How to Calculate and Solve for Lag Time | Irrigation Water Requirement

The image above represents lag time. Three essential parameters are needed to calculate lag time: Inflow Rate (Qn), Manning’s Co-efficient (n), and Border Strip Slope (S_o).

The formula for calculating lag time:

T_L = ^{Q_n0.2 . n1.2} / _120So^1.6

Where:

T_L = Lag Time
Q_n = Inflow Rate
n = Manning’s Co-efficient
S_o = Border Strip Slope

Let’s solve an example;
Find the lag time when the inflow rate is 16, the manning’s coefficient is 4, and the border strip slope is 6.

This implies that;

Q_n = Inflow Rate = 16
n = Manning’s Co-efficient = 4
S_o = Border Strip Slope = 6

T_L = ^{Q_n0.2 . n1.2} / _120So^1.6
T_L = ^{(16)0.2 . (4)1.2} / _120(6)^1.6
So, T_L = ^{1.741 . (5.278)} / _120(17.58)
T_L = ^9.189 / _2109.71
T_L = 0.00435

Therefore, the lag time is 0.00435.

Read more: How to Calculate and Solve for Inflow Rate | Irrigation Water Requirement

How to Calculate Lag Time Using Nickzom Calculator

Nickzom Calculator – The Calculator Encyclopedia is capable of calculating the inflow rate.

To get the answer and workings of the inflow rate using the Nickzom Calculator – The Calculator Encyclopedia. First, you need to obtain the app.

You can get this app via any of these means:

Web – https://www.nickzom.org/calculator-plus

To get access to the professional version via web, you need to register and subscribe for NGN 2,000 per annum to have utter access to all functionalities.
You can also try the demo version via https://www.nickzom.org/calculator

Android (Paid) – https://play.google.com/store/apps/details?id=org.nickzom.nickzomcalculator
Android (Free) – https://play.google.com/store/apps/details?id=com.nickzom.nickzomcalculator
Apple (Paid) – https://itunes.apple.com/us/app/nickzom-calculator/id1331162702?mt=8
Once, you have obtained the calculator encyclopedia app, proceed to the Calculator Map, then click on Agricultural under Engineering.

Now, Click on Irrigation Water Requirement under Agricultural

Now, Click on Inflow Rate under Irrigation Water Requirement

The screenshot below displays the page or activity to enter your values, to get the answer for the inflow rate according to the respective parameters which is the Inflow Rate (Q_n), Manning’s Co-efficient (n) and Border Strip Slope (S_o).

Now, enter the values appropriately and accordingly for the parameters as required by the Inflow Rate (Q_n) is 16, Manning’s Co-efficient (n) is 4 and Border Strip Slope (S_o) is 6.

Finally, Click on Calculate

As you can see from the screenshot above, Nickzom Calculator– The Calculator Encyclopedia solves for the inflow rate and presents the formula, workings and steps too.