Specific Yield 

Compilation of Specific 

Yields for Various 

Materials

By A. I. JOHNSON

HYDROLOGIC PROPERTIES OF EARTH MATERIALS

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1662-D

Prepared in cooperation with the 

California Department of 

ff^ater Resources

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1967
U.S. DEPARTMENT OF THE INTERIOF 

MANUEL LUJAN, Jr., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

First printing 1967 

Second printing 1976 

Third printing 1992

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government

For sale by the Books and Open-File Reports Section 

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

Page

Abstract___..__...._...._.....__..........__...._.._..__. Dl

Introduction __-__-____--__-____.____----_----__.--_-___-____..-__-- 1

Purpose and scope..----------------___---__-_---__---_-____--_ 1

Definition of terms._-_--_----__-_-_-_-_--__-_---__-_----_--__. 2

Acknowledgments ___-_-__---__-_-------_-------.-----__---_--. 3

Some factors affecting specific yield.___--_-_---_-------------__--_--_ 3

Methods of determining specific yield_-_-____---__-__-___-_---____--_ 5

Laboratory methods.___-_-___-__---_____-_-____---_--_-__-____ 5

Sample saturation and drainage._____________-_-_---_-.___-_ 5

Correlation with particle size. -_____--_---_.--_-____-____-__ 7

Centrifuge-moisture equivalent--___-__-_----_--__-----___-__ 7

Moisture-tension techniques._-_--_-------__-__----___-____ 9

Field methods__-__-__--________-_-___----___--_-__-____-____ 11

Field saturation and drainage. _-___-_ x_ _____________________ 11

Sampling after lowering of water table.--_____.___-_..._-____ 11

Pumping method...______.____._..____._.._..._.___.___.__ 12

Recharge method___-___--_--______-. .__.....__._.____._ 13

Review ol literature.____--.-_-__-_----_-_.----_------------.____._ 14

Summary . _--______._.___--__.___--__._--.____________.._______ 68

References cited_______________ ._._._...___-..___-._._-.._.__..__ 71

ILLUSTRATIONS

Page 

FIGURE 1. Soil-classification triangle showing relation between particle

size and specific yield._..__._--____-_____-._.___ ..__ D8 

2-7. Graphs showing 

2. Relation of moisture equivalent to specific retention. 10

3. Porosity, specific retention, and specific yield for

sediments of the South Coastal Basin, Calif. _... 22

4. Relation of porosity to depth in certain types of 

sedimentary materials of the South Coastal Barm, 

Calif.....--.--.----.-.--....-..-.-..._._--. 24

5. Relation between texture and specific yield of naterials that were drained for approximately 100 

days---------------__--_-----_-_-_---_----- 29

6. Relation between moisture equivalent and specific 

retention of water-bearing materials that wire 

drained for 50-400 days.........._.._.._._... 30

7. Variation of specific yield in relation to durat'on 

of pumping for a pumping test at Grand Island, 

Nebr.--.----..-.-....-----..-..-..-......-. 31

in
IV CONTENTS

Page 

FIGURE 8. Map showing ground-water storage units of Sacrarrento

Valley, Calif_._____....__.____._....._._..._.. ._ D34

9-17. Graphs:

9. Textural features and hydrologic properties of the 

dominant unweathered sediments in the groundwater reservoir of the Friant-Kern Canal service 

area. ______________________________________ 39

10. Mechanical-analysis data and hydrologic properties 

of four representative course and medium sands 

in the ground-water reservoir of the Friant-Kern 

Canal service area___________________________ 40

11. Mechanical-analysis data and hydrologic properties 

of five representative fine sands and silty s«nds 

in the ground-water reservoir of the Friant-Kern 

Canal service area-___--______-_----_-_-_---_ 41

12. Mechanical-analysis data and hydrologic properties 

of seven representative silts and clays in the 

ground-water reservoir of the Friant-Kern Canal 

service area__--__----_---_---_- .___._.___-__ 42

13. Grade-size distribution of cored samples from the

Tia Juana Basin, Calif_______-___-_-------_-_- 44

14. Porosity, specific yield, and specific retention of sediments from the Tia Juana Basin, Calif__________ 46

15. Distribution and specific yield of sediments froir the

Tia Juana Basin, Calif__.-____-____-________ 47

16. Relation of specific retention to sorting coefficient in 

alluvium of the Little Bighorn River valley, 

Montana.__________________________________ 59

17. Relation of specific yield to particle size for sediments sampled at Rechna Doab, West Pakistan. 63

18. Map showing specific yield of sediments of Rechna Eoab,

West Pakistan_____________________________ ._._____ 64

19. Graph showing colinear plot of Dgo to specific yield for various values of porosity.______________________________ 69

TABLES

Page 

TABLE 1. Quantity of water retained and given up by different s^nds

that were drained for 2J^ years-______________________ D15

2-29. Specific yield:

2. Alluvial deposits in the Morgan Hill area, S T nta

Clara Valley, Calif________-__-_-_-_-_------_._ 15

3. Valley-fill materials in San Diego County, Calif 16

4. Water-bearing materials in the Mokelumne area,

near Lodi, Calif__________________-__-__-_ 18

5. Unconsolidated sediments in the Escalante Valley,

Utah__-____________________-____--------.- 20
CONTENTS V

TABLK 2-29. Specific yield Continued Page

6. Estimated values for sediments of the South Ciastal

Basin, Calif..____________________________ D21

7. Water-bearing sediments in the Platte River valley,

Nebraska_ .^............................... 26

8. Water-bearing sediments of the Mokelumne area,

California__ ..-..^......................... 31

9. Water-bearing sediments in the Sacramento Valley,

Calif...----- --- --_----- - __- - 33

10. Water-bearing sediments in the Lompoc plain,

Santa Barbara County, Calif._---_----__.-__. 36

11. (Effective porosity) of core samples from Bureau of 

Reclamation test holes in the Friant-Kern Canal 

service area, as determined from measured porosities and moisture equivalents._________________ 36

12. Water-bearing sediments in Santa Margarita Valley,

Calif-..------------------.--------.--------- 37

13. Sediments in Ventura County, Calif_____-__--_._-- 43

14. Values for the various lithologic materials used in 

estimating ground-water storage on the Smith 

River plain, California.____-____--_____--____ 43

15. Water-bearing sediments in Tia Juana Basin, Calif __ 46

16. Water-bearing sediments in San Luis Obispo County,

Calif.--------.-----....--..--.----.----.--. 48

17. Water-bearing sediments in the San Joaquin Valley,

Calif-----..-.------.---_.-------.----------- 49

18. Alluvial deposits of the Eel, Van Duzen, and1 Mad

Rivers, Humboldt County, Calif _-_____ _ 54

19. Sediments from Beaverdam Creek basin, Maryland 55

20. Alluvial deposits of the Santa Ynez River basin,

California. _ __-__ __ -_____-_ __-_-___- 56

21. Alluvium in Napa and Sonoma Valleys, Calif------ 57

22. Unconsolidated materials in the Little BVhorn

River valley, Montana._______________________ 58

23. Used to estimate total ground-water storage caoacity

in the Putah area, California. ._____ _______ _ 60

24. Values used in coastal plain of Los Angeles County,

Calif ---- - ----------------- 62

25. Alluvium from Rechna Doab, West Pakistan__ __ 63

26. Water-bearing sediments in the Sacramento valley,

Calif .-- --__--_----_----_----__--- 65

27. Alluvial deposits in the Humboldt River valley,

Humboldt County, Nev__.___._-___-____-.___. 66

28. Unconsolidated alluvium___-___--__-__-_____.__- 68

29. Compilation of specific yields for various materials. 70
HYDROLOGIC PROPERTIES OF EARTH MATERIALS

SPECIFIC YIELD COMPILATION OF SPECIFIC YIELDS 

FOR VARIOUS MATERIALS

By A. I. JOHNSON

ABSTRACT

Specific yield is defined as the ratio of (1) the volume of water that a srturated 

rock or soil will yield by gravity to (2) the total volume of the rock or soil. 

Specific yield is usually expressed as a percentage. The value is not definitive, 

because the quantity of water that will drain by gravity depends on variables 

such as duration of drainage, temperature, mineral composition of the water, 

and various physical characteristics of the rock or soil under consideration. 

Values of specific yield, nevertheless, offer a convenient means by which hydrologists can estimate the water-yielding capacities of earth materials and, as such, 

are very useful in hydrologic studies.

The present report consists mostly of direct or modified quotations from many 

selected reports that present and evaluate methods for determining specific 

yield, limitations of those methods, and results of the determinations made on a 

wide variety of rock and soil materials. Although no particular values are recommended in this report, a table summarizes values of specific yield, and their 

averages, determined for 10 rock textures. The following is an abstract of the 

table:

Specific yields, in percent, of various materials 

[Rounded to nearest whole percent]

Number of _______Specific yield______

Material determination* Maximum Minimum Average 

Clay.----..-----.---.------.-- 15 5 0 2

Silt_------------------_------- 16 19 3 8

Sandy clay....__________ 12 12 3 7

Fine sand__. ___. ______ 17 28 10 21 

Medium sand____. __ ___ 17 32 15 26 

Coarse sand____...__..__ 17 35 20 27 

Gravelly sand......__--__--._-- 15 35 20 25

Fine gravel-______--._.___ 17 35 21 25 

Mediumgravel ------------ 14 26 13 23

Coarse gravel.__.___.__.. 14 26 12 22

INTRODUCTION 

PURPOSE AND SCOPE

The purpose of this report is to assist hydrologists in estimating the 

quantity of water in storage in ground-water reservoirs by providing

Dl
D2 HYDROLOGIC PEOPEETIES OF EARTH MATERIALS

a compilation of specific yields representative of a variety of aquifer 

materials. The data presented here were compiled from prblished reports which have presented specific yields in relation to the texture 

of rock and soil materials. No attempt is made to evaluate the specificyield data, but a table summarizes the published values f -»r the convenience of the reader.

Not all specific yields from all published reports are listed in this 

report. However, this report does present a representative cross section of the publications noted as a result of rather lengthy library 

research. Along with pertinent tables or illustrations of data on specific yield, those parts of the text describing special methodology or 

the limitations of the data are quoted directly from each publication. 

Also presented are brief descriptions of all laboratory and field methods for determining specific yield and specific retention, to assist the 

reader in understanding the data compiled herein.

This report was prepared as a part of the specific-yieM research 

studies made by the U.S. Geological Survey in cooperation with the 

California Department of Water Eesources. The research testing was 

done at the Hydrologic Laboratory of the U.S. Geological Survey at 

Denver, Colo. The project was under the general supervision of Fred 

Kunkel, then district geologist of the Ground Water Branch of the 

Survey, Sacramento, Calif., and was under the direct supervision of 

A. I. Johnson, chief of the Hydrologic Laboratory.

DEFINITION OF TERMS

Most rock or soil materials contain interstices, or void peaces. The 

space commonly is described quantitatively by a property known as 

porosity. Porosity is defined by the American Society for Testing and 

Materials (1961) as the ratio, usually expressed as a percentage, of the 

volume of voids of a given soil mass to the total volume of the soil 

mass. For all practical purposes, ground water fills all void spaces 

in the saturated zone. From the previous definition, therefore, it follows that porosity is a measure of the quantity of water contained per 

unit volume (Todd, 1959).

Not all water contained in the saturated zone can be removed from 

the rock or soil by drainage or by pumping wells. Gravity ground 

water is that part of the water that will drain by gravity s.nd thus be 

available to wells. That part of the water retained by modular and 

surface tension forces in the void spaces of the rock and soil materials 

usually is known as retained water. The water-yielding capacity and 

water-retaining capacity of rock or soil materials are knowr as specific 

yield and specific retention. The specific yield plus the specific retention of a rock or soil is equal to the porosity of the rock or soil.
COMPILATION OF SPECIFIC YIELDS D3

Meinzer (1923a, p. 28) defined the specific yield (<av ) of a rock or 

soil, with respect to water, as the ratio of the volume of water that 

will drain by gravity from a saturated rock to the total volume of the 

rock, This ratio usually is expressed as a percentage.

Because specific yield represents the void space that will jdeld water 

to wells and is effective in furnishing water supplies, it is # Iso known 

as effective porosity. However, because of the possible confusion with 

similar terms with slightly different meanings used by soil scientists 

(who also occasionally call it "noncapillary porosity") anc1 by petroleum geologists, the term "specific yield" is preferred by the author 

and is used in this report exclusively.

The specific retention (wr) of a rock or soil, with respect to water, 

has been defined by Meinzer (1923a, p. 28) as the ratio tl at will be 

retained against gravity drainage from a saturated rock to the total 

volume of the rock. It usually is expressed as a percentage. Soil scientists and engineers use a similar measure called "water-holding 

capacity," but it is expressed as a percentage of the dry weight rather 

than of the volume. Water-holding capacity is defined (Am. Soc. Testing Materials, 1961, p. 1418) as "the smallest value to which the water 

content of a soil can be reduced by gravity drainage." The waterholding capacity can be converted to specific retention by multiplying 

by the dry unit weight of the rock or soil and then dividing by the 

unit weight of the water.

ACKNOWLEDGMENTS

Valuable information on publications suitable for this r^rcort was 

provided by Robert T. Bean, Hal C. Hanson, Helen J. Peters, and 

Raymond Richter of the California Department of Water Resources, 

and by Joseph F. Poland, U.S. Geological Survey, all of Sacramento, 

Calif. Their assistance is gratefully acknowledged.

SOME FACTORS AFFECTING SPECIFIC YIELD

Meinzer (1923b, p. 52) indicated that the distinction between gravity water and retained water is not definitive, because the quantity 

of water that will drain from a rock or soil material depends on the 

length of time the rock or soil is allowed to drain, on the temperature 

and the mineral composition of the water both of which affect its 

surface tension, viscosity, and specific gravity and on various physical characteristics of the rock or soil under consideration. He noted 

(1923a, p. 29), for example, that a smaller proportion of water will 

drain from a short sample than from a long sample of the same mate 

rial because a larger proportion of the short sample will regain sat-
D4 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

urated as part of the capillary fringe. Meinzer pointed out that 

methods for determining specific yield have been so little standardized 

that specific-yield data always should be accompanied by r. statement 

indicating the methods used and, particularly, the size of rample and 

the period of draining under consideration.

The quantity of water yielded to wells from a body of saturated rock 

or soil thus depends upon the specific yield of the rock or soil and not 

upon its porosity. For example, the specific yield is 8 percent if a volume of saturated rock 10 feet thick and 100 feet square (100,000 cu ft) 

will supply 60,000 gallons (8,000 cu ft) of water when drained by 

pumping wells. If the rock still retains a total of 13,000 cubic feet of 

water in its void spaces after drainage, its specific retention would be 

13 percent and its porosity would be 21 percent (8 +IS). Certain 

materials, such as clay, have high porosities and, thus, are capable of 

holding large quantities of water but yield only a small part of it 

under gravity drainage, even after a long period of time; consequently, 

these materials usually are worthless as aquifers.

The effect of duration of drainage upon specific yield has been noted 

by a number of hydrologists. Meinzer (1923b, p. 65) statec1 that most 

of the gravity water in a rock or soil material is yielded e^.rly in the 

drainage cycle but that there is apparently almost no limit to the 

duration that the slow draining will continue. He noted that finetextured materials not only yield less water than coarse-textured materials but also yield it more slowly. He also indicated that, for most 

water-bearing materials, the volume of water drained by the rapid 

lowering of the water table in the immediate vicinity of a heavily 

pumped well is definitely much less than the total that would" be yielded 

by long-term draining, but that the draining that accompanies the 

annual fluctuation of the water table is virtually complete.

Williams and Lohman (1949, p. 213, 220) stated that the true value 

of specific yield is obtained only after the saturated material has been 

drained for a long period of time. Using pumping-test methods in the 

field, the above authors concluded that their laboratory determination 

of about 25 percent specific yield were probably correct ard that the 

apparent specific yield of 15 percent obtained near the beginning of 

the pumping period would have increased to about 19 percent by the 

end of the second year of pumping and probably would have reached 

the true value of 25 percent sometime during the third year of pumping. A report by Prill, Johnson, and Morris (1965, p. 51) presents 

quantitative information on the phenomenon of time-of-drainage effects on specific yield, as determined by laboratory drainage of long 

columns of material. These authors concluded that, even for sand-size 

materials, a period of 2 months to more than 1 year would b^ required
COMPILATION OF SPECIFIC YIELDS D5

for the drainage to reach equilibrium and, thus, give the maximum 

specific yield.

METHODS OF DETERMINING SPECIFIC YIELD

The specific yield of the rock or soil materials composing the zone 

of water-table fluctuation must be determined in order to estimate the 

available water supply represented by each increment of ris^ in the 

water table during a period of recharge. The specific yielc1 is also 

needed to estimate the water supply obtainable from the materials for 

each increment that the water table is lowered. Although most field 

methods determine specific yield directly, most laboratory methods 

determine specific retention, and specific yield is found indirectly by 

subtracting the specific retention from the porosity.

Todd (1959, p. 24) stated that all methods have limitations laboratory samples may be disturbed or may not be representative. The 

measurement and control of variables in field tests is difficult and many 

estimates lack accuracy.

Tolman (1937, p. 482) noted that "perhaps the greatest difficulty in 

the application of quantitative methods' lies in the variability in the 

texture and hence in the hydrologic properties of the water-bearing 

materials. The hydrologic properties vary greatly, even with apparently slight differences in texture. Hence the ordinary geologic descriptions are quite inadequate for hydrologic purposes, and quantitative descriptions based on laboratory determinations have become essential."

During the past 6 or 7 decades, a number of laboratory and field 

methods have been developed for the determination of specific yield 

or specific retention. However, from the early 1900's until th*. writer 

started the specific-yield research project discussed in the report by 

Johnson, Morris, and Prill (1961), little work had been done by hydrologists in this country to determine specific yield by laboratory 

methods. To assist the reader in understanding the data compiled in 

this report, the various laboratory and field methods for determining 

specific yield are summarized briefly in the following paragraphs. 

(Also see Meinzer, 1923b, p. 53-76.)

LABORATORY METHODS 

SAMPIJ3J SATURATION AND DRAINAGE

The method of sample saturation and drainage consists of draining 

columns of saturated materials by gravity and determining both the 

volume of material drained and the volume of water yielded. The volume of water yielded can be measured directly or can be computed 

from the porosity and the moisture content after draining, but the
D6 HYDEOLOGIC PROPERTIES OF EARTH MATEBIALS

columns must be long enough to avoid having an undue percentage of 

the column occupied by the capillary fringe. Meinzer (1932, p. 114) 

pointed out that care must be taken to prevent loss by evs t>oration and 

that the tests must be made at a uniform temperature or corrections 

for temperature variations must be applied. Because drainage continues for a long time at a diminishing rate, Meinzer al^o noted that 

the specific yield should be determined for specific periods of drainage.

As early as 1892 Hazen studied the water-retaining and wateryielding capacities of filter sands as related to their particle size. By 

alternately saturating and draining different-size sands, he found that 

the amount of water retained after the sand had drainec1 increased as 

the particle size decreased. He found that the percentage of water retained by the fine materials was greater in the lower part of the bed 

than in the upper part. He explained this by stating th^t the height 

to which capillary attraction was effective was in inverse proportion 

to the square of the effective size of particles.

King (1899) published results of tests of the water-yielding and 

water-retaining capacities of five different sizes of sand. Five galvanized-iron cylinders 8 feet long and 5 inches in diameter were filled 

with sand, and water was introduced at the bottom of each cylinder 

until the sand was saturated. The columns were then allowed to drain 

for a period of 21/2 years. Discharged water was measured or weighed 

at frequent intervals initially, and later only every few days, weeks, 

or months. At the conclusion of the tests, the quantity of water remaining in each 3-inch-thick layer of sand was determined. The results of King's tests showed discrepancies of about 5-7 percent between the porosity (representing the total water content possible under 

saturated conditions) and the total quantity of water accounted for. 

King's tests seemed to give lower values for specific retention than 

Hazen's tests, especially for the coarser samples.

Meinzer (1923b, p. 57) stated that the results obtained by Hazen 

and King are inadequate and cannot be used as a reliable basis for 

very definite conclusions as to water-yielding capacity. He concluded 

that many more tests of the same sort obviously were nQ«ded.

More recently, Johnson, Prill, and Morris (1963) made a detailed 

study of the column-drainage method and determined many of the 

factors affecting specific yield as determined by this method.

After a standard method was developed for packing columns of 

porous media (Morris and Kulp, 1961), the research determined that 

the column diameter (1- to 8-in.) made little difference ir the moisture 

distribution after drainage, that the drainage characteristics made 

little difference when the media were cleaned with acid, r.nd that similar results were obtained no matter what procedure was used for satu-
COMPILATION OF SPECIFIC YIELDS D7

rating the media. The distribution of moisture after drainage was similar when any one of four designs of column was used for the tests. 

Later research (Prill, Johnson, and Morris, 1965) studied the effect 

of time on column drainage and concluded that even for the sand-size 

materials used in the study, a very long time would be required to 

reach drainage equilibrium.

CORRELATION WITH PARTICLE SIZ(B

Particle-size analysis can be considered as one method of estimating 

specific yield. By determining the specific retention by some other 

method and the effective size, or median diameter, by particle-size 

analysis, the relation of the two can be graphically represented by a 

curve (Meinzer, 1923b, p. 64). By determining the effective size, or 

median diameter, of a sample and referring to the curve, the approximate specific retention can be obtained. After determining the porosity, the specific yield can then be obtained, as mentioned before. 

Probably, at best, this method represents a speedy but only approximate means for estimating specific yield.

Briggs and Shantz (1912, p. 72) determined the water-holding 

capacity by interpreting particle-size analyses and developed the 

following equation: Water-holding capacity = (0.03 sand + 0.35 

silt -I- 1.65 clay) -I- 21, where the water-holding capacity and the sand, 

silt, and clay are expressed as percentages of the weight of the dry 

sample. Middleton (1920, p. 160) developed several similar equations 

which appeared to provide more precise relations than those of Briggs 

and Shantz.

As a part of the specific-yield-research study discussed earlier, Prill 

and Johnson (unpub. data, 1966) developed a relation between specific yield and soil texture for samples from the San Joaquin and 

Antelope Valleys, Calif. The data are shown by lines of equal specific 

yield on a trilinear graph of textural classification (fig. 1). The 

specific yields were determined by both laboratory and field methods, 

and the textural classes were determined by particle-size analysis 

of samples.

CENTRIFTJOB-MOISTURJB EQUIVALENT

Specific yield can also be estimated from the centrifuge-moisture 

equivalent. The latter is defined as the moisture content of a soil after 

it has been saturated with water and then subjected for 1 hour to a 

force equal to 1,000 times that of gravity (Am. Soc. Testing Materials, 

1961, p. 1404). The centrifuge-moisture equivalent is multiplied by 

the dry unit weight of the soil and divided by the unit weight of water 

to obtain the moisture equivalent, expressed as a percentage of the 

volume.
D8 HYDKOLOGIC PROPERTIES OF EARTH MATERIALS

EXPLANATION

Line of equal specific yield 

Interval 1 and 5 percent

PARTICLE SIZE, IN MILLIMETERS 

Sand 2-0.0625 

Silt 0.0625-0.004 

Clay <0.004

10

S <§> <§> 

SILT SIZE. IN PERCENT

<§> <§>

FIGURE 1. Soil-classification triangle showing relation between particle size and specific

yield.

The concept of moisture equivalent was introduced by Briggs and 

McLane (1907) by determinations made on more than 100 soils of the 

moisture retained under a centrifugal force 3,000 times the force of 

gravity. Stearns (1927) pointed out that the moisture-equivalent 

method is based on the theory of applying a centrifugal force great 

enough to reduce the capillary fringe enough that it can be ignored 

without introducing much error, even in small samples, and yet not 

so great as to withdraw a large proportion of the water that is held 

more securely above the capillary fringe. Stearns noted that if a 

material will lift water 100 inches by capillarity acting against gravity, the material will theoretically be able to hold the water only 0.1 

inch against a centrifugal force that is 1,000 times greater than the 

force of gravity. Prill (1961) discussed this relation in more detail 

and pointed out that water retention after centrifuging is comparable 

to that obtained by gravity drainage of long columns.

Briggs and McLane (1907) made their early determinations under 

a centrifugal force of 3,000 times gravity, but in a later publication 

Briggs (1910) suggested that a force 1,000 times gravity could be used.
COMPILATION OF SPECIFIC YIELDS D9

In 1912 Briggs and Shantz conducted moisture-equivalent tests 

employing a force 1,000 times gravity, and since then, that force has 

been accepted as standard by most investigators, including the U.S. 

Bureau of Public Roads (1942), American Society for Testing and 

Materials (1961), and American Association of State Highway Officials (1942). However, many studies have been made since 1912 

concerning the relation of many other factors to the moisture equivalent obtained.

Considerable experimental work has indicated that for at least 

some medium-textured materials the moisture equivalent approximately equals specific retention. Israelson (1918) stated that correlations between the moisture equivalent and the water retention 

after irrigation closely correspond. In 1933 Piper determined a relation (fig. 2) between centrifuge-moisture equivalent and specific 

retention, as determined by the field drainage of long columns of 

various materials. Since that time, the centrifuge-moisture equivalent, 

as a percentage of the volume, has been adjusted to specific retention 

by multiplying by the ratio-correction factor determined by Piper 

(1933). This value is then subtracted from the porosity to obtain the 

specific yield.

In 1963 Johnson, Prill, and Morris reported a detailed study of 

the centrifuge-moisture-equivalent method. This research showed, for 

example, that the effect of temperature was of sufficient magnitude to 

warrant establishment of a standard temperature for the test (Prill 

and Johnson, 1959). Since 1959, centrifuge-moisture equivalents determined by the Hydrologic Laboratory have been made at a constant 

temperature of 20°C., and the American Society for Testing and 

Materials now (1966) has adopted this temperature as their standard 

for the test. (Prill and Johnson, 1966).

MOISTURE-TENSION TECHNIQUES

Moisture tension has been defined as the equivalent negative gage 

pressure, or suction, in the soil moisture. It is equal to the equivalent 

negative pressure to which water must be subjected to be in hydraulic 

equilibrium through a porous permeable plate or membrane with 

the water in the soil.

For tensions less than one atmosphere, the moisture-tension relations are determined by porous-plate apparatus consisting of a lightduty pressure chamber in which porous ceramic plates are installed. 

An air compressor maintains the air within the pressure chamber at 

a value equivalent to a given tension force.

Duplicate samples of the soil, retained in ^-inch-high plrstic rings, 

are placed on the porous plates in the pressure chamber and are al-
D10 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

SPECIFIC RETENTION ((?), IN PERCENT OF DRY WEIGHT

1.0 1.5 2.0 2.5 

SPECIFIC RETENTION (ft) 

MOISTURE EQUIVALENT (M)

FIGURE 2. Relation of moisture equivalent to specific retention. (After Piper, 1933.)

lowed to saturate by capillary action. The samples are subjected to 

a pressure equivalent to the desired tension until the water outflow 

from the pressure chamber has attained equilibrium. The samples are 

then removed from the pressure chamber, and the moisture content, 

by weight, is determined.

The moisture content at y10- to % -atmosphere tension has been 

considered as approximately equivalent to the field capacity 

(Coleman, 1947; Richards and Weaver, 1944), which if converted 

to moisture content by volume, would approximate specific retention. 

Prill and Johnson (1967) investigated moisture-tension techniques 

in detail in the interest of applying these techniques to the routine 

determination of specfic retention. They found, for example, that the
COMPILATION OF SPECIFIC YIELDS Dll

moisture distribution in porous media as determined by moisturetension techniques was comparable to that determined by gravity 

drainage of long columns.

Petroleum-reservoir engineers have used a mercury-injection method 

(Purcell, 1949) to determine the variation of capillary pressures (somewhat similar to moisture tensions) above the water table. The Hydrologic Laboratory currently is studying the adaptability of this method 

to the estimation of specific retention and specific yield.

FIELD METHODS 

FIEUUD SATURATION ANI> DRAINAGE

The field saturation and drainage method is similar in principle 

to the laboratory method. Meinzer (1932, p. 115) indicated that a plot 

of land should be selected where the water table and capillary fringe 

are at sufficient depth below the surface to permit gravity drainage. 

The material underlying the plot should then be thoroughly wetted and 

allowed to drain, and care should be taken to avoid all possible evaporation. After a sufficient period of drainage, samples are taken for determination of moisture content and porosity, and the specific yield is 

computed as the difference between these two.

Israelson (1918) conducted a series of field tests of the water-retaining capacities of different-type soils in Sacramento Valley, Calif. His 

method was to determine the porosity of the different soil? and their 

water content at successive depths immediately before irrigation and 

again about 4 days after irrigation. This second determination gave 

the approximate specific retention to be expected in a limited drainage 

time.

SAMPLING AFTER IA>WERING OF WATER TABUT,

After appreciable lowering of the water table, sample are collected from the zone immediately above the capillary fringe. The moisture content and porosity of the samples are determined, and the 

specific retention and specific yield are calculated. Meinzer (1932, p. 

116) cautioned that, when making tests of this kind, it is essential to 

ascertain that the part of the deposit from which the sample is taken 

has not received any recent contribution of water from rain or irrigation, or that it has not been exposed to evaporation or to absorption by 

plants both of which consume water that is retained against gravity 

by molecular attraction.

Experiments were made by Lee (Ellis and Lee, 1919) on samples 

of fill from the major stream valleys of San Diego County, Calif. His 

method was to collect samples immediately above the capillary fringe 

after the water table had been appreciably lowered, as commonly hap-
D12 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

pens in summer and autumn. Johnson and Kunkel (1963) discussed the 

results of this method in conjunction with moisture-content determination by nuclear meter, to determine the specific yield in tl Q- area of 

water-table lowering in the immediate vicinity of a large well field 

near Fresno, Calif. They found that the moisture distribution determined by this field method could be closely reproduced by data obtained 

by the centrifuge, moisture-tension, and column-drainage techniques in 

the laboratory.

PUMPING METHOD

This method consists of lowering of the water table by pumping 

a measured volume of water and then determining the volume of sediments drained. The specific yield is then obtained as the ratio of the 

volume of water pumped to the volume of sediments drained (Meinzer, 

1932).

Pumping water from a well lowers the piezometric surface around 

the well and creates a cone of depression. In a carefully controlled 

pumping test, data are obtained on rate of discharge, water levels, 

and duration of pumping. The drawdown data are then used in various 

formulas to calculate the magnitude of one of the most important 

hydraulic characteristics of an aquifer the coefficient of storage. 

Wenzel (1942, p. 87) defined the coefficient of storage as the cubic feet 

of water discharged from each vertical column of the aquifer with a 

base 1 foot square as the water level falls 1 foot. For water-table conditions, the coefficient of storage is equal to the specific yield of the material de-watered during the pumping. For artesian conditions the 

coefficient is equal to the water obtained from storage by compression 

of a column of water-bearing material whose height equals the thickness of the water-bearing material and whose base is 1 foot square.

Thiem (1906) apparently was the first hydrologist to envelop a 

formula to determine aquifer characteristics by a well-pumping 

method. However, the greatest advance in aquifer analysis by well 

hydraulics was probably made through the development of the nonequilibrium formula by Theis (1935). The theory advanced by Theis 

introduced both the time factor and the coefficient of storage. Since 

1935, many modifications of formulas or methods of interpretation 

have been developed.

Methods for computing storage coefficient (specific yield) by the 

pumping method were described in detail by Wenzel (1942), Ferris 

(1948), Brown (1953), Bruin and Hudson (1955), Remson and Lang 

(1955), Ramsahoye and Lang (1961), and Ferris, Knowles Brown, 

and Stallman (1962). Most of the methods are based on the following 

assumptions: (a) The aquifer is homogenous and isotropic, (b) the
COMPILATION OF SPECIFIC YIELDS D13

aquifer has infinite areal extent, (c) the discharging well penetrates 

and receives water from the entire thickness of the aquifer, (d) the 

well diameter is infinitesimal, and (e) water removed from storage 

is discharged instantaneously with the decline of head. Although 

very few field conditions meet these specified limitations, successful 

application of the pumping method seems to be possible for many 

ground-water problems. Ferris (1948) pointed out that these methods 

can assist in the interpretation of local geology, but he also emphasized 

that any discrepancy between the hydraulic and geologic evidence in 

a given problem is untenable and points to incorrect interpretation of 

either or both sets of data.

Specific yield can also be estimated from moisture contents determined by sampling or by nuclear-meter logging in the cone of depression around a pumped well.

RECHARGE METHOD

The recharge method is the converse of the pumping method and 

consists of observing the seepage losses from streams or canals, or 

determining the amount of water recharge^ into an aquifer through 

a recharge well, and making corresponding observations on the resulting rise of the water table. From these observations the volume 

of sediments saturated by the measured recharge is determined, and 

the specific yield can be computed (Meinzer, 1932, p. 116).

Moulder and Frazor (1957) used the recharge method to analyze 

aquifer characteristics near Amarillo, Tex., and foun<? that water 

levels may have risen as much as 5 feet during a 4-month recharge 

period. Moulder noted that slow drainage or slow filling of sediments 

with water made the data collected early in the test unusable for 

analysis by the nonequilibrium method. He concluded tl at conform - 

ance to theoretical conditions requires longer periods of time at greater 

distances from the pumping or recharging well.

Sniegocki (1963) made a detailed study of the fundamental principles of artificially recharging aquifers through wells Kesults of 

his study show that recharge data may be satisfactory fo^ calculating 

absolute values for hydraulic characteristics, such as the specific yield 

(or coefficient of storage), for an aquifer. He concluded (Sniegocki, 

1963, p. 22-23) that, if under certain conditions the fiel<? situation is 

readily adaptable for a recharge test, the testing period generally required to determine absolute hydraulic constants could be shortened 

as much as 90 percent. He noted that the coefficient of storage (specific yield) for the aquifer in his study was 0.30 (30 percent) after 

cyclical recharge for about 9 days; whereas, in the discharge situation,
D14 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

a value of 0.30 could not be obtained until pumping had continued 

for more than 100 days. Meinzer suggested earlier (1932, p. 136) that 

"better results can doubtless be obtained, however, if the specificyield test is made during a period immediately after the well has been 

shut down, when the quantity of water taken into storage, in the 

cylinder [cone of depression] will be equal to the total inflow during 

the period and the volume of material saturated can be computed 

from the rise of the water levels."

REVIEW OF LITERATURE

The following paragraphs present the results of library research 

to compile a list of specific yields for rock and soil materials of various 

textures. Pertinent parts of the publications describing the methods 

or limitations of the data have been quoted. All the following text is 

direct or only slightly modified quotation. Additions to quotations are 

indicated by brackets, and omissions are indicated by asterisks Figure 

and table numbers, however, have been changed to fit their order of 

appearance in this report.

Glark, W. O., 1917, Ground water for irrigation in the Morgan Hill area, California, in Contributions to the hydrology of the United States, 1916: U.S. 

Geol. Survey Water-Supply Paper 400, p. 82-83.

The alluvium is composed, according to 69 well logs, of about 69 percent clay, 

29 percent gravel, and 2 percent sand. From the available data on poros'ty * * * 

it has been concluded that the porosity of the sand and gravel is about 35 

percent of its volume, that of the clay 32 percent, and that of the all wium as 

a whole about 33 percent.

The vital question in this connection is not so much the total porosity of 

the materials and the total quantity of ground water present as the quantity 

of water that these materials will yield under a pump. Different materials by 

no means give up water to a pump in the proportion of the total water they contain. Fine materials are usually better sorted than coarser materials and therefore when saturated they may contain even more water than the coarser materials, but they permanently retain, a large percentage of this water, whereas 

the coarser materials readily part with a large percentage of their w.^ter content. The fine materials are therefore of comparatively little value as water 

producers and the coarse materials are the important water-bearing formations.

The following table [table 1] shows the relative amount of water retained 

by sands of different degrees of fineness.

It will be seen from this table that the coarsest of the five sand's tested 

gives up a quantity of water equal to 32.29 percent of the total voluire of the 

sand, or somewhat more than 83 percent of the water it contains. Tie gravel 

and sand of the Morgan Hill district are on the whole considerably coarser 

than this sand and would give up a larger proportion of their water. For purposes of calculation it is assumed that they would give up about 90 percent of 

their total water content If the alluvium includes 29 percent of gravel and 2
COMPILATION OF SPECIFIC YIELDS D15

TABLE 1. Quantity of water retained and given up by different sands that were

drained for #J/£ years

[Based on tables given by King (1890)]

Effective diameter

of sand grains, in 

millimeters

0.47

. 18

. 16

. 12

.08

Porosity of sands,

expressed in percentage of total

volume

38.86

40.07

40.76

40.57

39.73

Quantity of water 

retained, expressed

in percentage of 

total volume of

the sands

6.57

7.37

10.35

12.49

14.09

Quantity o' water 

given up by the

saturated sands, 

expressed IT percentage of total

volume of the sands

32.29

33. 70

30.41

28.08

25. 4

percent of sand, these materials will hold a quantity of water equal to 10.85 

percent of the total volume of the saturated alluvium; if they will yeild 90 

percent of this water they will furnish a quantity of water equal to 9.77 percent of the total volume of the saturated alluvium [ta'ble 2]. The clays form 

a'bout 69 percent of the alluvium, and their average porosity is about 33 percent of their total volume. Clays give up a very small percentage of the water 

they contain. It is stated by King [1899] that clays of fine texture may retain 

as much as 32 percent of their dry weight of water.

TABLE 2. Specific yields for alluvial deposits in the Morgan Hill area, 

Santa Clara Valley, Calif.

Specific yield Material (percent)

Gravel, with sandClay loam ___.

10

2

The materials called clay in the Morgan Hill area are not true clays but 

perhaps more nearly clay loam, so that the quantity of water they retained 

would be considerably less than that retained by fine clay. Tl > porosity of 

fine clays would be greater, but the clays from which the porosity data here 

used were obtained were not true clays, and hence it is believed that their 

average porosity represents the porosity of the clays of the Morgan Hill area. 

It is thought that 90 percent of the amount required for saturation is a liberal 

estimate for the quantity of water retained by the clays of the Morgan Hill 

area that is, they would give up 10 percent of the amount required to saturate 

them. As about 69 percent of the alluvium is clay and the porosity of this clay 

is taken as 33 percent of its volume, the pore space in the clay is equal to about 

22.77 percent of the total volume of the alluvium. If it gives up 10 percent 

of the water required for saturation the clay would yield a quartity of water 

equal to 2.28 percent of the volume of the saturated alluvium [table 2]. The 

total water that the saturated alluvium will give up is therefore calculated 

to 'be 12.06 percent of its volume.

Bllis, A. 3., and Lee, C. H., 1919, Geology and ground waters of the western 

part of San Diego County, California: U.S. Geol. Survey Water-Supply 

Paper 446, p. 121-123.

Experiments made by the writer on 36 samples from the fill of th<> major river 

valleys of San Diego County, the material varying from coarse sand to silt,
D16 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

indicated total voids expressed as percent by volume as follows: Coarse sand, 

39 to 41 percent; medium sand, 41 to 48 percent; fine sand, 44 to 49 percent; 

fine sandy loam, 50 to 54 percent. The average porosity of all 36 sairoles was 

45.1 percent. The classification of materials is that used by the Bureax^ of 'Soils 

of the United States Department of Agriculture. These percentages represent 

the porosity of the material under natural condition as to size and arrangement 

of grains [table 3].

TABLE 3. Specific yields of valley-fill materials in San Diego Count", Calif.

yield 

Material (percent)

Coarse sand _____________ __ _ 34

Medium sand- __________ _ _ ________ 37

Fine sand _____________________________ ___ 37

Fine sandy loam ____________ _ ___ ___ _ ___ _ ___ 30

A certain proportion of the moisture that occupies the voids of any saturated 

porous material does not readily drain out, even when the zone of saturation has 

fallen below the depth from which the capillary rise of water is rapid. This 

moisture can not be extracted by pumping nor does it represent water th*t drains 

out and is replenished during the natural fall and rise of the water table. To 

determine the water-retaining capacity of various valley-fill materials, s:x expert 

ments were made after the annual summer lowering of the water table 1 ^d taken 

place. The water-retaining capacity was found to range from 6 to 10 percent in 

the coarse, medium, and fine sands, but no finer materials were examined where 

the depth to the water table was great enough to enable the field capacity to be 

determined with certainty. Etcheverry [1915], quoting from Widtsoe's extensive 

experiments, gives the water-retaining capacity of sandy loam as 14% percent by 

weight, which is equal to about 22 percent by volume, and this percentage can be 

considered as representing roughly the condition in sandy loam soils of the major 

river valleys under consideration. The total volume of water that might be 

drained from the valley fill by the slow lowering of the water tabl* can be 

estimated as ranging from about 33 to 37 percent by volume. Such complete drainage, however, requires considerable time, and the relatively quick drainage 

resulting from the artificial lowering of the water table by pumping undoubtedly 

represents the extraction of far less of the total water content. In prr^tice the 

proportionate volume that could be extracted from the valley fill of the major 

valleys probably does not exceed 20 to 25 percent. * * *.

Stearns, H. T., Robinson, T. W., and Taylor, G. H., 1930, Geology and water 

resources of the Mokelumne area, California: U.S. Geol. Survey WaterSupply Paper 619, p. 151-172.

Experimental field tests were made on undisturbed soil columns to determine 

the specific yield of the soil directly above the water table. These soil columns 

were obtained during the fall, when the water table was at its lowest level. In 

this way a test was made of the soil within the belt of fluctuation of the water 

table.

A cylinder 18 inches in diameter and 36 inches long made of 16-gage galvanized 

iron was used for the x tests. The cylinder was butt-jointed and riveted, and the 

joints were floated with solder and scraped smooth on the inside. A 3-inch iron 

collar was riveted and spot welded to the top of the cylinder to prevent damage
COMPILATION OF SPECIFIC "YIELDS D17

to the cylinder in driving it. The bottom outside edge of the cylinder was 

beveled with a file to facilitate driving, and three equally space-' holes were 

drilled near the top, through which wires were placed to lift it.

A 4-foot square pit was dug within S 1/^ or 4 feet of the water table. The cylinder 

was then driven into the bottom of the pit, and the soil was excavated around 

the cylinder as driving progressed. A driving cap of 2-inch plank'ig was used 

on top and a 4 by 4 inch timber about 14 feet long, handled by two n^en, was used 

in a manner similar to a pile driver. Constant care was taken to keep the cylinder 

in a vertical position while it was being driven. Special care was taken as the 

soil neared the top of the cylinder to keep the soil from being compacted by the 

driving cap. Driving was stopped when the bottom of the cylinder was within a 

few inches of the water table. A strong flexible wice was then used to saw 

through the soil column at the bottom edge. Heavy wires were strung through 

the holes near the top of the cylinder by means of which the cylinder was lifted 

a fraction of an inch by either a lever or block and tackle. The cylinder was 

suspended only long enough to allow a 24 by 24 inch 16-gage galvani^-ed-iron base 

plate to be slipped under it. If the soil was not compact enough to remain in the 

cylinder when lifted this much, the plate was forced under the cylinder by means 

of an automobile jack, special care being used to keep the plate fl-sh with the 

bottom edge of the cylinder. The latter method proved to be the simpler of the 

two. The cylinder was then centered on the plate and leveled. It wf s found that 

for the base plate 12-gage galvanized iron is preferable to 16-gage.

Two 1%-inch holes were then drilled in the confined soil column about 4 inches 

from diametrically opposite sides of the cylinder. TJhese holes were drilled to the 

bottom of the soil column with a wood auger welded to an extersion. handle. 

They were then cased with 1%-inch nickel-plated brass pipes. One of the pipes 

was perforated the entire length, except 6 inches on the upper end, end the other 

pipe was perforated only in the lower 6 inches. The perforations vere one-sixteenth of an inch in diameter and were drilled in parallel rows about half an 

inch center to center. * * *.

Water was added to the soil in the cylinder by pouring it into the 1%-inch 

hole in which only the lower 6 inches of the casing was perforated The water 

was removed from the cylinder by drawing it up into a glass tube or rubber hose, 

and the amount of water removed or added was measured in a glass graduate.

The distance to the water level in the small holes was measured with a steel 

tape from the bottom edge of a spirit level placed across the top of the cylinder. 

A small lead weight, with a blunt point, was placed on the end of the tape, and 

the measurement was taken when the point of the weight broke the mirror 

surface of the water in the 1%-inch holes. Measurements were made in one hole 

immediately after measurements had been made in the other, to ascertain 

whether or not the water table in the cylinder was level.

***** * *

* * * the resulting specific yield would have been larger and more nearly the 

actual specific yield if the time interval between changes of water in the cylinder 

had been greater. Experiments conducted the following year proved that an 

interval of several days is necessary to obtain accurate results.

Tests 1, 2, and 5 are completed, but the remainder of the tests are still in 

progress, and the data obtained will be given in a later report. Additional observations are necessary and may change the results given here, hence these data 

are of a preliminary nature and subject to revision [table 4].
D18 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

TABLE 4. Speaiflo yields of water-bearing materials in the Mokelumne area, near

Lodi, Calif.

Specific yield 

Material (percent)

Medium sand _ ___ 20

Silty sand ____________-___ 10

Sandy silt _______ _ 2

Sandy clay _ 2

Clay ____________ __ 1

Test 1. The time interval allowed for each determination was not long enough 

for accurate results. The average specific yield for a rising water tabJe was 1.04 

and for a falling water table 0.59. The average of the two is 0.82. The soil tested 

consisted of fine black clay and coarse black sand. The test was made chiefly on 

the fine black clay, which has a low specific yield and the result obtained is 

about what would be expected.

Test 2. The soil was mainly a medium-coarse brown sand, hence the specific 

yield should be relatively high. The time interval for the first part of the experiment was short, being not over 45 minutes, but for the last part of the test the 

time interval ranged from about 1 hour to 50 hours. The specific yield was about 

20.

Test 3. The results of this test are not yet satisfactory, the specific yield 

ranging from 4.26 to 20.2. The soil is similar to that of test 2, and a specific yield 

of 15 or 20 would be expected. The temperature correction curve? were not 

definite, but the corrections obtained were 0.015, 0.0084, and 0.014 foot per degree.

Test 4. The soil tested was a very fine black sandy clay with a low specific 

yield. Owing to an undetected leak in the cylinder only one determination has 

been obtained so far. The specific yield was 4.4; corrected for temper? ture, 2.44. 

Two fairly well defined temperature correction curves have been obtained, showing corrections of 0.0096 and 0.0087 foot per degree.

Test 5. The soil tested was a brown silty sand. This is doubtless tie best test 

of the group and showed a specific yield of about 10. Very well defined temperature correction curves were obtained, giving corrections of 0.008, O.OT%, 0.0065, 

0.0079 and 0.006 foot per degree. The time required for the water table to reach 

an equilibrium was established as being at least 25 days.

Test 6. The soil tested was a fine black sandy silt. The specific yields were 

1.6 and 1.4; corrected for temperature, 1.2 and 2.6. Fairly well define! temperature correction curves were obtained, showing corrections of 0.0264, 0.0112, and 

0.0192 foot per degree. The time interval required for the water table to reach an 

equilibrium after a change of water was 43, 38, and 38 days for three series of 

observations.

Test 7. The soil tested was a hard fine brown and gray sandy clay. Leakage 

caused considerable difficulty and only one result of 13.6 for the specific yield 

was obtained. This result is believed to be high for soil of this texture, but 

additional data are needed to prove it. The result was obtained for a riMng water 

table and would be too high if there was a small undetected leak in th? cylinder. 

This is possible, for seven days after the last observation was made a leak appeared. Between February 5 and 16, 1929, a well-defined temperature correction 

curve was obtained, showing a correction of 0.055 foot per degree. Another 

series of observations gave no definite temperature correction curves, v^hich may 

be an indication that an undetected leak was present.

Test 8. The soil tested was a very hard sandy clay. The results are not consistent, for two tests gave a specific yield of 0.16 and 0.15 for a falling water table,
COMPILATION OF SPECIFIC TTTELDS D19

and two tests gave 0.64 and 0.62 for a rising water table. Application of the 

temperature corrections to the results did not make them more consistent. The 

temperature correction curves were fairly well defined and showed corrections 

of 0.55, 0.033, 0.0218, 0.0168, 0.0172, and 0.018 foot per degree.

If there were no recharge from April to September, and no discharge other than 

that by pumping from wells during this period, and if all the puirxring occurred 

during this period, the specific yield could be approximately computed by dividing the average volume of water withdrawn (53,800 acre-feet) by the average 

volume of material unwatered (360,200 acre-feet). Such a computation would 

give a specific yield of about 15. If allowances are made for the modifying factors, however, it appears that the specific yield is more nearly 10. Intensive 

investigation that is now in progress should give a more accurate figure for average specific yield. * * *.

White, W. N., 1932, A method of estimating ground-water supplies based on discharge by plants and evaporation from soil, in Contributions to the hydrology of the United States: U.S. Geol. Survey Water Supply Paper 659, p. 

74-76.

Determinations of specific yield were first made with the disturbed soils with 

which the tanks were filled, and it seemed for a time as if the questionable 

figures thereby obtained were the best that were to be had. After considerable 

experimenting, however, a method was developed by which determinations were 

made with undisturbed soils in the fields where ground-water plants were growing. The essential steps in the process were as follows: Cylinders of 16-gage 

galvanized steel were driven vertically downward so as to inclose undisturbed 

columns of soil. The cylinders were then sealed at the bottom to make them 

watertight, and they were also protected against evaporation at the top. Measured quantities of water were introduced into or taken from the cylinders, and 

the resulting rise or fall of the water table was observed.

Altogether nine cylinders were driven one 18 inches in diameter and 54 inches 

high, three 18 inches in diameter and 36 inches high, three 12 inches in diameter 

and 36 inches high, and two 12 inches in diameter and 18 inches high. With the 

exception of the 54-inch cylinder all were driven nearly to the water table. All 

were sunk as closely as possible to selected observation wells, and they were 

put down in the fall, so as to inclose the soils in which the summer water-table 

fluctuation had occurred.

In order to reach the water table with one of these cylinders a p't 4 by 6 feet 

was sunk to a level above the water table equal to the height of the cylinder, 

the proper level being determined by sinking a small test hole to wf ter and making observations with a wye level. The rim at one end of the cylinde~ was slightly 

beveled off in order to provide a cutting edge, and a heavy drive cap was provided consisting of short pieces of 3-inch plank under a block of undressed green 

oak. Operations were begun by placing the cylinder with cuttinf edge down, 

after which the cap was placed on its upper end and it was slowly driven downward, care being taken to keep it in a vertical position. Two methods of driving 

were used with about equal success in one the cylinder was driven with a maul 

wielded by one man in the bottom of the pit; in the other, the dr've was provided by a pole about 6 inches in diameter and 12 feet long used pile-driver 

fashion, two men being required to handle it, one in the pit and the other stand-
D20 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

ing on a plank over the pit. As the cylinder moved slowly downward tl ? pit was 

deepened, the bottom of the pit being kept about 6 inches above the lower edge 

of the cylinder. In this way the friction on the outside of the cylinder was kept 

at a minimum, and at the same time sufficient support was provided a t the bottom to keep the cylinder in a vertical position. When the lower edge of the 

cylinder reached the water table, the driving was stopped, but the outnde excavation was continued until it was slightly below the lower edge of the cylinder. 

Then with a wire the soil column was sawed off even with the bottom of the cylinder, a bale was attached, and with the aid of a lever the cylinder with its included soil was slightly raised and a bottom was soldered to it. * * * Two small 

wells were then sunk in the inclosed soil, one to the bottom of the soil column 

and the other to a somewhat lesser depth. These wells were cased and stopped 

with cork. Finally the cylinder was provided with a cover to prevent evaporation 

In making determinations of specific yield in these cylinders, water was gradually introduced into the wells until the soil column was saturated practically 

to the top. Withdrawals were then made until the water table had subsided to 

the desired position in the column. Then water was alternately take*1 from or 

added to the deeper well, and the resulting changes ir. the water talJe in both 

wells were observed. Equilibrium was not established until about 24 tours after 

the addition of water and about 48 hours after its removal. Pronounced changes 

in barometric pressure between the time of addition or withdrawal and subsequent water-level observations seriously interfered with the results [table 5]. 

On this account it was necessary to make the observations in fair wefther. Part 

of the time it was necessary to make corrections for fluctuations in the water 

table produced by changes in temperature.

Table 5. Specific yield of unconsolidated sediments in the Escalante

Valley, Utah

Spec'flc yield 

Material [average] (percent)

Sandy clay loam ___ _ _________ _ ___ _ ______ 5.3

Loam fill _____________________________ 5.1

Clay fill _______________________________ 4.2

Clay __________________ . ______________ 3. 4

Clay loam _____________ _ ______________ 2.7

Loam__________ _____ __ ___.. ______________ 2. 4

Bckis, Rollin, 1934, Geology and ground water storage capacity of valley fill: 

California Div. Water Resources Bull. 45, p. 91-246.

The results presented cover a period of two and one-half years of field and 

laboratory investigations. During this time many methods were tred for determining porosity, water retention, and actual water yield of different sediment * * *.

During the course of this investigation, the moisture retention of about 150 

samples was determined, four methods of study being used. In general the retention increases with the degree of fineness of the sediment [table 6]. From an 

analysis of the results, it is concluded that the approximate moisture retention 

of coarse sediments can be estimated from an index of fineness, called the surface 

factor, which is determined from the mechanical composition of the sample.
COMPILATION OF SPECIFIC YIELDS D21

TABLE 6. Estimated specific-yield values for sediments of the South Coastal Basin,

Calif. 

[Specific-yield values given in percent]

Unweathered

Surface alluvium. _ .. 

Subsurface alluvium. .

Weathered tubturface

Tight ^... .............

Clayey '....... ___ ..

Gravel

256+ mm 

(boulders)

(D...13.6 

(2).. .13

(3). ...9 \i-<,

64-256 

 mm

(coarse)

14.2 

14

9 

5 

1

16-64 mm 

(medium)

20.5 

20

13 

7 

1

8-16 mm 

(fine)

26.5 

25

17 

8 

1

Sand

(coarse 

and 

medium)

30.9 

28

1

mm 

(fine)

21.2 

16

6 

5

1

Clay

Sandy

10 

5

Clay

1 

1

1

1 Lime-cemented gravels are included in tight gravels.

2 Lime-cemented sands are included in clayey sand.

s The yield of 1 makes allowance for small sandy or gravelly streaks.

Five methods for the determination of specific retention were tri?d during the 

course of this investigation. Four of these are direct: (1) laboratory drainage 

method; (2) collection of samples from well pits and borings; (3) cylinders 

driven after a rain ; and (4) cylinders driven into av material, whicl is then saturated and drained in the field.

A fifth method, not an independent one, is the estimation of specific retention 

from a description of the properties of the material (surface factor). 

* * * Wherever possible, the surface factors have been computed, and the ratio 

of weight of water retained, to surface factor has been given to facilitate 

comparison.

The Specific Yield Curve. Since both the specific retention and the porosity 

have been shown to vary with size, the computed specific retention* of the individual samples were averaged for each maximum 10 percent gr»de size and 

plotted on the graph [fig. 3]. The measured porosities were average-1 and plotted 

in like manner. Values on the specific retention curve were subtracted from 

corresponding values on the porosity curve to obtain the points tl rough which 

the specific yield curve was drawn. The specific yield curve gives the average 

yield value for gravels of which grade sizes of maximum 10 percent of particles 

are known approximately. This curve can not be used to predict the specific yield 

of an individual sample. If coarse gravels are considered to be those with maximum 10 percent grade sizes greater than 64 millimeters, the thre^ grade sizes 

represented give an average specific yield of 14.1 percent for coarse gravel. If 

medium gravel be considered to occupy that part of the curve with maximum 10 

percent between 16 and 64 millimeters, the two grade sizes represented give an 

average specific yield of 20.6 percent for medium gravels. If gravels the maximum 

10 percent of which is 8 to 16 millimeters be considered fine gravels the average 

specific yield of fine gravel is 26.5 percent.

Specific Yield of the Sands. From the specific yield curve [fig. ?], the maximum yield of the alluvial series represented is reached in coarse sand (maximum 

10 percent size, 1-2 millimeters), and averages about 32.5 percent. r"he yield for 

all alluvial sand samples with maximum 10 percent size coarser than % milli-
D22 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

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(THE GRADE SIZE IN WHICH THE CUMULATIVE TOTAL, BEGINNING WITH THE

COARSEST MATERIAL, REACHES 10 PERCENT OF THE TOTAL SAMPLE)

FIGURE 3. Porosity, specific retention, and specific yield for sediments of the Scuth Coastal 

Basin, Calif. (After Eckls, 1934.)

meter averaged by grade size is 30.9 percent. These sands are mediunr to coarse 

sands, and are considered to be the materials commonly logged as sand and 

coarse sand by well drillers. The specific yield values for coarse an-t medium 

sands were seen to be so nearly the same from the curve, that no attempt was 

made to differentiate the two for storage capacity computation.

The samples the maximum 10 percent grade sizes of which were greater than 

% millimeter and less than % millimeter were considered to be fine sands and 

probably represent the material logged as fine sand or quicksand by weU drillers. 

The specific yield estimated by averaging grade sizes for fine sand is 21.3 percent.

Since the average specific yields of coarse and medium sand were found to 

differ only a few percent, no attempt was made to assign different yMd values 

for sand in different regions, as was done for gravels. The curve shows an average of 30.9 percent for the coarse and medium surface alluvial sands.

The sand samples used to obtain these specific yield values were taken from 

cuts or from borings at depths of a few feet below the surface in orde'' to avoid 

the abnormally high porosities of unburied sands.

Specific Yield of the Clays. Mechanical analyses were made of only a very 

few of these samples, and therefore the samples were grouped accordicg to maximum grade size by inspection of the grains under a binocular microscope. It was 

thought from inspection of about 30 samples in this manner that in those the 

maximum 10 percent grade size of which did not exceed Me millimeter, the
COMPILATION OF SPECIFIC YIELDS D23

specific retention was generally about equal to the porosity. This lower limit is a 

rather indefinite approximation, but at any rate the materials classed as sandy 

clays fall on that part of the specific yield curve lying between 11 percent yield 

and zero yield. It is thought that these materials are those generall~ called sandy 

clays by well drillers. More properly speaking they are very fine sands and silts. 

The moisture retention and porosity of several samples of sandy clay were 

obtained from post auger borings at the average depth of a little more than 10 

feet. The average computed specific yield of these samples was approximately 

10 percent. The specific yields of nine clay samples from post aufer holes were 

computed and found to average approximately zero.

*******

Specific yield values have been estimated for the different types of material 

that fill the freshwater-producing basins, by adaptation of the results of experiments with surface samples to similar materials encountered in wells.

In order to assign specific yield values to the various types of sediments in the 

ground water basins the unaltered sediments, with their specific yield values 

shown on [figure 3], were classified into gravel, sand, and clay groups with subdivisions under each. Then the corresponding types of materials encountered in 

wells were classified under each of these groups, and divided into four stages to 

represent various degrees of alteration, from fresh material to residual clay. The 

specific yield of each type for each stage of alteration recognized was estimated 

from the yield of its unaltered derivative. The classification with the yield values 

is shown in table 6.

The Unweathered Deposits. Line 1, table 6, gives yield values everaged from 

the specific yield of the unaltered gravel curve [fig. 3]. These value** having been 

derived from practically unaltered surface samples could not be directly applied 

to the subsurface materials. Line 2 gives the specific yields estimated for subsurface unweathered materials. These values were modified from those of Line 

1, because of settling.

The gravel values were reduced only slightly, as it seemed probable that the 

effects of settling, greatest in sand and clay, would become less with coarser materials and probably practically die out with very coarse poorly sorted gravel and 

boulders. Thus the specific yield of coarse to medium gravels was reduced an 

average of five-tenths of one percent (to the nearest whole number), fine gravel 

1.5 percent, coarse and medium sand 3 percent, fine sand and sar'Jy clay each 

about 5 percent. From Curves I and II, of [figure 4], the loss of porosity from 

the surface to the depth of 50 feet appeared to be about 5 percent porosity. The 

depth of 50 feet, being below the steepest part of the curves, was tl ought to represent a fair average for the amount of compaction, and to take into account 

practically all of the near surface consolidation due to settling. It seems that 

lowering the specific yield of these materials (fine sand and sandy clay) 5 percent 

is conservative, since the specific yield may drop even more than the porosity. The 

values for coarser sands and gravels, though not measured, were reduced correspondingly less, estimates in all cases being made to the nearest whole number.

These subsurface values (Line 2, table 6), estimated from the srrface sample 

averages, represent the unweathered materials of the water-producing section 

and include such types logged by well drillers, as loose water grave1 and loose or 

running sand, which are the best water-yielding sediments of the formation.

*******

The well samples showed significant size differences fom surface gravels only 

at considerable distances from the mountains and in the regions where the gravels
D24 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

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DEPTH,IN FEET

FIGURE 4. Relation of porosity to depth in certain types of sedimentary 

materials of the South Coastal Basin, Calif. (After Eckis, 1934.)

were interbedded with sands and fine gravels. In these areas the materials on 

the surface do not represent the true average coarseness because the coarser gravels are usually covered by finer material deposited during the later stages of 

flood. The well samples were, in such cases, relied upon for size estimates. Values
COMPILATION OF SPECIFIC YIELDS D25

for practically the entire coastal plain were determined in this manner. Well 

samples were not available for large parts of the upper slopes of the basins and 

in these areas it was necessary to apply the surface size distribution to the buried 

materials. The two were thought to be comparable because no significant average 

size differences were noted between surface and depth conditions where well 

samples were obtained from the regions of coarse gravel.

Although well samples showed some differences in gravel sizes at different 

depths, the data were not complete enough to make possible the assignment of 

correspondingly different values. This inaccuracy is thought to be unimportant 

since doubling the maximum 10 percent size changes the specific y'eld only a few 

percent, and well samples seldom indicate consistent size change? of one grade 

size with change of depth.

*******

The Weathered Deposits. Since all variations in specific yield from those of 

the unaltered deposits, to zero for residual clay, occur in weathered deposits, it 

was found necessary to make an arbitrary classification for the purpose of 

assigning specific yield values.

The specific yield of weathered gravels and sands depends on: (1) the specific 

yield of the unweathered deposit, and (2) the extent to which alteration has 

progressed. Slightly weathered gravels and sands that have retained their 

original structure are generally classified as tight gravels or tight sands by well 

drillers. Gravels and sands that have lost a large part of their original structure 

but retain resistant pebbles or cobbles embedded in a clayey sandy matrix are 

generally classed as gravelly clays and sandy clays. Gravels and sands that have 

been altered to red, brown, or gray clayey soite with gritty angular residual 

fragments embedded, are usually called clay by well drillers. Tl «se classifications were adopted and specific yield values assigned accordingly.

The specific yields of the weathered materials could not be successfully classified from measurements on actual samples because of the natur? of variation. 

Therefore specific yields were assigned by making an arbitrary d'vision according to the degree of alteration. Tight gravel was given a yield value of twothirds that of unweathered subsurface gravel, and gravelly clay, one-third the 

specific yield of unweathered gravel. Probably the typical residual clay has a 

yield of zero, but since it is highly variable in composition it undoubtedly contains streaks that yield small quantities of water. It was, therefore, assigned 

a specific yield of one to indicate a probable slight yield throughout the well 

section.

The estimation of yield values for weathered sand was less simple. It was 

found that the decomposition of sand reduced the specific yield sharply, so that 

materials logged as tight sand had a specific yield value less than two-thirds that 

of good sand. Sandy clay formed by decomposition, being similar in mechanical 

composition to unweathered sandy clay, probably has an average specific yield 

similar to that of unweathered sandy clay.

Since unaltered sands were classified according to coarseness as sand, fine 

sand and sandy clay, the two finer divisions were so similar to tight sand and 

sandy clay (weathered) that it was impossible to separate then in well logs. 

Therefore the value of 16 percent assigned to fine sand was used also for tight 

sand, and all sandy clays were considered to yield 5 percent.

Lugn, A. L., and Wenzel, L. K., 1938, Geology and ground-water resources of 

south-central Nebraska: U.S. Geol. Survey Water-Supply Paper 779, p. 

89-96.
D26 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

In the laboratory the samples of water-bearing material are saturated and 

subjected to a centrifugal force approximately 1,000 times the force of gravity. 

The samples are weighed, then dried and reweighed. The difference in weight 

represents the weight of the moisture that is retained after centrifuping. The 

moisture equivalent by weight is computed by dividing the weight of the moisture 

retained after centrifuging by the weight of the dry soil, and the moisture 

equivalent by volume is computed by multiplying the moisture equivalent by 

weight by the apparent specific gravity of the material.

The moisture-equivalent determinations are made to ascertain the specific 

retention [Meinzer, 1923b] that is, the quantity of water that a soil or rock 

will retain against the pull of gravity if it is drained after having been saturated, 

expressed as the ratio of the retained water to the total volume of material. 

The specific yield of a material is equal to the porosity minus the specific 

retention. * * *.

******* 

Tests for moisture equivalent were made on four samples of loess obtained 

in the Platte Valley near Lexington. * * * The average moisture equivalent 

by volume was 33.8, and the average porosity was 53.7. If the average moisture 

equivalent is taken to represent the average specific retention, the average specific yield of the four samples of loess is about 20 [table 7].

******* 

TABLE 7. Specific yields of water-bearing sediments in the Platte River valley,

Nebraska

Specific yield 

Material (percent)

Sand and gravel- _____ _____ __ ________ 24

Silt (loess)_______________________________ 20

Clayey silt______________________________ 13

The moisture equivalent of samples of the Pleistocene sand and gravel obtained 

near Grand Island, Kearney, and Lexington was also determined in the laboratory. * * * One sample was composed principally of clay, and its moisture 

equivalent was 27.1, and the specific yield 13.2. * * * The moisture equivalents 

of * * * 17 samples ranged from 1.9 to 3.9 and averaged 2.8. This average falls 

into the range where Piper found that the moisture equivalent was considerably 

less than the specific retention. By using his diagram, the specific retention 

corresponding to a moisture equivalent of 2.6 is found to be about 5. The porosity 

of the 17 samples of sand and gravel ranged from 21.5 to 41.8 and rveraged 

about 29. The average specific yield is therefore computed to be 29 minus 5, or 24.

******* 

The moisture equivalent was determined also for several samples o.f soil in 

the vicinity of Lexington. Most of the soil is developed from loess and therefore 

may be expected to possess similar hydrologic properties. * * * The specific 

yields of these samples are 4.4 and 21.7 respectively. * * *.

A pumping test was made on the farm of Fred Meyer, about 4 miles west of 

Grand Island, * * * and the specific yield of the water-bearing sand and gravel 

was determined in place. The method was suggested by Meinzer [19^2] and 

consists of determining the ratio of (1) the quantities of ground water which 

in a given time are taken from storage between concentric cylindrical sections 

around the pumped well to (2) the volume of sediments between the cylinders 

that are unwatered in that time, * * *
COMPILATION OF SPECIFIC YIELDS D27

The computed specific yield became larger as the pumping increased, for the 

reason that all the water in the material does not drain out of it immediately. 

When pumping starts, a comparatively large volume of material is unwatered, 

partly because only a small percentage of the water contained in the interstices 

of the sediments immediately drains down to the water table. As pumping is continued, more water gradually drains out of the unwatered sediments, and hence 

the specific yield computed from the first few hours of pumpir^ is relatively 

small. The specific yield computed from the volume of water-bearing material 

unwatered in the last few hours of pumping would be too large because of the 

addition of water that percolated down from the material previously unwatered. 

The average results for specific yield * * * plotted against the periods of pumping, fall on a smooth curve. By extending this curve the conclusion is reached 

that the true specific yield lies between 22 and 23.

The specific yield determined by this test applies only to the upper few feet 

of water-bearing material that was unwatered during the period of pumping. 

A sample of water-bearing material from the well drilled at the location of this 

test was obtained close to the water table. * * * The porosity was found to be 

27.1 and the moisture equivalent 2.6 in the hydrologic laboratory. Piper's relation 

between moisture equivalent and specific retention gave a specific retention of 

about 5, from which the specific yield is computed to be about £2.

Piper, A. M., Gale, H. S., Thomas, H. E., and Robinson, T. W., 1939, Geology 

and ground-water hydrology of the Mokelumne area, California: U.S. Geol. 

Survey Water-Supply Paper 780, p. 101-121.

Two methods have been used to determine the specific yield of typical waterbearing materials of the Mokelumne area (1) measuring the volume of material saturated and unwatered by alternate addition and withdrawal of measured 

volumes of water from columns of undisturbed soil; and (2) determining the 

difference between the porosity and the specific retention of samples of undisturbed material after drainage for periods as long as 390 days. T^se are * * * 

termed, respectively, the volumetric method and the drainage method. 

In 

*******

the [volumetric] tests * * * the mean elapsed time ordinarily ranged 

between 19 and 63 days. The shorter term was perhaps inadequate for equilibrium to be fully attained, but in contrast, the three columns for which the 

elapsed time was least * * * also afford results for specific yield after the lapse 

of 215 to 220 days and without further withdrawal or addition of water. The 

longer term increased the specific yield between 1 and 3 percent of the result 

derived from the shorter term. However, these three columns were coarse in 

texture; the increase in yield with longer term might well hav* been greater 

had the material been finer, * * *

Obviously, the lapse of time required for the water level to reach true equilibrium at any particular temperature depends largely upon the lag in replenishing 

the capillary fringe as water is added and in draining the frinre as water is 

withdrawn. In either case, the volume of material saturated or urwatered tends 

to diminish as the term of the test is lengthened that is, the remit for specific 

yield tends to increase. All the columns of material tested in the Mokelumne area 

have tended to give larger results for specific yield by saturation than by unwatering, whence it is inferred that the lag following withdrawal is the greatei. 

For example, among four columns tested in 1930 and 1931, the respective mean
D28 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

results for determinations by saturation are between 108 and 115 percent of 

the mean results for alternate determinations by unwatering, the particular 

materials being relatively coarse. That the range might have been mud greater 

for fine materials is suggested by the determinations for column ?626N in 

1928-29. For that column, two results for specific yield by saturation we-e about 

three times as large as two results by unwatering, although all were snrall. The 

experimental errors due to lag seem not to compensate in short-term tes'-.s which 

withdraw and add equal volumes of water alternately. Further, if the columns 

are too short to contain the full capillary fringe, the results for specific yield 

tend to be too small, and the error becomes progressively greater as the stage of 

the water table is raised in the column. All the foregoing considerations suggest 

that the respective average specific yields determined by the volumetric method 

are likely to be less than the true specific yields of similar materials in the field. 

Figure 5 shows the relation between the results for specific yield as determined 

by the drainage method and the mean size of the particles composing the 

respective samples. On that diagram the abscissas allot equal space to sr^cessive 

grades or classes whose limiting particle sizes are in the constant ratio 2:1; thus 

the silt fraction of the conventional nomenclature spans 3.6 classes, and the clay 

fraction is extended indefinitely. With three exceptions, the plotted points fall 

within a moderately narrow zone with parallel straight-line limits as indicated, 

the width of that zone being equivalent to one class interval. Without er^eption, 

the points that represent materials with small dispersion of particle size? (standard size-ratio deviation is small) fall to the right on the diagram; likewise, the 

points that represent the materials of higher porosity for any particular mean 

size and size-ratio deviation fall to the right. These relations suggest that the 

specific yield of these particular water-bearing materials is a systematic function of mechanical composition and texture, although obviously the 16 tests 

just described afford too few data for statistical treatment of that sunrestion. 

The drainage tests on the second set of samples * * * were terminate after 

about a year (322 to 390 days). In all the samples the quantity of retained water 

decreased steadily, though at a diminishing rate. Thus, the retention at the end 

of the tests ranged between 61 and 97 percent of the respective quantities retained 

after the lapse of 96 to 111 days; also, in general, the greater additional drainage 

came from the coarser-grained samples. * * * The specific yields derived from 

the longer term of drainage ranged between 106 and 167 percent of the respective 

results derived from the shorter term and averaged 127 percent. In general, the 

percentage increase was least for the materials of large specific yield and greatest 

for the materials of moderate specific yield.

The percentage increase in the results for specific yield derived from the 

longer term of drainage is greater than the increase in the few long-term tests by 

the volumetric method. However, it has been inferred that the volumetric method 

tends to yield results that are too small, whether the test is made by saturation 

or by unwatering, although the tests by saturation have consistently rfforded 

results somewhat greater than those by unwatering. Accordingly, the increased 

yield indicated by the long-term drainage tests may measure the actual lehavior 

of water-bearing materials under field conditions, whereas tests by the volumetric 

method as conducted in the Mokelumne area may not evaluate the finrl small 

increments of specific yield.

The graphs that constitute figure 6 show the mean specific retention of the 

materials tested by the drainage method in relation to their moisture equivalent, 

a property that has been used commonly as an approximate measure of the 

quantity of water that a material would retain against the pull of gravity. The
COMPILATION OF SPECIFIC YIELDS D29

35

30

uj 25

20

15

\

Sand, 

coarse

\ 

^ 

\

\ 

\

\

\ 

\

Sand, 

medium

\ 

\

\ 

\

\ 

\

\

\ 

\

\ 

\

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fine

\

\

\

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00

o

\

°\ 

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x-^x 

\ \ 

°\o \ 

\ \

\ V

\ \

\ \ <\ \ \ \ \ \

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Silt

MEAN SIZE OF PARTICLE (Wentworth scale)

FIGURE 5. Relation between texture and specific yield of materials that were drained for 

approximately 100 days. (After Piper and others, 1939.)

graphs are based upon the two sets of axial subsamples taken from the respective 

gross samples after the two terms of drainage. * * *

*****« * 

Records for 231 irrigation wells within the area that receive.** percolate are 

available in sufficient detail to show the physical character of the material in 

the two zones. Of these, 185 wells have driller's records, which commonly discriminate three general classes of material "gravel" and "coarse sand," "sand" 

or "standing sand," and "silt" or "clay." The remaining 46 wells have yielded 

samples that have been classified according to the standard grades or classes 

of granular material. * * * By comparing the two sorts of records for several
HYDBOLOGIC PROPERTIES OF EARTH MATERIALS

0.4

8 12 16 20 24 28 

SPECIFIC RETENTION (R), IN PERCENT OF DRY WEIGHT 

0.8 1.2 1.6 2.0 2.4 2.8 

SPECIFIC RETENTION ( K )

32

3.2

36

3.6

RATIO:

MOISTURE EQUIVALENT(M>

FIGURE 6. Relation between moisture equivalent and specific retention of water-bearing 

materials that were drained for 50-400 days. (After Piper and others, 1939.)

wells within selected small areas approximate correlations have been derived as 

follows: (1) By "gravel" and "coarse sand" the driller designates material whose 

dominant grade falls under one or the other of those same terms in the standard 

classification that is, material in which most particles are larger than 0.5 

millimeter in diameter; (2) "sand" and "standing sand" span the medium-sand 

and fine-sand grades of the standard classification that is, they include material 

in which the dominant fraction is 0.5 to 0.125 millimeter in diameter; (P) "silt" 

and "clay" include the very fine sand, the silt, and the clay fraction" of the 

standard classification that is, material composed largely of particles smaller 

than 0.125 millimeter in diameter. * * * Corresponding mean results for specific 

yield determined by the drainage method are interpolated from figure 5 as 

follows: Gravel and coarse sand, 35 percent; medium and fine sand, 26 percent; 

very fine sand, silt, and clay, 3.5 percent [table 8].
COMPILATION OF SPECIFIC YIELDS D31

TABU: 8. Specific yields of water-bearing sediments of the Ifokelumne area,

California

Material 

Gravel and coarse sand______

Medium and fine sand______

Very fine sand, silt, and clay.

Speciflc yield 

(percent)

35

26

3.5

Wenzel, L. K., 1942, Methods for determining permeability of water-bearing 

materials: U.S. Geol. Survey Water-Supply Paper 887, p. 110, 100.

It is generally recognized that saturated water-bearing materials when allowed 

to drain, may yield water rather slowly. Investigations have shov^n that a sample 

of material after being saturated may continue to drain for several years, although most of the water in it may drain out in a much shorter time. Thus the 

value for the specific yield of a material, as ordinarily determined in the laboratory, is not likely to be reached under conditions found in nature except 

when the water-bearing material is permanently unwatered. Hence, material 

that is unwatered and then saturated again may hold in the period when it is 

unwatered considerably more water than is represented by the specific retention 

of the material.

The slow draining of water-bearing material in the vicinity cf a pumped well 

causes the water table to decline rapidly at first and then more slowly as draining proceeds. * * *.

^Although the material may yield a very large percentage of the water in it in a 

few hours or days, it may continue to yield small amounts for several years. 

The sand and gravel unwatered during a pumping test near Grand Island, Nebr., 

drained in such a manner that the computed specific yield of the material was 

9.2 after 6 hours of pumping, 11.7 after 12 hours, 16.1 after 24 hours, 18.5 after 

36 hours, and 20.1 after 48 hours of pumping [fig. 7]. A much longer period of 

pumping would be required before the true specific yield of the material would 

have been reached. The true specific yield was estimated to lie between 22 and 23. 

[See Lugn and Wenzel, 1938.]

25

20

15

10

15 20 25 30 35 40 45 

TIME SINCE START OF PUMPING, IN HOURS

50 55 60

FIGURE 7. Variation of specific yield in relation to duration of pumping for a pumping test 

at Grand Island, Nebr. (Graph prepared by A. I. Johnson with data from Wenzel, 1942, 

p. 100.)
D32 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

Wenzel, L. K., Cady, R. C., and Waite, H. A., 1946, Geology and ground-water resources of Scotts Bluff County, Nebraska: U.S. Geol. Survey Water-Supply 

Paper 943, p. 66-67, 86.

The Brule formation * * * is chiefly a ruddy-buff, or flesh-colored si' 1:, massive and featureless in fresh exposures, but weathering into brick-shapec1 blocks 

or slabs. * * *.

***** * *

Eighty-eight percent of the material was composed of very fine sand and silt, 

and almost 70 percent was silt. * * *.

*******

The moisture equivalents determined in the laboratory for the two samples 

taken from the Brule formation were 24.9 and 20.9, respectively, an average of 

22.9. Because the values fall in the higher range referred to by Piper, tl ?y can 

be taken to represent the approximate specific retention. The porosities of the 

samples were 51 and 54, an average of 52.5. Thus the average specific yield of the 

samples is 29.6. This indicates that a cubic foot of Brule, if allowed to drain 

for a long period will yield about 0.296 cubic foot of water and will retain about 

0.229 cubic foot.

Investigations have shown that a sample of material after being saturated will 

not yield its water at once but the water will drain rather slowly, the rate of 

draining being somewhat proportional to the permeability of the material. The 

Brule, because of its tight character, yields water sluggishly, and several months 

to a year or more are doubtless required before the specific yield calculated in 

the laboratory is reached. As a result the quantity of water that is removed from 

storage by a decline of the water table in the Brule cannot be calculate^ from 

the specific yield determined in the laboratory unless the water table remains 

below the material for a long period. The comparatively large seasonal f uctuation of water levels in wells that tap the Brule results in part from the incomplete draining of the material during the time allowed. This means that the water 

table may decline for a considerable period before much water comes out of storage, except what drains from the cracks and fissures. This decline, however, will 

gradually slow up as the water table reaches lower stages, and a greater thickness 

of the formation thereby becomes available for draining.

Poland, J. F., Davis, G. H., Olmsted, F. H., and Kunkel, Fred, 1951, Ground-water 

storage capacity of the Sacramento Valley, California, Appendix D of Water 

resources of California: California Water Resources Board Bull. 1, p. 624- 

627.

In order to estimate the storage capacity of the water-bearing deposits it w?s necessary to classify the materials in the drillers' logs into a few groups to which 

arbitrary specific yield values could be assigned. Although many of the logs reported only gravel, sand, or "clay" (actually silt in most places), or gradations 

between these primary units, other logs reported as many as 10 to 20 different 

types of material. After a review of the many types of material described, it was 

decided to group the materials logged in five general classes, namely : (1) gravel; 

(2) sand, including sand and gravel, and gravel and sand; (3) tight sand, hard 

sand, or sandstone, with which were combined 26 different drillers' terms cohering 

material with more or less similar hydrologic properties; (4) cemented g'ravel, 

or clay and gravel, which embraced 19 additional drillers' terms; and (5) "clay,"
COMPILATION OF SPECIFIC YIELDS D33

which included 19 different types of material ranging from silt through clay to 

shale, and included lava. To obtain a reasonable geographic distribution of logs, 

the same well logs previously selected for the peg model on the basis of depth 

and representative geographic distribution also were utilized for tve classification 

of materials. Thus, for approximately 3,000 well logs, materials were classified 

in the five general classes described above.

Assignment of Specific Yield Values. It was not feasible to make an extensive 

field investigation to determine the specific yield of the different types of waterbearing materials in the Sacramento Valley. Therefore, it was n-^essary to assign an estimated specific yield value to each of the five general categories of 

material on the basis of available data.

* * * * * * *

On the basis of the results obtained in * * * two investigations [Eckis, 1934; 

Piper and others, 1939], together with specific-yield data fnm less detailed 

studies by others, * * * specific-yield values were assigned to the five groups 

of material classified in the well logs of the Sacramento Valley [table 9].

TABLE 9. Specific yield of water-bearing sediments in the Sacramento Valley,

Calif.

Specific yield 

Material (percent)

Gravel _________________________________ 25

Sand, including sand and gravel, and gravel and sand_____ 20 

Fine sand, hard sand, tight sand, sandstone, and related

deposits _ ______ ____________ 10 

Clay and gravel, gravel and clay, cemented gravel, and related deposits _ ______________________ 5 

"Clay," silt, sandy clay, lava rock, and related fine-grained 

deposits -______-_____________________ 3

For the purpose of estimating underground storage capacity, the Sacramento 

Valley was divided roughly into four storage groups and the^e in turn were 

subdivided into a total of 29 storage units, as shown on figure 8. The subdivision 

into groups and into the smaller storage units was first ma-le areally from 

physiography and soils; that is, from what can be seen at ti -i land surface; 

then the boundaries of the units were modified on the basis o* the subsurface 

geology to a depth of 200 feet, as shown by the peg model. In the modification, 

special emphasis was placed on the hydrologic character of tb« sediments and 

the continuity of water-bearing beds in the top 100 feet (the u^per and middle 

zones).

This was done for three reasons. First, it is believed that the storage units 

should be representative for the depth range most widely subje?t to unwatering 

or resaturation under present conditions or under moderately increased utilization to be anticipated in the near future. Second, for nearly all the storage 

units in the valley except the basin deposits, the specific yield is greater above 

the 100-foot depth than below it Lastly, with reference to natural or artificial 

recharge at or near the land surface, the distribution of water-bearing beds in 

the near-surface deposits is of primary importance. In this re^tiect, the coarse 

gravel tongues or blankets that are so well defined at shallow depths beneath 

the channels of Cache Creek (Al), and the Feather River (A5), are especially 

noteworthy.
D34 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

A Flood-plain and chance' deposit* 

B Low alluvial - plain and alluvialfan deposit*

C Diaaected alluvial deposit* 

D Basin deposit*

FIOUBB 8. Ground-water storage units of Sacramento Valley, Calif. (After Poland and

others, 1040.)

Computation of the ground-water storage capacity of the Sacramento Valley 

involved the following steps:

1. The valley deposits were divided areally into four storage grcnps and 

these were subdivided into 29 storage units.
COMPILATION OF SPECIFIC YIELDS D36

2. For each of the 29 units the area within each township cr portion of a 

township included was measured to the nearest 10 acre* with a scale 

or planimeter. The township or part of a township became the basic 

subunit for computation of storage capacity.

3. For each of three depth zones under consideration (20-5*K 50-100, and 

100-200 feet below land surface), logged material in selected wells in 

each basic subunit was classified into five categories of material. An 

arbitrary specific yield was assigned to each category.

4. Using these arbitrarily assigned specific-yield values, the average specific yield was computed for each depth zone in each basic subunit.

5. The storage capacity (to the nearest 100 acre-feet in each subunit was 

obtained as the product of average specific yield times volume of sediments in the depth zone.

6. Storage capacity for each storage unit was obtained as the sum of storage 

in all the subunits. These were then totaled by groups to give the estimated ground-water storage capacity for the Sacramento Valley.

Upson, J. E., and Thomasson, H. G., Jr., 1951, Geology and water resources of 

the Santa Ynez River basin, Santa Barbara County, Calif on-'a: U.S. Geol. 

Survey Water-Supply Paper 1107, p. 130-133.

The decline of shallow water level during the summer is a n^asure of the 

total discharge during that period. * * * The seasonal decline varies from year 

to year, apparently mainly in response to rainfall. The largest deoHnes occurred 

after the 1938 and 1941 winters of excessive rain when pumpage vras small, and 

probably are accounted for by relatively large seepage to the river in the ensuing summer seasons. * * * However, the average for the entire plain in tne 

period 1935-44 is taken as 3.5 feet

To determine the quantity of water represented by this decline of water level 

it is necessary to determine a value for the specific yield of the materials within 

the zone of water-level fluctuation. Specific yield is estimated approximately 

from the physical composition of the deposits by using a method similar to that 

employed by Piper (Piper, Gale, Thomas, and Robinson, 1939, p. 120-121) in the 

Mokelumne area. This method utilizes independently determined values for the 

specific yield of different grade sizes of material, together with the proportionate 

volumes of different sizes as revealed by well logs. * * *.

The total footage of each of several types of material within tve determined 

range of water-level fluctuations was obtained from well logs. The types are 

designated according to the drillers series, and are grouped irto four main 

classes as follows: Gravel and coarse sand; sand; silt, including fine sand, sandy 

clay, and soft clay; and clay [table 10]. * * * Next, the total footage of the 

different classes of material as recorded in drillers' logs and Surrey logs were 

added by areas, making allowance for a preponderance of wells bored in the 

coarse channel deposits; and new percentages were obtained. Tl *j percentages 

were weighted according to the acreage of the several areas and the following 

percentages by volume of the four classes of materials within the range of 

water-table fluctuations over the entire Lompoc plain obtained1 : Gravel and 

coarse sand, 7 percent; sand, 23 percent; silt, 32 percent; and clay, 38 percent.

The terms applied by drillers apparently correspond in general to standard 

terminology for grain sizes. By referring to the report on the Mckelumne area 

(Piper, Gale, Thomas, and Robinson, 1939, p. 117, fig. 8), the following values 

of specific yield for the grade sizes distinguished were taken: Gravel and coarse
D36 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

TABLE 10. Specific yields for water-bearing sediments in the Lompoc plain,

Santa Barbara County, Calif.

Specific yield 

(percent)

______________________________ 35

____________________ 30

Material

Gravel and coarse sand_____________ __. 

Sand _________ __ ______ 

Silt, including fine sand, sandy clay, and soft clayClay ___________________________ 

12

2

sand, 35 percent; sand, 30 percent; silt, 12 percent; and clay, 2 percent. Applying 

these values in proportion to the percentage volumes of the different classes of 

material, the average specific yield of the deposits within the zone of water-table 

fluctuation in the Lompoc plain is computed to be 14 percent.

Taking the total area as 16,300 acres, the average specific yield as 14 percent, 

and the average yearly decline as 3.5 feet, the amount of water represented by 

the decline is about 8,000 acre-feet a year. This represents the totM amount 

discharged during the season of no replenishment, or about half the y<*ar. Some 

discharge also occurs in winter, but its effect is masked by recharge. * * *.

Klein, I. E., written communication: Sacramento, Calif., U.S. Bureau of Reclamation.

LTable 11 and figs. 9 through 12 illustrate the relation between teTture and 

hydrologic properties, as determined by I. E. Klein.]

TABLE 11. Specific yield (or effective porosity) of core samples from Bureau of 

Reclamation test holes in the Friant-Kern Canal service area, as detemined from 

measured porosities and moisture equivalents

Hydrotextural classification

Well-sorted medium sand..... . ..............

Number 

of tests

127 

130 

35 

204

123 

44 

122 

329

372 

446 

34

Specific j^eld

Mean

30 

30 

29 

14

20 

23 

13

5

3 

1

Media"

30 

30 

3fi 

13

2' 

2? 

12 

4

2

Range 

of 90 

percent

18 -37 

23 -36 

26 -33

4 -25

9 -30 

13 -29

0 -2 

0 - H

California Department of Public Works, 1956, Santa Margarita River Investigation : California Div. Water Resources Bull. 57, v. 2, app., p. B65--B67.

In general, the procedure adopted followed that prescribed by the Division of 

Water Resources in its South Coastal Basin Investigation. Briefly, tlis method 

entailed estimating the volumes of various sedimentary types sucl as sand, 

gravel, clay, etc., occurring within appropriate depth intervals in e"»ch basin, 

multiplying each of these volumes by an appropriate weighted specific yield 

factor to obtain the volume of extractable water contained in each in*<?rval and 

finally summing the capacities of each interval to obtain the total storage capacity of the basin. Specific yield is defined herein as the volume of extractable
COMPILATION OF SPECIFIC YIELDS D37

ground water obtained from a unit volume of material expressed as a percentage 

of the volume of the material.

The logs of water wells provided the information upon which the storage 

capacity estimates were based. Clay, sand, and gravel and numerom gradations 

between these types were recognized on most logs. Some logs reported as many 

as 20 different types of material. In order to estimate the storage capacities of 

individual sedimentary types, it was first necessary to assign a specific yield 

value to each type appearing on the logs. The values assigned are those set 

forth in table 12 and were derived largely from laboratory determinations made 

at the time of the South Coastal Basin Investigation.

TABLE 12. Specific yield of water-bearing sediments in Santa Margtrita Valley,

Calif.

Type

Clay

Soil

Clay-sand

Silt

Sand

Tight sand

Gravel

Tight gravel

Gravel 

Clay

Description of material

Carbonaceous-silt 

Decomposed granite 

Hill formation

Hardpan 

Adobe

Loam 

Lake bed

Sand and clay 

Muck 

Sea mud and packed 

sand 

Silty clay 

Clay with lime rocks

Cement 

Sandy clay 

Cemented sediment

Sandy soil

Fine sand

Sandy-soil 

Silty-sand 

Unsorted angular sand 

Sand with trace of clay 

Sand and mud

Coarse sand 

Quicksand

Cemented sand 

Dirty sand

Gravel and sand 

Boulders 

Cobbles and sand 

Fill

Cemented gravel 

Gravel with clay layers 

Dirty gravel

Conglomerate (partially 

Clay and boulders

Sandy clay with 

gravel 

Packed sand with 

rocks

cemented)

Specific yield 

value assigned

1

4

5

10

28

16

22

15

7

Estimates of the storage capacities of ground water basins are necessarily 

approximate because of inherent difficulties in extending data from relatively 

few wells to apply to entire basins. The results, however, are believed to be use-
D38 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

 S ^-> o »

Illll

(H O

^: v>

Z "o

i 11 i i 111 

MSfsM!

J- B ;? J2 = . 

£ 0. "S Iff s"5 $

dOlOVJ ONIldOS
20

10 

98 - 

7 6 

5 4

(For further breakdown

see triangular diagram) / ° ILL-SORTED SILT

B. TEXTURAL CLASSIFICATION as a function of sorting and 

average grain size. Numbered points refer to specific illustrated samples detailed in figures 10,11,12.

_______li I i I I I I____I I____

V256 Vis % Vt Vi

MEDIAN DIAMETER (DK) OF GRAINS, IN MILLIMETERS

."AQUICLUDE LINE"

0.01 gpd permeability

and 1 percent

specific yield

50

C. TEXTURAL CLASSIFICATION in terms of percentage of 

sand, silt, and clay. Numbered points refer to sediments detailed in figures 10,11, and 12.

'100 

SILT

a

FIGURE 9. Teztural features and hydrologlc properties of the dominant unweathered sediments in the ground-water reservoir of the FriantKern Canal service area. (After unpub. data by I. E. Elein, U.S. Bur. Reclamation, 1954.)
D40 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

Vie Vs 1A Vi I 2 4 MILLIMETERS

90

« 50 

o

z

10

90

g 50

< 

z

UJ

o 

ac

UJ 

CL

10

TTTTf

10 100 

DIAMETER

1000 10.000 MICRONS

CLAY SILT

?*£

> =

F

a

 o 

£

V

j»

3

o

£ $»

>§

SAND

o>

II 

c

ID

C9

GRAVEL

U.S. Bur.

Reclamation

test hole

Depth

Textural classification

(based on average size and

sorting)

W

Microns

20/23-8D.. 

27/25-1 A.. 

28/24-23. .. 

25/26-16C.

418.0

401.5

364.3

482.3

Well-sorted coarse sand.. 

Ill-sorted coarse sand 

Well-sorted medium sand 

Ill-sorted medium sand.

125

74

125

28

600

690

340

320

1,800

2,300

720

1,190

3.8 

5.7 

2.4 

6.5

39.3

38.0

39.7

32.0

460

85

130

30

FIGURE 10. Mechanical-analysis data and hydrologic properties of four representative coarse and medium 

sands in the ground-water reservoir of the Friant-Kern Canal service area. (After unpub. data by I. E. 

Klein, U.S. Bur. Reclamation, 1954; table abstracted from regional laboratory reports on the core samples 

from the test holes represented.)
COMPILATION OF SPECIFIC YIELDS D41

Vie Vis '/4 Vz 1 24 MILLIMETERS

100 

DIAMETER

1000 10.00C MICRONS

CLAY SILT

£>« «

u.

F

a' o 

a 8

o

£-5!

« <o >8

SAND

£

a 

c 

<o

CO

GRAVEL

No. ence 

1

«

5

6

7

8

9

U.S. Bur. 

Reclamation 

test hole

20/23-8D....

23/25-9D....

31/25-27.....

20/23-8D....

20/23-8D....

Depth

(ft)

593.0

94.0

399.0

546.0

686.5

Textural classification 

(based on average size and 

sorting)

Well-sorted fine sand. ...

Very ill sorted silty sand

Well -sorted fine sand ....

Very ill sorted silty sand

Ill-sorted fine sand ......

o>

Effective si:

V>u)

a

Median di(Z>«) eter 

|il

Microns

90

5

45

4

7

210

180

120

100

110

430

1,000

240

570

370

_

!§

1 1

Q

2.2

14.1

2.3

11.9

7.3

r 

t_

|i

£

4\2

3^. 1

40.4

SIX 8

ST. 9

'K'-

ic yield (orjtive porosit ume percen

1*1

CO

33

10

34

6

17

§*3 D1

i*« SO-a

lil §^3 OD

150

.2

47

.2

.2

FIGURE 11. Mechanical-analysis data and hydrologic properties of five representative fine sands and silty 

sands in the gronnd-water reservoir of the Friant-Kern Canal service area. (After unpub. data by I. E. 

Klein, U.S. B'ir. Reclamation, 1954; table abstracted from regional laboratory reports on the core samples 

from the test holes represented.)
D42 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

V256

90

50

10

90

50

10

II IIII I I I I

Vis VB 14 % 1 24 MILLIMETER

\ i i i

i i i u |

Mini i 1111

1?

/

TT=rr

i i 111

1 1 11 1

10 100 

DIAMETER

1000 10,000 MICRONS

CLAY SILT >iC

01

c 

ul

Medium 01

(5

5

^1

SAND

<n

"a 

c

CD

O

GRAVEL

6

S

e 

1

10

11

12

13

14

15

16

U.S. Bur.

Reclamation 

test hole

23/23-33A....

23/23-33 A... .

20/23-8D.--.

25/23-28.-.--

28/22-9B.....

23/23-33A23/23-33 A .

Depth

(ft)

733.2

233.5

241.5

93.5

597.5

219.5

155.6

Textural classification

(based on average 

size and sorting)

Well-sorted silt. .......

Well-sorted silt. -.--.-.

Ill-sorted silt ..........

Ill-sorted silt.. ......

Clayey sandy silt.

Silty clay. ............

Clay................

S

qj

>

u

w

S

1 3

la^

'Pi's

dQ

-w S

C* '5?

§|

- 

Microns

22

10

4

3

 1

 1

50

30

58

40

18

13

3

110

70

350

250

140

120

40

fe

o

 2

«| SI S ' 3 l^ I Q * I'HQ

'S

CD

°

2.2

2.7

9.4

9.1 12

 11

 20

Xo.

g

3

°

s~

pPi

40.5

40.6

36.0

33.2

36.7

38.5

47.0

£§

« §

o-^- ^''^

11

o§.|

sis.

CO

28

17

7

2

^ V^

<v«

.2 g

E3 ^

Is

o

 «*H

 So"

Iai5 !& § s

9

.2

.07

.02

.007

.003

t<.001

 Calculated. 

t Estimated.

FIGURE 12. Mechanical-analysis data and hydrologic properties of seven representative s'lts and clays 

in the ground-water reservoir of the Friant-Kern Canal service area. (After unpub. data by I. E. Klein, 

U.S. Bur. Reclamation, 1954; table abstracted from regional laboratory reports on the core samples from 

the test holes represented.)
COMPILATION OF SPECIFIC YIELDS D43

ful and to reasonably represent the physical situation under the stated 

assumptions.

California Water Resources Board, 1956, Geology and ground wate- of Ventura 

County, California; California Water Resources Board, Ven*ura County 

Inv., Bull. 12, v. 2, app. B, p. 40-41.

In its South Coastal Basin Investigation, the Division of Water Resources 

conducted extensive field and laboratory investigations for the purpose of assigning specific yield values to various types of material appearing in well logs. 

These procedures are described in Bulletin No. 45, "Geology and Ground Water 

Storage Capacity of Valley Fill" (Division of Water Resources, 1934). With 

slight variations, the values determined in this earlier work and Bulletin 46, 

"Ventura County Investigation" were adopted for compiling the change of 

storage estimates presented here.

The task of assigning specific yield values to the sediments appearing in logs 

was simplified by dividing all basin sediments into eight general categories. 

These included soil, clay, clay-sand, clay-gravel, tight sand, sand, tight gravel, 

and gravel. Sand, gravel, and clay, which constitute the bulk of the basin sediments, were generally found to be well differentiated on the drillers' logs. 

Combinations of these materials, however, were frequently described by such 

unique terms as "ooze," "muck," "cement," etc. Materials so described were 

placed, based on the judgment of a geologist, into one of the above e'ght categories. Table 13 indicates specific yield values assigned to the general categories. In 

certain instances, these values were altered slightly whenever field observations 

indicated the advisability of changes.

TABLE 13. Specific yields of sediments in Ventura County, Cclif.

Specific yield 

Material (percent)

Soil, including silty clay ________________________ 3

Clay, including adobe and hardpan __________________ 0

Clayey sand, including sandy silt ___________________ 5

Clayey gravel ______________________________ 7

Sand ____________________________________ 25

Tight sand, including cemented sand _________________ 18

Gravel, including gravel and sand ___________________ 21

Tight gravel, including cemented gravel _______________ 14

Back, William, 1957, .Geology and ground-water features of the S'-nith River 

plain, Del Norte County, California: U.S. Geol. Survey Water-Supply Paper 

1254, p. 43-45.

Specific yields assigned to deposits on the Smith River plain were modified 

from specific-yield values used in a report on the Sacramento Valley (Poland, 

Da vis, Olmsted, and Kunkel, 1951). * * * Table 14 shows the specif e yields, in 

percent, used to estimate ground-water storage for the Smith River plain.

TABLE 14. Specific-yield values for the various litholoffic materials uxed in estimating ground-water storage on the Smith River plain, California

Poeciflc yield 

(percent)

Class 1: Gravel; boulders; sand and gravel ____________ 25

Class 2: Dune sand ___________________________ 15

Class 3: Sand; clay and sand; fine sand _______________ 10

Class 4: Clay and gravel; sandy clay ________________ 5

Class 5: Clay; blue shale _______________________ 1
D44 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

For each unit, * * * the drillers' logs were examined and the thickness of each 

class of material between 10 and 35 feet below the land surface was totaled. The 

total thickness for each class was divided by the total thickness for all classes 

to determine the percentage represented by each class. Each percentage was 

multiplied by the specific-yield value for that class; then these products were 

totaled and divided by 100 to determine the average specific yieM for the 

sediments in that storage unit.

California Water Rights Board, 1957, Determination of specific yield and storage 

capacity: California Water Rights Board Spec. Rept. 2 of Referee Tia Juana 

Basin, app. C., p. C12-C23.

In order to apply values of specific yield to materials described in drillers' 

logs, it was necessary to establish values that could be correlated with these 

descriptions. The primary bases for classification of materials in available 

drillers' logs being dominant or median grain sizes. In order to provide such a 

comparison the relationship between the maximum ten percent grad*> size and 

dominant grain size was determined from cored samples. This relationship is 

depicted on figure 13, which indicates that the maximum ten percent grade size 

is in genera] one grade size larger than the dominant particle size.

Many of the sediments reported in drillers' logs are broadly classified, necessitating the application of average specific yields to the large portion of the sediments so classified in the basin. Correlation of specific yields of cored samples 

with the general classification of that material shown by existing well logs in the 

test hole vicinity indicates a range of 17 to 32 percent specific yield for "sand" as 

described by the driller. Because of this variation average values of specific 

yields were applied to such general classification of sediments. Values so used 

are listed in table 15.

SPECIFIC YIELD, IN PERCENT 

30 32 32 28 21

Vk

'/4 

W 

1

2

4

V FINE 

SAND

FINE 

SAND

MEDIUM 

SAND

COARSE 

SAND

V. COARSE 

SAND

GRANULE

0

GRAVEL

GRANULE OC O

zl

a

/

V) O

II

C

O <

0

0

II

Xo

!i SILT

8 4 2 1 V, % Vi 

MAXIMUM 10 PERCENT GRADE SIZE, IN MILLIMETERS

1/128

FIGURE 13. Grade-size distribution of cored samples from the Tia Juana l>sln, Calif. 

(After California Water Rights Board, 1957.)
COMPILATION OF SPECIFIC YIELDS D45

Determination of specific yield of valley fill materials in type (2) samples 

[3-inch inside diameter by 3 feet long] was accomplished by use of the laboratory 

drainage method. * * *.

******* 

After saturation the samples were immediately weighed and placed in a 

moisture room, in which atmospheric temperature and humidity remained 

essentially constant, and allowed to drain freely. The temperature of the air 

was maintained at 70 degrees Fahrenheit and the relative humidity at approximately 100 percent. * * *.

Initial effluent was determined by weighing the samples daily for a period of 

twenty days; water loss thereafter was determined weekly. * * *.

After the samples had drained 34 or 35 days, at which time the remaining 

moisture content consisted essentially of moisture held as specific retention and 

capillary water, the samples were inadvertently subjected to ambient atmospheric 

temperature and humidity until 134 days of draining time had elapsed. * * *.

******* 

The values of specific retention and specific yield obtained from laboratory 

drainage of type (2) samples * * * are illustrated graphically on figure 14. 

Individual computed values * * * are represented by the average curve shown 

as a dashed line labeled Specific Yield-Partial Saturation on fgure 14 and 

values incorporating porosity are shown by the solid line labeled Fnecific YieldTotal Saturation. The latter values are believed more representative and were 

therefore utilized. Thus specific yields for materials contained in type (2) 

samples were taken as the difference between porosity and specie retention. 

A comparison of the specific yield values so determined for Tia Juana Basin 

sediments and the specific yields of South Coastal Basin sediments are shown 

on figure 15, where these values are both depicted in relation to grain size.

Although the origin and mode of deposition of sediments in Tia Juana and 

South Coastal Basins differ, the specific yields of sediments sampled' in Tia Juana 

Basin were found to be only slightly higher than those in the South Coastal Basin. 

The greatest variation (2^ percent specific yield) occurred in fine and medium 

sand, with less variation (1 percent specific yield) in the very fire and coarse 

sands. Figure 15 also illustrates the size distribution of Tia Juan* Basin sediments based upon the average percentages of the various grain sizes found in 

32 samples obtained from five test holes.

Specific yield values determined by the drainage method for Tia Juana Basin 

sediments varying from fine to coarse sand indicate an average of 1.9 percent 

(specific yield) greater value than the South Coastal Basin sediments. In view 

of the small variation in corresponding yield values and the more extensive 

studies of South Coastal Basin sediments, the specific yield value* based upon 

maximum ten percent grade size are considered valid for the problem under 

consideration and therefore have been adopted.

******* 

The greatest single factor contributing to error in computing storage capacity 

is the well drillers' interpretation of the material he encountered during well 

drilling and descriptions have been found to vary widely among drillers when 

describing similar sediments. A tendency exists among drillers to describe sediments on the basis of their permeability rather than water-yield ; ng capacity. 

Therefore, the problem for the investigator is to differentiate betveen the well 

logs and consider only the more reliable logs when assigning yieM values, although the less reliable logs are often of a qualitative value. For these reasons,
D46 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

MAXIMUM 10 PERCENT GRADE SIZE, IN MILLIMETERS

(THE GRADE SIZE IN WHICH THE CUMULATIVE TOTAL, BEGINNING WITH THE

COARSEST MATERIAL, REACHES 10 PERCENT OF THE TOTAL SAMPLE)

FIGURE 14. Porosity, specific yield, and specific retention of sediments from th? Tia Juana 

Basin, Calif. (After California Water Rights Board, 1957.)

all drilling logs have been classified broadly into two categories differentiated 

and undifferentiated. Sample test holes, test pit samples, test wells, and water 

wells that have good material descriptions are classified as differentiated, with 

the remaining sources of information called undifferentiated. Specific yield 

values assigned to the various types of materials in differentiated and undifferentiated well logs are listed in table 15. The values assigned to materials described 

in undifferentiated logs generally fall into the category of clay, sand or gravel.

TABLE 15. Specific yield of water-bearing sediments in Tia Juana Basin, Calif.

Differentiated description of material

Sandy clay. __. __ _ _ 

Silt....... ------------------

Very fine sand..-.. -----------

Fine sand.. _ _ ___ ___ Medium sand. . _________________

Coarse sand _ -----------------

Very coarse sand. ...............

Gravelly sand ------------------

Fine gravel. -_- _-_-_-_-_-----

Medium gravel . .---.---------

Coarse gravel.. _ ......... _ ..

Very coarse gravel and boulders.

Average 

specific yield 

(percent) 1

5

10

17

25

30

32

31

28

26

23

18

14

Undifferentiated 

description of 

material 2 

Clay.. .......

Silt........ ... 

Sand.. -----------

Boulders. --------

Average 

specific yield 

value used 

(percent) 

1

5

10

21

30

22

14

1 Determined from maximum 10 percent grade size of cored samples.

2 As contained in drillers' logs.
COMPILATION OF SPECIFIC YIELDS D47

100

80

60

20

Distribution and specific yield of 

the Tia Juana Basin sediments

are based on mechanical and 

drainage analyses of cored

SPECIFIC YIELD OF SEDIM 

FROM SOUTH COASTAL B

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5TRIBUTION OF SEDIMENTS 

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I YIELD OF SEDIMENTS

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GRAIN SIZE. IN MILLIMETERS

FIOUKE 15. Distribution and specific yield of sediments from the Tia Juara Basin, Calif. 

(After California Water Rights Board, 1957.)

Values assigned to these materials are averages of the values assigned to differentiated sources of information.

In addition, to estimates of specific yield obtained from sample test holes and 

wells, several other sources of information have been utilized. Curing March 

1948, tests were conducted at wells owned by the San Ysidro Irrigrtion District 

and during September, 1949, at the South Basin plant of the California Water and 

Telephone Company for a determination of permeability by the discharging well 

method. Values of specific yield have been determined from data corseted during 

these tests. The San Ysidro test revealed the affected water-bearing materials 

to have a specific yield of 31 percent which compares in magnitude to the estimated average specific yield of 25 percent for the subarea in which the test was 

performed. The South Basin test indicated shallow materials to have a yield of 

20 percent within the subarea which has an estimated average specif c yield of 21 

percent, average values being determined from the specific yield map. * * *.

California Water Resources Board, 1958, Geology and ground water of San Luis 

Obispo County, California: California Water Resources BoaH, San Luis 

Obispo County Inv., app. B, p. 26-27.

The changes in ground water storage occurring over selected periods of study 

were generally not estimated due to lack of historical data on ground water level 

fluctuations. A certain portion of the total storage can be considered usable 

storage capacity, but this amount is uncertain in most basins due to lack of data. 

In general, the estimating procedures required: (1) A determination of total 

volume of saturated sediments and, (2) an estimate of the percentage of this 

volume that contained extractable ground water. The first item was obtained by 

computing the volume of sediments that lay between the water tr*>le and the
D48 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

bottom of the basin. The second item was obtained by evaluating tl ^ average 

weighted specific yield of the sediments by analysis of available well logs. 

***** * *

With slight variations, the values determined in this [Eckis, 1934] earlier work 

were adopted for computing the change of storage estimates presented here.

The task of assigning specific yield values to the sediments appearing in logs 

was simplified by dividing all basin sediments into eight general categories. These 

included soil, clay, clay and sand, clay and gravel, tight sand, sand, tight gravel, 

and gravel. Sand, gravel, and clay, which constitute the bulk of the basin sediments, were generally found to be well differentiated on the drillers' logs. Combinations of these materials, however, were frequently described by s\\ch unique 

terms as "ooze," "muck," "cement," etc. Materials so described were placed, based 

on the judgment of a geologist, into one of the above eight categories. Table 16 

indicates specific yield values assigned to the general categories of material encountered. The Paso Robles formation is generally more compacted and weathered than the alluvium and some specific yields were lowered accordingly.

TABLE 16. Specific yield of water-bearing sediments in San Luis Obispo County,

Calif.

Specific yield (percent)

Paso Robles

Material Alluvium formation

Soil, including silty clay_____ ________...... .. 5 5

Clay, including adobe and hardpan_ ________... . .. 3 3

Clay and sand, including sandy silt.. _______ .. 5 5

Clay and gravel ...______... . .- __ .. 7 7

Sand.........--.... . .. . .. . 25 20

Tight sand, including cemented sand.. .._____.__ _ 18 15

Gravel, including gravel and sand__ . _________..___ 21 18

Tight gravel, including cemented gravel..._______... .. 14 13

Davis, G. H., Green, J. H., Olmsted, F. H., and Brown, D. W., 1959, Groundwater conditions and storage capacity in the San Joaquin Valley, California: 

U.S. Geol. Survey Water-Supply Paper 1469, p. 206-210.

The values chosen for specific yield were based largely on previous work by 

other investigators in California, with certain rational modifications to fit conditions in the San Joaquin Valley. * * *.

The results obtained by Eckis (1934), by Piper and others (1939), by the Sacramento laboratory of the Bureau of Reclamation, and by other lers detailed 

studies were modified somewhat for use in the San Joaquin Valley, and the 

specific yields listed in table 17 were assigned to the five major groups of material classified in the well logs.

The grouping of drillers' terms and the specific yield of one category S 

(sand) were different from those used by the Geological Survey in the Sacramento Valley investigation (Poland and others, 1951, p. 625), * * *. The 

specific yield of 25 percent assigned to the coarse gravelly deposits ws approximately a general average of the results * * * which ranged frorr 13 to 35 

percent. Probably much of the clean gravel and well-sorted sand near the apexes 

of the alluvial fans of the east-side streams in the San Joaquin Valley has a 

specfic yield substantially above 25 percent, as suggested by the,Bureau of 

Reclamation data * * *. However, the writers believe that figure to be a reasonable and conservative estimate of the valleywide average.
COMPILATION OF SPECIFIC YIELDS D49

Sand and gravel (mixed) was included in the gravel category instead of being 

grouped with sand as in the Sacramento Valley storage estimate. (See Poland 

and others, 1951.) Inasmuch as both the G and the S categories were assigned 

a specific yield of 25 percent in the San Joaquin Valley estimate, it would have 

made no difference in which category the sand and gravel was placed in computing weighted-average specific yields. However, for geologic interpretations 

of the data * * * grouping mixed sand and gravel with gravel was more useful 

and instructive.

TABLE 17. Specific yield of water-bearing sediments in the San Jocquin Valley,

Calif.

Specific

yield 

Group Material (percent)

G Gravel; sand and gravel; and related coarse gravelly deposits.__. 25

S Sand, medium- to coarse-grained, loose, and well-sorted._______ 25

F Fine sand; tight sand; tight gravel; and related deposits..------ 10

Cg Silt; gravelly clay; sandy clay; sandstone, conglomerate; and

	related deposits.________________________________________ 5

C Clay and related very fine grained deposits.__________________ 3

X Crystalline bedrock (fresh)___-_-_---__--___-_---_--_----__ 0

DRILLERS' TERMS USED IN ESTIMATING SPECIFIC YIELD 

Group G: Gravel, sand and gravel, and similar materials

(Specific yield 25 percent)

Boulders Water gravel

Coarse gravel Gravel and sand

Cobbles Gravel and sandrock

Cobble stones Rock and gravel 

Dry gravel (if above water table) Sand and boulders

Float rocks Sand and cobbles

Gravel Sand and fine gravel

Loose gravel Sand and gravel

Rocks Sandy gravel

Group S: Sand 

(Specific yield 25 percent)

Coarse sand Running sand 

Free sand Sand 

Loose sand Sand, water 

Medium sand

Group F: Fine sand, tight sand, tight gravel, and similar materials

(Specific yield 10 percent)

Sand and clay Sand and hard sand

Sand and clay strata (traces) Sand and lava

Sand and dirt Sand and pack sand

Sand and hardpan Sand and sandy clay
D50 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

TABLE 17. Specific yield of water-bearing sediments in the San Joaquin Valley,

Calif. Continued

DRILLERS' TERMS USED IN ESTIMATING SPECIFIC YIELD Continued

Group F: Fine sand, tight sand, tight gravel, and similar materials Continued

(Specific yield 10 percent)

Sand and soapstone

Sand and soil

Sand and some clay

Sand, clay, and water

Sand crust

Sand little water

Sand, mud, and water

Sand (some water)

Sand streaks, balance clay

Sand, streaks of clay

Sand with cemented streaks

Sand with thin streaks of clay

Coarse, and sandy

Loose sandy clay

Medium sandy

Sandy

Sandy and sandy clay

Sandy clay, sand, and clay

Sandy clay water bearing

Sandy clay with streaks of sand

Sandy formation

Sandy muck

Sandy sediment

Very sandy clay

Cloggy sand

Coarse pack sand

Compacted sand and silt

Dead sand

Dirty sand

Fine pack sand

Fine quicksand with alkali streaks

Fine sand

Fine sand, loose

Hard pack sand

Hard sand

Hard sand and streaks of sandy clay

Hard sand rock and some water sand

Hard sand, soft streaks

Loamy fine sand 

Medium muddy sand 

Milk sand 

More or less sand 

Muddy sand 

Pack sand

Poor water sand

Powder sand

Pumice sand

Quicksand

Sand, mucky or dirty

Set sand

Silty sand

Sloppy sand

Sticky sand

Streaks fine and coarse sard

Surface sand and clay

Tight sand

Boulders, cemented sand 

Cement, gravel, sand, and r->cks 

Clay and gravel, water bearing 

Clay and rock, some loose rock 

Clay, sand, and gravel 

Clay, silt, sand, and gravel 

Conglomerate, gravel, and boulders 

Conglomerate, sticky clay, sand and

gravel 

Dirty gravel 

Fine gravel, hard 

Gravel and hardpan strata 

Gravel, cemented sand 

Gravel with streaks of clay 

Hard gravel 

Hard sand and gravel 

Packed gravel 

Packed sand and gravel 

Quicksand and cobbles 

Rock sand and clay 

Sand and gravel, cemented streaks 

Sand and silt, many gravel 

Sand, clay, streaks of gravel 

Sandy clay and gravel 

Set gravel 

Silty sand and gravel (cobb^s)

Tight gravel

Sandy loam

Sandy loam, sand, and clay

Sandy silt

Sandy soil

Surface and fine sand
COMPILATION OF SPECIFIC YIELDS D51

TABLE 17. Specific yield of water-tearing sediments in the San Jo"-qwin Valley,

Calif. Continued

DRILLERS' TERMS USED IN ESTIMATING SPECIFIC YIELD C mtlnued

Gronp F: Fine sand, tight sand, tight gravel, and similar materials C ^tinned

(Specific yield 10 percent)

Silt and sand 

Soil, sand, and clay 

Topsoil and light sand

Brittle clay and sand

Clay and sand

Clay, sand, and water

Clay, with sand

Clay with sand streaks

More or less clay, hard sand and

boulders 

Mud and sand 

Mud, sand, and water 

Sand and mud with chunks of clay 

Silt and fine sand

Water sand sprinkled with clay

Float rock (stone) 

Laminated 

Pumice 

Seep water 

Soft sandstone 

Strong seepage

Gronp Cgs Clay and gravel, sandy clay, and similar materials

(Specific yield 5 percent)

Cemented gravel (cobbles) 

Cemented gravel and clay 

Cemented gravel, hard 

Cement and rocks (cobbles) 

Clay and gravel (rock) 

Clay and boulders (cobbles) 

Clay, pack sand, and gravel 

Cobbles in clay 

Conglomerate 

Dry gravel (below water table)

Gravel and clay 

Gravel (cement) 

Gravel and sandy clay 

Gravel and tough shale 

Gravelly clay 

Rocks in clay 

Rotten cement 

Rotten concrete mixture 

Sandstone and float rock 

Silt and gravel 

Soil and boulders

Cemented sand

Cemented sand and clay

Clay sand

Dry hard packed sand

Dry sand (below water table)

Dry sand and dirt

Fine muddy sand

Fine sand, streaks of clay

Fine tight muddy sand

Hard packed sand, streak^ of clay

Hard sand and clay

Hard set sand and clay

Muddy sand and clay

Packed sand and clay

Packed sand and shale

Sand and clay mix

Sand and tough shale

Sand rock

Sandstone

Sandstone and lava

Set sand and clay

Set sand, streaks of clay

Sticky sand and clay

Tight muddy sand

Very fine tight muddy sand

Dry sandy silt

Fine sandy loam

Fine sandy silt

Ground surface

Loam

Loam and clay

Sandy clay loam

Sediment

Silt

Silt and clay

Silty clay loam

Silty loam

Soft loam

Soil

Soil and clay
D52 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

TABLE 17. Specific yield of water-bearing sediments in the San Joaqvin Valley,

Calif. Continued

DRILLERS' TERMS USED IN ESTIMATING SPECIFIC YIELD Continued 

Group Cg: Clay and gravel, sandy clay, and similar materials Continue!*

(Specific yield 5 percent)

Soil and mud Clay and sandy clay 

Soil and sandy shale Clay and silt 

Surface formation Clay, cemented sand

Clay, compact loam and sand

Top hardpan soil Clay to coarse sand 

Topsoil Clay, streaks of hard packed sand 

Topsoil and sandy silt Clay, streaks of sandy clay 

Topsoil silt Clay, water

Clay with sandy pocket

Decomposed hardpan Clay with small streaks of sand 

Hardpan and sandstone Clay with some sand 

Hardpan and sandy clay Clay with streaks of fine sard 

Hardpan and sandy shale Clay with thin streaks of sand 

Hardpan and sandy stratas Porphyry clay 

Hard rock (alluvial) Quicksandy clay 

Sandy hardpan Sand clay 

Semihardpan Sand shell 

Washboard Shale and sand

Solid clay with strata of ceir^nted sand 

Cemented sandy clay

Hard sandy clay (tight) Ash 

Sandy clay Caliche 

Sandy clay with small sand

streaks, very fine Ohalk 

Sandy shale Hard lava formation 

Set sandy clay Hard pumice 

Silty clay Porphyry 

Soft sandy clay Seepage soft clay 

Clay and fine sand Volcanic ash 

Clay and pumice streaks

Group C: Clay and related materials 

(Specific yield 3 percent)

Adobe Gumbo clay

Brittle clay Hard clay

Caving clay Hardpan (H.P.)

Cement Hardpan shale

Cement ledge Hard shale

Choppy clay Hard shell

Clay Joint clay 

Clay, occasional rock Lava

Crumbly clay Loose shale

Cube clay Muck 

Decomposed granite Mud

Dirt Packed clay

Good clay Poor clay
COMPILATION OF SPECIFIC YIELDS D53

TABLE 17. Specific yield of water-bearing sediments in the San Joaquin Valley,

Calif. Continued

DRILLERS' TERMS USED IN ESTIMATING SPECIFIC YIELD Continued 

Group C: Clay and related materials Continued

(Specific yield 3 percent)

Shale Sticky 

Shell Sticky clay 

Slush Tiger clay 

Soapstone Tight clay 

Soapstone float Tulemud 

Soft clay Variable clay

Volcanic rock 

Squeeze clay

Group X: Crystalline bedrock (fresh) 

(Specific yield zero)

Granite Graphite and rocks

Hard boulders Bock (if in area of known crystalline

Hard granite rocks)

Ha rd rock

The S (sand) category was assigned a specific yield of 25 percent instead 

of the 20 percent used in the Sacramento Valley study. The Bureau of Reclamation laboratory data * * * indicate that 20 percent probably is much too 

conservative an estimate for the San Joaquin Valley, even allowing for the 

fact that many well drillers do not discriminate between tight or silty sands 

and relatively loose, well-sorted sands. Moreover, as the data of Eckis and 

Gross indicate * * * many sands have higher specific yield than gravels, owing 

to the higher porosity of the sands. In many places, as for example in the south 

coastal basin of southern California where Eckis and Gross conducted their 

study, most gravelly beds are much less well sorted than the sands; 1 ^nce, their 

porosity and specific yield are lower. Accordingly, in the San Joaquin Valley 

sand was assigned the same specific yield as gravel. * * *.

Tight sand, tight gravel, fine sand, and many similar terms sugresting restricted permeability and drainable void space were placed in an intermediate 

category having an assigned specific yield of 10 percent. Several types included 

here were assigned a specific yield of only 5 percent in the Sacramento Valley 

study (Poland and others, 1951) but the writers believe that the present grouping, which is supported by laboratory-test data of the Bureau of Reclamation, is more logical.

A fourth category comprising gravelly clay, sandy clay, sandstone, conglomerate, and related very poorly sorted or tightly cemented materials of 

low premeability was given a specific yield of 5 percent. This value is about the 

same as that obtained by Eckis and Gross for clayey weathered subsurface 

materials in the south coastal basin and is slightly higher than tl » average 

of 4 percent obtained by Piper for very fine sand, silt, and clay. .Although a 

specific yield of 5 percent may be too high for true silty olay, claye7 silt, and 

sandy clay, * * * such materials have higher specific yields than the "clay" 

described by drillers, and these materials accordingly were placed in the 5-
D54 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

percent category. However, where Bureau of Reclamation geologists rather 

than well drillers described these materials, they were assigned a specific yield 

of only 3 percent.

The finest grained deposits, mostly described as some type of "clay" were 

assigned a specific yield of 3 percent. This specific yield is higher than that used 

for clay in the south coastal basin study, but is midway betweer the values 

used for clay and sandy day in the unweathered subsurface alluvial deposits 

in that area. The term "clay" as applied by the driller, is likely to include many 

beds that are silty or sandy, if they contain much material so fine that it remains in suspension in the drilling fluid. Comparisons of sample descriptions 

by well drillers and Bureau of Reclamation geologists indicated that some of 

the materials classified by the drillers as "clay" were described by the geologists 

as silt or even fine sand.

Evenson, R. E., 1959, Geology and ground-water features of the Eureka area, 

Humboldt County, California: U.S. Geol. Survey Water-Supply Paper 1470, 

p. 35.

The deposits for which estimates of storage capacity are consid?red are the 

alluvium, channel deposits, and the lower terrace deposits of the Eel, Van Duzen, and Mad Rivers. The following specific-yield values, table 18, assigned to 

these deposits encountered in wells in the Eureka area, have been rdapted with 

slight modification from those figures used in estimating the ground-water storage capacity of similar deposits in the Sacramento Valley (Poland and others, 

1951).

******* 

Most of the material penetrated by shallow wells in the alluvial dcr>osits along 

the Eel, Van Duzen, and Mad Rivers consists of fine- to coarse-gTained sand 

and gravel and a few thin streaks of silt or clay ordinarily not thick enough 

to be noted on well logs. * * *

TABLE 18. Specific yields for the alluvial deposits of the Ee\ Van 

Duzen, and Mad Rivers, Humboldt County, Calif.

Specif" yield 

Material (percent)

Gravel _______________________________ 25

Sand and gravel, sand- _______ _____ 20

Sand and silt _____ _____ ____ 15

Sand and clay, soil and clay, gravel and clay_________ 10

Clay ________________________________ 3

Rasmussen, W. C., and Andreasen, G. E., 1959, Hydrologic budget of the Beaverdam Creek basin, Maryland: U.S. Geol. Survey Water-Supply Paper 1472, 

p. 83-92.

The ratio of the volume of drained, or gravity, water to the total volume of 

the rock or soil is called the specific yield * * *. The amount of water that 

saturated sediments will yield to gravity is equal to AHY, wher« AH is the 

change in ground-water stage and Y is the specific yield.

The same expression represents ideally the amount of water entering storage 

with a rising water level. However, in a sand that is fairly homogeneous except that a silt or few clay lenses are within the zone of ground-water fluctuation, a rise of the water table from below to above one of these lens?s would not
COMPILATION OF SPECIFIC YIELDS D55

result immediately in complete saturation of it. Though the silt or clay might 

be considerably more porous than the surrounding sand, its permeability might 

be so low that a rather long time would be required for the water to penetrate 

the lens, and even then some air would be trapped. Conversely, when the water 

table receded, leaving a partly or completely saturated silt-clay lens somewhere 

within the capillary fringe, the lens would not yield its gravity water as readily 

as the surrounding sand. Rather there would be a leakage from the s'It-clay lens 

down to the lowered water table. Further, the water table responds quickly to 

every sizable rainfall, and a rapidly rising water table entraps air in even the 

coarser sediments. Trapping of air results in a decrease in porosity and permeability, until the air is dissolved in the water.

Because of these considerations, a new term, gravity yield, will be denned 

here in such a way that the definition will include length of drainage time. The 

gravity yield of a rock or soil after saturation or partial saturation is the ratio 

of (1) the volume of water it will yield by gravity to (2) its own volrme, during 

the period of ground-water recession. Gravity yield, in effect is a "field" specific 

yield; it is a,function of time and of previous fluctuations of inflltenng water, 

as well as of the character of the rock or soil, * * *.

*******

The * * * estimates of gravity yield, which range from 8.7 to lf.0 percent, 

average 11.1 percent [table 19] * * *. These check values of grrvity yield 

were obtained under conditions of a rising water table, when the gravity yield 

percentage would be lower because of entrapped air. That is, the water levels 

would be too high, and the gravity yield thus would be computed too low. 

Hydrologists have noted the same phenomenon in the dunes of the Netherlands. 

Krul and Liefrinck (1946, p. 40) say: "An observation worth mentioning was 

that indications of water levels computed during an infiltration period with 

a rising water table were always found to be too high, a phenomenon which 

was attributed to compression of the air contained in the sand interstices * * *."

TABLE 19. Specific yield of sediments from Beaverdam Creek basin, Maryland

Sfedflc yield 

Material (percent)

Medium sand___________________________ 25 

Sandy clay_____________________________ 11

Porosity determinations for sediments from the Beaverdam Creek basin 

were * * *:

Porotity 

Type of material (percent)

Medium-grained sand_______________________ 38. 0

Sandy silt_________________________.___ 38.3

Sandy clay_____________________________ 30 5

Average _ ____________________ 37.6

The converted moisture equivalents, which range from 2.3 to 39.6 percent, are 

greatest for the clay and least for the sand. * * * The pit logs * * * indicate 

a predominance of sand, so that a single arithmetic average of the converted 

moisture equivalents, assumed to be equal to the specific retention, is reasonable. 

Substituting the average porosity and the average converted moisture equivalent 

in equation (6) gives a specific yield of 21.0 percent (37.6-16.6).
D56 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

It is possible that this high specific yield was due, in part, to inadequate 

sampling of the basin. Serious errors are apt to be brought in when co-nparatively 

large areas are represented by only a few samples. It is reasonable, however, that 

the specific yield would be higher than the gravity yield, because it is unlikely 

that ground-water drainage during the period of observation was ever accomplished so completely that all gravity water was released from storage.

Wilson, H. D., Jr., 1959, Ground-water appraisal of Santa Ynez Piver basin, 

Santa Barbara County, California, 1945-62: U.S. Geol. Survey Water-Supply 

Paper 1467, p. 24-25.

Laboratory methods are subject to the usual errors inherent in any method 

involving sampling. Also, for the preliminary estimate it was rot believed 

justified to sample the alluvial deposits in great detail. Pumping-test methods 

are of doubtful value in obtaining specific-yield values for the alluvial deposits 

of the Santa Ynez River basin because field conditions are far different from 

the ideal conditions which must be assumed in the derivation of the equations 

expressing pumping test theory * * *.

For the preliminary estimates of this report, specific yield was approximated by 

estimating the proportion of different classes of material as reported in the available well logs and assigring arbitrary specific-yield values to each class 

[table 20]. * * * The arbitrary specific-yield values selected for different classes 

of material as reported in the well logs were determined by comparison with 

other areas similar to the Santa Ynez River basin in which specific-yield values 

had been obtained from field and laboratory tests. The method is based in 

part on mechanical analysis of 'the material and was used rather successfully 

by Eckis (1934) in the south coastal basin of southern California. * * * In the 

Mokelumne area, California, estimates of specific yield by both th^ volumetric 

method and the drainage method were made by Piper and others (1939, p. 

120-121). * * *.

TABLE 20. Speoifio yield for attuvial deposits of the Santa Ynez River basin,

California

Specific yield 

Material (percent)

Gravel ____________________________________ 25

Sand _________________________ _____ 30

Fine sand________________________________ 20

Gravel, cemented or clayey_____________________ 10

Silt _____________________________________ 5

Clay ___________________________________ 5

The materials in the Santa Ynez River basin are roughly comparable to those 

in the south coastal basin. Accordingly, a specific-yield value of 25 percent was 

assigned to gravel, 30 percent to sand, 20 percent to fine sand, 10 percent to 

cemented or clayey gravel, and 5 percent to silt and clay. The deposits found in 

the south coastal basin are mostly in alluvial fans, whereas the deposits of the 

Santa Ynez are river-channel and flood-plain deposits in which the gravel is 

better sorted and contains less fine material. Possibly, therefore, tl ? gravel has 

a slightly higher specific yield than 25 percent. Conversely, coarse gravel, such 

as in the alluvium of the Santa Ynez River, contains an assortment of large 

pebbles, cobbles, and boulders that have no specific yield and fill considerable 

space, tending to lower the specific yield of the material as a whole. For this 

reason the lower value, close to that used by Eckis, was considered more appropriate for this area than Piper's value of 35 percent for gravel and coarse sand.
COMPILATION OF SPECIFIC YIELDS D57

Kunkel, Fred, and Upson, J. E., 1960, Geology and ground water in Napa and 

Sonoma Valleys, Napa and Sonoma Counties, California: U.S. Geol, Survey 

Water-Supply Paper 1495, p. 64-65,78-79.

Specific yield. Estimates of specific yield were made by classifying the materials in the younger and older alluvium, as reported in drillers' logs into groups, 

and assigning a specific-yield value to the material in each group. IE the drillers' 

logs, gravel, sand, clay, and volcanic rocks are usually identified. Tl« more complete logs mention the color, coarseness of grain, hardness, degree of cementation, and other characteristics readily related to the formations or lithologic 

types. The drillers' terms were grouped into five general classes of material of 

similar water-bearing properties * * * [table 21].

TABLE 21. Specific yields for alluvium in Napa and Sonoma Valleys, Calif.

Specific yield 

Napa Valley (percent)

Gravel, boulders, gravel and boulders._____________________ 25

Sand; sand and boulders; sand and gravel; sand, gravel, and boulders; 

water ______________________________________ 20

Clay and gravel alternating; clay, gravel, and water; clay and sand; clay, 

sand, and gravel; clay and gravel, sandy; clay, sandy, and boulders; 

gravel and sandstone ; sandy loam ; sand, gravel, boulders, and clay mixture ; sand, gravel, boulders, and some clay; sand and hard gravel; sand 

and rock; some water______ _______ ___ 10

Clay and gravel; cemented conglomerate; cemented gravel; cemented sand, 

gravel, and clay; cemented sand and boulders; clay and boulders; clay, 

gravel, no water; clay and gravel; clay with gravel; clay and rock ; sandy 

clay; clay with sand; gravel, boulders, and clay; hard gravel (cementing 

assumed); dry gravel (cementing assumed); hardpan and boulders; 

loam; dry sand (cementing assumed) ; sandrock ; sandstone.-_____ 5

Clay ; clay and soil; hardpan ; hardpan and clay ; broken rocks ; rocks; 

rock(s), water; soil; surface; tule mud____________________ 3

Sonoma Valley

Gravel, boulders, gravel and boulders______________________ 25

Sand; sand and boulders; sand and gravel; sand, gravel, and boulders; 

water _______________________________________ 20

Clay and gravel alternating; clay, gravel, and water; clay and sand; clay, 

sand, gravel; clay and gravel, sandy ; sandy clay, and boulders; f ravel 

and sandstone; sandy loam; sand and clay; sand, gravel, boulders, and 

clay mixture; sand, gravel, boulders, and some clay; sand and hard 

gravel; sand and rock; some water; volcanic ash ; tuff; pumice; tuff and 

gravel; tuff and boulders____________________________ 10

Clay with gravel; cemented conglomerate; cemented gravel; cemented sand, 

gravel, and clay; cemented sand and boulders; clay and boulders; clay, 

gravel, no water; clay and gravel; clay with gravel; clay and rock; sandy 

clay; clay with sand ; gravel, boulders, and clay ; hard gravel (cementing 

assumed) ; dry gravel (cementing assumed) ; hardpan and boulders, 

loam and dry sand (cementing assumed) ; sandrock; sandstone; bor'ders 

and red clay; volcanic rocks and rocks (agglomerate)__________ 5

Clay; clay and soil; hardpan; hardpan and clay; broken rocks; rocks; 

rock(s), water; soil; surface; tule mud; red volcanic rocks; soft rock; 

red rock; some water; porous rock_______________________ 3

Rock; hard rock; solid rock; basalt; granite_____________ __ 0
D58 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

It was not feasible in this investigation to attempt to make field determinations 

of the specific yield of the different types of water-bearing material. Therefore, 

an estimated specific-yield value was assigned to each of the five general classes 

of material on the basis of available data. These values are the saire as were 

applied in the Sacramento Valley investigation (Poland and others, 19*1, p. 625) 

on the basis of the work of Eckis (1934) and Piper and others (1939), and are 

applied to the same classes of material as nearly as could be determine^ from the 

drillers' logs. The names of the materials included in each group are those com« 

monly used and listed by drillers in the area.

******* 

To determine the average specific yield for each depth zone in each groundwater storage unit, the thickness, in feet, of each class of material in each depth 

zone was totaled. These thicknesses were converted to percentages of total 

thickness of all the materials in each zone; and these percentages w<°re multiplied by the specific-yield value assigned to the particular class of material. 

The sum of these products is the average specific yield for each d<H>th zone. 

In other words, the various specific yields are prorated according to tve relative 

thickness 

******* 

of the material that has each specific-yield value.

Because vertical boundaries are assumed for the ground-water storage units in 

Sonoma Valley, the volume of each storage unit is equal to the area of the unit 

multiplied by its thickness. * * * The specific yield of the younger and older 

alluvium is estimated on the basis of drillers' logs, as for Napa Valley. * * *.

Because the ground-water storage capacity of Sonoma Valley was estimated 

to a depth of 200 feet, some volcanic material beneath the older alluv'um at the 

edges of the plain was included in the estimate and in the classification of 

materials. In general, the pumice and tuff are assumed to be comparable in 

specific yield to sandy clay and gravel, the agglomerate to clay and fravel, and 

clayey volcanic rocks to clay. The flow rocks yield practically no water; therefore, in Sonoma Valley a sixth class of material, "rock," is added * * * [table 21].

Moulder, E. A., Klug, M. F., Morris, D. A., and Swenson, F. A., 1960, Geology 

and ground-water resources of the lower Little Bighorn River valley, Big 

Horn County, Montana: U.S. Geol. Survey Water-Supply Pape^ 1487, p. 

42-43.

The properties of the fine-grained sediments overlying the coarse-grair<*d terrace 

deposits are important in determining whether the land is irrigable ar'l whether 

it can be drained. Laboratory tests indicate that the hydrologic properties vary 

greatly even though the textural properties are similar [table 22]. For example, 

some samples classified as medium had a lower coefficient of permeability than

TABLE 22. Specific yield of unconsolidated materials in the Little Bighorn

River valley, Montana

[Specific yield values rounded to nearest whole number for present report]

Specific yield 

Material (percent)

Very coarse (predominantly gravel)_____________ 25 

Coarse (predominantly coarser than very fine sand) _____ 32 

Medium (loam, silty loam, and very fine sandy loam)___ 28 

Moderately heavy (clay loam, silty clay loam, and sandy clay

loam) ______________________________ 29 

Heavy (clay and silty clay)___________________ 17
COMPILATION OF SPECIFIC YIELDS D59

some samples classified as heavy. The specific retention generally proved to be 

the only property consistent with the particle-size analysis [fig. 16 was prepared 

by A. I. Johnson to illustrate this relationship], hence, the textural classification 

apparently is a good measure of the capillary retentiveness of the material and 

the height of the capillary fringe above the water table. Because of this relationship between capillary and soil texture, soil-classification maps vr^re used in 

deciding how deep the drains must be to lower the water table sufficiently to 

alleviate 

******* 

waterlogging.

A comparison of specific yields determined by laboratory tests with the 

storage coefficients determined by field tests suggests that the larger values 

obtained in the laboratory represent the storage coefficient to be expected after 

a very long period of draining and that the smaller values obtained from the field 

tests represent the storage coefficient of the fine-grained sediments during only 

the short period of the field test. Therefore, the laboratory value1* -are more 

nearly representative of the effectiveness of drainage measures.

Thomasson, H. G., Jr., Olmsted, F. H. ( and LeRoux, E. F., 1960, Geology, water 

resources, and usable ground-water storage capacity of part of Solano 

County, California : U.S. Geol. Survey Water-Supply Paper 1464, pp. 284-286, 

366-368.

The continental sediments examined in the south coastal basin investigation 

were composed chiefly of alluvial-fan deposits that were laid down b.v torrential 

but intermittent streams of steep gradient. In contrast, the rear-surface 

materials underlying most of the Putah area were transported by Futah Creek 

and the small streams to the south, and were deposited on the broac1 , relatively 

flat channel-ridged plain. Accordingly, the alluvial deposits in the south coastal

1.0 2.0 3.0 4.0 5.0 6.0 8.0 10 

SORTING COEFFICIENT (So)

FIGURE 16. Relation of specific retention to sorting coefficient in alluvium cl the Little 

Bighorn River valley, Montana.
D60 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

basin undoubtedly are much coarser than those in the Putah area, much of the

clay in the south coastal basin being of residual rather than depositlo^al origin.

*******

The samples tested in the Mokelumne investigation were obtained at depths 

of less than 15 feet from unconsolidated sediments of late Pleistocene and Recent 

age. On the other hand, wells drilled to a depth of 200 feet in the Futah area 

penetrate the Tehama formation and related continental sediments of Pliocene 

to early Pleistocene age in their lower portions throughout the area rnd almost 

from the land surface in some parts of the area. These older deposits- are more 

weathered and indurated and, group for group as described by drillers, presumably are of lower specific yield than the alluvium. Certainly the yield factors 

of wells tapping these older deposits in the Putah area are systematically much 

lower than the yield factors of wells tapping only the Recent and upper 

Pleistocene alluvial deposits, suggesting a decrease of permeability and probably 

of specific yield in the older deposits.

The results obtained in those two investigations, together with sp?cific-yield 

data from less detailed studies by others, were used as a basis frorr which to 

assign arbitrary percentages for specific yield of the five general classes of 

material in the Putah area. However, the figures obtained experimentally in the 

two detailed investigations were considered to be slightly higher than would 

be warranted for use in connection with the respective categories of material 

as classified from local drillers' logs in the Putah area.

Therefore, the percentages obtained in the earlier investigations were modified 

somewhat for use in the Putah area because of differences In the lithologic and 

hydrologic character of the sediments, which were considered to reflect differences in the source and composition of the materials and in the conditions 

under which the alluvial deposition occurred in the different areas Table 23 

shows the specific yield assigned to each of the five categories of material.

TABLE 23. Specific yield used to estimate total ground-water storage capacity in 

the Putah area, California

Specific yield 

Material (percent)

Gravel _ ______________________________________ 25

Sand, including sand and gravel, and gravel and sand______ ___ 20

Tight sand, hard sand, fine sand, sandstone, and related deposits -___ 10

Clay and gravel, gravel and clay, cemented gravel, and related deposits__ 5

"Clay," silt, sandy clay, lava and related fine-grained deposits_______ 3

[Cretaceous rocks_________________________________ 0]

The specific yield of 25 percent assigned to the gravel category was the highest 

figure used in the computations for the Putah area. This figure was a rough 

average of results * * * which ranged from 13 to 35 percent.

The sand category was assigned a specific yield of 20 percent, which was appreciably below the 24-percent average of the experimental data. However, it is 

believed that the material ordinarily logged as sand by drillers in the Putah area 

is somewhat more consolidated or silty and, hence, of lower specific yield than 

the sand obtained from the south coastal basin and from the shallow alluvial 

deposits of the Mokelumne area.

Such drillers' terms as tight sand, hard sand, sandstone, cemented1 sand, and 

similar descriptive terms suggesting relatively low permeability anc* drainable 

void spaces were mentioned in enough well logs to warrant an intermediate 

category, to which a specific yield of 10 percent was assigned.
COMPILATION OF SPECIFIC YIELDS D61

The fourth group comprised material described by means of 21 different terms 

of drillers, to refer to such materials as clay and gravel, "dry gravel," cemented 

gravel, and gravelly clay. Although obviously of low permeability and probably 

low specific yield, these materials doubtless include some moderately permeable 

beds of fair specific yield, and an average specific yield of 5 percent was assigned.

The finest grained deposits, including clay, silt, sandy clay, hardpan, muck, 

shale, and lava were assigned a specific yield of 3 percent. Deposits included in 

this category comprise more than two-thirds of the sediments in the 20- 200-foot 

zone in the Putah area ; only locally do the coarse-grained deposits exceed half the 

section. The specific yield of 3 percent is higher than that used for clay in the 

south coastal basin study, but it is midway between the values used for clay and 

sandy clay in the unweathered subsurface alluvial deposits in that area. The 

term "clay" as applied by the driller is likely to include many beds that are silty 

or sandy, if they contain much material so fine that it remains in suspension in 

the drilling 

****** 

fluid. * * *.

The total ground-water storage capacity * * * in the Suisur-Fairfield area 

was estimated by the same method as that used in the Putah area but with a 

few minor 

****** 

variations * * *.

As in the Putah area, the average specific yield for each depth range in each 

storage unit was estimated from the percentages of material * * * and the specific yields in table 23 plus a specific yield of zero for the Cretaceous rocks. The 

estimates of total storage capacity were then the product of the total volume of 

each subunit times its estimated average specific yield.

California Department of Water Resources, 1961, Planned utr'zation of the 

ground water basins of the coastal plain of Los Angeles Cou~rty: California 

Dept. Water Resources Bull. 104, app. A, p. 121, Attachment 2, p. 2-3, 2-4.

Specific yield values for the sedimentary deposits of Los Angeles County are 

given in table 24. These specific yield values were compiled from available data, 

including work done by the State Water Rights Board for the San Fernando 

Valley Reference, and from Bulletin 45 (Calif. D. W. R., 1984). They were also 

checked against figures obtained from well tests but no new determinations were 

made during this investigation. Specific yield values are multiplied by the thickness and areal extent of the water-bearing sediments to detemine the total 

storage capacity of these sediments. * * *.

Kazmi, A. H., 1961, Laboratory tests on test drilling samples from Rechna Doab, 

West Pakistan, and their application to water resources evalration studies: 

Athens, Internet. Assoc. Sci. Hydrology Pub. 57, p. 496, 500.

These tests have been used to calculate the specific yield of the samples, using 

the formulae:

g ,fi Centrifuge Correction Apparent

... = moisture X factor X specifi" retention equivalent (from tables) gravitr

and

Specific yield=Porosity Specific retention.

Specific yields of 76 samples from 7 test holes, thus calculated, have been shown 

in figure 17. [Table 25 has been interpreted from fig. 17 by A. I. Johnson.] From
D62 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

TABLE 24. Specific yield, values used- in coastal plain of Los Angeles

County, Calif.

[After State Water Rights Board Revised Values of Specific Yield as used for San Fernando 

Valley Reference, 7-9-59, which is based on values used in Bulletin 45, Geo'ogy and 

Ground Water Storage Capacity of Valley Fill]

Note : Specific jield values above base of Bellflower aquiclude = 00 

00 Percent Bellflower Aquiclude

03 percent Clay and shale

Adobe Granite clay Shale

Boulders in clay Hard clay Shaley clay

Cemented clay Hard pan Shell rock

Clay Hard sandy shale Silty clay loam

Clayey loam Hard shell Soapstone

Decomposed shale Muck

05 percent Clayey sand and silt

Chalk rock Rotten conglomerate Sediment

Clay and gravel Rotten granite Shaley gravel

Clayey sand Sand and clay Silt

Clayey silt Sand and silt Silty clay

Conglomerate Sand rock Silty loam

Decomposed granite Sandstone Silty sand

Gravelly clay Sandy clay Soil

Loam Sandy silt

10 percent Cemented or tight sand or gravel

Caliche Dead gravel Heavy rocks

Cemented boulders Dead sand Soft sandstone

Cemented gravel Dirty pack sand Tight boulders

Cemented sand Hard gravel Tight coarse gravel

Cemented sand and gravel Hard sand

14 percent Gravel and boulders

Cobbles and gravel Heaving gravel Silty sand

Coarse gravel Heavy gravel Tight fine gravel

Boulders Large gravel Tight medium grav?l

Broken rocks Rocks Muddy sand

Gravel and boulders Sand and gravel, silty

16 percent Fine sand

Fine sand Quicksand Sand, gravel and boulders 

Heaving sand Sand and boulders Tight sand

21-23 percent Sand and gravel

Dry gravel Gravelly sand Sand

Loose gravel Medium gravel Water gravel

26 percent Coarse sand and fine gravel

Coarse sand Fine gravel Medium sand

Value of one added to given value where streaks of sand or gravel occur in clay or clayey 

material.

this data the average specific yields of various grades of sediments have been 

computed and have been used to calculate the mean specific yield for a thickness 

of 400 feet of sediments penetrated by each test hole. Based on this' average 

specific yield, the subsurface sediments in the Rechna Doab have been zoned as 

shown in figure 18.
COMPILATION OF SPECIFIC YIELDS D63

Range of specific yields of 

75-90 percent of samples

FIGURE 17. Relation of specific yield to particle size for sediments sampled at Kechna 

Doab, West Pakistan. (After Kazml, 1961.)

TABLE 25. Specific yield of alluvium from Rechna Doab, West Pakistan 

Material Specific yield 

(percent)

Gravel, sand and silt__ 

Coarse sand _________

Coarse to medium sand-. 

Medium sand____ . 

Medium to fine sand____

Fine to very fine sand-__. 

Silty sand-____ 

Sandy silt, silt and clay.

26

23

23

28

27

15

5

3

Under the water table conditions the specific yield of an aquifer equals coefficient of storage. Thus the coefficient of storage as deduced from the behaviour 

of the rising water table * * *, in Rechna Doab varies from 0.2 to 0.3 * * *. 

As deduced from the laboratory studies, the average storage coefficient for the 

entire aquifer in the Rechna Doab, is 0.17; in the northeastern part of the doab 

the aquifer has an average specific yield of about 0.14; in the central zone
u

o 

*II

03

EXPLANATION

5-10 10-15 15-20

Specific yield, in percent

20-25

Test hole

25I

FIGURE 18. Specific yield of sediments of Rechna Doab, West Pakistan. (After Kazml, 1961.)

50 MILES $
COMPILATION OF SPECIFIC YIELDS D65

(largely waterlogged) the average is about 0.2 and in the southeastern portion 

of the doab the average is 0.19. However these figures are much higher than those 

obtained from aquifer tests according to which the storage coeff ?ient ranges 

from 0.0016 to 0.073 at various locations * * *. This wide range of variation is 

readily explained by the fact that some of the sand zones between th<? clay layers, 

in the pumped wells, have probably been under artesian or semiartesian pressure.

Olmsted, F. H., and Davis, G. H., 1961, Geologic features and rround-water 

storage capacity of the Sacramento Valley, California: U.S. Geol. Survey 

Water-Supply Paper 1497, p. 150-152.

Modified specific yields were assigned to the five groups of material classified 

in the well logs of the Sacramento Valley [table 26].

* * * * * * * 

TABLE 26. Specific yield of water-bearing sediments in the Sacramento Valley,

Calif.

Specific yield 

Material (percent)

Gravel ________________________________ 25 

Sand, including sand and gravel, and gravel and sand___ 20 

Tight sand, hard sand, fine sand, sandstone, and related

deposits ______________________________ 10 

Clay and gravel, gravel and clay, cemented gravel, and related deposits___________________________ 5 

"Clay," silt, sandy clay, lava rock, and related fine-grained 

deposits _________________ ____ 3

The lithologic and hydrologic character of the sediments of the Sacramento 

Valley necessitated certain modifications of the specific yields obtain ed by experiments in earlier investigations. The conditions under which alluvial deposition 

occurred in the Sacramento Valley were different from those in tl ? other area 

and are the principal reason for the modifications.

In contrast to the south-coast basin where continental sediments, composed 

essentially of alluvial-fan deposits, were laid down by intennittert streams of 

steep gradient, the sediments of the Sacramento Valley are predominantly 

slack-water deposits laid down by the Sacramento River and its tributaries on 

broad, flat, alluvial plains and fans. In general, the alluvial deposits of the 

south-coastal basin are much coarser than those of the Sacran^nto Valley. 

Also, most of the clay in the pre-Recent deposits of the south-oast basin is 

the result of weathering rather than deposition from water; hence, a gravel 

deposit may contain considerable, clay in the form of weathered pebbles that 

would not reduce the permeability of the deposit as much as would an equal 

amount of interstitial clay deposited from water.

The samples tested in the Mokelumne area are not considered representative 

of the sediments in the 20- to 200-foot depth range in the Sacrarrento Valley, 

because they were all taken at depths of less than 15 feet in unconsolidated 

deposits of late Pleistocene and Recent age. Most of the wells drilled to a 

depth of 200 feet penetrate sediments of early Pleistocene and Pliocene age 

throughout the eastern and northern parts of the valley. These elder deposits 

are more indurated and presumably of lower specific yield than the younger 

alluvium.

Probably the most important departure from the experimental results was 

the specific yield of 20 percent assigned to the sand category. It is believed that 

material ordinarily logged as sand by well drillers in the Sacramento Valley 

is somewhat more consolidated and hence of lower specific yield than sand in
D66 HTDROLOGIC PROPERTIES OF EARTH MATERIALS

the south-coastal basin and sand samples from the younger alluvial deposits of 

the Mokelumne area. Facts tending to support this idea are that drillers frequently distinguish the unconsolidated sand from the more or less consolidated 

sand by use of the terms "loose sand," "running sand," "quicksand," and "caving 

sand"; and that a considerable part of the water-bearing deposits of the eastern 

and northern parts of the Sacramento Valley are firm enough to stand without 

casing * * *.

Enough well logs mentioned tight sand, hard sand, sandstone, cemented sand, 

and other descriptive terms indicating restricted permeability that an intermediate category was set up with an assigned specific yield of 10 percent.

A specific yield of 5 percent was assigned deposits such as clay and gravel, 

"dry" gravel, cemented gravel, and gravelly clay, which although they are obviously of low permeability, supply small quantities of water to wells.

The fine-grained deposits, including clay, silt, sandy clay, hardpan, muck, shale, 

volcanic ash, and lava, were assigned a specific yield of 3 percent. In any one 

well log, deposits included in this category generally constitute mo^e than half 

the sediments penetrated in the 20- to 200-foot depth range; only locally do the 

coarse-grained deposits occupy more than half this depth range. The specific 

yield of 3 percent is higher than that used for clay in the study cf the southcoast basin, but it is midway between the values used for clay and sandy clay 

in the unweathered subsurface alluvial deposits in that area. Material logged 

by the drillers as "clay" is likely to include many beds that are silty, sandy, or 

even gravelly, if they contain much material so fine that it remains in suspension 

in the drilling fluid * * *.

The specific yield of 25 percent assigned to gravel agrees fairly closely with 

experimental results obtained by Eckis (Eckis and Gross, 1934) and by Piper 

(Piper and others, 1939).

Cohen, Philip, 1963, Specific-yield and particle-size relations of Quaternary alluvium, Humboldt River valley, Nevada: U.S. Geol. Survey Y^ater-Supply 

Paper 1669-M, p. 20-23.

The data and graphs [table 27] * * * show the relations, or lack of relations, 

that seem to exist between specific-yield, porosity, specific-retention, sortingcoefficient, and median particle-size-diameter values of 323 samples from the 

Humboldt River valley. In summary, these apparent relations are:

TABLE 27. Specific yields for alluvial deposits in the Humboldt River valley,

Humboldt County, Nev.

Specific yield

Material (percent) 

Fine gravel _______ __ ____ _ 19 

Very-fine gravel _____ _ __ 18 

Very-coarse sand ___ _ 21 

Coarse sand _ 27 

Medium sand _ 28 

Fine sand ______________________________ 26 

Very-fine sand _____ _ 20 

Silt ___________________________________ 19 

Clay ____________________-____________ .5

1. For most samples, porosity values are virtually independert of sortingcoefficient values alone.

2. Porosity values tend to increase as median particle-size-diameter values 

decrease.
COMPILATION OF SPECIFIC YIELDS D67

3. For most samples, specific-retention values do not correlate with sortingcoefficient values alone.

4. Specific-retention values tend to increase as median particle-size-diameter values decrease.

5. Specific-yield values do not correlate with sorting-coefficient values of 

samples whose median particle-size-diameter values fall within the 

silt- and gravel-size ranges but tend to increase as sorting coefficient 

values decrease in the intervening ranges.

6. There is a poor correlation between specific-yield values and median 

particle-size diameter values.

* * *****

* * * the specific-yield values of the samples from the Humboldt River valley 

differ markedly from those shown by the other writers. The n«ost striking 

difference is the tendency for samples from the Humboldt River valley to have 

considerably higher mean specific-yield values for samples whose median particle-size diameters fall within the silt-size range.

The relatively high specific-yield values of the samples whose median diameters are in the silt-size range probably partly is a result of the relatively high 

porosity of this material * * *.

Preuss, F. A., and Todd, D. K., 1963, Specific yield of unconsolidated alluvium: 

Berkeley, California Univ. Walter Resources Center Contr. 7C p. 2-4, 13, 

16, 19.

Because of the amount of data available from previous investigations, this 

study was restricted to the analysis of published data. However, it was necessary to assume (a) that the data from each of the four sources * * * were 

comparable; and (b) that the data were representative of what v^ould be expected from other alluvial sources.

Several studies have indicated that gravity drainage of fine-grained materials, 

such as clay or silt, is a very slow process. Therefore, specific yield, rs a measure 

of the ultimate volume of water drained, is seldom attained under field or 

laboratory conditions. Water yield is not constant but increases with time at an 

ever diminishing rate. Because the four data sources did not make ary particular 

distinction with regard to their values, it will be assumed here that the samples 

had undergone complete drainage.

* * *****

As the result of a thorough literature survey, four independent investigations were found to contain data presented in an usable form. From these 

investigations a total of 311 separate soil samples were selected for analysis in 

this study. The majority, 230 samples, was obtained from an expensive field 

investigation of the South Coastal Basin in the Los Angeles area o* California. 

Porosities and specfic retentions were determined in the laboratory, and specfic 

yields were obtained as the difference.

From an investigation of the ground water aquifer in South-Central Kansas, 

28 samples were obtained, and 32 samples came from a study in South-Central 

Nebraska. In both of these studies, porosities and moisture equivalents were 

determined in the laboratory. * * *.

The remaining 21 samples were obtained from a ground water ftudy of the 

Mokelumne area of California. The porosity and specific yield were determined 

in the laboratory for that study.
D68 HYDEOLOGIC PROPERTIES OF EARTH MATERIALS

To determine which grain diameter was the most representative, the average 

deviation of specific yield values within plus or minus one standard error of 

estimate was plotted against the representative grain diameter. * * * It indicates that a representative grain diameter of about DM has the least degree of 

specific yield deviation.

* * *****

It appears that a maximum value of specific yield occurs with a De-> of between 

0.4 and 0.5 of a millimeter. As the grain sizes become smaller beyond this point, 

the interstices also become smaller producing increased capillary forces. These 

increased forces result in greater retention of the water so that specific yield 

decreases. The large range in specfic yield for any particular grain size can be 

largely attributed to variations in porosity.

A relationship between uniformity coefficient and grain size resulted in no 

definite conclusions. However, it was noted generally that, for the samples used 

in this study, the uniformity coefficient decreases as the grain size 

decreases. * * *.

The results * * * indicate that porosity has perhaps the greatest single effect 

upon specific yield. It appears that a peak specfic yield of 32.5 percent occurs at 

a porosity of between 41 and 42 percent. After the peak the specfic yield seems 

to diminish quite rapidly.

* * *****

[Table 28 was interpreted by A. I. Johnson from data in this re'wrt.] * * * 

The resulting colinear graph [fig. 19] shows the relation of DM to specific yield 

for various porosities.

TABLE 28. Specific yields of unconsolidated alluvium

Specific yield 

Material (percent)

Coarse gravel___________________________ 12

Medium gravel___________________________ 13

Fine gravel_____________________________ 17

Gravelly sand _ _ 22

Coarse sand _ _ __ _ ____ _ 28

Medium sand__________ __ _____ _ _ 28

Fine sand __ __________ __ ____ _ _ 23

Very fine sand__-______________________ _ 16

Silt____________________________________ 4

It is interesting to note that the family of lines has a characteristic shape. 

The range of specific yield is relatively broad for the same grain size. This broad 

range shows the importance of porosity. The flattening of the line.'' of porosity 

toward a constant specific yield value, always less than the porosJty, indicates 

that specific retention approaches a finite value greater than zero.

SUMMARY

Table 29 summarizes the specific yields used in many of the previously listed investigations. A specific yield averaged from all values 

reported in the table also is reported for each texture of rock or soil 

material. The reported specific yields, in general, are representative of 

the ultimate amount of time for drainage. Corrections to k "^er values 

would have to be made for short drainage periods.
COMPILATION OP SPECIFIC YIELDS D69

40

35

30

Z 25

0 20

UJ

a. 15

10

/

////// '//// /

/ / / I

/////// I 

/ / / / / / / /

I I I I I I II

I l\l I/I /Hill/ I I

0.01 0.05 0.1 1.0 

, IN MILLIMETERS

10 100

FIGURE 19. Colinear plot of DBO to specific yield for various values of porosity. (After

Preuss and Todd, 1963.)

It should be remembered that the textures listed are, ir general, 

broad classifications based on the predominate particle size. One can 

observe that the highest specific yields tend to be around the medium 

and coarse sand texture this is due to the fact that these sands normally have a more uniform size distribution than do the gravels or the 

finer sands, silts, and clays.

Research on specific yield completed by the Hydrologic Laboratory 

indicates that many of the specific yields used in the past especially 

for fine-textured materials such as the silts, sandy clays, and fine 

sands are too small. Johnson and Kunkel (1963) pointed out that this
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Material

California fill, Valley 

1934) (Eckis, 

California area, Mokelumne 

1939) others, and (Piper 

basin, River Ynez Santa 

and (Upson California 

1951) Thomasson, 

Calif. Valley, Sacramento 

1949) oth»rs, and (Poland 

Cali- plain, River Smith 

1957) (Back, fornia 

Calif. County, Venture 

Resources Water (Calif. 

1956) Board, 

Valley, Margarita Santa 

Dept. (Calif. Calif. 

1956) Works, Public 

Calif. Basin, Juana Tia 

Rights Water (Calif. 

1957) Board. 

County, Obispo Luis San 

Re- Water (Calif. Calif. 

1958) Board, sources 

Calif. Valley, Joaquin San 

1959) others, and (Davis 

California area, Eureka 

1959) (Evenson, 

Calif. Basin, Ynez Santa 

1959) (Wilson, 

Pakistan Doab, Rechna 

1961) (Kazmi, 

Valleys, Napa-Sonoma 

and (Kunkel Calif. 

1960) Upson, 

Valley, River Humboldt 

1963) (Cohen, Nev. 

alluvium Unconsolidated 

1963) Todd, and (Preuss 

valley, River Bighorn Little 

and (Moulder Montana 

1960) Others, 

yield specific Average 

H 

w

OZd OIDOIOHdAH S3LLH3dOHd HXHV3 S1VIH3J,VH 
COMPILATION OF SPECIFIC YIELDS D71

conclusion is indicated by specific yields obtained by various field 

tests as well as by the centrifuge, column-drainage, and moirtare-tension tests in the laboratory. These authors also noted that th«, specific 

yield varies depending on the interrelation of textures; for example, 

a silt over a sand may not have as high a specific yield as would the 

same silt over a clay.

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D72 HYDBOLOGIC PROPERTIES OF EARTH MATERIALS

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D74 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

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o

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