Question

A tile drainage system draining 12 hectares, flows at a design capacity for two days, following a storm. If the system is designed using a drainage coefficient of 1.25 cm, how much of water will be removed during this period ?
1. 1500 m³
2. 4500 m3
3. 3000 m3
4. 3500 m3

Answer 1

Correct Answer - Option 3 : 3000 m3

Concept:

The drainage coefficient is defined as the depth of water to be removed in 24 hours from the entire drainage area.

• It is used for the design of drainage systems for agricultural lands.
• In agricultural lands, open ditches or drains are the most commonly used surface drainage structures.
• The rate at which the open drains should remove water from a drainage area depends on:
  • Rainfall
  • Size of the drainage area
  • Characteristics of the drainage area
  • Nature of the crops grown
  • The degree of protection required for them from waterlogging

​Calculation:

Given:

Drainage coefficient = 1.25 cm/day

Area = 12 ha = 120000 m2

(1 ha = 10000 m2)

Water removal period = 2 days

The volume of water removed = Drainage coefficient × Area × Time = (1.25/100) × 120000 × 2 = 3000 m3