Saturday, 1 December 2012

Forest Garden Notes - 1 : Further Thoughts on Water Management

Given the experience of over five months without rain here in Southern Crete I have been considering the water resource implications for growing fruit, nuts and vegetables on our plot of land.

Since my ultimate aim is to plant a food forest to produce fruit and nuts and a series of intensive vegetable plots to keep us self sufficient in vegetables and salads I decided to do some background reading and research to get a handle on the volume of water required to ultimately support such a venture.

As a starting point I started put together a rough list of what fruit and nuts grew best in the Cretan climate, what could tolerate the summer drought, what was available locally and best suited our particular growing conditions. 

Site of future food forest

In his excellent book "Mediterranean Kitchen Garden" Maiano Bueno suggests a basic mix of fruit trees for when planning an orchard to ensure a selection of healthy fruit throughout the year and good information about the most common vegetables found around the Mediterranean countries. I used this list and information to put together an ongoing that is evolving over time as additional information and personal preferences get incorporated. More on the actual list in a later post. What I was really trying to get at here was a rough idea of numbers of fruit and nut trees and the area to devote to vegetables in order to estimate water consumption for growing purposes during the long summer drought.

From my earlier research into Passive Solar Design (PSD) I found that for most purposes the Mediterranean climate of Southern Crete was similarly experienced in Southern Coastal California and warmer inland areas of California as a whole. I further discovered that the University of California (UC), as part of their UC Master Gardener Program, have produced an excellent series of articles entitled "Why Have a Backyard Orchard". These articles provided clear ideas and technical data that has helped me to check out whether what I am proposing is both feasible and possible.

My other source of reference was the excellent book "Creating a Forest Garden" by Martin Crawford. Not only is this a seminal account of how to achieve the goal of creating a forest garden - one of my aims for including in my overall permaculture design for my plot in Crete - and contains much practical and detailed information but is also a most beautifully presented book. A real bonus and contrast at the end of a harsh dry summer here in Crete.

From studying these sources, plus discussions with local nurseries and long term residents, plus the physical dimensions of the obvious area to devote to a forest garden, at least at the outset, I have arrived at the conclusion that I will be limited to about 40 - 50 fruit and nut trees at the core of our forest garden. In addition to the usual soil condition, natural drainage, varieties that suit local conditions etc the planning for suitable irrigation is obviously vital given the long, hot, dry summers in Crete. Since the plot is off grid it is essential that the finite resource of the spring water available on site, see previous Water Management post, I needed to explore how best to collect, conserve and distribute this vital resource. Since for longer term planning purposes (10 years, say) I wanted to ensure at the outset that I installed sufficient water storage to ensure that, when combined with the steady flow from the natural spring, I could meet the water requirements for the fully productive fruit and nut plot I was envisioning.

Temporary vegetable area
In Martin Crawford's book he states that "For example, a medium sized heavily fruiting tree (e.g.. apple or plum, 4m wide and high) might require in the region of 2.5cm of irrigation water per week in a drought, which works out as some 400 litres per week".

Meanwhile the  California Backyard Orchard section Orchard section on irrigation recommends that "water use for a medium sized semi dwarf fruit tree is about 16 gallons per day on a hot summer day on the coast of California without any fog influence". That of course is American gallons, (for those of us used to Imperial gallons!) which converts to approx 425 litres per week per tree.

For the vegetable beds the advice I gleaned from researching on the internet was that there seemed to be a general rule of thumb "that most vegetables need about an inch (2.5cm) of water (62 US gallons per 100 square feet)". This converts to approximately 25 litres per sq metre per week.

One of the many reasons for me choosing an earth sheltered house design, that will be "buried" into the hillside and not placed where what many would regard as a perfect site to construct a standard box design house, was that this land was now available for a series of intensive vegetable plots, on gently sloping land within a Permaculture Zone 2 area in relation to the positioning of the house. The maximum area that was thus released for vegetable growing purposes amounted to some 320 square metres. Allowing for plenty  access paths, to avoid compacting the soil, a rough maximum growing area is, say, 160 square metres. Therefore the irrigation requirement for the vegetable plots is 4000 litres per week during the growing period which will predominately be April to November each year. Whilst in April and November this requirement may be met by over winter in-ground water storage and rainfall, for the remaining 6 months irrigation will be required.

The combined irrigation requirement for, say 40 heavily cropping fruit and nut trees (or an equivalent mix of heavy and moderate cropping) at 400 - 425 litres per week per tree  plus, say 200 sq metres of vegetable beds at a total of 25 litres per week per sq metre is therefore 20,000 to 21,000 litres per week during the long dry summer months.

First food forest pomegranates
Previously (see earlier post on Water Management) I had estimated that the flow from the on plot spring water, in May 2011, was flowing at approximately 4000 litres per day. Given that all the snow on the mountains had melted by the end of July and it had not rained, apart from a couple of light showers for about 5 months I remeasured the spring water flow at the end of the first week in October and found that it was still flowing at just over 2000 litres per day. There was still evidence of water leaks etc around the outflow pipes from the storage tank so I happy to regard this as a minimum flow rate. For the period May to September, when there will be the peak demand for irrigation, I will therefore assume an average flow rate of 3000 litres per day  ie. 21000 litres per week which, reassuringly, equals the estimated irrigation requirement.

The current water storage tank has a capacity of approximately 15,000 litres. Whilst, given the above data, this should be adequate to manage the water requirement, my preference is to construct a second 15,000 litre holding tank and link this, in series, with the existing tank to provide some fall back capacity as and when required. Any overflow would be used to top up, as necessary, the main 60,000 litre storage tank I am proposing to install. This tank is designed to fill up during the winter and spring months, when the spring water flow will be at a maximum, to provide domestic and around house watering during the dry summer months.

 It is planned that any surplus water, particularly in the winter and spring when the flow of the spring will be at its maximum, will be diverted to store this surplus water in the soil of the major terraced areas of the plot. 


"Mediterranean Kitchen Garden" - Mariano Bueno

"Creating a Forest Garden" - Martin Crawford