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.
including a variety of tools for computing depth-discharge and
depth-storage curves for a variety of
outflow control devices and pond geometries.
trenches with multiple perforated and non-perforated pipes.
structures for separation of hydrograph components (e.g.
major and minor).
Culverts including storage
Cascade lets you route the current inflow
hydrograph through a short cascade of
The above detailed design tools are available at all points in
the developmetn of the drainage network.
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.
There is more pipe information in our FAQ section.
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.
There is more channel information in our FAQ section.
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
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
See a short 90 second demo on 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
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
There is more pond information in our FAQ section.
to expand this screen image.]
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
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
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.
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
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
There is more diversion information in our FAQ section.
The Culvert command lets you model the behaviour of a culvert
under various conditions of flow.
Because of the many variables involved, the process is largely
one of trial and error and MIDUSS does not suggest initial
feasible values for the design.
Culvert design can be carried out for either steady, (i.e. time
invariant) flow or for an inflow
hydrograph. When inflow is in the form of a hydrograph the
hydraulic design can be followed by
a routing process that shows the attenuation of the inflow
hydrograph caused by ponding that
occurs upstream of the embankment. In such cases the peak outflow
from the barrel will be less
than the peak inflow and you can refine the barrel design for the
reduced flow if desired.
Your Culvert design can be preceded by a Channel design with
either a trapezoidal or
complex cross-section. When this is done the cross-sectional shape
of the channel is ‘inherited’ by
the culvert design and used to describe the flow cross-section
upstream of the culvert. If the
inflow is a flow hydrograph, a channel design may be followed by a
Channel routing process from
which the channel outflow forms the inflow to the culvert.
The culvert is assumed to be located below a sag point in a
highway embankment that will form
an overflow weir in the event that the barrel flow capacity is
sufficiently surcharged. Flow
separation between barrel and weir flow is assumed to be
recombined downstream of the barrel.
The cross-section of the barrel conduit may be a circular pipe, a
rectangular box, a horizontal or
vertical ellipse or a pipe arch. Multiple barrels may be used but
cross-section and other hydraulic
parameters are assumed to be the same for all barrels.
The Cascade command lets you route the current inflow
hydrograph through a short cascade of
storage cells formed from a variety of cross-sectional shapes such
as pipes, rectangular boxes,
horizontal and vertical elliptical pipes and pipe arch sections.
The storage may be provided by a ‘superpipe’ or oversized storm
sewer with a modest slope and a reach length limited to 100 - 150m
(330 - 500 ft). Two reaches of superpipe can be used in series.
Each chamber is horizontal with a specified length, width,
height and invert elevation.
The outflow control from each chamber is assumed to be an
orifice of specified diameter and
coefficient of contraction with the orifice invert equal to the
bottom of the upstream chamber.
You can specify a pipe, box or any of three special pipe
sections (e.g. horiz elliptical, vert elliptical or pipe arch).
If you select the special pipes a drop-down list lets you browse
through a set of commercially available sizes. These are shown in
metric or imperial sizes depending on the choice of units.
If a cell is surcharged, the data box containing the Height is
highlighted to warn you that more
storage or a larger orifice is required.