Stormwater BMP

Introduction 

Stormwater runoff refers to the water from snowmelt or rainfall that flows over land. Generally, it includes runoff from natural drainage and storm drains serving residential, commercial, recreational, agricultural, industrial, and undeveloped lands. If uncontrolled, this water can cause erosion, pollution, and flooding problems. 

This is where stormwater management comes in! In essence, any construction project involving more than 1 acre of land is required to create a stormwater runoff management program. This program is intended to eliminate or reduce the negative effects of this runoff. Moreover, this can be achieved by implanting certain practices, popularly known as BMPs. 

Continue reading this article to learn more about BMPs and what they include! 

What are Stormwater BMPs? 

In stormwater management, BMPs is an acronym for the Best Management Practices. Therefore, stormwater BMPs are simple techniques and actions that prevent the pollution caused by stormwater runoff. 

According to the 2001 LA Municipality Stormwater Permit, BMP best practices are defined as the practices, methods, or means designed to eliminate or reduce the discharge of contaminants to surface runoff. Also, these practices may include non-structural and structural maintenance and control measures, either after, during, or before pollution-producing operations. 

Moving on, Stormwater BMPs involve land development design that proposes the most ideal techniques for managing the anticipated quality and flow of stormwater. This is usually based on an assessment of planning requirements and site conditions. 

Advantages of Stormwater BMPs 

Implementing the stormwater BMPs can offer the following benefits; 

  • Flood control. BMP best practices temporarily contain a large quantity of stormwater runoff and discharge it slowly. This helps to reduce the impacts of flooding. Moreover, it restores and preserves the natural flood-holding capacity of floodplains and streams. 
  • Improves water quality. Most stormwater management practices remove contaminants from the water. At the same time, the reduce soil erosion and contaminant loadings. Thus helping to improve and protect the quality of surface and groundwater. 
  • Environmental amenities. Some BMPs offer attractive environmental features. As an example, designing wet ponds and shallow marshes can create open water areas and wetland habitats. Such environments are suitable for use by marsh birds, waterfowl, and other wildlife. Besides, large water ponds are ideal for swimming, fishing, and other recreational activities. 
  • Reduce property damage. Reducing the impacts and frequency of flooding will ensure public safety. More notably, it will reduce damage to property, infrastructures, and public services. Even better, BMPs will significantly reduce the cost of maintaining stormwater handling facilities and infrastructure requirements. 

Limitations of BMPs 

Stormwater Best Management Practices have their own set of drawbacks as well. These may include; 

  • High initial cost. BMPs in stormwater management may help to reduce maintenance costs over time. However, the initial cost of designing and implementing these practices is very high. 
  • Requires Management plans. Similar to other developments projects, BMPs require management plans as well as agreements. Here, the agency, civil engineer, institution, or individual responsible for maintaining or operating the BMP must be identified at the beginning of the project. More importantly, the plan must demonstrate that the responsible party is committed and financially able to accomplish that responsibility. 
  • Increased responsibility. BMPs are increasing the responsibility of homeowners to reduce stormwater runoff and contaminants from their property. However, for this to happen, homeowners have to be educated about pollutant prevention measures and landscape practices. This will play a crucial role in addressing the ultimate source of excess runoff. 

Types of BMPs in Stormwater Management 

BMPs used to reduce, treat or prevent pollution from stormwater can be classified into various groups. These are; structural BMPs, Managerial BMPs, and Vegetative BMPS. That said, let’s have a look at them one by one; 

Structural BMPs 

  • Extended Detention ponds 

This involves the use of a detention pond to transport stormwater, rather than letting it flow directly into the river. The ponds then hold the stormwater until contaminants settle to the bottom. Once that happens, the water is slowly released into the river. Thus helping to reduce pollution and flooding in the rest of the river system. 

  • Wet ponds

A wet pond allows incoming runoff from stormwater to replace the water in the pond. As a result, pond water flows out, while the new runoff remains in the pond as it waits for the next storm. In the meantime, most pollutants in the runoff settle to the pond’s bottom. Although this offers minimal flood protections, it prevents contaminants from getting into the river. 

  • Water quality inlets/ grease (oil) separators

In essence, water quality inlets consist of separators that remove oil, grease, and sediments from parking lots before discharging runoff to the infiltration basin or storm drain. 

  • Porous pavement 

As the name suggests, this BMP involves installing porous pavement like bricks or interlocking tiles. Thus allowing the surface runoff to pass through the pavement into the soil. This helps to control erosion and removes fine-grain contaminants. 

  • Infiltration basins

An infiltration basin holds stormwater runoff and stores it until it gets into the surrounding soil. This approach effectively removes fine-grained pollutants from the runoff. However, the basins can be clogged by course-grained pollutants. 

Managerial BMPs 

This includes practices that are intended to prevent pollution caused by stormwater runoff. In other words, they reduce the number of contaminants contained in the runoff. Such techniques are; waste reduction and spill prevention practices. 

Vegetative BMPs

Finally, vegetative BMPs refer to various landscaping practices for controlling stormwater runoff. This includes practices like placing ditches or grassed swales in highway medians or residential areas. Such techniques reduce peak stormwater runoff flowing downstream through storage and infiltration. Moreover, this may include designing filter strips to direct surface runoff from impervious surfaces into stone trenches. The collected water will then be distributed uniformly over the grass strip. 

Final Word      

When choosing a stormwater management BMP, it’s good to consider the benefits and drawbacks of each technique. Here, you can consider factors like costs, management goals, and physical site constraints to come up with the ideal approach. However, implementing BMPs that need a lot of land area like basins and ponds on small sites or fully developed areas, isn’t practical. Similarly, vegetative BMPs might not be ideal for certain sites because of economic restrictions and space limitations. 

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