assessment of the vulnerability of surface runoff networks

Assessment of the Vulnerability of Surface Runoff

Networks to Climatic Changes

in the Trois-Rivières-Centre Area

• History and context

• PIEVC Protocol

• Step 1: Definition of the project

• Step 2: Data Gathering and sufficiency

• Step 3: Risk Assessment

– Definitions

– Infrastructure Components

– Climate Events

– Worksheet and Assessment Workshop

• Step 4: Engineering Analysis

• Step 5: Recommendations

CONTENT

• Problems identified during heavy precipitations and high water table

– Back-up problems on upper levels and at the basis of slopes

– Problems worsen to the point of becoming catastrophic for low levels that receive an unwanted volume of water overflowing from the upper levels

• The City of Trois-Rivières’s wish

– Protection against back-ups

– Protection against flooding on properties

– Protection against the effects of land slides and slope erosion

Description of the Problem

History and Context

Approach

Vulnerability Assessment of the Engineering of

surface runoff infrastructure in the area of Trois-

Rivières-Centre via the PIEVC protocol

History and Context

Application of the CVIIP protocol project

Engineers Canada, the Centre for Expertise and

Research on Infrastructures in Urban Areas (CERIU), and

the City of Trois-Rivières have signed a protocol

agreement to evaluate the vulnerability of the

municipality’s infrastructures to climate change, and

more specifically of the surface runoff evacuation

networks.

History and Context

5-step Procedure

• Step 1: Definition of the project

• Step 2: Data Gathering

• Step 3: Risk assessment

• Step 4: Engineering analysis

• Step 5: Recommendations

CVIIP Protocol

Step 1: Definition of the Project

Localization of the Areas under Study

Fleuve St-Laurent

Des Chenaux Boulevard

Saint Lawrence River

Step 1: Definition of the Project

• Located in the St. Lawrence lowlands

• Confluence of the St. Maurice and St. Lawrence rivers

• Rectangular territory oriented south-west/north-east

• 26 km X 17 km (440 km2)

• Generally flat topography consisting of plateaux

• Altitude of 75 m

Fleuve St-Laurent

• Trois-Rivières-Centre: 10 km2 surface

• Boundaries: North Des Chenaux Boulevard

South Highway 40

East St. Maurice River

West Des Forges and Récollets Boulevards

Geography of the City of Trois-Rivières

Area under Study

• General plan of the City’s equipment

Watershed boundaries

Main axis of collection of the sanitary network

Pumping station locations and characteristics

• General plan of the stormwater and sanitary networks

Network types

Diameters, materials and installation date of the conduits

• SEWERGEMS database

Conduit diameters and lengths

• Others

Plans for two problem areas

Step 2: Data Collection

Available Infrastructure Data


Plans for the Catchments and Subcatchments


Specific Areas: Infiltration Issues Related to the Groundwater Table

Level Profiles : Saint-Louis/Labadie


Missing or incomplete data

• Conduit inverts

• Subcatchment characteristics

• No network analysis model (SWMM)

• Master plan

• Anticipated modifications to the collection and

evacuation of surface runoff networks


Data on climatic events

Reference periods

Present climate: 1971 – 2000

Future climate: 2041 – 2070

Data and record sources

Environment Canada

Engineers Canada

Ouranos

CERIU


Definition

Risk: Function of an undesired incident and of its severity and consequences

R = P x S

Risk = Probability x Severity

Step 3: Risk Assessment

Definition

Probability: Occurrence of an event

within a determined time frame

Scale: 0 to 7

Step 3: Risk Evaluation

Scale Method A

to Calculate Probability

Number of Occurrences

per Year

0 Negligible or not applicable 0

1 Improbable / very improbable > 0 – 0.05

2 Small 0.05 – 0.10

3 Occasional 0.10 – 0.25

4 Moderate / possible 0.25 – 0.75

5 Often 0.75 – 1.25

6 Probable 1.25 – 2.00

7 Certain / very probable > 2.0

Severity: Consequences of an event if it has occurred

Scale: 0 to 7


Scale Severity of the Consequences and Impacts

Method E

0 Negligible or not applicable

1 Measurable change: small / improbable / rare

2 Change: small / rare / marginal in functionality

3 Occasional loss of some capacity

4 Moderate loss of some capacity

5 Loss of capacity and of function: probable / periodic

6 Loss of function: major / very probable / critical

7 Loss of asset: extreme / frequent / continuous


Risk Scale: Probability x Severity from 0 to 49

Risk Scale Threshold Reaction

< 12 Small Immediate measures not necessary

< 12-35 Medium Mitigating measures may be necessary

Engineering analysis may be required

> 35 High Immediate measures required


Selection of the Infrastructure Components Infrastructure Components

Networks

Drainage at individual lots

Streets (Major Drainage System)

Local stormwater serwers

Local Combined sewers

Local pseudo-separated sewers

Stormwater Collectors

Combiend Sewer Collectors

Pseudo-separated Collectors

Catch basins

Manholes

Natural streams

Outfalls

Special Structures

Pumping station

Diversion chamber

Retention basin

Operation and Maintenance

Pumping station

Diversion chamber


Selected Climate Events

2-year return period, 21,8 mm in 1 hour 1





Intense Rain (24 hour) 50 mm / 24 hours 1

Snow Storm 300 mm / 24 hours 1

Winter Rain 25 mm / 24 hours (December, January, February) 1

Strong Wind 63 km/h 2

Ice Storm 25 mm / 24 hours 2

Lightning 2

Frost/Thaw 85 days/year where Tmax > 0 and Tmin < 0 2

Water Table 2

Water Course Level 2

Intense Rain (1 hour)

Climate Events Threshhold and/or Duration Group

Group 1 events

The probability is calculated based on the average

number of occurrences in one year during the

observation period (recent observations do not

affect these probabilities)

Group 2 events

The probability is calculated based on the historical

average overrun during one year


Climate Events – Calculation of the Probabilities


Climatic Events – Calculation of the Probabilities

Present Climate Futur Climate

2-year return period, 21,8 mm in 1 hour 1 4 5





Intense Rain (24 hour) 50 mm / 24 hours 1 4 5

Snow Storm 300 mm / 24 hours 1 4 4

Winter Rain 25 mm / 24 hours (December, January, February) 1 4 5

Strong Wind 63 km/h 2

Ice Storm 25 mm / 24 hours 2 4 6

Lightning 2

Frost/Thaw 85 days/year where Tmax > 0 and Tmin < 0 2 4 4

Water Table 2

Water Course Level 2


Probability scoreClimate Events Threshhold and/or Duration Group


Example of Evaluation Matrix

Infrastructure Element

Performance Reaction

(✓ if Yes)

Climatic Event


C1

C2

C3

C4

C5

C6

C7

C8

C9

10-year Return Period

Y/N P S R

Networks

Local combined conduits

3


Performance Criteria

Performance responses ID

Structural integrity C1

Serviceability C2

Functionality C3

Operations and maintenance C4

Emergency response risks C5

Insurance considerations C6

Economics C7

Public health and safety C8

Environmental effects C9

City of Trois-Rivières:

– Engineering

– Operation

– Development and urbanism

– Claims

Engineers Canada

CERIU

Ouranos

BPR


Evaluation Workshop – September 19, 2011

Participants

Steps 3: Risk Assessment

Evaluation Workshop


Evaluation Workshop

Infrastructure Elements

Reaction

on Performance

(✓ if Yes)

Événements climatiques


Intense

Rain

(24 hrs)

Snow

Storm

Winter

Rain

Strong

Wind Ice Storm Lightning Frost/Thaw

Water

Table

Levels

in Water-

courses

C1

C2

C3

C4

C5

C6

C7

C8

C9

2-year

Return

Period

21.8 mm

in 1 hr

5-year

Return

Period

26 mm

in 1 hr

10-year

Return

Period

28.8 mm

in 1 hr

50-year

Return

Period

34.9 mm

in 1 hr

100-year

Return

Period

37.5 mm

in 1 hr

Threshold:

50 mm/

24 hrs

Threshold:

30 cm/

24 hrs

Threshold:

25 mm/

24 hrs

Dec., Jan.,

Feb.

Threshold:

63 km/hr

Threshold:

25 mm/

24 hrs

Threshold:

85 days/

year where

Tmax > 0

and

Tmin < 0

Y/N P S R Y/N P S R Y/N P S R Y/N P S R Y/N P S R Y/N P S R Y/N P S R Y/N P S R Y/N P S R Y/N P S R Y/N P S R Y/N P S R O/N P G R O/N P G R

Networks

Drainage at lot level ✓ ✓ 5 1 5 ✓ 4 1 4 ✓ 3 4 12 1 1 ✓ 5 6 30 ✓ 5 6 30 ✓ 4 6 24 ✓ 6 0 ✓ 7 0

Streets ✓ ✓ ✓ ✓ 5 0 0 ✓ 4 0 0 ✓ 3 3 9 1 1 ✓ 5 2 10 ✓ 4 3 12 ✓ 5 4 20 ✓ 1 0 ✓ 6 6 36 ✓ 4 2 8 ✓ 6 0

Local storm conduits ✓ ✓ ✓ ✓ ✓ ✓ 5 0 0 ✓ 4 3 12 ✓ 3 6 18 1 1 ✓ 5 1 5 ✓ 5 1 5 ✓ 1 0 ✓ 1 0

Local combined conduits ✓ ✓ ✓ ✓ ✓ ✓ 5 0 0 ✓ 4 3 12 ✓ 3 6 18 1 1 ✓ 5 1 5 ✓ 5 1 5 ✓ 1 0 ✓ 1 0

Local pseudo-separated conduits ✓ ✓ ✓ ✓ ✓ ✓ 5 1 5 ✓ 4 3 12 ✓ 3 4 12 1 1 ✓ 5 5 25 ✓ 5 4 20 ✓ 4 0 ✓ 1 0

Collecting storm conduits ✓ ✓ ✓ ✓ ✓ ✓ 5 0 0 ✓ 4 4 16 ✓ 3 5 15 1 1 ✓ 5 2 10 ✓ 5 2 10 ✓ 2 0 ✓ 1 0

Collecting combined conduits ✓ ✓ ✓ ✓ ✓ ✓ 5 0 0 ✓ 4 4 16 ✓ 3 5 15 1 1 ✓ 5 2 10 ✓ 5 2 10 ✓ 2 0 ✓ 1 0

Collecting pseudo-separated conduits ✓ ✓ ✓ ✓ ✓ ✓ 5 2 10 ✓ 4 4 16 ✓ 3 5 15 1 1 ✓ 5 2 10 ✓ 5 4 20 ✓ 4 0 ✓ 1 0

Catch basins ✓ ✓ 5 0 0 ✓ 4 0 0 ✓ 3 0 0 1 1 ✓ 5 6 30 ✓ 4 0 0 ✓ 5 0 0 ✓ 6 2 12 ✓ 4 2 8 ✓ 6 0

Manholes ✓ 1 1

Natural network ✓ ✓ ✓ ✓ ✓ ✓ ✓ 5 1 5 ✓ 4 2 8 ✓ 3 3 9 1 1 ✓ 5 6 30 ✓ 4 3 12 ✓ 5 4 20 ✓ 3 0 ✓ 6 4 24 ✓ 4 5 20 ✓ 4 0

Emissaries ✓ ✓ ✓ ✓ ✓ ✓ 5 0 0 ✓ 4 1 4 ✓ 3 5 15 1 1 ✓ 5 3 15 ✓ 5 2 10 ✓ 0 0 ✓ 6 0 0 ✓ 4 1 4 ✓ 7 0

Special Structures

Pumping Stations

Capacity ✓ 5 ✓ 4 ✓ 3 1 1 ✓ 5

Mechanical failure 1 1 ✓

Power failure 1 1 ✓ 4 ✓ 4 ✓ 6 ✓

Instrumentation & control 1 1 ✓ 4 ✓ 4 ✓ 6 ✓

Diversion chamber

(regulation)

Capacity ✓ 5 ✓ 4 ✓ 3 1 1 ✓ 5 6

Mechanical failure 1 1 6 ✓

Power outage 1 1 ✓ 4 ✓ 4 ✓ 6 ✓

Instrumentation control 1 1 ✓ 4 ✓ 4 ✓ 6 ✓

Retention basin Capacity ✓ 5 ✓ 4 ✓ 3 1 1 ✓ 5 ✓ 5 6 ✓

Opération and Maintenance

Pumping station

Staff ✓ 3 1 1 ✓ 5 ✓ 4 ✓ 5 ✓ 4 ✓ 6 ✓

Equipment 1 1 ✓ 4 ✓ 6 ✓ ✓

Transportation ✓ 3 1 1 ✓ 5 ✓ 4 ✓ 5 ✓ 4 ✓ 6 ✓

Instrumentaiton & control ✓ 3 1 1 ✓ 5 ✓ 4 ✓ 5 ✓ 4 ✓ 6 ✓

Diversion chamber

(regulation)

Staff ✓ 3 1 1 ✓ 5 ✓ 4 ✓ 5 ✓ 4 ✓ 6 ✓

Equipment 1 1 ✓ 4 ✓ 6 ✓ ✓

Transportation ✓ 3 1 1 ✓ 5 ✓ 4 ✓ 5 ✓ 4 ✓ 6 ✓

Instrumentaiton & control ✓ 3 1 1 ✓ 5 ✓ 4 ✓ 5 ✓ 4 ✓ 6 ✓ ✓



Intense

Rain

(24 hrs)

Snow

Storm

2-year

Return

Period

21.8 mm I

n 1 hr

5-year

Return

Period

26 mm

in 1 hr

10-year

Return

Period

28.8 mm

in 1 hr

50-year

Return

Period

34.9 mm I

n 1 hr

100-year

Return

Period

37.5 mm I

n 1 hr

Threshold:

50 mm/

24 hrs

Threshold:

30 cm/

24 hrs

Y/N P S R Y/N P S R Y/N P S R Y/N P S R Y/N P S R Y/N P S R Y/N P S R

✓ 5 1 5 ✓ 4 1 4 ✓ 3 4 12 1 1 ✓ 5 6 30

✓ 5 0 0 ✓ 4 0 0 ✓ 3 3 9 1 1 ✓ 5 2 10 ✓ 4 3 12

✓ 5 0 0 ✓ 4 3 12 ✓ 3 6 18 1 1 ✓ 5 1 5

✓ 5 0 0 ✓ 4 3 12 ✓ 3 6 18 1 1 ✓ 5 1 5

✓ 5 1 5 ✓ 4 3 12 ✓ 3 4 12 1 1 ✓ 5 5 25

✓ 5 0 0 ✓ 4 4 16 ✓ 3 5 15 1 1 ✓ 5 2 10

✓ 5 0 0 ✓ 4 4 16 ✓ 3 5 15 1 1 ✓ 5 2 10

✓ 5 2 10 ✓ 4 4 16 ✓ 3 5 15 1 1 ✓ 5 2 10

✓ 5 0 0 ✓ 4 0 0 ✓ 3 0 0 1 1 ✓ 5 6 30 ✓ 4 0 0

1 1

✓ 5 1 5 ✓ 4 2 8 ✓ 3 3 9 1 1 ✓ 5 6 30 ✓ 4 3 12

✓ 5 0 0 ✓ 4 1 4 ✓ 3 5 15 1 1 ✓ 5 3 15

✓ 5 ✓ 4 ✓ 3 1 1 ✓ 5

1 1

1 1 ✓ 4

1 1 ✓ 4

✓ 5 ✓ 4 ✓ 3 1 1 ✓ 5

1 1

1 1 ✓ 4

1 1 ✓ 4

✓ 5 ✓ 4 ✓ 3 1 1 ✓ 5

✓ 3 1 1 ✓ 5 ✓ 4

1 1

✓ 3 1 1 ✓ 5 ✓ 4

✓ 3 1 1 ✓ 5 ✓ 4

✓ 3 1 1 ✓ 5 ✓ 4

1 1

✓ 3 1 1 ✓ 5 ✓ 4

✓ 3 1 1 ✓ 5 ✓ 4

About the Infrastructure Components

• Drainage at lot level is generally not a problem. Some specific lots

located on lower grounds (at the basis of slopes) do receive exceeding

runoff from lots in higher grounds. This is the case for Terrasse Le

Corbusier and Des Berges Street.

• The Côte Récollets and Cyprès Street are cited as examples of severe

problems during rainfall events with return periods of 10 years or

more.

• Drainage of street with steep slopes has been added as an

infrastructure component at Spémont, Sainte-Marguerite and Des

Mélèzes.

• Tunnel drainage has been added as an infrastructure component at

La Vérendrye, Père-Daniel and La Violette.

• Regulation chambers have been added to the infrastructure

components.


Evaluation Workshop – Highlights

About the Climate Events

• Combined events seem to have more severe impacts than

separate events.

• Since the 2000s, “extreme” events, especially intense rain over

short periods of time, seem to occur more often.

• The particular situation of the City of Trois-Rivières, which is

located near two large bodies of water (the St. Lawrence River and

the St. Maurice River) seems to be a factor regarding the impact

of climate events.

• Water levels in watercourses, water tables and lightning require

complementary studies to determine the future climate trends and

to assess risks.


Evaluation Workshop – Highlights

Compilation of the Results

7 3 2 2 7 3 2 2

6 6 1 1 1 1

5 5 8 7 7 2 6 5 5

4 12 9 10 5 8 7 7 4 5 4 3 6 5 2 3

3 2 2 1 3 4 2 3 1 2 2 5 4

2 1 3 2 5 4 2 1

1 1 2 1 3 3 5 3 1 1 2 1 3 3 5 3

0 0

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

Legend Statistics Legend Statistics

Risk < 12 68 Risk < 12 57

12 <= Risk < 36 44 12 <= Risk < 36 54

Risk >= 36 0 Risk >= 36 1

Number of elements evaluated 112 Number of elements evaluated 112

Number of elements not evaluated 87 Number of elements not evaluated 87

% of elements evaluated 56% % of elements evaluated 56%

Present Climate Conditions Future Climate Conditions

Pro

bab

ilit

y

Pro

bab

ilit

y

Severity Severity

Compilation of the Results – Highlights

• Of the 442 possible interactions between the infrastructure

components and the climate events, 199 have been

deemed relevant for evaluation

• Of the 199 interactions deemed relevant, 87 were not

evaluated during the workshop because time did not

permit

• Based on the present climate conditions, no item has

been assigned a high risk. 44 items have been assigned a

medium risk and 68 a low risk

• Based on future climate conditions, one interaction has

been assigned a high risk, namely streets with steep

slopes during ice storms. 54 interactions have been

assigned a medium risk and 57 a low risk


Classification of Interactions Requiring Engineering Analysis


Climatic Event Infrastructure Element Risk

Frost / thaw

Drainage at individual lot level: Terrasse Le Corbusier 24

Natural streams: Millette and Récollets watercourses 20

Streets with steep slopes: Côte des Récollets, Cyprès Street, Vieux-Port Street 16

Water table

Pumping station - Capacity 35


Storm, combined and pseudo-separated conduits 21

Streets with steep slopes: Côde des Récollets, Cyprès Street, Vieux-Port Street 14

Winter rain

Retention basin - Capacity 30


Pumping station - Capacity 25



Streets with steep slopes: Côte des Recollets, Cyprès Street, Vieux-Port Street 20

Intense rain


Catch basins 30



Pumping station – Capacity and mechanical failures 25

Groundwater drainage at basis of slopes: Spémont, Sainte-Marguerite and Des Mélèzes 24

Tunnel drainage: La Vérendrye, Père-Daniel and La Violette 24

Collecting combined conduits: 6th Street, Père-Daniel, St-Sacrement, Papineau and St-Louis 16

Streets with steep slopes: Côte des Recollets, Cyprès Street, Vieux-Port Street 15

Snow storm Natural network: Millette and Récollets watercourses 12


Ice storm



Catch basins 12

Strong wind Natural streams: Millette and Récollets watercourses 12

Vulnerability Assessment

Ratio = Total charge anticipated

Total capacity anticipated

VR = ChT / CT

VR > 1 = Vulnerable infrastructure

VR < 1 = Infrastructure with a capacity to adapt

Step 4: Engineering Analysis

Limitations of the Analysis

• Incomplete data regarding conduit inverts does not

permit a quantitative analysis of the current and future

capacities, nor the sizing of the solutions to the drainage

problems

Solution (outside the scope of the project)

• Completion of the data in the SEWERGEMS database

• Analysis of the network with a numerical runoff model

Step 4: Engineering Analysis

Conclusions on the Process

• Several infrastructure/climate interactions were not evaluated

during the workshop due to time restrictions. We recommend

longer workshops (a day and a half long).

• The absence of critical data for the engineering analysis did not

allow the adequate completion of this task. It would better to

perform the required data collection and measuring prior to

undertaking any risk assessment project related to the

vulnerability of infrastructure engineering to climate changes.

• Rare rainfall events have low probability at the protocol scale.

Risk is small even if their severity is very high. These high impact

events could occasionally necessitate an engineering analysis

Step 5: Recommendations

Conclusions on the Process (2)

• Local weather phenomena, such as the influence of large

water bodies (St. Lawrence and St. Maurice rivers) on

climate and of the varying topography on the recurrence

of intense rain events in recent years could not be

explained due to the absence of specific knowledge on

the climate in the Trois-Rivières area. It is preferable to

conduct this type of study prior to undertaking any risk

assessment project related to the vulnerability of

infrastructure engineering to climate changes.


• The recommendations have been grouped based

on season (summer and winter) and priority (short, medium or long term).

• The recommended actions may be taken by the

internal resources of the City of Trois-Rivières to preserve the advantage of keeping collective

memory and specific knowledge of the networks. To

satisfy these specific needs, specialized consulting

firms may also be commissioned to contribute in these actions.



City of Trois-Rivières

Climate Events Infrastructure Components Recommendations Priority

Pumping Station - Capacity and Mechanical failure

Drainage at individual lots : Terrasse Le Corbusier

Catch basins

Natural streams : cours d'eau Millette et des Récollets

Stormwater, combined and pseudo-separated sewers

Ground water drainage at the basis of slopes : Spémont, Sainte-Marguerite et

des Mélèzes

Tunnel Drainage : La Vérendrye, Père-Daniel et la Violette

Combined Sewer Collectors : 6e Rue, Père-Daniel,

Saint-Sacrement, Papineau et Saint-Louis

Streets with steep slopes : côte des Récollets, rue des Cyprès, etc.

* Action may be taken by City staff or commisionned to specialized firms.

Summer interventions

Intense Rain

Water Table

Strong Winds

Catch basin maintenance program

Watercourse monitoring program

Emergency plan

and traffic monitoring

Publlc Information

Short Term

Analysis and assessment

of conduites, puming stations

and catch basin capacities *

Medium Term

Étape 5 : Recommendations

City of Trois-Rivières

Climate Events Infrastructure Components Recommendations Priority

Streets with steep slopes : côte des Récollets, rue des Cyprès, etc.

Drainage at individual lots : Terrasse Le Corbusier

Natural streams : cours d'eau Millette et des Récollets

Catch basins

Stormwater, combined and pseudo-separated sewers

Pumping Station - Capacity

Retention basins - Capacité

* Action may be taken by City staff or commisionned to specialized firms.

Short Term

Analysis and assessment

of conduites, puming stations

and catch basin capacities *

Medium Term

Winter interventions

Frost/Thaw

Winter Rain

Snow Storm

Ice Storm

Catch basin maintenance program

Watercourse monitoring program

Emergency plan

and traffic monitoring

Publlc Information

Thank you for your time

assessment of the vulnerability of surface runoff networks

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