• [ M98 ][ V2 ]   When I use the Channel design the only way I can define the shape is in terms of a simple trapezoidal cross section. My channel is more complicated than this. How can I do this?

The channel design in MIDUSSS can use a simple trapezoidal shape or an arbitrary cross section made up of lines joining a set of up to 50 coordinate pairs. To use this you must click on the check box labeled "Define arbitrary cross section." This will then allow you to draw and refine a channel cross section which can be as complicated as you wish.   [ V2 ] You can save the cross section to file for use later on or during another session.

• [ M98 ][ V2 ]    When I start to draw the channel cross section a line appears leading to the first point that I have defined. What is this for?

This line will disappear once you have specified the entire cross section and presses the [OK] button.

• [ M98 ][ V2 ]    I am defining an arbitrary cross section but don’t know how to finish.

You define the points of the arbitrary cross section moving from left to right. In order to mark each point you must use the primary (or left) mouse button. To finish defining the points you must click the last point using the secondary {or right} mouse button.

• [ M98 ][ V2 ]    I’ve defined an arbitrary cross section but the design button is still disabled. How can I can I design this channel?

After you have defined all of the coordinate pairs you must click on the [OK] command button in the bottom right of the form. This will enable the [Design] button.

• [ M98 ][ V2 ]    When designing an arbitrary cross section I am not able to define the total channel depth. Why is this?

The channel depth can be entered only for a simple trapezoidal cross section. When you define an arbitrary cross section with a number of points the channel depth is automatically computed and displayed for information.

• [ M98 ][ V2 ]    I was able to design a channel with an arbitrary cross section but after changing the gradient or the Manning ‘n’ value the computed water surface disappeared. Why is this?

Once a design has been completed any change in the data will cause the computed water surface to be erased. This forces you to use the [Design] command button once again to update the design.

• [ M98 ][ V2 ]    When trying to draw a channel cross section my points were not very accurate. I want to make the section symmetrical. How can I do this?

Once all of the points have been drawn approximately, you can edit these by typing in numerical values in the table below the drawing window. You can either specify the X and Y coordinates explicitly or you can change one of the secondary parameters such as the horizontal (dX) or vertical (dY) distance between points.

• [ M98 ][ V2 ]    In editing the data defining an arbitrary cross section I notice some of the values are negative. Why is this?

It is quite possible to have negative values since these represent the difference between two adjacent points moving from left to right. A negative value indicates a reduction in elevation. Similarly, the slope defined by the (dY/dX) parameter may be negative implying a downward slope.

• [ M98 ][ V2 ]    I designed a channel with an arbitrary cross section but it was too narrow. I want to change the design by widening the low flow channel. Do I have to enter all the points again?

No. You can increase the width of only one line segment in the cross section. This can be done by typing in a new value for the dX value for a line segment. When you do this all of the points to the right of that line segment will be automatically moved to the right.