Scientific Investigations Report 2006-5136
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006-5136
Applying these measuring methods to most large riverine systems, such as the Yakima River Basin, is challenging because many systems were extensively modified with diversions and return canals, and there are usually thousands of kilometers of stream network. In turn, many parts of such a network may provide habitat for several life-history stages of anadromous and resident salmonids and other fish. To partially address this issue, a method was developed to thermally profile long (about 5-25 km) river reaches. The profile is based on measuring water temperature at 1- to 3-second intervals at or near the streambed, and in some cases, concurrently measuring (profiling) the water temperature near the surface. Measurements are taken in a Lagrangian framework, which entails drifting at the ambient streamflow velocity. This method produces a longitudinal, Lagrangian profile of stream temperature near the streambed.
Electrical conductivity profiling of the cobble-bottom streambed of the Hanford Reach on the Columbia River, Washington, by Lee and others (1997) identified ground-water discharge areas. This method was similar to that of Lee and Dal Bianco (1994), who applied it to a small, gravelly bottom river. The profiling method was based on techniques to locate ground-water discharge areas in lakes (Lee, 1985; improved on by Harvey and others, 1997). Together, these studies demonstrated that profiling is an effective method for locating ground-water discharge areas, especially when combined with piezometer measurements.
The conceptual basis for development of the method was to determine if a robust, thermal-profiling method could be developed, and if so, to document the thermal profile, with its attendant diversity and structure, of selected reaches. Profiles should yield information related to salmonid habitat because the complexity in salmonid life histories is functionally related to diversity in thermal habitat (Rieman and Dunham, 2000). If a thermal profile could be documented, it then needed to be determined if areas of ground-water discharge could be identified from the thermal profile.
Profiling in a Lagrangian framework (moving downstream at the same velocity as the river) allows for tracking temperature of a parcel of water as it moves downstream in a reach. Deviations from the diurnal heating of a parcel should principally be due to ground-water discharge, surface-water inflows, and depending on setting, streamflow losses or riparian-vegetation shading. In particular, deviations (anomalies) from an overall heating response may represent ground-water discharge areas. Using temperature anomalies to identify ground-water discharge areas is not a new concept (e.g., Cartwright, 1970); discharge areas will have a larger vertical thermal gradient than recharge areas. Areas with sharp thermal gradients are candidates for more intensive studies.
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