Soil Permeability

Introduction

Permeability refers to the ability of water to penetrate soil. This is important because the water cycle, including the recharging of ground water and aquifers relies on this principle. Communities and farms around the world rely on underground water sources for drinking, bathing, watering crops, and other activities.

Places like New Orleans in Louisiana, which were originally built on wetlands, have spent the last few hundred years slowly covering the land with roads, buildings, and parking lots which have disrupted this natural system. 

Not only is there less water left for drinking or irrigation, but the land is now sinking, which damages building foundations, or can even cause explosions when gas mains or other infrastructure is damaged by land subsidence.

About This Page

This page covers various types of earthworks, plus living and inert tools we can use for increasing soil permeability. You can mix and match solutions, for example you may want to plant trees with mulch and compost to compound the ability of each to help improve soil permeability. Using plants and trees in conjunction with earthworks, or certain types of substrate can help improve infiltration and/or reduce erosion.

Animals

People often consider animals such as ant and insectivores such (including armadillos and moles) to be annoying pests, but in reality there are vital for healthy soil!

They not only help aerate soil, but their droppings and food caches (for those species who store extra food underground) can add nutrition to our soils too.

Bugs

Ants

Arthropods

"The burrowing by arthropods, particularly the subterranean network of tunnels and galleries that comprise termite and ant nests, improves soil porosity to provide adequate aeration and water-holding capacity below ground, facilitate root penetration, and prevent surface crusting and erosion of topsoil. Also, the movement of particles from lower horizons to the surface by ants and termites aids in mixing the organic and mineral fractions of the soil. The feces of arthropods are the basis for the formation of soil aggregates and humus, which physically stabilize the soil and increase its capacity to store nutrients."

Some species such as "The isopod, Helleria brevicornis Ebner, is known to excavate vertical burrows in soil up to 10 cm deep [23]." - Role of Arthropods in Maintaining Soil Fertility

Millipedes

Termites

Insectivores

Moles

Rodents

Rodents including mice and prairie dogs burrow which helps improve soil health.

Prairie Dogs

The Great Plains Restoration Council put together a list of soil benefits in Prairie Dogs and Soil Impacts, which also explains how humans are generally the cause of poor soil, particularly as we keep disturbing the soil, and pushing out native animals to make way for livestock.

Earth Works

This term refers to building or digging the ground into certain configurations for a variety of reasons. In this section we look at types of earthworks which help improve soil permeability, including diverting standing water from waterlogged locations and spreading it more evenly over the landscape for absorbtion.

Keylines

Berms & Swales

Half-Moons

Half-Moons Greening Mauritania

3:05 minute video about this traditional technique, and how it has helped farmers reduce run off, increase water infiltration, and boost their crop production.

Plants

Plants perform a variety of services for our water cycle including cleaning out pollution, reducing erosion and runoff, and respiring water back into the atmosphere. A plant's roots can be a key part of ground infiltration as their roots burrow through the ground, creating channels for water for move along. Similarly, these same roots can help bring water back up within reach of species who would otherwise struggle to survive through the drier months.

Grasses & Wildflowers

In places like Australia and the USA, native plants have been driven towards extinction as European settlers replaced common grassland species with European and African plant varieties to help feed their livestock. As a result the root structure in these grazing lands have suffered due to inapropriately short roots. When these non-native and invasive grasses are replaced with native grasses and flowers once more, the longer roots help the landscape handle long, dry months. The native plants also benefit from seasonal fires, resulting in greener grasslands after seasonal fires.

Check out our Wildflowers page to learn which species of flowers, grasses, and other species are appropriate for your area. Replacing non-native with native species can help reduce water use demand, improve soil permeability and health, while also encouraging the return of native pollinators and other wildlife.

12:35 minute video shows how native grasses can be planted in lines or curves to help slow down water enough to help it penetrate a hillside slope without disrupting the soil integrity.

The lady explains her choices of native tree species interplanted within the native grass, how the evergreens provide shade and protection to the rainforest species. She explains how the grasses help protect her saplings from freezing and baking hot weather. However she comes along periodically to weed away vines and grasses to prevent them from strangling the saplings, then uses the weeded materials as free mulch to further lock in moisture.

This example is in Australia so she also explains how the different species will support local natives including koalas.

Trees & Forests

Forest cover has been shown to improve ground permeability much like the smaller plants mentioned above. This paper talks about the ability of intermediate forest cover in maximizing aquifer recharge in seasonally dry tropics. Different species of trees may have different impacts in different climate regions, and in a variety of densities.

Deforestation is Driving Water Shortages

The speed of deforestation on the global scale is massively outpacing our ability to replant. Much more money is being spent by governments to promote deforestation than there is money being spent on tree planting. In addition to this problem, most tree-planting schemes (especially the larger projects) typically fail, resulting in ghost forests full of dead saplings. Even if they were more successful, it takes at least 2 years before a sapling starts to make much of an impact on CO2 or water retention, vs old growth trees which are much more valuable based on a variety of metrics. 

Click the Deforestation button to help "turn off the tap" of deforestation, as tree planting is the equivalent of mopping the floor while a mains pipe has exploded and continues to gush water.

Planting Trees

Planting trees is a great solution when done on a relatively small scale. Tree plantings are most successful when done in a place where they can be protected and cared for, such as farm land where a farmer understands their value, or in parks, along roadways, or in gardens where people appreciate their shade. Planting close to a source of water, and where there are roads for arborists to access the trees can significantly boost a tree planting project's success. Click the Trees button for some basic information about what makes or breaks a planting's success, as well as our directory for free or affordable trees. 

You can also click the Tree Planting & Care button to learn more about how to dig an appropriate hole that won't kill your sapling. We've also included information such as aftercare tips like appropriate trimming techniques. The page also looks as the how a tree's "drip line" affects watering, and helps determine appropriate planting locations for smaller, understory plants to survive or even thrive. 

Soil Amendments & Coverings

Soil ammendments are substances like sand, perilite, or compost which can be mixed into dirt to improve permeability. Some like much and compost can also help maintain moisture in the soil, while sand can help water filtrate through, instead of encouraging water to stay in unwanted places too long (which can rot plant roots).

Compost

Compost is a natural material made from waste products such as leaves, grass clippings, kitchen waste, and most biodegradable materials. When added to soil (preferably mixed in), it can improve permeability as well as the soil's ability to hold water. High clay content can prevent water from penetrating into the ground, while high sand content can cause soil to filter water faster without the ability to hold moisture for later use by plants. Compost is also highly nutritious, so it helps plants grow better, and plants with deep roots are better at both reaching water deeper in the soil, as well as helping water surface water (such as rain or snow melt) sequester into the soil.

Gravel

Gravel is a good solution for paths and parking areas. Gravel and river rock can also be a good way to reduce weeds in a swale or drainage system, while also reducing soil erosion.

Mulch

Mulch can be used to make paths, or places over garden areas to promote water retention in the soil. As it breaks down, mulch adds nutrients and improves the permeability of soils which may be compacted. Particularly heavy clay or loam soils.

For free mulch you may want to contact your local arborist or sign up with buy nothing groups or apps like Chip Drop.

Permeable Pavement

Life Expectancy:

Pro: "Permeable pavements add space for infiltration, especially in contexts such as alleyways or against the curbline, where nuisance flooding and other issues must be addressed without sacrificing space for mobility.

Many different types of pervious surface can be applied to different contexts, adding quality and performance to the urban environment." - NATCO

Con: "permeable pavements are often not appropriate for travel surfaces with high volumes, heavy vehicles, or where frequent starting and stopping place additional force on road surface.

Interlocking pavers may settle or buckle, reducing surface smoothness and creating accessibility issues.

Review adjacent surfaces and assess where soil is more likely to erode or be tracked onto the permeable pavement surface (such as from gravel driveways on private property). ..."  - NATCO

Solution: "More frequent street vacuuming of those areas may be required to remove sediment.

Permeable street surface requires regular maintenance to remain effective. Develop detailed plans and responsibilities for appropriate cleaning and maintenance of permeable  pavements installed in the right-of-way, which may include sweeping, washing, or vacuuming to remove grease, oil, and other sediment."  - NATCO

Resources: "Porous ashpalt, pervious concrete, permeable interlocking concrete pavers, and grid pavers provide infiltration of stormwater directly under the street surface, and can be applied on any portion of the street provided appropriate surface and sub-surface conditions." Snow ploughs and street cleaners are needed for maintenance.  - NATCO

Resources

Permeable Drains

Companies

Sand

Ground Water Maps

Understanding your local geological and hydrological conditions can help determine if a community should be focusing on increasing permeability, or if other water management methods would be more practical. Some aquifers are still in good condition, while others need significant assistance if they are going to support us and our descendants. 

International

Maps

North America

USA

Resources & Tools

Ground Work

Permeable Pavements