6.2 Quantify costs and effectiveness of stormwater best management practices

Key Message: 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.

Importance

Preventing nutrients from entering stormwater runoff is the most effective strategy for nutrient reduction. After that, BMPs play a critical role in intercepting and treating runoff to reduce nutrient pollution and safeguard water quality and recreational uses. BMPs use natural processes like sedimentation, biological uptake by plants and soil, and microbial denitrification to remove nitrogen and phosphorus before stormwater is discharged into receiving waters.

Overview

Conventional BMPs include wetlands, baffle boxes, retention ponds, street sweeping, and infrastructure upgrades (e.g., repairing undersized culverts or pipes). These systems often require extensive planning, construction, or coordination and are typically applied at a larger watershed scale.

In situations where larger infrastructure is impractical or too costly, green infrastructure—also known as Low Impact Development (LID)—can be implemented to manage runoff at its source, minimizing the volume of water and pollution flowing from the built environment (Figure 6.2.1).

Green infrastructure includes:

• Canopy trees and green roofs that intercept rainfall before it reaches the ground
• Rainwater harvesting systems like barrels or cisterns that store rainwater for reuse
• Vegetative buffers and shoreline littoral zones that filter runoff before it enters waterbodies
• Pervious pavements (e.g., pavers, gravel) that allow stormwater to infiltrate
• Rain gardens, vegetated swales, and recessed tree islands that slow and absorb runoff
• Stormwater parks that integrate recreation, habitat, flood control, and runoff treatment

While conventional BMPs are widely accepted and regulated under Florida law (see Chapter 6.3), green infrastructure BMPs are encouraged but not necessarily required for compliance. Yet these newer techniques have growing research support and may be essential for achieving nutrient reduction targets.

Adoption of green infrastructure has been limited by high upfront costs and uncertainty about long-term performance. Builders have been particularly slow to embrace systems like green roofs and pervious pavement. These practices may offer lifecycle savings but often involve higher initial costs that are difficult to justify, especially in low- to medium-density developments. However, in high-value urban areas or redevelopment projects, green infrastructure can be cost-effective and space-efficient. Retrofitting older neighborhoods should also be a priority (see Chapter 7.1).

BMP nutrient removal efficiencies vary considerably (Table 6.2.1). No single BMP achieves state nutrient reduction standards alone (see Chapter 6.3). Retention ponds that do not discharge to surface waters offer the highest nitrogen removal. Other effective BMPs include bioswales, stormwater harvesting, and use of engineered media like wood chips or biochar.

BMP performance and cost-effectiveness depend on land use, location, and scale. ROI varies significantly (Table 6.2.2), with nutrient-reducing media like sawdust and wood chips offering the greatest return per pound of nitrogen removed, followed by pervious pavement and stormwater harvesting. Floating aquatic vegetation islands, while effective in some settings, show much lower ROI. Additional case studies will help improve cost-benefit comparisons across BMPs.

Approach

Research on stormwater BMPs in Florida should be expanded and curated into a statewide cost-effectiveness database. Since performance varies by land use, location, and scale, BMPs particularly effective for conditions in Sarasota County should be identified and verified.