In hydrology, what is the primary purpose of conducting a Depth-Area-Duration (DAD) analysis for a storm event?
- ATo determine the probability of a storm occurring in a given year
- BTo analyze the maximum amount of rainfall for different storm durations over various area sizesCorrect
- CTo measure the velocity of flood flow in a river channel
- DTo calculate the evaporation rate from a reservoir surface
Solution
Concept
Depth-Area-Duration analysis in catchment storm hydrology
Formula
NONE
Step-by-step solution
1. A Depth-Area-Duration (DAD) analysis evaluates the spatial and temporal characteristics of severe storms. 2. For a storm of given duration, average precipitation depth is highest at the center and decreases outward with increasing area. 3. DAD curves plot maximum average rainfall depth against catchment area for various durations (e.g., 6h, 12h, 24h). 4. Hence, the primary purpose is analyzing maximum rainfall for different durations over various area sizes. Answer: B
Explanation
Depth-Area-Duration (DAD) analysis is a hydrological technique used to determine the maximum average rainfall depth that occurs over different catchment areas for various storm durations. Plotting these relationships produces DAD curves, which are essential for evaluating maximum probable precipitation and sizing major hydraulic spillways.
Why the other options are wrong
A) Storm return periods and annual occurrence probabilities are determined by frequency analysis (IDF curves). C) River flood flow velocity is measured using current meters and stream gauges. D) Reservoir evaporation is estimated using pan evaporimeters or water balance methods.
Shortcut
DAD analysis = Maximum rainfall depth for various Durations over different catchment Areas.
Common mistake
Confusing DAD analysis with Intensity-Duration-Frequency (IDF) analysis used for storm probability and return periods.
Correct answer: B) To analyze the maximum amount of rainfall for different storm durations over various area sizes