Using MIDUSS 98 by Alan A. Smith Alan A. Smith Inc. Dundas, Ontario, Canada.

Using MIDUSS 98

by

Alan A. SmithAlan A. Smith Inc.

Dundas, Ontario, Canada

Getting Started

Confirm that program is authorized

Accept statement of DisclaimerSelect system of unitsDefine an Output fileSet the time parameters

Required first steps:

Selecting Units

Metric/SI or Imperial

Units are all kinematic (no force or mass)mm/hr, metre/sec, cub.m, hectare-m

orinch/hr, feet/sec, cub.m, acre-feet

Units cannot be changed after time parameters have been defined

Output file

Contains a record of all commands, data and results to allow design session to be repeated exactly

Can be converted to an Input database to run in Automatic mode

Should be stored in special folder for each job

Time Parameters

Time step for hydrology

Maximum expected storm duration

Maximum expected hydrograph length

Routing or stability time step t = t/N, N = 1,2,3,...

Other features & options

Show or hide status barInclude full path in Output fileReview Output file at any

timeUse context sensitive helpShow or hide ‘tool-tips’Select from ‘Other Options’

Defining a Design Storm

Define the time parametersSelect storm type - 5 optionsEnter required parameters

e.g. Depth, duration etc.

Display rainfall as table and graphAccept the stormDefine a 5-character descriptor

Storm Types Available

Chicago hyetographHuff rainfall distributionMass rainfall distribution (can be user defined)

Canada AES (Atmospheric Environment Service)

Historic storm (user defined)

Chicago hyetograph

cd

avebt

ai

Huff Distribution

Huff storm - 1st quadrant

1st quadrant

Huff storm - 2nd quadrant

2nd quadrant

Huff storm - 3rd quadrant

3rd quadrant

Huff storm - 4th quadrant

4th quadrant

Mass Rainfall Distribution

Defined by series of uniformly spaced vertical coordinates which increase continuously from 0.0 to 1.0

Various standard distributions for North America included with MIDUSS 98

User defined distributions are easily defined using local data

Maximum number of points is unlimited

Mass Rainfall example

Historic Storm

Last value entered by user

15 valuesstill zero

City of Guelph Design StormsReturn a b c rperiod (mm/hr) (min)

2-years 743 6 .79890.4

5-years 1593 11 .87890.4

10-years 2221 12 .90800.4

25-years 3158 15 .93550.4

50-years 3886 16 .94950.4

100-years 4688 17 .96240.4

Estimating Catchment Runoff

Storm

Surface depressionstorage

Infiltration

Initial abstraction

Direct runoff or Effective rainfall

Losses

Infiltration methods

Soil Conservation Service (SCS) Curve Number (CN) method

Horton’s equation ‘moving curve’ method

Green & Ampt model

SCS Curve Number method

254400,25

101000

CNS

CNS inches

mm

))((

))(()(

2

a

a

IStP

ItPtQ

P(t) = depth of rainfall

Q(t) = depth of runoff

Ia = initial abstraction

S = potential storage

CN = curve number 100

CN depends on soil type and pre-wetting

Horton equation

Kt

cccapacity effff

0

Green & Ampt model

where

M=moisture deficit

S =suction head

K =hydraulic conductivity

K

MSKf 1

Rainfall-Runoff models (1)

Losses subtracted from rainfall to get effective rainfall which is then applied to catchment.

Rainfall

Infiltration Model

Losses Catchment ModelRunoff

Effectiverainfall

Rainfall-Runoff models (2)

Losses and infiltration calculated along with runoff as part of Runoff Model

Rainfall

Catchment ModelRunoff

Losses andinfiltration

SurfaceDepression

Storage

Calculating the Runoff (1)

Runoff from pervious and impervious fractions computed and added together

Flow lengths can be:-

(a) equal

(b) proportional

(c) user supplied


Overland flow length can be estimated as area divided by length of stream bank available for inflow.

Symmetrical catchmentArea = 2.2 ha

One-sided catchmentArea = 2.4 ha

mW

AL 47

9675632

22000

2

mW

AL 125

192

24000

75m

96m

63m

192m


Overland flow routing choices:

Combine effective rainfall with: triangular response function rectangular response function single linear reservoir response function

Combine infiltration & other losses with

outflow from idealized inclined plane.(Similar to SWMM RUNOFF method)

Design of a Pipe

In a tree network, each node can have only one outflow link. Therefore we use the convention that link numbers are the same as the upstream node number.

101

Outflow 101

102

103

Outflow 102

Runoff 102

Inflow 102

11

10

6

7

8

9

4 5

32

1 Link 101

Link 102

Get the Maximum Inflow

If no inflow hydrograph exists the user can specify a peak flow for the design

Use Hydrograph|Add Runoff to update Inflow hydrograph

Uniform Flow in Pipes

2cos1

2

2

sin8

2

21

03

2

Dy

DP

DA

SARn

MQ

Solve for y0 using 02

sin 52

53

fullQ

Qf

Critical Depth in Pipes

Solution for Ycr is based on the minimum energy criterion

13

2

Ag

TQ

yD

T

yDyT

g

Q

T

Ayf

2tan2

2

0

1

2

23

A Trial Pipe Design

Double click on a row to test trial design

Click [Design] to get results of part-full flow analysis

Table of feasible designs for given Q and ‘n’

Surcharged Pipes

0

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1y/D

Q/Qfull

When y = 0.93815 D Q = 1.07571 Qfull.

Due to closed top boundary resistance increases as depth y approaches diameter D.

At y = 0.81963 D Q = Qfull

Surcharged Pipes

Q > Qfull

Q = Qfull

Q < Qfull

Energy line

Water surface

MIDUSS 98 assumes uniform flow for part-full pipes

Exercise 4

Design a pipe to carry 2 c.m/s when

running 75% full with a gradient of 0.4%

and n = 0.013

Check for surcharged hydraulic grade line

if discharge increases to 3 c.m/s

Channel Design

Channel design based on use of Manning eq. to find normal depth Yo for a specified discharge.

GeometrynManningSlopeyfQ ,'',,00

Using Manning eq.

21

03

2

000 SRAn

MQ

M = 1.49 imperial 1.00 metricA = flow areaR = hydraulic radiusS = bed slope

Channel Flow Assumptions

Flow is fully developed rough turbulent.Channel is prismatic, i.e. cross-section

is constant along length.Flow is uniform, i.e. Sf = S0.

A0, P0, R0 = f(Y0, geometry).Cross-section is fixed boundary.

Simple Cross-section

B

T

y0GL GRGeneral Trapezoidalsection can be:

rectangulartrapezoidaltriangularnon-symmetrical

Complex Cross-section

1

54 7

6

8

910

2

3

Y

X

X3

Y3WL

Datum

Cross-sections can be defined by a set of straight lines joining up to 50 coordinate pairs. These can be drawn graphically and edited numerically.

Defining the Discharge

Peak value of current Inflow hydrograph if one exists.

User specified discharge if no Inflow hydrograph is defined

Peak flow is from current Inflow hydrograph

Design of a simple channel

Display table of Depth - Grade - VelocityEnter channel depth and slope, press [Design]Plot and design details appear.

Design of a complex channel (1)

Draw section and specify peak flow = 15 c.m/s


Check low flow channel for reduced flow = 1.5 c.m/s


Increase width of low flow channel to 3.5 m

Reduce

Manningn=0.025


Check modified section for maximum flow of 15 cm/s

Exercise

Design a trapezoidal channel to carry 2 c.m/s

with gradient of 0.3% and n=0.04Design a channel which includes a low flow

channel to carry maximum flow of 12 c.m/s and low flow of 2 c.m/s. Allow freeboard of 0.3 m. Try for gradient = 0.3%, n=0.04 for main channel and n=0.02 in low flow channel

Flood Routing definitions

Q(t)Peak flow attenuation

time

lag

Inflow at x

x

time t time t+tc t

tp

Recession limbRising limb Outflow at x+x

Flood Routing methods

Hydraulic Uses both dynamic and continuity equations Allows backwater effects to be modelled Solution advanced by timestep t

Hydrologic Uses only continuity equation Cannot model backwater effects Solution advanced downstream by x

Kinematic Wave Equation

0

t

A

x

Q

dA

dQ

A

QthatsoWLfQ

)(

t

Q

ct

Q

dQ

dA

x

Q

1

Continuity with no lateral inflow yields:

For quasi-uniform flow:

Substitute and separate variables to get wave eq.

01

t

Q

cx

Qor

Q Q+Q

x

t+ t

t A

where c = dQ/dA is wave celerity

Space-Time Coordinates

Time t

Distance x

8

7

65

43

21

t

x

x

tNucleus

Flow Q4 unknown

Continuity Around the Nucleus

x

QQ

x

Q

56

t

QQ

t

Q

78

438

217

246

135

1

1

1

1

QQQ

QQQ

QQQ

QQQ

07856

QQQQx

tc0

1

t

Q

cx

Q

8

7

65

43

21

dx

dt

Generalized Muskingum equation

011

11

2143

1324

QQQQ

QQQQ

xtc

Let

and get Q4=f(Q1 , Q2 , Q3)

1

11

1

4

3

2

1

33221144

C

C

C

C

QCQCQCQC

Collecting terms,

where

KtX

KtX

KtX

KtX

21

2

21

2

Setting = 0.5 yields

Deriving the Diffusion equation

01

t

Q

cx

QNon-centered finite difference scheme creates a numerical error

2

21

x

QD

t

Q

cx

Q

Convert the Wave equation

to a Diffusion equation

2

2

2

3

2

1

x

Q

dhdKQ

K

t

Q

cx

Q

Diffusion coefficient is

related to channel conveyance

012212

12

2

x

Qx

t

Q

cx

Q or

Determine weighting coefficients

xshwhere

dhdQh

Qff

f

1221

122122

x

dhdQs

QD

f

Compare the two equations for the diffusion coeff. D

5.0;2

1 dh

dQh

Q

f

f(,,D)=0 leads to multiple sets of (,) coordinates for any value of D.

Numerical Stability Criteria

1

1

x

tc

Unstable

Condition for numerical stability is

Limits for x and t

122x

tcFor = 0.5 x

D

212 and

For very long channels, route hydrograph over multiple sub-reaches of length x=Length/N, N = 2,3,4...

From parts 1 & 2

tcDxx

tc

x

D

22

1 or

Limits for x and t

122x

tcFor = 0.5 x

D

212 and

For very long channels, route hydrograph over multiple sub-reaches of length x=Length/N, N=2,3,4...

For very short channels, use routing time-step equal to sub-multiple of hydrology time step, t=t/N, N=2,3,4...

From parts 2 & 3 c

Dxt

x

D

x

tc 2212

or

From parts 1 & 2

tcDxx

tc

x

D

22

1 or

MIDUSS 98 Route Command

MIDUSS 98 Route Command

Details of last conduit design are displayed

Changes to x or t reported for information

User can change computed X or K values

Estimated values of weighting coefficients

Results of Route command

Calculating celerity

2Q

Design of a Detention Pond

Peak outflow ison recessionlimb of inflow.

Inflow

Outflow

Time

Q(t)

Volume

DischargeOutflow

Inflow

WL

Types of Detention Pond

On rooftops of proposed new commercial buildings

On-site storage on parking lots or below ground in oversized storm sewers or trench

‘Off-line storage reservoir with connection above normal hydraulic grade line

‘In-line’ storage reservoir with outflow control device to reduce peak flow

Theory of Reservoir Routing

t

QI1

QI2

QO1

QO2 = ?

Inflow Outflow

Inflow = Outflow + Rate of change of storage

Assume:-

(1) Storage depends only on outflow(2) Reservoir surface is horizontal(3) Water surface elev. is function of outflow

Law of

Continuity

Theory of Reservoir Routing (2)

12112

222

21

12

2

21

2

21

QOQOt

SQO

t

SQIQI

t

SSQOQOQIQI

1221)1()2( QOQIQIQOfQOf

Inflow = Outflow + Rate of change of storage

Outflow QO

f(QO)

QI1 + QI2 - 2QO1

Outflow Orifice Controls

dHfordHgdCQ c 322

42

5.057.1

25

04.0496.0

d

H

d

H

d

Hfwhere

dHfordgCd

HfQ c

Submerged orifice

Non-submerged orifice

Hd

Ccd

Hd

Outflow Weir Controls

Rectangular weir

Hy

ygBCQ

cr

crdcr

3

2

23

Hy

ymgCQ

cr

crdcr

5

422

25

Triangular weir

HYcr

HYcr

Storage Models

MIDUSS 98 provides 4 tools to assist in defining the depth-storage relation.

“Rectangular” reservoir or pondOversized storm sewersWedge shaped storage (parking lots)Rooftop storage

Rectangular Pond storage

H

Aj+1 = Lj+1 x Bj+1

Aj = Lj x Bj

Lj

Lj+1

mAm

mHBmHLA

mHBmHLA

BLA

AAAH

V

jjj

jjm

jjj

jmj

22

46

1

1

Aspect ratio R = L/B

For irregularly shaped ponds the aspect ratio R is defined by:

Area

PerimeterRRRf

2

844)(

Oversized Storm Sewers

Weir & orificeoutflow control

Datum

WL

IL

D

S0

Wedge shaped Storage

Parking lot storage created by restricting capacity of catch basins

32221

2118

HggggV

Typical depth of exit pipe below rim elevation

Ponding depth H

3 ft/ 0.92 m

R2

R1

g1

g2

Roof top Storage

Roof slope S0

HL/2 L/2

H

Q = K.H

e.g. Q = 24 litres/min/25mm head

Vol = f(H, L S0)

Linear Discharge weir

On-Site Storage Control

Rooftop storageParking lot storageUnderground storage

Commercial developments may have a percentage of impervious areas of 85% or more. On-site storage is often preferred to centralized storage for cost sharing, quality control and spill control. Methods include:-

Roof

structures

12

3

Parking95%

impervious

Roads90%

impervious

Buildingfootprint

30%Parking and Roads

65%Pervious

5%

Total Width W

Roof

stora

ge

75%

tota

l ro

of

are

a

Tota

l B

readth

B

Par k

i ng

67%

B

Roads

33%

B

Schematic of Commercial Site

Example of On Site control

Totalarea 10 ha

Imperv. 90% 1.95

Pervious 10% 0.22

Parking 4.33

Roads 2.17

Roof 3.00

Parking &roads 6.50

Grass 0.50

73%imper

v

0.50

Imperv. 95% 4.11

Pervious 5% 0.22

Part 3 pervious areaPart 3 impervious area

0.72

1

3

2

Part 3 total area 2.671.95

Example of On Site control

Model Rooftop storage

Roof areahectares

Store areahectares

Area/drainsq.metre

Drain flow L/min/25m

m

Roof slopegH:1V

3.000 2.250 450.0 24.000 200.00

Outflow from Rooftop

Parking Lot storage

99.0

100.0Inlet Control Device

100.5

Define Wedge storage

Wedge invert

Grade 1 g1H:1V

Grade2 g2H:1V

Angle subtended

Number of wedges

100.00 60.00 120.00 90.00 67.00

Outflow from Parking storage

Parking lot storage (2)

Rim elevation

Catch basinInvert level

Volume

Discharge

Rim capacity

Compare outflow with and without on-site storage

0.889

0.492

Working with Files

Topics discussed Types of files Commands that use files Storage arrays that interact with

files Naming a file File formats

Type Typical Name Purpose

Output Def ault.out Records commands, data, results

I nput data Miduss.Mdb Database f or Automatic use

Hyetograph 5year.stm Rainf all intensities

Hydrograph Pond flow.hyd Flowrates

Rainf all dist. Huff 1.mrd Fractions of total rain depth

Diversion Div12345.hyd Flow removed f rom inflow

J unction Hyd12345.J NC Flow accumulated at junction

Help Miduss98.hlp Help system

Log Miduss.log Error reporting

Types of Files

Commands that use Files

File Type Related Command

Output Most commands except Windows, Help, Show(Table, QGraph),

I nput Automatic (Create, Edit, Run)

Hyetograph Hydrograph (FileI _O)

Hydrograph Hydrograph (FileI _O)

Mass Rain Dist. Storm (Huff , Mass distribution)

Diversion Design (Diversion)

J unction Hydrograph (Combine, Confluence)

Rules for File Names

Long names allowed. More than 11 characters used by DOS “nnnnnnnn.eee”

Names can include spaces, periods, e.g. “Pond Inflow.Pre.005hyd”

Only 11 illegal characters, e.g.“ \ / : * ? < > |

Array Name Size ContentsRainTemp() NRain Temporary storm until accepted by user

Rain() NRain Defined design storm

RainEffI() NRain Effective rainfall on Impervious areas

RainEffP() NRain Effective rainfall on Pervious areas

OvHyd() MaxHyd Total runoff hydrograph

OvHydI() MaxHyd Runoff from Impervious areas

OvHydP() MaxHyd Runoff from Pervious areas

Inflow() MaxHyd Inflow to pipe, channel, pond etc.

Outflow() MaxHyd Outflow from pipe, channel, pond etc.

TempHyd() MaxHyd Temporary junction or diverted flow

BkupHyd() MaxHyd Backup storage to allow ‘Undo’ command

Storage arrays that use Files

Record Content Example

1 Description “Hydrograph #1…”

2 File type 4

3 Peak value “0.432”

4 Gravity 9.81

5 Time step 5

6 No. of values 36

7 Value 1 0.000

8 Value 2 3.456E-03

: : :

N+6 Value N 4.567E-04

Hydrograph File Formats

The FileI_O Command

The FileI_O Command

Select Read or Write

Choose Rainfall hyetograph or flow hydrograph

Select type of hyetograph or hydrograph

Pick drive from drop down list

Navigate to folder where file is found or is to be created

Define type of file or “All files”

If file exists (‘Read’) pick file from this list

If file is to be created, enter the name here

Exfiltration Trench

Idealized diagram of exfiltration trench

Perforated distribution pipe Outflow Control Device

Exfiltration XWater table

Outflow Q

Inflow I

Purpose of Exfiltration

Encourage return of storm runoff to the groundwater

Reduce the hydraulic load on the minor (e.g. piped) system

Improve quality of runoff by removal of some particulate matter

Reduce thermal impact on the runoffSplit inflow hydrograph into two

components of Outflow and Groundwater recharge

Basic Theory

Inflow = Outflow + Exfiltration + Change of storage

t

VVXXQQII

12212121

222

11111

222

21 2222

XQXQt

VXQ

t

VII

1111122221 22,,,, XQXQVfXQVfII

211112 22)( IIXQQfQf

IQ

X

V

Trench Cross-section

GIL

yGIL

yGILS f

21

2

For laminar flow:

fKSqA

Q

where

K = hydraulic conductivity

Water table elevation G

Topwidth T

Height H

Invertelevation IL

Filter

Clear stone

Dep

th y

P +

y/2

P=IL-G

B

yeff

Define Trench parameters

Data window is opened by using Geometry/Trench menu command from Trench Design form.

Define Trench parameters

Define outflow control

[Compute]

Plot V,Q=f(H)

Defining the Trench Pipes

Main storm sewer is solid 450 mm pipe with invert =100.85

Two 200 mm diam. perforated pipes are plugged at down stream end to distribute inflow along trench

Pipes positioned graphically with clearance shown. Position refined by editing table.

Press [Compute] to update volume table

Results of Routing

The Etobicoke Trench

What is Automatic mode?

In Manual mode all commands and required data are entered by the user. These commands, data and main results are copied to the Output file. This information allows the design session to be repeated.

In Automatic mode, commands and data are read from an input file with no entry required from user.

Reasons for Automatic mode

User can complete a design in two or more sessions

Repeat a design with a different storm

Revise and compare the design of one or more components

Add or insert commands in Manual mode to change hydrology simulation or design

Files used in Automatic mode

‘Output’ is the file created in a previous Manual session.

‘New Output’ is modified output file created during Automatic design session.

‘Miduss.Mdb’ is a database file created by the Create Miduss.Mdb command.

Create Miduss.Mdb

Edit Miduss.Mdb

Run Miduss.Mdb

Automatic

Structure of the Database

Command

Index

Parameter valueDescription, data or results

Advantages of a Database

Direct access to records speeds processingDatabase file can be ‘bound’ to a gridFile can be viewed, edited and used as

input source simultaneouslySetting a command as a negative number

causes a continuous Automatic run to stop and revert to step-by-step EDIT mode or switch to Manual mode

Automatic processing can re-start where it was halted

Steps to Run Automatic mode

Create the input database Miduss.Mdb using the Creat Miduss.Mdb command

Review and/or Edit the database - e.g. change Command numbers to negative value to halt processing.

Use the Run Miduss.Mdb command to process the file in any of three modes EDIT, STEP or RUN

Using the Control Panel

The Control Panel is displayed when the Run Miduss.Mdb command is used

RUN starts continuous processing of the data

STEP executes commands one by one without any chance to modify data

EDIT executes next command and lets you alter data and [Accept] the result

Using MIDUSS 98 by Alan A. Smith Alan A. Smith Inc. Dundas, Ontario, Canada.

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Transcript of Using MIDUSS 98 by Alan A. Smith Alan A. Smith Inc. Dundas, Ontario, Canada.