Controlling Erosion and Runoff on Construction Sites

Published November 30, 2015 by Whirlwind Team

site erosion control

Metal building contractors are constantly reminded, "water is the enemy," encouraged to choose the right site location, building materials and techniques to avoid long-term moisture exposure. This time of year however, it's important to review the building practices you're implementing from job site to site, making sure rainfall, snow melt and mudslides aren't creating irreversible damage to the property and/or its surrounding environment.

Erosion control is nothing to take lightly. In addition to posing a threat to the environment via sediment run-off that pollutes storm drains, nearby streams and other bodies of water, storm water-related erosion poses immediate health and safety concerns to your employees, site occupants and neighbors.

Additionally, failure to observe careful and methodical erosion control methods can be costly in terms of litigation from adjacent and/or down-slope property owners, not to mention the fines associated with potential local building code violations.

Types of erosion

Erosion is typically a multi-phase process, starting at the surface via wind and splash erosion and then quickly making its way through deeper and larger sections of the earth.

  • Wind erosion. This type of erosion takes place on the surface of dry earth. Sand dunes are a dramatic example of severe wind erosion. Surfaces eroded by the wind are also more susceptible to water erosion.
  • Water erosion. Typically, erosion caused by water begins at the surface and as the first layer of dirt and vegetation or ground cover is washed away, the ensuing water will continue to etch it's way through longer and deeper sections of earth. In worst-case scenarios, water runoff causes cause deep, wide areas of stream and channel erosion, resulting in thousands of pounds of displaced earth that winds up being deposited elsewhere.

The following tips can be used to mitigate erosion and mudslides throughout the winter and spring, or during severe weather scenarios.

Understand the basic principals of erosion control

There are six basic principals of erosion control:

  1. Reduce erosive forces and increase resistive forces. Reducing the amount of power exerted by water and wind, combined with implementing techniques that resist these forces are the overarching goals of any erosion control program.
  2. Implement sediment control. It is almost always more cost-effective to prevent the erosion of sediment than it is to pay for the equipment/man power required to remove sediment that has been deposited elsewhere.
  3. Modify topography. Short, shallow slopes will erode slower and allow erosion-preventative vegetation to take root more firmly than longer, steeper slopes.
  4. Limit soil exposure. The less contact soil has to water and wind, the less it will erode. Leave vegetation and other shelter in place wherever necessary and try to divert excess water away from exposed soil when possible. Also, try to schedule activities that disturb established soil during the dryer seasons, avoiding ground disturbance when water and wind are more likely.
  5. Reduce runoff velocity. Altering slope, and increasing surface roughness via specialized grading, rock dams and so on will help to reduce runoff velocity. Keep in mind that rock dams are not recommended for steeper slopes.
  6. Inspect and repair regularly. Once in place, erosion control techniques should be inspected on a regular basis. They should be evaluated within 24-hours after a storm, at least every seven days while a site is active and approximately every 14-days on inactive job sites.

The goal is always to use the smallest time and cost investment initially, implementing thoughtful and efficient erosion control methods, to avoid costly repairs, fines and damage down the road.

Meet with the local building department

In an effort to reduce erosion on active construction sites, many city councils and building departments have put specific ordinances into place. These ordinances are designed to accommodate the region's typical climate patterns and may also have stipulations in place for more severe weather patterns as well. In many cases, erosion and sediment control measures are required to be put in place between certain calendar dates, regardless of whether or not it rains or snows.

Observe drainage patterns on the property

If you have the luxury of observing a job site in the midst of, or directly after, a storm - lucky you. You'll be able to watch water runoff in action. If not, walk the property and look for evidence of water runoff and sediment deposits via rivulets, seasonal stream beds or recent sand and gravel deposits. This will give you an idea of how water moves naturally, and you can augment this movement accordingly.

Keep soil covered

Recall that Basic Erosion Control Principal #4, above, advocates minimizing soil exposure. Do this by:

  • Limiting the amount of vegetation removed from and/or disturbed during construction.
  • Seeding exposed construction with fast-growing, native ground cover.
  • Covering exposed areas with two to four inches of straw.

In addition to anchoring the soil, vegetation simultaneously slows down the flow of water so these steps serve a two-fold purpose.

Note: If your job site is located in a protected or sensitive habitat, consult with a biologist to ensure the control methods you put in place - including seeding methods - will not negatively impact it.

Use erosion control blanket on steep slopes

As mentioned above, some of the most basic erosion control methods will not work - or are not safe to use - on steep slopes. If you are working on a steep slope, especially one where topographical modifications are not possible, erosion control blankets are an excellent option. They can be used alone or in combination with seeding. If you opt for the latter method, the seeding should take place prior to placing erosion control blankets in place.

Apply sediment control methods

Any additional water runoff can usually be controlled using additional sediment control methods:

  • Straw rolls can be applied on slopes, at the base of slopes, in trenches and around drainage devices. Ideally they should be placed along the natural contours of the land and staked down to keep them in place.
  • Slit fences are designed to capture sediment at the base of slopes but are not intended for use on slopes or around storm drains. Incorrect installation and use of slit fences can actually increase erosion damage so use best practices when implementing this method.
  • Gravel bags work similarly to sand bags but are filled with drain rocks and are used to protect drain inlets. The larger rocks allow sand to filter through without creating a dam.
  • Rock entrances and roads to mitigate the disturbance to exposed soils. You can also use large rock or concrete pieces as energy dissipaters at the outlet of outlet of pipes, conduits or channels to slow the speed of water that flows through them.

Make sure to keep additional supplies on hand so modifications can be made when you perform routine inspections. You can learn more about erosion control - and determine which types are most appropriate for your construction site - Erosion Control Treatment Selection Guide, a joint effort published by the US Departments of Agriculture, Forest Service, National Technology & Development Program and the Department of Transportation.

Taking the extra time to implement erosion control methods on the job site protects the environment and makes for safer and more pleasant job site conditions for you and your employees.

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