Flood frequency analysis (FFA) Flashcards
1
Q
Definition
A
Statistical assessment of floods is done based on their return period T. Is the average elapsed time T in years between occurrences of an event (or its characteristic) which exceeds a certain magnitude X > x.
Tflood = 1/Pe = 1/(1-Pne)
2
Q
Procedure
A
- Selection of sample (e.g. annual series)
- Plausibility of data (homogeneity, consistency)
- Selection of probability distribution F(x)
- Estimation of parameters
- Test for goodness of fit, confidence intervals
- Application for design
3
Q
Recommended distribution functions
A
Generalised extreme value (GEV) → 3 par → shape B, D, C
4
Q
Estimation of parameters for probability distributions:
A
Probability weighted moments/ L-moments (NEW):
- Using relation between L-moments and parameters
- Exponent r at probability (see Eq. 6.4) → more robust against outliers
5
Q
Extreme Value
A
- Extreme value distribution type I (EI, Gumbel):
Simple, often used PD with 2 parameters c-location, d-scale - Generalised extreme value distribution (GEV):
- 3 parameters: a-shape, c-location, d-scale, very flexible shape
- Contains as special cases EI, EII, EIII