Components of the Catch Basin

Despite being just a small part of the larger storm water management plan, the catch basin itself is complex enough to contain multiple important parts. Without an understanding of why a basin contains certain features, it’s all too easy to overlook something essential until the feature stops working. Precast concrete catch basins feature fixed openings for inflow and outflow pipes, limiting your installation options. If you’re going to build a custom design, with a greater volume or a lower depth for better trash collection, you’ll need to know what goes into a quality catch basin.


Starting from the top down, durable metal grates cap the top of most catch basins. If they’re attached to a separate surface or curb drain, these basins may feature a separate manhole cover instead for direct access. Grates are most commonly used because they allow storm water to flow in along with small bits of trash. Large debris is trapped on the surface of the grate for easy removal. Small bits of debris are allowed through the grate so it can accumulate in the bottom of the basin rather than flowing into the rest of the drainage system.


The term sump is often associated with pumps used in basements to remove unwanted water. But the sump part of the pump’s name actually refers to the small hole it sits in that accumulates water from the surrounding floor. Sumps are also a part of the catch basin’s design. The basin is deeper than it is wide so that water entering the feature shoots rapidly to the bottom. This helps settle out solid debris.   Light trash, like wrappers and paper, floats on the surface along with any grease or oil mixed into the run off. Careful placement of the outflow pipe in the sump ensures that only water flows out with none of the trash at the bottom and top of the space.

Inflow and Outflow Pipes

If the catch basin only consisted of a sump and a grate on top of it, the container would quickly fill up and overflow. All basins require at least one outflow pipe to let wastewater escape after debris settles or floats out. Catch basins, accepting water from another underground source will also feature an inflow pipe. Most basins process water from both direct surface grates and pipes, to keep everything flowing smoothly. Both types of pipes can clog, so it’s important to know how many connections to check for debris during every maintenance visit.

Basin Structure

Regardless of the volume capacity of the basin or the depth of its sump, the catch basin needs some kind of structure to keep the soil around it from collapsing in. Precast concrete basins are popular, but they’re highly limited and often fail to provide the right solution for a specific purpose. Custom fabricated basins are generally built with concrete block and reinforcement plates made from steel. This provides plenty of stability and reinforcement against soil movement. However, concrete block offers even less protection from leaks and seepage than poured concrete. Both forms of the material will leak steadily, with the amount of water lost increasing over time.


That’s where a flexible liner product comes in. Concrete performs best when it remains sealed, but liquid sealant products are far from easy to apply or reliable over time. Wrapping a flexible polymer liner, preferably a multi-layered RPE product, around the inside of the basin will prevent leaks and water loss for years to come. It’s also easier to replace than other sealants that often need stripping or scraping before new material is applied.

Don’t let the size and shape limitations imposed by precast basin manufacturers control your project. Building a custom basin may take some extra time or effort, but protection against flooding is well worth it. When it comes time to order the liner for your site built basins, turn to BTL Liners for everything you’ll need.

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AquaArmor Pond Liner

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