Which of the following statements regarding Water Distribution Efficiency ($\eta_d$) is/are TRUE?
Options:
(A) It is defined by $\eta_d = 100 \left( 1 - \frac{\bar{y}}{\bar{d}} \right)$, where $\bar{d}$ is average water depth stored and $\bar{y}$ is average numerical deviation from $\bar{d}$
(B) A distribution efficiency of $100\%$ implies completely uniform penetration depth throughout the length of run
(C) Under-irrigation at the lower end of a border strip lowers the distribution efficiency
(D) Distribution efficiency accounts for evaporation losses from the supplying reservoir
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
1. $\eta_d = 100 (1 - \bar{y}/\bar{d})$ evaluates how uniformly water infiltrates along the run (A is true).
2. Perfect uniformity means $\bar{y} = 0$, giving $\eta_d = 100\%$ (B is true).
3. Incomplete penetration or non-uniform soaking widens deviation $\bar{y}$, reducing $\eta_d$ (C is true).
4. Distribution efficiency is strictly a field-level uniformity index; reservoir evaporation is unrelated (D is false).