Rising from a tiny headwater in Bodham the river starts 2+1⁄2 miles before Selbrigg Pond where three small streams combine.

[1] The river has a catchment area of approximately 115 km2 and from its source falls 50 metres to the present tidal limit at Cley sluice The sub-surface geology is predominantly chalk and in parts of the lower valley the river runs over chalk beds.

The Glaven has two major tributaries: Stody Beck joins just above Hunworth Mill (Map Ref TG 066 356), and the Thornage Beck joins close to the unbridged ford on the Thornage to Hunworth road (Map Ref TG 062 363).

The long, thin lake at Bayfield Hall in many ways epitomises the beauty of the lower Glaven valley.

In the late 19th century an "extravaganza" tunnel was built into the valley side so that the Glaven could be partly diverted around the lake.

This tunnel stopped operating in 2010 when the Bayfield hall project set out to create a new 1.2-mile long river channel to save the wildlife including many species of fish, especially Trout.