Southern California’s modified channels tend to be in poor biological condition as measured by stream bioassessment scoring tools – especially compared to streams in more natural condition.

Previous SMC research has illuminated the management challenges associated with improving the biological integrity of modified channels, particularly fully hardened channels.

• In a 2015 SMC analysis, researchers found that Southern California modified channels achieve lower-than-expected bioassessment scores even in the absence of environmental stressors that bring down scores for other types of streams. These stressors include specific conductivity, total nitrogen, and percent sands and fines on the streambed. The study concluded that channel hardening along the banks and bottom is strongly associated with poor biological condition, and that even if water quality improved in these modified channels, it may be insufficient to boost bioassessment scores. At the same time, the study also found that modified channels with less channel hardening may have more potential to see their ecological condition improved through management of water quality and physical habitat. The study’s findings are based on an analysis of benthic macroinvertebrate stream scoring data calculated using the California Stream Condition Index.
• A follow-up 2017 SMC study completed a similar analysis using stream algae scoring data calculated via the Algal Stream Condition Index, and reached similar conclusions.

As a result, managers need insights about specific actions they could take – other than removing channel hardening – that are most likely to improve the biological health of the greatest number of modified channels across Southern California. An ongoing SMC study is working to get these answers.