D--048966 - CALFED Bay-Delta Program - State of California

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Sacramento ~ Core Sierra Nevada ecoregion -- River ~ Lake ¯ Dam Site 887 Hydrology and Water Resources ¯ ¯ evada ¯ ’: 0 10 20 30 40 50 60 70 80 90 I00 l~0r~ters 0 10 20 30 40 50 60 70 z r Source: Department of Fish and Game; ArcUSA data; Department of Water Resources SNEP GIS Center FIGURE 30.4 Larger dams that are regulated by the California Division of Dam Safety are found on almost all major streams of the Sierra Nevada. D--048999 D-048999
888 VOLUME II, CHAPTER 30 16 14 12 Snow ~nd Glacier Melt Only: Maclure Croek,~ 3500 m, 0.9 .sq. km.,1967 contamination of the enclosed water and provides greater operational flexibility. However, a finding by the staff of the State Water Resources Control Board held that improvements to effectively constitute a new diversion that the ditch owner ~ does not hold rights to. Leakage currently provides water for 6 improvement of wildlife habitat and other uses. A decision is 4 pending on this case involving the Crawford Ditch of the E1 2 0 ~~ , Dorado Irrigation District (Borcalli and Associates 1993). Occasional failures of these (and more modern) canals result in serious erosion or debris flows. Four flume failures occurred 4000 3~ Mostly Seowmelt a,~,~uturn,~ Rain: Merce,~ River A at Happy Isles. 1200 m. 460 sq. km..1967 II along the Tule River just between 1962 and 1965. In 1992, the Cleveland fire in the South Fork of the American River Basin destroyed a large portion of the El Dorado Canal, which sup- 2so0 2000 I I plies about a third of the total water to the E1 Dorado Irrigalion District. In November 1994, a fallen oak blocked the ~ger 150o 10oo 1 J/I 1 , II Creek Canal, diverting water to the slope below and eroding hundreds of cubic meters of soil. o Environmental Consequences 3500 3000 2~oo 2ooo Rainfall and Snowmelt: South Fork Merced River. 1200 m, 250 sq. km., 1967 The construction, existence, and operation of dams and diversions have a variety of environmental effects. Inundation of a section of stream is the most basic impact. A river is transformed into a lake. The continuity of riverine and riparian habitat is interrupted. To creatures that migrate along such ~soo corridors, this fragmentation has consequences ranging from ~000 altering behavior of individuals to devastating populations. 500 Dams have the potential to alters downstream flows by oro -- ders of magnitude and, at the extreme, can simply turn off the water and dry up a channel. Changing the natural transs0o port of water and sediment fundamentally alters conditions 4~o ~ ~o ~00 200 200 lso too 60 o ~ R~n~, O~y: Ma~e, Creek. 500 rn, 44 sq. kin., 1967 | ~J~ for aquatic and riparian species. Changing stream flow also has dramatic impacts on chemical and thermal attributes of downstream water. The abundance of impoundments in the Sierra Nevada is impressive when one realizes that virtually all flat water at the lower elevations of the west slope is man- made. The terrain is simply not conducive to the formation of natural lakes below about 1,500 m (5,000 ft). An obvious impact of water management is alteration of the natural hydrograph (temporal pattern of stream flow). For example, during the snowmelt season, the daily cycle of run- 14000 ~o00 t0000 ~o00 Combined Sources: Merced River Near Briceburg. 360 m, 1,800 sq. km., 1967 ~ ]/ ,. off and recession may be transformed into a constant flow. A series of hydrographs from streams in and near Yosemite National Park illustrate natural stream flow patterns generated under various watershed and climatic conditions at dill000 ferent elevations (figure 30.5). Dams are built to change those ~00o ~oo ~~v~ ~~,~a~ patterns (figure 30.6). Diversions not associated with large impoundments change the volume without much effect on o ~ O N D J F M A M J J A S timing (figure 30.7). Large projects usually alter both volume and timing (figure 30.8). FIGURE 30.5 Watersheds with different elevation ranges and sources of High Flows runoff have different patterns of stream flow over a water year (October to September). The most obvious alterations in formerly natural hydrographs are decreases in peak flows. The size of an impoundment and D--049000 [9-049000
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D--048966 - CALFED Bay-Delta Program - State of California

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