Difference between revisions of "Water management"
(Originally Chapter 5.1. in Permaculture and Climate Change Adaptation)
Revision as of 15:09, 1 July 2017
Changing climatic conditions mean a need to plan for altered and often unpredictable future precipitation patterns. In some places precipitation will decrease; elsewhere drought will be more common and/or pronounced; other areas will experience erratic rainfall, storms or other extreme weather events.1 Applying the principle of 'capture and store energy', permaculture practitioners have designed strategies to regulate the movement of water across a site or landscape, either through controlled mechanical processes or within natural flows through soil and vegetation.2
A straightforward water retention technology used in many permaculture projects is swales, or earth bunds: elongated mounds dug along contours or in flat areas to intercept surface water runoff and allow its absorption in to the soil and groundwater.3 In Guatemala, the Mesoamerican Permaculture Institute has identified swales as an element of traditional Maya water management practices, now part of a wider strategy to promote and strengthen indigenous knowledge.
Another simple technique is mulching: covering the soil surface with a layer of organic matter that is allowed to rot down. This reduces surface evaporation and enhances the physical capture of rainwater and surface water runoff, especially when combined with swales. It also stabilises soil surface temperatures, adds organic matter to the soil, and improves habitat quality for soil organisms, and so combines water retention with soil improvement.4
The Chikukwa Project in Zimbabwe combines several techniques in an integrated strategy for water management that has reversed rapid degradation in water supplies. Creating swales and replanting natural vegetation on slopes above the fields has improved water retention in soils and reduced erosion. Areas around springs have been reforested and fenced against grazing livestock, improving availability and quality of water. Villagers have constructed simple systems to harvest and store rainwater and use household greywater to irrigate cultivated trees and vegetables. Villagers nowadays resolve disputes arising over access to water and other resources using sophisticated conflict transformation techniques.5
Widely adopted in broadscale permaculture, the Keyline Plan technique combines water retention and soil protection. A complex of off-contour ridges, channels and ditches direct water from potentially flood-prone sites to where it is most needed. A common addition is large-scale storage of surplus water that would otherwise run off the land, for later use by rapid, gravity powered flood irrigation.6
The Jordan Valley permaculture project has rehabilitated a four hectare desert site affected by declining rainfall, increased groundwater salinity, and erosion resulting from intermittent heavy run-off from an adjacent road. Building 1.5 kilometres of swales across the site, planting these with nitrogen-fixing and fruit-bearing trees, and extensive mulching of surrounding soils allowed establishment of initial tree cover. This was later interplanted with vegetable crops, along grasses that improve the soil and provide forage for livestock. Crop yields match those in adjacent areas that use conventional high-input agricultural methods, with far higher efficiency of water use and steady declines in soil salinity and heavy metal content.7
Tamera Ecovillage in the seasonally arid Mediterranean climate of South Portugal is experimenting with landscape-scale retention of rainwater using large artificial lakes. Water slowly infiltrates the surrounding soil, replenishing aquifers. Lakeside vegetation also absorbs water, maximizing evapotranspiration and condensation and increasing local humidity.8 Tamera’s water landscape project was inspired by Krameterhof in the Austrian Alps, where a network of pools and water channels supports aquaculture, irrigation, and consumption by livestock, as well as the creation of microclimates.9