Rainwater harvesting is a very old technique to collect and storage water from the rain for drinking, domestic or irrigation purposes.
In south Spain, were water can be very scarce, structures called “aljibe” were used for the collection of running water after raining, for later use as irrigation and drink water for livestock. They were very spread in south Spain since the romans, but were abandoned in recent times with modern supply of water.
One of the ideas to provide water to Quemao Viejo could be the building of one of this “aljibe”.
The collection area could be either the space between two hills, which should naturally get running water, o by giving some slope to an area with almond trees, and covering it with plastic sheeting to avoid water filtering into the soil. This second option seems less green, but the water collected would be less saturated with debris, and so reducing the risk of getting the “aljibe” clotted with soil swept along in the water. The plastic sheeting used should be strong enough to avoid degradation and be able to be removed from the land if the project would not carry on.
Let’s do some maths:
In this region of South Spain, the average precipitation is 300 mm per year. That means, if I am not wrong, 300 litters per year. Using for collection about 200 square meters, that would mean 60,000 litres a year (considering a system 100% efficient). An “aljibe” two meters deep, two meters wide and 5 meters long would give us a capacity of storage of 20,000 litres, which I believe is more than enough for irrigation and domestic water for a year.
The cost could be in the range of 1,000£ ( contracting a digger for 2 or 3 days (500£), buy the plastic sheeting (200£), building material to cover the “aljibe”-labour not included).
If the water storage were to be used as domestic, it should be treated. Easy! Sun can do that for us! I’ll do another post about that.