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

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

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

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 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’

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

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

Chicago hyetograph

Huff Distribution

Huff storm - 1st quadrant

Huff storm - 2nd quadrant

Huff storm - 3rd quadrant

Huff storm - 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 15 values still zero Last value entered by user

City of Guelph Design Storms Return a b c r period (mm/hr) (min) 2-years 743 6 .7989 0.4 5-years 1593 11 .8789 0.4 10-years 2221 12 .9080 0.4 25-years 3158 15 .9355 0.4 50-years 3886 16 .9495 0.4 100-years 4688 17 .9624 0.4

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

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

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

Horton equation

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

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.

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

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

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

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)

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.

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 Solve for y0 using

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

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

Surcharged Pipes Due to closed top boundary resistance increases as depth y approaches diameter D. At y = 0.81963 D Q = Qfull Q/Qfull When y = 0.93815 D Q = 1.07571 Qfull. y/D

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

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. Using Manning eq. M = 1.49 imperial 1.00 metric A = flow area R = hydraulic radius S = 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 T y0 GL GR General Trapezoidal section can be: B rectangular trapezoidal triangular non-symmetrical B

Complex Cross-section 1 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.

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

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

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

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

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

Design of a complex channel (4) 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=0.04 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

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

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

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

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

Continuity Around the Nucleus 8 7 6 5 4 3 2 1 bdt adx

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

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

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.

Numerical Stability Criteria Condition for numerical stability is Unstable

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...

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...

MIDUSS 98 Route Command

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

Results of Route command

Calculating celerity

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

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

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

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

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

Outflow Weir Controls Rectangular weir H Ycr Triangular weir H Ycr

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

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:

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

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

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)

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

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

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

Example of On Site control 1 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

Example of On Site control

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

Outflow from Rooftop

Parking Lot storage 100.5 Inlet Control Device 100.0 99.0

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) Volume Discharge Rim capacity Rim elevation Catch basin Invert level 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

Types of Files

Commands that use Files

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. “ \ / : * ? < > |

Storage arrays that use Files

Hydrograph File Formats

The FileI_O Command

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”

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

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

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

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

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 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

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. 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.

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

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

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