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Introduction
Successful upstream passage of adult and juvenile fish through artificial structures (channels, culverts, fishways) depends on the selection of appropriate passage design flows. It is recognized that fish passage through artificial structures cannot practically be provided at all flows. A high design flow is selected to be the upper limit of the range through which upstream fish passage criteria are satisfied. The limitation of passage above the passage design flow may be due to velocity, drop height or turbulence. Structural design flows are also important, especially in terms of passage of debris and bed material. WAC 220-110-070 (Water Crossing Structures) requires that the high flow design discharge be the flow that is not exceeded more than 10 percent of the time during the months of migration. This report provides regional regression equations for ungaged catchments to estimate this flow.
For gaged catchments the 10 percent exceedance flow for any month can be easily determined by developing a flow duration curve. For ungaged catchments, the two-year peak flood can be used to estimate this flow (Cummans, 1975). The two-year peak flow is often much higher (300 to 400 percent) than the 10 percent exceedence flow. Bates (1988), reviewed current agency criteria and developed two regression equations relating basin parameters to the 10 percent exceedence flow.
The U.S. Geological Survey (USGS) are in the process of updating regional regression equations for flood frequencies in Washington. This report utilizes the same regions and basin parameters to develop regression equations for the 10 percent exceedence flow for the months of January and May. These months were selected to represent the high fish passage design flow (QFP) for two periods when upstream passage has been observed (Peterson, 1982) and (Cederholm, 1982). January represents the month of highest flow when adult salmonids are passing upstream, and May represents the most critical month for upstream passage of juvenile salmonids. Other months are also important, but January and May represent the two extreme combinations for design considerations. Equations were developed for three regions of Western Washington (Figure 1 - Sumioka et al 1998). Data was also analyzed for Eastern Washington, but no correlation between design flows and basin parameters could be found.
Description of Regions
The state of Washington was divided into subsections based on their drainage flow characteristics. These regions were derived from "The Catalog of Information on Water Resources Data" (1972), "Water Resources Regions and Subregions for the National Assessment of Water and Related Land Resources" by the U.S. Water Resources Council (1970), "River Basins of the United States" by the Inter-Agency Committee on Water Resources, Subcommittee on Hydrology (1961), and State planning maps. The regions defined are those regularly employed by the U.S. Water Resources Council and USGS for water resources planning.
The Coastal Lowland Region (Region 1) includes parts of Clallam, Jefferson, Mason, Thurston, Pacific, Lewis, and all of Grays Harbor counties and consists of streams that drain directly into the Pacific Ocean.
The Puget Sound Region (Region 2) includes sections of Clallam, Jefferson, Mason, Thurston, Pierce, and all of King, Snohomish, Whatcom, and Skagit counties. Region two consists of streams that drain into the Puget Sound. In order to find the best correlation, the Region 2 data was divided into highland and lowland streams. The division was defined at gage elevations of 1000 feet. In addition, Region 2 had a high percentage of urbanized streams (defined arbitrarily as greater than 20 percent impervious surfaces). Separate regression equations were run for this data.
The Lower Columbia Region (Region 3) is based on rivers that flow west of the Cascade Mountain Range and drain into the Columbia River. This region includes Wahkiakum, Cowlitz, Clark, and sections of Skamania, Pacific, and Lewis Counties. Again the best correlation was found when the region was divided into highland and lowland subregions. Again, the classification was based on the gage elevation.
Region four (Eastern Washington) is defined as the rivers in counties east of the Cascade Mountain Range. As defined by the USGS and U.S. Water Resources Council, Eastern Washington is divided into six regions. Too few fluvial systems fit the required criteria however to analyze any one region as a whole. Therefore, it was necessary to condense all of Eastern Washington into one region. No correlation was found amongst the small, unrepresentative data pool gathered within this large, diverse region.
Methodology
To create a usable model for estimating fish passage design flows, a data selection process was
necessary. Parameters selected required the drainage areas to be less than 50 square miles with at
least five years of data compiled by the USGS for January and May. All selected data were reported
by USGS as either fair, good or excellent. Sites where the measured data was reported poor or had
large periods of estimation during the months of interest were excluded from the analysis. Certain
sites were also rejected because of major upstream diversions, lakes or reservoirs acting as stream
controls. Data was compiled from USGS Hydrodata (Daily Values) and USGS Open File Reports
84-144-A, 84-144-B, 84-145-A, and 84-145-B. Basin drainage areas were gathered from the USGS
Hydrodata. Mean annual precipitation and precipitation intensity were gathered from the USGS
Open File Reports. When figures were not available in the Open File Reports, values were
determined by locating the latitudinal and longitudinal coordinates of the gage stations on Plates
1 and
2. The 10 percent exceedence flow values were calculated using the Hydrodata software via the
Weibul formula:
where N is the number of values and M is the ascendant number in the pool of values.
Regression Analysis
A least squares multiple regression analysis was run on a logarithmic transformation of the data. Drainage area and mean annual precipitation (precipitation intensity for Region 1) were the independent values. The independent variables used were those specified in the 1996 USGS report.
Reasonable correlations were found within the Western Washington regions. Correlation improved
upon further division of the individual regions. Gage less than 1000 feet were classified lowland,
gages more than 1000 feet were classified highland. Separate analyses were run for the high passage
flows during January and May migration periods for each region/subregion defined. Percent
standard error (Tasker 1978), was derived from the formula;
where the units of the mean are natural log units. A table was included in the paper by Tasker that allowed for simple derivation of standard error in percent from logarithmic units.
The user is reminded of the non-symmetrical nature of the log-normal distribution. The higher the calculated design flow, the greater probability that the upper design flow will fall higher than one standard error above the regression line and less than one standard error below the regression line. It is, however, correct to assume an equal probability within one standard error above or below the regression line when the calculated flow and the standard error are expressed in logarithmic (base 10) units. However, the imprecise nature of accurately predicting high passage design flows would more often than not influence the user to add the standard error, making the probability distribution somewhat unimportant. The above statement remains to maintain scientific accuracy.
Results and Applications
Table 1 is a summary of the regression equations that were developed. Region one stations were all lowland (elevation <1000 ft), Region 2 had lowland, highland (elevation > 1000 ft) and urbanized stations, and Region 3 has lowland and highland stations.
Computation of a fish passage design flow at an ungaged site is made as follows:
| Example 1: Lake Creek Tributary (Lake Cavanaugh Road) | ||
|---|---|---|
| From Table 1: | Region 2, Elev <1000 ft, January | |
| A = 1.82 sq mi | ||
| Latitude: | 48o22' | |
| Longitude: | 122o11' | |
| From Plate 2: | P = 80 in/yr | |
| Qfp = | 0.125(A).93(P)1.15 | |
| Qfp = | 0.125(1.82).93(80)1.15 | |
| Qfp = | 34 cfs, Standard Error is 48.6% | |
| Qfp = | 18 to 50 cfs ................. Answer | |
| Example 2: S. Branch Big Creek (SR 101) | ||
|---|---|---|
| From Table 1: | Region 1, May | |
| A = 0.87 sq mi | ||
| Latitude: | 47o09' | |
| Longitude: | 123o53' | |
| From Plate 1: | I24,2= 4.5 in/24 hours | |
| Qfp = | 2.25(A).85(I24,2)0.95 | |
| Qfp = | 2.25(0.87).85(4.5)0.95 | |
| Qfp = | 8.3 cfs, Standard Error is 30.6% | |
| Qfp = | 6 to 11 cfs..................... Answer | |
| Table 1. - Regional regression equations for fish passage design flows in Washington. Qfp, fish passage design flow; A, drainage area, square miles; I, 2-year, 24-hour precipitation, in inches; P, mean annual precipitation, in inches. | |||||
|---|---|---|---|---|---|
| Constant | Coefficients | Standard error of prediction | |||
| Equation | ab | c | (%) | ||
| REGION 1 | |||||
| January | Qfp=aAbIc | 6.99 | 0.95 | 1.01 | 25.7 |
| May | Qfp=aAbIc | 2.25 | 0.85 | 0.95 | 30.6 |
| REGION 2 | |||||
| Lowland Streams < 1000 feet Elevation | |||||
| January | Qfp=aAbPc | .125 | 0.93 | 1.15 | 48.6 |
| May | Qfp=aAbPc | .001 | 1.09 | 2.07 | 75 |
| Highland Streams > 1000 feet Elevation | |||||
| January | Qfp=aAb | 141 | 0.72 | 59.8 | |
| May | Qfp=aAbPc | 3.25 | 0.76 | 0.48 | 56.9 |
| Urban Streams > 20% Effective Impervious Area | |||||
| January | Qfp=aAbPc | .052 | 0.96 | 1.28 | 40.7 |
| May | Qfp=aAbPc | .003 | 1.10 | 1.60 | 43.3 |
| REGION 3 | |||||
| Lowland Streams < 1000 feet Elevation | |||||
| January | Qfp=aAbPc | .666 | 0.95 | 0.82 | 38.1 |
| May | Qfp=aAbPc | .014 | 0.87 | 1.42 | 38.1 |
| Highland Streams > 1000 feet Elevation | |||||
| January | Qfp=aAbPc | .278 | 1.41 | 0.55 | 59.8 |
| May | Qfp=aAbPc | 3.478 | 0.85 | 0.38 | 28.2 |
| Table 2. - Maximum and minimum values of basin characteristics and R squared values used in the regression analysis, by region and land type. | ||||
|---|---|---|---|---|
| Drainage Area | Mean Annual Precipitation | 2-year 24-hour Precipitation | R2 | |
| (sq mi) | (inches) | (inches) | (January/ May) | |
| REGION 1 | ||||
| Maximum | 48 | -- | 7.5 | (0.91/0.84) |
| Minimum | 2.72 | -- | 2.5 | |
| REGION 2 | ||||
| Lowland Streams < 1000 ft Elevation | ||||
| Maximum | 48.6 | 160 | -- | (0.81/0.77) |
| Minimum | 1 | 28 | -- | |
| Highland Streams > 1000 ft Elevation | ||||
| Maximum | 45.8 | 170 | -- | (0.68/0.76) |
| Minimum | .19 | 60 | -- | |
| Urban Streams > 20% Effective Impervious Area | ||||
| Maximum | 24.6 | 47 | -- | (0.74/0.76) |
| Minimum | 3.67 | 35 | -- | |
| REGION 3 | ||||
| Lowland Streams < 1000 ft Elevation | ||||
| Maximum | 40.8 | 130 | -- | (0.84/0.86) |
| Minimum | 3.29 | 56 | -- | |
| Highland Streams > 1000 ft Elevation | ||||
| Maximum | 37.4 | 132 | -- | (0.73/0.81) |
| Minimum | 5.87 | 70 | -- | |
Limitations and Comments
The equations presented in this study can be used within certain limitations to predict fish passage design flows for Western Washington. With the exception of urbanized streams in region two, the relationships were determined from gaging-station data for natural-flow streams and should not be applied where artificial conditions have altered stream hydrology. These equations are not a substitute for hydrologic synthesis within a region, where flows are actually measured to develop a correlation to gaged data. Extrapolations beyond the limits of the basic data used in each region is not advised. Relationships can be used with the most confidence in lowland areas with runoff dominated by rainfall, and with least confidence in highland or desert areas with little rainfall. Many urbanized streams in Puget Sound have been modeled using continuous simulation models. Watershed basin plans may be available from local governments with data that should be used to generate flow duration curves for a specific stream location.
For Eastern Washington, since no correlation was found it is recommended that the two year peak flood flow (USGS, 1996) be used as the high fish passage design flow.
Bates, K. and P.D. Powers. 1988. Design flows for adult salmon passage. Washington Department of Fisheries. Unpublished.
Cederholm, C.J., W.J. Scarlett. 1982. Seasonal immigration of juvenile coho salmonids into four small tributaries of the Clearwater River, Washington. University of Washington Press. Seattle.
Cummans, J.E., M.R. Collins and E.G. Nassar. 1975. Magnitude and frequency of floods in Washington. United States Geological Survey. Open-file report 74-336.
Peterson, N.P. 1982. Immigration of juvenile coho salmon into riverine ponds. Canadian Journal of Fisheries Aquatic Sciences. 39:1308-1310.
USGS, 1996. Flood frequencies in Washington. United States Geological survey. In preparation.
Tasker, Gary D. 1978. Relation between Standard Errors in Log Units and Standard Errors in Percent. WRD Bulletin.
Williams, J.R., and Pearson, H.E. 1985. Streamflow statistics and drainage basin characteristics for the South Western and Eastern Regions, Washington. Volume I. USGS. Open-file report 84-145-A. Volume II Open-file report 84-145-B.
Williams, J.R., and Pearson, H.E. and Wilson J.D. 1985. Streamflow statistics and drainage basin characteristics for the Puget Sound Region, Washington. Volume I. USGS. Open-file report 84-144-A. Volume II. Open-file report 84-144-B.
Fish Passage Technical Assistance Index
