Climate Impacts on People, Places and the Economy
Four Forms of Floods
Sea level rise is just one adaptation challenge facing Delray Beach and surrounding region, but one that is inextricably tied to several interralated hydrological challeges. The first of these challenges is flooding
Rising sea levels will very gradually inundate low lying areas of coastal communities. In Miami Beach and areas south, communities have experienced severe “sunny day” flooding for several years. This “nuisance flooding” is prevalent in Monroe, Miami Dade and Broward counties, lower case when in a list urbanized areas are less than 2-feet above sea level. This also occurs periodically in Delray Beach and other Palm Beach County locations, especially during high tide events, called King Tides.
Residents of low-lying property on either side of the Intracoastal are prone to this periodic flooding, which is anticipated to become more frequent in the coming decades. The adjacent map illustrates areas that are predicted to be flooded when sea levels rise.
Sea level threatens to gradually inundate coastal communities, it also diminishes the capacity of our complex stormwater management system to effectively drain inland areas. Canals which drain stormwater to the ocean utilize simple gravity. When a control structure is closed, water rises on the land side of the canal. When the tide is low on the ocean side, the South Florida Water Management District (SFWMD) opens the control structure and the water drains through. As seas rise, there will be less of a differential, less “head” between the land side and the ocean side of the control structure, thus diminishing that rate of drainage. During high tides, the fresh water will not drain unless pumped from the freshwater side of the control feature to brackish water side. The increase frequency of heavy rain falls associated with climate variability may increase both the number of times the SFWMD is challenged to drain the canals and the duration of time it takes to lower the canals.
Rising Water Table
Changing precipitation patterns may increase the frequency of heavy rainfalls and prolong periods of rainy weather. After several days of rain, soils become saturated and unable to absorb and convey water to the aquafer quickly resulting in ponding. Many of communities plan for this with retention lakes and dry retention areas. However, as precipitation events become more extensive the water table will rise, resulting in dry retention areas remaining wet for extended periods. The rising water table can create problems for septic systems, and become breeding ground for insects.
Floridians are aware of the dangers and potential damage from hurricane winds and associate storm surge, which can wash buildings off their foundations and flood coastal homes and businesses. As the climate warms, there is a potential that hurricanes will pack a harder punch on coastal communities, as warm oceans fuel stronger storms, with higher precipitation levels. Add this to rising sea levels and there is a likelihood that communities would experience higher storm surge waves, impacting beaches and surrounding neighborhoods more severely. Protecting communities from these impacts requires a consistent investment in our beaches and dune systems, along with smart building practices that properly anchor and elevate structures high above the predicted water levels. The City of Delray Beach is a national leader in proactive beach nourishment and dune maintenance. Since the 1970s, XXX billion metric tons of sand were place on the City’s public beach, and a sizable vegetated dune systems has developed, providing barrier island homeowners protection from coastal storms.
Drought Conditions and its Impacts
Southeast Florida is at risk of saltwater intrusion due to the permeability of the Biscayne Aquifer and the dense population along our coast, which both draws down the supply of fresh water and limits recharge because of the highly paved built environment. Why does saltwater intrusion occur? The Biscayne Aquifer is a shallow lens of freshwater saturating a porous limestone base under the ground surface. It is bounded by saltwater from the Atlantic Ocean that extends under the land mass and abuts the aquifer on the bottom and sides. Where they meet, a narrow area called the dispersion zone, there is a mix of salt and fresh water and it is not geographically fixed. The boundary is dependent on the amount of freshwater recharge from precipitation that filters into the aquifer and creates a head of pressure that keeps the saltwater at bay. Wells tap the aquifer and continually draw water. This depletion of freshwater can change the head pressure, allowing the dispersion zone and saltwater line to move landward.
Climate variability is often associated with increases in precipitation, especially rain downpours that can create flash flood conditions. Conversely, climate change will also result in periods of extended droughts. Drought periods pose challenges to our agricultural sector, tourism economy, water supply and increase the risks of wild fires. Water conservation techniques, including restrictions on irrigation and planting drought resistant landscape, are common adaptation approaches, new systems of long term water storage and additional aquafer recharge will become increasingly important.