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

VOLUME II, CHAPTER 30
additions. Downstream of Lake Tahoe, the Truckee River has in association with major rainstorms and so can be considlargely
recovered from the intense insults to water quality of ered episodic in nature. Nevertheless, streams tend to adjust
the 1870s to 1930s (log transportation on artificial floods, saw- their form to accommodate the long-term sediment supply.
dust dumping from lumber mills, and chemical waste from a Processes that detach and transport particles of soil and rock
pulp and paper mill) (Pisani 1977)o Today, the principal prob- downslope and downstream can be lumped together as erolem
in the Truckee River above Reno is elevated temperature sion. Sedimentation occurs when these particles come to rest
resulting from water storage in Martis Creek, Prosser, Boca,
and Stampede Reservoirs (Bender 1994). Total dissolved sol-
in transitory or long-term storage.
ids have been in the 6 to 210 mg/l range. Naturally occurring
uranium is found in Sagehen Creek, and iron is high in a few
Aquatic Effects
places within the Truckee River system (Bender 1994). Water Alteration of stream sediments can seriously impact populaquality
problems have been identified on Leviathan/Bryant tions of fish and other aquatic organisms. Aquatic ecosystems
Creeks (bacteria, nutrients), Little Truckee (nutrients), and have developed in response to a particular regime of water
Trout Creek (total dissolved solids, suspended sediments) and sediment flows and channel conditions. When conditions
(California State Water Resources Control Board 1984). change, such as when annual floods cease because of a dam
~cotr
Although the surface waters of the Sierra Nevada are no
nger pristine in terms of quality or other attributes, most
eams could rank as excellent or outstanding compared with
onventional standards or water elsewhere in the state, naor
the proportion of silt-size sediments increases because of a
road built next to the stream, some organisms will benefit and
some will suffer. Trout and other salmonids require streambed
deposits of gravel-size particles in which to prepare nests
ion, or world. However, water quality in the Sierra Nevada, (redds) for their eggs where there is substantial flow of water
as elsewhere, is intimately connected to water quantity. Re- and dissolved oxygen. Until the fry emerge after two to six
duction in natural flows because of diversions is perhaps the months, the redds are vulnerable to scour and deposition of
most widespread water quality problem. Water remaining in other sediments that could block flow of water through the
~-the stream must support the same habitat needs and dilute redd (Lisle 1989). When sediment inputs to a stream exceed
whatever material and heat loads that arrive downstream of the transport capacity of the channel, fine sediments (clays,
the points of diversion. For these reasons, what is usually silts, and sands) tend to accumulate on the bed surface (Lisle
considered a quantity problem is also a problem of quality, and Hilton 1992). Fine sediments have been found to fill sub-
Additionally, there are persistent problems in different river stantial fractions of pools in streams on the Sierra National
basins. In the Lake Tahoe Basin, nutrient loads that would be Forest that were known to have high sediment yields, such
considered small anywhere else are accelerating eutrophi- as Miami Creek (Hagberg 1993). These fine sediments often
cation of the lake. Within many parts of the Feather River smother invertebrates, reduce permeability of streambed
Basin, unstable stream banks resulting from long-term over- gravels and fish-egg nests (redds), impede emergence of fish
grazing and roads are producing sediment yields at the basin fry, and cause poor health or mortality of fry at emergence
scale that are up to four times greater than natural yields, because of reduced levels of dissolved oxygen (Burns 1970).
Throughout much of the Sierra Nevada, a few problem mines Sedimentation also adversely impacts invertebrate habitat
continue to leach heavy metals into streams, and mercury re- (Erman 1995). In many streams in the Sierra Nevada, suitable
mains in the beds of many streams from a century ago. Iso- gravels for spawning are found only in isolated pockets and
lated problems such as poorly designed and located septic lower-gradient reaches (Kondolf et al. 1991; Barta et al. 1994).
systems and roads impact local portions of streams and should The limited extent of such areas increases their importance
be correctable by moderate investments for improved water for fisheries maintenance. Fortunately, scour and deposition
quality, processes are highly variable within and between streams, so
that some spawning areas are almost always available (Lisle
1989). Sediment transport processes in streams of the Sierra
Nevada have been the subject of few studies (e.g., Andrews
and Erman 1986), and even basic information is scarce. Much
E R O S I O N A N D S E D I M I= N TAT I O N of the sediment in mountain streams consists of large particles
known as bedload. In fourteen streams of the eastern
Soil erosion, mass wasting, channel erosion, and sedimenta- Sierra Nevada, the proportion of bedload varied between 0%
tion are natural processes that alter the landscape and streams,
They are important disturbance mechanisms in terrestrial and
and 65% of the total sediment load (Skau et al. 1980).
aquatic ecosystems. These geomorphic processes are critical
in nutrient cycling, transport of organic matter, and creation
Natural Sediment Yields
of fresh surfaces for colonization (Naiman et al. 1992). The Natural surface erosion is generally r~garded as small in the
rates at which they occur are highly variable across the land- Sierra Nevada because of high infiltration capacity of the soils,
scape and over time. These processes operate most intensely predominance of snowmelt as a water input to soils, rarity of
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