Check Dams: Slowing the Flow of Stormwater Runoff and Protecting Waterways

As part of many Stormwater Pollution Prevention Plans (SWPPPs), check dams play a critical in erosion and sediment control. These simple yet effective structures help slow water flow, reduce erosion, and trap sediment, protecting downstream water quality and ensuring regulatory compliance. 

What are Check Dams and Why are They Important?

Check dams are small, temporary barriers constructed across drainage ditches, swales, or other areas with concentrated flow. Their primary function is to reduce the velocity of stormwater runoff, allowing sediment to settle out and preventing it from being carried downstream. This is crucial on construction sites where exposed soil is vulnerable to erosion. By slowing the flow, check dams also reduce the overall volume and peak flow rate of runoff, minimizing the risk of downstream flooding.

Types of Check Dams

Several types of check dams are available, each with its own advantages and disadvantages. Choosing the right type depends on site-specific factors such as flow rate, slope, soil type, and project duration. Here are three common types:

Wattles:

• Description: Wattles are cylindrical, biodegradable barriers made from compacted straw, coconut fiber, or other natural materials encased in netting. They are flexible and conform well to uneven terrain.

• Best Use: Wattles are ideal for areas with low to moderate flow rates, such as small ditches, swales, and around storm drain inlets. They are particularly useful in environmentally sensitive areas as they are biodegradable.

• Advantages: Environmentally friendly, easy to install, and relatively inexpensive.

• Disadvantages: Less durable than other types and may not be suitable for high flow rates or long-term use. They can also be susceptible to damage from heavy equipment or foot traffic.
  

Hay Bales:

• Description: Hay bales are rectangular blocks of compressed hay or straw. They are readily available and relatively inexpensive.

• Best Use: Hay bales are suitable for temporary applications in areas with low to moderate flow rates. They can be used to create check dams in ditches, swales, and around construction perimeters.

• Advantages: Readily available, inexpensive, and easy to install.

• Disadvantages: Hay bales decompose quickly, especially when exposed to moisture, and may need frequent replacement. They are also less effective than other types for controlling fine sediments and can become a source of pollution if not properly maintained. They are generally discouraged for use as a primary sediment control measure due to these issues.

Rock Weirs:

• Description: Rock weirs are constructed from appropriately sized rocks or gravel placed across a drainage channel. They are more durable than wattles or hay bales and can handle higher flow rates.

• Best Use: Rock weirs are best suited for areas with moderate to high flow rates, such as larger ditches, channels, and outlets. They are also suitable for longer-term applications.

• Advantages: Durable, effective at trapping sediment, and can handle higher flow rates.

• Disadvantages: More expensive and labor-intensive to install than wattles or hay bales. They also require careful sizing and placement of rocks to ensure effectiveness and stability.

Installation Methods

Proper installation is crucial for the effectiveness of any check dam. Here are some general guidelines:

• Site Preparation: Clear the area where the check dam will be installed, removing any debris or vegetation.

• Wattle Installation: Place the wattle across the drainage channel, ensuring it is in close contact with the ground. Secure the wattle with stakes driven through the netting at regular intervals. For areas with higher flow, consider using multiple rows of wattles.

• Hay Bale Installation: (Generally discouraged) If used, place hay bales across the drainage channel, ensuring they are tightly butted together. Secure the bales with stakes or wire, and consider using a geotextile fabric on the upstream side to improve sediment trapping efficiency.

• Rock Weir Installation: Place the largest rocks in the center of the channel and gradually decrease the size of the rocks towards the edges. Ensure the weir is keyed into the banks of the channel to prevent water from bypassing it. A geotextile fabric placed under the rocks can enhance filtration and prevent soil erosion.

• Spacing: Space check dams appropriately based on the slope and flow rate of the channel. Steeper slopes and higher flow rates require closer spacing.

Maintenance Requirements

Regular inspection and maintenance are essential to ensure the continued effectiveness of check dams.

• Inspection: Inspect check dams weekly and after each significant rainfall event. Look for signs of damage, such as erosion, displacement, or deterioration.

• Sediment Removal: Remove accumulated sediment when it reaches one-third to one-half of the check dam's height. Dispose of the sediment properly, following local regulations.

• Repair or Replacement: Repair or replace damaged sections of the check dam promptly. Replace deteriorating wattles or hay bales as needed.

• Rock Weir Maintenance: Periodically check rock weirs for displaced rocks and readjust them as necessary. Ensure the weir remains keyed into the channel banks.

Conclusion

Check dams are a vital component of many effective Stormwater Pollution Prevention Plans (SWPPPs). By understanding the different types of check dams, their proper installation methods, and necessary maintenance practices, construction professionals can significantly reduce erosion and sediment runoff, protecting our waterways and ensuring compliance with environmental regulations. Proactive erosion and sediment control is not only good for the environment, but it also saves time and money in the long run by preventing costly repairs and potential environmental fines.

Not sure what erosion and sediment controls you need on your construction site?

Contact the Certified Professionals in Erosion & Sediment Control (CPESC) at Eco Permit Pros today to get started on your plan!

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