Baseline Hydrologic Analyses for South Fork Battle Creek

Transcription

1 Baseline Hydrologic Analyses for South Fork Battle Creek Report Prepared for Rugraw, LLC Redding, CA Upstream View of Proposed Diversion Site 28

2 Table of Contents 1. Introduction Available Data Water Year Classification Regional Water Year Classifications Application to SF Battle Creek Synthetic Project Inflow Record Observed Streamflow Comparison Seasonal Flow Relationships Synthetic Time Series Development Estimated Accuracy of Synthetic Flows Additional Uncertainties Flow Data Analysis and Applications Water Year Characterization Mean Daily Flow Metrics Flow Frequency Analysis Flow Duration Analysis Instantaneous Peak to Mean Daily Flow Relationships References Appendix A Period of Record Water Year Type Classifications List of Figures Figure 1. Project Area Map... 2 Figure 2. Normalized Annual Discharge Comparison... 7 Figure 3. Seasonal Flow Comparisons (area-normalized flow in cfs/sq mi) Figure 4. Seasonally Transposed Mill Creek to SF Battle Creek Normalized Flows Figure 5. Spring Flow Comparison by Year Figure 6. Dry Year and Wet Year Spring High Flow Regressions Figure 7. Transposed Spring Flows Using Dry Year and Wet Year High Flow Regressions Figure 8. Observed vs. Synthetic Flows for SF Battle Creek near Mineral, WY Figure 9. Observed vs. Synthetic Flows for SF Battle Creek near Mineral, WY Figure 10. Maximum Daily Flow Frequency Curve for SF Battle Creek near Mineral Hydrologic Analyses for South Fork Battle Creek i Northwest Hydraulic Consultants

3 List of Tables Table 1. Streamflow Data Sources... 3 Table 2. Selected Watershed Characteristics (from USGS StreamStats)... 4 Table 3. Percentile Thresholds for Regional Water Year Types... 5 Table 4. Regional Water Year Types Table 5. Comparison of Summer and Annual Water Year Type Classifications... 6 Table 6. Annual Runoff Comparison for SF Battle Creek Period of Record... 7 Table 7. Summary of Estimated Bias of Synthetic Streamflows for SF Battle Creek Table 8. Summary of Estimated Accuracy of Synthetic Streamflows for SF Battle Creek Table 9. Post-2000 Water Year Classifications for SF Battle Creek Table 10. Seven-Day Low Flow Frequency Table 11. Maximum Daily Flow Frequency for SF Battle Creek near Mineral Table 12. Project Inflow Durations for February 1 - May Table 13. Project Inflow Exceedance Probabilities for Sediment Analysis Table 14. Observed Flow Exceedance Probabilities for Selected Representative Water Years Table 15. Estimated Instantaneous Peak Flow Frequency for SF Battle Creek near Mineral Hydrologic Analyses for South Fork Battle Creek ii Northwest Hydraulic Consultants

4 1. Introduction The proposed is located on upper South Fork (SF) Battle Creek, roughly between Lassen Lodge and Mineral, California (see Figure 1). The Project proposes to divert flow from the creek at approximately RM 23.0 (above Angel Falls) and return powerhouse discharges to the creek at RM 20.6 (1.7 miles upstream of Panther Grade). The FERC licensing process requires an assessment of Project operations and potential impacts on the 2.4-mile bypass reach between the diversion and powerhouse return. The impact assessment includes evaluation of potential impacts of Project operations on stream hydrology, biology, sediment transport, and geomorphology under a range of hydrologic conditions. To address data needs identified by FERC and Project reviewing agencies (including the State Water Quality Control Board (SWRCB), California Department of Fish and Wildlife (CDFW), and National Marine Fisheries Service (NMFS)), Rugraw LLC contracted with NHC to conduct a hydrologic assessment to develop streamflow data needed for Project operations and impact assessments. Data needs include annual hydrographs representing a range of hydrologic year types (e.g., dry, normal, wet) and a longterm streamflow record suitable for statistical analysis of flow frequency and duration characteristics and support of other analyses. As documented in this report, NHC conducted this work in three phases. a. First, long-term streamflow records from nearby watersheds were used to characterize the range of hydrologic conditions represented by the relatively short observed streamflow record available within the Project s bypass reach on SF Battle Creek. b. Subsequently, an extended synthetic flow record was developed for upper SF Battle Creek by regression against a long-term daily flow record from an adjacent watershed. c. Various flow metrics were computed from the extended synthetic record. The synthetic record will also be used as input to a Project operations model to provide additional data on flow splits. Hydrologic Analyses for South Fork Battle Creek 1 Northwest Hydraulic Consultants

5 Figure 1. Project Area Map Hydrologic Analyses for South Fork Battle Creek 2 Northwest Hydraulic Consultants

6 2. Available Data The primary data sources for the hydrologic analyses were daily streamflows collected by the U.S. Geological Survey (USGS) and California Department of Water Resources (DWR) in SF Battle Creek and adjacent watersheds (Figure 1). Peak streamflow data for these sites were also used to help determine flow levels for hydraulic modeling (see Section 5.3). Table 1 summarizes the streamflow data reviewed for this study, including the collecting organization, station ID (if known), data type, and available period of record. The SF Battle Creek near Mineral gage was located upstream of the Old Highway 36 Bridge (approximately RM 22.5), just downstream from the proposed Project diversion location and within the Project bypass reach. The eight-year daily record ( ) for this site provided the basis for NHC s hydrologic analysis. This was supplemented by long-term streamflow data from Deer Creek near Vina and Mill Creek near Los Molinos. Both of these gages are located farther downstream (at the edge of the Sacramento Valley) and their watershed areas are significantly larger than the tributary area to the Project, but the basins have similar orientation, geology, and headwater elevations. The Deer Creek below Slate Creek watershed is most similar in size and elevation to SF Battle Creek. However, like SF Battle Creek, it has a relatively short (10-year) daily streamflow record. Hydrologically relevant parameters for each gaged watershed were computed using the USGS StreamStats application for California (USGS, 2014) and selected values are summarized in Table 2. NHC was unable to locate longterm records for watersheds in close proximity to SF Battle Creek with similar elevation and drainage areas. NHC obtained the daily data for SF Battle Creek indirectly through the study team (Deas, pers. comm., 12 Aug 2014). This dataset included continuous daily flows from October 1959 through September 1967, reportedly collected by DWR (Hydmet, 2012), as well as more sporadic data in water years and collected by Rugraw. Based on observation and measurement records provided by Rugraw, NHC re-estimated daily flows from recorded stage measurements for the period; there was insufficient documentation of the monitoring, so those data were not used. Table 1. Streamflow Data Sources Station Source Station ID Data Type Period of Record (WY) South Fork Battle Cr near Mineral USGS DWR Rugraw Peak Daily Daily Mill Cr near Los Molinos USGS Peak, Daily Deer Cr below Slate Cr/Deer Cr at Hwy 32 USGS DWR DCH Daily Hourly Deer Cr near Vina USGS Peak, Daily ; As reported by Hydmet (2012); no station information or data found on CDEC website. Data from not used because of lack of documentation. Hydrologic Analyses for South Fork Battle Creek 3 Northwest Hydraulic Consultants

7 Table 2. Selected Watershed Characteristics (from USGS StreamStats) Station Drainage Area (sq mi) Mean Annual Precipitation (in) Mean Basin Elevation (ft) South Fork Battle Cr near Mineral Mill Cr near Los Molinos Deer Cr below Slate Cr/Deer Cr at Hwy Deer Cr near Vina The long-term record from the downstream Battle Creek gage (USGS , Battle Creek below Coleman Fish Hatchery) was not used because the Battle Creek system is highly regulated and basin hydrology is notably non-homogeneous, with demonstrated differences in hydrologic response from the North Fork and South Fork basins (USBR, 2001; Jones & Stokes, 2005). In addition to streamflow data, snow course data from Feather River Meadow (CDEC FEM) and Lower Lassen Peak (CDEC LLP) were used as reference data in investigating seasonal flow relationships (see Section 4.2). The snow course data, which extend back to 1930, include snow depth and snow water equivalent collected on a monthly basis from late winter through spring. Hydrologic Analyses for South Fork Battle Creek 4 Northwest Hydraulic Consultants

8 3. Water Year Classification The purpose of the first phase of the hydrologic analysis was to characterize the range of hydrologic conditions represented by the eight-year SF Battle Creek streamflow record in order to determine the extent to which the observed record could be used to select representative dry, normal, and wet year hydrographs that can be utilized for potential impact assessments. To the extent possible, it would be desirable to use observed data as a foundation for impact assessments; however, limited observations require the construction of a synthetic record to provide a representative long-term flow record. California water managers are familiar with the DWR water year hydrologic classifications designating individual years as wet, above normal, below normal, dry, or critical. For purposes of water supply planning and management, DWR releases water year classifications every spring for the Sacramento (and San Joaquin) Valley. Our approach was to develop similar runoff-based water year classifications for the long-term Mill Creek and Deer Creek records to confirm regional consistency in hydrologic year types, then to validate the classifications for SF Battle Creek based on relative annual runoff volumes for SF Battle Creek, Mill Creek, and Deer Creek within the SF Battle Creek period of record. 3.1 Regional Water Year Classifications DWR s annual water year type classification for the Sacramento Valley the Sacramento Valley Index is based on combined fall/winter runoff, forecast spring runoff, and prior year conditions at four stream gages within the greater Sacramento River watershed. Index values are classified into five categories critical, dry, below normal, above normal, and wet based on thresholds corresponding to percentile rankings. DWR recently published reconstructed historical water year classifications (based on index values computed from actual, rather than forecast, spring runoff) extending back to the early 1900s (DWR, 2013). NHC used a similar classification scheme to rank and classify water years from the long-term Deer Creek and Mill Creek records and compare to the historic DWR classifications. Since we are not concerned with water supply and over-year storage, total annual runoff was used as the basis for classification rather than the DWR approach encompassing wet season and prior year runoff. After computing annual runoff for each water year (October-September), percentile rankings were used as the basis for classification into the five water year hydrologic types. Thresholds were set at the 15-, 30-, 50-, and 70-percentile levels, based on the original DWR hydrologic classification weightings (DWR as reported in Null and Viers, 2013) as shown in Table 3. Table 3. Percentile Thresholds for Regional Water Year Types Water Year Type Percentile Range Critical C 0-15% Dry D 15-30% Below Normal BN 30-50% Above Normal AN 50-70% Wet W % Although based on a slightly different volume metric than the DWR index, the water year types determined for the Deer Creek and Mill Creek historic records (Appendix A) compare quite well with DWR s reconstructed classifications for the Sacramento Valley index. Table 4 compares the year types Hydrologic Analyses for South Fork Battle Creek 5 Northwest Hydraulic Consultants

9 for water years 1960 through 1967, the period for which daily flow data are available for SF Battle Creek. The similarities in water year types between the Project region and the Sacramento Valley indicate a broad regional consistency that would support the assumption that relative runoff volumes on SF Battle Creek would have a similar long-term distribution to the neighboring watersheds. Table 4. Regional Water Year Types Water Year Sacramento Valley Index Mill Creek Annual Runoff Deer Creek Annual Runoff 1960 D BN D 1961 D BN BN 1962 BN BN BN 1963 W W W 1964 D D D 1965 W W W 1966 BN BN BN 1967 W W W NHC performed a similar ranking and classification (using the same percentile thresholds) of summer runoff only for Deer Creek and Mill Creek, using total runoff volume in July through September of each water year in place of total annual runoff. This low flow period is critical for understanding the seasonal operation timeframes and for evaluating Project impacts. As shown in Table 5 and Appendix A, water year types closely match classifications based on the summer-only period. This alignment between annual and seasonal flow indicates that selection of representative years based on (annual) water year types should provide representative summer conditions for the same year type. Table 5. Comparison of Summer and Annual Water Year Type Classifications Water Year Sacramento Valley Index Mill Creek Deer Creek Annual Summer Annual Summer 1960 D BN BN D D 1961 D BN BN BN BN 1962 BN BN BN BN BN 1963 W W AN W AN 1964 D D D D BN 1965 W W W W W 1966 BN BN BN BN BN 1967 W W W W W 3.2 Application to SF Battle Creek The eight-year record for SF Battle Creek is too short to support the DWR water year type classification. However, the regional consistency in water year type demonstrated above suggests that the relative wetness of the years for which data are available for Battle Creek would correspond with that for the neighboring watersheds. This conclusion is further supported by comparison of annual volumes between the three gages over the SF Battle Creek period of record. Hydrologic Analyses for South Fork Battle Creek 6 Northwest Hydraulic Consultants

10 Annual Discharge (inches) Table 6 compares annual volume, expressed in inches over the watershed area to facilitate comparison, for SF Battle Creek, Mill Creek, and Deer Creek over water years 1960 through Relative wetness of individual years within that period is indicated by comparison of annual runoff to the period mean for each watershed. To provide a broader long-term context, annual runoff is also compared to the longterm mean for Mill Creek and Deer Creek. Table 6. Annual Runoff Comparison for SF Battle Creek Period of Record Water Year SF Battle Creek (33.2 sq mi) Runoff (in) % Period Mean Runoff (in) Mill Creek nr Los Molinos (131.4 sq mi) % Period Mean % Longterm Mean Runoff (in) Deer Creek nr Vina (208.7 sq mi) % Period Mean % Longterm Mean % % 73% % 64% % % 81% % 72% % % 81% % 82% % % 133% % 134% % % 62% % 55% % % 142% % 154% % % 72% % 68% % % 134% % 142% Relative wetness of each year is generally consistent across all three gages, and the period averages for the Mill Creek and Deer Creek records indicate that the 1960 through 1967 period was slightly drier than the long-term average. As shown in Figure 2, normalized SF Battle Creek runoff consistently falls between those of Deer Creek and Mill Creek. Figure 2. Normalized Annual Discharge Comparison Water Year SF Battle Creek Deer Creek Mill Creek Hydrologic Analyses for South Fork Battle Creek 7 Northwest Hydraulic Consultants

11 Based on the consistency in seasonal and annual runoff patterns demonstrated in this analysis, it is reasonable to conclude that water year types for nearby Deer Creek and Mill Creek also apply to the Project watershed on SF Battle Creek. The available observed record for the Project bypass reach covers a diverse range of hydrologic conditions, from a dry year in water year 1964 through wet years in 1965 and Related analyses requested by FERC and other regulatory agencies require assessment of Project impacts on representative dry, normal, and wet year conditions. In selecting representative annual hydrographs needed for further analyses, preference should be given to observed data over synthetic estimates where possible. Based on that consideration, NHC recommends the following years for representative daily flow hydrographs over the range of conditions represented in the observed record: Dry year 1964 (1 Oct Sept 1964) Below Normal year 1962 (higher spring runoff) or 1961 (larger winter events) Wet year 1967 (high spring snowpack and runoff) or 1965 (large winter storms) This analysis and visual inspection of the annual hydrographs indicate that these years will provide suitable sample inputs to the Project operations model to simulate potential Project effects on flows, sediment, and temperatures for their respective water year types. However, in some cases, use of observed hydrographs may not be possible due to needs for paired data or other observations not available within the observed period of record. In those cases, or for year types not represented in the observed record (i.e., Critical or Above Normal), representative annual hydrographs can be selected from the synthetic record (see Section 4) based on year types listed in Appendix A (see also Section 5.1). Hydrologic Analyses for South Fork Battle Creek 8 Northwest Hydraulic Consultants

12 4. Synthetic Project Inflow Record Although observed data cover a sufficient range of hydrologic conditions to provide representative annual flow hydrographs, the observed daily flow record for SF Battle Creek is too short for reliable statistical analysis of annual and seasonal flow frequencies and durations. The second phase of NHC s work focused on the development of a long-term daily flow record for SF Battle Creek to support statistically-based analysis of Project inflows, operations, and impacts. Our approach was to assess correlations between the SF Battle Creek record and available long-term flow records, select the longterm record that related most closely to SF Battle Creek, and develop regression equations to transpose flows from the long-term record to the Project reach to extend the observed flow record there. 4.1 Observed Streamflow Comparison The observed daily streamflow record for SF Battle Creek near Mineral (at the Old Highway 36 Bridge) consists of a nearly complete record for water years and more sporadic data collected in and The eight-year continuous record was used as the basis for development of the extended synthetic flow record. This period was compared to coincident data from the long-term records for Mill Creek near Los Molinos (Mill Creek) and Deer Creek near Vina (Deer Creek) and to Deer Creek below Slate Creek (Upper Deer Creek). Although Upper Deer Creek does not have an extended record, if the Upper Deer Creek record correlated well with both SF Battle Creek and (lower) Deer Creek, one possible approach would be to transpose the long-term Deer Creek record through Upper Deer Creek to SF Battle Creek. SF Battle Creek flows for the period were initially plotted against flows from Mill Creek and Deer Creek for the same period. SF Battle Creek flows were also plotted against Deer Creek below Slate Creek (Upper Deer Creek) for , which is the period of overlap for the two gages. All flow comparisons used area-normalized flows (flow divided by basin area) to provide more direct comparison of runoff generation and flow patterns. Scatter plots of the full analysis period for all three gage comparisons essentially produced clouds of data with no distinct relationships or discernible trends. Recognizing the differences between basins in elevation and precipitation, which would suggest distinct seasonal runoff responses, separate flow comparison plots were produced for fall (October through December), winter (January through March), spring (April through June), and summer (July through September). The seasonal plots (Figure 3, next page) show much stronger correlations and patterns that are more readily explained by physical differences between the watersheds. The blue trend lines shown on the fall, winter, and spring plots are high flow regressions only, as discussed in Section 4.2; the black trend line on the summer plot is based on all summer flows. Hydrologic Analyses for South Fork Battle Creek 9 Northwest Hydraulic Consultants

13 Winter (January March) SF Battle Creek (cfs/sq mi) Fall (October December) SF Battle Creek (cfs/sq mi) Figure 3. Seasonal Flow Comparisons (area-normalized flow in cfs/sq mi) R² = Mill Creek (cfs/sq mi) Deer Creek nr Vina (cfs/sq mi) Upper Deer Creek (cfs/sq mi) R² = Mill Creek (cfs/sq mi) Deer Creek nr Vina (cfs/sq mi) Upper Deer Creek (cfs/sq mi)

14 Summer (July September) SF Battle Creek (cfs/sq mi) Spring (April June) SF Battle Creek (cfs/sq mi) Figure 3 (continued) R² = Mill Creek (cfs/sq mi) Deer Creek nr Vina (cfs/sq mi) Upper Deer Creek (cfs/sq mi) R² = Mill Creek (cfs/sq mi) Deer Creek nr Vina (cfs/sq mi) Upper Deer Creek (cfs/sq mi)

15 The scatter plots in Figure 3 show that SF Battle Creek has a consistently stronger correlation with Mill Creek than with Deer Creek. Not surprisingly, there is significantly more scatter in the winter and spring seasons, when differences in elevation and relative contribution of precipitation processes (snow and rain) are most important. The summer relationship between SF Battle Creek and Mill Creek is remarkably consistent. This period is particularly important for planned application of the synthetic flow record, since low flows are critical for potential temperature impacts and will largely dictate periods when operations shut down to maintain minimum instream flows. In most seasons (with the notable exception of summer), SF Battle Creek correlates most closely with Upper Deer Creek. This is not surprising since Upper Deer Creek is most similar to SF Battle Creek in terms of watershed size and elevation. The winter and spring relationships, in particular, are much tighter than those to either of the long-term, lower elevation records. However, the correlations between Upper Deer Creek and (lower) Deer Creek are no better than SF Battle Creek to Mill Creek or Deer Creek. Since development of a long-term synthetic record for SF Battle Creek requires transposing from one of the two long-term records, use of the Upper Deer Creek record provides no advantage and would introduce additional uncertainty in transposing through two locations. Based on these results, and particularly the strong summer correlation, the long-term Mill Creek record was selected as the reference time series for a synthetic SF Battle Creek record. 4.2 Seasonal Flow Relationships The next step in creating the synthetic record was the development of regression equations to transpose Mill Creek daily flows to the Project area on upper SF Battle Creek. Recognizing the seasonal shifts in flow relationships, separate equations were developed for each season. Summer in this region is largely dry, so differences in summer flows are likely driven primarily by watershed geology, particularly the influence of perennial springs. Since geologic characteristics (including the occurrence of baseflow springs and groundwater seeps) are similar for the Mill and SF Battle Creek watersheds, they are assumed essentially constant on an annual time scale; therefore, the summer regression equation ( baseflow equation ) was further assumed to apply for baseflow levels throughout the year. Separate high flow regressions were applied in the fall, winter, and spring to account for other factors affecting the flow relationships in those seasons. All flow relationships discussed in this section were developed for area-normalized flows. Synthetic daily flows were computed by multiplying normalized flows computed from the equations presented in this section by the SF Battle Creek basin area (see Section 4.3). The baseflow equation (Equation 1) represents the best-fit regression of Mill Creek to SF Battle Creek normalized flows for July through September (line shown in Figure 3): (Equation 1) where q bf is transposed Mill Creek baseflow and q M is Mill Creek flow. Equation 1 was applied for all summer flows and for baseflows (q M less than 2 cfs per square mile) throughout the year. The seasonal high flow regressions are linear relationships representing the best-fit line to SF Battle Creek vs. Mill Creek data above the baseflow threshold. (Power series regressions were also checked but linear regressions provided a better fit in all cases.) These are the blue trend lines shown in the fall, winter, and spring plots in Figure 3. The seasonal high flow regressions, which apply only to normalized Mill Creek flows greater than 2 cfs per square mile, are presented in the following equations, where q B is Mill Creek flow transposed to SF Battle Creek and q M is Mill Creek flow (as in Equation 1). Hydrologic Analyses for South Fork Battle Creek 12 Northwest Hydraulic Consultants

16 SF Battle Creek (cfs/sq mi) SF Battle Creek (cfs/sq mi) SF Battle Creek (cfs/sq mi) SF Battle Creek (cfs/sq mi) Fall (October-December) (Equation 2) Winter (January-March) (Equation 3) Spring (April-June) All (Equation 4) The transposed flows resulting from application of the low and high flow relationships are illustrated in the seasonal plots in Figure 4. In each plot, the blue points represent transposed Mill Creek flows vs. SF Battle Creek observed flows, and the red line is the unity relationship between transposed Mill Creek flows and observed SF Battle Creek flows. Figure 4. Seasonally Transposed Mill Creek to SF Battle Creek Normalized Flows Summer (Jul-Sep) Fall (Oct-Dec) Transposed Mill Creek (cfs/sq mi) Transposed Mill Creek (cfs/sq mi) Winter (Jan-Mar) Spring (Apr-Jun) Transposed Mill Creek (cfs/sq mi) Transposed Mill Creek (cfs/sq mi) Hydrologic Analyses for South Fork Battle Creek 13 Northwest Hydraulic Consultants

17 SF Battle Creek (cfs/sq mi) For the summer, fall, and even winter seasons, the majority of the transposed flows fall along the unity line. However, for spring, a large number of points fall well off the line, and there appear to be several different tracks in the flow relationship. We hypothesized that the different relationships between SF Battle Creek and Mill Creek spring flows could be related to snowpack, since the magnitude and timing of snowmelt is a key component of spring flows, especially for the higher elevation SF Battle Creek watershed. To evaluate this hypothesis, spring flows were plotted by individual years. Figure 5 shows the same SF Battle Creek vs. Mill Creek spring flow comparison included in Figure 3 with individual water years designated by symbols; the orange color designates relatively dry years (dry and below normal from Table 4) and blue designates wet years. Figure 5. Spring Flow Comparison by Year Mill Creek (cfs/sq mi) It is immediately apparent from the figure that the more erratic departures on the right side of the plot are all associated with overall wet years (1963, 1965, and 1967), while the correlation is much tighter in overall dry years. There is no simple correlation with spring snowpack however. Snow depth and snow water equivalent data from the Feather River Meadow snow course (CDEC FEM), located at 5,400 feet just east of the SF Battle Creek and Mill Creek headwaters, show 1963 as having the lowest spring snowpack in the 79-year record while 1967 had the highest, with snowpack continuing to build up through May. The remaining years in the SF Battle Creek flow record had spring snowpack near the longterm average; 1962 (a dry year) was the second highest snow year in the analysis period. Absent a convincing snowpack correlation, NHC explored developing separate spring high flow regressions for dry years and wet years. Results are shown in Figure 6. Data scatter is significantly lower for the dry years, producing a very good regression fit. For the wet years, fit continues to be relatively poor. NHC explored the effect of eliminating outliers from the high flow data used to determine the regression, including eliminating data from 1967 altogether due to the extreme snowpack, but resulting Hydrologic Analyses for South Fork Battle Creek 14 Northwest Hydraulic Consultants

18 Battle Creek (cfs/sq mi) Battle Creek (cfs/sq mi) shifts did not significantly improve the fit or ability to match observed flow hydrographs (see Section 4.3), so results are presented including all of the wet year data. Figure 6. Dry Year and Wet Year Spring High Flow Regressions Equations 5a and 5b represent the regression relationships shown in Figure 6. Transposed spring flows based on the dry and wet year regressions (and the baseflow regression for low flows) are shown in Figure 7. Spring (April-June) Dry Year (Equation 5a) Spring (April-June) Wet Year (Equation 5b) Figure 7. Transposed Spring Flows Using Dry Year and Wet Year High Flow Regressions Dry Year Spring (Apr-Jun) Wet Year Spring (Apr-Jun) Transposed Mill Creek (cfs/sq mi) Transposed Mill Creek (cfs/sq mi) Hydrologic Analyses for South Fork Battle Creek 15 Northwest Hydraulic Consultants

19 4.3 Synthetic Time Series Development The entire USGS Mill Creek daily flow record (water years 1930 through 2014) was transposed to SF Battle Creek using the relationships developed in Section 4.2. Daily flows were divided by the square mile Mill Creek watershed area to produce normalized daily flows. The baseflow transposition was applied to summer flows and low flows throughout the year. The appropriate seasonal high flow regression was applied depending on month of the year and for the series calculated with multiple spring regressions the Mill Creek water year classification (Section 3.1 and Appendix A). The transposed flow was multiplied by the 33.2-square mile SF Battle Creek watershed area to produce an estimated daily flow for SF Battle Creek at the Old Highway 36 Bridge. Figure 8 and Figure 9 (at the end of this section) show the synthetic time series versus observed SF Battle Creek flows for the periods when observed data are available for SF Battle Creek near Mineral. Figure 8 includes the period used to develop the transposition equations; plots are shown at two scales to better illustrate peaks as well as more typical flow levels. Figure 9 compares the more sporadic data collected in , which effectively serves as a validation period. The figure includes two synthetic hydrographs, one using the single spring high flow regression (Equation 4, labeled Synthetic) and one using separate wet year and dry year spring high flow regressions (Equations 5a and 5b, labeled Syn W/D). It should be noted that the only differences between the two synthetic data sets are in the high flow portions of the April through June periods; both series use Equation 1 for low flows and summer flows and Equations 2 and 3 for fall and winter high flows, respectively. The figures show little difference between the two synthetic data series Estimated Accuracy of Synthetic Flows As with any statistically-based approach, it is unreasonable to expect to match the full range of observed flows equally well. This analysis places an emphasis on more accurately reproducing (and estimating) low flow conditions in the Project reach, which will be critical for operational considerations. Expected accuracy for estimations during the summer baseflow period is improved by the tight correlation of SF Battle Creek and Mill Creek flows during this period. Moving into the wet season, the physical mechanisms affecting runoff production become more complex (with spatially and orographically variable precipitation, differences in snow accumulation and melt, etc.) and the observed flow relationships show significantly more scatter, making it more difficult to capture variability and accurately transpose flows with a consistent set of equations. Since regression relationships seek to even out departures from the mean, it can be difficult to accurately estimate peak flows, with larger events in particular often being somewhat anomalous from day to day runoff generation mechanisms. Both synthetic SF Battle Creek streamflow records tend to under-estimate large peaks (Figure 8), with the notable exception of December 1964, which was the largest event in the observed period. For this reason, peak flow estimates based on the synthetic record, especially those greater than about 300 cfs, should be used with caution. Another factor that may affect accuracy of the estimated flows is relative flow timing between SF Battle Creek and Mill Creek. Since the Mill Creek gage is much farther downstream, flow from the headwaters would be expected to take longer to reach the gage location than in SF Battle Creek. NHC evaluated shifting Mill Creek flows back one day to account for timing differences, but overall seasonal correlations were consistently better when comparing flows recorded the same day. In a visual comparison of observed and simulated hydrographs, however, timing shifts are apparent in places. These timing shifts can result in large errors compared to observed flows. Table 7 summarizes positive (estimated greater than observed) and negative (estimated less than observed) residuals for all days with observed data. The table is broken out into several categories to Hydrologic Analyses for South Fork Battle Creek 16 Northwest Hydraulic Consultants

20 provide information about potential bias in different seasons and at different flow levels. The summary results indicate a slight negative bias. Table 8 lists the standard error of estimate for the two synthetic flow series for the same seasons and flow levels. As visual inspection in Figure 8 and Figure 9 suggested, there do not appear to be significant differences between the two synthetic series. Based on a marginally better visual match to the observed hydrograph (e.g., spring 1962 and 1966), the series using separate wet/dry spring high flow regressions (Synthetic W/D) was selected as the most representative estimate of SF Battle Creek flows. Table 7. Summary of Estimated Bias of Synthetic Streamflows for SF Battle Creek Flow Category No. of Positive Residuals Mean of Positive Residuals (kcfs) No. of Negative Residuals Mean of Negative Residuals (kcfs) % of Residuals > 10% of Obs. Mean Days in Category Summer % 820 Fall % 776 Winter % 735 Synthetic (Single Spring Flow High Flow Regression) Spring % 755 Q obs % 1223 Q obs % 1259 Q obs % 553 Q obs > % 52 All % 3086 Synthetic W/D (Wet Year/Dry Year Spring High Flow Regressions) Spring % 755 Q obs % 1223 Q obs % 1259 Q obs % 553 Q obs > % 52 All % 3086 Hydrologic Analyses for South Fork Battle Creek 17 Northwest Hydraulic Consultants

21 Table 8. Summary of Estimated Accuracy of Synthetic Streamflows for SF Battle Creek Flow Category Mean Observed (cfs) Mean Estimated (cfs) Std. Error of Estimate (cfs) % of Observed Mean Summer % Fall % Winter % Synthetic (Single Spring Flow High Flow Regression) Spring % Q obs % Q obs % Q obs % Q obs > % All % Synthetic W/D (Wet Year/Dry Year Spring High Flow Regressions) Spring % Q obs % Q obs % Q obs % Q obs > % All % Additional Uncertainties The synthetic flow data for South Fork Battle Creek near Mineral represent our best estimate of Project reach inflows over an extended time period, based on available data. An additional factor that may affect Project inflows, especially during the summer growing season, is agricultural diversions from SF Battle Creek upstream of Highway 36. We understand that there are extensive irrigated lands upstream of the Project site, but do not have information about the magnitude and timing of associated withdrawals and whether they were occurring (and thus implicitly accounted for in the observed flow record) during the period in the 1960s used to develop flow correlations. Hydrologic Analyses for South Fork Battle Creek 18 Northwest Hydraulic Consultants

22 Figure 8. Observed vs. Synthetic Flows for SF Battle Creek near Mineral, WY Hydrologic Analyses for South Fork Battle Creek 19 Northwest Hydraulic Consultants

23 Figure 9. Observed vs. Synthetic Flows for SF Battle Creek near Mineral, WY Hydrologic Analyses for South Fork Battle Creek 20 Northwest Hydraulic Consultants

24 5. Flow Data Analysis and Applications The final extended flow record for SF Battle Creek near Mineral is a composite of the synthetic flow data (computed as described in Section 4) and observed flow data, where available. Again, the synthetic flows derived with separate wet year/dry year spring high flow regressions were selected as the most representative time series for SF Battle Creek. These flows represent our best estimate of baseline daily inflows to the Project reach from water years 1930 through The following sections describe results of several initial applications of the extended inflow record. 5.1 Water Year Characterization Temperature, fisheries, and sediment impacts analyses are being conducted as part of this study using flow data from representative water year types. While years with observed data are preferred because they most accurately represent flow patterns in the Project reach, some of the analyses require other kinds of contemporaneous data, such as water temperature and fish use, that are not available for the earlier periods. To facilitate selection and characterization of appropriate years for these analyses, the composite SF Battle Creek near Mineral record was classified by water year type using the same methods employed for Mill Creek and Deer Creek, described in Section 3.1. Classifications for SF Battle Creek based on annual and summer runoff volumes are included in Appendix A. The Project temperature analysis requires selection of a representative year of each water year type in the post-2000 period, to correspond with available water temperature and meteorological data. The objective in selecting representative years is to identify, where possible, water years with runoff near the midpoint of the percentile range for each category with relatively typical runoff patterns. Table 9 groups the post-2000 period by water year classification for SF Battle Creek, with annual runoff percentile rank shown in parentheses. Some suggested representative year selections are indicated in bold. Note: water year 2013 is categorized as a Below Normal (BN) water year; however, it is somewhat unique because it was extremely wet in the fall, then critically dry through the rest of the year. Therefore, analyses and results produced from this year should be compared to the other two more representative BN years (2002 and 2012) where possible. Table 9. Post-2000 Water Year Classifications for SF Battle Creek Water Year Type 5.2 Mean Daily Flow Metrics Flow Frequency Analysis Low Flows Percentile Range Percentile Target Years in Category ( ) (annual runoff percentile in parentheses) Critical C 0-15% 7% 2014 (3) Dry D 15-30% 22% 2001 (16), 2007 (21), 2008 (24), 2009 (29) Below Normal BN 30-50% 40% 2002 (48), 2012 (32), 2013 (31) Above Normal AN 50-70% 60% 2000 (55), 2004 (56), 2005 (53), 2010 (57) Wet W % 85% 2003 (79), 2006 (95), 2011 (84) As mentioned previously, magnitude and timing of flow during low-flow periods are critical for potential impact assessments in the Project bypass reach. Table 10 presents the results of seven-day minimum flow frequency analysis on the Project inflow time series. The analysis indicates that sustained zero flow Hydrologic Analyses for South Fork Battle Creek 21 Northwest Hydraulic Consultants

25 conditions entering the Project reach occur about once every ten years on average and that sustained flows as low as 1.5 cfs occur about once every five years on average. This recurrence corresponds quite well with the frequency of Critical-type water years (15 percent). Table 10. Seven-Day Low Flow Frequency Return Interval 7-day Minimum Flow (cfs) 2-year year year < year year year 0.00 High Flows An understanding of high flows is important for hydraulic design of the diversion structure as well as sediment transport considerations. Although the largest events in this region have occurred in fall to early winter, some of the highest flows have also occurred in the spring, likely associated with rain-onsnow events. Figure 10 and Table 11 show annual maximum (mean) daily flow frequency analysis results based on a Log Pearson Type III fit using the methods of Bulletin 17b (USGS, 1981). Again, these values should be used with caution as higher peaks tend to be under-estimated in the synthetic SF Battle Creek record. Table 11. Maximum Daily Flow Frequency for SF Battle Creek near Mineral Return Interval Maximum Daily Discharge (cfs) 2-year year year year year year 1550 Hydrologic Analyses for South Fork Battle Creek 22 Northwest Hydraulic Consultants

26 Figure 10. Maximum Daily Flow Frequency Curve for SF Battle Creek near Mineral Flow Duration Analysis Inflow Exceedance Probabilities February 1 to May 15 Table 12 summarizes Project inflow exceedance probabilities for a range of flows from February 1 to May 15, which encompasses key seasons of potential upstream spawning migrations in the bypass reach by both spring Chinook and steelhead. Table 12. Project Inflow Durations for February 1 - May 15 Flow Category Exceedance Probability (% of time period) for Flow Threshold (cfs) Feb Feb 16 28/ Mar Mar Apr Apr May Full Period (Feb 1 May 15) Hydrologic Analyses for South Fork Battle Creek 23 Northwest Hydraulic Consultants

27 A consideration related to fish passage is the ability of migratory fish to pass Panther Grade, located 1.7 miles downstream of the Project powerhouse, and other physical fish migration barriers between Panther Grade and the Project reach. The studies of Douglas Parkinson and Associates (2012) established, with detailed measurements of jump heights and pool depths at Panther Grade, that the channel feature was clearly impassable at each of the flows studied (24, 100, and 180 cfs). It has been hypothesized that Panther Grade could become passable at some flow substantially greater than 180 cfs. If passage were to become possible at 300 cfs, for example, Table 12 indicates that Panther Grade would be passable about 1.4 percent of the days between February 1 and May 15 (on average, approximately a day and a half per year). As discussed in Section 4.3.1, peak flows tend to be underestimated in the synthetic data, so this estimate may be somewhat low. The 300-cfs exceedance probability for the observed data between 1960 and 1967 is about two percent (on average, approximately two days per year) during the period February 1 through May 15. Sediment Transport The sediment transport analysis will use a hydraulic model to identify the flow thresholds needed to initiate transport or deposition of different bed material sizes found approaching the diversion structure and in the Project reach. s of sediment transport and/or deposition can then be estimated from information related to flow durations for each flow threshold and material size category. To support the hydraulic and sediment analyses, flow exceedance probabilities (expressed in days per year) over a range of flows up to 500 cfs were computed for the entire composite record (Table 13) and for the representative years of observed data identified in Section 3.2 (Table 14). Table 13. Project Inflow Exceedance Probabilities for Sediment Analysis Exceedance Probability (days per yr) for Flow Threshold (cfs) Table 14. Observed Flow Exceedance Probabilities for Selected Representative Water Years Water Year Exceedance Probability (days per yr) for Flow Threshold (cfs) (dry) (below normal) 1962 (below normal) (wet) (wet) Instantaneous Peak to Mean Daily Flow Relationships The USGS collected instantaneous peak ( peak ) flow data for SF Battle Creek near Mineral over the same 1960 through 1967 period for which daily data are available. This period is too short for a reliable peak flow frequency analysis, but NHC compared recorded peak flows to corresponding mean daily flows to determine whether a reasonable scaling factor could be identified to support at least an Hydrologic Analyses for South Fork Battle Creek 24 Northwest Hydraulic Consultants

28 approximate peak flow analysis. Of the seven peaks in the USGS record, six are from the same event that produced the maximum daily flow for the year. The annual peak for water year 1963 is missing from the peak flow record, but it is likely associated with the maximum daily flow on 12 October 1962, which was the second highest daily flow in the observed record (and produced the peak and maximum daily flow on Mill Creek for that year). Instantaneous peak to mean daily flow ratios for the six events range from 1.44 to 1.89, which is a reasonably consistent relationship for something as variable as peak flows. Based on this comparison, NHC recommends a multiplier of 1.62 (slope of the best-fit peak to maximum daily flow linear regression) on maximum daily peaks as a reasonable estimate of peak flows from the daily time series. Table 15 shows estimated peak discharges based on scaling maximum daily flow values in Table 11 by the 1.62 multiplier. Table 15. Estimated Instantaneous Peak Flow Frequency for SF Battle Creek near Mineral Return Interval Estimated Peak Discharge Near Mineral (cfs) 2-year year year year year year 2500 Note that these values are much lower than peak flow quantiles that would be estimated from the USGS regression equations for flood flows in California (USGS, 2012) (or from the superseded USGS regression equations in the StreamStats web application). For the Sierra region, the USGS identified basin area, mean basin elevation, and mean annual precipitation as the dominant peak flow parameters, and coefficients and exponents on those parameters were estimated from available gage records in the region. The resulting equations produce an estimate of 1,340 cfs for the 2-year peak discharge and 9,300 cfs for the 100-year discharge for SF Battle Creek. The December 1964 event, which is approximately a 25-year event on Mill Creek, had an observed instantaneous peak of 2,050 on SF Battle Creek near Mineral. The regression estimate of the 25-year peak for SF Battle Creek is 5,630 cfs, clearly indicating that regression results are too high for this watershed. It is worth noting that the USGS regression estimates for Mill Creek are reasonably consistent with flow frequency results for the long-term Mill Creek peak flow record. Because there are so few long-term gage records for smaller, higher elevation watersheds (as discussed in Section 2), these types of basins are not well-represented in the regressions, and it is reasonable to expect greater error in the peak flow predictions. Hydrologic Analyses for South Fork Battle Creek 25 Northwest Hydraulic Consultants