Gradient Road V's Terraces
- David Spicer
- May 30
- 4 min read
Updated: Jun 5
Gradient Roads or Terraces: Why I Choose One or the other is context driven
Water and Access
In landscape design, choosing between a gradient road with a slight fall or a level terrace is critical for balancing water management and access. Both systems harvest water and provide pathways, but their outcomes vary based on the land’s needs. Drawing from years of experience Dave Spicer of Doc Spice Permaculture, aims to articulate the differences in this article, exploring why you might choose a gradient road or a terrace, highlighting their differences in water control, access, and ecological benefits of hydrating landscapes and increase localised water cycle restoration.
Gradient Roads: Channeling Water to Storage
Gradient roads, with a gentle 1 in 400 fall (0.25% grade), channel rainwater to storage systems like dams, ideal for water-scarce areas. Six years ago, I designed a gradient road for Tim, a holistic management grazer on 2,500 acres, where water was the limiting factor. The road, tilted inward to prevent water from spilling over the outer bank, directed runoff to a dam while keeping a drivable outer edge.
Gravel roads excel at water harvesting, with ~85% of rainfall running off due to low absorption. For a 450-meter-long, 3-meter-wide road during a 10mm (0.01-meter) rain event:
Volume = Length × Width × Rainfall Depth
Volume = 450 m × 3 m × 0.01 m = 13.5 cubic meters
13.5 cubic meters × 1,000 liters/cubic meter = 13,500 liters
With 85% runoff, about 11,475 liters reach the dam per event, enhancing water security for grazing.
When paired with Holistic Management for livestock grazing, gradient roads complement the increased soil sponge capacity from higher humus content. This enhanced soil health, driven by managed grazing, increases the rainfall needed to trigger runoff events, as the soil retains more water before saturation, optimizing water delivery to the dam.
Why Gradient Roads?
Efficient Water Delivery: Quickly directs water to dams, ideal for arid regions.
Dual Purpose: Provides access while harvesting water.
Supports Holistic Management: Complements soil-building practices by channeling excess water to storage.
Drawbacks: Installation is slow, requiring precision for the 0.25% slope.
Terraces: Hydrating Landscapes and Boosting Rainfall
Level terraces allow water to infiltrate until the soil reaches field capacity, after which surplus water flows to storage. Unlike gradient roads, terraces prioritize groundwater recharge and watershed restoration while offering flat, wide surfaces for easy access—perfect for homesteaders. Compared to swales, which I used early at Doc Spice Permaculture, terraces are easier to maintain and provide better access, avoiding the steep slopes of swales (see my article, “To Swale or Terrace or Both and Why”).
Hydrating landscapes through terraces yields significant ecological benefits, driven by increased vegetation:
Soil Health: Enhanced moisture supports microbial activity and nutrient cycling, improving fertility.
Vegetation Growth: Hydrated soils foster dense plant cover, reducing erosion and boosting biodiversity.
Increased Localized Rainfall: More vegetation produces cloud condensation nuclei (CCN)—like pollen and organic compounds—that act as cloud seeding agents, promoting rain formation. This creates microclimates that can increase localized rainfall in dry areas.
Carbon Sequestration: Thriving plants and soils store more carbon, supporting climate resilience.
These benefits make terraces my go-to for watershed restoration and homesteading, where access encourages land interaction for planting or livestock management.
Why Terraces?
Groundwater Recharge: Prioritizes soil hydration before runoff.
Superior Access: Flat surfaces support vehicles and foot traffic.
Ecological Impact: Enhances soil health, biodiversity, and rainfall via cloud seeding.
Low Maintenance: than swales or gradient roads.
Drawbacks: Terraces delay water delivery to dams until soil saturation, less ideal for rapid storage needs.
Spillways: Flexibility with Terraces, Not Gradient Roads
Level terraces allow spillways at specific points to direct overflow to other landscape elements, like dams, swales, or additional terraces, enabling precise water management. For example, a spillway can channel excess water to a dam only after hydrating a specific area. Gradient roads, however, direct all water along their length to a single destination, offering no option for strategic spillways, limiting flexibility in complex landscapes.
Choosing the Right Design
The choice depends on your priorities:
Gradient Road: Best for quickly directing water to a single storage point in water-scarce areas, like Tim’s operation, and supports Holistic Management by channeling excess water after soil sponge capacity is enhanced. Choose this for immediate dam replenishment without spillway flexibility.
Terrace: Ideal for hydrating soils, restoring watersheds, promoting localized rainfall via cloud seeding, and enabling spillways for flexible water distribution. Choose this for homesteading or ecological restoration.
Consider rainfall, soil type, topography, and maintenance. Gradient roads need precise construction, while terraces require planning for spillways and overflow drainage.
Conclusion
Gradient roads and terraces are powerful tools for water harvesting and access, each suited to specific needs. Gradient roads, as used in Tim’s 2,500-acre holistic grazing operation, efficiently deliver water to storage while supporting enhanced soil sponge capacity through Holistic Management. Terraces hydrate landscapes, increase localized rainfall through water cycle restoration, and allow spillways for versatile water distribution, all while providing excellent access for homesteaders. By aligning your choice with your land’s needs—rapid water capture or ecological restoration with flexible flow control—you can create a sustainable, functional landscape.
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