Composite drains are manufactured using different materials, hence the roughness coefficient of each of the materials will be different. Therefore, the n is modified according to Horton-Einstein equation

Horton-Einstein equation is as below:

$$ {(\frac{\mathrm P1{({\mathrm n}_{\mathrm{culvert}})}^{1.5}\;+\;\mathrm P2{({\mathrm n}_{\mathrm{culvert}})}^{1.5}\;+\;\dots.}{{\mathrm{Total}}_{\mathrm P}})}^\frac23\; $$

We carried out examples to benchmark the calculation with MiTS by using different coefficient with different types of drains. We also provide the project file and the spreadsheet of calculation for users to understand better.

**1)** **Box Drain**

The **project file** can be referred as per link.

The n used in the project is as below:

Left side = 0.03

Bottom side = 0.02

Right side = 0.03

The perimeter, cross sectional area, velocity, peak discharge and other relevant calculations including the composite n can be referred to in the **benchmark** spreadsheet provided.

**2)** **V Shape Drain **

The n used in the project is as below:

Left side = 0.03

Bottom side = 0.02

The **project file** and the **benchmark** are provided for your reference.

**3)** **Half Round Drain **

n used in the project is as below:

Left Side n = 0.03

Bottom n = 0.02

Right Side n = 0.03

Bottom Curve n = 0.02

**Project File** and **benchmark** spreadsheet is as per link.

**4)** **Trapezoidal Drain **

n used for composite trapezoidal drain is as below:

Left Side n = 0.03

Bottom Side n = 0.02

Right Side n = 0.03

The **benchmarking** is carried out based on the **project file.**

**5)** **Block Drain **

n used in the composite block drain is as below:

Left Side n = 0.03

Bottom Side n = 0.02

Right Side n = 0.03

Bottom Curve n = 0.02

The **benchmarking** is carried out based on the **project file.**

**6)** **UDrain **

n used in the composite Udrain is as below:

Left Side n = 0.03

Bottom Side n = 0.02

Right Side n = 0.03

You can obtain the **project file** and the **benchmark** as per link.

**7) UDrain DWF**

n used in the composite UDrain DWF is as below:

Left Side n = 0.03

Bottom Side n = 0.02

Right Side n = 0.03

You can refer to the **benchmarking** and the **project file** for your perusal.