours, more than 10,500 linear feet of the flood wall system had been installed. More than 4,700 tons of sand were used. The flexibility of the system enabled it to contour to uneven ground surfaces with minimal prep work, makes angles and curves, while being lightweight and man portable for ease of placement. A simple tarp was secured atop the system for additional support against the rising waters.