Model-This.com

Occasionally I encounter a set of grading plans with nothing but contour lines as a guide to building a site. Seldom, if ever, does contour lines provide sufficient data to properly establish an accurate DTM from which to work. Allow me a chance to illustrate:

Looks simple and straightforward does it not, put a little more thought into it. A section from a not so arbitrary, direction wise anyway, baseline yields this section :

What are the odds that the design engineer actually intended to break the –2% slope to –2.8%? Or is it more likely that the -2% was intended to strike the 2:1 slope? In this example the later is the true statement.  Then why does it show the change in grade? Simple, the contour interval is set at 1-foot, so with a 2% slope there are only two contour lines generated every one hundred feet. Anything that happens inside this interval is not propery represented by contour lines. Just one example why the design engineer should always include alignments and typical sections.