Riparian Restoration at the San Joaquin River National Wildlife Refuge
Past Successes and the Future
By Chris Stevenson, Restoration Biologist, San Joaquin Valley
River Partners’ History on the SJRNWR
In 1999, San Joaquin River National Wildlife Refuge purchased 3,166 acres of agricultural land (known as the West Unit) adjacent to the San Joaquin River. The major reason for the sale was that repeated levee failures, most recently in 1983 and 1997, made future farming unprofitable. At the time of purchase, the US Army Corps of Engineers (USACE) agreed to develop a non structural flood management project that called for abandoning or breaching the USACE flood control levees damaged in the 1997 flood. In 2001, a series of studies were contracted to determine the potential benefits for designed levee breaches on the San Joaquin River National Wildlife Refuge to lessen the negative effects of flooding downstream. The designed levee breaches would reconnect the river with its floodplain and provide spawning habitat for the Sacramento splittail (Pogonichthys macrolepidotus) and juvenile foraging habitat for salmon and steelhead.
River Partners began restoration efforts on 777 acres of the San Joaquin River Wildlife Refuge (Refuge) in 2002. Since that time, River Partners has restored and enhanced approximately 2,350 acres of riparian habitat on the Refuge on old agricultural fields. In 2006, widespread flooding began in early April and inundated areas of the Refuge for up to four months. The 2006 flood was critical in determining the future course of restoration work on the Refuge.
Lessons from the 2006 Flood
As part of its adaptive management process, River Partners conducted post flood surveys on restoration plantings throughout the Refuge. These surveys recorded high mortality of elderberry, and coyote brush. The species that showed the best tolerance for longduration flooding included black willow (Salix gooddingii), sandbar willow (Salix exigua), Fremont cottonwood (Populus fremontii), buttonbush (Cephalanthus occidentalis) and Oregon ash (Fraxinus latifolia). River Partners has used the results from this survey to develop a specific flood-tolerant plant community and another community which consists of the species which prefer higher and drier conditions. These community types were first implemented on the Vierra Unit of the Refuge.
The Vierra Unit is comprised of 511 acres of wetlands and riparian habitat located within the area identified by the USACE for a non structural flood management project. River Partners implemented active restoration on 311 acres of the unit by planting native woody species and an herbaceous understory. Approximately 200 acres of managed wetlands adjacent to the riparian habitat were constructed in the lower portions of the Vierra Unit.
The Vierra Unit restoration was completed in November 2008. At the time this project was completed, River Partners had documented over 70 % survival for all planted woody species. The herbaceous component, installed in the Fall of 2007, has become well-established. Although River Partners has been planting riparian vegetation on historic floodplain acreage, the riparian areas of the San Joaquin River have also been impacted by dams, levees and water diversions which have altered the historic annual hydrologic cycle and prevented flooding onto these areas. Flooding is a critical part of the natural cycle in riparian areas. It provides sediments and nutrients (natural fertilizers) critical for the health of riparian ecosystems and drowns many non-native weeds and rodents.
Restoration and Floodplain Management on the Refuge
The next phase of restoration on the Refuge is the Ecosystem Restoration and Floodwater Attenuation (ERFA) Project. In addition to restoring 633 acres on the west bank of the San Joaquin River, River Partners will work with the California Department of Water Resources to implement the USACE goals for the nonstructural flood control project.
Levee breaches are a critical part of the ERFA project during flooding events since this is an ideal site for transitory storage of flood water. Models of flood flows in this section of the San Joaquin River show that the Refuge acres will have the capacity to hold 1,535 acres of flood storage, covering a depth of 2-14 feet, which will reduce the effects of flooding on downstream levees. This flooding will also reconnect the restored riparian areas on the Refuge with the San Joaquin River by restoring natural river function to the restored riparian acres.
The ERFA project will also reengineer the drainage system associated with the restored acres. Drainage of flooded areas on the Refuge during the 2006 floods was complicated because the only drainage outlet for a large portion of the Refuge was a 36 inch culvert. Slow drainage of riparian areas can cause fish entrapment because there is no current directing the fish to go back to the river. Slow drainage can also be a problem because ponding can increase the water temperature and be lethal to native fishes. The ERFA project will improve this drainage as part of its flood management component.
The ERFA project is the culmination of River Partners collaboration with the US Fish and Wildlife Service to restore riparian habitat on the Refuge. By drawing on the lessons learned from the 2006 postflood surveys and the re-designed Vierra Unit plantings, River Partners was able to integrate an innovative flood management plan with efforts to restore fish and wildlife habitat.