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MIDUSS

 

Hydrology Features

The hydrologic modelling methods used in MIDUSS are well recognized and very versatile.  You can select from a choice of:

  • Five single event storms (including custom Malaysia storms),
  • Three rainfall abstraction models, and
  • Four overland flow routing methods

This combination provides a wide range of modelling options. This allows you to examine the sensitivity of results to the choice of algorithm a feature appreciated equally by both professional engineers and teachers.

In addition to alternative methods for generating runoff from a catchment there are capabilities to add baseflow and to model a large, reasonably homogeneous catchment as a 'lumped area' without having to resort to unreasonable values for the overland routing parameters.

You can use either Metric or US units throughout MIDUSS.

If you have generated hydrographs using another software product, you can use the them in MIDUSS and takes advantage of the MIDUSS design capabilities you don't get with other packages.

The MIDUSS user manual includes comprehensive engineering theory for all the available hydrology models. In fact, the MIDUSS user manual has been used as a supplementary text book at many Universities and Colleges.

Learn more about the MIDUSS hydrology features below.

STORM

The Storm command allows you to define a rainfall hyetograph either of the synthetic, design type or a historic storm.

Available storms are:

  • the Chicago hyetograph
  • the 4 Huff quartile design storms
  • a Mass rainfall distribution curve
  • the Canada Atmospheric Environment Service storms
  • a user defined Historic storm

Storms may also be defined by importing a hyetograph file in simple text format.

CATCHMENT

The Catchment command lets you define a single sub-catchment and computes the total overland flow hydrograph for the currently defined storm. You can, of course, combine an unlimited number of catchments within a drainage network.

The roughness, degree of imperviousness and surface slope of both the pervious and impervious fraction are defined in this command. The effective rainfall on these two fractions is computed and stored for future use.

The runoff hydrographs from the pervious and impervious areas are computed separately and added to give the total runoff.

MIDUSS offers a choice between three different models for estimating infiltration and rainfall losses and four alternative methods for routing the overland flow.

Model rainfall losses with:

  • SCS CN
  • Horton
  • Green & Ampt

Route flow with

  • Triangular SCS
  • Rectangular
  • SWMM method
  • Linear reservoir

Rainfall loss can also be estimated using the simple runoff coefficient which is converted to a corresponding SCS CN for the current storm depth. All rainfall loss methods can be used with any of the flow routing algorithmns with the exception of the SWMM runoff method*.

The Triangular SCS is a dynamic triangular response function in which time of concentration varies with the intensity of the effective rainfall

The Rectangular response function varies dynamically in the same manner as the triangular response.

The SWMM RUNOFF algorithm uses a stage-discharge relation based on the Manning equation coupled with a non-linear reservoir. *Use of the SWMM routing method limits infiltration methods to either Horton or Green & Ampt.

The Linear reservoir response function is defined by the impulse response of a single linear reservoir. Use of this method is similar to the OTTHYMO procedure.

MIDUSS lets you compare methods and to examine the sensitivity of the resulting runoff hydrograph to the methods used. This flexibility means, however, that you must exercise some care and consistency in the selection of procedures and parameter values for a particular application.

This window shows the first of many options in the catchment command. The runoff is computed as the sum of the direct runoff hydrographs from the pervious and impervious fractions. These can be specified and computed from the appropriate tabs on this form.

LAG and ROUTE

This command helps you model the runoff from a very large sub-catchment without having to resort to specifying unrealistically long overland flow lengths.

The command computes the lag time in minutes of a hypothetical linear channel and linear reservoir through which the runoff hydrograph is routed. Typically this results in a smaller, delayed runoff peak flow.

Lag and Route is intended to simulate a very large catchment (>30 ha or 75 acres) using a hypothetical linear reservoir in series with a linear channel at the downstream end of the catchment. The lag of the two components is roughly 2/3 of the total travel time in the conduits from the most remote point in the drainage network to the outflow. The linear reservoir lag is roughly 2/3 of the total. These fractions are defined by an empirical curve built in to the program and which can be edited.

The travel time is dependant on the type of conduit, the slope, roughness and average flow. The reservoir and channel lags are computed and displayed but you can modify these as a special option.

The modified peak flow is shown on the form along with a graphical and tabular display.

BASE FLOW

This command lets you specify a constant positive value of base flow to be added to the current inflow hydrograph.

The direct runoff hydrograph computed by the Catchment command does not include any baseflow. This command lets you add an estimated baseflow to the current Inflow hydrograph. If some baseflow has been added previously, a negative value can be used as long as it does not result in a negative ordinate in the inflow hydrograph.

 

Design Features

Design options in MIDUSS include:

  • Pipe sizing(in which hydraulic gradient is reported if the pipe is surcharged)
  • Open channels of either a generalized trapezoidal shape or a more complex cross-section defined graphically and modified with up to 50 co-ordinate pairs.
  • Hydrograph flood routing in part-full pipes or open channels.
  • Detention ponds including a variety of tools for computing depth-discharge and depth-storage curves for a variety of outflow control devices and pond geometries.
  • Exfiltration trencheswith multiple perforated and non-perforated pipes.
  • Diversion structuresfor separation of hydrograph components (e.g. major and minor).

The above detailed design tools are available at all points in the development of the drainage network.

PIPES

You can design a pipe to carry the peak flow of the current Inflow hydrograph. If no hydrograph has been calculated you can specify a desired constant flow.

For the peak flow you will be shown a table of diameters, gradients and average velocities which represent a feasible design. You can either choose one of these diameter-gradient pairs by double clicking on a row in the table or you can enter explicit values for diameter and gradient.

MIDUSS carries out a uniform flow analysis and reports the actual and relative depth, velocity, pipe capacity and also the critical depth. You can experiment by changing either the pipe roughness (i.e. the Manning 'n') or the diameter or gradient and press the [Design] button to see the results.

CHANNELS

MIDUSS lets you design channels with two types of cross-section to carry the current peak flow in the Inflow hydrograph. If no hydrograph has been calculated you can enter a constant flow value.

The cross-section can be:

  • A general trapezoidal shape defined by a base width and left and right sideslopes.
  • An arbitrary shape defined by up to 50 pairs of coordinates.

In both cases a table of depth, gradient, velocity values is displayed which represent feasible designs. You can select from this list by double clicking on a row of the table or you can specify a total depth and gradient explicitly.

Pressing the [Design] button causes a uniform flow analysis to display the uniform flow depth, critical depth, average velocity and channel capacity.

You can experiment with alternative schemes until satisfied. Pressing the [Accept] button saves the current design.

An arbitrary cross sectin can be drawn with the mouse pointer and the coordinates iof the selected points are shown automatically in a grid. These coordinates can be edited to refinen the drawing. If the length dX of a segment is altered all the points to the right are adjusted automatically.

ROUTING

Once a drainage conduit has been designed - either a pipe or channel - you can route the Inflow hydrograph through a reach of specified length to obtain the Outflow hydrograph at the downstream end.

For each conduit design MIDUSS adjusts the time step and reach length to acceptable sub-multiples in order to ensure numerical stability in the routing process. You are advised of these changes but need not take any action.

The result of the routing operation is displayed in both graphical and tabular form. When an outflow hydrograph has been created by some routing operation you may choose from two possible courses of action. Either the outflow can be copied to the inflow array in order to continue to the next downstream link, or the outflow may be stored at a junction node to be combined with other flows at a confluence point.

DETENTION POND

MIDUSS helps you to design a detention pond to achieve a desired reduction in the peak flow of a hydrograph.

The current peak flow and the total volume of the inflow hydrograph are reported and you are prompted to specify the desired peak outflow. MIDUSS estimates the maximum storage requirement to achieve this.

The storage routing through the pond requires a table of values defining the outflow discharge and the storage volume corresponding to a range of stage or depth levels. You can enter this data directly into the grid if you wish, but it is usually easier to use some of the features of the Pond command to automate this process.

The outflow control can be designed using multiple orifices and weir controls. The Stage - Storage values can be estimated for different types of storage facility. These may be a multi-stage pond with an idealized rectangular plan shape and different side slopes in each stage; one or more "super-pipes" or oversized storm sewers; wedge storage formed on graded parking lots; or a combination of these types of storage.

Rooftop storage can also be modelled to simulate controlled flow from the roof of a commercial development. Following use of the ROUTE command you can experiment by changing any of the flow or storage data until the desired result is obtained.

 

 

 

 

 

 

 

 

 

 

 

 

EXFILTRATION TRENCH

The Trench command lets you proportion an exfiltration trench to provide underground storage for flow peak attenuation and also to promote return of runoff to the groundwater.

The trench usually consists of a trench of roughly trapezoidal cross-section filled with clear stone with a voids ratio of around 40% and with one or more perforated pipes to distribute the inflow along the length of the trench.

The exfiltration trench splits the inflow hydrograph into two components. One of these is the flow which infiltrates into the ground water; the balance of the inflow is transmitted as an outflow hydrograph. Obviously an exfiltration trench requires reasonable porosity of the soil and a water table below the trench invert.

The design involves several steps including definition of the trench and soil characteristics, definition of the number, size and type of pipes in the trench and description of the outflow control device comprising orifice and weir controls as used in the Pond command.

The outflow control devices are similar to those used in the detention Pond command. Water from the inflow hydrograph enters the stone fill through one or more perforated pipes running the length of the trench. The trench may also have a conventional, un-perforated storm sewer between the manholes to convey the Outflow. The positioning of the various pipes in the trench can be defined graphically using the Trench pipes window. The diameter and type (perforated or non-perforated) can be specified and the location set by dragging the pipe to the desired position or by editing the numerical data in a grid. During the drag and drop procedure the current pipe cover is shown to assist in ensuring adequate clearance.

DIVERSION DEVICE

A diversion structure allows the inflow hydrograph to be split into two separate components, the outflow hydrograph and the diverted flow hydrograph.

Below a user-specified threshold flow all of the inflow will be transmitted to the outflow hydrograph. When the inflow exceeds the threshold value, the excess is divided in proportion to a specified fraction. For example, if the inflow is 25 cfs and the thresh-hold is 5 cfs so the excess flow is 20 cfs. Now if the capture fraction is F = 0.8 this means that 80% of the excess flow is diverted and the diverted flow will be 16 cfs and the outflow will be 9 cfs.

Instead of specifying the diverted fraction F you can define this implicitly by specifying the desired peak outflow. MIDUSS will then work out the necessary fraction to be diverted.

The diverted flow hydrograph is written to a file so that it may be recovered at a later time and used to design the necessary conduit or channel.

Use of the diversion command is the only instance in which the topology of the network changes from a tree to a circuited network.

 

 

System Requirements

System requirements
(recommended)

  • PII-266 with 128 MB RAM
  • 1024 x 768 colour video
  • 150 MB hard disk space for installation of program files including installation of 120 minutes of audio visual tutorials
  • CD ROM access
  • 3.5" floppy (for MIDUSS license transfers if required)
  • sound card (if you wish to hear the audio in the tutorials)
  • Windows 9X, NT4, Me, 2000, XP
    (Note: Windows 3.1 is not supported)

System requirements
(bare minimum)

  • P75 with 16 MB RAM
  • 800 x 600 colour video
  • 20 MB hard disk space for installation
  • CD ROM access
  • Windows 9X, NT4, Me
    (Note: Windows 3.1 is not supported)

MIDUSS provides many hydrology and design features. Just click on a heading below to learn more about the features you need.. MIDUSS provides a blend of simulation and design features intended to help you be more efficient in producing effective designs.

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