archaeological & built heritage assessment - The Heritage Council

However, the Lough Allen canal had not generated the expected traffic, and the shallow and neglected
state of the upper Shannon made it unsuitable for the deeper draft steamers, which did not go north of
Athlone (ibid.). It was still expensive to transport coal and in reality the canal was little used possibly due
to the cheap availability of ‘sea-coal’ at all the ports and to the fact that the imported coal was considered
to be of superior quality during the mid-nineteenth century.
A commission set up in 1831 implemented a survey on the condition of the Shannon and recommended
enlarging the lateral canals and locks and opening up the Boyle Water into Lough Key as well as improving
drainage along the course of the river Shannon, including widening Tarrant’s old cut and constructing a
weir at Ballantra to hold Lough Allen at a fixed level. Works commenced in the 1840s and at Roosky the
lateral canal was abandoned and a channel was dredged in the river with a lock, weir and new bridge
erected. The Jamestown Canal was enlarged and straightened with a new lock constructed nearer the
downstream end of the canal. Tarrant’s cut was widened to divert more of the Arigna waters directly into
Lough Allen. The Carnadoe Waters were opened up into the Carnadoe Waters and a new bridge was
erected at Carrick-on-Shannon. The Boyle Water was opened up into Lough Key with a new lock and the
bridges at Cootehall and Knockvicar were replaced. Many shallows were removed in the bed of the river
using four steam dredgers. The new bridges were fitted with opening spans to a design by Thomas Rhodes
but by the time the works reached the Jamestown Canal funds were running low and fixed bridges were
built from here upstream. The locks became smaller as the works moved upstream. The works carried
out by the Shannon commissioners failed to come to grips with the problems of flooding, and in the early
1860s sluices had to be fitted to the open weirs including Roosky and Jamestown which ensured better
control of the levels. By 1925, the Lough Allen Canal was rarely used and subsequently abandoned with
Lough Allen becoming a storage reservoir with sluices to control its flow into the river. The Shannon
navigation had almost exclusively become dependent on the Grand Canal trade and there was very little
traffic north of Athlone.
Bridges
River navigation works, the construction of canals, and drainage schemes had a considerable impact on
road bridges in Ireland in the period 1700-1850. The navigation works necessitated the construction of
many large new river bridges, particularly on the Shannon, and also the underpinning, alteration and repair
of many others – all major undertakings. Hundreds of public road and accommodation bridges were built
across approximately 400 miles of new canals (O’Keefe & Simington 1991). The arterial drainage works
resulted in the removal and replacement of hundreds of ancient bridges and the underpinning and
alteration of thousands of others (ibid.).
The first bridges were formed accidentally by fallen trees. Gradually, early settlers began to make for
themselves crude timber bridges across small rivers and streams. The archaeological evidence relating to
bridges is largely dependent on the early medieval literature of the time in the form of monastic annals.
They imply that the great rivers forming boundaries between the provinces were rarely bridged for fear of
invasion and cattle raids. Of those bridges that were constructed, O’Keefe & Simington (1991) have
identified six types of droichet [bridge]: a cesaigh droichet or wicker bridge; cliath droichet or hurdle-bridge
[stronger wicker]; clar droichet, or woodbridge [planks and beams]; a cloch droichet or stone bridge; a
droichet clochaeltra or bridge of stone and mortar, and a droichet long or bridge of boats.
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