POINTE DU BOIS GENERATING STATION SPILLWAY REPLACEMENT PROJECT NUMERICAL AND PHYSICAL MODELING Kara Hurtig, Northwest Hydraulic Consultants, North Vancouver, BC, Canada David S. Brown, KGS Group, Winnipeg, MB, Canada Brian Hughes, Northwest Hydraulic Consultants, North Vancouver, BC, Canada Kevin Sydor, Manitoba Hydro, Winnipeg, MB, Canada
Project Description Existing Facility Winnipeg River, 150 km northeast of Winnipeg, Manitoba, Canada. Owned and operated by Manitoba Hydro (since 2002) Oldest hydroelectric plant operating in Manitoba (1909 to 1926) Run of River Facility Average River Flow: 850 m 3 /s (range 225 2840 m 3 /s) 16 horizontal turbines (78 MW) and operates at a head of 14 m. 92 spillways and 5 sluiceways (only 6 automated) N Pointe du Bois satellite mosaic from Canada Centre for Remote Sensing Winnipeg River Drainage Basin
Project Description Proposed Upgrades Spillway facilities require replacement for: Public and dam safety Concrete deterioration Spillway capacity & operation issues provide a safer working environment for staff Spillway Replacement Project includes: Replacing the existing spillways and sluiceways with a new East Spillway Existing gravity dams maintained and enhanced for dam safety New earthfill dam constructed downstream of the existing spillway facilities. Safely passes floods up to the Inflow Design Flood (IDF) of 5,040 m 3 /s Maintains operation of the powerhouse East Spillway
Project Description Project Objectives Spillway performance Constructability Costs Timelines Risk management Environmental considerations Integrated Hybrid Modeling Approach Understand the hydraulic design complexities Optimize the arrangement of the spillway s approach and discharge channels, Investigate construction cost saving alternatives, Evaluate spillway operation Numerical Modelling Physical Modelling
Integrated Hybrid Modeling Approach Numerical and Physical Modeling Each has distinct advantages for analyzing and comparing design alternatives Typically, the two types of model studies complement each other For this project, both models were applied simultaneously for an integrated approach to provided a broader and more efficient analysis Fast-tracked design process to meet strict construction schedule requirements
Numerical Modeling Description CFD model to Evaluate alternative spillway arrangements and configurations, Provide preliminary hydraulic assessment of the spillway structures, and Establish the initial design of the project. CFD model consists of: Model Dimension: 1200 m of river reach (600 m upstream and 600 m downstream) Mesh sizes ranged: 4m x 4m x 1m 1m x 1m x 0.5m Existing Spillways New Guideberms Existing Gravity Dams Existing Powerhouse New Earthfill Dam New Approach Channel, Spillway, Discharge Channel
Physical Modeling Description 1:50 scale 150 m of the forebay Existing spillway and sluiceway facilities Exit from the powerhouse draft tubes 800 m downstream from existing sluiceways Model footprint was 22 m by 24 m Objectives included: Optimization of the approach and discharge channel designs Evaluation of hydraulic performance of the spillway Confirmation of spillway operations
Approach Channel Optimization Objectives Reduce excavation volumes and costs Minimizing headlosses Maintaining adequate spillway capacity to safely pass the IDF Design Initial Design developed in numerical model Optimized using an integrated approach Confirmed and analyzed in physical model
Approach Channel Optimization Upstream Boundary Condition CFD model results used to define the inflow characteristics for the physical model since the CFD model encompassed a larger area of the outer forebay Performance of the approach channel guide berms is affected by flow direction Velocity magnitudes ±10% and velocity vectors ± 6 degrees Flow rate 4 % lower than that predicted by CFD model
Approach Channel Optimization Optimization Process Channel geometry was adjusted and rapidly tested in physical model Guideberms were shaped in physical model to provide smooth approach flow with no flow separation Confirm: Froude number within the channel remained low enough to ensure stable hydraulics Control would remain at the spillway structure Rockfill sizing adequate
Approach Channel Optimization Optimization Process CFD model allowed for: Detailed water level and velocity data Continuous mapping and estimation of Froude numbers Physical Model: Data at key points were used to confirm the results from the CFD simulation Design team combined efforts and expertise at model witness tests to expedite the design process Observations over a large range of flow conditions
Discharge Channel Optimization Objectives Minimize risk of a hydraulic jump at base of the spillway structure Minimize rock excavation costs Confirm acceptable operation Confirm spillway capacity Confirm acceptable hydraulic conditions at powerhouse tailrace on west bank Design Numerical modeling provided initial design Physical modeling to efficiently optimize the width and curvature of the discharge channel
Discharge Channel Optimization Optimization Process Several full-day working model demonstrations to resolve concerns, determine limitations, and compare alternatives Results from CFD model simulations prepared in the days prior to the meetings to help interpret and complement results taken from the physical model Provided the opportunity to efficiently test and visualize several designs Physical model considered better at handling transitional flows and wave activity Ongoing collaboration to ensure designs being evaluated were practical, economical and accurate
Discharge Channel Optimization Optimization Process Integrated use of CFD and physical models allowed the project team to: expediently optimize the discharge channel design confirm its performance met the required hydraulic criteria over a range of spillway discharges Testing showed significant potential for a reduction in the width of the discharge channel without: adversely impacting the spillway capacity increasing wave activity in the vicinity of the spillway creating water levels that exceed the channel walls The optimization of the discharge channel eliminated approximately 150,000 cubic meters of excavation (a total excavation reduction of 20%) Final Geometry Initial Geometry
Summary and Conclusions Numerical Modeling Can be more efficient for evaluation of: Large areas or extended river Major changes such as adjusting structure locations or significant bathymetric alterations Collection of detailed data Physical Modeling Visual, tangible and understandable to most observers Can be more efficient for evaluation of: Localized design refinements Complex hydraulic phenomenon Rapid assessment of wide range of flow conditions & geometric changes Often used to validate CFD models and confirm the final design developed for a project
Summary and Conclusions Integrated Hybrid Model Approach Allowed the Project Team to: Expediently optimize the design (channels and guideberms) Confirm detailed data (i.e. Froude Number) in entire channel Understand & visualize the more complex hydraulic conditions (i.e. wave patterns in a channel) Integration of the CFD model and physical model allowed for the expedient interpretation of model results by Project Team The combination of the detailed results from the CFD model and the rapid assessment & visualization of the physical model proved to be invaluable Provided Manitoba Hydro with the confidence that the new arrangement could be constructed on schedule and with reduced project costs.
POINTE DU BOIS GENERATING STATION SPILLWAY REPLACEMENT PROJECT NUMERICAL AND PHYSICAL MODELING THANK YOU FOR YOUR TIME QUESTIONS? Presenters: Kara Hurtig, Northwest Hydraulic Consultants, North Vancouver, BC, Canada, KHurtig@nhcweb.com David S. Brown, KGS Group, Winnipeg, MB, Canada, DBrown@kgsgroup.com Co-Authors: Brian Hughes, Northwest Hydraulic Consultants, North Vancouver, BC, Canada Kevin Sydor, Manitoba Hydro, Winnipeg, MB, Canada