Environmental Management


Walsh Ditch Stream Reconnection Fatal Flaw Analysis, Seattle Public Utilities, Seattle, WA

Walsh Creek formerly joined Rock Creek and the Cedar River in the Seattle water supply watershed above the water supply intake. Due to potential pollutants in the creek, Walsh Creek was diverted in the 1920s via Walsh Ditch to a point further downstream, away from the water supply intake. In recent years, maintenance of the artificial ditch became expensive, so Seattle Public Utilities contracted Cardno TEC to evaluate flows and water quality pollutants to help identify potential water quality risks in reconnecting the creek to its natural confluence with the Cedar River.

Cardno TEC conducted flow monitoring and storm event and base flow water quality monitoring to support development of a water quality and one-dimensional mixing model to evaluate potential contaminant levels downstream in the Cedar River. The report prepared by Cardno TEC showed low probabilities of concentrations in the river and supported the City of Seattle in their capital planning for reconfiguration of the watershed.

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