We’re thrilled to announce our latest Smart Pond installation at Seascape Resort! This CMAC (Continuous Monitoring & Adaptive Control) system delivers real-time flood control and improved water quality, protecting both local communities and Florida’s natural ecosystems.
We’re proudly serving businesses, municipalities, and residential communities across Florida with sustainable stormwater solutions. Want your own Smart Pond? 📩 Contact us at info@nationalstormwater.com
With the implementation of Florida’s updated stormwater rule, design flexibility has increased—particularly through the use of off-site compensatory treatment and Regional Stormwater Management Systems (RSMS). However, these strategies may lead to the discharge of partially treated stormwater runoff to wetlands.
While this approach offers permitting efficiency, it also raises a key technical question:
How do we demonstrate that a wetland has the assimilative capacity to receive this runoff without causing an adverse impact?
📜 Regulatory Background: Rule 62-611, F.A.C.
The good news is wetlands are consumers of nutrients. In fact, wetlands need nutrients to thrive. The issue is determining the total amount of nutrients that can be assimilated by a wetland system while remaining within healthy limits. The answer lies in Chapter 62-611, F.A.C., Florida’s Wetlands Application Rule, which outlines procedures to evaluate wetland assimilative capacity. Originally developed for wastewater treatment wetlands, this rule can also be applied to stormwater discharges—especially in the context of project designs that discharge partially treated runoff to natural wetlands while using off-site compensatory treatment within the same watershed.
🔬 Key Wetland Capacity Criteria
Rule 62-611 sets specific hydraulic and nutrient loading limits for discharges to artificial treatment wetlands and natural (receiving) wetlands. We will use the more stringent limits for natural wetlands in this procedure:
– Hydraulic Loading:
≤ 2 inches/week (annual average)
Detention Time: > 14 days (annual average)
– Nutrient Loading (Assimilative Capacity)
Total Nitrogen (TN): < 25 g/m²/year
Total Phosphorus (TP): < 3.0 g/m²/year
– Discharge Limits:
To Receiving Wetlands: TN = 3 mg/L, TP = 1 mg/L
🚧 How This Applies to Projects
Typical event mean concentrations (EMCs) for project runoff are already below the discharge limits. For example, the EMCs for roadway projects are:
– TN: 1.52 mg/L
– TP: 0.20 mg/L
This means that for many projects, discharges to wetlands may comply with Rule 62-611 without additional nutrient treatment, as long as the wetland has sufficient assimilative and hydraulic capacity.
📌 Why This Matters
By applying the wetland assimilative loading criteria under Rule 62-611, engineers can demonstrate regulatory compliance for wetland discharges from partially treated stormwater systems. This can support more cost-effective stormwater designs, reduce the need for additional BMPs or treatment infrastructure, and allow the use of off-site compensating treatment to achieve full compliance with the new, more stringent performance criteria later this year.
📂 Downloadable Design Example
To help illustrate this approach, we’ve provided a downloadable spreadsheet example that walks through the process of evaluating a wetland’s assimilative and hydraulic capacity for a representative stormwater discharge scenario. Note that other developments that discharge to the same wetland system may add to the cumulative loading, so provisions for calculating this loading are included in the spreadsheet.
📥Download the Design Example Spreadsheet
🧰 Tips for Stormwater Engineering Consultants:
– Use Rule 62-611 procedures to evaluate wetland assimilative loading capacity.
– Ensure discharge concentrations and loading rates from your project are within allowable thresholds for the receiving wetlands.
– Consider the cumulative loading from other developments within the same basin that may discharge to the same wetlands.
– Larger wetland systems are more likely to assimilate additional nutrient loading without adverse impact.
– Coordinate with the WMD early in design to confirm consistency with the ERP Rules and Applicant’s Handbook.
Stormwater Nutrient Credits (SNCs) are available for purchase in the Tampa Bay HUC-8 Service Area within the Southwest Florida Water Management District (SWFWMD). This program functions like wetland mitigation banking, allowing public and private developers to meet stormwater treatment requirements by purchasing off-site credits.
By utilizing SNCs, developers can streamline compliance, reduce on-site infrastructure costs, and contribute to regional water quality improvements. This approach provides a flexible, cost-effective solution for meeting regulatory requirements while supporting sustainable development.
If you are interested in purchasing credits or learning more, please fill out the contact form, or email us at info@nationalstormwater.com.
Stormwater Nutrient Credits (SNCs) are available for purchase in the Halifax River HUC-12 Service Area within the St. Johns River Water Management District (SJRWMD). This program functions like wetland mitigation banking, allowing public and private developers to meet stormwater treatment requirements by purchasing off-site credits.
By utilizing SNCs, developers can streamline compliance, reduce on-site infrastructure costs, and contribute to regional water quality improvements. This approach provides a flexible, cost-effective solution for meeting regulatory requirements while supporting sustainable development.
If you are interested in purchasing credits or learning more, please fill out the contact form, or email us at info@nationalstormwater.com.
The June 28, 2024, updates to Chapter 62-330, F.A.C. and the Environmental Resource Permit Applicant’s Handbook Volume I (AH I) brought significant changes to stormwater design and treatment standards. For projects with Conceptual Environmental Resource Permits (ERPs) issued prior to this date, the key question is: Do the new treatment performance standards apply to future construction phases under an existing conceptual ERP?
📝 Rule Background: AH I, Section 3.1.2(e)3
Section 3.1.2(e)3 of the updated AH I provides that if a construction phase is consistent with an unexpired conceptual ERP, it may continue using the stormwater criteria that were in effect at the time the conceptual approval was issued—commonly referred to as grandfathering. However, if modifications to the construction phase cause substantially different water resource impacts, the project will be subject to the new standards.
📌 Why Verifying Grandfathering Status Is Important
While the grandfathering provision is clearly stated, the determination of what constitutes “substantially different water resource impacts” can be subjective. This is why it is highly advisable for consulting engineers to seek confirmation from the Water Management District (WMD) that a project phase remains eligible for grandfathering.
🛡️ Benefits of a Grandfathering Verification Request:
📄 How to Submit a Request
The verification request should include:
📂 Get a Head Start:
To assist you, we have provided a draft Grandfathering Verification Request letter that you can tailor to your projects.
📥 Download the Draft Grandfathering Verification Request Letter
By taking this proactive step, consulting engineers can streamline the permitting process, protect their project timelines, and reduce uncertainty under Florida’s evolving stormwater regulations.
1. What is a Regional Stormwater Management System (RSMS)?
An RSMS is a facility designed, constructed, and maintained to manage stormwater for one to multiple parcels and may serve one or more projects within a defined drainage area (you can think of this like the service area of a mitigation bank). Its purpose is to prevent flooding, reduce pollution, and manage stormwater discharges for a larger area compared to a conventional system.
2. How does an RSMS differ from traditional stormwater management systems?
Unlike stormwater management systems that are integrated within a development project, an RSMS is permitted as a standalone stormwater management system to serve multiple projects in a defined area. It also provides a mechanism for accountable nutrient reduction across a HUC 12 or potentially larger watershed, enabling more efficient land use and potentially lower development costs through offsite compensatory treatment credits (aka Stormwater Nutrient Credits).
3. What are the main advantages of using an RSMS?
– Cost Efficiency: Offsite treatment infrastructure can reduce site development costs.
– Improved Water Quality: Centralized treatment in larger, professionally managed stormwater facilities achieve higher pollutant removal rates.
– Flexibility in Development: Developers may reduce on-site treatment requirements by utilizing offsite credits.
– Comprehensive Watershed Management: Better tracking and accountability of stormwater nutrient reduction at a watershed scale.
4. How are pollutant load reductions allocated in an RSMS?
RSMS facilities track pollutant removal in pounds or kilograms, ensuring allocations do not exceed their permitted treatment capacity. Records of these allocations must be maintained permanently by the RSMS permit holder and reported as specified in Sections 9.7.3 and 12.6(d) of the Applicant’s Handbook.
5. What permitting requirements apply to RSMS?
RSMS must be permitted under the Environmental Resource Permit (ERP) program. This includes demonstrating reasonable assurance of compliance with water quality standards, long-term operations and maintenance, and accurate tracking of nutrient load reductions.
6. How does an RSMS provide stormwater nutrient credits (SNCs)?
An RSMS can generate SNCs by documenting excess treatment capacity in an accounting ledger, much like a wetland mitigation bank. These credits can then transferred to other entities within the same service area (e.g. hydrologically connected or within the same watershed) to offset their pollutant loading requirements. Keep in mind that the user of an SNC must still meet the water quantity requirements of ERP (e.g. pre-post rate control) and must demonstrate that the discharge of less than fully treated stormwater does not adversely impact any downstream waters.
7. Who is responsible for maintaining an RSMS?
The permit holder of the RSMS is responsible for its operation, maintenance, and compliance with all applicable regulations. This includes maintaining accurate records of stormwater treatment allocations and ensuring that the system operates within its design capacity.
8. Does the user of SNCs have any ongoing responsibilities after the credits are transferred to their project from an RSMS?
No. Like a wetland mitigation credit, the purchaser bears no long-term responsibility for the continued operations and maintenance of the nutrient credit generating project. That obligation falls solely on the RSMS permit holder.
Our collaboration with Babcock Ranch ensured effective stormwater management during Hurricane Ian. The innovative smart pond systems diverted water and recharged wetlands, preventing flooding and protecting the community. By integrating advanced technology and sustainable design, Babcock Ranch remained resilient while surrounding areas were severely impacted. This partnership demonstrates how smart stormwater solutions enhance community resilience against extreme weather events.
NST is proud to have played a key role in the stormwater infrastructure at Babcock Ranch, highlighted as a FEMA case study for its remarkable performance during Hurricane Ian. As America’s first solar-powered town, Babcock Ranch stands as a testament to the power of smart stormwater technology and resilient design.
Through smart stormwater technology and sustainable design, we’re helping shape communities built to endure Florida’s most challenging weather events while protecting water quality and the environment.
By: Mark Thomasson, P.E., Chief Stormwater Engineer
A common point of confusion with the new Florida stormwater rules involves how they apply to ongoing developments, especially for projects involving outparcels within previously approved master development plans. Here’s a quick breakdown using a typical scenario to help clarify how the new rule applies.
Scenario:
Imagine a multi-parcel commercial subdivision with interior roads, parking areas, and a large stormwater pond, all designed and permitted under a comprehensive stormwater master plan. The development is mostly built out and the stormwater system is already in the operational phase and managed by a commercial property owners’ association. One commercial outparcel—sold recently to a new buyer—remains undeveloped. The buyer intends to use the land consistent with the original assumptions for land use type and impervious coverage in the master plan.
How the New Rules Apply:
Since the master plan was properly permitted under the prior rules, the new stormwater requirements only apply to the outparcel project itself. This means:
Key Takeaway:
For outparcels in fully permitted developments, requirements of the new stormwater rules are limited to the outparcel itself. There is no need to retroactively adjust or re-permit the existing infrastructure, as long as the new construction is consistent with the original permit’s assumptions.
As Hurricane Milton brought unprecedented rainfall to Hillsborough County, our smart pond at SR-676 effectively demonstrated its advanced capabilities. The system initiated the lowering of water levels 24 hours before the storm’s peak, facilitating proactive flood management. The animation below illustrates the varying water levels in the pond at different times throughout the day.
With a staggering 13.2 inches of rain falling in less than a day—an event classified as a 200-year storm—our pond effectively handled the runoff, despite the adjacent Delaney Creek overtopping its banks. Importantly, this meant the pond did not contribute to any local flooding, helping to protect the surrounding community.
We take pride in the role this technology played in minimizing stormwater impacts during such an extreme weather event. Our thoughts are with those affected by Hurricane Milton, and we are committed to advancing our flood mitigation efforts to safeguard our communities in the future.
"*" indicates required fields
© 2025 National Stormwater Trust. All Rights Reserved.
