Rainwater Harvesting Principles

by Giovanni Castaldo, Santa Cruz Permaculture Design Course alum

This series of blog posts about Rainwater Harvesting is provides an overview of some of the key practices. It’s informed and guided by the book Rainwater Harvesting for Drylands and Beyond, one of Brad Lancaster’s approachable and inspiring works. This is the first in a series of blog posts by Giovanni Castaldo.

The recurrent droughts and the yearly summer and fall dry spells that characterize California’s arid Mediterranean climate make water a particularly precious resource for this state. Today we are confronted with the need to reverse the degradation of water globally. We must also reestablish the health of the natural systems that humans damaged. These natural systems are our life-support infrastructure for clean, abundant and safe water, food and oxygen. We also face the threat to water security brought along by global warming. Although the challenges are global, the solutions can start locally in our own backyards.

The Role of Government

Centralized governments have been in charge of the environment for too long. They pushed for short-sighted initiatives, large-scale and money-intensive projects that played into the hands of powerful interests while furthering water instability globally. Faced with the drawbacks of such mishandling, governments have created “band-aid” approaches. These so-called solutions perpetuate the logic of intensive engineering of the landscape without taking on the systemic issues that are the root causes of water insecurity.

Even a government such as California that is proactive when it comes to water legislation is missing the point. As the first state in the U.S. to recognize the human right to water in 2012, California’s efforts on integrative regional water management, sustainable groundwater management, and overall conservation and restoration are shadowed by its colossal projects. These projects continue to be proposed, such as the Water Fix Tunnels and the avoidance to engage in a comprehensive reform of the agricultural system, whose practices have been so damaging to the water resources and the people of the State.

The California aqueduct. Photo credit: Ian Kluft

It is necessary for the people to keep governments accountable and to require that they give the information, resources, and assistance that empowers citizens to use their creativity to build water sustainability and locally. It is time for people to reclaim direct personal and collective responsibility in honoring water as the source of all life.

Rainwater Harvesting Locally

A variety of practices for rainwater harvesting empower humans at the household, neighborhood, and town level to provide water for their communities while being stewards of the broader watershed and ecosystem.

Brad Lancaster lays out what the guiding principles of rainwater harvesting ought to be:

1. Begin with long and thoughtful observation.

Be it your garden or neighborhood park, observe the slopes of the land and how the water flows on it when it rains.

2. Start at the top.

Begin working at the top, or highpoint, of your watershed and work your way down. Start where water flow begins.

3. Start small and simple.

Human-scale water harvesting earthworks reduce the need for maintenance and enable us to do it ourselves. Small-scale trials also allow us to see what works and what doesn’t, avoiding large-scale mistakes.

4. Spread and infiltrate the flow of water.

The objective is to spread out the flow of water so it can slow down and infiltrate into the soil. Multiple techniques are available for spreading water with the purpose of planting water just like we would think of planting crops.

A flooded road showing poor infiltration of water and pooling on the compacted dirt. Photo credit: Evelyn Simak

In landscapes that have channels for water flow, this “channelization” increases the velocity of water flow through and downstream of the channelized area. This reduced infiltration of water into the soil and increases erosion. This landscape is like a drain, where water, soil, and organic matter drain out of the system causing erosion and downstream flooding. Upstream areas are left dry while downstream areas require expensive stormwater management.

Lydia Neilsen demonstrating how to use a bunyip to measure the height of a newly-built berm-and-swale during the Santa Cruz Permaculture Design Certificate Course. The swale is the trench portion, and the berm is the elevated mound of dirt that is formed with the dirt from the trench. Berms and swales are always built on contour and allow water to slow and infiltrate as it moves down a slope.

Alternatively, in a net landscape, water, soil and organic matter are captured, slowed and spread. This improves soil fertility, water infiltration, vegetative production, and resistance to drought. It reduces erosion, flooding, and their related costs. Overall, the ecosystem stability improves. One way to achieve this is with berms and swales in sloped areas, as shown above.

5. Always plan for an overflow route, and manage that overflow water as a resource.

Overflow is not a problem or a waste, but a resource. In huge storms, extra runoff can be directed from one harvesting structure to the next until it reaches the bottom of the site. Overflow spillways should be stabilized with heavy tightly packed rock or well-rooted vegetation to hold up to large flows.

6. Maximize living and organic groundcover.

Bare dirt is prone to compaction and the surface tends to seal up. Then the water either runs off or pools, supporting mosquito breeding before evaporating. Covering the soil with organic groundcover increases infiltration.

This video of a rain simulator demonstrates the role that vegetative, living groundcover can play in reducing or eliminating soil erosion compared with bare soil. The video was produced by South Dakota State University Extension.

Plants’ roots with surface mulch and the associated soil life makes a living sponge that can more than double infiltration. Plants bring to fruition the harvested water in the form of fruits, vegetables, grains, lumber, fiber for clothes and medicinal herbs. They also stabilize spillways, control erosion, provide shade, and act as windbreaks. Native plants make the best groundcover as they are adapted to the local climate.

7. Maximize beneficial relationships and efficiency by “stacking functions.”

Design the water-harvesting structures in relationship to the overall landscape to perform multiple beneficial functions. The vegetation helps us harvest water while giving many things back. Contour berms can act as raised footpaths. Check dams stabilize path and road crossings over drainages. Rainwater cisterns can act as privacy walls, pillars supporting porches, property fences, retaining walls, shading structures, etc.

8. Continually reassess your system: the feedback loop.

No matter how good a plan or design is, maintenance and adaptation are required over time. Landscapes continually evolve and we need to continually work with them

Up Next: Surveying

Now that we’ve outlined these principles, we’ll explore in the next blog post how to survey a site to assess the water resources and observe the landscape before designing a rainwater harvesting system. Stay tuned for the next post, coming soon!

Learn More

Want to go deeper with all of this? Join us for our Permaculture Design Certificate Course! We spend an entire weekend focused on Regenerating Watersheds & Soils, and part of your design project includes assessing a landscape for rainwater harvesting. Learn more and register today at santacruzpermaculture.com/permaculture-design-course/

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