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Breaching levees can restore river habitats and reduce flood damage, but combining these objectives takes innovative planning, according to research by geologist Jeffrey Mount at the University of California, Davis. 

Mount is studying two intentional breaches in levees created by The Nature Conservancy on the lower Cosumnes River. Floodwater spilling out through the breaches spread sand over former agricultural fields, says Mount. Seeds and twigs trapped in this sand have grown into thickets of cottonwood and willow trees. These "accidental" forests attract abundant wildlife and, when flooded in winter, are home to juvenile Chinook salmon. 

When located properly, these breaches reduce the impacts of small and intermediate floods by storing water on the floodplain. This stored water helps lower the flood level and reduces the threat to nearby communities. 

To reduce damage from major floods, new approaches in flood management may be needed, says Mount. Levee failures at the height of a major flood cause a sudden drop in flood level that protects downstream areas, he says. If these failure points are pre-planned, major flooding can be confined to agricultural land, and farmers compensated for cleanup. 

Mount thinks that parts of the Sacramento and San Joaquin valleys would be appropriate for a combination of both schemes. A major obstacle to this scheme is the current trend toward conversion of floodplain farms into housing developments, says Mount. 

The findings were presented at the scientific meeting of the CALFED Bay-Delta Program in October. CALFED was established in 1994 to bring together state and federal agencies involved in management of the Bay-Delta system.