Hydraulic Modeling to Aid TDG Abatement at Boundary and Cabinet Gorge Dams

Transcription

1 Hydraulic Modeling to Aid TDG Abatement at Boundary and Cabinet Gorge Dams Joe Orlins, P.E., Ph.D. NWHA Technical Seminar May 15, 2014

2 Boundary and Cabinet Gorge Dams

3 The Problem: Too Much Gas Boundary and Cabinet Gorge are high head dams with deep plunge pools Results in TDG levels that exceed 110% state standards during periods of spill Boundary Dam (Seattle City Light) Cabinet Gorge Dam (Avista Utilities)

4 The Problem TDG supersaturation can cause gas bubble trauma in fish Like a diver getting the bends TDG production in spillway discharge is related to: the depth of plunge the residence time of bubbles at depth

5 The Facilities: Facts and Figures Boundary Dam (Seattle City Light) Cabinet Gorge Dam (Avista Utilities) Type variable-radius concrete arch variable-radius concrete arch Dam Height 340 feet 208 feet Crest Length 508 feet 395 feet 7Q10 Flood Discharge 108,300 cfs 118,400 cfs Primary Outlet Works Spillway (108,000 cfs) Powerplant (55,000 cfs) Low level sluices (252,000 cfs) Spillway (206,000 cfs) Powerplant (38,000 cfs) No. of Spillway Bays 2 8 Spillway Gate Type/Size Radial: 50-foot-wide by 45-foot-high Vertical lift: 40-foot-wide by 35-foot-high Approximate Height of Fall 177 feet ~40 feet

6 Background Addressing TDG as part of FERC relicensing / settlement agreements Cabinet Gorge license issued 2000 Boundary license issued 2013

7 Background Owners have been studying TDG since 1996 (Cabinet Gorge) and 1999 (Boundary) Many of the personnel have remained Similar suite of tools Field data collection Physical modeling CFD modeling Prototype testing

8 TDG Abatement Strategies 1. Reduce air entrainment Almost impossible to achieve in practice 2. Reduce flow energy via head loss or turbine Expensive, limited return on capital investment 3. Reduce jet penetration / air entrainment depth Most promising approach, with several variations

9 Structural Mitigation Measures Spread jet impact area and reduce tail water penetration Sluices (at Boundary) Throttle sluice gates Requires modification to sealing system for partially open operations Roughen sluice flow Installation of deflectors at lower lip to disperse flow Spillways (at Boundary & Cabinet Gorge) Roughness elements Dissipate energy, disperse flow, increase impact area, decrease depth Spillway flow splitter / aerator Dentated flip bucket, humped apron

10 Roughness Element Concept Add roughness Break up jet Reduce depth of plunge

11 Concept Development - Overview Physical modeling Iterative development Optimize placement, height, spacing, number, etc. Can t simulate bubble rise CFD modeling Simulate bubble path TDG predictive tool Estimate effect of change on TDG Field testing

12 Concept Development - Physical Model Boundary Dam 1:25 scale model Includes: Spillways Sluices Plunge pool

13 Spillway Turbulence Elements Physical & CFD Models

14 Concept Development Physical Model 13,000 cfs Baseline 13,000 cfs Modified

15 Spillway Turbulence Elements CFD Model

16 Spillway Turbulence Elements Model Comparisons

17 Concept Development - CFD Model Sluiceway and Spillway: Combined Operation

18 Numerical Predictive TDG Model

19 Boundary: Iterative Evaluation & Improvement

20 Cabinet Gorge: Prototype Testing (2013) Single bay modified Roughness elements Flip bucket Treated as 1:1 scale model Good: TDG performance Not-so-good: Durability

21 Cabinet Gorge: Design Refinement (2014) Tools for design of remedial measures: CFD Model (cavitation/air supply assessment) STAAD model (structural design) Excel based calculations (air supply system design)

22 Summary Physical model Plunge depth reduced by up to approx. 50% CFD model Maximum plunge depth reduced Duration at depth reduced Prototype testing TDG supersaturation at compliance site reduced Design refinement

23 Next Steps Boundary Construct roughness elements on bay 2 Test in 2015 Model spillway bay 1 modifications Use complete suite of tools to optimize Cabinet Gorge Evaluate performance of modified design Optimize configuration for build out Construction & field testing

24 Conclusions Sharing information has been win-win faster implementation and proof of concept Multiple ways to reach a solution Reduction of TDG by roughness elements Concept works Not directly transferable between sites

25 Thank You! Joe Orlins, P.E., P.Eng., Ph.D. Guy Paul, P.E. Kim Pate, L.G., P.E.