March 7, 2017 | By Shoal Creek Conservancy
This blog post was written by Andy Sobchak. To learn more about the author, please visit this site.
In a race to flood resiliency, cities around the world are taking vastly divergent paths. Some are building mega infrastructure to store or divert floodwater. Others are returning urban watersheds to more natural states to reduce the quantity and peak rate of runoff. Others still are building amphibiously and letting the floodwaters in.
The Shoal Creek Conservancy released last week the City + Water showcase to highlight some of these methods, but with space for only 10, a number of radical yet plausible ideas didn’t quite make the cut. In the spirit of outside-the-box thinking, its worth unpacking a few of them here:
In 2016, the Universities of Birmingham and Southampton in the United Kingdom jointly released a study which suggested planting trees in creek floodplains and upper areas of a watershed could reduce downstream flooding by up to 20%. The trees in sufficient density provide a flow barrier which slows down runoff and could be used strategically to manipulate runoff timing throughout a watershed. By way of their ever-expanding root network, trees also loosen the soil (i.e., increase porosity) increasing infiltration and reducing runoff quantity. Planting floodplain trees or implementing any green infrastructure which slows down runoff in Shoal Creek’s upper watershed could allow runoff from mid-to low-watershed areas to drain out of the Shoal Creek system before upper-watershed runoff arrives in the downtown core.
Parking Garages, Basements and Vacant Lots
In 2011, Rotterdam put the finishing touches on an underground parking garage which also doubles as a water storage tank during floods. Reportedly, the garage can store up to 10,000 cubic meters of water, or the equivalent of approximately four Olympic-sized swimming pools.
In Detroit, the Detroit Land Bank Authority is converting vacant lots and the basements of demolished homes into green infrastructure and stormwater storage opportunities. Unlike other cities in America pushing the envelope of low-impact development – or redevelopment – Detroit has the unusual luxury of space. The DLBA controls 66,125 vacant parcels and in 2016 alone razed 2,112 structures.
In 2013, the City of Cedar Rapids (Iowa) completed construction of the 5,000-person McGrath Amphitheater, a Cedar River-adjacent concert venue which converts to floodwater storage facility. Indeed, flooding amphitheaters is a practice dating back to the Roman era as emperors of the time, including Caesar, Claudius and Nero, would flood amphitheaters to re-enact naval battles. The most significant of these bloody naumachiae was staged in 80 A.D. when Rome’s Colosseum was flooded. Although the Roman focus was entertainment, the Cedar Rapids approach of flood mitigation could be applied in Austin. Could House Park Stadium be redesigned to provide effective flood storage?
Communities in Australia, California and Florida are all experimenting with using stormwater to replenish groundwater supplies in a process known as aquifer storage and recovery (ASR). The typical approach to ASR includes pumping or infiltrating drinking-quality water into under-capacity aquifers – permeable layers of soil or rock – as a form of storage during times of surplus. The water would then be pumped out of the aquifer during times of need.
Aquifer storage of stormwater requires considerations for water quality. To prevent contamination of the aquifer, either the stormwater is pre-treated or only clean stormwater (i.e., harvested rainwater) can be used. If these quality issues can be resolved, storing stormwater in natural locations underground could provide great benefit. Whether aquifers can be used as a flood mitigation tool depends on how quickly water can be directed underground.
Bridges or culverts can often cause riverine flooding if they present a constriction to watercourse flow, especially during very large storms. Conversation in our community has speculated if removing bridges, specifically the West Avenue or the W. 9th Street bridges, could help reduce Shoal Creek’s flooding in the downtown core. Many of the bridges over Shoal Creek have historical value and consideration of their removal would need to occur in this context, but if there is no desire for their preservation and traffic impact is limited, their removal could provide some benefit.
For the same reasons bridges can constrict flow, online control of a creek by a man-made weir is a contentious issue. Some municipalities in North America forbid it; others consider it under certain circumstances. A weir (think a small, low-profile dam made of natural or artificial materials which allows water to flow around, over or through it) or series of weirs could be implemented along Shoal Creek to help maximize flooding in locations deemed low risk (e.g., parkland) and minimize flooding in high risk areas. During low flow, the weirs could also help restore the swimming holes which made the creek a recreational attraction in Austin’s early days.
Video: House Park Stadium courtesy Perry Henderson | YouTube
Discussion of radical ideas can lead to real, creative solutions. For lively conversation about water management in Shoal Creek, join representatives from the Shoal Creek Conservancy at the City of Austin’s first open house as part of the Shoal Creek Flood Mitigation Study.
Thursday, March 9, 6pm-8pm
Cirrus Logic, 700 West Avenue