Staying dry with rising tides – case study miami beach inc2

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STAYING DRY WITH RISING TIDES – CASE STUDY MIAMI BEACH

Author: Kerry Olsson, Marketing Director, Wapro AB

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ABSTRACT

The City of Miami Beach, Florida, USA is a beautiful resort community nestled between the Atlantic

Ocean and Biscayne Bay. Miami Beach is built on natural and man-made barrier islands.

Infrastructure which ensures residents and tourists in Miami Beach aren’t regularly flooded by sea water

is often taken for granted however with a changing climate it has become evident to residents that

there are issues that need to be dealt with.

Much of the system that transports stormwater directly to the sea was built just a few centimeters to

one to two meters above sea level. Over the years these outlet structures have settled, and sea levels

have risen, often causing seawater to flow into the stormwater system.

Overfilled stormwater systems cause seawater to push up onto streets as well as residential and

commercial properties causing blocked roads, inconvenienced pedestrians, closed businesses, and

damaged homes.

A team of scientists of the Potsdam Institute for Climate Impact Research (PIK) in Potsdam, Germany

has detected a clear upward trend in the past few decades toward more unprecedented daily

rainfall events. The institute found that these once anomalous events have increased in frequency 24

percent in central and eastern US1.

Miami Beach is spending more than US$500 million in infrastructure to brace for the scientific projection

that the sea level will rise 1.5m by the turn of the century. This paper will present issues surrounding

aging infrastructure, and solutions put in place during phase 1 & 2 of this monumental project

exhibiting the success of the project and potential issues surrounding trying to flood-proof a city.

1 Jayalakshmi K - Potsdam Institute research links record-breaking daily rainfall to global warming

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Flooded streets during sunny weather caused by high tides flooding the stormwater system.

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1 Introduction

Water management is one of the greatest challenges Southeast Florida faces as sea level rises.

During wet periods, the system discharges high volumes of rainfall runoff through the canal network to

minimize potential flood impact to both developed and natural areas. Conversely the system retains

water during dry periods to make it available for man-made and natural system supplemental water

needs. Water levels in the regional system of canals and the Water Conservation Areas are maintained

to recharge the underground freshwater aquifers.

2 Location

Miami Beach is located on a variety of natural and man-made barrier islands between the Atlantic

Ocean and Biscayne Bay, in Southeast Florida. It has a total land area of approximately 48km2 and is

home to 91,000 people.

It is connected to the neighbouring City of Miami by a series of long bridges.

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The highest point of Miami Beach is actually the beach, and that is only 11.41ft (3.47m) Above

Mean Sea Level (AMSL).

Parts of the western side of South Beach are at virtually level with normal high tide, with the entire city

averaging only 4.2ft (1.3m) Above Mean Sea Level (AMSL).

With forecast sea level rises of up to a metre over the next 20 – 30 years, stormwater management is

one of the greatest challenges Southeast Florida faces in the coming years.

Graphic courtesy of: http://interactive.fusion.net/pumpit/

Approximate height above sea level across Miami Beach

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3 Background

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The central and Southern Florida Project for Flood Control and other Purposes (C&SF Project), was

authorized by Congress in 1948 at the request of the State of Florida. Primary objectives of the project

are:

-Flood Control

-Water Supply

-Prevention of saltwater intrusion

-Environmental Preservation

The water management system consists of canals, levees gated spillways, pumping stations and

surface water impoundments. All of which were constructed by the U.S Army Corps of Engineers

between 1950 and 1970. (http://www.iscvt.org/, 2015).

Traditional sea level rise and storm mitigation measures including sea walls and dykes, such as those in

the Netherlands and New Orleans, may not work in South Florida due to the porous nature of the

ground and limestone beneath the surface.

3.1 THREE-TIERED SYSTEM

The primary canal system is managed at a regional level by the State of Florida, federal interests in the

system are managed by the U.S Army Corps of Engineers. The secondary system is managed by local

governments, such as cities, counties or special taxing districts. The secondary system accept runoff

from individual residential communities or commercial/agricultural areas and convey that water to the

primary canal system. The smallest subdivision, system of drainage ditches, swales, storm sewers and

water detention ponds that are owned and maintained by private land owners, home owner

associations, etc. These community-based systems not only retain water to avoid serious flooding, but

they also provide a source of groundwater recharge and support supplemental irrigation during dry

periods.

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There are two major roles of the Primary Canals.

1. To remove excess rainfall runoff from urban and agricultural areas to minimize impact from flooding.

2. Recharge groundwater. Water levels in the canals are raised in dry times, when there is low risk of heavy rains.

(http://www.iscvt.org/, 2015)

During wet periods, the stormwater system discharges high volumes of rainfall runoff through the canal

network to minimize potential flood impact to both developed and natural areas. Conversely the

system retains water during dry periods to make it available for man-made and natural system

supplemental water needs. Water levels in the regional system of canals and the Water Conservation

Areas are maintained to recharge the underground freshwater aquifers.

All levels of the system have a part to play in these functions.

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These controls were needed as the South Florida area developed at a rapid pace after the Second

World War. Many of the new residents and tourists were ex-servicemen that had been through the

numerous training camps in the area during World War 2.

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The canals are still a common means of transport for people and produce. Although the transport and

surroundings have certainly changed.

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4 Origin of Problem

Most of Florida was planned in the 1940-50s. The planners expected a rise in tourism in the post-war era

and aimed to reclaim vast submerged land. Research and investment on stormwater management

gained impetus in the United States after the 1972 enactment of the federal Water Act, five regional

water management districts were initiated, which had authority to regulate stormwater management

systems for new development.

Fig 1. Assumed urban areas and now! Source: (http://www.iscvt.org/, 2015)

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These systems were intended to deal with increased rainfall runoff originating from impervious surfaces

in new developments mainly by constructing storage ponds to attenuate flood flows. To estimate

runoff capacity the single-event approach is commonly used in the United States. Storm event of

specified return interval and duration, 24h or 48h durations are commonly used to calculate

stormwater quantity and quality in management operations. (California Regional Water Quality

Control Board 2014).

With rising sea levels due to the change in global climate, south Florida will become more and more

susceptible to a wide variety of negative effects, primarily due to its very low topographic elevation.

Sea level has risen about 200 mm (8’’) the last 100 years. (http://www.iscvt.org/, 2015). As a result, the

water management system has become under dimensioned.

On top of all this, Miami Beach must contend with a fairly new phenomenon that has come to be

known locally as “sunny-day flooding”, in which Alton Road and its neighbouring streets are awash in

water even when no rain has fallen. This is a consequence of southeast Florida’s geology. Unlike, say,

the island of Manhattan, whose bedrock is composed of hard, relatively impermeable marble, granite,

and schist, Miami Beach and its neighbouring towns sit upon a foundation of porous limestone.

When the tides are at or nearing their seasonal highs—the highest, which occur in March and October,

are known as king tides—seawater surges inward from the bay and the ocean, bubbling up through

the limestone and infiltrating the sewer system. The very drains and gutters built to channel

water off the streets function in reverse, becoming the conduits through which water gushes onto the

streets.

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Fig 2. Common sights in the Miami area when high tides occur in combination with higher sea levels.

The control of discharge water quality, known as an allowable discharge, is accomplished by

calculations that determine the size of lakes and ponds needed for a water control structure that

meters the water flow volume to a determined particulate range of water levels in the water

management system. Stormwater (or storm runoff) is a major source of water-quality degradation

[(United States Environmental Protection Agency (USEPA), 2004); (Shaver, 2007)] and poses flood

hazards in urban areas (Damodaram, 2013).

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Drivers splash through saltwater caused by annual high tides between Fifth and Eighth streets on West

Avenue in Miami Beach on Oct. 7, 2010. MIAMI HERALD

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5 Solutions

There are several attempts to map out the vulnerability of the coastal areas, using down-scaled

climate models with historical data to evaluate the extent to which climate change may damage or

harm a system. Mapping of these vulnerabilities helps determine which areas are most susceptible to

flooding, providing visuals or stakeholder engagement and assessing next steps to reduce current and

future risk.

In the City of Miami Beach a comprehensive Stormwater Management Master Plan (SWMMP) has

been put in place in order to evaluate and update its stormwater management practices and

infrastructure. The plan is based on comprehensive data collection of rain data and tidal data from

gauges in pre-existing monitoring wells. The SWMMP is a long-term planning document that provides

guidance for the upgrades to the City’s stormwater infrastructure performance improvements for the

next 50 years. The plan takes into consideration sea level rise as well as how infrastructure is designed

to handle water from storms and tidal waters that enter the system when the tides are higher than the

outfalls. The plan includes installing approximately 60 pumps as well as back flow preventers.

(http://www.iscvt.org/, 2015). The cost of US$50m for these systems may appear high, however when

you consider that there is an estimated $400 Billion worth of built environment that requires protection,

it could be seen as a good investment.

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City of Miami Beach, Fla., Mayor Philip Levine, left, addresses officials and members of the media, as

workers prepare to install part of a new storm water pump station, Wednesday, Sept. 17, 2014 in Miami

Beach. (AP Photo/Wilfredo Lee)

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This new system collects flood waters, screens out large debris like plastic bottles and pumps it back

out into Biscayne Bay through one-way valves that keep rising Biscayne Bay waters from flooding

drainage pipes. The plan also calls for raising seawalls, most of which are on private property, and

raising some roads.

The first new pumps were installed in 2014 -2015 in some of the city’s worst hot spots and they have

kept roads dry through a first round of fall tides.

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An energy dissipater, seen here at 14th Street and West Avenue in Miami Beach on Monday, Oct. 6,

2014, is the last part of the water removal process. Water moves from street level into the bay, having

gone through the pumping station, which is underground. Walter Michot Miami Herald Staff

Recent groundwater studies by the U.S. Geological Survey (USGS) have revealed some interesting

results specific to the response of the surficial aquifer in Miami-Dade County associated with sea level

rise. The increase in groundwater levels associated with rising sea level will be greater along the

coastal fringe than in inland areas.

The Biscayne aquifer underlies Miami Beach to a depth of approximately 200 feet or more (USGS,

2014). The groundwater in the Biscayne aquifer is unconfined and will likely fluctuate in direct response

to variations from precipitation and sea level rise.

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This fluctuation occurs as the underlying ground consisting of porous limestone which allows water to

flow freely.

As means to increase storm water runoff capacity, vertical wells have been installed in several

locations throughout Southern Florida. The vertical wells were meant to discharge storm water into the

ground water table but with a risen sea water level the increased pressure from the sea water elevates

the ground water. A reversal of flow in the vertical wells means water comes up through the wells into

the storm water system and floods the streets. This is occurring today.

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To mitigate the flooding WaStop inline check valves have been installed in some locations allowing

storm water to recharge the ground water and preventing ground water flooding the surface area

through the vertical wells.

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Fig 3. Installation of WaStop check valves in vertical wells to stop flooding of streets.

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So far during 2014 and 2015, check valves have been installed into 2 vertical wells and about 400

normal outfall pipes in the Miami beach stormwater system.

WasStop inline check valves have a pulsating flow which allows sediment and debris to pass

through, making clogs and costly maintenance virtually non-existent. At the same time as

providing 100% secure seal against backflow – even in low pressure events. With its market

leading low headloss the WaStop inline check valve allows the maximum flow through the valve

ensuring that stormwater is removed from the streets quickly and without hinderance.

Since the installations in Miami beach other coastal communities such as Delray Beach, Boynton

Beach, and Hollywood (Florida) have expressed an interest in WaStop check valves. There is no

other easy solution to the issues.

Conclusion

With rising sea levels increasing ground water levels and climate change causing more frequent storm

events, flooding is now common event. The inevitability and the massive scale of the problem will

demand for actions both short term and long term. Solutions are pumping stations ‘lifting’ storm water

discharging it into the sea in case of both high tide and rain. Another solution is installing check valves.

This ensures that the system only needs to deal with storm water and is not inundated with seawater or

ground water that has infiltrated into the system. This creates a larger retention capacity in the existing

network. Both solutions increase the capacity of the storm water management system. Increasing

storage capacity or elevation of infrastructure are other potential solutions, there is no one-size fits all

solution to a growing problem.

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For more information contact Wapro

USA

Worldwide

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References

Damodaram, C. a. Z. E. M., 2013. Simulation-optimization approach to design low-impact

development for managin peak flow alteration in urbanizing watersheds, u.o.: J. Water Resour. Plann.

Manage.,.

http://www.iscvt.org/, 2015. Regional Impacts of Climate Change and Issues for Stormwater

Management, Miami: Southeast Florida Reginoal Climate Change Compact.

Shaver, E. H. R. S. J. M. C. a. R. G., 2007. Fundamentals of urban runoff management: Technical and

institutional, Madison,: North American Lake Management Society.

United States Environmental Protection Agency (USEPA), 2004. Water quality standards for coastal and

Great Lakes, u.o.: Fed. Regist.

Engineering

Staying dry with rising tides – case study miami beach inc2