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