Floodplain mining occurs throughout Washington and is highly concentrated on the alluvial floodplains of the Yakima River (Norman et al., 1998). Currently, the Yakima River floodplains contain 141 active or abandoned gravel mines. Floodplain mining results in open pits on riparian land that typically intersect the water table at least seasonally (Kondolf 1997). The resulting open-water ponds are separated from the adjacent main channel by a narrow strip of unmined land or dike (Kondolf, 1997). On the Yakima River, flood revetments create varying degrees of hydraulic disconnection between the ponds and the adjacent river. Floodplain gravel mining impacts the structure and function of alluvial systems (Kondolf, 1997; Norman et al., 1998).
Recently, efforts were made to connect the Hansen Ponds gravel-pit complex to the Yakima River to increase hydrologic connectivity and provide off-channel habitat to anadromous salmon. The surface-water connection was established in February 2004 by constructing an ingress notch in the dike that separated the Hansen Ponds system from the Yakima River. In addition to reconnection, efforts have been made to re-establish native vegetation, introduce large woody debris, and improve shoreline complexity in the ponds to provide a productive lotic environment that adds to the juvenile salmon rearing habitat. Little is known about the magnitude of ecological change in this system following reconnection or whether these changes are providing adequate habitat. An understanding of these factors is critical in assessing the effectiveness of salmon habitat restoration.
The intent of this project was to develop an ecological monitoring protocol to characterize the response of the Hansen Ponds system to reconnection efforts by comparing it to similar, disconnected site. To isolate the ecological response of the system to reconnection and provide a description of the effectiveness of creating new off-channel salmon habitat, the explicit objectives of this ecological characterization were to examine: (1) possible differences in the degree of hydrologic connectivity in the reconnected and disconnected sites; (2) any ecological differences between the reconnected and disconnected sites, including differences in characteristics such as water quality (temperature, dissolved oxygen, pH, conductivity, and clarity), sediment composition, and aquatic vegetation.; and (3) whether restoration has provided adequate habitat for salmon in the Hansen Ponds system.
Gabriel, A., and D. Parrish. 2006. Ecological characterization of salmon habitat restoration efforts for abandoned gravel pits, Yakima River, Washington. Presented at the Yakima Basin Aquatic Science and Management Conference, June 14-15, 2006, Central Washington University, Ellensburg, WA.
David Parrish. 2005. Ecological Characterization of Salmon Habitat Restoration Efforts of Abandoned Gravel Pits, Yakima River, Washington. Unpublished M.Sc. thesis, Resource Management Program, Central Washington University.