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Flooding Part of Natural Central Valley Riparian Ecology

Flooding at the San Joaquin River National Wildlife Refuge, 31 March 2011.

Springtime rainstorms and heavy snowfall in the Sierra Nevada have required large dam releases throughout the Central Valley. As temperatures continue to rise, snowmelt feeds our valley reservoirs, causing dam operators to continue to release high flows to make room for additional runoff coming from the upper watershed. Springtime flooding is a natural part of the riparian ecology of the San Joaquin watershed, and our native forests are rejuvenated by this type of disturbance.

The photograph above shows the extent of flooding at the San Joaquin River National Wildlife Refuge, 31 March 2011.

In the background, the restored fields of the Arambel, Lara and Hagemann tracts of the Refuge display cottonwood and willow canopies poking above the floodwaters. Prior to restoration, these flood prone fields were farmed. Floods like this one, which occur approximately every seven years in this region, would create significant economic losses for these farmers in lost crops and clean-up costs.

In the foreground, a constructed elevated refuge for terrestrial species is visible as a small rectangular “island” in the river. Through a generous grant from the Central Valley Project Improvement Act Habitat Restoration Program / Central Valley Project Conservation Program (U.S. Bureau of Reclamation and U.S. Fish and Wildlife Service) River Partners was able to plant the levee surrounding the Lara tract in November 2010 to provide cover for riparian brush rabbits and other terrestrial species threatened by this flooding. While this 1.8-mile linear habitat restoration project is not mature enough to provide cover today, it will provide invaluable high elevation refuge for threatened species in coming years.

Three riparian brush rabbits are seen on a constructed "bunny mound" at the Refuge.

Riparian brush rabbits, whose numbers have been increasing significantly in recent years at the Refuge, began retreating to high ground as the river started swelling on 27 March 2011. In the above photo, three riparian brush rabbits are seen on a constructed “bunny mound” at the Refuge. USFWS, USBR, River Partners and the Endangered Species Recovery Program at CSU Stanislaus have been working together since 2002 to restore this population of flood-threatened riparian-obligate rabbits. Floods like this one decrease population numbers, however, strategic adaptive management has lead to the creation of vegetated high ground refugia and vegetated levees at the Refuge which should help to mute this decline and allow rabbits to repopulate the area once the floodwaters recede.

The above article originally appeared in the March 2011 issue of the River Partners Journal.