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How to prevent soil erosion and runoff from seeping into shed?

Hi everyone,

As a resident in a unit block with a shared garden – I’m seeking advice on drainage issues regarding a sloped garden area and a concrete bin shed. We have a paved sloped path up the side of the house, which levels to a flat paved area that sits above the garden bed. Anytime it rains, rainwater absolutely decimates the slope and carries all the soil and water to the bottom of the hill to the base of the shed, and has raised the soil level which washes soil into the shed floor. Located Northern Sydney on the coast, so the rain and wind can get brutal sometimes. This erosion has also completely claimed the brick edging that once lined this bed.

Agapanthus at the top of the slope provides bare minimum stability. Camellia tree also provides some stability, but has proved a contributor to the soil levelling issues – garden was previously mulched, the mulch collected at/washed away to the base of the tree, and over time, has compacted into a very thick layer of what looks like mycelium. I’m fairly certain that the soil is just that, no clay or sand to worry about.

Due to major issues with Anredera cordifolia necessitating arduous manual tuber removal, I was already planning to essentially excavate the area where the soil level is higher at the base of the shed. Truthfully, I believe that there is probably access to a storm drain, however I'm working under the assumption of no access because strata have made it clear that they would prefer not to shell out for a plumber, so this probably rules out a French drain or something similar. Leading to the shed is a pebble path, and the other side backs onto a retaining/property boundary wall, so the practicality of digging a trench and redirecting with berms etc. would be null, since I think the water would then just seep under the shed gate. Would a soakwell be a recommended solution in this instance?

Regarding the slope, of course soil leveling and planting of natives to reduce erosion is a high priority – this issue may be addressed/rectified when property is assessed by a landscaper, but in the meantime, I was also wondering how to best reclaim the edging? It has been overrun by a thick root system, which I have begun to remove already, however I’m not sure of the best way to dig out and level the soil surrounding the edging…perhaps this is best left to the potential landscaper?

I’m in my early 20s and have done lots of bush and wetland regen, but since my strata doesn’t take the suggestions of young people too seriously, I’m looking to provide as much of a concrete solution as possible to spur them into action. Any advice will be sincerely appreciated.

Thanks again in advance,

Neo 😊

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JacobZ

Hi @neowest,

What you are dealing with is less a planting problem and more a hardscaping and water control issue. The slope is currently acting like a chute, with water accelerating off the paved area above and stripping soil as it moves downhill. Until that slope is physically stabilised, any soil, mulch, edging, or planting will continue to wash out, no matter what species are added.

The first priority should be hardscaping the slope to slow and hold the soil in place. This usually means regrading the slope slightly and introducing retaining features such as low timber or masonry steps, sleepers, or terracing, combined with geotextile or erosion control matting. These elements break the slope into shorter sections, reduce water velocity, and give soil and plants a chance to establish. Once this is done, soil can be rebuilt in controlled layers and planted out with appropriate groundcovers and shrubs to provide long term stability.

Only after the slope is physically stabilised does it make sense to address drainage. At that point, simple surface interception along the edge of the paving, such as a shallow swale or gravel strip, can make a big difference by stopping water from freely dumping onto the slope. A soakwell can be part of the solution, but it is not a standalone fix and should only receive relatively clean, slowed water. Otherwise, it will clog up with sediment and eventually fail.

Realistically, any drainage solution in a strata setting should be designed or at least signed off by a professional. Shared structures, unknown stormwater connections, and responsibility boundaries make DIY drainage risky and hard to defend if something goes wrong.

Presenting this to strata as a staged, professional solution starting with hardscaping and erosion control, then drainage if required, will give you the best chance of being taken seriously and getting action. If you aim to install retaining structures as a first step, then plant out the terraces with soil stabilising plants, you may find that drainage becomes less of an issue as the soil will better be able to hold moisture with the root structures in place.

Ultimately, I think the main issue is erosion control and drainage will need to be addressed later when you can get the rest of the strata owners on board.

Allow me to tag our helpful members @Dave-1, @Noelle and @Nailbag to see what they think.

Jacob

neowest

@JacobZ, thank you for such a detailed response.

I think we are on the same page regarding the stabilisation of the slope as the highest priority. In reality, I was unwilling to try a drainage solution myself anyway, so now I'm able to strongly recommend engaging the services of a professional in my proposal.

In the meantime, I think I would be able to at least begin to try and install some retaining features while waiting for the strata response to my proposal. Out of the options you mentioned, is there a particular method you recommend that won't pose too much of a hindrance in the future (in the event that strata does hire a landscaper)?

Thanks for your time again.

Neo

Dave-1

Good Evening @neowest

@JacobZ has really set out the issues nicely. A profesional landscaper will cost a resonable amount of money, so not sure if a Strata group will pick it up and run. However I do think they would be happy if you suggest a planned approach to handling the yard as a whole. Fixing the garbage storage shed first would be a good way to get it passed to work on the rest of the issues.

For slowing the water and capturing the silt I am suggestion a Gabion bench or bench seat such as

https://www.workshop.bunnings.com.au/discussion/175994/gabion-wall-bench-seats

Resloping your pavers so you channels the water to go the way you want is another thing I would do.

But first I would install a gabion cage dig out the high side of the shed (around 600mm from the shed so you can pave) and install a gabion basket wall. Only low but it will become a garden bed on the high side of this. weedmat will stop the fines from drifting through the cage. You can buy premade cages from Bunnings in teh garden section.

Swales would also work well in channeling and slowing the water. With that area near the clothesline I would lift the pavers just before the steps and dish drain it buy lowering the soil under say three pavers and then put them back, have them slope towards the right of the steps and a swale then funnels and curvers the water around and down the terraced styled yard (in the future)

Having someone look after a garden area in a strata is a bit hard (not everyone like gardening) so maybe plant it out days for sections while you do the backend work of swales and walls?

Dave

EricL

Hello @neowest

I can only suggest what Jacob has recommended and that is to regrade the soil and perhaps place a retaining wall at the bottom of the garden. I personally prefer a terracing option as it looks much more organized and literally slows down the flow of water.

Eric

Nailbag

Hi @neowest

Your first issue to address which you have already highlighted is the body corp. Until you get them on board you potentially will be up for a more serious scenario than the water run-off. If the issue is its your word against their then seek advice from a professional. Get a couple of opinions into a report that you can take to them independent of yourself. At the very least this will give you a more definitive plan of attack other than ones provided in an online forum. Especially as drainage issues can have multiple cause and effect influences.

Nailbag

neowest

@Dave-1 Wow, thanks for such in-depth advice, especially regarding the swales. It sounds quite effective given the super smooth suface of the pavers. I'm definitely going to have a look into incorporating that into the terracing of the slope, as @EricL has also helpfully suggested. I agree that pitching the gabion wall as a bin shed fix should help with the overall likelihood of cooperation with strata.

@Nailbag You're right about the issues with the strata/body corp management, and given they are so notorious here, I want to do this right. A neighbour (non-strata) has recently let me know that she has reached out to a couple of professionals regarding potential landscaping options, so hopefully if and when they get back to her, I will be able to include their observations/suggestions in my report.

Thanks again for all of your help, it's really appreciated.

Neo

Nailbag

Your very welcome @neowest last thing you want to do is upset the BC.

Regards Nailbag

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