Grading and Drainage Surface Water-Section E LARE

Grading and Drainage Surface Water Overview

Review The Basics and Prepare for the LARE Exam

Drainage is one of the most critical activities that landscape archtitects regularly perform that impacts the health, safety, and welfare of the public. The LARE has many challenging questions and vignettes that test your ability to grade a site without adversly impacting the natural environment while protecting your client’s interests. Brush up on the basics of grading while you prepare to take the LARE. 

What is Surface Drainage?

Surface drainage techniques involve manipulating the ground plane in order to move water from one location to another place without the use of drain pipes or other constructed drainage systems.

You create efficient drainage by grading the landscape so storm water or irrigation water accumulates and flows from a higher elevation to a lower elevation and away from structure and other protected areas. 

Regardless of soil drainage characteristics, slope is the most significant element to consider. For effective drainage, paved areas should have a minimum of a 1 percent slope. Turf or landscaped areas ideally have a minimum slope of 2 percent. Exceeding the 2 percent standard by too much can cause erosion problems. Inclines of more than 4 or 5 percent could seem very steep in a lot panorama situations.

Determine the Slope

The formula for calculating slope is rise/run = % slope

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For example, every foot of elevation decrease over a 100-foot length equals a 1 percent change in grade. For example, it will take 2 feet of elevation change over each 100-foot length of a swale to create a 2 percent slope. If the span is 10 feet, you'll necessity a slide of 0.2 feet (about 2.5 inches) to create a 2-percent slope.

You will use this calculation frequently during the LARE exam. CLARB rules allow you to bring a non-programable calculator to use during the exam. (Unfortunately, you can’t use your iPhone or other cool gadget.)

Practical Considerations

Different areas and different functions have different grading requirements and restrictions. 

Paved Areas

Paved areas with permeable or impermeable surfaces, like driveways or parking lots, are easy to drain by simply grading them so they slope way from buildings and other protected areas and flow towards a lawn, storm sewer, catch basin, or street gutter. Ensure that any water that leaves your client’s site does so in a way that does not negatively impact surrounding areas down-stream and complies with all applicable laws and regulations.

Turf and Landscape Areas

In open turf areas, you can create a swale by making a downward-sloping channel in the landscape where water is conveyed to areas where it can be retained, detained, infiltrated, or moved to other drainage systems. 

Control erosion is important after site grading. Immediately after you create a swale in the landscape, there needs to be some sort of temporary erosion control to keep sediment from flowing off-site. In many areas, siltation in streams due to construction activity has significantly impacted riparian environments. 

Prepare for the LARE Exam

Prepare for the LARE. Many candidates find the LARE to be extremely challenging. Increase you odds of success by studying. Read all the landscape architecture technical books recommended by CLARB, take a practice exam, join a Google LARE group, or attend a LARE workshop. Candidates who come prepared do much better than those who think the don't need to study.