The world’s water supply is at risk. If we take a “water’s eye view” and look around, it’s not hard to understand why: human development is breaking the natural hydraulic cycle by intervening in it in many ways:
- Deforestation worldwide decreases the infiltration rate of soils and cuts off transvaporation.
- Modern agricultural practices of plowing and soil manipulation with heavy machinery create a layer of non-permeable hardpan clay that prevents infiltration and increases runoff and soil erosion.
- City sprawl, roads, industrial zones and suburbs create large impermeable surfaces with similar results.
- All these activities also require ground water for irrigation, domestic use, and processing. The more this broken cycle is perpetuated, the more our water supply decreases.
The equation is simple: less water infiltrating into the ground + more water pumped out of the ground = water table dropping.
The damage expands as rivers and waterways are flooded during heavy rainfall and mix with pollutants from sewers, agricultural fertilizers, biocides, etc.
A dear friend of mine, Tom Newmark, started an initiative called “The Carbon Underground.” Its purpose is to promote carbon-negative agricultural practices. I loved the idea and am very impressed with his project’s research and information sharing. I am a keen permaculturist and very interested in carbon sequestration through regenerative agriculture. This initiative got me thinking about the fundamental importance of building back the earth’s water reserves to allow regenerative practices and carbon sequestration to take place.
A solution to these problems lies in an elegant and noble method developed by Australian agronomist and engineer P.A. Yeomans, called “keyline design.”
The basic idea behind keyline design and any other water retention techniques is to “slow, spread and soak” the water into the ground. When applied, these techniques help to reduce runoff and soil erosion, and also recharge the water table. Other benefits are extended flow and season from springs, and more regulated flow in creeks and rivers.
The keyline method consists of recognizing the key points on a slope and the contour line that extends from them. The key point location can be found in a primary valley where the lower and flatter portion of the primary valley floor suddenly steepens.
The key point and extending keylines create water retention opportunities for us in the landscape: Earthen dams would be placed at the key point. Terraces would be placed on slopes above the keyline of a more than 30% slope, swales and furrows would be installed on mild slopes of less than 30%, below and parallel to the keyline.
Swales are trenches that are cut into the soil on hillsides with mild slopes. They stop water from running and deposit it under the ground. If rain deposits water into a swale at more than its capacity, it should be designed to overflow on a mild slope into the next retention.
A swale has a secondary function as a nutrient pump. As water collects and sinks in along the swale, any nutrient washouts from decomposing material or manures uphill would stop there and be integrated into the soil.
Once this system is in place, the regeneration process starts without further intervention, as biomass and nutrients are trapped in swales and begin to grow native species and accelerate forest growth. Well-managed regenerative agricultural practices can be implemented to produce grain, cattle, fruit trees, or agroforestry. In any case, the cultivars would benefit from the water, soil, and nutrient retention and would build up their resilience and productivity.
Other practices that combine very well with keyline design are holistic management for cattle or other animals, food forests, and organic farming.
In the last few years, I have been involved in different projects of varying magnitudes and have integrated water retention landscapes or keyline design into all of them. The results are very encouraging. Landscapes that suffer from harsh compaction, erosion, and nutrient depletion have started to grow lush greenery. Plant growth has accelerated and irrigation water in the summer is abundant. Even microclimates have changed and are moderated by the presence of a large body of water nearby.
Water retention in the landscape has many other indirect benefits, as it attracts wildlife such as migratory birds and frogs. Some of these animals directly benefit us and some do not, but all occupy a niche in the larger ecosystem.
Another aspect is the possibility of integrating aquaculture into the system, increasing net yield and building up nutrient-rich fertilizer in the irrigation water.
From the time I first stepped into the Pachamama community in Nosara, Costa Rica in 2008, I saw a tremendous need for water retention, as the land formation, the soil type and the heavy rain pattern in a short season all caused massive erosion. Water in the dry season was very scarce.
At the time, I tried to promote the creation of such a system, but the community was not open to the idea.
Some years passed and the idea took root with great help from another permaculturist who came to live in the community – Apurva Jivan. Last year, we began to use keyline design on the land. We created two main retention ponds to recharge the water table, and a series of swales, ripraps, and diversions to slow the water flow, spread it and soak it into the ground.
The construction of the dams is done by selecting the best clay and placing it in the core at layers not exceeding 30 cm, compacting it with a sheepsfoot roller, and building up the embankments with poorer clay soils at a 1: 3 slope. It took us four weeks to build two ponds. Together, they will hold 5,000 cubic meters of water per rain event. This has the potential of injecting a total of 5,000,000 liters a year into the aquifer (the calculated volume of water that flows through the watershed).
Our success indicator is the spring that flows downstream from the ponds and is reduced to a trickle in the dry season. If that spring revives, the volume will increase by next year, and we will know exactly how much we’ve been able to charge the water table.
So, in order to trap carbon underground in plant matter, water must go underground too.
This post was previously published on www.gaiauniversity.org and is republished here with permission from the author.
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