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

2. Getting Started Required first steps:
Confirm that program is authorized
Accept statement of Disclaimer
Select system of units
Define an Output file
Set the time parameters

3. Selecting Units Metric/SI or Imperial
Units are all kinematic (no force or mass) mm/hr, metre/sec, cub.m, hectare-m or inch/hr, feet/sec, cub.m, acre-feet
Units cannot be changed after time parameters have been defined

4. 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

5. 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,...

6. Other features & options
Show or hide status bar
Include full path in Output file
Review Output file at any time
Use context sensitive help
Show or hide ‘tool-tips’
Select from ‘Other Options’

7. Defining a Design Storm
Define the time parameters
Select storm type - 5 options
Enter required parameters e.g. Depth, duration etc.
Display rainfall as table and graph
Accept the storm
Define a 5-character descriptor

8. Storm Types Available Chicago hyetograph Huff rainfall distribution
Mass rainfall distribution (can be user defined)
Canada AES (Atmospheric Environment Service)
Historic storm (user defined)

9. Chicago hyetograph

10. Huff Distribution

11. Huff storm - 1st quadrant

12. Huff storm - 2nd quadrant

13. Huff storm - 3rd quadrant

14. Huff storm - 4th quadrant

15. 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

16. Mass Rainfall example

17. Historic Storm
15 values still zero
Last value entered by user

18. City of Guelph Design Storms
Return a b c r period (mm/hr) (min)
2-years
5-years
10-years
25-years
50-years
100-years

19. Estimating Catchment Runoff
Direct runoff or Effective rainfall
Storm
Initial abstraction
Losses
Infiltration
Surface depression storage

20. Infiltration methods
Soil Conservation Service (SCS) Curve Number (CN) method
Horton’s equation ‘moving curve’ method
Green & Ampt model

21. SCS Curve Number method
CN depends on soil type and pre-wetting
inches
P(t) = depth of rainfall
Q(t) = depth of runoff
Ia = initial abstraction
S = potential storage
CN = curve number  100 mm

22. Horton equation

23. Green & Ampt model where M=moisture deficit S =suction head
K =hydraulic conductivity

24. Rainfall-Runoff models (1)
Effective rainfall
Infiltration Model
Runoff
Losses
Catchment Model
Losses subtracted from rainfall to get effective rainfall which is then applied to catchment.

25. Rainfall-Runoff models (2)
Losses and infiltration calculated along with runoff as part of Runoff Model
Rainfall
Runoff
Catchment Model
Surface Depression Storage
Losses and infiltration

26. 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

27. Calculating the Runoff (2)
Symmetrical catchment Area = 2.2 ha
Overland flow length can be estimated as area divided by length of stream bank available for inflow.
75m
96m
63m
One-sided catchment Area = 2.4 ha
192m

28. Calculating the Runoff (3)
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)

29. Design of a Pipe 7
101
Runoff 102 1
Link 101 8
Inflow 102
102 9
Outflow 101 2
Link 102 3 10
103 11
Outflow 102 4 5 6
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.

30. 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

31. Uniform Flow in Pipes
Solve for y0 using

32. Critical Depth in Pipes
Solution for Ycr is based on the minimum energy criterion

33. A Trial Pipe Design Table of feasible designs for given Q and ‘n’
Double click on a row to test trial design
Click [Design] to get results of part-full flow analysis

34. Surcharged Pipes Due to closed top boundary resistance increases
as depth y approaches diameter D.
At y = D Q = Qfull
Q/Qfull
When y = D Q = Qfull.
y/D

35. Surcharged Pipes Q > Qfull Q = Qfull Q < Qfull
Energy line
Q > Qfull
Water surface
Q = Qfull
Q < Qfull
MIDUSS 98 assumes uniform flow for part-full pipes

36. 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

37. Channel Design
Channel design based on use of Manning eq. to find normal depth Yo for a specified discharge.
Using Manning eq.
M = imperial metric A = flow area R = hydraulic radius S = bed slope

38. 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.

39. Simple Cross-section T y0 GL GR General Trapezoidal section can be: B
rectangular trapezoidal triangular non-symmetrical B

40. Complex Cross-section1 5 4 7 6 8 9 10 2 3 Y X X3 Y3 WL
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.

41. Defining the Discharge
Peak value of current Inflow
hydrograph if one exists.
User specified discharge if no Inflow hydrograph is defined

42. Design of a simple channel
Plot and design details appear.
Enter channel depth and slope, press [Design]
Display table of Depth - Grade - Velocity
Peak flow is from current Inflow hydrograph

43. Design of a complex channel (1)
Draw section and specify peak flow = 15 c.m/s

44. Design of a complex channel (2)
Check low flow channel for reduced flow = 1.5 c.m/s

45. Design of a complex channel (3)
Reduce Manning n=0.025
Increase width of low flow channel to 3.5 m

46. Design of a complex channel (4)
Check modified section for maximum flow of 15 cm/s

47. Exercise
Design a trapezoidal channel to carry 2 c.m/s with gradient of 0.3% and n=0.04
Design 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

48. Flood Routing definitions
lag
Q(t)
Peak flow attenuation
Inflow at x
Outflow at x+Dx
Recession limb
Rising limb tp
time
c Dt x
time t
time t+Dt

49. Flood Routing methods Hydraulic Hydrologic
Uses both dynamic and continuity equations
Allows backwater effects to be modelled
Solution advanced by timestep Dt
Hydrologic
Uses only continuity equation
Cannot model backwater effects
Solution advanced downstream by Dx

50. Kinematic Wave Equation
Continuity with no lateral inflow yields: Q
Q+Q x
t+ t t A
For quasi-uniform flow:
Substitute and separate variables to get wave eq. or
where c = dQ/dA is wave celerity

51. Space-Time Coordinates
Time t
a Dx
Flow Q4 unknown 3 8 4 5 6
Nucleus Dt
b Dt 1 7 2 Dx
Distance x

52. Continuity Around the Nucleus8 7 6 5 4 3 2 1
bdt
adx

53. Generalized Muskingum equation
Let
and get Q4=f(Q1 , Q2 , Q3)
Collecting terms,
Setting b = 0.5 yields
where

54. Deriving the Diffusion equation
Non-centered finite difference scheme creates a numerical error or
Convert the Wave equation to a Diffusion equation
Diffusion coefficient is related to channel conveyance

55. Determine weighting coefficients
Compare the two equations for the diffusion coeff. D
f(a,b,D)=0 leads to multiple sets of (a,b) coordinates for any value of D.

56. Numerical Stability Criteria
Condition for numerical stability is
Unstable

57. Limits for Dx and Dt For b = 0.5 and From parts 1 & 2 or
For very long channels, route hydrograph over multiple sub-reaches of length Dx=Length/N, N = 2,3,4...

58. Limits for Dx and Dt For b = 0.5 and From parts 1 & 2 or
For very long channels, route hydrograph over multiple sub-reaches of length Dx=Length/N, N=2,3,4...
From parts 2 & 3 or
For very short channels, use routing time-step equal to sub-multiple of hydrology time step, dt=Dt/N, N=2,3,4...

59. MIDUSS 98 Route Command

60. MIDUSS 98 Route Command Details of last conduit design are displayed
Estimated values of weighting coefficients
User can change computed X or K values
Changes to Dx or Dt reported for information

61. Results of Route command

62. Calculating celerity

63. Design of a Detention Pond
Volume
Inflow WL
Discharge
Outflow
Q(t)
Inflow
Peak outflow is on recession limb of inflow.
Outflow
Time

64. Types of Detention Pond
‘In-line’ storage reservoir with outflow control device to reduce peak flow
‘Off-line storage reservoir with connection above normal hydraulic grade line
On-site storage on parking lots or below ground in oversized storm sewers or trench
On rooftops of proposed new commercial buildings

65. Theory of Reservoir Routing
QO2 = ?
QI2
Law of
Continuity Dt
Inflow
Outflow
QI1
QO1
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

66. Theory of Reservoir Routing (2)
Inflow = Outflow Rate of change of storage
f(QO)
QI1 + QI2 - 2QO1
Outflow QO

67. Outflow Orifice Controls
Submerged orifice
Ccd H d
Non-submerged orifice d H

68. Outflow Weir Controls
Rectangular weir H
Ycr
Triangular weir H
Ycr

69. Storage Models
MIDUSS 98 provides 4 tools to assist in defining the depth-storage relation.
“Rectangular” reservoir or pond
Oversized storm sewers
Wedge shaped storage (parking lots)
Rooftop storage

70. Rectangular Pond storage
Aj+1 = Lj+1 x Bj+1
Lj+1
Aspect ratio R = L/B Am H m Lj
Aj = Lj x Bj
For irregularly shaped ponds the aspect ratio R is defined by:

71. Oversized Storm Sewers
Weir & orifice outflow control D S0 WL IL
Datum

72. Wedge shaped Storage
Parking lot storage created by restricting capacity of catch basins g2 R2 R1
Ponding depth H g1
Typical depth of exit pipe below rim elevation
3 ft/ 0.92 m

73. Roof top Storage L/2 L/2 H Roof slope S0 Linear Discharge weir H
Q = K.H
e.g. Q = 24 litres/min/25mm head
Vol = f(H, L S0)

74. On-Site Storage Control
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:-
Rooftop storage
Parking lot storage
Underground storage

75. Roof storage 75%total roof area
Schematic of Commercial Site
Building footprint 30%
Parking and Roads 65%
Pervious 5%
Parking 95% impervious
Parking 67% B
Roof storage 75%total roof area 2 1
Total Breadth B 3
Roads 90% impervious
Roads 33% B
Roof structures
Total Width W

76. Roof storage 75%total roof area
Schematic of Commercial Site
Building footprint 30%
Parking and Roads 65%
Pervious 5%
Parking 95% impervious
Parking 67% B
Roof storage 75%total roof area 2 1
Total Breadth B 3
Roads 90% impervious
Roads 33% B
Roof structures
Total Width W

77. Example of On Site control1 2
Imperv. 95% 4.11
Roof 3.00
Parking 4.33
Pervious 5% 0.22
Total area 10 ha
Parking & roads 6.50
Imperv. 90% 1.95
1.95
Roads 2.17
Pervious 10% 0.22
0.72
Grass 0.50
0.50 3
Part 3 pervious area
Part 3 impervious area
73% imperv
Part 3 total area
2.67

78. Example of On Site control

79. Model Rooftop storage Roof area hectares Store area hectares
Area/drain sq.metre
Drain flow L/min/25mm
Roof slope gH:1V
3.000
2.250
450.0
24.000
200.00

80. Outflow from Rooftop

81. Parking Lot storage
100.5
Inlet Control Device
100.0
99.0

82. 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

83. Outflow from Parking storage

84. Parking lot storage (2) Volume Discharge Rim capacity Rim elevation
Catch basin
Invert level
Rim capacity

85. Compare outflow with and without on-site storage
0.889
0.492

86. Working with Files Topics discussed Types of files
Commands that use files
Storage arrays that interact with files
Naming a file
File formats

87. Types of Files

88. Commands that use Files

89. 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. “ \ / : * ? < > |

90. Storage arrays that use Files

91. Hydrograph File Formats

92. The FileI_O Command

93. The FileI_O Command Select Read or Write
Choose Rainfall hyetograph or flow hydrograph
If file is to be created, enter the name here
Pick drive from drop down list
Select type of hyetograph or hydrograph
If file exists (‘Read’) pick file from this list
Navigate to folder where file is found or is to be created
Define type of file or “All files”

94. Exfiltration Trench Idealized diagram of exfiltration trench
Perforated distribution pipe
Outflow Control Device
Inflow I
Outflow Q
Exfiltration X
Water table
Idealized diagram of exfiltration trench

95. 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 runoff
Split inflow hydrograph into two components of Outflow and Groundwater recharge

96. Basic Theory Inflow = Outflow + Exfiltration + Change of storage I V Q

97. Trench Cross-section For laminar flow: where
Topwidth T
For laminar flow:
Filter
Clear stone
where
Height H
Depth y y
eff
Invert elevation IL
P + y/2 B
P=IL-G
Water table elevation G
K = hydraulic conductivity

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

99. Define Trench parameters

100. Define outflow control
[Compute]
Plot V,Q=f(H)

101. Defining the Trench Pipes
Main storm sewer is solid 450 mm pipe with invert =100.85
Pipes positioned graphically with clearance shown. Position refined by editing table.
Press [Compute] to update volume table
Two 200 mm diam. perforated pipes are plugged at down stream end to distribute inflow along trench

102. Results of Routing

103. The Etobicoke Trench

104. 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.

105. 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

106. Files used in Automatic mode
‘Output’ is the file created in a previous Manual session.
Create Miduss.Mdb
Edit Miduss.Mdb
Run Miduss.Mdb
Automatic
‘Miduss.Mdb’ is a database file created by the Create Miduss.Mdb command.
‘New Output’ is modified output file created during Automatic design session.

107. Structure of the Database
Index
Command
Parameter value
Description, data or results

108. Advantages of a Database
Direct access to records speeds processing
Database file can be ‘bound’ to a grid
File can be viewed, edited and used as input source simultaneously
Setting 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

109. 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

110. 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