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Tidal flooding


Regardless of the causes, southeast Florida, with a population of 5.6 million (one-third of the State’s population), is among the most vulnerable areas in the world for climate change due its coastal proximity and low elevation (OECD, 2008; Murley et al. 2008), so assessing sea level rise (SLR) scenarios is needed to accurately project vulnerable infrastructure (Heimlich and Bloetscher, 2011). Sea level has been rising for over 100 years in Florida (Bloetscher, 2010, 2011; IPCC, 2007).  Various studies (Bindoff et al., 2007; Domingues et al., 2008; Edwards, 2007; Gregory, 2008; Vermeer and Rahmstorf, 2009; Jevrejeva, Moore and Grinsted, 2010; Heimlich, et al. 2009) indicate large uncertainty in projections of sea level rise by 2100. Gregory et al. (2012) note the last two decades, the global rate of SLR has been larger than the 20th-century time-mean, and Church et al. (2011) suggested further that the cause was increased rates of thermal expansion, glacier mass loss, and ice discharge from both ice-sheets. Gregory et al. (2012) suggested that there may also be increasing contributions to global SLR from the effects of groundwater depletion, reservoir impoundment and loss of storage capacity in surface waters due to siltation.

Why is this relevant?  The City of Fort Lauderdale reported last week that $1 billion will need to be spent to deal with the effect of sea level rise in Fort Lauderdale alone.  Fort Lauderdale is a coastal city with canals and ocean property, but it is not so different from much of Miami-Dade County, Hollywood, Hallandale Beach, Dania Beach and host of other coastal cities in southeast Florida.  Their costs may be a harbinger of costs to these other communities. Doing a “back of the napkin”  projection of Fort Lauderdale’s cost for 200,000 people to the additional million people in similar proximity to Fort Lauderdale means that $5 billion could easily be spent over the next 100 years for costal impoundments like flap gates, pumping stations, recharge wells, storm water preserves, exfiltration trenches and as discussed in this blog before, infiltration galleries. Keep in mind that would be the coastal number and we often ignore ancillary issues.  At the same time, an addition $5 to 10 billion may be needed for inland flooding problems due to the rise of groundwater as a result of SLR.

The question raised in conjunction with the announcement was “is it worth it?”  I suggest the answer is yes, and not just because local politicians may be willing to spend money to protect their constituents.  The reality is that $178 billion of the $750 billion economy of Florida, and a quarter of its population, is in the southeast. With nearly $4 trillion property values, raising a few billion for coastal improvements over 100 years is not an insurmountable task.  It is billions in local engineering and construction jobs, while only impacting taxpayers to the tune of less than 1/10 of a mill per year on property taxes. This is still not an insurmountable problem.

I think with good leadership, we can see our way.  However, that leadership will need to overcome a host of potential local community conflicts as some communities will “get more” than others, yet everyone benefits across the region.  New approaches to working together will need to be tried.  But the problem is not insurmountable, for now…

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A recent Rolling Stone article outlines a potentially dismal future for south Florida.  I was quoted in the article and give the author a bunch of information.  It is hard to write articles that “pop” in the popular press while conveying facts and figures.  But I would suggest that the future is not quite as dismal as the article depicts.  The sea level rise has been ongoing for at least 140 years as indicated by the Key West tidal station, the longest running tidal gauge in the world, but the amount has been 9 inches since 1920.  True it appears that the sea level rise may be accelerating as a result of warming temperatures in the atmosphere that causes the oceans to expend, plus the loss of ice that runs off from glaciers, but 3 feet by 2100 seems the average or maybe the high average.  That is unlikely to inundate all of south Florida, but keeping the water table low will be a challenge.  I suggest that the challenge can be met and accomplish two goals.  In low lying areas the impact of sea level rise is really manifested as increasing groundwater tables.  An increased groundwater table means less soil storage capacity, which means smaller rainstorms will cause flooding.  The increased flooding is already creating a demand by residents for solutions from local public officials.  We have used exfiltration trenches (French drains) for many years, but increasing water tables will mean many of these systems will not function as they may be currently.  But what if we reverse the concept?  Instead of exfiltration, what if we allowed the water to infiltrate the pipe and go to a central wet well, and then pump the water out of the wet well?  I further suggest that the dumping large quantities of groundwater to the ocean or canals may not be permittable as a result of high nutrients, so what if this water is instead pumped to a water plant as a raw water supply?  Wouldn’t that solve two problems at once? Lots of excess fresh water supplies in an era where there are significant limitations in fresh water supplies?  Just thinking….. 

 

 


The concept of horizontal wells arises from riverbank filtration concepts.  Riverbank filtration has been practiced for nearly 200 year in Europe, where the concept was to remove debris form polluted waters by drawing through the banks of rivers.  Much of the concepts for groundwater flow are related to the filtration ability of water to move through a porous media.  The concept was to dig trenches along the river and draw water from the trenches as opposed to the polluted rivers.  The concept worked relatively well.  The result is an abundant, dependable supply of high-quality water with a constant temperature, low turbidity, and low levels of undesirable constituents such as viruses and bacteria. Riverbank filtration also provides an additional barrier to reduce precursors that might form disinfection byproducts during treatment.

Now let’s look at this from another perspective, and we’ll pick on southeast Florida as is provides a great case study.  Sea level rise will inundate coastal property, both via coastal flooding and from a rise in groundwater. Since most stormwater drainage depends on gravity flow, drainage capacity will suffer as sea level rises reducing the head differential between interior surface waters and tide. Saltwater intrusion will be exacerbated. Furthermore, reduced soil storage capacity, groundwater flow and stormwater drainage capacity will contribute to increased flooding during heavy rain events in low-lying areas.  In low lying areas, current practices like exfiltration trenches will become impractical, as will dry retention will become wet retention.

Stormwater utilities will be faced with dramatic, currently unanticipated increases in capital expenditures and operating costs, and time will be needed for planning, design, securing permits and compliance. Additional local pumping stations on secondary canals will be needed to supplant the storm drainage system in order to prevent unacceptable ponding. Design capacities of these stations will depend on local rain patterns, drainage basin size and secondary canal system design.  Many will operate continuously, which means ongoing operations will increase substantially. Hundreds of pumping stations may be needed in some communities.

Permits will be a major challenge due to contaminants in the runoff as regulated by MS 4 Stormwater permits, and the inability to treat this water under the current structure. The cost and energy required for stormwater treatment would be a major concern going forward. But what if we sent this continuous flow to water plants as raw water?  All of a sudden we have a solution to two problems – stormwater and raw water supplies.  How often do you see a 2 for 1 solution?


If you live on an island, and your groundwater table is tidal, what should your datum be for storm water planning purposes?  Average tide?  High tide?  Seasonal high tide?  If you are the local official with this problem, what do you do, realizing that the difference from mean tide and seasonal high tide (when most flooding occurs) is 1.5 feet?  Realizing that property and infrastructure is at much higher risk for periodic inundation, does the failure to address the problem indicate a lack of willingness, understanding, hope or leadership?  We see all four responses among local officials, but the “head in the sand” mode is the most curious.  It’s tough challenges that often define leaders.  With sea level rise, there is time to plan, construct infrastructure in stages, arrange funding, and lengthen the life of infrastructure and property.  Meanwhile, those insurers, banks and the public we talked about in a prior blog wait and watch.


Talk Radio discussion

Hi All.

This is a radio show I did this week.  One of 4 I have scheduled.  It talks about me and my company, outlook, thoughts.  Take a listen.  Let me know what you think!

Fred


Based on my last blog, his inquiry came to me.  And I think I actually have an answer:  when bakers and insurance companies decide there is real exposure.  Let’s see why it will take these agencies.  There is very little chance, regardless of good faith efforts, significant expertise, or conscientious bureaucrats to stop growth and development.  The lobby is simply too strong and local officials are looking for ways to raise more revenues.  Development is the easiest way to increase your tax base.  As long as there are no limits placed on develop-ability of properties (and I don’t mean like zoning or concurrency), development will continue.  But let’s see how this plays out.  Say you are in an area that is likely to have the street inundated permanently with water as a result of sea level rise (it could be inland groundwater, not just coastal saltwater).  For a time public works infrastructure can deal with the problem, but ultimately the roadways will not be able to be cleared.  Or say you are located on the coast, and repeated storm events have damaged property.  In both cases the insurance companies will do one of three things:  Refuse to insure the property, insure the property (existing) only for replacement value (i.e. you get the value to replace) but no ability to get replacement insurance, or the premiums will be ridiculous.  We partially have this issue in Florida right now.  Citizen’s is the major insurer.  It’s an insurance pool created by the state to deal with the fact that along the coast, you cannot get commercial insurance.  So Citizens steps in.  The state has limited premiums, and while able to meet its obligations, in a catastrophic storm would be underfunded (of course in theory is should have paid out very little since 2006 since no major hurricanes have hit the state, but that’s another story). 

As the risk increases, Citizens and FEMA, the federal insurer, have a decision to make.  Rebuilding where repeated impacts are likely to happen is a poor use of resources and unlikely to continue.  Beaches and barrier islands will be altered as a result.  The need will be to move people out of these areas, so the option above that will be selected will be to pay to replace (move inland or somewhere else).  Then the banks will sit up.  The banks will see that the value of these properties will not increase.  In fact they will decline almost immediately if the insurance agencies say we pay only to relocate.  That means that if the borrowers refuse to pay, the bank may not be able to get its money out of the deal on a resale.  We have seen the impact on banks from the loss of property values as a result of bad loans.  We are unlikely to see banks engage in similar risks in the future and unlikely to see the federal insurers (Fannie Mae, Freddie Mac) or commercial re-insurers like AIG be willing to underwrite these risks.   So where insurance is restricted, borrowing will be limited and borrowing time reduced.  That will have a drastic impact on development.  The question is what local officials will do about it?

There are options to adapt to sea level rise, and both banking and insurance industries will be paying close attention in future years.  Local agencies will need a sea level rise adaptation plan, including policies restricting development, a plan to adapt to changing sea and ground water levels including pumping systems to create soil storage capacity, moving water and sewer systems, abandoning roadways, and the like, and hardening vulnerable treatment plants.  Few local agencies have these plans in place.  Many local officials along the Gulf states refuse to acknowledge the risk.  What does that say about their prospects?  Those who plan ahead will benefit.  Southeast Florid a is one of those regions that is planning, but it is slow process and we are only in the early stages.

Regardless of the causes, southeast Florida, with a population of 5.6 million (one-third of the State’s population), is among the most vulnerable areas in the world for climate change due its coastal proximity and low elevation (OECD, 2008; Murley et al. 2008), so assessing sea level rise (SLR) scenarios is needed to accurately project vulnerable infrastructure (Heimlich and Bloetscher, 2011). We know that sea level has been rising for over 100 years in Florida (Bloetscher, 2010, 2011; IPCC, 2007). Various studies (Bindoff et al., 2007; Domingues et al., 2008; Edwards, 2007; Gregory, 2008; Vermeer and Rahmstorf, 2009; Jevrejeva, Moore and Grinsted, 2010; Heimlich, et al. 2009) indicate large uncertainty in projections of sea level rise by 2100. Gregory et al. (2012) note the last two decades, the global rate of SLR has been larger than the 20th-century time-mean, and Church et al. (2011) suggested further that the cause was increased rates of thermal expansion, glacier mass loss, and ice discharge from both ice-sheets. Gregory et al. (2012) suggested that there may also be increasing contributions to global SLR from the effects of groundwater depletion, reservoir impoundment and loss of storage capacity in surface waters due to siltation. The loss of groundwater, mainly from confined aquifers, is troubling, and currently completely unknown. The contribution of carbon dioxide, commonly occurring in deep groundwater is also unknown. To gauge the risk to property in southeast Florida, Southeast Florida Regional Climate Compact and Florida Atlantic University reviewed twelve different projections of SLR and its timing. The consensus was 3” to 7” by 2030 and 9” to 24” by 2060. From the literature review and analysis, it was concluded that approximately 3 ft. of sea level rise by 2100 would a suitable scenario and time frame to illustrate the methodology presented in this article. To allow flexibility in the analysis due to the range of increases within the different time periods, an approach that uses incremental increases of 1, 2, and 3 feet of SLR was considered for risk scenarios. An issue normally ignored in sea level rise projections is groundwater. The importance of the groundwater table in the model is that it is responsible for determining the soil storage capacity. Soil is composed of solids, water, and air (voids). Soil storage capacity depends on physical and chemical properties, water content of the soil, and depth to the water table or confining unit (Gregory et al 1999). As the rain infiltrates the soil, unsaturated pores quickly fill up, effectively raising the water table (Gregory et al 1999). For example efforts, a groundwater surface elevation map was derived based well site information available from the USGS (http://groundwaterwatch.usgs.gov) that had a minimum of 35 years of continuous data. Using GIS, an inundation model was created in GIS by subtracting the groundwater surface model from the digital elevation model with the difference in elevation being the soil storage capacity. The photo shows the evolution of these features as applied to a section of northwestern Miami-Dade County. What this indicates it that the impact of sea level rise on low-lying inland areas may be far different that the projections using the bathtub models. It also means that wellfields, sewer mains, roadways and storm water systems will be affected far more quickly than projected from bathtub models. The method used here suggested that the estimated may be off by a factor of two of three.

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