Flooding is a natural part of the water cycle, but the way water moves through communities has changed significantly over time. As towns and cities grow, more land is covered by roads, rooftops, parking lots, and other hard surfaces that prevent water from soaking into the ground.

When rain falls faster than it can infiltrate, drain, or be stored, flooding can occur.

Understanding how stormwater moves through a community is the first step toward understanding why flooding happens—and what can be done to reduce its impacts.

Natural landscapes absorb rainfall.

Grasslands, forests, wetlands, and healthy soils allow water to soak into the ground, where it becomes part of the natural water cycle.

Developed areas work differently.

Roads, parking lots, sidewalks, and rooftops prevent infiltration. Instead of soaking into the soil, rainfall becomes stormwater runoff that moves quickly across the surface.

As communities develop, runoff volumes often increase while infiltration decreases.

This means more water reaches streams, lakes, and storm drainage systems in a shorter period of time.

Stormwater systems are designed to manage rainfall, but every system has limits.

During intense storms, large amounts of rain can fall in a short period of time. When runoff enters drainage systems faster than it can be conveyed away, water may temporarily pond on streets, collect in low areas, or contribute to localized flooding.

This does not necessarily mean the system has failed. It often means the storm exceeded the capacity for which the system was designed.

As rainfall intensity increases, communities must continue evaluating how best to manage runoff and reduce flood risk.

Infrastructure is built to serve communities for decades, but communities do not remain static.

Over time:

• Development patterns change
• Drainage areas expand
• Infrastructure ages
• Rainfall records evolve

Stormwater systems that once performed adequately may face new challenges as communities grow and conditions change.

Managing flood risk often requires a combination of maintenance, rehabilitation, upgrades, and new approaches to stormwater management.

Water needs somewhere to go.

Streams, rivers, lakes, wetlands, and drainageways serve as part of the larger stormwater system by temporarily storing and conveying water during storm events.

These natural features help reduce flooding by providing space for water to spread out and slow down.

Protecting and maintaining these systems is an important part of community resilience.

There is no single solution to flooding.

Most communities rely on a combination of strategies that work together.

Traditional infrastructure includes:

• Storm sewer systems
• Culverts
• Channels
• Detention basins
• Pump stations

These systems are designed to move or temporarily store water during storm events.

One of the most effective ways to reduce runoff is to increase infiltration.

When rainfall soaks into the ground, it is temporarily removed from the surface runoff system. This reduces peak flows and helps lessen pressure on storm drainage infrastructure.

Infiltration also supports groundwater recharge by allowing water to replenish underground aquifers.

For many communities, infiltration provides both flood reduction and long-term water resource benefits.

Resilience is the ability of a community to prepare for, respond to, and recover from challenges.

Flood resilience involves more than infrastructure alone.

It includes:

• Long-term planning
• Infrastructure maintenance
• Responsible development
• Public education
• Stormwater management
• Natural resource protection

Communities that combine these approaches are often better equipped to manage changing conditions and future storm events.

Residents can help reduce runoff and improve resilience by:

   ✓ Redirecting downspouts to vegetated areas

   ✓ Maintaining healthy lawns and landscapes

   ✓ Installing rain gardens or rain barrels

   ✓ Keeping storm drains free of debris

   ✓ Supporting local stormwater initiatives

Small actions across many properties can have a meaningful impact.

Flooding is closely connected to stormwater management, water quality, and community infrastructure. Explore these related topics to learn how stormwater systems work, how pollution reaches local waterways, and how residents can help manage runoff on their own properties.

• Stormwater 101
• Homeowner’s Guide to Stormwater
• Green Infrastructure 101
• Flooding, Runoff, and Resilience
• Understanding MS4 Programs
• Stormwater Pollution Sources