BY CAROL E. BECKER

An Australian town decides what to do with a spent quarry.

FROM THE JULY 2018 ISSUE OF LANDSCAPE ARCHITECTURE MAGAZINE.

Hornsby Quarry is like many quarries that roared with life in the 19th and 20th centuries and then suddenly fell silent because their resources were tapped out or became too expensive to extract. It is deserted today. The quarry, in Hornsby, New South Wales, Australia, has for a generation remained “the big hole in the ground”—300 meters roughly square, 100 meters to the bottom—and a major safety hazard that Hornsby Shire was forced to buy at the market rate of AU$25 million (about $16 million U.S.) after CSR Limited, a private company, ceased extracting hard rock basalt for road base material and gravel in 2001.

The Hornsby Shire Council acquired the quarry in 2002. Because it was built before reclamation laws and it was zoned as Local Public Recreation Land (technically called Open Space A) by the New South Wales Environmental Planning Act in 1994, CSR had no obligation to mitigate the site before ceasing operations, and the Shire was required by state legislation to buy it back. The huge cost of the land, set by the solicitor general, was ultimately reduced in court by AU$9 million, but the final price still cost each rate-holder (taxpayer) approximately $50 per year, for a total of 10 years, says Kurt Henkel, a landscape coordinator at Hornsby Shire.

The quarry will not remain dormant, however. Its stories—physical, historical, geographical—parallel the long development of Australia and are about to get a bold retelling. The vision for Hornsby Quarry is to move from accidental money pit to extraordinary new parkland, and it’s all about politics, geology, preservation, conservation, and, of course, landscape architecture at one of its most interesting callings.

A rendering produced by the Hornsby Shire Council shows how the strong topographic and vegetative features of the quarry and surrounding landscape could create an extraordinary park on the northern edge of Sydney. Image courtesy Hornsby Shire Council.

Practical considerations alone prevented the quarry from being filled after its closing. Its location and size were prohibitive. The quarry lies less than a kilometer from the city center, having been established around 1900, long before the town of Hornsby became a major suburban rail stop northwest of Sydney. It would require eight years of running trucks through the city center to provide the estimated four million cubic meters of fill that would be required, according to a study by Clouston Associates, a Sydney-based landscape and strategic planning firm. The council deemed it a “too-painful consequence” for the residents, Henkel recalls. “We already knew [at that point] the more we filled the hole, the more the distinctive landscape would be lost,” he told me.

A soil scientist, Simon Leake, says that what remains today owes to the unique characteristics of this quarry. Leake is known in Australia for creating the soils in Sydney’s new Barangaroo Park (see “Peter Walker’s Point,” LAM, November 2016). He has more recently evaluated the Hornsby site. The eastern face of the quarry has exposed the cross section of a basaltic diatreme, a geological feature said to be rare worldwide. In simple terms, Leake says, it’s a remnant of an ancient explosive tube that erupted with force through existing rock to create not a mountain, as we think of volcanic eruptions, but a large, deep valley with basaltic rock soils, rare and therefore commercially valuable in the Sydney area. The quarry’s operations dug deep—nearly to sea level in this case—to reach the hard rock basalt and mine it until it was spent. Today, the site itself is largely volcanic basalt with a sandstone overlay. Leake also mentions a rare finding of granite “that can only have landed here from a volcanic eruption.” To his surprise and research interest, he adds, deep pockets of healthy soil have returned in selected areas of the site in just 30 years.

The steep walls of the quarry make the bottom of the pit feel remote; that the city of Hornsby lies less than a kilometer away seems improbable. At the bottom, spring-fed water fills the lake. Stormwater from the upstream catchment bypasses the quarry hole before draining into Berowra Creek, a tributary of the Hawkesbury–Nepean River system. The old crusher plant still sits above the quarry to the southwest, silent and derelict for the time being. High above the quarry walls, the feeling of remoteness is enhanced by gum trees that are already 20 feet high. Until all the talk about what to do with the quarry started, many people did not even know the quarry was here.

Image courtesy Hornsby Shire Council.

Given the fact that the site remained vacant and untouched for a generation, natural bushland vegetation has regrown quickly. But the area surrounding the quarry is more than just a native parkland. It has, thanks to its volcanic soil, become a small and critically endangered ecological community called Blue Gum (Eucalyptus saligna) High Forest. Tucked in the embayment of the quarry itself is also the Higgins Family Cemetery, resting place of 23 pioneers who settled this valley two centuries ago. In all, the site of 59 hectares includes the quarry, the surrounding bushland, an open area known as Old Man’s Valley, and the adjacent Hornsby Park, which already contains bush walks and mountain bike trails.

What to do with it suddenly took on new life with the Clouston study in 2014. A Clouston principal, Crosbie Lorimer, believed that the rare geological heritage alone “almost requires us to express it rather than hide it.” Clouston is known for its work in restoring industrial heritage sites, of which the greater Sydney area has many. Its study points to the old crusher not as an eyesore, but as an artifact that should be restored, repurposed, and used to teach visitors about the history of the place. These considerations led to Clouston’s recommendation to retain “the quarriness of the place,” creating a park that might offer everything from heritage bush walks to extreme sports: zip lines, rope climbing, rock climbing, and non-snow tobogganing. Although there are critical safety challenges to be met to implement this recommendation, it would go a long way to increasing open green space in the region, currently at about half of the Shire Council’s own plan projections. It also falls in line with the community’s desire to see something result from its massive investment in the quarry land.

But how? For so long, the focus had been on the constraints of the site, and it seemed that new thinking was required to help turn Clouston’s recommendation into real possibility. Then landscape architecture students at the University of New South Wales were introduced to the project. They hiked to the bottom of the quarry in 2016. Their task, said Jessica Hodge, a landscape architect and the author of the Quarry Project brief, assigned as one of two projects for students in the Site Planning 2031 course, was outlined thus:

“Develop a structure plan for the Hornsby Park site, identify appropriate recreational and open space uses for the site, and determine the best location for each element. Develop a detail plan for one chosen part of the site, demonstrating a variety of site specific uses and consider the overall landscape setting for the park.”

From among the 50 students in the class, Henkel cites five renderings that shifted the focus to future possibilities. It was “an unshackling,” he says, because the students were “not always following the constraints.” Their renderings demonstrated wide-ranging approaches to the site and “showed [us] the fun that can come from the site when it is developed as a park.” Nearly two years after completing their assignments and graduating, these landscape designers talk enthusiastically about the future of Hornsby Quarry.

The filling operation as of February 2018. The imported material is deposited via conveyor belt, seen at top right. Image courtesy Hornsby Shire Council.

The first step is stabilization. The quarry won’t be filled, but fill is needed on a monumental scale to shape the new parkland and stabilize the void for parks development. “If we fill about a quarter [of the void], we remove almost half of the problems of stabilizing, and we still have a water body and a very dramatic site with space at the bottom for visitors,” Lorimer says. What developed is an agreement among the Shire Council, the state government, and the federal government to place fill from NorthConnex, a roads project that is digging a motorway tunnel in Sydney. At a rate of 35 truckloads dumping 800 cubic meters per hour, NorthConnex is currently providing one million cubic meters of the necessary fill in a project that will run throughout the winter, finishing in August of this year.

Before the operation began, there had to be permitting, noise abatement construction, including a new access road into the park, and a conveyor system to deposit fill into the quarry. Work could not begin until 2016.

As the filling by NorthConnex continues, landform studies are under way in consultation with geotechnical engineers, constructability specialists, and environmental impact analysts who study the proposed landform works. While the Shire may spend AU$4 million to AU$7 million more to complete stabilization, the exact plan will not be known until the end of the year, Henkel says. Hornsby Quarry Park is expected to be complete in five to seven years, by which time the area’s population, including the suburbs of Hornsby, Asquith, and Waitara, is projected to grow about 15 percent and require an additional 1,000 jobs. Hornsby Quarry Park will be the only local destination adventure park and will go a long way to closing the gap between actual and recommended green space in the region, connecting to adjacent Berowra Valley National Park and the Great North Walk 250 kilometers along the east coast from Sydney to Newcastle.

Carol E. Becker is a writer, teacher, and landscape designer in Chicago, specializing in sustainability in the built environment. Reach her at carol@sage-advice.net or on Twitter @ladysage14.