Land Subsidence in the 

Santa, Clara Valley, California, 

as of 1982 

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 497-F 

Land Subsidence in the 

Santa Clara Valley, California, 

as of 1982 

By J.F. POLAND and R.L. IRELAND 

MECHANICS 0 F AQUIFER SYSTEMS 

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 497-F 

A history of land subsidence in the 

Santa Clara Valley from 1916 to 1982 

caused by water-level decline 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1988 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Library of Congress Cataloging-in-Publication Data 

Poland, J.F. (Joseph Fairfield), 1908-

Land subsidence in the Santa Clara Valley, California, as of 1982. 

(Mechanics of aquifer systems) (U.S. Geological Survey Professional Paper 497-F) 

Bibliography 

Supt. of Docs. No.: I 19.16:497-F 

1. Subsidences (earth movements)-California-Santa Clara Valley (San Benito County and Santa Clara County). I. 

Ireland, R.L. II. Series. III. Series: U.S. Geological Survey Professional Paper 497-F. 

QE75.P9 No. 497-F 557.72 s 87-600268 

[QE600.3. U6] [551.3'53] 

For sale by the Books and Open-File Reports Section, 

U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225 
CONTENTS 

Page Page 

Abstract Hydrology-Continued 

Introduction - - - - - - - - - - - - - - - - - - - - - - - - -

Location and general features- - - - - - - - - - - - - - -

Scope of study and purpose of report - - - - - - - - - - -

Well-numbering system - - - - - - - - - - - - - - - - - -

Acknowledgments- - - - - - - - - - - - - - - - - - - - -

Fl 

1 

1 

1 

3 

3 

Recovery of artesian head, 1967-80------------

Land subsidence - - - - - - - - - - - - - - - - - - - - - - -

History of leveling control - - - - - - - - - - - - - - - -

Extent and magnitude of subsidence - - - - - - - - - - -

Economic and social impacts - - - - - - - - - - - - - - -

F18 

21 

21 

23 

30 

33 

33 

39 

39 

40 

42 

43 

45 

Annotated bibliography of reports by U.S. Geological Survey 

authors - - - - - - - - - - - - - - - - - - - - - - - - -

Hydrogeology - - - - - - - - - - - - - - - - - - - - - - - - -

Hydrology - - - - - - - - - - - - - - - - - - - - - - - - - -

Rainfall - - - - - - - - - - - - - - - - - - - - - - - - - -

Ground-water pumpage - - - - - - - - - - - - - - - - - -

Surface-water imports --- ---------------

Decline of artesian head, 1916-66-------------

3 

5 

14 

14 

14 

14 

14 

Monitoring of compaction and change in head - - - - - - - -

Measurement of compaction - - - - - - - - - - - - - - -

Analysis of stresses causing subsidence - - - - - - - - - -

Example of stress-strain graph - - - - - - - - - - - - - -

Computer simulation of aquifer-system compaction - - - - - -

Compaction-subsidence ratios - - - - - - - - - - - - - - - - -

Computer plots of field records - - - - - - - - - - - - - - - -

Selected references - - - - - - - - - - - - - - - - - - - - - -

ILLUSTRATIONS 

' Page 

FIGURE 1. Generalized geologic map of north Santa Clara County - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - F2 

2. Geologic section A-A' from Alviso southeast to Edenvale Hills ------------------------------ 7 

3. Geologic section B-B' from Los Altos east to Milpitas- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 8 

4. Geologic section C-C' from near Los Gatos northeast to Alum Rock --------------------------- 9 

5. Composite log of core hole 6S/2W-24C7 in Sunnyvale ----------------------------------- 10 

6. Composite log of core hole 7S/1E-16C6 in San Jose - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 11 

7-12. Graphs showing: 

7. Consolidation-test curves for samples from core hole 6S/2W-24C7 ------- ------------------ 12 

8. Consolidation-test curves for samples from core hole 7S/1E-16C6 - - - - - - - - - - - - - - - - - - - - - - - - - 13 

9. Cumulative departure of rainfall at San Jose from the seasonal mean for the 106-year period 1874-75 to 

1979-80 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 15 

10. Ground-water pumpage in north Santa Clara County, 1915-80 ---------------- ----------- 15 

11. Surface-water imports to north Santa Clara County, 1955-80 --------------------------- 18 

12. Artesian-head change in San Jose in response to rainfall, pumpage, and water imports - - - - - - - - - - - - - - 20 

13-17. Maps showing: 

13. Generalized water-level contours for spring and summer, 1915, north Santa Clara County------------- 21 

14. Change in water level, 1915-67, north Santa Clara County----------------------------- 22 

15. Network of level lines in the San Jose subsidence area; initial numbering of level lines -------------- 23 

16. Network of level lines in the San Jose subsidence area; numbering of level lines revised to three digits in the late 

1950's - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 24 

17. Times and extent of leveling in the San Jose subsidence area --------------------------- 25 

18. Graph showing artesian-head change and land subsidence, San Jose- - - - - - - - - - - - - - - - - - - - - - - - - - - - 29 

19-21. Maps showing: 

19. Land subsidence from 1934 to 1960, north Santa Clara County - - - - - - - - - - - - - - - - - - - - - - - - - - 30 

20. Land subsidence from 1960 to 1967, north Santa Clara County -------------------------- 31 

21. Land subsidence from 1934 to 1967, north Santa Clara County -------------------------- 32 

22. Profiles of land subsidence, D-D ', Redwood City to Coyote, 1912-69 - - - - - - - - - - - - - - - - - - - - - - - - - - - 33 

23. Profiles of land subsidence, E-E ', Mountain View to Milpitas, 1933-67 - - - - - - - - - - - - - - - - - - - - - - - - - - 34 

24. Profiles of land subsidence, F-F', Los Gatos to Alum Rock Park, 1934-69 ------------------- ----- 35 

25. Diagram of recording extensometer installations - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 36 

26-30. Graphs showing: 

26. Elastic response of multiple extensometers at the Sunnyvale site 6S/2W-24C, 1981-82- -- - - - -- - - - - - -- 37 

27. Measured annual compaction in wells 1,000 ft deep in Sunnyvale and San Jose ------------------ 40 

28. Stress change and compaction, San Jose site------------------------- ----------- 41 

29. Simulation of compaction based on water-level data for well 7S/1E-7Rl (1915-74) and on subsidence measured at 

bench mark P7 - - - - - - - - - - - - - - - - - ::- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 43 

30. Compaction/subsidence ratios versus depth at extensometer wells in north Santa Clara County - - - - - - - - - - 45 

III 
IV CONTENTS 

Page 

FIGURES 31-48. Computer plots showing: 

31. Hydrograph, change in applied stress, compaction, subsidence, and stress-strain relationship, 6S/1 W -23E 1- - F 48 

32. Hydrograph, change in applied stress, compaction, and stress-compaction relationship, 6S/2W-24C4 - - - - - 49 

33. Hydrograph and change in applied stress, 6S/2W-25Cl; compaction and stress-compaction relationship, 

6S/2W-24C4------------------------------------------------- 50 

34. Hydrograph, change in applied stress, compaction, and stress-compaction relationship, 6S/2W-24C3 ----- 51 

35. Hydrograph and change in applied stress, 6S/2W-25Cl; compaction and stress-compaction relationship, 

6S/2W-24C3- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 52 

36. Hydrograph and change in applied stress, 6S/2W-24C4; compaction and stress-compaction relationship, 

6S/2W-24C3 and 6S/2W-24C4---------------------------------------- 53 

37. Hydrograph and change in applied stress, 6S/2W-25Cl; compaction and stress-compaction relationship, 

6S/2W-24C3 and 6S/2W-24C4---------------------------------------- 54 

38. Hydrograph and change in applied stress, 6S/2W-24C7; compaction, subsidence, and stress-compaction 

relationship, 6S/2W-24C3 and 6S/2W-24C7 ------------- ------------------- 55 

39. Hydrograph, change in applied stress, compaction, subsidence, and stress-compaction relationship, 

7S/1E-9D2- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 56 

40. Hydrograph, change in applied stress, compaction, subsidence, and stress-strain relationship, 7S/1E-16C5 -- 57 

41. Hydrograph and change in applied stress, 7S/1E-16C5; compaction, subsidence, and stress-strain relationship, 7S/1E-16C6-11----------------------------- --------------- 58 

42. Hydrograph, compaction, and subsidence, 7S/1E-16C6-11---- -------- --------------- 59 

43. Hydrograph and compaction, 6S/2W-24C3 ---------------------------------- 59 

44. Hydrograph and compaction, 6S/2W-24C4 ---------------------------------- 59 

45. Hydrograph and compaction, 6S/2W-24C7 ---------------------------------- 60 

46. Hydrograph and compaction, 7S/1E-16C5----- ------------------------------ 60 

47. Hydrograph 7S/1E-16C5; compaction 7S/1E-16Cll - - - - - - - - - - - - - - - - - - - - - - -,- - - - - - 60 

48. Hydrograph and compaction, 7S/1E-16Cll ------------ -------- -------------- 60 

TABLES 

Page 

TABLE 1. Ground-water pumpage, north Santa Clara County, 1915-80 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - F16 

2. Surface-water imports to north Santa Clara County, 1955-80 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 19 

3. Annual compaction at compaction-measuring sites in north Santa Clara County - - - - - - - - - - - - - - - - - - - - - 38 

4. Values of parameters used for simulating observed compaction at selected sites in north Santa Clara County ------ 42 

5. Compaction versus subsidence for periods of leveling in north Santa Clara County - - - - - - - - - - - - - - - - - - - - 44 

6. Wells for which records are included in figures 31-42 ----------------------------------- 61 

CONVERSION FACTORS 

The inch-pound system of units is used in this report. For readers who prefer the International System 

of Units (SI), the conversion factors for the terms used are listed below: 

Multiply 

acre 

acre-ft (acre-foot) 

ft (foot) 

gal/min (gallons per minute) 

(gallmin)/ft (gallons per minute per foot) 

in. (inch) 

mi (mile) 

mi2 (square mile) 

By 

4047 

1233 

0.3048 

.003785 

.207 

2.54 

1.609 

2.590 

To obtain 

m2 (square meter) 

m3 (cubic meter) 

m (meter) 

m3/min (cubic meters per minute) 

(Lis)lm (liters per second per meter) 

em (centimeter) 

km (kilometer) 

km2 (square kilometer) 

National Geodetic Vertical Datum of 1929 (NGVD of 1929): A geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called mean sea level. 

NGVD of 1929 is referred to as sea level in this report. 
MECHANICS OF AQUIFER SYSTEMS 

LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, 

CALIFORNIA, AS OF 1982 

By J.F. PoLAND and R.L. IRELAND 

ABSTRACT 

From 1916 to 1966 in the San Jose area of the Santa Clara Valley, 

California, generally deficient rainfall and runoff was accompanied by 

a fourfold increase in withdrawals of ground water. In response, the 

artesian head declined 180 to 220 feet. As a direct result of the artesianhead decline, the land surface subsided as much as 12.7 feet in San Jose, 

due to the compaction of the fine-grained compressible confining beds 

and interbeds as their pore pressures decreased. The subsidence resulted 

in flooding of lands bordering the southern part of San Francisco Bay, 

and the compaction of the sediments caused compressional failure of 

well casings in several hundred water wells. The gross costs of subsidence 

to date are estimated to be $30 to $40 million. 

The recovery of artesian head since 1967 has been substantial. In 

downtown San Jose, the artesian head recovered 70 to 100 feet in the 

8 years to 1975. Recovery of water levels was due to a fivefold increase 

in surface-water imports from 1965 to 1975, favorable local water supply, 

decreased withdrawal, and increased recharge. 

In 1960, the U.S. Geological Survey installed extensometers in coreholes 1,000 feet deep in San Jose and Sunnyvale. Measurements obtained 

from these extensometers demonstrate the marked decrease in annual 

compaction of the confined aquifer system in response to the major head 

recovery since 1967. In San Jose, for example, the annual compaction 

decreased from about 1 foot in 1961 to 0.24 foot in 1967 and to 0.01 

foot in 1973. Net expansion (land-surface rebound) of 0.02 foot occurred 

in 1974. 

INTRODUCTION 

LOCATION AND GENERAL FEATURES 

The Santa Clara Valley is a long, narrow structural 

trough that extends about 90 mi southeastward from San 

Francisco. San Francisco Bay occupies much of its northem one-third. The valley is bounded on the southwest by 

the Santa Cruz Mountains and on the northeast by the 

Diablo Range (fig. 1). The San Andreas fault system is 

a few miles southwest of the valley, and the Hayward fault 

borders the valley on the northeast. Both fault systems 

are active. 

Land subsidence occurs in the central one-third of the 

valley in an area of intensive ground-water development. 

This report discusses only this densely populated central 

one-third of the valley, which extends southeastward 

about 30 mi from Redwood City and Niles to Coyote, at 

the bedrock narrows about 10 mi southeast of downtown 

San Jose. 

The subsidence area is almost wholly in Santa Clara 

County. Southeast of Coyote Hills, the subsidence area 

extends into Alameda County, and north of Palo Alto it 

extends into San Mateo County (fig. 1). 

Santa Clara County extends 30 mi southeast of Coyote. 

Ground water is pumped from wells in this area. Therefore, to avoid confusion, the project area is defined as 

north Santa Clara County when clarification is needed. 

For example, tables of ground-water pumpage and 

surface-water imports listed in this report are for north 

Santa Clara County, as indicated by their titles. 

Minor subsidence also has occurred in the Hollister area 

(not shown). It is reported that as of the late 1960's, subsidence of 1 to 2 ft had occurred at bench marks in 

Hollister (T .H. Rogers, Woodward-Clyde Consultants, 

oral commun., November 1983.) However, Hollister is in 

San Benito County, 10 mi south of the south boundary 

of Santa Clara County, and thus this subsidence is not 

discussed further in this report. 

SCOPE OF STUDY AND PURPOSE OF REPORT 

Since the late 1950's the U.S. Geological Survey has 

carried on a modest study of land subsidence in the Santa 

Clara Valley, financed by Federal funds for study of the 

mechanics of aquifer systems. The study has been similar 

to concurrent studies of land subsidence in the San 

Joaquin Valley (Poland and others, 1975; Ireland and 

others, 1984), but on a much smaller scale. The principal 

field activities of the program have been twofold. First, 

in 1960 the Geological Survey drilled core holes at the 

centers of subsidence in San Jose and Sunnyvale. They 

were drilled to a depth of 1,000 ft-the maximum depth 

tapped by most water wells as of 1960. Cores were tested 

in the laboratory for physical and hydrologic properties 

and for clay-mineral analysis. Results have been released 

F1 
F2 MECHANICS OF AQUIFER SYSTEMS 

in several publications (Johnson and others, 1968; Meade, 

1967). 

Second, in 1960 extensometers (compaction recorders) 

were installed in the 1,000-ft core holes and in nearby 

satellite holes in order to measure the compaction or expansion of the sediments in that depth range and compare it with change in artesian head and with subsidence 

in the same time interval. Aquifer-system compaction and 

expansion and water-level change (change in applied 

stress) have been measured for 22 years. The change in 

artesian head was monitored by the Geological Survey, 

and subsidence was monitored by the National Geodetic 

Survey. These records from 1960 to 1980 are included in 

full in this report as computer-plotted stress-strain or 

stress-compaction relationships (see figs. 31-42). The 

Geological Survey terminated measurements of water 

level and of compaction or expansion at the end of 1982. 

Measurements of these data for the 3 years 1980-82, 

inclusive, have also been included in this report (table 3; 

figs. 43-48). 

122"00' R 1 W R 1 E 

T 

4 

s 

37° 

30' 

T 

5 

s 

T 

6 

s 

T 

7 

s 

37° 

15' 

T 

8 

s 

I 

I 

I 

I -----t---

report 

I 

I 

I 

I 

0 

0 

1 

I 

I - ---t--~--'-"M~A'lt'....,..-c 

5 KILOMETERS 

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I 

EXPLANATION D Alluvium and bay deposits 

~ Santa Clara Formation and assoc- ~ fated deposits 

~ Consolidated rocks 

----Fault-Dashed where approximate, dotted where concealed 

~'Trace of geologic section- See 

figures 2-4 

Types of observation wells and identification numbers 

~M 1 Water level 

:JE 1 Extensometer (listed in tables) 

24C7 

® Well and (or) extensometer 

xP7 Bench mark and number 

FIGURE !.-Generalized geologic map of north Santa Clara County. 
LAND SUBSIDENCE IN THE SANTA _9LARA VALLEY, CALIFORNIA, AS OF 1982 F3 

In addition to the principal field activities, development 

of a one-dimensional mathematical model that calculates 

idealized aquifer-system compaction and expansion was 

a highly significant accomplishment. The model has been 

applied to observed water-level fluctuations and to the 

resulting observed transient compaction and expansion 

behavior of a total thickness interval at several sites in 

the Santa Clara Valley (Helm, 1977). 

The principal purposes of this report are (1) to present 

a summary of measured land subsidence through 1982, 

including the overall extent and magnitude; (2) to report 

the measured annual compaction and water-level change 

from 1960 through 1982 at extensometer sites; (3) to show 

the relationship between water-level change (stress 

change), measured compaction, and subsidence, chiefly by 

use of computer plots of Geological Survey field data; (4) 

to record the yearly pumpage of ground water in north 

Santa Clara County from 1915 to 1980; and (5) to report 

the yearly surface-water imports from 1955 to 1980 via 

the Hetch Hetchy and South Bay Aqueducts. 

Reports and papers published to date on various aspects 

of the Geological Survey study in the Santa Clara Valley 

have been published in several different sources. Therefore, to assist the interested reader, this report includes 

a brief annotated bibliography of published reports prepared by Geological Survey authors as a result of these 

studies. 

WELL-NUMBERING SYSTEM 

The well-numbering system used in California by the 

U.S. Geological Survey and the State of California shows 

the locations of wells according to the rectangular system 

for the subdivision of public land. That part of the number 

preceding the slash (as in 7S/1E-16C6) indicates the 

township (T. 7 S.); the number following the slash is the 

range (R. 1 E.); the digit following the hyphen is the section (sec. 16); and the letter following the section number 

indicates the 40-acre subdivision of the section. Within 

each 40-acre tract the wells are numbered serially, as 

indicated by the final digit. 

In this report, wells are referenced to the Mount Diablo 

base and meridian; all wells are south of the base but are 

both east and west of the meridian. 

ACKNOWLEDGMENTS 

We acknowledge the cooperation of Federal, State, and 

local agencies, private companies, and individuals. All 

leveling data used in the preparation of the subsidence 

maps and graphs and in calculating magnitude and rates 

of subsidence were by the National Geodetic Survey 

(formerly the U.S. Coast and Geodetic Survey). Waterlevel data utilized in this report were chiefly from field 

measurements by the Geological Survey, but the Santa 

Clara Valley Water District was most helpful in supplying records of ground-water levels from its well-measuring programs. The California Division of Highways and 

the San Jose Water Works granted permission to drill 

core holes and maintain compaction-measuring equipment 

on their properties. 

Core descriptions in the field were by W.B. Bull, J.H. 

Green, R.L. Klausing, R.H. Meade, G.A. Miller, and F.S. 

Riley (all of the Geological Survey). J.H. Green prepared 

figures 2, 3, and 4 (geologic sections), figures 5 and 6 (composite logs of core holes), and figure 19 Oand subsidence 

from 1934-60). 

ANNOTATED BIBLIOGRAPHY OF REPORTS BY 

U.S. GEOLOGICAL SURVEY AUTHORS 

1962, Poland, J.F., and Green, J.H., Subsidence in the 

Santa Clara Valley, California-A progress report: U.S. 

Geological Survey Water-Supply Paper 1619-C, 16 p. 

By maps and profiles, this report illustrates the subsidence that had occurred by 1954; bench mark P7 in 

San Jose had subsided 7.75 feet. The first complete 

survey of the bench-mark network was in 1934. Subsidence maps are included for 1934-54, 1940-54, and 

1948-54. 

1962, Green, J.H., Compaction of the aquifer system and 

land subsidence in the Santa Clara Valley, California: 

U.S. Geological Survey Professional Paper 450-D, p. 

175-178. Results of laboratory tests on the compressibility of fine-grained cores from two 1,000-ft core holes 

and records of the fluctuation of artesian head since 

1915 were used to compute the compaction of the confined aquifer system up to the 1960 releveling of the 

bench-mark network. Computed compaction was in 

general agreement with actual subsidence, but the procedure is highly subjective when applied to such heterogeneous deposits. 

1964, Green, J.H., The effect of artesian-pressure decline 

on confined aquifer systems and its relation to land subsidence: U.S. Geological Survey Water-Supply Paper 

1779-T, 11 p. This report summarizes the use of onedimensional consolidation tests on cores and known 

declines of artesian head to compute compaction of finegrained clayey beds. It also describes the use of void 

ratio values derived from one-dimensional consolidation 

tests to compute change in porosity in response to 

change in effective stress. 

1967, Meade, R.H., Petrology of sediments underlying 

areas of land subsidence in central California: U.S. 

Geological Survey Professional Paper 497 -C, 83 p. This 

paper describes petrologic characteristics that influence 
F4 MECHANICS OF AQ"Q_IFER SYSTEMS 

compaction of water-bearing sediments in the San 

Joaquin and Santa Clara Valleys, including particle size, 

clay minerals, and associated ions. The analytical procedures used in the clay-mineral studies are discussed. 

In addition, particle-size data for cored sediments in the 

Santa Clara Valley are tabulated, as are clay minerals 

and associated ions from fine-grained cored sediments 

and from fine-grained surface sediments (seep. 38-45 

and 63-78). Montmorillonite is the dominant clay 

mineral, comprising between 5 and 25 percent of the 

sediments, depending on the general fineness of their 

particle size. Calcium is the dominant exchangeable 

cation. 

1968, Johnson, A.I., Moston, R.P., and Morris, D.A., 

Physical and hydrologic properties of water-bearing 

deposits in subsiding areas in central California: U.S. 

Geological Survey Professional Paper 497-A, 71 p. To 

provide information on the water-bearing deposits in 

the areas of maximum subsidence (in San Jose and in 

Sunnyvale), two core holes were drilled in the Santa 

Clara Valley. In all, 87 samples from these core holes 

were tested by the Geological Survey for physical and 

hydrologic properties, and 21 samples were tested by 

the U.S. Bureau of Reclamation for engineering properties, including one-dimensional consolidation tests. 

The report presents core-hole logs and laboratory data 

in tabular and graphic form, describes methods of 

laboratory analysis, and shows interrelationships of 

some of the physical and hydrologic properties. For a 

summary of the results of laboratory analyses, see 

p. 43-45. 

1968, Meade, R.H., Compaction of sediments underlying 

areas of land subsidence in central California: U.S. 

Geological Survey Professional Paper 497-D, 39 p. A 

study, partly statistical, of the factors that influence the 

pore volume and fabric of water-bearing sediments compacted by effective overburden loads ranging from 40 

to 1,000 lb/in2• Paper includes summary of pertinent 

previous studies that identify these factors and that indicate the nature and degree of their influence on compaction processes (p. 3-14). 

1969, Poland, J.F., and Davis, G.H., Land subsidence due 

to the withdrawal of fluids: Geological Society of 

America, Reviews in Engineering Geology, v. 2, 

p. 187-269. A review of the known (1963) examples of 

appreciable land subsidence due to fluid withdrawal 

throughout the world, with a brief examination of the 

principles involved in the compaction of sediments and 

of aquifer systems as a result of increased effective 

stress. Special emphasis is given to subsidence studies 

in the San Joaquin (p. 238-252) and Santa Clara 

(p. 252-262) Valleys and to the Wilmington oil field 

(p. 200-214) in the Los Angeles and Long Beach Harbor 

area. 

1969, Poland, J.F., Land subsidence and aquifer-system 

compaction, Santa Clara Valley, California, USA: in 

Tison, L.J., ed., Land subsidence, v. 1, International 

Association of Scientific Hydrology Publication 88, (is 

now International Association of Hydrological Sciences), p. 285-292. Intensive withdrawal of ground 

water from the confined aquifer system, 800 ft thick, 

in the San Jose area of the Santa Clara Valley has 

drawn down the artesian head as much as 220 ft since 

1915. Resulting land subsidence, which began about 

1916, was 12.7 ft in 1967. Report includes graphs of 

measured compaction, water-level change, and subsidence to 1969 in Sunnyvale and San Jose, log-log plots 

of compressibility of fine-grained sampJes from the 

Sunnyvale core hole, and a map of land subsidence from 

1934 to 1967. 

1972, Poland, J.F., Lofgren, B.E., and Riley, F.S., 

Glossary of selected terms useful in studies of the 

mechanics of aquifer systems and land subsidence due 

to fluid withdrawal: U.S. Geological Survey WaterSupply Paper 2025, 9 p. The glossary defines 25 terms 

as they are used in Geological Survey research reports 

concerned with the mechanics of stressed aquifer 

systems and of land subsidence. Most are terms that 

have appeared in engineering or hydrologic literature, 

but several have been· introduced as a result of the 

Survey's studies. 

1973, Webster, D.A., Map showing areas bordering the 

southern part of San Francisco Bay where a high water 

table may adversely affect land use: U.S. Geological 

Survey Miscellaneous Field Studies Map MF-530, 1 

sheet, scale 1:125,000. Map presents general information about the depth to the top of the saturated zone 

(water table), shown in four depth zones 0-5, 5-10, 

10-20, and >20ft below land surface. Depth zones are 

based on data obtained from more than 1,000 soil 

borings made for foundation engineering studies. The 

problems caused by a shallow water table are also 

discussed. 

1977, Helm, D.C., Estimating parameters of compacting 

fine-grained interbeds within a confined aquifer system 

by a one-dimensional simulation of field observations: 

International Association of Hydrological Sciences, 

International Symposium on Land Subsidence, 2d, 

Anaheim, California, December 1976, Publication 121, 

p. 145-156. A one-dimensional mathematical model that 

calculates idealized aquifer-system compaction and expansion has been applied to observed water-level fluctuations and to the resulting observed transient 

compaction-and-expansion behavior of a total thickness 

interval at several sites in the Santa Clara Valley. For 

established values of total cumulative thickness of finegrained interbeds (aquitards) within the confined aquifer 

system, the weighted average thickness of these inter-
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F5 

beds, and the initial distribution of preconsolidation 

pressure, it is demonstrated that carefully evaluated 

values of the vertical components of hydraulic conductivity and nonrecoverable compressibility can be used 

to predict aquifer-system behavior with reasonable 

accuracy over periods of several decades. The paper 

includes plots of simulated compaction based on measured water level and compaction data at eight sites in 

the Santa Clara Valley for periods of record ranging 

from 12 to 59 years. 

1977, Poland, J.F., Land subsidence stopped by artesianhead recovery, Santa Clara Valley, California: International Association of Hydrological Sciences, International Symposium on Land Subsidence, 2d, Anaheim, 

California, December 1976, Publication 121, p. 124-132. 

From 1916 to 1966, generally deficient rainfall and 

runoff was accompanied by a fourfold increase in 

withdrawals of ground water. In response, the artesian 

head declined 180 to 220 ft, causing the land surface 

to subside as much as 12.7 ft in San Jose, due to compaction of the fine-grained compressible aquitards as 

the pore pressures decreased. From 1967 to 1975 the 

artesian head recovered 70 to 100ft. This water-level 

recovery was due to a fivefold increase in surface-water 

imports from 1965 to 1975, favorable local water supply, 

decreased withdrawal, and increased recharge. Extensometers installed in 1960 to measure change in thickness of the confined system demonstrated the marked 

decrease in annual compaction in response to the major 

head recovery. In San Jose, the annual compaction 

decreased from about 1 ft in 1961 to 0.01 ft in 1973. 

1978, Helm, D.C., Field verification of a one-dimensional 

mathematical model for transient compaction and expansion of a confined aquifer system: in Verification of 

mathematical and physical models in hydraulic engineering: American Society of Civil Engineers, Proceedings of Specialty Conference, College Park, 

Maryland, p. 189-195. Land subsidence due to groundwater withdrawal from a confined aquifer system is an 

expression at land surface of net compaction (vertical 

consolidation) at depth of compressible layers within the 

system. Water-level fluctuations within coarse-grained 

aquifers produce stress changes on the upper and lower 

boundaries of slow-draining aquitards. Within a confined system, any lag in compactive response to such 

a load increase is usually ascribed to slow vertical 

drainage from the aquitards. The emphasis of this paper 

is threefold: First, the author describes the trial-anderror method used to find vertical hydraulic conductivity, K', and nonrecoverable specific storage, S~kv; 

second, the values of these parameters so estimated are 

listed in table 1; and finally, based on these values, 

predictions of critical stress and ultimate compaction 

values are presented. 

HYDROGEOLOGY 

A generalized geologic map of north Santa Clara County 

(the central part of the Santa Clara Valley) is shown in 

figure 1. The map was compiled chiefly from geologic 

maps prepared by Jennings and Burnett (San Francisco 

sheet, 1961), Rogers (San Jose sheet, 1966), and Dibblee 

(Palo Alto 15-minute quadrangle, 1966). The consolidated 

rocks, shown as a single unit on the map, range in age 

from Jurassic to Pliocene; they consist principally of consolidated sedimentary rocks but also include substantial 

areas of metamorphic rocks-the greenstones of the Franciscan Formation, which are probably metamorphosed 

submarine basalt flows (Dibblee, 1966). These rocks are 

highly compressed but yield small quantities of water to 

domestic wells from fractures induced by tensional and 

compressional forces. 

Except for the two major regional faults-the San Andreas and Hayward faults-no attempt has been made to 

include faults on this generalized map because detailed 

geologic mapping was beyond the scope of the study. For 

more geologic detail, in addition to the sources cited, the 

reader is referred to a geologic map published by the 

California Department of Water Resources (1967, pl. 3). 

That map shows subsea contours on the buried surface 

of rocks of the Franciscan Formation for much of the 

valley. From the Dumbarton Bridge southeast to Sunnyvale, the buried surface plunges from 300 to 3,000 ft below 

sea level. 

The Santa Clara Formation of Pliocene and Pleistocene 

age unconformably overlies the consolidated rocks and is 

exposed intermittently along both flanks of the valley. 

Dibblee (1966) designated a type area as the exposures 

between Saratoga and Stevens Creeks, with a type section as exposed in Stevens Creek. About 2,200 ft of the 

Santa Clara Formation is exposed in the type area. Where 

exposed, the formation consists of semiconsolidated 

conglomerate, sandstone, siltstone, and claystone. The 

conglomerate and sandstone are poorly sorted and have 

a fine-grained matrix; thus the formation has a low 

permeability and, where exposed or at shallow depth, 

yields only small to moderate quantities of water to wells, 

rarely enough for irrigation purposes. 

Along the western border of the valley, the Santa Clara 

Formation was warped and folded during the last uplift 

of the Santa Cruz Mountains. Dips of 25 o to 35 ° are common. Beneath the valley the formation may be undisturbed and in part conformable with overlying beds. 

In his map of the Palo Alto 15-minute quadrangle, 

Dibblee (1966) discriminated a geologic unit overlying the 

Santa Clara Formation that he calls "older alluvium." The 

only extensive outcrop covers about 4 mi2 in the Saratoga 

area. He described the unit as stream-laid gravel composed of cobbles and pebbles in a matrix of sand and silt, 
F6 MECHANICS OF AQUIFER SYSTEMS 

derived from adjacent hills, generally undeformed, dissected where elevated, as much as 50 ft exposed, and age 

presumably late Pleistocene. 

Because this unit has been mapped only on the west side 

of the valley and is of little importance in water supply, 

its outcrop area has been combined with that of the Santa 

Clara Formation in the stipple pattern of figure 1. 

Unconsolidated alluvium and bay deposits of clay, silt, 

sand, and gravel of late Pleistocene and Holocene age 

overlie the Santa Clara Formation and associated 

deposits; their upper surface forms the valley floor. Well 

logs indicate that permeable alluvial deposits attain a 

thickness of 1,000 ft or more in the valley trough. Wells 

range in depth from 200 to 1,200 ft (California Department of Water Resources, 1967, pl. 4). The deeper wells 

probably tap the upper part of the Santa Clara Formation, although the contact with the overlying alluvium and 

bay deposits has not been distinguished in well logs 

because of the lithologic similarity. 

Coarse-grained deposits predominate in the alluvial-fan 

and stream-channel deposits near the valley margins, 

where the stream gradients are steeper. The proportion 

of clay and silt layers increases hayward. For example, 

a well-log section extending 12 mi northward from Campbell to Alviso (Tolman and Poland, 1940, fig. 3) shows that 

to a depth of 500 ft the cumulative thickness of clay layers 

in the deposits increases from 25 percent near Campbell 

to 80 percent near Alviso. 

Well yields in the valley range from 300 to 2,500 gallons 

per minute (gal/min), and the specific capacity [(gal/min)/ft 

drawdown] ranges from 10 near the valley margin to 70 

in mid-valley, exceeding 300 in both San Jose and Santa 

Clara (California Department of Water Resources, 1967, 

pl. 6). 

Geologic sections A-A' (fig. 2), B-B' (fig. 3), and C-C' 

(fig. 4) illustrate the general nature of the alluvial waterbearing deposits that underlie the valley floor. Finegrained materials such as clay, silt, and sandy clay, which 

retard the vertical movement of confined ground water, 

constitute the major part of the valley fill near the bay 

(figs. 2, 3). Sand and gravel occur in lesser amounts near 

the bay, but they are more abundant near the valley 

margins, where locally they are predominant. None of the 

distinctive layers or lenses can be traced laterally for mor€ 

than a mile or two. Inspection of the three figures indicates that the well-log section B-B' (fig. 3), which 

traverses mostly lowland areas near the bay, contains a 

preponderance of clay. On the other hand, sections A -A' 

and C-C' (figs. 2, 4) traverse chiefly upland areas, and 

many of the well logs indicate a preponderance of coarsegrained material. 

In the central two-thirds of the valley below a depth of 

150 to 200 ft, ground water is confined. The confinement 

extends northward from the southern part of San Jose 

to Palo Alto and Milpitas and beneath the bay. In much 

of the area of confinement, wells more than 200 ft deep 

flowed in the early years of urban development (see 

fig. 13). The confined aquifer system is as much as 800ft 

thick. Around the valley margins, grotind water is 

generally unconfined, and most of the natural recharge 

to the ground-water reservoir percolates from stream 

channels crossing alluvial-fan deposits. 

The confining member overlying the confined aquifer 

system has a thickness of 150 to 200ft (see fig. 3, central 

part; also see fig. 5). Although predominantly composed 

of clay and silt, it also contains some channel fillings and 

lenses of permeable sand and gravel. This confining 

member supports a shallow water table distinguished by 

an irregular surface. As of 1965-70, the shallow water 

table overlying much of the confined system was less than 

30ft below the land surface (Webster, 1973). At least near 

the bay, the shallow water table did not fluctuate appreciably during the period of prolonged artesian-head 

decline terminating in 1966, indicating little change of 

stress in the shallow confining member. j 

In 1960, the Geological Survey drilled core holes 1,000 

ft deep at the two centers of subsidence: in Sunnyvale 

(well6S/2W-24C7) and in San Jose (well7S/1E-16C6). An 

electric log was obtained for each core hole after coring 

was completed. Graphic logs and generalized lithologic 

descriptions were prepared from the geologists' logs made 

at the drill site, supplemented by interpretation of the 

electric log in zones not cored or of poor recovery. These 

three elements were combined to give a composite log for 

each core hole (figs. 5, 6). The depths of the samples tested 

also were plotted on the composite logs. 

In all, 87 samples from these core holes were tested by 

the Geological Survey in the laboratory for physical and 

hydrologic properties, including particle-size distribution, 

specific gravity of solids, dry unit weight, porosity and 

void ratio, hydraulic conductivity (normal and parallel to 

bedding}, and Atterberg limits (Johnson and others, 1968, 

p. A1 and tables 5 and 6). 

Compressibility characteristics of fine-grained compressible layers (aquitards) can be obtained by making 

one-dimensional consolidation tests of "undisturbed" finegrained cores in the laboratory. As one phase of the 

research on compaction of the aquifer system, laboratory 

consolidation tests were made by the U.S. Bureau of 

Reclamation on 21 selected fine-grained cores from the 

two core holes (see sample depth and number in composite 

log). Properties tested included the compression index, 

Cc, a measure of the nonlinear compressibility of the sample, and the coefficient of consolidation, Cv, a measure 

of the time rate of consolidation. Complete results of these 

laboratory tests have been published (Johnson and others, 

1968, tables 8 and 9, and figs. 12 and 21c). The 21 samples 

tested spanned a depth range from 141 to 958 ft below 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F7 

land surface. The range of the compression index, Cc, was 

small compared with the range in the San Joaquin Valley: 

the maximum value was 0.33, the minimum was 0.13, and 

the mean was 0.24. Of the 21 samples, 15 had Cc values 

falling between 0.20 and 0.30. This suggests that the 

nonlinear compressibility characteristics of the aquitards 

in the confined aquifer system do not vary widely. The 

NW 

ALVISO 

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sample, can be obtained graphically from the e-log p 

5 KILOMETERS 

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500 

600 

700 

800 

900 

1000 

·~ 

·.~_6, 

v ·~ 

~ -.-

i:D -o.= -:_-_-

=~- ~ •:-;:;; ~:~ ~--::: 

~l,~ -;-= -:-:::- _:.. :::-:..: -:::-::- ~ 

-~"- illim~ ~~~ ~~~ ~ :-;:=: _._._ 

·=- -·- -,_ 

~ 

See figure 2 for explanation 

0 

0 

2 3 4 5 KILOMETERS 

2 3 4 

.... en en ...... .....,. I 

5 MILES 

.... 

en 

...... 

I 

=.:=.:.= .:..--:-:::.:-: -_-__ ~-:- ----_ 

~~ ~-=.:.-=-==-

See figure 1 for 

location of section 

FIGURE 4.-Geologie section C-C' from near Los Gatos northeast to Alum Rock. 

~ a: CO L0 

N ("') I I w w 

.... 

en 

...... 

NE 

C' 

ALUM 

ROCK 

F9 
FlO MECHANICS OF AQUIFER SYSTEMS 

SAMPLE NUMBER SPONTANEOUS GENERALIZED LITHOLOGIC 

POTENTIAL ~~~:~~~:y GR~;:IC lfrom co~E~!!'~~~. drilling 

USBR 1 USGS 5 millivolts AM -16 in. FEET performance, and lllctric logsl 

~------~~--------~--~-~~~+~--~~------------~~50~---o-.~.-------~~~~~~~~~---------1 

60 CAL10 

23 L255 

60 CAL 20 

23 L256 

23 L 258 

23 L 257 

60 CAL 30 

23 L259 

23 L 261 

23 L262 60 CAL 40 

23 L263 

23L265 

60 CAL 50 

60 CAL 60 23 L 267 

23 L269 

60 CAL 69 

500 

0-150 Clay, silty, sandy, and gravely. Olive to blue. 

Calcareous nodules 

150-185 Clay. Greenish gray to olive. Calcareous nodules 

-t-----=:::::::=::::====t- 200-:~.;,-;.: 185-215 Gravel, clayey, silty, and sandy. Greenish gray 

~~~~~~~~~~~~~~~-! 

;-=-~~ 256-318 Clay, silty, sandy, and gravely. Greenish gray 

1------=+--+--~::;;..,,....------~ 300 --~-_:::.:~ to olive brown. Calcareous nodules 

~ 318-328~G~ra~v~el~,s=a~nda--------------1 

328-415 Clay and dt, sandy. Olive gray .to yellowish 

brown. Calcareous nodules 

415-434 Sand, gravelly and . silty. Olive brown to vellow brown 

434-506 Clay, silty, and sandy . Olive gray to yelow 

brown. Calcareous nodules 

r----~5:--t----.~======r- 500 ~ 506-516 Gravel 

!':0~:0. 516-536 Clay, silty, sandy, and graveHy. Ohe gray to 

yellowish brown. Calcareous nodules 

::~-:_- ~-547 Sand, silty and clayey .. Yelow brown to gray 

54 7-6 7 8 Clay and silt , sandy. Oarll greenish gray to olive 

---- brown 

678-742 Clay, silty. Greenish gray 

~~~~~-~-~-~~-------~-4 

-:~=~:-~:~: 742'-752 c~r.:.iltlilc~~o::nn~:.liv• brown to greenish 

752-802 Clay, silty. Oarll greenish gray to olive gray. 

1----""""""1'..:;__+-.....:::.-....:::-------+- BOO~ Calcareous nodules. Gatropod shels at 755-760 It 

~ 802-814 se::,dJ:ta~:W'J::dv· clayey silt. Olive gray 

~ :~ 814-839 Sil'.iod~'f:Y and sandy. Olive gray. Calcareous 

~- 839-845 - ...... ·-.... 

1-----........L..--+-~-....... ,---------+-- 900 --=::.:~ 845-1000 Clay, silty and sandy. Greenish gray to olive brown. 

~ ~ Calcareous nodules 

~----------L----------~------------~-L~--------------------~1000~~-------------------------------~ 

1

~ Prepared by J. H. Green u.s. Bureau of Reclamation 

FIGURE 5.-Composite log of core hole 6S/2W·24C7 in Sunnyvale. 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 

SAMPLE NUMBER SPONTANEOUS RESISTIVITY GRAPHIC GENERALIZED LITHOLOGIC 

POTENTIAL oluns m21m LOG DESCRIPTION 

USBR 1 USGS 5 millivolts AM -16 in. (from core descriptions. drillinQ 

~------------+-------------+-~-~~~·~----~o~o------------------------s~:~~+--F~T~-~-~-~----------~P~•rl~o-~~·~~~·~.end~~·~c~•~~-~~~~~·'~---------4 

1-- 60 CAL 70 

r23L271-I23 L 272 -III23 l 273 -~-

23 L 275 -1- 60 CAL 80 1-

23 L 277 -

23L 279-

-60 CAL 90 

23 L 282-

23 L 283-

23 284 -- 60 CAL96 

0-70 Clly and dt 

== r---------------~ -==~ .. -_;. ~_=.·· 70-75 Clly. grevely and sendy. Gr11nish gray to yelowish brown. Wood It 7 3 It 

r-----+----------+ 100-:~~ 

{ ::. ~ 

"---= 

75-148 Gravel. sandy and cllyey 

;: .0: 

=~-·-----------------~ 

148-214 Clly end slit. sendy. Greenish grey to olive 

brown. Grevel 11 1 72- 1 7 4 h L t-~o:::!"---+---c-""- ....... ,-----+ zoo-::-.::-~ 

---::. ~ ~214-246 Cley, silty IIIII sillily. Greenish grey to Ytlowish 

--=-=- brown. Pltnt r1111ains at 230-231 It, grevll 

at 240-241 ft 

246-290 Grevtl. sendy end clayey. Rock fragments as 

···- largt IS 3 in. . 

~ c 290-303 Clay, silty. sandy, end gravely. Light olive 

r---~-;--~--~===--------+300-~ grey "5 ------=== >--· 303-326 liancl. clayey 8RCI grevlly. Modlrete lll'own 

1 E ~ -~:~::.~_=-~-=-:..=·-~ to dirk vtllowish brown 326-390 Clay. silty. sandy, and grevely. Greenish grey 

_ _ _ _ to olive gray. Calcareous 

----

~---.::~=-+-----.,;.;~~~§==1400-• .~ ~ 390-426 Send 1nd grevel Sand is pale olive to yelowish .•. ••. brown. Calcareous 

:._·~:...-426-438 tlly end silt, sandy. Yelowish brown. Cal· :..-=-..:. careaus 

- ? ~--~-~-~ _4_3_8_-4_7_3_G_re_vtl_._•_•ndy---end--silt--y._Modl__ r_••_•_brow __ n ____ -l 

< 473-512 Silt end clay, sendy. Greyish red to llllldlrete 

500 - ~ -==: olive brown. Cerbone-•. caltereous 

I <-----------~ ~--------------------~ ~ 512-528 Greve!. Rock freg111111ts u largt as 2.5 in. 

=----

~ :=: --:_: 528-583 S~t IIIII clay, sandy. Bluish grey to yelowish 

~- - - - · brown. Celcereous. Cerboneceous et 

L_ ---- 530-531 h. gravel It 546-550 ft 

~ -.~ 

r--~~----+-7---------------+600-:~~ 

~ t ~---=-=------=-= j~ 58HI70---.. _, 7--- 670-706 Silt. clayey. sendy, end gravely. Olive brown 

~ ~ -::: to yelowish brown. Caltereous 

~ 700 -~ 706-722 Clay end grevel Yelowish brown 

~ L _ _ 721-748 ... , ...... -· ........... 

~ 748-785 Grevtl, sendy, end dty. Silt 11 756-759 It } J ~ _s------ ~----------1 r--__:;~r--+---~~;::;:.. _____ + 800 -~-; 785-817 Silt end clay, sendy end grevely. Olrk bluish 

{_______ __. ~~ -8-1-7--8-:34--:-Gr-::-:-.-':-ye-.~-n-:-is:-. -~-:-~-cla--ye_y _____ -1 

~-

~- ~ 834-855 Silt end sand. clayey end grevely. Olive -~= grey to olive brown 

- ~ 855-865 Grevel 

~ :::: 865-897 Silt end clay 

J----:;~~+-::-====;§§§§:=~=:f- 900 -'?.~ 897-929 GriYII end sind. Green to yelow~h b~wn. ~ • ~-.~ Rock fregments II llrge IS 2 II., silt II 

~ 

~ 903-906 h 

_- _-: 929-973 Silt end clay. slndy. Yelowish brown to 

: : olive. Send or grevelly slllll at 964-967 It 

~-------------~ ---"'~ 973-981 Sand 

'-------IL-------1~-==-=---1~---=5:10..-----...&. 1000 =-= :-= 981-1000 Silt end clay 1u.s. Bureau of Reclamation Prepered by J. H. Gr11n 

FIGURE 6.-Composite log of core hole 7S/1E-16C6 in San Jose. 

Fll 
F12 MECHANICS OF AQUIFER SYSTEMS 

0.90 SAMPLE DEPTH 141 FEET SAMPLE DEPTH 437 FEET 

0.70 

0.80 0. 60 

0. 70 0.50 

0.60 0.40 

0. 50 0.30 

0.40 SAMPLE DEPTH 522 FEET 

0.60 

0.30 0.50 

SAMPLE DEPTH 191 FEET 

0.70 0.40 

0.60 0. 30 

0. 50 0.20 

SAMPLE DEPTH 605 FEET 0.40 0.80 

0.30 0. 70 

O. BO SAMPLE DEPTH 253 FEET 0.60 

0.70 0. 50 Q) 

. o. 60 0.40 0 

1-

....: 0.50 0.30 a: 

c 0.40 0.80 SAMPLE DEPTH 715 FEET 

0 

;:::oo. SAMPLE DEPTH 308 FEET 

0.70 0. 70 

0.60 0.60 

0. 50 0.50 

0.40 0. 40 

0.30 0.30 

0.70 

SAMPLE DEPTH 344 0. 70 SAMPLE DEPTH 865 FEET 

0.60 0.60 

0. 50 0.50 

0.40 0.40 

0.30 0.30 

0 10 100 1000 SAMPLE DEPTH 958 FEET 

0. 70 

0.60 

0.50 

0.40 

0 1 10 100 1000 10,000 

LOAD, IN POUNDS PER SQUARE INCH 

FIGURE 7.-Consolidation-test curves for samples from core hole 6S/2W-24C7. Sample depths are in feet below land surface. 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F13 

curve: It is the slope of the straight-line portion of the 

loading curve or its dashed extension. Note that several 

points were obtained on the rebound as well as the loading 

branch of the curve in order to compare void-ratio increases due to unloading. 

Based on a study of the cores recovered from the two 

core holes, Meade (1967, table 1 and p. 39-43) described 

SAMPLE DEPTH 301 FEET 0.70------~----~----~-----

0.60 

0. 50 

0.40 

0.30------------~--~~--~~ 

0. 60 SAMPLE DEPTH 354 FEET 

Q) 0. 50 

~ 

C) 0. 40 I--

cc a:: 0. 3 0 .___ __________ ....._ ____ ~ ____ ....... 

0.60 

0.50 

0.40 

SAMPLE 0.70~----~----~----~----~----~ 

0.60 

0.50 

0.40 

0.30 

0.20 .___ ____ ....._ ____ ~----~----~----~ 

0 10 100 1000 10,000 

the types of deposits encountered to the 1,000-ft depth 

as nonmarine and mostly alluvial, with possibly a few 

lacustrine deposits at depths below 700 ft. Although both 

core holes are near San Francisco Bay (the Sunnyvale hole 

is only 3 mi from the bay), Meade reported that neither 

core contained sediments that could be recognized as 

estuarine. He listed several pieces of evidence indicating 

SAMPLE DEPTH 554 

0.60 

0. 50 

0.40 

0.30 REBOUND 

0. 2 0 L..,_ ____ ....._ ____ ........._ ____ .....J... ____ __.. ____ __J 

0. 50 

0.40 

0. 30 L...-____ ....._ ____ __.__ ____ ---L,. ____ __.. ___ ____, 

0.6 0 SAMPLE DEPTH 790 FEET 

0. 50 

0.40 

0.30 

0.20L------~----__.__ ___ ---L,. ___ __.. ___ __J 

O. 60 SAMPLE DEPTH 832 FEET 

0. 50 

0.40 

0:30.__ ___ ....._ ____ ~-------L..-~~~---.J 

SAMPLE DEPTH 937 FEET 0.70~----~--~~--~---~------

0.60 

0.50 

0.40.__---~---~---_.---~~--__j 

0 10 1000 10,000 

LOAD, IN POUNDS PER SQUARE INCH 

FIGURE B.-Consolidation-test curves for samples from core hole 7S/1E-16C6. Sample depths are in feet below land surface. 
F14 MECHANICS OF AQUIFER SYSTEMS 

the absence of estuarine sediments, including a complete 

lack of marine or estuarine fossils. 

It is of interest to note that at the Dumbarton Bridge 

crossing of San Francisco Bay, 9 mi northwest of the 

Sunnyvale core hole, Atwater and others (1977, pl. 1, 

cross section C-C') found two intervals of estuarine 

deposits above a depth of 180 ft, respectively 0 to 60 ft 

and 120 to 160 ft below sea level and each about 6 mi wide. 

Their study of late Quaternary depositional history is 

based on detailed examination of sediments from 18 

boreholes at three San Francisco Bay toll crossings (Bay 

Bridge, San Mateo Bridge, and Dumbarton Bridge). Three 

geologic cross sections show detailed descriptions of 

samples to a maximum depth of 200 ft below present sea 

level. Emphasis is on the estuarine deposits. 

X-ray diffraction studies of 20 samples from the two 

core holes indicate that montmorillonite composes about 

70 percent of the clay-mineral assemblage in these 

deposits. Other constituents are chlorite (20 percent) and 

illite (5 to 10 percent) (Meade, 1967, p. 44, fig. 33, and 

tables 14 and 15). Montmorillonite is the most compressible of the clay minerals. 

HYDROLOGY 

RAINFALL 

Precipitation that falls within the drainage basin is the 

ultimate source of all local ground water. The rainfall at 

San Jose has developed definite trends in the past 100 

years (fig. 9). A plot of the cumulative departure of rainfall at San Jose from the seasonal mean for the period 

of record clearly defines these trends. 1 The rainfall record 

for San Jose began in 1874-75. For the 106-year period 

to 1979-80, the seasonal mean rainfall (July 1 to June 30) 

was 14.13 in. From about 1890 to about 1915 the generally 

rising curve defined by the yearly points indicates that 

the cumulative surplus exceeded the cumulative deficiency 

by about 55 in. Thus, the average yearly surplus in this 

wet 25-year period exceeded the seasonal mean by about 

2 in. 

On the other hand, for the 50 years from about 1916 

to about 1966 the declining curve defined by the yearly 

points indicates that the cumulative deficiency exceeded 

the cumulative surplus by about 60 in. Thus, the average 

yearly deficiency in the 50-year dry period was below the 

seasonal mean by about 1.2 in. 

1

The cumulative departure curve is detennined by calculating the seasonal mean 

for a period of record, calculating each season's departure (plus or minus) from 

that mean, and then summing those departures. Thus, the first season had a deficiency of 6 in. and the second season had a surplus of 5 in., resulting in a cumulative 

deficiency of 1 in. for the first two seasons. 

GROUND-WATER PUMPAGE 

The intensive development of irrigated agriculture in 

the valley began about 1900. Tibbetts and Kieffer (1921, 

pl. 7) reported that the number of irrigation wells in north 

Santa Clara County increased from 115 in 1890 to 1,590 

in 1920. 

Year 1890 1900 1910 1920 

Wells 115 235 440 1,590 

Agricultural pumpage increased from about 40,000 acreft/yr in 1915-20 to a maximum of 103,000 acre-ft/yr in 

1945-50 (fig. 10, table 1). After 1945, population pressures caused a great transition of land use from agricultural to urban and industrial development. By 1970-75 

most of the orchards had been replaced by houses, and 

agricultural pumpage had decreased to 20,000 acre-ft/yr. 

Municipal and industrial pumpage, on the other hand, increased from 22,000 acre-ft/yr in 1940-45 to 131,000 acreft/yr in 1970-75. Total pumpage (fig. 10, table 1) increased 

nearly fourfold from 1915-20 to 1960-65-from 49,000 

to 185,000 acre-ft/yr-but then decreased 19 percent to 

150,000 acre-ft/yr by 1970-75 in response to a rapid increase in surface-water imports. 

SURFACE-WATER IMPORTS 

The import of surface water to Santa Clara County 

began about 1940 when San Francisco began selling surface water imported from Hetch Hetchy Reservoir in the 

Sierra Nevada to several municipalities. This import increased from 6,000 acre-ft in 1955 to 12,000 acre-ft in 

1960 and to about 50,000 acre-ft in the 1970's (fig. 11, 

table 2). Imports before 1955 are not known. 

Surface water imported from the Central Valley 

through the State's South Bay Aqueduct first became 

available in 1965; during the 1970's, deliveries through 

the aqueduct exceeded 100,000 acre-ft four different years 

(table 2, fig. 11). 

Unused imported water was recharged to the groundwater reservoir through stream channels and percolation 

ponds. The yearly quantity diverted to channels (stippled 

segment of yearly bars, fig. 11) in the 15 years has averaged about 40,000 acre-ft and represents about 48 percent of the total import from the South Bay Aqueduct. 

DECLINE OF ARTESIAN HEAD, 1916-66 

In the spring of 1916, the artesian head in index well 

7S/1E-7R1 in San Jose stood 12ft above the land surface 

(fig. 12). At that time there were only about 1,000 irrigation wells in north Santa Clara County. The cumulative 

departure graph of rainfall at San Jose (fig. 9) shows that 
UJ 

j: en 40 

UJ-' ><C 

~en 

-~ 

~ i::5 20 

LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 

:::Een 

::::J (AVERAGE RAINFALL FOR 106 SEASONS IS 14.13 INCHES,SEASONAL YEAR JULY 1 TO JUNE 30) 

(.) 

F15 

40~----~----~------L-----J-----~----~~----J-----~----~~----~-----L----~ 

1860 1880 1900 1920 

YEAR 

1940 1960 1980 

FIGURE 9.-Cumulative departure of rainfall at San Jose from the seasonal mean for the 106-year period 1874-75 to 1979-80. (Data from 

U.S. Weather Bureau and National Weather Service.) 

1920 1930 1940 1950 

YEAR 

MUNICIPAL AND INDUSTRIAL 

1960 

FIGURE 10.-Ground-water pumpage in north Santa Clara County, 1915-80. 
F16 MECHANICS OF AQUIFER SYSTEMS 

TABLE 1.-Ground-water pumpage, north Santa Clara County, 1915-80, in acrejeet 

[From 1915 to 1966 agricultural pumpage was estimated by the Santa Clara ValldY Water District from ~cultural power sales of Pacific 

Gas and Electric Company and is reported~ fiscal ~ear. To 1966 municipal an industrial pump~ is listed by calendar year; municipal pumpage is metered, industrial is estimated. ince 1 6 ~umpage is metered and is reporteil here ~ fiscal year July 1-June 30. Indust:fial 

fuumpage was estimated as follows: 1915-34, 5,000 acre- yr; 1935-43, 10,000 acre-ftlyr; 1944-50, 1 ,000 acre-ftlyr; 1951-60, 20,000 acre- yr; 1961-66, 22,000 acre-ftlyr] 

Agricultural Municipal Total Year and Yearly 5-year average industrial Yearly 5-year average 

1915-16 22,800 8,600 31,400 

1916 31 '500 9,200 40,700 

1917 41,300 9,800 51,100 

1918 45,500 10,700 56,200 

1919-20 56,000 39,420 10,200 66,200 49,120 

1920-21 63,000 10,800 73,800 

1921 54,600 10,500 65' 100 

1922 56,700 10,700 67,400 

1923 97,500 10,800 108,300 

1924-25 82,500 70,860 14,700 97,200 82,360 

1925-26 76,000 12,600 88,600 

1926 74,000 12,500 86,500 

1927 90,000 12,000 102,000 

1928 118,000 12,700 130,700 

1929-30 102,000 92,000 15,400 117,400 105,040 

1930-31 122,000 14,600 136,600 

1931 84,000 17,000 101,000 

1932 104,000 14,400 118,400 

1933 108,000 14,900 122,900 

1934-35 56,000 94,800 15,100 71, 100 110,000 

1935-36 68' 100 18,900 87,000 

1936 63,700 19,800 83,500 

1937 61,400 20,100 81,500 

1938 77' 600 20,200 97,800 

1939-40 73,000 68,760 22,100 95' 100 88,980 

1940-41 72,600 20,700 93,300 

1941 84,000 20,000 104,000 

1942 97,600 18,700 116,300 

1943 117,900 19,600 137,500 

1944-45 96,100 93,640 33,500 129,600 116, 140 

1945-46 100,800 34,200 135,000 

1946 104,900 36,400 141,300 

1947 114, 100 38,200 152,300 

1948 98,200 41,600 139,800 

1949 95,700 102,740 44,200 139,900 141,600 

1950-51 84,000 49,500 133,500 

1951 81,100 46,600 127,700 

1952 95,700 50,700 146,400 

1953 92,500 52,700 145,200 

1954 121,800 95,020 55,600 177,400 146,040 

1955-56 90,200 64,900 155,100 

1956 94,300 66,100 160,400 

1957 78,600 77,100 155,700 

1958 102,600 79,800 182,400 

1959 90,000 91,140 93,200 183,200 167,360 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F17 

TABLE 1.-Ground-water pumpage, north Santa Clara County, 1915-80, in acre-feet-Continued 

Agricultural Year Yearly 5-year average 

1960-61 84,800 

1961 63,400 

1962 54,400 

1963 76,200 

1964-65 57,200 67,200 

1965-66 40,200 

1966-67 29,800 

1967-68 35,400 

1968-69 28,600 

1969-70 29,320 32,660 

1970-71 23,710 

1971 24,090 

1972 17,450 

1973 15,940 

1974-75 16,903 19,620 

1975-76 20,036 

1976-77 16,714 

1977-78 11,702 

1978-79 12,027 

1979-80 9,793 14,050 

1980-81 9,568 

1916 was the end of a wet period beginning about 1890. 

Hunt (1940) reported that in 1912, 29 percent of the valley 

lands were irrigated, but that by 1920, 67 percent were 

irrigated, including 90 percent of the orchards; nearly all 

of these lands were irrigated with ground water from 

wells. By the autumn of 1966, the head in well 7S/1E-6M1 

in San Jose was about 210ft below land surface (fig. 12).2 

The principal factors in this major 50-year decline of 

about 220 ft are shown in figure 12. The upper line is a 

replot (fig. 9) of the cumulative departure, in inches, from 

1910 to 1980 of the seasonal rainfall at San Jose from the 

seasonal mean for the 106-year period since 1874-75. Except for the 6-year wet period 1936-42, the departure in 

the 50 years from 1916 to 1966 was substantially negative, 

and the cumulative departure represents a cumulative 

deficiency of 60 in. 

2The record of depth to water in index well 7S/1E-7R1 extends from 1915 to 

date. However, during the last two decades the artesian head in this well has been 

higher than the head in nearby representative deep wells, such as well 7S/1E-6M1 

(803ft deep). Accordingly, the composite hydrograph of figure 12 represents the 

artesian head in well 7R1 to 1959 and the head in well 6M1 from 1959 to 1980. 

Municipal Total and 

industrial Yearly 5-year average 

106,400 191,200 

121,300 184,700 

119,400 173,800 

109,700 185,900 

131,400 188,600 184,840 

122,300 162,500 

140, 100 155,390 

139,200 174,630 

136,670 165,270 

126,040 155,360 162,630 

124,500 148,210 

142,390 166,480 

137,820 155,270 

129,125 145,060 

120,526 137,430 150,490 

148,764 168,800 

136,329 153,043 

115,581 127,283 

137,678 149,705 

139,764 149,557 149,680 

151,558 161,126 

The bottom graph of figure 12 shows the estimated total 

ground-water pumpage for the 65-year period 1915-80; 

the plot is similar to figure 10 except that the increase 

in pumpage is plotted downward to reflect its influence 

on the artesian head in the index wells. Estimates from 

1915 to 1965 are based chiefly on electric-power consumption for agricultural use and are graphed as 5-year 

averages; since then, virtually all pumpage has been 

metered. 

The 50-year decline in artesian head plainly was caused 

by generally deficient rainfall and constantly increasing 

pumping draft. The curve of artesian-head decline conforms reasonably well with the cumulative departure 

curve of the seasonal rainfall at San Jose. 

Water levels in a relatively full ground-water basin at 

the end of the prolonged wet period beginning in 1890 

are shown in figure 13. The water-level contours are 

generalized from plate XIV of Clark (1924), which was 

drawn from measurements of depth to water in wells in 

the spring and summer of 1915. Both figures 13 and 14 

are maps prepared by P.R. Wood and K.S. Muir (U.S. 

Geological Survey, written commun., June 1972). Clark's 

area of artesian flow as of 1915 (from pl. XIV) and his 

"boundary of former area of artesian flow" (from pl. XV) 
F18 MECHANICS OF AQUIFER SYSTEMS 

are both shown in figure 13. Obviously the confined 

aquifer system must extend beyond Clark's ''former area 

of artesian flow." The boundary between confined and 

free ground-water conditions is not easily determined or 

recognized in parts of the Santa Clara Valley. In this 

report, however, the 1-ft subsidence line of 1934-67 

(fig. 21) is considered to be a general approximation of 

the boundary of the confined area, and accordingly it is 

plotted in figure 13. 

It is of interest to note that the California Department 

of Water Resources (1967, p. 85 and pl. 11) defined the 

boundary of the confined aquifer system as the boundary 

of their San Jose subarea. That boundary agrees in 

general with the 1-ft subsidence line of 1934-67 (fig. 21), 

except near Oak Hill and Penitencia Creek. 

In general, the water-level contours of figure 13 are 

assumed to represent a free water table near the valley 

margins and the potentiometric surface of the confined 

aquifer system in the central area included within the 1-ft 

subsidence line. The water-level contours by 1915 had not 

yet been distorted appreciably from the conditions that 

prevailed before man began the steady increase in groundwater withdrawal. The water-level contours indicate a 

1-

w 

w 

LL. 

200.---------~~--------~----------~ 

~ 150r--------------------------- o: 

u 

<( 

LL. 

0 

en 

0 

z 

<( 

en 

SOUTH BAY 

AQUEDUCT 

~ 100r-------------------~ 0 

:I: 

1-

z 

1--

0: 

0 

0.. 

SOUTH BAY 

AQUEDUCT 

Diverted to channels 

; 50 ~---------------illll\~~~fili'~::t:::~~ 1-

0 

1-

o~--~~~~~~~~~~~~~~~~ 

1950 1960 1970 1980 

YEAR 

FIGURE 11.-Surface-water imports to north Santa Clara County, 

1955-80. 

generally northwesterly movement of ground water 

toward San Francisco Bay in 1915. In the San Jose area, 

the water levels in wells ranged from 60 to 100ft above 

sea level, and artesian wells were still flowing in downtown San Jose. 

By 1967, after a half century of exploitation, water 

levels in wells had been drawn down below sea level in 

much of the ground-water basin. The hydraulic gradient 

toward San Francisco Bay in wells tapping the confined 

system had been reversed, and movement was now 

toward large cones of pumping depression as much as 

200ft below 1915 levels, surrounding heavily pumped 

municipal well fields. In central San Jose, the artesian 

head of 1967 was 160 to 180ft below 1915levels (fig. 14). 

In part of the confined aquifer system in 1967, water 

levels in wells had been drawn down below the base of 

the confining member, which near the bay is 150 to 200 

ft below the land surface. Therefore, it is not practical 

to draw a boundary between water table and confined conditions as of 1967 on the basis of figure 14. 

RECOVERY OF ARTESIAN HEAD, 1967-80 

The recovery of water level since the middle 1960's has 

been substantial. By 1975, the spring high-water level at 

index well 7S/1E-6M1 (fig. 12) was 60ft higher than in 

1966 and about equal to the 1935 level. Subsequent 

recovery was affected by the drought of 1976 and 1977, 

but the high level of 1980 was still 60 feet higher than 

the 1963-66 lows. 

From 1958 through 1982, the Geological Survey 

measured depth to water in well 7S/1E-16C5 at the 12th 

and Martha Street well field of the San Jose Water 

Works. This well is 908ft deep and is about 1.5 mi east 

of well 7S/1E-7R1 (fig. 1). The record of depth to water 

in well 7S/1E-16C5 is shown from 1958 through 1979 in 

figure 41A and from 1980 through 1982 in figure 47A. 

The recovery of artesian head in this index well from the 

1966 low to the 1978 low was about 80ft. 

This major recovery of artesian head was due to several 

factors, including increased imports of surface water, 

favorable local water supply, decreased pumpage, and increased recharge (fig. 12). The most important factor was 

the increase in imports. 

The import of surface water to Santa Clara County 

began in about 1940. As shown by table 2, by 1966-67 

yearly import through the Hetch Hetchy and South Bay 

Aqueducts was 36,000 and 32,000 acre-ft, respectively. 

By 1979-80, total import was about 158,000 acre-ft, considerably more than double the import of 1966-67. 

The average seasonal rainfall at San Jose was above 

normal in the 14-year period 1966-80. The cumulative 

departure graph (fig. 9) indicates a positive increase of 

about 15 in. in the 14 years. 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F19 

TABLE 2.-Surface-water imports to north Santa Clara County, 1955-80, in acrefeet per fiscal year 

[Data from Santa Clara Valley Water District; total imports rounded to 5 acre-ft] 

Year Hetch Hetchy 

(July 1-June 30) Aqueduct 

1955-56 5,965 

1956 6,300 

1957 7,445 

1958 9,690 

1959-60 12,300 

1960-61 12,765 

1961 15,578 

1962 22,970 

1963 24,072 

1964-65 29,536 

1965-66 33,572 

1966 35,784 

1967 39,902 

1968 41,675 

1969-70 47,203 

1970-71 45,288 

1971 49,744 

1972 48,890 

1973 49,467 

1974-75 53,273 

1975-76 58,229 

1976 47,657 

1977 38,052 

1978 49,434 

1979-80 51' 806 

The average yearly pumpage of ground water, which 

reached a peak of about 185,000 acre-ft in 1960-65, 

decreased to about 150,000 acre-ft in 1970-75 and 

1975-80 (table 1). A principal reason for this 19-percent 

decrease is the tax on ground-water pumpage applied 

since 1964 for water extracted from the ground-water 

basin. In 1970-71, for example, the ground-water tax was 

levied at $8 per acre-ft for ground water extracted for 

agricultural purposes and at $29 per acre-ft for ground 

water extracted for other uses. For water delivered on 

the surface in lieu of extraction, the cost was $10.50 per 

acre-ft for water used for agriculture and $31.50 per acreft for water used for other purposes. The economic advantage of using surface water where available is obvious 

when one considers the cost of ground-water extraction 

in addition to the tax. 

Local agencies have been working since the 1930's to 

obtain water supplies adequate to stop the ground-water 

overdraft and raise the artesian head. Their program has 

South Bay Aqueduct Total Diverted to Total channels imports 

495. 495 30,030 

29,680 29,680 63,250 

31,785 31,480 67,570 

63,032 55,213 102,935 

57,663 46,466 99,340 

77,234 38,072 124,435 

88,486 44,024 133,775 

92,432 43,596 142,175 

92,582 47,586 141,470 

86,565 41,076 136,030 

104,052 36,196 157,325 

118,692 52,607 176,920 

89,693 29,318 137,350 

79,776 20,126 117,830 

105,107 41,308 154,540 

105,868 35,628 157,675 

involved (1) salvage of flood waters from local streams 

that would otherwise waste to the bay, and (2) importation of water from outside the valley. In 1935-36, five 

storage dams were built on local streams to provide detention reservoirs with combined storage capacity of about 

50,000 acre-ft, to retain flood waters, and to permit controlled releases to increase streambed percolation (Hunt, 

1940). The storage capacity of detention reservoirs was 

increased to 144,000 acre-ft by the early 1950's (California State Water Resources Board, 1955, p. 51). 

Recharge from stream channels and percolation ponds 

to the ground-water reservoir has been augmented since 

1965 by water from the South Bay Aqueduct that could 

not be delivered directly to the user. The quantity diverted 

to recharge areas in the 15 years has averaged about 

40,000 acre-ft per year and represents 48 percent of the 

total import from the South Bay Aqueduct. (See stippled 

segment of yearly bars, fig. 11, and upper right graph, 

fig. 12). 
Cl) 

wo 

:::J:oo um 

z ..... ;o 50 

-1-

w'Lt') 40 

a:,..... 

;::::) co 30 .......... 

a:: a: <o 

fbu. 

oz 

w< >W 

i=~ 

<-' -'< :::lz 

:Eo 

;::)(I) 

u< w -'Cf.l 

_, 

<~ 

u.o 

za:: 

~.u. 

a: 

Land surface 

I I I I 

1

2oo 

HETCH HETCHY 

AQUEDUCT 

50 

1 r-rrr11TT11 ll··+llll++ ::::·:·:··l··:··:··:·:··.··.····l·'···· t· ·l·-·1·-·1· n. -1-1 I o 

-0 

WELL 7S/1E-6M1 

[ , I WELL 7S/1E ,7R1 I ~~ w w~ I I J200 

160 

~~~~~~ 

I ~~ l 

I I I I = I I -200 

150 

1910 1920 1930 1940 1950 1960 1970 1980 

YEAR 

FIGURE 12.-Artesian-head change in San Jose in response to rainfall, pumpage, and water imports. 

Cl) 

0 

z 

< Cf.IJ-

::::.w 

ow 

:::J:U. I-I w za:: - u ._:< 

a::U. 

oo 

Q.. 

~ 

~-w 

wu 

u.< u. Za:: 

-;::::) 

a::' (I) 

we 

1-z 

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~-~ 

0~ 

1-c 

:::J:-1 

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Q..aJ 

w 

0 

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0 

z 

< Cf.IJ-

::::.w 

ow 

:::J:U. 

1-' w za:: - u w'< 

(!:)u. <0 

Q.. 

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~ 

0 

a:: 

tr.l 

0 

~ -

0 

00 

0 

~ 

~ c::: -

~ 

tr.l 

~ 

~ 

~ a:: 

00 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F21 

LAND SUBSIDENCE 

HISTORY OF LEVELING CONTROL 

The first precise leveling of bench marks within the subsiding area in Santa Clara County was carried out in 1912 

on a line from Bingham, Utah, to San Francisco through 

Niles, San Jose, and Redwood City. This initial line and 

all subsequent leveling described in this report were accomplished by the National Geodetic Survey (formerly the 

U.S. Coast and Geodetic Survey). 

T 

4 

s 

T 

6 

s 

T 

7 

s 

37° 

15' 

T 

8. 

s 

i 

I 

I 

I 

I 

I 

I 

I I ----~-----------~--

1 I 

0 1 2 3 4 5 KILOMETERS : 

0 2 3 4 5 MILES 

In 1919, a line of first-order levels was run southward 

from San Jose. This leveling revealed subsidence of 0.4 

ft at San Jose (fig. 22, bench mark P7). The first releveling early in 1932 showed subsidence since 1912 ranging 

from 0.35 ft in Palo Alto (bench mark I7) to 3.66 ft in San 

Jose. More extensive leveling early in 1933 confirmed the 

subsidence and provided additional control on its extent. 

As a result of the great scientific interest in this regional 

subsidence, and through the joint efforts of A.L. Day, C.F. 

Tolman, and the National Geodetic Survey (Tolman and 

R 1 E 

EXPLANA D Alluvium and bay deposits 

~ Santa Clara Formation and 

l..!.!.i..!l associated deposits 

~ Consolidated rocks 

----- Fault-Dashedwhereapproxlmate, dotted where concealed 

----Boundary of area of artesian 

low, 1915. (Data from Clark, 

1924,Piate XIV) 

----Boundary of former area of 

artesian Row (pre-1915). 

(Data from Clark, 1924, 

plate XV). 

----Approximate boundary of pressure area (Line of 1 foot subsidence, 1934-67)-Dashed 

where uncertain 

--10--Water-level contour-Generalized contour' on the water 

table In the recharge area 

and on the potentiometric 

surface of the confined 

aquifer system in the conlined area. Dashed where 

approximately located. Contour interval 10 and 20 feet. 

Datum is sea level. Contours 

Clark, 

FIGURE 13.-Generalized water-level contours for spring and summer, 1915, north Santa Clara County. 
F22 MECHANICS OF AQUIFER SYSTEMS 

Poland, 1940, p. 29), an extensive network was laid out 

in 1933 to determine by periodic releveling the extent, 

magnitude, and rate of subsidence. 

The extent of the network is shown in figures 15 and 

16. Initially numbered with single or double digits (fig. 15), 

the lines were renumbered by the National Geodetic 

Survey in the late 1950's using three-digit numbers 

(fig. 16). The network was completely leveled for the first 

time in the spring of 1934. The total length of survey lines 

composing this bench-mark net is about 250 mi. As shown 

in figure 15, level line 1 extends from Morgan Hill northT 

4 

s 

37° 

30' 

T 

5 

s 

T 

6 

s 

T 

7 

s 

37° 

15' 

T 

8 

s 

0 5 KILOMETERS 

0 5 MILES 

westward to San Jose and then northward along the east 

side of San Francisco Bay past Niles. Line 2 extends along 

the west side of the bay from San Jose northwestward 

past Redwood City. Three transverse lines (3, 18, and 9) 

extend southwestward across the San Andreas fault, and 

three (1, 4, and 6) extend eastward across the Hayward 

fault. 

The times and extent of leveling of the net are shown 

in figure 17. Heavy lines drawn on the screened background define the leveling accomplished in a designated 

year, which may range from a single line to complete 

R 1 E 

D 

EXPLANATION 

Alluvium and bay deposits 

Santa Clara Formation and 

associated deposits 

~ Consolidated rocks 

-----Fault-Dashed where approximate, 

dotted where concealed 

--2o--Line of equal water-level change, 

1915-67-Dashed where approximate. Interval 20 feet 

FIGURE 14.-Change in water level, 1915-67, north Santa Clara County. 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F23 

coverage of the net, as in 1954 and 1960. In 1956, the 

National Geodetic Survey published a chronologie compilation of adjusted elevations, in feet, through 1954 for 

all bench marks in the network (U.S. Coast and Geodetic 

Survey, 1956). 

Since the late 1950's, the primary control for identifying bench-mark elevations is the National Geodetic 

Survey's 30-minute quadrangle (for example, see parts 

of National Geodetic Survey quadrangles 371221, 371222, 

371213, and 371214 in figure 16). Almost all the network 

is in National Geodetic Survey quadrangles 371213 and 

0 5 10 KILOMETERS 

0 5 10 MILES 

371222. When requesting bench-mark elevations in subsiding areas from the National Geodetic Survey, one 

should specify quadrangle, line number, and year or years 

of leveling. 

EXTENT AND MAGNITUDE OF SUBSIDENCE 

The subsidence record for bench mark P7 in San Jose 

is plotted in figure 18, together with the fluctuation of 

artesian head in nearby index well 7S/1E-7Rl-6Ml taken 

from figure 12. The black dots on the subsidence curve 

' ' 

EXPLANATION 

~ Bedrock 

----•• Fault- Dashed where approxi· 

mate, short dash where infer· 

red, dotted where concealed 

--1--

5-- Number of level line 

0 

0 

City 

Airport 

FIGURE 15.-Network of level lines in the San Jose subsidence area; initial numbering of level lines. 
F24 MECHANICS OF AQUIFER SYSTEMS 

indicate times of bench-mark surveys. The fluctuation of 

artesian head represents the change in stress on the 

aquifer system, and the subsidence is the resulting strain. 

Subsidence at bench mark P7 began about 1916 and was 

5.4 ft by 1938. From 1938 to 1947, subsidence stopped 

during a period of artesian-head recovery but resumed 

in 194 7 coincident with a rapidly declining head. It attained its fastest average rate in 1960-63 (0.7 ft/yr). By 

1967 the bench mark had subsided 12.67 ft. Releveling 

of bench mark P7 in 1969 showed a further small increase 

in subsidence to 12.88 ft. 

371221 

371222 

0 5 10 KILOMETERS 

0 5 10 MILES 

Maps showing lines of equal subsidence for the periods 

1934-54, 1948-54, and 1940-54 have been published 

earlier (Poland and Green, 1962, figs. 4, 5, and 6). Three 

additional subsidence maps are included in this report. 

They show subsidence from 1934 to 1960 (fig. 19), subsidence from 1960 to 1967 (fig. 20), and overall subsidence 

from 1934 to 1967 (fig. 21). To date (1984), 1967 was the 

last year of releveling of the bench-mark network. 

From 1934 to 1960, maximum subsidence exceeded 5 ft 

at centers in San Jose and Sunnyvale (fig. 19). In that 

period subsidence beneath the bay tidelands ranged from 

122"00' 

EXPLANATION 

~ Bedrock 

----··Fault-Dashed where approximate, short dash where inferred, dotted where concealed 

371221 Quadrangle numbers 

110 (National Geodetic Survey) 

---- Number of level line 

0 City 

371214 

371213 

FIGURE 16.-Network of level lines in the San Jose subsidence area; numbering of level lines revised to three digits in the late 1950's. 
-.:._"', 

?, 

~~~-

~) \ ~;.\\\s .>-,.., ~~ ~t· ' .. ~~~<.,:o. "/ ~: '· \ /, \ '1- ' / /~'-----"' ·, :X / ,·> ~ \" 

~ "· "-) / ( \! 'l /' / / .!, 'l>l-~·· • ·<: ... < "'~-J. y / '· ;> , , "y'\ .. .:;:.....- \ .. 'v "'-··~ I · •. ~\~)-.0~<.:: 'Y/ ,?·. . / ~)?';., 

~ \\, \ Morgan Hill 

1912 

MARCH 

1933 

JANUARY~EBRUARY 

~ "'\ 

\,, ' ' ' . '- ., N~ ;: ~~' >\- ~~''. ·. ·.A---~ 'Y 

\.~---~- /. "' \\ R / v,· (>. X '· - ,-- . ") \-.:.: . . edwood C \ -v -. . r : >~ "t ·~ .' "ty . '>I ~ . · ' ' I · y 

' (~":'~~~:_"':w\>·-\ ,:" \(() ~\. 1 •· '?\ ~- ; L · \Sa \ -...j >;--. . .,:.J I 

"-,, ·~ \i t~; .. ..., ·; \, I 1!i i '\ 'i-..J A .-•'{ \ ;., : /'··,._/"-..::::, . ''-·~," / !">~\~ f""/ }· ,' 

~\ 

1919 

NOVEMBER 

1934 MAY~EPTEMBER 

FIGURE 17.-Times and extent of leveling in the San Jose subsidence area. 

::<('\ '\ 

~-- Nile~..,_, 

(j ,~· \'< .. ,..,. A .. -(' '\(() . X , \ ' 'v' ... •. "" \\. ' 

'-·1 \~\.< "*"_1.--·~ ·,.-: \ ~ \~I 

~ 1~---

" .> ' i / '··<. / 

y 

·-; ~; \~'1 : / ·-~ /', 

' / ~- /' .··. ~ \__ 1<' ·,, ;\.c/Y i/ '"1".:;_/'l·J "" . '/-, 7 ;r:~~:·~~-~- v, /'r-/· '"~'· </""~·<· 

':('; 

; y,_;'\ 

~ '· 

\ " , Morgan Hi~ 

1932 

MARCHMMAY 

Morgan Hill 

1934 

NOV EMBE R"DECEMBE R 

f; 

z 

t::l 

r:n 

c::: 

t:O 

r:n 

8 

t_%j 

z 

0 

t_%j 

z 

t-3 

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~ sz 

0 

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~ > 

~ t-t 

t-t 

t_%j 

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&? 

t-t 

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z 

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(.0 

00 

~ 

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en 
-''l 

Morgan Hill\ 

1935 

MAY·JUNE 

Morgan Hill' 

1937-38 

NOVEMBER 1937 • MARCH 1938 

' ' 

. ..:) 

\ Morgan Hill 

1936 

MARCH-JUNE 

Morgan Hill 

1938·39 

OCTOBER 1938 • JANUARY 1939 

FIGURE 17.-Continued. 

~ 

1937 

MARCH-DECEMBER 

Mo,gan ~ 1939 

FEBRUARY-MARCH 

~ 

~ 

0") 

a:: 

t_:Ej 

0 

~ 00 

0 

to:j 

~ 

9 

;1 

~ 

; 

a:: 

00 
Morgan 

1939-40 

NOVEMBER 1939 • MARCH 1940 

1954 

APRIL-JULY 

1940 

MARCH-MAY 

v' 

Morgan 

FIGURE 17.-Continued. 

1956 

AUGUST 

:::-:'! 

'\.-

1948 

JANU ARY·JULY 

Morgan Hill 

1960 

OCTOBE~NOVEMBER 

§ 

r:n 

53 

r:n 

~ 

~ t:r;j 

z 

1-3 

gj 

r:n 

C) 

~ 

~ 

~ t"' 

t:r;j 

~to< 

~ 

t: 

d 

~ 

~ 

> r:n 

0 

lozj 

~ 

c.o 

~ 

l'%j 

~ 

-::J 
)' .. />-\... ~';'; 

- ;-.~-' 

Redwood· jv.~.;'( · CitY )j 

Nile~. /·-/'· '.·' ·.... ' .. ~ /-

>0~'" '"7':'·.; ·.~"""''""' / :'·'·, . '1.· .. . '\ 

Redwo : . --(j-~ ... · · j, 

City 1, ! ,";>. ' · : ', I 

/, ... ~').,! . --~ \,.,, .· ~ ··,)·-,J .s ' \_..,., 5 . ·/, r I ""f--..._)\ 

"'- \ \ /\ sf: L ·····,,,\ \ '.,_ / ) >--..'J /' 

,, \ ""--....1 f·l--)' '-, ,,- I i / ' 

'-1 ;, t / / ~·- & 

'\ A, ':>("-..;-'\~ 

~--~ J- \ ..,.')'-,...,_ / Y' ~''l•_,...., /'-f-'> \<';' 

l 

\ 

Morgan 

1963 

FEBRUARY 

1969 

MARCH-MAY 

y 

\"'<' 

\ '-!' '-\( 

" \t .. ' '\· ,, c.J \V,_, 

\ ! 't '<~/ r• . ' ~ ~.,, _ _\~, '-.., ·~ ... 

~ \. f:1( ,~-~-A~. aiY\.X "{\, 1 · -,· , ( i ... , · o t<v 

".,_, ' 7>>-t ! / ' -~' .A " '. / \ I, \-·1 /·c........ '/ ,~ . 

'" ' f \ i / / 't'J:., ('.>.,~ \ t, , \ ~.·,,/ ' ,. { .• , '\z-::! ... /.'< .,v ' ,..., '/'-, -~1 ~ \ "'--.-~. />. .. 'Y; \ .r;-- ~' ' ~;.... ' ;:"'>..,~,~~-... :>.~--.., __ <..< 

/'.f.,.// j''? '-•. ' 7r ' 

f / \.\, 

.) ~' ' 

\ Morgan Hill'-

1965 

FEBRUARYRMARCH 

FIGURE 17 .-Continued. 

1967 

FEBRUARYRAPR IL 

~ 

t..:> 

00 

a:: 

t?:l 

0 

= 

~ ~ 

0 

r:n 

0 

~ 

§ 

~ 

~ 

t?:l 

~ 

~ 

~ t?:l 

a:: 

r:n 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F29 

1 to 3 ft. As of 1960, the area of subsidence lay wholly 

within the area of alluvium and bay deposits. From 1960 

to 1967, maximum subsidence exceeded 3.5 ft in San Jose 

and Santa Clara (fig. 20) and at one bench mark in San 

Jose was 3.9 ft. The average rate of subsidence was 0.5 

ft/yr, the most rapid rate of subsidence in any 7-year 

period. 

From 1934 to 1967, the National Geodetic Survey resurveyed the network from "stable" bedrock ties a dozen 

times to determine changes in altitude of the bench marks. 

During the 33-year period 1934-67, subsidence ranged 

from 2 to 5 ft under the bay and its tidelands to 8 ft in 

San Jose and Santa Clara (fig. 21). The volume of subsidence (pore-space reduction) planimetered from the 

1934-67 subsidence map is about 500,000 acre-ft. If thE~ 

ratio of the pre-1934 subsidence volume to the 1934-67 

subsidence volume is assumed to be equal to the ratio o:f 

the pre-1934 subsidence of bench mark P7 to the 1934-67 

subsidence of that bench mark, then the total subsidencE~ 

volume from 1912 to 1967 is about 800,000 acre-ft. 

When a line of bench marks in a subsidence area has 

been releveled a number of times, one of the most informative means of presenting subsidence information is to 

draw a series of subsidence profiles (figs. 22-24). 

Land-subsidence profiles along line D-D I from Redwood 

City to Coyote from 1912 through 1969 are shown in 

0 

2 1-

w 

w 

1.1-

!: 4 

u.i SUBSIDENCE BENCH MARK P7 (.) 

z 

w 

c 

en 6 r:::a 

::I 

Cl) 

8 

10 

Note: 

Dotted segments show 

12 author's interpretation 

1910 1920 1930 1940 

YEAR 

figure 22 (for location oflineD-D~, see fig. 21). The spring 

1934leveling was used as a reference base because it was 

the first complete leveling of the net. Subsidence before 

1934 is plotted above the reference base, and subsidence 

after 1934 is shown below it. The marked increase in rate 

of subsidence after 1948 from Palo Alto to San Jose plainly is due to the increased decline of artesian head (fig. 18) 

in response to increased ground-water withdrawal (fig. 

10). Note that from 1934 to 1967 maximum subsidence 

of 8.6 ft was near bench mark W111 3 mi northwest of 

bench mark P7; in addition, note that from 1934 to 1960 

the greatest subsidence along line D-D I was 5. 7 ft at 

bench mark J111 reset in Sunnyvale. Changes in the rate 

and magnitude of withdrawal and of artesian-head decline 

doubtless have caused much geographic variation in subsidence rate and magnitude with time. 

Profiles of land subsidence along transverse line E-E I 

from Mountain View to Milpitas from 1933 to 1967 

(fig. 23) have a pattern similar to that of the profiles in 

figure 22. The rate of subsidence prior to 1948 is low compared with the great increase in the rate thereafter. 

Benchmark J111 reset is common to both linesD-DI and 

E-E~; from 1934 to 1967 it subsided 7.8 ft. 

Land-subsidence profiles along line F -F~ from Los 

Gatos through San Jose to Alum Rock Park from 1934 

to 1969 are displayed in figure 24. Bench mark 119 in San 

40 

ARTESIAN HEAD 

0 WELL 7S/1E-7R1 WELL 7S/1E-6M1 w 

(.) 

cc 

1.1-

a: 

40 ::I 

Cl) 

c 

z 

cc 

_. 

80 ~ c 

_. 

w 

r:::a 

a: 

c 

120 w 

> 

c 

r:::a 

cc 

1-

160 w 

w 

1.1-

!: 

a: 

w 

200 1-

cc 

3:: 

c 

1-

240 ~ Cl.. 

w 

c 

280 

1950 1960 1970 1980 

FIGURE 18.-Artesian-head change and land subsidence, San Jose. 
F30 MECHANICS OF AQUIFER SYSTEMS 

Jose is common to both line D-D' and F -F'; it subsided 

7. 7 ft from 1934 to 1969 and was exceeded only by bench 

mark E 176, which sank 8. 7 ft in the same period. 

Although line F -F' crosses the concealed Hayward fault 

at Alum Rock, about 2.5 mi from the east end of the line, 

the relevelings from 1934-69 do not indicate any differential displacement across the fault. 

ECONOMIC AND SOCIAL IMPACTS 

Subsidence has caused several major problems. Lands 

adjacent to San Francisco Bay have sunk 3 to 9 ft since 

37° 

15' 

0 1 2 3 4 5 KILOMETERS 

0 2 3 4 5 MILES 

1916, requiring construction and repeated raising of 

levees to restrain landward movement of the saline bay 

water as well as construction of flood-controllevees near 

the hayward ends of the valley streams. The subsidence 

has affected stream channels in two ways: Channel grades 

crossing the subsidence bowl have been down warped, and 

saline bay water has moved upstream. These changes tend 

to cause channel deposition near the bay and reduce channel capacity, creating the need for higher levees. Intrusion may occur where wells tapping shallow aquifers are 

pumped, inducing downward movement, especially 

through rusted well casings. 

EXPLANATION D Alluvium and bay deposits 

.. ·,, ~ 

, .. .. Santa Clara Formation and 

associated deposits 

~ Consolidated rocks 

-----Fault-Dashed. where approximate, dottetl where concealed 

-4-- Une of equal subsidence-Dashed 

where poorly controlled. Compded from leveling of National 

Geodetic Survey in MaySeptember 1934 and OctoberNovember 1960. Interval, in 

feet, is variable 

Compiled by J. H. Green 

FIGURE 19.-Land subsidence from 1934 to 1960, north Santa Clara County. 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F31 

About 30 mi2 of evaporation ponds from Palo Alto 

around the south end of the bay are used for salt production. Behind the landward chain of dikes bordering these 

ponds, at least 17 mi2 of land lie below the highest tide 

level of 1967. Currently these lands are protected by the 

dikes and stream-channel levees, but they as well as the 

bay-front levees are considered inadequate. Extensive 

flooding of the Alviso area in March to April1983 attests 

to the inadequacy of the stream-channel levees. 

By making use of the table of annual compaction (table 

3) and the compaction-subsidence ratios for the 1,000-ft 

core holes (table 5), we can derive a rough estimate of the 

37° 

15' 

0 1 2 3 4 5 KILOMETERS 

0 2 3 4 5 MILES 

subsidence that occurred from 1969 through 1982. The 

measured compaction at 6S/2W-24C7 from 1969 through 

1982 was 0.24 ft. If the ratio of compaction to subsidence 

for the 13-year period remained at 105 percent, the subsidence would be about 0.25 ft. The measured compaction at 7S/1E-16C11 from 1969 through 1982 (table 3) was 

0.44 ft. If the ratio of compaction to subsidence for the 

13-year period remained at 99 percent, the subsidence 

would also be 0.44 ft. These figures suggest that the subsidence for the 13-year period was on the order of half 

a foot at San Jose (16C11) and a quarter of a foot in 

Sunnyvale (24C7). 

EXPLANATION D Alluvium and bay deposits 

• •e I 

::.:• Santa Clara Formation and 

associated deposits 

Consolidated rocks 

-----Fault-Dashed where approxImate. dotted where concealed 

-O.t""':""Une of equal subeidence-DMhed 

where poorly controllecl. Compiled lrom leveling of Natioul 

Geodetic Survey In OctoberNovember 1960 and FebruaryMarch 1967. Interval 0.5 

and 0.1 foot 

FIGURE 20.-Land subsidence from 1960 to 1967, north Santa Clara County. 
F32 MECHANICS OF AQUIFER SYSTEMS 

About $9 million of public funds had been spent to 1974 

on flood-control levees to correct for subsidence effects, 

according to Lloyd Fowler, former Chief Engineer of the 

Santa Clara Valley Water District. In addition, the Leslie 

Salt Co. has spent an unknown but substantial amount 

maintaining levees on the 30 mi2 of salt ponds to counter 

as much as 9 ft of subsidence in the Alviso area. Several 

hundred water-well casings have failed in vertical compression as a result of compaction of the sediments. The 

protrusion of well casings as much as 2 to 3 ft above land 

surface also has been observed (Tolman, 1937, p. 344). The 

cost of repair or replacement of such damaged wells has 

been estimated as at least $4 million (Roll, 1967). Including 

funds spent on maintaining the salt-pond levees, establishing and resurveying the bench-mark net, repairing 

railroads, roads, and bridges, replacing or increasing the 

size of storm and sanitary sewers, installing drainage 

pumping plants, and making private engineering surveys, 

the direct costs of subsidence must have been at least $30 

to $40 million to date. Fowler (1981) has estimated that 

the direct costs of subsidence, including the estimated cost 

of a proposed new levee system, all figured in 1979 dollars, 

would exceed $100 million. 

A major earthquake could cause failure of the baymargin levees, which would result in the flooding of areas 

presently below sea level. The bay-margin levees were 

R 3W R 2 W 1 22000' R 1 W R 1 E 

T 

4 

s 

T 

5 

s 

T 

ii 

s 

T 

7 

s 

37° 

15' 

T 

8 

s 

I 

~ I 

I 

I 

I 

I -;-----t---

1 

I 

I 

I 

I 

I 

I 

I 

I I --- -r-----------

1 I 

I I 

I I 

I : 

I 0 1 2 3. 4 5 KILOMETERS 

I 0 2 3 4 5 MILES 

EXPLANA 

D Alluvium and bay deposits 

~ Santa Clara Formation and 

• • • assocIated deposits 

~ Consolidated rocks 

-----Fault-Daahed where approxImate, dotted where concealed 

--2--Line of equal subaldence-Daahed where approximately 

located. Interval, In feet, Is 

D D' variable 

1---.JAIIgnment of subsidence profiles24C7 See figures 22-24 

e Core hole and number 

OC5 Observation well and number 

JG2 

)( Bench mark and number 

FIGURE 2C-Land subsidence from 1934 to 1967, north Santa Clara County. 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F33 

constructed of locally derived weak materials and were 

designed only to retain salt-pond water under static conditions (Rogers and Williams, 197 4). The potential for such 

an earthquake poses a continuing threat to flooding of the 

estimated 17 mi2 of land standing below the high-tide 

level of 1967. Such a threat has probably reduced the value 

of this land substantially compared with its value if it all 

still stood above sea level as it did in 1912. This decrease 

in land values should be included in the gross costs of 

subsidence. 

MONITORING OF COMPACTION AND 

CHANGE IN HEAD 

MEASUREMENT OF COMPACTION 

Two principal objectives of the Federal program on 

mechanics of aquifer systems are to determine the depth 

1-

w 

w 

u. 

~ 

w 

u 

z 

D 

4 

2 

,..... ~ w 

0 

~ 2 

u; 

Ill 

=> 

en 

4 

6 

Menlo 

Redwood Park 

City Palo 

Alto 

Ill 

(.!) ,..... 

Dashed lilies indicate 

no control between 

bench marks 

Note: All leveling 

to bench marks 

by the National 

8 Geodetic Survey 

Sunnyvale 

interval in which compaction is occurring and to measure 

the magnitude and time distribution of the compaction 

where possible. Such information, together with periodic 

measurement of land subsidence as determined by spiritlevel surveys to surface bench marks, is essential for 

determining the cause of subsidence and for monitoring 

the magnitude and the change in rate of subsidence. When 

coupled with measurement of water-level or head change 

in the stressed aquifer systems, these data supply the 

numbers required for stress-compaction or stress-strain 

analysis. 

The first extensometer (compaction recorder) in the 

Santa Clara Valley was installed in 1958 at well 6S/1W23E 1 in Agnew. In 1960, extenso meters were installed 

in the cased core holes 1,000 ft deep at the centers of subsidence in San Jose (7S/1E-16C6) and in Sunnyvale 

(6S/2W-24C7), in two satellite holes in Sunnyvale (24C3 

and 24C4), and in two unused water wells. They have 

San Jose 

"'<» 

(l. .... 

D' 

\ 

\ 

1940 ~ 

FIGURE 22.-Profiles of land subsidence, D-D ', Redwood City to Coyote, 1912-69. 
F34 MECHANICS OF AQUIFER SYSTEMS 

0 

co 

1-

2 

1-

w 

w 

u. 

~ 3 

w· 

(.) 

z 

w 

0 

CJ) 

m 

:::> 4 CJ) 

5 

6 

(0 

0 

..... 00 N coco > 

a: ::::> > 

Note: Dashed lines 

indicate no leveling 

0 0 co co 

~ X 

I 

Note: All leveling by the 

National Geodetic Survey 

N .... E ~ Q) 

a: a: 

t9 ~ 

~- ~-

0 

w 

t9 ~ 

I co 

>-

.... 

~ Q) 

a: 

::; 

~191_3 --- 1934 BASE 

- ---- ---- -- / 

- / 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

0 

0 

~ Q) 

a: ~ Milpitas Q) 

a: co 

'o:t 

:::c 

00 c; (0 'o:t ..... :::c L.O 

X u 

co ~ 'o:t Q) 

a: l!) (0 

00 ..... 

'o:t 0 l!) w· 'o:t 

..... ..... 

0 N 

E' 

-

--

/ 

/ 

/ 

/ 

4 KILOMETERS 

4 MILES 

SL-----------------------------------------------------------------------------------~ 

FIGURE 23.-Profiles of land subsidence, E-E', .Mountain View to Milpitas, 1933-67. 
Los Gatos 

fUJ 

UJ 

0 

2 

3 

u.. 4 

w· 

(.) 

z 

UJ 

Cl 

~ 5 

=> 

U) 

6 

8 

,.... ,.... ...... ,.... 

u ;;; 

F 

,.... 

,.... 

z 

0 

0 

LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F35 

~ ~ ~ ~ QJ QJ QJ 

a: a: a: a: co co co co San Jose ,.... ,.... ,.... ,.... 

en 5 i= ;n cr (.!) 

co (I) cO cO cO co" tO tO ,.... ,.... :::l ,.... ,.... ,.... ,.... ,.... ,.... ,.... 

ill 5 i= cr a: ~m 

s: M (I) z :::E:= 

I I I 

4 KILOMETERS 

4 MILES 

~ QJ 

a: 

co 

~ 

u. 

tO co cO ,.... ,.... ,.... 

w :2 ~ 

QJ 

QJ 

a: 

~ <0 

"C 

c: "3 ~ ~ <0 ,.... u. i5 Alum Rock QJ 

co a: 1:i 8 > co lii co ~- COco~ N ,.... COr-.,_ > co o~co 

a:l 

a: > OJ:r 

I I( 

Note: All leveling by the 

National Geode.tic Survey 

Park 

9~----------------------------------------------------------------------------------------~ 

FIGURE 24.-Profiles of land subsidence, F-F', Los Gatos to Alum Rock Park, 1934-69. 
F36 MECHANICS OF AQUIFER SYSTEMS 

recorded compaction or expansion of the confined aquifer 

system for 22 years. 

Extensometers of two types are in use (fig. 25). In the 

cable type (fig. 25A), an anchor weight is attached to the 

extensometer cable, lowered into the well, and set below 

the bottom of the well casing. This anchor acts as a depth 

bench mark. The extensometer cable is maintained 

Core hole 7S/1E-16C6 was destroyed in 1969 during the 

construction of a freeway. It was replaced in 1969 by 

another 1,000-ft extensometer, well 7S/1E-16C11. 

Sheaves 

mounted in 

A 

Recorder 

Compaction tape -

Steel tab I e __ __. 

Clamp 

/Bench mark 

_...J::::::L-.....C::::::;).,._ Con c r e t e .--~___.___.____, I I 

~"'":":'T":"r."':"":"'''~~sl ab~+.-:-:-~~~~ 1 1 

··=;<) <?¥K~:}-??H~t~\; 1 11!+!-t:;m:...--r;x-~/(--);~~._.....(~.~:--;!,_; .. :j....... :~·=·~.:.-~:~::.: 

Cab I e, 1/8-inch stain I ess \~~~} I I ;~t~\: steel, 1 x 19 stranded :::.:.:\· 1 }/: Extensometer 

reverse I ay ·:·:.:.:.: 1 1 ·:;.::: pipe 

p e r f o r a ted cas i n g ~-~.;:11-:'~~;-t::~~iT-: ~~ r ;f[f. 

··?n I I :~?;;;; Well casing t..:.,:..;;:.......----

4 to 13 inches 

Anchor weight, 200 to 

300 puunds, in open 

hole 

---:.:.:.::.:,.·~ ... : .. =::··~ I I ::.~:··:~·. 

·;lt/~ I @!iA 

8 

Extensometer 

pipe cemented 

in open hole 

FIGURE 25.-Recording extensometer installations. A, Anchored cable assembly. B, Pipe assembly. 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 

(ideally) under constant tension by a counterweight at the 

land surface. As the aquifer system compacts, an 

equivalent length of cable appears to emerge from the 

well; this movement is measured by a mechanical recorder 

attached to the compaction cable at land surface. In the 

free-standing pipe extensometer (fig. 25B), the pipe is 

lowered into the well and set below the bottom of the well 

casing. A mechanical recorder attached to the extensometer pipe measures the movement of the land surface 

relative to the nonmoving pipe and thus measures the 

compaction or expansion of the aquifer system. 

The accuracy of the compaction record is dependent 

largely on the ability of the extensometer cable or pipe 

to maintain a constant length between the bottom-hole 

reference point and the above-ground reference point. 

Friction tends to develop between the extensometer cable 

or pipe and the deforming well casing, which shortens and 

moves downward in the grip of the compacting sediments. 

Because of its much greater cross section, the pipe is more 

competent than the cable to resist frictionally induced 

length changes. Therefore it generally produces a better 

record in typical wells of moderate depth, but other factors may be involved in selecting the design for a specific 

site. 

When initally installed, all the extensometers were of 

the anchored-cable type. To reduce the friction problem 

and increase the accuracy of measurement, the three 

paired Sunnyvale extensometers (6S/2W-24C3, C4, and 

C7) and 7S/1E-16Cll in San Jose were modified in the 

early 1970's by replacing the anchored cable with a freestanding pipe of 1.5-in. diameter (fig. 25B) in the casing. 

Well 16Cll has 6-in. casing, the other three have 4-in. 

casing. 

The kind of field record being obtained in 1981 at the 

multiple extensometer site at Sunnyvale (wells 6S/2W24C3, C4, and C7) is illustrated in figure 26. The compaction was recorded on a chart with a vertical scale 

(compaction) of 10:1 and a horizontal scale of 10 days/in. 

The compaction records from the three extensometers 

were traced on a common chart base for a 1-year period 

from March 20, 1981, to March 26, 1982. The maximum 

compaction occurred on October 3, 1981. 

Compaction and expansion in feet 

[minus (-) indicates expansion] 

C4 C3 C7 

Date (250ft) (550ft) (1,000 ft) 

4/1/81 0 0 0 

10/3/81 0.015 0.061 0.076 

3/26/82 -.015 -.061 -.076 

Net change 

from 4/1/81 

to 3/26/82 0 0 0 

These compaction plots are of interest for two reasons. 

First, they illustrate the sensitivity of the recording 

,... 

.,...~ 

»-

~ ;g. 

N '<t 0 0 

0 0 

133:1 Nl 'SS3N)f::JIH1 Nl 38NVH::J 

"' 0 

0 

:r:: 

1-

2 

0 

:2 

F37 

~ 00 

I 

....... 

00 

(j) 

....... 

6 

""" C'\1 

~ C\J 

00 

~ 

Q.l 

~ 

·;.; 

Q.l 

~ 

~ ~ 

§ 

rn 

Q.l 

...c: 

~ 

~ 

1:1! 

00 

""' Q.l 

~ 

Q.l 

s 

0 

00 

~ 

Q.l 

~ 

>< Q.l 

Q.l 

-a 

·.o 

"3 

s 

<+-! 

0 

Q.l 

00 

~ 

0 

0.. 

00 

Q.l 

""' <:.) 

·.p 

00 

1:1! 

~ 

I 

~ C\J 

r.::l 

ll:: 

:;:J 

(.!1 

~ 
F38 MECHANICS OF AQUIFER SYSTEMS 

extensometers to very small changes in applied stress. 

Secondly, we can see from the plots in figure 26 that the 

measured compaction from April1, 1981, to March 26, 

1982, at the Sunnyvale site all occurred within the elastic 

range of stress; that is, no permanent deformation 

occurred in the aquifer systems. 

Continuous or periodic water-level measurements are 

also necessary in a subsidence-monitoring program in 

order to define the cause-and-effect relationship of the 

subsidence process. Moreover, in order to produce reliable 

stress-strain or stress-compaction plots that can be utilized 

to derive storage and compressibility characteristics of 

the aquifer system, water-level measurements must represent the average change in stress in the compacting interval being measured. 

At the Sunnyvale site, for example, wells 24C4 (250-ft 

depth) and 24C3 (550-ft depth) are open-bottom blank 

casings drilled primarily as extensometers. Periodic 

water-level measurements have been made and are 

recorded in the computer plots of field records (figs. 32, 

34, 36) and supplementary records of 1980-82 (figs. 43, 

44). The hydrograph for the 250-ft well (24C4) shows an 

annual fluctuation of about 50 ft and may be a fair 

representation of stress change for the confined depth 

interval from 200 to 250ft (fig. 32A). The hydrograph for 

the 550-ft well (24C3), on the other hand, was very sluggish from 1964-74 (fig. 34A) and is not considered reliable 

as a measure of stress change in the depth interval 250 

to 550ft. 

The Geological Survey terminated field monitoring of 

compaction and water-level change on this study in 

January 1983. At that time, extensometers were in use 

in five wells at two compaction and water-level monitoring sites (wells 6S/2W -24C3, C4 and C7 in Sunnyvale and 

wells 7S/1E-16C5 and C11 in San Jose; for location, see 

fig. 1). The five wells will continue to be monitored by the 

Santa Clara Valley Water District for compaction of the 

aquifer system and water-level change. 

The net annual compaction or expansion (negative compaction) at each site for the entire period of record 

through 1982 is summarized in table 3, as are records of· 

compaction or expansion in two additional depth intervals defined by multiple-depth installations. For example, 

at 6S/2W-24C, wells C3, C4, and C7 are respectively 550, 

250, and 1,000 ft deep. The extensometer in well C7 

records total compaction from land surface to the 1,000-ft 

depth, and the extensometer in C3 measures the compaction from land surface to the 550-ft depth. By subtracting the compaction in C3 from that in C7, the 

compaction of the 550- to 1,000-ft depth interval is 

calculated. 

The marked decrease in the annual compaction in 

response to the substantial head recovery since 1966 is 

demonstrated graphically by the compaction records from 

the two deep extensometers in Sunnyvale and San Jose 

(fig. 27). The annual compaction in well 7S/1E-16C6-11 

in San Jose decreased from about 1 ft in 1961 and 1962 

to 0.24 ft in 1967 and to 0.01 ft in 1973. Net expansion 

Oand-surface rebound) of 0.02 ft occurred in 197 4. In 1976 

the drought caused a sharp decline of artesian head (fig. 

40), which in turn increased compaction to 0.11 ft at the 

San Jose site. In Sunnyvale, compaction of the aquifer 

system in well24C7 decreased from about 0.45 ft in 1961 

to 0.04 ft in 1973; net expansion of 0.016 ft and 0.04 ft 

occurred in 1974 and 1975, respectively. 

The subsidence of surface bench marks from 1960 to 

1967 (or 1969), plotted on the long-term compaction plots 

for wells 6S/2W-24C7 (fig. 38) and 7S/1E-16C6-11 (fig. 

TABLE 3.-Annual compaction at compactionlin order to arrive at consistent sums, the amount of annual compaction is shown to 0.001 ft; however, many 

Anchor Depth Start ~Tell depth when . 1 of 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 . 1nterva number Installed (f ) record (feet) eet 

6S/1W-23E1--- 425 0-425 9/10/58 0.093 0.214 0.141 0.270 0.253 0.119 0.153 0.142 0.145 0.027 

6S/2W-24C4--- 250 0-250 1/29/60 .037 .058 .040 .030 .053 .018 .027 .017 

-24C3--- 550 250-550 1/29/60 .200 .151 .152 .123 .144 .104 .125 .070 

-24C3--- 550 0-550 1/29/60 .237 .209 .192 .153 .197 .122 .152 .087 

-24C7--- 1,000 550-1,000 6/30/60 .244 .172 .177 .182 .174 .144 .126 

-24C7--- 1,000 0-1,000 6/30/60 . 211 .453 .364 .330 .379 .296 .296 .213 

7S/1E-9D2---- 605 0-605 5/5/60 .094 .333 .408 1.047 

-9D2---- 605 0-605 1/14/65 .210 .200 .087 

7S/1E-16C5--- 908 0-908 8/16/60 .080 .712 .918 .429 .394 .397 .418 .226 

-16C6--- 1,000 0-1,000 6/30/60 .276 .966 1.021 .399 .506 .410 .477 .236 

-16Cll-- 1,000 0-1,000 6/2/69 

1Record ends April 22, 1963 (equipment failure) 2Site abandoned May 1978 

3c6 record ends June 2, 1969, and Cl1 star.ts on June 2, 1969 

' 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F39 

41), demonstrates that the measured compaction to the 

1,000-ft depth is approximately equal to the measured subsidence as determined by bench-mark surveys. The close 

agreement of the compaction and subsidence values at the 

Sunnyvale and San Jose sites is shown in table 5. At the 

San Jose site (16C6), measured subsidence from October 

1960 to May 1969 was 4.21 ft, and measured compaction 

for the same time period was 4.17 ft; thus the ratio of compaction to subsidence was 99 percent, which means that 

all of the subsidence is due to the measured compaction 

to the 1,000-ft depth. 

ANALYSIS OF STRESSES CAUSING SUBSIDENCE 

Increase in effective stress (grain-to-grain load) is the 

cause of compaction of sediments. The withdrawal of 

water from wells reduces the head in the aquifers that 

are tapped and increases the effective stress borne by the 

aquifer matrix. The reader interested in a quantitative 

analysis of stresses causing subsidence is referred to 

Lofgren (1968) and to Poland and others (1975, p. 39-44). 

In summary, water-level fluctuations change effective 

stresses in the following two ways: (1) A rise of the water 

table provides buoyant support for the grains in the zone 

of the change, and a decline removes the buoyant support; 

these changes in gravitational stress are transmitted 

downward to all underlying deposits. (2) A change in position of either the water table or the artesian head, or both, 

may induce net vertical hydraulic gradients across confining or semiconfining beds and thereby produce a net 

seepage stress. The vertical normal component of this 

stress is algebraically additive to the gravitational stress 

that is transmitted downward to all underlying deposits. 

A change in effective stress results if the preexisting 

measuring sites in north Santa Clara County 

seepage stress across the bed is altered in direction or 

magnitude. 

The change in applied stress within a confined aquifer 

system, due to changes in both the water table and the 

artesian head, may be summarized concisely (Poland and 

others, 1972, p. 6) as 

where Pa is the applied stress expressed in feet of water, 

he is the head (assumed uniform) in the confined aquifer 

system, hu is the head in the overlying unconfined 

aquifer, and Ys is the average specific yield (expressed 

as a decimal fraction) in the interval of water-table 

fluctuation. 

EXAMPLE OF STRESS-STRAIN GRAPH 

Field measurements of compaction and correlative 

change in water level serve as continuous monitors of subsidence and indicators of the response of the system to 

change in applied stress. They also can be utilized to construct stress-compaction or stress-strain curves from 

which, under favorable conditions, one can derive storage 

and compressibility characteristics of the measured part 

of the aquifer system, as demonstrated by Riley (1969). 

Nineteen years (1960-79) of measured water-level 

change (well 7S/1E-16C5) and compaction (well 7S/1E16C6-11) in San Jose are shown in figure 41, together with 

a computer plot of stress change versus strain. Well16C5 

is 908ft deep, and compaction in well16C6-11 is measured 

to 1,000 ft, spanning the full 800-ft thickness of the aquifer 

system from the 200- to the 1,000-ft depth. As the water 

levels at this San Jose site rose rapidly after 1967 (fig. 

measured yearly values are not accurate ~o less than a few hundredths of a foot. Minus (-)indicates expansion] 

Total 

1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 measured 

compaction 

(fE>et) 

0.028 -0.022 -0.031 0 0.024 -0.021 -0.024 -0.012 0.043 0.018 -0.027 0.003 1. 536 

.009 0 .009 .044 -.027 -.006 -.002 -.005 .004 .003 -.003 -.005 -0.001 0.003 -0.005 .298 

.064 .021 -.008 -.032 .028 -.023 -.020 -.016 .022 -.002 .001 .004 -.002 .002 -.005 1.103 

.073 .021 .001 .012 .001 -.029 -.022 -.021 .026 .001 -.002 -.001 -.003 .005 -.010 1.401 

.092 .081 .020 .018 .024 .069 .006 -.016 .025 .008 .023 .001 -.004 .008 -.001 1. 573 

.165 .102 .021 .030 .025 .040 -.016 -.037 .051 .009 .021 0 -.007 .013 -.011 2.948 

.882 

.041 .038 .010 .007 .057 -.003 -.019 -.014 .043 2 .036 .693 

.156 .054 .044 .106 .123 .030 .021 .026 .095 .049 .027 .029 -.027 .040 -.028 4.319 

.129 3 .023 4.443 

.071 .075 .064 .050 .007 -.019 .011 .114 .043 .006 .042 -.018 .028 -.035 .439 
F40 MECHANICS OF AQUIFER SYSTEMS 

41A), the stress-strain curves obtained from the paired 

measurements of compaction and artesian head began to 

show seasonal expansion during the winter months when 

the water level was highest and the effective stress on 

the confined system was lowest (fig. 41D). These stressstrain loops can be used to obtain the compressibility of 

the confined system in the recoverable or elastic range 

of stresses (less than preconsolidation stress). The stressstrain curve for 1967-74 has been enlarged in figure 28. 

Depth to water is plotted increasing upward. Change in 

depth to water represents an average change in stress 

in all aquifers of the confined aquifer system tapped by 

well16C5. The lower parts of the descending segments 

of the annual loops for the winters of 1967-68, 1969-70, 

and 1970-71 are approximately parallel, as shown by the 

dotted lines, indicating that the response is essentially 

elastic in both aquifers and aquitards when the depth to 

water is less than about 180 ft. The heavy dashed line 

drawn parallel to the dotted lines represents the average 

slope of the segments in the range of stresses less than 

preconsolidation stress. The reciprocal of the slope of this 

...... 

w 

w 

u.. 

2 

z 

line is the component of the storage coefficient attributable to elastic or recoverable deformation of the aquifersystem skeleton, Ske, and equals 1.5 x 10- 3. The 

component of average specific storage due to elastic 

deformation, Sske, equals Ske/800 ft = 1.87 x 10-6/ft. If 

stresses are expressed in feet of water, and if Yw (the unit 

weight of water) equals unity, the average elastic compressibility of the aquifer system skeleton, ake, is-equal 

numerically to Sske. 

In these computations we have assumed that in the 

range of stresses less than preconsolidation stress, the 

compressibility of the aquitards and of the aquifers is the 

same. Therefore, the full thickness of the confined aquifer 

system, 800 ft, was used to derive the average specific 

storage component, Sske, in the elastic range of stress. 

COMPUTER SIMULATION OF 

AQUIFER-SYSTEM COMPACTION 

As stated by Helm (1978), land subsidence due to 

ground-water withdrawal from a confined aquifer system 

SUNNYVALE 

WELL 6S/2W-24C7 

0 1.2~~--~---r--li---~--r---r-~--~--~---,---,---,---,--,---,---.--.,--.---~--~~ ...... 

u 

<( 

c.. 

~ o.a~~~~~~~~~~~~~~~~~~~~ WELLS 7~~1~!~~~ and C11 

o.: l!lillilllllillillll ililillilllillilill! 11111111111111111111 :::~:::::::::::=:::: ::;:;::;: :::;:;:;:: ·:·:·:·:· .·.·.·.·.· 

1962 1964 1966 1968 1970 1972 

YEAR 

FIGURE 27.-Measured annual compaction in wells 1,000 ft deep in Sunnyvale and San Jose. 

1982 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F41 

is an expression at land surface of net compaction (vertical consolidation) at depth of compressible layers within 

the system. Water-level fluctuations within coarse-grained 

aquifers produce stress changes on the upper and lower 

boundaries of slow-draining aquitards (compressible finegrained interbeds). Indirectly, irregular and cyclic pumping drawdowns generate complex loading and unloading 

stress patterns in the aquifer system, causing compaction 

and expansion of the aquitards. Within a confined system, 

any lag in compactive response to such a load increase 

is usually ascribed to slow vertical drainage from the 

aquitards. After water levels in coarse-grained material 

rise during a period of water-level recovery, it has been 

observed during the next cycle of declining water levels 

that nonrecoverable compaction is reinitiated before 

water levels reach their prior lowest level. 

Helm (1977) developed a one-dimensional mathematical 

model of vertical deformation based on a modification of 

Karl Terzaghi' s consolidation theory; the model computes 

transient aquitard compaction and expansion due to arbitrarily specified changes in effective stress within an 

340 

300 

• • • 

260 • 

Iw 

w 

LL. 

~ 

r£ 220 

w 

I-

<{ 

~ 1967 

0 

I- 180 

:I: 

Ia.. 

w 

0 • 

140 • • • • • 

100 • • • • 

adjacent aquifer. This model has been applied by Helm 

(1977) to observed water-level fluctuations and to the 

resulting observed transient compaction-and-expansion 

behavior of the confined aquifer system at seven sites in 

the Santa Clara Valley. 

According to Helm, values for total cumulative thickness b' sum of fine-grained interbeds within the confined 

aquifer system, the weighted-average thickness b' equiv of 

these interbeds, recoverable vertical compressibility S~ke, 

and the initial distribution of preconsolidation pressure 

p' max (z, 0) must be approximated from field data independently of any subsequent simulation process. Only 

values for vertical components of hydraulic conductivity 

K' and nonrecoverable compressibility S ~kv are adjusted 

by trial-and-error to fit calculated-to-observed compaction 

history. The estimated values forK' at the sites studied 

range from 0.56 x 10-6 to 12.5 x 10-6 ft/d, those for 

s~kv range from 1.4 X 10-4 to 13.1 X 10-4fft, and those 

for s~ke range from 2.2 X 10-6 to 15.8 X 10-6/ft 

(table 4). 

For established values of b' sum, b' equiv, and p' max (z, 0), 

I • • • 

~ • • • 

• • • + • • ..... 

4) 

...... • • • • • 7 • • • 

• "' • 1972 • 

• • / • 

• 

/1973 

• 

COMPACTION, IN FEET 

FIGURE 28.-Stress change and compaction, San Jose site. Depth to water in well 7S/1E-16C5, and compaction in well 7S/1E-16C6-11. 
F42 MECHANICS OF AQUIFER SYSTEMS 

TABLE 4.-Values of parameters used for simulating observed compaction at selected sites in north Santa Clara County 

[Modified from Helm (1977, table 1)] 

Period of record Estimated thickness Estimated values of parameters (years) (feet) 

Site of 

water-level 

data Water-level Compaction Total 

data data b' 

sum 

6S/1W-23E1 1958-72 1958-72 189 

6S/2W-24C3 1960-72 1960-72 225 

6S/2W-24C7 1960-72 1960-72 422 

6S/2W-25C1 1960-72 1960-72 255 

6S/2W-25C1 1921-74 1932-74 255 

7S/1E-7R1 1915-74 1916-74 477 

7S/1E-9D2 1958-72 1960-63, 258 

1965-72 

7S/1E-16C5 1958-72 1960-72 477 

Helm (1977, figs. 9, 10) demonstrated that carefully 

evaluated values of K' and S~kv can be used to predict 

aquifer-system behavior with reasonable accuracy over 

periods of several decades. A good example of the simulation result for six decades of record using values listed 

in table 4 is shown in figure 29 (from Helm, 1977, fig. 10). 

COMPACTION-SUBSIDENCE RATIOS 

The amounts of measured compaction and measured 

subsidence at extensometer sites where leveling data are 

available are shown in table 5. The ratio of measured compaction to measured subsidence, expressed as a percentage, was computed for the period of record available. 

Percentages are sometimes erratic for short periods of 

control at some sites, as shown by table 5; some periods 

of measured compaction and leveling are combined to 

make the compaction/subsidence ratios more consistent, 

and some are not shown as a result of incomplete data 

or mechanical problems at the extensometer site. 

At extensometer site 6S/2W-24C, the compaction/subsidence ratio for the full period of the leveling record 

(November 1960 to February 1967) increased from 11 percent for C4 (the 250-ft extensometer) to 50 percent for 

C3 (the 550-ft extensometer) and to 105 percent for C7 

(the 1,000-ft extensometer). For the shorter periods 

between levelings, the ratio for 24C3 was surprisingly 

consistent, whereas the ratio for 24C4 was erratic. For 

extenso meter 24C7, the measured compaction during 

each of the shorter periods exceeded the measured subsidence and averaged 105 percent for the six years to 

Weighted K' S' S' skv ske 

feetx 10 

_6 

- 1-x10 

4 

- 1-x10 

6 average - - b' equiv day foot foot 

15.1 1.18 1.4 7.5 

18 .56 13.1 3.96 

53.1 12.5 3.35 2.60 

18 .75 3.26 15.8 

18 .72 3.29 

18 1.87 2.25 

18 .82 6.1 7.92 

18 3.28 2.3 2.2 

February 1967. The 5-percent excess is attributed to 

mechanical problems in recording the compaction. 

At extensometer site 7S/1E-16C5 (908 ft deep) the 

aquifer system is about 800-ft thick, from 200 to 1,000 

ft below land surface. If the compaction potential was 

uniform with depth, the part measured by extensometer 

16C5 would be 708/800, or 88.percent of the subsidence. 

Actually, for the 8.5 years from October 1960 to May 1969 

the compaction measured at 16C5 equaled 87 percent of 

the subsidence. 

At extensometer site 7S/1E-16C6, the extensometer 

cable anchor was landed at the 1, 000-ft depth, believed 

to be the bottom of the aquifer system. For the full 

8.5-year period to May 1969, the measured compaction 

was equal to 99 percent of the subsidence, indicating that 

the anchor truly was landed at the base of the compacting system. 

In the 13.5 years from May 1969 through 1982 the cumulative compaction at the two 1,000-ft extensometers, 

6S/2W-24C7 in Sunnyvale and 7S/1E-16C6-11 in San 

Jose, was 0.24 ft and 0.44 ft, respectively (table 3). During the six years 1977 to 1982, inclusive, the cumulative 

compaction was very small, about 0.03 ft at 6S/2W-24C7 

and 0.07 ft at 7S/1E-16C6-11. 

A.K. Williamson (U.S. Geological Survey, oral commun., 

1981) noted an interesting relationship in the San Joaquin 

Valley between extensometer depth and the compactionsubsidence ratio (Ireland and others, 1984, p. 153 and fig. 

67). We have plotted a similar figure for the few extensometers in north Santa Clara County (fig. 30). Compaction/subsidence ratios based on the full period of available 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F43 

records were used in preparing figure 30. Although there 

were only seven ratios to plot, they surveyed a wide range 

of extensometer depths: one was at shallow depth, three 

were at mid-depth (400 to 600ft deep), and three were 

at full depth of the aquifer system (about 1,000 ft). All 

were centrally located within the confined system and at 

either of the two centers of maximum subsidence. 

Together, they defined a relatively "tight" curve, which 

indicates that all the compaction due to ground-water 

withdrawal occurs at depths between about 200 and 1,000 

ft. Between these depths the compaction/subsidence ratio 

is shown to approximate a linear function of the logarithm 

of the depth. The least-squares regression equation of the 

function has an R-squared value of 0.95, which indicates 

that 95 percent of the variation of the ratio is explained 

by the equation, whereas 5 percent of its variation is random (or attributable to other factors not considered). 

On the basis of the relation shown in figure 30, a 300-ft 

extensometer in a subsidence area in the Santa Clara 

Valley would record approximately 18 percent of the total 

subsidence measured at the well site, and a 700-ft extensometer would record approximately 72 percent of the 

total subsidence at the site. 

~ 

w 500 

zwa:: -LL.w 

w z ~ 600 

(!)-<( 

zen~ 1oo 

<Ccn n ~ ~ 800 ~ 

en 

0 

2 

3 ~ 

w 

w 4 LL. 

z 5 

z 6 0 

i= 

u 7 

<( 

~ 8 ~ 

0 

u 9 

10 

11 

12 

13 

1920 1930 1940 

COMPUTER PLOTS OF FIELD RECORDS 

The records of compaction and of depth to water in the 

extensometer wells or in nearby observation wells have 

been computerized on a daily basis, and computer plots 

of these records through 1979 are included here as figures 

31-42. Graphs of subsidence of a surface bench mark 

located at the measuring site, determined by periodic 

instrumental surveys to a stable bench mark, are also included for the first part of the period of compaction 

measurements. (No bench-mark surveys have been made 

since 1969.) Site locations are shown in figure 1. 

The Geological Survey continued collecting field records 

of compaction and depth to water at these sites in the 

three years 1980-82 (figs. 43-48). Early in 1983 the operation and maintenance of the principal sites was taken over 

by the Santa Clara Valley Water District. 

The computer program and extensometer and waterlevel data collected on this long-term (mechanics of 

aquifers) study on land subsidence are stored on computer 

tape Number 220691, type 6250BPI, at the U.S. Geological Survey Information Services Division, Reston, 

Virginia. 

1950 1960 1970 

FIGURE 29.-Simulation of compaction based on water-level data for well 7S/1E-7R1 (1915-74) and on subsidence measured at bench mark P7 

(from Helm, 1977, fig. 10). 
F44 MECHANICS OF AQUIFER SYSTEMS 

TABLE 5.-Compaction versus subsidence for periods of leveling in north Santa Clara County 

[Ratio of compaction/subsidence: value shown on total line is ratio for period of record] 

Ratio of 

Extensometer Depth Bench Dates of Subsidence Compaction compaction mark number (feet) number leve;Ling (feet) (feet) to subsidence 

(percent) 

6S/1W-23El 425 Al76 11/60-2/67 2.392 1.033 43 

6S/2W-24C4 250 Jlll 11/60-2/63 .807 .091 11 

2/63-4/65 .683 .085 12 

4/65-2/67 .544 .045 8 

Total ..................... 2.034 .221 11 

6S/2W-24C3 550 Jlll 11/60-2/63 .807 .414 51 

2/63-4/65 .683 .341 so 

4/65-2/67 .544 .267 49 

Total ..................... 2.034 1.022 so 

6S/2W-24C7 1,000 Jlll 11/60-2/63 .807 .845 105 

2/63-4/65 .683 .738 108 

4/65-2/67 .544 .547 101 

Total ..................... 2.034 2.130 105 

7S/1E-9D2 605 JG4 10/60-2/63 1. 552 .762 48 

2/63-2/67 1. 551 (1) 

2/67-5/69 .230 .118 51 

7S/1E-16CS 908 JG2 10/60-2/63 l. 919 1. 677 87 

2/63-3/67 1. 923 1.604 83 

3/67-5/69 .366 .365 100 

Total ..•...........•...... 4.208 3.646 87 

7S/1E-16C6 1 '000 JG2 10/60-3/67 3.842 3.812 99 

3/67-5/69 .366 .363 99 

Total .............•....... 4.208 4.175 99 

1No extensometer data from 4/22/63 to 6/18/65. 

The primary purpose of including these records is to 

show graphically the measured compaction and subsidence at specific sites, and (so far as possible) the change 

in effective stress in the pertinent aquifers at these sites, 

as indicated by the hydrographs. Because of the confining beds and multiple-aquifer/aquitard system, it is difficult to obtain water-level measurements that specifically 

represent the average stress change for the interval in 

which compaction is being measured. 

stress-strain relationships are plotted for figures 31-41. 

In these figures, compaction equals the change in thickness of the compacting interval, and strain refers to the 

compaction divided by the thickness of the compacting 

interval. 

As indicated in table 6, stress-strain relationships 

are shown for figure 31 (extensometer 68/1 W-23E1) 

and for figures 40 and 41 at the San Jose core-hole 

site (extensometers 7S/1E-16C5 and 16C6-11, 

Change in applied stress and stress-compaction or respectively). 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F45 

120.-------------r-------------~------------~------------~------------~----------~ 

• 

100 

RATIO (%) = 149{LOG10 OEPTH)-352 • 

..._ 

z 

I.U 

(.) 

a: 80 I.U 

0... 

~ 

w 

(.) 

z 

I.U 

c 

Ci) 

co 

:::::> 

(/) 

0 60 ..._ 

z 

0 

i= 

(.) • cs:: 

0... 

~ 

0 

(..') 

~ 

0 

0 40 

i= 

cs:: 

a: 

EXPLANATION 

20 • EXTENSOMETER WELL 

OL-------------L-L-----------L-------------L-------------L-------------~----------~ 

0 200 400 600 800 1000 1200 

DEPTH OF EXTENSOMETER, IN FEET 

FIGURE 30.-Compaction/subsidence ratios versus depth at extensometer wells in north Santa Clara County. 

SELECTED REFERENCES 

Atwater, B.F., Redel, C.W., and Helley, E.J., 1977, Late Quaternary 

depositional history, Holocene sea-level changes, and vertical crustal 

movement, southern San Francisco Bay, California: U.S. Geological 

Survey Professional Paper 1014, p. 1-15. 

California Department of Water Resources, 1967, Evaluation of groundwater resources, South San Francisco Bay, appendix A, Geology: 

Bulletin 118-1, 153 p. 

__ 1975, Evaluation of ground water resources, South San Francisco Bay, v. 3, Northern Santa Clara County area: Bulletin 118-1, 

133 p. (contains 11 geologic sections, fault map, and 10 sheets of 

subsurface deposits by depth intervals). 

California State Water Resources Board, 1955, Santa Clara Valley 

investigation: Bulletin 7, 154 p. 
F46 MECHANICS OF AQUIFER SYSTEMS 

Clark, W.O., 1924, Ground water in Santa Clara Valley, California: U.S. 

Geological Survey Water-Supply Paper 519, 209 p. 

Dibblee, T.W., 1966, Geologic map and sections of the Palo Alto 

15-minute quadrangle, California: California Division of Mines and 

Geology, map sheet 8. 

Fowler, L.C., 1981, Economic consequences of land surface subsidence: Journal of Irrigation and Drainage Division, Proceedings 

of the American Society of Civil Engineers, v. 107, no. IR2, 

p. 151-158. 

Green, J.H., 1962, Compaction of the aquifer system and land subsidence 

in the Santa Clara Valley, California: U.S. Geological Survey Professional Paper 450-D, p. 175-178. 

__ 1964, The effect of artesian-pressure decline on confined aquifer 

systems and its relation to land subsidence: U.S. Geological Survey 

Water-Supply Paper 1779-T, 11 p. 

Helm, D.C., 1977, Estimating parameters of compacting fine-grained 

interbeds within a confined aquifer system by a one-dimensional 

simulation of field observations: International Association of 

Hydrological Sciences, International Symposium on Land Subsidence, 2d, Anaheim, California, December 1976, Publication 121, 

p. 145-156. 

__ 1978, Field verification of a one-dimensional mathematical model 

for transient compaction and expansion of a confined aquifer system, 

in Verification of mathematical and physical models in hydraulic 

engineering: American Society of Civil Engineers, Proceedings of 

Specialty Conference, College Park, Maryland, p. 189-195. 

Hunt, G.W., 1940, Description and results of operation of the Santa Clara 

Valley Water Conservation District's project: American Geophysical 

Union Transactions, part 1, p. 13-32. 

Ireland, R.L., Poland, J.F., and Riley, F.S., 1984, Land subsidence in 

the San Joaquin Valley, California, as of 1980: U.S. Geological 

Survey Professional Paper 437-1, 93 p. 

Jennings, C.W., and Burnett, J.L., 1961, Geologic map of California, 

Olaf P. Jenkins, ed.: California Division of Mines and Geology, San 

Francisco sheet, scale 1:250,000. 

Johnson, A.l., Moston, R.P., and Morris, D.A., 1968, Physical and 

hydrologic properties of water-bearing deposits in subsiding areas 

in central California: U.S. Geological Survey Professional Paper 

497-A, 71 p. 

Lofgren, B.E., 1968, Analysis of stresses causing land subsidence: U.S. 

Geological Survey Professional Paper 600-B, p. B219-B225. 

Meade, R.H., 1967, Petrology of sediments underlying areas of land subsidence in central California: U.S. Geological Survey Professional 

Paper 497 -C, 83 p. 

__ 1968, Compaction of sediments underlying areas of land subsidence in central California: U.S. Geological Survey Professional 

Paper 497-D, 39 p. 

Poland, J.F., 1969, Land subsidence and aquifer-system compaction, 

Santa Clara Valley, California, USA, in Tison, L.J., ed., Land subsidence, v. 1: International Association of Scientific Hydrology (is 

now International Association of Hydrological Sciences) Publication 

88, p. 285-292. 

__ 1977, Land subsidence stopped by artesian-head recovery, Santa 

Clara Valley, California: International Association of Hydrological Sciences, International Symposium on Land Subsidence, 

2d, Anaheim, California, December 1976, Publication 121, 

p. 124-132. 

__ 1984, Case history No. 9.14, Santa Clara Valley, California, USA, 

in Poland, J.F., ed., Guidebook to studies of land subsidence due 

to ground-water withdrawal: United Nations Educational, 

Scientific and Cultural Organization, 7 Place de Fontnoy, 75700 

Paris, France, p. 279-290. 

Poland, J.F., and Davis, G.H., 1969, Land subsidence due to the 

withdrawal of fluids: Geological Society of America, Reviews in 

Engineering Geology, v. 2, p. 187-269. 

Poland, J.F., and Green, J.H., 1962, Subsidence in the Santa Clara 

Valley, California-A progress report: U.S. Geological Survey 

Water-Supply Paper 1619-C, p. C1-C16. 

Poland, J.F., Lofgren, B.E., Ireland, R.L., and Pugh, R.G., 1975, Land 

subsidence in the San Joaquin Valley, California, as of 1972: U.S. 

Geological Survey Professional Paper 437-H, 78 p. 

Poland, J.F., Lofgren, B.E., and Riley, F.S., 1972, Glossary of selected 

terms useful in studies of the mechanics of aquifer systems and land 

subsidence due to fluid withdrawal: U.S. Geological Survey WaterSupply Paper 2025, 9 p. 

Riley, F.S., 1969, Analysis of borehole extensometer data from central 

California, in Tison, L. J., ed., Land subsidence, v. 2: International 

Association of Scientific Hydrology (is now International Association of Hydrological Sciences) Publication 89, p. 423-431. 

Rogers, T.H., 1966, Geologic map of California, Olaf P. Jenkins, ed.: 

California Division of Mines and Geology, San Jose sheet, scale 

1:250,000. 

Rogers, T.H., and Williams, J.W., 1974, Potential seismic hazards in 

Santa Clara County, California: California Division of Mines and 

Geology, Special report 107, 39 p., 6 pl. 

Roll, J.R., 1967, Effect of subsidence on well fields: American Water 

Works Association Journal, v. 59, no. 1, p. 80-88. 

Santa Clara Valley Water Conservation District, 1964, Hydrologic data 

for north Santa Clara Valley (California), seasons of 1935-36 to 

1960-61, v. 3, surface-water summary and ground-water fluctuation: Santa Clara Valley Water Conservation District, mimeo report, 

p. 828-1230. 

__ 1967, Hydrologic data for north Santa Clara Valley (California), 

seasons of 1961-62 to 1965-66, v. 4, precipitation, evaporation, 

reservoir fluctuation, surface-water flow, surface-water summary, 

ground-water fluctuation, and ground-water quality: Santa Clara 

Valley Water Conservation District, mimeo report, p. 1231-1705. 

__ 1977, Historical ground-water level data, 1924-1977: Santa Clara 

Valley Water District, mimeo report, 423 p. 

Tibbetts, F.H., and Kieffer, S.E., 1921, Report to Santa Clara Valley 

Water Conservation Committee on Santa Clara Valley Water Conservation project: Santa Clara Valley Water Conservation District, 

unpublished typwritten report, 243 p. 

Tolman, C.F., 1937, Ground water: New York, McGraw-Hill, first edition, 

593 p. 

Tolman, C.F., and Poland, J.F., 1940, Ground-water, salt-water infiltration, and ground-surface recession in Santa Clara Valley, Santa Clara 

County, California: American Geophysical Union Transactions, pt. 1, 

p. 23-35. 

U.S. Bureau of Reclamation, 1961, Central Valley Project, San Felipe 

Division geology and ground-water resources appendix: U.S. Bureau 

of Reclamation, Geology Branch, Project Development Division, 

118 p. 

U.S. Coast and Geodetic Survey, 1956, San Jose area, California, 

1912-54leveling (190A California); 42 p. (A compilation of adjusted 

elevations for all bench marks in the level network.) 

Webster, D.A., 1973, Map showing areas bordering the southern part 

of San Francisco Bay where a high water table may adversely affect 

land use: U.S. Geological Survey Miscellaneous Field Studies Map 

MF-530, scale 1:125,000. 
FIGURES 31-48; TABLE 6 
F48 

e 200 

!;~ 160 QC 

~~ 120 to 

:~ 80 

~­z- 40 

MECHANICS 1JF AQUIFER SYSTEMS 

Stress-strain 

~ ~o----~------,~o----~,5~----~20------2~5------3~0------3~5----~40~----~45------5~0------5~5------s~o----~65~~--~----~75x10~ 

STRAIN 

D 

FIGURE 31.-Hydrograph, change in applied stress, compaction, subsidence, and stress-strain relationship, 6S/1W-23El. A, Hydrograph of well 

6S/1 W -23E 1, perforated 170-177, 244-255, 311-315, and 343-350 ft. B, Change in applied stress, water table assumed constant. C, Compaction to 425-ft depth at well6S/1W-23E1 and subsidence of bench mark A176, 0.6 mi west. D, Stress change versus strain (225-ft thickness). 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F49 

Q ! i! :li FRt·-.. -- -1---... t.~r·.t .. !-- ... : -RSi---._,.- f·</•·i··--. --1·----+·~ .... :,-...,. -·r .. ---'1 ~-:_ ---,---------,--------r -... :---~· 1 ~w 8 

i ~ 1:i I I I I I I I I I I I I I I +-~ .. ,. 1-· I I I I I 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 

~ 160 

Q 

~~ c 120 .... ~ 

~~ ~ Q 80 c.,_ 

: ~ 40 c,:,Z 

z-

~ 0 

0 0.1 0.2 0.3 0.4 

COMPACTION, IN FEET 

D 

c 1977 1978 1979 1980 

FIGURE 32.-Hydrograph, change in applied stress, compaction, and stress-compaction relationship, 6S/2W-24C4. A, Hydrograph ofwell6S/2W-24C4, 

depth 250ft. B, Change in applied stress, water table assumed constant. C, Compaction to 250-ft depth at well6S/2W-24C4. D, Stress change 

versus compaction of deposits above 250-ft depth. 
F50 MECHANICS OF AQUIFER SYSTEMS 

c ji: J!l~ 1 n~--1----l-===:=--tf~-[-----J-~-J-1~----1--~--r-r~=:=:==+~~r·~=--;-~I I u 8 

~ i l~ [? I I I I I I c~~K'"'~ o-250 jMt I I I I I I I ~ 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 . 1970 1971 1972 1973 1974 1975 

u c 

h ·:: b· ............... ' ~ .... ~ ~ 40 

!!:t: 

~ ~ 0 ~!! 0 0.1 0.2 0.3 0.4 

~ COMPACTION, IN FEET 

D 

FIGURE 33.-Hydrograph and change in applied stress, 6S/2W-25Cl; compaction and stress-compaction relationship, 

6S/2W-24C4. A, Hydrograph of well 6S/2W-25Cl, depth 500ft. B, Change in applied stress, 6S/2W-25Cl, water 

table assumed constant. C, Compaction to 250-ft depth at well6S/2W-24C4. D, Stress change versus compaction 

of deposits above 250-ft depth. 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F51 

~ i 

u 

1it!! 

1960 1961 1962 

ft 

1963 1964 

I 

1965 1966 1967 

I I I 

1968 

I 

1969 

I 

1970 

I 

1971 

I 

1972 

t~·~t· 1973 1974 1975 .. ·rt~l 1976 I 

1977 

I 

1978 1979 

I~ I~ 1980 

c 

160 r 

120~ 

::f.~. o~~~~--~~0.~5~--~~~~~.-o~~--~~~1.5 

~ 

COMPACTION, IN FEET 

D 

FIGURE 34.-Hydrograph, change in applied stress, compaction, and stress-compaction relationship, 6S/2W-24C3. A, Hydrograph ofwell6S/2W-24C3, 

depth 550ft. B, Change in applied stress, water table assumed constant. C, Compaction to 550-ft depth at well6S/2W-24C3. D, Stress change 

versus compaction of deposits above 550-ft depth. 
F52 MECHANICS OF AQUIFER SYSTEMS 

A 

B 

~ i I!!tffll i I I ,r .. ··t·"l ... I I II 1:r I I I i 1: I I L) 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 

c 

s; 8o ~'4- a..C 

~ ~ 120~ c ..... 40 Stress-compaction 

~~ 

~z o~~~~--~~~~~~~~~~--~~~ 

~- 0 0.5 1.0 1.5 

~ COMPACTION, IN FEET 

D 

FIGURE 35.-Hydrograph and change in applied stress, 6S/2W-25Cl; compaction and stress-compaction relationship, 6S/2W-24C3. A, Hydrograph 

of well6S/2W-25Cl, depth 500ft. B, Change in applied stress, 6S/2W-25Cl, water table assumed constant. C, Compaction to 550-ft depth 

at well 6S/2W-24C3. D, Stress change versus compaction of deposits above 550-ft depth. 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F53 

c 

D 

1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 

E 

.n 

~ 160 

e:cz: 

Cl) ~ 120 QC 

~~ 

~~ 80 

""t- z ... -~ 40 ... t:)Z 

z-

"" % 0 u 0 0.2 0.4 0.6 0.8 1.0 1.2 

COMPACTION, IN FEET 

FIGURE 36.-Hydrograph and change in applied stress, 6S/2W-24C4; 

compaction and stress-compaction relationship, 6S/2W -24C3 and 

6S/2W-24C4. A, Hydrograph of well 6S/2W-24C4, depth 250ft. B, 

Change in applied stress, 6S/2W -24C4, water table assumed constant. 

F 

C, Compaction to 250-ft depth at well 6S/2W-24C4. D, Compaction 

to 550-ft depth at well 6S/2W-24C3. E, Compactio11 in 250-550-ft depth 

interval. F, Stress change versus compaction of deposits from 

250-550-ft depth. 
F54 MECHANICS OF AQUIFER SYSTEMS 

c 

D 

~~~!11ft I m I I .I c~·r .. ~t~"ll I : M 

2.5 L..--..L......-...L.......--L--.......L-~-L-........l..-........L--..I--'---.J......-~..J....--...L--.......__-J...._....J.... _ __, 

1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 

u) 

~ 120 e:ffi "'tcc 

!!!~ 80 

~ .. ~c 

c ..... 40 zw 

.... 

-~ 

tDZ 0 zc 

X 

(.) 

0 0.2 

E 

Stress·compaction 

0.4 0.6 0.8 

COMPACTION, IN FEET 

F 

1.0 1.2 

FIGURE 37.-Hydrograph and change in applied stress, 6S/2W-25Cl; compaction and stress-compaction relationship, 

6S/2W-24C3 and 6S/2W-24C4. A, Hydrograph of well 6S/2W-25Cl, depth 500 ft. B, Change in applied stress, 

6S/2W-25Cl, water table assumed constant. C, Compaction to 250-ft depth at well 6S/2W-24C4. D, Compaction 

to 550-ft depth at well6S/2W-24C3. E, Compaction in 250-550-ft depth interval. F, Stress change versus compaction of deposits from 250-550-ft depth. 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F55 

ll:~ ! ! 1~ 1~-1-------1~-g;ot:·j"'---·1· ·---1--i<,l·····----1-··--···1·---i·--···1--------1---~~1--~-~·-~ ~c c-' A 

1~ Jill I ft I I~ I I I 

c 

-0.5 

~ 0.0 

~ 0.5 .... 

~ 1.0 

z 1.5 C) 2.0 ~ 2.5 : 

~ 3.0 

8 3.5 

I 

~ ~r----... 

"'----r-.... Compaction, 0-1000 feet 

-- '-------... -r--- ---t----. 

Bench mark J 111 

-- ....___ r--... 

I r-- 4.0 

D 

iliEIII : I I I I I I I 'tt·-.. ·1···1 I I I 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 

E 

!f::f~~/}~ ~~ 

; m 40 Stress-compaction 

~~ o~~~~~--------~~~----~~--~~-------~~~._~ 5 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 

COMPACTION, IN FEET 

F 

~ 

~ 

~ 

0.0 ~ 

0.5 ;:. 

1.0 ~ 

1.5 2 2.0 ~ 

2.5 ~ 

FIGURE 38.-Hydrograph and change in applied stress, 6S/2W-24C7; 

compaction, subsidence, and stress-compaction relationship, 

6S/2W-24C3 and 6S/2W-24C7. A, Hydrograph of well 6S/2W-24C7, 

perforated 807-851 and 880-903 ft. B, Change in applied stress, 

6S/2W-24C7, water table assumed constant. C, Compaction to 550-ft 

depth at well 6S/2W-24C3. D, Compaction to 1,000-ft depth at well 

6S/2W-24C7, and subsidence at bench mark J111, 400ft southeast. 

E, Compaction in 550-1,000-ft depth interval. F, Stress change versus 

compaction of deposits from 550-1,000-ft depth. 
F56 MECHANICS OF AQUIFER SYSTEMS 

-0.5 ,_ 0.0 .... 

.... 0.5 

iE 1.0 

z 1.5 0 

2.0 t; 

: 2.5 

.........____ 

1'---. .........__ 

.......... 

~ 

Bench mark JG4 

2 3.0 0 

(..) 3.5 

4.0 

---t----- t--

--- ----t--

1--

I I 

I 

I l 

Compaction, 0-605 feet 

0.0 t;:; 

0.5 ~ 

1.0 iE 

1.5 ~ 

2.0 ffi 

2.5 ~ 

3.0 ~ 

3.5 U) 

1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 

en 

~ 160 

~~ oc 

!!:!ll: 120 

~~ c,_ 80 z .... 

.... 

-~ 

~z 40 zc 

5 0 

0 

Stress-compaction 

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 

COMPACTION, IN FEET 

D 

FIGURE 39.-Hydrograph, change in applied stress, compaction, subsidence, and stress-compaction relationship, 7S/1E-9D2. A, 

Hydrograph of well 7S/1E-9D2, depth 605 ft. B, Change in applied 

stress, water table assumed constant. C, Compaction to 605-ft depth 

from May 1960 to April1963 and from January 1965 to January 1978, 

c 

en 

~ 160 

~ffi 

~ !« 120 .... :J: 

~ :5 80 c,_ 

: ti! 40 ~z 

zc 

5 0.1 0.2 0.3 0.4 0.5 0.6 0.7 

COMPACTION, IN FEET 

E 

and subsidence of bench mark JG4 at well7S/1E-9D2. D, Stress change 

versus compaction of deposits above 605-ft depth, May 1960 to April 

1963. E, Stress change versus compaction of deposits above 605-ft 

depth, January 1965 to January 1968. 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F57 

-0.5 

0.0 

0.5 

8 10 

... 1.5 

:!!!: 2.0 

~ 2.5 

~ 3.0 

~ 3.5 

Q 4.0 

(.) 4.5 

5.0 

5.5 

'-

'--. ........ '\. ~ ........._.._ 

'-., 

r----..... ~--.....__ 

............_ "---

~- Bench mark JG2 .................. 

B 

'---

-- --. 

Compaction. ·o-908 feet 

0.0 

0.5 ..... 

1.0 ~ 1.5 :!!!: 

2.0 ... · 

2.5 ~ 3.0 ~ 

3.5 ~ 

4.0 "' 

4.5 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 

~ 200 

180 

160 

Q 140 

120 Q.. 

Q.. 100 .. 80 :!!!: 

s 60 

z 40 

~ 20 

0 

0 10 15 20 25 

FIGURE 40.-Hydrograph, change in applied stress, compaction, subsidence, and stress-strain relationship, 7S/1E-16C5. A, Hydrograph 

of well 7S/1E-16C5, depth 908ft. B, Change in applied stress, water 

table assumed constant. C, Compaction to 908-ft depth at well 

c 

30 

STRAIN 

D 

35 40 45 50 55 60 63 x 1o-• 

7S/1E-16C5 and subsidence of bench mark JG2, located in top of northeast concrete curb of 12th Street, approximately 20 ft west of well 

7S/1E-16C5. D, Stress change versus strain (708-ft thickness). 
F58 MECHANICS OF AQUIFER SYSTEMS 

~ .:! I ... 160 

Q 200 ji,Qg'~iFfi\fvf~J qq Gf'1it9t9?=f'1YEtffH I 

-0.5 

0.0 

0.5 

..... 1.0 

1.5 

~ 2.0 

~ 2.5 

3.0 

~ 3.5 

ri 4.0 

8 4.5 

'----+---.. 

\ 

f--... ........ Bench mark JG2 '--.... _'-..,. 

'--.... .._____,_ 

""'-.., ----......_,_ 

---...... Bench mark JG3 

I ----- 5.0 

5.5 

B 

----.... ........... 

----- ""----- ---.... 

------ - 1-

I I 

l l 

I I 

I I 

Compaction 0-1000 feet 

0.0 

0.5 

1.0 

1.5 

2.0 

2.5 

3.0 

3.5 

4.0 

4.5 

6.0 5.0 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 

180 

"" 160 

..... 140 c 

~ 120 

:5 100 

..... 80 Stress·strain 

60 

~ 40 

20 

0 

0 10 15 20 25 

FIGURE 41.-Hydrograph and change in applied stress, 7S/1E-16C5; 

compaction, subsidence, and stress-strain relationship, 7S/1E-16C6-ll. 

A, Hydrograph ofwell7S/1E-16C5, depth 908ft. B, Change in applied 

stress, 7S/1E-16C5, water table assumed constant. C, Compaction to 

1,000-ft depth at well 7S/1E-16C6-ll (see fig. 42B) and subsidence 

at bench mark JG2 from October 1960 to February 1963 and bench 

c 

30 

STRAIN 

D 

35 40 45 50 55 60 63 x 10-4 

mark JG3 from February 1963 to May 1969. (Bench mark JG2 is 

located in top of northeast concrete curb of 12th Street, approximately 

20ft west ofwell7S/1E-16C5; bench mark JG3 is located approximately 300ft north of bench mark JG2.) D, Stress change versus strain 

(800-ft thickness). 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F59 

-0.5 

0.0 

0.5 

t;:; 1.0 

~ 1.5 

~ 2.0 

z 2.5 

§ 3.0 

~ 3.5 

:::E 4.0 

8 4.5 

5.0 

5.5 

6.0 

~ 

"\. 

"'"h. Bench mark JG2 ~ h. 

"\. 

~"' 

" 

!--.. 

--r-----... .........._ ......_ Bench mark JG3 

I 

r---... .............. 

---- "'---,......_ -...... -

Compaction 0-1000 feet 

- 1-

0.0 

0.5 ..... 

1.0 ~ 

1.5 ; 

2.0 • 

2.5 ~ 3.0 ::!l 3.5 ~ 

4.0 ~ 

4.5 

1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 5.0 

FIGURE 42.-Hydrograph, compaction, and subsidence, 7S/1E-16C6-ll. 

A, Hydrograph of well 7S/1E-16Cll, perforated 551-571, 598-618, 

and 640-660 ft. B, Compaction to 1,000-ft depth at well 7S1E-16C6-11 

(7S/1E-16C6 from June 1960 to June 1969 and 7S/1E-16Cll from June 

1969 to January 1980) and subsidence at bench mark JG2 from October 

0 

~~-- ow _,w 

wLL. 40 

mz 

Hydrogr~ph, 24C3 

. . . 

- /'.... ............__. -----...: ..... - ........__, a:-

w • 80 1-w <Cu 

~~ 120 oa: 

~--~ 

:z:c 160 

1-z 

Q.<( 

~...I 200 . . . A 

1.1 . . . 1- 1.2 w 

w LL. 

~ 1.3 

z Compaction, 0-550 feet 

0 1.4 

i= 

u 

_.,. 

<( 1.5 

-~rv 

~ ~ 

Q. 

~ 

0 

u 1.6 

1.7 . . 1980 1981 1982 1983 

B 

FIGURE 43.-Hydrograph and compaction, 6S/2W-24C3. A, Hydrograph 

of well 6S/2W-24C3, depth 550ft. B, Compaction to 550-ft depth at 

well 6S/2W-24C3. 

8 

1960 to February 1963 and bench mark JG3 from February 1963 to 

May 1969. (Bench mark JG2 is located in top of northeast concrete 

curb of 12th Street, approximately 20ft west of well 7S/1E-16C5; 

bench mark JG3 is located approximately 300 ft north of bench mark 

JG2.) 

~ 1- 0 

g~ 

wLL. 40 

IDz 

a:-

~ u.i 80 

<(~ 

~ ~ 120 

~--~ 

i=·~ 160 Q.<( 

~...I 200 

0.0 

1-

w 0.1 w LL. 

~ 0.2 

z 

0 0.3 i= 

u 

<( 

Q. 0.4 

~ 

0 

u 0.5 

0.6 

.... !' -, T ..... 

Hydrograph, 24C4 .....--.. .A. ___...-'\ 

\.__/ r--' v \ I 

'V 

A 

....,.. "TO , . ' ' I I I I I ' . . ... ' 

Compaction, 0-250 feet 

-

.. . 1980 1981 

B 

1982 1983 

FIGURE 44.-Hydrograph and compaction, 6S/2W-24C4. A, Hydrograph 

of well6S/2W-24C4, depth 250ft. B, Compaction to 250-ft depth at 

well 6S/2W-24C4. 
F60 MECHANICS OF AQUIFER SYSTEMS 

~~--- ow 0 ...JW 

wu.. 

mz 

a:- 40 w • 1-w <(u 80 ~~ ------r - ----- _I 

Hydrograph, 24C7 

0~ 1- (/) 120 

J:c 1-z a..<( 160 ~...J A 

2.6 -r 

1-

w 2.7 w 

u.. 

~ 2.8 

z Compaction, 0-1 000 feet 

0 2.9 

i= 

u <( 3.0 a.. ~---~/ ~ / 

::iii - 0 

u 3.1 

3.2 . . . . . 1980 1981 1982 1983 

B 

FIGURE 45.-Hydrograph and compaction, 6S/2W-24C7. A, Hydrograph 

of well6S/2W-24C7, perforated 807-851 and 880-903 ft. B, Compaction to 1,000-ft depth at well 6S/2W-24C7. 

40 

~~--- ow 80 ...JW 

wu.. 

Hydrograph, 16C5 

mz 

a:- 120 w . 1-w <(u 160 ~~ 

0~ I-(/) 200 

J:c 

1-z a..<( 240 

~...J 

280 

A 

4.0 -T . 1-

w 4.1 w 

u.. 

~ 4.2 

z· Compaction, 0-908 feet 

0 4.3 i= 

u <( 

a.. 4.4 

v ~ 

~ /~ 

::iii 

0 

u 4.5 

4.6 

1980 1981 1982 1983 

B 

FIGURE 46.-Hydrograph and compaction, 7S/1E-16C5. A, Hydrograph 

of well 7S/1E-16C5, depth 908ft. B, Compaction to 908-ft depth at 

well 7S/1E-16C5. 

40 

~~--- Hydrograph, 16C5 

ow 80 ...JW 

wu.. 

lllz 

a:- 120 w • 1-w <(u 

~~ 160 

0~ I- (f) 200 

J:c 

1-z a..<( 240 ~...J 

280 

A 

4.6 . -r .. 1-

w 4.7 w 

u.. Compaction.! 0-1000 feet 

~ 4.8 

z 

0 4.9 i= 

u 

I~ _,...-...., ............ 

-- - "-.../ ....__., 

<( 

a.. 5.0 

::iii 

0 

u 5.1 

5.2 

1980 1981 1982 1983 

B 

FIGURE 47.-Hydrograph 7S/1E-16C5, and compaction 7S/1E-16C11. 

A, Hydrograph of well 7S/1E-16C5, depth 908ft. B, Compaction to 

1,000-ft depth at well 7S/1E-16C11. 

0 

~~--- ow 40 ...JW 

wu.. 

mz 

a:- 80 

Hydrograph, 16C 11 

w • 1-w <(u 120 ~~ 

0~ I- (f) 160 

J:c 

1-z a..<( 200 ~...J 

240 

A 

4.6 ' -.- ~ 

1-

w 4.7 I 

w 

u.. Compaction, 0-1 000 feet 

~ 4.8 

z 

0 4.9 

i= 

u 

I~ ~ ~ 

-- - "-.../ ....__., 

<( 5.0 a.. 

::iii 

0 

u 5.1 

5.2 __.__._ . 1980 1981 1982 1983 

B 

FIGURE 48.-Hydrograph and compaction, 7S/1E-16Cll. A, Hydrograph 

of well 7S/1E-16Cll, perforated 551-571, 598-618, and 640-660 ft. 

B, Compaction to 1,000-ft depth at well 7S/1E-16Cll. 
LAND SUBSIDENCE IN THE SANTA CLARA VALLEY, CALIFORNIA, AS OF 1982 F61 

TABLE 6.-Wellsfor which records are included in.figures 31-42 

Figure Well 

number number 

31 6S/1W-23E1 

32 6S/2W-24C4 

33 -24C4 

-25C1 

34 -24C3 

35 -24C3 

-25C1 

36 -24C4 

-24C3 

37 -24C4 

-24C3 

-25C1 

38 -24C3 

-24C7 

39 7S/1E-9D2 

Type of 

extensometer 

Cable 

Cable 

and pipe. 

---do---

None 

Cable 

and pipe. 

--do---

None 

Cable 

and pipe. 

---do---

---do---

---do---

None 

Cable 

and pipe. 

---do---

Cable 

40 -16C5 Cable 

41 7S/1E-16C6-11 Cable 

and pipe. 

42 

-16C5 Cable 

-16C6-11 Cable 

and pipe. 

Water-level 

recorder or 

observation 

well 

Recorder 

Observation 

----do-----

----do-----

----do-----

----do-----

----do-----

----do-----

----do-----

----do-----

----do-----

----do-----

----do-----

----do-----

Recorder 

---do---

---do---

---do---

---do---

Depth 

of well 

(feet) 

425 

250 

250 

500 

550 

550 

500 

250 

550 

250 

550 

500 

550 

1,000 

605 

908 

1,000 

908 

1,000 

Perforated 

interval 

(feet) 

170-177 

244-255 

311-315 

343-350 

unknown 

unknown 

unknown 

807-851 

880-903 

unknown 

unknown 

551-571 

598-618 

640-660 

Remarks 

Stress-strain plot 

for 225-ft interval. 

Changed from cable to 

pipe assembly in 

October 1973. 

Changed from cable to 

pipe assembly in 

October 1973. 

Changed from cable to 

pipe assembly in 

October 1973. 

Stress-strain plot for 

708-ft interval. 

Stress-strain plot for 

800-ft interval. 

Changed from cable to 

pipe assembly in 

April 1972. 
GPO SBS-045/78029