Looking for how to calculate the size of an attenuation tank? An attenuation tank is a storage solution designed to temporarily hold excess stormwater, preventing it from overwhelming drainage systems during heavy rainfall. These tanks play a crucial role in both urban and rural areas, where managing stormwater is essential to reduce the risk of flooding and protect infrastructure.
They work by storing the runoff and slowly releasing it back into the environment at a controlled rate. Sizing an attenuation tank correctly is crucial for its effectiveness. The tank needs to be large enough to handle the expected water flow but not oversized, which could lead to unnecessary costs.
In this guide, we’ll explore the factors that help to decide the size of the attenuation tank & how to calculate the size.
Let’s start!
What Are the Main Factors That Go into Deciding How to Size an Attenuation Tank?
1. Assessing rainfall intensity and duration
Understanding local rainfall patterns, including the intensity and duration of downpours, is critical for determining the size of your attenuation tank. Different regions experience varying levels of rainfall, so accurate data is necessary to ensure your tank can handle the expected water volume.
2. Evaluating the impermeable surface area
The size of impermeable surfaces like roofs, driveways, and roads contributes to runoff. The larger the area, the more stormwater will be generated, requiring a larger tank to manage the excess water effectively.
3. Calculating the discharge rate
Discharge rate regulations set by local authorities determine how quickly water can be released back into drainage systems. Your tank needs to be sized to store excess water until it can be safely discharged at an allowable rate.
4. Factoring in soil infiltration rates
Infiltration rates affect how much water is absorbed into the ground naturally. If your project site has low soil infiltration, the tank needs to store more water to prevent flooding.
5. Considering future climate changes
Climate change can increase the frequency and severity of storms. To future-proof your project, it’s essential to size your tank with potential increases in rainfall and extreme weather in mind.
6. Taking into account local regulations and guidelines
Local planning and water management authorities provide specific guidelines on stormwater management. Your attenuation tank must comply with these regulations to ensure it meets legal and environmental standards.
How Can You Calculate the Size of an Attenuation Tank?
To calculate the size of an attenuation tank, the basic formula considers the water that comes from your roof, not the amount you will use. For most cases, this method is effective. Here’s the calculation:
Footprint of property (m²) x Drainage coefficient x Filter efficiency x Annual rainfall x 0.05 = recommended tank size
While this might sound complicated, let’s make it simple:
- Footprint of property: This is simply the area of your roof, calculated by multiplying the length and width of your building in metres.
- Drainage coefficient: Not all rainwater will make it into the tank; some evaporates or overflows during heavy rain. Typically, 80% of the water will enter the tank, so we use a factor of 0.8 for this.
- Filter efficiency: Some water is lost as it passes through the filter. If your filter is 95% efficient, like ours, you’d use a factor of 0.95.
- Annual Rainfall: This is the amount of rainfall your location gets in a year, which can be found from local weather sources or websites.
Finally, the result from this calculation gives you the volume of water your tank will collect in a year. The 0.05 at the end helps determine 5% of the annual water, which is the recommended tank volume for your needs.
Conclusion
Sizing an attenuation tank correctly is essential to effectively manage stormwater for any project. By considering factors like the property’s footprint, drainage coefficient, filter efficiency, and annual rainfall, you can calculate the appropriate tank size to prevent flooding and ensure proper water management. With the right tank in place, you can protect your property and the surrounding environment.
If you need expert guidance on choosing or installing the right attenuation tank, contact Resolute Civils today. We’re here to provide products for all your stormwater management needs.
FAQs
What is an attenuation tank used for?
An attenuation tank stores excess stormwater during heavy rain and slowly releases it to prevent flooding and damage to the drainage system.
How do you calculate the size of an attenuation tank?
The size is calculated based on the property’s footprint, drainage coefficient, filter efficiency, and annual rainfall, using a specific formula to determine the optimal tank volume.
Why is drainage coefficient important in sizing an attenuation tank?
The drainage coefficient accounts for the percentage of rainwater that will reach the tank, typically around 80%, helping ensure the tank size is appropriate for the water collected.
Does my property’s location affect the size of the attenuation tank?
Yes, areas with higher rainfall will require larger tanks, as they need to accommodate more stormwater compared to drier regions.
Can attenuation tanks be installed in both urban and rural areas?
Yes, attenuation tanks are essential for managing stormwater in both urban and rural projects to prevent flooding and ensure efficient drainage.
What factors influence the volume of water stored in an attenuation tank?
Key factors include the size of the roof, local rainfall data, and the efficiency of the drainage and filtration systems in capturing rainwater.