The Coastal Built Environment in Southeast Florida and Sea Level Rise
Prognosis for potential damage and needed change
Ricardo A. Alvarez
NOTES FOR PRESENTATION
Today I will focus on sea level rise and its effects on storm surge generated by hurricanes. Regarding sea level rise it is my opinion that the current discussion focusing on a historical rate of rise of 1 mm a year, or even the more recent increased rate of 2.5 mm/year and rising, misses the point and gives the impression that it is happening so gradually and in such minute increments that, the potential for damage is equally minute and will only become significant over the course of centuries or millennia in the future. I believe we need to focus on the more immediate and clear threat that we can see every year with each storm surge generated by an approaching hurricane, or with every high tide that coincides with a full Moon and generates a highest high water mark, where we already see the ‘footprint’ of the accumulated sea level rise included in these progressively higher levels of water reaching our shores.
It is in the hazard of storm surge that we can see the real potential for damage being exacerbated by sea level rise. And truly damaging it is! I don’t know how many of you have had the opportunity of witnessing first hand the potential for catastrophic damage that can be caused by storm surge. To illustrate such potential for damage let me share with you a brief collection of photos, from my own collection gathered over 25 years of researching the impact of hurricanes: backgroundSTORMSURGE
The Built Environment
Often in our discussions of global climate change and sea level rise, we speak of urban planning, land use and the built-environment. Having been involved in this dialog for the last fifteen years, it occurs to me that we refer to the built-environment with some detachment, almost in abstract terms, along the same lines of what we do when speaking of urban infrastructure.
Yes, we all know what the built environment is; it is something important, out there, something that may be impacted by climate change and sea level rise, something, almost in the nature of a catch-all term that most of us have no time to think about let alone define.
Given how high the stakes are, let me offer the following thoughts:
- The built environment consists of the homes and buildings where we live, work, and play, where we procreate, where we take shelter from the elements and from hazards;
- The built environment is invaluable not because of how much it cost to build or how much it might cost to replace, but because of the function it provides;
- The built-environment fulfills a critically essential function in sheltering the full range of human activity.
Vulnerability of the Coastal Region
Like in many other regions, coastal communities in southeast Florida are exposed to sea level rise. The coastal built-environment in Southeast Florida is vulnerable to sea level rise.
How may sea level rise (SLR) cause or contribute to potential damage to the built-environment?
- Rate of SLR continues to increase;
- SLR will exacerbate storm surge;
- Deeper storm surge water will translate into faster flow (approx. 10% increase in flow velocity for every 300 mm in depth);
- Faster flowing storm surge equals an exponential increase in the energy of impact on buildings; hydrodynamic pressure increases in direct proportion to the square of the velocity of flow;
- Deeper storm surge will result in higher waves above still-water level;
- Breaking waves against buildings will increase by 120 mm for each 100 mm of sea level rise, and generate much higher impact loads on buildings;
- The horizontal component of sea level rise ranges from 150 to 200 times the rise, which means an increase of 300 mm over current levels will result in one additional square kilometer of land becoming vulnerable to storm surge, for every 16.5 kilometers of coast line;
- Increased sea level, faster flowing water will contribute to higher rate of beach erosion and loss of sand;
- This vulnerability is a dynamic process; as more urban development takes place to accommodate increments in population, there will be more people and property at risk from a hazards that will grow gradually more damaging because of continued SLR.
State of Preparedness
How prepared is our coastal built environment for these additional impacts? What is the state of our current defenses?
- The state of our defenses ranges from inadequate to non-existent, and tentative at best!
- Natural defenses such as: barrier islands, wide sandy beaches, dunes, and mangrove forests have been destroyed or rendered ineffective;
- Construction of inlets as an aid to navigation has disrupted natural transport of sand as a result approximately 50% of beaches are in critical condition because of loss of sand;
- Water management effective in reducing coastal flooding, but as SLR continues to increase system is becoming gradually less effective; in reality it does not protect the built environment against storm surge;
- Evacuation of the coastal zone, required by emergency management authorities when a hurricane warning is issued, protects human life but does nothing for the built environment;
- Beach nourishment using off-shore sources of sand is a temporary fix that does not address the root causes of the problem;
- Except for a few coastal structures specifically engineered to withstand the impact of storm surge and breaking waves, the vast majority of new buildings and existing stock have been built on the basis of design criteria that ignores sea level rise and the future impact of storm surge;
- Building codes and standards, even in southeast Florida with its reputation of having the toughest hurricane building code, are woefully inadequate. While the High Velocity Hurricane Zone of the Florida Building Code establishes strong minimum requirements to defend against the impact of wind, when it comes to the impact of water, which is 800 times denser than air at sea level, it basically ignores the problem;
- Flood maps and storm surge atlases used in Florida provide an idea of the extent and depth of flooding, but they lack the critical information on storm surge velocity of flow, which is required to quantify potential loads acting on buildings;
Potential for Damage
A recent study [2011] on vulnerability of residential structures to storm surge in Miami-Dade indicates there were 254,864 low-density residential properties, valued at $53.6 Billion, at risk of being damaged by storm surge as of 2009. This study only took into account the construction cost of the building, but not the value of contents or human life.
Limited as this study was it provides us with a glimpse of what the true value at risk could be in the tri-county [Broward, Miami-Dade and Palm Beach] region. The study could be used in combination with U.S. Census data to extrapolate and include the value of commercial buildings, schools, health-care facilities, transportation, communication and public services infrastructure that may also be at risk not only in Miami-Dade, but in the larger tri-county region. By adding the value of contents, and more importantly the value of function and services rendered from all of the buildings at risk, we could arrive at an approximation for the true potential for damage.
What is that number today, $600.0 – $800.0 Billion? More than a trillion dollars? Taking into account the dynamic nature of this process, perhaps the question should be: what will the value at risk be in 2020 or 2050?
In reality, more than the cost of replacing structures, the cost of contents, the cost of services and functions, it is our way of life as we currently know it for those who reside in coastal southeast Florida that is truly at risk. How do we attach a dollar sign to that?
Essential Change
It is clear critical changes are needed on several fronts to reduce the potential for damage to the coastal built environment from the impact of SLR.
Not only is such critical change needed, but it is essential to the survival of southeast Florida as a viable region.
In considering this need for essential change, it is critically important to view this not as one single action or a few significant changes that are implemented by a given date. We must think of this as a long term process involving a continuum of essential changes that will take place over the long term.
Some changes can be identified and assessed now, but others will require research and studies in order to determine their viability or methodology of implementation. What we can do now is identify areas of research that will help in this process.
Changes we can assess now:
- Change design methodology for all new buildings in the coastal region, so that design criteria includes hydrodynamic loads from storm surge and wave action on the basis of expected conditions during service life of structure;
- Establish required re-certification of all buildings currently vulnerable to SLR/storm surge and incorporation of adaptation measures;
- Modify regulatory framework [land use, zoning] to limit/preclude projects that increase overall value-at-risk either through new construction or renovation of existing buildings;
- Consider gradual modification of water-management methodology to migrate from a drainage-dependent system to one where water storage becomes an incrementally larger and growing component;
These changes are based on a building-by-building approach to the design of every new buildings and the gradual modification, through retrofit or renovation, of the existing stock of vulnerable structures.
While this will improve our defenses it will not address the hazard itself. This approach will allow buildings to interact with the hazard and offer enhanced resistance to causes of potential damage, but as SLR continues to increase and exacerbate coastal hazards this approach may also prove to be inadequate over the longer term.
In view of this, it is also essential that we consider alternatives for regional protection by way of measures that will essentially keep the hazard away or at the very least reduce or dampen the energy of future impacts. Here we are talking about developing a Southeast Florida SLR Adaptation model, which may borrow from existing models such as the Dutch or the Venetian.
Areas of Needed Research
- Research velocity of storm surge flow on a basin-specific basis to develop data base to assist design professionals in calculating hydrodynamic loading conditions for new or existing buildings on the coastal zone;
- Research development of new, or modification of existing, building materials or components to address new conditions that may affect their performance, such as corrosion because of salt water contact, or resistance to higher impact loads;
- Research how soil saturation, as a function of SLR, will contribute to hydrostatic loads applied to the foundations and underside of buildings and structures. Use research to develop maps of the coastal region showing range of expected hydrostatic loads by location. This will assist design professionals in designing for such loading conditions;
- Research alternatives for issue of permeability of limestone to determine feasibility of erecting off-shore protective structures;
- Research feasibility of developing large scale water storage capacity on the western fringes of the tri-county urban area, as well as combining that with deep water injection into the aquifers;
- Research viability of floating cities;
- Research/develop time-lines for implementation of various adaptation alternatives taking into account time for necessary research, impact studies, other regulatory issues, funding and design/construction phases;
- Research future worst-case scenarios where relocation or abandonment may become more cost-effective than adaptation.
In closing let me leave with the following thought: When it comes to sea level rise, Humankind, WE are already at a crossroads, and we have two alternatives: (1) We continue with the business as usual approach and let Nature take its course, while we remain passive bystanders, or (2) We take action and guide the process of adaptation son our built-environment interacts with nature and we reduce the potential for damage!