Will adding soil to the lawn affect drainage?

[Snakeytail]

So my house is built a meter or so above street level. The front lawn near the house slightly slopes away, then has a steeper slope near the property lawn. I am slowly converting the entire lawn into a native garden but the ground is pretty hard clay with crappy drainage. I've sheet mulched a strip near the property line and it was fine to just add extra compost and dirt on top to plant into while the organics slowly work at the clay underneath. But between mulch, compost and soil, I added about 30cm of height. Im worried if I do the same to the "flat area" that I will be redirecting water towards the house rather than down the hill? In a perfect world I would dig out the top layer of lawn before adding anything to keep it at the same level, but not a lot of extra money for landscaping so it would have to be by hand and will take forever.

How much could I build the area up before affecting drainage? If I keep the dirt layer smaller, I'm guessing the mulch shoudnt affect drainage as much? If I spend the next 6 months topically applying clay breaker is that going to do enough to help the existing soil? 

[EricL]

Hello @Snakeytail 

Thank you for sharing your question about your lawn. It would definitely help if we could see your lawn and slope layout. I have a general idea of what you are describing but would like to see the actual slope of the soil and how adding soil to your lawn might push rainwater back to the house. Would it be possible for you to post a photo of the garden and lawn? Once we see how it's situated we'll be able to offer recommendations on how to best layout your vegetable garden.

Generally speaking, I sometimes suggest transforming the slope into a terrace configuration which staggers the rainwater and slows its flow down the slope. I've placed an image below to give you an idea of how it can be done with sleepers.

Let me call on our experienced members @Dave-1, @Nailbag and @AlanM52 for their recommendations.

If you need further assistance, please let us know.

Eric

[Snakeytail]

Photo will give you a better idea of what I mean. So I basically sheet mulched the slope already; the top edge of the mulched area is there the yard starts to slope. So adding some addition dirt on top really didn't change anything.

What I'm talking about now is the area between the mulched strip and the house. It's essentially flat (very slight slope) and pretty much level with the house so I'm worried if I add another 30cm of material that water could pool next to the foundation.  I can't plant in the ground as is, even if I kill the grass first which is why I though if I add a layer of dirt and mulch on top, I could plant tubestock right away. 

I just don't know how much affect adding like 15 cm of dirt and 10cm of mulch is going to have or if I'm overthinking.  If all else fails I could spend the next couple years trying to amend the current soil to make it plantable, but that will make for a lot of digging! 

[AlanM52]

Hi @Snakeytail,

As suggested by @EricL please post some photos.

Thanks

[EricL]

Hello @Snakeytail 

If you are worried about back flow from the garden, I suggest installing sleepers at the very top to serve as a border to prevent the soil from eroding and prevent water from flowing to your home. You also have the option of putting in an agi-drain at the top to re-direct the water back down.   

Eric

[Nailbag]

Hi @Snakeytail 

It simply comes down to gravity. If you can maintain a small steady slope away from the home then water will run away naturally. If you make it dead level, then you're still good as long as you don't cover any weep holes that allow the sub-floor to breath and prevent mould and moisture traps. So, essentially either of those and obviously avoid any fall back to the house and you will be right.

Nailbag

[Snakeytail]

So if I were to build a small wall about  30cm tall next to the cement that surrounds the house (like Eric suggested) and added 30cm of material at that edging that slowly sloped away from the house, would that small wall be enough to keep the water back and direct it down the hill? I really like the look of some of those stone walls but with the gaps wasn't sure if that would contain water.

I guess if all else fails I get a jack hammer to help breakup the clay then mix in some amendments in thr top layer! 

[EricL]

Hello @Snakeytail 

I propose doing a mock up and see if you are ok having a 30cm wall close to your house wall. I recommend using cardboard so that you have a visual reference. I would suggest having the wall at least a meter away from your house wall or in line with the concrete walkway. I would also suggest putting in agi pipe at the bottom of the wall to make sure the water is redirected back to the bottom as your clay soil will definitely not absorb it.

If you need further assistance, please let us know. 

Eric