Flood Modeling Midterm

FEMA definition of flood

a general and temporary condition of partial or complete inundation of 2 or more acres of normally dry land area

Benefits of small flood

disease regulation, water regulation, water quality, food suply, recreation

Benefits of extreme floods

soil formation, drinking water, tourism

BFE

base flood elevation

height of floodwaters resulting from a 100-year flood event

Floodway

designated area reserved to discharge the base flood

Flood fringe

an area that can contain slow-moving or standing water

Hazard vs Impacts

Hazard is a process or event that could cause loss of life and damage

Impacts are the effects that have been caused by such hazards

When does a hazard become a disaster

when there is severe impacts or disruption in the functioning of a community

Flood insurance rate map (FIRM) definition

map of an area where FEMA has labeled the special flood hazard areas, base flood elevation, and risk zones

Color code for high, moderate, and low risk flood areas (FIRM)

High = blue

Moderate = orange

low= unshaded

What is a special flood hazard area

any area with the possibility of experiencing a 100-year flood event in any given year

(Zones, A & V)

What is a non-special flood hazard area

Zone outside the 100-year flood areas. Can be in between the 100- and 500-year flood

(Zones B, C, D, or X)

What does flood zone D mean

possible risk, but no flood hazard analysis has been performed yet

Stillwater vs total water level

total water level includes the effects of waves on the water elevation while still water does not

T/F: BFE accounts for the effects of waves

T, BFE includes waves

T/F: Climate change has not affected the water cycle

F: climate change and human activity have affected the quantity, quality, timing, and use

3 natural functions of floodplains

Water resources, ecological and biological resources, societal resources

Examples of water resources functions of floodplain

reduces flood damages

erosion control

groundwater recharge

Examples of ecological functions of floodplain

natural retainers of sediments

biodiversity

carbon storage

Examples of societal functions of floodplain

recreation

education

research

Types of flood drivers

Pluvial

Fluvial

Coastal

Compound

Pluvial Flooding

Intense rainfall or sustained moderate rainfall (flash flooding)

Fluvial flooding

accumulation of large volumes of excessive rainfall/snowmelt

Coastal flooding

One or a combination of high tides, storm surge, and waves that are above sea level

Compound flooding

Multiple flood drivers (extreme or not) that occur in combination and cause greater impacts than an independent event alone

What do flood hazards refer to

the duration, depth, and velocity of floodwaters

Duration definition

length of time where floodwaters are above a given threshold

Flood depth definition

vertical distance between water surface elevation and ground elevation with respect to a common datum

Velocity definition

average rate of floodwaters moving through a floodplain

Flood impacts refer to

fatalities, injuries, and extensive infrastructural damages

Hydrodynamic flood impacts

force due to moving water

Hydrostatic flood impacts

vertical and lateral forces due to standing water

Debris flood impacts

floating and rolling debris

Soaking flood impacts

damages to materials (wood)

Sediment flood impacts

trapped in building material and structure

Infrastructure flood impacts

damage to critical infrastructure and utilities

Safety and health flood impacts

mental stress, fatigue, mold, mosquitoes

Flood Zone: V

Coastal areas

What does the “E” indicate in flood zones

elevation of water has been determined and is designated on the Flood Insurance Rate Maps (FIRM)

Flood Zone: A

Areas subject to inundation by 1% annual flood chance (100-year flood) that do not meet criteria for V zone

Subject to breaking waves, storm surge, and wave runup

LiMWA meaning

Limit of moderate wave action

boundary between moderate and minimal wave action zones

Flood Zone: X

Outside the areas of a 100-year flood event , beyond the insurance limit

subject to 0.2% or 500-year flood event

Flood Zone: Unshaded

Outside of the 500-year flood event

Flood Zone: AO

Inside 100-year (1%) flood and on sloping terrain

Flood Zone: AH

Inside 100-year (1%) flood and a pond

Flood Zone: AR

Areas with temporary increased flood risk due to flood control system (dam or levee)

Structural measures for flood management

designed to keep floodwaters away from infrastructure

Nonstructural measures for flood management

Designed to keep building away from floodwaters

FEMA flood management strategies

Prevention

Control

Mitigation

Preservation and restoration

FEMA flood management prevention strategies

floodplain regulation

redevelopment of policies

land acquisition

restore and preserve

flood proof building

FEMA flood management control strategies

Develop projects/infrastructure

Channel restoration

Runoff control

land treatment

detention ponds

flow diversion

FEMA flood management mitigation strategies

Information and education

flood emergency measures

financial support

post-flood recovery plans

FEMA flood management preservation strategies

land use regulations

policies

information and education

tax adjustments

beach nourishment

What kind of data do flood events use

Spatial, temporal, and spaciotemporal data

Spatial Data

satellite imagery, radar data, LiDAR data, drone imagery

Temporal data

tide gauge

river gauge

rain gauge

high water marks

Spatiotemporal data

inundation maps made from hydrodynamic models

What is complete duration series

all available data records

What is partial duration series

data records that exceed a given threshold value

What is annual exceedance series

partial duration series in which the number of data points is equal to the number of years (avoids double counting the same event)

What is extreme value series

partial duration series containing the largest or smallest values in equal intervals

Baseflow definition

low flow rate added to a channel from subsurface (groundwater)

Bankfull definition

flow rate that fills a channel to its maximum capacity

Flood flow definition

flow rate that overtops the banks

Peak flow definition

maximum flow rate within a period of interest

In terms of probability what is an extreme event

The probability of a random variable (X) being greater than or equal to a threshold value (xt)

Time between extreme event occurrences

recurrence intervals

Return period (T)

average recurrence intervals

average time until the next extreme event

Continuous variable

can take on an infinite number of values

What is the non-exceedance (probability the value is less thn or equal to) known as

Cumulative Distribution Function (CDF)

What do histograms show

frequency distribution of a random variable arranged in bins

What is the kernel density function

Nonparametric method to estimate the probability density function (PDF)

How to find the probability that a value does NOT exceed the threshold value

CDF

How to find the probability that a value does exceed the threshold value

EP = 1- CDF

Exceedance probability

How often will a value exceed the threshold value

T = 1/EP

return period

Univariate analysis steps

sample extreme data

Empirical CDF

Develop hypothesis for CDF

Maximum likelihood estimation

goodness of fit

evaluate hypothesized distribution

Block maxima process

dividing data into non overlapping periods of equal duration and selecting max data results from each period

Limitation of block maxima

ignores other extremes within the same block as the top extreme

Peaks over threshold (POT) process

samples data records by selecting values that exceed a threshold (percentiles, usually 95%)

Peaks over threshold (POT) requirement

extreme values are independent and identically distributed (IID)

What is the ECDF

Empirical cumulative density function

What does the “i” represent in the ECDF

the rank, where 1 is the smallest

What does the “a” represent in the ECDF

type of plotting position formula

set value based on the type

Null hypothesis

The hypothesis to be tested

skeptical perspective

Alternate hypothesis (HA)

Contradicts H0

What kind of distribution for river flow

Pearson 3

What kind of distribution for coastal water level

GEV (generalized extreme) and pareto (generalized pareto)

What kind of distribution for rainfall

G2 (gamma), Pearson 3, kappa

Moment 1 of a PDF

mean

Moment 2 of a PDF

variance

Moment 3 of a PDF

skewness

Moment 4 of a PDF

kurtosis

What conda package estimates parameters for distributions

fitter

For goodness of fit what is used to reject the H0

significance

set at typically 0.05 (95% confidence)

What does the p-value represent

the risk involved in rejecting the H0 given the data

When do we reject the H0

when p-value < 0.05

Visual assessment of goodness of fit

Quantile-Quantile (Q-Q) plot

Statistical tests for goodness of fit

anderson-darling

Cramer von mises

kolmogorov-smirnov

What does anderson-darling test

data from a given distribution

What does Cramer von mises test

symmetry of PDF