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, and commenced the construction of roads in the north of Devon. In August 1824 he was employed by the Earl of Morley in making a bridge across the Catwater, an estuary of the Plym within the harbour of Plymouth at Lara. To guard against the undermining effects of the current, he formed an artificial bottom. The bridge, which cost 27,126l., was opened on 14 July 1827. With the exception of Southwark Bridge over the Thames, it was the largest iron structure then existing, and Rendel received a Telford medal from the Institution of Civil Engineers. He soon entered into partnership at Plymouth with Nathaniel Beardmore, and his practice rapidly grew. In 1826 he erected Bowcombe Bridge, near Kingsbridge, Devonshire, when hydraulic power was first applied to the machinery for making swing bridges. In 1831 he introduced a new system of crossing rivers by means of chain ferries worked by steam, and in 1832 he constructed a floating bridge on this principle, crossing the Dart at Dartmouth. Between 1832 and 1834 similar floating bridges were erected at Torpoint and Saltash across the Tamar, which greatly facilitated the intercourse between Devonshire and Cornwall. For these achievements a second Telford medal was awarded to Rendel.

During this period Rendel was also engaged in reporting on harbours and rivers in the south-west of England, and thus acquired that mastery of hydraulic engineering on which his fame chiefly rests. In 1829 he designed the harbour which was afterwards executed at Par in Cornwall; in 1835 he carried out works on the Bude harbour, dock, and canal, and in 1836 he designed Brixham harbour and the breakwater at Torquay. In 1836–7 he designed, as a terminus to the Great Western railway, the Millbay Docks, Plymouth, afterwards executed by Isambard Kingdom Brunel [q. v.] In 1843–4 he constructed canals in Devonshire, and was engaged on the Colchester and Arundel navigation; and in 1844 he designed harbour improvements for Newhaven and Littlehampton in Sussex. At the same time he was largely employed on marine works by the admiralty and other government departments, as well as by public companies. The exchequer loan commissioners engaged him in 1835–7 in the repair of the Montrose suspension bridge after its fall. There he introduced the principle of trussing the framing of the roadway. This system of preventing the undulation, by which so many structures of the kind have been destroyed, is now acknowledged to be essential to their safety.

About 1838 Rendel dissolved partnership with Beardmore at Plymouth, and settled in London, but still was chiefly employed on work for his native county. In 1841 he constructed the Millbay pier, Plymouth, a work of considerable difficulty owing to the depth of water in which it was built. Here he first introduced the method of construction since employed in Holyhead and Portland harbours. In 1839 he was engaged in preparing schemes for a railway between Exeter and Plymouth, running over Dartmoor. At the time sufficient funds could not be raised, but an alternative coast line was afterwards carried out by I. K. Brunel. In 1843 he made plans for docks at Birkenhead, which he defended before parliamentary committees against hostile local influence. The contest was long protracted, and the incessant labour served to shorten Rendel's life; his published evidence forms a valuable record of engineering practice of the period. In 1844–53 he constructed docks at Grimsby; in 1848–53 extensions of the docks at Leith; in 1850–3 docks at Garston on the Mersey, with extensions of the East and West India and the London docks. As constructor of the Grimsby docks he was one of the first to apply W. G. Armstrong's system of hydraulic machinery for working the lock gates, sluices, cranes, &c. For this work he received a grand medal of honour at the Paris exhibition of 1855. For the admiralty he planned in 1845, and afterwards constructed, the packet and refuge harbour at Holyhead, and in 1847 he constructed the harbour of refuge at Portland. In the making of these great harbours he contrived, by means of elevated timber staging, to let down masses of stone vertically from railway trucks, and, by building up the masonry with unexampled rapidity to a point above the sea-level, contrived to reduce to comparative insignificance the force of the sea during building operations. As many as twenty-four thousand tons of stone were deposited in one week. In 1850 he commenced making a new harbour at St. Peter Port, Guernsey.

Rendel was much occupied in the improvement of rivers. In 1852, in conjunction with Sir W. Cubitt and Richard John Griffith, C.E. (afterwards Sir R. J. Griffith, bart.), he examined and reported to the treasury upon the arterial drainage works in Ireland, and in 1855 he completed the suspension bridge across the Ness at Inverness for the commissioners of highland roads and bridges. His aid was also sought by foreign countries. In 1852–3 he designed docks for Genoa; in 1853–5 he reported on the harbour of Rio de Janeiro; in 1854 he reported to