Tip 4 – how to keep stormwater at your place with a sunken pond

A sunken pond allows you to keep rain water whilst the surface soil is sodden from the rain and unable to absorb your surplus rainwater.

When your rain tank or garden overflows into a sunken pond the water will be absorbed down there where the soil still has absorption capacity.


Dig a hole, squarish in shape, at least half a metre deep and half a metre square.  Line it with sturdy blocks, preferably sandstone or some other soft and partly porous material that’s easy to work with.  Stack them so they’re stable but only use bits of stabilizing mortar or cement in a few places so they’ll stay stacked.  Put sand or porous material behind the walls about 150 deep.  If you’ld like a permanent pond at the base also lay down some pool liner leaving a permanent water storage area about 150 deep for frogs and fish and water lilies and plants.

Another option is to turn your lawn or garden into a temporary ‘tank’.  Build a retaining wall or garden ‘edge’ – a 100 mm board will do the trick – around the sides to hold the water that falls there so it can be absorbed into the soil after the peak rain has ended.

With my sunken pond, rain tank and porous garden no stormwater has left my house in inner Sydney in 17 years except for about 5,000 litres in total on two heavy rainfall events.

That’s over 1.7 million litres of stormwater I’ve kept in my tiny backyard which measures 5 m  x  5 m.

Drawings, photos, details in Sustainable House p 184, 187, 191



Getting water down to where the plant and trees roots are helps grow your garden to its natural capacity, sustains the life that’s in the soil and provides a habitat that attracts birds, butterflies.  If you grow water chestnuts or watercress there you’ll also have something else to eat from your garden.  And it stops your place adding to the pollution of rivers and oceans.

Oh; and it can be a home to elegant, wispy, water plants . . . lovely to behold with a cuppa at the beginning or end of the day.  And it’s fun to see the water falling into it from your tank and know you’re not wasting a drop; with a bit of thought you can make that waterfall a passing thing of beauty.


If you do it yourself the pool liner will cost about $50 and the rocks and wall material can be free from building sites or you may have enough lying around your garden.

Enjoy your rain,


One Response to “Tip 4 – how to keep stormwater at your place with a sunken pond”
  1. Bridget says:

    We dug a hole in our front garden (Lane Cove) before the heat last Summer to catch all the stormwater that was running off the side of the house and the edge of the property. It now has volunteer tomatoes and pumpkin growing in it, and I’ve planted Taro. The front garden has never looked so good, and has needed very little or no watering over summer.

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  • Michael Mobbs

    Michael is a former Environmental Lawyer who is uniquely placed to consult in four main areas:

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