Groundwater Maps

A new groundwater surface map that includes projected sea level rise is now used when reviewing surface water management license applications. In May 2017, the Broward County Board of Commissioners enacted Ordinance No. 2017-16 amending Section 27-200 (b) (5) a. 3. b) of the Broward County Code of Ordinances ("Code") to read:

“Antecedent conditions: Ground water and surface water stages antecedent to a design event shall be the higher of the average wet season water levels or the applicable control elevations. Plate WM 2.1 may be used for determining the average wet season ground water levels for use in calculating a design event for existing projects, except for applications for major redevelopment as defined in Section 27-192 or for a major modification to a surface water management license. Plate WM 2.1 - Future Conditions shall be used for determining the average wet season ground water levels for use in calculating a design event for new applications for a surface water management license, applications for major redevelopment of existing sites, and applications for major modifications to existing surface water management licenses submitted after June 30, 2017.

In addition, Ordinance No. 2017-16 amended Section 27-200, Definitions, of the Code to read:

Major redevelopment means construction activities which involve the demolition or removal of the principal structure on a site or of more than fifty percent (50%) of the impervious surface of a developed area on a site. Major redevelopment also means minor redevelopment with the cumulative expansion of developed area greater than or equal to twenty-five percent (25%) of the existing developed area of a site or greater than or equal to two (2) acres over a period of ten (10) years.

These changes were necessary because the previous Code version utilizes an average wet season groundwater elevation map, Plate WM 2.1, which does not provide an adequate basis for surface water management system design for future flood protection and drainage. Application of Plate WM 2.1 – Future Conditions to surface water management system designs for new development, major redevelopment, and major license modifications will phase in better flood protection and drainage for future development. Further, the definition of "major development" was amended to correct a typographical error and to clarify that either the demolition or removal of the principal structure on a site or the demolition or removal of more than 50% of the impervious surface of a developed site qualify as a major redevelopment.

These changes will:

1) Account for conditions expected during the lifecycle of new structures;

2) Provide an appropriate tool for long-term infrastructure and site planning;

3) Ensure the resiliency of current and future infrastructure investments by addressing future flood risk in the design and licensing of surface water management systems in Broward County; and

4) Advance the resiliency standards and investments needed across the region, ultimately protecting both public and private infrastructure, preserving the quality of our environment, and ensuring a vibrant and competitive economy.

The Environmental Protection and Growth Management Department, as the local planning agency for the Broward County Comprehensive Plan, and the Broward County Planning Council, as the local planning agency for the Broward County Land Use Plan, held public hearings on March 23, 2017, and April 27, 2017, respectively, at which time it was recommended to the Board of County Commissioners that the proposed Ordinance was generally consistent with the Broward County Comprehensive Plan and Land Use Plan.

The Plate WM 2.1 – Future Conditions map represents the expected future average wet season groundwater elevations for Broward County. The average is based on model outputs for the months of May through October over the period of 2060-2069. The models used are The Broward County Inundation Model and the Broward County Northern Variable Density model, both developed by the United States Geological Survey (USGS) and MODFLOW based. The future conditions that are modified in the models are both precipitation and sea level rise. The future precipitation pattern is based on the Center for Ocean-Atmospheric Prediction Studies (COAPS) downscaled Community Climate System Model (CCSM) global model and represents an increase of 9.1% rainfall from the base case of 1990-1999 (53.4 inches/year to 58.2 inches/year). Sea level rise was based on the United States Army Corps of Engineers (USACE) National Research Council Curve 3 (NRC3) curve which equates to an increase of 26.6 inches to 33.9 inches to the future period from 1992 levels. Final groundwater elevation results are presented in the North American Vertical Datum of 1988 (NAVD 88).

The Plate WM 2.1 – Future Conditions map is the first map in a planned series of storm water design aids entitled the "Future Conditions Map Series. While this first map is an important tool in establishing design standards for drainage and surface water management systems, it does not address predicted changes in surface flood elevations anticipated with the rising groundwater table and loss of regional storage for rainfall. County staff is currently working on developing a second map, the "Future Conditions Broward County 100-year Flood Elevation Map," that, when completed, will represent predicted changes in surface flood elevations by integrating the anticipated rise in the groundwater table and the associated loss of regional storage during the 100-year design storm event. The "Future Conditions Broward County 100-year Flood Elevation Map" will be one of the tools used to determined appropriate finished floor elevations for residential and commercial structures in Broward County. Completion and adoption of this second map is expected by the end of 2019, and will constitute an important resiliency advancement by evaluating the effect of sea level rise on flood elevations across the County, inclusive of both eastern and western communities. This information will ultimately help reduce flood risk and flood insurance premiums by informing more resilient planning standards.