• [ M98 ][ V2 ]    I opened the pipe design window and found that the current peak flow is zero. Why is this and what can I do about it?

You are trying to use the pipe design before the inflow has been specified. This is a convenient way of designing a pipe or channel for any arbitrary discharge that you care to type into the text box.

• [ M98 ]    When I open the pipe design window the values for diameter and gradient are initially zero. Are there no default values for this?

The default values are shown in the form of a list that contains a set of feasible designs that will carry the current peak flow under full bore conditions. You can either type in the values of diameter and gradient into the text boxes or if you double click on one of the rows the values in that row will be copied to the diameter and grade data boxes.
[ V2 ]  You are presented with an automatic pipe design as a starting point.

• [ M98 ][ V2 ]    If I double click on one of the rows in the list of feasible designs the gradient copied to the text box is not the same as shown in the table. Why is this?

When you double click on a row in the list of feasible designs the diameter is copied precisely because this corresponds to a set of industrial standard sizes. However the gradient is rounded up the nearest one tenth of one percent.

• [ M98 ][ V2 ]    I have entered the diameter and gradient for a pipe design but all the answers are still zero. What do I have to do to get this design?

The [Design] command button must be pressed in order to obtain the values of depth and flow capacity and velocity etc.

• [ M98 ][ V2 ]    The pipe design results show something called the critical depth. What use is this?

The critical depth is the depth of flow at which the total energy is a minimum. The comparison between the critical depth and the depth of uniform flow will indicate if the pipe will be sub-critical or super-critical under normal flow conditions. Super-critical flow is undesirable as it implies that a hydraulic jump will occur somewhere downstream.

• [ M98 ][ V2 ]    When designing a pipe I changed the gradient but the [Accept] button is grayed out and not available. What have I done wrong?

You have done nothing wrong because each time the design data is changed the [Accept] command is disabled to make sure you press the design button to update the results before accepting the results.

• [ M98 ][ V2 ]    I specified a pipe diameter and gradient but MIDUSS tells me the pipe will be surcharged. Is this a fatal error on my part?

Normally you would not accept a design in which the pipe is surcharged. However if a previous design is being subjected to a more severe storm it is quite likely that the pipe is unable to carry all of the increased peak. You may want to accept a surcharged condition and then use the Diversion command to separate the total hydrograph into the minor and major system flow hydrographs.