Land Subsidence Due To 

Ground-Water Withdrawal in the 

Los Banos-Kettlemaii City Area, 

California, Part 3. Interrelations of 

Water-Level Change, Change in 

Aquifer-System Thickness, 

and Subsidence

GEOLOGICAL SURVEY PROFESSIONAL PAPER 437-G

Prepared in cooperation with the 

California Department of Water Resources
Land Subsidence Due To 

Ground-Water Withdrawal in the 

Los Banos-Kettleman City Area, 

California, Part 3. Interrelations of 

Water-Level Change, Change in 

Aquifer-System Thickness, 

and Subsidence

By WILLIAM B. BULL and JOSEPH F. POLAND

STUDIES OF LAND SUBSIDENCE

GEOLOGICAL SURVEY PROFESSIONAL PAPER 4 3 7-G

Prepared in cooperation with the 

California Department of Water Resources

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1975
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress Cataloging in Publication Data

Bull, William B. 1930-

Land subsidence due to ground-water withdrawal in the Los Banos-Kettleman City area, California.

(Studies of land subsidence) (Geological Survey Professional Paper 437-E-G)

Pt. 2 by W. B. Bull; pt. 3 by W. B. Bull and J. F. Poland.

Includes bibliographies and indexes.

CONTENTS: pt. 1. Changes in the hydrologic environment conducive to subsidence. pt. 2. Subsidence and compaction 

of deposits, [etc.]

Supt. of Docs. No.: I 19.16:437-G 

1. Subsidences (Earth movements) California San Joaquin Valley. 2. Aquifers California San Joaquin Valley. 3.

Water, Underground California San Joaquin Valley. I. Miller, Raymond E. II. Poland, Joseph Fairfield, 1908- III.

California. Dept. of Water Resources. IV. Title. V. Series. VI. Series: United States. Geological Survey. Professional

Paper 437-E-G. 

QE75.P9 No. 437-E-G [GB485.C2] 557.3'08s [551.3'5] 74-28239

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402

Stock Number 024-001-02611
CONTENTS

Abstract _________________________________ Gl Interrelations of water-level change, etc. Continued

Introduction _____________________________ 2 Relation of changes in aquifer-system thickness, etc. Con.

Purposes of report _______________________ 2 Elastic and inelastic changes, etc. Continued

Definition of terms _____ ___ ___ ________ __ 2 Relation of monthly compaction to water-level

Acknowledgments ______________________ 4 change ____________________ G13

Analysis of stress changes tending to cause compaction __ __ 4 Relation of compaction and expansion to change in

Stress change due to change in seepage forces _______ 4 artesian head _________________ 17

Stress change due to fluctuation of the water table ___ 5 The Lemoore site _________________ 18

Buoyancy effects _ _____ 5 The Yearout site _________________ 21

Effect of specific retention in the unsaturated zone __ 5 Well 19/16-23P2 _________________ 22

Equation summing change in applied stress ______ __ 6 Relation of lower-zone compaction to change in applied

Combined effect of man-induced stress changes tending to stress _________________________ 27

cause additional compaction of the lower zone __ 6 Criteria for the prediction of future subsidence __ ___ __ 35

Interrelations of water-level change, change in aquifer-system Timelag of compaction ____________________ 35

thickness, and subsidence __________________ 8 Conditions before delivery of canal water _________ 37

Relation of subsidence to artesian-head decline ____ 8 Computation of aquifer-system pore-pressure decay __ 44

Relation of changes in aquifer-system thickness to change Conditions after delivery of canal water ___________ 49

in artesian head _____________________ 11 Summary _______________________________ 57

Elastic and inelastic changes in aquifer-system thick- References ______________________________ 60

ness___________________________ 11 Index __________________________________ 61

ILLUSTRATIONS

 Page

FIGURE 1. Map showing location of bench marks, observation wells, compaction recorders, core holes, and lines of section referred to in this report ________________________________________ G3

2. Diagrams showing the effect of water-table change on lower-zone applied stress _______ __ 7

3. Profiles of subsidence and artesian-head decline, 1943-66, Tumey Hills to Mendota _______ ___ 9

4. Profiles of subsidence and artesian-head decline, 1943-66, Anticline Ridge to Fresno Slough __ 9 

5-10. Graphs of subsidence and artesian-head decline near bench mark:

5. GWM59 ___________________________________________-_________________ 9

6. B1042 ______________________________________________________________ 10

7. S661 ________________________________________________________________ 10

8. H237 (reset) _________________________________________________ __________ 10

9. N692 _____________________________________________________ __________ 10

10. PTS21S ____________________________________________________ __________ 11

11. Graphs of subsidence, compaction, and artesian-head decline near Huron __ ___ 12 

12-18. Graphs showing relation of:

12. Annual compaction rates to change in artesian head at the Oro Loma site _______ 13

13. Monthly compaction to lower-zone water-level change at the Mendota site, well 14/13-11D6-- . 14

14. Computed virgin compaction to lower-zone water-level change at well 14/13-11D6 _ 15

15. Monthly compaction to lower-zone water-level change at the Cantua site ________ 16

16. Monthly compaction to lower-zone water-level change at well 19/16-23P2 __ _ __ 16

17. Monthly compaction to lower-zone water-level change at the Westhaven site, 20/18-11Q2, 11Q3 __ 17

18. Aquifer-system compaction or expansion to water-level change, well 18/19-20P2 ____ 19

19. Stress-strain plot for well 18/19-20P2______________________________________ __________ 20 

20-23. Graphs showing relation of aquifer-system compaction or expansion to water-level change:

20. Well 13/15-35D5 ____________________________________________________________________________ 22

21. Well 19/16-23P2, February-July 1967 ____________________________________________________________ 24

22. Well 19/16-23P2, March 14-April 13, 1967___________________________________ 25

23. Well 19/16-23P2, summer 1964 _____________________________________ ____ 26

HI
IV CONTENTS

Page

FIGURES 24-29. Maps showing:

24. Change in applied stress on the lower zone resulting from change in the position of the water table, 1943-60-- G28

25. Increase in applied stress an the lower zone resulting from artesian-head decline between 1943 and 1960 30

26. Increase in total applied stress on the lower zone, 1943-60 ____________________________ 31

27. Estimated compaction in the lower zone, 1943-59______________________________________ 32

28. Specific compaction of the lower zone, 1943-60 _________________________ _________ 33

29. Depth to lower-zone pumping level, summer 1965 _______________________________ 38

30. Plots of cumulative subsidence and subsidence rate for bench mark S661 _______________- 39

31. Map showing number offset of lower-zone head decline associated with each foot of subsidence, 1943-60 -_ 40

32. Map showing specific subsidence, 1943-59___________________________________________ 41

33-39. Graphs showing:

33. Applied-stress increase and subsidence relations at bench mark GWM59 ______________ _ 42

34. Applied-stress increase and subsidence relations at bench mark H237 (reset) ___________ 42

35. Applied-stress increase and subsidence relations at bench mark PTS21S _____________ _ 43

36. Changes in the mean daily compaction rate of deposits for selected applied stresses _ ___ ______ __ 45

37. Decrease in the mean daily compaction rate in the 703-2,000-foot-depth interval at the Cantua site 46

38. Estimated time needed for residual compaction to occur after mid-1961, 703-2,000-foot-depth interval,

Cantua site ___________________________________________ ________ 47

39. Decrease in the mean daily compaction rate of the lower-zone deposits at the multiple compaction-recorder sites ________________________________________________ 48

40. Map showing areas to receive water from the San Luis Canal section of the California Aqueduct __ _____ _ 51

41. Maps showing the effect of delivery of Delta-Mendota Canal water on subsidence rates in the northern part of

theLos Banos-Kettleman City area __________________________________________ 52

42. Graphs showing interrelations of subsidence rates, artesian-head decline, and surface-water imports near

Stratford and Lemoore ________________________________________________ 53

43. Map showing estimated annual subsidence rates in the Los Banos-Kettleman City area in 1970 if summer

lower-zone water levels rose 60 feet and the seasonal fluctuation were reduced to 10-20 feet _ ____ 55

TABLES

 Page

TABLE 1. Variation in net specific unit expansion during a period of seasonal head recovery at well 18/19-20P2__ _ _ G21 

2. Estimated annual subsidence rates in the Los Banos-Kettleman City area if summer lower-zone water levels rose

60 feet and the seasonal fluctuation were reduced to 10-20 feet______________________________ 54
STUDIES OF LAND SUBSIDENCE

LAND SUBSIDENCE DUE TO GROUND-WATER WITHDRAWAL 

IN THE LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA,

PART 3. INTERRELATIONS OF WATER-LEVEL CHANGE, 

CHANGE IN AQUIFER-SYSTEM THICKNESS, AND SUBSIDENCE

By WILLIAM B. BULL and JOSEPH F. POLAND

ABSTRACT

By increasing the stresses tending to compact the deposits by as 

much as 50 percent, man has created the world's largest area of 

intense land subsidence in the west-central San Joaquin Valley, Calif. 

As of 1966, more than 2,000 square miles had subsided more than 1 

foot, and the area that had subsided more than 10 feet was 70 miles 

long. Maximum subsidence was 26 feet.

The increase in stress caused by pumping of ground water can be 

expressed in feet of water. A seepage stress of 1 foot of water occurs for 

each foot of head differential resulting from either artesian-head 

change or change in water-table position. Stress increase resulting 

directly from artesian-head decline has caused most of the compaction 

and subsidence. Each foot of water-table change also causes a 0.6-foot 

stress change because of removal or addition of buoyant support of the 

deposits within the interval of water-table change and a 0.2-foot stress 

change because of part of the pore water being changed from a 

neutral-stress condition to an effective-stress condition, or vice versa. 

The effect of water-table change is to alter the grain-to-grain stress in 

the unconfined aquifer by ±0.8 foot of water per foot of water-table 

change. The effect of water-table change on stress in the deeper 

confined zones is to alter the stress by only ±0.2 foot of water because 

the seepage-stress change more than offsets the sum of the two other 

stress changes.

Changes in aquifer-system thickness may be both elastic (are reversible and occur with minor time delay) and inelastic (are irreversible and occur with large time delay). As of 1966 excess pore pressures 

existed in many of the aquitards and net aquifer-system expansion 

occurred briefly or not at all, but elastic changes did affect the monthly 

amounts of measured compaction. Compaction rates were maximal 

during times of head decline because elastic compaction is additive 

with virgin compaction, and compaction rates were minimal during 

times of head rise because expansion is subtractive from virgin compaction. In the study area, the elastic component of seasonal compaction varies from less than 5 to about 90 percent. The percentage 

depends not only on the lithology and permeability of the deposits, but 

also on the magnitude and rate of increase of present applied stress as 

compared with past effective stress maximums and durations.

Three concurrent processes are tending to change aquifer-system 

thickness during times of applied-stress decrease elastic expansion 

with no measurable time delay (presumably chiefly of the aquifers), 

delayed elastic expansion (presumably chiefly of the thin aquitards 

and the outer parts of the thick aquitards), and virgin compaction 

(presumably of the thick aquitards and aquicludes). Compaction due 

to decay of excess pore pressures may still occur in thick clay beds

after 60 feet of head recovery in adjacent aquifers, but only 1 foot of 

head recovery may be needed to reverse the trend from recorded 

compaction to recorded net expansion, even when water levels are 

near historic lows. The approximate modulus of expansion (net 

specific unit expansion) of the upper-zone aquifer system at the 

Lemoore and Yearout sites is about 3.5 x lO^ftr1 (foot per foot of 

aquifer-system thickness per foot of decrease in applied stress). Dur 

ing a period of seasonal head recovery at the Lemoore site, the net 

specific unit expansion varied from 0.6 to 3.6 x 10~6ft~1 as the rates of 

residual compaction and nondelayed and delayed expansion varied 

concurrently with changes in the magnitude and rate of applied-stress 

decrease.

Little time is needed to raise pore pressures in many of the 

aquitards. Compaction ceases when aquifer pore pressures rise to 

equilibrium with the maximum pore pressure in a contiguous 

aquitard, thus preventing further expulsion of water. Further porepressure increases in the aquifers are transmitted fairly rapidly into 

the aquitards because their specific storage in the elastic range is 

small.

The prediction of subsidence is largely empirical, and reasonable 

predictions can be made only if the rates and magnitudes of future 

applied-stress changes can be predicted accurately. The timedependent nature of the pore-pressure decay in the aquitards and 

aquicludes greatly complicates estimates of compaction for 

heterogeneous aquifer systems.

Most of the subsidence since 1960 has been the result of prior 

applied-stress increases. In many of the thick beds of low permeability, the applied stress has not yet become effective because of 

insufficient time for pore pressures in the aquicludes and aquitards to 

reach equilibrium with the head in the aquifers. Determination of the 

rates and changes of rates of residual compaction is important in the 

prediction of subsidence.

The rate of decrease of aquitard-aquifer pore-pressure differentials 

can be evaluated at some sites through study of change of mean daily 

compaction rates for selected applied stress levels. In the 

703-2,000-foot depth interval at the Cantua site, the relation between 

mean daily compaction rate (y) and time (x) for the 1961-67 period is

y=0.0028e-°-096)r .

Because increase in applied stress was negligible from 1961 to 1967, 

the decrease in the post-1961 rate of daily compaction can be used to 

estimate future residual compaction. A 10-percent decrease in residual compaction rate had occurred as of mid-1962 and 45 percent as 

of 1968, and a 90-percent decrease is predicted by about 1986, assumGl
G2 STUDIES OF LAND SUBSIDENCE

ing a hydrologic environment similar to that of the 1961-67 period. 

Exponents of similar equations for other compaction-recorder sites 

indicate that the rate of pore-pressure decay is twice as rapid in the 

northern as in the southern part of the study area.

Importation of surface water has resulted in alleviation of subsidence in the Delta-Mendota Canal service area and in the vicinity of 

Stratford and Lemoore. Deliveries of water from the San Luis Canal 

section of the California Aqueduct should result in widespread alleviation of subsidence.

INTRODUCTION

By increasing the stress tending to compact the unconsolidated deposits by as much as 50 percent, man has 

created the world's largest area of intense land subsidence in the west-central San Joaquin Valley. Withdrawal of ground water for agriculture has caused more 

than 2,000 square miles to subside more than 1 foot. As 

of 1966, the area that had subsided more than 10 feet 

was 70 miles long and included 500 square miles; maximum subsidence was 26 feet.

Water-level changes in the aquifer systems have increased the applied stresses and have caused accelerated compaction of the deposits. Detailed knowledge of 

the interrelations of water-level change, change in 

aquifer-system thickness, and the concurrent changes 

in the altitude of the land surface is necessary for a 

better understanding of the mechanics of aquifer systems and the compaction of sediments, as well as for the 

development of criteria in predicting future land 

subsidence.

This paper is the third of three reports discussing land 

subsidence due to ground-water withdrawal in the Los 

Banos-Kettleman City area, California. Part 1 (Bull 

and Miller, 1974) is a factual presentation of the hydrologic factors conducive to land subsidence in the 

study area. Part 2 (Bull, 1974) contains basic data and 

interpretation about the land subsidence and compaction that have been measured in the area and discusses 

geologic factors influencing the amounts, rates, and distribution of compaction.

The introduction to all three parts, in Part 1 (Bull and 

Miller, 1974), includes descriptions of the geographic 

setting of the study area, the formation and objectives of 

the Inter-Agency Committee on Land Subsidence, the 

scope of the field and laboratory work for the cooperative and federal subsidence programs, and brief summaries about land subsidence and compaction. For a 

summary of the hydrologic environment, and the maninduced changes in the hydrologic environment, the 

reader is referred to the summary and conclusions of 

Part 1 (Bull and Miller, 1974). The principal areas of 

land subsidence due to ground-water withdrawal in 

California and the topographic and cultural features of 

the Los Banos-Kettleman City subsidence area are 

shown in figures 1 and 2 of Part 1 (Bull and Miller, 

1974).

The boundaries of the Los Banos-Kettleman City 

study area, bench marks, observation wells, compaction 

recorders, core holes, and lines of section referred to in 

this report are shown in figure 1. The northeastern 

boundary as shown in figure 1 is along the valley 

trough, but as of 1966, as much as 8 feet of subsidence 

had occurred east of the valley trough. Therefore, in 

much of the study, the 1-foot subsidence line of 1920-28 

to 1966 (Pt. 2, Bull, 1974, fig. 9) was used as the east 

boundary of the subsidence area.

PURPOSES OF REPORT

The overall purpose of Part 3 is to relate water-level 

changes to changes in thickness of the aquifer-system 

skeleton in the west-central San Joaquin Valley. This 

goal consists of three purposes. The first is to review how 

grain-to-grain stresses are changed by water-level 

changes. The analysis of stresses has been discussed by 

Lofgren (1968), but a modified method of applied-stress 

computation is used in this study. The second purpose is 

to show the effects of change in applied stress on 

aquifer-system thickness. Three components of change 

in aquifer-system thickness are discussed. The third 

purpose is to provide criteria for predicting future subsidence in the study area and to assess the reliability of 

the possible ways of predicting future subsidence.

The bulk of the information presented in this paper 

concerns events that occurred before April 1966, which 

was the time of a complete survey of the bench-mark 

network by the U.S. Coast and Geodetic Survey (now 

National Geodetic Survey of the National Ocean Survey, National Oceanic and Atmospheric Administration). Post-March 1966 data are presented and discussed only to present facts or concepts that cannot be 

demonstrated with the earlier data.

DEFINITION OF TERMS

The geologic and engineering literature contains a 

variety of terms that have been used to describe the 

processes and environmental conditions involved in the 

mechanics of stressed aquifer systems and of land subsidence due to withdrawal of subsurface fluids. The 

usage of certain of these terms in reports by the U.S. 

Geological Survey research staff investigating 

mechanics of aquifer systems and land subsidence is 

defined and explained in a glossary published separately (Poland and others, 1972). Several terms that 

have developed as a result of the Survey's investigations are also defined in that glossary.

The aquifer systems that have compacted sufficiently 

to produce significant subsidence in California and 

elsewhere are composed of unconsolidated to semiconsolidated clastic sediments. The definitions given in the 

published glossary are directed toward this type of sed-
R. 10 E.

LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3

12 13 120°30' 14 15 16 17 120°00' R.19 E.

G3

37°00

EXPLANATION

Boundary of deformed 

rocks -J 

ive Points \

Boundary of the Los Banos-Kettleman City 

area

Core hole and well number

Compaction recorder; if more than one, 

number indicated inside symbol

Observation well and number; if more than 

one, number indicated inside symbol

Irrigation well from which water-level record has been obtained and well number

Bench mark and number

5 10 15MILES

36°30

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 1. Bench marks, observation wells, compaction recorders, core holes, and lines of section referred to in this report.

iments; they do not attempt to span the full range of contribution of membrane effects due to salinity or elecrock types that contain and yield ground water. In trical gradients has been discounted as relatively

denning the components of the compacting stresses, the insignificant in the areas studied.
G4 STUDIES OF LAND SUBSIDENCE

In our research reports, pressures or stresses causing 

compaction are usually expressed in equivalent "feet of 

water head" (1 ft of water = 0.433 Ib in" 2 (pounds per 

square inch)).

A committee on redefinition of ground-water terms, 

composed of members of the Geological Survey, recently 

issued a report entitled "Definitions of Selected 

Ground-Water Terms" (Lohman and others, 1972). The 

reader is referred to that report for definitions of many 

ground-water terms.

ACKNOWLEDGMENTS

The cooperation of numerous ranchers, landowners, 

and companies is acknowledged for supplying essential 

information to the subsidence project and for giving 

permission to install and maintain wells and equipment 

for obtaining water-level and compaction information. 

Particular assistance was given by the Pacific Gas and 

Slectric Co., Westlands Water District, and Russell Giffen, Inc.

The financial cooperation of the California Department of Water Resources made this study possible, and 

information provided by the U.S. Bureau of Reclamation from core holes and observation wells contributed 

significantly to the essential data.

This work could not have been completed without the 

discussions, interest, and assistance of the many people 

who have been associated with the land-subsidence 

studies since 1956. We appreciate particularly the helpful discussions and review of the manuscript by our 

colleagues B. E. Lofgren, F. S. Riley, D. C. Helm, and G. 

H. Davis. Mr. Bull enjoyed working together with R. L. 

Ireland and R. G. Pugh on a variety of jobs in the field, 

and the authors appreciate their extensive help in coliection and assembling of field data. Special credit is due 

Mr. Ireland for his meticulous care and thoughtful 

foresight in the installation and operation of the equipment for recording compaction and water-level changes 

during the entire period of record.

ANALYSIS OF STRESS CHANGES TENDING TO 

CAUSE COMPACTION

Compaction is caused by the grain-to-grain load 

which results from all the stress-producing factors in 

the overlying stratigraphic section. In the Los Banos 

-Kettleman City area, and elsewhere, stress changes 

caused by man's changes of the hydrologic environment 

are superimposed on the prior natural stresses tending 

to compact the deposits. The ratio of manmade to 

natural applied stress varies considerably with geographic area and with depth, but can be large. For 

example, the applied stress at the 600-foot depth at the 

Cantua recorder site was increased from about 330 to 

about 500 Ib in~2 as the result of 400 feet of artesianhead decline. About 52 percent increase in applied 

stress has occurred as a result of man's change in the 

hydrologic environment at the 600-foot depth. However, at the 200-foot depth at the same site, no change in 

applied stress has occurred. The 200-foot depth is about 

10 feet below the water table, which has not changed 

position substantially at the site during the past 60 

years.

Water-level changes in both the confined and 

unconfined parts of the aquifer systems cause changes 

in applied stress and thereby alter the preexisting 

stress distribution within each sedimentary bed. Applied stresses become effective stresses only as rapidly 

as water can be expelled from a given bed.

A stress that does not tend to cause compaction is the 

hydrostatic (neutral) stress, which is equal to the depth 

below the water surface times the unit weight of water, 

and is transmitted downward through the water between the grains. The hydrostatic stress is considered 

neutral because, although it tends to compress each 

grain, it does not tend to change the grain-to-grain 

relationships significantly.

The basic theory used by the Geological Survey regarding the stresses produced by water-level change 

within an aquifer system has been discussed by Lofgren 

(1968, 1969) and Poland (Poland and Davis, 1969). The 

theory is summarized briefly in this paper, first, to provide the reader necessary background before applying 

the theoretical concepts to the actual mechanics of 

aquifer systems, and second, because a different approach from that described by Lofgren will be used in 

computing the changes in stress that result from 

water-table change.

STRESS CHANGE DUE TO CHANGE IN SEEPAGE FORCES

A major contribution to the theory of mechanics of 

aquifers was made by Lofgren by the application of the 

seepage-stress concept (Taylor, 1948; Scott, 1963) to the 

distribution of stresses in a compacting aquifer system 

(Lofgren, 1968; Lofgren and Klausing, 1969). Although 

several methods can be used to obtain the same results 

(Taylor, 1948, p. 203; Poland and Davis, 1969), the 

seepage-force concept provides the most logical 

dynamic explanation of how changes in confined and 

unconfined water levels affect stress relations in porous 

media.

Seepage forces are developed by the establishment of 

a hydraulic gradient across an aquiclude or aquitard. 

The hydraulic gradient may be caused by either watertable or artesian-head change and may induce flow 

either upward or downward across the bed responsible 

for the head differential. Flow through the bed is accompanied by dissipation of the hydraulic head. The
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G5

seepage force corresponding to this loss of hydraulic 

head is transferred to the granular skeleton and is exerted in the direction of the overall route of flow. Lofgren and Klausing (1969, p. B67) stated,

Within an aquiclude compacting under the stress of downward seepage, the hydraulic gradient and therefore the seepage force per unit 

thickness vary from a minimum at the upper surface to a maximum at 

the lower surface until steady-state conditions are reached. ***. Although the distribution of these forces within the aquiclude may be 

indeterminate, the total seepage force accumulated through the 

aquiclude is equal to the total head differential across it.

The large artesian-head decline that has occurred in 

the Los Banos-Kettleman City area has produced seepage forces within the upper confining bed that have 

tended to cause changes in effective stress in all underlying beds within the depth interval of artesian-head 

decline. Because seepage stresses are equal (assuming 

no water-table change) to the changes in artesian head, 

it is convenient to express the seepage stresses in units 

of feet of water (1 ft of water equals 0.433 Ib in~2 ). If the 

other factors tending to change the applied stress in the 

aquifer system also are expressed in feet of water, then 

the various components tending to change the stress 

condition at a given point in the aquifer system can be 

added algebraically to obtain the net change in applied 

stress.

STRESS CHANGE DUE TO FLUCTUATION 

OF THE WATER TABLE

Water-table fluctuations will be discussed mainly as 

an influence on stress changes within the lower zone 

(confined aquifer system) the zone in which most of 

the manmade compaction in the study area has occurred. Changes in the position of the water table affect 

the applied stress on the lower zone in three ways: by 

changing the head differential and therefore the seepage stresses across the confining clays; by removing or 

supplying buoyant support of the grains within the 

depth interval affected by water-table change, depending on whether the water table declines or rises; and by 

eliminating or developing water of specific retention as 

the deposits become saturated or unsaturated.

Water-table rise tends to increase the seepage stress 

on the lower-zone deposits, each foot of water-table rise 

being equivalent to 1 foot of (water) increase in applied 

stress on the lower zone. Thus, water-table rise has the 

same effect on the seepage stress as an equivalent decline in lower-zone artesian head. However, as will be 

shown later, the tendency toward increase of seepage 

stress as a result of water-table rise is largely offset by 

the two other components of stress resulting from

water-table rise is largely offset by the two other components of stress resulting from water-table rise.

Conversely, water-table decline tends to decrease the 

seepage stress on the lower zone, with each foot of 

water-table decline tending to decrease the applied 

stress on the lower zone by 1 foot of water.

BUOYANCY EFFECTS

The effect of change in buoyant support of the granular skeleton of the deposits within the depth interval of 

water-table change has been described by Lofgren 

(1968). The dry unit weight, y d, of deposits above a 

water table can be expressed as

7d =(l-n)-G- 7W,

where n is the mean porosity, G is the mean specific 

gravity of the mineral grains, and 7W is the unit weight 

of water. The submerged unit weight of the deposits, y ', 

below the water table is expressed as

WPhysical tests of cores from the Los Banos-Kettleman 

City area indicate that a mean porosity of 0.40 and a 

mean specific gravity of the grains of 2.70 is appropriate 

for the deposits in the zone of water-table change (Johnson and others, 1968). Substituting in the preceding 

equations, the applied stress due to weight of deposits 

above the water table equals about 1.6 feet of water per 

foot of thickness, and the applied stress due to the 

weight of deposits submerged below the water table is 

about 1.0 foot of water per foot of thickness. Thus, the 

change in applied stress on all underlying deposits resulting from the buoyancy component is +0.6 foot of 

water for each foot of water-table decline and -0.6 foot 

of water for each foot of water-table rise. This type of 

water-level change results in large changes in stress, 

per foot of water-table change, above the first aquiclude. 

However, the effect of this buoyancy component of 

water-table change on stress in the lower zone is to 

cancel much of the change in seepage stress induced by 

the water-table change.

EFFECT OF SPECIFIC RETENTION 

IN THE UNSATURATED ZONE

The effects of the two results of water-table change 

discussed earlier pertain to seepage and buoyancy processes. A stress component caused by a third process also 

is used in this paper for computations of applied stress 

in areas of water-table change.

The weight of the water contained in the deposits 

above the water table is part of the applied stress tending to compact the underlying saturated deposits. If the
G6 STUDIES OF LAND SUBSIDENCE

additional weight of this water is not considered, the net 

computed stress change on the lower zone due to watertable change will be twice as large as it should be. The 

effect of specific retention on applied stress is discussed 

in detail because it pertains to a process of stress change 

that is different from those of the other two stress components.

Change from a saturated to an unsaturated condition 

causes the stress condition of the retained water to be 

changed from a neutral to an applied stress. Where the 

contained water is supported by underlying pore water, 

it represents a neutral stress. If the water table should 

decline, not all the water will drain from the deposits. 

The weight of the water retained represents a change 

from a neutral stress to a stress that is applied to all the 

underlying deposits. Conversely, under conditions of 

water-table rise, the weight of water that was part of the 

applied stress becomes a neutral stress.

The amount of water retained in the deposits above 

the water table varies with clay content. Nearly all the 

water-table deposits are Diablo1 alluvial fans. Large 

differences in clay content commonly occur in adjacent 

beds. Clay content (Johnson and others, 1968) in most 

sand beds ranges from 5 to 20 percent, but the finer 

grained beds usually contain 30-50 percent clay. Data 

on specific yield and specific retention for various materials (Johnson, 1967) suggest that a mean specific 

retention of 20 percent (by volume) is a reasonable approximation for the alluvial-fan deposits.

Therefore, for purposes of computing the change in 

applied stress resulting from the water of specific retention, a value of 0.2 of the volume is used. (This represents a moisture content of 12.4 percent of the weight of 

the solids in deposits assigned a porosity of 0.40 and a 

specific gravity of 2.70.) The amount of retained water 

will be more than the value used in this report where 

the clay content of the deposits exceeds roughly 20 percent and where the moisture content of the deposits 

above the water table exceeds specific retention but is 

less than saturation.

Use of the assigned value of 0.2 of the volume of the 

deposit for the water of specific retention has the following effect on the computed applied stress resulting from 

water-table change. During a water-table decline, as 

each foot of deposits becomes unsaturated, an increase 

in applied stress equivalent to 0.2 foot of water will be 

applied to all the underlying deposits as half of the 

water in material assumed to have a porosity of 0.40 is 

transferred from a neutral to an applied-stress condition. The effect of a water-table rise will be to decrease

'Principal source of deposits, where identified, is indicated as Diablo (derived from the 

Diablo Range) or Sierra (derived from the Sierra Nevada).

the applied stress on the underlying deposits as a result 

of this component. As in the case of buoyancy of the 

granular skeleton, the water of the specific retention 

component will tend to offset the seepage-stress change 

applied to the lower zone as a result of change in the 

position of the water table.

EQUATION SUMMING CHANGE 

IN APPLIED STRESS

The change in applied stress within a confined aquifer 

system due to changes in the potentiometric surfaces 

may be summarized as

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

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

system, hu is the head in the overlying unconfined 

aquifer, andFs is the average specific yield (expressed as 

a decimal fraction) in the interval of water-table 

fluctuation (Poland and others, 1972, p. 6). Change in 

stress applied to a fine-grained bed becomes effective in 

changing the thickness of the bed only as rapidly as the 

diffusivity of the medium permits decay of excess pore 

pressures and thus allows the internal grain-to-grain 

stress (effective stress) to change.

COMBINED EFFECT OF MAN-INDUCED STRESS

CHANGES TENDING TO CAUSE ADDITIONAL

COMPACTION OF THE LOWER ZONE

Compaction of the lower-zone aquifer system accounts for at least 55-95 percent of the subsidence in 

different parts of the study area (Pt. 2, Bull, 1974, fig. 

45). Therefore, the following computation of stresses 

will use the lower zone as an appropriate example.

Changes in lower-zone artesian head cause changes 

in applied stress on the lower-zone deposits that are 

equal to 1 foot of water for each foot of head change. 

Because of the convenient way in which the stresses 

have been expressed, changes in lower-zone water 

levels are numerically equal to changes in applied 

stress where no water-table change has occurred during 

a given period. The position of the water table has not 

changed more than 50 feet since 1951 in most of the 

study area; therefore, the recorded head changes in the 

confined aquifer systems approximate the appliedstress changes.

Locally, the water table has risen more than 100 feet 

and in another part of the area has declined more than 

350 feet. In all areas of significant water-table change, 

the resulting change in applied stress on the lower zone 

has been computed as discussed subsequently and 

added algebraically to the change in applied stress indicated by lower-zone water-level change.
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G7

The applied stress diagrams in figure 2 show the 

effect of the three components of change in applied 

stress on the lower zone that are concurrent with 

water-table change. Derivation of the assigned values 

was discussed in the previous section. Head changes 

affect the seepage processes by 1 foot of water per foot of 

head change. The absence or presence of buoyant support for the granular skeleton results in an applied 

stress due to the dry weight of deposits above the water 

table of 1.6 feet of water per foot of thickness and an 

applied stress due to the weight of the deposits below the 

water table of 1.0 foot of water per foot of thickness. The 

applied stress due to contained water in deposits above 

the water table is equal to 0.2 foot of water per foot of 

thickness.

The conditions shown in figure 2A represent the initial conditions in a diagrammatic aquifer system. Unsaturated deposits extend to a depth of 200 feet, which is 

the initial position of both the water table and the 

potentiometric surface of the confined aquifer system. 

An unconfined aquifer occurs between 200 and 340 feet, 

and a 50-foot aquiclude occurs between 340 and 390 

feet. A confined aquifer system occurs below a depth of 

390 feet, and the top of an aquitard at a depth of 500 feet 

has been selected as the reference plane for which to 

compute applied stresses and changes in applied stresses. Because the water table and the potentiometric surface occur at the same level, a head differential does not 

exist across the aquiclude and no seepage stress is 

present. The distribution of neutral pressures is hydrostatic, the same as if no confining bed were present. The 

vectors Ps, Pw, andP^ represent the three components of 

stress applied to the top of the aquitard at a depth of 500 

feet. The initial total applied stress is 660 feet of water.

The applied stress due to the dry weight of the iinsaturated deposits is the largest component even though it IP 

derived from a thickness of deposits that is only two 

thirds as thick as the saturated section above the 

aquitard.

Conditions after a water-table decline of 100 feet are 

depicted in figure 2B. The vector of applied stress due to 

the weight of the dry deposits above the water table ie 

greater than the sum of the other two vectors, and the 

total gravitational stress applied to the top of the 

aquitard at a depth of 500 feet is 740 feet of water. The 

gravitational components tending to increase applied 

stress as a result of the water-table decline total 80 feet 

of water ( AP6 +APS + &PW). Sixty feet of the increase is 

the result of loss of buoyancy of the grains in the dewatered section, and 20 feet of the increase is the result of 

transfer of the retained pore water from a neutral to an 

applied-stress condition. The 100 feet of water-table 

decline also caused a head differential across the aquiclude that has resulted in an upward seepage stress of 

100 feet. The net effect of the three water-table compo 

nents of stresses tending to change the stress applied to 

the top of the lower-zone aquitard is to decrease th^ 

applied stress by 20 feet of water.

Conditions after a water-table rise of 100 feet ar<p 

depicted in figure 2C. The component of applied stres? 

due to the weight of the submerged deposits is the dom 

inant source of stress applied to the top of the lower-zone 

aquitard, and the total gravitational stress applied to 

the top of the aquitard is 580 feet of water. The gravitational components tending to decrease the applied 

stress (from the initial condition shown in fig. 2A) as a 

result of the water-table rise total 80 feet of water. Sixty 

feet of the decrease in applied stress is the result of

400

a

UJ

_J

0. 

Q_ 

<OC

200 U >

Z LL <0 I . o £

DC UJ 

O"-

400 W ~ 

UJ W 

DC W

(/) DC

600 QNEUTRAL STRESS, IN FEET OF WATER

FIGURE 2. Effect of water-table change on lower-zone applied stress. A, Water table and lower-zone potentiometric surface at same level. B, Water table lowered, potentiometric surface 

constant. C, Water table raised, potentiometric surface constant. All stresses in feet of water; based on assumed porosity of 0.40, specific gravity of 2.70, and specific retention of 0.20 by 

volume. Ps = applied stress due to dry weight of unsaturated deposits;Pfe = applied stress due to buoyant weight of submerged deposits; Pw = applied stress due to weight of contained 

water in unsaturated deposits; J=seepage stress; AP=change in total applied stress from condition A.
G8 STUDIES OF LAND SUBSIDENCE

buoyancy effects tending to lift the grains in the section 

that has been submerged, and 20 feet of the decrease is 

the result of transfer of the pore water from an appliedstress to a neutral-stress condition. The 100 feet of 

water-table rise also caused a head differential across 

the aquiclude that has resulted in a downward seepage 

stress of 100 feet. The net effect of the three water-table 

components of stress change applied to the top of the 

lower-zone aquitard is to increase the applied stress by 

20 feet of water.

The net effect of stress change on the lower-zone deposits per unit change in the position of the water table 

will be minor. Changes in stress resulting from 

buoyancy changes and changes in the stress condition of 

the contained water are more than offset by the change 

in seepage stress that also results from change in the 

position of the water table. A net change of applied 

stress on the lower zone of 0.2 foot of water per foot of 

water-table change is the resultant of the three components tending to change the applied stress. If the contained water above the water table is not taken into 

account, the net change in applied stress would be 0.4 

foot of water twice as large as it should be.

During 1951-65, local water-table declines caused as 

much as 40-70 feet of water applied-stress decrease on 

the lower zone. Locally, change from a confined to a 

water-table condition below the Corcoran Clay Member 

of the Tulare Formation has decreased the rate of 

applied-stress increase from 1.0 to 0.8 foot of water per 

additional foot of lower-zone water-level decline. 

INTERRELATIONS OF WATER-LEVEL CHANGE,

CHANGE IN AQUIFER-SYSTEM THICKNESS, 

AND SUBSIDENCE

Part 1 (Bull and Miller, 1974), Part 2 (Bull, 1974), and 

the preceding section of this paper have discussed the 

hydrologic environment, the stress changes caused by 

changes in the hydrologic environment, and the compaction of the ground-water reservoir and resulting 

land subsidence. The purpose of this section is to show 

the interrelations of change in applied stress caused by 

changes in the positions of the potentiometric surfaces 

including the water table, decrease or increase in 

aquifer-system thickness, and land subsidence.

In most of the area the decline in artesian head approximates the increase in stress, expressed in feet of 

water, tending to compact the lower-zone deposits. 

Changes in the position of the water table have been 

minor at most observation-well sites during the periods 

of record. Also, about 5 feet of water-table change causes 

a net change in applied stress on the confined zones that 

is equivalent to only 1 foot of change in artesian head. 

Therefore, the plots of change in artesian head shown in 

figures 3-23 are representative of the general changes

in applied stress (in feet of water) that have occurred in 

the deposits in which the wells are perforated.

First, the records from two lines of section and specific 

sites throughout the area are interpreted. Then, the 

regional change in applied stress on the lower-zone deposits that has resulted from changes in the positions of 

the potentiometric surfaces of the lower zone and the 

water table is analyzed for a 17-year period as the basis 

for a specific compaction map of the lower zone.

RELATION OF SUBSIDENCE TO 

ARTESIAN-HEAD DECLINE

A comparison of the regional declines in land-surface 

altitudes and the artesian head of the lower zone between 1943 and 1966 is shown in figures 3 and 4. The 

plots showing change in head do not extend as far 

southwest as the plots showing change in the landsurface altitude, because the area near the foothills of 

the Diablo Range had not been developed agriculturally 

in 1943 and hence no head measurements were made 

west of those shown.

Profiles of subsidence and artesian-head decline between Tumey Hills and Mendota are shown in figure 3. 

The subsidence profiles reveal a slightly asymmetrical 

change in the altitude of the land surface. The profiles of 

artesian-head decline roughly parallel each other, but 

do not have the same overall configuration as the subsidence profiles. The profiles of head decline show progressively larger amounts of decline to the west, 

whereas the subsidence profiles have a pronounced reversal about midway along the line of section. By 1966 a 

maximum of 24 feet of subsidence had occurred since 

1943 where the head had declined only 190 feet; farther 

to the southwest, only 14 feet of subsidence had occurred 

where the head had declined 350 feet.

The profiles of subsidence and artesian-head decline 

between Anticline Ridge and Fresno Slough in figure 4 

reveal a history that is roughly similar to that shown in 

figure 3. The subsidence profiles show a markedly 

asymmetrical change in land-surface altitude. The 

profiles of head decline parallel each other in the east 

half of the line of profile, but show a marked divergence 

in the west half. The 1955 head-decline profile is similar 

to the subsidence profile in that it reverses its trend and 

is asymmetrical. The trough of the head-decline profile 

is 1-2 miles southwest of the trough of the subsidence 

profile. By 1966, the head-decline profile did not show a 

reversal, but instead had an overall trend of increasing 

depth to the west. The subsidence maximum of 18 feet 

occurred where the head had declined 200 feet, but 5 

miles to the southwest only 3 feet of subsidence had 

occurred where the head had declined 275 feet.

It is readily apparent from figures 3 and 4 that al-
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G9

8 12 

DISTANCE, IN MILES

16 20

350

FIGURE 3. Profiles of subsidence and artesian-head decline, 1943-66, Tumey Hills to

Mendota.

though subsidence is associated with head decline, the 

quantitative relation between cause and effect varies 

within the study area. For example, the 

subsidence/head-decline ratio varies along the line of 

profile 3 from 0.12 to 0.04, and the ratio varies along the 

line of profile for figure 4 from 0.09 to 0.01. Geologic 

reasons for the variability of the subsidence/head decline ratio are discussed in Part 2 (Bull, 1974).

Comparisons of subsidence and change in artesian 

head are shown for selected bench marks and nearby 

wells in figures 5-10. The ratio of the water level to the 

subsidence scales is 20:1. The hydrographs consist of 

selected measurements that represent times of maximal applied stress during the intensive pumping 

periods of late winter and summer. Description of the

8 12 

DISTANCE, IN MILES

FIGURE 4. Profiles of subsidence and artesian-head decline, 1943-66, Anticline Ridge to 

Fresno Slough.

six sites is from north to south, and the locatipns of the 

bench marks and wells are shown in figure 1.

Subsidence and artesian-head decline near bench 

mark GWM59, 15 miles west of Mendota, are shown in 

figure 5. Subsidence rates increased between 1940 and 

1955, and since then have undergone a slight, but con300

- 400

5 5 50°

0- (/) 

00HZI <

H-" 600

Well 13/12-22N1 

perforated 400- 

- 1223 feet

Well 13/12-22Q1 

perforated 602- 

1090 feet

10 Q

1950 1960

 115 

1970

FIGURE 5. Subsidence and artesian-head decline near bench mark GWM59.
G10 STUDIES OF LAND SUBSIDENCE

tinuing, decrease. The water-level record reveals a 

parallel history of accelerating, then decelerating, rate 

of decline. Since 1960, summer low water levels have 

undergone little decline, while the subsidence has continued at a moderately rapid rate.

Subsidence and artesian-head decline near Mendota 

are shown in figure 6. This site provides the longest 

bench-mark record of subsidence in the Los BanosKettleman City area. The overall trends of both the 

subsidence and water-level plots have been toward 

gradually increasing rates of subsidence and head decline.

Subsidence and artesian-head decline 10 miles 

southwest of Mendota are shown in figure 7. Bench

UJ u.

,r 100

0. U_

5 oc

D D 

Q. V)

o a

H 2

200

30C

Well 14/15-18ES 

perforated 525- 

888 feet

10

920 1930 1940 1950 1960 1970

FIGURE 6. Subsidence and artesian-head decline near bench mark B1042.

200

300

400

500 -

600

700

800

vBench mark S661

Well 14/13-26N2 

perforated 831- 

1703 feet

Well 14/13 26E2 

perforated 809- 

1526 feet

10

15

20

25

1950 1960 1970

FIGURE 7. Subsidence and artesian-head decline near bench mark S661.

mark S661 has subsided more than any other bench 

mark in the San Joaquin Valley, even though the period 

of record extends only as far back as 1943. Rapid compaction has destroyed well casings within a few years. 

Thus, the records from several wells are necessary to 

show the trend in water levels. Both the rates of subsidence and head decline have decreased since the 

mid-1950's.

Subsidence and artesian-head decline near bench 

mark H237 (reset), 6 miles northwest of Cantua Creek, 

are shown in figure 8. Well 16/15-6N1 was one of the 

first wells drilled in the vicinity of the bench mark, and 

the water-level record during the early 1940's indicates 

that little head decline occurred during initial agricultural development. Between 1944 and 1961, the artesian head declined rapidly, and since 1961 the head 

has continued to decline but at slower rates than previously. The rate of subsidence increased until about 1960 

and has been roughly constant since then.

Subsidence and artesian-head decline southwest of 

Five Points are shown in figure 9. The head-decline

600

1940 1950 1960 1970

FIGURE 8. Subsidence and artesian-head decline near bench mark H237 (reset).

|B

£L LL 

5 DC

O Q 1-2

300

400

1940 1950 1960

FIGURE 9. Subsidence and artesian-head decline near bench mark N692.
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 Gil

trend is similar to that shown in figure 8, although the 

head decline since 1940 has been about 90 feet greater 

near bench mark N692 than near bench mark H237. 

The subsidence histories of the two bench marks are 

similar until 1960, but since 1960 the rate of subsidence 

at bench mark N692 has decreased slightly, while that 

at bench mark H237 has been constant.

Subsidence and artesian-head decline near Westhaven are shown in figure 10. Wells in the vicinity of 

this bench mark provide the longest record of head 

decline in the Los Banos-Kettleman City area. The 

water-level record begins in 1918, and the bench-mark 

record begins in 1923. The rapid decline in artesian 

head between 1947 and 1953 coincided with a period of 

marked agricultural expansion after World War II. The 

subsidence rate increase after 1947 coincided with the 

increased rate of head decline.

The relation between subsidence and the change in 

applied stress on the lower-zone deposits is discussed for 

three of the preceding sites with reference to figures 

33-35.

1920 1930 1940 1970

FIGURE 10. Subsidence and artesian-head decline near bench mark PTS21S.

RELATION OF CHANGES IN AQUIFER-SYSTEM 

THICKNESS TO CHANGE IN ARTESIAN HEAD

The history of subsidence, compaction, and changes 

in artesian head near Huron from 1954 to 1960 is shown 

in figure 11 by means of graphs of subsidence of the land 

surface at B889, compaction in a well 2,030 feet deep as 

recorded by shortening of a cable anchored at the bottom of the well (Lofgren, 1961), and change in head as 

recorded by a float-type water-level recorder on well 

19/18-27M1. The compaction record was the result of 

the first attempt to measure compaction in the study 

area. A good record was obtained from mid-1955 until 

the fall of 1960, when the cable of the compaction 

recorder failed because of corrosion. Attempts to install 

new equipment were unsuccessful. Bench mark B889 

and well 19/17-35N1 are close together about ll/2 miles

north of Huron, but well 19/18-27M1 is about 5 miles 

east of the compaction-recorder site. Wells suitable for 

water-level recorders were not available nearer the 

compaction recorder.

The plots of subsidence and compaction in figure 11 

are about parallel, indicating that most of the compaction causing the subsidence occurred above the depth of 

the compaction anchor at 2,030 feet. From October 1955 

to January 1960, measured compaction was 85 percent 

of the total subsidence as observed by releveling of the 

nearby benchmark. The hydrograph for well 

19/18-27M1 reveals an overall rate of head decline of 

about 8 ft yr" 1 (feet per year). Superimposed on the 

long-term trend are seasonal fluctuations of 40-70 feet. 

Comparison of the compaction and water-level plots 

shows that maximum compaction rates occur during 

seasons of declining head. Compaction rates are small 

or net compaction ceases during seasons of rising artesian head.

The trends of annual compaction rates and lowerzone artesian-head decline at the Oro Loma site near 

the Delta-Mendota Canal are shown in figure 12. The 

amounts of annual compaction measured by a cabletype recorder anchored at 1,000 feet in well 12/12-16H2 

decreased from 0.44 ft yr" 1 in 1959 to 0.08 ft yr" 1 in 

1965. The water level in well 12/12-16H6 indicates that 

the summer low water levels have been almost the same 

since 1960 but that the recovery of the water levels 

during the winters has become progressively less. 

Hence, the seasonal fluctuations decreased from 23 feet 

in 1960 to 9 feet in 1965.

The compaction shown in figure 12 is virgin compaction occurring in the thicker more clayey aquitards and 

aquicludes that still are characterized by residual excess pore pressures. The decrease in annual compaction 

rates reflects a progressive decrease in pore-pressure 

differences between aquifers and aquitards in the 

aquifer system as water drains to the more permeable 

strata.

ELASTIC AND INELASTIC CHANGES IN 

AQUIFER-SYSTEM THICKNESS

Not all virgin compaction is inelastic. A small part of 

the virgin decrease in aquifer-system thickness is elastic. The next two sections will describe some aspects of 

elastic compaction and expansion of the aquifer system, 

as well as virgin compaction, in response to change in 

applied stress as indicated by change in artesian head.

The following modification of Jacob's (1940) equation 

for the coefficient of storage provides a convenient way 

to visualize the relative importance of the elastic and 

inelastic components of compaction due to artesianhead decline:
G12

tUJ

" Si 

z >

STUDIES OF LAND SUBSIDENCE

360

Q< 

D UJ 

I- </)

< UJ *s

OC UJ

358

356

354

352

'Subsidence, bench mark B889

UJ 

CO

tUJ QJ

UJ o

"-<

Z u-

- cc

QJ "'

I- Q

< Z

280

320

360

400

/Compaction, well 19/17-35N1

Hydrograpn, well 

19/18-27M1

FIGURE 11. Subsidence, compaction, and artesian-head decline near Huron. 

Elastic components

Inelastic 

component

Total water 

from storage 

per unit decline 

in head

Expansion 

of water

JmnlE

Compression Compression Compaction 

of aquifers of aquitards of aquitards

VmJE1 s

y is the specific weight of water, n is the mean porosity 

of the aquifer system, m^ is the thickness of the aquifers, rri2 is the thickness of the aquitards, m is the 

thickness of the aquifer system, Ew is the bulk modulus 

of elasticity of water, Es andEc are the moduli of elasticity of the aquifers and aquitards respectively, and (3 c is 

the modulus of compressibility for the inelastic compaction of the aquitards. Assumptions for this equation are 

that the aquifer system consists of uncemented granular material and that the release of water from all parts 

of the aquifer system is instantaneous. These assumptions are met for the first three terms of the equation. 

Because a timelag exists for the compaction of 

aquitards, the field determination of the fourth term is 

only an approximate minimum value.

The water that is obtained from storage as a result of 

head decline is obtained from the elastic expansion of 

the water contained in the pore spaces and the compression of the aquifer-system skeleton containing the 

water.

The following example compares the general magnitude of the storage components yielded as a result of 

artesian-head decline for well 19/16-23P2: 

St =

36xl(r3 = 2.5 + 32)xlO-3

The component of l.OxlO"3 is the amount of water 

released from storage per unit head decline as a result of 

expansion of water, assuming a porosity of 0.4, a thick-
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G13

DC 

< 

UJ .

< K^

cc o 

r- O

O O

< 7

Q. O

<0

3 LL

Z 

Z

180

- 190

O UJ

_l UJ 

Ul LL 

ffl z

cc -

200 h

UJ <

O _i

210

1959 1960 1961 1962 1963 1964 1965

FIGURE 12. Relation of annual compaction rates to change in artesian head at the 

Oro Loma site.

ness of 1,800 feet, and 3x 105 Ib in~2 for the modulus of 

elasticity for water.

The component of 2.5x10-3 is an estimate of the 

minimum amount of water released from storage per 

unit head decline as a result of elastic compression of 

the aquifers and aquitards within the 1,800-foot thickness and thus combines the second and third terms of 

the original equation. The estimate is based on the 

mean recorded net expansion measured during 18 

periods of .head recovery in which recorded expansion 

exceeded 0.01 foot. It is assumed that elastic compression is equal to elastic expansion and that change in 

thickness in the elastic range of deformation is linear 

with change in effective stress. As will be discussed 

later, amounts of recorded expansion generally are less 

than amounts of actual expansion because of concurrent 

delayed compaction in beds with residual excess pore 

pressure. Thus, the value of 2.5xlO~3 should be regarded as a minimum.

The inelastic component of 32 x 10~3 (the fourth term 

of the equation) is an estimate of the minimum amount 

of inelastic compaction of the aquifer system per unit 

head decline. The amount is based on the total subsidence that has occurred at well 19/1&-23P2 as of 1966

minus the estimated elastic compaction that has occurred for the historic increase in applied stress. About 

8 feet of inelastic subsidence has occurred as a result of 

250 feet of increase in applied stress. Continued recording of compaction during times of nonrising water 

levels, when potentiometric levels are above the historic low levels at well 19/1&-23P2, indicates that the 

applied stress has not become fully effective in the finer 

grained parts of the aquifer system and that ultimate 

amounts of compaction have not occurred yet. Thus, the 

value of 32xlO~3 should be regarded as a minimum.

The thickness of the deposits affected by changes in 

applied stress was estimated on the basis of the following information. The compaction anchor is set at a depth 

of 2,200 feet in well 19/1&-23P2. Pumping of well 

19/16-23P1, about 500 feet from the recorder well, controls to a large extent changes in applied stress at the 

compaction-recorder site. The casing of the gravelpacked irrigation well is perforated from 660 to 2,155 

feet below land surface. It is assumed that the drawdown in the irrigation well affects the artesian head for 

aquifers below a depth of about 400 feet. Hence, the 

storage components are based on an estimated thickness of 1,800 feet.

For the example at well 23P2, most of the water 

derived from storage is yielded by inelastic compaction 

of the aquifer system. The amount of water yielded by 

elastic compression of the aquifer system is at least two 

or three times that yielded by elastic expansion of the 

water. Inelastic aquifer-system compaction has provided at least 32 times the amount of water of expansion.

The estimates of the components of the storage 

coefficient in those parts of the study area where large 

amounts of land subsidence have occurred indicate that 

less than one-tenth of the long-term compaction of the 

aquifer system is the result of elastic compression. A 

similar conclusion was reached by Poland (1961). It will 

be shown later, however, that in one area of minor 

subsidence, the elastic component of compaction accounted for most of the compaction during a 6-month 

period. (See end of section "The Yearout Site.")

RELATION OF MONTHLY COMPACTION 

TO WATER-LEVEL CHANGE

The monthly compaction that has been recorded at 

four sites is compared with the record of change in 

lower-zone water level in figures 13-17. The times of the 

measurement of the compaction usually are 28 days 

apart, but range from 26 to 32 days.

The amount of compaction measured since the previous visit to the recorder site is dependent on several 

factors other than the change in aquifer-system thickness. Casing-cable friction at most sites makes it neces-
G14 STUDIES OF LAND SUBSIDENCE

sary to stress the cable manually during each visit. 

Manual stressing of the cable overcomes the friction 

that may prevent recording of compaction. The cable is 

stretched more than the amount of compaction that 

occurred during the month, but if friction characteristics remain the same from month to month, cable 

stresses between and below the points of contact between the casing and the cable should return to approximately the same tensions after each manual stressing. 

Examination of many records indicates that the friction 

characteristics of a given recorder system do not change 

noticeably with time. A more important source of error 

for a given measurement is the variation in the individual mode of manual movement of the counterweights. However, little variation is apparent between 

the results obtained from a single operator from month 

to month.

Errors introduced into measurements of compaction 

by individual differences in stressing are not cumulative and are compensated for in succeeding measurements. As the total amount of measured compaction 

accumulates during a period of several months, the 

ratio of error to total compaction decreases.

No attempt has been made to compensate for possible 

errors introduced into the measurements of a single 

month. Where the measurement of a given month appears to be in error, the amount of measured compaction 

is simply added to the compaction of an adjacent month 

and a mean value is shown for the combined periods. In 

addition, all records of apparent expansion of the 

aquifer system have been removed by averaging the 

measured expansion with the measured compaction of 

an adjacent month, or months. Recorded expansion was 

removed because it was not possible at some sites to 

separate objectively the records of net expansion that 

result from head recovery from the records of apparent 

expansion that are the result of operator error.

At some sites, such as the Oro Loma site, friction was 

large and the operator error was large compared to the 

small amount of monthly compaction. For this reason, 

the evaluation of the monthly compaction record for the 

Oro Loma site is not included; instead, annual compaction rates and water-level changes at Oro Loma are 

shown in figure 12.

At the four other sites (see figs. 13-17), friction was 

small or the amount of operator error was small compared with the large amounts of monthly compaction 

being measured. The records from these sites provide 

useful information about the changes in compaction 

rates as related to the changes in applied stress, as 

indicated by changes in water level.

The relation of monthly and bimonthly compaction to 

lower-zone water-level change for 1961-66 at the Mendota site is shown in figure 13. The water-level record is 

continuous, and the time of measurement of the compaction is at the end of each period shown. Casing-cable 

friction is moderate in well 14/13-11D6. Most of the 

compaction is recorded when the cable is stressed. The 

total recorded compaction is the sum of the relative 

cable movement during the period and the relative 

cable movement resulting from cable stressing at the 

end of the period.

The general relation at the Mendota and other sites is 

that the maximum amounts of monthly compaction are 

recorded during times of declining head. During times 

of rising head, the amounts of monthly compaction 

commonly are less than half the maximum values, even 

when water levels are within 20 feet of historic low 

levels. As a result, the inverted bar graph in figure 13 

gives the general impression that most of the compaction occurs before seasonal low water levels have occurred.

The pattern just described is interpreted as being the 

result of elastic compaction and expansion of the aquiFIGURE 13. Relation of monthly compaction to lower-zone water-level change at the Mendota site, well 14/13-11D6.
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G15

fers and thin aquitards that is superimposed on continuing virgin compaction of the thicker aquitards and 

aquicludes. Most elastic changes in thickness of the 

aquifer system are assumed to be rapid and linear in 

response to change in applied stress. Virgin compaction 

rates should be more rapid at times of low water levels 

than at times of high water levels because the applied 

stress is greater. During times of applied-stress increase, elastic compaction is added to virgin compaction, but during times of applied-stress decrease, elastic 

expansion is subtracted from virgin compaction.

An estimated elastic component was removed from 

the recorded compaction values of the 1963 record for 

well 14/13-11D6 at the Mendota site to evaluate the 

validity of the foregoing interpretation.2 The elastic 

changes were estimated for those deposits assumed to 

be sufficiently permeable to have little or no time delay 

for thickness changes during times of applied-stress 

change. Cores from the Mendota site suggest that the 

sandy deposits undergoing elastic changes consist 

chiefly of sands, silts, and thin-bedded clayey sands. A 

total of 118 feet of clayey deposits was not included in 

the computation of elastic change in thickness because 

of the time needed to expel water from aquitards upon 

increase in applied stress. Also, those aquitards within 

which virgin compaction was continuing would continue to expel water during times of decrease in applied 

stress. The core record indicates that 540 feet of sandy 

deposits occur in the 658-foot interval between the base 

of the Corcoran Clay Member at a depth of 700 feet and 

the anchor depth of 1,358 feet. An additional 60 feet of 

sand is in that part of the upper zone that is assumed to 

be compacting to cause about 19 percent of the subsidence during 1963-66.

The pattern of computed monthly virgin compaction 

for the 1963 data varies, depending on the values assigned to specific unit expansion for the 600 feet of 

sandy deposits within the compacting interval. Low 

values, such as 1.6xlO~6ft-1, reduce the variation in 

compaction between the periods, but tend to retain the 

general pattern of figure 13, where maximum compaction values occur before the times of maximum applied 

stress. A specific unit expansion of S.OxlO^ft" 1 was 

tried, but resulted in 3 of the 6 months of water-level 

decline being associated with assigned amounts of elastic compaction that exceeded measured compaction for 

those months. Thus, a specific unit expansion of 

5.0xlO~"6ft~ 1 is above an upper limit for assigning a 

reasonable value of specific unit expansion.

An intermediate value between the extremes of 1.6 

and 5.Ox lO^ft" 1 appears to be reasonable for the purpose of evaluating gross changes in the pattern of 

monthly and bimonthly compaction. Accordingly, a 

value of 3.3xlO~6ft-1 for elastic specific unit compaction (or expansion) was assigned as a reasonable compromise. The computed elastic specific compaction or 

expansion of the aquifers, using this assumption, would 

be 3.3xlO-6 x600=2xlO~3 feet per foot of water-level 

change. The assigned value of specific unit expansion 

appears to be a reasonable approximation when compared with a mean upper-zone value of S.SxlO"6^;" 1 

measured at the Lemoore site.

The elastic change in gross aquifer thickness at the 

Mendota site that occurred as a result of net water-level 

rise or decline was computed for each month. When this 

change was added to the measured compaction during 

times of rising water level and subtracted during times 

of declining water level, computed values of estimated 

virgin compaction were obtained. The cumulative computed monthly virgin compaction for the period 

January 2,1963, to January 7,1964, was 0.49 foot. The 

cumulative measured compaction during the same time 

interval was 0.48 foot. Water levels at the end of this 

period were only 4 feet higher than at the beginning, 

and so it is assumed that net elastic change in aquifersystem thickness was negligible during 1963.

The monthly plot of the computed virgin compaction 

is shown in figure 14. The amounts of computed 

monthly virgin compaction seem to bear a closer relation to change in applied stress, as indicated by the 

water-level plot, than does the plot of total monthly 

compaction in figure 13. Computed virgin compaction is 

distributed more uniformly throughout the year, and 

the rate of computed virgin compaction is less during 

the seasons of high water level. Distortions due to fric-

-0.03

0.06

o

UJ H

I- O

O <

0. 0.

1 ^

O O

O O

2 It should be recognized that during the seasonal rise and fall of artesian head for the 

aquifers, the boundaries within the aquitards between expanding and compacting thicknesses are constantly changing.

1963 1964

FIGURE 14. Relation of computed virgin compaction to lower-zone water-level change at 

well 14/13-11D6.
G16 STUDIES OF LAND SUBSIDENCE

tion within the recorder system and the grossness of the 

method of removing the elastic component preclude 

more detailed interpretations of figure 14.

The relation of the recorded compaction to lower-zone 

water-level change at the Cantua site is shown in figure 

15. The compaction-recorder system in well 

16/15-34N1 probably has more casing-cable friction 

than any other compaction-recorder system in the San 

Joaquin Valley. The friction caused by contact of the 

vinyl-coated cable and the 4-inch casing in this 

2,000-foot well is such that compaction rarely is recorded if the cable is not stressed during each visit.

Well 16/15-34N4 provided a good water-level record 

for the lower zone from 1960 to April 1963 when the 

effects of 2 feet of casing shortening caused the casing to 

rupture in two places. The ruptures allowed upper-zone 

water to enter the well, causing anomalously high 

water levels. The well was repaired in December 1964 

and a good water-level record has been obtained since.

The casing in the compaction-recorder well apparently has not ruptured, despite the 9 feet of casing 

shortening that occurred between mid-1960 and 1967.

There are two reasons why the compaction-recorder 

casing has not ruptured: The compaction-recorder well 

has a 4-inch casing, which is stronger than the 8-inch 

casing in the water well (Pt. 2, Bull, 1974, fig. 39), and 

also has three slip joints which appear to have been 

effective in relieving much of the stress placed on the 

casing as a result of compaction.

Despite the large amount of casing-cable friction in 

well 16/15-34N1, a consistent record of monthly and 

bimonthly compaction has been obtained. The times of 

rising water levels are the times of minimum compaction, and the times of declining water levels are the 

times of maximum compaction. Those months of rapid 

decline in water level commonly are the months of maximum measured compaction a situation suggestive of 

elastic compaction superimposed on virgin compaction 

of the aquifer system, such as was decribed for the 

Mendota site.

The relation of recorded monthly compaction to 

lower-zone water-level changes at well 19/16-23P2, 

about 8 miles northwest of Huron, is shown in figure 16. 

Well 19/16-23P2 was an unsuccessful oil test drilled in

/[Compaction well 

16/15-34N1

No record due to casing rupture

Water level, well 

16/15-34N4

1961 1962 1963 1964 1965

FIGURE 15. Relation of monthly compaction to lower-zone water-level change at the Cantua site.

1966

1961 1962 1963 1964 1965

FIGURE 16. Relation of monthly compaction to lower-zone water-level change at 19/16-23P2.
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G17

1950. Subsequently, the surface string of 13 %-inch 

casing was plugged with cement below 2,200 feet, and 

the upper part was gun perforated. The well was used as 

an irrigation well for several years.

The mode of operation of the compaction recorder at 

this site has not been as consistent as at the other sites. 

Problems with the cable have been frequent, and the 

cable had to be replaced five times during the period of 

record shown in figure 16. The well-casing diameter is 

13 inches, which results in less casing-cable friction 

than if the casing diameter was smaller. However, except for the period since August 1966, friction has been 

sufficient to require cable stressing at each visit. Prior 

to August 1966, monthly amounts of compaction tended 

to be erratic during those periods when the cable was 

not stressed during each servicing of the installation.

Apparent expansion of the aquifer system has occurred at well 19/16-23P2, but has been removed from 

the record shown in figure 16 in order to be consistent 

with the type of presentation shown in figures 13-17.

A float-operated water-level recorder has been used 

in the same well to obtain a record of the artesian head. 

Parts of the record, particularly in 1961, are missing 

because of a tendency of the float to be caught between 

the compaction cable and the casing. The sharp 

fluctuations in water level result from the intermittent 

pumping of irrigation well 19/16-23P1 about 500 feet 

southwest of the observation well.

Several general features of the records shown in 

figure 16 are apparent. The times of minimum measured monthly compaction occur mostly during times of 

rising water levels. Monthly compaction in excess of 0.1 

foot occurs during times of rapid artesian-head decline, 

which suggests that most of these large monthly 

amounts of compaction are the result of elastic compaction of large thicknesses of deposits. Comparison of the 

compaction and water-level records is better during 

those times when the cable was stressed at each visit, 

such as during 1965 and 1966, than during periods in 

which the cable was rarely stressed, such as during 

1963 and 1964.

No attempt has been made to separate the elastic and 

virgin components of compaction in the 19/16-23P2 record because of the frequent equipment changes and the 

inconsistent stressing of the cable.

The relation of compaction to lower-zone water-level 

changes at the Westhaven site is shown in figure 17. 

Both the water-level and compaction records are based 

on monthly measurements. The compaction recorder is 

described by Poland and Ireland (1965).

The amounts of monthly compaction were small. 

Most of the compaction occurred during times of declining water levels, and little net compaction was measured during times of rising water levels.

DEPTH TOWATER BELOW SURFACE, LAND INFEET

4* W 

4^ 0)0O0000

-^& ^

v A .

^ ^"

1963

'/ /' 

Corripaction, well

20/18-1 1Q3

f\

V V/ V v \/

Water level, well 

20/18-1 1Q2

P

~n

-

v'Y

1964 1965

poo

'-* bi 

o

MONTHLY COMPACTION IN0-1930 THE 

FOOT DEPTH INTERVAL, FEET IN 

FIGURE 17. Relation of monthly compaction to lower-zone water-level change at the West 

haven site, 20/18-11Q2, 11Q3.

RELATION OF COMPACTION AND EXPANSION 

TO CHANGE IN ARTESIAN HEAD

The records of monthly compaction in the preceding 

section indicated that thickness changes within the 

elastic range greatly affect the pattern of short-term 

recorded compaction of the aquifer system. However, 

the excessive friction at most sites and the low sensitivity of the graphical analysis of figures 13-17 permit only 

general interpretations. Three sites within the study 

area have sufficiently low friction that the records can 

be used to obtain quantitative estimates about the 

mechanics of the aquifer systems. The net expansion 

characteristics of the aquifer-system skeleton can be 

approximated in some cases, and the types of inelastic 

processes can be identified.

The reader is cautioned to regard the quantitative 

estimates as being only general approximations. Even 

at sites where changes in aquifer-system thickness are 

being measured accurately, two types of questions arise 

regarding the water-level data. First, in a heterogeneous aquifer system, "What is the interval that is being 

affected by the head changes indicated by the waterlevel record?" Where additional data are available, the 

water-level records of nearby irrigation wells are compared with the observation-well record to see if they are 

similar and if the times of water-level change coincide 

with the times of aquifer-system compaction or expansion. In the absence of these cross-checks, it is assumed 

that the water-level record is representative of the 

aquifer system. The second question is, "What are the 

variations in pore pressure in the aquifers and 

aquitards within the thickness of deposits opposite the 

perforated casing?" This question cannot be resolved 

unless piezometers are installed in many aquifers and 

aquitards. It is assumed that the water-level record 

represents an integrated pore-pressure distribution for 

the aquifers and that the pore pressures in the 

aquitards not only lag behind the pore-pressure
G18 STUDIES OF LAND SUBSIDENCE

changes in the aquifers but also have less seasonal 

fluctuation than pore pressures in the aquifers. Excess 

pore pressures in the central parts of the thicker 

aquitards may have no seasonal fluctuation, only a variable rate of decay, depending on the magnitude of the 

hydraulic gradient to contiguous aquifers.

Therefore, the general purposes of this section are to 

provide some gross approximations of the physical constants of the aquifer systems, to illustrate techniques of 

relating water-level change to change in aquifersystem thickness, and to provide tentative interpretations of the figures and tables of this section.

Most of the following interpretations are based on the 

classical hydrodynamic theory of soil consolidation 

(Terzaghi and Peck, 1948, p. 233-242). Field compaction and water-level records help verify parts of the 

theory of consolidation of clays that has been developed 

through laboratory investigations. Also, field studies 

can add to those aspects of the theory that cannot be 

tested in the laboratory.

Eleven compaction recorders in the study area have 

recorded net expansion during water-level rise. The 

records of net expansion from three of the sites are 

presented in this section. Water-table changes are negligible at all three sites during the periods of record, and 

so the artesian-head changes are the only causes of the 

applied-stress changes.

THE LEMOORE SITE

Excellent records of aquifer-system compaction and 

expansion and the associated water-level changes have 

been obtained from well 18/19-20P2, about 10 miles 

northeast of Westhaven. This upper-zone well taps the 

confined aquifer system above the Corcoran. A 

float-operated recorder monitors water-level changes 

through a perforated interval 497-537 feet below the 

land surface. The well is 577 feet deep, has a 6%-inch 

casing, and has a reverse-lay stainless steel cable that 

does not require stressing when the charts are changed 

on the 1:1 and 24:1 recorders.

The depth range of deposits affected by the change in 

recorded artesian head has been estimated from an electric log of well 18/19-20P1 (Pt. 2, Bull, 1974, fig. 47) and 

from the water-level record in a nearby well 260 feet 

deep. The electric log indicates that a continuous sand 

occurs between depths of 294 and 565 feet, which is 

confined by lacustrine (Croft, 1972) clay beds at depths 

of 277-294 and 565-577 feet. The lower clay is the upper 

part of the Corcoran. Nearby well 18/19-21R3 is perforated in the depth interval 220-260 feet and has a water 

level that is 40-50 feet higher than the level in well 

18/19-20P2 but fluctuates annually about 45 feet. Thus, 

substantial long-term artesian-head decline has occurred to at least as shallow a depth as the base of a clay

bed between depths of 230 and 245 feet, and seasonal 

fluctuations are sufficiently large to cause elastic compaction and expansion in the sand interval between 245 

and 277 feet. For purposes of this discussion, the section 

penetrated by well 18/19-20P2 that is compacting and 

expanding is estimated to be between 230 and 577 

feet a thickness of 347 feet. The total thickness of the 

three clay beds affected by head decline is 44 feet.

The water-level record of well 18/19-20P2 represents 

the applied-stress changes at the site. Good hydraulic 

continuity exists in the thick sand sequence between 

the depths of 294 and 565 feet, which constitutes 89 

percent of the aquifer material within the 347-foot 

thickness. The aquifer between depths of 245 and 277 

feet is only 32 feet thick. The rate and amount of head 

changes differ moderately from that of the aquifer 

below the 294-foot depth, and it is known that both 

aquifers undergo head declines during the late winter 

and summer and have rising heads during the autumn.

Changes in aquifer-system thickness during regional 

water-level recovery are shown in figure 18, which includes the summer low water level of 214 feet and the 

winter high water level of 157 feet. The water-level 

recovery needed to record net expansion generally is 

only 1-2 feet. The fact that only 1 foot of applied-stress 

decrease was needed to initiate net aquifer-system expansion when the depth to water was 214, 201, and 169 

feet shows that the aggregate virgin compaction of the 

beds was small. Virgin compaction may continue at a 

slow rate in a few tens of feet of clay beds during times of 

water-level rise, when most of the deposits are expanding. The net result is recorded expansion almost as soon 

as applied stress starts to decrease. Furthermore, the 

1-foot rise in water level needed to reverse the trend 

from compaction to net expansion indicates that the 

amounts of casing-cable friction and lag in the recorder 

system are minimal.

In a major contribution, Riley (1969) developed a 

graphical method for plotting field measurements of 

water-level change and compaction as stress-strain 

curves. Under favorable circumstances, these can be 

used to obtain quantitative values for gross elastic storage and compressibility parameters and other characteristics of compacting aquifer systems. A stress-strain 

plot for well 18/19-20P2 is shown in figure 19. Consecutive periods of repeated applied-stress increase and decrease produce a series of loops, or nearly parallel segments, that are displaced with increasing time toward 

the right side of the plot as a result of cumulative inelastic compaction. Cumulative compaction between two 

dates can be determined along any line of equal applied 

stress.

The descending segments of the stress-strain plot are 

of particular interest because they represent the times
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G19

Q Ilil UJ

\- UJ

< uo z

Q ~

Z UJ

- CJ

OT <

< U.

w

CC Q

 to

ISO160

170

-1 180 -O2- -1

< 190

O Iu. I

°t

UJ UJ

^ Q 200 

co m

210

220

ExpansiorK

September October November December

1967

January February

1968

0.01

0.02

0.03

2s

> O

cc z

UJ <

0.04 < 

u. 

O

UJ

0.05

0.06

FIGURE 18. Relation of aquifer-system compaction or expansion to water-level change, well 18/19-20P2.

of net aquifer-system expansion. The mean slope of the 

lower parts of the descending limbs provide a means of 

approximating the modulus of expansion of the aquifer 

system the specific expansion. The net specific expansion indicated by the mean slope shown in figure 19 is 

1.2xlO~3 . This is the component of the storage 

coefficient attributable to elastic response of the 

confined aquifer system skeleton. The net specific unit 

expansion is

1.2XHT3

 =3.5xl(T6ft- 1 ; 

347 feet

this is the component of specific storage attributable to 

elastic response of the confined system skeleton.

The descending and rising limbs of the plot are not 

congruent. At times of equal applied stress, the rising 

limb may be to the left of the descending limb (5/8/67

and 4/19/67) or to the right of the descending limb 

(2/10/68 and 12/20/67). These variations can be explained by differences in the rates of delayed changes 

that are occurring in the aquifer system. The greatest 

sensitivity of the stress-strain plot is in determining the 

approximate elastic properties of the aquifer systems. A 

graphical procedure that is sensitive in determining 

virgin changes (fig. 18) will be used to describe the 

hydrodynamic processes and to explain the variations 

in the stress-strain plot.

Figure 18 shows the effects of variation in the rates 

and types of time-delayed changes on aquifer-system 

thickness. The previous discussion about the relation of 

monthly compaction to water-level changes showed the 

importance of elastic changes on recorded compaction 

during times of changing applied stress, and so it can be 

assumed that much of the thickness change in figure 18 

is elastic. If all the thickness changes were elastic and
G20 STUDIES OF LAND SUBSIDENCE

220

Note: Date (month/day/year)

150-3 0 +4 

COMPACTION, IN FEET X10" 2

FIGURE 19. Stress-strain plot for well 18/19-20P2. (Modified from Poland, 1969a, p. 19.)

occurred without time delay, the expansion and com- change represented by the water-level record. Only a 

paction plot would parallel the plot of applied-stress small part of the two plots is parallel near the 175-foot
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G21

depth-to-water part of the record. At deeper water 

levels, convergence of the plots from September into 

December is interpreted as being the result of continuing virgin compaction that is concurrent with elastic 

expansion. The result is that net expansion is less than 

if virgin compaction were not continuing. At rising 

water levels above 175 feet, the divergence of the plots is 

interpreted as being the result of delayed expansion. 

Delayed expansion may have been occurring at deeper 

water levels also, but was masked by large rates of 

virgin compaction.

The relative magnitudes of convergence and divergence at selected times are shown by the dimensionless numbers in figure 18. The rate of convergence is 

more rapid during times of deep than shallow water 

levels, indicating that virgin compaction rates are 

larger during times of larger applied stress.

The large rate of convergence during the period of 

declining water levels early in February as compared 

with the divergence rates preceding the start of head 

decline indicates that time-delayed compaction was occurring at water levels of less than 170 feet. It cannot be 

determined if part of the delayed compaction is inelastic, because either elastic or inelastic compaction would 

cause the convergence patterns in figure 18. Three thick 

clay beds are influenced by water-level changes in well 

18/19-20P2. Apparently, one or more of the beds is 

sufficiently thick and of sufficiently low diffusivity to 

retain excess pore pressures after 57 feet of head recovery from the summer low water level of 214 feet. These 

excess pore pressures have resulted from years of 

cumulative head decline. The linear plot for the same 

time period in figure 19 suggests that most of the change 

in aquifer-system thickness at water levels above 170 

feet is elastic. It should be kept in mind, however, that 

concurrent delayed compaction and delayed expansion 

tend to offset each other to an unknown degree that 

varies with applied-stress level.

The presence of delayed expansion shows that three 

concurrent processes are tending to change aquifersystem thickness during times of applied-stress 

decrease elastic expansion with no measurable time 

delay (presumably chiefly of the aquifers), delayed elastic expansion (presumably of the thin aquitards and 

outer parts of the thick aquitards), and virgin compaction (presumably of the thick aquitards and aquicludes). It is assumed that the rates of elastic change in 

the aquifers occur linearly and that inelastic compaction rates decrease and delayed expansion rates increase with decreasing applied stress. The amounts of 

delayed expansion at the Lemoore site cannot be estimated, because virgin compaction was occurring at the 

same time. However, it appears that during times of 

high water levels the rates of delayed expansion exceed

the rates of virgin compaction, for a given rate of 

applied-stress decrease.

Variations in net specific unit expansion during the 

seasonal decrease in applied stress are shown in table 1.

T AB LE 1. Variation in net specific unit expansion during a period 

of seasonal head recovery at well 18/19-20P2

Date

1967

Sept. 20

Sept. 22

Sept. 24

Oct. 2 __

Oct. 8__

Oct. 13

Oct. 31

Nov. 10

Do

Nov. 18

Do

Dec. 4__

Do

Dec. 18

Do

1968

Jan. 10

Do

Jan. 21

Depth

to water

(ftl

______ 214.0

_ 211.5

212.0

___ 202.5

___ 204.0

_ _ 198.0

______ 201.5

______ 195.0

_ _ _ 195.0

__ 190.0

_- __ 190.0

__ _ 177.0

__ __ 177.0

___ 169.7

_ ___ 169.7

_ ___ 159.0

159.0

___ 157.0

Water-level

rise

(ft)

2.5

9.5

4.0

6.5

5.0

13.0

7.3

10.7

2.0

Mean rate of

water-level rise

(ft per day)

1.2

1.1

.8

.6

.6

.8

.5

.5

.2

Recorded net 

expansion

(ft)

0.0005

.006

.003

.004

.004

.013

.009

.012

.0025

Specific unit 

expansion

0.6 

1.8 

2.2 

1.8 

2.3 

2.9 

3.5

3.2 

3.6

The mean rates of water-level rise were 1.2 feet per day 

immediately after the summer low water level, but decreased to 0.2 foot per day for an 11-day period preceding the winter high water level. Most of the periods had 

mean rates of water-level rise of 0.6-0.8 foot per day. 

The values of net specific unit expansion for the nine 

intervals of head recovery at well 18/19-20P2 given in 

table 1 form a logical sequence when considered in a 

context of the combined effects of decreasing rates of 

water-level rise (decrease in applied stress), concurrent 

decrease in virgin compaction rates, and increase in 

delayed expansion rates. Table 1 shows that net specific 

unit expansion reaches a value of 3.5 x 10~6 more than 1 

month before the winter high water level. Low values of 

net specific unit expansion occur during the three 

periods after the summer low water level, even though 

the rates of head recovery are the most rapid during 

these periods. The low values of net specific unit expansion are interpreted as being the result of rapid rates of 

virgin compaction. Between October 8 and December 

18, the rates of water-level rise are roughly constant, 

but the values of net specific unit compaction increased 

from 2.2xlO~6 to S.SxlO^ft" 1 . This increase can be 

attributed largely to a decrease in the rate of virgin 

compaction with decrease in applied stress and to an 

increasing rate of delayed expansion.

THE YEAROUT SITE

Monthly compaction and expansion and water levels 

have been measured in upper-zone well 13/15-35D5, 

about 4 miles east of Mendota. The 4-inch well casing is 

perforated opposite Sierra micaceous sands and silts at 

depths of 373-433 feet. The bottom of a pipe-type compaction gage is set in the upper part of the Corcoran at a 

depth of 440 feet (Pt. 2, Bull, 1974, table 1).
G22 STUDIES OF LAND SUBSIDENCE

The depth range of deposits affected by change in 

recorded artesian head was estimated from an electric 

log of well 13/15-35D1 (200 ft west of well 35D5) and 

water-level data from observation well 35D5 and irrigation well 13/15-34A1 (325 ft west of well 35D5 and 

perforated at depths of 100-276 ft). Comparison of the 

compaction and water-level records indicates that the 

water levels of the two wells are about the same during 

times of no pumping. However, head decline is larger in 

well 13/15-34A1 because pumping is more intense in 

the 100-200 -foot-deep sand section than in the 

280-430-foot-deep sand and silt section. Comparison of 

a 10:1 expanded-scale compaction record and the two 

water-level records shows that the detailed variations 

of the compaction record coincide with short-term 

water-level fluctuations in well 13/15-34A1. For purposes of this discussion, the section penetrated by well 

13/15-35D5 that is compacting and expanding is estimated to be between depths of 100 and 440 feet a 

thickness of 340 feet.

The monthly water-level measurements for well 

13/15-35D5 represent the approximate trend in 

applied-stress change at the site. Because larger seasonal fluctuations occur in the upper part of the aquifer 

system, the seasonal changes indicated by the waterlevel record for well 13/15-35D5 should be regarded as 

minimal mean changes in head. Monthly instead of 

continuous water-level measurements also result in 

minimal seasonal recorded head changes.

The relation of water-level and aquifer-systemthickness changes in well 13/15-35D5 are shown in 

figure 20. The general trends of the plots are parallel, 

but short-term departures from parallelism are apparent for some months.

Maximum values of net specific unit expansion can be 

computed for the fall and winter of 1966-67 and 

1967-68. For 1966-67, the specific unit expansion was

0.051-ft increase in thickness _. n x iQ-6ft-l

(340-ft thickness) x (38-ft decrease 

in applied stress 

as indicated by 

water-level rise)

FIGURE 20. Relation of aquifer-system compaction or expansion to water-level change, 

well 13/15-35D5.

The specific unit expansion for the 0.045 foot of expansion and 39 feet of head recovery in 1967-68 was 

3AxW~Gft~l. These values are regarded as maximal 

because the upper part of the aquifer system probably 

had larger seasonal water-level changes than the lower 

part represented by the record from well 13/15-35D5. It 

is concluded that the specific unit expansion at the 

Yearout site is not greatly different from that at the 

Lemoore site (3.5 xKT6^1 , from fig. 19).

Most of the upper-zone thickness changes at well 

13/15-35D5 are elastic. Between August 2, 1966, and 

August 1, 1967, the net cumulative compaction at the 

site was only 0.013 foot, during which time a net waterlevel rise of 1 foot occurred. Between August 2, 1966, 

and February 14,1967, a seasonal water-level recovery 

was accompanied by a net expansion of the aquifer 

system of 0.051 foot. Assuming that half of the delayed 

compaction occurred during each of the two halves of 

the year, 0.058 foot (0.051 ft+0.0065 ft=0.058 ft) of 

expansion occurred during the 6y2-month period of head 

rise, and 0.058 foot (0.064 ft-0.0065 ft=0.058 ft) of 

elastic compaction occurred during the 5% months of 

head decline. The elastic component of seasonal compaction (0.58 ft/0.064 ft) is estimated to be about 90 

percent. Thus, as at most of the other sites, elastic 

changes greatly affect short-term recorded compaction 

during times of head change.

WELL 19/16-23 P2

In August 1966, the compaction recorder in well 

19/16-23P2 was rebuilt to obtain a better record of 

aquifer-system compaction and expansion. The recorder system is described in Part 2 (Bull, 1974). The 24:1 

expanded-scale record assists in evaluating small 

amounts of compaction and net expansion and in determining the times of change from recorded compaction to recorded expansion. A discussion of the thickness 

of Diablo alluvial-fan deposits affected by the applied 

stress changes was presented on page G13 of the present 

report.

The record from well 19/16-23P2 can be used to determine long-term cumulative compaction to illustrate 

the importance of the relative magnitudes of rates of 

head recovery and delayed compaction in determining 

whether net expansion or compaction occurs to demonstrate the large mechanical lag in this compaction recorder 2,200 feet deep, and to evaluate the relative 

friction and stretch characteristics of the different types 

of cables that have been used in the well.

In addition to casing-cable friction, the type of well 

construction also requires scrutiny. The casing is 

plugged with cement below the compaction anchor and 

is encased to the land surface in a cement jacket, a 

system which poses the question of whether the casing-
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G23

cement construction seriously distorts the response of 

the aquifer system to changes in effective stress.

The casing has been telescoped by vertical shortening 

of the adjacent deposits. About 97 percent of the compaction measured at the site results in casing shortening, and only 3 percent results in increased protrusion of 

the casing above the land surface. Although it cannot be 

proved that casing shortening is distributed identically 

to formation shortening, the assumption is made that 

casing deformation conforms with aquifer-system deformation. Poland and Ireland (1965, p. B182) also 

made this assumption at the Westhaven site on the 

basis of casing shortening being equal to 95 percent of 

the compaction.

Compaction and water-level records for February 

-July 1967 are shown in figure 21. The effects of intermittent pumping of nearby irrigation well 23PI are 

superimposed on a regional water-level rise. Net 

aquifer-system expansion was recorded during times of 

rapid decrease in applied stress as indicated by waterlevel rise, and aquifer-system compaction occurred during times of increase in applied stress as indicated by 

water-level decline. A brief 10-foot recovery in potentiometric level in early June was sufficient to cause a 

reversal from recorded compaction to recorded expansion.

The fact that compaction exceeded expansion in 

figure 21 during a net rise in potentiometric level is 

attributed to delayed compaction as water was expelled 

gradually from aquitards that had residual excess pore 

pressures. In March, water levels were deeper than 580 

feet. In June, water levels declined to only 575 feet, but 

0.08 foot of delayed compaction had occurred since 

March.

Detailed compaction and water-level changes for a 

1-month period, March 14 to April 13, 1967, are shown 

in figure 22. The 1:1 and 24:1 records of compaction and 

expansion have been traced directly from the field 

charts, and the water-level record has been replotted 

and positioned vertically so that the April 3 compaction 

and water-level plots coincide. The stepped compaction 

record is the result of casing-cable friction.

The water level in observation well 23P2 rose 19 feet 

between March 18 and 22, while the nearby irrigation 

well pump was turned off, and declined 17 feet when the 

well was pumped again. The water level rose about 2 

feet between March 29 and April 3, as a result of regional head rise (fig. 21). After the irrigation well pump 

was turned off on April 3, the water level rose 31 feet in 

10 days.

The water level had been drawn down below the 

570-foot depth six times in the preceding years, but had 

been drawn down below the 580-foot depth only once 

(during February and March 1967, fig. 21). About 0.006

foot of compaction was recorded during the March 13-18 

head-decline period. The shortening probably was 

largely delayed virgin compaction from prior head de 

clines.

The recorded net aquifer-system expansion of 0.015 

foot between March 18 and March 22 resulted from a 

19-foot rise in potentiometric level. The first measured 

expansion was about 19 hours after the irrigation well 

pump had stopped and after about 10 feet of water-level 

recovery had occurred. After expansion was first recorded, about 5 feet of water-level recovery occurred for 

each 0.01 foot of recorded net expansion.

When the irrigation well pump started again on 

March 22, a new period of compaction began. By the 

time the applied stress had increased 17 feet, 0.01 foot of 

compaction had been recorded. Then, while the applied 

stress decreased 2 feet between March 29 and April 3, 

an additional 0.015 foot of net virgin compaction was 

recorded. This delayed compaction is interpreted as 

being the result of continuing slow explusion of water 

from aquitards whose pore pressures greatly exceeded 

the pore pressures in the adjacent aquifers.

A second period of aquifer-system expansion began 

April 3 when the irrigation-well pump was turned off 

After 14 hours, and 10 feet of water-level rise, expansion was recorded again. By April 13, 31 feet of waterlevel recovery and 0.025 foot of net aquifer-system expansion had been recorded. After expansion was first 

recorded, about 9 feet of water-level recovery occurred 

for each 0.01 foot of expansion. The high points on the 

24:1 record of aquifer-system expansion from April 4 to 

13 form a curve similar to the curve of applied-stress 

reduction.

The similarity of the expansion and decrease-inapplied-stress curves is interpreted as suggesting that 

little time is needed to raise pore pressures in many of 

the aquitards. Compaction ceases when the pore pressures in the aquifers rise to the maximum pore pressure 

in a contiguous aquitard, thus preventing further expulsion of water. Further increases in pressure are 

transmitted fairly rapidly, even in aquitards, because 

in the elastic range their specific storage is very small.

The mechanics of elastic aquifer-system compaction 

is in distinct contrast to inelastic compaction, in regard 

to the volumes of water involved. During periods of 

decreasing aquifer pressures (water-level decline), elastic expansion of the water and elastic decrease in pore 

volume occur, and these volumes are small. When the 

effective stresses in the aquifers exceed prior effective 

stresses in adjacent aquitards, virgin compaction occurs. The volume of water moving out of the aquitards 

at such times generally is many times larger than the 

volume of water moving into the aquitards to establish 

pressure equilibrium during periods of rising water
G24

STUDIES OF LAND SUBSIDENCE

FIGURE 21. Relation of aquifer-system compaction and expansion to water-level change in well 19/16-23P2, February-July 1967.

levels and elastic expansion of the aquitards. to-grain stress, even when net compaction is continuing

The time lag at the reversals from compaction to within some aquitards. When the aggregate expansion

recorded expansion is due to the mechanics of the of the aquifers and thinner aquitards exceeds aggregate

aquifer system and to the mechanics of the recorder, shortening of the thicker aquitards still compacting, net

Elastic expansion is concurrent with decrease of grain- expansion of the aquifer system will occur.
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G25

-

 ___ ______ r^~

i i i i

^ " -_

i i i i

Compac

 

1 1 1 1 1

ion, well 19/16-23P2,

i i > i

1 : 1 scale -

-

0.05

550

Well 19/16-23P2, 24:1 scale

590 0.0333

FIGURE 22. Relation of aquifer-system compaction and expansion to water-level change in well 19/16-23P2, March 14-April 13, 1967.

Expansion will not be recorded, however, until the 

direction of movement of the recording equipment has 

been reversed. When a system that has casing-cable 

friction is recording compaction below the uppermost 

point of contact between the casing and the cable, cable 

tension is reduced below that point. The counterweights 

move down relative to the concrete pad, when the cable

tension is reduced by an amount that exceeds friction in 

the system. On the other hand, expansion is recorded 

after cable tension has increased to the point where 

friction is overcome and the counterweights begin to 

rise. The amount of movement needed to reverse the 

loaded gear train in the recording equipment is negligible compared with the amount of movement necessary
G26 STUDIES OF LAND SUBSIDENCE

to change cable stresses in a system where casing-cable 

friction is significant.

Because of the mechanical lag in the recorder system, 

the water levels at which net expansion is first recorded 

are higher than when the net expansion first occurred. 

For the periods of aquifer-system expansion shown in 

figure 21, net expansion was first recorded when the 

water level had risen about 10 feet, but net expansion 

probably had begun earlier.

The proportions of elastic and virgin compaction 

probably changed during periods of declining potentiometric levels. For the period of record shown in figure 

21, the proportion of elastic to virgin compaction, per 

unit decline in head, probably was largest when water 

levels were higher than 550 feet and probably was 

smallest when water levels were lower than 580 feet.

The initial stages of rapid compaction that coincided 

with the rapid declines in water level that occurred from 

the 547-foot depth to water in April and the 535-foot 

depth to water in May probably are largely elastic. As 

water levels continued to decline, a progressively larger 

number of beds within the aquifer system began to 

contribute to the virgin component of compaction.

The relation of aquifer-system compaction and expansion to water-level change at well 19/16-23P2 during a typical summer pumping season is shown in figure 

23. The nearby irrigation well was pumping during the 

entire summer, except for a 12-day period in May and a 

4-day period in September. Again, the times of recorded 

compaction coincided with times of increasing applied 

stress, and the times of recorded expansion coincided 

with times of decrease in applied stress. However, the

500

580

June

^Compaction

July August September

1964

-0.1

X

UJ

CC

O

0,1 

o

0.2

0.3

FIGURE 23. Relation of aquifer-system compaction and expansion to water-level change, well 19/16-23P2.
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G27

curves of change in applied stress and change in 

aquifer-system thickness do not show the parallelism of 

the plots in figure 22. The plots in figure 23 suggest that 

much more friction was present in the recorder system 

in 1964 than during the period shown in figure 22,

Many of the apparent differences between figures 22 

and 23 can be explained by comparing the differences in 

the equipment used to measure changes in aquifersystem thickness for the two time periods. Such a comparison also illustrates the need to manually stress the 

compaction cable at each monthly visit at some recorder 

sites. A Vk-inch stainless steel 7x7 stranded uncoated 

cable was used during the period of record shown in 

figure 23. The cable had twice the stretch characteristics (B.E. Lofgren, April 22, 1968, written commun.) of 

the reverse-lay cable used during the period of record 

shown in figure 22. Therefore, before installation of the 

reverse-lay cable, larger changes in aquifer-system 

thickness were necessary during expansion to increase 

cable tension below the uppermost friction point 

sufficiently to overcome the casing-cable friction.

Although expansion was recorded many times at the 

site, net recorded expansion exceeded 0.01 foot only 18 

times during the 1962-67 period. Maximum recorded 

expansion was 0.094 foot. The following data and interpretations pertain to the above 18 times of expansion.

The delay between the start of water-level recovery 

and the start of recorded expansion is a function of the 

rate of applied-stress decrease, the difference in cable 

stress above and below the uppermost casing-cable friction point at the start of applied stress decrease, the 

magnitude of cable-casing friction, and the stretch 

characteristics of the cable. The delay ranged from 38 

hours for vinyl-coated cable (large stretch and friction 

properties) to 6 hours for the reverse-lay cable (low 

stretch and friction properties). The associated waterlevel recoveries were 21 and 6 feet, respectively.

The number of hours between the start of water-level 

recovery and the start of recorded expansion does not 

seem to be related to the depth to water at the beginning 

of water-level recovery. For example, the six times in 

which 7-10 hours of water-level recovery occurred before recorded expansion started were associated with 

initial water levels ranging from 545 to 587 feet below 

the land surface.

The specific unit expansion of the 18 times when 

recorded expansion exceeded 0.01 foot ranged from 0.6 

to S.lxlO"6!!" 1 . The presence of delayed compaction 

indicates that minimum values of net specific unit expansion are being obtained for the amounts of expansion and applied-stress decrease that occurred after expansion was first recorded. It is concluded that the mean 

value of l^xlO'^f1 for the 18 times is a minimum

value for the net specific unit expansion and that a 

representative value for the 1962-67 period may be 

larger than 2.0xlO~6ft~1 .

RELATION OF LOWER-ZONE COMPACTION TO 

CHANGE IN APPLIED STRESS

Regional applied-stress increases have resulted from 

the changes in the positions of the lower-zone potentiometric surface and the water table. The algebraic 

sum of stresses caused by these two types of regional 

water-level change provides information regarding the 

increase in lower-zone applied stress during a selected 

17-year period. Then, by estimating the lower-zone 

compaction, the specific compaction (compaction per 

unit applied-stress increase) can be derived. The specific 

compaction map relates the estimated compaction to 

the observed change in applied stress on a regional 

basis, thus permitting examination of the effect of hydrologic (other than long-term water-level change) and 

geologic factors on compaction.

The period between 1943 and 1960 was selected as the 

interval to appraise the specific compaction. The period 

is sufficiently long to eliminate some short-term factors 

that might affect the results of a 3- to 6-year appraisal. 

The 1943-December 1959 subsidence map (Pt. 2, Bull, 

1974, fig. 10) shows only the subsidence that has resulted from artesian-head decline. The earliest widespread water-level control within the study area is 

based largely on measurements made by the Pacific Gas 

and Electric Co. in 1943. Most of these measurements 

were made during the summer pumping season. The 

1960 water-level map (Pt. 1, Bull and Miller, 1974, fig. 

33) also is based on measurements made largely during 

the summer pumping season. Some recent maps have 

many control points, but are based on water-level 

measurements made at the time of winter high water 

levels. Thus, the 1943-60 period fills the requirements 

of being long and having good control regarding 

changes in the position of the potentiometric surface 

and altitude of the land surface.

The regional change in total applied stress on the 

lower zone was determined as a result of the seepagestress change, the gravitational change resulting from 

the gain or loss in buoyancy of the grains caused by 

water-table change, and the gravitational change resulting from the change of pore water from a saturated 

to an unsaturated condition, or vice versa.

The change in applied stress on the lower zone resulting from change in the position of the water table between 1943 and 1960 is shown in figure 24. For those 

areas that were developed agriculturally by 1960 but 

not in 1943, the water table was assumed to have remained constant until irrigation began. Electric logs of 

the first water wells drilled within a given part of the
G28 STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

37°00'

36°30' -

EXPLANATION

Boundary of deformed 

rocks

Line of equal change in applied stress on the 

lower zone resulting from change in the 

position of the water table, in feet of 

water

Interval 10 feet. Based on maps showing 

change in the position of the water table, 

1951-65 and 1962-65, a map showing the 

history of increase of irrigated area, and 

changes in the position of the water table 

as indicated by electric logs of wells 

drilled in the 1940's and the early 1960's.

Western boundary of the Corcoran Clay 

Member of the Tulare Formation

Coahnga

VALLEY

15 KILOMETRES 36 °00'

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 24. Change in applied stress on the lower zone resulting from change in the position of the water table, 1943-60.

area provided valuable information about the position graphs from shallow wells and from maps showing the

of the water table at the onset of irrigation. The rates of position and change of the water table during much of

water-table change were derived largely from hydro- the 17-year period.
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G29

Within the areas of near-surface subsidence (Pt. 2, 

Bull, 1974, fig. 10), little change in the position of the 

water table has been noted. Within these areas, the 

moisture-deficient deposits apparently absorbed most of 

the moisture that percolated below the root zone during 

the 1943-60 period. This moisture added above the 

water table increased the applied stress on the lower 

zone. However, because the quantity is small and is 

unknown, this increment of stress increase was not 

included.

The change in applied stress on the lower zone that 

has resulted from change in the position of the water 

table between 1943 and 1960 is small. The total range in 

applied-stress change is 100 feet, from about +25 feet to 

 75 feet, but the stress change for more than 90 percent 

of the area is within ±20 feet of water.

Water-table rise is characteristic of most of the area 

east of the west boundary of the Corcoran Clay Member 

of the Tulare Formation. In much of the area, watertable rise has caused less than 10 feet of increase in 

applied stress on the lower-zone deposits. In the small 

area southwest of Mendota, about 20 feet of increase in 

applied stress has occurred as the result of 100 feet of 

water-table rise.

Large water-table declines occurred in all the area 

west of the Corcoran because of pumping of wells perforated 400-1,900 feet below the water table. Water-table 

decline extended as much as 5 miles east of the west 

boundary of the Corcoran aquiclude and may have 

influenced the rates of water-table rise for even greater 

distances to the east. The areas of maximum watertable decline coincide with the areas in which vertical 

permeability in the upper zone is greatest. The maximum decrease in applied stress on the lower zone was 

70 feet, southwest of Huron, and was the result of 350 

feet of water-table decline. The good vertical permeability of the deposits southwest of Huron has permitted 

recharge from streamflow with a high concentration of 

dissolved solids to move down into the main groundwater body (Davis and Poland, 1957, p. 459).

The change in applied stress on the lower zone that 

has resulted from lower-zone artesian-head decline is 

equal to the head decline in feet of water. The decline of 

the lower-zone potentiometric surface from 1943 to 

1960 (fig. 25) represents the increase in applied stress as 

a result of the component, which is large compared with 

the stress increase resulting from water-table change. 

Areas of applied-stress increase of 300 feet are widespread, and locally the applied stress increased as much 

as 400 feet.

The change in total applied stress on the lower zone is 

the algebraic sum of the data shown in figures 24 and 

25. Artesian-head decline has occurred throughout the 

area during the 1943-60 period. The net water-table

component has been added to the head-decline component in areas of water-table rise and has been subtracted in areas of water-table decline. Figure 26 shows 

the 1943-60 total applied-stress increase, which ranges 

from 75 feet in the northern part of the area to a maximum of 350-400 feet near the Big Blue Hills. The 

general pattern of the map conforms to the change in 

artesian head because change in head is the dominant 

component. Except for the area between Huron and 

Westhaven, the maximum increase in applied stress is 

near the west boundary of the study area, which is the 

side of least ground-water recharge to the lower zone.

Not all the land subsidence, however, is the result of 

compaction of the lower-zone deposits. Information 

from 12 compaction-recorder sites in different parts of 

the area provides estimates of the amounts and proportions of compaction occurring above and below the principal confining bed the Corcoran. The minimum proportion of compaction occurring in the lower zone 

ranges from about 95 percent at the Oro Loma site in the 

northern part of the area to about 58 percent at the 

Westhaven site in the southern part of the area. North 

of the road between Five Points and Anticline Ridge, 

more than 80 percent of the compaction occurs in the 

lower zone, except within a small area near Fresno 

Slough where most of the pumpage is from the upper 

zone.

The proportions of compaction in the two zones (Pt. 2, 

Bull, 1974, fig. 45) are based on post-1958 information, 

which is considered applicable for the 1943-59 period 

because the proportions of water pumped from the two 

zones (based on well-perforation data) apparently have 

not changed materially since 1943.

The compaction isopleths for the lower zone (fig. 27) 

for the 1943-59 period were derived from the 

1943-December 1959 subsidence map, using the information noted. The values of lower-zone compaction for 

most of the area are nearly as large as the amounts of 

land subsidence due to artesian-head decline during the 

period (Pt. 2, Bull, 1974, fig. 10). However, the amounts 

of lower-zone compaction are considerably less than 

subsidence along most of Fresno Slough and south of the 

Five Points-Anticline Ridge road. The overall trend of 

maximum amounts of lower-zone compaction increases 

northward from the vicinity of Huron to the area 

southwest of Mendota.

The ratio of the lower-zone compaction (fig. 27) to the 

lower-zone increase in applied stress (fig. 26) specific 

compaction is shown in figure 28. In a general sense, 

compaction of unconsolidated deposits increases with 

increasing applied stress. One purpose of computing the 

compaction per unit change in applied stress is to gain 

an insight into factors, other than long-term change in 

applied stress, that may affect the amounts of compac-
G30 STUDIES OF LAND SUBSIDENCE

120°30'

37°00

36°30' -

36° 00

EXPLANATION

Boundary of deformed 

rocks

Generalized line of equal increase in applied 

stress on the lower zone due to artesianhead decline between 1943 and 1960, in 

feet of water

Interval 50 feet. Based on map showing the 

maximum decline in the altitude of the 

potentiometric surface at the lower zone, 

1943-1960 (pt 1, fig. 41)

Area in which the lines for the 1960 map 

are drawn on the basis of minimum water 

levels that occurred between 1950 and 

1958

WesthavenQ

Water levels in this area rose for several 

years prior to 1960 because water from 

the Delta-Mendota Canal has, in general, 

replaced ground water for the irrigation Coalinga 

VALLEY

Western and eastern boundaries of the 

Corcoran Clay Member of the Tulare 

Formation

Kettleman BED 

City

Base from U.S. Geological Survey Central 

Valley map, 1:254,000, 1958

FIGURE 25. Increase in applied stress on the lower zone resulting from artesian-head decline between 1943 and 1960.
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3

120°30' 120°00'

G31

37°00'

36°30'

36°00'

EXPLANATION

Boundary of deformed 

rocks

Line of equal change in applied stress on the 

lower zone, expressed in feet of water

Interval 25 feet. Map was derived from maps 

showing lower-zone artesian-head decline 

and change in the position of the water 

table 1943-60

10 15MILES

10 15 KILOMETRES

Kettleman 

City

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 26. Increase in total applied stress on the lower zone, 1943-60.
G32 STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

37°00

36°30' -

36° 00'

EXPLANATION

Boundary of deformed 

rocks

Generalized line of equal compaction in the 

lower zone

Interval 2 feet, except the 1-foot line. Map 

based chiefly on the 1943-59 subsidence 

map, the estimated proportion of upperand lower-zone compaction at 12 compaction-recorder sites, and a map showing 

the variation in the amount of water 

pumped from the lower water-bearing 

zone. Maps showing depth to the base of 

the Corcoran and thickness of the lower 

water-bearing zone were used also

Coalinga 

VALLEY

15 KILOMETRES

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 27. Estimated compaction of the lower zone, 1943-59.

tion. If there were no variation in the other factors values of specific compaction would be characteristic of

affecting lower-zone compaction and the history of the entire area. However, a pronounced anomaly is

applied-stress increase was similar regionally, uniform readily apparent in figure 28. The specific compaction of
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3

120°30' 120°00'

G33

37°00' -

EXPLANATION

Boundary of deformed 

rocks

Generalized line of equal ratio; interval 

0.01

Lower-zone compaction, 1943-59 

(fig-27)

Increase in applied stress on lower 

zone, 1943-60 (fig. 26)

PLEIASANT

Coalinga

VALLEY

Kettleman BED 

10 15 KILOMETRES City

36°30' 

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 28. Specific compaction of the lower zone, 1943-60.

much of the northern third of the area is twice that of hydrologic and geologic affect compaction and subthe southern two-thirds of the area. The variations in sidence within the Los Banos-Kettleman City area. The 

specific compaction demonstrate that other factors geologic and hydrologic factors affecting specific com-
G34 STUDIES OF LAND SUBSIDENCE

paction and specific unit compaction are discussed in 

detail in Part 2 (Bull, 1974).

A map showing estimated specific unit compaction of 

the lower water-bearing zone, 1943-60, was introduced 

in Part 2 (Bull, 1974, fig. 54 ) That map was obtained by 

dividing the specific compaction of figure 28 by the 

thickness of the lower zone to derive values of compaction per foot of applied stress increase per foot of 

aquifer-system thickness. The resulting specific unit 

compaction was about four times as great in the northern part of the area as in the south. The geologic factors 

evaluated in part 2 are prior total applied stress, mean 

lithology, and the source and mode of deposition of the 

different genetic types of deposits.

Based on the detailed analysis of the specific unit 

compaction map in Part 2 (Bull, 1974), it is concluded 

that the higher specific compaction in the northern area 

(fig. 28) is due principally to the following factors:

1. The prior total applied stress as of 1943 was less in 

the northern part of the area than in the southern 

part, and thus the compressibility of deposits of a 

given lithology is higher. In general, values of 

compressibility decrease as effective stress increases.

2. Genetic differences of the deposits are conducive to 

more rapid expulsion of water from the deposits in 

the northern area. The aquitards of the flood-plain 

deposits in the northern subarea are thinner than 

the aquitards of the alluvial-fan and lacustrine 

deposits in the southern subarea. Also the 

flood-plain aquitards may be twice as permeable as 

the alluvial-fan and lacustrine aquitards (Pt. 2, 

Bull, 1974, table 6). More rapid expulsion from the 

thinner more permeable beds should produce values of specific compaction for the 1943-60 period 

that are closer to ultimate values than those to the 

south. These geologic factors contribute toward the 

higher specific compaction in the northern part of 

figure 28.

Another hydrologic parameter that shows the concentric, or enclosed, pattern of isopleths that is similar 

to the pattern of specific compaction within the study 

area is the overall pattern of seasonal head decline. The 

seasonal head decline shown in Part 1 (Bull and Miller, 

1974, fig. 43) is for the period between December 1965 

and August 1966. However, the pattern probably is 

representative of the latter part of the 1943-60 period 

because the area irrigated with ground water was about 

the same as in 1966. Seasonal variations in head during 

the early part of 1943-60 period probably were less 

along the west and south sides of the study area and 

probably were greater in the northern part. The small 

amount of seasonal head decline in the northern part of 

the area in 1966 (Pt. 1, Bull and Miller, 1974, fig. 43) is

due chiefly to the small number of wells taking water 

from the lower zone. Formerly, large amounts of water 

were pumped from the lower zone in the north end of the 

area, prior to delivery of water from the Delta-Mendota 

Canal in 1954.

Geologic factors likewise affect the pattern of seasonal head decline. The seasonal head decline in 1966 

was extreme near Kettleman City because of the barriers to recharge provided by the Kettleman Hills and 

the clay plug beneath Tulare Lake bed. Opposite the Big 

Blue Hills, seasonal head decline is largely influenced 

by wells tapping the Pliocene marine and estuarine 

sequence of the Etchegoin Formation (Miller and 

others, 1971, p. E16-E17) that receives negligible recharge.

The seasonal variations in head in the study area do 

not consist of a simple winter high and a summer low. 

The most common pattern, reflecting the irrigation 

schedule, is for the winter recovery high to be followed 

by a water-level decline in February and March that 

approaches the depth to water during the summer. During April and May, water levels recover almost to the 

winter high before declining to the summer lows. Thus 

it is common in areas of large specific compaction for the 

lower-zone head to undergo two fluctuations each year 

that exceed 60 feet. Examples of hydrographs with large 

seasonal fluctuations in areas of large specific compaction are shown in figures 13 and 15-17.

One possible explanation for the relation between the 

magnitudes of seasonal fluctuations in head and specific 

compaction is that hysteresis may be important in areas 

of large seasonal fluctuations in head. On the basis of 

laboratory tests, Terzaghi and Peck (1948, p. 107) 

stated, "If the load is removed at the same rate at which 

it was previously applied, the elastic recovery is smaller 

than the preceding compression. If the load is again 

applied, the recompression curve joins the main branch 

without any break, and the decompression and recompression curves enclose a hysteresis loop." The rejoining 

of the recompression curve with the main branch of the 

curve of a stress-strain plot indicates that in situations 

of recurrent application of stress on either sands or clays 

in laboratory consolidation tests (1) short-term decreases in applied stress do not appreciably change the 

amount of ultimate consolidation from what it would 

have been if periodic decreases in stress had not occurred and (2) the maximum applied stress is the dominant control in consolidation tests where stress is 

periodically decreased and reapplied gradually.

The results of laboratory testing as just described 

suggest that the dominant controlling stress in areas of 

recurrent application of stress to unconsolidated deposits as a result of artesian-head decline may be the 

summer pumping lows. Little is known about the effect
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G35

of periodic loading on the compaction characteristics of 

different types of naturally occurring materials, but the 

preceding discussion suggests that detailed studies of 

the relation between seasonal fluctuation in artesian 

head and specific compaction might be productive.

CRITERIA FOR THE PREDICTION OF 

FUTURE SUBSIDENCE

Estimates of the amounts, rates, and distribution of 

future subsidence are important in the planning, construction, and maintenance of large engineering structures. The economic aspects of subsidence are particularly important for large water-distribution systems. 

The cost of the San Luis Canal section of the California 

Aqueduct was increased substantially because of the 

additional freeboard that had to be included for the 

estimated subsidence that would occur between the 

time the canal was constructed and the time when delivery of imported water would raise ground-water 

levels sufficiently so that subsidence would cease. The 

canal passes through the areas of most intense subsidence caused by change in water levels. A master drain 

will be built low on the west slope near the valley trough 

to alleviate the problems associated with locally high 

water tables and to remove waste irrigation waters. 

This drain will be within the subsidence area.

Another major expense caused by land subsidence is 

damage to well casings. Damage to the casings of wells 

pumped to supplement the surface-water imports will 

continue as long as compaction of the deposits adjacent 

to the casings continues.

The prediction of subsidence is largely empirical. Although data about many of the factors affecting compaction have been obtained, the interrelations of these factors are so complex that it is difficult to predict future 

amounts of subsidence with confidence. Prior attempts 

to predict subsidence by the use of laboratory data will 

be discussed, but the main purpose of this section will be 

to describe empirical techniques and criteria for estimating future subsidence criteria that are based on 

the past history of relations between change in applied 

stress and compaction within the study area.

Compaction of the deposits in the Los Banos 

-Kettleman City area has occurred because large increases in effective stress have occurred, highly compressible deposits are present, and the compressible 

deposits are thick. These are the fundamental factors 

that determine the magnitude of ultimate compaction 

and subsidence. In those parts of the area where the 

deposits are generally of low compressibility or highly 

compressible deposits are thin, the magnitude of future 

subsidence would be small, even if future increases in 

effective stress were large. For example, 600 feet of 

applied-stress increase has resulted in only 1 foot of 

subsidence in the area adjacent to the Big Blue Hills

where wells tap the thick Etchegoin Formation. Conversely, in those parts of the area where thick compressible deposits occur (southwest of Mendota and near 

Huron), large amounts of ultimate compaction and subsidence would occur even if future increases in effective 

stress should be moderate. However, the rate of future 

subsidence in some areas of thick compressible deposits 

may not be large because of the time required for the 

applied stresses to become effective in thick beds of low 

permeability.

The factor subject to future variation is the change in 

applied stresses resulting from water-level changes. 

Because future rates of water-level change cannot be 

predicted with precision, the following discussion will 

be limited mainly to criteria for prediction, rather than 

the actual prediction of land-surface altitudes at specific 

future times. Sufficient information is available to estimate the subsidence rates that will prevail after 60 

feet of water-level recovery in the study area.

TIMELAG OF COMPACTION

Compaction of fine-grained beds (aquitards) and resulting land subsidence are time-dependent processes 

because water cannot be expelled rapidly from beds of 

low permeability when applied stress is increased. For 

this reason and because the compressibility of water is 

much less than the structural compressibility of 

fine-grained beds, the additional load applied to 

aquitards and aquicludes is initially borne almost entirely by the pore water. If stress is applied to the 

aquifer system by loading at the land surface, the immediate result is an absolute increase in pore pressure 

within the fine-grained beds. If the stress is applied by 

lowering head in confined aquifers, the immediate result in the adjacent aquitards is an unchanged absolute 

pore pressure, which represents an increased pore pressure relative to the newly reduced head in adjacent 

aquifers.

The increased pore pressures in the aquitards, 

whether absolute or relative, induce flow of water from 

these aquitards to adjacent aquifers and concurrent reduction in pore volume of the aquitards. The rate of flow, 

and hence the rate of compaction, is, at any time, a 

function of the magnitude of the pore-pressure differences between the aquitards and the aquifers. During a 

specified interval, the volume of water expelled, decrease in pore volume, and volume of compaction are 

equivalent.

Flow from aquitards to aquifers continues until the 

compaction of the aquitards produces a structure strong 

enough to withstand the increased applied stress. When 

the required compressive strength is attained, the pore 

water in the aquitards no longer bears a portion of the 

applied stress, and pore pressures thereafter are con-
G36 STUDIES OF LAND SUBSIDENCE

trolled by the heads in the adjacent aquifers. Within the 

aquitards, as long as effective stresses do not exceed 

preconsolidation stresses, changes in pore pressures are 

characterized by steady-state vertical flow and negligible changes in storage.

During the period of nonsteady-state outward flow 

from the aquitards and gradual progression toward 

steady-state flow conditions, the difference between the 

pore pressure at a point in a fine-grained bed and the 

pore pressure that would exist at that point if steadystate flow conditions prevailed is termed "excess pore 

pressure." At any time during the compaction of a clay 

bed, the average excess pore pressure within the bed is a 

measure of additional compaction that will occur ultimately if the increase in applied stress is maintained 

until all excess pore pressures have decayed.

The time required to dissipate excess pore pressures 

in a clay stratum is determined by the volume of water 

(per unit area) that must be expelled to attain the required reduction in pore volume and by the average rate 

(per unit area) of outward flow. The volume of water to 

be expelled varies directly with the magnitude of the 

increase in applied stress, Apa, the compressibility of 

clay, mv , and the thickness, b', of the bed. The average 

flow rate varies directly with the increased stress and 

the vertical permeability of the clay, K', and inversely 

with the bed thickness. Thus, the time required for the 

decay of excess pore pressures in a clay bed is a nonlinear function of a time constant for the bed defined by 

(mvywb'kpa)l(kpaK'lb''), in which 7W is the unit weight 

of water. Multiplying mv byjw converts the stress term 

in compressibility from units of force per unit area to 

units of equivalent head. In the latter form, it is dimensional ly compatible with the conventional units for 

permeability (vertical hydraulic conductivity, K') in 

which the hydraulic gradient is defined in units of head. 

Thus, the time constant, mvywb' 2/K', is seen to be the 

ratio of the square of the bed thickness to the hydraulic 

diffusivity,l^'/Ss', and to have the dimension of time. In 

the case of a clay losing water to both upper and lower 

sands, the half thickness, 672, rather than b' determines the time constant. For a given sustained increase 

in applied stress on an individual clay bed, an interval 

of one time constant is required to permit dissipation of 

93 percent of the resulting excess pore pressures in that 

bed. An interval corresponding to half the value of the 

time constant will permit 76 percent of the ultimate 

compaction to occur, but twice the time constant is required to achieve 99 percent of ultimate compaction.

In the study area, the diffusivities (equivalent to cv , 

the coefficient of consolidation) of the aquitards in the 

lower zone are low, typically 1-100 square feet per year 

(Johnson and others, 1968, table 9), and the aquitard 

thicknesses, though widely variable, may be substantial. At the Cantua site, for example, 22 of the 138 

aquitards in the lower zone range in thickness from 15 

to 50 feet (Pt. 2, Bull, 1974, table 8). Thus, even if heads 

in the aquifer system are stabilized, many years may be 

required to approach steady-state pore pressures in adjacent aquifers and aquitards.

The time-dependent nature of the pore-pressure 

decay in the aquitards and aquicludes is an important 

factor that complicates the problem of developing 

criteria for estimating or predicting compaction of 

heterogeneous aquifer systems, even when a substantial history of change in applied stress and correlative 

land subsidence is known, as in the Los Banos 

-Kettleman City area.

If applied stress has increased during some time 

period and then has stabilized and the subsidence rate is 

observed for a number of years thereafter, methods are 

available for estimating the future subsidence by use of 

exponential decay curves (Prokopovich and Hebert, 

1968).

If, following a period of known applied-stress increase 

and observed subsidence, applied stress decreases 

sufficiently to stop subsidence, approximate values for 

the average compressibility of the compacting deposits 

can be computed. These computed compressibilities can 

be utilized to estimate the magnitude of ultimate compaction (or subsidence) that would occur as a result of 

any future increase in applied stress beyond the preconsolidation stress (Poland, 1969b).

The applied stress has continued to increase with 

time and in an irregular pattern in much of the study 

area, making it difficult to establish criteria for estimating future subsidence under an assumed future change 

in applied stress. One of the principal reasons for this 

difficulty is that there is no economically practical way 

to measure vertical distribution of excess pore pressures 

in numerous aquitards at several sites.

Some appreciation of the difficulty of developing 

criteria for estimating future subsidence under an assumed hydrologic change in the study area can be obtained at sites where long-term information about subsidence and applied-stress increase is available. The 

variation in the ratios of subsidence to increase in 

lower-zone applied stress and head decline to subsidence is instructive in illustrating the problem. If it 

were not for the time lag inherent in the compaction of 

the fine-grained sediments, the ratio of subsidence to 

increase in applied stress would represent the product of 

the compressibility and thickness of the aquifer system. 

At a given site, this product would be a constant that 

could be used to calculate the subsidence that would 

result from any specified future stress increase. It will 

be seen, however, that this ratio is far from constant and 

is, in fact, a complex function of stress history.
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G37

CONDITIONS BEFORE DELIVERY 

OF CANAL WATER

Maximum canal deliveries are not scheduled until 

the mid-1970's, and widespread compaction and subsidence will continue until the distribution systems to deliver the canal water are completed. Additional compaction is anticipated in some of the thicker clays after 

maximum deliveries of imported water are attained 

because the rise in potentiometric levels in the aquifers 

probably will not be sufficient to eliminate all excess 

pore pressures in these clays. Wells will still supply 

nearly one-third of the irrigation water used in the Los 

Banos-Kettleman City area.

The economics of pumping ground water will determine, in part, the rates and amounts of subsidence before canal water is available. Because the amounts of 

water pumped exceed recharge in the area, water levels 

have declined as much as 500 feet in the last 20 years. 

By 1966, the cost of pumping ground water had increased to more than $15 per acre-foot in large parts of 

the area. Equipment needed to pump the water has 

become progressively more expensive as pump bowls 

have been lowered to maintain submergence. Larger 

pump motors and additional electricity have been 

needed to raise the water to the land surface. The result 

has been one of the greatest concentrations of electric 

power use for agriculture in the world.

The depths from which lower-zone water had to be 

pumped in the summer of 1965 are shown in figure 29. 

The depth to pumping level ranged from less than 200 

feet to more than 1,000 feet, and in most of the area, 

water had to be pumped from depths of more than 400 

feet. The increased costs of pumping water have reduced 

profit margins. In those areas where the depth to pumping level was 700-1,000 feet in 1965, the land is not 

farmed as intensively as it was when water levels were 

as much as 300 feet higher.

The past rate of subsidence can be used to predict 

future subsidence if it is appropriate to assume that the 

past trend in subsidence rate will be maintained into 

the future. Two types of subsidence plots at a given 

bench mark are shown in figure 30. The plot of cumulative subsidence provides information about the total 

amount of subsidence that has occurred at any particular time, and changes in the slope of the cumulative 

subsidence plot are indicative of the general changes in 

rate of subsidence that have occurred.

A plot of subsidence rate is much more instructive 

than a cumulative plot for predicting future amounts of 

settlement. The plot of subsidence rate in figure 30 is a 

generalized curve derived from a graphical integration 

of a rate bar graph. For examples of rate bar graphs and 

curves, see Part 2 (Bull, 1974, fig. 22).

Unforeseeable changes in rate make extrapolations 

of either cumulative subsidence or subsidence rate 

curves of limited value. For example, the changes in 

subsidence rate at bench mark S661 in 1954,1957, and 

1962 shown in figure 30 would have been most difficult 

to predict in advance and actually were not noticed until 

several years after they occurred. In those parts of the 

study area where surface water has been available in 

some years but not in others, the trend in subsidence 

rates has changed more frequently and abruptly than in 

the example shown in figure 30. (See fig. 42.)

Another approach is to estimate the amount of 

applied-stress increase per foot of subsidence. The 

amount of potentiometric level decline per foot of 

subsidence during a 10-20-year period can form the 

basis for predicting minimum amounts of future 

subsidence, should the rate of increase in applied stress, 

as indicated by water levels, continue to be the same.

The number of feet of lower-zone head decline associated with each foot of subsidence during the 

1943-60 period is shown in figure 31. The change in the 

lower-zone potentiometric surface was chosen because 

three-fourths of the water pumped to cause the increase 

in applied stress and subsidence has been withdrawn 

from the lower zone, and at least three-quarters of the 

compaction has occurred there (Pt. 2, Bull, 1974, fig. 45)- 

The near-surface subsidence component has been removed from the total subsidence measured by benchmark surveys for this period. The change in head is 

based on the maximum head decline during the period; 

therefore, in the northern part of the area where water 

levels were recovering in 1960, water levels of the 

mid-1950's were used.

The number of feet of lower-zone head decline associated with each foot of subsidence during the 

1943-60 period generally ranged from 15 feet to 400 

feet. For large parts of the area, less than 25 feet of head 

decline were associated with each foot of subsidence for 

the 1943-60 period.

The use of this map to make empirical predictions of 

the minimum amounts of subsidence that would occur 

in the future as a result of an assumed head decline 

would be dependent on the following assumptions.

1. It is recognized that substantial draft is from the 

upper zone in parts of the area where wells are 

perforated in both the upper and lower zones. It is 

assumed that the proportion of perforated interval 

in the upper and lower zones and the lateral recharge characteristics of the two zones will not 

change. If this assumption is true, then a given 

amount of head decline in the lower zone will be 

associated with a proportionately similar head decline in confined aquifers in the upper zone. In 

effect, the technique described here would utilize
G38 STUDIES OF LAND SUBSIDENCE

120°30' 120°00'

37°00

EXPLANATION

Boundary of deformed 

rocks

Generalized line of equal depth to pumping 

level, in feet

Interval 100 feet. Compiled from 1965 

pump-test records and from U.S. Geological Survey summer well rounds in 

1965 and 1966

15 KILOMETRES

36°30

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 29. Depth to lower-zone pumping level, summer 1965.

estimated future head declines in the lower zone as 

indicators of the change in applied stress in all the 

confined and semiconfined zones, using the assumption that future patterns of water-level 

change will be proportionately the same as the past 

history of water-level change in the different parts
LOS BANOS--KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G39

2.0

1950 1960 1970

FIGURE 30. Cumulative subsidence and subsidence rate for bench mark S661.

of the aquifer systems.

2. The water table has risen in some parts and has 

declined in other parts of the area. If the head 

decline/subsidence technique were to be used, it 

would be assumed that the trend of water-table 

change in the future would be the same as in the 

past.

The values shown in figure 31 are maximum values of 

the ratio because the head decline/subsidence ratio so 

derived does not take into account the time lag of compaction.

Although figure 31 may be of use to administrators 

and planners, the reciprocal of the head 

decline/subsidence ratio may be of more interest to hydrologists. The specific subsidence the ratio of subsidence to head decline is shown in figure 32 and approximates a minimum value of the storage coefficient 

component for virgin compaction of the aquifer-system 

skeleton. If the 1943-59 subsidence values were the 

ultimate compaction amounts that would result from 

the applied-stress increase for the same period, then 

figure 32 would represent the sum of two components of 

storage per unit head decline the inelastic compaction 

and the elastic compaction. The component of storage 

due to elastic compression of the aquifer system probably accounts for less than 5 percent of the storage values 

approximated in figure 32. The biggest unknowns in the 

use of specific subsidence as an approximation of the 

storage coefficient of the aquifer-system skeleton are 

the magnitudes and areal variations of excess pore pressures in 1943 and 1960. If the mean aquifer-aquitard 

pore-pressure differentials were roughly the same at 

the two times, then the values of figure 32 would be a 

fair approximation of the sum of the two storage components for virgin compaction. They would also be a reliable tool for predicting ultimate subsidence from a 

postulated additional head decline.

Long-term changes in the importance of delayed 

compaction as related to the rate of applied-stress increase are shown in figures 33 through 35 for points in 

the northern, central, and southern parts of the study 

area.

Applied-stress increase and subsidence relations for a 

site in the northern part of the study area are shown in 

figure 33. Bench mark GWM59 is about 8 miles south of 

the Oro Loma compaction-recorder site. About 90 percent of the subsidence of this bench mark can be attributed to lower-zone compaction. Cumulative plots of subsidence and head decline for the site are shown in figure 

5.

The history of increase in applied stress in the vicinity of bench mark GWM59 is shown in figure 33A. The 

amount of water-table rise is estimated to be 31 feet 

since 1940, as compared with 200 feet of head decline 

during the same period. The overall rise in the water 

table accounts for only about 3 percent of the stress 

increase on the lower zone. However, the proportion of 

applied-stress increase resulting from water-table rise 

is important for some periods. For example, during the 

1963-66 period, water-table rise accounted for onefourth of the increase in stress applied to the lower zone.

The history of applied-stress increase in the vicinity 

of bench mark GWM59 reveals an increasing rate of 

applied-stress increase until 1956 and a decreasing rate 

since then. A maximum rate of increase in applied 

stress of 17.8 ft yr ~ l occurred during the 1953-55 

period, but the rate of increase in applied stress had 

decreased to only 1.7 ft yr" 1 during the 1963-66 period.

In figure 336, each bar in the graph portrays the 

relation between the lower-zone applied-stress increase 

and the concurrent subsidence for the time period between two bench-mark surveys. The subsidence/ 

increase-in-lower-zone-applied-stress ratio is shown on 

the right side of the graph and the equivalent head 

decline/subsidence ratio is shown on the left 

side. If water-table rise had not affected the increase in 

lower-zone applied stress, the numbers along the left 

side of the graph would represent the number of feet of 

head decline associated with each foot of subsidence. 

Because water-table rise has increased the stresses applied to the lower zone, the left sides of the graphs in 

figures 33-35 treat the stress increases as equivalent 

lower-zone head declines.

The subsidence/increase-in-lower-zone-appliedstress ratio at bench mark GWM59 has increased exponentially during the period of record, and the head 

decline/subsidence ratio has decreased from 50 to 6.

The changes in the ratios shown in figure 33B are 

interpreted as the result of a progressive increase in
G40 STUDIES OF LAND SUBSIDENCE

120° 30' 120° 00'

37°00' 

EXPLANATION

Boundary of deformed 

rocks

Line of equal lower-zone head decline 

associated with 1 foot of subsidence, 

1943-60, in feet; interval variable. Dashed 

where approximate

Based on:

1. Subsidence due to artesian-head decline, 1943-59; estimated near-surface subsidence component subtracted from total subsidence in 

near-surface subsidence areas

2. Maximum artesian-head decline for 

the lower water-bearing zone, 

1943-60 PLEIASANT

Coalinga

VALLEY

15 KILOMETRES

36°30' 

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 31. Number of feet of lower-zone head decline associated with each foot of subsidence, 1943-60.

excess pore pressure in the aquitards during the con- graph of figure 33B would have a uniform height that

secutive time periods. If the time delay associated with would be a function of the compressibility and thickness

much of the compaction were not present, the bars of the of the deposits at the site. The changes in the ratios
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3

120°30' 120°00'

G41

37°00'

36°30' -

36°00

EXPLANATION

Boundary of deformed 

rocks

San Luis Canal - California Aqueduct

Generalized line of equal ratio; interval 0.01 

and 0.02

Subsidence due to artesian-head decline, 1943-59

Lower-zone artesian-head decline 

1943-60

1. Subsidence due to artesian-head decline, 1943-59; estimated near-surface subsidence component subtracted from total subsidence in 

near-surface subsidence areas

2. Maximum artesian-head decline for 

the lower water-bearing zone, 

1943-60

Coalinga

VALLEY

15 KILOMETRES

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 32. Specific subsidence, 1943-59.

between 1940 and 1956 indicate that average excess become even more important since 1956 because the

pore pressures doubled during this period of accelerat- rate of applied-stress increase has declined progresing increase of applied stress. Delayed compaction has sively. Nearly all the 2 feet of subsidence that occurred
G42 STUDIES OF LAND SUBSIDENCE

a z

1960 1970 1940 1950 1960 1970

0.20 0.16

-0.16

LU

Z

o

N 

CC

1°

-0.12

- co

LU CO

tfl LU 

<C

LU H- ir w

O Q

Z LU

- 0.08 r- -

-0.04

Z <

LU 

O 

COm 

D 

CO

1940 1950 1960 1970

FIGURE 33. Applied-stress increase and subsidence relations at bench mark GWM59. A, 

Change in rate of increase of applied stress on the lower zone. B, Change in the ratio of 

subsidence to increase in lower-zone applied stress.

from 1959 to 1966 is interpreted as being the result of 

stresses initially applied before 1959.

The history of increase in applied stress in the vicinity of bench mark H237 (reset) is shown in figure 34. The 

bench mark is in the central part of the study area about 

6 miles northwest of the town of Cantua Creek. About 

85-90 percent of the subsidence of this bench mark is 

the result of lower-zone compaction. The estimated 

amount of water-table rise during the period of record is 

about 56 feet as compared to 270 feet of head decline. 

Thus, the change in the position of the water table

1940 1950 1960 1970

FIGURE 34. Applied-stress increase and subsidence relations at bench mark H237 (reset). A, 

Change in rate of increase of applied stress on the lower zone. B, Change in the ratio of 

subsidence to increase in lower-zone applied stress.

accounts for about 4 percent of the change in stress 

applied to the lower zone.

The rate of increase in applied stress on the lower 

zone has been moderately high for most of the period of 

record. Between 1943 and 1959 little change in rate 

occurred, the rate fluctuating about a mean increase of 

about 14 ft yr" 1 for the three periods shown. Since 1959 

the rate of applied-stress increase has decreased steadily. During the 1957-59 period, the applied stress was 

increasing at a rate of 16 ft yr" 1 , but during the 1963-66 

period, the rate of increase had declined to only 5 ft yr" 1 .

Figure 34B shows that the subsidence/increase-inlower-zone-applied-stress ratio for bench mark H237 

(reset) did not increase greatly until after 1959. Between 1943 and 1959, the ratio ranged from 0.020 to 

0.033. After 1959, the ratio increased greatly. Between
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G43

1959 and 1963 the ratio was 0.048, and between 1963 

and 1966 the ratio increased to 0.114. The equivalent 

head decline/subsidence ratio decreased from 50 during 

the 1943-53 period to about 9 during the 1963-66 

period.

Comparison of figures 34A andfi shows that between 

1943 and 1963, when the rate of applied-stress increase 

ranged from 11.4 to 16.0 ft yr" 1 , the ratio of subsidence 

to stress increase more than doubled from 0.020 to 

0.048. This change in the ratio is interpreted as representing a substantial increase in the magnitude of excess pore pressures during a 20-year period of steady 

head decline with no intervening periods of stable head 

to provide sufficient time for the aquifer system to approach a steady-state pore-pressure distribution. The 

1963-66 period was characterized by slightly lower 

compaction rates and a decrease in the rate of appliedstress increase to only 5 ft yr" 1 . Most of the compaction 

that occurred during the 1963-66 period is interpreted 

as being delayed virgin compaction resulting from prior 

periods of head decline.

The variations of increase in applied stress in the 

vicinity of bench mark PTS21S are shown in figure 35. 

The bench mark is in the southern part of the study area 

about 2 miles north of Westhaven. About 60 percent of 

the subsidence of this bench mark has been the result of 

lower-zone compaction. Change in applied stress that 

can be attributed to change in the position of the water 

table is minor in the vicinity of the bench mark. The

FIGURE 35. Applied-stress increase and subsidence relations at bench mark PTS21S. A, 

Change in rate of increase of applied stress on the lower zone. B, Change in the ratio of 

subsidence to increase in lower-zone applied stress.

estimated water-table rise has been only 15 feet as 

compared with 422 feet of lower-zone head decline (fig. 

10). Water-table rise accounts for less than 1 percent of 

the applied-stress increase at the site.

Because about 40 percent of the compaction at bench 

mark PTS21S has occurred in the upper zone, the ratios 

of subsidence to increase in lower-zone applied stress 

are apt to be misleading, unless head changes have been 

similar in the upper and lower zones. Similar head 

changes have occurred in the two zones at the Westhaven compaction-recorder site 5 miles to the south of 

bench mark PTS21S (Pt. 1, Bull and Miller, 1974, fig. 

14). It is tentatively assumed that the heads above and 

below the Corcoran also are similar in the area near 

bench mark PTS21S, but such an assumption is tenuous 

in an area of highly lensing alluvial-fan deposits.

The history of applied-stress increase in the vicinity 

of bench mark PTS21S does not have a consistent trend 

and is dominated by a period of 35 ft yr" 1 applied-stress 

increase between 1947 and 1954.

The ratio of subsidence to increase in lower-zone applied stress at bench mark PTS21S decreased between 

1923 and 1954, the ratio being only 0.007 during the 

1937-47 period as compared with 0.019 during the 

1923-33 period. The overall trend since the mid-1940's 

appears to have been one of overall increase of the ratio, 

which may be the result of the increasing importance of 

delayed compaction. The head decline/subsidence ratio 

ranges from about 140 feet during the 1933-47 period to 

14 feet during the 1954-57 period. The apparent lesser 

proportion of delayed compaction occurring at PTS21S 

as compared with that at bench marks GWM59 and 

H237 (reset) may be because the post-1960 head declines have been roughly twice as large at PTS21S or 

perhaps because relatively thick-bedded alluvial-fan 

deposits of low permeability at bench mark PTS21S do 

not permit delayed compaction to occur as rapidly as at 

the other two bench-mark sites.

Figures 33 and 34 demonstrate the importance of 

time-delayed virgin compaction for those attempting to 

predict future subsidence, and figure 35 shows the extreme variations that can occur in cause-effect type 

ratios. The lack of consistent ratios at all three sites 

demonstrates the hazard of attempting to predict future 

subsidence by an extrapolation of such ratios when 

based on short time intervals.

However, cumulative ratios derived for periods ranging from 2 to more than 4 decades can be used to furnish 

minimum estimates of the subsidence that would occur 

ultimately from a given additional increase in applied 

stress that is, subsidence in response to a given increase in effective stress. The cumulative ratios are 

computed from the total subsidence and applied-stress 

increase for the period of record before a given date.
G44 STUDIES OF LAND SUBSIDENCE

Such minimal values would serve as a floor for estimates of subsidence obtained by other methods. The 

cumulative values of the ratios for figures 33-35 are 

shown by the x's. As with other cumulative graphical 

techniques, the effect is to smooth out the short-term 

variations. The cumulative values of these ratios as 

plotted for 1966 agree with the ratios in figure 32.

Another factor that should be considered in areas of 

intense land subsidence is the permeability decrease 

caused by compaction. Compaction of the aquitards has 

reduced their vertical permeability, thereby tending to 

increase the time required for excess pore pressures in 

the aquitards to reach equilibrium with those in adjacent aquifers. Locally, the overall water-bearing section 

has been decreased in thickness by 2 percent or more. 

The actual decrease in thickness of some of the compressible and rapidly compacting beds may be more than 4 

percent. Under conditions of uniform increase in applied stress, decreasing permeability of the compressible beds that occurs as a consequence of compaction 

results in a decrease in the rate of pore-pressure decay 

and compaction of the aquitards.

COMPUTATION OF AQUIFER-SYSTEM PORE-PRESSURE

DECAY

The compaction during a time period is a function of 

the rate of flow of water from the aquitards and aquicludes, which in turn is a function of aquitard-aquifer 

pore-pressure differentials. Thus, prediction of the rate 

of pore-pressure decay and delayed compaction at a site 

provides estimates of future subsidence, assuming that 

the applied stress will remain relatively constant.

Two methods of predicting aquifer-system porepressure decay can be illustrated by field data from the 

Los Banos-Kettleman City area. In much of the northern part of the study area, an equilibrium has been 

approached between ground-water inflow and outflow. 

Although the applied stress has been increased greatly 

from the preagricultural development conditions, little 

seasonal or long-term change in applied stress has occurred during the 1960-67 period. Thus, bench-mark 

surveys in these areas provide information about decrease in the rate of aquifer-system compaction under a 

constant stress. Future compaction can then be estimated by graphical projection or through the use of 

power-function equations of the type described by Prokopovich and Hebert (1968, p. 920).

The preceding technique cannot be used in most of the 

study area because the artesian head has not been 

stabilized and hence applied stress has not been constant during 2-3 bench-mark surveys, as in the northern area. However, at some sites the rate of appliedstress increase has decreased greatly since 1960, and 

the total post-1960 applied-stress increase is only 2-6

percent of the pre-1960 stress increase. Thus, when 

compared with the prior periods of stress increase, the 

load on the aquifer system may be considered roughly 

constant since about 1960. The lack of sufficient 

bench-mark surveys can be circumvented at some sites 

by using compaction-recorder data. The problem of 

large seasonal variations in applied stress can be 

largely eliminated by using recorded compaction 

amounts for selected ranges of applied stress. This technique works best at those sites where large amounts of 

compaction are being measured and where seasonal and 

longer term applied-stress changes are minimal.

The minimum rate of decrease of delayed compaction 

after a given date at the four multiple compactionrecorder sites can be determined by computing the 

changes in the mean daily compaction rates of lowerzone deposits for selected applied stresses. The selected 

applied stresses for the four sets of graphs in figure 36 

are ranges of applied stress. The minimum applied 

stress was placed at a lower-zone potentiometric level 

below which compaction was generally recorded each 

month. The maximum applied stress was the maximum 

depth to water for a given year. At all four sites, the 

maximum summer depths to water (minimum lowerzone potentiometric levels) during the last half of the 

period of record shown in figure 36 were deeper than the 

maximum summer depths to water during the first half 

of the period of record; however, the change was not 

large, and at three of the sites the summer low-water 

level increased 4-20 feet. The maximum depth to water 

had the following ranges: the Oro Loma site, 202-206 

feet; the Mendota site, 496-516 feet; the Cantua site, 

600-618 feet; and the Westhaven site, 419-458 feet. The 

component of change in applied stress that can be 

attributed to water-table change at the four sites is 

negligible; hence, it is not portrayed in figure 36.

Decrease in the mean compaction rate at the Oro 

Loma site for those days when the depth to water in well 

16H6 exceeded 190 feet is shown in figure 36A. The 

compaction was measured in the depth interval extending from 35 to 535 feet below the Corcoran. During the 

1963-66 period, 55 percent of the subsidence was the 

result of compaction in the upper 1,000 feet of deposits, 

and 45 percent of the subsidence was the result of compaction occurring below 1,000 feet. For most of the 

period of record, the depth to water exceeded 190 feet for 

365 days a year. The curve showing the trend of the 

mean daily compaction rate shows a progressive decrease in slope with time. In 1961 the mean daily compaction rate was 0.0009 foot per day, but by 1967 the 

rate had decreased to 0.0003 foot per day.

Decrease in the mean compaction rate at the Mendota 

site for those days when the depth to water exceeded 470 

feet is shown in figure 36B. The compaction was meas-
CO

< 200

Q

 

- ^

^ 

LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3

0

G45

Number of days that depth to water exceeded 190 feet

200

220

>. 0.001

Mean compaction- rata for those days when the depth to 

water excaeded 190 feet

200

365

480

500

Number of days that depth to water exceeded 470 feet

520

0.002

Maximum depth to weter

0.001

1961 1963 1965 1967

Mean compaction rate for thosa days when the depth to 

water exceeded 470 feet

B

200

365 

Number of days that depth to water exceeded 560 feet

H 600

LU

LU

LL

con

~ - *~--^

^-~^\

^.

Maximum depth to water

0.003

0-002

0.001 1961 1963 1965 1967

Mean compaction rate for those days when the depth to 

water exceeded 560 feet

CO

< 200

Q

365 -

^+^"* ^

^ ^^ ^

^. _

Number of days that depth to water exceeded 410 feet

420

ILU 

LU

LL 440 

AKCI

\

X

X

X_-~*^^

Maximum depth to water

Q 0.0010

r- 0.0005

Mean compaction rate for those days when the depth to 

water exceeded 410 feet

D

FIGURE 36. Changes in the mean daily compaction rate of deposits for selected applied stresses. A, Oro Loma site; depth interval 500-1,000 feet. B, Mendota site; depth 

interval 780-1,358 feet. C, Cantua site; depth interval 703-2,000 feet.D, Westhaven site; depth interval 830-1,930 feet.

ured in the depth interval extending from 80 feet to 658 ence occurred below the 1,358-foot depth. During the

feet below the Corcoran. During the 1963-66 period, 31 period of record, the number of days that the depth to

percent of the compaction that was causing the subsid- water exceeded 470 feet increased from 91 to 365 days.
G46 STUDIES OF LAND SUBSIDENCE

The curve shows an overall decrease in the mean daily 

compaction rate with time. In 1962 the mean daily 

compaction rate was 0.002 foot per day, but by 1967 the 

rate had decreased to 0.0007 foot per day.

Decrease in the mean daily compaction rate at the 

Cantua site for those days when the depth to water 

exceeded 560 feet is shown in figure 36C. The compaction was measured in the depth interval extending from 

128 feet to 1,425 feet below the Corcoran. During the 

1963-66 period, 12 percent of the compaction causing 

subsidence at the site was the result of compaction 

below 2,000 feet. The number of days that the depth to 

water exceeded 560 feet increased from 98 to 359 days 

during the period of record. The curve showing the trend 

of decrease in daily compaction rate is close to all the 

points. Data are not available for 1963 and 1964 because of a casing failure in the well used to observe 

changes in water level. In 1961 the mean daily compaction rate was 0.0028 foot per day, but by 1967 the rate 

had decreased to 0.0016 foot per day.

Decrease in the mean daily compaction rate at the 

Westhaven site for those days when the depth to water 

exceeded 410 feet is shown in figure 3QD. The compaction was measured in the depth interval extending from 

100 feet to 1,185 feet below the Corcoran. About 95 

percent of the compaction is estimated to occur above 

the 1,930-foot depth. During the period of record, the 

number of days that the depth to water exceeded 410 

feet increased from 161 to 335 days. The curve at this 

site also is suggestive of a decrease in the rate of daily 

compaction. In 1963 the mean daily compaction rate 

was 0.0010 foot per day, but by 1967 the rate had decreased to 0.0007 foot per day.

The rate at which applied stress becomes effective in 

the fine-grained, poorly permeable parts of the aquifer 

system decreases progressively with time in an exponential manner. All four mean-daily-compaction-rate 

plots in figure 36 are best fitted with exponential curves.

The mean daily compaction rates in 1967 are only onethird to two-thirds the rates at the beginning of the 

5-7-year periods.

The mean-daily-compaction-rate plots may be represented by a general exponential equation of the type

y=cemx,

in which c and m are determined by the data for each 

site. A semilogarithmic plot of the decrease in the mean 

daily compaction rate of the Cantua site data (fig. 37) 

shows that the points have virtually no scatter about 

the regression line. The daily compaction rate is decreasing exponentially in the 703-2,000-foot-depth 

zone for those days in which the depth to water exceeds 

560 feet. The equation for the linear plot of mean daily 

compaction rate (y) and the time since mid-1961 in 

years (x) is

y =0.0028

The intercept that controls the coefficient was selected 

arbitrarily as mid-1961, but the exponent includes 

m the rate of change ofy with respect tojc ( 0.096) of 

the plot in figure 37. Comparison of values of m for 

similar plots in other depth zones, or areas, should provide some general useful information regarding the 

rate of completion of pore-pressure decay in the aquifer 

systems.

The curve in figure 37 may be extrapolated as an 

example of predictive technique if it is assumed that the 

maximum depth to water will continue to fluctuate between 610 and 620 feet and that the water level will be 

deeper than 560 feet for 365 days each year. Despite the 

continued decrease in compaction rate, 0.4 foot of compaction would still be occurring in the 

703-2,000-foot-depth interval during the year 1971. 

During the period between the 1963-66 bench-mark

fl.

On

0.003

I- IQ. W

O UJ O >

F I & g 0.002

O § UJ IO W O UJ

. X UJ

- 0 CC

UJ I0.001

y=0.0028e"°- 096;)c

1962 1964 1966

FIGURE 37. Decrease in the mean daily compaction rate in the 703-2,000-foot-depth interval at the Cantua site.
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G47

surveys, 18 percent of the compaction measured in the 

upper 2,000 feet of deposits occurred above 703 feet, and 

12 percent of the subsidence was the result of compaction below 2,000 feet. If these proportions were the same 

in 1971, the amount of subsidence during the year 

would be about 0.56 foot (0.09 ft would be occurring in 

the 0-703-ft-depth interval, 0.40 ft would be occurring 

in the 703-2,000-ft-depth interval, and 0.07 ft would be 

occurring below a depth of 2,000 ft). Thus, the minimum 

amounts of future compaction and subsidence at the 

Cantua site would be large even if the water levels 

never exceed historic low levels.

Importation of surface water in the next decade probably will invalidate the assumption made for the purposes of the preceding discussion that the water level 

would be deeper than 560 feet at all times of the year. 

An estimate of the rate of subsidence after an assumed 

water-level rise will be presented in the next section.

The time needed to approach steady-state pore pressures in the 703-2,000-foot-depth interval at the Cantua site can be estimated on the basis of figure 37. The 

total head decline at the site of roughly 400 feet is large 

compared with the 18-foot head decline of 1961-67. 

Therefore, for purposes of the projection shown in figure 

38, it is assumed that mid-1961 is the time of an unknown mean aquitard-aquifer pore-pressure differential and that the mean head in the aquifers remains 

constant thereafter. The rate at which the 1961 excess 

pore pressures would be dissipated can be expressed as a 

function of the change in mean daily compaction rate, 

using 1961 as the initial time. The curve in figure 38 

describes the same equation as shown in figure 37. The 

solid line represents the controlled time period shown in 

figure 37, and the dashed part of the curve, the 

post-1967 extrapolation of the curve, which after six 

decades, is essentially asymptotic to a zero-compaction 

rate line. Figure 38 shows a decreasing rate of completion of post-1961 residual compaction. By mid-1962, 10

percent of the residual compaction had occurred, and by 

1968, 45 percent had occurred. The estimate of the future percent completion of post-1967 compaction indicates that it would be 1975 and 1991 before 50 and 90 

percent, respectively, of the residual compaction had 

occurred. By the year 2033, the yearly compaction 

would have decreased to only 0.001 foot.

The decrease in the mean daily compaction rate of the 

lower zone at all four multiple compaction-recorder 

sites (derived from figure 36) is shown in figure 39. The 

plot for the Cantua site has little scatter, but the plots 

for the other sites have large amounts of scatter. The 

scatter is larger at those sites with low compaction 

rates, thus reflecting the problems in measuring small 

amounts of compaction with the equipment presently in 

use. The degree of scatter is so large for the Oro Loma 

site data that the points for 1962 and 1965 were rejected 

as being unreasonable. Computation of m values for the 

four lines shown in figure 39 gave the following results: 

Cantua site, -0.096; Mendota site, -0.21; Westhaven 

site, -0.091; and the Oro Loma site, -0.18 (a minimum 

value). The m values are indicative of only the general 

rates of decrease of compaction rates at the sites because 

the applied stresses were not constant during the 

periods of record.

The implication in figure 39 is that the rate of decrease in the mean daily compaction rate for the two 

southern sites is only about half that for the two northern sites. The mean daily compaction rate at the Westhaven site has been decreasing less than at the Cantua 

site, but would have decreased more rapidly if there had 

not been an overall head decline of 39 feet from 1963 to 

1966.

The overall lithology of the lower zone (Pt. 2, Bull, 

1974, fig. 61) is more clayey at the Oro Loma and 

Westhaven sites than at the Mendota and Cantua sites. 

Therefore, the overall amounts of clay in the lower zone 

at the sites does not appear to explain the more rapid

0.0000024

* I- I-

< 0. UJ

EC 111 m 

Q LL

O § UJ H

O V) O UJ

- Q EC

Z O <

< I §

UJ I0.001 -

0.002 -

-80 

/

j>=0.0028e-°- 096*

0.003' 

1960

-i5.65

UJ

r- O

2 uj

-60

-40

-20

O 

Z Z

o o

I- IUJ O 

0- 0-

o| 

o o

UJ

Q- 3 

W

1980 2000 2020 2033

FIGURE 38. Estimated time needed for residual compaction to occur after mid-1961, 703-2,000-foot-depth interval, Cantua site.
G48 STUDIES OF LAND SUBSIDENCE

0.003

0.002 -

0.001

0.0005

0.0003 -

1961 1965 1969

FIGURE 39. Decrease in the mean daily compaction rate of the lower-zone deposits at the 

multiple compaction-recorder sites. (Derived from fig. 36.)

compaction rates at the Oro Loma and Mendota sites. 

The bedding of the lower-zone deposits is different in the 

northern and southern parts of the area and is described 

in detail in Part 2 (Bull, 1974). Flood-plain deposits 

predominate in the northern part of the area, clayey 

alluvial-fan deposits predominate in the southern part, 

and a mixture of alluvial-fan, lacustrine, and 

flood-plain deposits occurs in the lower zone of the central part (Miller and others, 1971).

Because the time needed to dissipate excess pore 

pressures is a function of the square of aquitard thickness, a bed thickness factor can be substituted for the 

time needed to dissipate a given excess pore pressure 

from an aquitard of a given lithology. If aquitard thickness is expressed as (aquitard thickness/2)2 and weighted mean aquitard-thickness factors are derived from 

the micro logs of the core holes, comparisons of the relative ease of pore-pressure dissipation can be made. Micrologs are not available for the Westhaven site. The 

Oro Loma, Mendota, and Cantua sites have weighted 

mean aquitard-thickness factors of 16, 11, and 34, respectively (Pt. 2, Bull, 1974, table 7). Thus, the sites 

with the most rapid decrease of mean daily compaction 

rates (fig. 39) have thinner lower-zone aquitards than 

does the Cantua site. Therefore, the rates of decrease of

mean daily compaction indicated by the regression plots 

in figure 39 may be in large part a function of areal 

variations in aquitard thickness.

The difference in the rates of decrease of mean daily 

compaction rates in the northern and southern parts of 

the study area implies that for a given head decline, 

greater excess pore pressures exist, as of 1967, in the 

lower-zone deposits in the southern part of the area 

than in the northern part. The situation may simply be 

that response to a given increase in applied stress has 

caused more rapid compaction in the northern than in 

the southern part of the area.

The preceding discussion concerned prediction of 

compaction based on empirical compaction relations of 

large thicknesses of deposits at multiple compactionrecorder sites. The time delay involved in the compaction of saturated fine-grained deposits can also be computed from consolidation tests of core-hole samples from 

subsidence areas.

Direct computations of ultimate compaction for a 

given increase in applied stress, based on laboratory 

consolidation tests, have been made by Miller (1961). 

The method is a refinement of a technique outlined by 

Gibbs (1959, p. 4, 5) based on Terzaghi's consolidation 

theory (1948). The chief merit of the approach is that the 

time delay associated with virgin compaction is considered. A chief problem is that because of the high cost of 

consolidation tests, generally relatively few test results 

have been available from a given core hole. For the four 

Inter-Agency core holes in the Los Banos-Kettleman 

City area, consolidation tests were made on 60 cores, an 

average of 15 per hole. The average depth of the core 

holes was 1,700 feet, and so the mean spacing of 

consolidation-test cores was 110 feet. As a result of the 

paucity of tests, hundreds of feet of deposits may be 

assigned consolidation characteristics on a subjective 

basis. The results of Miller's computations of future 

compaction at the Oro Loma site have been published 

(1961). Because of the limited number of consolidation 

tests, it was decided not to include updated computations in this paper. However, the computations of ultimate compaction made for the Oro Loma site in 1960 on 

the basis of consolidation tests should be reviewed as of 

7 years later, in order to compare earlier predictions 

with actual subsidence.

The basic procedure used by Miller (1961) is as follows: (1) The fine-grained part of the aquifer system is 

divided into thickness segments and each segment is 

assigned consolidation-test results considered to be typical of the deposits of that segment. The results of one 

consolidation test may be used for many segments. (2) 

The change in applied stress for a given time period is 

determined. (3) Estimates of compaction are computed 

on the basis of the void-ratio change determined graphi-
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G49

cally from the straight-line part of the one-dimensional 

consolidation curves. (4) The effect of thick clay beds on 

rates of pore-pressure decay is taken into account using 

the Terzaghi equation. (5) A sum of the computed compaction for all the segments is determined for one or 

more time periods.

The attempt to compute residual compaction on the 

basis of consolidation tests resulted in estimates of compaction and subsidence that are too low. Miller (1961, p. 

57, 58) estimated that 0.8 foot of residual compaction 

would occur at Oro Loma after 1959 in the depth interval 465-1,000 feet, as a result of prior decline in artesian pressure that occurred between 1937 and 1959. 

The maximum summer depths to water at the Oro Loma 

site have remained about the same in each year since 

1959 (fig. 36A). However, as of 1968, the amount of 

residual compaction measured since 1959 within the 

depth interval was already twice the amount computed 

on the basis of laboratory consolidation tests.

The chief problem of using consolidation-test results 

to estimate subsidence in the San Joaquin Valley has 

been an insufficient number of consolidation tests to 

define variations in compressibility due to the wide 

range in character of aquitard materials. In addition to 

the limited number of tests, the subjective decision as to 

what constitutes the "fine grained" deposits within the 

aquifer system may lead to underestimations of future 

subsidence.

The use of consolidation tests to estimate compaction 

or subsidence for a given change in applied stress appears to have much greater potential in the Santa Clara 

Valley, Calif. (Poland, 1969b, p. 288-290). The 

fine-grained beds in the Sunnyvale and San Jose core 

holes that were sampled for consolidation tests have 

compressibilities or compression indices that group 

rather closely. Poland suggested that the well section 

be divided into zones not more than 200 feet thick, a 

suggestion that would reduce the effects of nonlinear 

compressibility decrease with increasing effective 

stress. He concluded that approximate ultimate compaction for a zone can be computed using the equation

where

Az is the computed ultimate subsidence or compaction, 

mv is the mean compressibility of the compacting

beds, 

m is the aggregate thickness of the compacting

beds, and

Ap' is the change in effective stress. 

Better estimates should be obtained for the Santa 

Clara Valley than for the San Joaquin Valley because of

the lesser variation in the compressibility of the deposits. The most subjective element in the equation is 

m, the aggregate thickness of the compacting beds.

Computation of future subsidence that would result 

from the compaction of a given bed also can be made. For 

example, useful computations of the compaction rate of 

the Corcoran Clay Member of the Tulare Formation at 

the Oro Loma site have been made by Miller (1961, p. 

57, 58), using the Terzaghi equation. He used the entire 

thickness of the Corcoran because compaction of the 

clay occurs by drainage into the underlying aquifer as a 

result of the downward head differential. A value of the 

consolidation coefficient of 0.92 square foot per year 

obtained for the load (effective stress) range 200-400 Ib 

in ~2 was used by Miller, who assumed that this 

coefficient applied to the entire thickness of the Corcoran at the site that is, that the Corcoran had uniform 

vertical permeability throughout its 86-foot thickness. 

Under these assumptions, Miller found that 8,000 years 

would be required for about 93 percent of the compaction to occur in response to a given applied stress, that 

1,600 years would be required for 50 percent of the 

compaction to occur, and that 60 years would be necessary for only 10 percent of the compaction to occur. He 

also concluded that the Corcoran is compacting very 

slowly at the Oro Loma site at a rate of roughly 0.01 ft 

yr" 1 .

The consolidation characteristics of the fine-grained 

materials in the various types of deposits are given in 

Part 2 (Bull, 1974, table 9). Many of the fine-grained 

beds from which cores were obtained for consolidation 

tests are not thick nor do they have a large areal extent. 

Except for the lacustrine clays, the beds within the 

study area characteristically are intertonguing lenses.

CONDITIONS AFTER DELIVERY 

OF CANAL WATER

Importation of surface water into the study area by 

the San Luis Canal section of the California Aqueduct 

should eliminate much of the ground-water overdraft 

that has caused large artesian-head decline and subsidence since 1920. Canal water will not be delivered to all 

areas at the same time, and even after maximum deliveries can be made through the completed distribution 

system, ranchers will continue to pump 

400,000-500,000 acre-feet of ground water per year 

after full development of the project area.

The San Luis Canal section of the California 

Aqueduct is a federal-state joint-use facility.3 It is part 

of the major canal under construction for transporting

3The authors are indebted to many Bureau of Reclamation employees for furnishing 

statistics and general information about the San Luis project. Most of the following information was obtained from Richard Bateman, Ralph Cole, William Cooke, Alfred Harvey, and 

David Magleby.
G50 STUDIES OF LAND SUBSIDENCE

water from areas of abundant water in northern 

California to areas needing water in central and southern California. At the north boundary of the San Luis 

service area, the canal has a bottom height of 85 feet, 

and the width at the top of the lining is 217 feet. The 

depth from the canal floor to the top of the lining is 35 

feet, and the design capacity of the canal is 13,100 cubic 

feet per second. Water will be withdrawn for irrigation 

at many points along the canal, and at Kettleman City, 

on the south edge of the study area, its design capacity is 

8,100 cubic feet per second. The gradient of the canal is 

only 4xlO~5 (2% ia/mi).

The canal was completed in 1968 at an estimated cost 

of $548 million for the canal and storage features. At 

least an additional $284 million is expected to be spent 

in the construction of distribution systems both upslope 

and downslope from the canal. Upon completion of the 

distribution systems, a maximum of 1,200,000 acre-feet 

of water can be delivered to the San Luis service area 

each year. The ultimate demand of the service area is 

estimated to be 1,600,000 acre-feet per year, which 

means that about 400,000-500,000 acre-feet of ground 

water will have to be pumped in order to satisfy the 

demand. The location of the canal, service area, and 

proposed master drain are shown in figure 40.

One reason for continued pumping of ground water 

will be to provide a mix of irrigation water that will 

percolate into the surface soils more readily than the 

sodium chloride water of 200-300 milligrams per liter 

total dissolved solids that will be delivered from the 

Sacramento River system to the San Luis service area.

The schedule of delivery of water to the San Luis 

service area is the determining factor in how rapidly the 

pumping rate will decrease and the artesian head will 

rise, resulting in the alleviation of subsidence in parts of 

the area and elimination of subsidence in other parts of 

the area. The delivery of water is based to such a large 

extent on political and economic factors that as of 

mid-1968 it is not possible to estimate the schedule of 

water delivery. Some of the problems that have to be 

solved before delivery of water include these: the 

160-acre limitation landowners have to agree to before 

they are eligible to receive canal water; funds for the 

construction of distribution systems are becoming increasingly difficult to obtain during a period of war-time 

economy; and appropriate means of removing waste 

irrigation water have to be made from those parts of the 

area where the water table is close to the root zone. 

Furthermore, farmers may prefer to continue to use 

some of the wells drilled shortly before imported surface 

water becomes available.

Delivery of water is expected to occur in three stages. 

The first area to receive large amounts of canal water is 

downslope from the canal in the northern part of the

area. The next area will be downslope from the canal in 

the southern part of the area. The area upslope from the 

canal will receive canal water last because the time 

needed to construct facilities to move water upslope is 

greater than that for the gravity-flow structures to be 

used downslope from the canal.

One method of evaluating the influence of importation of canal water is to study the effect of past imports 

of water. The following discussion will make such an 

evaluation in the northern and southern parts of the 

area. Then a prediction of future subsidence rates will 

be made under assumed conditions.

In the Los Banos-Kettleman City area as a whole, the 

subsidence rates were accelerating during the 1943-53 

period. In most of the area, subsidence rates increased 

until 1955-60, but have decreased since 1960. Despite 

the reversal in subsidence rate in the middle and late 

1950's, rates in 1959-63 were more than twice those in 

1943-53 in much of the area.

A pronounced exception to the general increase in 

subsidence rates was the northern part of the Los 

Banos-Kettleman City area, the area that had been 

receiving Delta-Mendota Canal water since 1953. The 

effect of delivery of Delta-Mendota Canal water on subsidence rates in this northern area is shown in figure 41. 

Large-scale deliveries of water from the Delta-Mendota 

Canal began in 1954. Parts of the area within, and the 

area to the north of, the Delta-Mendota Canal service 

area shown in figure 41 were receiving surface-water 

imports from other smaller canals prior to delivery of 

Delta-Mendota Canal water. In 1960, a local water 

company completed the construction of a lift system 

upslope from the Delta-Mendota Canal and began to 

irrigate a large area near the foothills with imported 

surface water.

The subsidence rate in the northern part of the Los 

Banos-Kettleman City area during the period 1943-53 

is shown in figure 4 LA. Rates in part of the area that 

later received canal water exceeded 0.4 ft yr" 1 , as compared with maximum subsidence rates farther south of 

slightly more than 0.6 ft yr^ 1 during the same period. 

The pattern of rate isopleths for the 1943-53 period 

continues from the southeast directly into the middle of 

the area later to receive water imports from the DeltaMendota Canal.

Figure 41B shows the change in mean subsidence 

rates from 1943-53 to 1959-63. The most apparent 

change between the patterns of isopleths of figures 4L4. 

and B is that the trough defined by the isopleths that 

extended to the Merced County line in the 1943-53 

period stops abruptly at the south edge of the service 

area of the Delta-Mendota Canal. The maximum subsidence rate within the service area during the 1959-63 

period was 0.5 ft yr" 1 at the south edge. Water levels in
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3

120°30' 120°00'

G51

37°00' 

36°30'

36°00

EXPLANATION

Boundary of deformed 

rocks

San Luis Canal section of the California 

Aqueduct

--<£---- x- - 

Proposed alinement of the San Luis Drain

Boundary of the San Luis service area

Hachured where prior imports of water have 

been made by the Delta Mendota Canal

10 15MILES

0 51015 KILOMETRES

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 40. Areas to receive water from the San Luis Canal section of the California Aqueduct.

the southern part of the service area were maintained at zone pumping in the area immediately to the south,

the previously low levels or were still declining at slow Within a 100-square-mile area of figure 4 IB, which

rates because of the large overdraft caused by lower- includes most of the area that has received large
G52 STUDIES OF LAND SUBSIDENCE

37°00'r'

EXPLANATION

Boundary of deformed rocks

 0.40 

A. Line of equal subsidence rate between 

1943 and 1953, in feet per year ; interval 

0.20 foot, except for the 0.10-foot line. 

Compiled chiefly from levelings of the 

U.S. Coast and Geodetic Survey in 1943, 

1953

Received large Received large 

amounts of water amounts of water

since 1953 since 1959 

Areas receiving water from the Delta 

Mendota Canal, for which large amounts 

of surface water were not available before 

construction of the canal

-0.60-

B. Line of equal increase in average subsidence rate, in feet per year, from the 

1943-53 to the 1959-63 period; interval 

0.20 foot, except for the 0.10-foot line. 

Compiled chiefly from levelings of the 

U.S. Coast and Geodetic Survey in 1943, 

1953, 1954, 1958, 1959,and 1963

Area in which the rate of subsidence was 

less during the 1959-63 period than during 

the 1943-53 period

37-00'-7-'

10MILES

10 KILOMETRES

FIGURE 41. Effect of delivery of Delta-Mendota Canal water on subsidence rates in the northern part of the Los Banos-Kettleman City area.

amounts of surface water since 1953, the subsidence draft south of the service area. Within the service area,

rate was less during the 1959-63 period than during the local pumping of lower-zone water continued, but

1943-53 period. Subsidence was alleviated in varying lower-zone water levels rose more than 40 feet between

degrees within this 100-square-mile area, despite the 1955 and 1966 in some wells,

continued acceleration of subsidence rates and over- The area near the foothills that has received large
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G53

amounts of canal water since 1959 has undergone only a 

slight increase in subsidence rate since the 1943-53 

period. Much of this area was not farmed until after 

1947. The area immediately to the south also shows 

negligible increase in subsidence rate, but was yet to be 

farmed as of 1968.

Subsidence alleviation in the Delta-Mendota Canal 

service area was the result of sustained importation of 

surface water. The effect of intermittent importation of 

surface water in part of the southern part of the Los 

Banos-Kettleman City area is shown in figure 42.

The interrelations of subsidence rates, artesian-head 

decline, and surface-water imports near Stratford and 

Lemoore show that even occasional surface-water imports influence the subsidence rate. Before construction 

of Pine Flat Dam on the Kings River in the Sierra 

Nevada, the rate of subsidence of bench mark L157 

increased as follows: 1933 to December 1942,0.0 ftyr" 1 ;

275

1942 to May 1947, 0.06 ft yr^ 1 ; and May 1947 to March 

1954, 0.37 ft yr" 1 . Since completion of Pine Flat Dam in 

1954, subsidence rates have varied markedly, ranging 

from 0.3 ft yr" 1 between January 1958 and January 

1959 to 0.44 ft yr- 1 between January 1960 and March 

1963.

The inverted bar graph of annual discharge downstream from the Lemoore weir indicates the trends in 

availability of surface water for agriculture in the 

Stratford-Lemoore area that resulted from the construction of Pine Flat Dam. Discharge downstream 

from the Lemoore weir has ranged from 0 acre-feet in 

1961 to more than 500,000 acre-feet in 1958. The 2 years 

when annual discharge exceeded 200,000 acre-feet were 

times of greatly reduced subsidence rate at bench mark 

L157. Periods of marked reduction of surface water imports, such as in 1957 and 1960 to early 1963, were 

associated with an eightfold increase in subsidence

425

Annual discharge of Kings River 

downstream from the Lemoore 

Weir (from Kings River Water 

Association)

Bench mark L157

FIGURE 42 Interrelations of subsidence rates, artesian-head decline, and surface-water imports near Stratford and Lemoore.
G54 STUDIES OF LAND SUBSIDENCE

rate, when compared with the mean subsidence rate in 2 

years of abundant surface water.

Measurements of the pumping level in well 

21/19-2B1, although infrequent, show general trends 

that agree with the records of subsidence rates and 

surface-water imports. This well is 1,990 feet deep and 

taps only the lower zone. The time of maximum recorded depth to pumping level late in 1961 coincides 

with the year of minimum availability of surface water 

and occurs in the period of maximum subsidence rate. 

The time of minimum recorded depth to pumping level 

late in 1956 is associated with a year of large surfacewater import and with a period when the subsidence 

rate was only 0.07 ft yr-1.

The interrelations shown in figure 42 indicate that 

little residual compaction would occur if water levels 

were raised more than 50 feet.

Accurate prediction of subsidence rates for an entire 

region at a specified future date may not be possible 

because of the many highly variable factors that 

influence change in applied stress. However, it can be 

assumed that importation of canal water will decrease 

pumping and will cause artesian heads to rise, and 

thereby alleviate subsidence to varying degrees in all 

areas of decrease in applied stress and possibly eliminate subsidence in parts of the area. The following discussion, although made in the form of a prediction, is 

intended as an example of the application of criteria for 

the prediction of future subsidence after a postulated 

decrease in applied stress.

Estimated subsidence rates based upon a postulated 

increase in lower-zone artesian head are made in table 2 

and in figure 43. The estimates were made on data 

available as of December 1967. The year 1970 is used as 

the time of the hypothetical head rise. It is necessary to 

specify a date for the estimated rates because of the 

continuing decay of excess pore pressures that have 

resulted from previous head declines. The year 1970 

may or may not be the time of major recovery of lowerTABLE 2. Estimated annual subsidence rates in the Los BanosKettleman City area if summer lower-zone water levels rose 60 feet 

and the seasonal fluctuation were reduced to 10-20 feet

Estimated rate if water levels 

rose 60 feet in 19702

(ft/yrl

0

0 -0.1 

0 -0.1 

0.1-0.2 

0.2-0.3 

0.1-0.2 

0 -0.2 

0 -0.1 

0.2-0.3 

0.3-0.4 

0 -0.1 

0.2-0.3 

0 -0.2 

0 -0.1

1Based on 1963-66 subsidence rate map, compaction rate after 60 ft of water-level rise at 

compaction-recorder sites, lithofacies maps, and lower-zone seasonal fluctuation map. 

Correction of estimated 1968 rates based on residual compaction graphs (figs. 38, 39).

Subarea 

1A _ __ _ __

2 _ _

3 _ __ _ _

4 _ _ __

6 _______ _ __

8 _ __ ___ _ _

9 __ ________

10 ____________

11

12 __ ___ __ _

13 __ ________

Estimated rate if water levels 

rose 60 feet in 19681

(ft/yrl

________ 0

________ 0 0.2

0.1 0.3

_ _ _ 0.3-0.5

0.1 0.3

0.1-0.2

__ __ __ 0 0.2

___ ___ 0.2-0.4

0.4-0.6

________ 0 0.2

_ _____ 0.2-0.4

_ _ _ 0.1-0.2

0 -0.2

zone artesian head. It can be stated with certainty, 

however, that increase in head as the result of canalwater imports will not be uniform, nor will it occur at 

the same time in all parts of the area.

A 60-foot increase in head was selected for several 

reasons. It is a reasonable minimum amount of rise in 

the summer potentiometric level that will occur after 

large-scale deliveries are underway, but probably is less 

than the ultimate amount of head recovery that will 

occur in much of the area after the maximum delivery of 

surface water. It is possible that the lower-zone artesian 

head will rise more than 200 feet in parts of the study 

area, despite the estimate that total ground-water 

pumpage under full import conditions will still be about 

half a million acre-feet.

About 60 feet of seasonal water-level recovery has 

occurred at many of the compaction-recorder sites. If a 

larger value of postulated head rise had been 

selected 100 feet, for example then the compaction 

records would be of little use in determining the rate of 

compaction after given amounts of head recovery.

The estimates of future subsidence rates after a postulated head recovery represent an integrationof knowledge regarding many aspects of the hydrology and 

geology of the Los Banos-Kettleman City area. Because 

many different types of knowledge and experience are 

involved, the results should be considered in part to be 

subjective. However, the large amount of factual data 

that is available makes the estimates more objective 

than the reader might first suspect. The general pattern 

of subsidence rates is well established from the 1963-66 

subsidence rate map (Pt. 2, Bull, 1974, fig. 19).

The compaction rate after 60 feet of seasonal lowerzone head recovery is available from most of the 

compaction-recorder sites. In evaluating the compaction records, it is important to remember that the 

amounts of recorded compaction during a period of 

water-level rise are the net result of two components 

tending to change aquifer-system thickness: Delayed 

compaction of the aquicludes and many of the aquitards 

will tend to cause compaction to be recorded; elastic 

expansion of the aquifers and some of the aquitards also 

will tend to cause expansion to be recorded. The net 

result of these two components is dependent on the rates 

of delayed compaction and water-level rise. If the rates 

of water-level rise are sufficiently rapid, net expansion 

may be recorded, even though delayed compaction is 

continuing in parts of the aquifer system. In this case, 

recorded compaction may resume after a period of 

water-level rise, assuming that water levels are constant after the head recovery. Rates of delayed compaction that are recorded while water levels are rising are 

minimum rates.

Two lithofacies maps (Pt. 2, Bull, 1974, figs. 63, 66)
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3

120° 30' 120°00'

G55

37°00

EXPLANATION

Boundary of deformed

rocks

4

Boundary and number of hydrologic or 

geologic subarea

ES3

0-0.1

0-0.2 0.3-0.4

Estimated rate of subsidence in each subarea in feet per year

Based on the 1963-66 subsidence map, 

compaction rate after 60 feet of waterlevel rise at compaction-recorder sites, 

lithofacies maps, and lower-zone seasonal 

fluctuation map; corrected on the basis of 

graphs showing the decrease in the rate of 

delayed compaction at selected applied

Coalmga 

VALLEY

36°30' -

Base from U.S. Geological Survey Central 

Valley map, 1:250,000, 1958

FIGURE 43. Estimated annual subsidence rates in the Los Banos-Kettleman City area in 1970 if summer lower-zone water levels rose 60 feet and the seasonal

fluctuation were reduced to 10-20 feet.

were used in the evaluation. One map shows the general other map shows the distribution of genetic classes of 

patterns of the mean lithology of the lower zone, and the deposits with different types of bedding, which have an
G56 STUDIES OF LAND SUBSIDENCE

important influence on the rate at which water can be 

expelled from the compressible deposits and hence on 

the rate of compaction. Most of the subarea boundaries 

that trend generally east-west in figure 43 were selected 

on a hydrogeologic basis. Subarea boundaries that 

parallel the length of the area also parallel the lines of 

equal subsidence rate, or boundaries of Sierra and Diablo deposits.

The lower-zone seasonal fluctuation had to be considered also. A 60-foot head rise for summer levels would 

raise the minimum seasonal water level 50 feet above 

the 1967 winter high water levels in parts of the area. In 

other parts of the area, 60 feet is only half the seasonal 

fluctuation that was occurring in 1967. It is assumed 

that seasonal fluctuation of artesian head will decrease 

as the ground-water pumpage decreases. A range of 

10-20 feet of seasonal fluctuation was selected for the 

purposes of table 2 and figure 43. The amount of seasonal fluctuation that is postulated is about the same as 

has been occurring in that part of the area that already 

has received large-scale surface-water imports the 

service area of the Delta-Mendota Canal. In 1966 and 

1967, seasonal fluctuations in most of the DeltaMendota Canal service area were 5-20 feet.

The factors just described were the principal sources 

of information used to estimate the subsidence rates if 

summer water levels had risen 60 feet in 1968 (table 2). 

Maximum estimated subsidence rates after a postulated water-level rise in 1968 exceed half a foot per 

year in subarea 9, but in most of the area would be 

0.1-0.3 ftyr- 1 -

The estimates of 1968 subsidence rates if the postulated water-level rise had occurred were made only 

to form a basis for predicting future rates within small 

areas, or at given points, after a summer head recovery 

has actually occurred. The potentiometric levels during 

the summer of 1968 actually reached historic lows in 

most of the area.

To estimate subsidence for some future year, the decrease in the rates of delayed compaction has to be 

estimated and applied as a correction to the 1968 estimates. The selected year of 1970 for a postulated 60 feet 

of summer head rise is 2Vz years after the December 

1967 base date. The plots of decrease in the rate of 

delayed compaction in figures 38 and 39 indicate that 

after a 2%-year period, residual compaction in the 

northern part of the area would be roughly 35 percent 

complete and would be roughly 15-20 percent complete 

in the southern part of the area. The larger correction 

factor was applied in subareas 1 through 4, and the 

smaller correction factor was applied in subareas 5 

through 13.

The end result of the foregoing computations and 

corrections is the set of estimated subsidence rates in 

1970 if the summer water levels in that year should be

60 feet above the 1967 summer levels. These estimates 

do not take into account the elastic expansion, principally of the aquifers, that will occur as a result of the 

postulated 60 feet of head rise. The only data available 

at the time of the writing of this paper are the amounts 

of net specific unit expansion at three sites. The net 

values are considered as minimum values of specific 

unit expansion, but at least 0.1 foot of expansion should 

occur in most of the area as a result of 60 feet of lowerzone head recovery. Change in altitude of bench marks 

surveyed before and after an actual 60-foot head recovery would include the effects of the elastic expansion of 

the more permeable beds within the aquifer system and 

thus may result in lower observed subsidence rates than 

shown in figure 43. The rates given in table 2 and figure 

43 are based on the premise that summer water levels 

will not change significantly after the 60-foot waterlevel recovery.

Over long time periods, elastic expansion of the lower 

zone in response to substantial recovery of artesian 

head may be offset by compaction resulting from increase in stress that will be applied to the lower zone as 

a result of water-table rise. The water table is rising at 

the present time in most of the study area. Importation 

of additional supplies of water for agriculture probably 

will result in an acceleration of water-table rise. Every 

5 feet of water-table rise will tend to offset 1 foot of 

lower-zone head recovery. For example, 50 feet of 

water-table rise in an area where the lower zone is 

confined and the lower-zone head remains constant will 

result in an increase in applied stress on the lower zone 

of 10 feet of water.

Surface-water deliveries have been made in subarea 

1A for a long time, and the head decline that has caused 

subsidence began in this area before 1920 (Pt. 1, Bull 

and Miller, 1974, fig. 21). Sixty feet of head rise should 

cause compaction to cease, except in the Corcoran, and 

probably will result in minor net expansion in much of 

the subarea.

Subarea IB is that part of the Delta-Mendota Canal 

service area adjacent to the area of excessive groundwater pumping to the south. Much of the delayed compaction may have already occurred in the Diablo 

flood-plain deposits that underlie this subarea, and so it 

is anticipated that subsidence rates would be low should 

water levels rise.

Most of subarea 2 bordering the foothills of the Diablo 

Range has never been irrigated, but the proportion of 

irrigated land increases to the northeast. Much of the 

head decline and associated subsidence that has occurred in the past has been the result of ground-water 

movement to the areas of intense pumping to the 

northeast of subarea 2.

The lower-zone deposits underlying subarea 3 consist 

chiefly of Diablo flood-plain deposits. The thin aquitards
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G57

typical of this class of deposits have contributed to rapid 

expulsion of water during past periods of applied stress.

Subarea 4 also is underlain principally by Diablo 

flood-plain deposits. Although this has been the area of 

maximum subsidence rate in the past (Pt. 2, Bull, 1974, 

fig. 18), the potential for future delayed compaction is 

considered to be about the same as subarea 11, where 

lower subsidence'rates have occurred in the past.

Subarea 5 is underlain chiefly by Sierra flood-plain 

deposits, but these deposits are finer grained than the 

Sierra flood-plain deposits to the east in subarea 6. 

Future subsidence is expected to occur within this subarea, but the amounts should be small.

Nearly all the head decline that has occurred in subarea 6 has been the result of excessive lower-zone overdraft to the west. Thus, 60 feet of head rise would consist 

mainly of a decrease in the gradient of the potentiometric surface to the west. Subsidence rates may decrease to 

nearly 0 in parts of the area where the lower-zone deposits consist mainly of sand that has few interbeds of 

fine-grained material. However, expansion of agricultural development and additional pumping of lowerzone water in those parts of the subarea outside of the 

San Luis Canal service area may result in subsidence 

rates of as much as 0.2 ft yr- 1 .

Most of the wells in subarea 7 tap sands and thick 

clays of the Etchegoin Formation. Subsidence rates 

were low during the 1963-66 period, but probably will 

not decrease markedly because of the large excess pore 

pressures that probably exist in very thick clay beds. 

Also, 60 feet of head rise is minor when compared with 

the 400-500 feet of head decline that has occurred in the 

subarea.

Subareas 8 and 9 have lower-zone deposits that are 

similar to those of subarea 4, except that the Diablo 

deposits consist of alluvial-fan instead of flood-plain 

deposits. Sierra and lacustrine deposits make up a large 

portion of the section.

Records from the Cantua recorder site indicate that 

maximum delayed compaction may occur within subarea 9. At least 100 feet and possibly more than 200 feet 

of head recovery may be necessary to eliminate excess 

pore pressures at this site. The area is underlain by 

several types of deposits.

The water-table rise that should occur in the coarsegrained deposits of subarea 10 southwest of the 

confining influence of the Corcoran should cause a 

steady and rapid decline in applied stress on the aquifer 

system which approaches a water-table type of aquifer 

next to the foothills. The lensing clay beds in the fan 

deposits of the subarea generally are not thick, and 

periods of rapid water-level rise at one site (19/16-23P2) 

are accompanied by recorded net aquifer expansion.

The amount of subsidence after delivery of canal 

water may be greater in subarea 11 than elsewhere in

the study area because of the thick section of interbedded fine-grained deposits from both Diablo and Sierra 

sources that constitute the lower zone in this subarea. 

Head declines have been large, but the rates of compaction have not been as rapid as in subarea 4, where much 

less head decline has occurred. These facts are interpreted to mean that excess pore pressures are large in 

subarea 11, thus favoring large amounts of delayed 

compaction. Net expansion is recorded in the subarea, 

but only because of the rapid rate of head recovery that 

occurs after extremely large seasonal water-level declines (Pt. 1, Bull and Miller, 1974, fig. 43).

Subarea 12 is much the same as subarea 6, except 

that heavy pumping has occurred in the upper as well as 

in the lower zone. The estimates of future subsidence 

are based on the premise of 60 feet of head rise in the 

upper as well as in the lower zone in subarea 12 and in 

the southeastern part of subarea 11.

In many respects, the situation in subarea 13 is similar to that in subarea 7, except that the deposits from 

which the water is being pumped are the lower part of 

the continental Tulare Formation.

SUMMARY

Water-level changes resulting from pumping of 

ground water and irrigation have changed the stresses 

tending to compress the alluvium of the Los Banos 

-Kettleman City area. Change in stress applied on the 

confined lower zone, in which three-fourths of the compaction is occurring, is the algebraic sum of the following components of stress change:

1. A seepage stress equal to the lower-zone artesianhead change.

2. A seepage stress equal to the head differential 

caused by change in water-table position.

3. A stress caused by change in buoyancy of the deposits within the depth interval that is being dewatered, or saturated, as a result of water-table 

change.

4. A stress caused by part of the pore water being 

changed from a condition of neutral to applied 

stress, or vice versa, that occurs within the depth 

interval being affected by water-table change. 

The magnitudes of the various stresses on the 

confined zones (expressed in feet of water) is as follows, 

assuming a porosity of 0.4, a specific gravity of 2.7, and a 

moisture content (specific retention) of the dewatered 

deposits of 0.2 the volume: Seepage stresses resulting 

from either artesian-head change or change in watertable position cause 1 foot of change in applied stress per 

foot of change in head differential. Each foot of watertable change also causes a 0.6-foot stress change because of removal or addition of buoyant support of the 

deposits within the interval of water-table change and a 

0.2-foot stress change because of part of the pore water
G58 STUDIES OF LAND SUBSIDENCE

being changed from a neutral-stress condition to an 

effective-stress condition, or vice versa. The effect of 

water-table change is to change the effective stress in 

the unconfined aquifer by ±0.8 foot of water per foot of 

water-table change. The effect of water-table change on 

stress changes in the deeper confined zones is to change 

the stress by only ±0.2 foot of water because the 

seepage-stress change more than offsets the sum of the 

two other stress changes.

Applied-stress increase on the lower-zone deposits 

has been as much as 500 feet of water as a result of 

artesian-head decline, and water-table change has 

caused as much as 25 feet of stress increase in the 

northern part of the area and as much as 75 feet of stress 

decrease in the southern part.

Over long time spans, the rates of compaction (and 

subsidence) per unit applied-stress increase accelerate 

with additional applied-stress increase, but vary widely 

because of geologic and hydrologic factors. For example, 

in some areas applied-stress increases of less than 200 

feet have resulted in 20 feet of compaction, but locally 

along the west margin of the area, increase in applied 

stress of 400 feet has caused only 1 foot of compaction.

Changes in aquifer-system thickness are elastic (are 

reversible and occur with minor time delay) and inelastic (are irreversible and occur with large time delay). 

Under the pore-pressure conditions of the sixties, in 

much of the area net aquifer-system expansion occurred 

briefly or not at all, but elastic changes affected the 

monthly amounts of measured compaction. Maximum 

compaction rates occur during times of head decline 

because elastic compaction is additive with virgin compaction; minimum compaction rates occur during times 

of head rise because expansion is subtracted from virgin 

compaction. Removal of the estimated component of 

elastic change of aquifer-system thickness shows that 

virgin compaction is distributed more uniformly 

throughout the year than is the observed net monthly 

compaction and decreases during times of appliedstress decrease.

The elastic component of seasonal compaction varies 

from less than 5 to about 90 percent, depending on the 

lithology and permeability of the deposits and on the 

magnitude and rate of applied-stress increase as compared with previous effective stress maximums and durations.

Good records of net aquifer-system expansion have 

been obtained at three sites. Amounts of net expansion 

of almost 0.1 foot have been recorded during times of 

decrease in applied stress indicated by rise in artesian 

head. Under the conditions of excess pore pressures 

existing in aquitards in the sixties, three concurrent 

processes were tending to change aquifer-system thickness during times of applied-stress decrease elastic

expansion with no measurable time delay (presumably 

chiefly of the aquifers), delayed elastic expansion (presumably chiefly of the thin aquitards and the outer 

parts of the thick aquitards), and virgin compaction 

(presumably of the aquicludes and thick aquitards). 

Delayed compaction due to continuing decay of excess 

pore pressures may still occur in thick clay beds after 60 

feet or more of head recovery in contiguous aquifers.

The net change in aquifer-system thickness that results from these three concurrent processes is chiefly a 

function of the rate of change of applied stress and the 

hydraulic conductivities of the different materials constituting the aquifer system. During rapid appliedstress decrease, net expansion may be recorded while 

some aquitards are still undergoing virgin compaction. 

Delayed expansion rates increase with decreasing applied stress and may exceed the decreasing virgin compaction rates for short time periods of rapid appliedstress decrease. During periods of slow applied-stress 

decrease, virgin compaction rates may continue to exceed delayed expansion rates and net compaction results.

The approximate modulus of expansion (net specific 

unit expansion) of the upper-zone aquifer system at the 

Lemoore and Yearout sites is about 3.5x 10~6ft~ 1 . During a period of seasonal head recovery at the Lemoore 

site, the net specific unit expansion varied from 0.6 to 

3.6xlO~6ft-1 , as the rates of virgin compaction and of 

nondelayed and delayed elastic expansion varied concurrently with changes in the magnitude and rate of 

applied-stress decrease.

Little time is needed to raise pore pressures in many 

of the aquitards. Compaction ceases when aquifer pore 

pressures rise to equilibrium with the maximum pore 

pressure in contiguous aquitards, thus preventing 

further expulsion of water. Additional pore-pressure 

increases in the aquifers are transmitted fairly rapidly 

into the aquitards because their specific storage in the 

elastic range is small.

The time lag between the start of head recovery and 

the start of recorded expansion depends on the 

mechanics of the aquifer and recorder systems. Net 

aquifer-system expansion will not occur until the expansion rate exceeds the compaction rate. Net expansion will not be recorded until cable tension below the 

uppermost friction point between the casing and the 

cable is increased to the point where it overcomes the 

friction, reverses the sense of movement in the recorder 

system, and raises the counterweights. The minimum 

amounts of head recovery that occurred before net expansion was first recorded were 6 feet at well 

19/16-23P2 and I foot at well 18/19-20P2.

Prediction of the amounts, rates, and distribution of 

subsidence during future time periods in the Los
LOS BANOS-KETTLEMAN CITY AREA, CALIFORNIA, PART 3 G59

Banos-Kettleman City area is not meaningful unless 

the magnitude and time distribution of change in applied stress can be predicted with reasonable accuracy. 

The time-dependent nature of the pore-pressure decay 

in the aquitards and aquicludes also complicates estimates of compaction of heterogeneous aquifer systems. 

Therefore, the most practical approach is to provide 

criteria for the prediction of subsidence rate, assess the 

critical factors affecting compaction rates, and make 

predictions of future subsidence rates on the basis of 

postulated hydrologic changes.

Prediction of trends of future subsidence based on 

historic subsidence graphs is most likely to be useful 

when based on subsidence-rate plots, rather than 

cumulative subsidence plots.

Head decline/subsidence or subsidence/head decline 

ratios determined for long time periods on an areal basis 

are a useful tool for predicting minimum ultimate subsidence from a postulated additional head decline. 

These ratios also are useful for predicting the rate of 

future subsidence if the future rate of applied-stress 

increase is the same as the rate of applied-stress increase during the period for which the head 

decline/subsidence ratios were determined. If the rate of 

applied-stress increase accelerates in the future, estimates of subsidence based on past ratios will most likely 

be less than the amounts of subsidence occurring in the 

future. If the rate of applied-stress increase decelerates 

in the future, estimates of subsidence based on past 

head decline/subsidence ratios will probably also be low 

compared with actual amounts of subsidence, because of 

the large amounts of residual compaction that will continue even during times of little or no increase in applied stress.

Most of the subsidence since 1960 has been the result 

of increase in applied stress prior to 1960 that did not 

have sufficient time to become fully effective in many of 

the thicker aquitards because of their low vertical permeabilities. The occurrence of residual compaction is 

particularly apparent in areas of large head decline and 

subsidence that continue to have seasonal fluctuations 

in artesian head of more than 40 feet. In much of the 

area, the rate of increase in applied stress has been 

decreasing since the mid-1950's because the rate of 

lower-zone head decline has decreased from more than 

10-15 ft yr" 1 to only 1-5 ft yr"" 1 . The rates of compaction 

and subsidence have not undergone a proportionate decrease. Instead, the rate of compaction has continued to 

be Vs-% of the earlier rates as a result of a large component of residual virgin compaction that is occurring in 

thick beds with low permeabilities. The increase in the 

delayed compaction component occurring during the 

past few decades is readily apparent in plots of the ratio 

of subsidence to lower-zone increase in applied stress.

The rate of decrease of aquitard-aquifer porepressure differentials can be evaluated at some sites 

through study of change of mean daily compaction rates 

for selected applied stress levels. In the 

703-2,000-foot-depth interval at the Cantua site, the 

relation between mean daily compaction rate (y) and 

time Or) for the 1961-67 period is

A 10-percent decrease in residual compaction rate had 

occurred as of mid- 1962 and 45 percent by 1968, and a 

90-percent decrease is predicted to have occurred by 

about 1986, assuming a hydrologic environment similar to that of the 1961-67 period. Exponents of similar 

equations for other compaction-recorder sites indicate 

that the rate of pore-pressure decay is twice as rapid in 

the northern as in the southern part of the study area. 

Weighted mean aquitard thickness factors (aquitard 

thickness/2)2 derived from micrologs of core holes show 

that the sites of most rapid decrease of mean daily 

compaction rates have thinner aquitards than does the 

Cantua site in the southern part of the area.

Laboratory consolidation test results are useful in 

predicting the rates and amounts of compaction of the 

clay beds from which the samples were cored, but estimates of future amounts of compaction of entire aquifer 

systems may be of doubtful value if based on only a few 

consolidation tests. Prior attempts to estimate future 

subsidence on the basis of consolidation-test results 

from the study area have resulted in underestimation of 

future subsidence because of an insufficient number of 

consolidation tests to define variations in compressibility due to different types of aquitard materials.

Importation of surface water in the past has resulted 

in marked reductions in subsidence rate. In the service 

area of the Delta-Mendota Canal, the subsidence rate 

during the 1959-63 period was less than that during the 

1943-53 period, but in the area south of the service area, 

the rate of subsidence had doubled between the same 

time periods. Intermittent delivery of water from the 

Kings River in the vicinity of Stratford and Lemoore, 

after construction of the Pine Flat Dam, has caused 

temporary rise in artesian head and decrease in subsidence to rates that were as low as 0.03 ft yr" 1 during 

years of abundant surface water. During years when 

surface water was not available, the artesian head declined, and subsidence rates increased to more than 0.44 

ft yr-l. Delivery of water from the San Luis Canal 

section of the California Aqueduct should result in 

widespread alleviation of subsidence, even before maximum deliveries are obtained.

Assuming that as of 1970 lower-zone summer water 

levels throughout the study area will be raised 60 feet
G60 STUDIES OF LAND SUBSIDENCE

and seasonal fluctuation will be reduced to 10-20 feet, 

the rate of subsidence should be reduced substantially 

for two reasons. First, the rate of subsidence would be 

less even if water were not imported, because the rate of 

applied-stress increase has been decreasing and the delayed compaction rate has been decreasing exponentially. Secondly, a 60-foot water-level rise would eliminate excess pore pressures in some beds and would decrease the applied stress on those beds still having excess pore pressures. On the basis of many types of information available in December 1967, a postulated 

60-foot water-level rise by 1970 would result in maximum subsidence rates of only 0.3-0.4 ft yr" 1 , and large 

areas that were subsiding 0.2-0.4 ft yr" 1 between 1963 

and 1966 would be subsiding less than 0.2 ft yr" 1 . Water-level rises of 100-200 feet should eliminate or 

reduce subsidence rates to negligible amounts throughout the Los Banos-Kettleman City area.

REFERENCES

American Geological Institute, 1960, Glossary of geology and related 

sciences [2d ed.]: Washington, D.C., Am. Geol. Inst., Natl. Acad. 

Sci.-Natl. Research Council, 325 p. with 72 p. supp.

American Society of Civil Engineers, 1962, Nomenclature for hyraulics: Am. Soc. Civil Engineers, Manual and Repts. on Eng. 

Practice, no. 43, p. 85.

Bull, W. B., 1964, Alluvial fans and near-surface subsidence in western Fresno County, California: U.S. Geol. Survey Prof. Paper 

437-A, 71 p.

 1974, Land subsidence due to ground-water withdrawal in the 

Los Banos-Kettleman City area, California Part 2. Subsidence 

and compaction of the deposits: U.S. Geol. Survey Prof. Paper 

437-F,90p.

Bull, W. B., and Miller, R. E., 1974, Land subsidence due to groundwater withdrawal in the Los Banos-Kettleman City area, 

California Part 1. Changes in the hydrologic environment conducive to subsidence: U.S. Geol. Survey Prof. Paper 437-E, 71 p.

Croft, M. G., 1972, Subsurface geology of the late Tertiary and 

Quaternary water-bearing deposits of the southern part of the 

San Joaquin Valley, California: U.S. Geol. Survey Water-Supply 

Paper 1999-H, 29 p.

Davis, G. H., and Poland, J. F., 1957, Ground-water conditions in the 

Mendota-Huron area, Fresno and Kings Counties, California: 

U.S. Geol. Survey Water-Supply Paper 1360-G, 588 p.

Gibbs, H. J., 1959, A laboratory testing study of land subsidence: 

Pan-American Conf. Soil Mech. and Found. Eng., 1st, Mexico 

City 1959, Proc., v. 1, p. 13-36.

Jacob, C. E., 1940, On the flow of water in an elastic artesian aquifer: 

Am. Geophys. Union Trans., 21st Ann. Mtg., pt. 2, p. 574-586.

Johnson, A. I., 1967, Specific yield Compilation of specific yields for 

various materials: U.S. Geol. Survey Water-Supply Paper 

1662-D, 74 p.

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

hydrologic properties of water-bearing deposits in subsiding 

areas in central California: U.S. Geol. Survey Prof. Paper 497-A, 

71 p.

Kings River Water Association, 1953-62, Annual Water Master Reports: Reports on river discharge, canal diversions, and schedule

administration published in separate volumes for each water 

year.

Lofgren, B. E., 1960, Near-surface land subsidence in western San 

Joaquin Valley, California: Jour. Geophys. Research, v. 65, no. 3, 

p. 1053-1062.

 1961, Measurement of compaction of aquifer systems in areas 

of land subsidence, in Geological Survey research, 1961: U.S. 

Geol. Survey Prof. Paper 424-B, p. B49-B52.

 1968, Analysis of stresses causing land subsidence, in Geological Survey research 1968: U.S. Geol. Survey Prof. Paper 600-B, p. 

B219-B225. 

-1969, Land subsidence due to the application of water, in Varnes, D. J., and Kiersch, George, eds., Reviews in Engineering 

Geology, v. 2: Boulder, Colo., Geol. Soc. America, p. 271-303.

Lofgren, B. E., and Klausing, R. L., 1969, Land subsidence due to 

ground-water withdrawal, Tulare-Wasco area, California: U.S. 

Geol. Survey Prof. Paper 437-B, 103 p.

Lohman, S. W., and others, 1972, Definitions of selected ground-water 

terms revisions and conceptual refinements: U.S. Geol. Survey 

Water-Supply Paper 1988, 21 p.

Miller, R. E., 1961, Compaction of an aquifer system computed from 

consolidation tests and decline in head, in Geological Survey 

research 1961: U.S. Geol. Survey Prof. Paper 424-B, p. B54-B58.

Miller, R. E., Green, J. H., and Davis, G. H., 1971, Geology of the 

compacting deposits in the Los Banos-Kettleman City subsidence area, California: U.S. Geol. Survey Prof. Paper 497-E, 46 p.

Poland, J. F., 1961, The coefficient of storage in a region of major 

subsidence caused by compaction of an aquifer system, in Geological Survey research 1961: U.S. Geol. Survey Prof. Paper 424-B, 

p. B52-B54.

 1969a, Status of present knowledge and needs for additional 

research on compaction of aquifer systems, in Land Subsidence, v. 

1: Internat. Assoc. Sci. Hydrology Pub. 88, p. 11-21. 

-1969b, Land subsidence and aquifer-system compaction, Santa

Clara Valley, California, USA, in Land Subsidence, v. 1: Internat. Assoc. Sci. Hydrology Pub. 88, p. 285-292.

Poland, J. F., and Davis, G. H., 1969, Land subsidence due to withdrawal of fluids, in Varnes, D. J., and Kiersch, George, eds., 

Reviews in Engineering Geology, v. 2: Boulder, Colo., Geol. Soc. 

America, p. 187-269.

Poland, J. F., and Ireland, R. L., 1965, Shortening and protrusion of a 

well casing due to compaction of sediments in a subsiding area in 

California, in Geological Survey research 1965: U.S. Geol. Survey 

Prof. Paper 525-B, p. B180-B183.

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

terms useful in the studies of the mechanics of aquifer systems 

and land subsidence due to fluid withdrawal: U.S. Geol. Survey 

Water-Supply Paper 2025, 9 p.

Prokopovich, N. P., 1963, Hydrocompaction of soils along the San Luis 

Canal alignment, western Fresno County, California in Abstracts for 1962: Geol. Soc. America Spec. Paper 73, p. 60.

Prokopovich, N. P., and Hebert, D. J., 1968, Land subsidence alongthe 

Delta-Mendota Canal, California: Am. Water Works Assoc. 

Jour., v. 60, no. 8, p. 915-920.

Riley, F. S., 1969, Analysis of borehole extensometer data from central California, in Land Subsidence, v. 2: Internat. Assoc. Sci. 

Hydrology Pub. 89, p. 423-431.

Scott, R. F., 1963, Principles of soil mechanics: Palo Alto, Calif., 

Addison-Wesley Pub. Co., Inc., 550 p.

Taylor, D. W., 1948, Fundamentals of Soil Mechanics: New York, 

John Wiley & Sons, Inc., 700 p.

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practice: New York, John Wiley & Sons, Inc., 566 p.
INDEX

[Italic page numbers indicate major references]

A, B Page

Alluvial-fan deposits _____________ G6, 34, 57

Anticline Ridge ___________________ 8, 29

Applied stress change_______ 6, 13, 36, 37, 39, 44

relation to lower zone ________________ 42, 58

relation to lower-zone compaction _______ 27

relation to subsidence ______________ 43, 59

relation to water-level changes ______ 4, 27, 35

Yearout site _________________ 22

Applied stress computation_____________ 5, 7

Aquifer system, compaction ____________ 23,26

expansion ______________________ 23

pore-pressure decay prediction__________ 44

relation to lower zone compaction __________ 6

thickness, changes _________ 8, 17, 18, 22, 58 

relation to artesian-head changes ______ 11

unconfined ____________________ 4, 7

Aquitard ________________________ 11,35 

Aquitard permeability decrease __________ 44

Aquitard pore pressure _____________________ 23

Artesian-head change _____ 8, 11, 17, 27, 29, 53, 56 

Big Blue Hills _________________________ 29, 34, 35

Buoyancy effect _______________ 5, 8, 28, 57

California Aqueduct _______________ 35, 49, 59 

Canal water ____________________ 37,49, 59 

Cantua site _________ 4, 16, 44, 46, 47, 48, 57, 59 

Casing-cable friction _________ 14, 18, 23, 25, 27 

Clay deposits_____________ 6, 18, 36, 37, 57, 59 

Compaction _______ 11, 26, 43, 46, 47, 48, 54, 58 

cause _______________________ 4

Lemoore site ______________________ 18,21

mean daily rate __________________ 44,46,47

measurement _________ 14, 17, 23, 24, 49, 59 

Lemoore site ________________________ 18

Yearout site ______________________ 22

relation to aquitards _______________ 35,44

relation to artesian-head change__________ 17

relation to Corcoran Clay Member of the

Tulare Formation_______ _____ 29 

relation to lower-zone aquifer system ______ 6, 29

relation to water-level fluctuation _______ 13

Compaction recorder, mechanical lag________ 22

Compression _ _ _ _ _ _ _ _ _ _ ______ _ _ 12

Confined aquifer system _________ 4, 5, 6, 7, 18

Consolidation coefficient ________________ 36

Consolidation tests __________________________ 49

Corcoran Clay Member of the Tulare

Formation ______ 8, 15, 18, 21, 29, 49

D, E, F

Damage from subsidence _______________ 35

Definition of terms ______ _ _ _ _ __ _ ______ 2

Delayed compaction _____ _ 23, 41, 43, 44, 54, 58 

Delayed expansion __________________ 21,58

Delivery of canal water ________________________ 50

Delta-Mendota Canal __________ 11, 34, 50, 59

Diablo flood-plain deposits_____________ ____ 57

Diablo Range__________________ _____ 56 

Effective stress ___________________ 13,35

Elastic change, relation to aquifer-system

thickness ________________ Gil 

Elastic compaction _______ 15, 17, 23, 26, 39, 58

Lemoore site ___________________________ 19

Yearout site _____________________ 22 

Elastic compression,_____________________ 13

Elastic expansion_____ 13, 15, 16, 17, 23, 54, 56, 58

Yearout site _____________________ 22 

Elastic specific unit compaction __________ 15

Electric log ______________________ 18, 27 

Equipment __________ 11, 14, 16, 17, 23, 25, 27 

Etchegoin Formation.___________________ 34, 35, 57

Expansion ________________________ 17, 23

measurement _____________ 17, 23, 25, 27 

Lemoore site _______ ______ 21

Yearout site __________________ 22 

Expansion of water _ __ _ _ ___ _ _ _____ _ 12

Five Points ___________ _____________ 10, 29

Flood-plain deposits______________ 34

Fresno Slough _____________________ 8, 29

G, H

Gravitational stress______________________ 7

Ground-water pumpage costs _______________ 37

Head changes _____________________ 7

Head decline ______________ 8, 34, 37, 57, 59 

Head decline/subsidence ratio ________ 9, 39, 43

Head increase_____________________________ 54, 58

Huron ____________________._________ 11

Hydraulic diffusivity __________________ 36

Hydraulic head dissipation _____________ 4

Hydrodynamic theory of soil consolidation ______ 18

Hydrographs ______________________ 9

I, K, L

Inelastic change, relation to aquifer-system

thickness _____________ 11

Inelastic compaction __________________ 13,23,39,58

Lemoore site _____________________ 21

Kettleman Hills _____________________ 34 

Klausing, R. L., quoted ______________________ 5

Lacustrine deposits ___________________ 34, 49

Lemoore __________________________ 53, 59

Lemoore site __________________ 15, 18, 58

Lofgren, B. E., quoted________________ 5

Los Banos-Kettleman City area, compaction _ ___ 4

location _____________________ 2

Lower zone, aquifer system ______________ 5

aquitards _______________________ 49

artesian head ____________________ 11, 54

compaction-related applied-stress change ____ 27 

deposits __________________ 57, 58

bedding _______________________ 48

head decline __________________ 37,38

potentiometric level_________________ 44

water-level change ________________ 16

Lower-zone applied-stress/subsidence ratio ______ 39

M, N, O, P

Mendota__-______________ ________ 8, 10

Mendota site ________________ 14, 15, 44, 47, 48

Neutral pressure ________________________ 7

Page 

Neutral stress __________________ G58

Oro Loma site___________ 11, 14, 44, 47, 48, 49 

Peck, R. B., quoted ___________________ 34 

Pine Flat Dam __________________ 53,59

Pore pressure _____________________________ 21

relation to aquifers and

aquitards ___ 17, 35, 36, 40,44, 58, 59 

Pore pressure decay, relation to effective stress __ 6 

Potentiometric level______________ 7, 54, 56

lower zone ___________ _ _____ 44

Preconsolidation stress _____________________ 36

Predicted compaction __ ___ ____ 48,54 

Predicted subsidence_______ 35, 37, 50, 54, 59, 60 

Previous work ___________________ 2

Protrusion of casing ______________________ 23

Pumpage costs of ground water ____________ 37

R,S

Rate, applied-stress increase __________ 39, 42, 43

compaction__ 15,16,17,23,44,46,47,48,49,54, 58 

elastic change __________________ 21

expansion _______________ 15, 16, 17, 23 

Lemoore site ____________________ 21

pore-pressure change ______ _ _________ 40, 47

subsidence ________ 37, 50, 52, 53, 54, 56, 57, 59

Recharge.________________________________ 34

Recorder mechanics_______ _________ 25

Residual compaction________ _____ 49, 59

Residual excess pore pressure ____________ 11,23

San Joaquin Valley __ ________________ 2

San Luis Canal __________________ 35,49,59

Santa Clara Valley ____________________ 49

Saturated deposits ___________ _______ 5, 27

Seasonal head decline_____________________ 34

Seepage force __________________ 4, 8, 27, 57 

Sierra flood-plain deposits ___ _____ _ 57

Sierra sands and silts ________________ _____ 21

Specific compaction_____________ 27, 32, 33, 34

Specific gravity__________________________ 5

Specific retention __________________ 5,6

Specific subsidence ___ ____ _ ___ 39 

Specific unit compaction ____________ 27,29,34

Specific unit expansion _____ 15, 19, 21, 27, 56, 58 

Yearout site ______________ ________ 22

Specific yield ____________________________ 6

Steady-state pore pressure ______________ 36, 47

Storage coefficient _______________ 11, 13, 39 

Stratford___________________________ 59

Stress changes ______________________ 4

Stress increase/subsidence ratio ___________ 44

Stress-strain plot _____________ __ 18,19,34 

Study area ________________ ______ 2 

Subsidence_________________________ 8, 29

after delivery of canal water.____________ 49

alleviation ____________________________ 52, 53

before delivery of canal water ______ 37,50

future ________________ 35, 50, 54, 59, 60

Subsidence/head-decline ratio _________ 9, 39, 43 

Subsidence/lower-zone applied-stress ratio_______ 39

Subsidence rate ____ 37, 50, 52, 53, 54, 56, 57, 59 

Subsidence/stress increase ratio ________ 44

Surface-water deliveries-_______________ 56

Surface-water imports _________ 50, 53, 54, 59

G61
G62 INDEX

T, U, V Page 

Terzaghi, Karl, quoted _______________ G34

Timelag of compaction._____________ 35, 58

Total applied stress _________________ 29

Tulare Lake bed _____________________ 34 

Ultimate compaction _________________ 36, 48

Unsaturated deposits_________________ 6, 7, 27

Upper-zone head decline ______________ 37

Virgin compaction ______ 11, 15, 16, 21, 23, 43, 58

W, Y ec

Water-table change _____ G6, 7, 27, 28, 29, 39, 56 

relation to applied stress _______ 4,27,35 

relation to aquifer-system thickness ____ 8, 23

relation to compaction _________ 13, 23, 54, 57

relation to expansion ________________ 27

relation to pumping ___________ 17, 57

relation to subsidence ________________ 8, 60

Water-level fluctuations, Lemoore site _______ G18

Yearout site _____________________ 22

Well casing rupture__________________ 16

Well construction______ ____________ 22

Westhaven ______________________ 11,43 

Westhaven site _____________ 17, 44, 46, 47, 48 

Yearout site _____________________ 22, 58

U.S.GOVERNMENT PRINTING OFFICE:1975-0-689-905/13