Balfour predicted the deal would be worth up to £250m for the firm. Individual projects are expected to be awarded from the third quarter of this year with each expected to be worth up to £10m.
The £300m programme presents the largest single flood risk asset management programme ever awarded in the country.
It is designed to manage and deliver capital investment works to the Thames tidal flood defences along the 170km length of the Thames Estuary, protecting 1.25 million people from flooding risk across Kent, Essex and London and £200 billion worth of property.
The programme will involve creating tidal walls and embankments, refurbishing major flood barriers new pumping stations.
Packages of major or complex maintenance works will include repairing fixed flood defence walls or subsidence of earth embankments.
CH2M Hill will be working alongside their delivery partner, Balfour Beatty and specialist suppliers including Critigen, Hunton Engineering Ltd, KGAL and Qualter Hall.