1. This work is supported by the National Science Foundation’s
Directorate for Education and Human Resources TUES-1245025, IUSE-
1612248, IUSE-1725347, and IUSE-1914915. Questions, contact education-AT-unavco.org
MODELING FLOOD HAZARD MODULE
Unit 1 – Introduction to Flooding
Version: April 15 , 2019
2. FLOODS
• What do you know about flood or flooding?
• When is the last time you heard about it?
• Have you (or anyone you know) ever
experienced a flooding situation? Are floods
always bad or damaging?
• Can you think of any reason(s) why floods
might be beneficial
4. FLOODING - DEFINITION
• Occurrence of water that is beyond the
handling capacity of any natural or
engineering system
5. WHAT KIND OF FLOOD DO YOU SEE?
Riverine
Flooding
Coastal Flooding Shallow Flooding
Source: Jocelyn Augustino, FEMA.
https://www.fema.gov/media-library/assets/images/54208#details
Source: Jocelyn Augustino, FEMA.
https://www.fema.gov/media-library/assets/images/50150
6. WHAT KIND OF FLOOD DO YOU SEE?
Riverine
Flooding
Coastal Flooding Shallow Flooding
Source:
https://commons.wikimedia.org/wiki/File:Fort_Kent_Maine_Bridge_during_fl
ood_2008.jpg
Source:
https://commons.wikimedia.org/wiki/File:Van_Buren_Maine_aerial_during
_2008_flood.jpg
7. WHAT KIND OF FLOOD DO YOU SEE?
Riverine
Flooding
Coastal Flooding Shallow Flooding
Source: https://www.usgs.gov/media/images/boulder-creek-colo-flood-
stage
Source: https://www.usgs.gov/media/images/souris-river-flooding-1
8. WHAT KIND OF FLOOD DO YOU SEE?
Riverine
Flooding
Coastal Flooding Shallow Flooding
Source: https://coastal.er.usgs.gov/hurricanes/sandy/photo-comparisons/newjersey.php
9. WHAT KIND OF FLOOD DO YOU SEE?
Riverine
Flooding
Coastal Flooding Shallow Flooding
Source: https://coastal.er.usgs.gov/hurricanes/sandy/photo-comparisons/northcarolina.php
10. FLOODPLAIN
Topographically: relatively flat
land adjacent to a stream
Geomorphologically: landform
composed primarily
unconsolidated
sedimentary deposits (alluvium)
from the adjacent stream
Hydrologically: area subjected
to periodic flooding from the
adjacent stream
Redrawn after: http://www.yourdictionary.com/floodplain
A flat area of land adjacent to a stream, composed of alluvium, and is subjected to
flooding or inundation during periods of high water in the stream.
11. NATURAL FUNCTIONS OF FLOODPLAINS
• Water resources
– Flood and erosion control
– Groundwater recharge
• Ecological/biological resources
– Natural filters of sediments and nutrients
– Enhances biodiversity
– Habitat for fish and wildlife
• Societal Resources
– Recreational activities
– Fertile agricultural land
– Educational and research opportunities
12. HUMAN IMPACTS (RIVERINE DEVELOPMENT)
• Alteration of flood conveyance
• Obstruction/diversion of flow
13. HUMAN IMPACTS (WATERSHED DEVELOPMENT)
• Decrease in
infiltration
• Increase in
run-off and
flooding
Redrawn after:
http://auburnhills.org/departm
ents/community_development
/low_impact_development/ind
ex.php
14. HUMAN IMPACTS (COASTAL DEVELOPMENT)
• Coastal erosion resulting from anthropogenic
actions, including building structures and sand
mining
15. HOW FLOODS IMPACT HUMANS AND PROPERTY
• Hydrodynamic force
– Force due to moving water
• Hydrostatic force
– Vertical and lateral forces due to standing water
• Debris impact
– Floating and rolling debris from flood water
• Soaking
– Damage to wood, drywall and other building materials
• Sediments and contaminants
– Trapped in building material and structures after
drying
16. SAFETY AND HEALTH HAZARDS
• Damage to utilities – electrocution, drinking
water contamination, sewage, gas leaks, fire
hazard
• Breeding ground for mosquitos, mold, mildew
• Mental stress and fatigue
17. FLOODPLAIN MANAGEMENT
• Floodplain Management: “a decision-making
process that aims to achieve the wise use of
the nation’s floodplains.” “Wise use” means
both reduced flood losses and protection of
the natural resources and functions of
floodplains.
18. FLOODPLAIN MANAGEMENT
• Structural Measures: building of dams, levees
and other structure to manage floods and
floodplains
• Non-structural measures – retain natural
characteristics of floods and floodplains;
regulations; policies
19. FLOODPLAIN MANAGEMENT STRATEGIES AND TOOLS
• Strategy 1: Modify human susceptibility to flood
damage
• Reduce disruption by avoiding hazardous,
uneconomic or unwise use of floodplains by:
– Floodplain Regulation: zoning codes to steer
development away from hazardous areas or natural
areas deserving preservation, establishing rules for
developing subdivisions, and rigorously following
building, health and sanitary codes.
– Development and re-development policies: on the
design and location of public services, utilities and
critical facilities.
20. STRATEGY 1 CONTINUED
• Land acquisition: to preserve open space and
permanently relocate buildings from
floodplains.
• Flood-proof building: by elevating new
buildings and retrofitting existing ones.
• Restore and preserve the natural resources
and functions of floodplains
21. STRATEGY 2: MODIFY THE IMPACT OF FLOODING
• Assist individuals and communities to prepare for,
respond to and recover from a flood by
• Providing information and education to assist self-help
and protection measures.
• Following flood emergency measures to protect people
and property.
• Providing financial support through disaster assistance,
flood insurance and tax adjustments.
• Preparing post-flood recovery plans and programs to
help people rebuild and implement mitigation
measures to protect against future floods.
22. STRATEGY 3: MODIFY FLOODING ITSELF
• Develop projects that control floodwater.
– Dams and reservoirs along streams/rivers to store
excess water upstream from developed areas.
– Dike, levees and floodwalls to keep water away from
developed areas.
– Channel restoration or alteration to make them more
efficient, so overbank flooding will be less frequent.
– Flow diversion around developed areas.
– Land treatment to hold more water through
infiltration
– Detention ponds to store on-site excess runoff
– Runoff control measures from areas under
development outside the floodplain.
23. STRATEGY 4: PRESERVE AND RESTORE NATURAL RESOURCES
• Renew the vitality and purpose of floodplains by re-
establishing and maintaining floodplain environments in
their natural state through:
• Floodplain, wetlands and coastal barrier resources or land
use regulation to steer development away from sensitive or
natural areas.
• Development and redevelopment policies on the design
and location of public services, utilities and critical facilities.
• Land acquisition; open space preservation; permanent
relocation of buildings; restoration of floodplains and
wetlands, and preservation of natural functions and
habitats.
24. STRATEGY 4 CONTINUED
• Information and education to make people
aware of natural floodplain resources and
functions and how to protect them.
• Tax adjustments to provide a financial
initiative for preserving lands or restoring
lands to their natural state.
• Beach nourishment and dune building to
protect inland development by maintaining
the natural flood protection features.
25. HYDROLOGY OF FLOODING
• How to quantify and characterize a flood
event?
• This is typically done using the concept of
return period or frequency of occurrence
• Requires knowledge of probability and
statistics related to streamflow time series
27. HYDROLOGIC DATA SERIES CONTINUED
Partial duration series: Magnitude greater than some base value.
Annual exceedance series: is a partial duration series with # of
values = # years
28. HYDROLOGIC DATA SERIES CONTINUED
Extreme value series
Includes largest or smallest values in equal intervals
Annual series: interval = 1 year
Annual maximum series: largest values
Annual minimum series : smallest values
29. RETURN PERIOD
• Random variable:
• Threshold level:
• Extreme event occurs if:
• Recurrence interval:
• Return Period:
Average recurrence interval between events equaling or
exceeding a threshold
TxX
Tx
X
TxX ofocurrencesbetweenTime
)(E
30. ANNUAL MAXIMUM SERIES FOR WABASH RIVER AT LAFAYETTE, IN
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
200000
1901
1908
1912
1916
1920
1924
1927
1932
1936
1940
1944
1948
1952
1956
1960
1964
1968
1972
1976
1980
1984
1988
1992
1996
2000
2004
2008
2011
2015
Discharge(cfs)
Year
What is the return period of 75,000 cfs at this site?
31. RETURN PERIOD FOR 75,000 CFS
• Number of times flow exceeded 75, 000 cfs in 114 years = 13
• Average recurrence interval = return period = 114/(13-1) = 9.5 years
(approx. 10 years)
• Probability of occurrence of 75,000 cfs every year = (1/10) x100 = 10 %
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
200000
1901
1908
1912
1916
1920
1924
1927
1932
1936
1940
1944
1948
1952
1956
1960
1964
1968
1972
1976
1980
1984
1988
1992
1996
2000
2004
2008
2011
2015
Discharge(cfs)
Year
32. 100-YEAR FLOOD
• A flow that has a return period of 100-years is
called the 100-year flood
• For most practical purposes (e.g., building
house, buying insurances, etc.), area that gets
inundated from 100-year flow is considered as
the “floodplain”
• Approaches to finding the 100-year flow and
how to map the corresponding floodplain will
be covered in Units 2-4 of this module
33. SUMMARY
• Floodplains provide many natural functions and
benefits to the society
• Some human actions alter the natural functioning
of floodplains, thus increasing the flow discharge
• A flood with very high discharge becomes a
hazard
• There are several ways to manage floodplains and
mitigate the flood hazard
• The 100-year flow is used in practice for flood
hazard management
Editor's Notes
This introductory slide is meant for generating some initial discussion on what students know about floods and their experience with it. This slide is animated to generate one question per click.
Potential benefits of floods include ground water recharge, habitat dependence, and sedimentation of valuable soil elements.
Students are expected to have the basic understanding of hydrologic cycle and its processes so they know what happens on the landscape after rainfall, and why some areas get ponded. If students do not have this background information, the instructor may look at or have students look at the GETSI Water resources module: https://serc.carleton.edu/getsi/teaching_materials/water_resources/unit1.html
This is just a simple definition of flooding.
This slide is animated. Instructor may ask the students to guess the type of flooding (riverine, coastal or shallow) by looking at the images. After a click a box will appear to show the correct answer.
Photos:
Left: Cars drive through flood water in Texas. Taken in Houston, TX Sep 13, 2008. Photo by Jocelyn Augustino (owned by FEMA-open access)
https://www.fema.gov/media-library/assets/images/54208#details
Right: Local residents play in shallow flood water in neighborhoods where heavy rain occurred in Lawrence, MA. Photo by Jocelyn Augustino (owned by FEMA- open access)
This slide is animated. Instructor may ask the students to guess the type of flooding (riverine, coastal or shallow) by looking at the images. After a click a box will appear to show the correct answer.
photos
On the left (public domain) : Fort Kent, Maine bridge flooded. Original source; NOAA (original website doesn’t work). https://commons.wikimedia.org/wiki/File:Fort_Kent_Maine_Bridge_during_flood_2008.jpg
On the right (public domain): Van Buren Port, Maine during the 2008 flood . Courtesy of General Services Administration (GSA)
https://commons.wikimedia.org/wiki/File:Van_Buren_Maine_aerial_during_2008_flood.jpg
This slide is animated. Instructor may ask the students to guess the type of flooding (riverine, coastal or shallow) by looking at the images. After a click a box will appear to show the correct answer.
photos
On the left (public domain image) : Boulder Creek at flood stage; “This bridge is at 75th Street east of Boulder showing Boulder Creek at flood stage (5000 cfs) on Friday, September 13, 2013. When looking west (upstream), the USGS streamgage is on the right.
Numerous rivers flooded during a significant September 2013 rain event along Colorado's Front Range, damaging or destroying several USGS streamgages. In response, USGS field crews measured flood flows, made gage repairs, and assessed sites to replace those gages destroyed. ”
Photographer
Kit Fuller
USGS
kitfuller@usgs.gov
https://www.usgs.gov/media/images/boulder-creek-colo-flood-stage
On the right (public domain image): “The Souris River downstream of the Sherwood, ND gage.
Photo taken by USGS personnel on a Civil Air Patrol flight.”
Photographer
Joel M. Galloway
GS-W-NDbmk_Webmaster@usgs.gov
https://www.usgs.gov/media/images/souris-river-flooding-1
This slide is animated. Instructor may ask the students to guess the type of flooding (riverine, coastal or shallow) by looking at the images. After a click a box will appear to show the correct answer.
“Oblique aerial photographs of Mantoloking, NJ. View looking west along the New Jersey shore. Storm waves and surge cut across the barrier island at Mantoloking, NJ, eroding a wide beach, destroying houses and roads, and depositing sand onto the island and into the back-bay. Construction crews with heavy machinery are seen clearing sand from roads and pushing sand seaward to build a wider beach and protective berm just days after the storm. The yellow arrow in each image points to the same feature.” - https://coastal.er.usgs.gov/hurricanes/sandy/photo-comparisons/newjersey.php
This slide is animated. Instructor may ask the students to guess the type of flooding (riverine, coastal or shallow) by looking at the images. After a click a box will appear to show the correct answer.
“Oblique aerial photographs of Rodanthe, NC. View looking west along the North Carolina shore. Beach erosion moved the shoreline landward to reach houses built on the beach. Sand on the roads behind the beach indicates landward transport of sand by overwash. The yellow arrow in each image points to the same feature.” -
https://coastal.er.usgs.gov/hurricanes/sandy/photo-comparisons/northcarolina.php
Definition of floodplain can vary depending on the different perspectives. These perspectives are presented here and a generic definition is provided in the box (animated).
Definition derived from text at : https://www.oas.org/dsd/publications/Unit/oea66e/ch08.htm
This slide just mentions some natural and/or beneficial functions of floodplains.
Humans can affect the occurrence of high flows/floods in many ways. For example, this slide shows how development along the floodplain will increase the flow depth and extent by altering the flow conveyance in a river.
These images were recreated by Diana Krupnik by looking the food management manual from FEMA.
Floods will also occur when more water (runoff) will move faster over a landscape. This slide show how converting a natural land into urban development increases the runoff by decreasing infiltration. This increased runoff will move faster to the stream to cause flooding.
Image adapted by Diana Krupnik from http://auburnhills.org/departments/community_development/low_impact_development/index.php
Building of structures along coasts including sand mining alters the beach dynamics leading to beach erosion and flooding
Image adapted by Diana Krupnik from http://auburnhills.org/departments/community_development/low_impact_development/index.php
This slide describes how flooding impacts properties. This slide is animated to only show the title before the text. Before clicking, ask students what are their thoughts on “how floods impact humans and property”. After getting some answers, click to display the impacts.
This slide describes the broader impact of floods on the overall infrastructure and societal health. This slide is animated to only show the title before the text. Before clicking, ask students what are their thoughts on “safety and health hazards related to flooding”. After getting some answers, click to display the impacts.
This slide shows the federal emergency management agency’s (FEMA) ‘view of floodplain management.
There are two broader ways of managing floods or floodplains. Structural and non-structural as described on this slide.
FEMA advocates four management strategies for managing floodplains. These strategies include both structural and non-structural changes and are often combined to achieve the required goal. As you will see strategy 1 primarily involves non-structural measures.
Strategy 2 also involves non-structural measures, but is focused on educating the community so they are well prepared and consequently less impacted with flooding occurs.
Strategy 3 involves structural measures, but some of these measures, which are not directly along the stream or in the floodplain can also be considered non-structural.
This is similar to strategy 1, but these measures in strategy 4 purely applies to preserving natural resources such as wetlands and beaches; whereas strategy 1 involved measures for new or existing development within the floodplains.
As we have learned floodplains are defined by how often the water flows over bank into the surrounding flat terrain. In most practical cases, floodplains are defined by looking at how frequently they get flooded from the adjacent stream, and hence we need information to quantify the frequency of occurrence of floods. This is usually accomplished by using the concept s of return period and flood frequency, which are based on probability and statistics related to the streamflow data.
Streamflow data can be plotted and analyzed in different ways for flood frequency analysis. The basis streamflow series is a complete duration series. What you see here is 20 years of daily data plotted for the Wabash River near Lafayette, IN
A commonly used data serise is partial duration series. A partial duration series is extracted from the complete duration series by only using data above a certain threshold value. A special type of partial duration series is the annual exceedance series in which the threshold is defined such that the number of values in the partial duration series is equal to the number of years of data. In this case, the red line on the data series is defined such as there are only twenty values greater than the red line. 20 values for 20 years of data.
Extreme value series is a plot of either the minimum or maximum value for a given time interval. The most commonly used data series of flood frequency analysis is the annual maximum series which shows the maximum value for each year for the duration of the data.
The topic of quantifying flood is generally done by using the concept of return period. If we consider the flow (discharge) as a random variable X, then the flood occurs when this random variable exceeds a threshold (XT). The easiest way to find a return period for a given threshold (or flow value) is to see how many times this threshold has been exceeded and what is the interval (recurrence interval) between these exceedances. The average recurrence interval between all the exceedances is called the return period. In literature, you will find return period and recurrence interval used interchangeably, but in this unit we will use return period.
This plot shows the annual maximum series for Wabash River at Lafayette since 1901. We are interested in finding the return period for 75,000 cfs flow.
This slide shows the calculations for getting the return period for the 75, 000 cfs flow.
It is good to emphasize that to get the 100-year flow one should have more than 100 years of data, which is not always possible so statistical approaches are used to find this value, which will be covered in Unit 2 of this module
