Introduction to traditional Rainwater Harvesting Technology Practices

Growing Water

Since the beginning of agriculture, farmers, especially those in arid areas, have sought to develop techniques to collect runoff from slopes, to direct it to crop areas and facilitate its infiltration near the roots of the crops or to direct it to reservoirs.

The very diversified traditional techniques of rainwater harvesting deserve to be known, because they are implemented with the local resources of the environment and they are manageable by the communities. Their relevance has been evaluated over the long term, and their efficiency has been measured more recently by scientific methods.

Growing Water

Introduction to traditional Rainwater Harvesting Technology Practices

Traditional rainwater management and harvesting techniques

Archaeology has unearthed vestiges of rainwater harvesting and management devices in China, the Middle East and America. A part of the ancient knowledge in the field of hydraulics has been lost, but many ancient skills remain alive in Afghanistan, Australia, Botswana, Burkina Faso, Egypt, India, Iran, Israel, Kenya, Mexico, Mali, Niger, Pakistan (Thar desert), Palestine, Sudan and in the Nile valley before the construction of the Aswan dam.

In the Peruvian Andes, the rehabilitation of pre-Inca and Inca installations has made it possible to recultivate land that had been abandoned and to provide communities with fresh water.

Inhabitants of the village of Huamantanga, in the Peruvian Andes, rehabilitate and maintain the 1400 year old amunas, canals that collect, preserve and make water available during the long dry season.

In the Sahel, the "traditional" techniques of stone lines and cordons and pit cultivation irrigated by small impluviums, which had once fallen into disuse, are regaining popularity and are making it possible to rehabilitate land that has become barren; the combination of the heritage of local techniques and those from the European heritage of knowledge of bocage development is making it possible to regreen arid areas.

Bocage sahélien

Mobilizing ancient knowledge and know-how could therefore contribute to implementing dynamics of regeneration of degraded environments.

Among these developments we can distinguish:

filtering devices whose function is to slow down and spread runoff: lines and cordons of stones or plants, fascines, filtering dikes and low walls,

Obstacles and retaining "traps" that do not simply slow down runoff, but retain it, concentrate it and force it to infiltrate: earth, sand and stone dikes sometimes reinforced with living hedges; jessour in Tunisia, fanya juu system in Kenya, Hopi waffle gardens, ôno or ôgo gardens of the Dogons in Mali, ditches and swales...

very diverse terrace designs depending on the slopes, climates, cultivation methods and social organizations: rain-fed with the stone terraces of the Konso country on the high plateaus of Ethiopia and the Mofu terraces on the Mandara Mountains in Cameroon; irrigated with the Inca andenes; flooded with the rice paddies in Asia...

Designs including an impluvium, i.e. a catchment area and a water reception and concentration area.

Among these developments can be distinguished:

◦ models with small impluviums: (wégou, zaï, tassa, half-moon... of the Sahel; ngoro of Matengo of Tanzania; gawan of Somalia; teras and negarim of the Near East...

◦ and models with large impluviums: Tunisian tabiâ; liman irrigation system in Palestine and Israel; khadin of Rajasthan...

water conveyance networks to cultivated or inhabited areas: Persian qanats; Algerian foggaras, Moroccan khettaras and faljs of the Sultanate of Oman; Pre-Incan amunas and Inca puquios; Arabo-Andalusian acequias spread in the former Spanish colonies...

All these developments were designed to provide three functions :

- to collect rainwater

- to guide runoff and carry it to places cultivated and inhabited by humans

- to store water in the ground or in reservoirs

Most of these devices are not only water "management" systems, they are also erosion control and soil fertility preservation systems. They were developed by agrarian societies that, by cutting down forests and cultivating the cleared areas, have generated environments that tend towards desertification. Indeed, as soon as the soils are no longer protected by their vegetal "skin" that are the forests and the natural meadows, as soon as they are exposed and exposed, they are directly subjected to the rigors of the impact of rainfall and winds that carry them away by erosion. To counter the processes of water and wind erosion, which they have generated, humans are forced to tirelessly work to stop it. They must deal with fragile environments and invent devices that preserve their habitability. In Europe, the reintroduction of trees and living hedge around field in agricultural landscapes during Middle-Age was a response among others in the world to remedy the catastrophe of the disappearance of forest cover.

The natural forest is a system that maintains the water cycle, minimizing and compensating for water "losses" by generating the water it needs. The creation of an agricultural system tends to create an unbalanced environment where water leaks from all sides.

In such a system, water is lost:

- by evaporation from the soil surface

- by surface runoff

- by percolation and deep drainage

As shown in the diagram above, water loss can be variable:

- evaporation will be all the more massive at the surface of the soil, if it is bare and if it is compacted;

- Surface runoff will also be more pronounced if the soil is not covered and if the water does not encounter obstacles that slow it down and facilitate its infiltration;

- percolation and deep drainage will lead to a complete loss of water in the absence of trees whose roots would bring the deep water to the surface.

Traditional water harvesting methods are remedial devices for leaky agricultural production systems. They are an essential technical and social heritage whose value must be recognized and their uses revalued.

The essential objective of these methods and techniques consist in transforming the "blue water" of precipitation into productive and fertile "green water" for the agroecosystems managed by humans.

Today, it seems essential to make the most of ancient knoledge and to integrate this heritage into a paradigm of environmental regeneration that aims not only to "harvest water", but to "cultivate water" to generate fertile and perennial living environments.

This implies thinking jointly about water, soil, plants and other living beings – micro and macro fauna – residing under and on the land. For this we need to combine ancestral and contemporary knowledge, popular and scientific, and also to equip ourselves with an ethic that considers land and water as a living common that must be taken care of and does not consider the territories where we live and cohabit with multiple other living beings as mere environments to be exploited for the sole benefit of a tiny minority.

We propose to the reader a series of articles on the different techniques of water harvesting and cultivation to make known the principles, the modalities of implementation and the potential.

The various articles to come will be the following:

- Filtering and retaining devices: (lines and cords, bunds, low walls and dikes of stones and plants

- Terrace systems (dry and rain-fed, irrigated, flooded)

- Impluvium: micro and macro catchment areas designs

- Traditional water conveyance systems

These technical devices have been developed in semi-arid environments where dry and rainy seasons alternate.

Concerning the management of water and agricultural soils in environments where water is very present or even excessive, we refer the reader to the following articles:

- Floating Gardens of Bangladesh

In progress

- Floating Gardens of the World

Published online by La vie re-belle
 9/04/2022
 http://lavierebelle.org/introduction-aux-techniques

Articles 7

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