U.S. Army Corps of Engineers Broward County Planning Assistance to States. Flood Risk Management Study for Tidally Influenced Coastal Areas

Transcription

1 U.S. Army Corps of Engineers Broward County Planning Assistance to States Flood Risk Management Study for Tidally Influenced Coastal Areas Initial Stakeholder Resiliency Meeting Wednesday, November 9, 2016, 2:00 PM 4:30 PM Broward County Main Library 100 S Andrews Ave, 6th Floor Conference Room Fort Lauderdale, FL I. Welcome SUMMARY MINUTES Dr. Jennifer Jurado brought the meeting to order at 2:02pm. II. Focus on Resiliency in Broward Dr. Jurado introduced the U.S. Army Corps of Engineers (USACE) and Broward County coastal flood resiliency study. Major issues include: What are the flooding impacts to local communities? What infrastructure investments are needed to protect communities? How much investment and flood risk are communities willing to afford? Local development is rapidly occurring and is outpacing the regulatory framework and ability to analyze new infrastructure impacts. Cities are actively reducing flooding with stormwater valves and pumps. However, numerous areas are being inundated through overtopping of existing infrastructure, which will worsen with sea level rise. Broward County reached out to the USACE for assistance in developing resiliency standards, in particular seawall height elevations and other possible adaptation measures, such as raising roads and other infrastructure. Future scenarios and modeling will not only include sea level rise effects, but the impacts of storm surge and tidal flooding. The economic impacts of flooding on infrastructure and economic activity in vulnerable areas will also be analyzed in the study. III. Community Expectations Introduction Dr. Samantha Danchuk presented a summary of coastal climate change impacts in Broward County: Sea level rise has been accelerating in the past three decades and is projected to increase about one foot by year 2030 and two feet by year Page 1 of 9

2 2060, based on the Unified Sea Level Rise Projection developed by the Southeast Florida Regional Climate Change Compact. Groundwater has increasingly been impacted by saltwater intrusion into underground aquifers, which has required the closure and movement of several water supply wells. In addition, rising groundwater levels reduces the stormwater infiltration and drainage capacity of local soils. Regional water management is increasingly affected by sea level rise, as canals lose the ability to drain stormwater by gravity to the ocean. Adequate drainage will require the installation and use of pumps. Annual king tides are causing up to one additional foot of sea level rise during periods in the Fall season, which causes flooding in certain lowlying areas of the community Storm surge can impact many coastal and inland areas of the community, depending on the intensity of the storm. The U.S. currently spends about 10% of its Gross Domestic Product (GDP) on climate change impacts Broward County has responded to these challenges by developing a Climate Action Plan, Unified Sea Level Rise Projection, and 3D visualizations of storm surge flooding, among others. Additional areas of focus include: Infrastructure resilience by assessing transportation and property vulnerability, which can prevent up to 40% of losses Natural resilience provided by green infrastructure can save $20 in avoided losses for every $1 spent Economic resilience through adaptive redevelopment, which reduces climate risk and insurance premiums through programs such as the Community Rating System. The outcome of these efforts and this current study is to understand current and future conditions and develop tools, policies, and resilience standards. The resiliency study will involve both community input and a technical analysis to downscale regional information to local communities, while examining local economic effects and adaptation options. IV. USACE Planning Assistance to States Program Glenn Landers presented the USACE perspective on sea level rise and additional details on the USACE-Broward County resiliency study. The USACE s sea level rise guidance is about 1.5 meters (5 feet), with an upper limit of 2 meters (6.5 feet) by year 2100 which are inline with projections from Page 2 of 9

3 the National Oceanic and Atmospheric Administration (NOAA) and the Intergovernmental Panel on Climate Change (IPCC). Future IPCC projections may indicate higher sea level rise as contributions from Antarctic ice melt is considered. Sea level rise is a design requirement for all USACE projects, as are changing precipitation patterns and temperatures. Sea level rise will continue well beyond year 2100 and geologic history indicates about 7 to 8 feet of sea level rise for each degree Celsius of global warming. The uncertain factor is exactly how fast this rise will occur. Buildings and land values will depreciate as it becomes economically infeasible to protect. Coastal ecosystems will require space to naturally adapt to changing sea levels, as they have always done. The gravity-based drainage canals in South Florida are less effective as sea levels rise and saltwater intrusion into the Everglades are oxidizing peat soils, causing land subsidence. In northern Florida, the St. Johns River is experiencing major changes in salinity, affecting river and marine ecosystems. The ADCIRC storm surge model will be used to study two areas in Broward County, the Las Olas Isles and Hollywood Lakes area, and model the effects 5, 10, and 20 year tidal storm surge as it moves through inlets and transmitted through the Intracoastal Waterway and neighboring communities. Mr. Landers described several areas of recent tidal flooding in Fort Lauderdale and Hollywood. Elements of the study include LiDAR elevation surveys of streets, seawalls, and stormwater infrastructure and local tide gauge data to obtain accurate water elevations to customize the ADCIRC model. In addition to existing seawall conditions, an initial seawall height of 2.5 feet will be modeled in ADCIRC. Risk is a measure of the probability of a future event and the consequences of that event. We have limited experience with sea level rise, thus it will be a learning process to improve community resilience. This process will occur in three steps: (1) risk assessment, (2) risk management, and (3) public communication. This is a technical study and not a detailed benefit-cost analysis of alternatives. The project timeline is approximately 20 months and scheduled to conclude in Spring Dr. Jurado added that the results of the study will be useful to other coastal areas of Broward County outside the immediate study locations. In addition, Broward County is currently undertaking three related projects that will further advance resiliency efforts: (1) wet season groundwater elevation maps for sea level rise, (2) proposed coastal resiliency standards, and (3) updated 100 year flood maps. V. Status of Drainage Improvements Alan Dodd detailed the efforts that the City of Fort Lauderdale is undertaking to protect areas from the short and long-term effects of flooding due to climate change. The City has installed temporary tidal plugs in storm drains, until tidal Page 3 of 9

4 valves are installed. Currently, 116 valves have been installed and 27 are in construction. Valves can alleviate 70-90% of the roadway flooding issues, with alternative measures, such as catch basins and bioswales, accounting for other areas. The City cannot correct the flooding problems solely by improving public infrastructure. The biggest issue moving forward are private seawalls, thus the City implemented a revised seawall elevation ordinance in 2016, requiring properties with seawalls that experience overtopping that impacts public rightof-way or other properties to raise their seawalls within one year to a height of 3.9 feet NAVD, which is the current maximum height allowable. The City owns about 4.25 miles of seawalls, some of which require raising or replacement. In the longer term, the City s stormwater master plan is being implemented in three phases. Phase 1 identifies 37 areas of flooding, 17 of which are completed and 8 in construction, with a final completion target of early Phase 2 identifies the City s water basins and designs engineered and natural infrastructure to manage water, using LiDAR and survey data. By the end of 2017, designs should be completed that are anticipated to require approximately $175-$200 million of critical neighborhood improvements needed to reduce flooding impacts. Phase 3 is planned to address the rest of the City. In total, approximately $750 million of investment will be needed to fully implement the stormwater master plan. Rob Taylor from Hazen and Sawyer stated the value of high-definition LiDAR elevation data to analyze the existing stormwater infrastructure for future design purposes. A 10 year level of service is used for stormwater infrastructure. Some areas may require installation of pumps to move stormwater, as seawall heights are raised. Mr. Dodd added that a phased approach with adaptable infrastructure will need to be implemented, since conditions 50 years from now will be much different than 10 years. Rares Petrica noted that the condition of seawalls is also important, since water is leaking through damaged seawalls in some locations that are sufficiently elevated. In other areas, water is percolating up from the ground or through storm drains. VI. Community Expectations Discussion Dr. Danchuk asked the meeting attendees for feedback on local flooding and infrastructure issues. Attendee responses included: Study areas are at high risk of flooding Causes of flooding are king tides, rainfall, and overbuilt areas Conditions will get worse in the future Will seawalls be ineffective due the porous underground limestone? Areas closer to the coast generally experience a greater groundwater response to sea level rise and existing salinity control structures limit the extent of the groundwater response South Florida has a finely controlled water management system that requires modeling to understand the impacts and subsequent responses Page 4 of 9

5 Seepage under and through seawalls into low-lying areas can be controlled by pumps to an extent, but engineered solutions do have limits Up to 15 days of flooding a year is tolerable, however intermittent flooding is more tolerable than a continuous flooding Damage to buildings and vehicles are important considerations Delayed emergency response times can have dire consequences Increased flooding and other climate change effects can erode city services and the desire for people to live or work there Increased inflow into sanitary sewers increases treatment costs Flooding damages landscaping that must be repaired or replaced Indirect economic effects from relocation and decreased local investment should be considered along with the direct physical damage and cost to infrastructure and property Subsidies should be available for private seawall owners who are required to raise or modify their seawalls. In some areas, seawall caps or earthen berms may be suitable. It is unfair for those not living in vulnerable waterfront areas to pay for the risk taken by waterfront property owners Examples exist for governments to collectively improve properties through uniform assessment and large bid contracts, such as lakeshore stabilization and soundproofing buildings near airports. Modeled projections will include 5, 10, and 20 year storm surge, coupled with 1 and 2 feet of sea level rise, and high tide water levels VII. Community Input on Adaptation Strategies Real-time feedback from Kahoot.it online survey: 1. Have you experienced hardship from a flood in the study area? Yes = 16 No = Do you think we can adapt to increased flooding? Yes = 28 No = 6 3. Do you have flood insurance? Yes, it is required = 6 Yes, but it's not required = 5 No = 21 I don't know = 1 4. Do you receive warnings about flooding? Yes, from local meetings or events = 8 Yes, from the news or weather forecast = 14 Yes, from neighbors and friends = 0 No = 4 Page 5 of 9

6 5. Could you raise your seawall? Yes = 2 No, because of cost = 3 No, because of space = 0 No, because of view = 1 6. Could you elevate your house? Yes = 0 No, because of cost = 13 No, because of street level, space on property or other = 4 7. Is raising a seawall affordable for homeowners? Yes = 2 No = 16 I do not know how much seawalls cost = How long have you lived in Broward? Less than 2 years = 6 2 to 5 years = 5 5 to 10 years = 2 More than 10 years = How often do you participate in community events or initiatives? A few times per year = 12 Weekly = 6 Monthly = 9 Never, this is my first = Do you feel the building code should be changed to increase resilience to flooding? Yes = 31 No, let owners build what they want and take on risk = Which option would you like to understand better? Berms or levees = 0 Seawalls = 0 Living shorelines and natural protection = 11 Pumping systems and temporary water storage areas = 13 Comments: Where will you store the water? Underground injection as a possible solution? Some areas will become infeasible to pump water from, which may necessitate converting the area to a water storage area. 12. Should natural solutions and shorelines offering habitat be prioritized? Yes, I would volunteer to use my property = 6 Yes, in general = 16 No = 1 Page 6 of 9

7 13. Would you volunteer to transform your seawall into living shoreline? Yes = 2 No, I do not have a seawall = 7 No = 1 Comments: Living shorelines should be considered because they are naturally adaptive over time, not fixed to a specific location and elevation, and require less management. Additional questions and comments: What building standards exist to promote resiliency in areas vulnerable to flooding, such as finished floor elevation? Many cities follow the FEMA flood standards. The focus of this study is not to recommend building floor elevation standards, but the results can inform future decisions. The 100 year flood maps will tie into the Community Rating System, which is being modified to encourage climate resilient development. VIII. Community Decision-making Process Alan Dodd summarized the next steps for the City of Fort Lauderdale. The seawall ordinance was developed over six months and is final. The current focus for the next six to eight months is on the modeling, analysis, and community engagement with the targeted neighborhoods in the stormwater master plan. Afterward, the design is planned to be completed by December Finally, a discussion about project costs with elected officials will occur. For the USACE-Broward County resiliency study, preliminary results should be available by Spring-Summer 2017, after which another stakeholder meeting will be scheduled. The 100 year community flood map will have its own community engagement meetings specifically for that project. USACE guidance apply to projects that Congress approves, typically related to large water resource related infrastructure projects, such as ports, levees, dams, canals, etc. The USACE guidance is required to consider sea level rise and changing rainfall patterns. The White House has released guidance on considering climate resilience in infrastructure. IX. Question and Answer Session and Wrap Up Where will the money come from to pay for infrastructure improvements? Has relocating the salinity barriers been considered to better mitigate saltwater intrusion? Are there regional efforts to adjust water levels to protect areas from high tide flooding? Moving the G-54 control barrier on the North New River canal further eastward has been considered, but to have a significant water supply Page 7 of 9

8 benefit would likely require coordinated movement of multiple control barriers eastward and concessions from the community and marine industry that would restrict waterway access to these areas. In addition, it would require significant operational changes to the hydrologic system. Broward County relies heavily on the South Florida Water Management District on their analysis of operational changes to the primary canal network. What is the difference between the FEMA map and the 100 year community flood map? The intent of the update to the 100 year community flood map is to proactively stay ahead of the FEMA flood maps by incorporating projected sea level rise into the results, which FEMA does not include. This will likely insulate the County from incurring massive FEMA flood insurance adjustments in the future. In addition, the 100 year community flood map includes areas of the County outside of FEMA flood zones, which do not have a finished floor elevation listed. FEMA maps differ for inland and coastal areas. Inland maps focus on flooding from precipitation and river systems, while coastal maps focus on storm surge flooding. Congress has prohibited FEMA from including sea level rise into its maps. Can you describe the economic analysis in the study? Based on the flood elevations from the scenario modeling, the economic analysis will estimate the physical damage costs to infrastructure, plus the economic losses from business operations. This will better inform which adaptation strategies to pursue. Broward County will be working with RMS on the economic analysis. RMS is a major risk management advisor for local governments, who has recently worked with the City of San Francisco on climate resiliency. RMS will do a comparative analysis of their in-house hydrodynamic model with the USACE ADCIRC model. How do you decide between adaptation resiliency planning and potential development of exit strategies in high-risk areas, because they appear to have competing time horizons and end goals. Also missing is a broad discussion of environmental justice, because no matter if you plan for resilience or for exit strategies, there will always be those that do not have the ability to pay. A specific strategy to ensure environmental justice does not currently exist. However, these conversations are occurring at a regional level. There will likely be multiple drivers of retreat from an area. Cost of living or operations may become cost prohibitive, driving changes in land use and investment. Isolated incidences like hurricanes may prompt mass migrations or justify redevelopment, however chronic vulnerability due to climate change may not result in reinvestment. An organized relocation is Page 8 of 9

9 not likely, given the large populations living on the coasts, especially in South Florida. Surface water management and drainage infrastructure strategies differ between counties. Miami-Dade is more inclined to provide fill and pumping to reduce flooding, while Broward leans toward on-site engineered water features, such as wet/dry retention areas and French drains, etc. X. Adjournment Dr. Danchuk adjourned the meeting at 4:30pm. Page 9 of 9