Allowing stormwater to recharge groundwater may help solve urban water problems
The Indonesian capital of Jakarta is a dramatic example of some increasingly common water problems because it faces a triple threat:
- The sea level is rising from climate change.
- The city is sinking due to low aquifer water levels from overuse.
- Impervious concrete covers so much ground that the rain can no longer recharge the aquifer.
Rain that could keep wells from running dry and stop Jakarta from sinking instead flows over pavement and into the Java Sea. As much as 40% of Jakarta is already below sea level, so the stakes should not be underestimated.
Mitigating Water Problems
Many cities worldwide have faced some variation of these problems and have successfully been using new mitigation strategies. Take, for instance, the widespread use of impervious concrete. When too much of a city is covered in concrete, stormwater is lost as runoff instead of filtering through the ground to replenish aquifers.
Solutions range widely in scale, from individual residential features such as rain gardens, green roofs, ponds, and rainwater harvesting systems, to municipal infrastructure solutions like curb cuts, lagoons, swales, and meadows.
Another urban solution is pervious pavement, which allows stormwater to flow freely back into the ground and into aquifers. Until recently, perviousness was achieved mainly by coating gravel aggregate with cement paste, which leaves air space through which water can pass. Pervious pavement has found limited use, mostly in urban parking lots and applications with little traffic because its porousness limits its durability and, consequently, its suitability for many applications.
Environmentally Friendly Solution
Researchers from the Department of Civil and Environmental Engineering at Washington State University in Pullman, however, have found an inexpensive way to increase the tensile strength of pervious concrete and solve an industrial waste problem in the process.
Nearby Boeing donated a quantity of carbon fiber waste from aircraft production, and the researchers, led by Karl Englund and Somayeh Nassiri, used inexpensive milling techniques to create a composite with pieces of ideal shapes and sizes. They then used the aggregate to create a pervious concrete that actually matches the tensile strength of traditional concrete while still allowing water to flow through freely.
This new material is very useful in several ways:
- Strengthening pervious pavement could widen its use.
- Full-scale production would also dispose of carbon fiber waste, which has been a problem for industry. Since the material requires a great deal of recycled carbon fiber waste, it stands to make a significant dent in disposal needs.
- The process achieves these benefits with minimal use of chemicals and energy.
The research team has now turned its energy toward testing and mainstreaming the material, as well as creating a supply chain in cooperation with industry.
Once tested and proven, such a pervious pavement could help solve the water crises of sinking, concrete-bound cities by allowing the rain to do its natural job of replenishing groundwater.