Environmental Earthworks

Project Type

Project Summary

Working in an environmentally sensitive area which requires careful earthworks to control water flow, provide water catchment, build silt traps, swales for habitat regeneration, control erosion and landslides, provide access and build specialist bridges over watercourses to meet the requirements of environmental laws.

Project Description

This is work on three separate properties on the north coast of NSW, Australia, all 3 properties are within Byron Shire and all 3 are environmentally sensitive as defined by local government. We introduced permaculture concepts to the clients who agreed to work within permaculture principles to meet the stringent requirements of local council as well as take advantage of many opportunities to be able to provide good water management and increase the environmental habitat, tree planning opportunities and food producing areas as food forests.

In these photos we are diverting water, which successfully control further landslips. The fall in the diversion drain was 1:100 which provided adequate runoff in heavy rainfall. As this was a diversion drain as opposed to a swale, the intention is to move water out of the landscape rather than have water percolate into the landscape. A diversion drain can be designed to drain into a catchment pond as a water harvesting technique.

This is a benched swale which means it is level in sections (on contour) before it falls into the next level. This allows some sections to absorb water for tree planting and still maximize flow of drainage to a defined endpoint.

 1:100 fall to accelerate drainage from the hillside and reduce land slippage on lower slopes with sections on contour to work as a tree planting swale.

Stabilizing the earthworks is essential, a mixture of fast germinating seed and longer-term seeds work best. Show is 15 days after earthworks. 

In the photos you will see a construction of three silt traps as small dams, in 2 of these silt traps we have constructed dam walls complete with keyways. In one of the silt traps we have not built a dam wall, simply dug into the existing watercourse as a collection pit. It is important that the silt traps are designed to be cleaned out with relatively small machines so the silt traps are designed to be fully accessible for a 3 tonne mini excavator.

Small silt traps work well and can be cleaned out with small machinery. The silt caught makes excellent seed raising mix.

Silt trap with swale that leads into a large dam.

Clearing the site needs to be carefully marked out and well planned for easy recovery of the site aesthetic.

Pond serves as both a silt trap for the larger dam below and as a higher water source in the catchment.

Environmental law requires that specialist bridges be constructed over watercourses to allow the migration of fish. In this case we constructed box culvert bridges rather than using round pipes. Any drainage needed to be designed to minimize erosion and be as silt free as possible before entering the watercourse.

Environmental Law requires specialist waterway crossings and silt management.

Building the box culvert bridge as per engineering specifications.

Approved to meet environmental standards.

Swales were built above roadways to minimize water management at the roadway and to create an opportunity for water to be absorbed into the landscape and provide an area for reforestation or growing of fruit trees.

We did note to the clients that there was an opportunity to use the road verge as an excellent area to plant fruit trees. The road verge is often where we collect increased amounts of topsoil that is collected on the edge when the road is first cut in.

The earthworks described here were done over a 2-year period and represent multiple projects with approximately 5000 cubic meters of earth moved.

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