Slotted Drain Length Calculator

Calculate the required length of a slotted drain for a design flow using Manning’s equation.
\[ L = \frac{Q}{\frac{1.49}{n} A R^{\frac{2}{3}}\sqrt{S}} \]

* Flow depth \(d\) must be ≤ 0.18 ft. Enter the design flow rate \(Q\) (ft³/s), slot width \(b\) (ft), flow depth \(d\) (ft), slope \(S\) (ft/ft), and Manning’s \(n\).

Step 1: Enter Parameters

Design Flow Rate, \(Q\) (ft³/s):

Example: 1.0 ft³/s

Slot (Drain) Width, \(b\) (ft):

Example: 0.2 ft

Flow Depth, \(d\) (ft):

Example: 0.15 ft (must be ≤ 0.18 ft)

Channel Slope, \(S\) (ft/ft):

Example: 0.005 ft/ft

Manning’s Roughness, \(n\):

Example: 0.015

Step 1: Enter Parameters

Required Slotted Drain Length