Impervious surface is any hard surface that does not let water pass through. Common examples include roofs, driveways, patios, sidewalks, paved parking lots, and roadways. Impervious surface generates more runoff at faster rates than vegetated or undeveloped land.

A few illustrative comparisons:

• A forested acre typically retains the majority of rainfall, releasing only a small fraction as runoff after infiltration and evapotranspiration
• A fully paved acre releases close to all of the rainfall as runoff, and releases it faster, causing peak flows that the system must handle
• A roof with gutters directs concentrated flow to specific discharge points, often at high velocity during heavy rain

Higher impervious coverage leads to higher peak flows and greater stress on drainage infrastructure. This is why increasing impervious surface — through development, paving, or roof expansion — translates directly into higher demand on the public stormwater system. It is also why site-level runoff management, including green infrastructure and low-impact development, reduces the load on the public system.

Newport’s stormwater system includes:

• 55 miles of storm drain pipe in a range of materials including reinforced concrete, corrugated metal, HDPE, and in some older areas clay
• 3,291 catch basins of varying age, some dating to the late 1800s
• 161 outfalls discharging to Narragansett Bay, the harbor, Almy Pond, Easton Pond, and other receiving waters
• Tide gates at outfalls in tidally influenced areas to prevent seawater backflow during high tides
• Pump stations in low-lying areas where gravity drainage is not feasible
• Detention and treatment facilities at select locations to manage runoff volume and quality

Hydraulic capacity varies across the system and is influenced by pipe size, condition, and downstream constraints including tide. Tide gates play a critical role in coastal areas but can also restrict discharge during high tide conditions, which can compound flooding during coincident rain and high tide events.

System age is a significant operational consideration. Much of the infrastructure is over 70 years old, and some components date to the 1870s original construction under Colonel George Waring. Age affects both hydraulic capacity and structural condition.

Stormwater is a leading source of non point source pollution in coastal communities. Unlike wastewater, stormwater does not receive centralized treatment before discharge. The pollutants that wash into catch basins end up in receiving waters.

Typical stormwater pollutants include:

• Sediment from construction sites, eroding landscapes, and paved surfaces
• Nutrients (nitrogen and phosphorus) from fertilizers, pet waste, and organic debris
• Hydrocarbons from vehicles — motor oil, gasoline, and tire wear particles
• Heavy metals from vehicle brakes, roofing materials, and industrial activity
• Pathogens from pet waste and illicit sanitary discharges
• Trash and debris including litter and yard waste
• Chlorides from road salt in winter

Source control is the most cost-effective approach: street sweeping, catch basin cleaning, pet waste management, reduced fertilizer and pesticide use, and cleanup of spills before they reach a storm drain all reduce pollution loads. End-of-pipe treatment (for example, detention ponds and filtration) is also used where site conditions and capital investment allow.

Stormwater management is governed by a layered federal and state framework:

• Clean Water Act (federal). Administered by EPA. Requires NPDES permits for stormwater discharge from municipal systems and certain industrial and construction activities.
• MS4 Permit. Newport is a regulated Municipal Separate Storm Sewer System (MS4) operator under RIPDES. The permit requires six minimum control measures: public education, public involvement, illicit discharge detection and elimination, construction site runoff control, post-construction stormwater management, and pollution prevention and good housekeeping. MS4 compliance focuses on pollution prevention rather than end of pipe treatment.
• Rhode Island Department of Environmental Management (RIDEM). Administers RIPDES stormwater programs, inspects compliance, and enforces requirements. Annual reporting documents system inspection, maintenance, and program implementation.
• Consent Decree (EPA and RIDEM). Newport operates under a consent decree covering CSO and sewer separation work. While focused on sewer, this decree also shapes stormwater infrastructure investment.
• Local ordinances. City code addresses illicit discharges, construction site runoff, and post-construction stormwater management.

Residents and property owners can take specific actions that reduce runoff and improve stormwater quality:

• Never put anything down a storm drain. Storm drains lead directly to the bay, harbor, and ponds — not to a treatment plant. Dumping motor oil, paint, yard waste, or anything else down a catch basin is an illicit discharge and is illegal.
• Pick up pet waste. Pet waste left on the ground washes into storm drains and contributes bacterial contamination to receiving waters.
• Reduce fertilizer and pesticide use. Apply only what your lawn or garden needs, and avoid application before rain.
• Manage runoff on your property. Rain barrels, rain gardens, pervious pavement, and conserving or increasing vegetated area all reduce the runoff leaving your property.
• Check your downspouts. Disconnecting downspouts from the sewer system (in older areas with combined connections) and directing them to a pervious area or rain barrel reduces load on the public system.
• Keep catch basins clear. Do not pile leaves, snow, or debris on or near catch basin grates.
• Report illicit discharges. If you see pollution entering a storm drain or a suspicious discharge from an outfall, contact the Department at 401-845-5600.