Catch Basins &Drainage Inlets

A catch basin is an underground drainage structure that collects surface water runoff through a grated opening. Water enters through the top grate, debris settles in the sump at the bottom, and cleaner water exits through an outlet pipe connected to the drainage system. The sump traps sediment, leaves, and debris to prevent clogging downstream pipes.

Catch basin sizing depends on the drainage area, rainfall intensity, and flow rate requirements. Small yard drains (6"-9") handle residential applications up to 2,000 sq ft. Medium basins (12"-18") suit larger residential or light commercial areas. Large basins (24"+) are used for parking lots, commercial properties, and municipal applications. Calculate the required flow capacity using local rainfall data and drainage area to select the appropriate size.

A catch basin is a point collection system—water enters through a single grated opening and is piped away. A French drain is a linear collection system—a perforated pipe surrounded by gravel that collects water along its entire length through infiltration. Catch basins are better for collecting surface runoff at low points, while French drains excel at intercepting subsurface water or collecting runoff along edges.

Yes, catch basins are excellent for collecting downspout discharge. You can connect multiple downspouts to a single catch basin using underground pipes, then route the combined flow to a single outlet. This consolidates multiple drainage points and allows for easier debris removal. Use a catch basin with adequate capacity for your total roof drainage area.

Inspect catch basins at least twice per year—before and after the wet season. Clean them when sediment accumulates to within 6 inches of the outlet pipe, or sooner if debris is visible at the surface. High-debris environments (near trees, construction sites) may require quarterly or monthly cleaning. Regular maintenance prevents backups and extends system life.

Catch basins are manufactured in several materials: High-density polyethylene (HDPE) and polypropylene are lightweight, corrosion-resistant, and easy to install. Concrete offers maximum durability and load capacity for heavy traffic areas. Cast iron and ductile iron frames and grates provide high strength for vehicle traffic. Each material suits different applications based on load requirements, soil conditions, and budget.

Catch basin grates come in multiple styles: Flat grates sit flush with the surface for pedestrian and vehicle traffic. Atrium grates have a domed profile to prevent clogging from leaves and debris. Slotted grates have narrow openings that are heel-safe and ADA compliant. Perforated grates offer maximum water intake. Decorative grates add aesthetic appeal for visible installations. Select based on traffic type, debris load, and accessibility requirements.

P-traps are required when connecting catch basins to sanitary sewer systems to prevent sewer gases from escaping. For storm sewer connections, traps are typically not required but may be specified for odor control in certain applications. Check local codes—some jurisdictions require trap primers or water seal maintenance for trapped installations.

Load ratings range from Light Duty (pedestrian only, no vehicles) to Class A (passenger vehicles), Class B (light trucks), Class C (commercial vehicles), Class D (heavy trucks), and Class E/F (aircraft and ports). Match the grate and frame rating to your actual traffic: residential driveways typically need Class A-B, parking lots need Class C, and loading docks or public roads require Class D or higher.

DIY installation is feasible for small residential catch basins in simple soil conditions. The process involves excavating the hole, creating a gravel base, setting the basin level, connecting inlet and outlet pipes, backfilling carefully, and installing the grate. However, proper slope, pipe connections, and load-bearing capacity require expertise. For larger basins, vehicle traffic areas, or tie-ins to municipal systems, professional installation is recommended.