Understanding contour lines and how they work is critical when it comes to passing the ARE Site Grading Vignette. Part of the Site Planning and Design exam, the Site Grading Vignette basically requires you to re-grade an existing site to meet a variety of requirements.
In some cases, candidates are required to provide a new building pad or structure and re-grade the site to accommodate these changes. In other conditions, candidates may be asked to simply re-grade an existing site condition in order to provide proper drainage on that site. Either way, it will be essential to understand how site contours work so you can pass the SPD exam.
No matter what your experience level is with site planning and grading, it’s always important to review the terms so that there are no surprises when you sit down to take your exam. Here’s a quick summary of a few of the basic terms used with site grading:
These are lines on a site plan that equal a uniform elevation height. These lines will curve in all directions but it’s important to remember that it’s simply marking a specific elevation. Look for a number near this line that defines that specific elevation. Depending on the severity of the grading, contour lines will vary in terms of their spacing so it’s important to pay attention to the difference between adjacent grade elevations.
A swale is a depressed area of land that is typically used to direct surface water. Swales are important to recognize and draw on the Site Grading Vignette because they can help you control and regulate water runoff on your site. Depending on the program, you will most likely have to use a swale to direct water around certain site elements so it’s important to know what they look like.
For the most part, swales “point” in a general direction on a site plan. In some cases, they almost come to a point like a triangle. Water will typically flow between these points.
To properly draw a swale on the SPD vignette, you will want these points/peaks to point in the direction of the HIGHER elevation. See the diagram below from the Dorf Solutions book for a comparison between swales and crowns.
Crowns and swales are very similar except a crown is not a depressed area; it is an area with a peak that is also used to direct surface water runoff. Crowns are usually used on roads or parking lots because the goal is to move the surface water off of that surface as quickly as possible where as a swale gathers water and then moves it together.
When it comes to recognizing crowns on a site grading plan, they are the exact opposite of swales. They will still point in a general direction, but crowns point in the direction of LOWER elevation.
This diagram below does a wonderful job explaining the difference between swales and crowns on a site grading plan. Notice how they look very similar in nature but they both perform different tasks on a site plan. Again, swales are used to collect and direct surface water runoff while crowns are used to direct runoff off of a specific surface.
Image credit to “Solutions” by Norman Dorf
Part of the Site Planning Vignette will test you on your ability to draw new contour lines that connect back to the existing grade lines. When doing this, remember that you must connect your new contour lines with the existing lines in 2 points. What I mean by this is that you’re not allowed to draw a new grade line that connects different contour elevations. If you’re going to draw a new line, it must start and end along the same contour line.
Understanding this basic principle may sound easy, but it’s definitely a common mistake made by ARE candidates on the SPD exam.
Another thing to remember when it comes to adding new contour lines on the ARE is that you shouldn’t add new grade lines where you don’t need them. Just like the other ARE vignettes, you will be graded on your ability to NOT over-design a solution. What I mean by this is that you should aim to provide the minimal site disturbance possible while still meeting the rules and requirements given in the program of the vignette.
An easy way to understand this is that it costs money to re-grade a site, so adding new contour lines where you don’t necessarily need them is wasting valuable money. There’s no hard rule for over-designing on the Site Grading Vignette, but there are definitely people that have failed the SPD exam for adding too many extra lines. This is nothing to freak out about, simply design your solution as efficiently as you can just like you would any other vignette on the ARE.
Your understanding of contours on the ARE Site Grading Vignette is very important for a number of reasons. This vignette is very straightforward and should be completed fairly quickly in order to give candidates more time on the Site Design Vignette. Remember, the Site Grading Vignette is only one of 2 vignettes that make up the Site Planning and Design exam.
Without getting into too much about the SPD exam as a whole, you will basically have 2 hours to complete both the Site Planning and the Site Grading Vignettes. The way you divide up the time is up to you but based on experience, the Site Design Vignette will take you more than double the time that the Site Grading will take so it’s important to save as much time as you can while still designing a passing solution.
For more information on the Site Grading Vignette, see here!
Since you will be asked to analyze, modify, and design new contour lines, your understanding of these basic elements will be even more important. You’d be surprised with the number of ARE candidates that aren’t that familiar with site grading based on a lack of experience in the real world. To be honest, I had to spend a lot of time trying to understand site grading and contours before taking the SPD exam because I lacked that experience before taking the ARE.