When all else fails, just go with the flow: unintended lessons from an experiment in the Goulburn River

In upland rivers, densities of detritus can be strongly related to amounts of “retentive” features (slack flows, wood, etc.) that trap and hold detritus on the riverbed. Experiments to augment channel retentiveness can increase detritus and dependent organisms and we attempted such an experiment in the Lower Goulburn River. Using established methods we increased retention at four sites by adding woody structure to treatment areas, but not control areas. Over 24 months, the experimental areas were sampled five times at baseflow (1000 ML / day).Unfortunately, our intervention was ineffective and treatment areas did not accumulate more detritus than control areas. However, our data show that temporal patterns in densities of detritus were strongly negatively associated with mean antecedent flows (60 day average), suggesting that rates of flow-driven export may override retention effects in this system.

Management interventions to increase retention, detritus and dependent organisms can be effective in upland streams but may not be viable in large rivers with large magnitude variations in flow.

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