Recommendations from hydrologist Stephen Suau in the wake of Tropical Storm Debby
At the 10/24/24 SCAN meeting, professional engineer and hydrologist Stephen Suau presented his independent study and preliminary findings following Tropical Storm Debby. He has now prepared and submitted constructive recommendations to the Sarasota County Stormwater Department which is provided below.
If any of these recommendations ring true to you or your community, SCAN encourages to let your County Commissioners know that the County should consider if not embrace them at a minimum to protect existing and future residents from flood damage and improve stormwater service to its customers.
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| Teresa Mast Mark Smith Tom Knight Joe Neunder Ron Cutsinger |
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| Laurel Meadows after Debby, August 5, 2024 |
REVIEW OF FLOODING IN THE PHILLIPPI CREEK BASIN DUE TO TROPICAL STORM DEBBY
RECOMMENDATIONS
Background
The recommendations herein are provided by Stephen M. Suau, P.E. Engineering and Consulting, LLC following an independent review and preliminary technical evaluations of the flooding resulting from the rainfall associated with Tropical Storm Debby (TSD); discussions with Sarasota County staff; and input from members of the community.
Flooding such as that experience from TSD occurred in the Phillippi Creek drainage basin in 1962 and 1992 with the latter resulting in the advancement of the Stormwater Environmental Utility (SEU) by Sarasota County. The SEU was established specifically to manage both rainfall flooding and stormwater quality and provides a committed source of annual revenue for these purposes. Currently, this annual revenue is approximately $25,000,000. Properties are assessed independent of millage rates based generally upon their impervious coverage. The revenue generated is utilized for administration, planning, regulation, and maintenance of the public stormwater infrastructure. Stormwater capital improvement projects, as needed, have been funded by separate basin-specific assessments. The SEU enabled the public acquisition and utilization of the large historical floodplain now known as the Celery Fields Regional Stormwater Facility (CFRSF); the adoption of the 100-year design storm criteria for public and private infrastructure constituting the most stringent criteria in and inclusive of the Southwest Florida Water Management District; the development and adoption of sophisticated hydrodynamic flood models and floodplain maps; and the establishment of a County-wide rainfall and water level monitoring network. Similarly, the recommendations contained herein are intended to further protect the enviable quality of life of existing and future residents from flood damage in the wake of Tropical Strom Debby.
Sarasota County has also established an Environmentally Significant Lands Protection Program (ESLPP) by voter referendums in 1999 and 2005. The ESLPP currently generates revenue based upon a portion of property millage assessments for the acquisition and protection of natural lands, many containing designated floodplain areas.
Recommendations
Based upon the independent review performed by Stephen M. Suau, P.E. Engineering and Consulting, LLC, and in the context of applicable Sarasota County Comprehensive Plan Goals, Objectives and Policies (refer to Appendix A), the following operational and administrative recommendations are provided:
Operational Recommendations
A significant portion of SEU’s annual operating budget and efforts are allocated to the operation and maintenance of the public stormwater infrastructure system. Annual SEU revenues have increased over the past decades due to both increases in the stormwater assessment fees and the population base. At the same time, the public stormwater infrastructure (i.e. network of ditches and drainage structures) has not dramatically increased as commercial and residential development projects are responsible for the construction and maintenance of their private stormwater management systems. Yet, public input in the wake of TSD has cited a perceived lack of maintenance of the public stormwater infrastructure by the SEU.
It is in this context that the following operational recommendations are provided to: (1) improve the quality and utility of the current monitoring and modeling technologies; (2) utilize the latest cost effective technologies; (3) increase coordination and collaborations between SEU planning, design, permitting, and operations staff; and (4) re-engage with the public as valued SEU customers to overcome their perceptions and concerns.
1. Use of Technology and Engagement for Maintenance of Stormwater Infrastructure
Sarasota County’s Municipal Separate Storm Sewer System (MS4) Permit specifies the frequency of inspection and maintenance activities required for each asset type of the public stormwater infrastructure. To facilitate this process, the SEU created a web-based stormwater infrastructure database (SID) available at the following link: Sarasota Stormwater Map (arcgis.com). SID categorizes stormwater infrastructure based upon its drainage hierarchy and maintenance frequency, consistent with the County’s MS4 Permit.
Concurrently, SEU manages the inspection and maintenance of stormwater assets through an asset management software (AMS) with each stormwater asset assigned a unique identifier. The AMS provides work orders that are either scheduled activities, such as routine ditch maintenance; or non scheduled activities when non-anticipated and emergency actions are warranted. The scheduled activities are programmed based on the minimum frequency set forth in the MS4 permit.
It is recommended that Sarasota County’s asset management software (AMS) be linked to the stormwater infrastructure database (SID) so that the public and SEU customers can track public stormwater infrastructure inspection and maintenance activities in real time.
It is recommended that the SEU conduct annual if not routine open houses with community representatives within each of the five (5) primary watersheds: Sarasota Bay, Little Sarasota Bay, Dona/Roberts Bay, Lemon Bay, and Myakka River. SEU should utilize the open houses to review maintenance schedules with existing and new residents and to solicit input on other maintenance needs from SEU customers.
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2. Transparency and Engagement regarding Pre-Storm Action Plan
The SEU has identified approximately 200 hot spots where known drainage issues have arisen in the past. These drainage issues include trash or litter debris build up, illegal dumping, excessive vegetation growth, etc. These hot spots are identified in the stormwater infrastructure database (SID) available at the following link: Sarasota Stormwater Map (arcgis.com).
With the identification of an oncoming storm, between 72 and 24 hours preceding the storm, SEU staff generates and is assigned hot spot work order assignments from the Asset Management Software (AMS) for inspection, and if warranted, corrective action. The intent of this program is to ensure that public stormwater assets perform as intended.
It is recommended that the SEU also solicit input from customers on existing and potentially additional hot spots as part of the annual and/or routine open house.
3. Identification, Inspection, and Maintenance of Dikes (or Levees)
Properties protected by dikes (or levees) can be uniquely susceptible to unexpected and potentially significant flooding if such dikes are breached or fail. Recent examples include the Laurel Meadows subdivision from TSD and Hidden River from Hurricane Ian in 2022.
It is recommended that SEU inventory all dikes (or levees) within the City of Sarasota and unincorporated Sarasota County. The inventory should identify the ownership and entity responsible for maintenance of all dikes (or levees). Finally, the SEU should require that all dikes (or levees) are inspected and certified annually by a professional engineer to ensure proper operation and maintenance.
A sample inspection report required for the annual inspection and certification of above ground impoundments (AGIs) by the SFWMD is provided in Appendix B.
4. Flood Management of the Celery Fields Regional Stormwater Facility
As discussed in Section 3.3.1, the operation of the Main C structure gates can potentially impact flood elevations upon private properties downstream and adjacent to the CFRSF. The precise protocol is somewhat uncertain.
It is recommended that the SEU pursue the creation of additional floodplain storage within the CFRSF as a high priority.
It is recommended that the SEU pursue the feasibility of creating additional floodplain storage on public lands adjacent to the CFRSF.
It is recommended that SEU re-evaluate the efficacy of the Main C structure gates operation in terms of resulting flood impacts both upstream and downstream. If it is determined that the operation of the Main C weir gates is warranted, automation should be pursued, and transparent notification protocol should be established in coordination with affected upstream private properties. Once the protocol is established, it should also be incorporated into the County’s existing text / email alert systems and sent to the potentially affected properties.
5. Contract with the USGS to manage ARMS Data
The SEU operates over 50 automated rainfall and stream monitoring stations within the City of Sarasota and throughout unincorporated Sarasota County. Referred to as the Automated Rainfall Monitoring System or ARMS, this data provides both invaluable real time information and a permanent record of past events for subsequent analyses and evaluations. Yet the potential value of this investment is not fully realized due to understaffing for sufficient quality control/assurance and data reduction.
The United States Geological Survey (USGS) operates and maintains several stream stage and discharge monitoring stations within the Sarasota County region. The USGS protocols are the gold standard for stream monitoring, setting the bar for quality control/assurance, field measurements, and data reduction.
It is recommended that SEU contract with USGS to manage ARMS, including the development of rating curves and publishing of rainfall, stream stage/elevation, and discharge data.
Administrative Recommendations
These recommendations are applicable to the planning and regulatory side of SEU and are also intended to (1) improve the quality and utility of the existing monitoring and modeling technologies; (2) utilize the latest proven and cost-effective technologies; (3) increase coordination and collaborations between SEU planning, design, permitting, and operations staff; and (4) re-engage with the public as valued SEU customers to overcome and rebuild their perceptions and concerns.
6. Continue to Build Internal Expertise and Capacity of SEU
Since the creation and adoption of the original flood prediction models several decades ago, SEU has at times periodically relied on consultants to update the models and perform development reviews. This resulted in an overreliance of consultants as well as a corresponding thinning of internal technical expertise. While the assistance of consultants is important to assist in the design and permitting of major stormwater improvement projects, it is important that SEU staff be of sufficient number with the broad core expertise to direct and manage both consultants and the direction of major projects. It is understood that in recent years SEU has begun to re-internalize both model maintenance and development reviews. This effort should be continued with a goal of broad internal cross-training of technical expertise with the latest state-of-the-art and cost-effective technologies.
It is recommended that the internal core expertise and capacity of SEU staff continue be built to proactively manage the technical, operational, and customer service aspects of the stormwater program using state of the art technologies. This may require at least a partial restructuring of leadership, organization, and staff expertise. As such, market competitive salaries must be considered to attract competent and qualified full-time employees. The creation of a culture of multidisciplinary collaboration and a proactive sense of purpose must be a priority of leadership.
7. Proactively Protect Significant Floodplain Areas
Since Sarasota County’s formal adoption of the local detailed flood prediction models and maps over 20-years ago, the SEU has been slow to move this best available information into the Federal Emergency Management Agency’s (FEMA) Flood Insurance Rate Maps (FIRMS). At the same time, these local flood maps have not been readily available and accessible to the public. Moreover, these established local flood maps could and should be used proactively in planning to assist in meeting applicable goals, objectives, and policies of the Sarasota County’s Comprehensive Plan.
Recognizing that not all floodplains are created equal, and that FEMA has defined several floodplain categories, it is recommended that SEU make provisions to widely publish the SEU floodplains utilizing such categories for ease of public access.
It is recommended that SEU proactively prioritize floodplains for planning and protection through acquisition of public easements. Such a proactive program should include coordination, if not a partnership with other agencies and programs such as Sarasota County’s Environmentally Significant Lands Protection Program (ESLPP) to implement floodplain, water quality, and ecological function enhancements; facilitate public access and recreation opportunities; and assure perpetual management (i.e. operation and maintenance), as applicable. The 1994 purchase and subsequent enhancement of the Celery Fields Regional Stormwater Facility established a successful model for proactive floodplain planning, protection, enhancement, and public access by SEU.
8. Minimize Density Increases in Designated Floodplain Areas
As evidenced by TSD and other previous flood producing rainfall events, there is a nexus between flood damage and designated floodplain areas. Fortunately for Sarasota County, the existing floodplain areas have long been mapped and are a known. In fact, these floodplain areas are recognized and used as a constraint when planning by several large and long-term developments.
In this context, rezoning to increase densities within designated floodplains is a unique opportunity to apply basic planning principles to assure that such proposals avoid or minimize flood damage to existing and future residents. Consistent with applicable Comprehensive Plan goals, objectives, and policies (refer to Appendix A) these assurances should be considered prior to increasing densities in designated floodplains. Granting such density increases without sure upfront assurances and based just upon a reliance of the “models” and development “codes” to address floodplain issues should be avoided.
It is recommended that the available floodplain models and maps be used proactively to more rigorously evaluate rezoning applications that propose to increase densities in designated floodplains. As an example, this evaluation could include the following:
⮚ For rezoning proposals that do not include a binding site plan, it should be stipulated that the development will be clustered so that no encroachment into the 100-year would occur or be allowed. However, the applicant may elect to demonstrate that adequate onsite floodplain mitigation measures would be provided using the applicable flood model to offset any potential increases in flood elevation for the 100-year design storm as part of the rezoning process.
⮚ For rezoning proposals that include a binding site plan, a binding floodplain encroachment map shall be included with the application clearly identifying the proposed development footprint overlaid with the limits of the County established and adopted floodplain. The percentage of the horizontal extent of each 100-year floodplain category (AE, AH, etc.) which would remain and be lost based on the proposed development footprint should be determined and displayed on the map. If greater than 5%, the applicant shall demonstrate using the applicable flood model that such encroachment will not result in an increase in offsite flood elevation for the 100-year design storm.
9. Update Design Storm Criteria
While the Southwest Florida Management District (SWFWMD) and other municipalities in the region utilize 8 inches of rainfall corresponding to the 25-year, 24-hour design storm for regulatory purposes, SEU utilizes 10 inches of rainfall corresponding to the 100-year, 24-hour design storm. However, all federal, state and local municipalities typically require that the finished floor of habitable structures be set at or above the 100-year flood level (aka base flood elevation). Regardless, the current regulatory design storm criteria utilized by SEU and established by the SWFWMD is based upon the evaluation of rainfall data and records prior to 1996. As such, the current design criteria do not consider the last 29 years of rainfall data. Several authoritative rainfall analyses have been conducted since 1996 including by the University of Central Florida’s Stormwater Management Academy in 2011, the National Oceanic and Atmospheric Administration (NOAA) in 2013, and the United States Geological Survey (USGS) and South Florida Water Management District (SFWMD) in 2022.
It is recommended that SEU engage with the SWFWMD, Unites States Geological Survey, and any other appropriate authoritative and academic agencies to update the design rainfall volumes for planning and regulatory purposes.
10. Engagement of Stormwater Environmental Utility Advisory Committee
The Stormwater Environmental Utility Advisory Committee (SEUAC) consists of 10 Sarasota County residents appointed by the Board of County Commissioners. Pursuant to Sarasota County Resolution No. 2022-205, SUEAC “shall act solely in an advisory capacity, without compensation, reporting directly to the Board” with the purpose “to support and advise the SEU in the development of the stormwater related goals and objectives, and serves a venue for deliberation, consideration, and recommendation of public input regarding SEU issues from the residents of Sarasota County to the Board. To accomplish this purpose, the SEUAC shall:
⮚ Review each Fiscal Year’s SEU budget and work program and provide a letter of recommendation;
⮚ Assist the SEU in the development of Stormwater-related goals and objectives, including the Comprehensive Plan required by F.S. Ch. 163, Pt. II (F.S. Chapter 163.3161 et seq.); ⮚ Make recommendations on matters relating to stormwater management, including the scope of services for consulting planning efforts;
⮚ Serve as a forum to review proposals by the public;
⮚ Stimulate citizen involvement in stormwater issues; and
⮚ Periodically, evaluate the SEU’s program, facilities, and services to assure ha objectives and goals are being achieved consistent with the Comprehensive Plan.”
It is recognized that the SEUAC is a voluntary committee so their time is limited and should be used as efficiently as possible.
It is recommended that SEU utilize the SEUAC to the maximum extent possible regarding further vetting of the recommendations contained herein; evaluation of cost-effective technologies and approaches to implement these recommendations; and strategies for broader engagement of SEU customers.
APPENDIX A
WATER GOAL 1: Sarasota County shall provide programs which prevent and mitigate the losses, cost, and human suffering caused by flooding; protect natural and beneficial functions of the floodplain; protect water quality by preventing further degradation of the water resources; enhance water quality where appropriate; enhance, protect and conserve the hydrologic and ecological functions of natural systems including estuaries, the Gulf of Mexico, freshwater and groundwater systems; and ensure safe, efficient, economical, and sustainable water supplies that provides customers the appropriate water quality for the intended use.
WATER OBJECTIVE 1.1: Address the maintenance of existing facility capacity and ensure the adequacy of facilities to meet future needs.
WATER POLICY 1.1.1: The county shall continue to operate a Stormwater Environmental Utility (SEU) to provide for monitoring, maintenance, and improvement of the county's stormwater management system. The Utility shall manage the county's stormwater system to minimize pollutants, flooding, and sedimentation wherever possible. The Utility shall continue cooperation with the municipalities, other appropriate governmental agencies, and public and/or private utilities, which will implement Watershed Management Plans. Replacement and correction of existing facility deficiencies as well as providing for future facility requirements shall be identified and prioritized for inclusion in the County's Capital Improvement Program (CIP).
WATER POLICY 1.1.2: The county and private developments shall monitor and maintain stormwater management and conveyance facilities to ensure that the stormwater management systems are adequately maintained and functioning in compliance with design and permit requirements.
WATER POLICY 1.1.3: The county shall continue to fund the continuous maintenance of watershed maps and models for each drainage basin in the County through the Basin Master Planning Program to provide a basis of review for new development and other watershed alteration proposals as well as assure that stormwater management systems are developed to attain the adopted level of service. Each detailed master plan shall be developed, in accordance with the Basin Master Plan Schedule, as a Sarasota County inter-department effort to ensure consideration of natural drainage functions. Basin master plans shall be developed in cooperation with the municipalities and adjacent Counties to address stormwater quality and quantity problems in basins crossing more than one political boundary. Each plan shall be designed to protect downstream and estuarine water from degradation by stormwater runoff. Each basin plan shall define the level of service and a cost- effective capital improvements program shall be developed. As each basin plan is completed, the comprehensive plan, including the Capital Improvements Plan, shall be amended to incorporate and reflect the stormwater management system improvements identified in the basin plan.
WATER POLICY 1.1.4: As part of the basin master planning program, the county shall identify: 1) the extent of the existing 100-year floodplain; 2) all drainage facilities which fall below adopted level of service standards; 3) costs associated with improving such facilities to meet minimum drainage level of service standards; and 4) funding sources for those improvements. Where the improvements of drainage facilities are not feasible or desirable, alternative methods may be employed including, but not limited to, off-line reservoirs, parks designed for flooding, and floodways. If the completion of improvements to provide the adopted minimum level of service standards for existing development or existing roadways would result in unacceptable adverse economic or social impacts to specific areas, a level of service less than the adopted minimum may be accepted for the specific area.
WATER POLICY 1.1.5: The county shall pursue providing regional stormwater management systems, including those that could take the place of site-specific attenuation facilities. These regional systems should be developed by the county and, when appropriate, funded by development in lieu of construction of onsite, private attenuation facilities. Privately owned water quality treatment facilities should be located and maintained onsite to promote source control of pollutants before they enter the County stormwater system.
WATER POLICY 1.1.6: As the county develops stormwater management facilities, all system improvements shall be developed with consideration for aesthetics and the possibility of incorporation into the county park system.
WATER POLICY 1.1.7: The County shall support creation, implementation, and update of Watershed Management Plans, that includes holistic management practices, quantitative water quality readings, and protect the health of surface waters.
Relative to operation and maintenance, the SEU’s Stormwater Management Program is based on requirements set forth in the Unified Development Code, the County’s Comprehensive Plan and permit requirements set forth in the State of Florida Municipal Separate Storm Sewer System Permit, issued to Sarasota County pursuant to Permit No. FLS000004-005 - MAJOR Facility (MS4 Permit). As part of the MS4 Permit, the County is required to implement a Stormwater Management Program (SWMP). The SWMP requires the inspection and maintenance of stormwater infrastructure, known as structural controls in the permit. Structural controls are generally associated with the collection, storage, attenuation, treatment and conveyance of stormwater runoff.
The permit specifies the frequency of inspection and maintenance activities required for each type of structural control. The SEU has identified and categorized stormwater structural controls, identified as “assets” in the SWMP. The assets include inlets, catch basins, curb/gutter, culvert pipes, swales, ditches, canals, weirs, bridges, levees, retention and detention ponds, floodplain compensation areas, pump stations, and other similar facilities.
APPENDIX B
ABOVE GROUND IMPOUNDMENT
INSPECTION/CERTIFICATION REPORT
This checklist is to be used as a suggested guide for annual above ground impoundment inspections/certifications. Although it is fairly complete, it should not be interpreted as being limited and/or all inclusive in any particular case. The certifying engineer is responsible for the scope of the inspection(s) and the contents of the report(s). A “YES” response requires that alterations or repairs be specified to be accomplished by a special calendar date. If additional room is needed to comments, please add extra sheets.
PERMIT NUMBER __________________ DATE OF INSPECTION _______________
1. ARE THE IMPOUNDMENT TOP ELEVATION, TOP WIDTH AND SIDE SLOPES AS PERMITED?_________IF NOT, PLEASE EXPLAIN.
2. ARE THE DIMENSIONS, ELEVATIONS AND MATERIALS (I.E. FIXED PLATE METAL WEIR, ETC.) OF THE IMPOUNDMENT DISCHARGE STRUCTURE(S), DISCHARGE CULVERT(S) AND EMERGENCY OVERFLOW STRUCTURE(S) AS PERMITTED? _________ IF NOT, PLEASE EXPLAIN.
3. IS THE REST OF THIS IMPOUNDMENT SYSTEM CURRENTLY AS PERMITTED AND DOES IT SHOW EVIDENCE OF BEING OPERATED AS PERMITTED? __________ IF NOT, PLEASE EXPLAIN.
4. ADDITIONAL COMMENTS
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