The Herford East branch line is part of a collection of London consumer routes called the Lea Valley lines that run along which river?
Hertford East branch line: The Hertford East branch line is a railway line in Hertfordshire in the United Kingdom, running between Hertford and Broxbourne . Hertford East branch line:  It branches off the West Anglia Main Line north of Broxbourne , and could be seen as part of the Lea Valley lines—a collection of commuter routes into London. Lea Valley lines: The Lea Valley lines are two commuter lines and two branches in North East London, so named because they run along the Lower Lea Valley of the River Lea.
River Lea