November 09, 2020

Swale Science: Unpacking the Math Behind Earthworks

50 minutes

This episode of "The Poor Proles Almanac" focuses on the importance of water management in creating sustainable and resilient agricultural systems. Host Andy emphasizes that effective water management can not only reduce the need for artificial irrigation but also improve soil health and enhance the overall ecological integrity of a property.

The Significance of Watersheds and Groundwater Systems

The episode starts by explaining the concept of watersheds and their role in channeling water into bodies of water like streams and ponds. The hosts emphasize that watersheds play a vital role in water purification and that understanding the local watershed is crucial for effective water management on any property. The episode then discusses the importance of groundwater systems, particularly aquifers, for long-term water availability. The hosts highlight the detrimental effects of unsustainable practices like over-pumping from the Ogallala Aquifer, drawing a connection to the broader theme of regeneration and resilience.

Soil Health and Water Retention Capacity

The episode emphasizes the critical role of healthy soil in water management. The hosts explain that soils rich in organic matter have a significantly higher water holding capacity than compacted, depleted soils. They note that even a small decrease in organic matter can lead to substantial losses in plant-available water. The episode advocates for practices that enhance soil health, such as reducing tillage, incorporating organic amendments, and using perennial crops and rotations, highlighting the interconnectedness of soil health and water management.

Challenging Conventional Irrigation Practices

The episode challenges the conventional approach to irrigation, which often relies on pumping water from streams, ponds, wells, or municipal sources. The hosts argue that these methods can have negative environmental impacts, particularly in water-scarce regions. They propose that by focusing on regenerative practices, farmers and homesteaders can reduce their reliance on artificial irrigation and create more sustainable water management systems.

The Importance of Perennial Systems

The episode argues for prioritizing perennial crops and grazing systems over annual gardens, especially in a post-collapse scenario. The hosts explain that perennial systems offer greater food security and resilience, as they are less vulnerable to seasonal fluctuations and require fewer inputs. They suggest that by establishing robust perennial systems, individuals can produce a larger proportion of their own food sustainably, reducing their dependence on external sources.

Introducing Swales and Berms for Water Management

The episode introduces the concept of swales and berms, which are earthworks designed to slow down and infiltrate rainwater into the soil. The hosts acknowledge that swales have become a popular permaculture technique but caution against their overuse, emphasizing the importance of understanding the site-specific conditions and potential downsides of implementing swales.

Debunking Permaculture Myths and Emphasizing Evidence-Based Practices

The hosts critique the tendency within the permaculture movement to rely on anecdotal evidence and "rule of thumb" approaches, advocating instead for a more rigorous, data-driven approach to water management. They express skepticism towards permaculture practitioners who promote swales as a universal solution without considering the specific needs and constraints of a particular site. The episode emphasizes the importance of understanding the science behind water movement and infiltration, urging listeners to engage in critical thinking and informed decision-making when designing water management systems.

Calculating Runoff and Swale Sizing

The episode provides a detailed explanation of the rational method, a mathematical formula used to estimate the peak runoff rate from a given area. The hosts break down the formula into its components, explaining the concept of runoff coefficient and how it varies depending on the surface type (e.g., grass, pavement). They demonstrate how to calculate the volume of water that needs to be absorbed by a swale based on the peak runoff rate and the area contributing to the swale. The hosts emphasize the importance of using accurate calculations to ensure that swales are appropriately sized and can effectively handle the anticipated water volume, preventing overflow and potential damage to the surrounding landscape.

Key Considerations for Swale Implementation

The episode outlines several key considerations for designing and implementing swales:

Observation and Site Analysis: The hosts stress the importance of observing the natural flow of water across the property over different seasons to understand the topography and identify areas prone to runoff or compaction.

Starting Small and Simple: The hosts encourage listeners to begin with small, manageable swale projects, gradually increasing complexity as they gain experience and confidence.

Working with Existing Trees: The episode provides guidance on how to integrate swales around existing trees, emphasizing the importance of avoiding damage to the root systems.

Addressing Overflow and Potential Risks: The hosts emphasize the need for overflow management, explaining that unplanned overflow can undermine the effectiveness of swales and potentially damage other parts of the property. They also advise listeners to consider the potential impacts of water saturation on nearby structures or features.

The episode concludes by highlighting the suitability of swales for specific site conditions, noting that they are generally better suited for smaller properties with unique features and less steep slopes than alternative water management techniques like keyline systems, which will be covered in the next episode.

For sources, transcripts, and to read more about this subject, visit: www.agroecologies.org

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By The Poor Prole’s Alamanac, Bleav

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