BONNYBROOK WASTEWATER TREATMENT PLANT –
FLOOD BERM GROUNDWATER MODELING
Presentation by Mundzir Basri, Ph.D., P.Eng.
Outline1. June 2013 Flood Event
2. BBWWTP Site Flood Protection
3. Groundwater Modeling
4. Questions
June 2013 Flood Event
Flood Event at Bonnybrook WWTP
Impacts to Bonnybrook WWTP
Before the Flood…
After the Flood… Saturday, June 22, 2013
June 2013 Flood Event at Bonnybrook
• Approximately 1:100 yr event on Bow River
• Bow River flows approached 2500 cms adjacent to BBWWTP
• Highest influent sanitary flows ever experienced at BBWWTP:
Peak flow of 1,138 MLD measured prior to loss of power (peak flow measured 9:30 AM, no data after 12:15 PM)
Previously measured net high 938 MLD (May 27, 2011)
1:100 year Bow River Flood Level
Varies across the site from approximately: • 1029.3m at Calf Robe
• 1030.8m at NE corner of Plant D site
• Historic flood impact reports (Reid Crowther)list 1030.1
FLOODWAY
FLOOD
FRINGE
June 2013 Flood Impacts at Bonnybrook
• Estimated Total Damages ~ $20 Million
• Major Impacts:
– Process infrastructure (tankage / channels) surcharged
– Flooded tunnel systems
– Lost electricity to the entire site
– UV facility and equipment flooding
– Headworks flooding / bypassing
– Lost treatment capabilities – 15 days to recover process
– Solids deposition throughout facility
– Extensive post flood clean up required
UV Facility
Pumphouse & Tunnels
BBWWTP Site
Flood Protection
Flood Protection Concept
Flood BermOutfall Relocation
Schedule Critical System
FLOOD PROTECTION
CONCEPT
KEY FLOOD PROTECTION SYSTEM COMPONENTS
BBWWTP Site Flood Protection System is an array of components that combined provide total flood protection to this critical infrastructurefor the 1:100 year Bow River flood.
• Flood Berm and Cutoff Wall
• Plant Outfall Relocation
• Storm Sewer System Modifications
• Plant Bypass System Modifications
FLOOD BERM
BERM
BERM
PLANT D
FLOOD BERM
Plant D Access Road
Compacted Clay
Rip Rap Self-Launching
ApronGeometry TBD
Oil Pipeline
R/W
1500 Storm Sewer
3.1m to 3.7m
Groundwater
Interceptor
BBWWTP Site
3m Wide Top
1:100 Yr Flood Level1.0m
Freeboard
Parks Land
15.8 to 17.6m
Vegetated Rip Rap
Cu
toff
Wa
llGroundwater Flow During
Flood
River Hydraulic Modeling
• 1-D Hydraulic Model (HEC-RAS)
• 2012 Model developed by other consultant– Based on 2011 surveyed cross sections
– Includes the entire city (Bow River and Elbow River)
• Existing 2012 Model shows a slight variation in the water levels as compared to the Bylaw Flood Steps
1028
1029
1030
1031
1032
1033
1034
1035
1036
40000 40500 41000 41500 42000 42500 43000
Ele
va
tio
n (
m)
Station (m)
2012 Existing WaterLevel (2752 cms)
2013 Flood HWM(2500 cms)
Bylaw Step Elevations
Abandoned Rail Bridge
CP Rail Bridge
Bonnybrook Bridge
Calf Robe Bridge
Objective of Modeling Study
The objective of the modeling study was to
evaluate a subsurface groundwater cutoff
wall and dewatering pipe to minimize future
impacts from high river water (i.e., flood)
levels.
Model Domain (“Study Area”)
Refined Mesh in Vicinity of the Bonnybrook
WWTP Site
Refined Mesh along Flood Berm and Cut-off
Wall and at Well Locations
Location of Calibration Targets
Cross Section showing 100-year Flood (red),
Flood Berm (blue), & Cut-Off Wall (dark blue)
Oblique Slice Through the 3D
Hydrostratigraphic Model
Groundwater Head Distribution in the Study Area
without Flood Berm and cut-off Wall at the
Bonnybrook WWTP
Model Boundaries
• Bow River
• Elbow River
• Glenmore Reservoir
• Groundwater levels recorded at five
monitoring wells were used to calibrate the
model.
Water Elevation Data recorded at Bow River at
Calgary (05BH004) in 2013
Water Elevation Data recorded at Glenmore Reservoir
at Calgary (05BJ008) in 2013
Groundwater Elevation Data recorded at 8
Groundwater Monitoring Stations in 2013
Calibration Results of Groundwater Elevations
at B06A-LI163A
Calibration Results of Groundwater Elevations
at B04A-LI161A
Flood Berm Design Cut-of Wall (m) Maximum Groundwater Flux (m3/s)
Bow River flood berm with cut-off wall1 0.263
Bow River flood berm with cut-off wall3 0.255
Bow River flood berm with cut-off wall5 0.239
Bow River flood berm with cut-off wallBedrock 0.000
South access flood bermN/A 0.061
Groundwater Seepage Rate under Different Cut-off Wall depths
Seventeen Key and Near-Field Locations Used to
Assess Groundwater Levels with
Different Cut-Off Depths
Predicted Hydraulic Head Elevations for Different
Cut Off Wall Depths and Different Silt Layer
Thickness at 17 Locations
FourteenKey
Locations
GroundSurface
Elevation
Silt Layer No Silt Layer
3 m 1 m 0 m
1 m COW 3 m COW 5 m COW Bedrock COW 0 m COW 0 m COW
PPH#2 1031.85 1028.24 1028.18 1028.24 1028.23 1029.05 1029.05
TPH#1 1031.99 1028.20 1028.15 1028.20 1028.19 1028.96 1028.96
PPH#1 1030.58 1028.25 1028.19 1028.25 1028.24 1028.97 1028.97
DPH#1 1032.02 1028.11 1028.05 1028.11 1028.11 1028.87 1028.87
DPH#2 1031.62 1027.99 1027.94 1028.00 1028.01 1028.76 1028.74
DAF BLOG 1031.21 1027.97 1027.92 1027.97 1027.99 1028.66 1028.66
TUNNEL 1 1030.06 1027.88 1027.82 1027.88 1027.91 1028.56 1028.56
POW BLDG 1030.02 1027.81 1027.76 1027.82 1027.86 1028.51 1028.51
TUNNEL 2 1030.17 1027.68 1027.62 1027.69 1027.74 1028.28 1028.29
TUNNEL 3 1029.49 1027.54 1027.50 1027.56 1027.64 1028.21 1028.21
TUNNEL 4 1029.83 1027.43 1027.39 1027.45 1027.56 1027.53 1027.45
TUNNEL 7 1028.16 1026.95 1026.92 1026.98 1027.29 1027.87 1027.88
TUNNEL 5 1028.50 1027.16 1027.12 1027.20 1027.36 1027.89 1027.92
TUNNEL 6 1027.95 1026.66 1026.62 1026.68 1027.09 1027.66 1027.71
NorthBermP 1028.73 1027.22 1027.14 1027.09 1026.98 1028.67 1028.77
MidBermP 1028.90 1026.61 1026.51 1026.48 1027.08 1028.07 1028.19
SouthBermP 1028.10 1026.45 1026.35 1026.21 1026.78 1027.82 1027.94
Results• The Elbow River is an important boundary condition as it influences the
groundwater levels below the BBWTP site including during a flood
• While the cutoff wall all the way to bedrock reduces the groundwater
seepage from the Bow River it actually restricts the flow from the Elbow
River
• Based on modeling results, flood berm with no cutoff wall was
recommended
• The dewatering pipe near the toe of the cutoff wall provides minor
relief at the BBWTP buildings from elevated groundwater levels during a
flood but is good practice in terms of managing the integrity of the
flood berm
• The dewatering system around some of the BBWTP buildings provides
only minor relief from elevated groundwater levels during a flood
Acknowledgments
• City of Calgary
• Stantec Hydrogeology Team –
Mundzir Basri, Niloofar Firoozy and
David Alberti
QUESTIONS