What Is a Catch Basin? The Differences Between a Catch Basin vs. Inlet vs. Storm Drain

Top view of dual stormwater catch basins, highlighting the structure and components of what is a catch basin for effective stormwater drainage.

What Is a Catch Basin? The Differences Between a Catch Basin vs. Inlet vs. Storm Drain

Last Updated on June 25, 2024 by Stormwater Compliance Solutions

Catch basins, inlets, and storm drains are crucial in stormwater management, preventing flooding and maintaining proper drainage. While these terms are sometimes used interchangeably, they have distinct differences. Understanding these differences is essential for effective stormwater management. Read on to learn more about the characteristics, functions, and key distinctions of stormwater catch basins vs. inlets and storm drains.

Stormwater Catch Basins

Also known as storm drains or curb inlets, catch basins are structures designed to collect and channel excess water from paved surfaces such as roads, parking lots, and sidewalks. They typically have a grated ground-level opening leading to an underground collection system. Catch basins for stormwater are typically made of precast concrete, metal, or plastic and have a removable grate for easy access and maintenance.

Functions and Types of Catch Basins

The primary function of a stormwater catch basin is to capture and separate debris, sediment, and pollutants from stormwater runoff before it enters the drainage system. The removable grate helps prevent large objects and debris from entering the underground pipes, reducing the risk of clogging and blockages. Catch basins and drainage pipes also help avoid the accumulation of standing water, which can lead to flooding and property damage. Different types of catch basins may include:

  • Industrial catch basins
  • Road catch basins
  • Residential basins
  • Collection basins
  • Street catch basins

There are also different types used for various purposes, depending on the state standards and DOT specifications in the region.
Internal view of a stormwater catch basin showing water accumulation and debris, illustrating the function of a catch basin in stormwater management.

Differences Between Catch Basins in Pennsylvania and New Jersey

It is important to note that there may be specific differences in catch basin design and regulations between different states and regions. In Pennsylvania, catch basins are typically constructed with a sump and a hooded outlet pipe to prevent the release of sediment and pollutants into the waterways.

In New Jersey, catch basins are designed with a bypass structure to redirect excess stormwater flow during heavy rainfall events.

Catch Basins vs. Inlets

Inlets, also known as curb inlets, yard inlets, or drop inlets, are another type of structure used in stormwater management. Inlets are typically located at the edge of roads or parking lots and have a grated opening, allowing water to enter the underground drainage system. Like catch basin drainage systems, inlets are usually made of concrete or metal and can vary in size depending on the anticipated flow of stormwater runoff.

Overall, the main difference between a catch basin and an inlet is that a catch basin is designed to catch debris before it moves into the stormwater system, whereas an inlet is meant to convey water and debris downstream and not collect anything.

Functions of Inlets

The main function of inlets is to provide an entry point for stormwater runoff into the drainage system. They are designed to efficiently capture and convey excess water from paved surfaces, preventing it from pooling or causing damage. Inlets work with other stormwater management structures, such as catch basins and pipes, to ensure proper drainage and to avoid flooding.

Differences between Inlets in Pennsylvania and New Jersey

Similar to stormwater catch basins, inlet design, and regulations may vary between Pennsylvania and New Jersey. In Pennsylvania, inlets are typically designed with a hooded outlet to minimize the release of sediment and pollutants. In New Jersey, inlets may be equipped with a bypass structure to redirect excess flow during heavy rainfall events.

What Is a Storm Drain Catch Basin?

Storm drains, or storm sewers, are integral to stormwater management systems. Large, underground pipes collect and convey stormwater runoff from stormwater catch basins and inlets to a suitable discharge point, such as a river, lake, or detention pond. Storm drains are typically made of concrete or corrugated metal and are designed to handle large volumes of water.


The primary function of storm drains is to transport stormwater runoff away from developed areas and into natural water bodies or storage facilities. They help prevent flooding by providing a network of underground pipes that efficiently move water away from urban and suburban areas. Storm drains also play a crucial role in preventing erosion and protecting infrastructure by directing water away from roads, buildings, and other structures.

Differences Between Storm Drains in Pennsylvania and New Jersey

While storm drains and stormwater catch basins in Pennsylvania and New Jersey serve the same purpose, there may be variations in design and construction standards. Local regulations and environmental considerations often dictate these differences. The Department of Transportation (DOT) in each state sets the standards and specifications for each.

It is important to consult local guidelines and work with experienced professionals when planning and implementing storm drain systems.

More About Storm Drains and Stormwater Catch Basins

What Is the Purpose of a Catch Basin?

The primary purpose of a precast concrete catch basin is to collect and temporarily store stormwater runoff. Catch basins are strategically placed in areas with high water flow rates to capture and prevent water from pooling on the surface. They are typically connected to a storm sewer or drainage system, which directs the collected water away from the area to a suitable disposal or treatment location.

What Is the Difference Between a Storm Drain and a Catch Basin?

While “storm drain” and “stormwater catch basin” are often used interchangeably, there is a slight difference between storm drains vs. catch basins. A storm drain is a system of pipes, channels, and structures that collect and convey stormwater runoff. On the other hand, a storm sewer catch basin refers explicitly to the underground structure or container that collects the water before it enters the storm drain system.

Does Water Sit in a Catch Basin?

You might wonder how catch basins work. Water accumulates in a stormwater catch basin but is not meant to sit there indefinitely. The catch basin is designed with an outlet pipe that allows the collected water to flow into the storm drain system. The catch basin’s purpose is to temporarily hold the water and capture any debris or pollutants before they enter the drainage system.

Where Does Water from a Catch Basin Go?

The water collected in a stormwater catch basin is directed to a storm sewer or drainage system. From there, it is transported to a suitable location for disposal or treatment. The exact destination of the water depends on local regulations and the specific design of the water drainage catch basin stormwater management system in place.

How Deep Should a Catch Basin Be?

If you’re wondering, “What size catch basin do I need,” the depth of a catch basin can vary depending on its intended use and the local requirements. In general, stormwater catch basins are designed to be deep enough to allow for the pipes to enter and exit the structure and promote positive drainage. The depth of each catch basin is usually 4-8 feet to accommodate cover, and the pipe diameter, and allow for 2-4 feet below the depth of the lowest pipe.

What Happens to the Water in the Bottom of the Catch Basin?

The water that collects in the bottom of a stormwater catch basin will either stay in a permanent pool of water and transfer over each storm event or it will seep into the ground via a sump in the bottom of the basin. Other designs exist to allow the pool of water to drain over time.

How Do You Install a Storm Drain Catch Basin?

Installing a stormwater pit catch basin requires careful planning and adherence to local regulations and guidelines. The process typically involves the following steps:

  1. Excavation: A hole is dug at the desired location for the catch basin.
  2. Setting the basin: The stormwater catch basin structure is placed in the hole, ensuring it is level and securely positioned.
  3. Connecting pipes: Inlet pipes from the surrounding area are connected to the catch basin, allowing water to flow into the structure.
  4. Backfilling: The area around the catch basin is backfilled with suitable material to provide stability and support.
  5. Surface grating: A grating or cover is installed on top of the stormwater catch basin to prevent debris and unauthorized access.

It is important to consult with a professional and follow local regulations to ensure proper installation and functionality of the storm drain catch basin.

What is the Difference Between a Catch Basin and a Manhole?

While stormwater catch basins and manholes are similar in structure, they serve different purposes within a stormwater management system. A catch basin is primarily designed to collect and temporarily store stormwater runoff, while a manhole provides access to underground utility lines, pipes, or chambers for maintenance or inspection purposes. Manholes are typically larger and may have multiple access points, while catch basins are specifically designed for water collection.

What Is the Difference Between a Catch Basin and a Drain Inlet?

Catch basins and drain inlets are both components of stormwater management systems, but they serve different functions. A catch basin is an underground structure that collects and temporarily stores stormwater runoff, while a drain inlet is an opening or grate on the surface that allows water to enter the drainage system. The drain inlet directs water into the underground pipes or channels that lead to the stormwater catch basin.

What Is an Inlet for Stormwater?

An inlet for stormwater, also known as a stormwater inlet or drainage inlet, is an opening or structure that allows stormwater runoff to enter the drainage system. Inlets are typically located at low points or along the edges of roads, parking lots, and other paved surfaces. They are designed to capture and direct water into underground pipes or channels, preventing water pooling and minimizing the risk of flooding — another stormwater risk management measure.


In summary, stormwater catch basins, inlets, and storm drains are essential to effective stormwater management systems. While they share the common goal of preventing flooding and maintaining proper drainage, each has distinct characteristics and functions.

Stormwater catch basins are designed to capture and filter debris and pollutants from stormwater runoff. Inlets provide entry points for stormwater runoff into the drainage system, facilitating efficient conveyance. Storm drains transport stormwater runoff away from developed areas and protect infrastructure from flooding and erosion.

Understanding the differences between these components is crucial for designing and implementing effective stormwater management strategies. Regional variations and regulations, such as those between catch basins in Pennsylvania and New Jersey, must also be considered to ensure compliance and optimal performance.

Contact Stormwater Compliance Solutions today at [email protected] to discuss your catch basin, inlet, and storm drain options today.

Daniel Flynn has been with Stormwater Compliance Solutions for over 10 years working on a wide range of engineering and construction projects in the stormwater field. He is responsible for business development, engineering analysis and design, project scheduling and management. He has extensive experience in hydrology and hydraulic of small watersheds and this experience has allowed him to expand the company’s stormwater management services to a wide array of clients. He has a bachelor of science in Forest Engineering from the State University of New York, College of Environmental, Science and Forestry. He is a licensed Professional Engineer in the State of New Jersey and a Certified Erosion Sediment and Stormwater Inspector (CESSWI).