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Scientists at the Columbia River Research Laboratory (CRRL) are using two-dimensional hydraulic modeling techniques along with geographic information systems (GIS) to estimate the spatial distribution of fish habitats on the Columbia and lower Snake Rivers. Two-dimensional hydraulic modeling allows investigators to calculate a depth and mean column water velocity for anywhere, and everywhere, on a river and under any flow conditions chosen. Modeling is advantageous to real-world measurements because of the cost, difficulty, or improbability, of collecting this data in the field. Depths and water velocities taken from the hydraulic model, along with other features of the river such as the material that makes up the river bottom (sand, cobbles, etc.) can be analyzed within a GIS to determine if an area of the river meets the needs of a fish during a given stage in its life, such as in the case of a spawning white sturgeon, for example. Thanks to work being done by the White Sturgeon Ecology Section at CRRL, we know the type of physical environment a white sturgeon prefers when spawning. When releasing its eggs, a white sturgeon seeks out fast water that is not too shallow, and a river bed composed of cobbles, boulders, or even bedrock. If we apply specific criteria to a section of the John Day Reservoir(see map) under two scenarios, 1) present impounded conditions and 2) natural river, or pre-dam, conditions, we can see how the spatial distribution of suitable white sturgeon spawning habitat may have changed since John Day Dam was constructed on the Columbia River in 1968.
The pair of figures above show the results of the rising of the water level over a fifteen mile-long section of the Columbia River when the John Day Reservoir was filled, merging the river where it was orginally separated into two parts, and flooding a wide area of land including the large island that was known historically as Blalock Island.
The second two figures illustrate the dramatic differences in velocity between the slow-moving reservoir and the fast-flowing natural river. Keep in mind that white sturgeon prefer fast water when spawning.
The final pair of figures show the spatial distribution of habitat suitable for spawning in the impounded reservoir and what we predict would have been present under natural river conditions. Note how the analysis reveals no suitable habitat today in this section of John Day Reservoir, though historically there could very well have been white sturgeon spawning in the area. In addition to John Day Reservoir, similar analyses are being conducted on the lower Snake River and the Hanford Reach of the Columbia River. Other fish species and life stages under study include rearing and spawning fall chinook salmon, smallmouth bass, and northern pikeminnow. The two-dimensional hydraulic model used in this study was provided by Dr. Peter Steffler, Dept. of Civil Engineering, University of Alberta, Edmonton, Alberta, Canada. Related BRD Studies:John Day Reservoir Decision Support System Project Spatially Explicit Aquatic Habitat Model Project Contact James R. Hatten Email: jim_hatten@usgs.gov Publications
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