Evaluation of Etobicoke Exfiltration System in The City of Barrie

• Parto Peyvandisani• MEng student, Environmental

Engineering, Ryerson University• Toronto, Ontario• BEng, Civil Engineering, University of

Birmingham, 2013

1

Evaluation of Etobicoke Exfiltration System in the

City of BarrieParto Peyvandisani

Prof. James Li and Dr. Darko Joksimovic

Ryerson University, Toronto, Canada

2

Presentation Outline

• Background• Aim of the study• Modelling Scenarios• Validation• Screening for retrofit opportunities• Conclusions

3

Background• Etobicoke exfiltration system (EES)

was constructed as a conveyance system control in 1993 in the City of Etobicoke (now Toronto)

• Runoff/Capture of 15mm storm• Perforated pipe conveys flows to

the void space provided by granular trench

• Exfiltration to the surrounding soil• Recharge the groundwater

4

Advantages

5

FOUR SEASONS RECHARGE GROUNDWATER

FLOODING, WATER QUALITY, EROSION,

ETC.

NO SURFACE SPACE WITHIN THE RIGHT-

OF-WAY

ECONOMICAL

Limitations

6

PERCOLATION RATE > 15 MM/HR

GROUNDWATER LEVEL > 1M BELOW BEDDING

LOCAL RESIDENTIAL ROADS

Aim of this studyEvaluate the runoff control performance of EES retrofit• focus on quantity control • Kidd’s Creek watershed area in the City of Barrie Methodology:• develop a SWMM model to simulate the EES retrofit• validate the modelling approach using flow test data• screen for retrofit opportunities in the Kidd’s Creek drainage area• apply the EES model and analyze results

7

EES Modelling Approaches

Orifice – storage – pump (older version of SWMM)SWMM LID module (infiltration trench)This study:

- Scenario 1: storage unit with seepage- Scenario 2: conduit with seepage

8

Scenario 1:Storage Unit with seepage

MH2: Upstream manholeMH3: Downstream manholeC1: Storm sewerOrifice 1 & 2 : Connections to perforated pipesSU: Storage UnitC2 and outfall: Dummy conduit

9

Exfiltration Storage Model

Exfiltration from a storage unit

• Equation 1. Green Ampt Infiltration Rate

• 𝑓𝑓 = 𝐾𝐾(𝜓𝜓𝜓𝜓𝜓𝜓𝐹𝐹 𝑡𝑡

+ 1)

• Equation 2.The Cumulative Infiltration

• 𝐹𝐹 𝑡𝑡 = 𝐾𝐾𝑡𝑡 + 𝜓𝜓𝜓𝜓𝜓𝜓ln(1 + 𝐹𝐹 𝑡𝑡𝜓𝜓𝜓𝜓𝜓𝜓

)

Where • K= hydraulic conductivity• Ψ= Suction head• θ= Soil moisture content

10

Scenario 1:Storage Unit with seepage

Storage Curve:

• Tabular Curve• Trench depth: head difference of MHs + Inlet offset of the conduit

11

0102030405060708090

100

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Surf

ace

Area

(m2)

The depth of Water(m)

Tabular Curve, between two manholes

Wedge storage

Scenario 2: conduit with seepage

MH2: Upstream manholeMH3: Downstream manholeC1: Storm sewerOrifice 1 & 2 : Connections to perforated pipesC2 and outfall: Dummy conduitC3: Conduit with seepageJ1: Dummy manhole

12

Scenario 2: conduit with seepage• It is suitable to represent

perforated pipes or natural channel

• The seepage loss rate would depend on:

1- The flow depth in the conduit

2- The hydraulic conductivity for the surrounding soil

3-The variation in moisture content of the soil

13

Leaky Conduit Modeling

Scenario 2: conduit with seepage

• It does not present continued exfiltration into the surrounding soil

14

Validating the Modelling approach

• Fire hydrant test on the original EES

• Flow and level measurements between MH2 and MH3

• Duration of the flow test was about 110 minutes

15

Monitoring Location & Equipment• Pressure

Transducers in the upstream and downstream of the stone trench

• Data logger in manholes

16

Validation Result

17

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

Wat

er D

epth

(m)

Time(min)

Water Depth in the Stone Trench

Measured Data Simulation Result

ValidationResult

14

28

11

31

0

5

10

15

20

25

30

35

Exfiltration loss (m3) Final stored Volume (m3)

Volu

me

(m3)

Exfiltration Loss AnalysisExperimental Result Simulation Result

18

Sensitivity Analysis

0

50

100

150

200

250

0

5

10

15

20

25

30

Sand LoamySand

SandyLoam

Loam Silt Loam SandyClay Loam

Clay Loam Silty ClayLoam

SandyClay

Silty Clay Clay

Hydr

aulic

Con

duct

ivity

(mm

/hr)

Exfil

trat

ion

loss

(m3)

Sensitivity Analysis

Exfiltration loss(m3) in SU Hydraulic Conductivity(mm/hr.)

19

Seepage Properties Sensitivity Analysis

Pros and Cons

The exfiltration rate is compatible with Green Ampt method

Flooding occurs when the inflow rate to the manhole > inflow to the main storm sewer in case of large event or when there is a deficiency in the conventional system

20

Flooding News, Barrie

21

Screening for retrofit opportunities

• All local public roads

• Wellhead zone A-B is excluded

• The groundwater > 8 ft is considered

• Storm sewer installed before 1998 are considered

• Pavement installed before 1993 are considered

• Soil group A and B have been selected

22

Kidd’s Creek Watershed Area• Area 26-ha

• 47% imperviousness

• 33 EES retrofit

• Required trench depth achieved for 25 mm design storm

• SCS-5 year-6 hours design storm event (present and future conditions)

• Peak flow analysis for 72 hours

23

EES locations throughout Kidd’s Creek watershed area

Results

0%

20%

40%

60%

80%

100%

120%

C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29 C30 C31 C32 C33

Max

imum

Per

cent

Util

ized

Link ID

Maximum Storm Sewer Utilization

Conventional EES

24

Results

0

10

20

30

40

50

60

70

SU1 SU2 SU3 SU4 SU5 SU6 SU7 SU8 SU9 SU10 SU11 SU12 SU13 SU14 SU15 SU16 SU17 SU18 SU19 SU20 SU21 SU22 SU23 SU24 SU25 SU26 SU27 SU28 SU29 SU30 SU31 SU32 SU33

Max

imum

Per

cent

Ful

l

Trench Storage ID

Maximum Utilization of Trenches

25

ResultsOutfall flow rate to the creek :

• Conventional system: 2,612 L/s

• With EES: 1,499 L/s

• 42 % reduction in outlet to the creek

• Exfiltration loss: 2,542 m³

26

Outfall flow rate (L/S) to the creek

Conclusions

27

Kidd’s Creek watershed would benefit from significant capacity improvements through

EES retrofit

Storage node with seepage appropriately models EESLimitations due to HGL simplification (horizontal) in the trench: overestimate levels, possible node flooding

Recommendations and Further Studies

28

New experimental data needed to validate the modelling approach

Enhance SWMM to explicitly model buried, exfiltrating stone trench hydraulically

Acknowledgement: City of Barrie

Thank you

29