The hydrologic modelling methods used in MIDUSS are well recognized and very versatile. You can select from a choice of:
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.
Available storms are:
Storms may also be defined by importing a hyetograph file in simple text format.
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.
Model rainfall losses with:
Route flow with
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
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.
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 options in MIDUSS include:
The above detailed design tools are available at all points in the development of the drainage network.
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.
The cross-section can be:
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.
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.
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.
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.
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 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.
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.
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.
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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