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Win-Win Situation. Retrofitting Farm Dams to Increase Freeboard and Increase Wildlife Habitat and Productive Edge

The first thing I look for in a dam retrofit other than the spillway, is the freeboard. The freeboard is the height of the dam wall above the spillway. The freeboards presence is critical to the safety of the dam. 

After looking at the spillway and the freeboard, I would look at the batters of the dam wall bot. inside and outside. 

What degree slope are they? 

Can you build the dam wall any higher? 

As you go up the dam wall, you’ve got to go out to keep the batter grade reasonable. That’s how we can get an idea of how high we can raise the wall.

Once we work out our desired new height of the top of the dam wall, we then come down to our spillway height which gives the dam wall its freeboard and new water level. Transferring this height around the dam’s edge gives you a height of where the new water level will be.

From this process we get an idea of how much material in cubic metres we need to excavate to repair the dam wall to give it enough freeboard. I would call having ample freeboard the insurance policy. This builds natural capital by increasing habitat and a productive edge.

My general approach to dam retrofitting is to cut a bench in one side of dam edge, ideally closest to the dam wall as possible or sometimes on both sides. Its all about logistics of time and energy to move the material into position. This decision also depends on the topography/slope above the high watermark of the dam edge.

A bench cut into side of dam for material to repair the dam wall, this bench is 300mm below the water level when the dam is full.

 

This high water mark gives us a measurement to work from for our bench excavation, so we can either cut the bench so it’s under the water, above the water or both. 

This opens up the opportunity for putting in a productive crop around the waters edge or creating a human sanctuary: a place to sit comfortably and observe or just chill by the water’s edge.

We can also utilise fallen trees, stumps or large rocks to position around or in the dam for extra habitat creation.

 

Habitat creation for farm dams and aesthetic beauty

 

 

There is also the classic edge effect which you can install such as chinampas, which you can see in the video below from Green Cauldron Farm video link https://www.facebook.com/greencauldronfarm/videos/283680772134211/

 

There are so many opportunities for retrofitting existing dams for many reasons. In Australia, Landcare gives grants to fence off farm dams and install water troughs for livestock. This results in improved wildlife habitat while the livestock get better water quality. A win win situation. 

 

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David Spicer

David Spicer’s approach to design and education is based upon a proven emphasis on practicality, having over 18 years experience in Permaculture education working and teaching with Bill Mollison at the Permaculture Institute (Tasmania) and Geoff Lawton, the managing director of the Permaculture Research Institute of Australia and Zaytuna Farm. He is renowned for his ability to explain concepts and ideas simply, conveying the basics. David previously worked as farm manager of the renowned Tagari Farm and Zaytuna Farm in northern New South Wales. He has taught and worked extensively within Australia and internationally on various projects, covering six Australian states, Morocco, Jordan, New Caledonia and Palestine covering a broad array of different climate zones. David is a valued member of the permacultureconsultants.com team headed up by Geoff Lawton. He has the distinction of being Registered Teacher #5 with the Permaculture Research Institute of Australia. David currently serves as Lead Consultant and Educator for permacultureworks.org.

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