Water Retention Landscapes (WRL) are systems for the restoration of the full water cycle by retaining the water in the areas where it falls as rain. A WRL is a landscape with no rainwater run-off, where only spring water leaves the land. The rain which falls on such an area is taken up by the vegetation or the water-bodies and recharges the groundwater. The retention areas act in place of the fragile humus layer and, through their high water absorbing capacity, they also help to prevent fatal landslides and floods, which nowadays are caused more and more often by intense rainfall. There are many measures that can be used in various combinations to create WRLs (several of them have been used in Tamera as well):
- The construction of water retention spaces in the form of lakes and ponds;
- Reforestation and planting of mixed-culture ground cover vegetation;
- Holistic grazing management;
- Keyline design: a planning technique for maximizing beneficial use of water resources that considers topography and landscape features such as ridges, valleys and natural water courses, seeking optimum water storage sites and potential interconnecting channels;
- Swales: low tracts of land, usually moist or marshy. Artificial swales are often designed to manage water runoff, filter pollutants, and increase rainwater infiltration;
- Infiltration of road and roof runoff water by different means.
Four elements are particularly important for the shaping of such water retention spaces:
- The vertical sealing layer of the dam (of a water retention space) consists of fine materials (ideally clay), usually using the material excavated from the deep zones. It is connected to a watertight layer of subsoil that sometimes lies a few meters below the surface. The sealing layer is compacted and built-up layer by layer with fine, earth-moist material. Then it is piled up from both sides with mixed earth-material, covered with humus or topsoil, and can then be landscaped and planted on. Through this natural construction method the water retention spaces fit in with the landscape and do not become incongruous with their surroundings.
- The longer side of the retention space is, if possible, laid out in the same direction as that of the prevailing wind. The wind then blows over a long surface, thereby forming waves which oxygenate the water: oxygen is an important element for the purification of water. Wind and waves carry particles of debris to the shores where they are trapped by aquatic plants and eventually absorbed by them.
- Banks are never artificially straightened or reinforced, but created in meandering forms with both steep and gently sloping parts so that the water can roll and swirl. At least one part of the shore is planted with aquatic and waterside plants.
- Deep and shallow zones are created. In this way different temperature zones emerge providing healthy thermodynamics in the water. Shaded shore areas support this process. Thus a diversity of habitats allow for a high diversity of aquatic organisms to be established.
In Tamera, the creation of lakes has proven to be a faster and more effective method to reduce erosion than reforestation which is a much slower process. It was used as a first step to allow for reforestation to be done in the most eroded areas. A series of interconnected retention areas (from swale sized to pond-sized to lake-sized) were created using the local earth and stone material. The construction of the first water retention space, “Lake 1”, located in the centre of the Tamera site, was realised in 2007. “Lake 1”, with a total capacity of 6,400 m2, was totally filled during the second winter after its’ creation. Already within the first year a new seepage spring arose which since then has flowed continuously throughout the year from Tamera to the nearby farms. In 2011, another retention area, with about three times the capacity of “Lake 1”, was built.
From 2006 to 2015, 29 lakes and retention spaces were created and the area of water bodies was increased from 0.62 ha in 2006 to about 8.32 ha. After 2015, the efforts shifted from the construction of open water bodies and mainly focused to other interventions aiming to support water infiltration, vegetation growing and soil formation, such as swales, planting of ditches, mulching with wood chips and charcoal, and check and maintenance of dams.
Tamera is now prepared to fully absorb even strong continuous rainfall. This large retention area is located at the highest point of the valley. The water pressure is therefore high enough to irrigate all of the land, without additional energy needs for pumping. This highest-situated retention space can then provide enough water to maintain stable all year round the water level of the further down retention spaces. The water retention landscape creates space for riverside forest plants and fruit trees; in Tamera, chestnut, alder, ash and elder tree were planted. Forest corridors offer a protected path for wild animals to reach the lakes and ponds. Also, further away from the water bodies, olive trees, cork oaks and a huge variety of native trees were planted to increase diversity and productivity.