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IECA Pulse: Understanding the Difference: Structural BMPs vs. Non-Structural BMPs in Erosion and Sediment Control

By Jerry B. Sanders,CPESC posted Jun 20, 2023 02:25 PM

  

As erosion and sediment control experts, we are dedicated to protecting our environment and mitigating the adverse effects of soil erosion. In this article, we will delve into the world of Best Management Practices (BMPs) and shed light on two key categories: structural BMPs and non-structural BMPs. Understanding the distinction between these approaches is essential for implementing effective erosion and sediment control strategies.

First, let’s keep in mind that Structural BMPs (SBMP) almost always have a Non-structural BMP (NSBMP) associated with them to make the SBMP work. Silt fence (SBMP) needs planning, budgeting, proper installation, maintenance, and care not to destroy (NSBMPs) to work effectively throughout the project. If any of the NSBMP is left out the silt fence is not going to work effectively.

Let's explore the characteristics and applications of each.

Structural BMPs: Structural BMPs encompass physical structures or engineered solutions designed to control erosion and manage sediment runoff. These measures involve the construction or installation of specific features that directly intercept, contain, or treat sediment-laden stormwater. Here are some common examples:

  1. Sediment Basins: These are temporary retention ponds designed to capture sediment-laden runoff, allowing sediment to settle out before the water is discharged. They are typically constructed with sediment forebays, outlet structures, and overflow spillways.
  2. Retaining Walls: These structures are built to prevent soil erosion on slopes or embankments. They provide stability, preventing slope failure and minimizing sediment runoff.
  3. Riprap and Gabion Systems: Riprap involves the placement of large, durable rocks or concrete blocks along shorelines or waterways to protect against erosion. Gabion systems utilize wire mesh containers filled with rocks or other materials to stabilize slopes and control erosion.
  4. Silt Fences: These vertical barriers, usually made of geotextile fabric, are installed along construction sites or disturbed areas. Silt fences trap sediment-laden runoff, allowing water to flow through while retaining the sediment.

Non-Structural BMPs: In contrast to structural BMPs, non-structural BMPs focus on modifying practices and behaviors to minimize erosion and sediment runoff. These strategies do not involve physical structures but instead emphasize planning, education, and the adoption of specific practices. Here are some examples:

  1. Erosion Control Planning: Developing a comprehensive erosion and sediment control plan before initiating any construction activities. This includes identifying potential erosion sources, determining appropriate BMPs, and scheduling site activities accordingly.
  2. Vegetative Measures: Implementing practices such as seeding, mulching, and revegetation to establish vegetation cover, stabilize soil, and reduce erosion. Vegetative measures play a vital role in preventing soil displacement and enhancing sediment filtration.
  3. Stormwater Management: Utilizing practices like retention ponds, bioretention areas, or permeable pavement to manage stormwater runoff. These measures help to infiltrate, treat, and control runoff, reducing sediment transport.
  4. Education and Training: Conducting educational programs, training sessions, and workshops to promote awareness and understanding of erosion and sediment control practices among construction workers, contractors, and landowners.

Conclusion: Both structural BMPs and non-structural BMPs are integral to effective erosion and sediment control. While structural measures involve the construction of physical features, non-structural practices focus on planning, education, and modifying behaviors. By combining these approaches appropriately, we can achieve sustainable erosion and sediment control, preserving our environment and ensuring the long-term health of our ecosystems. Remember, implementing the right combination of BMPs tailored to specific site conditions is the key to success.

As erosion and sediment control experts, let's continue striving for innovative solutions and promoting responsible practices that protect our soil, waterways, and the environment. Together, we can make a significant difference in preserving our natural resources for future generations.

Be sure to check out the webinar on July 11, 2023, Common BMPs: A Practical Approach, Bridging Theory and Practice

Stay safe!

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Thomas W. Schneider,CPESC
Jun 21, 2023 09:15 AM

Jerry, I really appreciate you mentioning the connection between Structural BMPs (SBMP) and Nonstructural BMPs (NSBMP).  In our industry, the erosion control BMPs are tested and designed with more of a scientific approach than the sediment control SBMP.  On the sediment control BMP side many times the SBMP is blamed for the failure when in fact it was the omission or failure to implement a NSBMP that the SBMP relied on.  The first NSBMP you listed was planning.  A bad plan will result in bad performance.  It still amazes me how many people will blame and inanimate object for the failure of the design.  If the SBMP fails, the first place to look is the planning and the design.  How many time have we heard someone say we removed this SBMP from the approved list because the SBMP does not work.  The reality is the failure is in the design in most cases.  Proper installation is also a NSBMP, but I will refrain for discussing that topic for now. All SBMPs will work if they are utilized in the right conditions.  If we look at the soil type, the topography and climatic condition when we design, we can determine the which SBMPs will work, and which will fail.  On the sediment control side of our industry failures are routinely blamed on the BMP.  The standards and practices committee as done a great job of developing a design standard for silt fence that will assist the user in determining if silt fence is appropriate SBMP for the site.  

For sediment control planning, as an industry, I think we need to look at the options for removal of the suspended sediment from the water.  Once we understand how the sediment is removed we can start to apply science to the problem.  This might be a totally new discussion but I believe there are only two practical ways to remove the suspended sediment.  Sedimentation or filtration.

Sedimentation is a process of gravity acting on the sediment particles so the particulate settles out of the water column.  This process takes time.  If you provide enough time it will settle out if you fail to provide enough time it won’t.  It as simple as that. 

Filtration is the act of placing something in the path of the water and allowing the water to pass through while preventing the particulates from passing through.  How many times have we heard people say filters do not work.  Filters do work if they are design and used in the correct conditions.  Every morning I utilize a coffee filter and it provides me with coffee to drink without any coffee grounds. Filtration is all about flow rates, particulate size, and the opening size of the filter media. It is a balancing act.  You need to let the water through, so it does not bypass the filter while also making the openings in the filter small enough to capture the particulate.  Easier said than done in most cases.

Planning and design is a NSBMP.  If we can, on the sediment control side, match the efforts of the erosion control side I believe we can eliminate many failures of the sediment control BMPs.