Gardening Techniques: Site Levelling
Site levelling is probably the most major task that will ever be undertaken in any garden. It must therefore be one of the first tasks to be undertaken, if it is to be undertaken at all. If you start with a sloping site you may well have to level it; certainly some level areas will improve the general appearance of the garden. If you start with a level site you may well want to introduce into it some changes in level to relieve the monotony of a single-level garden.
The first operation in any site levelling or change of level job is to remove all the top-from the area to be levelled: of course if the builder has already done this for you it saves some trouble. The top-soil, which is the upper layer of soil, is usually darker than the soil below. It may vary in depth from a few inches to a few feet. The sub-soil, which lies below the top-soil, is lighter in colour and more tacky.
To determine the levels of a sloping site use thick bamboo canes of different lengths, a thick straight edge about six feet long and a spirit level. Put a tent peg at the highest point of the garden and place a cane just under six feet from it, making the top of the cane level with the peg with the help of the straight edge and the spirit level. The distance and height of the cane will then give you the angle of your slope. In this way the whole garden can be covered by a series of canes. To make different levels and slopes place other canes beside the marker canes you used to map the slopes. With these other canes you can work out absolutely horizontalby using the spirit level and straight edge or devise new angles of slopes by making the other canes fall short or rise above the marker canes. T-shaped boning rods are used for sighting the angles of slopes by lining them up by eye over the top of the ‘T’.
The best way to get a completely flat surface is by the ‘cut and fill’ method. Having first removed the top-soil, you then remove the sub-soil, transporting it from higher levels to the lower levels, until the desired new level has been achieved. You then replace the top-soil, or import some, as the case may be, and level off with pegs and a spirit level.
According to the way in which the pegs are worked out, this method may be used either to level an entire sloping site, or to convert the sloping site into a series of terraces. Similarly, higher areas can be created in the garden, as can sunken gardens. Where there are changes of level, measures will have to be taken to ensure that the levels remain constant and do not slip away through weathering and natural subsidence. If the change in level is not great, a gentle slope covered either with grass (which may be difficult to mow) or with a shrub or mixed border can be used. Generally more satisfactory, however, is the use of retaining walls. These may be of either dry stone construction (which is useful in assisting drainage) or of bonded brick. In either case, the walls should be built on a firm foundation of concrete, and should be sloped back slightly against the level above them. An alternative is to use the change of level to create a, but it is usually necessary to use fairly-substantial blocks for this purpose.
Having created changes of level it is then obviously necessary to create a means of passing from one level to another: this will necessitate building a sloping path or a flight of steps. At this stage it is merely worth bearing in mind that not only will you and your family want to pass from one level to another, but also that you will have to move such things as lawn-mowers and wheel barrows from one level to another.