 As an eminent engineer, Donkin was often consulted on civil engineering matters.He supported Thomas Telford's 1814 proposals for a massive suspension bridge at Runcorn, and in 1821 reported along with Henry Maudslay on an iron bridge erected by Ralph Dodd at Springfield, Chelmsford.Thomas Telford employed Donkin in his survey of rivers in the London area for the Water Supply report, completed shortly before Telford's death.