Gordon Williams 's Profile
Gordon Williams
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Joined:
02/02/2011
Last Updated:
20/02/2011
Location:
NSW, Australia
Climate Zone:
Warm Temperate
Gender:
Male





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Ridge Dam Construction at Zaytuna

Posted by Gordon Williams over 8 years ago

The most recent PRI earthworks course saw the construction of a new ridge dam and swales at Zaytuna Farm.

On the 31st of January the Permaculture Earthworks course at Zaytuna farm began with good weather and a group of enthusiastic students ready to see the process of laying the groundwork for functional rainwater harvesting features in landscapes. During the week a variety of works were conducted across the property, including a new dam and swale, swale pipe crossings, building site levelling and, to make everyone's life a little bit easier, the excavator divided some clumping bamboo.

 

The first project for the 25 ton excavator was to construct a ridge point dam connected to the end of an existing swale that would increase the catchment. If the dam were to be built independent of the swale it would not naturally fill. The primary purpose of this dam is to increase the volume of water stored on the property at a height where it can be gravity fed to areas below for use.

 

removing topsoil

 

The first step was to remove the topsoil from the dam site and set it aside so that it could be laid out over the dam wall once it was finished. This gives the best conditions for a cover crop to be sown to protect the dam wall from erosion and get ahead of any weeds that are in the soil.

 

topsoil stockpiled outside dam area

 

Once the site was cleared work began on digging the keyway which serves as a means to lock the dam wall into the subsoil. The keyway consists of a trench dug into the undisturbed subsoil along the line of the wall and is filled, ideally with the best clay from the dam excavation. This material is then compacted into the trench to make it impervious, in this case the track of the excavator was used.

 

The excavated keyway

 

Compacting material into the keyway

 

Once the keyway has been compacted the process of building the wall begins. As the material is excavated it is spread out in layers and then compacted down onto the one below in a repeating process until the wall reaches the required height.

 

Track rolling the wall

 

Getting out every last bit

 

Because the dam was constructed at the end of an existing swale the high water mark of the swale (300mm of water in the swale) determines the height of the spillway, which is located at the other end of the dam wall. The wall is then raised further than this to create a freeboard to stop water flowing over the wall.

In large rain events water can be coming into a dam faster than it can exit and as a result of this the water can back up at the spillway and rise to a few feet in depth. As this ridge dam has a small catchment the wall was built up to obtain a freeboard of 700mm. For dams with larger catchments a freeboard of upwards of a meter would be ideal.

By having the swale attached to the dam allows not only for increased catchment but when the dam fills the swale will back flood and rehydrate the land below.

 

Once the wall is completed the stockpiled topsoil is laid out to cover the wall and the cover crop sown.

 

Dressing the wall with topsoil

 

The finished dam half full with the cover crop of cow pea doing well.

The finished dam with cover crop

 

The dam with the swale entering to the right of the tree.

Dam and swale opening

 

The spillway that will only overflow when the swale is full and there is still water coming in.

The spillway

 

The dam has been full continually since nine weeks after completion

full to the swale

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Comments (5)

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jordan lowery
jordan lowery : what a beautiful spot for a dam/pond. also done very well.
Posted over 8 years ago

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Darren J.  Doherty
Darren J. Doherty : No lockpipe? For such a great position this would have been a fantastic addition...Of all the dam types Ridge, Hillside or Contour Dams the installation of a lockpipe serves such an important function lest the dam is so much less utile. Nice job though...Also how many days did it take and what was the cost? Cheers, Darren
Posted over 8 years ago

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Gordon Williams
Gordon Williams : I wondered the same thing about the lockpipe but Geoff didn't feel the need as there are three more valley dams at the same level all with pipes. Would have been a good opportunity to demonstrate the installation of a pipe to students. The excavation cost roughly $1800 and took about a day and a half to build with the machine operator stopping for a few chats with students about the process along the way. It has about a 600,000L capacity and makes a pretty neat natural swimming pool with a nice view. Gordon
Posted over 8 years ago

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Darren J.  Doherty
Darren J. Doherty : G'day,

Thanks for this Gordon. Fair enough then...Nice job for that amount of cash....All the best, Darren
Posted over 8 years ago

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My Badges
Consultant Pdc teacher
My Permaculture Qualifications
Other course verified
Permaculture Earthworks
Type: Earthworks
Teacher: Geoff Lawton
Location: The Channon, NSW
Date: Jan 2011
Other course verified
Keyline Design
Type: Earthworks
Teacher: Darren J. Doherty
Location: Richmond, NSW
Date: Jan 2010
Other course verified
PDC Teacher Training Course
Type: Teacher Training
Teacher: Rowe Morrow
Location: The Channon, NSW
Date: Feb 2011
Other course verified
Compost and Soil Biology
Type: Soil Biology/Compost
Teacher: Paul Taylor
Location: The Channon, NSW
Date: Mar 2011
Other course verified
Permaculture Project Aid Worker course
Type: Aid Worker
Verifying teacher: Geoff Lawton
Other Teachers: Nadia Lawton
Location: The Channon, NSW
Date: Mar 2011
Other course verified
10 week internship
Type: Internship
Verifying teacher: Geoff Lawton
Other Teachers: Nadia Abu Yahia Lawton
Location: The Channon, NSW
Date: Jan 2011
Verified
PDC Course
Type: Permaculture Design Certificate (PDC) course
Verifying teacher: Darren J. Doherty
Other Teachers: Penny Pyett, John Champagne, Peter Brecknock
Location: Ryde, NSW
Date: Jan 2009
Other course verified
Holistic Management
Type: Other
Teacher: George Gundry
Location: Tarago, NSW
Date: Aug 2011
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Climate Zones
Gordon Williams has permaculture experience in:
Cool Temperate
Warm Temperate
Mediterranean

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