Download Sacramento River Fluvial Geomorphology

Sacramento River Fluvial Geomorphology –
Red Bluff to Tehama
River Mile 243 to 230
June 15, 2007
SACRAMENTO RIVER FIELD TRIP GUIDE
By Koll Buer, Retired Annuitant-DWR
INTRODUCTION
The 14-mile Red Bluff to Tehama reach of the Sacramento River is an area of profound
change. Above Red Bluff is the magnificent 60 mile long canyon reach, characterized by
tall cliffs of sedimentary and volcanic rocks. The river is mostly entrenched into
“bedrock”, hard rocks and deposits that erode slowly over time.
Below Red Bluff, the river flows into the Sacramento Valley. The river changes
character. Tall cliffs are replaced by eroding river banks and expanses of gravelly
alluvial deposits. The river channel is dynamic and restless, changing from year to year.
The vegetation changes dramatically as well. Above Red Bluff, riparian vegetation hugs
the stream bank in narrow belts. Below, expanses of tall cottonwoods extend far away
onto the floodplain from the channel proper. Agriculture thrives in the deep alluvial
soils, but walnut trees toppling into the river along eroding banks testify to the struggle
between man and nature.
A float trip along this stretch of the river reveals a lot. Some of the same geology as the
upstream reaches occurs here as well, but more subtly, sometimes buried in the lower
layers, sometimes revealing themselves locally with higher banks, yellow or reddish hues
distinct from the gray-brown sandy loams of the floodplain deposits. Bank protection,
mostly consisting of rock riprap, protects some banks, but also can be found abandoned
in sloughs away from the river.
Aerial photos provide a different perspective. Evidence of past river movement is
apparent, with multiple channels, oxbow lakes, islands, meander scrolls, and scars
occurring on the expansive floodplain. The recent meander belt is constrained by older
terraces on both sides of the river. Riparian forests occur mostly on gravelly point bars
and on recent river deposits. Rectangular orchards and fields predominate in most places.
Creeks joining the river in this reach include Red Bank Creek draining the west side of
the valley, pouring red mud and gravel into Lake Red Bluff a few feet above the Red
Bluff Diversion Dam. Salt Creek, Craig Creek, Antelope Creek, and farther south Mill
Creek drain the volcanic hills of the Cascade Range to the east. Elder Creek, joining the
Sacramento River across from Mill Creek, drains the valley foothills to the west.
Sources of Information
There is a huge reservoir of information on this section of the river, mostly collected by
agencies such as the Army Corps of Engineers, U.S. Fish and Wildlife, Department of
Fish and Game, and the Department of Water Resources. Universities, including Chico
State, U.C. Berkeley, and U.C. Davis have done research projects and theses, and
Conservation groups such as The Nature Conservancy and the River Partners conduct
research and restoration projects. Some of the information is available on the Internet,
but much of the information is buried in dusty archives. The Sacramento River Portal at
www.sacramentoriverportal.org is an excellent introduction to the resource.
DWR (1980) prepared the Middle Sacramento River Spawning Gravel Study for the
Department of Fish and Game to evaluate the condition of spawning gravel in the middle
Sacramento River. The report identified factors resulting in a loss of spawning gravel
quality. These include gravel mining on the river and its tributaries, construction of
Shasta and Keswick dams, and the loss of gravel recruitment from areas above dams.
DWR also published the Sacramento River Bank Erosion Investigation in 1994, detailing
the geology, meander belt, bank erosion, and other significant factors.
Harwood and Helley (MF-1790, 1985) produced a series of maps showing the Late
Cenozoic geology of the Sacramento Valley. The accompanying geologic map is
modified from this work. The USGS Red Bluff Sheet also is a handy reference for this
section of the river.
Location and Access
The field trip area is Tehama County. The reach begins at Red Bluff, River Mile 243,
and extends to the town of Tehama at RM 229, a river distance of about 14 miles.
Towns in the reach are Red Bluff and Tehama. Vehicular access is available from Lake
Red Bluff, with launch ramps at Red Bluff River Park, the Sacramento River Discovery
Center, and below the Red Bluff Diversion Dam on the left bank. Private launch ramps
are sometimes seasonally available at Bow River Mobile Home Park and Hunter’s
Resort. A launch ramp also is at the end of the reach at Tehama River Park directly
upstream of the Tehama Bridge. The river is navigable with small craft such as canoes,
rafts and jet boats. During the late-fall and dry springtime, low flows and snags cause
some of the riffles to be difficult to navigate. Caution should be used because of snags
and low, overhanging bank vegetation that in places can ambush the unwary.
Historic Changes
Since about 1850, the Sacramento River area has undergone a number of hydrologic,
geomorphic, and environmental changes, some of which have been detrimental to locally
adapted species. These changes are caused by dams and diversions, bank protection,
urbanization, stream gravel removal, hydraulic mining, agriculture, and logging. Some of
these changes have had long-reaching effects, including alteration of river characteristics,
such as depth, width, gradient, sinuosity, sediment, bed material, and bank erosion. This
in turn has reduced riparian vegetation, water quality, hydrologic diversity, and fish and
wildlife resources.
A large number of chinook salmon (Oncorhynchus tshawytscha) migrated up the
Sacramento River each year to spawn. Although there were probably four runs then, as
there are today, the two largest runs were thought to have occurred in the fall and spring.
The other two runs, winter and late fall, are not as well documented historically,
especially their numbers. Most of the spring-run and winter-run salmon, as well as part
of the fall and late fall salmon, were thought to have spawned upstream from the present
location of Shasta Dam. However, large numbers of spring-run and fall-run salmon also
spawned in many Sacramento tributaries. A large part of fall run spawned in the
Sacramento River between Redding and Red Bluff.
Before Shasta Dam, the Sacramento River was free flowing. Late summer flows were
low, averaging 3,000 cubic feet per second (cfs), and in dry years dropping as low as
1,000 cfs. The river and its tributaries, however, would fluctuate widely in response to
winter rains and spring snowmelt. Large amounts of suspended sediment and gravel
bedload moved from the mountains in response to intense winter storms.
In 1944, Shasta Dam was completed for flood control and water storage purposes.
Regulation of the discharge has dampened low and high extreme events below the dam,
resulting in a regulated flow in the summer averaging 7,000 cfs to 13,000 cfs and a
regulated peak winter flow near Redding of 80,000 cfs. The reservoir was constructed by
the U. S. Bureau of Reclamation on the upper Sacramento River above Redding. Shasta
Dam stores 4.5 million acre-feet and, to a large extent, regulates flows from the Pit,
McCloud, and upper Sacramento Rivers. Keswick Dam, 9 miles downstream from
Shasta, provides power, water regulation, stops salmon migration, and acts as a
fish-trapping facility. The dam traps most of the sediment in deltas in the upper reaches
of the lake. Sediment-free flow below the dam scours the river channel and transports all
but the coarsest sediment. The resulting substrate is armored by cobbles and boulders
that are in many places too coarse for salmon to spawn.
Whiskeytown Dam controls flows on Clear Creek. Since December 1963, water has
been diverted from the Trinity River Basin through the Clear Creek Tunnel and Judge
Francis Carr Powerhouse to Whiskeytown Lake. The Spring Creek Tunnel then diverts
Trinity water and most Clear Creek water through Spring Creek power plant into
Keswick Lake. The effect of the Trinity River diversion on post-Shasta flows has been to
increase average Sacramento River discharge by about 1,000 to l,500 cubic feet per
second throughout most of the year. The diversion amount has recently been reduced to
improve water flows in the Trinity River. Flows, particularly flood flows, in Clear Creek
below Whiskeytown dam have been reduced. Recently minimum flows on Clear Creek
have been increased to provide spawning and rearing habitat for anadromous fish.
There is ample reason for encouragement. The U.S. Fish and Wildlife Service continues
to purchase and rehabilitate critical riparian lands along the river. Bank protection is no
longer “maintained” by the removal of riparian vegetation. No new bank protection has
been installed in this section of the river since 1983. Many of the poorly screened or
unscreened diversions of the past now have modern screens that allow the salmonid fry to
safely move downstream past agricultural diversions. The operation of the Red Bluff
Diversion Dam has been changed so that the dam gates are in the water only four months
of the year instead of 12. Water temperatures are maintained cooler during the critical
spawning season by a temperature curtain allowing the release of cold bottom water at
Shasta Dam. Fishing restrictions on the ocean and in the river allow more fish to return
to the river to spawn.
WILDLIFE AND WETLAND-RIPARIAN HABITAT
About 150 years ago, the Sacramento River south of Red Bluff was bordered by up to a
half million acres of riparian forest and wetland. A wide array of species, including
shorebirds, wading birds, amphibians, reptiles, fish, mammals, invertebrates and plants
depend on this type of habitat. Fifty-five percent of the threatened and endangered
species in California are associated with wetlands.
As agriculture and urban areas developed along the river, the riparian vegetation was
gradually reduced, until less than five percent of the original acreage now remains. A
large amount of credit is due the U.S. Fish and Wildlife Service’s Sacramento River
Wildlife Refuge in protecting and enhancing the remaining riparian forests.
Native riparian forest vegetation includes mixed cottonwood, box elder, and sycamore
groves as well as mature stands of valley oak and live oak. The mixed cottonwood
forests are highly complex, with a mixture of ages, stages, and species occurring in
arcuate or linear swaths, a testament to the active movement of the river across the
floodplain. Most of the valley oak and live oak forests occurred on the flat, elevated
terraces adjacent to the river floodplain, but most of these have been converted to
agricultural uses.
USFWS Draft Comprehensive Conservation Plan and Environmental Assessment (July
2004) provides in Chapter 3-The Refuge Environment- a summary of plants and animals
in the river and riparian forests. The list of Threatened and Endangered species is long,
and includes the bank swallow, Chinook spring-run and winter-run and the now famous
valley elderberry longhorn beetle.
Riparian lands provide a multiplicity of complex, highly suitable and critical habitat for a
wide range of birds, mammals, amphibians, insects, and other wildlife. State and/or
Federal listed species of special concern include the bald eagle, western yellow-billed
cuckoo, Swainson's hawk, valley elderberry beetle, giant garter snake and others.
Sloughs and side channels provide nurseries for juvenile salmonids. Backwaters,
oxbows, and tributary mouths provide warmwater fishery and wetland habitat.
Riparian habitat may be divided into a number of zones, beginning on the gravel bar next
to the water surface, followed by the riparian scrub, and extending out to the riparian
forest on the floodplain and terrace.
The gravel bar habitat (gravel) is normally inundated and scoured by high flows on a
yearly basis. There are no soils present and the substrate consists of silt, sand, gravel,
cobbles and woody debris with a minimum of woody vegetation. Bare areas are the
norm, but thin lines of young willows, annual forbs and grasses occur in places. The
density and diversity of the gravel bar habitat is variable and depends upon streamflow,
length of time between flood events, summer moisture availability, shade, substrate, and
mechanical disturbance.
The riparian scrub habitat generally extends from the gravel bar to the edge of the high
water channel. The substrate is typically gravel overlain by sand and silt of varying
depth. Woody debris piled up by floodflows occurs in places. The vegetation generally
consists of brush and young woody vegetation of the type that occurs outside the channel
on the floodplain. The density of this vegetation is also highly dependent upon the flow
regime during the previous few years. The vegetation is adapted to winter flooding that
scours and removes most of the growth and allows for the periodic rejuvenation of this
habitat.
The riparian forest (cottonwood forest and mixed forest) is on the floodplain outside the
active channel. The substrate is generally organic silt and sand. The riparian forest is
normally inundated once or twice a decade. Instead of the scour that characterizes the
channel, deposition of sand and silt is the norm. Typical riparian forests consist of an
over-story of cottonwood, sycamore, box elder, alder, black walnut, valley oak, live oak
and other tree species with an under-story of brushy vegetation such as poison oak, valley
elderberry, blackberries, willows, and grapes as well as forbs and grasses. Meander
migration of the river within the riparian corridor results in erosion of the high banks with
mature riparian forest and deposition of point bar sediments on the opposite bank. This
results in the constant destruction of the mature forest and regeneration of the young
forest.
Artificial and natural ponds (marsh and part of open water), along with backwater areas
and oxbow lakes provide for transitory wetland habitat. The wetland habitat is created by
erosion and channel changes, but converted back to forest over time by flood deposition.
GEOMORPHOLOGY AND GEOLOGY
River geomorphology is the study of the origin and development of river form and
function as a result of the underlying geology. Geology includes geologic units,
structure, tectonics, and geologic changes caused by major climatic shifts.
River Geomorphology
The geomorphic characteristics of the study reach are an intrinsic function not only of the
geology underlying and surrounding the river, but also of the regional climate and river
hydrology. Human induced changes, such as dams, levees, and diversions have also had
a profound effect. Rivers with a natural shape and hydrologic condition generally
support the most diverse mixture of habitats and fish and wildlife species, since that is
what they originally adapted to.
If a river has incised (i.e., eroded down below the original channel bed surface) as a result
of natural or human-induced factors, the abandoned upper floodplain may become a
“terrace” (former floodplain). This is true of the Sacramento River as far south as about
Ord Ferry. Below Ord Ferry, basin deposits predominate with no terrace development in
the middle of the valley. Terraces allow vegetation to escape from periodic inundation,
resulting in valley oak woodlands or grassland-oak savannahs.
The river between Red Bluff and Tehama has been divided into 2 reaches (DWR 1980),
designated 6A and 6B. Reach 6A begins at the Red Bluff Diversion Dam and ends
downstream at RM238.5. This 4.5 mile-long reach has a relatively low slope of 5 feet
per thousand feet, low bank erosion rates, low sinuosity, and a fairly narrow meander
belt.
Reach 6B from RM238.5 to RM231, in contrast, has a fairly high gradient of about 8 feet
per thousand, overall high bank erosion rates, and a sinuous, anabranching channel. This
reach also has a wide meander belt.
The width of the river’s active meander belt varies from a low of 600 feet near Tehama,
to 5,300 feet at River Mile 237.
Bank erosion rates vary from 0 to about 50 feet per year with an average of 12.7 feet per
year in the Red Bluff to Chico Landing reach. The average bank height from thalweg to
top of bank is 25 feet, with 16 feet of sand and gravel at the base and 9 feet of silt on the
top.
Geology
Shasta and Tehama Counties lie within the Sacramento Valley, in the Great Valley
geomorphic province. The province extends throughout the Great Central Valley of
California. Most of the rocks and deposits are sedimentary, ranging in age from Upper
Jurassic to Recent, with volcanically derived rocks occurring along the eastern valley
margin.
The Great Valley province is a 400-mile-long by 60-mile-wide sedimentary basin. The
geomorphic provinces surrounding the northern Great Valley here include the Coast
Ranges to the west and the Cascade Range to the east. Geologic units cropping out
consist of sedimentary and volcanic deposits of Tertiary and Quaternary age, such as the
Tehama, Tuscan, and Red Bluff Formations. Terrace deposits include the Upper and
Lower Modesto and Upper and Lower Riverbank formations. Quaternary stream channel
alluvium and older alluvium occur in the stream corridor. The Redding Basin to the
north is part of the Sacramento Valley, but separated by uplift along the Battle Creek
fault zone and the Inks Creek fold system.
Tehama Formation. Regionally, the Tertiary Tehama Formation (Tte) is composed of
fluvial sedimentary deposits of semi-consolidated pale-green, gray, and tan sand,
tuffaceous sand, silt, and clay. The Tehama Formation has scattered, discontinuous
lenses of gravel that are coarser and more abundant toward the west. The clast lithologies
indicate that they were derived from the Coast Ranges and Klamath Mountains to the
west and northwest (Russell, 1931). The formation has a low regional dip towards the
center of the valley and the Sacramento River and is several thousand feet thick. The
Tehama Formation becomes finer away from the mountains of origin. In general, the
Tehama Formation forms rounded hills with moderate relief and has a thin soil cover.
Along the river at and below Red Bluff, the Tehama forms erosion resistant banks that
delineate geologic control in those areas.
The Tehama Formation is exposed along the west bank of Lake Red Bluff in the lower
part of the lake. The dam is founded on this formation here. More Tehama is exposed
downstream below this reach, specifically at Woodson Bridge, Hamilton City, and as far
downstream as Ord Ferry and below.
Tuscan Formation. The Pliocene Tuscan Formation (Tt) outcrops primarily along the
eastern side of the valley to the Sacramento River, but is a very small player below Red
Bluff. The Tuscan consists of interbedded lahar deposits, volcanic conglomerates, and
fluvial volcanic sandstones and siltstones. In general, it is intercalated with the Tehama
Formation along the axis of the Sacramento Valley. The Tuscan outcrops on the banks of
the eastside tributaries primarily. A single outcrop may or may not be in the lower left
bank at RM 232, where the river smashes directly into a tall vertical bank of consolidated
gravel underlain by ashy deposits.
Red Bluff Formation. The Pleistocene Red Bluff Formation (Qrb) crops out in the
northern part of the valley as a veneer or pediment surface overlying the Tehama and
Tuscan Formations. The Red Bluff Formation consists of very-coarse gravel with a red
(2.5-5YR) color, and a clay, sand, and silt matrix. The Red Bluff Formation west of the
Sacramento River was derived from metamorphic rocks of the Coast Ranges and
Klamath Mountains. A volcaniclastic fanglomerate on the eastern side of the Sacramento
River along Mill Creek, was derived from the Tuscan Formation and lava flows and is
correlated with the Red Bluff Formation in the west. The Red Bluff Formation is
overlain by the Rockland ash bed that has been dated as 0.4 Mya. Maximum thickness of
the Red Bluff is measured at 15 feet.
The Red Bluff Formation is exposed on the top of the Tehama along Lake Red Bluff,
from which the formation and the town got its name. The Red Bluff also occurs along
the valley east side. The Red Bluff originally consisted of a uniform, gently sloping
surface. Deformation of this surface is the primary indicator of Quaternary structural
deformation, including the Corning Dome, Inks Creek fold system and the Battle Creek
Fault.
Terrace Deposits. The river and major tributary streams have developed a series of
terrace levels flanking the stream channels. These terraces stair-step up in elevation away
from the active channel, with the upper terraces being the oldest.
Terrace deposits are typically complexly intertwined, and each mapped terrace may have
several minor deposits of different age and elevation associated with it. These are
typically not differentiated.
The four Pleistocene terraces that occur in the area, from oldest to youngest, are the
Lower Riverbank, Upper Riverbank, Lower Modesto, and Upper Modesto. These
terraces have been correlated by their absolute age, soil stratigraphy, and geomorphic
expression to the Riverbank and Modesto Formations of the San Joaquin Valley (USGS,
1984).
Terrace deposits are older and above present stream channel deposits. They average
about 6 to 10 feet thick but may exceed 20 feet in places. The lower half or two-thirds of
the deposit is similar to the stream alluvium. The upper part is generally finer, and
consists of a flood plain deposit of organic material, clay, sand, and silt. Terrace deposits
are abundant along the Sacramento River and tributaries such as Red Bank and Mill
Creeks.
The lower member of the Riverbank Formation (Qrl) is lithologically similar to the Red
Bluff Formation and has nearly the same red color. It consists of gravel, sand, silt and
clay. It occurs on the higher of two flat terraces that have been cut and filled into the
surface of the older Red Bluff and/or Tehama and Tuscan Formations. The deposits are
generally weathered and have a matrix generally rich in clay and silt.
The upper member (Qru) is younger. It formed during a long period of stable climatic
conditions. This member occurs as extensive flat stream terraces along most of the
westside and some of the eastside tributaries. Soils developed on the member display
medial development with strong textures. The soil contains a B-horizon and local
hardpan but profile development is not as great as on the lower member.
The upper member occurs extensively along westside tributaries and the lower member
occurs in smaller areas adjacent to the upper member.
The lower member (Qml) of the Modesto Formation consists of unconsolidated, slightly
weathered gravel, sand, silt, and clay. It generally has a silt layer on top that is several
feet thick. It is similar to the Upper member except that the soils created from this unit
do contain a faint B-horizon. The unit varies in thickness, but is generally less than 20
feet thick.
The upper member (Qmu) is composed of unconsolidated, unweathered gravel, sand, silt,
and clay. It forms alluvial fans along the east side of the Sacramento Valley from Red
Bluff to Oroville. Extensive deposits also occur along the Sacramento River and most
west-side streams. Soils at the top of the member have A/C horizon profiles, lacking the
B-horizon. Both the upper and lower members border existing channels and are
generally less than 20 feet thick.
The upper Modesto is the low terrace along the river and tributaries including the eastern
side of the river. There are a few exposures of Modesto terrace along this stretch of the
river.
Surficial Deposits. Quaternary surficial deposits in the area include floodplain deposits,
point bar deposits, oxbow lake deposits, basin deposits, and active stream channel
deposits.
Stream channel deposits (Qsc) are un-weathered gravel, sand, and silt in the channel of
present day stream and river systems. Point bar deposits occur on the inside of meander
bends and are differentiated only by the mode of deposition.
Floodplain Deposits (Qfp) are sand, silt and minor lenses of gravel deposited by floods
and during high water stages. These deposits form low but extensive surface adjacent to
the river channel. These deposits are generally highly erodible, so river banks composed
of this deposit generally have high erosion rates. The photo below shows floodplain
deposits with bank swallow nests, with a distinct contact with point bar deposits below.
Stream Channel Deposits (Qsc) include as a subgroup Qpb, or point bar deposits. These
are geomorphically distinct deposits that form on the inside of eroding bends. They
typically grade from gravel on the upstream end of the bar to sand on the downstream
end. As the river meanders and moves farther away, the younger deposits become finer.
When the river returns later, this characteristic deposit may be recognized in eroding
banks.
Tectonic Setting. The area is in the northern part of the Sacramento Valley in the Great
Valley Geomorphic province. This province includes a thick sequence of marine and
continental sedimentary and volcanic rocks in a large, elongated northwest-trending
structural trough. The trough is floored with basaltic and ultramafic oceanic crust and
mantle. The age of the deposits ranges from Jurassic to Recent. The trough is a region of
relative tectonic stability that has persisted in approximately its present structural form
throughout most of Cenozoic time.
Plate tectonics have played a major role in the tectonic development of California. From
late Jurassic to mid-Tertiary, the eastern Pacific oceanic lithosphere (Farallon plate) was
subducted beneath the western margin of the North American continental plate. This
subduction resulted in the formation of an arc-trench system that included an accretionary
prism, a forearc basin, and a volcanic-plutonic magmatic arc. Today these terranes are
represented by the Franciscan Complex, the Great Valley Sequence, and the Klamath and
Sierran plutonic/metamorphic belt. Throughout Cretaceous time rocks eroding from the
surrounding plutonic and metamorphic belts were deposited by submarine turbidity
currents into the deep forearc basin. These sediments, the Great Valley Sequence,
continued to accumulate, filling the forearc basin to near sea level by Paleogene. During
this same period, ocean floor and trench deposits of the Franciscan Complex were being
dragged down by the Pacific plate, and under thrust in a wedge against the continental
margin and beneath the Great Valley sediments. As more oceanic material was deposited
beneath the continental plate, the accretionary wedge increased in size. Subsequent under
thrusting resulted in the sediments of the forearc basin to be uplifted and tilted to the
south and east.
As subduction ceased during mid-Tertiary, uplift became more rapid and the transition to
a strike-slip regime began offshore in southern California. This transition led to the
formation of the San Andreas Fault. As the San Andreas Fault evolved, the Mendocino
triple junction between the Pacific-Farallon, North American, and Gorda lithospheric
plates began to develop and migrate slowly northward. During this period, the Great
Valley experienced several episodes of uplift and subsidence, until by early Miocene,
most of the northern valley had emerged from the inland seas and was subjected to fluvial
erosion and deposition. Concurrently, volcanic eruptions were occurring along the
northern Sierra Nevada, damming streams and filling narrow valleys with volcanic
debris.
During the Pliocene, continental stream lain sediments of the Tehama and Tuscan
formations were deposited as large coalescing alluvial fans over the Great Valley
Sequence sedimentary rocks at the foot of the emerging Coast Ranges. The Nomlaki
Tuff Member, which occurs locally at or near the base of the Tehama, is an ash fall from
volcanic eruptions that blanketed much of the northern valley about 3.4 million years
ago. Lava flows and mudflows flowed down the Cascades into the Sacramento Valley
from the east, forming the Tuscan deposits.
Eventually the Tehama and Tuscan formations filled the valley with sediments to a depth
up to 2500 feet. Subsequent erosion and re-deposition have formed the present outcrop
patterns of geologic units.
The Mendocino triple junction continued to move northward offshore, structures in the
valley began to simultaneously exhibit compressive deformation along a similar
northward-progressive pattern. Beginning with activity at the Sutter Buttes (2.5 my) and
continuing to the recent activity in the Battle Creek Fault region (0.5 my), the progressive
northward pattern of valley deformation correlates with the latitudinal positioning of the
Mendocino triple junction.
North of the Mendocino triple junction, the Gorda plate is presently subducting beneath
the North American plate. Activity associated with this movement can be seen in the
surface folding, faulting and uplift of the northern Coast Ranges, and in the 152-mile long
zone of intermediate-focus earthquakes dipping eastward below the North American
plate. Beneath the northern Sacramento Valley, several intermediate and deep-focus
micro seismic events correlate with the Gorda plate subduction.
Presently, the northern Sacramento Valley lies between the large-scale right-lateral
transform tectonism of the San Andreas Fault to the west, and the major east-west crustal
extension of the northern Basin and Range province to the east. The current state of
compressional stress is a result of regional forces manifesting their stress regime upon the
valley, rather than localized forces originating within the valley. The direction of stress
may vary locally, but in general, the direction of maximum compressive stress is
approximately northeast-southwest.
Evidence of this stress regime manifests itself as a series of northwest trending folds and
faults along the western Sacramento Valley. The faults dip steeply east, with reverse and
minor left-lateral movement. In the north and northeastern valley, the structural trend
shifts and, folds and faults become oriented in a more east-to-northeasterly direction.
These faults typically dip steeply to the south, with normal offset and minor right-lateral
movement.
Recent studies suggest that uplift along folds paralleling the western valley is active, and
may represent the shallow expression of deeper thrusting. Additional evidence suggests
that this zone of faulting (commonly referred to as the Coast Ranges-Sierran Block
boundary zone) extends the full length of the western valley and is most likely
responsible for the two 1882 Winters/Vacaville earthquakes (Magnitude 6-7) and the
1983 Coalinga earthquake (Magnitude 6.7). Fluvial processes and regional uplift have
formed the terrace and alluvial deposits as they appear today.
SACRAMENTO RIVER TRIP LOG
RED BLUFF DIVERSION DAM TO THE CITY OF TEHAMA
RM 243 TO 229
Map from http://www.sacramentoriver.org showing the trip reach. Yellow areas are
public lands managed by the U.S. Fish and Wildlife Service.
River Mile 243: Red Bluff Diversion Dam- The put-in is on river left below the
Diversion Dam. Exiting I-5 in Red Bluff at the Highway 36 East exit, take the first right
at Sale Lane where McDonalds Restaurant is located. Drive to the end of Sale Lane and
enter the USFS Mendocino Forest Red Bluff Recreation Area. Boat launching for the
lake is at the right. At the Sacramento River Discovery Center, turn left, go past
campground to the boat launch.
Red Bluff Diversion Dam- The Sacramento Canals Unit of the U.S. Bureau of
Reclamation Central Valley Project was designed to provide irrigation water to about
100,000 acres in Tehama, Glenn, and Colusa Counties. The dam is a gated concrete weir
structure 52 feet high and 5,985 feet long that diverts a maximum of 3,030 cfs into the
Tehama-Colusa and Corning canals. Work began on the dam in 1962 and was finished in
1964. See www.usbr.gov/dataweb/html/sacramento.html for more information.
The dam blocks the river and interferes with fish moving both upstream and downstream.
A fish ladder on each side, and a temporary subsurface opening in the center of the dam
improved migration problems, but led to a problem with predatory pike-minnows. Since
1987, the dam gates were opened during the winter, but presently are opened between
September 15 and May 15 to reduce the effect on fish.
Downstream winter-run Chinook are migrating downstream after the gates are closed and
still affected by the turbulence and predation problem below the dam. Upstream
migrating white and green sturgeon also appear to be held up by the dam.
There is a project afoot to remove the dam and replace the diversion capacity with a
series of low-lift screw pumps.
Fish Ladders and Fish Screens- Viewing platform on the left abutment has a video
screen to monitor fish moving up the ladder. A similar ladder exists on the right
abutment, and a temporary opening is maintained on the center gate when the rest of the
gates are down.
Tehama-Colusa and Corning Canals- The Tehama-Colusa Fish Facilities at the head
of the canal consists of a number of rotating screens and a bypass facility that allows
downstream and upstream migrants to pass the dam. A sediment settling basin was
constructed at the head of the canal. The TC canal is 110.9 miles long and follows the
west side of the valley all the way to Yolo County. The diversion capacity is 2.530 cfs.
The Corning Canal diverts water from the TC canal settling basin by lifting up to 500 cfs
of water 56 feet at the Corning Pumping Plant. These features are shown in the aerial
photo below.
Sacramento River Discovery Center- The center is an educational facility dedicated
to providing information on the Sacramento River watershed, its evolution and
dynamism. See the following website for more information
www.fs.fed.us/r5/mendocino/recreation/srdc
River Safety- This reach of the Sacramento River is considered Class I in a
classification system from I being the easiest to VI being the most difficult. It has riffles
but no rapids, and is navigable by canoes, rafts, and boats. Shallow riffles and snags
make propellers inadvisable. Despite the easy nature of the river, snags and overhanging
vegetation can be extremely dangerous if the boat becomes entangled or pinned.
Lifejackets should be worn, and attention to navigation is important to prevent accidents.
River Mile 242L: Bank Protection of the Sacramento River Bank Protection Project.
This project, between Red Bluff and Chico Landing, was authorized by Congress in
1963, and resulted in over 83,000 linear feet of rock riprap being installed in this 50 mile
reach. The plan was to protect every bend, thereby “locking in” the river. Concern over
the Valley Elderberry Longhorn Beetle resulted in the cessation of construction in the
early 1980’s. The last length of riprap was installed in 1983 at RM241. More than
several miles of riprap have been bypassed by the river, and presently occurs in sloughs
and side channels.
Bank protection causes changes in bank morphology, including channel narrowing and
deepening. Bank protection may also increase the tendency of a river meander to cut off.
Also note scour hole at the end of the riprap.
River Mile 241R: Bank Protection installed in 1983. Only one tree was left on the bank
after construction. The County of Tehama is responsible for maintaining the riprap by
spraying and removing vegetation. The purpose of removing vegetation was to inspect
the bank, look for damage, prevent roots from displacing rock, and discouraging rodents.
A lack of funds resulted in no maintenance and the growth of streambank vegetation you
see today. There is a recent movement afoot to begin the bank maintenance program
again…….
River Mile 240L: Mouth of Salt Creek
River Mile 240R: La Barranca is part of the U.S. Fish and Wildlife Service Sacramento
River Wildlife Refuge. Several projects are ongoing, including soils studies, fish
stranding reduction work, and others. USFWS lands are shown on the Location map in
yellow.
River Mile 239.5L: Blackberry Island, no longer an island, the old channel has been
filled in and is now a slough. Craig Creek, a distributary channel of Antelope Creek,
emerges at the downstream end of the “island”.
River Mile 239L: Bow River Trailer Park. Sometimes the private boat launch is
available.
River Mile 239R and L: Todd Island. This part of the river is highly dynamic, with
meander scars and oxbow lakes several thousands of feet out on each side of the river
floodplain. Todd Island was an island prior to 1983. A large flood event of that year cut
a new channel across the middle, resulting in two islands. Riprap was abandoned by the
river in both of the old channels. Large gravel deposit on right bank was the old main
channel that filled up during the flood event. Because the filling occurred during a single
event, the gravel deposit was too high above the groundwater table to establish riparian
vegetation. Because bank erosion is highly active here, you will see large gravel point
bars forming on the inside of bends.
River Mile 237L and R: Complex and diverse riparian forest developing and evolving
on the point bar on the inside of the bend, and bank erosion on the right side. The
eroding bank is not uniform but has several geologic units:
Floodplain deposits- consisting of silt and sand in the upper part of the bank.
Point Bar Deposits- exposed on the bar and in the lower eroding bank on the outside of
the bend, and consisting of sand and gravel.
Oxbow Lake Deposits- More clay rich silt, these deposited in abandoned meanders away
from the river, allowing finer clay to settle out. Clay forms a binder, making this type of
deposit more erosion resistant.
River Mile 236L: Hunters Resort. This is a clear demonstration that river front property
is ephemeral in this section of the river. Both the riprap and the resort are now in a
slough. Only a few years ago the resort was on the river.
River Mile 235L: Sacramento Bar. This is also an area of extremely active river
meandering, as well as periodic channel cutoffs. In the 1970s, LeClaire Avenue, about a
mile to the east was prosperous riverfront property protected by U.S. Army Corps of
Engineers riprap. A cutoff occurred across the bend, abandoning LeClaire Avenue. Two
more successive cutoffs have occurred since then.
River Mile 235R: Note tall, mature vegetation, with overhanging vines along the eroding
bank. This part of the bank is an oxbow lake deposit, with erosion resistant clay banks
also capable of retaining moisture. Just downstream are unvegetated banks of a gravelrich point bar deposits. Vegetation is limited by the low moisture retention of the gravel.
River Mile 234.5L: Mouth of Antelope Creek is hidden in the slough. The creek
parallels the river for several miles, following the course of a structural trough. The
Chico Monocline occurs along the base of the eastern foothills. The feature is an active
fault zone characterized by extension faults and down-folding of the valley margin.
Basin deposits occur along Antelope Creek as well, indicating that water may pool here
for extended periods.
Deseret Farms, Spanfelner property. Rapid changes in the flow direction caused by the
cutoffs have resulted in some interesting erosion along the left bank. A few years ago,
the high velocity flow of the river, resulting from the cutoff, flowed perpendicularly into
the bank causing severe erosion. Erosion is still occurring, but at a slower rate because
now the flow angle of incidence is reduced.
River Mile 233R: Mouth of Coyote Creek. The eroding bank at Shasta View Farms
below the confluence was protected with private rock riprap in the early-1990s. The
riprap washed out in a series of flood events beginning in 1994. The property was sold to
the U.S. Fish and Wildlife and planted with riparian vegetation. Note the large size of the
planted trees in less than 10 years.
Coyote Creek is a DWR bank erosion monitoring site. Erosion in the last twelve years
has been quite high, with the river moving westward more than 500 feet. See the figure
below for the successive bank lines since 1986. Also note that the locus of erosion has
moved upstream.
Some of the line work showing bank erosion on this 2004 aerial photograph is hard to
see, but the Spring of 2006 bank line is several hundred feet inland.
A “typical” eroding bank, compiled by averaging all eroding banks between Red Bluff
and Ord Ferry, is about 25 feet tall measured from the deepest part of the river to top of
bank. Approximately 16 feet of this bank consists of a sand-to-gravel point bar deposit,
with about 9 feet of a silt-and-sand floodplain deposit on top. During major flow events,
the banks erode, and the gravel is released back to the river to deposit on riffles and point
bars. DWR estimated that more than 85 percent of spawning size gravel comes from
bank erosion, with the remainder provided by tributaries. This is another powerful reason
for limiting bank protection and allowing banks to erode.
River Mile 232.5L: Multiple Channels, Islands, and Backwater Sloughs caused by active
meandering of the river. These features increase hydraulic and geomorphic diversity,
resulting in more diverse habitat for fish, plants, and wildlife. The diversity in habitat
results in more species occupying the area. Many of the species also have different needs
at different life stages and thereby require complex habitats created by the dynamic river
system. Juveniles of salmon and steelhead generally rear in these off channel
environments. Meandering, erosion and deposition maintains a range in depths to
groundwater, resulting riparian forest species diversity.
River Mile 232L: Tall erosion-resistant banks of the Lower Modesto Formation are
exposed on the left bank. The bank consists of semi-consolidated river deposits,
cemented by clay and volcanic ash. This deposit is considered “Geologic Control”, a
term used to define the extent of the meander belt. The river has not been east of this
point for more than 10,000 years. Geologic control does erode when the river migrates to
the geologic control, but much more slowly. The landowners on the top of the Modesto
terrace installed concrete revetments to keep their houses from eroding into the river.
You can see the riprap at the base and the concrete on the right. It is not clear if the entire
height of the bank is Modesto, or if the lower bank is Tuscan Formation.
River Mile 231L: More geologic control. Upper (geologically younger) Modesto
Formation has been protected by rock riprap. These houses are generally protected from
flooding because the Upper Modesto terrace level is above the active floodplain of the
river. Several distributary channels of Mill Creek are part of a large delta that was active
during the last glacial period when sediment production and runoff were much higher.
River Mile 230.5R: Mouth of Elder Creek. Elder Creek drains the Sacramento Valley
western foothills. Because of the long, low gradient traverse across the valley, the creek
discharges mostly clay, silt, sand, and fine gravel to the Sacramento River. A delta may
occur for a period of time, but the feature tends to be ephemeral, washed away by the
next high flow on the river.
River Mile 230L: Mouth of Mill Creek. Mill Creek is the only tributary in this reach
that has significant flows all year round. It is fed by snowmelt from Lassen volcano, and
in spring the flow may be milky white from glacial rock flour and ash from the
headwaters. Runs of spring-run Chinook and steelhead use the creek for spawning and
rearing. Note the coarse gravel at the mouth of the creek. Because of Mill Creek’s
steeper gradient at the base of the eastern volcanic foothills, it is capable of transporting
larger size sediment than Elder Creek to the west. Mill Creek is a significant producer of
spawning size gravel to the river.
River Mile 229.4: Boat Launching Ramp at Tehama River Park and takeout for the trip.
The park is accessed on the east abutment of the Tehama Bridge, by a left turn under the
railroad tracks, then to the right, across the old bridge, then turn left into the park.