STUDY OF THE STORM DRAIN SEWER OF THE URBAN CATCHMENT OF LA RIERETA, SAN BOI DE LLOBREGAT,

SPAIN

TEAM 3:1. Aline Veról2. José Rivero3. Pedro Ramos4. Ramiro Pighini

07.2012

IntroductionThe traditional canalization approach for flood control has been complemented or replaced by new concepts that consider a systemic approach, with distributed interventions over the catchment intending to recreate flow patterns prior to the urbanization. LID measures have been proposed to fulfill this aim.

The spatio-temporal variability of the phenomenon gives particular characteristics to each catchment. In this context, a systemic evaluation of flood control projects is needed, providing adequate spatial coverage without superimposing effects in time.

Mathematical modeling emerges as a useful tool to represent the integrated behavior of urban drainage and landscape.

Study area

Description “La Riereta” catchment

ObjectiveThe general objective of this project is to perform an analysis on the model of the storm drain sewer of “La Riereta”, an urban catchment located in Spain, and propose a sewer rehabilitation process. To carry out this process, a hydrological and hydraulic model will be developed using the EPA Storm Water Management Model (EPA SWMM 5.0).

LID – Low Impact DevelopmentLID: A set of procedures that try to understand and reproduce hydrological behavior prior to urbanization.

The main principles of this approach may be briefly described by the following points:

• Minimise runoff, acting on impervious rates reduction and maintaining green areas;

• Preserve concentration times of pre-development, by increasing flow paths and surface roughness;

• Use of retention reservoir for peak discharge control and improve water quality;

• Use of additional detention reservoirs to prevent flooding, if necessary.

Examples of LID measuresBio retention

Infiltration trenches

Examples of LID measuresVegetated roof covers

Permeable pavements

Examples of LID measuresRain Barrels

MethodologyTo develop the proposed case study, the group followed the methodology suggested by the organizers and detailed below:

• Basin discretisation;• Determination of the input data (for sub-catchments,

conducts and manholes);• Calibration and validation of the model using three

different rain events and hydrographs registered at the outlet of the urban basin;

• Determination of the design rainfall for TR 10;• Simulation of the drainage network diagnosis;• Analysis of the catchment to evaluate and propose the

use of LID measures;• Simulation of the drainage network considering the

implementation of the proposed LID measures;• Analysis and discussion of results.

Case StudyThe present case study is an urban catchment located in Sant Boi de Llobregat, a town near Barcelona, Spain.

This catchment has a surface area of approximately 17 ha and it presents high indexes of impermeability. Its slope varies from high to medium values. Roof drainage discharges directly to the streets through downspouts. Additionally, a group of inlets distributed in the streets ensure the collection of the generated runoff after the occurrence of rainfall.

The drainage system of “La Riereta” is a combined sewer network and it is mainly composed by circular cross-section pipes with different diameters and made by concrete.

Results - Discretization

Results - RainfallThree different rainfall events, with their corresponding flows – measured at the catchment outfall – were assigned for each group. Each of these events is identified by the name of the saint of the day in which the registration started.

Results - Calibration/ValidationThe chosen rainfall events for calibration of the model were: Susana and Efrén.

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0.05

0.1

0.15

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0.25

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0.35

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0.45

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0 10 20 30 40 50

Susana Rainfall Event

Measured flow(m3/s) Calculated flow (m3/s)

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0.15

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Time [min]

Efrén Rainfall Event

Measured flow (m3/s) Calculated flow (m3/s)

Results - Calibration/ValidationSanta Cecilia rainfall event was used to validate the model

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0.35

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Santa Cecilia Rainfall Event

Measured flow (m3/s) Calculated flow (m3/s)

Parameters adopted for sub catchments

Total Pcnt. Pcnt. Curb N-Imperv N-Perv S-Imperv S-Perv PctZero RouteToName Raingage Outlet Area Imperv Width Slope LengthS06 Pluv1 N12 0.5 81.16 500 2.28 0 0.04 0.15 0.65 2.6 30 OUTLETS12 Pluv1 N9 0.66 94.87 660 1.52 0 0.04 0.15 0.65 2.6 30 OUTLETS13 Pluv1 N2 2.06 90.73 2060 4.09 0 0.04 0.15 0.65 2.6 30 OUTLETS01 Pluv1 N13 0.77 87.8 770 6.63 0 0.04 0.15 0.65 2.6 30 OUTLETS02 Pluv1 N14 0.44 92.23 440 3.16 0 0.04 0.15 0.65 2.6 30 OUTLETS03 Pluv1 2 1 71.73 1000 4.65 0 0.04 0.15 0.65 2.6 30 OUTLETS05 Pluv1 N12 0.66 84.08 660 1.9 0 0.04 0.15 0.65 2.6 30 OUTLETS07 Pluv1 N11 0.55 98.06 550 4.09 0 0.04 0.15 0.65 2.6 30 OUTLETS08 Pluv1 N11 0.9 88.5 900 4.39 0 0.04 0.15 0.65 2.6 30 OUTLETS09 Pluv1 N6 0.69 92.64 690 6.46 0 0.04 0.15 0.65 2.6 30 OUTLETS4A Pluv1 N10 0.6 89.3 600 2.34 0 0.04 0.15 0.65 2.6 30 OUTLETS4B Pluv1 N10 0.09 89.3 90 2.34 0 0.04 0.15 0.65 2.6 30 OUTLETS4C Pluv1 N10 0.5 89.3 500 2.34 0 0.04 0.15 0.65 2.6 30 OUTLETS10A Pluv1 N7 0.87 96.37 870 4.72 0 0.04 0.15 0.65 2.6 30 OUTLETS10B Pluv1 N15 0.57 96.37 570 4.72 0 0.04 0.15 0.65 2.6 30 OUTLETS11B Pluv1 N16 1.1 95.97 1100 4.01 0 0.04 0.15 0.65 2.6 30 OUTLETS11A Pluv1 N9 0.95 95.97 950 4.01 0 0.04 0.15 0.65 2.6 30 OUTLETS14A Pluv1 N4 0.2 95.3 200 5.49 0 0.04 0.15 0.65 2.6 30 OUTLET

Parameters adopted for conduits

Inlet Outlet Manning Inlet Outlet Init. Max.Name Node Node Length N Offset Offset Flow Flow Link Shape Geom1 Geom2 Geom3 Geom4 Barrels

C2 N2 N4 70.86 0.013 30.89 24.18 0 0 C2 CIRCULAR 0.5 0 0 0 1C4 N4 N5 50.56 0.013 23.33 22.51 0 0 C4 CIRCULAR 0.4 0 0 0 1C6 N6 N7 80.59 0.013 26.46 24.57 0 0 C6 CIRCULAR 0.4 0 0 0 1C7 N7 N8 59.12 0.013 24.57 23.28 0 0 C7 CIRCULAR 0.4 0 0 0 1C9 N9 N11 123.33 0.013 21.46 15.46 0 0 C9 CIRCULAR 1 0 0 0 1C10 N10 N11 61.14 0.013 21.73 18.06 0 0 C10 CIRCULAR 0.3 0 0 0 1C11 N11 N12 108.06 0.013 15.46 15.9 0 0 C11 CIRCULAR 1 0 0 0 1C12 N12 2 36 0.013 15.7 14.2 0 0 C12 CIRCULAR 1 0 0 0 1C13 N13 N14 120.34 0.013 16.22 13.73 0 0 C13 CIRCULAR 0.6 0 0 0 1C14 N14 1 45.52 0.013 13.13 12.51 0 0 C14 CIRCULAR 1.2 0 0 0 1C5 N5 N9 64.88 0.013 22.31 21.46 0 0 C5 CIRCULAR 0.6 0 0 0 1C8 N8 N9 10.73 0.013 23.18 22.87 0 0 C8 CIRCULAR 0.5 0 0 0 1C15 N15 N7 105 0.013 28.518 24.574 0 0 C15 CIRCULAR 0.5 0 0 0 1C16 N16 N9 145 0.013 26.193 22.87 0 0 C16 CIRCULAR 0.6 0 0 0 1

C12A 2 N14 50 0.013 14 13.13 0 0 C12A CIRCULAR 1.2 0 0 0 1

Results - Diagnosis of drainage networkOnce the model was calibrated and validated, the team modelled the diagnosis of the drainage network for a design rainfall.

A design rainfall of 10 years of recurrence time is used not only in the city of Barcelona, but also in some municipalities around it, like Sant Boi de Llobregat. In this case, the design rainfall should be obtained from the IDF curve Barcelona-Fabra, based on precipitation series registered between the years of 1927-1993. This IDF curves are described by the following expressions:

Where:I: (mm/h)T: (years)D: (minutes)

Design rainfall obtained for TR 10

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mm

/hr.

min.

Design rainfall obtained for TR 10Water Elevation Profile: Node N6 - 1

07/24/2012 00:24:00

Distance (m)500450400350300250200150100500

N6

N7

N8

N9

N11

N12

2 N14

1

Elev

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n (m

)

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Water Elevation Profile: Node N2 - 1

07/24/2012 00:24:00

Distance (m)550500450400350300250200150100500

N2

N4

N5

N9

N11

N12

2 N14

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Ele

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n (m

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Water Elevation Profile: Node N13 - 1

07/24/2012 00:24:00

Distance (m)1601501401301201101009080706050403020100

N13

N14

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Elev

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n (m

)

17

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Water Elevation Profile: Node N10 - 1

07/24/2012 00:24:00

Distance (m)300280260240220200180160140120100806040200

N10

N11

N12

2 N14

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Elev

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n (m

)

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Water Elevation Profile: Node N16 - 1

07/24/2012 00:24:00

Distance (m)500450400350300250200150100500

N16

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Water Elevation Profile: Node N15 - 1

07/24/2012 00:24:00

Distance (m)500450400350300250200150100500

N15

N7

N8

N11

N12

2 N14

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Elev

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n (m

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Results - Diagnosis of drainage networkLID measures: Porous pavements, Bio retention cells and Rain barrels

Results - Diagnosis of drainage network

Type/Layer ParametersPP1 PPPP1 SURFACE 2 0 0.018 2 5PP1 PAVEMENT 120 0.18 0 100 0PP1 STORAGE 250 0.75 10 0PP1 DRAIN 0 0.5 0 6

PP2 PPPP2 SURFACE 2 0 0.018 3 5PP2 PAVEMENT 120 0.18 0 100 0PP2 STORAGE 250 0.75 10 0PP2 DRAIN 0 0.5 0 6

RB1 RBRB1 STORAGE 1500 0.75 10 0RB1 DRAIN 2 0.5 0 2

BR1 BCBR1 SURFACE 4 0.5 0.2 0.5 5BR1 SOIL 500 0.3 0.2 0.1 0.5 10.0 3.5BR1 STORAGE 500 0.75 100 0BR1 DRAIN 0 0.5 0 6

Results - Diagnosis of drainage networkSubcatchmentLID Process Number Area Width InitSatur FromImprv ToPerv Report File

S06 RB1 15 0.8 0 0 70 0S12 RB1 15 0.8 0 0 70 0S12 PP1 1 700 7 0 12 0S13 PP1 1 2150 7 0 12 0S13 RB1 22 0.8 0 0 40 0S13 BR1 1 1200 40 0 48 0S01 RB1 28 0.8 0 0 75 0S01 PP1 1 800 7 0 12 0S02 RB1 32 0.8 0 0 80 0S02 PP1 1 500 5 0 13 0S03 PP1 1 500 7 0 8 0S03 RB1 30 0.8 0 0 30 0S05 PP1 1 700 7 0 13 0S05 RB1 15 0.8 0 0 80 0S07 RB1 23 0.8 0 0 80 0S07 PP1 1 868 7 0 17 0S08 PP1 1 812 7 0 11 0S08 RB1 24 0.8 0 0 85 0S09 PP1 2 900 7 0 30 0S09 RB1 30 0.8 0 0 70 0S4A PP1 1 500 5 0 11 0S4A RB1 23 0.8 0 0 85 0S4B RB1 2 0.8 0 0 65 0S4B PP1 1 280 7 0 35 0S4C PP1 1 500 5 0 12 0S4C RB1 25 0.8 0 0 85 0S10A PP1 1 942 6 0 12 0S10A RB1 15 0.8 0 0 80 0S10B PP1 2 1040 7 0 19 0S10B RB1 21 0.8 0 0 80 0S11B RB1 20 0.8 0 0 75 0S11B PP2 2 700 7 0 10 0S11A RB1 30 0.8 0 0 70 0S11A PP1 1 840 7 0 10 0S14A PP1 1 400 7 0 21 0S14A RB1 6 0.8 0 0 60 0

Results - Diagnosis of drainage network

Design Rainfall Tr=10 and Flow Discharge

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Time [min]

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nsity

[mm

/h]

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Time [min]

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ge [m

3/s]

Desing Rainfall Tr=10

Flow Discharge

Flow Discharge with LIDmeasures

Results - Diagnosis of drainage network

Water Elevation Profile: Node N6 - 1

07/24/2012 00:24:00

Distance (m)500450400350300250200150100500

N6

N7

N8

N9

N11

N12

2 N14

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n (m

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Water Elevation Profile: Node N2 - 1

07/24/2012 00:24:00

Distance (m)550500450400350300250200150100500

N2

N4

N5

N9

N11

N12

2 N14

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Elev

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n (m

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Water Elevation Profile: Node N10 - 1

07/24/2012 00:24:00

Distance (m)300280260240220200180160140120100806040200

N10

N11

N12

2 N14

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Elev

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n (m

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Water Elevation Profile: Node N16 - 1

07/24/2012 00:24:00

Distance (m)500450400350300250200150100500

N16

N9

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Elev

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n (m

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Conclusions• The calibration of the model showed a reasonable

result, but the validation showed an exaggerated over estimation in the total volume.

• Considering the design rainfall, the nodes N4, N7 and N10 surcharged.

• The main purpose of this work was to treat this flooding problem using the LID concept.

• The use of LID, such as permeable pavements, rain barrels and bio retention cells, showed a good result on the main drainage line, where the actions in the catchment context are more sensible. The nodes that were flooded in the borders of the catchment were less sensible to LID measures because the surfaces related to these nodes were small and the distributed measures could not be as effective as they were in the catchment context.

Conclusions• Another problem was that in the borders of the

catchment there may occur, in reality, a diversion to the neighbouring catchments. As it has not been considered in the modelling, possibly the discharge in these nodes may be overestimated.

• This problem may also be the explanation for the calibration/validation results.

• In a real situation, a good result could be achieved by the use of LID combined with other flooding control measures. As an example, detention catchments or drainage net rehabilitation could be jointly considered.

Thank you for your attention