This Is an Audio-Enhanced Powerpoint Presentation. 0:00:03.350,0:00:10.330 to Hear The

This is an audio-enhanced PowerPoint presentation.
0:00:03.350,0:00:10.330
To hear the audio, please open this presentation
in “Slide Show” view.
0:00:10.330,0:00:14.570
This presentation will overview one way that
depth grid information can be paired with
0:00:14.570,0:00:18.970
local information to analyze the depth of
flooding at a number of locations throughout
0:00:18.970,0:00:20.160
the community.
0:00:20.160,0:00:25.770
This presentation will focus on a depth grid
that describes a storm equal to a 1 in 100
0:00:25.770,0:00:31.410
chance of occurring each year, also known
as the 1-percent annual chance storm event.
0:00:31.410,0:00:36.730
This event is the national standard used to
define areas as “flood prone” on FEMA’s
0:00:36.730,0:00:38.980
Flood Insurance Rate Maps.
0:00:38.980,0:00:44.170
This presentation is intended to describe
how the Percent Annual Chance and Percent
0:00:44.170,0:00:48.810
30-year Chance Grid information may be paired
with local spatial information to better understand
0:00:48.810,0:00:54.539
the probability of flood risk at a point within
the community related to certain time periods.
0:00:54.539,0:00:58.930
- A Recipe Card with limited instructions
on coupling the depth grid with local Address
0:00:58.930,0:01:03.460
Location Points, or “Building Footprints”,
to identify the flood depth at site-specific
0:01:03.460,0:01:06.799
locations is available for your use.
0:01:06.799,0:01:11.850
- This information allows communities to convey
flood risk in simple terms and provides a
0:01:11.850,0:01:18.609
data point to determine possible flood losses
within a structure, prioritize between elevation/acquisition
0:01:18.609,0:01:21.860
projects, and inform grant applications.
0:01:21.860,0:01:27.329
- Through a series of screen shots, this presentation
will take you through those same steps outlined
0:01:27.329,0:01:29.649
on the recipe card.
0:01:29.649,0:01:34.289
- Our hope is that these non-regulatory datasets
can provide additional understanding of the
0:01:34.289,0:01:39.279
natural hazard risk.
0:01:39.279,0:01:43.000
A variety of information is produced by Flood
Risk Studies.
0:01:43.000,0:01:47.639
- Regulatory Flood Risk Products include the
Flood Insurance Rate Map, or FIRM, and the
0:01:47.639,0:01:51.110
Flood Insurance Study (also known as the FIS).
0:01:51.110,0:01:56.759
- These two items have been delivered to communities
across the nation since the early 1970s.
0:01:56.759,0:02:01.719
- The FIRM and FIS should be used to assist
residents and business owners in determining
0:02:01.719,0:02:06.219
whether their structures are inside or outside
of the Special Flood Hazard Areas.
0:02:06.219,0:02:11.950
- The FIRM, FIS and its Water Surface Elevation
profiles contained within the text remain
0:02:11.950,0:02:14.180
the basis of a flood determination.
0:02:14.180,0:02:19.060
FEMA’s Risk MAP program allows us to provide
communities with a variety of non-regulatory
0:02:19.060,0:02:23.790
tools to better understand flood vulnerability
throughout their community.
0:02:23.790,0:02:28.319
- These datasets, if prepared, will be made
available to community staff and officials
0:02:28.319,0:02:32.400
during the Flood Risk Review or Resilience
meetings as part of the Flood Risk Database
0:02:32.400,0:02:38.380
- These datasets may be used by community
officials as they prioritize elevation/acquisition
0:02:38.380,0:02:41.250
projects
- These datasets may assist communities in
0:02:41.250,0:02:45.959
reviewing local development protocols, or
assist in supporting higher standards or more
0:02:45.959,0:02:49.940
stringent building codes in some areas of
the community.
0:02:49.940,0:02:55.019
- Knowledge of flood prone areas can aid local
building permit and inspection staff in reviewing
0:02:55.019,0:02:59.500
development permits for correct building codes
in areas that are flood prone.
0:02:59.500,0:03:03.870
You may wonder what types of data are used
to prepare these analyses, let’s take a
0:03:03.870,0:03:07.290
closer look.
0:03:07.290,0:03:11.609
Flood Risk Studies use engineering analysis
to determine updated flood risk along streams
0:03:11.609,0:03:12.920
and channels.
0:03:12.920,0:03:16.360
The engineering analysis is prepared in three
steps:
0:03:16.360,0:03:21.330
• Hydrologic analysis estimates the amount
(or volume of water) that is expected during
0:03:21.330,0:03:24.569
a storm event
• Hydrologic analysis reviews the historic
0:03:24.569,0:03:28.739
flooding of streams by referencing stream
gage readings.
0:03:28.739,0:03:32.799
• Hydrology is affected by the amount of
pavement within a study area.
0:03:32.799,0:03:37.610
• Hydraulic analysis determines how the
streams, channels and rivers will convey that
0:03:37.610,0:03:38.610
water.
0:03:38.610,0:03:42.080
• In the event there is too much water for
the stream channel, the storm water may leave
0:03:42.080,0:03:47.920
the stream channel and expand into parks and
roadways to transport the flood waters downstream.
0:03:47.920,0:03:53.319
• Some development practice constrict streams
and hurry flow with concrete lined channels.
0:03:53.319,0:03:58.849
• Other development practices maintain greenspace
and floodplain areas with community parks
0:03:58.849,0:04:02.720
to allow some relief to other residential
areas within a community.
0:04:02.720,0:04:07.469
• The result of these analysis is a series
of water surface elevations along the stream
0:04:07.469,0:04:10.250
channel that are then able to be mapped.
0:04:10.250,0:04:14.130
• These calculated water elevations are
mapping on terrain models that describe the
0:04:14.130,0:04:15.130
ground.
0:04:15.130,0:04:20.000
• This mapping effort assists FEMA in determining
flood prone areas in the vicinity of the streams
0:04:20.000,0:04:21.530
analyzed.
0:04:21.530,0:04:26.030
With different land use practices and different
ground elevation variation, comes a variability
0:04:26.030,0:04:28.200
of flood inundation area.
0:04:28.200,0:04:32.080
Some areas of your community are likely more
flood prone than others.
0:04:32.080,0:04:36.340
Low lying culvert and bridge crossings may
be overtopped, some areas of the community
0:04:36.340,0:04:40.880
are closer to streams and some are built on
elevated foundations to reduce their likelihood
0:04:40.880,0:04:42.320
of flooding.
0:04:42.320,0:04:47.610
Across the 1-percent annual chance floodplain
extent there is a variety of flood depth.
0:04:47.610,0:04:52.510
The flood potential of each location within
the floodplain can be described with the gridded
0:04:52.510,0:04:54.610
datasets prepared.
0:04:54.610,0:04:59.110
With the information provided we can investigate
the different flood potential throughout the
0:04:59.110,0:05:02.420
flood extent described on the Flood Insurance
Rate Map.
0:05:02.420,0:05:07.190
Well, there is no way to predict when the
next flood will happen, or how severe it will
0:05:07.190,0:05:08.190
be.
0:05:08.190,0:05:12.560
However, engineers and scientists can use
statistical data (what has happened in the
0:05:12.560,0:05:17.820
past) to estimate the probability or chance
that floods of a certain size will occur in
0:05:17.820,0:05:18.940
the future.
0:05:18.940,0:05:23.760
The chance of a flood of a certain size occurring
and then re-occurring is like flipping a coin
0:05:23.760,0:05:24.900
or spinning a wheel.
0:05:24.900,0:05:30.280
Just because heads comes up on one try, doesn’t
mean the next try will come up tails.
0:05:30.280,0:05:35.720
The annual chance analysis grids delivered
to your community define the variable possibility
0:05:35.720,0:05:40.160
of flooding throughout the floodplain, highlighting
locations within a community that may be more
0:05:40.160,0:05:41.510
vulnerable to flooding.
0:05:41.510,0:05:46.020
Two probability grid datasets will be available
for the streams studied.
0:05:46.020,0:05:50.270
These datasets describe the probability of
flooding related to location and water/or
0:05:50.270,0:05:55.630
ground and finished floor elevations at any
location within the 1-percent annual chance
0:05:55.630,0:05:56.630
floodplain.
0:05:56.630,0:06:01.690
Here are three examples of homes that are
built at different locations along the stream.
0:06:01.690,0:06:05.860
- On the left side of the screen you can see
the ANNUAL chance of flooding depicted by
0:06:05.860,0:06:10.840
the Percent Annual Chance grid, which described
the possibility of flooding in each individual
0:06:10.840,0:06:14.790
year
- House C, which is not only closest to the
0:06:14.790,0:06:20.050
stream, but built directly on the ground elevation
is more likely to flood than the home at location
0:06:20.050,0:06:22.770
A.
- The probability of flooding at the location
0:06:22.770,0:06:25.060
of House C is 10%.
0:06:25.060,0:06:28.160
- This means that the chance of flooding EACH
year is 10%.
0:06:28.160,0:06:34.539
- While the chance of flooding at House A
is lower at 0.2% possibility EACH year
0:06:34.539,0:06:38.790
- Most home mortgages are signed for a 30
year period.
0:06:38.790,0:06:43.410
For that reason, we have also created the
Percent 30-Year Chance grid, that describes
0:06:43.410,0:06:47.070
the possibility of flooding during a 30 year
period.
0:06:47.070,0:06:50.890
The information on the right side of your
screen shows the probability of flooding across
0:06:50.890,0:06:54.000
30 years for these same home locations.
0:06:54.000,0:06:58.570
- House B is located at the edge of the 1-percent
annual chance floodplain.
0:06:58.570,0:07:02.530
- Each year there is a 1% chance that this
home would flood.
0:07:02.530,0:07:06.740
- When we review the possibility of flooding
over the 30 year mortgage term, the probability
0:07:06.740,0:07:12.410
of flooding is determined to be 26%
With this information local officials can
0:07:12.410,0:07:16.750
identify vulnerable areas throughout the community
and through their local hazard mitigation
0:07:16.750,0:07:21.970
plan, identify areas to employ mitigation
projects to reduce the long term risk of flooding
0:07:21.970,0:07:26.460
throughout the community.
0:07:26.460,0:07:29.800
As discussed previously:
Two gridded datasets will be available for
0:07:29.800,0:07:31.690
each stream studied.
0:07:31.690,0:07:35.750
They are delivered to local communities in
the Flood Risk Database at the Flood Risk
0:07:35.750,0:07:38.960
Review Meeting and the Resilience Meeting.
0:07:38.960,0:07:43.930
The data, if available, can also be downloaded
from FEMA’s Map Service Center.
0:07:43.930,0:07:47.440
- The Percent Annual Chance grid describes
the chance of flooding each year
0:07:47.440,0:07:54.090
- The Percent 30-YEAR Chance grid describes
the probability of flooding in a 30-year period
0:07:54.090,0:07:59.420
The visualization may be beneficial to communities
preparing the flood hazard profile in a Local
0:07:59.420,0:08:01.120
Hazard Mitigation Plan.
0:08:01.120,0:08:05.900
The information may be used to describe the
flood extent and/or the vulnerability of a
0:08:05.900,0:08:06.900
community.
0:08:06.900,0:08:10.870
It may also be of use to local community officials
to determine areas that are more susceptible
0:08:10.870,0:08:16.700
to flooding, or to prioritize areas of risk
communication efforts.
0:08:16.700,0:08:22.970
“Targeting Mitigation to High Risk Properties”
is just one of our “Recipe Cards” intended
0:08:22.970,0:08:27.150
to assist local officials in the use of the
data prepared as a part of the Flood Risk
0:08:27.150,0:08:28.230
Project.
0:08:28.230,0:08:33.050
The Recipe Cards are intended to promote better
understanding of areas within a community
0:08:33.050,0:08:38.000
that may benefit from mitigation planning,
floodplain management, emergency response
0:08:38.000,0:08:41.380
plans, and flood risk awareness communications.
0:08:41.380,0:08:47.060
• The next few slides describe in greater
detail the GIS steps needed to create a visualization
0:08:47.060,0:08:49.520
tool to describe depth of flooding.
0:08:49.520,0:08:53.380
• These instructions and screenshots for
this tutorial were developed using ESRI’s
0:08:53.380,0:08:54.380
ArcMap.
0:08:54.380,0:08:56.720
It is a part of the ArcGIS Package.
0:08:56.720,0:09:01.140
• In order to perform the analysis described
in the ArcMap Software you will also need
0:09:01.140,0:09:04.390
to have access to the Spatial Analyst Extension.
0:09:04.390,0:09:08.130
The steps defined in this presentation are
applicable in other software, however the
0:09:08.130,0:09:11.490
software tools used may utilize a different
naming convention.
0:09:11.490,0:09:15.640
• Pair your local spatial building data
with the Percent Annual Chance grid to determine
0:09:15.640,0:09:19.700
the probability of flooding to structures
in the vicinity of the 1-percent annual chance
0:09:19.700,0:09:21.090
floodplain.
0:09:21.090,0:09:25.770
• This analysis may assist community staff
in determining areas where structure acquisition
0:09:25.770,0:09:30.080
and elevation projects may be beneficial to
reduce the long term flood risk within the
0:09:30.080,0:09:31.790
community.
0:09:31.790,0:09:38.029
Let’s begin with loading the Data to ArcMap
or comparable software.
0:09:38.029,0:09:43.800
• Open the software and using the Add Data
tool add the Percent Annual Chance data.
0:09:43.800,0:09:48.420
• The Percent Annual Chance data will be
found in the Flood Risk Database.
0:09:48.420,0:09:54.870
• Load the file named PctAnnChance.
0:09:54.870,0:10:04.060
• Also load the Percent 30-year Chance data,
which will be named Pct30yrChance
0:10:04.060,0:10:10.670
At this time, also load the structure location
point file, building footprints, aerial image
0:10:10.670,0:10:15.230
or other reference layer to assist you in
the identification of structures located in
0:10:15.230,0:10:18.440
the vicinity of the 1-percent annual chance
floodplain.
0:10:18.440,0:10:25.260
• For this example, we will be using a structure
location point file.
0:10:25.260,0:10:29.200
To assist in better communicating the changes
that are being shown in the Percent Annual
0:10:29.200,0:10:34.500
Chance grid, it is suggested that the symbology
be modified after the data is loaded.
0:10:34.500,0:10:39.639
To change the symbology (the manner in which
a polygon appears in your window) begin with…
0:10:39.639,0:10:46.250
• Right-click on the Depth_01pct layer and
from the menu on the left of your screen,
0:10:46.250,0:10:50.500
select Properties ( at the bottom of the list)
from the selection list that appears.
0:10:50.500,0:10:55.190
• In the Layer Properties box that appears
on your screen, select the Symbology Tab (it’s
0:10:55.190,0:10:59.190
the final tab on the right hand side of the
Layer Properties window shown in the example).
0:10:59.190,0:11:02.240
• And In the left pane of the window, select
“Stretched”
0:11:02.240,0:11:06.900
• Stretch removes the “no data areas”
of any raster allowing the software to increase
0:11:06.900,0:11:12.170
the visual contrast of the data within the
display, resulting in a crisper image, making
0:11:12.170,0:11:14.769
some features easier to distinguish.
0:11:14.769,0:11:18.910
• In the middle of the Layer Properties
window, locate the Color Ramp and select a
0:11:18.910,0:11:21.760
color schema to assist your review of the
information.
0:11:21.760,0:11:26.290
• We have selected the color schema showing
Green to Red (from left to right) for this
0:11:26.290,0:11:29.670
example
• This color selection will display areas
0:11:29.670,0:11:34.990
with small percent chance of flooding as Green
and progress to Yellow (middle range percent
0:11:34.990,0:11:39.420
chance) and Red cells for the areas of greatest
probability of flooding.
0:11:39.420,0:11:42.690
• Click Apply, then OK to close the window
when you are done.
0:11:42.690,0:11:46.120
Repeat these steps for the Percent 30-Year
Chance grid.
0:11:46.120,0:11:50.250
It is suggested that you choose a different
Color Ramp in order to distinguish the difference
0:11:50.250,0:11:55.300
between the two grids shown in your data frame.
0:11:55.300,0:11:59.470
The range of values for the percent chance
will vary for each study due to differences
0:11:59.470,0:12:05.190
in stream alignment, channel geometry, flood
flow, development throughout the floodplain
0:12:05.190,0:12:06.870
and other variations.
0:12:06.870,0:12:11.800
In order to review a set range of probability
across the dataset, it is advisable to classify
0:12:11.800,0:12:16.529
the values for the color ramp to a select
set of values to better understand the information
0:12:16.529,0:12:17.920
in the dataset.
0:12:17.920,0:12:22.960
In order to focus on a range of flood probability,
we advise the following classification of
0:12:22.960,0:12:28.910
the grid data set:
- 0 to 0.2% flood chance (equivalent to areas
0:12:28.910,0:12:36.180
within an Unshaded Zone X)
- 0.2% to 1% flood chance (equivalent to areas
0:12:36.180,0:12:40.350
within a Shaded Zone X)
- 1% to 4%
0:12:40.350,0:12:45.260
- 4% to 10%
- 10% or greater (the items within this are
0:12:45.260,0:12:49.960
highly flood prone and may be reviewed for
elevation/acquisition projects)
0:12:49.960,0:12:53.440
In order to classify the Percent Annual Chance
Grid in this manner:
0:12:53.440,0:12:58.920
-Once again, right click on the PctAnnChance
layer and from the menu on the left side of
0:12:58.920,0:13:02.750
your screen, select Properties (at the bottom
of the list) from the selection list that
0:13:02.750,0:13:03.750
appears.
0:13:03.750,0:13:08.430
-In the Layer Properties box that appears
on your screen, select the Symbology tab (it’s
0:13:08.430,0:13:12.170
the final tab on the right side of the Layer
Properties window shown in the example).
0:13:12.170,0:13:15.350
-In the left pane of the window, select “classify.”
0:13:15.350,0:13:21.410
-In the right pane of the window, click the
“Classify” button.
0:13:21.410,0:13:25.720
- When the Classification window opens, the
classification method should automatically
0:13:25.720,0:13:31.600
default to Natural Breaks, if it is not, set
it to Natural Breaks.
0:13:31.600,0:13:36.250
- Then select the desired number of classes
from the Classes drop down menu, which in
0:13:36.250,0:13:38.230
this case is 5.
0:13:38.230,0:13:43.850
- Then, in the Break Values window , click
the first value and replace it with a zero
0:13:43.850,0:13:50.690
point two, click the second value and replace
it with a one, repeat this for the next two
0:13:50.690,0:13:53.660
values using a four and ten respectively.
0:13:53.660,0:14:00.630
The last value will remain unchanged as this
is the highest value found in the data set,
0:14:00.630,0:14:04.050
which in this particular example is also 10.
0:14:04.050,0:14:08.610
- You should notice that as you manually change
the break values, the classification method
0:14:08.610,0:14:12.410
in the upper left corner will automatically
set itself to Manual.
0:14:12.410,0:14:18.440
- Once you finish replacing the break values,
click the OK button to return to the Symbology
0:14:18.440,0:14:23.700
Tab
-Now that the break values have been manually
0:14:23.700,0:14:26.130
adjusted, you can set the color ramp.
0:14:26.130,0:14:30.630
As before, it is recommended to use the green
to red ramp so that lower values appear in
0:14:30.630,0:14:33.730
green and higher values appear in red.
0:14:33.730,0:14:38.090
You may want to repeat these steps to review
the Percent 30-year Chance grid with the following
0:14:38.090,0:14:41.620
value classification:
- 0 to 5%
0:14:41.620,0:14:48.710
- 5 to 10%
- 10-26% (structures with 26% or greater chance
0:14:48.710,0:14:54.480
are within the 1-percent annual chance floodplain)
- 26%-30%
0:14:54.480,0:14:59.050
- 30%-40%
- 40%-50% and lastly,
0:14:59.050,0:15:06.040
- 50% or greater
To complete the analysis shown in this presentation,
0:15:06.040,0:15:09.160
you will need to add or create a dataset of
structure points.
0:15:09.160,0:15:14.170
Here are some examples of data sources that
you can use to complete this analysis, and
0:15:14.170,0:15:17.040
how some other data sources could be used.
0:15:17.040,0:15:23.100
1 – Address Points – This data is usually
available through Emergency Response or community
0:15:23.100,0:15:25.070
E911.
0:15:25.070,0:15:29.170
Point files will need to be reviewed against
an aerial image to assure that the location
0:15:29.170,0:15:32.550
data points are placed at structure locations.
0:15:32.550,0:15:36.250
These data is likely the most accurate for
the analysis shown in this example.
0:15:36.250,0:15:41.240
You will need to determine whether the community
needs to remove points on garden sheds and
0:15:41.240,0:15:44.380
other auxillary buildings when reviewing the
analysis.
0:15:44.380,0:15:50.870
2 – Building Footprints or Parcel Data – This
data is usually available through Planning/Zoning
0:15:50.870,0:15:54.180
departments or the county/parish Tax Assessor.
0:15:54.180,0:15:58.150
Building footprints describe the perimeter
of structures and parcel data describes the
0:15:58.150,0:16:00.660
perimeter of property boundaries.
0:16:00.660,0:16:05.220
These polygons may be used to analyze average
flood depth within the building footprint
0:16:05.220,0:16:07.790
or on the property parcel.
0:16:07.790,0:16:12.720
Another way to use this information is to
convert the data from polygon to point data,
0:16:12.720,0:16:17.889
which is easily transformed using GIS tools
available in the ArcToolbox.
0:16:17.889,0:16:24.170
• In order to convert the polygons to points,
open ArcToolbox, clicking on the Toolbox icon
0:16:24.170,0:16:26.139
above the data frame.
0:16:26.139,0:16:31.930
• ArcToolbox Menu window options that appear,
click on plus sign next to Data Management
0:16:31.930,0:16:34.990
Tools to expand the menu.
0:16:34.990,0:16:40.680
• From the menu under Data Management Tools,
click on the plus sign next to Features.
0:16:40.680,0:16:46.180
• Under the Features menu - double right
click on the Feature to Point tool.
0:16:46.180,0:16:50.170
• This will allow you to input the polygon
layer, and define the name and location of
0:16:50.170,0:16:51.860
the Point Layer.
0:16:51.860,0:16:56.690
You may need to review the output point file
against an aerial image to verify the points
0:16:56.690,0:17:00.850
created are within the structures you are
interested in analyzing.
0:17:00.850,0:17:05.529
3 – Aerial Imagery
If you are unable to find a readily available
0:17:05.529,0:17:09.600
point file, you can create one using ArcGIS.
0:17:09.600,0:17:15.429
- Using the Add Data button, you can add basemap,
or use local imagery if your community has
0:17:15.429,0:17:16.529
it available.
0:17:16.529,0:17:22.610
- Next, create a point Shapefile in ArcCatalog
and save it to your local computer following
0:17:22.610,0:17:25.629
the prompts in the ArcCatalog window.
0:17:25.629,0:17:32.239
- Finally, add point features to your shapefile
in ArcMap by placing points on the center
0:17:32.239,0:17:36.669
of structures that fall within the floodplain
- It is advisable to add pertinent address
0:17:36.669,0:17:43.480