Pacific Gas and Electric Company s Drum-Spaulding Project (FERC No. 2310) Rollins Transmission Line Project (FERC No. 2784)

Transcription

1 Nevada Irrigation District s Yuba-Bear Hydroelectric Project (FERC No. 2266) Pacific Gas and Electric Company s Drum-Spaulding Project (FERC No. 2310) Rollins Transmission Line Project (FERC No. 2784) Hydrology and Water Balance Model Technical Workshops June 11 and 14, 2007

2 Assessment of Regulated Hydrology and Development of Unimpaired Hydrology presented by Rick Jones, P.E. Devine, Tarbell and Associates, Inc. Page 2

3 Hydrologic Basin Locations GENERAL LOCATION Page 3

4 Unimpaired Hydrology Period of Record Methodologies Ideally >25 years of recent data Selected WY WY 2004 (29 year record; 10/1/1975 9/30/2004) Captures wettest (WY 1983) and driest (WY 1977) years on record Sufficient variability exists within record to analyze range of water year conditions as well as consecutive year types Page 4

5 Unimpaired Hydrology Methodologies Gage-Summation Begin with basin outflow via stream gage Remove reservoir regulation: Remove inter-basin transfers Proration Method Begin with a gage-summation hydrograph from a representative, largely unimpaired reference basin Apply via proration to other basins of interest: 2 nd ΔS Q target = Q = inflow A A Q target reference outflow Q Q reference losses nd and 3 rd order adjustments (avg. precipitation, basin elevation) Page 5

6 Gage-Summation Limitations General Missing gages Missing WY s Missing periods Poor data quality Stream gage errors Intermittent data collection Control type/accuracy Incomplete flow (spillway circumvention, compliance gages) Reservoir gage errors Intermittent data collection Storage rounding Evaporation Area-Capacity curves Wind run-up up Through-flow gradients Page 6

7 Typical Gage Summation Results Illustrating Poor Data Quality and Density in the Texas Creek Region Culbertson Lake - WY 1989 to Oct-1988 Apr-1989 Oct-1989 Apr Page 7

8 Typical Gage Summation Results Illustrating Missing WY s s and Data Scatter in the NFk NFk American River Region NFk NFk Amer R / LV Canal - WY 1976 to Page 8

9 Synthetic Unimpaired Hydrographs by Means of Proration 1 st order proration by area: Q = target A target q reference Page 9

10 Synthetic Unimpaired Hydrographs by Means of Proration 1 st order proration by area: Q = target A target q reference 2 nd order adjustment to resolve rainfall/long term volume differences: Q target 2 P = P target reference Q new Page 10

11 Comparison of NWS Isohyets vs. SCAS 4-km 4 Grid Data Page 11

12 Synthetic Unimpaired Hydrographs by Means of Proration 1 st order proration by area: Q = target A target q reference 2 nd order adjustment to resolve rainfall differences: Q target 2 = P P target reference Q new rd order adjustment to resolve runoff timing differences due to elevation: 3 rd 8to9k Qtarget 3, m = Atarget, efe, mqreference, e, m e= Bear/Drum-Spaulding/Rollins 5to6k Relicensings Page 12

13 Elevation Differences in Upper Basin Page 13

14 Snowpack Runoff Intensities across the Snowmelt Season, by Elevation Page 14

15 Upper Basin Reference Watershed Page 15

16 Upper Basin Reference Watershed South Yuba above Cisco Representative of the upper basin hydrology A subset of the upper basin, with the same elevation spread Largely unimpaired with good data Stream data at basin s s outflow was excellent Includes three reservoir sub-basins, basins, but their spatial extent was very small, roughly 4% Regulation from small reservoirs adjusted through gage-summation (where feasible) Page 16

17 South Yuba above Cisco Reconstruction Issues South Yuba River flow reconstruction Several missing periods (including significant storm events) Lake evaporation estimates Summer low-flow gage-summation errors: methods for data refinement Recession limb 7-day rolling average Manual adjustments Peak flow estimation Prorated Onion Creek Summer Base Flow Analysis Page 17

18 South Yuba above Cisco Reconstruction Issues Example during summer low-flow period, WY 1987 Cisco Unimpaired M-87 J-87 J-87 A-87 S-87 O-87 N-87 D-87 flow sum 7-day manual regression proration peak flow Page 18

19 South Yuba above Cisco Summer Peak Flow Analysis Summer Base Flow Trends during Dry, Normal, and Wet Years Area-Normalized Flow (cfs/sq mi) Dry Below Normal Above Normal Wet South Yuba at Cisco Onion Creek near Soda Springs Page 19

20 South Yuba above Cisco Period of Record Trends Monthly Runoff Volume (ac-ft) South Yuba River at Cisco Water Year Oct Nov Dec Jan Feb Mar Month Apr May Jun Jul Aug Sep Page 20

21 Unit Hydrograph by Elevation Band Each basin has a unique distribution of elevations Typical relative runoff intensities were developed for 1,000 ft elevation bands in the project vicinity using historic monthly snow pack data at a range of elevations A generic monthly distribution was then developed for the South Yuba at Cisco watershed based on elevation distributions Using period of record average monthly runoff at Cisco, this distribution was then given a second-order order calibration Page 21

22 Unit Hydrograph by Elevation Band (cont d) Annual differences in watershed runoff patters were honored using the following convergence algorithm: The months of August, September and October were ignored due to insignificant snowmelt impacts (all elevation bands given the same area-adjusted adjusted runoff) For the remaining months, the "recompiled hydrograph" must be +/- 2% the volume of the original reference hydrograph (monthly mass balance) For each water year, the individual elevation band volumes must be +/- 2% of the proportional volume expected from the original reference hydrograph (assumes equal annual area-adjusted adjusted runoff from each elevation band) For each water year, the total recompiled hydrograph must be +/- 1% of the volume of the original reference hydrograph (annual mass balance) ance) Page 22

23 Monthly Runoff Distribution (Period of Record Average) South Yuba River at Cisco ft ft ft ft Error 3.0 Area/Month 6.3% 50.4% 40.9% 2.4% Factor k 6-7k 7-8k 8k Month For each month in the above graph, the size of the factors represent the proportion of runoff contributed by that elevation band relative to what would be expected by a simple area-based proration. Error Page 23

24 Resulting Watershed Runoff Differences Canyon Creek at Pulp Mill Diversion (PCWA) Lower Basin method applied Drainage Area: 3.90 sq mi Average basin elevation: ~4,500 ft Rucker Lake, Rucker Creek Region Upper Basin method applied Drainage Area: 1.41 sq mi Average basin elevation: ~6,000 ft White Rock Lake South Yuba River Region Upper Basin method applied Drainage Area: 1.12 sq mi Average basin elevation: ~8,500 ft Page 24

25 Resulting Watershed Runoff Differences (WY scaled to 1 sq. mi. each for comparison) /1/2002 1/1/2003 4/1/2003 7/1/2003 Canyon Ck Pulp Canal Rucker Lake White Rock Lake Page 25

26 Upper Basin Gage Summation Limitations Page 26

27 Gage Summation Limitations in the Upper Basin Seven regions with thirty-seven locations Seventeen locations were either not gaged, had extensive missing data, or very sparse data Twenty locations with sufficient data were analyzed Examples of three locations Middle Yuba River Region Jackson Meadows Res Canyon Creek Region Jackson Lake South Yuba River Region Fordyce Lake Reference Basin on South Yuba at Cisco Page 27

28 Middle Yuba River Jackson Meadows Reservoir Principle gage-summation errors Missing WY s s within the POR 6-year gap between old and new stream gage locations Measurement rounding at reservoir gages Flow banding: USGS-reported daily storage rounded to 100 ac-ft means flows will band at ~50 cfs intervals Circumvention of stream gages 2 nd data set records regulated flow only; spillway flow will bypass the gage location Water surface evaporation at reservoir gages Roughly estimated to be 6 cfs in the summer Page 28

29 Canyon Creek Region Jackson Lake Principal gage summation errors: Missing WY s s within the POR Stream flow data begins in WY Data for WY s s 1996 and 97 was extremely sparse Range of stream gage Gage records compliance flows (up to 2.9 cfs) Circumvention of stream gage Spillway flows bypass the stream gage Measurement rounding at reservoir gage Clear evidence of flow banding at ~5 cfs intervals later in the POR (10 ac-ft rounding of storage data) Page 29

30 Canyon Creek Jackson Lake Comparison of gage-summation data with the synthetic hydrograph for the entire POR: Jackson Lake - WY 1976 to Jackson Lake - Synthetic Cumulative Unimpaired Data Jackson Lake - Gage Summation Data Page 30

31 South Yuba River Fordyce Lake Missing WY s s and months, and generally poor data quality, but excellent agreement in some instances (raw storage data is not rounded before submittal to USGS, thereby providing a reasonable check): Fordyce Lake - WY Oct-84 Jan-85 Apr-85 Jul Fordyce Lake - Synthetic Cumulative Unimpaired Data Fordyce Lake - Gage Summation Data Page 31

32 Lower Basin Extensive missing gage data/large number of inter-basin transfers meant reliable gage summations were not feasible Pilot Creek above Stumpy Meadows was used as reference basin 2 nd order precipitation correction only (lack of snowmelt improves the use of a simplified proration approach) Results deemed much more consistent than any summation approach could provide Page 32

33 Representative Hydrographs Normal, Wet, and Dry Years (Water Year 2003, 1995 and 2001) Bowman Lake (NID W.S. El. 5,562 ) 10,000 Normal Water Year Dry Water Year Wet Water Year 1,000 Flow (cfs) Oct 1-Dec 1-Feb 1-Apr 1-Jun 1-Aug Page 33

34 Representative Hydrographs Normal, Wet, and Dry Years (Water Year 2003, 1995 and 2001) Lake Spaulding (PG&E W.S. El. 5,014.6 ) 10,000 1,000 Flow (cfs) Normal Water Year Dry Water Year Wet Water Year 1 1-Oct 1-Dec 1-Feb 1-Apr 1-Jun 1-Aug Page 34

35 Representative Hydrographs Normal, Wet, and Dry Years (Water Year 2003, 1995 and 2001) Rollins Reservoir (NID W.S. El. 2,171 ) 10,000 1,000 Flow (cfs) Normal Water Year Dry Water Year Wet Water Year 1 1-Oct 1-Dec 1-Feb 1-Apr 1-Jun 1-Aug Page 35

36 Unimpaired Hydrology - Summary Gage data was generally insufficient for period of record unimpaired development Reference basins for upper and lower watersheds provided event detail South Yuba above Cisco Pilot Creek above Stumpy Meadows Reservoir Conditioned reference basin data to show unique characteristics of other sub-basins basins Drainage area proration Precipitation factor Snowmelt adjustment Page 36

37 Hydrology CD Hydrology CD will include: Excel spreadsheets with unimpaired and/or regulated hydrology for each node shown in Modeling Schematic (where data is available) DSS database with all available hydrology Matrix describing flow gages (compliance flow, full range, etc.) Page 37

38 Questions?

39 Development of Water Balance Model presented by Rick Jones, P.E. Devine Tarbell and Associates, Inc. Page 39

40 Model Selection Developed a Model Selection Matrix Key Criteria OS/Platform Interface (pure GUI, pure code, everything in between) Hydraulic/water allocation capabilities Hydropower-specific capabilities Presentation and aesthetics Cost and technical support Experience and acceptance Page 40

41 Model Selection List of Model Candidates ARSP (Acres Intl.) CALSIM (CDWR/USBR) CHEOPS (Devine Tarbell and Associates) MIKE BASIN (Danish Hydrologic Institute) MODSIM (Colorado St. Univ.) OASIS (HydroLogics( HydroLogics,, Inc.) HEC-ResSim (USACE-HEC) RiverWare (TVA/USBR/Univ Univ.. of Colorado) WEAP (Stockholm Environment Institute) Page 41

42 Model Selection Ultimate Selection HEC-ResSim Determining Factors Public Domain Windows/Java platform for PC usability Solid GUI HEC-DSS interface for relicensing workshops Model rule transparency HEC software has solid track record Noted Limitations Lack of technical support by developers Lacks various power calculation capabilities Page 42

43 Model Installation HEC-ResSim on the web: hecressim.htm Download ResSim Version 2.0, all Users Manuals, and HEC-DSSVue Optional Items MS Excel Data Import Add-In DSSVue Plug-Ins (Excel Export, USGS/CDEC Import) Page 43

44 Model Installation Virtual Memory Allocation ResSim has a relatively low default setting for virtual memory allocation; this is a problem when running a model as complex as Yuba- Bear/Drum-Spaulding Navigate to C:\Program Files\HEC HEC\ResSim,, open ResSim.config Modify Line 16 (vmparam( Xmx m)) to use nearly all of your Windows allocated virtual memory (e.g. vmparam -Xmx1350m) this number should be slightly less than your machine s s total RAM The model will not start if this number is too large, so this may y help you iterate the ideal memory settings. Always make a copy of any config file (ResSim.OLD( ResSim.OLD) ) in case something goes wrong! Page 44

45 Tour of the Water Balance Model Page 45

46 Development Status Model currently remains in development Aware of new ResSim (Version 3.0) recently released; no decision has been made at this time on upgrade of model Page 46

47 Modeling Simplifications and Water Balance Conventions Model does not perform system-wide optimization of storage Limited spill prevention techniques; limited to reservoirs connected cted by river reaches (Fordyce Spaulding) Rule curves based primarily on historic targets Flashboard operations based on typical timing Hydraulics No routing/travel time used due to one day time-step Page 47

48 Modeling Simplifications and Conventions Time-Step (Computational) Load shapes (peak vs. off-peak) are not possible with the multi-year simulations due to a 1-day 1 time-step; this can result in average modeled efficiencies that are inconsistent with actual operations (generation can be post-processed processed to improve accuracy) Certain small reservoirs (typically diversion impoundments or afterbays) are not modeled as storage reservoirs but as simple diversions Other small reservoirs modeled as inflow = outflow to avoid computation decision errors which propagate downstream, causing unnecessary spills and other unrealistic decisions Power Calculations Tailwater elevations are backed-out in some cases where plants have an artificially high forebay elevation (e.g. Chicago Park PH) Model cannot calculate efficiencies based on head and flow; design head conditions assumed Page 48

49 Modeling Simplifications and Feeder Diversions Conventions Modeled as diversions (versus reservoirs) Rules can be implemented for these diversions using external spreadsheets which create time series for use within ResSim decision logic Water Deliveries Monthly distribution based on averages, prorated to future license demands (where applicable) Monthly varying flows at each node Rules exist at major storage reservoirs (Jackson Meadows, Bowman, Spaulding, Rollins) to provide adequate downstream availability at Rollins and in Bear River Canal system Page 49

50 Questions?