Lecture 2 - Hydrologic Statistics and Frequency Analysis Flashcards
What is a random variable?
variable described by a probability distribution
What is a probability distribution?
function representing the frequency of occurence of a random variable
What do you call a set of observations from the random variable?
sample
What is a return period?
number of years, on average, between events of equal or larger magnitude, inverse of the annual exceedance probability (AEP) of occurence of an event of equal or larger magnitude in any given year
What chance of occurence does a 1 in 100 yr flood have in any given year?
1/100 or 1%
What are the two functions which describe a probability distribution?
probability density function and cumulative distribution function
How do you calculate the mean?
sum of all values/# of values
How do you calculate the standard deviation?
How do you calculate the coefficient of skew?
What are the 3 probability distributions commonly used in hydrology?
log-normal distribution, gumbel distribution, log-pearson III distribution
Which probability distribution is commonly used in hydrology, espescially for rainfall?
gumbel
Which probability distribution can be applied directly without use of frequency factors?
gumbel
Which probability distribution is recommended by the US Water Resources Council for Flood Frequency Analysis?
log-pearson III
What probability distribution is bell shaped and symmetric? Which variables is this distribution described by?
normal distribution, mean and variance
What is the max return period of an estimate?
double the length of the data record (need 50 years of records to estimate 100 yr flood)
What do Flow-Duration (F-D) show?
frequency or percentage of time the streamflow falls within various ranges
