Section 4: Soil and Water Conservation Engineering
Hydrology
Subtopic: Analysis of precipitation data
Question Statement:
Which of the following statements regarding Double Mass Curve analysis for precipitation records are correct?
Options:
(A) It is used to detect, test, and adjust inconsistency in the long-term hydrological precipitation record of a base rain gauge station
(B) It plots the cumulative precipitation of the test station against the concurrent cumulative average precipitation of surrounding base stations
(C) A marked persistent change in the slope of the plotted line indicates a physical change in gauge exposure, station relocation, or instrument drift
(D) It can only be applied if all surrounding rain gauges have completely identical annual rainfalls
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
- Statements A, B, and C are correct:
1. Double Mass Curve is the standard engineering tool for testing hydrological record homogeneity.
2. The slope $c = \frac{\sum P_x}{\sum P_{avg}}$ remains constant as long as the record is consistent.
3. A slope break identifies the year of inconsistency, corrected via slope ratio $P_{corrected} = P_x \times \frac{c_a}{c_0}$.
- Statement D is incorrect: Surrounding stations do not need equal rainfalls; their long-term average simply provides a stable regional benchmark.