Two silver threads run down the Derbyshire Derwent Valley between Matlock and Derby, the River Derwent and the Cromford Canal.

The valley bristles with monuments of industrial history, and the stretch of canal south from its terminus in Cromford is particularly rich in structures that typify and explain the archaeology of Britain’s inland waterways.

One of the most impressive – though difficult to see and photograph except in winter – is the Wigwell Aqueduct, designed by William Jessop to cross the River Derwent on a wide arch that carries the date 1793.

In its progress up the Amber and Derwent valleys the canal crossed both rivers by masonry-arch aqueducts – low arches in a long embankment over the Amber at Bull Bridge, now demolished, and a much higher, elegant single span across the Derwent at Lea Wood.  Both of these structures failed during construction and each had to be partly rebuilt at Jessop’s voluntary expense:  his famous comment on the injudicious economy of using Crich lime in the masonry of the Leawood aqueduct was,–

…Painful as it is to me to lose the good opinion of my Friends I would rather receive their censure for the faults of my head than of my heart.

The Wigwell Aqueduct (sometimes called the Leawood Aqueduct) has since stood the test of time, and it’s an outstanding example of the masonry-arch construction that James Brindley had pioneered at the Barton Aqueduct (1761) taking his Bridgewater Canal across the River Irwell west of Manchester.

A short walk further south along the canal stands an example of the successor to the masonry arch – the iron-trough aqueduct that Thomas Telford developed to span the wide Dee Valley at Pontcysyllte, east of Llangollen in North Wales. 

Telford showed that it was possible to carry a waterway in an iron trough at far greater height than was possible with masonry.  On the Cromford Canal, the iron-trough technique proved useful in other ways.

Twice in a decade, railway engineers needed to burrow a way under the canal for double-track railways.  In the late 1830s the North Midland Railway at Bull Bridge pierced the canal embankment to take its main line north towards Rotherham, and within ten years the Manchester, Buxton, Matlock & Midland Junction Railway needed to tunnel through Lea Wood, where the canal main line and a private branch to Lea Mills had hugged the hillside.

In each case, iron troughs in segments were fabricated at Butterley Works near Ripley and floated down the canal.  Dropping them into place and making the join watertight was accomplished in a matter of hours over Saturday night, when canal traffic could be paused, and then the embankment below was excavated and railway track laid.

The iron-trough rail arch and the original gothic road-arch at Bull Bridge were demolished in 1968.  Of the two aqueducts at Lea Wood, the one over the main line survives, and stopping trains to Matlock pass by.  The corresponding aqueduct on the Leawood branch was demolished sometime soon after the Second World War and has been replaced by a footbridge. 

Anyone seeking to understand the difference between the two types of aqueduct found on British canals need only park at the High Peak Junction car park and walk down the canal.

A short distance beyond the Leawood Aqueduct is a bijou example of the other major civil-engineering achievement of the Canal Age, the 42-yard Gregory Tunnel.

The towpath continues south as far as Ambergate, where the line of the canal was lost to a natural gas processing plant in the 1960s.

The hourly Derby-Matlock train service provides opportunities to explore the canal from Cromford, (rather than High Peak Junction), returning from Whatstandwell or Ambergate stations.