Making florida flood impact resilient by nature 041216

© Marco Pluijm, 04/12/2016

Artist's conception of what encroaching water could do to the mid-beach area. Ref. Photo-Illustration by Darrow; © Richard Cavalleri / Vanity Fair

Making Florida Flood Impact Resilient by Nature Marco Pluijm M.Sc. Senior Expert Ports and Coasts Key Elements: Climate Change; Extreme Event Impacts; Flooding, Adaptation; “Resilient by Nature” Summary

This paper is about which mitigation and protection strategies are seen as viable solutions for solving the challenges Florida is facing in terms of sea level rise, flood control and hurricane impact safety and resilience.

Based on the Resilient by Nature approach, which finds its origin in what can be learned from coastal zones which face similar impact exposures or even worse and suffer less damage or hardly any at all. Translating those capabilities to areas less flood and extreme weather impact resilient, such as large parts of Florida.

Solutions for the affected areas are presented as input towards a safer and much more resilient coastal system for Florida and similar places, with regard to a rapid changing climate, accelerated sea level rise and overall related extreme weather impacts.

In order to prevent the situation that large parts of the built environment of Miami and the Keys will become the new Atlantis, sunken and lost cities.


Introduction

Florida is in one of the US States, challenged extensively by accelerated sea level rise and climate change extreme weather impacts, such as hurricanes and excessive downpour. Events, which are happening more often and with much greater intensity than before and ever anticipated for in terms of response and mitigation. Additional challenge is the low-lying character of large parts of Florida, such as Miami and the Keys. Due to which combination of factors, flooding is beginning to rise to excessive proportions. In order to be able to reduce the effects of inundations and flooding, the authorities have invested large sums of money in pumping installations.

Which for the short term seems to be a viable solution. However, for the longer term, without investing in proper means to keep the floodwater out and under control in the first place, this is probably not to be considered as a feasible option.

Complicating factor in some areas is the porous and highly permeable limestone which forms part of the geological profile and which may require additional measures and mitigation in this respect.

Due to frequent flooding, there’s the risk of depreciation of property and devaluation of the affected areas, often those areas which have invested most, such as the ones along a waterfront. A trend which has clearly taken off.

In addition, the floods create sanitation issues and impacts on the terrestrial environment. Valuable vegetation and other characteristic features will get affected by salt water and can disappear, in which case the landscape is about to change and some of it can disappear completely.

In order to provide adequate overall response, it is crucial to differentiate between relative slow developing processes such as sea level rise and high impact events such as hurricanes. Consequently asking for different solutions.

Plan and Design Data under Pressure

Climate change comes faster and is much more intense than so far anticipated for. The challenge now is to assess how much faster and the increase in intensity.

Traditionally plan and design data are based on historic data, trend analyses and statistical forecasting. All with their own uncertainties and bandwidth. As a consequence of which, given the number of variables involved and the way they interact, it’s basically unknown what tomorrow will bring in terms of increased weather activities and how those will impact the plan and design conditions of today. In all respect, demonstrated by the sheer endless number of scenario’s and data analysis which are continuously produced in high numbers, without actually delivering data which can be used for adequate planning and design of extreme weather impact solutions.

With in there, the given fact that if and when a trend breach will occur, one will only know when it happens. Simply because you can’t forecast a trend breach.

Reason why alternative plan and design procedures and approaches are required in order to be able to keep up and encounter the challenges nature is delivering time and time again.


Resilient by Nature Approach

The Resilient by Nature approach is based on what can be learned from coastal systems which appear to have a built in natural resilience. Coastal systems and features which are hit by extreme weather phenomena, often over and over again, without suffering too much damage or hardly any damage at all. And are able to recover soon after by themselves or with just a little help from outside.

Within the Resilient By Nature approach, a number of coastal systems with such natural resilience have been identified and their characteristics analyzed and translated into parameters, which can be transferred to other, more vulnerable coastal stretches. By translating and implementing these characteristics as system components rather than adjusted, engineered designs. Thus delivering sustainable and resilient solutions. Instead of following a traditional maintenance approach such as for instance sand nourishments, often applied in those parts of the world with abundant quantities of sand and contractors who can handle those effectively. Sand nourishment is an approach which is some kind of effective for the time being, but by no means a sustainable solution for the longer term. Not even in aforementioned areas.

Therefore, in order to be able to deal with the climate change impacts as they appear today and are expected to intensify much faster than originally anticipated for, tomorrow, such an alternative approach is definitely required. A holistic approach rather than engineering on the basis of unreliable input data.

Resilient by Nature is such an holistic approach, suitable and appropriate for proper planning and implementation of safe and resilient coastal impact solutions when it comes down to dealing with accelerated climate change impacts for coastal areas.

More information about the Resilient by Nature approach and toolbox can be found on :

www.slideshare.net/MarcoPluijm/hurricane-‐impact-‐preparedness-‐and-‐resilient-‐by-‐nature-‐recovery Towards a Sustainable and more Resilient Approach

Where areas get flooded on frequent basis, such as Miami and the Keys, usually the first ones to take action are the affected individuals who take the initiative to protect their assets and limit the damage. For instance to build or raise flood protection around their land plots or raise the properties themselves by putting them on stilts or terps (raised grounds). Basically doing the same as the original inhabitants in the old days when colonizing low lying areas such as the Netherlands.

Which today is basically no longer an option, because many things have changed since, such as population density and the need for additional infrastructure and utilities. Reason why such individual solutions are no longer a viable solution when it comes down to protect communities. And why a more integrated, less individual approach is an absolute requirement. Which today is supported by many authorities.

Because when an integrated approach fails to get sorted properly and implemented, the individual efforts will fail eventually as well. Which in this case could mean that


large parts of the built environment have to be given back to the sea. A trend which already has taken off.

Consequently there’s an urgent need for integrated solutions which make optimal use of the assets and resources which are available, sharing what can be shared and differentiate between various needs and solutions, reducing impacts and directing the negatives to where they do the least harm.

Adequate sets of coherent and reliable inundation maps and topographical data are a key element for drawing up such integrated, adequate solutions.

Resilient by Nature based Solutions

The accelerated climate change induced phenomena to deal with here are :

• Accelerated sea level rise, including King Tides, both in frequency and intensity and so the need for adequate drainage, storage and discharge capacity

• Extreme weather impacts, leading to beach erosion and decay of coastline infrastructure, wave set up and storm surges, extreme downpour and flooding all together and therefore to the need for impact reduction, adequate surface water run off, storage and discharge.

The current response strategy in Miami (and to lesser extend the Keys) is to encounter and limit the effects of King Tides and Sea Level Rise induced floods by means of pumping the water out, once it has got in, in combination with raising flood defenses and foundation heights in parts of the affected built environment.

As such rather adequate mitigating measures for the moment, but as outlined earlier by no means a sustainable solution for the longer term.

Differentiation between affected areas on the basis of topography, sea-level rise predictions and inundation risks can provide fairly reliable indications about how to prioritize between most and least affected and valued areas and how to direct the incoming water to adequate storage areas and free run off drains and discharge facilities. For plan and design purposes, the affected built environment is sub-divided into mini-watershed areas, zones with equal flood and inundation risk, storage and run-off capabilities.

One of the essential base materials for planning and design are up-to-date flood maps and topographic data for all affected and also not yet affected areas, as one complete set of documents.

Additional feature, when preparing for this Florida flood and impact analysis, is that multiple references were found with regard to the porosity of large parts of the subsoil. Which is believed to be a relevant given, however of limited impact with regard to flood-water intrusion and management.

The actual impact of subsoil porosity with regard to salt water intrusion and related flooding is considered limited due to the characteristics of groundwater flow in direct relation to the water surface elevation (gradient during the tidal cycle) and the limited duration of that tidal cycle. However under those circumstances where the internal, landside response would be almost equal to the outside waterlevel changes, solutions like enhanced vertical drainage and/or deep penetration with artificial or


natural sealants (silt, clay) can be considered as options to reduce and redirect the seepage in combination with adequate horizontal drainage, storage and discharge, either natural (free flow during low tide) or by pumping.

In case of the additional extreme weather challenges Florida is facing, such as hurricanes and storm-surges, most appropriate natural solutions are considered to be the creation of hurricane impact barriers and sub-division of coastal stretches into low impact entities, all together reducing wave attack, set up and surge by means of creating guided flow and overflow (wash) conditions.

Hurricane shaped barriers as referred to in the Resilient by Nature approach and toolbox, differ from traditional offshore breakwaters in the sense that their efficiency is based on controlled over-wash and gradual wave energy dissipation and surge reduction.

With respect to the net effect of sub-dividing coastal stretches into smaller hydro-morphological units, reference is made to a paper about the subject called “Hurricane Impact as Resiliency Master Class”, to be accessed via :

www.slideshare.net/MarcoPluijm/hurricane-impacts-as-resiliency-master-class-11112016

Sub-dividing coastal stretches in more stable hydro-morphological units, with proven net results under hurricane conditions, properly laid out, can make a substantial difference of decimeters reduction in wave set up, surge and related currents. And so reduction of dynamic and static waterlevels along the affected coastlines, limiting impacts such as erosion and flooding.

In addition, these overflow barriers can be designed as such that activities on the surface can be developed within the clear understanding that during the extreme event ,free flow over the barrier is guaranteed.

Conclusions

Time’s up if we don’t want Miami and the Keys to become the new Atlantis, to become lost and sunken cities.

Current initiatives by local authorities and individual efforts deserve all respect and support, but may eventually fail without further integration and system implementation. Which may result in the fact that part of the built environment needs to be given up.

Adequate solutions with appropriate funding go hand in hand. Using natural processes and phenomena are expected to contribute significantly to cost reductions and savings for all involved.

The Resilient by Nature approach is based on what can be learned from systems with proven safety features and natural resilience built in, translated to areas which are less safe and resilient, such as in this case large parts of Florida.

In order to prevent such loss of land and assets, integration of efforts and concentration of functionalities is an absolute requirement. To secure safe flood protection infrastructure by connecting flood walls and other infrastructure of sufficient elevation relative to storm surge levels, including adequate safety margins and internal redundancy and flexibility. Cost savings can be achieved when


combinations can be made with existing road- and coastal infrastructure and plots of land with sufficient elevation. Sub-dividing the entire affected area into mini-watershed entities of manageable size and characteristics.

Equipped with adequate drainage capacity and facilities in order to direct flood water to the desired locations, such as direct discharge and storage ponds. Instead of allowing water-masses to accumulate at accidental low lying depressions without proper discharge capacities.

Free run off and discharge is to prefer over pumping, depending on the level of the drainage system relative to low water tidal levels.

In addition, where seepage contributes significantly to the overall quantities of incoming water, enhanced vertical drainage may be required in order to concentrate the seepage to where it does least harm. Which may require additional deep-injection with natural sealants, such as clay or silts.

In order to enhance shore line protection against direct storm hits, set up and surge can be achieved by creating over-wash breakwaters at adequate distances according to the planning and dimensions as they follow from the Resilient by Nature toolbox of solutions with proven natural resiliency.

Where needed and effective, in combination with creation of additional onshore over-wash and discharge capacity in order to reduce water level set up along the shoreline.

Traditional offshore rubble mound type of breakwaters won’t deliver the required performance due to their limited dimensions, size, height and hydraulic characteristics.

Phasing and funding of what’s proposed against what needs to be protected and when, is subject of further detailing, to be provided upon request.

Resilient by Nature Community The Resilient by Nature Community is an informal platform for exchange of information and experiences between people who are interested and/or involved in coastal systems in relation to extreme weather impact, safety and more effective resilience. Systems ideally with the potential and capacity to get implemented elsewhere and to be included as part of the Resilient by nature approach and toolbox. More information can be obtained via email on [email protected]

Making florida flood impact resilient by nature 041216

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