Comprehensive Monitoring of 

Meteorology, Hydraulics, and Thermal 

Regime of the San Diego Aqueduct, 

California
Comprehensive Monitoring of 

Meteorology, Hydraulics, and Thermal 

Regime of the San Diego Aqueduct, 

California

By HARVEY E. JOBSON and ALEX M. STURROCK, JR.

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1137

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1979
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

H. William Menard, Director

Library of Congress Cataloging in Publication Data

Jobson, Harvey E

Comprehensive monitoring of meteorology, hydraulics, and thermal regime of the

San Diego Aqueduct, California.

(Geological Survey Professional Paper; 1137)

Includes bibliographical references.

Supt. of Docs. No.: I 19.16:1137

1. San Diego Aqueduct, Calif. 2. Meteorology-California, SouthernObservations. 3. Hydraulic me asurements-California, Southern. I. 

Sturrock, Alex M., joint author. II. Title. III. Series: United States. 

Geological Survey. Professional Paper; 1137.

TC764.J6 628.1*5 79-607792

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

Washington, D.C. 20402

Stock number 024-001-03238-4
CONTENTS

Page

Conversion table ______________________________ IV

Abstract ________________________________________________ 1

Introduction ______________________________________________ 1

Acknowledgments ____________________________________ 2

Site description _________________________________________ 2

Instrumentation _________________ ______________ 3

Recording system _____ ___________________________ 3

Wind _________________________________________________ 6

Radiation _______________________________________ 7

Temperature __________________________________________ 8

Stage _________________________________ 8

Flow rate ______________________________ 9

Other data _____________________________ 10

Procedure ________________________________ 10

Data collection __________________________10

Data processing ______________________ 10

Calibration ________________________——— —— ______— 11

Results __________________________________ 13 

General ________________________________ 13

Wind ________________________________________________ 22

Radiation __________________________________ 24

Air temperature ____________________________ 26

Vapor pressure __________________________ 26

Water temperature ______________________________ 27

Discharge _______________________________ 28

Summary and conclusions _____________________ 29

References cited ___________________________ 29

ILLUSTRATIONS

Page

FIGURE 1. Map showing the San Diego Aqueduct and data-collection points _____________________—_____ — _____ —— — 1

2. Diagram showing typical cross section of the canal _________________________________________ — _ —— ____ —— — 2

3. Graph showing variation of bank height with distance along the canal ______________________ — ________ ——— ____ 2

4. Map showing the San Diego Aqueduct, the diversion points, and locations of siphons and stage recorders ____—_____ 2 

5-20. Photographs showing:

5. Diversion of water from the Casa Loma Canal at the entrance to the San Diego Aqueduct __ — ————— __— 3

6. Skinner end of San Diego Aqueduct _______________________________________________ 3

7. Recording system at downstream end of the canal _____________________________________ ——— —— — 3

8. Wind exposure at Cottonwood meteorologic station _________________________________ ———— ___— 6

9. Wind exposure at Skinner _____________________________________________________--__-----_ — ___— 6

10. Wind exposure at Skinner ________________________________________________________________________ 6

11. Psychrometer and supplementary anemometer at Cottonwood _______________________________—_ 6

12. Closeup of supplementary wind sensor and psychrometer at Cottonwood _______________——____ — _— 7

13. Closup of supplementary wind sensor and psychrometer at Skinner ____________________—______ 7

14. Radiation instrumentation at Cottonwood _____________________________________________ 7

15. Closeup of psychrometer _________________________________________________________ 8

16. Recorder and stilling well at the Cottonwood gage __________________________________________—_____ 8

17. Canal at the Cottonwood gage _________________________________________________________ 9

18. Simpson gage _____________________________________________________________________ 9

19. Newport gage _______________________________________________________________________ 9

20. So. End gage and diversion ____________________________________________________________ — ____——— 9

21-23. Graphs showing:

21. Monthly mean windspeed __________________________________________________________________ 22

22. Frequency of occurrence of daily windspeeds _________________________________________________________ 22

23. Mean annual diurnal variation in windspeed, averaged by 10-minute time periods for the period July 24, 1973,

to July 23, 1974 ______________________________________________________________________________ 23

24. Diagram showing frequency of occurrence, in percentage of time, of winds from various directions _________________ 23

25-31. Graphs showing:

25. Daily solar radiation ____________________________________________________________________________ 24

26. Daily atmospheric radiation ___________________________________________________________________ 25

27. Typical diurnal variation in atmospheric radiation as measured by the pyrgeometer and by subtracting the

measured instantaneous solar radiation from the all-wave radiation measured by the flat-plate radiometer ___25 

28. Daily average air temperature _____________________________________________________________ 26

29. Daily average vapor pressure _______________________________________________________________ 27

30. Daily mean water temperature, averaged over depth ______________________________________________ 28

31. Mean diurnal variation in water temperature __________________________________________________ 28

in
IV CONTENTS

TABLES

Page

TABLE 1. Locations of structures on San Diego Aqueduct (information furnished by the Metropolitan Water District of

Southern California) ____________________________________________________________________ 1

2. Calibration factors (for use in equation 3) of instrumentation used at the San Diego Aqueduct _________________——— 11

3. Profiles of centerline depth for the San Diego Aqueduct under nearly steady flow conditions ____________________ 12

4. Daily averaged values of meteorologic and temperature data for San Diego Aqueduct (July 25, 1973-July 23, 1974) __ 13

5. Daily averaged values of hydraulic and rainfall data for San Diego Aqueduct (July 25, 1973-July 23, 1974) _____— 17

6. Comparisons of vapor pressures estimated by four data-transfer methods _______________________________—_ 27

CONVERSION TABLE

[Factors for converting metric (SI) units to inch-pound units are shown to four significant figures]

Multiply metric unit By To obtain inch-pound unit

meter (m) 3.281 foot (ft)

millimeter (mm) 0.03937 inch (in)

meter per second (m/s) 35.31 foot per second (ft/s)

cubic meter per second (m3/s) 0.02832 cubic foot per second (ft3/s)

pascal (Pa) 10.00 millibar (mb)

watt per square meter (W/m2 ) 2.065 calorie per square centimeter per day [(Cal/cm2 )/d]
COMPREHENSIVE MONITORING OF

METEOROLOGY, HYDRAULICS, AND THERMAL REGIME OF THE 

SAN DIEGO AQUEDUCT, CALIFORNIA

By HARVEY E. JOBSON and ALEX M. STURROCK, JR.

ABSTRACT

Water temperature, as well as meteorologic and hydraulic variables which influence the energy budget of the San Diego Aqueduct 

in southern California, were continuously monitored for a 1-year 

period beginning July 24, 1973. The incoming solar and atmospheric 

radiation, windspeed and direction, water temperature, and the wetand dry-bulb air temperatures were recorded at 10-minute intervals 

at each end of the 26- kilometer concrete-lined canal, while the flow 

rates and stages were determined at hourly intervals for five locations. While only daily averaged values are presented in this report, 

a magnetic tape containing all the data can be obtained from the 

Automatic Data Processing Unit, U.S. Geological Survey, Water Resources Division, Reston, VA 22092. This report presents all information necessary for the use and interpretation of these data.

Windspeeds were typically low during the early morning hours 

and at maximum during the late afternoon; however, they were variable spatially. On the other hand, incoming radiation and absolute 

vapor pressure appeared to vary little from point to point. At a point 

where only the air temperature is known, the most accurate method 

to estimate vapor pressure is to compute it from the wet- and drybulb temperatures obtained at a remote site.

INTRODUCTION

The ability to predict the effects of man-induced activity on various physical and biological water-quality 

factors is becoming increasingly important. Water 

temperature, while being an important water-quality 

characteristic in itself, affects nearly every physical 

property of water and influences the rate of nearly all 

chemical and biological reactions. A major obstacle to 

accurate temperature prediction in open channels is 

the estimation of the heat exchange due to evaporation.

In 1973 a comprehensive study of evaporation from 

open channels was initiated. The San Diego Aqueduct, 

owned and operated by the Metropolitan Water District of Southern California, was selected as the study 

site. The San Diego Aqueduct is a concrete-lined, open 

channel originating near Hemet, Calif, (about 120 km 

southwest of Los Angeles), and flowing generally south 

for about 26 km. The canal has a 3.66-m bottom width 

and side slopes of 1.5 to 1m. At full capacity it will 

deliver about 28 m3/s, but it generally flows near half

capacity. Since it carries water for municipal purposes, 

the flow rate is steady for long periods of time. Only 

three diversion points exist. Two of these are seldom 

used, and the third is insignificant in size.

Water temperature, as well as meteorologic and hydraulic variables which influenced the energy budget 

of the canal, were continuously recorded for a 1-year 

period beginning July 24, 1973. The incoming solar 

and incoming atmospheric radiation, windspeed and 

direction, water temperature, and wet- and dry-bulb 

temperatures were recorded at 10-minute intervals for 

each end of the canal, and the discharge and stage were 

recorded at hourly intervals for five locations.

The purpose of this report is three fold: (a) to present 

a description of the site, instrumentation, and procedures used in the study of the San Diego Aqueduct, (b) 

to present daily averaged values of the data obtained 

and provide the information necessary for the use of 

the complete data set, and (c) to present a general 

analysis of the temporal and spatial variability of the 

recorded data.

All data obtained during the study are available on 

magnetic tape and can be obtained from the Automatic 

Data Processing Unit, U.S. Geological Survey, Water 

Resources Division, Reston, VA 22092. The tape contains 10-minute values of all meteorologic and temperature data, hourly values of hydraulic data, and daily 

values of rainfall, pan evaporation, and supplementary 

windspeed measurements.

The spatial and temporal variations in windspeed 

and direction are analyzed in this report. The frequency of winds of various speeds and directions is also 

presented for each end of the canal. In addition to a 

presentation of the spatial and temporal variations in 

incoming atmospheric and solar radiation, the measurements are compared to computed clear-sky values, 

and the dependence of the measured diurnal variation 

in atmospheric radiation on sensor type is illustrated. 

Because the wet-bulb temperature is such a difficult
METEOROLOGY, HYDRAULICS, AND THERMAL REGIME, SAN DIEGO AQUEDUCT, CALIFORNIA

parameter to measure, an analysis is presented which 

determines the most accurate method of predicting the 

vapor pressure using wet- and dry-bulb temperatures 

from a remote site. The variations in resistance to flow 

which occurred throughout the year are also presented.

ACKNOWLEDGMENTS

The authors acknowledge the excellent cooperation 

extended by the Metropolitan Water District of Southern California. They granted the U.S. Geological Survey permission to install instrumentation on their 

premises, furnished copies of their operating records, 

and provided valuable assistance in the routine operation of the data-collection program. Especially helpful 

were Messrs. Paul Singer and Charles Voyles who 

were instrumental in granting the Survey permission 

to use the canal and to Mr. Kenneth Gandee who provided for the routine operations of the data collection.

SITE DESCRIPTION

Evaporation was the process of major concern in the 

study and thus influenced the selection of a study site. 

Since the energy exchange due to evaporation is often 

small in comparison to radiation exchange and energy 

convected into and out of a stream-flow system, the 

most desirable site for study would be one where evaporation would be large and variations in the other elements of the energy budget small. Thackson and 

Parker (1971) presented monthly averaged 

meteorologic conditions for 88 locations in the United 

States. After a thorough study of these conditions, it 

was decided that the hot, dry climate found in southern 

California and southern Arizona provided the best 

general location for the study. Restricting attention to 

this general region of the country, a canal or other 

open-channel reach was sought which would have: (a) a 

traveltime of approximately 12 hours; (b) fairly constant and easily defined geometric and hydraulic 

characteristics; (c) reasonably steady flow rate; (d) very 

few tributary inflows of diversions; (e) a maximum 

depth of about 3 m; and (f) a fairly uniform wind exposure along the reach. After considerable reconnaissance, it was found that the San Diego Aqueduct most 

nearly met all the requirements. The San Diego 

Aqueduct carries water from the Casa Loma Canal to 

Lake Skinner (fig. 1).

Water for the San Diego Aqueduct is diverted from 

the Colorado River, below Parker Dam, and carried by 

the Colorado River Aqueduct to a point just west of the 

San Jacinto Mountains (fig. 1, northeast corner). At 

this point, the water can be diverted to the Casa Loma 

Canal or directly to the city of San Diego by underground pipe lines. Water for the San Diego Aqueduct is 

diverted from the Casa Loma Canal.

The general topography in the region consists of 

mountain massifs separated by the flat San Jacinto 

Valley floor. Areas with elevations above 610 m are 

shaded in figure 1. The elevation of the valley floor is 

approximately 450 m. The upper 40 percent of the 

canal traverses the approximate center of the valley, 

and the lower 60 percent of the canal runs along the 

extreme eastern edge of the San Jacinto valley; the 

land generally rises sharply to the east of the canal but 

is fairly flat to the west. A few short reaches in the 

lower part of the canal pass through cuts as deep as 18 

m with steep side slopes. In general, the hilly areas of 

the region are used only for grazing, and the valley is 

grazed or used for the production of hay or other dryland crops. The National Atlas of the United States 

(U.S. Geological Survey, 1970) describes the natural 

vegetation as Coastal Sagebrush or Chaparral. Vegetation is of minor importance to the exposure of the 

water surface to either wind or radiation.

Thornthwaite (1931) described the climate as 

semiarid. The National Atlas (U.S. Geological Survey, 

1970) shows the mean annual precipitation as ranging 

from 200 to 400 mm, with 30 days per year having 

more than 0.3 mm. The average annual runoff for the 

region is low, ranging from 10 to 30 mm; however, up 

to 130 mm of runoff may be expected in the mountains. 

Almost no precipitation occurs during the months of 

May-October. The average solar radiation is 121 W/m2 

in January and is 315 W/m2 in July, and the mean 

temperature ranges from a low of 10°C in January to a 

high of 24°C in July. The mean dew point temperature 

is 2°C in January, whereas it is 10°C in July.

The San Diego Aqueduct is concrete lined, with a 

bottom slope of 0.00012. The cross section of the canal 

is trapezoidal, measuring 3.66 m for bottom width and 

1.5 to 1 m for side slopes. The maximum design depth is 

3.05 m, and it has a 0.305-m freeboard. Its capacity is 

about 28 m3/s. The spoil dirt from the canal was piled 

along the sides so that the typical cross section appears 

as shown in figure 2. The spoil bank height varies 

along the length of the canal as shown in figure 3. The 

three very large bank height values represent places 

where the canal passes through deep cuts, but for the 

rest of the canal the bank height is more or less representative of the height of the spoil bank.

The 16 siphons which carry water under roads and 

drainageways for the San Diego Aqueduct are shown 

in figure 4. The longest, just south of Holland Road, is 

197 m long, and the shortest, under Cottonwood 

Avenue, is 13 m long. The length, type, and location of 

all siphons are summarized in table 1. All siphons here 

have smooth transitions in the channel cross section 

upstream and downstream.

Three points are available for diverting water from
INSTRUMENTATION

117°

33°45'

Colorado River 

Aqueduct^

EXPLANATION 

A Gaging station 

^ Meteorologic station

<X> Evaporation pan

---- Underground aqueduct

———— Canal

10 KILOMETERS

0 5 MILES

FIGURE 1.—San Diego Aqueduct and data-collection points. Shaded areas are above 610 m.

the canal. The first diversion structure, near Simpson 

Avenue, allows water to be diverted into the underground aqueduct shown in figure 1. This structure was 

in operation during 35 percent of the study and 

diverted a maximum of 3.02 m3/s. The second diversion, known as EM-8, is insignificant in size. The 

maximum diverted flow was 0.15 m3/s, but it generally 

diverted only about 0.03 m3/s for 1 or 2 hours during 

the day. This diversion structure is just below Holland 

Road and supplies water for a chicken farm. The third 

diversion structure, the So. End diversion, allows 

water to be diverted to San Diego without passing 

through Lake Skinner (fig. 1). The So. End diversion 

was not used except during the last 71 days (20 percent) of the study, when it was in continuous operation. 

The diversion of water from the Casa Loma Canal at 

the entrance to the San Diego Aqueduct is shown in 

figure 5. The Casa Loma flows from east to west just 

behind the diversion structure. The outlet of the canal 

into Lake Skinner is shown in figure 6.

INSTRUMENTATION 

RECORDING SYSTEM

Three types of recording systems were used for the 

study. Windspeed, wind direction, solar radiation, atmospheric radiation, wet- and dry-bulb temperatures, 

and water temperatures for each end of the canal were
METEOROLOGY, HYDRAULICS, AND THERMAL REGIME, SAN DIEGO AQUEDUCT, CALIFORNIA

Concrete

FIGURE 2.—Typical cross section of the canal.

036 

Cottonwood

24 27 

Skinner

9 12 15 18 21 

DISTANCE, IN KILOMETERS

FIGURE 3.—Variation of bank height with distance along the canal.

recorded digitally at 10-minute intervals. Analog recorders were used to continuously record the stage at 

five points along the canal, the discharge of the EM-8 

and Simpson road diversions, and after February 28, 

1974, the discharge at the lower end of the canal. 

Analog records were digitized manually at hourly 

intervals. Rainfall, pan evaporation, pan windspeed, 

prevailing wind direction, and general weather conditions were observed daily.

The primary recording system to monitor radiation, 

wind, and temperatures consisted of Esterline Angus 1 

D2020 recorders coupled with Pertec magnetic tape 

recorders. At 10-minute intervals the time, as well as 

the millivolt values of all 10 parameters, were recorded 

on magnetic tape. No averaging of the readings was 

possible, so recorded values were the millivolt readings 

at the instant they were sampled. A sampling of all 10 

channels took only about 5 seconds. At approximately 

1-hour intervals, the same information was printed in 

digital form on a paper tape. The paper tape allowed 

field monitoring of the system and served as a backup 

record on a few occasions when the magnetic tape system failed. At weekly intervals the magnetic and paper 

tapes were removed and mailed to NSTL Station, 

Miss., for processing. A total of 12 tapes was sufficient 

to allow them to be copied, cleaned, and returned to the 

field for reuse without a shortage occurring. The sys-

'The use of brand names in this report is for identification purposes only and does not imply 

endorsement by the U.S. Geological Survey.

NEWPORT GAGE 

NEWPORT RD

EXPLANATION 

A Stage recorder 

© Siphon 

(^) Diversion point

SOUTH END GAGE

^SKINNER GAGE

0 1 3 KILOMETERS

1 MILES

FIGURE 4.—San Diego Aqueduct, the diversion points, and locations 

of siphons and stage recorders.
INSTRUMENTATION

TABLE 1. — Locations of structures on San Diego Aqueduct

[Information furnished by the Metropolitan Water District of Southern California]

Siphon characteristics

Name of structure

Florida .

Olive

French

South Bachelor Mountain

Distance from 

canal intake (m) 1

— - 297.5

____ 593.7

1,978.6

4,453.4

.___ 5,275.8

6,982.8

. _ 8,019.6

____ 8,793.8

_ 9,134.2

___ 10,135.8

____ 13,460.3

_ _ 13,604.5

— - 15,155.7

.___ 15,353.2

_ _ 15,932.6

_ 17,042.0

_ _ 19,571.5

_ _ 20,519.8

_ _ 22,525.7

. 23,852.1 

_ _ 24,978.4

__ .24,978.4

____ 25,978.1

_ - 25,982.7

Length 

(m)

13.0

75.3 

40.3 

66.3 

65.0 

107.8

61.1

142.9

"55.9 

197.5

133.8 

158.5 

36.4 

61.1 

158.5 

36.4

Size

pipe, 3.96 m I.D.2

box, 3.81x3.35 m 

box, 3.81x3.35 m 

box, 3.81x3.35 m 

box, 3.81x3.35 m 

box, 3.81x3.35 m

box, 3.81x3.35 m 

pipe, 3.96 m I.D.

box, 3.81x3.35m 

pipe, 3.96 m I.D.

pipe, 3.96 m I.D. 

pipe, 3.96 m I.D. 

box, 3.81x3.35 m 

box, 3.81x3.35 m 

pipe, 3.96 m I.D. 

box, 3.81x3.35 m

'Locations for siphons are determined by location of the siphon intake. 

2Inside diameter.

FIGURE 5.—Diversion of water from the Casa Loma Canal at the 

entrance to the San Diego Aqueduct. Photograph taken from the 

east bank; view is to the north.

tern at the Cottonwood (north) end was housed in a 

plywood shelter (fig. 14). and at the Skinner (south) 

end it was housed in a concrete building (figs. 6 and 7). 

The water stage was recorded on vertical-drum 

graphic recorders. These recorders had an unlimited 

range in stage because a stylus-reversing device was 

activated for each 0.3-m change in stage. A distance of 

12.7 mm on the chart corresponds to a stage change of 

0.305 m, and a distance of 4.6 mm corresponds to a time 

lapse of 24 hours. The stage records were collected as a 

part of the Metropolitan Water District's routine 

operating data. Charts were changed on a weekly 

basis, and copies of the charts were furnished to the 

Survey for analysis. These charts were read manually 

to determine the stage to the nearest 3 mm each hour.

FIGURE 6.—Skinner end of San Diego Aqueduct. Photograph taken 

from Lake Skinner dam; view is to the west.

FIGURE 7.—Recording system at downstream end of the canal.

The head on a Venturi meter at the Simpson road 

diversion was also determined from records of this 

type. The recorded head was converted to a discharge 

by use of a rating curve.

The diversion discharge to the chicken farm (EM-8) 

was recorded on a circular graphic chart which made 

one revolution per week. The chart was activitated by 

the head on a Venturi meter and was calibrated to read 

flow rate directly. The discharge could be easily read to 

the nearest 0.01 m3/s. After February 28,1974, the flow 

into Lake Skinner was recorded on a circular graphic 

chart which made one revolution per week. The flow 

rate could be easily read to the nearest 0.3 m3/s. All
6 METEOROEOGY, HYDRAUEIGS, AND THERMAL REGIME, SAN DIEGO AQUEDUGT. CALIFORNIA

circular charts were changed weekly; copies were sent 

to the Survey and digitized on an hourly basis. A supplementary windspeed was recorded on a weekly circular chart which contained a pip mark for the passage of 

each 16 km of wind. These charts were changed 

weekly, and the mean windspeed for each day was estimated.

WIND

Propeller-type anemometers were used as the primary wind-sensing devices. The starting speed of the 

propeller is about 0.45 m/s, with complete tracking at 

about 1.40 m/s. The wind direction was measured by 

the movement of a wiper arm on a potentiometer 

housed in the main body of the anemometer.

The general exposure of the anemometer at Cottonwood is illustrated in figure 8. The sensor head was 

located approximately 2 m above the concrete platform, approximately 2.4 m above the elevation of the

FIGURE 8.—Wind exposure at Cottonwood meteorologic station.

FIGURE 9.—Wind exposure at Skinner. Photograph taken from dam 

with view generally to the north.

asphalt parking lot surrounding the concrete structure, and approximately 3.1 m above the surrounding 

ground level. The sensor was 3.8 m above the top of the 

canal. The valley floor is flat in this area, and no major 

obstructions occur within 1 km.

The wind exposure at the Skinner station was quite 

different from the Cottonwood station. The terrain 

rises steeply to the north as shown in figure 9, whereas 

it falls off rather rapidly to the south and west (fig. 10). 

The exposure of the primary anemometer at Skinner 

was adequate for south or west winds, poor for north 

winds, and only fair for east winds. The effective height 

probably varies with wind direction. The sensor was 

mounted 0.86 m above the roof of the building shown in 

figure 6. The railing (which was added after the study 

began) partly hides the sensor in the figure. The buildFIGURE 10.—Wind exposure at Skinner. Photograph taken with view 

to the south.

FIGURE 11 —Psychrometer and supplementary anemometer at Cottonwood.
INSTRUMENTATION

ing roof is 3.05 m above the level of the parking lot. The 

parking lot is generally lower than the surrounding 

terrain but about 0.3 m above the top of the canal.

Supplementary windspeed measurements were obtained over the water. At Cottonwood the supplementary anemometer was mounted on a swing-out arm 

which projected 3.0 m from the canal edge. The 

anemometer was 3.3 m above the top of the canal lining. The general location of the anemometer is illustrated in figure 11. Windspeed measurements were obtained by use of vertical axis cup anemometers 

equipped with totalizing dials. An electrical contact 

was closed upon the passage of each 16 km of wind, and 

the contact closure times were recorded on a circular 

chart. A closeup of the anemometer used at Cottonwood is shown in figure 12. At Skinner the supplementary anemometer was mounted on a short arm projecting to the west of the bridge over the canal shown in 

figures 6 and 13. The anemometer was 2.0 m above the 

top of the canal and was located near the center of the 

bridge.

Average daily windspeeds were obtained at the 

evaporation pans by reading a totalizing dial on the 

anemometers at approximately 0900 hours daily. The 

anemometers were mounted on the northwest corner of 

the evaporation-pan platform 0.15 to 0.20 m above the 

lip of the evaporation pan. The location of the evaporation pans is shown in figure 1.

RADIATION

The total incoming solar radiation was determined 

by use of Eppley precision spectral pyranometers. 

These instruments are sensitive to radiation with a 

wavelength between 0.3 and 3 ^tm (micrometers). At 

Cottonwood the sensor was mounted on top of the

*• 1

^te^>v*\\;;

FIGURE 12.—Closeup of supplementary wind sensor and psychrometer at Cottonwood, view to the southeast.

plywood shelter housing the recording system (the instrument to the right in fig. 14). At Skinner it was 

mounted 1.14 m above the roof of the building (fig. 6). 

Incoming atmospheric (longwave) radiation was determined by use of two types of instruments. From July 

24, 1973, until November 27, 1973, atmospheric radiation was determined by use of Eppley (longwave) 

pyrgeometers which are sensitive to radiation in the 

range of 4 to 50 ^tm. These instruments were mounted 

beside the pyranometers (figs. 6 and 14). After 

November 27, 1974, a flat-plate radiometer of the 

Gier-Dunkle type was used to determine the incoming 

atmospheric component at Cottonwood. The flat-plate 

radiometer is sensitive to radiation of all wavelengths. 

Accordingly, the solar component, determined by use of 

the pyranometer, was subtracted from the total incomFIGURE 13.—Closeup of supplementary wind sensor and psychrometer at Skinner, view to the south.

FIGURE 14.—Radiation instrumentation at Cottonwood, view to the

south.
8 METEOROLOGY, HYDRAULICS, AND THERMAL REGIME, SAN DIEGO AQUEDUCT, CALIFORNIA

ing radiation to give the atmospheric component. The 

flat-plate radiometer was also mounted on top of the 

plywood shelter.

TEMPERATURE

All temperatures were determined by use of 

platinum resistance temperature devices (RTD's). A 

10-volt regulated d-c power supply furnished the required voltage to all the sensors. Capsule-style sensors 

with a sheath length of 63 mm and diameter of 3.2 mm 

were used for the dry- and wet-bulb temperatures. For 

measurement of water temperatures, a sensor with a 

sheath length of 127 mm and diameter of 6.3 mm was 

used.

Measurements of wet- and dry-bulb temperatures 

were made with a ventilated psychrometer as shown in 

figures 12 and 13. To insure proper wet-bulb depression, a vane axial fan with a constant output of 4.5 m/s 

was used to draw air through the tube. The total length 

of the tube was 203 mm, and the entire assembly was 

shielded from radiation by a curved aluminum sheet 

380 mm long and curved in a semicircle with a 190-mm 

radius (fig. 15). The wet- and dry-bulb temperatures 

were measured by probes projecting across the tube 

mounted 139 mm and 51 mm behind the tube intake, 

respectively. The wet-bulb probe was covered by a wick 

which was continuously wetted by distilled water. The 

wick was a common white cotton shoelace which had 

been boiled in detergent to remove sizing and rinsed in 

distilled water. Water was supplied to the wick by 

gravity flow from a 1-gallon plastic bottle through a 

capillary tube. The rate of flow in the tube was controlled by a needle valve at the base of the bottle.

At Cottonwood the psychrometer was mounted 

under the swing-out arm as shown in figure 12. It was 

2.7 m above the top of the canal. The general location of

FIGURE 15.—Closeup of the psychrometer.

the psychrometer is illustrated in figure 11. At Skinner 

the psychrometer was mounted on a short arm which 

projected to the west of the bridge shown in figures 6 

and 13. The psychrometer was 1.4 m above the top of 

the canal and near the center of the bridge.

Water-temperature probes were fastened to a 

wooden plank in such a manner that they would be 

0.15, 0.61,1.1, and 1.5 m above the bottom of the canal. 

At Cottonwood the plank was mounted to the west side 

of the canal so that it sloped downward with the canal 

side. The top of the plank can be seen in Figure 11. The 

temperature probes were held about 44 mm away from 

the concrete wall. Water temperatures were always 

found to be uniform, so on November 29, 1973, the 

bottom probe at Cottonwood was removed and not used 

during the remainder of the study. At Skinner a plank 

was mounted to the bridge so that it was held vertically 

near the center of the canal. The vertical locations of 

the probes at Skinner were the same as those used at 

Cottonwood.

STAGE

The stage in the canal was recorded at the five locations shown in figure 4. In all cases, a float-stilling-well 

arrangement was used, and zero stage corresponds to 

zero depth in the canal. The Cottonwood gage was located on the right bank 0.593 km downstream of the 

canal entrance. The outlet of the Cottonwood Avenue 

siphon was 0.28 km upstream of the gage, and the entrance to Esplanade Avenue siphon was 1.38 km 

downstream. A gentle curve to the right begins 0.07 

km below the gage. A photograph of the recorder and 

top of the stilling well is shown in figure 16, and the 

general canal conditions with a flow of about 2.8 m3/s is

FIGURE 16.—Recorder and stilling well at the Cottonwood gage, with 

view upstream.
INSTRUMENTATION 9

shown in figure 17. Current meter measurements, 

made from the bridge shown in figure 17, were used to 

determine a stage-discharge relationship. The Cottonwood stage record was used to determine the discharge 

during times of unsteady flow.

The Simpson gage, located 9.13km downstream from 

the canal entrance, is mounted over the center of the 

canal as shown in figure 18. It is 1.01 km downstream 

of the railroad siphon and 0.28 km upstream of the 

Simpson Road siphon. The Newport gage, located on 

the right bank 13.46 km downstream of the entrance, 

is shown in figure 19. The Newport gage is 3.18 km 

downstream of the Olive Avenue siphon and 0.14 km 

upstream of the entrance to the Newport Road siphon. 

The So. End gage, shown on the left side in figure 20, is 

located at the entrance to the So. End diversion (fig. 1). 

Before the construction of Skinner reservoir, the So.

FIGURE 17.—Canal at the Cottonwood gage, with view downstream.

FIGURE 18.—Simpson gage, view to the south.

End diversion was the south end of the open part of the 

San Diego Aqueduct. The diversion is to the left in 

figure 20, and the flow into Lake Skinner continues 

toward the lower right. The Skinner gage was housed 

in the concrete building shown in figure 6 and is at the 

downstream end of the canal 25.98 km downstream of 

the canal entrance. The use of this gage was discontinued on February 20,1974. The discharge at the time 

the photographs in figures 17, 18, 19, and 20 were 

taken was about 2.8 m3/s.

FLOW RATE

Canal and diversion discharges were furnished by 

the Metropolitan Water District from their operating 

records during times of steady flow. The flow rate at 

Cottonwood was determined by the Metropolitan 

Water District from an analysis of gate openings which 

were periodically calibrated by current-meter measFIGURE 19.—Newport gage.

11:

T

FIGURE 20.—So. End gage and diversion, view to the west.
10 METEOROLOGY, HYDRAULICS, AND THERMAL REGIME, SAN DIEGO AQUEDUCT, CALIFORNIA

urements at the Cottonwood gage. The diversion discharge at Simpson road is determined by use of a calibrated weir. At the EM-8 diversion a Venturi meter 

was used. After February 28, 1974, the flow rate into 

Lake Skinner was continuously monitored by use of a 

sonic flow meter. The flow rate at the So. End diversion 

was not measured but can be obtained from continuity 

considerations.

OTHER DATA

The Metropolitan Water District maintains two 

evaporation pans at the locations indicated in figure 1. 

The daily rainfall, pan evaporation, pan windspeed, 

general weather observations, and wind direction are 

recorded at about 0900 each day. On October 9, 1973, 

the observation station near the So. End diversion was 

moved to a point near the Lake Skinner outlet. Both 

locations are shown in figure 1.

PROCEDURE

DATA COLLECTION

All meteorologic instrumentation was designed to 

operate unattended for time periods of up to 1 week. 

However, on alternate days, the canal patrolman: (a) 

wiped dust from the radiometer bulbs; (b) checked the 

wick on the psychrometer (clean or change if necessary); (c) filled bottle with distilled water if necessary; 

(d) checked the printed output tapes for obvious malfunctions; (e) checked blower motors on the psychrometers; and (f) reported any malfunction to the 

Survey for correction. On a weekly basis, Water District personnel changed the magnetic and paper tapes 

as well as all weekly charts. The junior author visited 

the site on an approximately monthly basis to perform 

maintenance, check on the overall operation of the 

data-collection system, and carry out special measurements.

When the field magnetic tapes were received at the 

office, they were copied in compacted form on an inhouse tape. At the same time, a complete listing was 

produced as well as a time plot of the millivolt level for 

each channel. The computer listing and plots were 

compared with the output on the paper tape and 

instructions for further processing generated. At this 

point the major concern was to be sure the correct data 

were associated with each data block, the recorded 

times were correct, and that each day contained 

exactly 144 entries for each parameter. Corrections to 

the recorded times were frequently necessary because 

of short-term power outages, and so forth. Power outages were easily detected because the recorder clock 

would automatically start over at 0000 hours (midnight). All data were referenced to Pacific daylight

time. Time checks written on the paper tape served as 

a reference for time corrections.

The hourly stage and discharge values were read 

from charts and keypunched. Likewise, the daily 

values of the supplementary windspeed, pan 

windspeed, pan evaporation, and daily rainfall were 

computed from recorded parameters and the values 

added to the data set. The declination of the sun was 

determined from a solar ephemeris.

DATA PROCESSING

The next step in the processing of the data was to 

convert the millivolt values to engineering units and to 

delete all questionable values from the set. Converting 

to engineering units was simply a matter of applying 

the appropriate calibration factors to the millivolt 

readings, but detection of bad data in the set required 

considerable patience and systematic sorting.

Judgment as to the authenticity of the data was 

based primarily upon plots of the data as a function of 

time. Two types of plots were used: the original plots 

from the field data tapes where each 10-minute value 

was plotted as a function of time, and daily averaged 

plots where the entire year's data for a single parameter at each end of the canal could be displayed on one 

illustration. The recorder at Cottonwood developed a 

malfunction early in the study which caused the data 

to drift slowly off the true value. Comparison of the 

daily average plots from Cottonwood and Skinner on a 

channel-by-channel basis enabled the processor to 

determine the time at which a particular channel 

started drifting.

Considerable difficulty was experienced in keeping 

the wick on the psychrometer sufficiently wet. Time 

periods for which the wick was not sufficiently wet 

were obvious when a plot of the wet- and dry-bulb air 

temperature was inspected. In a like manner, times 

during which one of the water temperature probes was 

out of the water, owing to low stage, were also easily 

detected from a plot of the four water temperatures. 

Each channel of data was scanned several times, and 

data which were questionable were deleted. As a final 

check, after the data sets had been transferred to engineering units and questionable data deleted, a program was written which searched each channel of data 

for each station and printed the 20 largest values, 20 

smallest values, and 20 largest changes to occur in 10 

minutes, along with the date and time of occurrence of 

each event. The data on these listings were then 

rechecked for consistency and accuracy. As a final step 

the data were replotted on the 10-minute-interval 

basis and the plots scanned a final time.

Hydraulic data were processed in a similar fashion
PROCEDURE 11

except that only hourly values and not 10-minute 

values were involved. The EM-8 diversion discharge 

was read directly from the circular chart, and no processing was necessary. An analog chart of the head on 

the weir at the Simpson Road diversion was furnished 

as well as the diversion discharge during times of 

steady flow. An analysis of the recorded head and discharge indicated that the flow could be computed from 

the formula

Qs = l.62Yw l - 317 (1)

in which Yw is the head on the weir in meters, and Qs is 

the Simpson Road diversion discharges in cubic meters 

per second. Equation 1 was used to determine the 

Simpson Road diversion discharge during time periods 

when the flow was changing.

For each day during which the flow was constant 

(209 out of 365), the Manning's roughness coefficient 

applicable to the Cottonwood stage was determined. 

The coefficients ranged from 0.0135 to 0.191 and could 

not be directly correlated with either stage or discharge. The variation appeared to result primarily 

from algal growth on the canal lining and therefore 

was more related to time of year than anything else.

Variable flow, extending over periods of 1-15 days, 

occurred on 27 occasions. During these time periods, 

the upstream flow was computed for each hour using 

the measured Cottonwood stage and Manning's equation. The roughness coefficients, obtained before and 

after the period of unsteady flow, were averaged for use 

in this computation.

Between February 28, 1974, and May 15, 1974, the 

discharge, as determined from the sonic flow meter at 

Skinner, was used to determine the flow in the canal. 

This value was read directly from an analog chart. The 

So. End diversion was in operation after May 15, 1974. 

Subsequent to that date the stage at Cottonwood was 

used to determine the flow into the upstream end of the 

canal, and the sonic flow meter was used to determine 

the flow at the downstream end. The flow at the So. 

End diversion could then be determined indirectly.

CALIBRATION

Table 2 contains a summary of the calibration factors for instruments used in the study. All calibration 

equations were of the form

O = a + bE (2)

in which O is output in the engineering units shown in 

table 2, E is recorder output in millivolts, and a and b 

are constants shown in table 2.

TABLE 2.—Calibration factors (for use in equation 3) of instrumentation used at the San Diego Aqueduct

Parameter

Cottonwood wind direction _ _ 

Skinner wind direction _ _

Cottonwood atmospheric _ _ 

Cottonwood atmospheric _ _ _ 

Cottonwood total incoming 

Cottonwood total incoming 

Cottonwood total incoming

Skinner atmospheric ________ 

Skinner atmospheric _ _ ___.

a

0.11

.08

1.2

_ n

6

0

-.03

0 

0 

0 

0 

0 

0

0 

0

b

0.1984

.1997

2.114 

2.089 

110.0

103.1

4.995

145.2 

145.6 

562.4 

355.0 

474.2 

145.6

145.2 

145.6

Units

degree 

degree W/m2 W/m2

°C

W/m2 W/m2 W/m2 W/m2 W/m2

W/m2 W/m2

Applicable dates

07-25-73—07-23-74

07-25-73—07-23-74

07-25-73—07-23-74 

07-25-73—07-23-74

07-25-73—07-23-74

07-25-73—07-23-74

07-25-73—08-28-73 

08-29-73—11-27-73 

11-28-73—01-31-74 

03-07-74—04-24-74 

06-05-74—07-23-74 

07 25-73 08-29-73

08-29-73—03-24-74 

04-24-74—05-28-74

After the study the anemometers were recalibrated, 

and their calibration constants had changed by less 

than 3 percent. Temperature probes were periodically 

checked against mercury thermometers and always 

found to be within ±0.1°C. The pyranometers were 

calibrated before and after use, and their calibration 

coefficients were found to have remained constant to 

within ±1 percent.

Considerable difficulty was experienced with the 

measurement of atmospheric radiation. Both 

pyrgeometers were calibrated before installation on 

July 25, 1973. By the end of August 1973, the measured atmospheric radiation at Cottonwood appeared 

to be drifting to the high side. To see if the difference 

between Cottonwood and Skinner readings was real or 

due to a drift in the calibration of pyrgeometers, on 

August 29, 1973, the sensors were interchanged. No 

shift in the daily average values at either end of the 

canal was observed after the sensors were interchanged, so it was assumed that the sensor calibrations 

were still valid. Although the recorder at Cottonwood 

malfunctioned three times between September 1, 1973, 

and November 28, 1973, the atmospheric radiation 

values measured at each end of the canal and the computed clear-sky values were all in general agreement.

On November 28, 1973, the pyrgeometer at Cottonwood was removed for a calibration check and replaced 

by a flat-plate radiometer of the Gier-Dunkle type. 

During December 1973, the measured atmospheric 

radiation at Skinner was 30 percent higher than that 

measured at Cottonwood. Unfortunately, it was impossible to determine whether one or both sensors were 

out of calibration. On January 31, 1974, the flat-plate 

radiometer failed, and it was replaced on March 7, 

1974. This second flat-plate radiometer was operated 

until April 24, 1974, when it also failed. The first flat 

plate, which had been repaired and recalibrated, was 

reinstalled at Cottonwood on June 5, 1974. This 

radiometer operated continuously until the end of the 

study on July 23, 1974.

Meanwhile, difficulty was also being experienced at
12 METEOROLOGY, HYDRAULICS, AND THERMAL REGIME, SAN DIEGO AQUEDUCT, CALIFORNIA

the other end of the canal. On March 24, 1974, the 

output of the pyrgeometer at Skinner started dropping 

sharply, falling essentially to zero by March 31, 1974. 

Unfortunately, the instrument could not be calibrated, 

so only the original calibration factor is available.

On April 24, 1974, the pyrgeometer removed from 

Cottonwood on November 20, 1973, was installed at 

Skinner. Although it had been recalibrated locally, the 

output using the new calibration factor appeared to be 

too large, so it was assumed that the original manufacturer's calibration factor was still valid. This instrument failed in a manner similar to the first pyrgeometer on May 28, 1974. After this date, no atmospheric 

radiation measurements were available at Skinner.

The hydraulic data were furnished by the Metropolitan Water District, and no extensive check on their 

accuracy was made by the Survey. However, the accuracy of the stage recorders at Cottonwood and Simpson 

Road were checked by measuring the centerline water 

depth from the bridge and comparing the results to the 

recorded stage. The centerline depth and stage always 

agreed to within ±6 mm. On January 15-16, 1974, the 

discharge was measured and the results compared with 

the value provided by the Metropolitan Water District. 

The results agreed to within 4 percent, which is considered to be about the accuracy of the flow measurements. Personnel of the California District of the Geological Survey made current-meter measurements 

which were used to calibrate the sonic flow meter at 

Skinner. The sonic flow meter was installed during the 

latter part of February 1974 and calibrated in early 

March.

It was realized that the five measured stages may not 

be representative of depths at all points along the 

canal. The word "depth" is used to mean the centerline 

(maximum) depth, which is also the stage (fig. 2) in all 

cases. An attempt was made to measure a longitudinal 

depth profile under several flow conditions to determine how to predict mean local depths from the recorded stages. These profiles were determined in the 

following manner. First an automobile odometer was 

used to place reference marks on the canal fence. No 

reference mark was placed closer than 160 m to either 

the intake or outlet of a siphon. Water depth was 

measured at each of these reference points for seven 

conditions which included flows ranging from 2.8 to 

23 m3/s.

It was impossible to measure the centerline depth 

(stage) directly except at a few points along the canal; 

however, it was fairly easy to measure the slope distance from the top of the canal lining to the water 

surface. The stage could then be computed from the 

known geometry of the canal. Comparisons of the 

stage, as determined from the slope measurements to

the stage as measured directly, where possible, indicated that the slope measurements allowed the stage to 

be estimated within about ±9 mm. 

The results of these measurements and calculations 

are summarized in table 3, which gives the centerline 

depth (stage) and the distance from the canal intake for 

each of seven runs. The flow variations during any run 

were very small, and the measured stages and discharges at the time of the runs will be presented later. 

Runs 1 and 7 were conducted on March 6 and April 24, 

1974, respectively, when the hydraulic conditions were 

essentially constant. Unfortunately the flow was 

slightly unsteady during run 2 made on March 24,

TABLE 3. — Profiles of centerline depth for the San Diego Aqueduct 

under nearly steady flow conditions 

[All values are in meters]

Distance 

from 

intake

593 

1,398 

2,444 

3,249 

4,054 

4,897 

6,147 

7,450 

8,529 

9,135 

9,794 

11,083 

11,888 

12,692 

13,497 

14,143 

15,594 

16,871 

17,602 

18,407 

19,212 

20,011 

20,333 

21,385 

22,190 

23,489 

24,532 

25,015

......

— —

— —

______

______

— —

______

__ _ _

Stage 

run

1

2.98 

2.86 

2.84 

2.80 

2.79 

2.77 

2.77 

2.76 

2.78 

2.79 

2.78 

2.77 

2.70 

2.65 

2.60 

2.64 

2.62 

2.70 

2.76 

2.75 

2.72 

2.72 

2.71 

2.56 

2.61 

2.51 

2.45 

2.39

______

______

— —

— —

Distance 

from 

intake

148 

477 

811 

1,145 

1,477 

1,811 

2,294 

2,614 

2,935 

3,254 

3,574 

3,893 

4,214 

4,835 

5,080 

5,611 

5,927 

6,266 

6,580 

6,715 

7,223 

7,541 

7,780 

8,355 

8,679 

9,004 

9,654 

9,955 

10,439 

10,778 

11,078 

11,399 

11,718 

12,038 

12,357 

12,705 

12,996 

13,317 

13,944 

14,258 

14,574 

14,888 

15,540 

15,775 

16,314 

16,644 

17,441 

17,760 

18,081 

18,402 

18,723 

19,043 

19,364

19,864

20,183

20,976

21,293

21,608

21,925

22,241 

22,892 

23,212

23,532 

24,017

24,338

24,657

25,139

25,459

25,780

Run 

2

1.02 

1.17 

1.12 

1.03 

1.03 

1.03 

1.06 

1.04 

1.03 

1.01 

1.03 

1.02 

1.01 

1.02 

.98 

.99 

1.01 

.98

.95 

.96 

.95 

.98 

1.01 

.98 

1.01 

.95 

.91 

1.06 

1.06 

1.03 

1.02 

1.01 

.98 

.96 

.92 

.87 

.84 

.92 

.88 

.84 

.77 

.84 

.80 

.92 

.92 

1.09 

1.09 

1.09 

1.12 

1.17 

1.20

______

Run 

3

— —

-_.___

______

______

______

— —

0.91 

.87 

.82 

.75 

.82 

.77 

.89 

.89 

1.05 

1.05 

1.05 

1.08 

1.13 

1.17 

1.12

1.19

1.20

1.22

1.20

1.26

1.33

1.37 

1.57 

1.58 

1.61

1.68

1.71

1.77 

1.81

1.84 

1.87

St

Run

4

1.01

1.17

1.10 

1.03

1.02

1.03

1.05

1.02

1.02

.99 

1.01

.99

.98 

.98

.96 

.96

.98

.95 

.91

.92

.94

.92

.94 

.96

.95

.96

.92

89 

1.05 

1.03

1.02

1.01 

.98

.94 

94 

91 

85 

.80

— —

— —

______

— —

age

Run 

5

______

______

______

——

— —

______

______

~L66 

1.60 

1.57 

1.53 

1.68 

1.67 

1.84 

1.87 

2.05 

2.05 

2.05 

2.11 

2.19 

2.22 

2.19 

2.25 

2.26 

2.30 

2.29 

2.37 

2.43 

2.47 

2.67 

2.70 

2.71 

2.78 

2.82 

2.87 

2.91 

2.94 

2.98

Run 

6

1.81 

1.98 

1.89 

1.82 

1.81 

1.82 

1.84 

1.81 

1.80 

1.77 

1.80 

1.77 

1.75 

1.75 

1.71 

1.73 

1.74 

1.70 

1.75 

1.68 

1.70 

1.69 

1.71 

1.73 

1.71 

1.74 

1.69 

1.67 

1.81 

1.78 

1.77 

1.75 

1.74 

1.68 

1.68 

1.64 

1.58 

1.54 

1.61 

1.55 

1.53 

1.46 

1.57 

1.55 

1.68 

1.69 

1.85 

1.84 

1.82 

1.85 

1.89 

1.92 

1.87 

1.89 

1.89 

1.88 

1.84 

1.88 

1.92 

1.95 

2.11 

2.09 

2.11 

2.15 

2.16 

2.27 

2.32 

2.34 

2.37

Run

7

2.47 

2.65 

2.58 

2.48 

2.45 

2.46 

2.46 

2.44 

2.43 

2.40 

2.42 

2.40 

2.36 

2.36 

2.33 

2.33 

2.33 

2.30 

2.25 

2.25 

2.26 

2.26 

2.27 

2.23 

2.16 

2.16 

2.17 

2.15 

2.25 

2.23 

2.23 

2.18 

2.19 

2.05 

2.13 

2.13 

2.11 

2.11 

2.17 

2.13 

2.13 

2.13 

2.16 

2.16 

2.25 

2.26 

2.24 

2.41 

2.43 

2.40

2~44 

2.48 

2.50 

2.48 

2.46

2~58 

2.60 

2.58 

2.74 

2.75 

2.78 

2.80 

2.85 

2.85 

2.87 

2.91
RESULTS 13

1974, as well as during runs 3 and 4 made on March 25, 

1974, and runs 5 and 6 made on March 26, 1974. The 

effect of the slight unsteadiness was accounted for by 

noting the time at which each measurement was obtained. All measurements were obtained by working in 

the downstream direction at a very nearly constant 

rate. The beginning times of runs 2, 3, 4, 5, and 6 were 

1354, 0635, 1100, 0632, and 1012 hours, respectively, 

and the ending times were 1922, 0903, 1325, 0829, and 

1705 hours, respectively.

RESULTS 

GENERAL

All data obtained during this study are available on 

magnetic tape from the Automatic Data Processing 

Unit of the U.S. Geological Survey. The tape contains 

10-minute values of all meteorologic and temperature 

data, hourly values of hydraulic data, and daily values 

of the supplementary data.

Table 4 contains daily averages of all meteorologic

TABLE 4.—Daily averaged values of meteorologic and temperature data for San Diego Aqueduct (July 25, 1973-July 23, 1974)

Day 

of 

month

Windspeed

(m/s)

COT1 SKN2

Wind 

azimuth3 

(degree)

COT SKN

Solar 

radiation

(W/m2 .

COT SKN

Atmospheric 

radiation

(W/m2 )

COT SKN

Air 

temperature <°C)

COT SKN

Vapor 

pressure 

(kPa)

COT SKN

Water 

temperature (°C>

COT SKN

July 1973

25 ____ _ ____

26 _ _________ __.

27 __ ______ ___

28 ___ ______ __

29 ___ ________

30 ____ _________

31 ______ __ ___.

._________!. 74

_________1.43

_________!. 22

_________1.66

_________1.66

1.31 

1.23 

1.27 

1.14 

1.18 

1.33 

1.26

______

______

211 

192 

222 

203 

204 

215 

199

326 

320 

310 

304 

306 

310

332

331 

326 

319 

319 

310 

309

390 

386 

391 

396 

398 

410

394 

385 

378 

382 

381 

385 

401

26.2 

24.5 

24.3 

24.4 

24.8 

25.9

27.1 

25.5 

25.2 

24.7 

25.1 

25.8

1.45 

1.28 

1.22

______

1.38

__ __ 25.4

25.7 25.5 

25.8 25.7 

25.8 25.7 

26.1 25.8 

26.2 25.9 

26.0 26.0

August 1973

i__ _ _ ______

2________________

3______ ____

4 _ __ __ ____

5_____ _____ _ __

6____ _--___.

7_ ____ _____

8______ _______ _

9__ ________ ____

10 ___ _____ ___.

11 _

12 ____ ______

13 ___ ___ _ _ ..

14 _

15 _ __ ___ ____

16 ________

17 __ _____

18 _______________

19 ___ __ _ ____ _

20 _____ ____ _

21 ____________ .

22 ___ _____

23 ____ ____

24 _____________ _

25 ___ ____ _ __

26 _______________

27 __

28 ____ ____

29 ____ _____

30 _______________

31 _ ____, _ ___

!_____ ____

2________, ________

3__

4 _

5_ _ ___ _ _____

6______ ______

7___

8 _____ _ ___

9 _ __ _ ____

10 _____ _______

11 __

12 _ ._

13 ____ _______

14 ___ _ ______

15 _______________

16 _ _.__ ___

17 _______________

18 ___ _ __

19 _ ___ ___ ___

20 ______________

21 _ ___.

22 _____ _________

23 ___ _____

24 _______________

25 __ ____ 

26 ____ _ ____

27 _____ __ _.

28 ____ ________ _

29 _______________

30 ____ _______ _

______ __1.14

______ _ 1.61

______ _ 1.24

_________1.39

____!. 27

._________!. 16

._-_____-_!. 12

_____ ___1.06

.-____. 1.22

. _____ -1.30

________ _1.20

.-_______ .92

____ _ ___1.31

_________!. 15

_________!. 16

_-______2.21

.__ _ ___1.47

___ _____2.02

1 69

_________1.93

_ _____ _2.30

___ ____1.05

_______ _ 1.54

_________ .83

_______1.21

____ __1.36

_____1.05

_ 1.40

___ _ ___1.31

_ _____ 1.27

______ __1.62

1 98

_ _ _____!. 72

___ _ _ .93

_________ .86

_ _____ .93

_ ____ 1.23

___ ____!. 25

99

_ ____ _1.55

___ ____1.39 

_ _____!. 11

____ _ ___1.18

-_____ 1.43

_ __ ___. .88

_____ __3.05

. _ _ ___1.60

___ ___1.66

__________3.33

._______, _1.24

_ _______ .91

._ _ ___,_1.02

_ ____ _1.62

1.18 

1.20 

1.45 

1.36 

1.42 

1.27 

1.06 

1.07 

1.18 

1.22 

1.10 

1.11 

1.36 

1.13 

1.31 

1.16 

1.23 

1.30 

1.61

1.29 

1.18 

1.24 

1.32 

1.50 

1.71 

1.44 

1.31 

1.15 

.99 

1.25

1.06 

1.31 

1.46 

1.09 

1.22 

1.00 

1.08 

1.35 

1.28 

1.24 

1.32 

.99 

1.15 

1.11 

1.02 

1.31 

1.17 

1.23 

1.09 

1.19 

1.08 

1.09 

1.54 

1.08 

1.68 

1.73 

1.28 

.87 

.85 

1.06

______

______

______

______

______

 

______

______

______

270 

207

225 

205 

220 

240 

29 

66 

211 

185 

191 

221 

52 

261 

259 

197 

196 

199 

206 

202 

210 

235 

190 

57 

216 

257 

245 

45 

70 

74 

219 

204

210 

203 

220 

207 

224 

238 

209 

218 

199 

204 

219 

226 

201 

198 

201 

217 

219 

230 

232 

248 

222 

184 

221 

229 

206 

226 

244 

208 

227 

207 

219

200 

218 

231 

209 

249 

252 

202 

219 

211 

254 

252 

192 

216 

230 

194 

206 

226 

208 

209 

188 

207 

202 

203 

218 

41 

231 

24 

212 

197 

197

269 

288 

310 

197 

297 

288 

308

300 

317 

302 

289 

239 

267 

288 

280 

260 

276 

291 

180

295 

318 

313 

277 

287 

290 

313 

289 

286 

282

 -

 -

284" 

267 

252 

243 

249

246 

308 

314 

208 

318 

290 

306

QOQ

318 

325 

308 

296 

269 

257 

303 

295 

287 

301 

299 

223

306 

323 

314 

292 

290 

299 

300 

294 

276 

271

September

262 

278 

__ 272 

165 

__ 257 

283 

285

247

252 

240 

220 

245 

232 

248 

265 

271 

255 

243 

253 

110 

195 

248 

249 

259 

256 

250 

242 

243

419 

426 

421 

408 

392 

391 

382

394 

383 

395 

414 

422 

426 

418 

420 

426 

420 

414 

431

385 

354 

351 

364 

368 

383 

405

413 

383

1973

406

427

______

397 

371 

376 

366

408 

413 

408 

396 

386 

392 

373 

377 

384 

369 

395 

402 

409 

413 

406 

407 

411 

413 

411 

424 

404 

381 

349 

355 

375 

370 

359 

353 

363 

372 

376

360 

366 

378 

379 

378 

366 

370 

384 

388 

394 

385 

374 

389 

379 

368 

356 

352 

339 

348 

359 

354 

381 

366 

354 

367 

353 

360 

362 

358 

344

26.4 

27.0 

28.0 

23.8 

22.5 

21.7 

22.5

23.9 

23.6 

23.6 

26.7 

26.5 

26.6 

25.7 

26.9 

27.2 

27.9 

27.6 

27.8

25.2 

22.4 

21.3 

17.6 

18.1 

19.8 

22.9 

24.6 

23.8 

19.7

21.3

______

24.4 

23.0 

20.6

26.4 

27.6 

26.5 

22.7 

22.1 

21.4 

21.4 

23.3 

23.7 

22.1 

22.3 

25.5 

24.2 

25.1 

25.3 

26.4 

26.3 

29.8 

29.9 

28.3 

27.3 

26.1 

22.6 

21.6 

20.0 

20.0 

20.0 

20.9 

23.0 

20.0 

18.9

18.4 

19.2 

19.6 

17.8 

19.5 

22.4 

22.5 

18.9 

18.5 

18.0 

20.3 

19.7 

18.7 

19.7 

18.1 

17.7 

18.0 

18.3 

19.5 

18.1 

19.2 

16.7 

17.5 

17.6 

20.9 

24.6 

25.8 

25.2 

23.7 

20.8

1.52

______

1.68

1.74 

1.61

------

1.20

1.35

1.19

______

1.36

______

".67"

1.56

1.78

1.66

1.56 

1.69

1.84 

1.82 

1.79 

1.80

1.92 

1.75 

1.28

1.54 

1.45

1.22 

1.21 

1.55 

1.49

1.39 

1.43 

1.57

"1.64 

1.68 

1.64 

1.48 

1.38 

1.25 

1.04 

1.15 

1.41 

1.47 

1.64 

1.48 

1.37 

1.15 

.54 

.52 

.59

26.2 26.0 

26.5 26.5 

26.3 26.6 

25.8 25.8 

25.9 25.8 

26.1 25.9 

26.0 25.7 

__ _ _ 25.6

25.9 25.7 

26.0 25.7 

26.1 25.8 

26.3 26.1 

26.5 26.2 

26.5 26.4 

26.4 26.3 

26.7 26.6 

26.8 26.6 

26.5 26.6 

26.5 26.5 

26.4 26.0 

______ 26.3

26.2 25.9 

25.9 25.3 

25.5 25.1 

24.6 24.5 

______ 24.0

24.1

______ 23.7 

______ 23.9

_ ___ 24.2 

______ 24.3

______ 24.2 

24.1 

24.0 

______ 23.7 

__ _ 24.2 

______ 24.5

24.4 

______ 24.4 

24.8 

___ 24.5 

24.2 

______ 23.8 

23.7 

______ 23.7 

_ 23.8 

23.8 

______ 23.4 

______ 23.5 

____ _ 23.4 

_ ___ 22.8 

22.4 

______ 22.3 

22.1 

22.2 

______ 22.4

See footnotes at end of table
14 METEOROLOGY, HYDRAULICS, AND THERMAL REGIME, SAN DIEGO AQUEDUCT, CALIFORNIA

TABLE 4.—Daily averaged values of meteorologic and temperature data for San Diego Aqueduct (July 25, 1973-July23, 1974)—Continued

Day 

of 

month

Windspeed

(m/s)

COT1 SKN2

Wind Solar Atmospheric Air 

azimuth3 radiation radiation temperature 

(degree) (W/m2 ) (W/m2 ) <"C) (kP

COT SKN COT SKN COT SKN COT SKN

Vapor Water 

pressure temperature

a) (°C)

COT SKN COT SKN

October 1973

6 ____________

g

g

10 ___________

12 ___________

1 1

15 ___________

17 ___________

18 ___________

19 ___________

20 ___________

21 ___________

22 ___ __ __ _

23 __________

24 ___________

25 ___________

26 ___________

27 __ ___ _

28 ___________

29 __ _ _ __.

30 ___________

31 ___________

^

2

3 ___ __ __ _

5 __ _ ________

7_ __ __ _ _.

9_ __ ___

10 ____________

11 ____________

12 ____________

13 ____________

14 __ ___ __ .

15 __ _ ___

16 ____________

17 ____________

18 ___________

19 ____________

20 ______ ____

21 __ ___ __

22 _______ .

23 ____________

24 ___ _ _.

25 ____________

26 _____ ___

27 _ ____ _ .

28 ___________

29 _ ___ __ _

30 ___________

1- _ _ ___ __.

2

3

4_ _ ____

5_________ ___

6 _ _____ __ _

g

g

10 _

11 ____________

12 ____-._____.

13

14 _____ __

15 _ __ _ __ _

16 ___ ______

17 ____________

18 ________ __

19 ____________

20 ___ __ ___.

21 ____________

22 ___

23 ___________

24 ___ ___

25 __. ______

26 _ ___ __ .

27 __..______-

28 ____ ___

29 ._ __ __ __

30 ___ ___

31 ____________

1 60

1 20

81

_______ _____ _1. 15

1 fW

95

_____________ .81

_____________ .91

95

1 16

____________ .1.11

__ __- 1.47

90

94

9 1 ft

Q CO

_____________ .80

1.44

_____________ 56

_____ _ _____ .62

_____________ .88

______ ___ __ .92

_____________ .94

.__- ___ ___ 1.08

1 09

___- _____ _1.47

_____________ .93

_______ __ __ .98

_ _ __ ___ .55 

_____________ .88

_ __ . __ _._ .88

_ __ _ ___ __ .93

1.39 

1.33 

1.04 

1.18 

1.19 

1.17 

1.31 

1.24 

1.40 

1.55 

.96 

.96 

1.05 

1.04 

1.01 

.91 

1.30 

1.10 

.94 

1.06 

.84 

1.06 

1.28 

1.38 

.88 

1.33 

1.55 

1.05 

1.38 

1.69 

1.16

1.44 

1.58 

1.17 

.79 

.78 

.70 

.66 

.82 

1.26 

1.32 

1.00 

1.17 

1.34 

.99 

1.09 

.98 

1.19 

2.17 

1.02 

.94 

1.08 

1.79 

1.22 

1.07 

1.09 

1.26 

1.41 

1.88 

1.05 

1.02

1.05 

1.07 

.84 

.57 

1.01 

1.54 

1.15 

.98 

1.55 

1.18 

1.00 

.82 

1.05 

.84 

1.64 

.65 

.76 

1.69 

1.55 

2.11 

.85 

1.01 

.93 

1.70 

.78 

.66 

.82 

81 

1.02 

1.17 

1.05

207 

213 

44 

199 

206 

207 

218 

219 

217 

83 

68 

64 

225 

205 

241 

246 

52 

48 

269 

214 

224 

213 

53 

36 

221 

74 

37 

251 

10 

26 

195

219 

224 

208 

185

196 

204

213 

201 

200 

202 

3 

13 

21 

205 

203 

5 

204

191 

244 

199 

37 

204 

229 

215 

196 

197 

184 

217

208 

243 

192 

90 

202 

197 

206 

217 

184 

44 

221 

62 

30 

226 

239 

239 

39 

29 

197 

200 

219 

213 

252 

36 

193 

27 

42 

191 

27 

20 

182

220 

225 

180 

202 

205 

257 

192 

184 

19 

39 

20 

200 

181 

237 

221 

187 

188 

225 

232 

189 

198 

189 

86 

193 

200 

41 

29 

8 

1 

199

226 

2 

43 

39 

10 

49 

4 

6 

4 

21 

232 

200 

27 

264 

17 

230 

207 

33 

80 

64 

241 

237 

7 

16 

188 

194 

233 

202 

186 

269 

200

203

176 

224 

242 

219 

218 

220 

217 

199 

211 

213 

207 

211 

198 

191 

151 

198 

191 

161 

204 

200 

191 

197 

191

163 

151 

173 

184

-_._

113 

139

49 

139 

126 

88 

136 

140 

134 

137 

141 

140 

107

137 

98 

104 

119 

125 

121 

128 

45 

32 

110 

101 

125

189

o-i Q

909

900

199 

118

186 

227 

218 

212 

217 

220 

214 

183 

197 

205 

203 

204 

203 

194 

168 

193 

193 

178 

201 

198 

191 

193 

188

November

166 

152 

158 

179

175

141

161

127

65

154

89

97

139

135 

146 

149

119

142

December

41 

142 

148 

84 

140 

144 

126 

142 

146 

144 

115

1 9^

104 

84 

132 

127 

134 

137 

130 

141 

98 

90 

121 

132 

119 

129 

38 

57 

118 

114 

129

363 

332 

346 

348 

365 

362 

376 

395 

395 

396 

383 

362 

343 

374 

357 

352 

341 

342 

335 

338 

335 

331 

348

1973

345 

367 

341 

323

301

1973

372 

403 

289 

283 

314 

299 

317 

310 

299 

299 

274

278 

277 

312 

302 

276 

283 

299 

317 

350 

448 

390 

312

358 

355 

356 

341 

343 

360 

357 

364 

345 

316 

325 

339 

355 

353 

358 

365 

367 

378 

368 

347 

337 

340 

350 

333 

333 

335 

329 

333 

329 

327 

340

342 

349 

322 

311 

306 

316 

339 

339 

334 

353 

360 

349 

329 

308 

309 

342 

376 

343 

293 

299 

345 

328 

320 

322 

297 

322

326

326 

312 

310 

320 

320 

325 

332 

339 

331 

332 

325 

317 

325 

339 

326 

334 

327 

309 

309 

305 

311 

325 

308 

300 

307 

313 

334 

353 

348 

337 

316

16.9 

16.4 

17.2 

22.2 

19.4 

14.4 

16.2

15.1 

14.2 

16.2 

17.6 

21.2 

21.5 

21.8 

23.3 

24.1 

23.8 

22.6 

19.0 

16.0 

14.8 

15.6 

16.7 

16.6 

17.3

11.6 

10.1

7.3 

6.9 

73 

7.5 

9.4 

10.6 

12.8 

12.3 

12.3 

12.6 

10.7

8.1 

8.4 

6.4 

7.4 

6.9 

7.6 

6.7 

10.1 

11.3 

10.7 

8.9

16.4 

15.5 

16.9 

21.6 

19.2 

15.5 

16.5 

15.2 

15.4 

15.6 

16.6 

19.0 

22.7 

23.6 

23.3 

24.2 

25.3 

24.8 

23.8 

20.1 

16.9 

14.9 

16.1 

17.1 

18.1 

18.8 

21.5 

21.8 

20.4 

20.2 

20.3

15.9 

14.4 

13.4 

14.0 

15.2 

15.1 

17.2 

18.6 

15.2 

18.7 

20.9 

17.9 

13.7 

12.2 

12.0 

12.4 

13.7 

11.5 

9.2 

9.1 

10.5 

10.0 

8.2 

8.0 

8.2 

9.7 

10.8 

14.4 

14.2 

12.3

9.2 

8.5 

9.5 

9.6 

11.3 

13.9 

14.4 

15.3 

15.5 

15.2 

12.7 

10.4 

8.6 

10.9 

14.1 

14.4 

13.4 

11.9 

12.8 

12.8 

10.6 

9.6 

8.4 

10.1 

9.5 

9.5 

8.8 

11.2 

11.9 

12.1 

10.2

0.98 ______

1.27 ______

1.16 ______

1.11 1.22 

.75 .85 

.60 .72 

.65 .76 

.61 .72 

_____ .70

_ __ .90

.89 ______

.81 ______

______ 1.14

______ 1.31

1.22 1.31 

______ 1.12

______ .97

______ .71

.48 

______ .36

.40

______ .28

_ _ .42

______ 0.94

______ 1.21

__ 1.04 

.95

.82

______ .79

_____ .89

______ 1.16

______ 1.24

______ 1.05

___ .98

_ _ 1.10

_ ___ 1.47

______ 1.20

.76

_____ .99

_____ .99

.76

______ .88

______ .71 

______ .60

0.65 .70 

.70 .80

0.84 0.91 

.63 .66 

.52 .53 

.67 .64 

.55 .61 

.45 .49 

.42 .51 

.53 .57 

.50 .52 

______ .56

.71 

.91

.43 I~~~~~ 

.78 ______ 

.68 ______

1.12 1.24 

1.08 ______ 

1.04 ______

 

______

15.1 

15.0

15.0 

14.9 

14.0 

13.6 

13.7 

13.8 

13.7 

13.6 

13.5 

13.5 

13.5

12.6 

12.4 

12.4 

12.4 

12.2 

11.8 

11.6 

11.9 

11.9 

12.3 

12.3 

12.0

22.5 

22.5

21.3 

20.9 

20.1 

20.3 

20.8 

20.9 

21.0 

21.1 

21.3 

21.4 

21.4 

21.2 

21.1 

21.0 

20.8 

20.7 

20.1 

19.8 

19.8 

19.5 

19.3 

19.2 

18.7

18.2 

18.6 

18.4 

18.4 

17.9 

17.6 

17.9 

18.3 

18.3 

18.5 

18.5 

18.5 

18.3 

17.9 

17.2 

17.3 

17.4 

16.8 

16.7 

15.8 

15.2 

15.4 

15.6 

15.0 

14.9 

15.0 

14.6 

14.5 

14.6 

14.4

13.9 

14.2 

13.8 

12.8 

13.2 

13.4 

13.3 

13.3 

13.2 

13.1 

13.1 

13.1 

13.1 

13.3 

13.2 

13.2 

13.0 

12.8 

14.0 

12.3 

12.0 

12.2 

12.1 

12.0 

11.5 

11.4
RESULTS 15

TABLE 4.—Daily averaged values of meteorologic and temperature data for San Diego Aqueduct (July 25, 1973-July 23, 1974)—Continued

Day 

of 

month

Windspeed

(m/s)

COT1 SKN2

Wind 

azimuth3 

(degree)

COT SKN

Solar Atmospheric 

radiation radiation

(W/m2 ) (W/m2 )

COT SKN COT SKN

Air 

temperature (°C)

COT SKN

Vapor 

pressure 

(kPa)

COT SKN

Water 

temperature (°C)

COT SKN

January 1974

i. _ _ __

2— _______

3_ __

4_____

5- _ ___ __

6______ __

7 ___ ...

8______ ___

9 __ .

10 — ..

11 — ... _

12 . .

13 — ._

14 _______

15 _ _

16 _______

17 ________

18 __ _

19 ________

20 ________

21 ___ __

22 __ _

23 ___ __

24 ______ _

25 _______

26 __ _

27 _________

28 ________

29 ________

30 _____

31 ____

________________3.72

________________!. 04

_______ _ _ ___ 2.44

— — ..___.____1.63

________________ .84

________________!. 13

_._—— — — .1.66

________________ .82

________________!. 18

_____ _ ____ _ 1.01

________________ .82

_ — _— — — -1.59

_____ ___ __ _ .74

97

___________ _ -1.48

_ _ _ _ ___ ___ 2.64

________________1.24

_ _ _ ___ ___ 2.60

________________2.08

_.______._.——— 1.69

_._____-_ —— —1.22

________________ .92

________________ .56

_____ _ ___ __ .72

_ ____ _ _____ .94

3.02 226 

1 

13 

233 

217 

188 

10 

239 

88 

219 

11 

21 

3 

9 

25 

223

211 

212 

223 

3 

5 

16 

214 

224 

192 

21 

10 

247 

208

242

______

______

128 

140

18 

95 

18 

15 

51

145 

111 

107 

140 

155 

146 

124

143 

23 

137 

170 

143 

162 

152 

20 

163 

164 

148 

150 

154

274

______ 316

00/1

______ 368

______ 417

______ 364

OQQ

164 304 

157 301 

36 280 

167 303 

164 309 

137 310 

139 308 

164 326

321

359 

355 

336 

336 

353 

356 

352 

367

7.2 

4.0

4.7 

5.7 

7.0 

7.3 

7.6

8.0 

7.6 

11.1 

11.8 

12.8 

13.5 

13.0

11.6 

10.8 

10.5 

8.4 

9.3 

12.5 

8.8 

6.9 

6.9 

8.0 

9.5 

8.5 

9.1

8.0

12.0 

10.6 

8.0 

8.9 

10.4 

11.3 

9.8 

10.3

0.53

.64 

.76 

.89 

.94 

.92

.88 

.73 

.84 

.96

1.01

1.19 

1.20 

.98 

.45

.83

0.85

______

11.5 

11.2

10.1 

10.5 

10.7 

10.7 

10.8

11.1 

11.1 

10.9 

11.1 

11.1 

11.1 

11.2

11.8 

11.7 

11.8 

11.9 

10.4 

10.2 

10.3 

10.6 

10.7 

10.4 

10.4 

10.7 

10.8

10.3 

10.2 

10.1 

10.0 

10.5 

10.3 

10.5 

10.8

February 1974

1 _ _

2______ _

3_ __

4______

5______ _

6_ _ _

7_____ ____.

8_______

9__________

10 _ _ __

11 ____ _

12 _________

13 __ _

14

15 ____ _ _

16 ________

17 __ _

18 ________

19 ________

20 _-_____.

21 _ _

22 ________

23 _____ __.

24 __

25 ____ _

26 __

27 _____

28 _____ __

_______ _ __ __ 1.04

___ —————. _1.43

. _ _ _ _ ___ _ 1.87

________ ___ -1.09

_ — _ — _—.. ..1. 52

___________ _ _ 1.61

________________ .83

________________4.09

_——— — — ___.!. 12

________________ .80

________________ .84

_____ __ _ __ _2.30

_ ____ _____ _ 1.98

_ — _ — ——— .-. 1.01

________________ .68

_ __ __ ...—1.76

_________ _ __ 2.36

________________1.05

. ___ __ ___ _1.57

___________ _ _1.70

.____._____ — _.1.07

________________ .69

------ --_- 2.37

_.__ —— _ — ——— 1.89

_ ___ ___ _-____1.41

——— — ————1.54

_ 1.11

______

______

194 

24 

30 

228 

19 

23 

49 

32 

189 

211 

193 

215 

213 

46 

268 

209 

230 

216 

235 

82 

25 

208 

42 

72 

22 

209 

200

______

______

______

69 

178 

178 

179 

181 

185 

186 

191 

163 

191 

147 

183 

166 

192 

184 

186 

132 

195 

90 

209 

196 

203 

213 

220 

223 

217 

223 

37

68 ______

182 ______

180 ______

1 QQ

161 ______

149 ______ 

190

197

191

185 ______ 

194

169

202

76 ______

209

211 ______

229 ______ 

230 ______

OOP;

79

341 

340 

351 

358 

350 

332 

336 

335 

347 

353 

348 

357 

342 

343 

363 

356 

352 

351 

331 

353 

361 

365 

368 

380 

393 

385 

371 

364

6.7 

8.1 

10.4 

11.1 

9.5 

7.3 

7.5 

10.4 

9.1 

10.0 

9.6 

9.8 

8.7 

8.4 

11.5 

10.1 

9.2 

8.4 

6.5 

9.2 

8.5 

91 

10.4 

11.2 

11.6 

12.0 

107

7.8 

10.6 

13.5 

13.9 

12.0 

9.8 

10.0 

11.0 

12.0 

12.8 

11.5 

12.2 

9.7 

9.5 

12.8 

11.9 

10.6 

10.6 

8.2 

10.7 

11.9 

11.7 

13.3 

14.3 

15.5 

14.0 

12.4 

11.8

______

0.61

______

______

______

10.8

______

11.5 

11.8 

11.2 

11.2 

11.6

10.7 

10.9

10.6

______

11.4 

11.5 

11.7 

11.2 

11.5 

11.7

March 1974

i_ ____

2 ______

3________ _

4 _

5 ____

6____ _

7__________.

8_ __ _

9_ ___

10 _._. ___.

11 ___

12 ________

13 ______ __

14 _______ .

15 ________

16 ___

17 _________

18 __ 

19 _____ __

20 ___

21 _________

22 ___

23 ______ _

24 __ _____

25 _ __

26 ______ _.

27 .__

28

29 _________

30 ______ _

31 _

__ _____________2.08

_ _______ _____ 1.27

_ -__ _ __ _ 2.84

._______— ______1.07

________ ______ .78

________________ .95

__ _____ __ _ _ 1.05

_ __ _ ____ _ __ .75

______ _ _ .73

_ ____ ____ __ .82

——— —————1.10

_______________ .90

—— —— — ——— 1.47

..—— —______!. 16

____________ _ .1.57

___ ______ __ 1.22

____________ —.1.08

.. _ — _________!. 88

__ _ __ ____ 2.06

—— ———————1.09

—— ——— — _.-_!. 03

_____________ _1.47

_________ 2.32

1.29 

2.01 

2.32 

.94 

.69 

] 06 

.77 

1 16 

.92 

1.13 

.72 

1.12 

.97 

1.14 

.81 

1.03 

1.06 

.83 

1.23 

.94 

1.37 

1.50 

.91 

1.18 

133 

1.24

______

207""" 

193 

201 

13 

22 

39 

23 

42 

35 

29 

86 

39 

218 

210 

215 

44 

230 

215 

79 

211 

222 

226 

39 

2 

35 

236

______

~~~224

210 

181 

46

81 

36 

244 

59 

185 

225 

236 

210 

231 

215 

188 

204 

218 

212 

265 

56 

222 

193

_____

23 2^ 

53 

58 

159 

196 

235 

231 

231 

244 

228 

214 

197 

148 

122 

37 

183 

102 

66 

202 

151 

153 

200 

217 

241 

163 

264

114 __________ 

142

007

82 ______

58 241 

160 255 

______ 239 

_____ 239

______ 253 

---_ 259 

244 256 

235 258 

218 258 

198 249 

203 268 

127 272 

72 250 

214 285

_____ 266 

239 267 

154 274 

181 265 

146 280 

194 268 

267 289 

148 263 

228 271

398 

362 

345 

352

346 

333 

344

390 

392 

394 

390 

378 

370 

367 

379 

373 

368

9.1 

8.6 

6.6 

6.8 

8.4 

10.8 

12.5 

14.1 

163 

16.3 

16.6 

16.5 

12.6 

11.2 

11.3 

130 

11.6 

10.6 

12.3 

11.9 

13.0 

13.2 

12.2 

149 

11.8 

12.4

15.9 

11.3 

8.2 

9.9 

11.0 

10.2 

9.5 

7.3 

7.7

______

" 17.1 

17.5 

18.2 

17.2 

13.2 

11.7 

12.2 

13.6

~~12.6 

12.2 

13.3 

13.2 

12.9 

15.7 

13.3

______

0.71 

.94 

.85 

.80 

.85 

.85 

.93 

1.08 

.97 

1.08 

1.10

______

1.06 ~ 

1.07 

1.15 

1.11 

1.04 

1.20 

1.10

______

0.99

______

1.15 

1.27

""1.22 

1.22 

1.14

______

______

12.4 

12.6 

12.6 

12.6 

13.2 

13.6 

13.9 

14.2 

14.5 

14.7 

15.0 

15.2 

15.0 

14.9 

14.9 

15.1

15.5 

16.0 

16.0 

16.1 

16.5 

16.7

12.8 

12.3 

12.1 

12.0 

11.7 

12.0 

12.2 

12.1 

12.5

14.1 

14.4 

14.7 

14.8 

15.0 

15.0 

14.8 

15.1

______

______
16 METEOROLOGY, HYDRAULICS, AND THERMAL REGIME, SAN DIEGO AQUEDUCT, CALIFORNIA

TABLE 4.

Day 

of 

month

1_ _ __

2 __ ____

3 ____

4__ _ _

5_ __ ___

6 __ __

7_ __ __

8________

9__ _ __

10 ____ _

11

12 __ ___

13 ______

14 ___ _

15 ______

16 ____ _

17 __ __

18 ______

19 ______

20 ______

21 ______

22 _ ____

23 ______

24 _ ___

25 ______

26 ______

27 ___

28 ______

29 ______

30 __

— Daily averaged values of meteorologic and temperature data for San Diego Aqueduct (July 25, 1973-July 23, 1974) — Continued

Windspeed

(m/s)

COT1

__________________3.83

1 OQ

-_____ — — ____.2.15

_ — .____ — -____1.23

_ ___ ____ ___ __1.32

__________________2.04

__________________2.75

1 OQ

__________________2.18

1 98

— __. — ._____— 1.84

- — ___— --____1.40

___ 1.49

___._ — _______— 1.70

__________________!. 50

SKN1.78 

2.34 

1.16 

2.15 

1.28 

1.41 

1.16 

1.15 

3.35 

1.71 

1.50 

1.19 

1.16 

1.01 

1.09 

1.05 

1.19 

1.87 

1.28 

.99 

1.49 

1.02 

1.63 

1.39 

1.53 

1.12 

1.07 

1.15 

1.69 

1.28

Wind 

azimuth3 

(degreel

COT

225 

218 

218 

46 

36 

235 

227 

221 

227 

267 

62 

204 

17 

2 

64 

196 

207 

226 

212 

228 

28 

225 

217 

85 

213 

232 

221 

217 

42 

36

SKN

205 

209 

242 

64 

254 

184 

255 

237 

247 

217 

53 

215 

195 

64 

207 

208 

204 

211 

208 

198 

56 

233 

194 

219 

197 

181 

216 

214 

44 

239

Solar 

radiation 

(W/m2 )

COT

139 

234 

287 

293 

297 

295 

291 

296 

258 

301 

302 

302 

301 

308 

310 

312 

318 

161 

249 

239 

309 

284 

304 

283 

312 

327 

308 

312 

326 

328

SKN

April

147 

233 

294 

300 

303 

295 

297 

299 

274 

305 

306 

307 

298 

308 

314 

317 

319 

232 

251 

232 

316 

291 

277 

111 

324 

323 

319 

317 

327 

328

May

Atmospheric 

radiation

(W/m2 )

COT

1974

237 

248 

276 

244 

251 

251 

273 

247 

248 

241 

251 

261 

265 

259 

255 

251 

249 

277 

288 

264 

276 

252 

248

______

1974

SKN

______

244 

251 

262 

266 

269 

276

Air 

temperature (°Ci

COT

10.7 

12.8 

12.2 

13.3 

15.8 

14.3 

16.6 

16.7 

11.0 

10.1 

13.0 

14.4 

16.0

11.3 

11.5 

14.2 

15.0

17.7 

19.4

SKN

13.4 

12.5 

16.1 

18.1 

16.2 

18.4 

17.4 

12.0 

11.4 

14.3 

15.9 

17.4 

._ 18.9

_ 14.9

._ 18.1

._ 12.8

12.2 

12.7 

15.0 

16.5 

19.5 

21.2

Vapor 

pressure 

(kPa)

COT

1.11 

.91

.93

.84

1.01

______

.97

.95

.72

------

SKN

0.91

.96 

.79 

.76

— —

.80 

.88 

1.06 

1.10 

1.16 

1.14 

.94 

1.06 

.94 

.77 

.88 

.94 

1.03 

.98 

1.11

Water 

temperature (°C)

COT

16.3 

16.4 

16.6 

16.0 

16.5 

16.8 

17.2 

17.4 

17.6 

17.3 

16.1 

16.8 

17.6 

17.3 

17.2 

17.5 

18.0 

18.2 

18.2 

17.3 

17.8 

18.3 

18.6 

18.7 

18.5 

18.5 

18.5 

18.7 

19.0 

19.2

SKN

18.0 

17.4 

17.9 

18.2 

18.5 

18.7 

18.5 

18.5 

18.7 

18.6 

19.2 

19.5

1 __ _ __ _ ....

2 ___ __

3

4

5__ ____ ___ ______ ______

6 ___ _

7

______ ______ ______

8_____ __ ____ ________

9________

10 ______

11 _ ___

12 ____ _

13

14 ______

15 _ _ _

16 ____ _

17 __

18 __ __

19 __ 

20 ____

21 __ _

22

23 _ ___

24 ___ _

25 ...

26 _____

27 __

28 _ __ _

29 ____ _

30 _

31 ____ _

1 __ ___

2____

3______

4 ... 

5

6__._ __

7__

8 _ __

9____ ___

10 ______

11 ______ 

12 _ __

13 _____ 

14

15 _ _

16 __. _

17 ______

18 ______

19 ___

20 ______

21

22 __ _ _ 

23 ___ _

24 __

25 

26 _ _.

27 ______

28 __ 

29 ___ _ 

30 ___ _

___________ _______!. 75

____ __ ____ ..1.72

___ _______ _ _ _3.15

__ ___ ____ __ 2.84

___ ___ _ _ ___ _2.79

__________________3.53

__________________3.06

____ __ ____ _ _2.54

___ ___ ____ ___1.39

— ___-. — -_____.1.07

___ __ ____ ___ 2.47

__________________1.31

_ _ ___ ____ __ 2.21

______-___________3.49

__________________5.17

__________________3.01

_ ___ ____ ___ 2.50

______.___________1.94

_ ___ _ _____ _ 2.58

_ ___ ___ ____ _3.69

__ __ ____ _ ___4.85

_______ ______ 4.08

________ _______.3.16

_____________ __2.11

____ __ _____ _2.04 

.______— _______.3.08

___ ___ ____ ___ 3.16

_______ __-__-__-__3. 97

____ ___ ___ _ 3.63

_________ ____3.96

__________________3.08

_ ___ _____ ___ __1.89

__ _.. _ _____ 3.50

.__ __ -.._ ___ __3.20

________________ _2.37

__________________!. 91

_ ___ __ _____ 3.09

_____ _ ____ __3.64

_________________ _4.18

1.38 

1.24 

1.37 

1.30 

1.46 

1.48 

1.53 

1.73 

1.54 

1.63 

2.18 

1.17 

1.37 

1.20 

1.35 

.93 

1.45 

.96 

1.14 

1.38 

1.34 

1.42 

1.30

1.34 

1.06 

1.02 

1.21 

1.28 

1.37 

1.51 

1.42 

1.51 

1.05 

1.11 

1.05 

1.04 

.91 

1.02 

1.43 

1.19 

1.42 

1.13 

1.10 

.96 

1.13 

.98 

1.11 

1.24 

.92 

1.13 

1.16 

1 29 

1.30

234 

225 

216 

213 

217 

226 

229 

219 

222 

218 

255 

66 

261 

229 

236 

48 

37 

239 

215 

225 

218 

220 

227

232 

220 

235 

206 

211 

212 

219 

213 

239 

231 

51 

85 

89 

57 

53 

210 

201 

215 

61 

208 

207 

60 

56 

59 

59 

57 

248 

205 

208 

217

212 

206 

237 

203 

213 

229 

225 

221 

218 

208 

194 

235 

230 

189 

201 

236 

81 

197 

198 

227 

212 

219 

224

222 

206 

225 

211 

227 

204 

233 

230 

238 

200 

200 

207 

199 

234 

210 

212 

216 

213 

217 

214 

203 

215 

216 

259 

234 

202 

208 

199 

205 

218

142 

224 

301 

216 

238 

164 

85 

275 

278 

271 

299 

352 

333 

328 

338 

333 

338 

331 

332 

326 

280 

307 

232

266

280 

251 

290 

315 

313 

74 

341 

345 

333 

310 

312 

323 

349 

346 

351 

351 

350 

343 

353 

354 

340 

333 

337 

332 

334 

333 

346 

348 

349

150 

257 

323 

220 

273 

213 

97 

261 

283 

241 

213 

350 

334 

339 

331 

336 

334 

337 

337 

334 

291 

312 

291

June

309 

313 

243 

299 

317 

301 

71 

343 

348 

335 

324 

334 

326 

340 

341 

353 

355 

357 

357 

359 

360 

355 

343 

343 

346 

338 

342 

356 

360 

362

-----

— —

______

1974

383 

394 

356 

318 

330 

340 

409 

327 

295 

317 

300 

298 

304 

298 

309 

310 

315 

325 

317 

318 

328 

325 

302 

297 

294

303 

299 

305 

306 

306 

307 

303 

310 

314 

302 

296 

333 

356 

367 

345 

365 

396 

404 

383

______

______

______

______

15.8 

16.4 

17.9 

15.2 

15.7 

14.2 

13.9 

14.4 

14.0 

12.9 

11.6 

14.8 

18.9 

19.3 

16.9 

20.0 

25.3 

26.3 

22.6 

17.6 

16.4 

16.5 

15.9

18.1 

17.4 

17.2 

18.9 

19.7 

18.6 

15.4 

20.1 

21.0 

21.7 

21.5 

22.0 

22.9 

24.1 

26.5 

23.1 

20.2 

19.1 

19.9 

22.4 

23.5 

24.8 

26.9 

28.6 

27.9 

28.5 

28.8 

28.0 

24.3 

22.0

15.2 

16.1 

18.2 

16.0 

16.0 

14.9 

15.3 

15.7 

15.4 

14.2 

12.8 

17.2 

20.7 

20.6 

16.9 

19.7 

26.7 

26.9 

23.0 

18.5 

16.7 

16.2 

16.2

18.2 

18.6 

16.8 

17.9 

19.6 

18.8 

15.3 

19.2 

20.8 

20.0 

20.0 

21.1 

20.6 

24.1 

27.7 

24.7 

22.0 

20.2 

20.0 

22.7 

24.0 

26.8 

29.2 

30.1 

30.4 

29.2 

29.2 

29.8 

25.1 

21.3

______

0.81 

.73

______

L22~~ 

1.25

1.28 

1.30

1.43" 

1.37 

1.40 

1.28 

1.24 

1.34

1.32 

1.17 

1.00 

.94 

.90 

1.00

— —

1.26 ~~

1.42 

1.38 

1.54 

1.47 

1.36 

1.23 

1.34 

1.27 

1.19 

1.07 

.93

.99

1.36 

1.65 

1.49 

1.41 

1.32 

1.24 

1.28

1.35 

1.52 

1.46 

1.53 

1.58 

1.66 

1.50 

1.48

1.73 

1.61

~~1.31 

1.13 

1.04

______

20.8 

20.9 

21.1 

21.4 

21.4 

21.2 

21.1 

21.4 

21.3 

20.9 

20.4 

19.7 

20.0 

20.8 

21.5 

21.6 

21.7 

22.5 

23.0 

23.2 

22.7 

22.3 

22.4

22.5 

22.8 

22.9 

23.2 

23.2 

23.3 

23.4 

23.6 

22.7 

22.8 

23.5 

24.0 

24.2 

24.4 

24.5 

24.5 

24.6 

24.6 

24.4 

24.4 

24.4 

24.8 

25.0 

25.1 

25.5 

25.3 

25.4 

25.5 

25.5 

25.3

20.6 

20.9 

21.3 

21.1 

21.3 

20.7 

20.4 

21.0 

20.7 

20.5 

19.7 

20.0 

20.0 

20.7 

21.3 

21.9 

22.0 

22.6 

22.9 

23.2 

22.7 

22.3 

22.1

22.5 

22.8 

22.6 

23.2 

23.2 

23.2 

22.5 

23.6 

23.3 

22.8 

23.5 

24.1 

24.2 

24.5 

24.7 

24.4 

24.3 

24.3 

24.3 

24.4 

24.4 

24.8 

25.1 

25.3 

25.5 

25.5 

25.4 

25.5 

25.3 

25.1
RESULTS 17 

TABLE 4. — Daily averaged values of meteorologic and temperature data for San Diego Aqueduct (July 25, 1973-July 23, 1974) — Continued

Dav 

of 

month

Windspeed

(m/s)

COT1 SKN2

Wind 

azimuth3 

(degree)

COT SKN

Solar 

radiation

(W/m2 )

COT SKN

Atmospheric 

radiation

(W/m2 )

COT SKN

Air 

temperature (°C>

COT SKN

Vapor 

pressure 

(kPa)

COT SKN

Water 

temperature <°C)

COT SKN

July 1974

i __ _ _ _

2____________

3____________.

4 _ _ _ _ ___

5______ __ __

6___ _____

7____ _ ___.

8

9___ __ ____.

10 ______ ____

11 _ ________

12 _____

13 __________

14 ____ _____

15 ___________

16 __ _ ____.

17 _____ ____.

18 ___________

19 ______

20 ____ ______

21 __

22 _ _____ _

23 ________

______________3.49

______________!. 75

______________3.14

______________4.12

4 25

______________4.43

__-__________3.76

4 00

______________2.30

— — ________2.50

9 3^

9 73

— — _-_____2.21

— — _— ____3.12

______________3.24

______________3.20

_________ _ _ 2.13

1.41 

1.51 

1.13 

1.07 

1.22 

1.44 

1.52 

1.59 

1.36 

1.67 

1.25 

1.21 

.95 

1.12 

1.07 

1.31 

1.14 

1.84 

1.52 

1.38 

1.20 

1.35

215 

217 

212 

60 

216 

222 

213 

216 

226 

231 

226 

248 

247 

73 

39 

266 

71 

223 

200 

67 

229 

218 

202

207 

227 

218 

222 

192 

214 

205 

209 

219 

215 

218 

222 

214 

32 

184 

194 

204 

237 

216 

199 

206 

223

330 

316 

346 

331 

341 

361 

349 

338 

343 

306 

330 

332 

272 

135 

286 

320 

321 

331 

209 

318 

319 

274 

216

317 

337 

354 

341 

346 

361 

345 

344 

343 

302 

344 

346 

235 

114 

269 

333 

342 

343 

225 

328 

322 

330

Q9C

391

OCC

315 ______

9QQ

276 ______

QQfl

QQQ

Ofll

360 ______ 

363 ______

QQ 1

306 

346

332 ______ 

307 

Q-i Q — —

334

one

01 n

306 ______

19.6 

19.6 

22.3 

25.4 

25.8 

22.6 

20.1 

19.3 

20.4 

18.8 

20.8 

22.8 

25.3 

26.4 

26.0 

26.4 

26.8 

26.7 

26.5 

26.9 

25.2 

24.8 

26.0

18.7 

19.4 

22.5 

26.3 

25.9 

23.1 

20.6 

19.8 

20.3 

19.1 

20.6 

22.6 

24.5 

25.6 

24.9 

26.8 

27.4 

27.3 

27.1 

27.3 

25.2 

24.9

1.10 - — _

1 9Q

1.34 1.47 

1.75 1.61 

______ 1.43 

______ 1.43

_ _ _ 1.71

______ 1.44

______ 1.69

____ 1.19

1.94

24.8 

24.8 

24.7 

24.9 

25.2 

25.2 

24.8 

24.4 

24.5 

24.9 

24.7 

24.5 

24.9 

25.2 

25.1 

25.5 

25.8 

25.9 

26.0 

25.8 

25.7 

26.3 

26.1

24.7 

24.6 

24.6 

24.8 

25.1 

25.1 

24.8 

24.2 

24.3 

24.5 

24.8 

24.6 

24.6 

24.9 

25.2 

25.5 

25.8 

25.8 

25.9 

26.0 

25.6. 

25.9

'Cottonwood (upstream) end of canal. 

2Skinner (downstream) end of canal. 

''Direction from which the resultant wind comes measured clockwise from north.

and temperature data. Averages are included in table 4 

only if sufficient data were present to adequately define 

the daily mean. The windspeed, solar radiation (shortwave), atmospheric radiation (longwave), and air temperatures represent averages of individual measurements. The wind azimuth represents the azimuth of 

the resultant wind vector for the day, and the water 

temperature represents the average obtained at all 

levels of measurement. A wind azimuth of zero represents a wind blowing from north to south. The vapor 

pressure was computed from the wet- and dry-bulb air 

temperatures for each 10-minute period and the results 

averaged. The conversion from wet- and dry-bulb temperatures to vapor pressures involved a two-step process. First the saturation vapor pressure of air at the 

wet-bulb temperature was computed using the formula

es = exp [ 52.418 - 6788.6/(273.16 + TW)

- 5.0016 In (273.16 + TW)] (3)

in which es is saturation vapor pressure in kilopascals, 

and TW is wet-bulb temperature in degrees Celsius.

The vapor pressure was then computed from

ea = es - 96.0(0.00066) (TA -

TW) (I + 0.00115 TW). . . (4)

in which ea is vapor pressure of the air in kilopascals, 

TA is dry-bulb temperature in degrees Celsius, the atmospheric pressure is assumed to be 96.0 kilopascals, 

and 0.00066 is the psychrometric constant.

Table 5 contains daily averages of all hydraulic data 

as well as daily rainfall values. The diversion discharge at EM-8 is not listed, because the mean daily 

value was always less than 0.1 m3/s. The diversion 

discharge at the So. End diversion was not measured 

but can be determined by continuity considerations, 

however. This diversion was zero prior to May 15, 

1974.

The rain gages were serviced at approximately 0900 

hours. The observed rainfall was assigned to the day 

preceding the date of observation. In some cases, the 

record had the word "trace" written in the rainfall 

column. In this case, the rainfall was recorded as 0.25 

mm.

TABLE 5.—Daily averaged values of hydraulic and rainfall data for San Diego Aqueduct 

(July 25, 1973-July 23, 1974)

Day Stage (cm)

of Cottonwood Simpson Newport South 

month gage end

Discharge (nvVs) Rainfall 1 (mm)

Skinner Cottonwood Simpson Skinner Cottonwood Skinner 

inlet inlet wood

July 1973

25 

26 

27 

28 

29 

30 

31

__ _ _ 241 __________

___________ 240

____________ 239 __________

__ _ __ 239 __ _ _____

_ __________ 238 _______

_ _ ___ _ 236 110

193 

192 

191 

191 

191 

191 

191

190 

189 

189 

190 

190 

190 

191

170 

170 

170 

170

13.9 

13.7 

13.7 

13.7 

13.7 

13.6 

13.4

0.0

.0 _ _______

.0 __ __ _ _ 

.0 _ _ ____

.0 __________

.0 __________

.0 __ __ __

0.0 

.0 

.0 

.0 

.0 

.0 

.0

0.0 

.0 

.0 

.0 

.0 

.0 

.0

See footnote at end of table.
18 METEOROLOGY, HYDRAULICS, AND THERMAL REGIME, SAN DIEGO AQUEDUCT, CALIFORNIA

TABLE 5.—Daily averaged values of hydraulic and rainfall data for San Diego Aqueduct

(July 25, 1973-July23, 1974)— Continued

Day

of Cottonwood 

month

Stage (cm)

Simpson Newport 

gage

Discharge (mj/s) Rainfall 1 (mm)

South Skinner Cottonwood Simpson Skinner Cottonwood Skinner 

end inlet inlet wood

August 1973

i

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31

____________ 229

____________ 229

____________ 229

____________ 230

____________ 232

____________ 232

____________ 232

_____________ 232

____________ 233

____________ 233

__________ 232

90 o

____________ 232

____________ 231

____ __ 231

____________ 232

____ _ _ _ 233

OQQ

____________ 233

____________ 233

____________ 233

____________ 233

____________ 233

____________ 233

208 

205 

205 

206 

206 

205 

207 

207 

208 

208 

208 

208 

208 

208 

208 

208 

207 

207 

206 

206 

206 

206 

206 

208 

207 

207 

207 

207 

207 

207 

208

187 

183 

183 

183 

183 

183 

184 

184 

185 

185 

185 

185 

184 

184 

184 

184 

184 

184 

183 

183 

183 

183 

183 

185 

184 

184 

184 

184 

184 

184 

185

188 

184 

185 

186 

186 

186 

187 

187 

188 

188 

188 

188 

187 

187 

187 

187 

186 

187 

187 

186 

186 

186 

186 

188 

188 

187 

187 

187 

188 

188 

210

168 

164 

164 

164 

164 

164 

165 

165 

166 

166 

166 

166 

166 

166 

166 

166 

166 

166 

165 

165 

165 

166 

166 

167 

167 

167 

166 

166 

166 

167 

198

12.9 

12.6 

12.6 

12.6 

12.6 

12.6 

12.6 

12.8 

12.9 

12.9 

12.9 

12.9 

12.9 

13.0 

13.0 

13.0 

12.9 

12.9 

12.9 

12.8 

12.7 

12.8 

12.9 

13.0 

13.0 

13.0 

13.0 

13.0 

13.0 

13.0 

13.0

.0 __________

.0 __________

.0 ________ __

.0 __________

.0 _____ __

.0 _ _- -___-

0.0 

.0 

.0 

.3 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.3 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.5 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0

September 1973

l 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30

____________ 233

____________ 233

____________ 233 

233

__ _____ _ 232

____________ 232

__ _ ______ 232

____________ 232

_____ _ _ 232

____________ 228

_ _ ___ 227

__ __ _ _ 225

____________ 223 

_____ _ _ 224

_____'_______ 225

____________ 226

___ _ _ __ 226

____________ 226

_ _ _ ___225

____________ 225

____________ 225

____________ 224 

____________ 223

_____ ____ 230 

____________ 232

_____ __ 232

208

__________

205 

204 

204 

204 

204 

204 

200 

199 

197 

195 

196 

198

197 

198 

200 

204 

207 

206

185 

185 

186 

186

183 

183 

183 

183 

183 

184 

181 

179 

176 

175 

175 

176 

176 

176 

176 

176 

176 

176 

175 

174 

176 

180 

182 

182

243 

242 

242 

242

273 

281 

291

182 

178 

179 

180 

180 

180 

180 

179 

180 

180 

179 

179 

180 

183 

185 

184

241 

240 

239 

239

178 

235 

234 

234 

237 

259

164 

158 

158 

159 

160 

160 

160 

160 

160 

160 

159 

159 

160 

163 

165 

165

13.0 

13.0 

13.0 

13.0

13.0 

13.0 

13.0 

13.0 

13.0 

12.7 

12.3 

12.2 

120 

118 

11.9 

11.8 

11.8 

11.8 

11.8 

11.8 

11.8 

11.8 

11.8 

11.8 

12.0 

12.4 

12.7 

12.7

.0 __ ___ -_

.0 __________

.0 _-__-- --

.0 __________

.0 __________

.0 _____ -- 

.0 -------- 

.0 _ - ___ -

.0 __________ 

.0 _ _ ___ _

.0 __________ 

.0 ___ _ _

.0 ____ _-- 

.0 -__ ___ __

.0 __ - _____ 

.0 __ _ _ _ _

.0 __________ 

.0 _ ___ _ _

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0

October 1973

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31

___ 231

____ _____ 231

____________ 228

____________ 218 

____________ 209

____________ 203

__ __ _ _ _ 201

-__ _____ 197 

___ __ _ 205

___ ___ ___ 210 

___ _ _ _ 208

__ _ 208

__ _____ _ 207

_____ ____ 205 

_____ _ 220

______ ___ 237 

----- -- 237

___ ______ 237

- — -_-_. .236

236 

____________ 237

___ ____ -237

— — ______ 237

_____ _-- 237

____-_ — —237 

____________ 237

____________ 238 

______ _ ___ 238

206 

206 

206 

205 

201 

198 

190 

184 

183 

180 

186 

196 

197 

197 

198 

198 

213 

242 

245 

245 

244 

244 

244 

241 

235 

232 

232 

231 

231 

231 

231

181 

181 

182 

180 

176 

174 

166 

160 

159 

156 

161 

172 

173 

173 

174 

174 

188 

208 

208 

208 

208 

207 

208 

206 

201 

198 

198 

198 

198 

199 

199

184 

185 

185 

184 

182 

180 

175 

170 

169 

167 

169 

180 

181 

181 

182 

183

207 

207 

207 

206 

206 

205 

201 

198 

198 

198 

199 

199 

199

164 

165 

165 

164 

162 

160 

156 

151 

150 

149 

150 

158 

159 

159 

159 

159 

166 

181 

181 

181 

181 

181 

181 

180 

177 

175 

175 

175 

175 

175 

175

12.7 

127 

12.8 

12.7 

12.1 

11.6 

10.7 

10.0 

10.1 

9.9 

107 

11.2 

11.3 

11.3 

11.3 

11.3 

13 2 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6

0.0 __________ 

.0 __________ 

.0 __________

.0 _ _ __ _

.0 _ -- _ -- 

.0 --_ __ __

.0 __________ 

.0 -__--_---_ 

.0 - — _- —

.0 -___--____

.0 __________

.0 __________ 

.0 _ _ ______

.0 -_-- _ -__

.0 __________ 

.0 __- _ --__

.0 --------- 

.6 __________ 

1.1 __________

1.3 — — — -

1.3 

1.3 

1.3 _ — --_-

1.3 ____ __ __ 

1.3

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.8 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0
RESULTS 19

TABLE 5.—Daily averaged values of hydraulic and rainfall data for San Diego Aqueduct

(July 25, 1973-July 23, 1974)—Continued

Diiy

of Cottonwood Si 

month

mpson

Stage (cm)

Newport 

gage

DischEirge (nrVs) Rainfall 1 (mm)

South Skinner Cottonwood Simpson Skinner Cottonwood Skinner 

end inlet inlet wood

November 1973

i 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30

_ _ _ _ _ 239

____________ 239

____________ 239

_ ___ _ 239

. ______ 239

____________ 239 

____________ 240

____________ 240

_ _ __ 239

____________ 239

____________ 240 

_ _ _ _ 238

____________ 229

-_-______-_. 224

_____ _ 221

219

_____ ___ 212

__ __ _ ___ 204

___ _____ 186 

____________ 174

__ ______ 170

____________ 161 

____________ 153

____________ 154

___ _ _ ____ 154

____________ 155

_ _______ 155

232 

227 

224 

225 

224 

224 

224 

223 

222 

221 

221 

221 

219 

209 

203 

199 

200 

197 

188 

171 

157 

153 

144 

135 

135 

134 

135 

135 

135 

135

199 

200 

203 

204 

203 

203 

203 

202 

201 

200 

200 

199 

197 

187 

181 

177 

178

151 

135 

131 

125 

115 

115 

115 

115 

115 

115 

115

199 

200 

201 

202 

201 

201 

200 

200 

199 

198 

198 

197 

195 

188 

184 

180 

181 

181

"~~~~~H8 

144 

140 

131 

131 

131 

132 

132 

132 

132

175 

176 

178 

178 

178 

177 

177 

177 

176 

175 

175 

174 

173 

167 

163 

160 

160 

159 

154 

145 

134 

130 

127 

119 

119 

119 

119 

118 

119 

118

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.6 

15.7 

14.6 

13.9 

13.6 

13.3 

12.5 

11.6 

9.7 

8.5 

8.1 

7.3 

6.9 

6.9 

6.9 

6.9 

6.9 

6.9 

6.9

1.3 __ _ _ 

1.1 __________

.9 __________ 

.9 _ __ _ __

.9 _______ __

.9 ___ _ — 

.9 ___ — — — 

.9 _ __ _____

9

.9 _ ___ __

9

9

.9 _ ________

.9 __________

.9 _____

.9 _ ________

.4 _ __ __

.0 _ _______

.0 ___ — — __

.0 __________

.0 __________

.0 _ _____ _

.0 __________ 

.0 __________

.0 __________ 

.0 _ _ __

.0 __________ 

.0 __________

.0 __________

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

1.8 

19.8 

7.1 

.0 

.0 

.3 

12.7 

.0 

2.8 

.0 

.0 

.0 

.0 

.0 

1.3

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

1.3 

14.0 

4.1 

.0 

.0 

.0 

17.5 

.0 

.8 

1.0 

.0 

.0 

.0 

.0 

.0

December 1973

l 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31

_____ ___ 156

_ _______ 156

___ ______ 156

_ __ __ _ _ 155

_ _______ 155 __.

____________ 154 __

___ ___ _ 154 _.

___ _ _ ___ 175 __.

_ __ __ _ 212

______ __ 211

____________ 210

___ __ _ __ 210

_ _______ 209

____________ 209

_ _ _ _ 209

209

____________ 205

__ __ __ __ 197

______ _ 197

197

__ _ _ 194

____________ 282

__ _ _ 289

____________ 289

136 

137 

138 

138 

136 

133

169 

175 

169 

161 

158 

157 

157 

157 

158 

157 

162 

164 

165 

165 

165 

162 

193 

250 

260 

260 

259

115

117 

117 

114 

110 

110 

123 

156 

162 

154 

144 

140 

140 

139 

139 

139 

139 

144 

147 

147 

147 

147 

144 

178 

235 

245 

244 

244

132 

133 

133 

134 

134 

134 

135 

134 

134 

142 

172 

177 

172 

166 

162 

162 

162 

162 

162 

162 

165 

168 

169 

169 

169 

167 

184 

231 

238 

238 

238

119 

119 

119 

119 

119 

120 

120 

120 

119 

126 

152 

157 

153 

148 

145 

145 

145 

145 

145 

145 

148 

150 

150 

150 

150 

149 

166 

206 

212 

212 

212

6.9 

6.9 

6.9 

6.9 

6.9 

6.9 

6.9 

6.9 

6.9 

8.7 

11.7 

12.4 

11.9 

11.9 

11.9 

11.9 

11.9 

11.9 

11.9 

11.9 

11.3 

10.5 

10.5 

10.5 

10.5 

10.2 

14.9 

21.5 

22.7 

22.7 

22.7

.0 ___ ____

.0 __________ 

.0 _____ _ 

.0 __________

.0 __________

.0 _ _____ _ 

.0 __________

.0 _ ___ _

.0 __________ 

.0 __________

.0 __________

.7 _____ _

1.8 __ _ —

2.1 __________

2.1 __________

2.1

2.1 __________

2.1 ___ ____

2.1 __________

1.2 _ __ _ __

.0 -—______

.0 —_.______

.0 __________

.0 __________

.0 -—_ — ___

.0 __________

.0 _ __ — ____

.0 __________

.0 __________

.0 _ _ ______

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.5 

.0 

.0 

.0 

.0 

.0 

.5 

.0 

.0 

.0 

11.9

1.3 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

1.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.3 

.0 

.8

January 1974

l 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31

289

____________ 312 

_ __ _ 314

____________ 314

____________ 312

____________ 287

____________ 286

____________ 285 

____________ 286

______________268

___ __ _ __218

____________ 163 

_ _ 145

____________ 147

_ 132

____________ 122

____ ___ _ 122

____________ 122

_ ____ _ _ _ 122

______________122 

_ ______ 123

260 

266 

278 

287 

289 

289 

284 

256 

255 

255 

257 

242 

199 

166 

161 

161 

143 

124 

123 

123 

125 

114 

104 

105 

105 

105 

105 

105 

105 

105 

105

243 

248 

260 

270 

271 

270 

264 

234

__________

143 

143 

127 

108 

108 

108 

110 

100 

88 

87 

86 

86 

86 

86 

85 

85 

85

238 

240 

245 

250 

151 

251 

249 

230 

229 

232 

244 

256 

267 

273 

277 

280 

283 

281 

208 

279 

278 

277 

271 

265 

260 

253 

248 

243 

235 

224 

212

213 

215 

221 

226 

227 

227 

225 

208 

206 

211 _____

223 

242 

262 

277 

282 

284 

287 

286 

284 

283 

282 

281 

276 

271 

265 

258 

253 

247 

237 

229 

218

22.7 

23.6 

25.4 

26.6 

27.0 

27.0 

26.6 

22.3 

22.1

22.1 

22.2 

19.6 

13.0 

9.8 

9.1 

7.6 

6.5 

6.5 

6.5 

5.9 

4.9 

4.1 

3.7 

3.7 

3.7 

3.7 

3.7 

3.7 

3.7 

3.7

0.0 __________

.0 _ _ ______

.0 __________

.0 _ _ ______

.0 __________ 

.0 __________

.0 __________

.0 __________ 

.0 _ _ ___ __

.0 __________ 

.0 __________

.0 _ _________

.0 _____ -_

.0 __________

.0 __________ 

.0 ______ ____

.0 __________

.0 __________

.0 _ ___ _ _

.0 __ ______ 

.0 __________

.0 _______ ___ 

.0 __________

.0 ___ _ _

.0 __________

.0 __________ 

.0 __________

.0 _ .______—

.0 __________

0.8 

.0 

.0 

59.7 

2.5 

29.5 

66.0 

5.6 

1.5 

.0 

.0 

.0 

.0 

.0 

.0 

2.8 

.3 

.0 

.0 

4.3 

.0 

.0 

.0 

.0 

.3 

.0 

.0 

.0 

.0 

.0 

.0

0.8 

.0 

.5 

53.6 

1.8 

18.5 

67.3 

.5 

1.0 

.0 

.0 

.0 

.0 

.0 

.0 

1.0 

.0 

.0 

.0 

2.3 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0
20 METEOROLOGY, HYDRAULICS, AND THERMAL REGIME, SAN DIEGO AQUEDUCT, CALIFORNIA

TABLE 5.—Daily averaged values of hydraulic and rainfall data for San Diego Aqueduct

(July 25, 1973-July 23, 1974)—Continued

Day

of Cottonwood Simpson 

month

Stage (cm) Discharge (m3/s)

Newport South 

gage end

Skinner Cottonwood Simpson 

inlet

Rainfall 1 (mm)

Skinner Cottonwood Skinner 

inlet wood

February 1974

l 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28

______________ 89

____________ 0

_____ 0

____________ 0 _____

____________ 0 _____

______________ 0 _____

___ _ __ 0

____________ 0 _____

_____ __ _ 0 _ ___

_____ ______ 0

____________ 0 _____

____________ 0 _____

___ ______ 0 _____

___ _______ 0 ___ _

____________ 0 _____

____________ 0 _____

_________ __ 0 ____

____________ 0 _____

____________ 0 _____

__ _____ __ 0 ___

___ _____ _ 0 _____

____________ 0 _____

___ ________ 0 _

____________ 184

____________ 215 _____

__ _ _ ____ 196 _ __

105 

100 

52 

53

202 

223

84 

82 

6 

3

196

150 __.

200 

188 

172 

152 

130 

108 

84 

60 

30 

12 

14

200 

200

205 

193 

177 

158 

136 

114 

90 

66 

42 

19 

14

3.7 

3.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

4.6 

9.2 

12.6 

10.4

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0

__________

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.3 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

1.3.

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.3 

.0 

.0 

.0 

.3 

.0 

.0 

1.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

2.3

March 1974

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31

___ ___ ___ 202

__ ________ 215

___ _____ 213

_______ __ 250

___ _______ 292

____________ 294 

_ 297

____________ 295

__ ___ ____ 291

___ ___ 291

____________ 292

___ __ _ 294

__ ___ ____ 294

____________ 294

____________ 294

294

294

____________ 248

_ _____ 217

____________ 214 

__ ____ _ 214

____________ 214

____________ 214

_ ________ 155

____________ 125

__ ___ __ 192

____________ 164

____________ 166

____ _____ 279

____________ 279

___ ___ ___ 279

178 

191 

190 

220 

272 

274 

278 

275 

271 

271 

271 

275 

275 

275 

275 

274 

274 

232 

194 

191 

190 

190 

191 

144 

95 

167 

160 

135 

256 

256 

256

154 __

168 _ .

167 __.

197 __

253 __.

254 

257 

256 

251 

251 

251 

254 

254 

254 

254 

254 

253 

214 

170 

166 

166 

166 

166 

123 

74 

145 

138 

108 

236 

235 

235

237 

238 

238 

233 

233 

235 

236 

236 

236 

236 

236 

236 

215 

178 

175 

174 

184 

196 

189 

145 

250 

232 

152 

270 

242 

240

__________

12.4 

12.4 

12.4 

12.4 

7.3 

4.6 

10.0 

7.7

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0

10.7 

12.4 

12.5 

15.5 

23.3 

23.5 

24.1 

24.0 

23.0 

23.2 

23.2 

23.7 

23.5 

23.6 

23.5 

23.4 

23.5 

19.0 

12.9

5.5 

19.9 

20.3 

20.3

9.4 

9.9 

.0 

.0 

.0 

.0 

20.6 

21.6 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.3 

.0 

.0 

.0 

.0 

.3 

.3 

.5 

.0 

.0 

.0 

.0

7.1 

4.3 

4.1 

.0 

.0 

.3 

13.2 

14.2 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.8 

.8 

.5 

.0 

.0 

.3 

.0

April 1974

i

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30

___ ____ __ 279

____________ 292 

______ __ _ 307

_ __ _____ 308

_ ______ 308

____________ 308

_ _______ _ 309

____ _____ 315 

____________ 321

__ __ __ 321

_ _________ 288

____________ 256 

____________ 255

____ _ __ 255

____________ 255

____________ 248

_____ __ 248

___ ______ 254

____________ 254 

_ __________ 255

___ _ ___ 256

____________ 256

_____ _ _ 256

____________ 257

_ _ _______ 258

_______ 259 

_ _________ 261

__ ___ _ 261

_ __________ 260

____________ 259

256 

267 

286 

287 

286 

287 

287 

293 

301 

301 

267 

229 

229 

229 

229 

218 

207 

208 

209 

210 

210 

211 

211 

212 

213 

214 

215 

216 

216 

216

235

267 

267 

267 

267 

273 

282 

283 

251 

211 

210 

211 

211 

200 

190 

191 

191 

191 

191 

192 

192 

192 

193 

193 

195 

196 

196 

196

239 

243 

257 

255 

245 

245 

245 

251 

261 

270 

268 

275 

279 

282 

286 

287 

286 

285 

284 

285 

285 

286 

286 

285 

285 

284 

283 

282 

281 

280

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.6 

1.7 

2.2 

2.2 

2.2 

2.2 

2.2 

2.2 

2.2 

2.1 

2.1 

1.9 

1.9 

1.9 

1.9

20.3 

21.5 

24.5 

25.6 

26.0 

26.0 

25.7 

25.5 

25.5 

24.4 

19.8 

15.9 

15.9 

15.7 

15.5 

13.9 

12.7 

12.9 

12.9 

12.9 

12.9 

12.8 

12.7 

12.7 

12.7 

12.7 

12.8 

12.9 

13.0 

13.0

6.4 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0

4.8 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0
RESULTS

TABLE 5.—Daily averaged values of hydraulic and rainfall data for San Diego Aqueduct

(July 25, 1973-July 23, 1974)—Continued

21

Day Stage (cm) Discharge (m3/s) Rainfall' (mm)

of Cottonwood Simpson Newport South Skinner Cottonwood Simpson Skinner Cottonwood Skinner 

month gage end inlet inlet wood

May 1974

l 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31

____________ 247

___ ___ __ 246

____ ____247

__ _ ___ __ 247

__ __ __ __ 247

_ _ _ __ 248

____________ 247

____________ 247

____ ___ __ 247

____________ 245

___ __ __ 245

__ -__ ___ 248

___ _ _ 248

___ ... _ _ 247

____________ 247 

__ ... __ __ 247

____________ 247

----- ___ __ 248

_____ ______ 249

___ _ __ 256

_ __ ____ 257

__ __ __ 260

210 

210 

210 

211 

211 

212 

211 

211 

211 

209 

208 

207 

210 

210 

210 

212 

214 

213 

215 

216 

217 

217 

217 

220

190 

190 

191 

191 

192 

192 

192 

192 

191 

190 

189 

189 

192 

193 

193 

194 

195 

196 

197 

197 

195 

198 

199 

202

283 __________ ___

283 __________ ___

284 _ _ __ ___

287 ___ __ ___ ___

288 ______ __ _

286 __ ____ _ 

283

279 __ _ _._

278 _ _ ______

278 _

278 _ _

278 ______

278 _ _____

275 _ ____ _

273 ___ _____

270 __________ 

270 ___ __ _ _

269 _

14.8 

14.8 

14.6 

14.6 

14.5 

14.9 

14.9 

14.8 

14.8 

14.8 

14.8 

14.9 

15.1 

15.5 

15.9 

16.0 

16.5

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

1.8 

2.5 

2.2 

2.3 

2.3

12.2 

12.2 

12.4 

12.4 

12.4 

12.4 

12.3 

9.9 

7.1 

7.2 

7.2 

7.4 

7.6 

7.8 

7.7 

7.8 

7.8 

7.8 

7.9 

8.0 

7.9 

8.0 

8.5 

8.5

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0

0.0 

.0 

.0 

.0 

.0 

.3 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.3 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0

June 1974

l

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30

____________ 265

__ ___ _ 266

____________ 267

____________ 267

_____ _ 267

_____ ______ 267

____________ 266

____________ 267

_ ___ _ _ 266

__ __ ____ 265

____________ 264

___ 265

_____ ______ 265

___ _ __ 265

____________ 264

___________ 264

___ _ __ 267

_____ ___ __ 270

____________ 270

____________ 272

________ ___ 274

_ _._ _ ____ 274

_______ ___ 275

_______ ___ 276

____________ 279

____________ 283

__ _ ___ __ 285

_______ _ __ 285

_____ ___ _ 285

224 

225 

225 

230 

238 

237 

237 

237 

237 

237 

236 

236 

236 

236 

236 

236 

235 

237 

240 

240 

240 

239 

240 

239 

238 

239 

242 

243 

243 

243

206 

206 

205 

211 

218 

217 

217 

217 

217 

216 

215 

216 

215 

216 

216 

215 

214 

217 

220 

220 

219 

219 

220 

218 

217 

218 

221 

223 

222 

222

270 _ 

270 _____ _

270 _ _____ _

271 _ ____ 

271 _ __ _ __

271 __________

272

273 _________

273 __ __ _ __

272 -__ ______

273 __________

273 __________

272 _

272 __________

272 _ _ _____

273 ___ _ ____

273 _____ _ 

272 __________

272 ___ ____ _

271 -___

270 __________

17.0 

17.2 

17.3 

17.3 

17.4 

17.3 

17.2 

17.3 

17.2 

17.1 

17.0 

17.0 

17.0 

17.0 

17.0 

16.9 

16.9 

17.4 

17.7 

17.7 

18.0 

18.2 

18.2 

18.4 

18.5 

18.9 

19.5 

19.8 

19.7 

19.9

2.4 

2.4 

2.5 

1.8 

1.1 

1.1 

1.1 

1.1 

1.1 

1.1 

1.1 

1.1 

1.1 

1.1 

1.1 

1.1 

1.1 

1.1 

1.1 

1.1 

1.4 

1.7 

1.7 

2.0 

2.2 

2.2 

2.4 

2.4 

2.4 

2.4

8.9 

9.0 

9.1 

9.7 

10.7 

10.7 

10.6 

10.6 

10.7 

10.8 

10.8 

10.7 

10.6 

10.5 

10.5 

10.5 

10.5 

10.8 

11.2 

11.2 

11.1 

11.0 

11.2 

11.0 

10.4 

10.5 

10.9 

11.1 

11.1 

11.3

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0

July 1974

l 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23

_____ ______ 285

_ __________ 285

_ ___ _____ 285

____________ 285

____________ 288

___ ___ _ 289

___________ 288

_ _________ 288

_ __ _ _ _ 290

_._ ________ 290

____________ 290

__ _ _ 290 

____________ 290

____ _______ 290

_—_____— 290

__ _ __ _ 289

____________ 288

___. _______ 288

-__ 287

_ __ _ __ _ 287

____________ 288

___________ 287

-________- 288

243 

243 

243 

244 

246 

248 

247 

247 

250 

250 

250 

250 

249 

250 

249 

244 

240 

238 

236 

236 

236 

235 

235

222 

222 

222 

222 

224 

224 

224 

224 

227 

228 

228 

225 

224 

224 

225 

224 

223 

223 __ —

223 _____

223 _____

224 __

224 _ __

269 __________

268 __________

267 _

267 __________

266 __________

266 __ _____ 

266 __________

267 __________

268 __________

268 _ _ _

269 _

273 _ __ _____

19.8 

19.8 

19.8 

19.9 

20.2 

20.4 

20.3 

20.2 

20.6 

20.6 

20.6 

20.6 

20.5 

20.6 

20.5 

20.3 

20.2 

20.2 

20.1 

20.1 

20.2 

20.1 

20.2

2.4 

2.4 

2.7 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8 

2.8

11.3 

11.2 

11.0 

10.8 

11.1 

11.2 

11.3 

11.3 

11.5 

11.4 

11.4 

11.4 

11.4 

11.3 

11.4 

11.4 

11.4 

11.4 

11.3 

11.4 

11.5 

11.5 

11.7

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

2.5

0.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.0 

.3

'Rainfall represents the accumulated amount between 0900 hours of the indicated day to 0900 hours of the following day.
22 METEOROLOGY, HYDRAULICS, AND THERMAL REGIME, SAN DIEGO AQUEDUCT, CALIFORNIA

WIND

The average windspeed at Cottonwood during the 

12-month period was 1.70 m/s, whereas that at Skinner 

averaged 1.24 m/s. The lower value at Skinner undoubtedly reflects the sheltering effect of the hill north 

of the anemometer. The yearly mean values of the supplementary windspeeds were 1.54 m/s at Cottonwood 

and 0.90 m/s at Skinner. The monthly mean 

windspeeds at Cottonwood and Skinner are shown in 

figure 21. A rather pronounced seasonal variation is 

seen at Cottonwood, but none is evident at Skinner. 

The frequency of occurrence of various daily average 

windspeeds is shown in figure 22. The uniform nature 

of the Skinner windspeed and the absence of high 

winds in comparison to Cottonwood is apparent. The 

highest wind gust observed at Cottonwood was 18.5

I I I 

Cottonwood

Q

§'

O 

LU 

CO

LU 0

Q- ASONDJFMA

CO 

CC 

LU

IJ J

1973 1974

D_ 

CO 

Q

? 3

——I——I——I——I——I——I——I——I——I——T 

Skinner

ASONDJ FMAMJ J 

1973 1974

FIGURE 21.—Monthly mean windspeed. Insufficient 

data were available for November at Cottonwood and 

for January and February at Skinner.

m/s and occurred at 1640 hours on July 18, 1974. The 

highest gust observed at Skinner was 9.9 m/s and occurred at 1420 hours on January 1, 1974.

A pronoumced diurnal variation in windspeed was 

observed at both stations. In order to illustrate this 

diurnal effect, the yearly mean windspeed was computed for each 10-minute interval of the day. The 

results of this averaging process are shown in figure 

23. It can be seen that the windspeed is usually low at 

night and in the early morning hours (2200-0800) and 

usually fairly high in the late afternoon hours (1400- 

1800).

The daily-average windspeeds at Cottonwood and 

Skinner were poorly correlated. The correlation coefficient for the entire year was only 0.43. For the months 

of March and April the correlation coefficient was 0.80, 

but for the months of May through August it was 0.32, 

and for the months of September through December it 

was 0.46. The correlation between the daily-average 

primary and supplementary windspeeds was also poor. 

Considering the entire year, the correlation between

co 0.20

£ 0.15 

O

LU

CJ 0.10

Iuj 0.05

O

QC

LU 

O

LU 

QC

I—i Cottonwood

a —— h^

"- VJ.^O

o

O

O 0.20

LL 

O

> 0.15

LU

D 0.10

a

LU

QC

u_ 0.05

n

I I I

Skinner

—

_

—

~

l~

—

—

_

—

-r-i-^ I

012345 

DAILY AVERAGE WINDSPEED, IN 

METERS PER SECOND

FIGURE 22.—Frequency of occurrence of daily 

windspeeds.
RESULTS 23

the primary and supplementary windspeeds was 0.64 

at Cottonwood and 0.47 at Skinner. These low correlation coefficients highlight the difficulty in attempting 

to measure a representative windspeed for a reach of 

any open channel. Surface winds are extremely variable from point to point.

The wind direction was recorded continuously at 

both ends of the canal. The percentage of the time during which the wind was coming from each of eight sectors (numbered counterclockwise from the north) was 

tabulated by month and year. The results of this tabulation are shown in figure 24. At Cottonwood the wind 

is from sector 4 (south-southeast) the largest percentage of the time, but the percentage is fairly uniformly 

distributed among all sectors. The two lowest percentages, for winds from the west, are probably due to a 

slight sheltering effect of the Lakeview Mountains (fig.

- 5

Q_

co 4

Q

i ' r

Skinner

8 12 16 20 24

TIME, IN HOURS

FIGURE 23.—Mean annual diurnal variation in 

windspeed, averaged by 10-minute time periods for 

the period July 24, 1973, to July 23, 1974.

1). The distribution of directions did not appear to vary 

with time of year. The largest percentage fell in sector 

4 for every month of the year. Local topography obviously had a great effect on the measured wind directions at Skinner. Notice the sheltering effect of the 

hill to sectors 1, 2, 7, and 8 and of the dam to sector 4 

(figs. 1, 6, 9, and 10). Sector 5 had the highest percentage for months March through September, and sector 3 

had the largest percentage for the months of October 

through December.

The mean windspeed, average speed irrespective of 

direction, and the resultant windspeed (vectorial average speed) were computed for each day. The ratio of 

these two windspeeds is a measure of how consistent 

the wind direction is and is called the wind consistency.

Cottonwood

Skinner

FIGURE 24.—Frequency of occurrence, in 

percentage of time, of winds from various 

directions.
24 METEOROLOGY, HYDRAULICS, AND THERMAL REGIME, SAN DIEGO AQUEDUCT, CALIFORNIA

The wind consistency was computed for each day and 

the monthly average determined by averaging the 

daily values. At Cottonwood the monthly average consistency varies from a low of 0.12 in February to a high 

of 0.76 in November, but no annual cycle was apparent. 

At Skinner the consistency values are probably less 

meaningful, but they varied from a low of 0.15 in December to a high of 0.71 in May. The months of May 

through August had values greater than 0.60, and October, November, and December had values less than 

0.25. Other months had values between 0.38 and 0.49.

RADIATION

The annual pattern of daily solar radiation is shown 

in figure 25. The yearly mean measured at Cottonwood 

and Skinner was 238 W/m2 and 242 W/m2 , respectively, a difference of less than 2 percent. The daily 

values at Cottonwood and Skinner were highly correlated. The correlation coefficient between daily average values for the entire year was 0.97. The standard 

deviation of the difference between the daily means at 

the two ends of the canal was 21.4 W/m2 .

Also shown in figure 25 is the variation of the estimated clear-sky solar radiation. This value was computed using the procedure suggested by the Tennessee 

Valley Authority (1972). The clear-sky solar radiation 

was determined from

sn sin 8 + cos 3> cos 8 sin hM ) (5)

77T

in which 3>rs. is clear-sky solar radiation, Io is effective 

solar constant, r is ratio of actual to mean Earth to Sun 

distance, hss is hour angle of sunset in radians, 3> is 

latitude, and 8 is declination of the Sun. The effective 

solar constant was varied by trial and error until the 

clear-sky curve appeared to form an envelope of the 

measured data. The value used in figure 25 is 1,046 

W/m2 . The value of r was approximated from

r = 1 + 0.017 (cos 360 (186 - £))) (6) 

365

in which D is Julian date (1 -365). The value of A,s,s was 

determined from

= arc cos /sin q,s 

\

sin (ft sin 8

cos <S> cos 8

(7)

in which a,, is solar altitude at sunset, which was assumed to be zero. The latitude of the Cottonwood and 

Skinner sensors was N. 33°47' and N. 33°36', respectively. The declination of the Sun was approximated by use of the expression

8 = 23.45 cos ( —— (172 - £>)). 365 (8)

From equations 5, 6, 7, and 8 the yearly average clearsky radiation at Cottonwood and Skinner is computed 

as 268.8 and 269.3 W/m2 , respectively, a difference of 

0.2 percent.

The annual variation of atmospheric radiation is 

shown in figure 26. The estimated clear-sky atmospheric radiation is also shown for reference. The clearsky value was computed from the formula presented by 

Idso and Jackson (1969)

= a- (Ta + 273.16)4

(1 - 0.261 exp (-0.000777 (Ta)2 ))

(9)

in which <&ca is incoming clear-sky atmospheric radiation, <r is Stefan-Boltzman constant (5.671 x 1CT8 

W/m2 ), and Ta is air temperature in degrees Celsius. 

The presence of clouds should increase the incoming

400

300

200 

CO

< 100

± IT 

* oi

Z. \- Q

D 01 O

££400

I I I

ASONDJFMAMJJ 

1973 1974

O 

cn

300

200

100

I I I I I I I I I I I

ASONDJFMAMJJ 

1973 1974

FIGURE 25.—Daily solar radiation.
RESULTS 25

atmospheric radiation over the clear-sky value by as 

much as 20 to 25 percent. The measured values would, 

therefore, be expected to be equal to or greater than the 

clear-sky values. In general, this appears to be the case 

as indicated in figure 26. Notable exceptions do occur, 

particularly at Cottonwood after March 1, 1974. After 

November 28, 1974, the atmospheric radiation at Cottonwood was determined for each 10-minute interval 

by subtracting the measured solar radiation from the 

all-wave radiation measured by a flat-plate radiometer.

The diurnal variation in atmospheric radiation, 

measured by the pyrgeometer for relatively clear days, 

is illustrated in figure 27. This mean diurnal variation 

was determined by averaging, on a time-period-bytime-period basis, the measured atmospheric radiation 

for 18 days. These days were selected between July 25, 

1973, and December 1, 1973, from both Cottonwood 

and Skinner, such that the ratio of the measured solar 

to the computed clear-sky solar radiation was greater

400 

300

CO

r- 200

<

-z. 

— 100 •z.

2S

I- t- n

I I I I I I I I I I I I

%lH I-M. .'-.-• :I'V'"L- ,,,Jf ' ~

••x-v---/)(v/i

Clear sky

Cottonwood

I I I I I I I I I I I < LU

o ^

< LU

CC OC

CO

ASONDJFMAMJJ

1973 1974

500

400

- 300

200

100

Clear sky

Skinner

J__L

ASONDJFMAMJJ 

1973 1974

FIGURE 26.—Daily atmospheric radiation.

than 0.97. Also shown in figure 27 is the mean diurnal 

variation in atmospheric radiation as determined by 

subtracting the instantaneous value of the measured 

solar radiation from the instantaneous value of the 

all-wave radiation measured by the flat-plate radiometer. This curve represents an average of the 4 days 

after November 28, 1973, for which the ratio of the 

measured solar to computed clear-sky solar radiation 

was greater than 0.97. Unfortunately these 4 days are 

not included in the set of 18 days represented by the 

pyrgeometer, because it was impossible to select any 

clear-sky days during which both instruments were 

operating satisfactorily. The diurnal variation in the 

atmospheric radiation, as measured by the pyrgeometer, follows very closely the diurnal variation computed 

by equation 9. On the other hand, the flat plate, with 

the solar component deducted, indicates a much

— CC

600

400

CO

r- 200

O LU p ^

< LU

5 g

LU LU 

I CL

a.

CO

O

I- 400

200

i—'—r

Clear

'Flat-plate radiometer

i i i i i i

8 12 16 20 24

Cloudy

/Pyrgeometer

Flat-plate radiometer

8 12 16 

TIME, IN HOURS

20 24

FIGURE 27.—Typical diurnal variation in atmospheric radiation as measured by the pyrgeometer and by subtracting the 

measured instantaneous solar radiation from the all-wave 

radiation measured by the flat-plate radiometer.
26 METEOROLOGY, HYDRAULICS, AND THERMAL REGIME, SAN DIEGO AQUEDUCT, CALIFORNIA

greater night-to-day variation. The mean value of 

these two curves should not be compared, because each 

curve represents the average of several but different 

days. The diurnal variation in the atmospheric radiation, as determined by deducting the solar radiation 

from the flat-plate all-wave radiation, appeared to be a 

function of the cloudiness. A comparison of the atmospheric radiation estimated by use of the pyrgeometer 

and the flat plate under cloudy to overcast conditions is 

also illustrated in figure 27. This figure represents the 

average of all days with a ratio of measured to clearsky solar radiation of less than 0.60. Thirteen days are 

included in the pyrgeometer curve and 20 days in the 

flat-plate curve. From an inspection of figure 27, it 

would appear that the flat plate is overly sensitive to 

the solar component of the radiation spectrum. A. P. 

Jackman (oral commun., 1975) found flat plates to be 

overly sensitive to solar radiation.

AIR TEMPERATURE

The annual pattern of daily average air temperature 

is shown in figure 28. The mean daily temperatures at 

Cottonwood and Skinner had a correlation coefficient 

of 0.99 for the period of record. This correlation coefficient remained stable throughout the year. The mean 

air temperatures at Cottonwood and Skinner were 

17.06 and 17.90°C, respectively. The rather sheltered 

location of the Skinner station, on a south hillside, is 

undoubtedly reflected in its higher mean temperature. 

The standard deviation of the difference between the 

daily average temperatures at the two ends of the 

canal was 1.45°C.

VAPOR PRESSURE

Other than atmospheric radiation, the vapor pressure of air proved to be the most difficult parameter to 

measure. More specifically the wet-bulb temperature 

was very difficult to measure continuously because of 

the problem of keeping the wick saturated. Overall, 

wet-bulb data are available for 44 and 56 percent of the 

10-minute time periods at Cottonwood and Skinner, 

respectively.

The annual pattern of daily averaged vapor pressure 

values is shown in figure 29. Daily averages are shown 

in figure 29 only if more than 130 of the 144 possible 

10-minute periods contained data. On a daily average 

basis the correlation between the Cottonwood and 

Skinner vapor pressures was good. The correlation coefficient was 0.96, and the standard deviation of the 

difference between the daily averaged values was 0.15 

kPa (kilopascals). The mean value at Skinner was 

higher than that at Cottonwood by 0.10 kPa. This 

higher value undoubtedly reflects the nearness of Lake 

Skinner. The standard deviation among daily values

was also higher at Skinner (0.38 kPa) than at Cottonwood (0.30 kPa). The higher variability at Skinner 

would also be expected because the presence or absence 

of the vapor blanket from Lake Skinner would depend 

on wind direction, which is of course quite variable.

Because of the large number of missing wet-bulb 

data and because most of the time complete data were 

available at either Cottonwood or Skinner, the 

transferability between Cottonwood and Skinner on a 

time-period-by-time-period basis was investigated. An 

obvious question arises: How can one best estimate the 

vapor pressure at one point given the dry- and wet-bulb 

temperatures at a remote site and the dry-bulb air 

temperature locally? There are four possible ways of 

estimating the vapor pressure under these conditions: 

(a) Assume it is the same as at the remote station (this 

method makes no use of the information known about 

the local dry-bulb temperature); (b) assume the wetbulb temperature is the same at both stations (this 

method makes no use of the dry-bulb temperature at

ASONDJ FMAMJJ 

1973 1974

DC

DC 

LU 

Q.

DC 

<

rniiiiiiiii

Skinner

A S O N D J F 

1973

A M J J 

1974

FIGURE 28.—Daily average air temperature.
RESULTS 27

the remote station); (c) assume wet-bulb depression 

(dry-bulb temperature minus the wet-bulb temperature) is the same at both stations; or (d) assume the 

relative humidity is the same at both stations.

Using the 11,688 10-minute periods for which 

complete data were available at both ends of the canal, 

the accuracy of these four transfer methods was 

checked by assuming one or the other of the wet-bulb 

temperatures was missing, estimating the vapor pressure by all four methods, and comparing the estimated 

value to the known local value. Morning, afternoon, 

and nighttime data were grouped separately to determine if time of day had any influence. The results are 

tabulated in table 6. In every case, transferring the 

vapor pressure directly resulted in the smallest rootmean-square error in the estimated vapor pressure. In 

two cases, the correlation ecoefficient resulting from 

the use of this method was slightly less than that 

resulting from the transfer of the wet-bulb temperaTABLE 6. — Comparisons of vapor pressures estimated by four datatransfer methods

Transferred 

quantity

Estimating Skinner 

vapor pressures

Estimating Cottonwood 

vapor pressures

Correlation Root-mean- Correlation 

coefficient square error coefficient

Root-meansquare error

All data

Vapor pressure ------- 

Wet-bulb temperature - 

Wet-bulb depression ___ 

Relative humidity - _ __

0.837 0.271 

.825 .327 

.528 .700 

.775 .302

0.837 

.774 

.780 

.806

0.271 

.326 

.348 

.312

Morning (0600-1200 hours)

Vapor pressure _______ 

Wet-bulb temperature _ 

Wet-bulb depression 

Relative humidity _____

0.875 0.225 

.860 .304 

.631 .509 

.830 .256

0.875 

.801 

.833 

.851

0.225 

.302 

.283 

.252

Afternoon (1200-1800 hours)

Wet-bulb temperature _ 

Wet-bulb depression ___ 

Relative humidity _ __

0.874 0.227

.834 .313 

.581 .606 

.819 .257

0.874 

.781 

.823 

.845

0.227 

.312 

.289 

.261

Night (1800-0600 hours)

Vapor pressure _______ 

Wet-bulb temperature _ 

Wet-bulb depression - _ _ 

Relative humidity _____

0.767 0.383 

.777 .386 

.500 1.061 

.723 .415

0.767 

.751 

.705 

.734

0.383 

.386 

.499

.447

CO_j 

< 

o

CO

<

Q_ 

O

d o

i—i—i—i—i—i—i—i—r

i Cottonwood

ASONDJFMAMJJ 

1973 1974

ASONDJFMAMJJ 

1973 1974

FIGURE 29.—Daily average vapor pressure.

ture, but no particular significance is attached to this. 

While transferring the vapor pressure directly was 

clearly the most accurate procedure, the least accurate 

procedure is not as well defined. It appears that 

transfer of the wet-bulb depression is probably the 

least accurate. Even on a minute-by-minute basis, the 

vapor pressures are faily well correlated between sites. 

Very little diurnal variation in vapor pressure was observed. It is also interesting that the correlation is 

poorer between Cottonwood and Skinner and the errors 

larger at night than during the day. This is probably 

due to the fact that the lake influenced Skinner to a 

larger degree at night, when winds were light, than 

during the day. During the day, the average Skinner 

vapor pressures were 7.0 percent greater than Cottonwood values, whereas at night they were 7.7 percent 

greater.

WATER TEMPERATURE

The annual pattern of the average water temperature in the canal is shown in figure 30. Daily average 

water temperatures at Cottonwood and Skinner were 

highly correlated with a correlation coefficient of 0.999 

and a standard deviation of 0.28°C. There was always a 

slight warming trend as the water passed through the 

canal. The average increase in temperature was 0.02°C 

during January through April, 0.11°C during May 

through August, and 0.42°C during December. Water 

temperatures at Cottonwood are not available for September through November. The water temperature 

was always observed to be uniform in the vertical.

The diurnal variation in water temperature is illustrated in figure 31, which shows the annual mean obtained for each 10-minute period of the day. These 

curves were obtained by averaging all available tern-
28 METEOROLOGY, HYDRAULICS, AND THERMAL REGIME, SAN DIEGO AQUEDUCT, CALIFORNIA

perature measurements at each individual time period. 

The mean annual diurnal range in temperature at Cottonwood is only 0.38°C as opposed to a range of 2.68°C 

at Skinner. The small diurnal variation in water temperature at Cottonwood results from the fact that the 

water entering the canal is diverted from the Colorado 

River Aqueduct, which passes under the San Jacinto 

Mountains just upstream of the entrance to the San 

Diego Aqueduct (fig. 1). The phase difference in the two 

distributions is also interesting. The Cottonwood temperature reached its low about midnight and its high at 

about 1100 hours, but the Skinner distributions 

reached a low at about 0730 hours and a high at about 

1700 hours.

DISCHARGE

Discharge values were provided by the Metropolitan 

Water District during days of constant flow. For each of 

these 209 days the average stage at Cottonwood was

OVJ

20

ELSIUS

o

O

CO

LU

LU 

DC

LU n

1 1 1 1 1 1 1 1 1 1 1 1 n Cottonwood J /Wr / v

: v/ :

_

i i i i i i i i i i

ASONDJFMAMJJ

1973 1974

LU 

DC

D

< 

DC 

LU 

Q.

CO o

g 20

h10

"1——T

Skinner

i i i i

ASONDJFMAMJJ 

1973 1974

FIGURE 30.—Daily mean water temperature, averaged 

over depth.

determined and Manning's n computed. During the 

summer and early fall, July 24, 1973, to October 9, 

1973, and May 1, 1974, to July 23, 1974, the n value 

remained fairly constant. The mean of 114 computed n 

values during these times was 0.0175 and the standard 

deviation was 0.0004. Even the extreme values of 

0.0182 obtained on May 8 and 0.0165 obtained on May 

22 would result in a variation of less than ± 5 percent. 

Starting about the first of October, the n values started 

steadily decreasing with time until October 18 when 

the n value was 0.0151. From October 18, 1973, to December 26, 1973, the values again remained fairly 

steady. The 53 values available during the latter 

period averaged 0.0152 and had a standard deviation of 

0.0004. During the winter and spring months, the n 

values varied widely in what appeared to be a random 

pattern, but a moving average seemed to increase more 

or less uniformly with time to about 0.0175. The 38

22

LU 

DC

D

21

CO 20

D 

CO 

LU

" 19

CO 

LU 

LU 

DC

g 18 

Q 0

Cottonwood

12 16 20 24

< 22

LU 

Q.

^ 

LU

I- 21

DC 

LU

20

19

18

Skinner

8 12 16 

TIME, IN HOURS

20 24

FIGURE 31.—Mean diurnal variation in water temperature.
REFERENCES CITED 29

values available for the period of January 16 to May 1, 

1973, averaged 0.0170 and had a standard deviation of 

0.0015. Extreme values of 0.0139 occurred on January 

19, 1974, and 0.0191 on April 27, 1974. Local operators 

attribute these shifts in the n values to biological activity of the water. Apparently algae and scum have 

some tendency to form at certain times of the year, 

varying the roughness of the concrete.

SUMMARY AND CONCLUSIONS

Meteorologic and hydraulic variables which influence the energy budget of the San Diego Aqueduct in 

southern California were continuously monitored for a 

1-year period beginning July 24, 1973. The incoming 

solar and atmospheric radiation, windspeed and direction, water temperature, and wet- and dry-bulb air 

temperature were recorded on 10-minute intervals at 

each end of the 26-km canal, and flow rates and stages 

were determined on hourly intervals at five locations. 

These data are available on magnetic tape and can be 

obtained by contacting the Automatic Data Processing 

Unit, U.S. Geological Survey, Water Resources Division, Reston, VA 22092. A detailed description of the 

study site, the instrumentation, and the procedures 

used has been given, as well as all other information 

necessary for the use of these data by interested persons. A general analysis of the spatial and temporal 

variability of the recorded data, as well as the daily 

mean values of all data, have been presented. From an 

analysis of these data, the following conclusions are 

drawn:

1. A pronounced diurnal variation in windspeed was 

observed at each end of the canal. Windspeeds were 

typically quite low during the early morning hours and 

at a maximum during the late afternoon.

2. Daily average windspeeds are quite variable from 

point to point, apparently depending on the local topography.

3. Solar radiation measured at Cottonwood was 

highly correlated to that measured at Skinner. The 

standard deviation between daily average values, obtained 26 km apart, was 21.4 W/m2 , and the mean difference was 4 W/m2 . This parameter is relatively easy 

to measure by use of pyranometers, and an accuracy of 

± 2 percent can be expected.

4. Atmospheric radiation values are difficult to 

monitor accurately, and results obtained by use of different instrument types are not always comparable.

5. Vapor pressure is another parameter which is difficult to accurately monitor on a continuous basis, but 

it is fairly uniform spatially. Instantaneous measurements taken simultaneously but 26 km apart had a 

correlation coefficient of 0.837 and a standard deviation of 0.27 kPa. The mean difference was 0.10 kPa.

6. At a point where only the dry-bulb temperature is 

known, the most accurate method to estimate the 

vapor pressure is to compute it from the wet- and drybulb temperatures obtained at a remote site.

7. Flow resistance, as defined by Manning's n, in the 

concrete-lined San Diego Aqueduct varied significantly 

with time of year. Local operators attribute this variation to biological growths.

REFERENCES CITED

Idso, S. B., and Jackson, R. D., 1969, Thermal radiation from the 

atmosphere: Journal of Geophysical Research, v. 74, no. 23, p. 

5397-5403.

Tennessee Valley Authority, 1972, Heat and mass transfer between 

a water surface and the atmosphere: Norris, Tennessee, Tennessee Valley Authority, Laboratory Report, no. 14.

Thackston, E. L., and Parker, F. L., 1971, Effect of geographical 

location on cooling pond requirements and performance: 

Nashville, Tennessee, Vanderbilt University, School of Engineering, report no. 5, 234 p.

Thornthwaite, W. C., 1931, The climate of North America according 

to a new classification: Geographical Review, v. 21, p. 633-655.

U.S. Geological Survey, 1970, National atlas of the United States of 

America: Washington, U.S. Government Printing Office, 417 p.

GPO689-143