Publication n° 117 de VAiiocÀJxtlon InteAnationaJte. deô Science* Hydn.ol0gi4u.eA Sympoiium de. Tokyo (Pécemb^e 1975)

PREDICTING UNGAGED LOW FLOWS IN DIVERSE HYDROLOGIC PROVINCES

USING RIVER BASIN GEOMORPHIC CHARACTERISTICS

John F. ORSBORN Professor and Hydraulic Engineer, Dept. of Civil and Environmental Engineering, Washington State University, Pullman, WA 99163 U.S.A.

SYNOPSIS: Hydrologists have been addressing the problems associated with determin­ing flows in ungaged streams since man began to conceive the hydrologic cycle as we now envision it. Low flows have taken on new importance in recent years as a limit­ed resource for which competition has sharply increased. State agencies desiring to regulate minimum flows must make low flow determinations at many ungaged sites. Horton's work on drainage basin characteristics is typical of fluvial-geomorphic con­cepts used to describe a river basin in quantitative terms. Computers have encour­aged the use of statistical regressions to generate ungaged low flow prediction equations based on relationships between stream flow records, precipitation, and many basin characteristics including: geographic factors, soil associations, land cover, basin area, percent of area in lakes, slopes of channels and side valleys, mean monthly temperatures, infiltration, antecedent moisture, transpiration and evaporation. All of these methods have been input-output, or precipitation-runoff models. New methods developed recently in the State of Washington apply an output-output model which determines the relationships between two low flows of different recurrence intervals in terms of basin characteristics. Regional correlation graphs are developed for gaged portions of streams between two-year and twenty-year seven-day average low flows, and basin characteristics such as drainage area, basin relief, and stream lengths as determined from maps. The ungaged basin characteristics are measured from maps, entered into the correlations, and the ungaged low flow recur­rence interval graph for the desired location is determined. Several combinations of basin characteristics are used to verify the results.

RÉSUMÉ: Des hydrologistes s'adressaient aux problèmes associés à la détermination des divers courants dans des rivières non jaugées depuis que l'homme commença à con­cevoir la forme physique du cycle hydrologique comme nous l'envisageons au présent. Des courants bas se revêtaient d'une nouvelle importance comme ressource limitée pour laquelle la compétition augmentait nettement dans les années récentes. Ces agences d'Etat qui désirent réguler des courants minimums doivent faire des détermi­nations quantitatives à plusieurs sites non-jaugées. Les travaux de Horton effectués sur les caractéristiques des bassins de réception sont typiques des concepts fluvial-géomorphiques employés à décrire un bassin en termes quantitatifs. Des ordinateurs ont permis l'emploi des regressions statistiques détailées dans la génération des équations pour la prédiction des courants bas non-jaugées, basées sur les relations entre les enregistrements du courant des rivières, la précipitation, et plusieurs caractéristiques du bassin, y incluent des facteurs géographiques, des associations du sol, la végétation du terrain, l'aire du bassin, le pourcentage d'aire dans des lacs, les pentes des canaux et des vallons, les températures moyennes mensuelles, l'infiltration, l'humidité antécédente, la transpiration et 1'evaporation. Tous ces travaux d'approche ont été des modèles de "input-output" (d'entrée-sortie) ou d'écou­lement de précipitation. Des nouvelles méthodes récemment développées à d'Etat de Washington appliquent un modèle de "output-output" qui détermine les relations entre deux courants bas des intervales de récurrence différentes quant aux caractéristiques du bassin. Des diagrammes de corrélation régionale sont développés pour des portions jaugées des rivières, montrants les moyens des courants bas pendant sept jours pour chaque deux ans et vingt ans, et des caractéristiques du bassin tel que l'aire de réception, le relief des bassins, et la longueur des rivières, sont déterminés des cartes. Les caractéristiques non-jaugées du bassin sont calcules des cartes, sont fait entrés dans les corrélations, et le diagramme de 1'intervale de récurrence du courant bas est déterminé pour le point désire d'une rivière non-jaugée. Plusieurs combinaisons des caractéristiques du bassin sont employés à en vérifier les résultats.

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17.2 INTRODUCTION

Definition of the Problem

The need to know the flow regime of ungaged streams is becoming increasingly more im­portant as pressures for development and allocation of those flows increase. State laws have been passed in an attempt to retain flows for instream uses, but in spite of extensive stream-gaging systems uncertainty about flows dominates. Low flows are particularly critical due to competition between natural and man-made needs during the annual low flow periods of summer and early fall. Numerous cause and effect, or input-output, models have been developed to predict low flows, and complex statisti­cal regressions and probabilistic-stochastic games have been played in search of un­bounded, repeatable and transferable methods for estimating ungaged low flows.

As yet, the capability for adequately simulating all the physical processes associ­ated with precipitation-runoff (input-throughput-output) relationships is not possi­ble. We must resort to at least several years of miscellaneous measurements, corre­lated against a long-term gage record, to provide the necessary confidence for water resources planning and allocation decisions. As stated by Thomas and Benson in their regression study of drainage basin and streamflow characteristics in four diverse regions of the O.S., "Low flou relations are unreliable in all study regions; they can provide only rough estimates of low-flow oharaoteristios at ungaged sites" (1).

To obviate this situation an output-output model has been developed, the details of which are described in this paper. By relating low flows of a certain return period, or recurrence interval (RI), to low flows of a longer recurrence interval, in terms of drainage basin characteristics for gaging stations in a hydrologie province, cor­relation graphs (hydromorphic models) are developed. Other geomorphic relations are generated to determine the low flows independently of the combined relationships. The characteristics of the RI graphs of other gaging stations in the province are noted. The geomorphic parameters for the ungaged streams are measured from maps and entered into the provincial correlation graphs to determine the ungaged low flows, and subsequently the RI graph at the site in question. The estimated flow values are verified using other combinations of geomorphic parameters, any available mis­cellaneous measurements at the site and/or the low flow characteristics of similar nearby streams.

Examples of Existing Methods

It has been 30 years since Horton published his first quantitative assessment of re­lationships between the geomorphic features of drainage basins and associated hydro-logic parameters (2). Examples of linear geomorphic basin characteristics, some of which are used in this new hydromorphic, output-output-model, are presented in Table 1. Strahler's use of dimensional analysis, more usually associated with the design of physical hydraulic models, enabled him to combine basin characteristics and streamflows into more meaningful physical force and form ratios (3).

The interactions of geology and hydrology were emphasized in studies of the low-flow characteristics of duration curves related qualitatively to geologic formations,

"Thomas, D. M., Benson, M. A., "Generalization of Streamflow Characteristics from Drainage-Basin Characteristics," 0.S.G.S., Water Supply Paper 1975, 1970.

'Horton, R. E., "Erosional Development of Streams and Their Drainage Basins; Hydro-physical Approach to Quantitative Morphology," Geol. Soc. Amer. Bull., Vol. 56, 1945,

Strahler, A. N., "Dimensional Analysis Applied to Fluvially Eroded Landforms," Geol. Soc. Amer. Bull., Vol. 69, 1958.

158

Table 1. Sample of Linear Geomorphic Characteristics Used in Drainage Basin Analysis*

Property Dimensions Relates to :

Stream Length, LS L Channel networks, percentage of input becoming surface runoff (output), soil type, geology, basin storage, contribution to low flow

Basin Length, LB L Aspect ratio LB/WB; concentration time Basin Perimeter, PB L Basin shape, concentration time Basin Relief, H L Potential energy, form of precipitation,

ground cover, etc. Basin Width, WB L Rectangular equivalent derived from AjLB Basin Area, A L2 Catchment size, volume of input, distribution

of precipitation input Drainage Density, LSI A £ _ 1 Soil types and runoff conditions, method of

determination not standardized Channel Slope, SC - Average rate of expenditure of energy as flow

moves through basin

For a more detailed list of basin properties and original references, see (3).

such as those reported by Schneider and Searcy (4,5). More recently, numerous in­vestigators, aided by computer power, have explored the relationships between low flows and drainage basin characteristics. As noted earlier, Thomas and Benson had little success in predicting ungaged low flows using multiple regression methods, although the regression methods had been used successfully earlier to develop pre­diction input-output models for floods (1). The best low flow results were 60 per­cent in error. Among the drainage basin characteristics indexes evaluated by Thomas and Benson were: drainage area, main channel slope and length, surface storage, ele­vation, forested area, soils index, basin width, and alluvial area.

In his discussion of methods for analyzing low flow data and estimating ungaged low flows, Riggs described the application of multiple regression methods under the con­cept of regionalizing relationships (6). "Attempts have been made to regionalize low-flow characteristics by multiple regression on several basin characteristics, including geologic indexes. Some of these regressions showed the geologic parame­ters to be statistically significant, but the standard errors of these regressions were too large to justify application of the relations to ungaged sites. One of the better regressions, which was derived for Connecticut, related 7-day 10-day low flow to drainage area, mean basin elevation, and percentage of basin covered by stratified drift; it has a standard error of 68 percent (Thomas and Cervione, 1970). The principal roadblock to régionalisation of low-flow characteristics is our inabil­ity to describe quantitatively the effects of various geological formations on low flows—even where detailed geologic maps are available."

Other methods of estimating low flow characteristics of ungaged streams deal with manipulations of existing low flow data into other forms. For example, Campbell was quite successful in developing drought frequency charts, converting the charts into percentages of the two-year low flow, and grouping watersheds according to flow

4 Schneider, W. J., Areal Variability of Low Flows in a Basin of Diverse Geologic Units," Water Resources Research, Vol. 1, No. 4, 4th Quarter, 1965.

Searcy, J. K., "Manual of Hydrology: Part 2. Low-Flow Techniques," U.S.G.S., Water Supply Paper 1542-A, 1959.

Riggs, H. C., "Low-Flow Investigations," Chap. Bl, Techniques of Water-Resources In­vestigations of the U.S. Geological Survey; Book 4, Hydrologie Analysis and Inter­pretation, 1972.

159

characteristics (7). He found that for 27 sample basins from across the United States: 1) basins could not be grouped by size of drainage area; and 2) that basins grouped by median flows had similar recurrence interval graph characteristics. Al­though these results speak to the similarity of low flow characteristics between certain streams, it does not provide a method for direct prediction of low flows in ungaged streams without some miscellaneous records.

Crippen recently summarized the various approaches to predicting ungaged stream flows (8). In predicting how future research efforts might approach this problem, he anticipated that: 1) there would be a shift away from gathering flow, basin and channel parameter data; 2) some researchers would look at the form of the model and refine the input to output physical rules; 3) there would be adjustments in desired versus real world accuracy; 4) there might be a concentration of the basin parameter concepts into smaller regions; and 5) a more complete melding of the talents of various disciplines would be needed. As stated by Solomon and noted by Crippen, "It is practically impossible to translate a hydrologie process into a functional relationship. The actual complexity in a hydrologie phenomenon has to be simplified by introducing assumptions and ignoring less important variables. Even if the exact relationships could be established, the errors involved by sampling the infinite population of data would still leave place for errors in predicting the effects" (9).

To avoid this complex situation we should recognize that the drainage basin inte­grates all the input and throughput processes into a series of outputs (annual mini­mum flows). Then one output of a certain probability (say 50 percent or 2-year EI) can be related to an output of a lesser probability (say 5 percent or 20-year RI), in terms of the more significant basin features and the natural flow stability. Thus we have a physical, hydromorphic, output-output, recurrence-interval, low-flow, pre­diction model for ungaged streams.

DEVELOPMENT OF ANALYTICAL PROCEDURES

The concepts described in this section were conceived as part of a minimum flow study in the State of Washington (10). Since the development of the original concepts for the entire state, improvements have been made in the procedures through studies of smaller regions as part of the State Water Program. In evaluating ways of predicting ungaged low flows, the primary objectives were to develop a method which could be: 1) transferred from one hydrologie province to another; and 2) operated by a tech­nician with a minimum amount of formal hydrologie training. Referring to the usual RI graph in Fig. 1, the 7-day average low flow RI curve will be used as the basis for the analytical development. The main reference "characteristic" flow is (Q7L2), the 7-day average low flow with a 2-year RI. The 7-day average low flow with a 20-year RI (Q7L20) is the second reference flow used to define the ungaged RI graph. This notation (Q7L2 for example) was designed for two reasons: 1) it can be used to con­sistently abbreviate flow terms with respect to Q (flow), 7 (averaging time period), L (type), and 2 (recurrence interval); and 2) this notation fits computer format and is much easier to type than subscripts.

Campbell, J. C., "Prediction of Seasonal-Low Streamflow Quantities," Water Resources Research Institute, Corvallis, Oregon, WRRI-10, Sept., 1971.

Crippen, J. R., "Basin Characteristic Indexes as Flow Estimators," ASCE Nat. Meeting on Water Resources Engineering, Preprint 2117, Los Angeles, Calif., Jan 21-25, 1974.

Solomon, S. I., "Statistical Association Between Hydrologie Variables," Proceedings, Hydrology Symposium No. 5 on Statistical Methods in Hydrology, Canada Dept. of Energy, Mines, and Resources, Ottawa, Ontario, CANADA, 1967.

Orsborn, J. F., et al., "A Summary of Quantity, Quality and Economic Methodology for Establishing Minimum Flows," State of Washington Water Research Center, Report No. 13, Vol. 1, June, 1973.

160

The U.S. Geological Survey (U.S.G.S.) has developed several measures of low flow characteristics which use the 7-day graph in Fig. 1 as a basis for comparing streams (11,12). A measure of the low-flow yield of a stream is the minimum 7-day average discharge, at the two-year RI, in cubic feet per second per square mile of drainage area. This value is called the "low flow index" (LFI). The LFI provides a quick appraisal of the low-flow yield of streams having different drainage areas.

A second value is the slope of the minimum 7-day frequency curve, which is a measure of the year-to-year variability of low flows. The "slope index" is the ratio of the minimum 7-day average discharges at two-year and twenty-year recurrence intervals. Variations in the slope indexes of frequency curves at different sites are due to differences in basin characteristics. A low value of the slope index means that year-to-year differences in low flow normally are small. A high index indicates a steep slope, and large variations in low flow.

The third index is the "spacing index". The spacing, or spread, between the minimum 7-day and 183-day frequency curves is the ratio of the discharges at the two-year RI on both curves, 183:7. The spacing between the curves for different durations of low-flow is influenced by the same basin characteristics that affect the slope.

For this new hydromorphic method of analysis, the 7-day low flow frequency (or RI) curve was converted from a log-probability to log-log scales as shown in Fig. 2, because: 1) the "slope index" can be defined by the dimensionless slope of the graph between 2 and 20 years ; and 2) the equation for the relationship between the 2- and 20-year flows can be written and used throughout the analysis. Between 2-and 20-year recurrence intervals, the plotted points usually form a straight line on log-log paper, whereas it is curved on probability paper. In Fig. 2, (Q7L1P), the projected 7-day average low flow at a 1-year RI, is used to compare the snythe-tic "maximum" low flows between basins. The slope of the graph (p) relates to the "slope index" mentioned earlier, and is an excellent indicator of basin storage stability. The relationship between the "slope index" as defined by (Q7L2/Q7L20), and the slope (p) in Fig. 2, is shown in Fig. 3 for a sample of stations in south­western Washington.

The low flow index (LFI), (Q7L2/A), where A is the drainage area, can be misleading in comparing basins. It can be used for comparing fairly small homogeneous basins, but as shown in Fig. 4 the unit values of (Q7L2) can vary widely even for basins in the same climatic region. Values of the LFI were found to have poor correlation with basin geomorphic characteristics, and therefore actual low flow values were selected for use in this analysis.

In the initial development of this methodology a sample of 29 gaging stations from throughout the State was selected for analysis (10). The average annual precipita­tion on these basins varies from 20 to over 120 inches per year. Geomorphic parame­ters and combinations were tested and selected based on how well they correlated with (Q7L2) and (Q7L20). Some of the combinations which worked best in various parts of the State were: (3/2-L1-H); (LT) (H) ; LT(H) 0- 5; and (v^DD-Ll). The terms are defined as: LI is length of first-order streams; H is relief or potential energy of the basin; LT is total length of streams; and DD is drainage density, with all units being in miles. Although a detailed study of parametric consistency in certain geographic areas has not been conducted, there appeared to be no particular geomor­phic combination which correlated consistently with (Q7L2) even in nearby basins.

"Pacific Northwest River Basins Commission, Puget Sound Task Force, "Appendix III, Hydrology and Natural Environment," Comprehensive Study of Water and Related Land Resources, 1970.

'Nassar, E. G., "Low Flow Characteristics of Streams in the Pacific Slope Basins and Lower Columbia River Basin, Washington," U.S.G.S., Open-File Report, 1973.

161

6 Therefore, for the state-wide sample, all of the geomorphic combinations were cal­culated and then averaged or selected for consistency between two or three of the combinations at each gage. Relief (H) is determined as the difference in elevation between the highest contour in the upper part of the basin and the gage elevation. Scale effects of maps on basin characteristics are discussed by Yang and Stall (13).

The basic equation developed for relating ungaged flows to the log-log RI graph was

Q7L(RI) = C(RI)"P (1)

In this equation, the left side is the unknown flow at a particular RI, and the coef­ficient C = Q7L1P at RI = 1.0 (see Fig. 2). Therefore, for the "characteristic" 7-day, 2-year low flow, Eq. 1 becomes

Q7L2 = Q7L1P/(2)P (2)

Using this definition of the RI log-log graph, and recalling that the slope (p) is an indication of natural low flow stability, a new relationship was developed using a "volume of the basin" term, (AH)/3, such that

(Q7L2) . 2 3 |-(AH)°^(Q7LlP)j°-5 (3)

(Q7L2) = 23(x)0-5 (4)

The 300 in the bottom of Eq. 3 is merely AH/3 divided by 100 for convenience. After estimating an ungaged (Q7L2) using the basin parameters (such as 3/2-L1-H), and esti­mating (Q7L1F) based on the ratio (Q7L1P)/(Q7L2) for the gages in the province, Eq. 3 is solved for (p). Then (Q7L20) is estimated by the ratio of (Q7L20)/(Q7L2) for the province, and/or by the best basin parameters for the province. The (Q7L2) and (Q7L20) values are plotted on log-log paper and (p) is measured graphically or solved mathematically using Eq. 2. If it agrees with the slope (p) determined in Eq. 3, the solution is complete. The (p) values for the ungaged stream can be compared with those at gaging stations in the province as a further verification.

The relationship in Eqs. 3 and 4 are presented graphically for the 29 statewide sta­tions, and the Lewis River Study Area in southwestern Washington, in Fig. 5, and are similar (14). An additional method for checking (Q7L2) was developed using the esti­mated values of (Q7L1P) and (p) in the equation

(Q7L2) - io[iilHSi!_!MM£i]0 - 6 (5)

where the coefficient (10) and the power of (0.6) vary slightly from province to prov­ince. If the value of (Q7L2) determined from the basin characteristics does not agree within reason with the value calculated by Eq. 5, then the first estimates should be checked, the geology of the area should be investigated for anomalies, and field measurements should be made during a low flow period if no miscellaneous records are available. Procedures for estimating low flow RI curves for ungaged streams are detailed in Ref. (14).

APPLICATION OF PROCEDURES

The general methodology developed for the sample of statewide gaging stations has been refined for parts of the State, such as the Lewis River Study Area, as discussed

13Yang, C. T., Stall, J. B., "Note on the Map Scale Effect in the Study of Stream Morphology," Water Resources Research, Vol. 7, No. 3, June, 1971.

14 Orsborn, J. F., Sood, M. N., "Technical Supplement to the Hydrographie Atlas, Lewis River Basin Study Area," State of Washington, Dept. of Ecology, State Water Program, Oct., 1973.

17.7 in the previous section. In addition, the methodology has been applied to other study areas in the southwest, northcentral and northeast portions of the State. Numerous smaller ungaged streams have been analyzed in connection with lake eutro-phication, timber and fish rearing studies.

The Okanogan-Methow River Basins Study Area, on the east side of the Cascade Moun­tains, contains two hydrologically diverse provinces. The provincial equations for (Q7L2) [like Eq. 4] are (15):

Okanogan Basin (Q7L2) = 36(x)°-h3 (6) and

Methow Basin (Q7L2) = 20(x)0-'43 (7)

The Okanogan Basin originates in a relatively dry region with an average annual pre­cipitation of 20 inches per year. Low flows are strongly influenced by storage and irrigation diversions. Numerous gaging stations are maintained in the Okanogan Basin, but in the Methow River Basin which is only slightly altered by diversions, only two continuous record gaging stations were available in a drainage area of 1790 sq mi. The average annual precipitation is 30 inches per year. Fortunately, numerous miscellaneous low flow measurements were made in 1971 at six sites. These records were correlated with the long-term records of the two continuous stations for the Methow Basin prediction model. The best parameter equations were

(Q7L2) = O.ISC^DD-Ll)1-22 (8) and

(Q7L20) - 0.07C/DD-L1)1-27 (9)

The 1971 low flow measurements were correlated with the long-term records by

(Q7L2) = 0.94(Q7L-1971) (10) and

(Q7L20) = 0.58(Q7L-1971) (11)

where (Q7L-1971) is the 7-day average low flow recorded in 1971. This type of special relationship between miscellaneous records and basin parameters is usually required in areas which lack continuous streamflow records. In the Little Spokane River Basin in northeastern Washington numerous miscellaneous records were available, and a common 10-year period was selected for correlating the miscellaneous and long-term records (16). The general equation for the Spokane Basin is

(Q7L2) = 10(x) 0- 7 0 (12)

and the models for estimating ungaged low flows are

(Q7L2) = QL(1961-70) (13) and

(Q7L2) = 0.57(3/2-Ll-H)1,25 (14)

In Eq. 13, QL(1961-70) is the average low flow for the 10-year period.

15 Orsborn, J. F., Sood, M. N., Technical Supplement to the Hydrographie Atlas, Oka­nogan-Methow River Basins Study Area," State of Washington, Dept. of Ecology, State Water Program, D e c , 1973.

Orsborn, J. F., Sood, M. H., "Technical Supplement to the Hydrographie Atlas, Spokane River Basin Study Area," State of Washington, Dept. of Ecology, State Water Program, publication pending.

163

17.8 TESTING OF PROCEDURES

Four examples are presented for comparing low flows predicted by the output-output hydromorphlc methodology with recorded values. None of the stations were used in developing the correlations. Predictions were made for a natural stream as shown in Fig. 6A on the east side of the Cascade Mountains, using the average state con­ditions in Eq. 3. The two predictions (using the average basin parameters and also Eq. 5) are in close agreement.

The model was used to determine the effects of regulation and diversion for the Yakima River at Cle Elum. The predicted low flow frequency curves (two parametric models were used) prior to 1917 (when regulation was begun) were compared with the existing curve. In Fig. 6B the steepness of the existing frequency curve reflects the large amounts of flow diverted for irrigation. The natural 2-year low flow has been reduced about 40 percent, and the 20-year flow by about 70 percent.

Low flow frequency curve predictions were made for numerous small streams entering Silver Lake in southwestern Washington in connection with a eutrophication study. In October, 1974, Hemlock Creek and Sucker Creek were measured and these low flows are plotted in Fig. 7 on the predicted frequency curves. The fact that the measured flows both plot at the same recurrence interval of 6 years reinforces the predicted values. Hemlock Creek has a drainage area (A) of 17.1 sq mi, an average annual pre­cipitation of 65 inches per year, and relief (H) of 0.21 miles. The smaller Sucker Creek has a drainage area (A) of 7.2 sq mi, precipitation of 63 inches per year, and relief (H) of 0.09 miles. Four small streams (4.6 to 37.8 sq mi) in the vicinity were used to develop prediction equations for the Silver Lake streams and the equa­tions were (in the form of Eqs. 3 and 5)

(Q7L2) = 13(x) 0- 6 0 (15) and

(Q7L2) = 8(B) 0- 5 0 (16)

where B = (LT)(H)°•5(Q7L1P)/(lOOOp).

Based on several streamflow measurements made on Elk Creek on the northwestern coast of Oregon and correlation with other gages, the Oregon Wildlife Commission salmon rearing project had predicted the 2-year low flows to be on the order of 3 to 4 cfs for the West and North Forks. Using output-output, hydromorphlc models for south­west Washington coastal streams, the West and North Fork 2-year flows were calculated to be 3.3 and 4.0 cfs. The general equation in the form of Eq. 3 was

(Q7L2) = 18(x) 0- 6 0 (17)

CONCLUSIONS

whereas regression analyses of streamflow and basin characteristics, and other meth­ods for predicting low flows have been shown to have a best accuracy of only about 60 percent, the output-output, hydromorphlc model predicts the entire low flow fre­quency curve with accuracies of a few percent and less. Geologic anamolies which increase or decrease low flows from predicted values can be anticipated. Natural low flows are predicted, and therefore the effects of regulation and diversion can be evaluated. In addition to low flows, the principles of the output-output, hydro­morphlc model, which is based on hydrologie province correlations of stream flow records and basin characteristics, has been used successfully to predict floods, average annual flows and sediment transport (17). Other possible applications in­clude correlations with natural water quality, and urbanization effects on floods and low flows.

1'Orsborn, J. F., "Determining Streamflows from Geomorphic Parameters," ASCE, Journ. Irrig. and Drainage Div., No. IR4, Paper 10986, D e c , 1974.

164

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(AH}°-5 (Q7LIP) 20

X- 300 p

Fig. 5. Correlation Graph for low flow estimation; Lewis Study Area and State of Washington

166

ul 300

o 200

q 100

60 -

• ' • t 1 I I

Q7L2 VALUES . RECORDED 140 CFS - PREDICTED 140, 139

l i i i

M i l '

Q7L20 RECORDED PREDICTED

1 1 I 1 1

1

VALUES 9 0 CFS 88, 92 .

) "—W ~-

1 1

1

1

Fig. 6A.

2 4 6 8 10 20

RECURRENCE INTERVAL, YEARS

Predicted and recorded natural low flow frequency graphs for the White River near Plain, Washington, for the period 1955-71

800

600 4

\ \

80

~1 I I I I I ' 1

Q7L2 VALUES (NATURAL) RECORDED 450 CFS

(1908-17) I f c — PREDICTED 4 4 0

TWO — 5 ^ = ^ -. I METHODS^ 4 ~~~- ;= = ~ ^

REGULATION AND DIVERSION EFFECTS Q7L2

EXISTING REGULATED, DIVERTED CONDITIONS" Q7L20

Fig. 6B.

_L I _J I I I I 20 30 2 4 6 8 10

RECURRENCE INTERVAL, YEARS

Predicted and recorded natural and regulated low flow conditions for the Yakima River at Cle Elum, Washington, 1908-70 (regulated after 1917)

3.0

a 2.0

o 0.6

0.4

i 0.2

I I I I I l l | ^

HEMLOCK CREEK

Q7L2 / Q 7 L 2 0

~TL30 ^ ,.0.82 I p

1.38,

-0.351

- SUCKER CR

'0.52

0.12

E I 2 4 6 8 10 20 RECURRENCE INTERVAL, YEARS

Fig. 7. Predicted and measured low flow graphs for small streams entering Silver Lake, Washington, 1974