What is a Catch Basin?

A catch basin, also known as a storm drain inlet or a stormwater pit, is an underground structure or chamber designed to collect and temporarily store stormwater runoff from impervious surfaces such as roads, parking lots, and sidewalks. Its primary purpose is to prevent sediment, debris, and pollutants from entering the drainage system and ultimately polluting nearby water bodies, such as rivers, lakes, and streams.

The catch basin is typically a rectangular or cylindrical container made of concrete, metal, or plastic. It is strategically placed at low points or along the curb lines of roads to capture runoff effectively. The basin is connected to a network of underground pipes that transport the collected water to a wastewater treatment facility or a natural water body.

The design of a catch basin includes several key components:

1. Inlet grate: Located at ground level, the inlet grate prevents large debris, such as leaves, branches, and trash, from entering the catch basin. It allows water to flow into the basin while capturing solid materials.
2. Sediment sump: The catch basin contains a sump or sump area, which is a depression at the bottom of the structure. The sump allows sediment and other particles to settle, separating them from the water. Sediment build-up can be periodically removed through maintenance procedures.
3. Outlet pipe: The catch basin is equipped with an outlet pipe connected to the drainage system. This pipe carries the treated stormwater away from the basin and transports it to a suitable discharge point, such as a water treatment plant or a natural water body.

Catch basins play a crucial role in stormwater management and help mitigate the impacts of urbanization on water quality. By capturing and treating runoff before it enters the drainage system, catch basins reduce the amount of pollutants reaching natural water bodies, protect aquatic ecosystems, and prevent localized flooding. Regular inspection and maintenance of catch basins are essential to ensure their proper functioning and effectiveness in managing stormwater runoff.

 

 

Additional Details About Catch Basins

1. Types of Catch Basins: Catch basins can vary in size and design depending on the specific requirements of the drainage system. They are commonly classified into two types:
   • Curb Inlet: This type of catch basin is located along the curb line of roadways. It collects runoff from the road surface and adjacent areas, preventing it from flowing directly into the drainage system.
   • Drop Inlet: Drop inlets are installed in areas where there is a significant change in elevation, such as at the bottom of slopes or depressions. They capture runoff as it flows down the slope and divert it into the catch basin.
2. Treatment Mechanisms: Catch basins employ various mechanisms to remove pollutants and debris from stormwater runoff. These mechanisms include:
   • Sedimentation: As runoff enters the catch basin, it slows down, allowing sediment and coarse particles to settle at the bottom. The sump area in the basin facilitates this sedimentation process.
   • Filtration: Catch basins may be equipped with filters or screens to trap smaller debris and pollutants suspended in the water. These filters help prevent clogging of the outlet pipe and improve the quality of the discharged water.
   • Oil/Water Separation: In some catch basins, oil and grease are separated from the runoff using specialized devices, such as oil-water separators. These devices use gravity and buoyancy to separate the oil, allowing cleaner water to flow through.
3. Maintenance and Cleaning: Catch basins require regular maintenance to ensure their optimal performance. Maintenance activities include:
   • Debris Removal: The inlet grates are inspected and cleaned regularly to remove leaves, trash, and other debris that may obstruct the flow of water into the basin.
   • Sediment Removal: Over time, the sediment sump in the catch basin accumulates sediment and solids. Periodic cleaning and removal of this sediment are necessary to maintain the basin’s capacity and effectiveness.
   • Inspection: Catch basins should be inspected for any damage, blockages, or signs of deterioration. If any issues are identified, repairs or replacements may be necessary.
4. Integration with Stormwater Management Systems: Catch basins are typically part of a larger stormwater management system that includes other components such as detention ponds, bioswales, and permeable pavements. These systems work together to capture, treat, and control stormwater runoff, minimizing its impact on the environment.
5. Environmental Benefits: Catch basins contribute to the protection of water quality by preventing pollutants and sediment from entering water bodies. By reducing the amount of pollutants reaching rivers, lakes, and streams, catch basins help preserve aquatic ecosystems and support biodiversity. They also play a role in reducing the risk of localized flooding by managing and controlling stormwater runoff.

It’s important to note that the design, specifications, and maintenance practices for catch basins can vary based on local regulations, climate conditions, and specific site requirements. Consulting with local authorities and stormwater management experts is crucial for implementing effective catch basin systems.

 

The construction of catch basins typically involves the following steps:

1. Planning and Design: The first step is to determine the location and size of the catch basin based on the site conditions, drainage requirements, and applicable regulations. This involves surveying the area, assessing the flow patterns of stormwater runoff, and considering factors such as nearby infrastructure and environmental considerations.
2. Excavation: Once the design is finalized, excavation work begins. The area where the catch basin will be installed is excavated to the required depth and shape. The excavation size will depend on the specific dimensions and design of the catch basin.
3. Formwork: Formwork is constructed to provide temporary support and shape to the catch basin structure during the pouring of concrete. It is typically made of wood or metal and follows the desired shape and dimensions of the catch basin.
4. Reinforcement: Steel reinforcement, such as rebar, is installed within the formwork to provide structural strength to the catch basin. The reinforcement is strategically placed to reinforce critical areas, such as the walls and base of the structure.
5. Pouring Concrete: Concrete is poured into the formwork, filling the space and surrounding the reinforcement. The concrete mixture used is typically designed to meet specific strength and durability requirements. Proper compaction and consolidation techniques are employed to ensure the concrete is dense and free of air pockets.
6. Inlet Grate Installation: After the concrete has sufficiently cured and achieved the required strength, the inlet grate is installed at the top of the catch basin. The inlet grate is securely fixed to prevent dislodgment and to effectively filter debris from entering the basin.
7. Outlet Pipe Connection: An outlet pipe is connected to the catch basin to facilitate the flow of captured stormwater. The pipe is typically made of a durable material such as PVC (polyvinyl chloride) or HDPE (high-density polyethylene). It is connected to the catch basin through an opening or outlet structure.
8. Backfilling and Site Restoration: Once the catch basin and outlet pipe are installed, the excavated area around the basin is backfilled with suitable material, such as gravel or compacted soil. The backfilled area is properly compacted to provide stability and support to the catch basin. Finally, the surrounding site is restored, which may involve regrading the area and restoring any disturbed landscaping.

It’s worth noting that the construction process may vary depending on the specific design, local regulations, and construction practices in different regions. Qualified engineers and contractors familiar with stormwater management construction are typically involved in the design and installation of catch basins to ensure compliance and effectiveness.