the river welland, with its tributaries, form a river system with a catchment area of . within this area, of waterway are designated as "main river", and are therefore managed for flood control by the environment agency under the river welland catchment flood management plan (cfmp). of this total, the below spalding are tidal, and have sea walls to protect the adjacent land from flooding, while are fresh water, but run through low-lying land, and are therefore embanked. within the catchment area, are below sea level, and would be flooded without such defences.