The "Useless" Backyard Drain: Why Filling It In Is a Flooding Disaster Waiting to Happen

The Dilemma

A homeowner recently asked:

I have a large, ugly grate in my backyard that isn't plumbed to anything. Since my pavers are porous, can I just get rid of this pit?

The GardenOwl Diagnosis

You have inherited a courtyard that is 90% beautiful. The herringbone pavers are crisp, the walls are solid, and the space feels private. But right in the middle, staring you in the face, is a massive, industrial steel grate—a primary defense against The Surge Capacity Deficit that serves as a vital relief valve, capturing high-velocity runoff before it can flood your interior floor space.

The Scenario

You have inherited a courtyard that is 90% beautiful. The herringbone pavers are crisp, the walls are solid, and the space feels private. But right in the middle, staring you in the face, is a massive, industrial steel grate.

You lift it up, expecting to see a complex sewer connection, but instead, you find... nothing. Just a dirt pit. It isn't plumbed to the street. It isn't connected to a sump pump. It looks like a relic left by a paranoid previous owner. Since your pavers are permeable (water drains through the cracks), you are tempted to just fill the hole with gravel, pave over it, and reclaim your floor space.

The Trap

Do not fill that hole.

That "useless" pit is likely the only thing stopping your living room from becoming a swimming pool during a flash flood.

Here is the physics of why: Permeable pavers are excellent, but they have a flow-rate limit. During a standard drizzle, water trickles down between the joints and into the sub-base just fine. But in a torrential downpour—what we call a "surge event"—the rain falls faster than the soil can absorb it.

If you are in an enclosed courtyard (which it looks like you are), that water has nowhere to go horizontally. It gets trapped between the walls. If you remove the pit, the water level rises until it finds the next lowest escape route: your back door threshold.

The previous owner didn't install that for fun. They likely learned a hard lesson after a flood. That pit is a Dry Well (or Soak-Away). It acts as a surge tank, holding a few hundred gallons of rapid runoff instantly, giving the ground time to slowly absorb it over the next 24 hours.

The Solution: Don't Delete It, Hide It

You are right about one thing: the grate is ugly. It looks like a storm drain in a warehouse parking lot. You can keep the flood protection without ruining the aesthetic.

1. Understand the "Unplumbed" Logic

The fact that it isn't plumbed is standard for this type of system. It relies on vertical infiltration. As noted by the University of Minnesota Extension, soil infiltration rates vary wildly. By digging a deep pit and filling it with void space (or leaving it open with a grate), you bypass the compacted topsoil and allow water to access deeper, more absorbent soil layers.

2. Swap the Grate for a Recessed Tray

Instead of that steel grid, you need a Recessed Tray Cover (sometimes called a Skimmer Lid or Inlay Cover).

• The Hardware: Buy a stainless steel tray frame that matches the dimensions of your pit opening. These are designed specifically for hardscapes.
• The Infill: You take your spare herringbone pavers and cut them to fit inside the metal tray.
• The Result: When the tray is placed over the hole, the pavers in the tray line up with the pattern on the floor. The only visible evidence is a tiny 1/4-inch gap around the perimeter of the square where the water slips through.

3. Check Your Pitch

While you are at it, ensure the surrounding pavers actually slope slightly toward this pit. We often see bowing retaining walls or damp masonry when water sits against the perimeter rather than flowing to a central drain. If the water pools against your house before it hits the drain, the drain is useless.

Visualizing the Result

Drainage is the unsexy part of landscaping that becomes very expensive if you ignore it. It’s easy to look at a dry patio and assume water isn't an issue, but "hidden" infrastructure like dry wells are often the safety net for your foundation.

Before you make any changes to hardscaping—especially in enclosed areas—you need to understand the water flow. If you want to spot hidden opportunities (or risks) in your own yard, upload a photo to our Exterior Design App to get an instant diagnosis and visualize the transformation. It acts as a second set of eyes, helping you see where a recessed drain might look best or where grading issues might be hiding.