The depths of penetrations along the length of a border strip at points 30 m apart were probed. The observed values are 2·0 m, 1·9 m, 1·8 m, 1·6 m and 1·5 m. The water distribution efficiency is :
- A0·905Correct
- B0·805
- C0·725
- D0·685
Solution
Concept
Water distribution efficiency
Formula
ηd = 1 − y / d
Step-by-step solution
1. Mean depth d = (2.0 + 1.9 + 1.8 + 1.6 + 1.5)/5 = 1.76 m. 2. Absolute deviations: 0.24, 0.14, 0.04, 0.16, 0.26 → mean deviation y = 0.168 m. 3. ηd = 1 − 0.168/1.76 = 0.905.
Explanation
Distribution efficiency measures the uniformity of water penetration along the strip. A value near 1 means a very uniform application.
Why the other options are wrong
0.805, 0.725 and 0.685 would need a mean deviation larger than 0.168 m.
Shortcut
ηd = 1 − (mean absolute deviation / mean depth).
Common mistake
Using the deviation from the maximum depth.
Correct answer: A) 0·905