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LTC 246-2009 Seasonal Tidal Flooding Impactsm MIAMIBEACH ~, _. _~. - , OFFICE OF THE CITY MANAGER NO. LTC # a ~+ 1. - ~-0 ° 9 LETTER TO COMMISSIORI z, TO: Mayor Matti Herrera Bower and Members ofthe City Commission r~•' r _ ~. FROM: Jorge M. Gonzalez, City Manager DATE: September 18, 2009 SUBJECT: Seasonal Tidal Flooding Impacts The purpose of this LTC is to provide the Mayor and City Commission with a report on the coastal flooding that is occurring throughout our City and in other parts of South Florida, as a result of the seasonal tidal impacts associated with lunar tides. Background For the past few days, several coastal communities in Broward: Miami-Dade and Monroe Counties have been experiencing the effects of the autumn tides, which are usually the strongest of the year. These tides are primarily due to fluctuations related to the lunar cycle in which the moon influences the sea level with its gravitational pull, which increases with its proximity to the Earth during the autumnal equinox. Yesterday, NOAH (National Oceanographic Atmospheric Administration) issued a statement expecting minor coastal flooding along portions of the Atlantic and Gulf Coast. It is predicted that as a result of the lunar conditions. low-lying coastal areas will experience minor flooding within a few hours of the high tide (Attachment 1). This cycle of coastal flooding caused by extremely high autumnal tides is expected to take place over the next few days. The temporary tidal flooding is also expected to naturally recede as the tide lowers and within the upcoming days it is expected to return to its natural cycle elevations. The City of Miami Beach, which is located on a barrier island, is extremely vulnerable to the impacts of these high tides. The City is particularly exposed by naturally low-lying topographic areas and climate variability. Low-lying areas that are prone to excessive flooding during these tides are primarily defined by: Alton Road and West Avenue between 5th Street and 10 Street, by Purdy Ave, adjacent to Maurice Gibb Park between Dade Blvd and 20th Street. and the west side of Palm Island. Since 2007, Public Works has implemented a pilot program that has installed eleven (11) tideflex valves at the discharge end of outfall pipes to protect stormwater from surcharging, or entering the drainage structures through open outfalls during high tides. The installation of tideflex valves provides reliable backflow prevention during these events. Inspection's of the recently installed tideflex valves have indicated that the structures are functioning as designed. Public Works continues to install the tideflex valves in response to flooding conditions at various locations throughout the City. (Attachment 2). Miami Beach is not the only municipality which has been affected by these lunar cycles. Key West has also been impacted severely and is experiencing flooding conditions over two (2) feet above the Mean Sea Level (MSL). In Broward County: the Ft. Lauderdale area is suffering narrowing of beaches as a result of these cyclical high tides {Attachment 3). In addition to the known factors that contribute to flooding, sea level rise along the Mid- Atlantic coastal zones may also be exacerbating the effects of seasonal high tides. According to the Environmental Protection Agency (EPA), sea level rose five (5) to (6) inches more than the global average along the Mid-Atlantic and Gulf Coasts in the last century because coastal lands there are subsiding (Attachment 4). In The Inundation ofour Coastline: Past, Present and Future with a Focus on South Florida. the University of Miami Rosenstiel School of Marine and Atmospheric Sciences (RSMAS), geologist Dr. Harold Wanless suggests that sea level rise along Florida's shoreline has accelerated to a rate of eight (8) to sixteen (16) inches per one-hundred years since 1932. The Administration will bring to the October 14'r City Commission Meeting, the recommendation to proceed with a Request for Qualifications (RFQ) for a Citywide Comprehensive Stormwater Management Master Plan, which will evaluate our current stormwater system, perform engineering modeling and analysis and provide recommended infrastructure solutions aimed not only at addressing the level of sen+ice of our citywide drainage infrastructure, but also provide solutions to the coastal flooding causing extreme tidal conditions. In addition, the City is currently investigating the feasibility of commissioning a technical/scientific study that will analyze the impacts of sea level rise from the past decades and the potential impacts to our City in the future. The high tide for Friday September 18, 2009 is predicted to reach 3.6 feet above MSL. This level of high tide could have a substantial and temporary impact to the most low-lying areas in the City. particularly Alton Road and 10'" Street: which is a main vehicular access to our City and which sits at an elevation of only 1.8 feet above MSL. The City intends to provide temporary precautionary measures such as VMS boards and cones in order to guide drivers to proceed with caution during the peak of the high tide. The City will continue to provide assistance to its residents in the attempt to mitigate the impacts associated to this force majeure event. Attachment 1. NOAA: Coastal Flood Statement, 09117/09. Attachment 2, Public Works Operations Log of Tide-Flex Valves at Outfalls. Attachment 3, "Moon River: Beaches: streets awash in rising tides." Miami Herald, 09117109. Ariachment 4. EPA -Coastal Zones and Sea Level Rise JMGHB ~,AVILEB FaworkGSALU(1) EMPLOYEE FOLDERSIFERNANDO VAZQUEZlLTCSCoastal Flooding IncidenLdoc Alcrt for Western C'ollicr; FLL168 ('?); PLL172 ('?); FLL173 ('?) (Florida) Issued by the V... Page 1 of 1 LoC21 forocast Dy "City, Sl° Clty, SY ~T.7 R5S Feods bYarnings Currant By StatolCOUnty... UV Abrts Obxervatlens Radar Satatlite Snow Covnr Surtace Wea:hor... Observed Procip Fo: ocasls Local Graphical Aviation rdarine Hurrkancs SEVero Weafher FirC Wo:+thcr Text Messages Ry state ©y Messago Typo National Foreras[ Models Numerical Models Statisbcat Models... MOS Prod GFS-LAMP Prod Climate Paxt Weather PredicUOns Woathor Safoty Weather Radio Hazattt Assort... StormReady TsunamiRaady Skywam'" EducationlOElreach In(ErmOtlEn CEnler Tsunamis Publlcadons... 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Page 1 of 4 ,,.~..w,, ,.., , , .. :, < . ~ , r r ~ ~ t:u;., .:~. i`.~oi~:Jc'.C`_ s .~..~, i"t c.i ., F ',1 E i:cii ,._} E_~.~_: "c!: :~: co::: EPA Home Climate Chanye Health and Envi ronmentat Effects •'ucxc::f Coastal Zones and Sea Level Rise Sea Level Rise Maps Sea Level Rise Reports Coastal Zones and Sea Level Rise ..:~is~t:::; s.i:;Ss Sea Level Rise ~ Land Loss ~ Storms and Flooding ~ Response CPA to Sea Level Rise ~ Coastal Water Supplies Climate Ready Estuaries Coastal zones are articular) vulnerable to climate variabilit Future Sea Level Change p Y Y Recent Sea Level Chanye and change. Key concerns include sea level rise, land lass, Ocean Acidification changes in maritime storms and flooding, responses to sea Saving Florida's Vanishing level rise and im lications far water resources. Shores (PDF) {3 pp., 1,284 p KB, About PDF) en Espanol (PDF, 3 pp., 356 KB, About Sea Level Rise PDF) Saviny New Jersey's Vanishing Shores (PDF} (3 Sea level is rising along most of the U.S. coast, and around the pp., 1,337 KB, About PDF) world. In the last century, sea level rose 5 to 6 inches more Coastal Sensitivity to Sea- than the global average along the Mid-Atlantic and Gulf Level Rise: A Focus on the Coasts, because coastal lands there are subsiding. Mid-Atlantic Region NOAA; Sea Levels Online Higher temperatures are EPA, in coordination with the expected to further raise sea State of Maryland Living U.S. Geoloyical Survey and level by expanding ocean Shorelines Proyram the National Oceanic and ;water, melting mountain "` `` Atmospheric Administration, ;glaciers and small ice caps, dnd Peen Center Report: Coasts has published a report, and Marine Ecosystems & " causing portions of Greenland Coastal Sensitivity to Sea Global Climate Change: and the Antarctic ice sheets Co Level Rise: A Focus on the Potential Effects on U.S. Mid-Atlantic Region." The melt. The International Panel Resources '' ••• study is one of 21 climate : on Climate Change (IPCC} chanye studies commissioned 'estimates that the global being conducted by the U.S. average sea level will rise between 0.6 and 2 feet (0.18 to Global Chanye Research 0.59 meters) in the next century (IPCC, 2007). Proyram (USGCRP). "Coastal Sensitivity to Sea-level Rise: ;The range reflects uncertainty about global temperature A Focus on the Mid-Atlantic ~ projections and how rapidly ice sheets will melt or slide into Region" discusses the possible ~ the ocean in response to the warmer temperatures. impacts of sea Icvcl rie and ;Furthermore, some processes affecting sea level have long how governments and (centuries and longer) time-scales, so that current sea level communities can respond to change is also related to past climate change, and some nsng eaaters. relevant processes are not determined solely by climate. Climate models, satellite data and hydrographic observations demonstrate that sea level is not rising uniformly around the world. Depending on the region, sea level has risen several times the global mean rise, or has actually fallen (IPCC, 2007}. Attaclmicnt 4 http aiw~~~a .cpa.gov:'clinrucchan~ c; sffixts'coastal.`indce.html Coastal Cones and Sea Level Rise Climak Chango -Health and F.nvirunmental F.fl'ects ', ... Pale 2 of 4 While current model projections indicate substantial variability in future sea level nse at regional and local scales, the IPCC has concluded that the impacts are "virtually certain to be overwhelmingly negative" (IPCC, 2007). Rising sea levels inundate wetlands and other low-lying lands, erode beaches, intensify flooding, and increase the salinity of rivers, bays, and groundwater tables. Some of these effects „~.,,. may be further compounded by other effects of a changing ~ +x- •• . climate. Additionally, measures that people take to protect :i~•:~k > 5r;1.< ~~;,-~ ' private property from rising sea level may have adverse effects ~~'~~~• on the environment and on public uses of beaches and waterways. Some property owners and state and local governments are already starting to take Irteasures to prepare far the consequences of rising sea level. Land Loss Coastal wetland ecosystems, such as salt marshes and mangroves are particularly vulnerable to rising sea level because they are generally within a few feet of sea level (IPCC, 2007). wetlands provide habitat for many species, play a key role in nutrient uptake, serve as the basis for many communities' econolric livelihoods, provide recreational opportunities, and protect local areas from flooding. As the sea rises, the Evoiuiion of a Marsh as Sea Level Rises outer boundary of these wetlands will erode, and new 5,000 Years Ana Today y .•vF wetlands will form '~~ ~"°' .................. inland as previously ~... ..,.~ ~ ~~' .. ?ya. .- `.c:. dry areas are ----------y-- ..._...._. san -oval Flooded by the higher water levels. Future rt J r I. I c {J1-_i i :.a r1I r.+ < t> .a I-• Prp4<.;;d.i The amount Of newly ~,t-:..>.^.~.,...I .. '.lr lv iul ..::a:1 v I i~ n, ;~.du ns_•: i a~n ..na; ~., a; created wetlands, however, could be ~ "" ': ` "` much smaller than -.. ..... - r ................. m the lost area of ~ `- ~' Leal wetlands -especially ieceuo in develo ed areas ~-~ '""'"" protected with ---------- -- bUlkheddS, dlkeS, `'"'r,auv;:~h«:h:nek.~pl pme ~.nm the sbx. rate or sea level nse that nzs cnaracteriza~melast sr,erat cnou~ano +ears. Thus. :he v.ea ct mar-'~ ha; .~xpanved o.m tir:~r us ne•n Ia:W:. ha:e beer. Inu noatnd. If In dnd Other SCrUCtU reS '~~*-tur^ =eo level rsez aster i:an the abic:f ofse ma sn:o aeep pace_Ne marsn area vnU COrtrac:. that kee neW ion5¢uN. bn o'hulkneaes l;r pnXe~ •::.^nm;~c tleoeloprnent s.ay pravent nea marsh from lOlmm({ P mla mv:x In z mtat az nr mar<.-, m ;ome areas. wetlands from s«•r:::....._c 1vr .ax.:,a.,,~..•e:a_;~na^:,.::.:v,.u,.,raa"r.=.,•n.+,•.-~~n<~;u~~-y.•r,<•,.cu~ltsasa forming inland. The IPCC suggests that by 2080, sea level rise could convert as much as 33 percent of the world's coastal wetlands to open water. (IPCC, 2007). Tidal wetlands are generally found between sea level and the highest tide over the monthly lunar cycle. As a result, areas with small tide ranges are the most vulnerable. An EPA Report to Congress estimated that a two foot rise in sea level could eliminate 17-43 percent of U.S. wetlands, with more than half the loss taking place in Louisiana (EPA, 1989). Nationwide, about 5000 square miles of dry land are within two feet of high tide. Although http: ~,•'~ti1~~m~.cpa.gov~ climatechange.~ e f7ecuicuar,tal?indc~.html 09r'18~ 2009 Coastal Zones and Seu Level Kise Climate Change - health and Environmental liffects' ... Page 3 of ~1 the majority of this land is currently undeveloped, many coastal counties are growing rapidly. Land within a few feet above the tides could be inundated by rising sea level, unless additional dikes and bulkheads are constructed. A two foot rise in sea level would eliminate approximately 10,000 square miles of land (PDF) (26 pp., 267 KB, About PDF) including current wetlands and newly inundated dry land, an area equal to the combined size of Massachusetts and Delaware (EPA, 1989). Some of the most economically important vulnerable areas are recreational resorts on the coastal barriers of the Atlantic and Gulf coasts. In many cases, the ocean-front block of these islands is 5 to 10 feet above high tide; but the bay sides are often less than two feet above high water and regularly flooded (see USGS's 7.5-minute map series). Erosion threatens Che high ocean sides of these densely developed islands and is generally viewed as a more immediate problem than inundation of their low bay sides. Many ocean shores are currently eroding 1 to 4 feet per year (FEMA, 2000). Storms and Flooding Sea level rise also increases the vulnerability of coastal areas to flooding during storms for several reasons. First, a given storm surge from a hurricane or northeaster builds on top of a higher base of water. Considering only this effect, a Report to Congress '^ " '~ by FEMA (1991) estimated that existing development in the U.S. -"'~ f x,k..,k~ Coastal Zone would experience a 36-58 percent increase in ~ > , : Z} annual damages fora 1-foot rise in sea level, and a 102-200 .•, percent increase fora 3-foot rise. Shore erosion also increases ,,, . ,,;,.__,,,. ,,,; ,' , :. .. vulnerability to storms, by removing the beaches and dunes that would otherwise protect coastal property from storm waves (FEh1A 2000). Sea level rise also increases coastal flooding froirr rainstorms, because law areas drain more slowly as sea level rises. Other impacts of climate chanye may further enhance or mitigate coastal flooding. Flooding from rainstorms may become worse if higher temperatures lead to increasing rainfall intensity during severe storms. An increase in the intensity of tropical storms would increase flood and wind damayes. Responses to Sea Level Rise along the Coast Property owners and federal, state, and local governments are already starting to take measures to prepare for the consequences of rising sea level. Most coastal states are working with the U.S. Arrny Corps of Engineers to place sand onto their beaches to offset share erosion. Property owners are elevating existing structures in many low-lying areas, encouraged by lower flood insurance rates. Several states have adopted policies to ensure that beaches, dunes, or wetlands are able to migrate inland as sea level rises. Some states prohibit new houses in areas likely to be eroded in the next 30-60 years (e.g. North Carolina Coastal Resources Commission - ). Concerned about the need to protect property rights, Maine, Rhode Island, South Carolina and Texas have implemented some version of "rolling easements," in which people are allowed to build, but only on the condition that they will remove the structure if and when it is threatened by an advancing shoreline (Titus, 1998). Historically, along sandy bay beaches, property oevners have erected various types of sea walls to halt erosion. Although these hard structures protect property, they can eliminate: bay http:i:'vv~~w.cpa.goviclimatcchance%effecls:coaslaUindcx.hlrnl 0911 &%2009 Coastal Lones and Sea Lcvcl Risc ~ Climate Chance - f Tealth and F.mironmental F.fl'ects ~ ... Page ~ of ~ beaches, evhich are usually less than 10 feet wide. Beaches are used for fishing, recreation, transportation, and landing small crafts, in addition to their environmental importance. The National Research Council . , ___, __i~ has released a report that examines ways to minimize the loss of bayshore habitat when protecting coastal property from shore erosion, such as the "Living Shorelines" '-> - =- ~''' approach. Coastal Water Supplies Rising sea level increases the salinity of bath surface water and ground water through salt water intrusion. New York City, Philadelphia, and much of California's Central Valley obtain {~^ i ,wy5~ 7~jy.~b~_~y,;. ,: some of their water from portions of rivers that are slightly upstream from the point where water is salty during drought. `' 'e` "~'~ " ' If sea level rise pushes salty water upstream, then Che existing water intakes might draw on salty water during dry K <~ 'V v , periods. Salinity increases in estuaries also can harm aquatic ~ ` ~~ plants and ammals that do not tolerate high salinity. - _. ~" +{:> ~! Shallow coastal aquifers are also at risk (IPCC, 2007). The freshwater Everglades currently recharge Florida's Biscayne aquifer, t[te primary water supply to the Florida Keys. As rising water levels submerge low-lying portions of the Everglades, portions of the aquifer would become saline. Aquifers in New Jersey east of Pltiladelpltia are recharged by fresh portions of the Delaware River which may become saline in the future. In all of these cases, water management authorities currently prevent excessive salinity by releasing fresh water from reservoirs during droughts. One possible response to sea level rise would be to stare more water during wet seasons so that more water can be released during droughts. However, other water management goals (e.g. flood prevention) may make it difficult to save extra water for the occasional drought. The impacts of climate change on local hydrology may offset or increase salinity increases due to sea level rise. Sea Level Rise Maps Sea Level Rise Reports References ^ IPCC, 2007: Climate Change 2007: Impacts, Adaptation and Vulnerability - .Contribution of 4Varking Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Parry, Martin L., Canziani, Osvaldo F., Palutikof, Jean P., van der Linden, Paul J., and Hanson, Clair E. (eds.)). Cambridge University Press, Cambridge, United Kingdom, 1000 pp. ^ Titus, J., 1998: Rising Scas, Coastal Erosion, and the Takings Clause: How to Save Wetlands and Beaches Without Hurting Property Owners. (PDF) (121 pp., 2.09 MB, Erosion Hazards " ~- ract of Relative Sea Level Rise on the National Flood 70 pp., 690 KB, About PDF) October 1991. ffects of Global Climate Change on the United States. igton, D.C.: U.S. EnviromYtental Protection Agency. EPA http:,'iwtivw.epa.gov,'climatechange;eftectti coastalindcx.hhtil OS)14?009