Chapter 6 Activities
6. Stormwater System Design & Maintenance
Introduction
Sarasota County receives about 54 inches of rainfall annually, though amounts can range from 35 inches in drought years to as much as 75 inches in particularly wet years. This rainfall deposits nutrients from the atmosphere onto both land and waterbodies (see Chapter 5). Some of the rain is intercepted by tree canopy, evaporates, or filters into the soil. However, in areas where natural pervious surfaces have been replaced by impervious features such as rooftops, roads, and parking lots, rain cannot infiltrate the ground and instead accumulates to form surface or subsurface runoff. Manmade drainage ditches and canals increase the volume and velocity of runoff, which can carry excess nutrients downstream through the watershed.
Nutrient concentrations in runoff vary with rainfall amount and intensity, as well as land cover characteristics—including the ratio of impervious to pervious surfaces, soil type, and vegetation. In urban areas, typical stormwater runoff contains about 2.0–2.4 mg/L of total nitrogen and 0.3–0.5 mg/L of total phosphorus—roughly five times higher than Florida’s ambient water quality standards for estuarine waters (Sarasota County 2023).
Florida law, first enacted in the 1980s and most recently updated in 2024, requires the use of stormwater best management practices (BMPs) in new developments to intercept and treat runoff before discharge to waterbodies. However, many older neighborhoods were built before these rules existed and may provide little or no stormwater treatment unless retrofitted. Once installed, stormwater BMPs must be properly operated and maintained to remain effective at pollutant removal.
Regulations differ for runoff entering natural waterbodies (see Chapter 6.1) versus runoff captured and detained in stormwater ponds (see Chapter 6.2). While BMPs such as ponds and swales help protect the ecological health and recreational uses of downstream waters, they are not themselves subject to the same water quality standards as natural waterbodies. The most effective BMPs not only treat runoff but also offer aesthetic, recreational, and ecological benefits.
Activity 1:
Estimate and Communicate Annual Nutrient Loads From Stormwater
Robust, long-term monitoring and modeling programs that account for surface and subsurface runoff, streamflow, and the composition of nitrogen species (organic and inorganic) are essential to accurately estimate and manage nutrient loads in watersheds.
Activity 2:
Quantify Costs and Effectiveness of Stormwater Best Management Practices
Stormwater Best Management Practices (BMPs) can capture and treat nutrient-laden runoff before it enters waterbodies, with varying degrees of efficiency. Where large-scale solutions like constructed wetlands or retention ponds are not feasible or affordable, smaller-scale green infrastructure should be encouraged—particularly in urbanized areas. These include green roofs, rain gardens, cisterns, pervious pavement, and multi-use “stormwater parks.” More research is needed to quantify and compare the costs and effectiveness of all BMP types.
Activity 3:
Encourage Implementation of Green Infrastructure and Resiliency in Site Plans of New and Redevelopment
New state and local stormwater policies now require development and redevelopment projects to better protect water quality. These updated regulations present an opportunity to decouple urban development from increased nutrient pollution. Development approaches that emphasize natural areas, green infrastructure, and low impact design (LID) are essential to meeting water quality goals.
Activity 4:
Adopt or Update Local Ordinances to Provide Guidelines for Stormwater Pond Management
Stormwater ponds and canals must be maintained to retain their nutrient removal efficiency, yet many lack consistent, long-term maintenance. Local ordinances can establish a framework for outreach, inspection, and certification to ensure that these systems are managed effectively to reduce nutrient pollution.
