Landscaping Drainage and Plant selection help

[DannyG]

There are very few certainties in life but death is one and me NOT being a gardener is another, so I need some help.

To gain the help I require I have spent 'hours' making a picture....a picture tells a thousand words and all that..........

Some clown decided to build a house up on a big hill. So he got his pick and shovel out and cut a large 'cut to fill' platform into the side of the big hill. This left the cut and fill areas all rocks and clay. And I mean massive rocks and lots of clay. Think abseiling and slippery slides......



Here is a photo of the cut side, or the abseiling area.....The rocks probably dont look that big in the first image due to the cars location, however if you look at the second photo you can see they are larger than a house.......



And this is the best indication I can give of the 'fill' side, or slippery slide area. See the massive rocks in the cut section and the massive clay and rock fill area. A very poor zoomed in phone photo from across the valley but shows what I am on about.



So what I need help with is to get some ideas as to what to do to these area's.

For the most part the areas above the cut will just go back to the native bushland and the areas below the fill will eventually be terraced and turned into grass and tree's.

So its mainly the cut batter (abseiling area) and the fill side that we need help with.

I was thinking of initially bringing in a few loads of some sort of mulch or wood chips to cover those areas to keep the dry dust from blowing all over the house. And then slowly start planting some sort of ground covers and shrubs to do my best to fill the area with greenery??
Whats your thoughts? Its all clay so obviously id need to dig out a far sized hole and replace it with decent soil anywhere that I plant things.

As for the massive rocks I was hoping to grow something above them that will drop down over the side or perhaps put some sort of wire lattice structure up and grow sh!t up them??

So any ideas or plant selection suggestions are welcome. The only criteria is that it needs to end up looking green and once established I dont really need to touch it!!


The other thing I need advice on is some drainage ideas.

In this first photo I want to put a drain in where the green line is along the driveway. Again, it is very undeveloped and yes all the weeds etc will be gone!!

However I am bringing in several truck loads of 20mm minus for the driveway so I am wondering if I dig a trench and put some 20mm in it, then lay a 65mm or 100mm slotted drain and then cover it with the 20mm minus driveway material would that be adequate?

Do I need the socked drain and will 65mm do or should I use 100mm? Will the 20mm minus be a suitable rock to use in the drain?

The drain will ultimately terminate into a pit drain down on the flat house site. (There are several pit drains on the flat house site)



In this next photo I am going to put up a small retaining wall (small in height, not length). So again I am anticipating putting down a drain and 20mm metal behind the wall as per the drain above. Is this going to be suitable?



Thanks for any advice or suggestions. The flat platform where the house and shed are sitting has a lot of pit drains for me to tap into and there is a massive spoon drain way up on the top side of the hill diverting most of the run off away from the platform as well.

[Bird]

For something like that would it be advisable to get some pro advice on the ground about it...

Certainly will be a lot of effort and would ****in suck to get it wrong.

[DannyG]

For something like that would it be advisable to get some pro advice on the ground about it...

Certainly will be a lot of effort and would ****in suck to get it wrong.

I have been given some 'expert' advice from the engineer and builder that went a bit like this.......

"plant out those areas over there" as he points to them, and "put a nice little retaining wall along there with a drain behind it and grow some shrubs on top of it" as he pointing along another section!!

The drain down the driveway is my idea, the builder said its not nescasary as the water will run down the driveway into the pit drains anyway but I am hoping to eliminate any corrosion from water by doing the drain.

[Mace]

Go for as many succulents as you can for a start Pal,  then look at other native species to infill spaces.

You dont want to be watering all summer, and they are easy maintenance.

http://www.wildseedtasmania.com.au/succulent.php

http://www.woodbridgenursery.com.au/3-succulents

[tryagain]

A couple of points worth considering, in regards to plants, I don't really know much about what is suitable for Tassie the advice I usually give is to start keeping an eye out in your local travels to see what is doing well and you like the look of and take some pics of it, you can usually either post a pic online or get a local nursery/landscaper to identify it for you.

If the fill side of the site isn't a rush to get completed, dumping a Deep (like 300mm layer) of leaf mulch over it can do wonders, it might take a couple of years to break down but when it does you have a good layer of planting material underneath. You can sometimes get tree loppers giving it away as they usually produce more than they can sell and want to avoid tip fees, if you are out of the way a bit though it's not as likely, although sometimes beer can be exchanged to sweeten the deal and a willingness to take whenever it suits them can help too.

[tryagain]

With your big back bank, I would potentially look at planting it out with some Tubestock as opposed to hoping something will grow from the top down and the bottom up, something like Lomandra longifolia (google tells me it grows in Tassie too) is pretty tough and should grow there, plant it at about 1m centres and it should fill up and stabilise the bank a bit and make it green. Probably not the "prettiest" plant but getting something that will survive there I would think is a higher priority.

With terminating to existing pits you need to be aware that they might not be designed to take the flow form additional catchment area's so you need to keep the overland flow path in mind for if/when they overflow.

With agline sizing, something the size you are looking at I wouldn't be considering 65mm.

[tryagain]

From the pictures the back bank looks too steep to keep mulch on it, I think it would wash down with any rain, that's if you could get it to stay in the first place. Some Jute mesh might be a good idea to stabilise it and keep the dust down a little until you get some growth happening on it.

The retaining wall at the bottom isn't a bad idea, but might not be necessary (gotta ask yourself what is it's intended purpose) and it might be better bang for your buck to spend your $$$ and time on other jobs, especially as it looks like it will be a bit out of the way behind the shed.

I have been given some 'expert' advice from the engineer and builder that went a bit like this.......

"plant out those areas over there" as he points to them, and "put a nice little retaining wall along there with a drain behind it and grow some shrubs on top of it" as he pointing along another section!!

As a Horticulturist who is in the midst of a career change to being a Civil Engineer, the last people you should be listening to in regards to landscaping are the builder and the engineer (structural and drainage components aside). It wouldn't be a bad idea to chat to a landscaper or two, You could just give them a call and say you are likely looking to do most of it yourself but would like someone to come and point you in the right direction and are happy to pay for a couple of hours of their time to have a chat about it. There might be some aspects that you think it's worthwhile to get them to quote on and possibly do as well.

[KeithB]

If the engineer says the excavated wall does not need to be retained, that's good. But a little retaining wall around the front with a drain with a drain behind it would be a good idea and, with a few plants in behind it to give a nice finished look. That's if you don;t mind the work an expense. I learned a long time ago that there is no such thing as a cheap retaining wall.

How do you intercept and deal with any runoff coming down the hill towards the excavated wall? Is that going the be a problem? You may need to divert that away from the house. I'd also make sure that all surrounding soil falls away from the slabs.

As Tryagain has said, it might also be worth thinking about fixing a load of screw pegs into the excavated wall and fixing some kind of mesh to hold the mulch in place.
Looks like a lovely location for your new home.

Keith

[Niley]

Hi Danny,

Not really a green thumb myself but have been involved in slope stabilisation for the past 30 years, predominantly the big stuff as pic below. Building a small retaining wall at the base of the cut is fine, however you need to eliminate surface water running down from the top of the hill and down the cut as the adequacy of any subsurface drainage behind the retaining wall you build will be insufficient in heavy rain and any weathered and loose surface material will just build up and flow down over the wall and onto your flat area. To prevent this and plant it with what ever you want, however I would suggest getting someone in with a machine and form a catch drain to the crest of the cut to divert water each side and away from the cut. You can line the catch drain with a non woven geofabric which should minimise erosion and vegetation growth. For the cut grab some jutemat and pin it to the face and cut holes in it for your plants.

Also remove any loose rocks on the crest when the machine is there as they are likely to end up in your shed some time down the track.

For the drain down the drive just leave open to collect into a sump, but just keep in mind to minimise slurry and soils from entering the drain.

Good luck with the landscaping!

[DannyG]

Some great advice gents thanks very much. Ill reply properly when I get an opportunity but just quickly here is a massive easement we put in above the cut to fill platform.  In fact the whole property (4 acres) has very large easements virtually around its perimeter.

[austastar]

Hi Danny
              If you are ever near Buckland, check out the Pulchella Native garden. It was once a quarry and a bunch of volunteers are turning it into a beautiful area.

https://maps.app.goo.gl/7bTYo

Cheers

Sent from my SM-T380 using Tapatalk

[gronk]

If the easement above your cut and fill stops all water, then the small amount that ends up down the embankment shouldn't be a major problem.
I personally dislike agi drains because after a few years, they either fill up with silt and stop working properly or the "rocks" above them become covered with soil etc and they stop getting free drainage.
Open drains, whether lined with hard material ( cement etc ) or largish rocks work much better.

[DannyG]

From the pictures the back bank looks too steep to keep mulch on it, I think it would wash down with any rain, that's if you could get it to stay in the first place. Some Jute mesh might be a good idea to stabilise it and keep the dust down a little until you get some growth happening on it.

The retaining wall at the bottom isn't a bad idea, but might not be necessary (gotta ask yourself what is it's intended purpose) and it might be better bang for your buck to spend your $$$ and time on other jobs, especially as it looks like it will be a bit out of the way behind the shed.

As a Horticulturist who is in the midst of a career change to being a Civil Engineer, the last people you should be listening to in regards to landscaping are the builder and the engineer (structural and drainage components aside). It wouldn't be a bad idea to chat to a landscaper or two, You could just give them a call and say you are likely looking to do most of it yourself but would like someone to come and point you in the right direction and are happy to pay for a couple of hours of their time to have a chat about it. There might be some aspects that you think it's worthwhile to get them to quote on and possibly do as well.

Thanks very much for your input.
You are correct the top bank in areas is most likely too steep to hold any mulch type product on it as it is now. I dont need a retaining wall although they (they being engineer and builder) have said to put something there. Its not so much to hold the hill up of course but more to retain any loose stuff that will find its way down the bottom.
But it will also help to make that area look nicer in the backyard, especially once I plant out the top of it.

I was hoping to 'step' the batter rather than have it just slope down, so I can get mulch to stay in place but I like the idea of the jute type mesh.

Go for as many succulents as you can for a start Pal,  then look at other native species to infill spaces.

You dont want to be watering all summer, and they are easy maintenance.

http://www.wildseedtasmania.com.au/succulent.php

http://www.woodbridgenursery.com.au/3-succulents

Thanks, I really need the good wife to 'approve' anything I plant so Ill show her those links.

If the engineer says the excavated wall does not need to be retained, that's good. But a little retaining wall around the front with a drain with a drain behind it would be a good idea and, with a few plants in behind it to give a nice finished look. That's if you don;t mind the work an expense. I learned a long time ago that there is no such thing as a cheap retaining wall.

How do you intercept and deal with any runoff coming down the hill towards the excavated wall? Is that going the be a problem? You may need to divert that away from the house. I'd also make sure that all surrounding soil falls away from the slabs.

As Tryagain has said, it might also be worth thinking about fixing a load of screw pegs into the excavated wall and fixing some kind of mesh to hold the mulch in place.
Looks like a lovely location for your new home.

Keith

Yeh the builder has put pit drains around the house site and the ground is being sloped away from the slabs and into those pit drains. Even though we have that big easement or spoon drain running above the house site, there would still be around 1500m2 of area between the drain the house site for water to collect.
I dont know a lot about how much water that would be but being out there when it is pouring with rain does tell me that the water will run down the side of the driveway and find its way into the pit drains at the front of the house site.
The water has even started to erode its own little path, hence I was considering making a drain there for it.

Hi Danny,

Not really a green thumb myself but have been involved in slope stabilisation for the past 30 years, predominantly the big stuff as pic below. Building a small retaining wall at the base of the cut is fine, however you need to eliminate surface water running down from the top of the hill and down the cut as the adequacy of any subsurface drainage behind the retaining wall you build will be insufficient in heavy rain and any weathered and loose surface material will just build up and flow down over the wall and onto your flat area. To prevent this and plant it with what ever you want, however I would suggest getting someone in with a machine and form a catch drain to the crest of the cut to divert water each side and away from the cut. You can line the catch drain with a non woven geofabric which should minimise erosion and vegetation growth. For the cut grab some jutemat and pin it to the face and cut holes in it for your plants.

Also remove any loose rocks on the crest when the machine is there as they are likely to end up in your shed some time down the track.

For the drain down the drive just leave open to collect into a sump, but just keep in mind to minimise slurry and soils from entering the drain.

Good luck with the landscaping!

Those engineered retaining walls you build are massive! The spoon drain we put in is quite large and we filled it with 200mm rock. It seems to be doing the job really well so far. We didnt line the drain with anything. It was discussed at the time but after the excavator driver spooned it out the 'experts' were happy enough that it would continue to drain for many years to come. I can only trust the 'experts'!!

I do plan on removing those loose rocks up the top of the hill or at the least we are bringing in some top soil and sewing grass as its not as steep up the top. I was able to use the ride on up there before it was all excavated!
Ill excavate a drain along side the driveway and fill it with a decent sized rock, I wont bother with ag pipe, thanks.

Hi Danny
              If you are ever near Buckland, check out the Pulchella Native garden. It was once a quarry and a bunch of volunteers are turning it into a beautiful area.

https://maps.app.goo.gl/7bTYo

Cheers

Sent from my SM-T380 using Tapatalk

No worries, that we shall do, thanks.

If the easement above your cut and fill stops all water, then the small amount that ends up down the embankment shouldn't be a major problem.
I personally dislike agi drains because after a few years, they either fill up with silt and stop working properly or the "rocks" above them become covered with soil etc and they stop getting free drainage.
Open drains, whether lined with hard material ( cement etc ) or largish rocks work much better.

Thanks, yep Ive made the decision to not bother with an ag pipe, ill just make an open spoon drain and fill it with some rock.

Again thanks very much for the advice, i appreciate it.