The report is sixty pages long. It contains forty-seven maps, twelve cross-section drawings, nine photographic plates, and a dedication that reads: “For the builders, whose names we do not know.”

Pella Strand, municipal surveyor, age twenty-nine, delivered her complete survey of the Lower Conduit to the Municipal Heritage Committee at half past ten on Friday morning. She arrived at the Municipal Chamber carrying seventeen notebooks in a canvas satchel and the report itself in a cardboard box. She had not, by her own admission, slept particularly well.

“I have been underground for two months,” she told the committee. “I would like to be above ground for a while.”

The Lower Conduit — the buried waterway beneath the Docklands and Bramblegate that Strand discovered during a routine subsurface survey in February — is, according to the report, a single interconnected hydraulic system of remarkable ambition and sophistication. It extends 947 metres from its stone-arched outfall beneath the old commercial wharf at Bramblegate Steps to its farthest traced point in the collapsed section beneath the former Chandler’s Brewery on Cooperage Lane.

The system comprises two principal branches. The eastern branch runs from the Bramblegate Steps outfall northeast toward the Docklands — 607 metres of brick-lined, arched conduit approximately two metres wide and one and a half metres tall, carrying flowing water. The western branch splits from the eastern at a junction 340 metres from the outfall and runs west-northwest for 340 metres beneath the old brewery district, terminating at the purpose-built cistern chamber discovered on 17 March beneath the former Ashwater Brewery site.

The cistern — roughly circular, four metres in diameter, with a two-and-a-half-metre vaulted ceiling — is a distribution chamber. Three brick channels converge at a central stone basin. Clear water flows through it to this day, fed by a spring source that has been active for at least 244 years.

“The system was engineered to supply freshwater to three breweries on Cooperage Lane,” Strand told the committee. “It was not an accident. It was not a drain. It was infrastructure.”

The report’s most significant finding concerns dating. The majority of the conduit — the eastern branch and the cistern — is dated by mason’s marks and brick analysis to approximately 1782, predating the city’s formal drainage system by nearly fifty years. But a section of the western branch, approximately forty metres west of the junction, is older. A carved mason’s mark — a fish within a circle, approximately six inches across, cut into a limestone keystone — belongs to the Ashwater Guild of Masons, active from the 1740s to the 1810s. The section uses rougher stone, a lower profile, and cruder mortar than the 1782 work.

“The oldest section was built in the 1760s,” Strand said. “Twenty years before the main system. Someone was channelling water under this city before anyone thought to write it down.”

The report recommends heritage listing for the entire conduit system. It also recommends structural monitoring of the cistern chamber ceiling, controlled access for future researchers, and preservation of the Bramblegate Steps outfall as part of any future development of the wharf.

Councillor Ida Pryce, who attended the presentation, described the report as “thorough, scholarly, and long overdue — not on Ms Strand’s part, but on the city’s.”

Strand is scheduled to lecture at the Bobington Polytechnic spring series on 17 April.

She was asked what she plans to do next.

“Dry out,” she said.