Page 54 - Green Builder Sept-Oct 2016

A large underground parking garage is under construction in CREDIT: WWW.GEOGRAPH.ORG.UK
Rotterdam, Netherlands, and will hold water instead of cars during
peak floods. Avoiding disaster. Managed retreat prevents construction too
close to vulnerable shorelines, which can lead to destruction of
A “village blue” has been proposed for several towns in the buildings as sea levels rise.
United Kingdom experiencing increasing river flood problems
and growing populations. This concept is a central recreation area, The “managed” part of retreating from the shoreline involves
complete with swimming and boating facilities, that becomes an establishing thresholds to trigger activities such as demolishing
expandable lake in flood conditions. buildings or abandoning efforts to control shoreline erosion. These
thresholds can be coupled with buy-back programs to compensate
The Good, the Bad and the Unknown property owners for loss, plus strict building codes that allow only
certain types of relocatable or floodable structures.
Advantages: Floodable development could take an effective small-
scale toolbox to the next level. It may best be thought of as a suite of Examples
tools (including LID) that can be selected based on which work best
at a given site. But unlike LID, the floodable development suite of Construction setback rules in most coastal areas and Great Lakes
tools is still experimental. Some tools may be better for fresh water, states allow development only within a certain distance of the water’s
salt water or a mix, while some may be better in urban areas versus edge. California has delegated this authority to local coastal programs
agricultural or rural areas. in partnership with the California Coastal Commission. Historically,
California set the line using calculations for a 100-year storm.
Disadvantages: Floodable development could be hazardous. Of course, many older structures don’t comply with current setback
Stormwater, particularly at the seaward end of a watershed, is usually rules.
polluted with heavy metals and organic chemicals, in addition to
sediment and bacteria. Large quantities of stormwater sitting on Funding programs in North Carolina and New Jersey allow
the surface or in underground storage facilities could pose a public states to purchase storm-threatened or coastal buffer properties.
health hazard during a flood or leave contamination behind. This
could be a particular problem in areas with combined sewer systems, Relocation is being tried with larger and larger structures.
such as San Francisco, where wastewater and street runoff go to the In 1999, the historic Cape Hatteras Lighthouse was moved 3,000 feet
same treatment system. inland from an eroding beach in the Outer Banks of North Carolina.

Also, wastewater treatment systems that commonly treat the Voluntary erosion-control “rolling” easements in Texas and
hazards of combined sewer effluent before releasing it into natural South Carolina vary landward from a rising high tide line. These
waters do not work well with salt water mixed in. If floodable rolling easements allow for continued private property ownership
development strategies are designed to hold and release brackish and development, with restrictions only on armoring and public
water, new treatment methods will be needed for the released water access.
to meet water quality standards. Finally, emergency communication
tools and extensive public outreach and management would be The Good, the Bad and the Unknown
required to prevent people from misusing or getting trapped in
flooding zones. Advantages: Managed retreat minimizes human suffering by
relocating buildings and infrastructure to safer ground before a
Unknowns: Floodable development is untested. We don’t know
if buildings and infrastructure can be designed or retrofitted to
accommodate occasional flooding in a cost-effective way. Also, it
is not clear exactly how much volume new floodable development
tools will hold. Some of the more heavily engineered solutions, such
as a water-holding parking garage, may not turn out to be more
beneficial than armoring or investments in upsizing an existing
wastewater system.

MANAGED RETREAT

What it is: The planned abandonment of threatened areas near
the shoreline.

Managed retreat is a strategy that safely removes settlement from
encroaching shorelines, allowing the water to advance unimpeded.
It involves abandoning, demolishing or moving existing buildings
and infrastructure to higher ground. It also includes banning
new development in areas likely to be inundated. It is used when
coastal armoring and other shoreline protection efforts become very
expensive, or are judged to be a losing battle.

52 GREEN BUILDER September/October 2016 www.greenbuildermedia.com