-----In 2004 we bought a falling-down house and 30 acres. This blog documents our progress-----

Tuesday, November 18, 2008

To terrace or not to terrace?

In parallel with the wastewater treatment decision, Dad is very insistent that we decide right away on the garden layout, and in particular that we put terraces in. I am less sure, not least because I'd never envisaged having terraces nor had it been something we'd discussed.

Much exchange of emails ensued... At one point I had talked myself into terracing, to the extent of having a giant HaHa... but then Dad talked me out of it again. So now we're back to square one, no decision on layout yet made and awaiting input from Michael from Septech on how detailed we need to be in specifying pipe layout.

I can't face summarising it all, so here's the email conversations recorded for posterity. ;-)

On 11th Nov Dad wrote:

I think terracing of the block is essential in order to retain water for garden beds. I believe each terrace can accommodate two rows of appropriate trees, at the high side and the low side. The stepdown of each terrace will give a place for trailing plants and for shrubs. The size of each terrace is dictated by your plans for the area other than as an effluence field. The pipes can be buried beneath the surface if it is more appropriate for the use you intend for the terrace. In fact, you may not want to put in terracing at all. But you need to take time to consider this in the light of needing to direct Michael, and when he proposes his pipes you need to accomodate these adequately. You are the one with the masterplan.

I replied:

In terms of terracing, I don't know yet. There are pros and cons. But at this stage, I don't see that whether we have terraces or whether we have the pipes simply laid on the surface with mulch would make a huge difference to the length of pipes we'd need. I will ask Michael though. For the moment I think we go with whatever layout in that specific area is the simplest for him to quote on, so we can get the plans submitted in order to get the building permit underway. If needed we can then revise the details of piping layout later as they'll remain in the same area so can't see it being a big deal

On 13th Nov Dad replied:

I suspect from your last email that you are not aware that the council health inspector will not permit us to move the field as established by the drainer before commissioning the system without another inspection. That is why I wanted you to consider the size of each of the terraces if terraces were to be used at all. Terraces make the area more efficient for use as a soakage of wastewater area. As the gradient is such that over the distance from the corner post under the master bedroom of the old house to the cornerpost under the kitchen on a diagonal is approximately 1 metre in fall. That translates to about 1m fall in approx 12 m. Since we can curve the terraces to the shape of the hill we can gain a slightly sloping open area with a width of 3m and a step down for each area of about 400mm. The 45m area available would permit 4 such terraces. The field has to be accounted for the minimum of 400m only on the parts where the pipes are going on the level along the length of the terrace. The drop down to the next terrace at either end does not apply to the overall capacity of the system to dispense water.

If you wanted to have only 2 terraces then the stepdown would be approx 1m. That may be more suitable to you. It would mean moving subsoil down to the lower area after scraping off any soil that could be used on the finished terrace. That applies to all terracing of course. The stepdown requires a slope rather than a sheer drop. This takes away from the available width of the area to accommodate the terraces, but a slope is more serviceable in the long run with less maintenance.

As long as you have a clear idea of this information you can make a considered choice about whether to have terraces or not. If you like you can simply distribute the pipes on the existing gradient. You also have the option of having the pipes buried at least 300mm under the ground or lying atop the ground with mulch atop them

I replied:

Yes, I understand we can't move the overall location of the field.. But, if the field is defined as simple a specific area - ie if you imagine we roped out a section of land between the house and the gums at top of driveway, then it may be that provided we stick to keeping the pipes within that specific area, we might have flexibility to change the precise details of pipe arrangement prior to implementation.

It all depends on how detailed Michael has to be in terms of how he describes things. Eg: if he has to describe the location of every single individual pipe and bend, then we wouldn't be able to alter a thing without having another inspection. But if all we need do for the permit is to commit to there being a set length of pipe in total and for it to be arranged over this particular plot of land (but not give details of precisely how the pipes would be arranged within the borders of that plot) then we would still have flexibility to decide the best garden (and thus pipe) layout closer to implementation.

Eg: do the pipes have to be evenly spaced within a given area, or can their arrangement be more finely targeted, so it only goes on those areas that have garden beds and not on the areas that are paths? As an illustration, see:

One idea for garden layout

If we went for a garden layout sort of like this, would we be able to focus the pipes in just the dark green bedding areas? This is what I want to find out from Michael. (nb: this is just one illustration: I would want to liaise with Prue before confirming precise shapes of beds etc, just showing to you so you get the gist of what I am asking).

Of course, it would be possible to still have terracing with this sort of garden although you wouldn't want too many... But, thinking about it more, there is another reason why having at least one terrace would be good - and that is so that we could use it as a Ha-Ha.

In case you don't know what a Ha-Ha is, it is basically an invisible fence. They used them a lot in old country houses here in the UK, as a way to keep sheep and cows out of the formal garden areas without having to build an obvious wall that blocked the view from the house.

I wonder if we could do a form of this encircling at least the bottom parts of the garden which had a HaHa type cliff edge - of a sufficient height to stop sheep/cows/etc. We could use the clay that we have excavated from other areas, supplemented with lovely topsoil that we buy in for the top for planting in - to help build up the height sufficient to give a high enough edge.

This would also solve a problem I have been worried about: how to be able to have a nice garden area without sheep getting into it and having to erect yet another fence. You mentioned if we had 2 terraces the step down would be 1m. So does that mean if we had only one terrace, that the step down at the outside edge would be 2m? This would be big enough to keep out sheep wouldn't it?

What do you think?

Dad replied:

1. A metre fence with a slope to complement it will be adequate. There are not slopes that a sheep or cow will not go up for good tucker, unless we are talking a sheer wall of sleepers or rock.

2. If we have only one terrace it will make a wall about 1.6m to 2m as a rough calculation. This terrace will not be level, most likely, but have a small gradient. Before beginning any excavation I would establish the gradients required to follow by placing markers for the man on the machine, and by frequent checks of gradient points as the excavation continues.

3 .The problem with moving the pipes is that you cannot handle them unless licensed to do so. They are a health hazard as they carry black water to be treated in the ground.

4. However you go about this there is sufficient area to get 400m of pipe in for the dispersal of the water. I would imagine there are guidelines as to how close together the row can be, and this relative to the percolation value of the soil. I am sure they will have it worked out to be certain all water delivered remains under the surface and doesn't seep to the surface because of saturation of the area.

I replied:

Hi Dad,

Re: 1)

We *are* talking about a sheer wall of rock. That is what a Ha-Ha involves.

I just realised I have some photos of a real HaHa that may help explain it better. In fact this is of the oldest HaHa in the world that was installed in the late 1600's and has been keeping out sheep ever since. I saw it with Mum at the Levens Hall garden a few years ago up in Cumbria. This is me standing on the edge of the Levens Hall HaHa with my toes nearly off the edge, taking a photo of the rock retaining wall. See, it's really clever, you can hardly tell there is a wall there even when standing right above it.

OA077 Lyn on the edge of the haha taking previous photo

And this is the photo I took, looking down. You can see they had pebbles at the bottom and rocks lining the wall side

OA076 it was a high wall and a big drop to the  bottom of the haha

I like the idea of a HaHa aka an invisible fence from the house side, because I really don't want to have everything looking like it is fenced in. The orchard wall was something that we were forced into and luckily you can't see the wire from the house, but it has spoiled my plans for that part of the garden... kind of hard to stroll through the trees down to the dam when you have to go through giant fencing. But hoping it will be OK in the end because we will grow things on the wall and make it look less like a prison fence encircling them. We had no choice anyway, protecting the trees was the top priority.

Re: 2)

A wall of 1.6 - 2m at it's highest point down near the driveway sounds great - although I want to discuss with Dave too. It would mean that even as we got up the hill towards the house there will still be a reasonable sized drop quite a way around. So it would only be near the house that we had to worry about having a low height fence.

We could have one small part where there were steps and a gate in the wall to allow you to walk up through the garden from the driveway.

Re: 3)

Of course I understand we can't move the pipes once they have been laid. But there is a long long time before a single pipe will go near the place. To spell it out more clearly, this is my understanding of the timing.

Dec 2008: Michael creates application including plan (to whatever level of detail is required)
Jan 2009: Dad gets building permit to start work on the old house
Sometime in 2011 or even 2012: We actually get round laying the pipes.

There is a lot of time between now and when the pipes need to be put on the ground. All I am saying is that why commit now to a detailed layout of exactly where each individual pipe will go, where it will bend, etc if we still have years to go before it will be implemented? The *only* reason to commit so early would be if the council required that level of detail for the permit, but that is for Michael to tell us.

Of course: the one thing I need to check in having just a single big terrace - which can't do until on site and can see the gradients - is whether having such a terrace would mean you couldn't see the dam from the house. I'm hoping not, am hoping that the slope is such that you would still be able to look down and see it, that the only parts that may be hidden are the driveway and part of the orchard...

Dad replied:

I did not say the wall was to be down near the driveway, but I referred to a terrace created by removing soil and subsoil layers to whatever size you wanted within the 45x45 area. The thought I had was that the terrace would ultimately regain the original level of the ground near the trees. I never thought you wanted to dig below the level of the trees to create a trench. Doing this may compromise the runoff prospect from the saturation field. You cannot go closer than the front of the house with any diggings because of the underground pipeline restrictions, so to manage a trench to runoff would have to be arranged in the other direction,across the road and thereby require a bridge of sorts.....I thought you would use the extra soil from the house excavation and from small terraces to build up a roadway between the trees. The idea of a Ha Ha for the wastewater area is going to greatly restrict the area available for pipes. I was talking about a wall or slope at the high side of the wastewater field. The vegetation of this field cannot be fruit trees or vegetables. Nothing that will be consumed. The area you have bending up towards the house is where the septic has to be put. This cannot be too far from the houses nor be too low as a very low gradient for the septic inflow pipes from bathroom and other area is required (apx 40/1 if it hasn't changed since I last laid such pipes). The tank could go under the area for the herb garden in your sketch, but must be not directly under as access needs to be readily available for service. A large terrace may require another percolation test as the test had only 600mm holes into the undisturbed terrain of the area. I think Michael's input is required before too much more detail is added to the area.

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