Design rule purpose

The purpose of this design rule is to ensure that the 'long section' (or 'vertical profile', used interchangeably later in the document) has a required 'sawtooth' shape. Water pipelines have to stay within limits of minimum and maximum gradients to ensure that water can be drained from the pipeline and to prevent unwanted hydraulic effects. The vertical profile of the pipeline is a feasibility requirement and has to be maintained in relation to terrain shape and a minimum cover required (while trying to keep the pipeline as close to minimum cover depth as possible, to minimize cost).

How to configure

This design rule is fairly straightforward to configure and expects that the used will will define the gradient limits on the pipe.

The gradient is defined as a ratio of change in depth (vertical dimension) to the distance between two sampling points along the pipeline chainage (horizontal dimension).

This calculation approximates the point-to-point sections as right-angled triangles and returns the gradient value at every sampling point along the route. Sampling points are spaced every ~30m on average. If any of these points exceeds the limits set by the user, a constraint break will be triggered and the option will be corrected by Optioneer until all of the gradient requirements are satisfied.

The limits on gradient are defined as follows. It is important to keep in mind the convention (see figure below):

positive means upwards - minimum positive gradient is more flat than maximum positive gradient
negative means downwards - minimum negative gradient is more flat than maximum negative gradient

Important notes

Sometimes sections of gradient might look very sharp when plotted in Optioneer. This is because of the relative scale - route length (x-axis) is often in tens of kilometers while pipeline depth is usually within a few meters range.
When using coarse-resolution elevation datasets, the vertical profile might appear unintuitive to users. Some open-source datasets only have a 1-meter vertical resolution so sections of terrain that the route is going through will appear very spiky. As a result, the vertical profile will be negatively affected - it will most likely satisfy design criteria, but the final outcome will look far from realistic.

Input / output summary

Input parameters

This design rule doesn't require a dedicated dataset and draws terrain data from the 'elevation' dataset.

Name	Default value	Unit
Minimum positive gradient	0.002	fraction
Maximum positive gradient	0.025	fraction
Minimum negative gradient	0.003	fraction
Maximum negative gradient	0.02	fraction

Output parameters