SWMM_Data

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Hydraulics and Lab. Seoul National University, Spring 2013

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Pipe Flow Modeling

1. Introduction

In this lab session a sewage system network will be studied. This will be performed by

using SWMM model (Storm Water Management Model) developed by the USEPA (United

States Environmental Protection Agency). With this software it is possible to simulate

rainfall-runoff events and runoff transport of urban drainage network taking into account

all the constraints that may exist: spillways, to pumps, to tanks, etc.

Each urban area has to be defined (set of buildings, roads, parks, etc..) and discharge on a

common sewage network defining an urban basin.

The hydrological phenomena of transformation of rainfall runoff hydrograph is analyzed

using a tank-model with cinematic-wave output. It assumes that each sub-basin, defined by

its area, width, slope, surface roughness, percentage of impervious area, etc. Assuming

some initial abstraction, so that until a certain rainfall threshold has not been reached

runoff will not be generated. The model does not describe the behavior of water in the

watershed, only the discharge at the outlet of the basin is given.

The model focuses on the parameterization of three main elements:

Contribution Basins Pipelines Junctions

For rainfall data, the application allows the analysis of both real rain values as with design

rainfall curves obtained from Intensity-Duration-Frequency.

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2. Main parameters of the model

2.1 Contribution basins

Name of the rain gauge associated to the basin. Name of the junction where runoff of the watershed is discharged. Catchment area in hectares (ha). Characteristic width of the basin, in meters. Average slope of the basin, in % Percentage of impervious surface % Coefficient of friction (N-IMPERV) for surface flow on impervious areas, by default

N-IMPERV= 0.2

Coefficient of friction (N-PERV) for surface flow on pervious areas, by default N-PERV = 0.2.

Water depth threshold to initiate runoff on impervious areas (Dstore-imperv), bydefault 2mm.

Water depth threshold to initiate runoff on pervious areas (Dstore-perv), by default6mm.

Percentage of impervious areas that have no initial water store (Zero-Imperv%), bydefault 25%.

Infiltration parameters pervious areas. It uses the curve number from the SCSmethod (U.S. Soil Conservation Service). In this study the value will be between 60

and 80.

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2.2 Junctions

The definition of link nodes is performed based on the following parameters:

Elevation of junction's invert (Invert El.) in meters Maximum water depth, distance from invert to ground surface. (Max Depth), in

meters.

water depth in the beginning of the simulation, in meters, by default 0.

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Hydraulics and Lab.

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2.3 Pipelines :

The characterization of the

Name of input and o Section geometry: ci Pipe length in meter Manning roughness

and 0.012 for polyet

Energy Loss coefficie

3. Flow propagation

Different approaches can be

3.1 Dynamic wave:

Solves the complete Representation of ba

reversal

Applicable to any net Small time steps are

Continuity equation:

Momentum equation:

Since :

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onduits is made by defining the following

tput junctions

cular, rectangular, ovoid .....

.

oefficient of the pipe. Generally n = 0.015

ylene.

nt along the conduit.

used in order to perform the water flow c

quations of Saint Venant unsteady flow u

ckwater effects, load flow, storage in the s

work

required (1 or 60 seconds)

0

l University, Spring 2013

parameters:

or concrete pipes

mputations:

idimensinal.

retch and flow

0

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3.2 Kynematic Wave:

Balance between gravity and friction is done. Applicable only arborescent networks with steep slopes.

Continuity equation :

0

Momentum equation: =

4. Study case

This example models runoff quantity in a small hypothetical drainage area. The study

domain consists of 8 subcatchments connected to a system of 1 to 2 m diameter conduits.

Rainfall data for both a short-term 36-hour period is provided.

1. Set up the model to run in single event mode for a period of 36 hours using Kinematic

Wave routing. Run the simulation.

2. View the Status Report for the run, noting the Continuity error.

3. Select some different output variables (e.g. subcatchment runoff, node flooding, link flow)

for viewing on the study area map. Use the Day/Time controls on the Map Browser to move

back and forth through time.

4. Animate the map by using the Animator Toolbar (make the toolbar visible by selecting

View | Toolbars | Animator from the Main Menu).

5. Generate some other types of reports, such as a time series plot and a profile plot.

6. Change the Simulation Options to use Dynamic Wave routing and re-run the analysis. Is

there any significance difference?

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7. Modify the model to run a continuous simulation as follows:

a) Edit the rain gage and change its Data Source to File, click on the File Name field

and specify the rain data file named sta310301.dat, and enter 310301 for the

Station Number.

b) Edit the Simulation Options as follows:

i. change the Routing Method back to Kinematic Wave

ii. make the End Date 01-02-2000 (for a 2-year simulation)

iii. change the Routing Time Step to 5 minutes.

8. Run the simulation (it may take several minutes). Try generating a Statistics Report to

see how the magnitude of various kinds of events (rainfall, runoff, , etc.) are distributed

over time.

Geometry and elements of the study area

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[SUBCATCHMENTS]

Name Raingage Outlet Area Imperv Width Slope

S1 RG1 J1 10 50 500 0.01

S2 RG1 J2 10 50 500 0.01

S3 RG1 J13 5 50 500 0.01

S4 RG1 J6 5 50 500 0.01

S5 RG1 J11 15 50 500 0.01

S6 RG1 J10 12 10 500 0.01

S7 RG1 J5 4 10 500 0.01

S8 RG1 O1 10 10 500 0.01

Name N-Imperv N-Perv S-Imperv S-perv PctZero RouteTo

S1 0.001 0.10 0.05 0.05 25 OUTLET

S2 0.001 0.10 0.05 0.05 25 OUTLET

S3 0.001 0.10 0.05 0.05 25 OUTLET

S4 0.001 0.10 0.05 0.05 25 OUTLET

S5 0.001 0.10 0.05 0.05 25 OUTLETS6 0.001 0.10 0.05 0.05 25 OUTLET

S7 0.001 0.10 0.05 0.05 25 OUTLET

S8 0.001 0.10 0.05 0.05 25 OUTLET

Name MaxRate MinRate Decay DryTime

S1 0.35 0.25 4.14 0.5

S2 0.7 0.3 4.14 0.5

S3 0.7 0.3 4.14 0.5

S4 0.7 0.3 4.14 0.5

S5 0.7 0.3 4.14 0.5

S6 0.7 0.3 4.14 0.5

S7 0.7 0.3 4.14 0.5

S8 0.7 0.3 4.14 0.5

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[JUNCTIONS]

Name Elevation Depth Name Elevation Depth

J1 1000 3 J8 984 3

J2 995 3 J9 980 3

J3 990 3 J10 990 3

J4 1005 3 J11 987 3

J5 1010 3 J12 990 3

J6 987 3 J13 995 3

J7 985 3

[OUTFALLS]

Name Elevation Type

O1 975 FREE

[CONDUITS]

Name Inlet node Outlet

Node

Length Manning n Type Diameter

C1 J1 J2 400 0.01 CIRCULAR 1.5

C2 J2 J3 400 0.01 CIRCULAR 1

C3 J4 J3 200 0.01 CIRCULAR 1

C4 J5 J4 200 0.01 CIRCULAR 1

C5 J3 J6 300 0.01 CIRCULAR 2

C6 J6 J7 300 0.01 CIRCULAR 2

C7 J13 J12 400 0.01 CIRCULAR 1.5

C8 J12 J11 400 0.01 CIRCULAR 1.5

C9 J11 J7 400 0.01 CIRCULAR 1.5

C10 J7 J8 100 0.01 CIRCULAR 2

C11 J10 J8 400 0.01 CIRCULAR 1

C12 J8 J9 400 0.01 CIRCULAR 2

C13 J9 O1 400 0.01 CIRCULAR 2

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RAINFALL TIMESERIES

Time Value

0:00 0

1:00 0.25

2:00 0.5

3:00 0.8

4:00 0.4

5:00 0.1

6:00 0.2

27:00 0.1

28:00 0.4

29:00 0.2

30:00 0.0

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