What is a catchment?

Land catching water

From the hill known as Old Joe, at the northeast corner of the Australian Capital Territory, Sullivan’s Creek flows southwest to Lake Burley Griffin. At the water’s edge, between Acton and Black Mountain Peninsulas, it spills towards the original course of the Molonglo River.

Between Old Joe and the Lake, water falls and runs into Sullivan’s Creek from an area bordered by Black Mountain and Crace Hill to the West, Mount Ainslie and Mount Majura to the east. It drains from steep slopes, gentle lowlands and open plains, through sheep paddocks and gardens, rubbish dumps and ruins, parks and ovals, across roadways and paths, schoolyards and backyards, over lips, between cracks, around obstacles, into streams to the lowest point.

Various surfaces conduct its passage: soft, hard, corrugated, smooth, vegetated, bare, dry, wet. Surface and volume affect its pace and style: seeping or trickling or dripping or flowing or pouring.

How much water eventually runs into the creek depends on rainfall and the extent to which it evaporates or is absorbed by the terrain. What is in the water depends on what is in or on its path.

Water carrier — groundskin

An outline of Sullivan’s Creek catchment area makes the creek look rather like the spine of a person kneeling and slightly crouched over. From nape to coccyx, right to left. Vertebrae visible beneath the skin.

But while this image says something about shape, it doesn’t express purpose. Think of the spine as a seam joining two lengths of fabric. Head, Old Joe, and bottom, the Lake, are the short edges. Fold the long sides together. Not a very effective bag.

The Aboriginal people of the Central Lake Eyre Basin make water bags with the skin peeled whole from a kangaroo. Neck opening out to body cavity, widest at the hind legs, drawn together at the root of the tail1.

Cup your palms together as you might under a running tap. There is the lifeline and its tributaries, the land bulging and folding, hatched and crossed.

Pipeline authority

There are maps for every suburb showing a network of lines and nodes following and traversing the outline of blocks and sections. These are pipes and their portholes. Main lines and branches channeling water to and from bathrooms and kitchens and laundries and gardens. Showers and taps, plugholes, basins, sink, sumps, drains and gulley traps. Visible manifestations of an underground engineering miracle. The essential substrata of urban life.

One day someone in orange overalls and a hard hat may kock on your door, map in hand. Access to a main pipe is in your backyard, your driveway, under the chookhouse.

Pools of water linger in your street. From across a neighbour’s fence you hear an intermittent glug-glug. A truck arrives and disgorges men in orange overalls and hard hats. Maps. Shouting. The local pipe is cleared.

Thunderstorm. Pelting rain drives all loose surface elements down any smooth avenue that presents itself. Water carrying leaves and tanbark, soil, paper litter and plastic swirls past and over the drains designed to catch and send it down. Clumps of its burden are trapped in the corners of gutters, along fences, against walls. A garden becomes a pond, a street a river.

In the same thunderstorm the concrete channel that was once a muddy bottomed, frondy grass-edged creek, whips up a violent torrent. Nothing stops or slows its passage. Danger: stormwater.

Canberra wasn’t built in a day, but between 1924 and 1927, a huge building effort was managed by the Federal Capital Commission. The offical photographer was WJ Mildenhall. On record are rows of pipes, fields of pipes, stacks of pipes. Made at the Canberra brickworks with pipeclay tested for the necessary properties. Layed according to the map. Seventy years later it may be necessary to dig up your street, your backyard, a main thoroughfare, and replace baked clay with plastic. An early morning knock on the door becomes a deep gash in the ground. Around it a pile of sour-smelling sodden clay tangled with tree roots, grows daily. After the operation the scar remains visible for months.

Fifty years since Sullivan’s Creek was lined with concrete it may be necessary to question the authority of impervious surfaces in urban water management.

The sign of the platypus

When the first wave of public servants moved into Ainslie, when building began on the land designated for the ANU, when the suburbs of Turner and O’Connor were planned, Sullivan’s Creek was still part of the good sheep paddock that Canberra ruined. Original vegetation along ridges and valleys had been cleared for grazing. The land was marked by fences and rough tracks. The Creek could still be seen in the way Eileen Mort portrayed it in her 1927 etching, as a romantic country stream.

Rainfall determined the the amount of water in the creek. At times it overflowed creating seasonal wetlands. An early resident in low-lying O’Connor hung out the washing in her gumboots.

As the city grew and the suburbs spread north through the Catchment, vegetation was cleared, large swathes of land were bituminised and concreted, rows of houses were installed. The activities of suburban life added new chemicals and minerals to the ground. The volume of unabsorbed rain water, or run-off, increased threefold and its rate seven-fold. The capacity for water to transport pollutants increased seven-ten times. It came to be recognised, in Canberra as elsewhere in Australia, that urban stormwater was a major environmental concern2.

Recent thinking about managing rate and volume of run-off and pollutants involves a technology that mimics the chain of ponds by constructing urban wetlands. Instead of moving stormwater as quickly as possible, this approach retains it as a resource. Carefully designed wetlands intercept and breakdown harmful pollutants, trap sediment, reduce the flow of stormwater and provide habitat for diverse plants and animals3.

A community group called Sullivan’s Creek Catchment Group is orchestrating the development of wetlands at key sites along the main channel of Sullivan’s Creek and its branches. The first wetland on the O’Connor channel near David Street was made with the support of a chain of people: residents of the catchment, Australian National University, CIC Pendon (land developer), Community Housing Canberra, Seeds and Plants Australia, CRC for Freshwater Ecology, Planning and Land Management (ACT Government), Young Consulting Engineers, Canberra Sand and Gravel, Natural Heritage Trust, Canberra Investment Corporation …

The Group’s logo is a creature that once swam in the creek and burrowed in its banks – the platypus. It’s a sign of commitment to the health of the Creek.

Frog

brown-striped frog, spotted grass-frog, toadlet, eastern sign-bearing froglet, peron’s tree frog, bat, eastern brown snake, common blue tongue, marbled gecko, bearded dragon, shingle back lizard, jack lizard, skink, pink-tailed legless lizard, eastern grey kangaroo, red necked wallaby, swamp wallaby, wallaroo, echidna, ring-tail possum, blakely’s red gum, yellow box, apple box, red stringy-bark, scribbly gum, cassinia, early wattle, urn heath, everlasting daisy, australian bluebell, common fringe-lily, blue caladenia, musky caladenia, hooded caladenia, wallaby grass, kangaroo grass, guinea flower, mountain violet, kunzea, leptospermum, plough-share wattle, parrot pea, egg and bacon, hardenbergia, billy buttons, lomandra, early nancy, eastern rosella, speckled warbler, painted button-quail, white winged chough, glossy black cockatoo, little wattle bird, bronze-wing pigeon, superb parrot, grey fantail, currawong, tree martin, red-capped robin, regent honeyeater, red-browed firetail, stubble quail, jacky winter, white-throated needle-tail, brown treecreeper

Crests, ridges, gullies, flats, boggy, dry, rocky, prickly, shady, edible …

What is a catchment?