The term ‘water harvesting’ generally refers to techniques used for the collection of water from a particular area (called the catchment) in order to provide water for human, animal, or crop use.
Water harvesting is an ancient practice that has enabled communities to grow and flourish even in semiarid and arid areas where other sources of freshwater (rivers, lakes, or aquifers) are scarce.
This concerns natural cycles such as rain, mist, condensation, evaporation, etc., and Permaculture integrates these practices for the purpose of assisting natural succession towards climax regenerative ecosystems.
The water collected can either be utilised immediately, for irrigation, or be stored in aboveground ponds or in subsurface reservoirs, such as cisterns or shallow aquifers, or in the soil.
While there is a very wide array of scales for the techniques of water harvesting, in this article I will focus on those linked to civil engineering; I will try to cover strategies that can be applied by individuals or, ideally, groups of individuals that coordinate their actions on a community scale.
Intercept water at the highest possible point in the landscape.
Ideally, this would start above the headwaters, above the formation of water streams, or the accumulation of water in the geology, that leads to the formation of springs. Oftentimes, these techniques have to be adapted to locally adapted materials and skills.
As it is practically impossible to work with imported materials, due to harvest and transport costs, and also to the impracticability of the terrain, it is more important to describe the function of “check dam type” features: to hold small volumes of water for a certain amount of time.
In drylands, some climate-appropriate techniques are leaky weirs, one-rock dams, or trincheras. All three aim at placing permeable obstacles in the path of water.
Place stable structures in advantageous positions.
As we go lower in the landscape, other techniques are possible: log dams, check dams, and earthen berms. These are slightly larger, and can also be more precise, allowing the diversion of water towards growing areas. Essentially, these types of structures enable more vegetation growth, more carbon breakdown as well as evapotranspiration.
Diverting water from the valley towards the ridge (keyline design), for slow infiltration on land used for cultivation, can be a stand-alone technique, or a complementary one to the ones mentioned above.
Create appropriate-sized water storage, in the landscape, for gravity irrigation
Some of the techniques mentioned above can be integrated into this “layer”, but here slopes are more gentle (< 20% ). Swales are an appropriate option, with the purpose of slowing, spreading, and soaking the water into the landscape. Where there is overflow, swales can be linked to check dams, keypoint dams, and contour dams, to create networks that hydrate larger areas while providing stability.
In dry climates, gabions are also a very effective, and even necessary, technique.
Where these techniques can be combined, projects are designed to also be flood-proof, fireproof, and drought-proof, through the holistic management of human and material resources. These systems can provide not only subsistence but also extra yield and possibilities for economic ventures, on condition that they are kept in scale and the operations are run ethically.
Direct rainwater off of hard surfaces (roofs, streetscape, etc.) towards storage or infiltration systems
This is a chapter in itself, as human beings have settled into almost every possible ecological niche on the planet. The use of fossil fuel has allowed us to go to even more diverse habitats, and colonize them with greater intensity. But rainwater harvesting from hard surfaces actually provides us with a baseline of survival: it’s a gauge of how much growth is actually possible, where we live.
The techniques that can be employed are numerous:
Nobody presents them better than Brad Lancaster: He is probably one of the leading authorities worldwide on the subject, and writing a few lines wouldn’t do justice to the wealth of content he provides through websites and books: https://rainwaterrunoff.com/ and https://www.harvestingrainwater.com/water-harvesting/water-harvesting-principles/passive-water-harvesting/resources/.
Aquaculture means life-rich systems that are fed by the water harvested using the techniques presented above. Where water is pacified throughout the landscape, and flows at speeds slower than the human walk, we encounter the conditions to build chinampas, paddies, flood irrigation systems, ponds, mangroves, floodplains, marshlands, etc.
These systems, in different iterations, combine land crops, water crops, and protein production in water (fish, crustaceans, shellfish), allowing for intricate, interdependent ecosystems to flourish.
Describing these techniques within this blog cannot compare to the wealth of information of a story by an independent video maker (Matt Powers) on Chinampas: https://www.youtube.com/watch?v=ijzL5IsF-Ow&t=11s
To conclude, I believe Humanity’s survival, and flourishing, both depend on our personal and community-level understanding of the importance of water harvesting. When human beings will be able to rise to the challenge of our times and move in the direction of assuming responsibility for their needs, and those of their families and communities, Civilisation will find a way forward.