Stormwater FAQ

Plain-English answers to common questions about stormwater runoff, drainage systems, flooding, green infrastructure, maintenance, and public responsibility.

What is stormwater?

Stormwater is rainwater or melted snow that runs off roofs, roads, parking lots, lawns, fields, construction sites, and other surfaces. Some of it soaks into soil, but some becomes surface runoff that must be managed through drainage systems or natural flow paths.

Is stormwater the same as sewage?

Usually, no. In many places stormwater and sanitary sewage use separate systems. Stormwater systems are intended for rain and snowmelt, while sanitary sewers carry wastewater from buildings. Older combined sewer systems may carry both, which creates special overflow and treatment challenges.

Why do streets flood if there are storm drains?

Storm drains have limited capacity and depend on clear inlets, pipe slope, downstream outlet conditions, and safe overflow routes. During larger storms, blocked inlets, undersized pipes, poor grading, or high downstream water can cause surface flooding.

What is a detention pond?

A detention pond temporarily stores stormwater and releases it at a controlled rate. It helps reduce peak flow downstream but does not eliminate water. It must be maintained to preserve storage, outlet function, and safe overflow capacity.

What is the difference between detention and retention?

A detention basin is often dry or partly dry between storms and focuses on temporary storage. A retention pond usually has a permanent pool of water and may also provide water-quality benefits. Local design manuals may define the terms differently.

What is green infrastructure?

Green infrastructure uses plants, soil, and natural processes to slow, absorb, filter, or store runoff. Examples include rain gardens, bioswales, permeable pavement, green roofs, and urban trees. It usually works best as part of a larger stormwater system.

Do rain gardens stop flooding?

Rain gardens can help manage smaller runoff events on suitable sites, but they do not stop all flooding. They need proper location, soil conditions, sizing, overflow routes, and maintenance. They should not be placed where they create foundation, slope, or neighbour-drainage problems.

Why do culverts matter?

Culverts let water pass under roads, driveways, embankments, and other crossings. If a culvert is blocked, damaged, or undersized, water can back up, overtop the road, erode soil, or damage nearby property and infrastructure.

Can property owners change ditches or drainage?

Local rules vary, but changing ditches, culverts, outlets, grading, or drainage paths can affect neighbours and public systems. Property owners should check with the responsible authority or a qualified professional before altering drainage features.

What pollutants can stormwater carry?

Stormwater can carry sediment, oil residue, metals, trash, nutrients, pet waste, bacteria, road salt, pesticides, and other contaminants. Pollution prevention, erosion control, street sweeping, and water-quality infrastructure can reduce impacts.

What is a stormwater fee?

Some communities charge stormwater fees to fund drainage maintenance, capital upgrades, flood reduction, water-quality programs, planning, and regulatory work. Fees may be based on property type, impervious area, or another local billing method.

Are flood maps enough to understand stormwater risk?

No. Flood maps are useful, but they do not show every local drainage problem. A property can face stormwater risk from street grading, blocked inlets, small creeks, poor lot drainage, culverts, or overland flow even outside a mapped floodplain.

Who owns stormwater infrastructure?

Ownership varies. Some assets are public, some are private, and some are shared through easements, developments, associations, utilities, or road authorities. Ownership should be confirmed before maintenance or changes are attempted.

Why does maintenance matter so much?

Stormwater systems collect sediment, leaves, trash, vegetation, ice, and debris. Ponds fill with sediment, culverts clog, inlets block, and channels erode. Maintenance often determines whether the design still works years after construction.

Is this site engineering advice?

No. Stormwater Explained is educational. Real drainage design, flood-risk review, construction controls, permits, and repairs should be handled by the responsible authority or qualified professionals under local standards.