How to temporarily backfill our stormwater pit?

[Tsu]

Hi,

We have a large stormwater pit (165 x 400 x 500 mm) in our backyard that was already there when we purchased the house. We have a 2-year-old toddler running around, and I really worry about the risk of him falling into it and getting hurt.

All our neighbours have the same pit, and they’ve permanently plugged theirs for years without any issues. So, we're looking for a temporary and budget-friendly solution to level the pit — possibly by covering the grating with mesh or fabric and backfilling it with drainage gravel.

We’re also thinking of placing something over the area, like a trampoline or a corner seating area around a fire pit, to make the space more functional and attractive. Would that be possible?

Thank you!!!

[EricL]

Hello @Tsu 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your backyard drain. 

Thanks for sharing that photo of your garden drain. Before you cover the area with anything, I suggest calling your local council and finding out what the rules and regulations are concerning large drains on your property. Just to give you an example, here in Queensland you're not allowed to cover or impede the natural flow of water to the drain. Any structural works that you plan on doing must first be submitted to the council for approval. Building over or permanently covering a drain, especially if it's part of a public stormwater system, may violate local council regulations or require specific approvals. 

Covering a drain pit can restrict the flow of stormwater, especially during heavy rainfall, potentially causing flooding of your property or neighbouring areas. Local water authorities or councils may need to access the drain for maintenance, repairs, or clearing blockages. Permanent coverings would hinder this access. 

I propose "temporarily" placing Saxon 170cm Black T Steel Fence Post near each corner of the drain and wrapping it in Coolaroo 1.83 Wide Black Light-Duty Screening Shade Cloth 70% UV Block. This will serve as a temporary fence and placing it over the drain will not hinder the flow of water and you can easily remove it if the drain needs to be serviced. The shade cloth can be fixed in place using Crescent 200 x 4.6mm Black Cable Ties - 100 Pack. Please remember to place a 30mm gap at the bottom so that there is no hindrance to the flow of water. The temporary fencing should be big enough that your child will not be able to push it out of the way. Please note that this temporary cover will eventually need to be removed when you begin your council approved modifications. 

If you are planning on renovating your backyard and filling in the soil to level it, I suggest visiting your local council and finding out what the rules and regulations are in regards to backyard drains. You also have the option of engaging the services of a local plumber to find out if the drain can be raised, if the garden is to be levelled. They will be familiar with the rules and regulations in regards to drains. My best advice is to gather more information so that any modification made is done to code.

If you need further assistance, please let us know.

Eric

[Tsu]

Hi @EricL,

Sorry for the super later reply. I took your advice and contacted a plumber to modify and raise our pit, he also did backfill and level our area with soil.

Now, my next project is to landscape it and maybe turn it into a play area with a cubby house for my toddler.

I love the idea of crazy paving/flagstone like the reference photo below.

Would you please give me some advice on how to prepare the floor and lay some stones without concrete? I am thinking of filling the gap between the stones with pebbles and glue them.

Thank you!

 

[JacobZ]

Hi @Tsu,

The process to prepare your area for paving is relatively simple, but very important. You'll start by adding a compactible material such as road base, then you'll level and compact it. Check out How To Lay a Base For Pavers for some guidance.

As you'd be creating a crazy paved area without a concrete base, I would suggest adding a layer at least 100mm thick of compacted road base.

You can then follow How to lay crazy paving for some guidance on how to lay your pavers.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob

[Tsu]

Hi @JacobZ 

Thank you! I am so glad it’s possible to do

Another question, as we will do the paving around the stormwater pit - do we necessarily need to create a little slope leading to the pit? The area is approximately 7x2.5 meters.

cheers,

T

[JacobZ]

Hi @Tsu,

Yes, ideally, you would create a slight slope leading toward the stormwater pit so that water naturally drains away from the paved surface. Without it, water can pool on top of the paving and cause issues such as staining, shifting, or erosion around the joints. A slope ensures efficient drainage and extends the life of both the paving and the pit system.

The usual recommendation is a gradient of around 1–2%, which means a drop of about 10–20 millimetres for every metre of paving.

Creating the slope would be done on the base material. You can use two stakes and a string line with a Line Level as a reference point over the pad. You can then measure down from that string line to ensure your base material is sloping down towards the drain.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob

[Tsu]

Hi @JacobZ,

thank you!

Back to the crazy paving, I want to simplify the process a bit by using stepping stones and fill the gap with pebbles. Would that work?

Cheers

T 

[JacobZ]

Hi @Tsu,

Yes, that would certainly work; you would just need to create your paver base with a slight slope, then set the stepping stones in place with mortar. 

You could then fill around them with decorative stones.

If you'd like to go one step further, you can apply Landscape Lock Concentrated Garden Glue over the decorative stones to lock them in place.

Let me know what you think.

Jacob

[Tsu]

Hi,

I just realised Bunnings has posted a similar idea to what I was planning to do!

https://www.bunnings.com.au/diy-advice/garden/garden-design/how-to-use-stepping-stones-to-create-a-p...

We’re getting started on the shopping list and have some stones ready. Can you please help us with how many bags of road base and sand I need for a 20sqm area?

Cheers,

T

[JacobZ]

Hi @Tsu,

To add a 50mm layer of road base to a 20sqm area, because of the compaction requirement, you would need approximately 1.1 cubic metres of road base. One 20kg Road Base is roughly 0.01 cubic metres, so you would need approximately 110 bags.

For a 30mm layer of sand, you would need 0.66 cubic metres, which is equivalent to 66 x 20kg bags of sand.

A simpler option is to speak with your local store's Special Orders team to explore what options for bulk bags of landscaping materials are available in your area. It is often simpler and more economical to have a bulk bag delivered than to lug over a hundred bags home.

Let me know if you have any further questions.

Jacob