Prediction Analysis

Flooding Sources – 5th Avenue BID

While 5th Avenue sits at a higher elevation, GAMA simulations and community input reveal that the corridor remains vulnerable to several systemic flood risks:

• Stormwater Runoff (High Risk)
  The natural slope of Park Slope funnels rainwater downhill. Without sufficient green infrastructure, 5th Avenue channels excess water toward lower avenues, especially during heavy rain events.

• Combined Sewer Backflow (Medium Risk)
  During high-intensity storms, NYC’s combined sewer system can overflow. GAMA models indicate potential for basement-level flooding along 5th Avenue through backflow in drainage lines.

• Insufficient Onsite Absorption (High Risk)
  GAMA simulations highlight the lack of permeable surfaces and bioswales, showing minimal water retention on-site. This exacerbates runoff and reduces flood buffering capacity.

• Lateral Spillover from Adjacent Areas (Low–Medium Risk)
  Severe flooding in lower zones (like 4th Ave and near Gowanus) can extend laterally via intersecting side streets, creating secondary risks for the BID area.

GAMA Insight:
Under high-risk scenarios, cells around 5th Avenue show increasing water height over time, especially in areas near side streets and drains. Without interventions, simulations project overflow cascading from elevated areas into low-lying zones — a problem preventable with upstream retention.

Conclusion: Preventing flooding on 5th Avenue is less about direct rainfall and more about managing how the corridor interacts with larger urban drainage systems. GAMA confirms that targeted interventions—bioswales, permeable sidewalks, and smart drainage—can intercept runoff and protect both 5th Avenue and downstream neighborhoods.

Our analysis utilizes three complementary simulation tools to evaluate different scenarios for 5th Avenue and their impact on the broader Park Slope area:

• StreetMix: Measures changes in foot traffic, flood prevention effectiveness, and traffic congestion based on different street configurations.
• FloodNet: Visualizes flooding patterns from the Gowanus Canal during major storm events, based on elevation data.
• GAMA: Models localized flooding from rainfall and storms showing water diffusion and barrier effectiveness. GAMA depicts generic flooding behavior across the terrain, regardless of whether water originates from rainfall, canal overflow, or runoff.

We modeled three distinct scenarios to assess potential interventions:

The FloodNet Elevation Map in Prediction Visualization 1 clearly illustrates the topographical reality of Park Slope - a neighborhood that truly lives up to its name. The color gradient shows how 5th Avenue sits at a significantly higher elevation (depicted in orange-yellow tones) compared to the progressively lower-lying areas to the west. The Gowanus Canal and its immediate surroundings (shown in blue-green) represent the lowest points in the area.

The Flood Vulnerability Map in Prediction Visualization 2 demonstrates the direct consequences of this elevation differential. Areas along the Gowanus Canal and 3rd Avenue display high vulnerability to flooding (indicated by the intense red zones), while vulnerability gradually decreases as elevation increases eastward toward 5th Avenue. This clear visual correlation between elevation and flood risk validates our upstream intervention approach.

By implementing water management solutions at 5th Avenue's higher elevation, we can intercept rainwater before it naturally flows downhill, preventing the accumulation of stormwater in the more vulnerable lower-lying areas. This preventative strategy addresses flooding at its source rather than merely reacting to flooding events after they've occurred in the canal area.

View 1: Average Flooding/Baseline Scenario

This view represents the current state of 5th Avenue with existing infrastructure and typical flooding patterns.

The current street design includes standard sidewalks, transit shelters, bicycle lanes, and parking areas, but lacks significant water management features. Two trees provide minimal stormwater interception.

Baseline Flooding Conditions in GAMA Model

The GAMA model reveals important baseline conditions:

• All cells start with low water height (~2.0).
• The Fifth Avenue BID area consistently exhibits lower water levels (light blue), indicating partial inundation but reduced severity compared to surrounding regions.
• The BID polygon border functions as a passive containment zone that limits water exchange.
• The interior maintains lower water accumulation, suggesting that its elevated position provides partial protection under low-risk scenarios.
• The square-shaped BID polygon reflects the inclusion of not only Fifth Avenue but also adjacent areas along 3rd and 4th Avenues, capturing the broader commercial and mixed-use zone it is meant to represent.

This confirms that while Fifth Avenue’s topography helps mitigate flood intensity during minor events, it does not fully prevent water intrusion and offers limited protection to downstream areas such as the Gowanus Canal.

View 2: Increased Flooding/High-Risk Scenario

This view illustrates what happens during severe weather events with the current infrastructure.

During heavy rainfall, the current configuration fails to adequately manage stormwater, leading to reduced pedestrian activity as the street becomes less hospitable.

The integrated simulation demonstrates severe flooding dynamics:

• Gowanus Canal overflows into surrounding area triggered by heavy rainfall
• All cells begin to flood; BID area gradually floods as dykes are overwhelmed
• Simulations show real-time water diffusion and barrier failure, helping visualize how low-lying areas transition from dry to saturated.

While the barrier/dyke model in GAMA does not replicate engineered flood infrastructure in precise detail, it effectively simulates the basic protective function of elevation-based or physical boundaries—such as raised sidewalks, berms, or zoning boundaries—that slow water ingress.

Even though the Fifth Avenue BID border lacks a physical barrier, simulating it as a virtual containment zone allows planners to:

• Visualize the impact of zoning boundaries on flood behavior
• Estimate timing of flood onset in targeted commercial zones
• Explore policy-driven interventions (e.g., permeable pavement, green buffers) within a defined footprint

This abstraction is useful for urban planning and resilience testing, helping stakeholders prioritize areas for real-world flood mitigation strategies.

The aerial view clearly shows the spread of floodwaters across lower-elevation areas, with 5th Avenue serving as a conduit that channels water toward lower avenues rather than absorbing or redirecting it.

View 3: Reduced Flooding/Intervention Scenario

This view represents our proposed intervention scenario with enhanced green infrastructure and stormwater management.

The redesigned street features expanded sidewalks, improved transit infrastructure, and critically, increased vegetation and permeable surfaces. The street view image reveals a dramatically greener environment, with tree canopy coverage significantly higher than in the current configuration.

The GAMA simulation results demonstrate the effectiveness of the intervention:

• BID area and surroundings are affected by increased water levels
• Vegetation (green patches) appear as water recedes and cells near the BID
• The intervention successfully manages the water that would otherwise flow downhill

The aerial view shows reduced blue coloration in lower areas, indicating that the 5th Avenue interventions are successfully intercepting and managing stormwater before it can accumulate downstream.

Key Findings

The intervention scenario demonstrating reduced funding shows that strategic modifications to 5th Avenue can have dual benefits: improved business conditions through enhanced foot traffic and aesthetics, alongside significant flood prevention capacity that protects not just 5th Avenue but the downstream neighborhoods as well.

Firstly, upstream flood prevention is critical and effective. Our simulations validate that targeted green infrastructure along 5th Avenue—Park Slope's higher-elevation commercial spine—can significantly intercept and manage stormwater. By addressing runoff at the source, these interventions protect more vulnerable low-lying areas like 4th Avenue and the Gowanus Canal from severe flooding.

Notably, these changes leverage the momentum of the Open Streets initiative, which already reimagines parts of 5th Avenue as a more pedestrian-friendly space. While the redesign introduces disruption—shifting the corridor’s balance away from car traffic—it aligns with a broader citywide vision for accessible, community-first streetscapes. In this context, 5th Avenue becomes a testbed for resilient urban design, where stormwater solutions integrate naturally into public space upgrades.

Beyond flood mitigation, the proposed interventions also yield strong community and economic co-benefits. Enhanced streetscapes with widened sidewalks, tree canopy, and permeable surfaces transform 5th Avenue into a greener, more inviting corridor. This attracts foot traffic, increases dwell time, and boosts retail activity—directly benefiting local businesses participating in or adjacent to the Open Streets program.

Even with these transformations, traffic flow remains resilient. StreetMix models show that despite the introduction of bioswales, rain gardens, and pedestrian zones, vehicular disruptions are modest and remain within a manageable 10% threshold. This confirms the feasibility of integrating climate adaptation features without sacrificing transportation performance.

Ultimately, this is about more than risk mitigation—it’s about community-building. A redesigned 5th Avenue becomes a climate asset and a cultural one: a model for how urban corridors can embrace sustainability without losing identity. It offers Park Slope and surrounding areas not just protection, but pride and permanence in the face of climate change.