Evaluation of Seepage 

From Chester Morse Lake 

and Masonry Pool 

King County, Washington

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1839-J

Prepared in cooperation with the city 

of Seattle Lighting Department
Evaluation of Seepage 

From Chester Morse L? ke 

and Masonry Pool 

King County, Washington

By F. T. HIDAKA and A. A. GARRETT

CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED fTATES 

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1839-J

Prepared in cooperation with the city 

of Seattle Lighting Department

Analysis of seepage losses from Chester 

Morse Lake and Masonry Pool and 

seepage gains to the Cedar and South 

Fork Snoqualmie Rivers

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1967
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

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

Washington, D.C. 20402 - Price 15 cents (paper cover
CONTENTS

Page

Abstract__ ______________________________________________________ Jl

Introduction._____________________________________________________ 1

Purpose and scope.____________________________________________ 1

Acknowledgments. ____________________________________________ 1

Location and general features.__________________________________ 2

History of Cedar River development and seepage from Chester Morse

Lake and Masonry Pool___ ___________________________________ 5

Earlier investigations._________________________________________ G

Study area____ _______________________________________________ 7

Climate ______________________________________________________ 7

Geologic setting.______________________________________________ 7

Hydrologic setting.____________________________________________ 9

Records used in the study._________________________________________ 10

Streamflow and stage records._______-------_______-____.______. 10

Well records.__----_-__---_-----_-_--_--_________-____________ 11

Precipitation records.._________________________________________ 12

Seepage estimates for water years 1957-64____________________________ 12

Seepage from Chester Morse Lake and Masonry Pool_______-_-___- 12

Seepage to Cedar River._______________________________________ 14

Seepage to South Fork Snoqualmie River_________________________ 14

Comparison of seepage estimates._______________________________ 17

Changes in runoff regimen following the Boxley Creek washout in 1918___ 19

Summary. ________________________________________________________ 26

References cited.__________________________________________________ 26

ILLUSTRATIONS

Page 

FIGURE 1. Map showing hydrologic data-collection sites in the vicinity

of Chester Morse Lake._____________________________ J3

2. Map showing physiographic setting and generalized geology

of the Cedar Falls-North Bend area_________-___--_- 4

3. Graphs showing comparison of stages of Chester Morse

Lake, Masonry Pool, and Rattlesnake Lake, 1961-64. __ 10 

4, 5. Graphs showing relation of monthly mean discharge increment to South Fork Snoqualmie River between 

Edgewick and North Bend to:

4. Index of stage of Masonry Pool for a range in precipitation indices, 1962-64____________-__-_--_ 16

5. A comparable value for Cedar River between Cedar

Falls and Landsburg, 1962-64._________-__---_ 17

in
IV CONTENTS

Page

FIGURE 6. Graph showing relation of cumulative discharge fo~ Cedar 

River near Landsburg to cumulative average precipitation for Landsburg and Cedar Lake, and of cumulative 

discharge for South Fork Snoqualmie River at North 

Bend to cumulative average precipitation for Snoqualmie 

Falls and Cedar Lake, 1908-26 and 1930-32. _ _ _ __ . _ _ J20

7. Graph showing relation of cumulative discharge fcr Cedar 

River near Landsburg and South Fork Snoqualmie River 

at North Bend to cumulative average discharge for Middle and North Forks Snoqualmie River, 1908-26 and 

1930-32_______________________-___--__--_________- 21

8. Graph showing relation of annual mean discharge fcr Cedar 

River near Landsburg to average of annual precipitation 

at Cedar Lake and Landsburg, and of annual m?an discharge for South Fork Snoqualmie River at Nortti Bend 

to average of annual precipitation at Cedar Lake and 

Snoqualmie Falls, 1908-18____________-__ _ __ __ 23

9. Graphs showing relation of annual mean discharge for Cedar 

River near Landsburg and South Fork Snoqualmie River 

at North Bend to average of annual mean dischrrges for 

Middle and North Forks Snoqualmie River, 190?-18____ 24

TABLES

Page

TABLE 1. Length and type of available records for selected stageand streamflow-gaging stations in Cedar and Sncqualmie 

River basins_______-_______________________________ Jll

2. Estimated seepage from Chester Morse Lake and Masonry

Pool, 1957-64____________.____________ 13

3. Estimated seepage to Cedar River between Ced<\r Falls

and Landsburg, 1957-64_____________________________ 14

4. Estimated seepage to South Fork Snoqualmie River between Edgewick and North Bend, 1957-64____________ 18

5. Comparison of estimated seepage from Chester Morse 

Lake and Masonry Pool with that to Cedar and South 

Fork Snoqualmie Rivers, 1957-64__________________ 18

6. Decreases in seepage from Cedar River above Landsburg,

1919-26 and 1930-32______________________________ 25

7. Increases in seepage to South Fork Snoqualmie River above

North Bend, 1919-26 and 1930-32____________________ 25
CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

EVALUATION OF SEEPAGE FROM CHESTER MORSE LAKE 

AND MASONRY POOL, KING COUNTY, WASHINGTON

By F. T. HIDAKA and A. A. GARRETT

ABSTRACT

Hydrologic data collected in the Cedar and Snoqualniie River basins on the 

west slope of the Cascade Range have been analyzed to determine the amount of 

water lost by seepage from Chester Morse Lake and Masonry Pool and the consequent gain by seepage to the Cedar and South Fork Snoqualmie Rivers. For 

water years 1957-64, average losses were about 220 cfs (cubic feet per second) 

while average gains were about 180 cfs in the Cedar River and 50 cfs in the 

South Fork Snoqualmie River.

Streamflow and precipitation data for water years 1908-26 and 1930-f2 indicate that a change in runoff regimen occurred in Cedar and South Fork Snoqualmie Rivers after the Boxley Creek washout in December 1918. For water 

years 1919-26 and 1930-32, the flow of Cedar River near Landsburg averaged 

about 80 cfs less than it would have if the washout had not occurred. In contrast, 

the flow of South Fork Snoqualmie River at North Bend averaged al out 60 

cfs more than it would have.

INTRODUCTION 

PURPOSE AND SCOPE

Under cooperative agreement with the city of Seattle Lighting Department, the U.S. Geological Survey analyzed hydrologic data for 

the water years 1957-64 to determine the approximate amount of 

seepage losses from Chester Morse Lake and Masonry Pool and the 

concurrent amounts of seepage to Cedar and South Fork Snoqralmie 

Rivers. The records for water years 1908-26 and 1930-32 were also 

used to investigate the effect that Boxley Creek washout of 1918 had 

on the runoff regimens of both the Cedar and South Fork Snoqralmie 

Rivers.

ACKNOWLEDGMENTS

Reports on previous investigations and data on reservoir altitudes 

were furnished by E. C. Brundage, power analyst with Seattle's 

Lighting Department. Valuable historical information was loaned

JJ
J2 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

by the division engineer of the Chicago, Milwaukee, St. Paul, and 

Pacific Railroad in Tacoma, Wash. I. S. Papadopulo^, hydraulic 

engineer, U.S. Geological Survey, provided assistance in the analysis 

of the available ground-water data.

LOCATION AND OENERAL FEATURES

The study area includes Chester Morse Lake (formerly called Cedar 

Lake), other parts of the Cedar River basin, and parts of the Middle 

and South Fork Snoqualmie River basins. The area comprises about 

250 square miles on the west slope of the Cascade Rarge in King 

County, Wash. The relation of the study area to the State as a whole 

and to the overall stream network is shown in figure 1; detailed 

features of the Cedar Falls-North Bend vicinity are shown in figure 2.

The part of the study area in the Cedar River valley includes the 

drainage system from Chester Morse Lake downstream to Landsburg. 

The Cedar River heads in the Cascade Mountains and flows westward 

12 miles to Chester Morse Lake. The only other large tributary to 

the lake is the Rex River. Chester Morse Lake lies at an altitude 

of 1,550 feet and is 5 miles long and half a mile wide,. The lake 

averages about 90 feet in depth and has a maximum depth of about 

115 feet.

A timber crib dam is half a mile downstream from the natural 

outlet of Chester Morse Lake. Another dam spans the narrow valley 

1.5 miles below the crib dam. Originally, this second dam was called 

Masonry Dam and the reservoir it formed was called Masonry Pool. 

These commonly used names have become the official designations of 

the dam and reservoir.

From Masonry Dam, Cedar River continues to flow westward on 

a fairly uniform gradient of about 40 feet per mile to Landsburg. 

Taylor Creek is the largest tributary to the Cedar River between the 

the dam and Landsburg.

The part of the study area in the Snoqualmie River valley is a 

6-mile reach extending from Edgewick to North Bend. This reach 

lies north of Chester Morse Lake, and includes segments of both the 

Middle and South Forks Snoqualmie River. The Snoqur.lmie Valley 

is separated from the Cedar River basin by a divide at an altitude of 

about 920 feet. The Snoqualmie flood plain ranges in altitude from 

440 feet at North Bend to about TOO feet near Edgewick.

The Cedar and South Fork Snoqualmie Rivers are about 3 miles 

apart at their closest point, in the vicinity of Cedar Falls. Rattlesnake Lake Hes half a mile north of Cedar River in the r.rea between 

the two rivers (fig. 2). The lake has no outlet, but any surface 

outflow would enter Boxley Creek, a tributary of South Fork Snoqualmie River, rather than Cedar River.
01234 SMILES 

I i i i I____I____|____I____|

FIGURE 1. Hydrologie data-collection sites in the vicinity o
47°30'

0

UJ l

1 2 MILES

CONTOUR INTERVAL

400 FEET WITH 

SUPPLEMENTAL 200-FOOT

CONTOURS 

DATUM IS MEAN SEA LEVEL

47°25'

Geology fro

and others 

FIGURE 2. Physiographic setting and generalized geology of the C
SEEPAGE, CHESTER MORSE LAKE AND MASONRY POOL, WASH. J5

HISTORY OP CEDAR RIVER DEVELOPMENT AND SEEPAGE FROM 

CHESTER MORSE LAKE AND MASONRY POOL

Cedar River is the source of municipal water supply for Seattle. 

In 1900, construction of a dam and diversion works was started at 

Landsburg, and in 1901, the first water was delivered to Seattle in 

gravity lines (McWilliams, 1955, p. 63).

The use of Cedar River in the vicinity of Chester Morse Lake for 

the development of hydroelectric power was investigated as early as 

1895. The large amount of potential storage in the lake, together 

with about 600 feet of fall in the river below the lake, were responsible for the early interest in development of the river. Construction 

of a powerplant at Cedar Falls began in 1902, and the first electricity 

was delivered to Seattle in 1905. The headworks was the timber 

crib dam half a mile below the natural outlet of Chester Morse Lake. 

The dam raised the lake level 18 feet, to 1,548 feet altitude, and 

provided 25,000 acre-feet of storage in addition to the 33,500 acre-feet 

in the natural lake. The water was carried 3 miles from the dam 

to the powerplant, and in this distance a gross head of 600 fee4: was 

available.

In 1910, construction of a new dam (Masonry Dam) 1.5 miles 

below the crib dam in the narrow valley was proposed. The dam 

was designed to have a spillway crest at 1,605 feet and was megut to 

provide an increase in storage capacity of 125,000 acre-feet. Because 

of seepage problems during the dam's construction, the spillway 

crest was lowered to 1,590 feet, and an opening in the dam was provided at 1,555 feet. "Water storage in the reservoir (Masonry Pool) 

created by the dam was started in December 1914. In the spring of 

1915, a rapid rise in the water level of Eattlesnake Lake (fig. 2) 

flooded the town of Cedar Falls. The flooding was attributed to seepage that resulted from storage of water behind Masonry Dam. To stop 

the seepage, the banks of Masonry Pool were flattened and sluiced 

with clay and other fine materials. This work was continued until 

1918 when it was believed that most of the larger leaks had been 

sealed. Water storage was started again, and the water-level rise 

in Masonry Pool caused increased flow from the south flank of Pouth 

Fork Snoqualmie Valley to Rattlesnake Lake and Boxley C~eek. 

Heavy rains helped to raise the level of Masonry Pool to 1,550 feet, 

and on December 23, 1918, a large slide and washout occurred above 

the source of Boxley Creek. The washout resulted in the release of a 

large amount of water and gravel outwash, which flooded a sawmill 

and half a mile of railroad grade near the Boxley Creek channel.

249-833 67-
J6 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

Following the washout, a continued effort was made to seal Masonry 

Pool by sluicing. This effort was discontinued in 1930. The dam 

has never been used to its capacity because of the excessive seepage 

and the possibility of additional washouts.

EARLIER INVESTIGATIONS

Many geologic and engineering investigations have been conducted 

in the vicinity of Chester Morse Lake since the washout of Boxley 

Creek. Some of the purposes of the studies were (1) to describe the 

geologic setting of the area and to analyze the Boxley Creek washout, 

(2) to determine the amount of seepage from Chester Morse Lake and 

Masonry Pool, (3) to determine the feasibility of sealing the reservoir banks to prevent the seepage, and (4) to evaluate the effect of 

replacing the timber crib dam with a higher and more solidly constructed dam at the outlet of Chester Morse Lake.

In 1919, an unpublished report regarding damage to the railroad 

right-of-way by the Boxley Creek washout of December 23, 1918, 

was prepared by J. C. Ealston for the Chicago, Milwaukee, St. Paul, 

and Pacific Railroad.

Reports were prepared in 1923 and 1952 by S. B. Hill for the city of 

Seattle. These unpublished reports evaluated the amount of seepage from Chester Morse Lake and Masonry Pool and considered the 

feasibility of sealing the banks of both reservoirs. In his earlier report, Hill stated that: "There was a large seepage loss' from Cedar 

Lake [Chester Morse Lake] after construction of the crib dam. This 

averaged for the first six years 122,000 acre-feet per year or an average of 168 second-feet" However, he also mentioned thr.t the amount 

decreased over the years: "The seepage loss from the lakes has decreased from year to year. * * * There is now but very slight seepage loss from Cedar Lake below 1,540 feet water level." Hill also 

concluded that seepage losses from Masonry Pool were large. According to his computations, the average loss per day during the 

period 1919-23 ranged from 200 acre-feet when the altitude of Masonry 

Pool was 1,520 feet to 983 acre-feet when the altitude was 1,550 feet.

Hill's later report supplemented and updated the earlier report. 

Benefits to the Lighting and Water Departments from additional 

storage in Chester Morse Lake were discussed.

New studies on the feasibility of reconstructing the crb dam at the 

outlet of Chester Morse Lake are currently (1964) being carried on 

by the consulting firm of Shannon and Wilson for the Seattle Lighting 

Department.
SEEPAGE, CHESTER MORSE LAKE AND MASONRY POOL, WASH. J7

STUDY AREA 

CLIMATE

Climate in the vicinity of Chester Morse Lake is mild ard wet, 

owing to the prevailing air currents that move inland from the Pacific 

Ocean. The Cascade Mountains to the east protect the area from 

the cold continental air masses. The combination of these two features produces a marine-type climate that is cool in the summer and 

relatively mild in the winter (Phillips, 1965).

Summer temperatures usually remain below 80°F and winter temperatures normally remain above freezing. The average monthly temperature ranges from 35°F in January to 61°F in July at Cedar Lake. 

(The U.S. Weather Bureau retains the old name, Cedar Lake, for its 

climatological station and records, although the lake's name was 

officially changed to Chester Morse.)

Precipitation over the area comes from warm, moisture-lader winds 

that move inland from the Pacific Ocean and are forced upward by 

the west slope of the Cascade Mountains. The rising air is cooled, 

and the moisture is condensed to produce rain or snow. Orogmphic 

influences cause a wide difference in precipitation within a relatively 

short distance, as illustrated by the records at Landsburg and Cedar 

Lake. Within a distance of only 12 miles between the two gages, 

average annual precipitation increases from 55 inches at Landsburg 

(altitude 535 ft) to 102 inches at Cedar Lake (altitude 1,560 ft).

GEOLOGIC SETTING

The study area, in the western foothills of the Cascade Range, 

includes a segment of the Puget lowland. The topography of the 

study area as a whole is that of a youthful upland, incised by steepsided stream valleys. The area has been modified greatly by glacial 

action. The crests of ridges show results of the characteristic eroding 

action of alpine glaciers, and the valleys have become filled with large 

quantities of morainal debris and outwash associated with the several 

Pleistocene continental glaciations.

The following topographic features are important parts of the study 

area: (1) The segment of the Puget lowland that has been called the 

Snoqualmie embayment by Mackin (1941b, p. 451), that extends into 

the mountains, and that is occupied by the South and Middle Forks 

of the Snoqualmie River, (2) the northwestward-trending valle;/ occupied by Chester Morse Lake, (3) the south westward-trending valley 

occupied by the Cedar River downstream from the lake, and (4) the 

extensive moraine that separates the Cedar River drainage from the 

Snoqualmie drainage to the north.
J8 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

Both the Snoqualmie embayment and the Cedar embankment are 

shown in figure 2, which presents a segment of the study area in detail. 

The Snoqualmie embayment includes virtually all the area presently 

underlain by alluvium or outwash in the northeast part of the segment as shown in figure 2. The Cedar embankment includes the 

east-central part underlain by outwash.

Prior to the onset of glaciation, the valley now occupied by Chester 

Morse Lake drained northwestward, converging with the valleys of 

the South and Middle Fork of Snoqualmie River. The depths of these 

valleys are not known. In Pleistocene time a, period of extensive 

glaciation a glacier entered the Snoqualmie embaymert from the 

northwest. It built a composite till-outwash moraine, the Cedar embankment of Mackin (1941b), opposite the Cedar Valley, to form 

Chester Morse Lake. The lake became a sizable water body shortly 

after glacial blockage of the valley mouth. According to Mackin 

(1941a, p. 457), the outwash gravel deposited during the advance of 

the glacier overlaps 'and grades into lacustrine deposits. These deposits represent successive positions occupied by the lake at later and 

later stages of ice advance. In other words, the lake war reduced in 

area by encroachment of the moraine, which covered th^ lacustrine 

deposits to a greater and greater depth as it advanced.

As a result of the blockage which dammed the Middle- and South 

Forks of the Snoqualmie as well as the Cedar River tli?, drainage 

pattern changed markedly. Most of the drainage from the Snoqualmie-Cedar area presumably escaped to the southwest (fig. 2) through 

the valley now occupied by the Cedar River. The drainage escaped 

in this direction by breaching the southwest divide at its lowest point. 

According to Mackin (1941a, p. 466), "Incision of part or all of the 

Snoqualmie-Cedar drainage in the course so determined, during one 

or more interglacial interstages, could then have produced the deep 

rock valley utilized as a spillway during the last glacial invasion." 

When the glacier withdrew, "the Middle and South Forks happened 

to begin downcutting in weak glacial detritus; these streams have 

subsequently trenched the valley mouth embankments, drained the 

glacial lakes, and cut deeply into the former lake floors " (Mackin, 

1941b, p. 20). In contrast, outflow from Chester Morse Lake by way 

of Cedar River had already become established across th°> southwest 

divide, just southwest of Rattlesnake Lake (fig. 2), so the retreat of 

the glacier had no effect on the Cedar River regimen. Furthermore, 

because the point where the Cedar River crosses the southwest divide 

is underlain by bedrock, "the river has been able only to cut a narrow gorge part way through * * * [bedrock] spurs [and] the Cedar 

morainal embankment is practically uneroded * * *" (Mackin, 1941b,
SEEPAGE, CHESTER MORSE LAKE AND MASONRY POOL, WASH. J9

p. 20). The near absence of head ward erosion has, of course, allowed 

Chester Morse Lake to remain intact, "only slightly lowered from its 

Pleistocene elevation."

HYDBOLOGIC SETTING

The Cedar Kiver basin and the Snoqualmie Kiver basin are separate 

physiographic entities. However, because of the permeable nature 

of the Cedar embankment, transfer of water takes place between the 

two drainage systems by means of subsurface leakage. In g?neral, 

water is lost from Masonry Pool and, to a lesser extent, from Caster 

Morse Lake and moves downgradient through the embankment. Part 

of this water enters the Snoqualmie drainage system and is intercepted 

by the South Fork of the Snoqualmie Kiver, within the reach between 

Edgewick and North Bend. Almost all of the remainder returns to 

the Cedar River system.

Rattlesnake Lake, which lies in the area between the two rivers, 

accepts some seepage from Chester Morse Lake and Masonry Pool. 

The area covered by Rattlesnake Lake has increased in size in the 

last century (many large tree stumps are now under water), anc1 much 

of the increase doubtless has occurred since the construction of 

Masonry Dam. In general, the lake stage responds to changes in the 

stage of both Chester Morse Lake and Masonry Pool. Figure 3 Shows 

the comparison of stages of Chester Morse Lake, Masonry Pool, and 

Rattlesnake Lake for water years 1961-64.

Water-level measurements in test wells constructed near the north 

end of Chester Morse Lake suggest that seepage occurs mainly from 

Masonry Pool. Water levels in the Cedar embankment are controlled 

in large part by the level in the Pool and to a significant extent also 

by precipitation that falls on the embankment.

As stated earlier (p. J2), Rattlesnake Lake is in the Snoqualmie 

River drainage system. Nevertheless, fragmentary data s iggest 

that the ground-water divide may be north of the lake, so that seepage 

from the lake may return to the Cedar River drainage system.

In the Snoqualmie River valley southeast of North Bend, ground 

water moves generally downgradient and parallel to the course of the 

South and Middle Forks. The available data suggest that no large 

transfer of water by ground-water movement occurs from the Middle 

to the South Fork. Doubtless, during times of changing stage in both 

forks, some water is taken into or out of ground-water storage. However, the amount of water in temporary storage is not critical compared to the amount transferred to the South Fork as underflow 

through the Cedar embankment.
J10 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

1560

1550 -

1540

JT 1530 -

1520 %.

1510

920

1961 1962 I 1963 

WATER YEAR

FIGUEE 3. Comparison of stages of Chester Morse Lake, Masonry Pool, and 

Rattlesnake Lake, 1961-64.

RECORDS USED IN THE STUDY

STREAMFLOW AND STAGE RECORDS

Many streamflow and stage records have been collected in and 

adjacent to the study area. Flow in the Cedar River near Landsburg 

has been gaged continuously since 1895. Other gaging stations in 

the Cedar River basin have been in operation for shorter periods.
SEEPAGE, CHESTER MORSE LAKE AND MASONRY POOL, WASH. Jll

Streamflow records on the three forks of the Snoqualmie River were 

started in 1908 but were collected only intermittently through 1964. 

Records were collected on the South Fork Snoqualmie River at Edgewick from 1962, after the start of this study, to 1964.

Stage records for Masonry Pool have been gathered by the Seattle 

Lighting Department since 1914. Stage records on Chester Morse 

and Rattlesnake Lakes are also available.

Sites at which streamflow and stage records were collected for use 

in this study are shown in figure 1. Lengths of records at these sites 

are listed in table 1.

TABLE 1. Length and type of available records for selected stage- and streamflowgaging stations in Cedar and Snoqualmie River basins

No.

on

fig. 1

Station name

Drainage

area

(sq mi)

Period of

record (water

years)

Type of record

Cedar River basin

1

2

3

4

5

ft

7

Cedar River near Cedar Falls (above

Chester Morse Lake).

Rex River near Cedar Falls (tributary

to lake) .

Chester Morse Lake _ ____ __ -_ _

Cedar River at Cedar Falls. ___ .__ _

40.7

13.4

78.4

81.3

84.2

17.2

117

1946-64

1946-64

1905-64

1918-64

1914-64

1957-64

1895-1964

Discharge.

Discharge.

Stage.

Discharge.

Snoqualmie River basin

8 

9

10 

11

12

Middle Fork Snoqualmie River near 

North Bend. 

North Fork Snoqualmie River near 

North Bend.

South Fork Snoqualmie River at 

Edgewick. 

Rattlesnake Lake__ __ _ __ ______

South Fork Snoqualmie River at 

North Bend.

169 

95.7

65.9 

1.86

81.7 

17.1

1908-26 

1930-32 

1908-26 

1930-38 

1960-64 

1962-64

1953-64

1908-26 

1930-38 

1945-50 

1960-64 

1946-64

Discharge. 

Discharge.

Discharge. 

Stage.

Discharge. 

Discharge.

! Not shown on map.

WELL RECORDS

From August 1962 to November 1964, a series of water-level measurements was obtained from each of about 50 domestic wells in the 

flood plain of the Middle and South Forks of Snoqualmie River and 

from several wells in the Cedar embankment. The measurements on 

the flood plain were made to determine the general features of ground-
J12 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

water occurrence in the interstream area, while those in wells on the 

embankment were made to determine whether the ground-water levels 

there fluctuate in response to changes in stage of Masonry Pool.

Virtually all the wells on the flood plain are near North Bend. No 

wells are known to exist in the area between the Middle and South 

Forks near Edge wick. This situation makes any evaluation of the 

ground-water features between the two streams difficult throughout 

much of the flood plain. Likewise, all wells in the embankment are 

concentrated on the steep northward-facing slope, whereas none are 

in the vicinity of Rattlesnake Lake or Masonry Pool. For that reason, 

the water-level gradient cannot be determined throughout much 

of the embankment.

PRECIPITATION RECORDS

Precipitation records used in the study were collected by the U.S. 

Weather Bureau at Cedar Lake (p. J7), Landsburg, and Snoqualmie 

Falls. The Landsburg precipitation gage has continuous records 

from 1904, whereas the Cedar Lake gage was started in 1903 and the 

Snoqualmie Falls gage, in 1899. The Landsburg and Snoqualmie 

Falls gage are at altitudes of 535 feet and 435 feet respectively, and the 

Cedar Lake gage is at the altitude of 1,560 feet. The gage sites are 

shown in figure 1.

SEEPAGE ESTIMATES FOR WATER YEARS 1957-64

Streamflow data collected in water years 1957-64 were used to estimate the seepage from Chester Morse Lake and Masonry Pool and the 

seepage to Cedar and South Fork Snoqualmie Rivers. Analysis was 

limited to the 8-year period by the length of records collected for 

Taylor Creek near Selleck. Any extension of the analysis to a longer 

period would require an estimation of discharge for Taylor Creek. 

This estimate is not considered necessary for the purposes of this 

study.

Annual values were used throughout this analysis except in the 

estimation of incremental flow to the South Fork Snoqualmie River 

between Edgewick and North Bend, where monthly estimates were 

computed and combined to obtain annual figures.

SEEPAGE FROM CHESTER MORSE LAKE AND MASONRY POOL

The seepage from Chester Morse Lake and Masonry Pool is assumed 

to be the difference between the estimated net discharge from the basin 

above the Cedar River gaging station at Cedar Falls and the measured 

discharge at that station, corrected for changes in storage in the lake 

and pool.

The estimated discharge from the basin above Cedar Fills was com-
SEEPAGE, CHESTER MORSE LAKE AND MASONRY POOL, WASH. J13

puted by summing the measured discharges of Cedar and Kex Eivers 

upstream from Chester Morse Lake (fig. 1, sites 1 and 2) and the estimated discharge for the remaining ungaged drainage area and subtracting the losses due to lake-surface evaporation. The basin above 

the Cedar Falls station has a drainage area of 84.2 square miles, and 

the two major tributaries to Chester Morse Lake drain 54.1 square 

miles. This difference leaves an ungaged area of 30.1 square miles. 

The discharge per square mile from the gaged area of 54.1 square miles 

was used to estimate discharge from the ungaged 30.1 square miles. 

Evaporation from Chester Morse Lake and Masonry Pool was estimated by assuming an annual loss of 24 inches from a water-surface 

area of 3 square miles. This evaporation rate is considered equal to 

the potential evapotranspiration value reported for Landsburg (U.S. 

Weather Bureau and U.S. Soil Conservation Service, 1961, p. 6). 

From these values, annual evaporation losses were computed to average 

5 cfs (cubic feet per second). For the present study, the 5-cfs value is 

assumed to be constant from year to year.

Values of annual mean discharge obtained at the Cedar Falls station were adjusted for changes in storage in Chester Morse Lake and 

Masonry Pool. The adjusted values represent the natural flow at the 

Cedar Falls station.

As mentioned previously (p. J12), the difference between the estimated discharge from tributary areas above the station at Cedar 

Falls and the adjusted discharge at the station itself was considered 

equivalent to the seepage from Chester Morse Lake and Masonry 

Pool. Table 2 summarizes the computations of seepage for water 

years 1957-64.

TABLE 2. Estimated seepage from Chester Morse Lake and Masonry Pool, 1957-64 

[Quantities in cubic feet per second]

Water year

1957..........

1958..........

1959. .-.._....

1960..........

1961--. 

1962--. 

1963... .... ...

1964_. 

Average. .

Rex

River

1

102

74.6

142

111

112

90.8

84.6

125

105

Cedar

River

above

Morse

Lake

2

260

202

373

286

288

232

218

309

271

Ungaged

area

3

201

154

287

221

223

180

169

241

210

Evaporation

from lake

and pool

4

5

5

5

5

5

5

5

Net discharge

at Cedar

Falls i

5

558

426

797

613

618

498

467

670

581

Cedar

River at

Cedar

Falls

6

336

230

456

395

290

433

357

Change

in

storage

7

+1

-4-9

+36 -33

-3

+6 1

+6

+2

Adjusted

discharge 2

8

337

232

492

409

392

296

277

439

359

Estimated

seepage 3

(rounded)

9

220

190

300

200

230

200

190

230

220

1 Net discharge at Cedar Falls (col. 5) for given water year is total of cols. 1, 2, and 3 minus evaporation 

from lake and pool (col. 4).

2 Adjusted discharge (col. 8) is total of cols. 6 and 7. 

8 Estimated seepage (col. 9) is cols. 5 minus 8.

249-833 67 3
J14 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

SEEPAGE TO CEDAR RIVER

Seepage to Cedar River downstream from Masonry Pool is assumed 

to occur in the reach between the gaging stations at Cedar Falls and 

Landsburg. Total discharge in this reach of river is the sum of the 

discharges of Cedar River at Cedar Falls and Taylor Creek near 

Selleck plus an estimated discharge from the remaining ungaged 

area of 15.6 square miles. The difference between this sum and the 

discharge at the Landsburg station was considered to be the seepage 

to Cedar River. The estimated discharge from the ungaged area was 

computed using the same discharge per square mile as that at the 

Taylor Creek station. The computations are summarized for the 

water years 1957-64 in table 3.

TABLE 3. Estimated seepage to Cedar River between Cedar Falls and Landsburg,

1957-64 

[Quantities in cubic feet per second]

Water year

1957

1958 _ __ _______

1959 _____________

1960_____-__--__-___

1961________________

1962__ _____________

1963__ --__-___-.__

1964 _______________

Average. ___ ___

Cedar 

River at 

Cedar 

Falls

1

336

230

456

442

395

290

278

433

357

Taylor 

Creek near 

Selleck

2

97.5

71.8

131

122

116

86. 1

94. 1

122

105

Ungaged 

area

3

88.4

65.5

119

111

105

78.1

85.3

111

95

Total estimated discharge at 

Landsburg 1

4

522

367

706

675

616

454

457

666

557

Cedar 

River mar 

Landsbnrg

6

716

535 90°

865

801

591

637

818

734

Estimated 

seepage a 

(rounded)

6

190

170

200

190

180

140

180

150

180

1 Total estimated discharge at Landsburg (col. 4) for given water year is total of cols. 1, 2, and 3.

2 Estimated seepage (col. 6) is cols. 5 minus 4.

SEEPAGE TO SOUTH FORK SNOQUALMIE BIVEF.

All seepage to South Fork Snoqualinie River is assumed to enter 

from the south: that is, from the general direction of the Cedar embankment and the flank of Rattlesnake Mountain (fig. 2). This assumption seems valid because seepage from the Middle to the South 

Fork has been proven insignificant.

In the method used to compute seepage to South Fork Snoqualmie 

River, a quantity of water was assumed to be contributed by surface 

runoff from the drainage area between the Edgewick and North Bend 

gaging stations. That quantity was subtracted from the difference
SEEPAGE, CHESTER MORSE LAKE AND MASONRY POOL, WASH. J15

between discharges at the two stations, and the resulting value was 

considered to be incoming seepage.

The computation of seepage to the South Fork for water ^ears 

1957-64: required an estimation of the difference between discharges 

at Edgewick and North Bend for about 6 years of no record. Estimates were needed for water years 1957-61 and parts of water years 

1962 and 1963. Because the available record is short, regression 

analyses were possible only on a monthly basis. The monthly data 

admittedly are not random because adjacent monthly values1 are 

usually related.

Two separate regressions were computed to estimate the increment 

of discharge between Edgewick and North Bend for the period of no 

record. Differences in monthly mean discharge for the 22 months 

of concurrent record at the two gaging stations were computed; these 

differences presumably consist not only of runoff accretions from 

precipitation over the intervening draining area but also of seepage 

from Cedar River basin.

In the first analysis, a multiple regression was computed, relating 

the increments of monthly mean discharge from the reach of the 

South Fork Snoqualmie River between Edgewick and North Bend 

to the stage in Masonry Pool and to precipitation. The amount of 

seepage and runoff accretions was assumed to be directly related to 

the stage and precipitation. A 2-month average value for stage of 

Masonry Pool, based on the current month and previous month, was 

used as an index of stage. An average of the monthly precipitation 

values recorded at Cedar Lake, Landsburg, and Snoqualmie Falls 

was computed for each month and then combined with half of the 

previous month's average to give an index of precipitation. The 

multiple regression using these variables is:

7= -130+4.0(^-1,500) +7.LP (1) 

where

7= discharge increment between Edgewick and North Bern?, 

/S=stage index for Masonry Pool, and 

P=precipitation index.

The relation is shown graphically in figure 4.

In the second analysis, the increment of discharge between Edgewick and North Bend was related to a similar increment in the Cedar 

River between the Cedar Falls and Landsburg gaging stations. The 

increments of discharge in both streams are assumed to be related because both presumably include seepage from Chester Morse Lake and
J16 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

Masonry Pool plus runoff accretion, 

from 22 months of record as:

The regression w\s computed

/=-69+ 0.49*7 (2) 

where

/= discharge increment between Edgewick and North Bend and 

G=comparable value for Cedar River between Cedar Falls and 

Landsburg.

The relation is shown graphically in figure 5.

These two regressions were used to estimate discharge increments 

for South Fork Snoqualmie River between Edgewick and North Bend 

for all months of no record at Edgewick during the 1957-64 water 

years. The monthly estimates were then combined to ol^ain annual 

figures. The average of the two annual figures was user1 as the estimated difference in discharge between Edgewick and North Bend.

Since the discharge increment includes both seepage ard runoff accretion, the runoff part must be subtracted to determine the seepage. 

The drainage area between Edgewick and North Bend gaging stations 

is 15.8 square miles. The runoff accretion from this area was estimated to be the same as the average of Taylor Creek, a tributary to 

Cedar River, and Griffin Creek, a tributary to Snoqualmie River.

OQ 

Oz

z o

(/> O 

* UJ

ct w

200

150

100

50

1530 1540 1550 

INDEX OF STAGE OF MASONRY POOL(S), IN FEET

1560

FIGURE 4. Relation of monthly mean discharge increment to South Fork 

Snoqualmie River between Edgewick and North Bend (/) to index of stage 

of Masonry Pool (8) for a range of precipitation indicesi (P), 1962-64. 

Numbers are precipitation indices, in inches.
SEEPAGE, CHESTER MORSE LAKE AND MASONRY POOL, WASH. J17

200 300 400 500

DISCHARGE INCREMENT TO CEDAR RIVER (C),

IN CUBIC FEET PER SECOND

600

FIGURE 5. Relation of monthly mean discharge increment to South Fork 

Snoqualmie River between Edgewick and North Bend (/) to a comparable 

value for Cedar River between Cedar Falls and Landsburg (C), 1962-64.

The estimated runoff accretion from the intervening drainage area 

was subtracted from the difference in discharge between Edgewick 

and North Bend, and the remainder was assumed to be seepage to 

South Fork Snoqualmie River. Table 4 presents a summary of the 

computations for the 1957-64 water years.

COMPABISON OF SEEPAGE ESTIMATES

Total seepage to the Cedar and South Fork Snoqualmie Rivers for 

the 1957-64 water years compares favorably with the estimated seepage from Chester Morse Lake and Masonry Pool. During this time 

span, the average seepage was computed to be about 180 cfs to the 

Cedar River and about 50 cfs to the South Fork Snoqualmie River, or 

a total of 230 cfs. Average seepage from Chester Morse Lake and 

Masonry Pool for the same period was computed to be about 220 cfs.

Although the two estimated seepage totals agree closely, within less 

that 5 percent, the amounts for some years do not agree as well. The 

greatest difference about 25 percent occurred in 1962. T?,ble 5 

summarizes the data used in making the comparisons.
J18 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

TABLE 4. Estimated seepage to South Fork Snoqualmie River between Edgewick

and North Bend, 1957-64

[Quantities in cubic feet per second]

Water year

1957

1958_______________

1959

1960. _ _ _

1961. ___ _ _

1962 _ _

1963_______.__.._-_

1964. ____________

Average---. _ _

Discharge increment between Edgewick 

and North Bend

From 

equation 1

1

103 

79 

154 

125 

117 

70 

93

From 

equation 2

2

117

81 

152 

139 

131 

79 

95

Average

3

110 

80 

153 

132 

124 

74 

94 

2 133

112

Surface 

runoff

4

63

48 

83 

76 

76 

55 

58 

77

67

Estimated 

seepage » 

(rounded)

5

50 

30 

70 

60 

50 

20 

40 

60

50

1 Estimated seepage (col. 5) for given water year is cols. 3 minus 4.

2 Measured discharge increment.

TABLE 5. Comparison of estimated seepage from Chester Morse Lake and Masonry 

Pool with that to Cedar and South Fork Snoqualmie Rivers, 1957-64

[Quantities in cubic feet per second]

Water year

1957

1958_________ - _ ___ _

1959_-___-.____-_ _ _ _____ _

1960__ _______ _ ___ ___ _____

1961

1962__ _______________________

1963

1964__ _______________________

Estimated seepage

To Cedar 

River

190 

170 

200 

190 

180 

140 

180 

150

180

To South 

Fork Snoqualmie River

50 

30 

70 

60 

50 

20 

40 

60

50

Total

240 

200 

270 

250 

2?0 ieo 2^0

210

2?0

Estimated 

seepage from 

Chester Morse 

Lake and 

Masonry Pool

220 

190 

300 

200 

230 

200 

190 

230

220

The computed discharges listed in some of the columns of tables 2-4 

may imply a greater accuracy than is warranted. The final seepage 

rates those in the last column of each table and in table 5 have been 

rounded to two significant figures, or to the nearest 10 cf s.

In general, errors in the computed seepage from Cl Q.ster Morse 

Lake and Masonry Pool probably are less than ±40 cfs and are based 

on the assumption that the errors in gaging-station record? and in estimated discharges for ungaged areas are no greater than ±2 percent 

and ±10 percent, respectively. Errors in the computed seepage to
SEEPAGE, CHESTER MORSE LAKE AND MASONRY POOL, WASH. J19

Cedar and South Fork Snoqualmie Rivers probably are less thp.n ±40 

cfs and ±20 cfs, respectively.

CHANGES IN RUNOFF REGIMEN FOLLOWING THE 

BOXLEY CREEK WASHOUT IN 1918

Streamflow records for Cedar River near Landsburg, South Fork 

Snoqualmie River at North Bend, and North and Middle Forl-s Snoqualmie River near North Bend in water years 1908-26 and 1930-32 

along with precipitation records collected at Cedar Lake, Landsburg, 

and Snoqualmie Falls during the same period were used to determine 

changes in runoff regimen following the Boxley Creek washout in 

1918.

Double-mass curves have been used to check the consistency of 

annual mean discharges of both Cedar River near Landsburg and 

South Fork Snoqualmie River at North Bend with records of p^ecipitation and runoff. Cumulative discharge for Cedar River was plotted 

against cumulative precipitation values obtained by averaging the records at Cedar Lake and Landsburg. Likewise, cumulative discharge 

for South Fork Snoqualmie River was plotted against cumulative precipitation values obtained by averaging the catches at Cedar Lake 

and Snoqualmie Falls. The double-mass curves for water years 1908- 

26 and 1930-32 are shown in figure 6.

If a change in runoff regimen occurred in 1918, after the Boxley 

Creek washout, the double-mass curve should show a break in slope 

at that time. The curves for both streams do show a definite, break 

in the relation between cumulative precipitation and discharge after 

1918. The Cedar River curve shows a flattening of slope, indicating 

less runoff per unit of precipitation, whereas the South Fork Snoqualmie River curve shows a steepening of slope, indicating the opposite 

effect. The two trends suggest that changes in seepage occurred 

relative to the pre-1918 conditions.

As a check, double-mass curves were drawn comparing cumulative 

discharges of the Cedar River and the South Fork Snoqualmie River 

with similar values obtained by averaging the annual mean discharges 

of North and Middle Forks Snoqualmie River near North Bend. 

These two curves (fig. 7) show post-1918 changes similar to those 

shown by discharge and precipitation in figure 6.

Statistical tests of the significance of the breaks in slope on the 

double-mass curves were computed in a manner described by Searcy 

and Hardison (1960, p. 51). An analysis of variance indicates that 

all breaks are significant at the 5-percent level. Thus, from a statistical evaluation, changes in the regimen of Cedar and South Fork 

Snoqualmie Rivers did occur between 1918 and 1919.
10

Projected c

E

So

R

5 10 

CUMULATIVE AVERAGE PRECIPITATION, IN HUNDR

FIGURE 6. Relation of cumulative discharge for Cedar Riv

lative average precipitation for Landsburg and Cedar 

discharge for South Fork Snoqualmie River at North 

precipitation for Snoqualmie Falls and Cedar Lake, 190
THOUSANDS IN DISCHARGE, CUMULATIVE 

SECOND PER FEET CUBIC OF 
J22 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

Quantitative values for seepage from Cedar River barin to South 

Fork Snoqualmie River have been obtained from records collected 

during water years 1908-26 and 1930-32. Annual mean discharges 

for Cedar River near Landsburg and South Fork Snoqualmie River 

at North Bend prior to the Boxley Creek washout in 1918 were each 

related to the average precipitation and average discharges used in 

the double-mass curve analysis. Simple regressions computed by the 

least-squares method express the relation between variables that would 

have existed if no change had occurred in 1918.

The following model was used in computing the regression between 

discharge and precipitation.

where

T annual mean discharge of Cedar River near Landsburg or

South Fork Snoqualmie River at North Bend, 

P=the respective average annual precipitation used in the

double-mass curves, and 

<z, 5= constants. 

The regressions for water years 1908-18 were computed as :

P (3) 

for the Cedar River near Landsburg, and

IF=- 100+ TAP (4)

for the South Fork Snoqualmie River at North Bend. The two curves 

and the points upon which they are based are shown in figure 8.

For the discharge-versus-discharge relations, the following model 

was used:

log Y=a+~b log X 

where

T = annual mean discharge of Cedar River or £outh Fork

Snoqualmie, 

X= average of the annual mean discharges of North and Middle

Forks Snoqualmie River, and 

#, &= constants. 

The regressions for water years 1908-18 were computed as :

log r= -0.64+1.18 log X (5) 

for Cedar River and

log r= -0.15 + 0.96 log X (6)

for South Fork Snoqualmie River. The curves in figure 9 express 

these two relations.
SEEPAGE, CHESTER MORSE LAKE AND MASONRY POOL, WASH. J23

1000

900

800

O 700 

m

600

500

400

300

EXPLANATION

Discharge of Cedar River near 

Landsburg versus average 

precipitation at Cedar Lake 

and Landsburg

Discharge of South Fork 

Snoqualmie River at North 

Bend versus average precipitation at Cedar Lake 

and Snoqualmie Falls

50 60 70 80 90 

ANNUAL AVERAGE PRECIPITATION (P), IN INCHES

100 110

FIGURE 8. Relation of annual mean discharge for Cedar River neai* Landsburg 

(Y) to average of annual precipitation at Cedar Lake and Landsburg (P), 

and of annual mean discharge for South Fork Snoqualmie River at North 

Bend (Y) to average of annual precipitation at Cedar Lake and Snoqualmie 

Falls (P), 1908-18.

The above regressions represent the relation between the variables 

prior to the Boxley Creek washout. If these relations were assumed 

to continue after the washout, estimates of annual discharge based 

on them would represent the hypothetical values under unchanged 

conditions. Differences between the estimated and measured discharges could then be considered to represent changes in the amount 

of seepage from the Cedar Biver drainage to the South Fork 

Snoqualmie River.
J24 CONTRIBUTIONS TO THE HYDROLOGY OP THE UNITED STATES

2000

Si 1000

500

250

A 

log ' -0.64 + 1.18 log X

2000

UJ O 

C3 O 

o: LJ 

< e/)

250

log r=-0.15 + 0.96 log X

500 1000 2000 ~~ 500 1000

AVERAGE OF ANNUAL MEAN DISCHARGES (X). IN CUBIC FEET PER SECOND

2000

FIGURE 9. Relation of annual mean discharge, 1908-18. A, Cedar River near 

Landsburg (Y) to average of Middle and North Forks Snoqualnie River (X). 

B, South Fork Snoqualmie River at North Bend (Y) to avenge of Middle 

and North Forks Snoqualmie River (X).

Annual mean discharges for Cedar Eiver were estimated for water 

years 1919-26 and 1930-32 using the two appropriate equations. The 

two estimates for each year were averaged, and the resulting values 

were considered to represent the hypothetical annual mean discharges 

for Cedar Eiver in the absence of a change in runoff regimen. Table 

6 shows a comparison of the measured and estimated discharges for 

the 11-year period. For all years of record, the estimated discharge 

was greater than the actual discharge.

The same procedure was followed for South Fork Snoqualmie 

River, but the computations show that estimated discharges were less 

than actual discharges (table 7).

For the 11-year period, 1919-26 plus 1930-32, the average annual 

seepage from Cedar River basin was computed as about 80 cfs, and 

the average annual seepage to South Fork Snoqualmie River was 

computed as about 60 cfs. Although the two average values agree 

closely, the comparison for individual years is not very close. Estimates for the 1920 and 1931 water years show the largest differences.

The computed discharges listed in some of the coluirris of tables 

6 and 7 may imply as did some of those in tables 2 to 4 a greater 

accuracy than is warranted. The final seepage value? have been 

rounded to two significant figures, or to the nearest 10 cfs. The errors
SEEPAGE, CHESTER MORSE LAKE AND MASONRY POOL, WASH. J25

TABLE 6. Decreases in seepage from Cedar River above Landsburg, 1919-26 and

1930-32

[Quantities in cubic feet per second]

Water year

1919 

1920 ___ _ _ _.._.

1921 _____ __ _ .-

1922 __ _ __ _ _ _

1923 _ __ __. _ _

1924___________-__-

1925 

1926 

1930 

1931 

1932.-. ---_--_--.--

Average. ___ _

Estimated discharge, based on relationships 

for 1908-18

From 

equation 5

791 

715

928 

727 

724 

669 

784 

562 

494 

598 

934

721

From 

equation 3

868 

797 

896 

668 

678 

561 

643 

563 

457 

611 

775

683

Average

830 

756 

912 

698 

701 

615 

714 

562 

476 

604 

854

702

Measured 

discharge

742 

654 

784 

626 

650 

556 

619 

470 

449 

483 

771

619

Decrease 

in seepage 

(rounded) '

90 

100 

130 

70 

50 

60 

100 

90 

30 

120 

80

80

i Decrease in seepage equals estimated discharge minus measured discharge.

in the computed seepages determined separately by the two independent methods are considered to be small because the final seepage 

values are in disagreement by only 20 cf s.

TABLE 7. Increases in seepage to South Fork Snoqualmie River above North Bend,

1919-26 and 1930-32

[Quantities in cubic feet per second]

Water year

1919_-____-_____- .

1920_____ __ _______

1921. __ _ __ _ __ __

1922_--__--____.___

1923 .

1924 _ _ 

1925 

1926 

1930 

1931-- - . .

1932_____._____.__.

Estimated discharge, based on relationship 

for 1908-18

From 

equation 6

535 

493 

610 

500 

498 

467 

531 

405 

365 

426 

613

495

From 

equation 4

578 

518 

596 

464 

474 

413 

449 

382 

336 

434 

547

472

Average

556 

506 

603 

482 

486 

440 

490 

394 

350 

430 

580

485

Measured 

discharge

627 

502 

719 

518 

551 

476 

626 

433 

363 

431 

698

540

Increase 

in seepage 

(rounded) '

70 

0 

120 

40 

60 

40 

140 

40 

10 

0 

120

60

i Increase in seepage equals measured discharge minus estimated discharge.
J26 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

SUMMARY

Interchange of water between the Cedar and South Fork Snoqualmie Rivers was computed for two periods, water years 1908-26 

plus 1930-32 and water years 1957-64. For the 1957-64 period, seepage from Chester Morse Lake and Masonry Pool was determined and 

compared with seepage to Cedar and South Fork Snoqu?,lmie Rivers. 

For the 1908-26 and 1930-32 period, the changes in regimens of the 

two rivers were compared before and after the Boxley Croek washout.

Average seepage from Chester Morse Lake and Masor.ry Pool was 

about 220 cfs for water years 1957-64. For the same period, average 

seepage to Cedar River between Cedar Falls and Landsburg and to 

South Fork Snoqualmie River between Edgewick and North Bend 

was about 180 and 50 cfs respectively, giving a total of 230 cfs.

A definite change in runoff regimen occurred in both the Cedar 

River above Landsburg and South Fork Snoqualmie River above 

North Bend after the Boxley Creek washout in 1918. For the combined 11-year period 1919-26 plus 1930-32, the changes in seepage 

from Cedar River basin and to South Fork Snoqualmie River averaged about 80 and 60 cfs respectively.

REFERENCES CITED

Huntting, M. T., and others, compilers, 1961, Geologic map of Washington: 

Washington Div. Mines and Geology.

Mackin, J. H., 1941a, A geologic interpretation of the failure of the Cedar Reservoir, Washington: Washington Univ. [Seattle] Bng. Expt. Sta. Series Bull. 

107, 30 p.

 1941b, Glacial geology of the Snoqualmie-Cedar area, Wasl ington: Jour. 

Geology, v. 49, no. 5, p. 449-481.

lie-Williams, Mary, 1955, Seattle Water Department History, 1854-1954: Seattle, 

Wash., Dogwood Press, 262 p.

Phillips, E. L., 1965, Climate of Washington : U.S. Weather Bur., Climatography 

of the United States, no. 60-45, 27 p.

Searcy, J. K., and Hardison, C. H., 1960, Double-mass curves: U.S. Geol. Survey 

Water-Supply Paper 1541-B, 66 p.

U.S. Weather Bureau and U.S. Soil Conservation Service, 1961, Normals of precipitation and evapotranspiration, State of Washington: Seattle, Wash., 

U.S. AVeather Bur. and U.S. Soil Conserv. Service, 15 p.

U.S. GOVERNMENT PRINTING OFFICE: 1967