Water Harvesting (I)
Harvesting rainwater for landscape use
Water in Jordan is a precious commodity, and rainwater is a seasonal gift. The process known as water harvesting can help you make effective use of rainwater by capturing rainfall for use in irrigation and other domestic uses.
Why harvest rainwater? The average amount of rainfall in Amman during January is over 60 mm, but goes down to zero during the summer months. Harvesting rainwater makes it possible to save the excess winter rainwater for use during the summer. Harvesting rainwater also can reduce your dependence on municipal water supplies and therefore result in considerable savings in your water bills. It also contributes to controlling off-site flooding and erosion by holding rainwater on the site, and also to reducing the load on the municipal storm water lines. Rainwater provides a source of water that is ideal for plants since it is clean, salt-free, and has a hardness of zero.
The practice of rainwater harvesting has been around in Jordan for centuries, and there is an abundance of historical structures that provide clear testimony to this practice. Such historical examples include the cut-stone reservoirs of the Nabatean city of Petra, as well as the underground cisterns found in the country’s Umayyad desert palaces, Crusader castles, and traditional village houses. Some of these historical water containers continue to be in use up to this day, and a number of those that fell into disrepair have been restored recently and are functioning again.
If you are interested in creating your own rainwater harvesting system, begin by carefully observing and analyzing your site during the rainfall period. Identify high and low rainwater areas, drainage patterns, gravity flow, and areas from which water can be harvested, such as rooftops, paved areas, and driveways (all known as catchment areas). The site’s natural topography also should be studied, in addition to the type of soil on the site, and the site’s existing plants and their water requirements.
There are two types of water harvesting systems: passive and active. In a passive water harvesting system no water storage containers are used, and rainwater is diverted immediately to the soil in the site, where it is stored for direct use by the plants. This method has the advantage of reducing salt accumulation in the soil since it increases the amount of rainwater percolating into the soil, which forces salts down and away from the root zone area (a process called leaching). This allows for greater root growth and water uptake, and eventually increases the drought tolerance of your plants. In active water harvesting systems, all or some of the rainwater falling on the catchment areas is channeled into water storage containers, where it would be kept for use during the dry season. A combination of both active and passive water harvesting techniques can be used in your garden.
Keep in mind that a water harvesting system also can provide an attractive landscaping and architectural design element that is functionally and aesthetically integrated within the site. For example, a downspout that directs water collected from the roof easily can be transformed from a mundane drainage element into a colorful sculptural piece that adds a touch of design to the garden. Developing your water harvesting system should be an on-going process that can be improved upon and expanded over time.
The main types of rainwater harvesting systems and their components will be further discussed in the upcoming article of this series.