Finding lost streams and springs captured in combined sewers: a multiple lines of evidence approach

Some streams and springs have been historically and intentionally captured into combined sewer systems. This is a source of clean baseflow to combined sewers and wastewater treatment works that, unlike groundwater, infiltration-inflow through pipe cracks and defective joints, has not been widely considered by the UK water industry. This study presents the first formal methodology, using multiple lines of evidence, to locate lost streams and springs and identify where they have been captured into the combined sewers. In a UK case study, approximately half the total stream length and over 100 natural springs have been apparently lost and could be flowing into the combined sewers. Evidence has demonstrated the suitability of tests to indicate captured flow in sewers, and has confirmed several streams and springs flowing into combined sewers.