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

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869 Hydrology and Water Resources umes. Dry periods may last for several years. From 1928 Variability in flow ~vmains a defining characteristic of Sierra through 1937, runoff was below average in each year. The past Nevada rivers. two decades have included record droughts for one year (1977), two years (1976-77), three years (1990-92), and six Even the limited variability in precipitation and runoff that occurred in this centvrv caused water managers to attempt years (1987-92). The recent six-year drought was similar to to augment supplies ihrough deliberate weather modifithe 1929-34 dry period. Total stream flow averaged across cation. Soon after the theoretical basis for cloud seeding to many rivers was about half of average in each case (Califor- increase precipita|ion was established, the world’s first opnia Department of Vkfater Resources 1994). Other indications erational program began in the eastern Sierra Nevada in 1948. of past climate suggest that severe droughts in the Sierra Within the next few ~,ears, cloud seeding programs were have persisted for periods from decades to more than two centuries (Graumlich 1993; Stine 1994, 1996; Millar 1996; started in the San Joa~luin, Kings, Mokelumne, and Feather Rivers (Henderson I~)95). Woolfenden 1996). The presence of tree stumps well below modern lake levels in Lake Tahoe and Lake Tenaya and else- A dozen programs were active in the Sierra Nevada i,1 I~)q4 a,ld 1995. Despite dozens of studies, the effectiveness of cloud seeding remains uncertain. Conwhere provides strong evidence for very arid conditions in ventional wisdom sug~4ests that a well-designed cloud seeding the past (Stine 1994). The period 1937 through 1986 was an program may yield up to ~’Y,, additional stream flow (Amerianomalously wet period in a 1,000-year-long reconstruction can Meteorological Society 1992). Hundreds of papers have of precipitation from dendrochronological evidence been written on environmental effects of cloud seeding (e.g., (Graumlich 1993). However, our water resources infrastruc- Berg and Smith 1980; Parsons Engineering Science 1995), but ture and institutions were largely developed during this pe- major impacts have not been h~und, perhaps because of the riod. Inferences about the climate of the past 100,000 years uncertainty in the amou,~t of precipitation augmentation. The (e.g., Broecker 1995) suggest that great variability in tempera- amounts of the prima ry seeding agent, silver iodide, released ture has been common and the temperature of the last 10,000 in a typical yea r (7-18 kg I 15--40 lb]) over a large river basin years was anomalously stable. Any resumption of such a vari- are several orders ~d magnit ude less than quantities naturally able climate would be challenging to California’s water resource system and society in general. Dramatic shifts in dimate could alter the distribution of vegetation over decades to centuries and could interact with a changed precipitation regime to alter runoff generation (Beniston 1994; Melack et present in soil. al. inpress), SURFACE WATER QUALITY The Sierra Nevada ix generally regarded as producing sur- Trends face water of excellent quality, meaning the water is suitable In both extremes of wet and dry conditions, there do not ap- for almost any use and c~mtains lower amounts of contamipear to be any strong trends in water becoming more or less available in the recent past. Concern was raised a few years nants than specified in state and federal standards. Most of the runoff would be suitable for human consumption except ago that the proportion of annual runoff occurring in the for the risk of path~gens. Very little of the water of the Sierra months of April through July in the Sacramento, Feather, Yuba, Nevada can be considered hi~4hly polluted (i.e., contaminated and American Rivers had declined since about 1910 (Roos with materials having potential adverse effects at concentra- 1987). However, this trend appears to be a result of increased tions above natural background). Areas of lower water qualrunoff for the remainder of the year and no change in abso- ity correspond to those areas with greater human activities lute amounts during spring (Wahl 1991; Aguado et al. 1992). and access. Head water streams are particularly sensitive to On the western slope of the Sierra Nevada, there have been pollution because of low fh~w conditions and nutrient limitano obvious trends in flood magnitude or frequency over the tions. The relatively few point sources of pollution throughhistorical period. In rivers of the eastern slope, clusters of out the range are mostly associated with inactive mines, events at both extremes have been evident in recent years (Kattelmann 1992). Five of the largest eight to eleven snowdumps, and towns. Many contaminants that enter Sierra Nevada streams can be c~nsidered non-point-source pollutmelt floods (in terms of volume) since the 1920s occurred from ants because they are generated over large areas. Livestock I978 to 1986. Five of the smallest thirteen or fourteen snow- waste is an example of n~m-point-source pollution. Sediment melt floods since the 1920s occurred from 1987 to 1991. In- is the most pervasive pollutant because its production may stantaneous peak flows have a similar distribution. For be increased above natural background levels by almost any example, in Rock Creek, four of the ten largest annual floods human activity that disturbs the soil or reduces vegetation and three of the six smallest annual floods occurred during cover. Sediment augmented above natural levels usually the 1980s. These events support theories of some climatologists that extreme events are becoming more common in the impairs some beneficial us~:*s of streams. Erosion and sediment are disc~sse .~d separately in another section of this chapwestern United States (Granger 1979; Michaelson et al. 1987). ter. Ground-water quality J~s discussed in the section about D--048981 D-048981
VOLUME II, CHAPTER 30 ground water. Water temperature is treated in Kondolf et al. Regional Water Quality Control Board 1991). Water quality 1996. was considered impaired in streams receiving wastewater Human activities in the watershed have the potential to from Nevada City, Grass Valle); Placerville, Jackson, and the alter nutrient cycling. A classic study in New England pro- Columbia-Sonora area (Centr~ Valley Regional Water Qualvided some of the first measurements of changes in nutrient budgets as a result of complete killing (but not removal) of ity Control Board 1991). trees in a small catchment (Likens et al. 1970). This study at Hubbard Brook found that loss of nitrates in stream flow in- Sewage creased by forty times in the first year following devegetation, Most communities with a centralized population in the Siand export of other nutrients increased several times. Studies erra Nevada have common sewage collection and treatment in Oregon (Fredriksen 1971; Brown et al. 1973) suggested that systems. Discharges from treatment facilities are regulated by typical harvesting procedures that impact less than half of a the regional water quality control board; however, short-terra watershed with deep soils will not significantly contaminate failures are a persistent dLfficult~: Disposal of treated wastesmall streams or risk serious declines in soil productivity waters on land instead of directly into streams is encouraged (Brown 1980). However, frequent harvesting of large portions where practicable (Central Valley Regional Water Quality of catchments with shallow soils and low cation exchange Contro! Board 1991). An experiment in Tuolumne County capacity can result in substantial nutrient losses from soils to demonstrated several problems with spraying treated effiustreams. Elevated concentrations of nitrates and phosphates ent on hillsides: the soil became overloaded with nutrients, may be expected in catchments with agriculture, fish farms, salts, and water, and alga! growth effectively sealed the soil and residences. Most of the work on nutrient cycling in the surface, minimizing infiltration (California Division of For- Sierra Nevada has been done in the Lake Tahoe area (e.g., estrv 1972). Effluent from a sewage treatment plant in the Lake Coats et al. 1976; Coats and Goldman 1993). In one catchment Tahoe Basin was sprayed over a 40 ha (100 acre) area from in the Tahoe basin, biological processes effectively prevented 1960 to 1965. Even five ),ears after application ceased, subrelease of nitrogen in nitrate form in surface water or ground stantial amounts of nitrates were entering a creek downwater (Brown et al. 1990). These authors cautioned that cre- gradient from the site. A stand of Jeffrey pine at the site was ation of impervious surfaces allows nitrates to bypass poten- also killed by the persistent high level of soil moisture (Perkins tial sinks. Human activities that decrease residence time of et al. 1975). water in soils have potential to increase nitrate export. Ni- A significant fraction of the residences in the Sierra Netrate concentrations sampled in seventy-seven streams of the vada are too dispersed to allow connection to community eastern Sierra Nevada were less than 1 mg/! in all cases and sewage facilities and rely on individual septic systems (Duane usually less than 0.1 mg/1, demonstrating that there is usu- 1996a). Septic systems in Nevada County have led to signifially little export of nitrates in streams (Skau and Brown 1990). car~t bacteriologica! contamination in streams below unsewered subdivisions (California Department of Water Point-Source Pollutants Resources 1974). Septic tank and leach field systems on individual lots prov-ide a good example of cumulative watershed There are very few known localized sources of water pollu- effects. The soils of a particular catchment have sufficient cation in the classic outfall-into-the-stream sense in the Sierra pacity to treat a particular quantity of sewage under a par- Nevada because of the virtual absence of industries that pro- ticular set of conditions. When the soil system is overloaded cess chemicals and continuing abatement of the few existing some fraction of the waste or its derivatives is discharged to sources. Point-source pollution has also been reduced very streams. Each residential septic system contributes only a effectively under the Clean Water Act of 1972 and subsequent small fraction of the total, but the community as a whole has amendments. Municipal and industrial discharges are con- polluted the catchment. Recreational developments such as trolled through National Pollutant Discharge Elimination ski areas and campgrounds also generate significant quanti- System permits. Most pollution of that general nature is as- ties of sewage and may have their own treatment faci!ities if sociated with active and abandoned mines and is discussed geographically isolated. In the 1950s, Yosemite Valley was the in the section on mining. Industrial-type pollutants may also most significant wastewater source in the upper-elevation be found in the vicinity of many cities and towns and aban- parts of the San Joaquin River Basin (Central Valley Regional doned lumber mills. However, serious problems of this na- Water Pollution Control Board 1957). ture are not known to exist (Central Valley Regional Water Urban storm water runoff can add a variety of contami- Pollution Control Board 1957; Central Valley Regional Water nants directlv to streams. Pet waste can be a significant source Quality Control Board 1991; Lahontan Regional Water Qual- of fecal coliform bacteria in some areas. Street runoff in the ity Control Board 1993). Over the entire western slope, there Lake Tahoe Basin is beginning to be routed into publicly are only ten "municipal and industrial discharger groups": owned lots to allow for some pollutant removal. Chester, Quincy, Paradise, Portola, Nevada City, Auburn, Even in the backcountr?’, inadequate disposal of human Placervi!le, Jackson, Sonora, and Bass Lake (Central Valley waste from dispersed recreationists has contaminated enough D-o48982 D-048982
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Page 3 and 4: 856 VOLUME II, CHAPTER 30 extensive
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D--048966 - CALFED Bay-Delta Program - State of California

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