Re-Engineering Urban Streams: The Effects Of Daylighting On Stream Ecology

The culverting of streams is widespread in cities and has been described as the most severe form of stream modification, because most interactions between the stream and the surrounding environment are lost. Daylighting, which involves recreating an open stream from a buried channel, has been promoted by some agencies (e.g. US EPA, CIWEM). Whilst daylighting can theoretically restore stream systems and natural processes, a review of projects across the world found that there were no empirical assessments of the effectiveness of daylighting projects.

The daylighting of two stream reaches in Auckland in 2013 provided an opportunity to address this knowledge gap and assess the effects of daylighting on stream ecology. Stream macroinvertebrates were sampled monthly pre- and post-daylighting and showed significant changes in community structure associated with improved habitat and increased food resources following daylighting. Whilst there were changes in the species living in the streams after daylighting, little change was observed in commonly used measures of stream health (i.e. species richness, MCI) post-daylighting. The response of the invertebrate community was different in the two reaches, with the reach that had more intact headwaters showing a greater change in ecology (71%) compared with the reach with extensively piped headwaters (58%).