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Frequently asked questions

 

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Ponds

 

V2 = applies to MIDUSS Version 2 (current release)
M98 = applies to MIDUSS 98

The pond does require a great deal of data. However MIDUSS contains many tools to help you obtain this data automatically. The first thing you should enter in the pond design is the target outflow. This will provide you with an estimate of the volume of storage that will be required. The next item you should define is the number of stages and typically this will be an odd number implying an even number of depth increments. The minimum and maximum water levels represent the total depth of the pond and can be expressed in terms of an actual elevation or an arbitrary depth depending on your choice.

  • [ M98 ][ V2 ]    The pond design form has a complicated table of levels, discharges and volumes. Do I have to enter values for all of these cells?

The table is available for direct data entry if you chose to do this. However it is much simpler to use some of the tools which are available in the storage geometry menu or the outflow control menu.

The outflow control is a device that will describe the relationship between the level in the pond and the rate of outflow from the pond. Typically an output control will comprise an orifice which controls the low flow conditions and a weir which will pass the larger flows for an extreme storm event.

  • [ M98 ][ V2 ]    In the pond design the storage geometry menu contains an item to setup grid levels but the grid levels appear to be already calculated. What is this for?

The setup grid levels option is included as a convenience to recalculate the levels at the different elevations of the pond. You do not need to use this.

  • [ M98 ][ V2 ]    In the pond design the storage geometry menu contains items for a rectangular pond. My pond is going to have a rather arbitrary geometry. Can I use this?

The rectangular pond represents an idealized shape that is defined by a set of contours that are nested rectangles. You can usually get a good approximation to the distribution of storage throughout the depth of the pond by using this feature.

The term super-pipe is a description of an oversized storm sewer which is intended to provide underground storage.

  • [ M98 ][ V2 ]    The storage geometry menu item in the pond design command shows something called wedge storage. What is this for?

Wedge storage is the name used to define storage that might occur on a graded parking lot in which ponding is encouraged in the vicinity of the catch basins. In fact the term "wedge" may be a misnomer as the shape of the storage volume will more likely be that of an inverted cone or pyramid with a circular or elliptical base at the top water level.

In the pond design command there is an item for rooftop storage. When you use this you will see a table that requires five pieces of information to be entered. You can click on the up arrow of the spin button and MIDUSS will display some typical values for the current peak inflow. MIDUSS assumes that only 75% of the roof area is available for storage with the rest used for roof structures. The drainage from the roof is provided through a set of roof drains that drain a contributing area of approximately 500 sq.m or 5000 sq ft. Each of these roof drains will have a flow capacity that depends on the depth at the roof drain. You can also define the slope of the roof in the vicinity of the roof drain.

  • [ M98 ][ V2 ]    I wanted to design rooftop storage but I was unable to enter data in the table. The reason seems to be a message saying "Roof not 100% impervious." What has happened?

Before you can define rooftop storage you must use the catchment command to define the area of the roof that will generate the runoff. The message you have described has been generated by MIDUSS to warn you that last catchment you designed had a significant amount of pervious area. This is normally not the case and this message is simply for your own protection.

  • [ M98 ][ V2 ]    I have managed to design a pond and I want to accept this design. However I notice a check box labelled "Keep all design data." What does this do?

When you press the [Accept] command button the information will be copied to the output file. If you do not check this box, the next time you use the pond design it will start with the default values that MIDUSS generates. If you want to refine the pond design or you anticipate that you will need to design a second pond with similar parameters you can check the "Keep all design data" box and the next time you use the pond design it will start up with the same information as your current design.

  • [ M98 ][ V2 ]    I want to model a pond which has an irregular shape.  I can get data from an AutoCAD drawing.  Do I have to calculate the storage volumes by hand and enter them in the 'Volume' column of the grid?

You can do this but there is an easier way that you can try.  It can be shown that the equivalent aspect ratio R = length/breadth is related to the perimeter P and area A of any plan section of the pond (i.e. base, top water level or in between).  The relationship is given by:
     f(R)   =    4R + 4/R + 8  =  P^2/A
You can get values of P and A at the base of the pond and work out the corresponding value of R.  Then use the Geometry|Rectangular menu command with this value of R as the aspect ratio for the base.  MIDUSS will work out the reducing aspect ratio at higher elevations.  At elevations where the sideslope changes fairly abruptly you can check the value or R from data taken from the AutoCAD drawing or contour plan and enter a preferred value o aspect ratio.

You can even model multi-cell ponds in this way.  At elevations below the berm which forms the cells the value of R will be quite large (e.g. 6 or even 10).  Above the top of the berm, the aspect ratio will reduce due to the abrupt reduction of the perimeter P.

 


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 Up ] FAQ General ] FAQ Operations ] FAQ Storms ] FAQ Catchments ] FAQ Hydrographs ] FAQ Pipes ] [ FAQ Ponds ] FAQ Channels ] FAQ Routing ] FAQ Automatic mode ] FAQ Diversions ]