GROUNDWATER HYDROLOGY
GROUNDWATER SUBAREAS
Groundwater occurs in the alluvial deposits underlying the alluvial fans, low plains, and basin
flats of the Colusa Basin Watershed. In California’s Groundwater Bulletin 118, DWR (2006)
recognizes the Colusa Groundwater Subbasin as comprising the part of the larger Sacramento
Valley Groundwater Basin lying approximately under the Colusa Basin Watershed footprint,
being “…bounded on the east by the Sacramento River, on the west by the Coast Range and
foothills, on the south by Cache Creek, and on the north by Stony Creek.”
The base of the Tehama Formation is the base of groundwater-bearing alluvial deposits in the
Colusa Groundwater Subbasin. Therefore the Tehama Formation forms both the bottom of the
subbasin and its western edge where the Tehama Formation contacts the non-water-bearing
Cretaceous marine sedimentary rocks in the western part of the watershed (Figure 1-Geology).
There is no boundary to inflow and outflow from the subbasin on the north, east, and south. The
groundwater-bearing geologic formations in the subbasin include all of the alluvial deposits
overlying the Cretaceous bedrock: the Tehama Formation of Tertiary age and the overlying
Quaternary alluvial fan, flood basin, and alluvial deposits.
The following descriptions of the composition, thickness, and general groundwater-bearing
characteristics of these geologic formations are adapted or paraphrased from DWR (2006) and
augmented with information from other sources. The distribution of these geologic units is also
described in the geology section of this assessment.
Pliocene Tuscan Formation. The Tuscan Formation occurs in the northern portion of the
subbasin where it lies about 400 ft below the ground surface. The Pliocene Tuscan comprises
volcanic mudflows, tuff breccia, tuffaceous sandstone, and volcanic ash layers. Younger layers
of the Tuscan consisting of massive mudflow or lahar deposits have a lower permeability than
the older underlying layers, creating confined groundwater conditions.
Pliocene Tehama Formation. The Pliocene Tehama Formation is the principal water-bearing
geologic unit within the Colusa Subbasin and the larger western Sacramento Valley, where its
reaches a maximum thickness of about 2000 ft (Olmsted and Davis 1961). The Tehama
Formation consists of moderately compacted sandy-silt and clay, with occasional gravel and
sand deposits and cemented conglomerate. Occasional deep sands and thin gravels and thin
gravels constitute a poorly to moderately productive deep water-bearing zone. This alluvium
derived from erosion of the Coast Range and Klamath Mountains and deposited under floodplain
conditions during the Pliocene. The depth to the top of the Tehama Formation is generally about
150-200 ft. Its depth is as much as several hundred ft near the Sacramento River and as little as
50 ft along the western edge of the valley. Deformation including folding and faulting as
expressed in the Corning anticline, the Willows arch, and possibly also the Dunnigan anticline
may affect the movement of groundwater through the Tehama Formation. Quaternary alluvium
has generally not been deformed. Groundwater typically occurs under semiconfined to confined
conditions in the Tehama Formation and unconfined conditions in the alluvial fans and alluvium
(Navigant Consulting, Inc. 2000).
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Pleistocene Modesto and Riverbank Formations. The Riverbank and Modesto Formations are
composed of alluvium derived from dissection by Pleistocene foothill streams of the uplifted
Tehama Formation siltstones and Cretaceous marine sedimentary bedrock. They have been
subsequently dissected by the same streams so that they now form terraces in the foothill valleys
and on the alluvial fans and interfan basin areas lying everywhere upslope from the valley flat.
The Modesto was deposited between 14,000 and 42,000 years ago and the Riverbank was
deposited between 130,000 and 450,000 years ago. The Modesto consists of moderately to
highly permeable gravels, sands, and silts ranging in thickness from 10-200 ft. The older
Riverbank terraces occur above the Modesto and consist of poorly to highly permeable gravel
and small cobble interlensed with reddish clay, sand, and silt. The Riverbank thickness ranges
from 1 ft to over 200 ft and yields moderate quantities of groundwater to domestic and shallow
irrigation wells and also provides water to deep irrigation wells with multiple depth perforation
zones.
Holocene Flood Basin Deposits. Flood basin deposits consist primarily of silt and clay
occurring between the natural levees of the Sacramento River and the low alluvial plains to the
west of the natural levees. Flood basin deposits also occur between abandoned channel ridge
deposits on alluvial fans and covering broader areas of low-gradient plains lying between the
alluvial fans and where the alluvial fans are not well developed, referred to elsewhere in this
assessment as interfan basin areas. The basin deposits are thin on the low-gradient plains along
the edge of the basin flat lands, but may reach hundreds of ft in thickness underlying the valley
flat. These deposits are clay-rich and of low permeability, and generally yield low quantities of
water to wells. Groundwater quality is also low from some depths in some basin deposits.
Holocene Alluvium. The recent alluvial deposits occur along the foothill streams and within the
natural levee and gently-sloping floodplain deposits bordering the western edge the Sacramento
River, and extend from the river into the Colusa Basin along the courses of the river’s
distributary sloughs. Recent alluvium consists of unconsolidated well sorted to poorly sorted
gravel, sand, silt, and clay. The maximum thickness of the recent alluvium is generally up to 80
ft (Helley and Harwood 1985) but it is as much as about 130 ft in the Sacramento River north of
Colusa (Navigant Consulting, Inc. 2000).
DWR (2006) describes the subareas of the Colusa Groundwater Subbasin as follows:
Stony Creek Fan. The Stony Creek Fan occupies the northern extent of the subbasin and
extends from the Black Butte Reservoir to the City of Willows, northeast from the City of
Willows to the Sacramento River, and north beyond the Tehama County line. The geologic units
within the fan area include Holocene alluvial deposits, Pleistocene deposits of the Riverbank and
Modesto formations, and Pliocene deposits of the Tehama and Tuscan formations.
Holocene alluvial deposits are observed along Stony Creek to the north and along the Sacramento
River to the east. Modesto and Riverbank deposits extend to the east along Stony Creek and
south and southeast within several ancestral stream channels (DWR 2000). Older alluviated
floodplain and channel deposits reach a thickness of 150 feet at Stony Creek and 110 feet along
the Sacramento River.
Thick clays of the upper Tehama formation underlie the intermediate water-bearing zone of the
Stony Creek plain at a depth of 300 feet, rising to a minimum depth of 40 feet on the axis of the
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Willows anticline. Wells installed 4 miles east of Highway 99W intersect occasional Tehama
formation gravels between 225- and 625-ft depths.
Tuscan Units A, B, and C are believed to extend into the Colusa Subbasin north of the City of
Willows. The sediments of the Tuscan Formation interfinger with the sediments of the Tehama
Formation in the subsurface (Lydon 1969). The degree of hydraulic conductivity between the
Tuscan Formation, the Tehama Formation, and the overlying Stony Creek fan deposits has not
been well established.
Willows-to-Williams Plain. Basin deposits overlie much of the flat alluvial plains in the area
between Willows and Williams. Permeabilities of the near-surface soils are extremely low.
Riverbank deposits are observed along the western subbasin boundary north of Maxwell. The
interstream areas of the Westside creeks contain little gravel and are underlain by poorly
pervious, occasionally alkaline, claypan soil. The Tehama Formation contains little gravel and is
not an important water-bearing material in this region.
Arbuckle and Dunnigan Plains. Quaternary surface deposits of alluvium, Modesto, and
Riverbank formations and basin deposits in the Arbuckle and Dunnigan plains occur east of
Hungry Hollow and Dunnigan hills from Williams to Cache Creek. Basin deposits overlie older
alluvial deposits. The region north of Arbuckle is alluviated to depths of 20- to 60-feet with
moderately to highly permeable sands and gravels from Sand and Cortina creeks. This zone
extends east of highway 99W and, in the College City area, appears to be Sacramento River
deposits. The area between Salt and Petroleum creeks is composed of poorly to moderately
permeable gravels, clayey sands, and silts. Petroleum and Little Buckeye creeks have deposited a
thin, moderately to highly permeable sandy gravel and sandy silts over older stream and terrace
alluvium.
The area in the vicinity of Zamora is underlain by a homogeneous section of gravels, sand, and
interbedded clays to minimum depths of 450 feet. Water producing members range from 25- to
35-percent of total material penetrated. Well production is high within gravel channels. A poorly
to highly productive water-bearing zone consisting of alder alluvial deposits and Tehama deposits
on the western and southwestern edges of the Arbuckle Plain ranges in depth from 100- to 300feet. The zone thickens easterly to depths of 400- to 450-feet.
Tehama deposits coarsen in this area and are an important water-bearing unit. The upper 800- to
900-feet contains 10- to 13-percent fine pebble gravel with a well-sorted, fine to medium sand
matrix. This portion of the Tehama Formation is highly pervious, loose, and well bedded. The
gravel beds range from 5- to 20-feet in thickness and are well confined within a silt and clayey
silt section.
Cache Creek Floodplain. Holocene stream channel deposits are observed along the entire extent
of Cache Creek (DWR 2000). The Cache Creek area is alluviated with floodplain deposits which
are exposed north of the town of Yolo and extend to Knights Landing. The relative proportion of
sand and gravel for the depth interval of 20- to 100-feet is approximately 27 percent.
Between depths of 100- to 200-feet the proportion is reduced to 24 percent. The percentage of
sand and gravel for deposits extending northward from Cache Creek averages 22 percent for the
20- to 200-ft interval. Farther east the proportion increases to 36 percent for the same depth
interval (Olmsted and Davis 1961). Tehama deposits are penetrated in the depth interval of 100to 200-feet.
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Historical Groundwater Studies and Data
Bryan (1923) appears to have conducted the first comprehensive study of the specific
groundwater resources in the Colusa Basin Watershed. During his extensive geologic studies
and groundwater well monitoring between 1912 and 1914, he noted the presence of small
artesian flows occurring in deep wells from College City northward to Willows, the most
southerly being the Chandler well and the most northerly being the well on the Spaulding
(formerly Rideout) ranch, near Norman station, south of Willows. Both of these wells had a
natural artesian flow of about 3 gallons per minute. Further Bryan (1923) observed:
The largest group of flowing wells in the valley is south of Colusa, along Dry and Sycamore
sloughs. The material encountered consists of thick beds of clays with streaks of fine sand in
which the artesian water is found. The wells range in depth from 100 feet to nearly 1,000 feet.
The pressure is rarely great enough to raise the water more than 2 or 3 feet above the surface of
the ground. In some wells, the water rises only a few inches above the normal water table, and
some of the wells only in winter. These variations in depth and pressure indicate that the beds
underlying the valley are not uniform in structure but that the flows are due to recurring favorable
structural conditions which have their origin in the manner in which valley filling took place.
Flood basins or similar depressions appear to have existed in approximately their present position
during most of the period of valley filling. In these depressions clays and similar impervious
deposits were for the most part laid down, but occasionally streams extended into the basins and
deposited beds of sand. These sands are connected with the sands and gravels of the low plains
and supplied by them with water. Where the level of the ground water in the plains is enough
higher than the surface of the adjacent basin to overcome the friction of flow through the sands,
wells in the basin will overflow. Fluctuations of ground-water level in the plains therefore cause
fluctuations in the flow of certain of the wells. As the difference in altitude of the basins and the
low plains is slight, only small pressures are obtained.
Bryan (1923) provides a detailed summary of the specific geologic conditions affecting depth to
groundwater and well production in each of several areas within or adjacent to the watershed:
Orland-Hamilton, Willows, Williams, Colusa-Meridian, Arbuckle, and Woodland. These
observations are of general interest but too detailed to be reproduced in this assessment. Bryan
(1923) measured depth to groundwater throughout the watershed and published a groundwater
elevation contour map of the Sacramento Valley. The contours in the vicinity of the Colusa
Basin Watershed were from measurements mostly made in the fall seasons of 1912-1913. A
copy of that Fall 1912-1913 groundwater contour map is reproduced in this assessment as Figure
2b-Groundwater.
The Colusa Basin Appraisal prepared by DWR (1990) includes a useful summary analysis of
groundwater elevation trends from Spring 1975 to Spring 1998 that reflected the substantial
groundwater recovery that followed from the imported irrigation water by the Tehama-Colusa
Canal in the 1970s. These results are summarized below and compared to updated groundwater
elevation trends for 4 of the representative groundwater wells.
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Current Groundwater Management
Sufficient data exist for monitoring changes in groundwater storage and to provide baseline data
for evaluating future groundwater management efforts. DWR monitors groundwater levels in 98
wells approximately semi-annually and maintains up-to-date published databases of period of
record well data (DWR 2006).
Groundwater management in the Colusa Basin Watershed is complicated by multiple
overlapping jurisdictions and water rights issues. Each of the 3 counties with lands in the
watershed has completed, or is in the process of completing, an individual county-level
groundwater management plan.
Glenn County adopted its Groundwater Management Plan 15 February 2000. For more
information about the Glenn County Groundwater Management plan the reader is directed to:
http://www.glenncountywater.org/management_plan.htm.
Yolo County adopted its
Groundwater Management Plan 6 June 2006. According to a March 26, 2008 press release from
Glenn County titled “Glenn County Groundwater Update”:
The semi-annual spring groundwater level measurements for Glenn County made by the
California Department of Water Resources, Northern District (DWR) were completed during the
week of March 10-14, 2008. Spring measurements are the basis for groundwater level Basin
Management Objectives (BMO) established to determine groundwater safe yield in many
groundwater management sub-areas of the County.
During the time of measurement, 8 wells within the County that utilize spring measurements for
BMO compliance were below average for this time of year. As a comparison, 16 wells were
below average at the same time last year. Overall, groundwater levels are much improved from
last year with an average 4 to 5 feet above where they were last year at this time.
Lower than average groundwater levels are the result of insufficient rainfall during the winter and
spring months, accentuated by the need for early irrigation to permanent crop plantings
throughout the County. Precipitation and surface application of irrigation water are the primary
sources of recharge in our area to meet the needs of the majority of wells used for irrigation. As
the irrigation season progresses, groundwater levels will experience seasonal fluctuation, which
may cause sporadic difficulty during the peak irrigation season. Keeping this in mind, consider
any and all methods of conservation available to you and remember your neighbor may be
pumping the same time you are.
BMO’s for groundwater levels were established and adopted by the Board of Supervisors in June,
2001. Currently, all of the wells utilized for BMO compliance are for domestic or agricultural
use. Over the years, there have been many dedicated monitoring wells installed by the County
and Water Advisory Committee (WAC) member irrigation districts to monitor groundwater
levels and quality. The intent of the monitoring wells is to develop a monitoring network
independent from these production wells. During the summer of 2007, 21 distinct aquifer zones
from dedicated monitoring wells throughout the County were utilized to establish Summertime
BMO’s for groundwater level. These established levels are considered interim until they are
finally adopted. The WAC is in the process of incorporating these wells towards the development
of Countywide BMO’s for spring, summer, and fall.
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Current and historic groundwater levels in our region can be viewed on DWR’s Water Data
Library. Their web page is: http://wdl.water.ca.gov/gw/map Point to Glenn County and navigate
regionally from there. Butte County has developed a regional groundwater information data base
program that provides access to groundwater-related information for agencies as well as
interested parties with information relating to established BMO’s for groundwater elevation,
water quality, and land subsidence monitoring. The website address for access to the program is:
http://bc-gis-ims-02/bmoic3”
Colusa County initiated the process of preparing a Groundwater Management Plan in February
2007. This planning process is expected to continue through 2007 and conclude in the spring of
2008. A public draft Groundwater Management Plan is currently undergoing public review and
comment and is expected to be adopted by the Colusa County Board of Supervisors in July 2008.
The adopted plan will serve as a long-term guide to manage the groundwater resources in Colusa
County.
Other groundwater management plans covering areas within the watershed include those adopted
by Glenn-Colusa Irrigation District (adopted 26 May 1995), Dunnigan Water District (adopted
15 February 2001); and Reclamation District No. 787 (adopted 16 November 2005).
Groundwater Level Trends
Bryan (1923) monitored the natural and pumping influenced fluctuations of the groundwater
table of the Colusa Basin during 1912-1913, observing:
The annual fluctuations of the water table are large. The rise begins in September and is gradual
until the coming of the rains, when the rate of increase is more rapid until some time in March.
Beginning about in March the water falls until, in the latter part of June, it reaches the summer
level, which is nearly constant except when affected by pumping. The characteristic fluctuations
in the basin lands are shown in figure 5, which gives the average depths to water observed weekly
in 24 wells in Colusa Basin. The curve is very similar to the curves given by Lee for the moist
lands in Owens Valley. The summer low stage is more protracted, however, and the rise and fall
before and after the winter rains are much sharper. The rise of ground water in the fall before the
winter rains begin is due chiefly to the decrease in loss by evaporation with cooler weather, while
replenishment by percolation from higher levels continues. In the plains areas, where depth to
water is 15 to 25 feet in summer, the winter rise brings the water within 5 to 15 of the surface.
Note that figure 5 referred to by Bryan shows an annual average groundwater elevation
hydrograph showing that the groundwater dips to about 4 ft below the ground surface in JuneOctober and maintains near about 1 ft below the ground surface during February-March.
As irrigated acreage increased through the 1960s, concurrently increasing groundwater
withdrawals generally resulted in gradually lowering groundwater elevations and, in some areas,
land subsidence. The Tehama-Colusa Canal began making deliveries to Glenn, Colusa, and
Yolo counties in the 1970s. This imported water resulted in reduced groundwater withdrawals in
some areas allowing groundwater elevations to rise up to 40 ft west of Willows and as much as
30 ft in the vicinity of Arbuckle between 1975 and 1988 (Figure 1-Groundwater). Navigant
Consulting, Inc. (2000) suggested that relatively stable groundwater levels between the Colusa
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Basin Drain and the Sacramento River during that same time interval may be maintained in part
by seepage from the Sacramento River.
According to DWR (1990) groundwater elevations ranged from 20 ft above sea level near
Knights Landing to about 220 ft above sea level near Orland in Spring 1988 (Figure 2Groundwater) and declined during the 1988 irrigation season in amounts varying by watershed
location (Figure 3-Groundwater). The groundwater table dropped about 10 ft in 2 Glenn
County locations: one centered about 1.5 mi north of Artois and the other about 2 mi northwest
of Willows. There was a 15-ft decline centered about 3 mi northeast of Williams and numerous
10-ft depressions along the fringe of the low plains from Williams to Dunnigan. A 25-ft
depression occurred just west of the Colusa Basin Drain about 5 mi northeast of Dunnigan.
DWR (1990) noted that these seasonal pumping depressions were not significant compared to
others that have developed in the larger Sacramento Valley Groundwater Basin. DWR (1990)
also noted that where there are rather minor seasonal groundwater fluctuations (about 5 ft is
considered minor) it reflects a general lack of groundwater storage space or near full
groundwater conditions which contributes to winter rainfall runoff and associated flood
management problems along the western edge of the Colusa Basin.
It is notable that the 5-ft and 10-ft seasonal groundwater elevation depressions that occurred
along the eastern edge of the low alluvial plains in 1988 along are similar to those Bryan (1923)
observed in this vicinity during 1912-1913.
In the latest update of California’s Groundwater Bulletin 118, DWR (2006) concluded generally
that neither the seasonal fluctuation nor long-term trend appeared to indicate overdraught:
Review of hydrographs for long-term comparison of spring-spring groundwater levels indicates a
slight decline in groundwater levels associated with the 1976-1977 and 1987-1994 droughts,
followed by recovery to pre-drought conditions of the early 1970’s and 1980’s. Some wells
increased in levels beyond the pre-drought conditions of the 1970’s during the wet season of the
early 1980’s. Generally, groundwater level data show an average seasonal fluctuation of
approximately 5-feet for normal and dry years. Overall there does not appear to be increasing or
decreasing trends in groundwater levels.
Representative Period of Record Groundwater Hydrographs
DWR (1990) reported 1970-1988 groundwater hydrographs for 4 representative wells in the
watershed (Figure 4-Groundwater). DWR (1990) observed that all of the wells except
17N/3W-10C1 showed seasonal groundwater elevation decreases, interannual and multiple-year
down trends associated with the 1976-1977 and 1986-1988 drought periods, and up trends
associated with Tehama-Colusa Canal water imports. Well 17N/3W-10C1 is east of Delevan
and is representative of shallow domestic wells that produce water from the basin deposits
underlying the Colusa Basin, an area that has been receiving water imports from the GlennColusa Canal since the early 1900s. There is little use of groundwater in this area and deep
percolation from surface water irrigation and possibly also seepage from the Sacramento River
keeps the ground water basin full. Naturally high groundwater levels in this vicinity are managed
down slightly to prevent evaporation leading to alkaline soils conditions and thereby improve
rice yields.
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The other 3 wells are representative of groundwater elevation conditions beneath the alluvial fan
deposits to the west of the Glenn-Colusa Canal, all of which showed a general water level
decline during the 1970s prior to the importation of water by the Tehama-Colusa Canal. Figure
1-Groundwater shows that the largest increases in spring groundwater levels form 1975 to 1988
were in the area that is upslope from the Glenn-Colusa Canal and downslope from the TehamaColusa Canal. The water level rise after the Tehama-Colusa Canal imports is due to both
reduced pumping and increased recharge from the applied irrigation water.
To evaluate groundwater level trends since 1988, we downloaded semi-annual groundwater level
data for each of the 4 representative wells evaluated by DWR (1990). We extended each of these
groundwater hydrographs back to 1963 and forward to 2008 (Figure 5-Groundwater). The
alluvial fan wells showed a multiple-year downtrend in elevations during the early 1990s drought
period ranging from 10-20 ft. Levels then gradually recovered to their late 1980s wet years
levels by the end of the wet years at the end of the 1990s. Well 19N/4W-12E1 has maintained
that relatively high level since 1998, but the other wells have declined somewhat. Well
17N/3W-10C1 continues to fluctuate within a narrow band of elevations most recently reflecting
a regular seasonal pattern from about 4 ft below the ground surface in spring to about 8 ft below
the surface in fall. This pattern may reflect recent changes to the groundwater table management
for alkali prevention and rice production.
Land Subsidence
Land subsidence is the lowering of the land surface over a broad area typically caused by
groundwater withdrawal from deep alluvial aquifers. When groundwater is pumped from an
alluvial aquifer, it reduces the pore water pressure in the spaces between grains of sand and
gravel. And reduced water pressure in the sand and gravel causes slow drainage of water from
any clay and silt beds adjacent to the sand and gravel aquifer. These clay and silt beds are
compressible and will compact after water is drained from them, resulting in subsurface and
surface settlement. The subsidence in the Davis-Zamora area appears to be attributable to this
mechanism; deeper clay layers compacted after sand and gravel pore water pressure was reduced
by groundwater pumping (Navigant Consulting, Inc. 2000).
Lofgren and Ireland (1973) identified 2 main areas on the southwestern part of the Sacramento
Valley near Davis and Zamora where land subsidence had exceeded 1 ft by 1973. The USGS
(1973) found that as much as 2 ft of subsidence had occurred in at least 2 areas of groundwater
pumping, east of Zamora and west of Arbuckle (Figure 6-Groundwater). USGS (1973) noted
that roughly 1 ft of subsidence results for each 10-100 ft of groundwater table elevation decline
below historic low levels. The maximum long-term groundwater level decline occurred near
Arbuckle, where a 100-ft pumping depression existed in 1969, before the Tehama-Colusa Canal
began importing water to the watershed (DWR 1990).
Land subsidence monitoring since 1973 showed some local land subsidence in the Davis-Zamora
area during the 1987-1992 drought period. Work to relevel the Zamora-Knights Landing line in
1988 revealed 3 ft of subsidence at Zamora, 3.9 ft about 2 mi east of Zamora, and 0.5 ft at
Knights Landing. As of 2000, total subsidence at Zamora was reportedly as much as 6 ft
(Navigant Consulting, Inc. 2000).
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DWR with assistance from the associated counties is currently establishing a cooperative GPS
subsidence network for the Sacramento Valley from Yolo County to Redding. The GPS network
will allow DWR or the county agencies to periodically resurvey the network to determine if and
how much land subsidence is occurring. Such networking will facilitate more cost-effective and
thus more frequent monitoring.
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Colusa Basin Watershed Assessment: Change in
Groundwater Levels Spring 1975-Spring 1988
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N:/Projects/2850-01/Figures/April 2008
Source: California Department of Water Resources, Northern District, Date.
Colusa basin appriasal.
1 - Groundwater
Note: Figure clarity is limited because this figure was scanned from the above
source. Please see the source for better figure clarity.
Colusa Basin Watershed Assessment:
Ground Water Contour Map 1988
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N:\Projects\2850-01\Figures\April 2008
2a - Groundwater
Source: California Department of Water Resources, Northern
District, Date. Colusa basin appriasal.
Note: Figure clarity is limited because this figure was
scanned from the above source. Please see the
source for better figure clarity.
Figure 2b-Groundwater. Excerpt s from Plate IV of Bryan (1923) showing groundwater
elevation contours of the Sacramento Valley including the Colusa Basin Watershed area
measured during 1912-1913.
Colusa Basin Watershed Assessment: Change in
Groundwater Levels Spring 1988 - Fall 1988
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N:\Projects\2850-01\Figures\April 2008
3 - Groundwater
Source: California Department of Water Resources, Northern
District, Date. Colusa basin appriasal.
Note: Figure clarity is limited because this figure was
scanned from the above source. Please see the
source for better figure clarity.
Figure 4-Groundwater. Representative groundwater well hydrographs 1970-1988
(adapted from DWR 1990).
Figure 5a-Groundwater. Representative groundwater well hydrographs 1963-2008.
GLENN COUNTY 21N/2W-9M2
(Source: DWR Water Data Library)
220
200
Groundwater elevation (ft)
180
GROUND SURFACE ELEVATION = 179 ft
160
140
120
100
80
1963
1968
1973
1978
1983
1988
Calendar Years
1993
1998
2003
2008
Figure 5b-Groundwater. Representative groundwater well hydrographs 1963-2008.
GLENN COUNTY 19N/4W-12E1
(Source: DWR Water Data Library)
200
180
GROUND SURFACE ELEVATION = 174 ft
Groundwater elevation (ft)
160
140
120
100
80
60
1963
1968
1973
1978
1983
1988
Calendar Years
1993
1998
2003
2008
Figure 5c-Groundwater. Representative groundwater well hydrographs 1963-2008.
COLUSA COUNTY 14N/3W-11A1
(Source: DWR Water Data Library)
180
160
Groundwater elevation (ft)
140
GROUND SURFACE ELEVATION = 136 ft
120
100
80
60
40
1963
1968
1973
1978
1983
1988
Calendar Years
1993
1998
2003
2008
Figure 5c-Groundwater. Representative groundwater well hydrographs 1963-2008.
COLUSA COUNTY 17N/3W-10C1
(Source: DWR Water Data Library)
160
140
Groundwater elevation (ft)
120
100
GROUND SURFACE ELEVATION = 94 ft
80
60
40
20
1963
1968
1973
1978
1983
1988
Calendar Years
1993
1998
2003
2008
Source: California Department of Water Resources, Northern
District, Date. Colusa basin appriasal.
Note: Figure clarity is limited because this figure was
scanned from the above source. Please see the
source for better figure clarity.
Colusa Basin Watershed Assessment:
Areas of Historical Land Subsidence 1926-1970
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N:\Projects\2850-01\Figures\April 2008
6 - Groundwater