magnitude and frequency of floods in western oregon · a method for estimating the magnitude and...

Magnitude and Frequency of Floods in Western Oregon

By D. D. Harris, Larry L. Hubbard, and Lawrence E. Hubbard

U.S. GEOLOGICAL SURVEY Open-File Report 79-553

Prepared in cooperation with theOREGON DEPARTMENT OF TRANSPORTATION,HIGHWAY DIVISION

1979

UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY H. William Menard, Director

For additional information write to:

U.S. GEOLOGICAL SURVEY P.O. Box 3202 Portland, Oregon 97208

ContentsPage

ABSTRACT ------------------------------------------ 1

INTRODUCTION --------------------------------------- 1

Purpose and scope --------------------------------- 2

Previous studies ----------------------------------- 2

GENERAL DESCRIPTION OF THE AREA ---------------------- 2

ANALYTICAL TECHNIQUE ------------------------------- 4

Drainage-basin characteristics --------------------------- 4

Magnitude and frequency of floods at gaged sites -------------- 5

Regression analysis --------------------------------- 5

APPLICATION OF RESULTS ------------------------------ 6

Method used ------------------------------------ 6

Evaluation of estimates ------------------------------ 8

Illustrative problems -------------------------------- 10

Limitations ------------------------------------- 13

SUMMARY ----------------------------------------- 14

SELECTED REFERENCES -------------------------------- 15

in

IllustrationsPage

Plate 1. Map showing locations of gaging stations in western Oregon - - - - In pocket

2. Map showing isopluvial of 2-year, 24-hour precipitation in tenthsof an inch for western Oregon --------------------- In pocket

Figure 1. Index map showing flood-frequency regions of western Oregon - - 3

2. Graph showing maximum observed peak discharges in relationto drainage areas ----------------------------- 9

3. Graph showing flood-frequency curve developed by regionalanalysis for the Willamette Region ------------------ 12

Tables

Page

Conversion factors ----------------------------- v

Table 1. Regional flood-frequency equations ------------------- 7

2. Basin characteristics used in multiple regression ----------- 16

3. Maximum discharges at gaging stations used in western Oregonflood-frequency analysis ------------------------ 23

4. Discharges for selected flood frequencies at gaging stations - - - - 29

IV

Conversion factors for inch-pound system and International System Units (SI)

[For use of those readers who may prefer to use metric units rather than inch-pound units, the conversion factors for the terms used in this report are listed below:]

Multiply inch-pound units By To obtain metric unit

Length

inch (in.) foot (ft) mile (mi)

25.40 0.3048 1.609

millimeter (mm) meter (m) kilometer (km)

Area

square mile (mi2 ) 2.590 square kilometer (km2 )

Specific combinations

cubic foot per second (ft 3 /s) 0.0283 cubic meter per second(m3 /s)

Afagnitude and Frequency of Floods in Western Oiegon

By D. D. Harris, Larry L. Hubbard, and Lawrence E. Hubbard

ABSTRACT

A method for estimating the magnitude and frequency of floods is presented for un regulated streams in western Oregon. Equations relating flood magnitude to basin charac teristics were developed for exceedance probabilities of 0.5 to 0.01 (2- to 100-year recur rence intervals). Separate equations are presented for four regions: Coast, Willamette, Rogue-Umpqua, and High Cascades.

Also presented are values of flood discharges for selected exceedance probabilities and of basin characteristics for all gaging stations used in the analysis. Included are data for 230 stations in Oregon, 6 stations in southwestern Washington, and 3 stations in north western California. Drainage areas used in the analysis range from 0.21 to 7,280 square miles. Also included are maximum discharges for all western Oregon stations used in the analysis.

INTRODUCTION

A special need for updated flood-frequency information for Oregon results from recent emphasis on flood-plain zoning, flood insurance, and design adequacy of hydraulic struc tures. Studies of flood magnitude and frequency are based on analyses of available streamflow records. Very few long-term records for streams with less than 10 mi2 of drainage area were available when the last flood-frequency reports were prepared for Oregon by the U.S. Geological Survey. Many data have been collected since a small-stream flood-data program was started in 1952 in cooperation with the Oregon State Highway Commission (now Oregon Department of Transportation, Highway Division). This program was ex panded in 1965, through funds provided by the U.S. Forest Service, to include many pre viously unsampled areas in national forests. Inclusion of these data has enlarged the flood- data base, both areally and in range of basin size.

This analysis was limited to western Oregon, because of the large number of gaging- station records available for the western part of the State and the deficiency of peak-flow information for many areas of the eastern part. Limiting the analysis to western Oregon allows timely use of urgently needed flood information in a rapidly developing area. An eastern Oregon flood-frequency analysis will be presented in a later report.

In describing flood frequency in this report, the term "exceedance probability" is used in preference to the term "recurrence interval." However, both terms are used in most of the tables, graphs, and illustrative problems. For example, a flood with a 0.01 exceedance probability is a flood that has one chance in a hundred of being exceeded in any one year. This is a 100-year flood under the "recurrence interval" terminology.

1

Purpose and Scope

This report describes methods for evaluating the magnitude and frequency of floods at sites on streams with natural flow. The purpose is to provide a method to estimate flood magnitude and frequency at ungaged sites in western Oregon. The report is based on data from all unregulated streams (or data from regulated streams prior to their regulation) where gaging stations have been operated for at least 10 years.

Records at the gaging stations provided the basis for estimating flood-peak discharges and frequency of occurrence at ungaged sites. Stations used in this analysis have records ranging from 10 to 70 years. Peak-flow records of 230 gaging stations are available for western Oregon, 73 of which are crest-stage gaging stations that have drainage areas as small as 0.21 mi2 . Locations of the gaging stations are shown on plate 1.

The magnitude of a flood is influenced by physiographic characteristics of the drainage basin. These characteristics, which include climate, topography, geography, soils, and vege tation, are referred to as basin characteristics throughout this report.

Multiple-regression analysis was used to correlate flood discharges with selected basin characteristics and to develop appropriate regional relation equations. Although many basin characteristics were determined and investigated, the number retained in the equations was reduced for simplicity and practicality, without undue sacrifice of the accuracy of the flow estimate. The characteristics used were selected on the basis of the results of prior investi gations, ease of determination, and the results of the regression analysis.

Previous Studies

A previous flood-frequency report by Hulsing and Kallio (1964), covering the Pacific slope basins in Oregon and lower Columbia River basin, contains peak-flow records for 173 gaging stations in western Oregon. Of these, 22 are for crest-stage gaging stations on small streams.

Regression equations for flood-peak discharge are presented in a report, "Evaluation of the streamflow data program in Oregon" (Lystrom, 1970), that is based on data from all stations with 10 or more years of record of unregulated flow through the 1967 water year (October 1966 through 1967).

GENERAL DESCRIPTION OF THE AREA

The area studied includes all that part of Oregon west of the crest of the Cascade Range. The principal physiographic areas in western Oregon include the Coast and Cascade Ranges and the Willamette, Rogue, and Umpqua River valleys, as shown in figure 1.

The western slope of the Coast Range is influenced directly by ocean-spawned storms and weather. Annual precipitation is commonly 60 to 80 in. in the area; some coastal mountains receive as much as 200 in. (U.S. Weather Bureau, 1964). Snowmelt is not nor mally a major factor in flooding.

In the Willamette, Rogue, and Umpqua River valleys, high streamflows are created by storms from the Pacific Ocean. High flows in some streams draining from the Cascade Range frequently are caused by runoff from snowmelt in combination with direct rainfall runoff. The proportional contributions from each source are difficult, if not impossible, to identify. Annual precipitation amounts range from lows of less than 20 in. in the Rogue River basin to more than 100 in. in the lower elevations of the Cascade Range.

In the higher elevations of the Cascade Range, flood peaks are predominantly from snowmelt runoff combined with heavy rainfall runoff. Much of the precipitation in this area falls as snow in late fall, winter, and early spring. Annual precipitation ranges from less than 20 in. in the south to more than 100 in. in the north.

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ANALYTICAL TECHNIQUE

Flood-frequency characteristics for gaged sites were related to drainage-basin charac teristics by the multiple-regression technique to define regional flood magnitude- frequency relations.

Drainage-Basin Characteristics

The drainage-basin characteristics computed for each gaging station and used as an independent variable in the multiple-regression study are listed in table 2 at the back of the report and are defined as follows:1. Drainage area (A), in square miles, the total contributing area upstream from the

gaging-station site, as shown in the latest Geological Survey water-resources data reports.

2. Main-channel slope (S), in feet per mile, determined from elevations at points 10 and 85 percent of the distance along the channel from the gaging station to the divide. This index was described and used by Benson (1962b, 1964).

3. Main-channel length (L), in miles, from the gaging station to the basin divide,measured in accordance with guidelines given by the U.S. Water Resources Council (1968) or taken in part from the various River Mile Index publications prepared by the Hydrology and Hydraulics Committee of the Pacific Northwest River Basins Commission (1963-68).

4. Mean basin elevation (E), in feet above mean sea level, determined by the gridmethod from quadrangle map of a practical scale by laying a grid over the map, recording the elevation at each grid intersection, and averaging those elevations. The grid spacing was selected to give at least 25 intersections within the basin boundary.

5. Area of lakes and ponds (ST), expressed as a percentage of the drainage area, determined from the most recent quadrangle maps available.

6. Forest cover (F), expressed as the percentage of the drainage area covered by forests, as shown on the most recent quadrangle maps available.

7. The values of soils index (SI), determined from a map compiled from computed values of soils indexes according to procedures described by the Soil Conserva tion Service (1959, 1964). Data for these computations were derived from soils- association and land-use maps included in the Columbia North-Pacific Framework Study (unpub. manuscript). Data were also furnished by the Soil Conservation Service staff, State office, Portland, Oreg.

8. Azimuth (AZ), in degrees from north, of a straight line connecting points 85 and 10 percent of distance from gage to divide.

9. Latitude at gage (LAT). Latitude of stream-gaging station in decimal degrees.10. Longitude of gage (LONG). Longitude of stream-gaging station in decimal degrees.11. Mean annual precipitation (P), in inches, determined from an isohyetal map pre

pared by the National Weather Service River Forecast Center, Portland, Oreg., (U.S. Weather Bureau, 1964), using adjusted climatological data (1930-57) and values derived by correlation with other physiographic factors.

12. Precipitation intensity (I), defined as the maximum 24-hour rainfall having a recur rence interval of 2 years (2-year, 24-hour rainfall), expressed in inches. These values were determined by the grid method, using plate 2 which was prepared by U.S. National Oceanic and Atmospheric Administration (NOAA) (1973).

13. Temperature index (TI), the mean minimum January temperature, in degrees Fah renheit, in the basin. This value was determined from a U.S. Weather Bureau publication (Sternes, 1960).

Magnitude and Frequency of Floods at Gaged Sites

Methods for estimating flow frequencies at gaged sites, presented in "Guidelines for Determining Flood Flow Frequency," published by the U.S. Water Resources Council (1977) were used in this study. Data from 230 gaging stations in Oregon, 6 in south western Washington, and 3 in northern California, representing basins that have virtually natural flow conditions and 10 years or more of record, provided the basic dependent variables (annual peak discharge). Historic flood information was used, when available, to supplement the systematic gaging-station record. For each station, the logarithms of the annual peaks were used to compute the mean, standard deviation, and skew co efficient that describe a log-Pearson Type-Ill distribution.

Frequency data from the log-Pearson Type-Ill frequency curve for each station are presented in table 4 at the back of the report. It lists flows for exceedance probabi lities of Q0 . 5 (2 yr), Q0 .2 (5 yr), Q0 . 10 (10 yr), Q0 . 04 (25 yr), Q0 . 02 (50 yr), and Q0>01 (100 yr). The figures in parentheses are the corresponding recurrence intervals. As an example, if a flow of 900 ft3 /s is shown under an exceedance probability of 0.5 in the table, it means that there is a 50 percent chance that the flow at the gaging station will exceed 900 ft 3 /s in any one year. Another way of describing the same peobability is that a 900-ft 3 /s flow has a 2-year recurrence interval. A flow shown under an exceedance probability of 0.01 has a 1 percent chance of being exceeded in any one year. (It could be described as having a 100-year recurrence interval.)

Regression Analysis

Multiple-regression analyses were used to define equations expressing flood discharges of selected exceedance probabilities as a function of the basin characteristics. This relation may be expressed by the mathematical model

QT=K Ci a C2 b C3 C . . . Cnnin which Qj is the discharge for a selected exceedance probability, T; K is a regression constant; C l , C 2 , C 3 , and Cn are basin characteristics; and a, b, c, and n are regression coefficients. A step-backward regression analysis of the variables was made using a STATPAC data matrix. The least significant independent variable (basin characteristic) was deleted at each step. An evaluation of the standard errors for the various steps of the multiple regression was made to determine the most suitable regional equation.

The program computes the logarithms of the regression constant, the exponents of the independent variables, and the logarithm of the standard error of estimate.

Data for the 230 gaging stations in western Oregon were used for the "first try" of regression equations. The residuals (the difference between the logarithms of the flood discharges estimated from the gaging-station record and the logarithms of the flood dis charges estimated from the regression equations) were plotted on a map of western Oregon. This plot and topographic maps were evaluated to delineate the boundaries of the four flood-frequency regions selected for use in the regression analysis. These four regions (Coast, Willamette, Rogue-Umpqua, and High Cascades) are shown in figure 1. Flood-frequency equations were then developed for each of these regions.

Few gaging-station data for the extreme southern end of the Oregon coast are usable for flood-frequency analysis. Peak-flow and basin-characteristics data for three gaging stations at the extreme northern end of the California coastal area were used to supplement the Oregon coast data. To determine the flood-frequency equations for the Coast Region, data from 37 stations in Oregon and three in California were used in the multiple-regression analysis.

To develop the flood-frequency equation for the Willamette Region, peak-flow and basin-characteristics data from six stations across the Columbia River in Washington were used to supplement data from 105 stations in Oregon.

Data from 60 Oregon stations in the Rogue-Umpqua Region and from 28 Oregon stations in the High Cascades Region were used to develop the respective regional equations.

The final regression equations for each of the four regions are shown in table 1. These equations relate floods having exceedance probabilities of Q0 5 , Q0 2 > QOIO' Q004 , Q002 , and Q001 to selected basin characteristics in each of the flood-frequency regions shown in figure 1. The general form of the equation and the standard error of estimate is also shown in table 1.

Drainage area (A) and precipitation intensity (I) were selected as the most signi ficant independent variables for the flood-frequency equation for the Willamette Region. Drainage area, precipitation intensity, and area of lakes and ponds (ST) were selected as the most significant independent variables for the Coast and Rogue-Umpqua Regions. For the High Cascades Region, drainage area, area of lakes and ponds, pre cipitation intensity, and nonforested areas proved to be the most significant indepen dent variables to use in the flood-frequency equation. In the frequency equation for the High Cascades Region, nonforested area is expressed as a function of forest cover (F).

Soils index and azimuth were not used in the final regression analysis. These two basin characteristics were not found to be significant in preliminary analysis, which was based strictly on data for Oregon stations.

APPLICATION OF RESULTS

Method Used

The design flow or peak discharge for selected exceedance probabilities (or recurrence intervals) can be estimated for sites on unregulated streams in Oregon by using the method described below.1. Locate the site on the map (pi. 1, in pocket) and determine which region it is in and

if it is on a gaged stream.a. If the site is at a gaging station used in this analysis or is on the same stream as

a gaging station used in this analysis and has a drainage area within 5 percent of that at the gaged site, USE THE GAGING-STATION DATA DIRECTLY FROM TABLE 4.

b. If the site is on a stream that has a gaging station listed in this report but has a drainage area estimated at 5 to 25 percent different from that at the gaging station, adjust the peak discharges of the gaged site (table 4) on the basis of drainage area by using the following equation: Qu =Qg (Au/Ag)a , where Qu and Qg are the discharges at the ungaged and gaged sites, Au and Ag are the drainage areas, and "a" is an exponent. The value for "a" can be selected from the expo nents for the drainage area (A) given in the equation in table 1.

2. If the site is on an ungaged stream or if the site is on a gaged stream shown in table 4 but the drainage area at the site differs by more than an estimated 25 percent from the drainage area at the gaging station, thena. Inspect the applicable regional equations in table 1 and identify which basin

characteristics are needed to estimate discharge for selected exceedance probabi lities.

Table {.-Regional flood-frequency equations

General form of equation QT=KAa(ST+l)b(101-F)cId where Qj=discharge for selected exceedance probability,K = regression constant,A = drainage area, in square miles,

ST = area of lakes and ponds, in percent,F = forest cover, in percent, andI = precipitation intensity, in inches.

(When the functions of F and ST are not significant, the factors (ST+l)b and (101-F)C are omitted from the equation.)

Exceedanceprobability

(RDL/

Qo.s(2)Qo. 2 (5)QQ j(10)

Qo.04 (25)Qo.o 2 (50)Q0 . 01 (100)

Equation

Percentstandard

error

(1) COAST REGION (40 stations)

4.59A°-96 (ST+l)-°-4S I 1 - 916.27A°-9S (ST+l)-°-4S I 1 - 9S7.32A°-94 (ST+l)-°-4s I 1 - 978.71A°-93 (ST+l)-°-4S I 1 - 999.73A°-93 (ST+l)-°-44 I 2 - 0110.7A°-92 (ST+l)-°-44 I 2 - 02

333233343537

(2) WILLAMETTE REGION (111 stations)

Qo.s(2)Qo. 2 (5)Q0 j(10)

Qo.04 (25)Qo.02 (50)Q0 . 01 UOO)

8.70A0 - 87 ! 1 - 7115. 6A°-88 I 1 - 5521. 5A0 - 88 ! 1 -4630.3A0 - 88 ! 1 - 3738.0A0 - 88 ! 1 - 3146.9A0 - 88 ! 1 - 25

3333

33343637

(3) ROGUE-UMPQUA REGION (60 stations)

Qo.s(2)Qo. 2 (5)Qo.i( 10 )

Qo.04 (25)Qo.02 (50)Qo.oidOO)

24.2A°-86 (ST+1)- 1 - 16 I 1 - 1536.0A°- 88 (ST+1)- 1 - 2S I 1 - 1544.8A°- 88 (ST+1)- 1 - 28 I 1 - 1456.9A°- 89 (ST+1)- 1 - 31 I 1 - 1266.7A°- 90 (ST+1)- 1 - 33 I 1 - 1077.3A°-90 (ST+1)- 1 - 34 I 1 - 08

4443444649

51

(4) HIGH CASCADES REGION (28 stations)

Qo.s(2)Qo. 2 (5)QoaOO)Qo.o4 (25)Qo.o 2 (50)Qo.oiOOO)

4.75A°-90 (ST+l)-°-62 (101-F)0 - 11 I 1 - 178.36A°- 86 (ST+l)-°- 81 (lOl-F) 0 - 08 ! 1 - 3011.3A0 - 8s (ST+l)-°-92 (101-F) 0 - 07 I 1 - 3715.4A°- 83 (ST+1)- 1 - 03 (101-F)°-OS I 1 -4618.8A°-82 (ST+1)- 1 - 10 (101-F)°-04 I 1 - S222.6A°- 81 (ST+1)- 1 - 17 (101-F)°-03 I 1 - S7

55505359

6672

]_/ Numbers in parentheses refer to recurrence intervals in years.

7

b. Determine the appropriate basin-characteristic values as follows:Drainage area (A) Compute the drainage area, in square miles, within the

surface-water divide upstream from the desired site on the stream, using the best available topographic map, generally U.S. Geological Survey ll/2- or 15- minute quadrangle maps. Determine the drainage area by planimetering.

Area of lakes and ponds (ST) Compute the percentage of the total drain age area occupied by lakes and ponds, using a planimeter or a transparent grid overlay on T/2- or 15-minute topographic maps. In the equation, the value (ST+1) is used to avoid introducing zero values that cannot be accom modated in the equations used in this study.

Forest-cover index (F) Compute the percentage of the total drainage area covered by brush or trees, as indicated by the extent of green overprint (vegetation) shown on U.S. Geological Survey topographic maps.

The value of 101-F is used in the equation for the High Cascades Region to reflect the percentage of "nonforest" cover. The value 101 is used rather than 100 to avoid having to deal with the logarithm of zero values. The use of nonforest cover rather than forest cover provided the most prac tical equation fit.

Precipitation intensity (I) Determine the maximum 2-year, 24-hour precipi tation, in inches, on plate 2 of this report by using the grid method as des cribed under drainage-basin characteristics section for mean basin elevation on page 11.

c. Compute the peak discharge for the desired exceedance probabilities, or recur rence intervals, directly through the use of the appropriate regional equations.

d. Compare, for reasonableness, the estimated peak discharge values particularlythose for small probabilities (long recurrence intervals) with (1) maximum peak discharges for nearby streams (table 3 at the back of the report) and (2) other maximum observed discharges (fig. 2).

Peak discharges for exceedance probabilities between 0.5 and 0.01, other than those shown in the equations, can be determined either by plotting station values from table 4 or by plotting computed values from the equa tions on probability paper and drawing a smooth curve through the points. Peak discharges for other exceedance probabilities can then be estimated from the curve.

Extrapolation of peak discharges for exceedance probabilities greater than 0.01 (the 100-year flood) exceeds the limits of this study. Such derived values should be qualified and used judiciously.

Evaluation of Estimates

Peak discharges estimated from the regression equation can be evaluated for credibi lity by comparison to maximum observed peak discharges for streams with similar drain age areas in the same regions. Maximum observed peak discharges for all gaging stations used in the analysis are listed in table 3. Figure 2 shows the maximum observed peak discharges for long-term gaging stations in western Oregon in relation to drainage area. Figure 2 also shows a maximum envelope curve developed by Matthai (1969). For drain age areas between 1 and 200 mi 2 , the equation for the Matthai curve is Q=11,OOOA°-61 . Also shown are the observed discharges that have the highest unit runoff measured in

Oregon and the highest peak discharges observed throughout the United States. Figure 2 can be used to judge the reasonableness or uniqueness of flood-peak discharges esti mated by use of flood-frequency equations. For example, if the 0.02 (50-year) flood discharge estimated for a site with a drainage area of 10 mi2 was 10,000 ft 3 /s, a com parison with figure 2 indicates the discharge could be too high for western Oregon. The user might then check the computations and also decide that the regional equations are not applicable if the basin being studied is not typical of the region.

On some streams the geology of the drainage basin can have a large effect on the magnitude of the flood peak. An example is the Clearwater River above Trap Creek near Toketee Falls (14314500) in the Umpqua River basin. Most of the Trap Creek drainage is located in a geologic area of recent volcanics (Wells and Peck, 1961). Ob served flood peaks at the Clearwater River above Trap Creek gaging station are much smaller in magnitude than are indicated by the regional equation. It appears that

1,000,000

UPPER LIMIT OF 1965 DATA (MATTHAI, 1969)

A North Carolina

EXPLANATION

Record peaks National

Record peaks Oretqon

1. Butter Creek tributary near Echo, OR2. Lane Canyon near Ecnp, OR3. Meyers Canyon near Mitchell, OR

O Maximum peaks at all stations in Western Oregon with at least 50 years of record and 10 square mile drainage areas, or 25 years of record and 10 square mile drainage area

10 100 DRAINAGE AREA, IN SQUARE MILES

1000 10,000

Figure 2.-Maximum observed peak discharges in relation to drainage areas.

peaks at this gaging station are greatly diminished because of temporary ground-water storage. Numerous springs along the Clearwater River above Trap Creek tend to support this assumption. Other streams in similar recent volcanic geology will probably respond in the same manner. Therefore, the geology map should be consulted to evaluate the possibility of the actual flood peaks differing from those indicated by the regional equation because of the local geology.

Some of the older peak discharges used in this analysis were based on once or twice daily gage readings which may be lower than the actual instantaneous peak and there fore would not represent the highest discharge during the day. The effect of such peaks on the analysis has not been thoroughly evaluated; however, because only about 2 percent of the peaks were determined in this manner, their use likely has little influence on the resulting equations.

Weather stations are sparsely located in the High Cascades Region; therefore, the precipitation intensity values shown on plate 2 are probably somewhat less reliable for the High Cascades than for the other three flood-frequency regions, where there are more precipitation gages. This lack of basic precipitation data probably contributed to the higher standard error for the High Cascades Region. This higher standard error may also be attributed to the lack of regional snowpack information. No basin charac teristics for snowpack were available for the regression analysis; however, it would be reasonable to assume that snowpack would influence the flood-frequency equations for the High Cascades.

Illustrative Problems

The method for estimating discharges of selected recurrence intervals is shown by thefollowing examples:

Example 1. (Determining a single flood in an ungaged area)Determine the discharge for an exceedance probability of 0.01 (100-year flood) for

a site in the Coast Region, where the drainage area is 20 mi2 and the area of lakes and ponds is 1.2 percent of the drainage area. According to the precipitation intensity map (pi. 2, in pocket), the site is at a location where the average 2-year, 24-hour precipita tion intensity over the drainage basin is 4.0 in.

From the Coast Region equation (see table 1), the 0.01 exceedance probability flood is:Q0 . 01 =10.7A0 -92 (ST+l)-°-44 I 2 -02

=(10.7)(20)°-92 (2.2)-°-44 (4) 2 -02

=(1Q.7)(15.7)(16.4)(1.41)

= 1,950 ft3 /s

Example 2. (Determining two floods in an ungaged area)Determine the discharge for exceedance probabilities of 0.5 and 0.1 (2- and 10-year

floods) for a site on a stream in the High Cascades Region. The drainage area is 9.8 mi2 ; the area of lakes and ponds (ST) is 2.5 percent; forest cover (F) is 96 percent; and the average 2-year, 24-hour precipitation intensity is 3.2 in.

From the High Cascades Region equation, the 0.5 exceedance probability flood is:

.17Q05 =4.75A0 - 90 (ST+l)-°-62 (101-F)0 - 11 I 1J=4.75(9.8)0 - 90 (2.5+l)-°-62 (101-96)0 - 11 (3.2) 1 - 17

=(4.75)(7.80)(0.46)(1.19)(3.90) =79 ft 3 /s

10

From the High Cascades Region equation, the 0.1 exceedance probability flood is:

= 11.3(9.8)0 - 85 (2.5+l)-°-92 (101-96)0 - 07 (3.2) 1 - 37

= 11.3(6.96)(0.32)(1. 12)(4.92)= 139 ft3 /s

Example 3. (Developing a flood-frequency curve)Develop a flood-frequency curve for a site in the Willamette Region. The drainage

area is 230 mi2 ; and the average 2-year, 24-hour precipitation intensity is 3.1 in.Based on the above basin characteristics, develop a flood-frequency curve by com

puting the flood discharges for Q0 5 , Q0 2 , Q 0 A , Q04 , Q 0 . 02 > m & QO.OI exceedance probabilities, as shown below:

=8.70(230)°- 87 (3.1) 1 - 71

=(8.70)(1 13)(6.92) =6,800 ft 3 /s

= 15.6(230)°-88 (3.1) 1 - 55

=(15.6)(120)(5.78) = 10,800 ft 3 /s

Q0 . 1 =21.5(A)°- 88 (I) 1 -46 =21.5(230)°- 88 (3.1) 1 - 46

=(21.5)(120)(5.22) = 13,500 ft 3 /s

Q0 . 04 =30.3(A)°- 88 (I) 1 - 37=30.3(230)°- 88 (3.1) 1 - 37

=(30.3)(120)(4.71) = 17,100 ft 3 /s

=38.0(230)°- 88 (3.1) 1 - 31

=(38.0)(120)(4.40) =20,100 ft 3 /s

Q0 . 01 =46.9(A)°-88 (I) 1 -25=46.9(230)°- 88 (3.1) 1 - 25

=(46.9)(120)(4.11) =23,100 ft 3 /s

11

Then plot the flood discharges on probability paper at the respective exceedance positionsand draw a smooth curve through the points, as shown in figure 3.Example 4. (Determining the exceedance probability or recurrence interval for a selecteddischarge)

Using the curve developed in example 3 (fig. 3), determine the exceedance probability and recurrence interval for a peak discharge of 16,000 ft3 /s.

At the 16,000-ft3 /s discharge magnitude on the graph, project horizontally to the frequency curve. Project up vertically at the intersection with the curve and read an ex ceedance probability of 0.05 and project down vertically and read a recurrence interval of 20 years.

EXCEEDANCE PROBABILITY

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20,000

10,000 -

5,000

2,000

1,0005 10 25

RECURRENCE INTERVAL, IN YEARS

100

Figure 3. Flood-frequency curve developed by regional analysis for an example computation at an ungaged site in the Willamette Region (example 3).

12

Example 5. (Determining a flood on a stream near an existing gaging station)Determine the discharge for an exceedance probability of 0.01 (the 100-year flood)

for a site upstream from the existing long-term gaging station on Salmon Creek near Oakridge (No. 1414650) in the Willamette Region. The gaged site has a drainage area of 117 mi2 , and the selected site has a drainage area of 100 mi2 . Therefore, the drainage areas differ by more than 5 percent but less than 25 percent. The flood for an exceed ance probability of 0.01 at the gaged site (table 4) is 14,000 ft3 /s. Use the relationship Q =Q (Au/Ag)a . The exponent "a" for an exceedance probability of 0.01 in the Willamette Region is 0.88.

Qu =Qg (Au/Ag)

=(14,000)(0.85) =(14,000)(0.87)

= 12,200 ft3 /s

0.88

Limitations

The equations in this report, developed through regional analysis, are usable, under certain limitations, for estimating flood magnitudes of selected exceedance probabilities or recurrence intervals at ungaged sites in western Oregon.

The equations are based on data representing natural flood conditions and are not appli cable to streams where storage or artificial structures have modified the flow appreciably such as sites downstream from large storage reservoirs. In general, the equations are not appli cable at any site where flow from 10 percent or more of the drainage basin is controlled.

Ranges of characteristics used for defining equations for each region are:

Region

1.2.3.4.

Drainagearea(A)

(mi2 )

Area oflakes and

ponds(ST)

(percent)

Forestcover

(F)(percent)

Precipitationintensity

(I)(in.)

Coast 0.27- 667 0-18.81 - - 3.0-6.2Willamette 0.37-7,280 - - - - 2.3-5.0Rogue-Umpqua 0.75-3,939 0- 4.40 - - 2.5-6.2High Cascades 0.21- 650 0- 3.65 48-100 1.4-4.3

Extrapolation beyond the limits of the data used for defining relationships is not advisable. Such extrapolations could produce erroneous discharge values. However, if extrapolations are made they should be used judiciously and qualified accordingly.

13

SUMMARY

The study describes a method for estimating the magnitude and frequency of floods on natural streams in western Oregon. The equations were developed by regional multiple- regression analysis. An evaluation of the differences between the flood discharges estimated from the gaging-station records and the discharges determined from the general regression equation were used to help delineate boundaries for four flood-frequency regions in western Oregon.

Drainage-area size was the most significant basin characteristic for all four of the flood- frequency regions in western Oregon. Precipitation intensity was also a significant basin characteristic for all the regions. By utilizing only the drainage-area size and precipitation intensity for the Willamette Region, the standard error of estimate ranged from 33 to 37 percent, as shown in table 1. The area of lakes and ponds was used in addition to drainagearea size and precipitation intensity in the flood-frequency equation for the Coast and Rogue- Umpqua Regions. The standard error of estimate ranged from 32 to 37 percent in the Coast Region and from 43 to 51 percent in the Rogue-Umpqua Region.

The standard errors of estimate were greatest in the High Cascades Region, where the range was 50 to 72 percent. Four basin characteristics (drainage area, precipitation inten sity, area of lakes and ponds, and forest cover) were required to reduce the standard error significantly in this region.

When used within the range of data used to define the relationships, the regional flood- frequency equations provide reasonably accurate estimates of floodflows of specified exceedance probabilities.

14

SELECTED REFERENCES

Benson, M. A., 1962a, Evolution of methods for evaluating the occurrence of floods: U.S.Geological Survey Water-Supply Paper 1580-A, 29 p.

____1962b, Factors influencing the occurrence of floods in a humid region of diverseterrain: U.S. Geological Survey Water-Supply Paper 1580-B, 64 p.

____1964, Factors affecting the occurrence of floods in the Southwest: U.S. Geological Survey Water-Supply Paper 1580-D, 72 p.

Columbia Basin Inter-Agency Committee, 1963, River mile index-Willamette River, ColumbiaRiver basin, Oregon: Hydrology Subcommittee report, 57 p.

_____1966, River mile index - Umpqua River and tributaries, Umpqua River basin, Oregon:Hydrology Subcommittee report, 25 p.

____1967, River mile index - Rogue River, Pacific slope basin, Oregon: Hydrology Subcommittee report, 28 p.

Friday, John, 1974, Cres,t-stage gaging stations in Oregon, A compilation of peak datacollected from October 1952 to September 1974: U.S. Geological Survey open-filereport, 160 p.

Hardison, C. H., 1971, Prediction error of regression estimates of streamflow characteristics atungaged sites, in Geological Survey Research, 1971: U.S. Geological Survey ProfessionalPaper 750-C, p. C228-C236.

Hulsing, Harry, and Kallio, N. A., 1964, Pacific slope basins in Oregon and lower ColumbiaRiver basin, part 14 of Magnitude and frequency of floods in the United States: U.S.Geological Survey Water-Supply Paper 1689, 320 p.

Lystrom, D. J., 1970, Evaluation of the streamflow-data program in Oregon: U.S. GeologicalSurvey open-file report, 28 p.

Matthai, H. F., 1969, Floods of June 1965 in South Platte River basin, Colorado: U.S.Geological S.urvey Water-Supply Paper 1850-B, 64 p.

Pacific Northwest River Basins Commission, 1968, River mile index - Coastal tributaries,Pacific coast basin, Oregon: Hydrology and Hydraulics Committee report, 84 p.

Riggs, H. C., 1968, Some statistical tools in hydrology: U.S. Geological Survey Techniques ofWater-Resources Investigations, book 4, chap. Al, 39 p.

_____1968, Frequency curves: U.S. Geological Survey Techniques of Water-Resources In vestigations, book 4, chap. A2, 15 p.

_____1973, Regional analyses of streamflow characteristics: U.S. Geological Survey Techniques of Water-Resources Investigations, book 4, chap. B3, 15 p.

Sternes, G. L., 1960, Climates of the States, Oregon, in Climatography of the United States:U.S. Weather Bureau, no. 60-35, p. 17.

Thomas, D. M., and Benson, M. A., 1970, Generalization of streamflow characteristics fromdrainage-basin characteristics: U.S. Geological Survey Water-Supply Paper 1975, 55 p.

U.S. Dept. of Agriculture, Soil Conservation Service, 1959, State engineering handbook, Oregon,sec. 4 in Hydrology: 10 p.

_____ 1964, Watershed planning, pt. 1 in Watershed planning, sec. 4 in Hydrology: U.S.Dept. Agriculture SCS Handb.

U.S. National Oceanic and Atmospheric Administration, 1965, Climates of the States Washing ton, of Climatology of the United States no. 60-45: Washington, D. C., 27 p.

_____1973, Precipitation-frequency atlas of the Western United States, NOAA Atlas 2,volume X - Oregon: Silver Spring, Md., 43 p.

U.S. Water Resources Council, 1967 [rev. 1977], A uniform technique for determining floodflow frequencies: Washington, D. C., U.S. Water Resources Council Bulletin 15, 15 p.

____1977, Guidelines for determining flood flow frequency: Washington, D.C., WaterResources Council Bulletin 17A, 26 p.

U.S. Weather Bureau, 1964, Mean annual precipitation, 1930-57, State of Oregon: Portland,Oreg., U.S. Soil Conservation Service Map M-4161.

Wells, F. G., and Peck, D. L., 1961, Geologic map of Oregon west of the 121st meridian: U.S.Geological Survey Miscellaneous Investigations Map 1-325, scale 1:500,000.

15

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(1) COAST

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)

Table 2. Basin characteristics used in multiple regressions continued

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(2) W1LLAMETTE REGION

1413500014137000141388001413865014141500

1414350014144000141446001414480014144870

1414490014145500141460001414650014147500

1414800014148700141503001415100014151500

1415200014152500141539001415450014155500

1415600014156500141570001415800014159000

1415920014159500141612001416150014161600

1416200014162500141630001416500014165500

100262

8.1747.922.3

10823.3.51258.50

52.7392113117246

924.44118186

52.5

134072.15.69211270

85.095.3529

2030348

160208.39

24.1.37

75.0930

47.6177

1340

129.092.2

370.0186.0196.0

57.0120.0240.0107.0710.0

259.075.0135.089.7112.0

64.5817.072.043.789.0

42.059.0

628.098.382.3

49.442.829.334.344.6

137.0123.0

1690.0258.01490.0

145.058.3101.039.813.7

24.837.63.610.513.6

23.910.71.3

32.71.3

14.542.133.024.751.0

53.31.2

18.727.018.0

78.516.43.3

24.031.7

21.3

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1610810560

43802150

40904080446041403760

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33702120263028502630

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26.2 429032.5 40801.19.51.0

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0.000.000.00.18

0.00

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4.23

1.380.000.000.000.00

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1.00.77

0.000.000.00

0.00.27

0.000.00.19

95.692.292.098.498.0

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3626223431

262122

4.34.13.43.53.5

4.23.74.03.63.5

3.53.43.43.63.5

3.63.63.53.43.3

3.21.42.63.03.0

2.63.03.0

22.522.022.029.423.0

21.021.023.022.023.0

24.023.023.020.021.0

20.021.020.023.022.5

24.022.025.022.024.0

25.027.026.0

22

Table 3.-Maximum discharges at ganinu stations used in western Oregon flood-freuuency analysis

Station number

1153085011531000115330001413400014134500

1413500014137000141388001413885014141500

1414350014144000141446001414480014144870

1414490014145500141456901414600014146500

1414740014147500141480001414870014150300

1415100014151500141520001415250014153900

1415450014155500141560001415650014157000

1415800014158250141585001415900014159200

1415950014161200141615001416160014162000

Yec

Station name rec

ars f 3rd Date

MIDDLE FK SMITH RIVER TRIB. NR OBRIEN,OR 12 12-22-64MIDDLE FK SMITH RIVER AT GASQUET,CA 16 12-22-6*LOPEZ CREEK NEAR SMITH RIVER, CA 12 03-02-72SALMON RIVER NEAR GOVERNMENT CAMP, OREG. 51 12-23-64SALMON RIVEH BELOW LINNEY CREEK, OREG. 23 03-31-31

SALMON RIVER AT WELCHES, ORtG. 13 03-31-31SANDY RIVER NEAR MARMOT, OREG. 65 12-22-64BLAZED ALDER CREEK NEAR RHODODENDRON, OREG. 13 12-22-64BULL RUN R NR MULTNOMAH FALLS, OREG. 10 01-20-72LITTLE SANDY RIVER NEAR BULL HUN, OREG. 58 12-20-74

WASHOUGAL RIVER NR WASHOUGAL, WA 28 01-20-72LITTLE WASHOUGAL R NR WASHOUGAL, WA 17 12-22-64GROENVELD CREEK NEAR CAMAS, WA 15 12-22-64MIDDLE FORK WILLAMETTE RIVE* NR OAKRIDGE OREG i b 12-22-6*MIDDLE FK WILLAMETTE R TRIB NR OAKRIDGE , OREG. 16 12-22-6*

HILLS CR AB HILLS CR RES, NR OAKRIDGE , OREG. 18 12-22-64M F WILLAMETTE R AB SALT CR., NR OAKRIOGE, OREG 26 12-28-45SWAMP CREEK NEAR MCCREDIE SPRINGS, OREG. 10 12-22-64SALT CREEK NEAR OAKRIDGE , ORtG. 19 10-29-50SALMON CREEK NEAR OAKRIDGE , OREG. 50 12-22-64

TUMBLE CREEK NEAR WESTF IP, OREG. 11 12-22-64N FK OF M FK WILLAMETTE R NR OAKR IDGE ,OREG. 46 12-22-64MF WILLAMETTE R NR OAKRIDGE OREG 39 12-28-45FERN CREEK NEAR LOWELL,OREG. 21 02-10-61FALL CR. NEAR LOwELL, OREG. 13 01-21-72

FALL CREEK BL WINBERRY CR N« FALL CR,OREG. 30 12-11-56LITTLE FALL CREEK NEAR FALL CREEK OREG. 13 12-28-45MF WILLAMETTE R AT JASPER OREG 10 11-23-09COAST FORK WILLAMETTE RIVER AT LONDON, OREG. 41 12-22-6*PRATHER CREEK NEAR DISSTON, OREG. 12 02-10-61

ROW RIVER ABOVE PITCHER CREEK, NEAR DORENA,OREG. 41 12-22-64ROW RIVER NEAR COTTAGE GROVE, OREG. 11 12-28-45MOSBY CREEK NEAR COTTAGE GROVE, OREG. 11 12-28-45MOSBY CR AT MOUTH, NR COTTAGE GROVE, OREG. 30 12-22-64COAST FK WILLAMETTE R AT SAGINAW OREG. 19 02-20-27

WILLAMETTE RIVER AT SPRINGFIELD, OREG. 36 12-29-45HACKELMAN CREEK NR UPPER SODA, OREG. 16 12-11-56MCKENZIE RIVER AT OUTLET OF CLEAR LAKE, OREG. 32 12-23-64MCKENZIE R AT MCKENZIE BRIDGE, OREG. 49 01-06-23S FK MCKENZIE R AB COUGAR LK NR RAINBOW, OREG. 19 12-22-64

SOUTH FORK MCKENZIE RIVER NR RAINBOW, OREG. 16 12-28-45LOOKOUT CR TRI NO 3 NR BLUE RIVER OREG. 11 12-20-57LOOKOUT C NR BLUE R OREG 19 12-22-64LOOKOUT CR TRIB NR BLUE R,OREG. 15 12-11-56BLUE RIVER NR BLUE RIVER, OREG. 30 12-22-64

Discharge (ft'/s)

10241100

57013003670

1300061400261086104280

2260024300

10339800

82

1070034000

120450011600

982440081800

5212100

247006110

9400012500

326

331002140085201410032500

140000102

33001650018400

2450052

666075

19600

23

Table 3. Maximum discharges at gaging stations used in western Oregon flood-frequency analysis continued

Station number

14162500 14163000 14165000 14165500 14166500

14167000 14169700 14170500 14171000 14171500

14172000 14172300 14173500 14174000 14174100

14178000 14178800 14179000 14181500 14181700

14182500 14183000 14184900 14185000 14185800

14185900 14186000 14187000 14187500 14188800

14189000 14189500 14190000 14190200 14190500

14190600 14191000 14198100 14192200 14192500

14192800 14193000 14193300 14194000 14195000

Ye o

Station name re«

ars f >rd Date

MCKENZIE R NR VIDA OREG 38 12-28-45 GATE CREEK AT VIDA. OREG. 24 l?-22-64 MOHAWK RIVER MR SPRINGFIELD* OREG. 31 IP-22-64 MCKENZIE RIVER NEAR C06URG,OREG. 18 IP-29-45 LONG TOM RIVFR NEAR NOTI. 03EG. 41 1P-P2-55

COYOTE CREEK NEAR CROW, OREG. 36 02-10-61 BEAR CREEK NEAR CHESHIRE. OREG. 20 01-15-74 HOCK CREEK NEAR PHILOMATH* OREG. 18 IP-24-64 MARYS RIVER NEAR PHILOMATH, OREG. 36 1P-P2-64 MUDDY CREEK NEAR CORVALLIS. OREG. 10 12-22-64

CALAPOOIA R AT HOLLEY 0»EG 41 12-22-64 BUTTE CR NR PLAINVIEW,OREG. 14 11-24-60 CALAPOOIA RIVER AT ALBANY, OREG. 36 12-22-55 WILLAMETTE RIVER AT ALBANY, OREG. 56 12-04-61 COX CREEK AT ALBANY, OPEG. 16 12-21-64

NORTH SANTIAM R BEL BOULDER CR NR DETROIT, OREG. 51 12-22-64 WIND CP NR DETROIT. OREG. 23 12-21-64 8REITEN8USH R A8V CANYON CR NR DETROIT, OREG. 44 IP-22-64 NORTH SANTIAM RIVER AT NIAGARA .OPEG. 26 11-22-09 N SANTIAM RIVER TRIB NR GATES, OREG. 17 01-30-65

LITTLE NORTH SANTIAM RIVER NEAR MEHAMA, OREG. 44 12-22-64 NORTH SANTIAM RIVER AT MEHAMA, OREG. 37 12-28-45 SHEEK CREEK NEAR CASCAOI A .OREG. 24 IP-22-64 SOUTH SANTIAM RIVER BELOW CASCADIA, OREG. 41 12-22-64 MIDDLE SANTIAM R NEAR CASCAOI A , OREG. 13 12-22-64

QUARTZVILLE CREEK NEAR CASCADIA, OREG. 13 IP-22-64 MIDDLE SANTIAM RIVER NEAR FOSTER, OREG. 16 12-P8-45 WILEY CREEK NEAR FOSTER, OREG. 26 01-21-72 SOUTH SANTIAM RIVER AT WATERLOO, OREG. 45 12-22-64 THOMAS CREEK NEAR SCIO.OREG. 14 12-22-64

SANTIAM R AT JFFFERSON OREG 23 11-21-21 LUCKIAMUTE RIVER NEAR HOSKINS, OREG. 42 IP-14-46 LUCKIAMUTE R AT PEDEE OREG 30 12-P2-64 WAYMIRE CR NR FALLS CITY, OREG. 15 12-22-64 LUCKIAMUTE RIVER NEAR SUVER. OREG. 42 IP-22-64

SOAP CREEK TRIBUTARY NEAR SJVER»OREG. 24 03-02-72 WILLAMETTE RIVER AT SALEM, OREG. 51 IP-04-61 GLENN CREEK NEAR SALEM, OREG. 25 12-21-55 GIBSON CREEK NEAR SALEM, OREG. 15 IP-23-64 SOUTH YAMHILL RIVER NEAR WILLAMINA, OREG. 42 12-22-64

SOUTH YAMHILL R TRIB NR WILLAMINA ,ORF.G. 23 12-21-55 WILLAMINIA CREEK NEAR WILLAMINA ,OREG. 43 12-22-64 MILL CREEK NEAR WILLAMINA, OREG. 15 12-22-64 SOUTH YAMHILL RIVER NEAR WHITESON,OREG. 36 12-23-64 HASKINS CREEK NEAR MCMINNVILLE, OREG. 21 03-31-31

Discharge (ft 3 /s)

64400 7140 13000 88200 6990

10600 530

2500 13600 6040

12600 647

32700 340000

1070

26700 231

16900 63200

132

36000 76600

116 27600 22900

36500 41800 9640

95200 27400

202000 5560 15700

598 32900

86 500000

172 434

19600

420 10BOO 6170

47200 610

24


Station number

1419650014197000141973001419850014199700

1420000014201000142015001420200014202500

1420300014203500142038001420400014P04100

14P0450014205500142060001420650014207500

1420800014208500142088501420900014209100

1420950014209900142100001421080014211500

1421180014223500142435001424500014248700

1425150014299000142995001430020014301000

1430140014301500143025001430300014303600

Years of

Station name record

NORTH YAMHILL RIVER NR PIKE» OREG. 11NORTH YAMHILL R AT PIKE. OREG. 25PANTHER CHEEK NEAR CARLTON,OREG. 16MOLALLA R AB PC NR WILHOIT, OREG. 41HULL CR NR COLTON,OREG. 13

MOLALLA R NR CAMBY» OREG. 44PUDDING PIVER NEAR MOUNT ANGEL* OREG. 26BUTTE CREEK AT MONI TOR, OREG. 22PUDDING RIVER AT AURORA. OREG. 38TUALATIN RIVFR NR GASTON,OR£G. 20

SCOGGIM CREEK NEAR GASTON. OxEG. 34TUALATIN RIVF.R NEAR DILLEY, OREG. 37BEAVER CREEK NEAP GLENWOOD.OKFG. 17GALES CREEK NR GALES CREEK, OREG. 17BATEMAN CHEE.K NEAR GLENWOOD ,OREG. 25

GALES CREEK NEAR FOREST GROVE, OREG. 22EAST FORK DAIRY CREEK AT MOUNTA INDALE » OREG. 11MCKAY CREEK NEAR NORTH PLAINS, OREG. 11TUALATIN RIVER AT FARMINGTON,OREG. 19TUALATIN RIVF.R AT WEST LINN, OREG. 46

CLACKAMAS RIVFR AT BIG BOTTOM, OREG. 50OAK GROVE FORK AT TIMOTHY MEADOWS, OREG. 16EAST FORK SHELLROCK CR NR GOVT CAMP, OREG. 10OAK GROVE FORK ABOVE POWERPLANT INTAKE, OREG. 43KINK CR NR GOVERNMENT CAMP, OREG. 19

CLACKAMAS RIVER ABOVE THREE LYNX CREEK, OREG. 38DUBOIS CREEK AT ESTACADA.OREG. 20CLACKAMAS RIVER AT ESTACADA, OREG. 47ROCK CR NR BORING OREG. 10JOHNSOM CHEEK AT SYCAMORE, OREG. 36

SALTZMAN CREEK AT PORTLAND, OREG. 25KALAMA R BL ITALIAN CR NR KALAMA,WA 26DELAMETER CREEK NEAR CASTLE ROCK, WA 19COWEMAN RIVER NEAR KELSO, WA 22BEAR CREEK NEAR SVENSEN.OREG. 10

YOUNGS RIVER NEAR ASTORIA, OREG. 31so FK NECANICUM RIVER NEAR SEASIDE, OREG. i&ASBURY CREEK NEAR CANNON BEACH, OREG. 25OAK RANCH CR NR VERNONIA OREG. 10NEHALEM RIVER NEAR FOSS. OREG. 37

PATTERSON CREEK AT BAY CITY, OREG. 17WILSON RIVER NEAR TILLAMOOK, OREG. 46TRASK RIVER NEAR TILLAMOOK, OREG. 37NESTUCCA RIVER NEAR MCMINNVILLE, OREG. 16NESTUCCA R NR BEAVER OREG 11

Discharge Date (ft3 Is)

02-10-49 478012-21-55 9530IP-21-64 612IP-22-64 2430011-24-60 293

12-22-64 4360012-22-64 1670001-21-72 731001-07-23 27900IP-21-55 8170

IP-21-55 5320IP-22-64 17100OP-02-63 472IP-22-64 397012-21-55 145

02-17-49 6410OP-17-49 142002-17-49 210012-22-55 24200IP-23-33 29300

12-22-64 1120001-07-23 97012-24-64 11801-07-23 5000IP-21-64 94

03-31-31 3480012-22-64 50803-31-31 6080011-20-62 28012-22-64 2620

12-21-55 30601-20-72 1790001-19-62 242011-20-62 972001-11-72 342

02-10-49 475001-25-64 3040OP-10-61 31412-21-64 51401-20-72 46900

01-28-65 30001-20-72 3600011-20-21 3000012-22-33 148001-11-72 29400

25


Station number

1430370014305500143061001430640014306500

1430670014306800143068101430683014307500

1430755014307610143077001430800014308500

1430870014308900143090001430950014310000

1431070014310900143110001431120014311500

1431200014312100143122001431230014313500

1431450014315500143160001431650014316700

1431750014317600143178001431800014318500

1431860014319200143195001432060014320700

Years of

Station name recordDischarge

Date (ft 3 /s)

ALDER BROOK NR ROSE LODGE.OREG. 23 01-21-72 218SILETZ RIVER AT SILETZ, OREG. 60N FK ALSEA R AT ALSEA. OREG. 18

11-20-21 4080012-22-64 14100

FIVE RIVERS NR FISHER. OREG. 14 01-21-72 17200ALSEA RIVER NEAR TIDEWATER. OREG. 37 12-22-64 41800

NEEDLE BRANCH NEAR SALAD0.03EG. 15 01-11-72 64FLYNN CREEK NEAR SALADO.OREG. 15 01-21-72 139DEF.R CREEK NEAP SALAOO.OREG. 15 01-28-65 201LYNDON CREEK NEAR WALDPORT .OREG. 11 01-28-65 162LAKE CREEK AT TRIANGLE, OR 32 01-15-74 4640

DEADWOOD CREEK TRI8 AT ALPHA, OR 12 12-22-64 89SIUSLAW R TRI8 NR RAINROCK ,OREG. 20 01-21-72 62JACKSON CREEK NEAR TILLER, OREG. 21SOUTH UMPQUA RIVER AT TILLER, OREG. 38ELK CREEK NEAR DREW, OREG. 22

12-22-64 2110012-22-64 6020012-22-64 8880

DAYS CREFK AT DAYS CREEK, OREG. 17 02-21-56 3450CANYON CREEK AT CANYONVlLLE. OREG. 15 IP-21-55 3810COW CREEK NEAR AZALEA. OREG. 48 01-15-74 10600WEST FORK COW CREEK NEAR GLENDALE ,OREG. 21COW CREEK NEAR RIDDLE, OREG. 22

SOUTH MYRTLE CREEK NEAR MYRTLE CREEK, OREG. 17W F FROZEN CR NR MYRTLE CREEK, OREG. 14NORTH MYRTLE CREEK NEAR MYRTLE CREEK, OREG. 21OLALLA CREEK NEAR TENMILE. OREG. 17LOOKINGGLASS CREEK AT BROCKWA Y ,OREG. 21

SOUTH UMPQUA RIVER NEAR BROCKWAY, OREG. 46PARROTT CREEK AT ROSEBURG.OREG. 25DEER CREEK NEAR ROSE8URG,OREG. 17MARKS CREEK NEAR ROSEBURG.OREG. 17NORTH UMPQUA R 8L LEMOLO LK NR T FALLS, OREG. 27

CLEARWATER RIVER AS TRAP CR NR TOKETTE FLS, OR 49NORTH UMPQUA RIVER AT TOKETEE FALLS OREG. 24FISH CP AT 6IG C R STATION NR T FLS, OREG. 28NO UMPQUA R AB COPELAND CR NR T FLS.OREG. 27STEAMBOAT CREEK NEAR GLIDE, OREG. 21

N UMPQUA RIVER AB ROCK CR NR GLIDE OWEG 23ROCK CREEK NEAR GLIDE, OREG. 17CAVITT CREEK NEAR PEEL, OREG. 12LITTLE RIVER AT PEEL, OREG. 22NORTH UMPQUA RIVER NEAR GLIDE, OREG. 20

NORTH UMPQUA R TRIB NR GLIDE OREG. 12SUTHERLIN CR AT SUTHERLIN OREG. 12NORTH UMPQUA R. AT WINCHESTER. OREG. 11CABIN CR TRIB NR OAKLAND, OREG. 19CALAPOOYA CREEK NEAR OAKLAND. OREG, 18

12-22-64 1570010-29-50 41100

12-11-56 305012-26-55 30001-20-64 326001-03-66 916012-26-55 35000

12-23-64 12500012-21-55 290IP-28-65 7910OP-10-61 26006-09-33 1190

12-23-64 102012-31-42 508012-22-64 12100IP-22-64 4070012-22-64 S1000

12-22-55 6800012-22-64 2280012-11-56 1060012-11-56 2110011-22-09 94000

12-26-55 188OP-10-61 225012-22-64 15000011-23-61 24611-23-61 26600

26


Station number

14321000 14321900 143P2000 14322400 14322700

14323200 14323300 14324500 14324600 14324700

14324900 14325000 14326500 14326600 14326800

14327000 14327100 14327240 143P7400 14327490

14327500 14328000 14330500 14331000 14332000

14333000 14333500 14335000 14335500 14337500

14338000 14339000 14339200 14339500 14341500

14342500 14343000 14347000 14353000 14353500

14359000 14359500 14361300 14362000 14363000

Ye c

Station name rec<

ars f 3rd Date

UMPQUA RIVER NEAR ELKTON, 0*EG. 70 12-23-64 YONCALLA CR NR YONCALLA OREG. 12 02-10-61 ELK CREEK NEAR DRAIN* ORES. 22 02-10-61 PASS CREEK NEAR DRAIN, ORES. 12 02-10-61 BEAR CREEK NEAR DRAIN, OREG. 14 02-10-61

TENMILE CREEK NEAR LAKESIDE , OREG. 19 12-26-64 EEL CREEK AT LAKESIDE, OREG. 19 01-17-74 WEST FORK MILLICOMA RIVER NEAR ALLEGANY, OREG. 22 ll-P.4-60 S FK COQUILLE R AB PANTHER CR, NR ILLAHE,OREG. 14 IP-22-64 SOUTH FORK COQUILLE RIVER NEAR ILLAHE,OREG. 16 12-22-64

SF COQUILLE R NR POWERS OREG 14 12-22-64 SOUTH FORK COQUILLE RIVER AT POWERS, OREG. 58 12-22-64 MIDDLE FK COQUILLE R NR MYRTLE POINT OREG. 17 10-31-24 GETTYS CREEK NEAR MYRTLE POINT, OREG. 24 OP-10-61 NORTH FORK COQUILLE RIVER NR FAIRVIEW»OREG. 13 03-02-72

N FK COQUILLE R NR MYRTLE POINT, OREG. 24 12-23-64 GEIGER CREEK NEAR BANDON,OREG. 16 02-10-61 MIL8URY CREEK NEAR PORT ORFORD,OREG. 11 01-04-66 DRY RUN CR NR PORT ORFORD»OREG. 22 01-18-71 NATIONAL CREEK NEAR UNION CREEK, OREG. 11 12-22-64

ROGUF RIVER ABOVE BYBEE CREEK, NR UNION CR, OREG 22 11-29-42 ROGUE RIVER ABOVE PROSPECT, OREG. 55 12-22-64 S FK ROGUE R AB IMNAHA CR NR PROSPECT OREG. 18 IP-01-42 IMNAHA CREEK NEAR PROSPECT, OREG. 18 02-13-45 SOUTH PORK ROGUE RIVER NEAR PROSPECT, OREG. 34 IP-22-64

MIDDLE FK ROGUE RIVER NR PROSPECT OREG. 30 12-22-55 RED BLANKET CREEK NEAR PROSPECT, OREG. 50 02-13-45 ROGUE R BL S FK ROGUE R NR PROSPECT OREG. 34 12-22-64 SOUTH FORK BIG BUTTE CR NR BUTTE FALLS, OREG. 56 IP-22-64 bIG BUTTE CREEK NFAR MCLEOD»OREG. 20 12-22-55

ELK CREEK NEAR TRAIL, OREG. 31 12-22-64 ROGUE R AT DODGE RR NR EAGLE POINT, OKEG. 38 12-22-64 CONSTANCE CR NR SAMS VALLEY OREG. 10 12-02-62 S FK LITTLE BUTTE CR AT BIG ELK RG STA,OR 22 05-25-42 SOUTH FORK LITTLE BUTTE CR NR LAKECREEK,OREG. 55 12-02-62

NO FK LITTLE BUTTE CR AT F L NR LAKECREEK ,OREG. 59 07-17-59 NO FK LITTLE BUTTE CR NR LAKECREEK, OWEG. 51 12-22-64 LITTLE BUTTE CREEK AB EAGLE POINT OREG. 10 10-30-24 W FK ASHLAND CREEK NEAR ASHLAND, OREG. 19 01-15-74 EAST FK ASHLAND CREEK NEAR ASHLAND, OREG. 19 01-15-74

ROGUE RIVER AT RAYGOLD, NEAR CENTRAL POINT, OREG 71 12-23-64 EVANS CR NR BYBEE SPRINGS NR ROGUE R OREG. 13 02-20-27 JONES CREEK NEAR GRANTS PASS, OREG. 25 OP-22-56 APPLEGATE RIVER NEAR COPPER, OREG. 38 01-15-74 APPLEGATE RIVER NEAR RUCH, OREG. 31 02-20-27

Discharge (ft3 /s)

265000 IS70

19000 10300

674

3330 316

8100 8840 12000

29600 48900 31800

245 7760

38400 206 286 213 475

4430 22400 2170 500

7010

3230 9900

55000 12600 8950

19200 87600

950 145

7660

163 1750 7000 4780 5630

131000 11100 1350

29800 20000

27

Table 3.-Maximum discharges at gaging stations used in western Oregon flood-frequency analysis-continued

Station number

1436600014368500143698001437000014370200

1437150014372300143725001437500014375500

14377000143775001437780014378000

Years of

Station name record

APPLEGATE RIVER NEAR APPLEGATE, OREG. 38POWELL CREEK NEAR WILLIAMS, OREG. 124UTCHF.RKNIFE CREEK NEAR WONDER, OREG. 16SLATE CREEK AT WONDER, OREG. 19ROUND PRAIRIE CREEK NR WILDERVILLE.OREG. 16

GRAVE CREEK AT PEASE 6PIDGE.NEAR PLACER, OREG. 34ROGUE RIVER NEAR AGNESS.OREG. 16E F ILLINOIS RIVER NEAR TAKILMA ,OREG. 39SUCKER CREEK MEAR HOLLAND, ORES. 24¥ FK ILLINOIS R RL ROCK CR NR 09PIEN. OR 22

ILLINOIS RIVER AT KERBY, OREG. 35DEF-R CREEK NEAR DRYDEN, OREG. 15SNAILBACK CR NR SELMA,ORFG. 17ILLINOIS R NP SELMA, OREG. 12

Discharge Date (ft'/s)

01-15-74 3720001-18-53 111001-03-66 43212-22-64 465001-03-66 375

12-22-64 624012-23-64 29000012-22-64 1570012-22-64 1750012-24-64 16100

12-22-55 5680001-18-53 500012-21-64 32912-22-64 160000

28

Table 4. Discharges for selected flood-frequencies at gaging stations

Station number

Peak discharge, in cubic feet per second, t'or selected exceedance probabilities (indicated recurrence interval)

0.50 (2-yr)

0.20 (5-yr)

0.10 (10-yr)

0.04 (2 5-yr)

0.02 (50-yr)

0.01 (100-yr)

(1) COAST REGION

11530850115J1000115330001424870014251500

1429900014299500143002001430100014301400

1430150014302500143030001430360014303700

1430550014306100143064001430650014306700

1430680014306810143068301430750014307550

1430761014323200143233001432450014324600

1432470014324900143250001432650014326600

1432680014327000143271001432724014327400

4014600

152147

2960

1900£12285

27900109

1740012900

72714500

88

2090051208680

2060030

6310355

223053

252190164

538037ao

4850131001530014800

137

498013400

95111107

6021100

286207

3590

2360253415

35200164

22600169001130

20100132

266007350

1200027300

39

8613588

340071

372910219

71504900

6650168002190021100

190

681021000

1^1190158

7425500

393249

3980

2650277509

39800205

26000195001440

24000163

302008S801420031700

45

101156112

424082

463340253

32405560

7760190002620025000

223

796026200

170256191

9130800

546304

4450

3000306636

45500259

30100229001880

28900204

34300109001710037100

51

12018?144

536096

573860293

95506330

9080215003160029700

262

933032800

206357231

10434800

671348

4780

3260327736

49600303

33200254002240

32600236

37300124001920041000

56

135201170

6230106

664220321

105006850

10000232003550033100

290

1030037800

232447261

11738700

805393

5110

3510347841

53600349

36300279002620

36300269

40200140002130045000

61

149219197

7140116

754560348

114007340

10900248003940036300

316

1120042700

257548289

29

Table 4.-Discharges for selected flood-frequencies at gaging stations-continued

Station number

Peak discharge, in cubic feet per second, for selected exceedance probabilities (indicated recurrence interval)

0.50 (2-yr)

0.20 (5-yr)

0.10 (10-yr)

0.04 (25-yr)

0.02 (50-yr)

0.01 (100-yr)


14135000141370001*1388001413885014141500

1414350014144000141446001414480014144870

1414490014145500141460001414650014147500

1414800014148700141503001415100014151500

1415200014152500141539001415450014155500

1415600014156500141570001415800014159000

1415920014159500141612001416150014161600

1416200014162500141630001416500014165500

549014000118061602270

13500125042

314025

201011700167031507350

2690023

614097002470

455003700207

1120011100

3570486018300555006360

49809500

331860

35

59202830029705820

49bOO

759021300165071803200

16600171057

1370044

333020800?830530011500

4490034

9640150004250

814005960288

1690017300

58207450

24300785009330

758015300

452850

55

89004010046108570

68700

899026600198077803850

185002020

6618300

59

4380284003760702014800

5920043

12300190005710

1110007670344

2090022000

75709360

284009450011400

948019800

543570

70

111004830058301050081800

1080033700239084704700

207002410

7724900

81

5890398005120952019300

7980053

16100245007880

15700010100

4172640028500

10100120003360011600014200

1210026200

664570

90

140005890075401320099000

1210039400270089405350

223002700

8630600

100

7170498006270

1160023000

9710062

19200290009750

19700012000

4753070033800

12100141003750013200016300

1420031400

755360107

1630067000894015300

112000

1340045300302094006030

238002990

9436900

122

8570610007550

1400027000

11600071

226003370011800

24200014100534

3510039500

144QO163004150014900018500

1640037000

846190124

18800753001040017500

126000

30

Table 4.-Discharges for selected flood-frequencies at gaging stations-continued

Station number

Peak discharge, in cubic feet per second, for selected exceedano: probabi (indicated recurrence interval)

0.50 (2-yr)

0.20 (5-yr)

0.10 (10-yr)

0.04 (2 5-yr)

0.02 (50-yr)

ities

0.01 (100-yr)


1416650014167000141697001417050014171000

1417150014172000141723001417350014174000

14174100U178000141788001417900014181500

1418170014182500141830001418490014165000

1418580014185900141660001418700014167500

1418880014189000141895001419000014190200

1419050014190600141910001419210014192200

1419250014192800141930001419330014194000

3150413023410705990

32205620237

12500106000

b337510

866260

21300

t>l1350034100

5511700

821012000209003410

37500

82507700030206410248

1180044

16500072

139

9520129

38503060

22300

4710768035315108630

419082/0391

20100160000

75011600

1278890

34700

661890048600

8017500

1180017900284005300

54200

12900120000

39608700384

1710060

241000117212

12300199

52404100

28300

5790106004191820

10500

482010200512

26000199000

90314600

1571070044900

1032270058500

9821700

1430022100336006730

65900

16500152000458010300486

2100071

298000152267

14100252

6210478033100

721014900

556222012900

561012800

68R34200

254000

111018700

1961310059300

1242760071200

12227300

1770027900402008730

81500

21500199000536012300

628

2630086

376000203343

16400324

75005660

38500

830018500649

252014700

620014800

83741000

299000

1?6021900

2261490071000

1413140080800

14131700

2020032400453001040093700

25600237000

594013900

744

3050097

439000246405

18000382

84906330

42600

941022600

746284016600

6790169001000

48200346000

143025400

2571670083600

1583530090600

16136300

22900372005050012100

106000

30000278000

653015500

867

34900108

507000293472

19700444

95307000

46800

31

Table 4. Discharges for selected flood-frequencies at gaging stations continued

Station number


0.50 (2-yr)

0.20 (5-yr)

0.10 (10-yr)

0.04 (25-yr)

0.02 (50-yr)

0.01 (100-yr)


1419500014196500141970001419730014198500

1419970014200000142010001420150014202000

1420250014203000142035001420380014204000

1420410014204500142055001420600014206500

1420750014208000142095001420990014210000

1421080014211500142118001422350014243500

28727704060224

7660

11613800b08030808650

2940181050902001890

6131701150954

10200

101003010

1690084

24400

1511170104

103001260

39735505630325

10800

1952020094704610136UO

3990261075302B9

2880

87464012901250

15000

147004750

25100163

37600

2341800168

129001770

47340606730399

13100

25724BOO12000573017500

470031909360360

3630

106571013RO1440

18500

180006030

30700231

46900

2962250217

145002110

57447108190499

16100

34631100155007260

22800

562039«0

11900468

4670

132717014701680

23300

224007780

38100335

59300

3792840287

165002560

65151909330579

18500

42136000164008480

27300

6330462014000

5615520

152833015401870

27100

259009170

43700426

68900

4463300344

179002910

732567010500664

20900

502412002140097bO

32100

7050530016300

6686420

173955016102050

31100

296001060049300

5?978700

5163770406

194003260

14245000 4860 6340 7300 8510 9410 10300

32


Station number


0.50 (2-yr)

0.20 (5-yr)

0.10 (10-yr)

0.04 (25-yr)

0.02 (50-yr)

0.01 (100-yr)


1430770014308000143085001430870014308900

1430900014309500143100001431070014310900

1431100014311200143115001431200014312100

1431220014312300143135001431450014315500

1431600014316500143167001431750014317600

1431780014318000143185001431860014319200

1431950014320600143207001432100014321900

1432200014322400143227001433800014339000

577017900291015802530

24307300

214001830147

203039201150049400

163

4000132710320

2560

21007750

15000245006270

35209740

3950055

1310

49300152

11700945001250

56004040370

550021100

9680?8600507023703140

449010200313002510232

250066001790076100

187

5390198929421

3560

379013700226003710010300

60901450057400

871920

74700217

19700141000

1490

106006720492

897035500

1280036600680029403510

609012100377002960294

27808620

2260094400

202

63002441070492

4250

522018700281004630013400

81501790069900

1112330

92900262

25800173000

1640

149008780572

1160046800

1720047500932036903960

833014500455003520380

31101140028800118000

218

7430305

1260586

5180

743026200357005870017800

112002250086400

1442880

117000320

34500216000

1810

2150011700

6731530063100

20900563001140042804280

10100162005120039SO449

33501360033700135000

229

8270353

1390660

5890

938032700418006870021500

137002600099100

1703300

136000364

41700249000

1930

2730014100

7471840076700

25000655001380048904590

1200017900567004370521

35801600038800153000

240

91104021530736

6640

1160040100483007910025500

1650029800112000

1983730

156000409

49400284000

2050

3380016700822

2170091600

33


Station number


0.50 (2-yr)

0.20 (5-yr)

0.10 (10-yr)

0.04 (25-yr)

0.02 (50-yr)

0.01 (100-yr)


1433920014359000143595001436130014362000

1436300014366000143685001436980014370000

1437020014371500143723001437250014375000

1437550014377000143775001437780014378000

425262003860319

6710

<t9409110<tlO228

2600

1801690

10600041903200

5840248001950157

54<tOO

6314650073<*0533

13300

977018700

937348

4070

3192840

18200063406150

8280381003500227

78600

7756330010200

6931R700

13800267001430431

5110

4273680

23600077908530

9810470004680273

94100

9658870014500

91226600

19900389002230538

6470

5804810

308000963011900

11700582006330329

113000

1110111000161001090

33300

25000492002960620

7520

7045690

363000110001480U

13000665007640370

127000

1260136000221001270

40600

30700605003800702

8580

8376600

4180001240017800

14200746009030410

140000

34


Station number


0.50 (2-yr)

0.20 (5-yr)

0.10 UO-yr)

0.04 (25-yr)

0.02 (50-yr)

0.01 (100-yr)

(4) HIGH CASCADES REGION

14134000141345001414569014147400I4lb8250

1415850014208500142088501420900014209100

1432749014327500143280001433050014331000

1433200014333000143335001433500014335500

1433750014339500143415001434250014343000

143470001435300014353500

2901380

123635

147050364

168049

17722504790735171

1050909569

9040618

3420104

1130121247

31009294

4442100

378060

203071293

243076

253307076201110286

187015101130

153001590

5540116

2290143

421

48502672/8

55926?0

6912479

?410855113

296095

307364098801380377

256019901680

20300?320

7170124

3310154573

6130467491

7173320135199106

29001040139

3660120

3814390132001760510

361027002620

279003560

9460132

4910167812

7880847900

8463860209271129

32701180159

4210140

4384970160002060622

453033003550

344004750

11300138

6330176

1030

927012401330

98244203133bO153

36401320179

4780161

4985560192002380745

559039604720416006210

13400144

7950183

1290

1070017601890

35

magnitude and frequency of floods in western oregon · a method for estimating the magnitude and...

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