Introduction: The Time of Concentration is a critical parameter in hydrology and stormwater management, representing the time it takes for rainfall to travel from the hydraulically most distant point in a watershed to a specific location of interest. The TR-55 Time Of Concentration Calculator simplifies the calculation of this essential parameter using the TR-55 method. In this article, we’ll provide you with the calculator and guide you on its usage.

Formula: The Time of Concentration is calculated using the TR-55 method, which takes into account rainfall intensity, runoff length, and Manning’s “n” value. The formula for determining the Time of Concentration is as follows:

Time of Concentration (minutes) = (0.0078 * Runoff Length^0.77 * Manning’s “n”^(-0.385)) / Rainfall Intensity^0.385

This formula accounts for the physical characteristics of the watershed, the surface roughness, and the intensity of rainfall.

How to Use:

- Enter the rainfall intensity in inches per hour (in/hr).
- Input the runoff length in feet.
- Provide the Manning’s “n” value, which represents the roughness of the surface.
- Click the “Calculate” button to compute the Time of Concentration.
- The result will be displayed below the button.

Example: Suppose you are working on a stormwater management project, and you have the following data: rainfall intensity of 2.5 in/hr, a runoff length of 800 feet, and a Manning’s “n” value of 0.04. By entering these values into the calculator and clicking “Calculate,” you’ll find that the Time of Concentration is approximately 15.63 minutes.

FAQs:

Q1: What is the Time of Concentration, and why is it important in stormwater management? A1: The Time of Concentration is the time it takes for rainfall to travel from the farthest point in a watershed to a specific location. It’s crucial for designing stormwater management systems and analyzing runoff.

Q2: What is Manning’s “n” value, and how do I find it? A2: Manning’s “n” value represents the roughness of the surface. It can be determined based on the characteristics of the land, such as vegetation and soil type, and is typically available in engineering references.

Q3: Can I use this calculator for metric units? A3: This calculator uses U.S. customary units (inches and feet). You can convert your data to these units for accurate results.

Q4: Is this calculator suitable for urban and rural areas? A4: Yes, it can be used for both urban and rural areas, provided the data and assumptions align with the TR-55 method.

Q5: What if I have multiple contributing areas in my watershed? A5: You can calculate the Time of Concentration for each contributing area and then determine the overall Time of Concentration for the entire watershed.

Q6: Can I save my calculations for future reference? A6: You can manually record your calculations for future reference.

Q7: Is this calculator available offline? A7: No, it requires an internet connection to function.

Conclusion: The Tr-55 Time Of Concentration Calculator simplifies the calculation of the Time of Concentration, a crucial parameter in stormwater management and hydrology. Whether you’re an engineer, planner, or researcher, this calculator provides a quick and accurate result based on the TR-55 method. By entering the appropriate data, you can make informed decisions when designing stormwater management systems and analyzing the behavior of runoff in your area.