\<!\-\-\--\>\<!\-- Created by: Tracey Serpi and Paul Baumann \--\>\<!\--
Dept. of Geography, University of Maryland Baltimore County \--\>\<!\--
Title: mod2.html \--\>\<!\-- Description: Module 2 \-- Flood Analysis
\--\>\<!\-- Version Number: 1 \--\>\<!\-- Origin date: September 12,
1996 \--\>\<!\-- Last Updated: September 12, 1996 \--\>\<!\-- Notes:
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INTRODUCTION:

Large sections of the upper Mississippi River Basin experienced major
flooding during the summer of 1993. Many small communities and local
governments throughout the region were faced with providing immediate
assistance and emergency services to the flooded areas. In the flood\'s
aftermath these same governments were requested to help the flood
impacted areas to recover with aid from the state governments and
federal agencies. To receive aid, in many cases the government units
were required to delineate the amount of area flooded. This lesson
module outlines a simple approach, using satellite imagery and basic
mathematical logic, to identify the amount and location of the flooded
areas. Major floods occur every year throughout the world impacting
hundreds of communities. The approach presented in this module might
help those communities with respect to future floods as well as those
communities still dealing with the recovery problems associated with the
1993 Mississippi flood.

The purpose of this lesson module is to present a methodology to
determine the amount of area directly affected by floodwater. This
methodology employs change detection requiring a base image data set and
an image during the flood period. Both data set s are from Landsat TM
images and cover a study area of 512 by 512 pixels. They are
geocorrected creating twenty-five meter pixels. The base image depicts
conditions present on July 4, 1988 and the flood image shows the region
on July 19, 1993 during the height of the flood. Figure 1, which is a
false color image taken over St. Louis, Missouri on July 29, 1993 using
a special NASA airborne scanner, shows the study area of St. Charles and
the Missouri River. It also shows a portion of St. Louis and the
Mississippi and Illinois rivers at flood stage. All analysis was
accomplished with the inexpensive (e.g. U.S. \$150) PEDAGeOG
microcomputer-based image processing software package.

BACKGROUND:

MISSISSIPPI BASIN

The Mississippi basin, the largest river basin in the United States,
forms a wedge of 1,243,000 square miles (3,220,000 sq. km.) in the
center of the continent. As the Mississippi River system drains toward
the Gulf of Mexico, the basin narrows, centering on the state of
Louisiana. Although the basin stretches into the alpine pastures of the
Rocky Mountains and the wooded valleys of the Appalachians, it covers
mainly the rich grain belts of the Midwest and the Great Plains.
Thirty-one states and two Canadian provinces contribute water to the
Mississippi system.

The Mississippi River suffers from a mistaken nomenclature. The main
trunk of the river is created by the union of three great branches, one
of which is the upper Mississippi. This branch, from which the entire
system is named, is the smallest of the three branches. The Missouri
branch is longer and covers a much larger drainage basin, and the Ohio
branch is larger in both size and volume of water. The upper
Mississippi, which terminates at the juncture with the Missouri River,
drains 171,500 square miles (444,300 sq. km.). In contrast, the Missouri
basin covers approximately 530,000 square miles (1,373,000 sq. km.) and
the Ohio basin about 202,000 square miles (523,000 sq. km.). The Ohio,
with its many tributaries draining the ridges and valleys of the
Appalachian Mountains, has a basin in which rainfall is more than twice
that in the larger Missouri basin. The Ohio basin pours a greater volume
of water into the Mississippi system than either of the other two main
branches combined. Below the Ohio, the lower Mississippi gathers water
from several other smaller basins, namely the Arkansas and the Red
River.

The lower Mississippi meanders considerably and has a quite wide
floodplain, especially in comparison to the floodplains of the Missouri,
upper Mississippi, and Ohio. The river also becomes very wide, usually
ranging from 800 to 1,500 yards (730-1,370 meters), and deep with the
center of the channel varying between 50 and 100 feet (15-30 meters).

HISTORIC FLOODS

The Mississippi system has experienced several major floods within this
century. Until the 1993 flood, the 1927 flood was considered the
greatest inundation of the Mississippi within the last hundred years.
Over 700,000 people were forced to leave their homes; 246 people and
165,000 head of livestock drowned; and property damage exceeded \$364
million. In 1937, heavy rains drenched the lower Mississippi, creating a
lake nearly the size of Lake Superior in area. Several smaller floods in
the 1940s and 1950s plagued the basin and severe floods hit the upper
basin in 1965 and 1973. The 1993 flood was concentrated in the upper
Mississippi basin and the middle and lower sections of the Missouri
basin. The Ohio basin, which generally accounts for about 70 percent of
the total volume within the system, was not experiencing any major
flooding. The discharge from the Ohio basin was being controlled during
the flood period by holding water back in the numerous reservoirs on the
river and its tributaries. This action plus the much larger channel and
floodplain of the lower Mississippi reduced greatly any flooding in the
lower Mississippi valley.

Within the flooded area, the 1993 flood reached record levels. On the
upper Mississippi at Keokuk, Iowa, peak discharges exceeded
significantly the previous record discharges in 1973 and 1851 and went
well above the 100 year flood mark. At Boonville, Missouri, the 1993
peak discharge on the Missouri matched the 1844 flood and exceeded the
1951 and 1903 floods, all three of which were identified as 100 year or
greater floods. The discharge might have been higher than the estimated
1844 peak if it was not for a number of reservoirs within the upper and
middle Missouri basin holding water back. The upper Mississippi basin
does not have as large reservoirs as the Missouri. At St. Louis, where
the Missouri and upper Mississippi merge, the 1993 peak discharge was
above the 100 year flood mark, but below the 1844 level. Again, flood
control through dams held the 1993 flood discharge level down; these
dams and their large reservoirs did not exist in 1844.

WEATHER CONDITIONS

Throughout the flooded areas, precipitation levels for the seven month
period of January through July 1993 ranged one and one-half to two times
higher than the average for the same seven months during 1961-1990. A
persistent eastward-flowing jetstream extending from central Colorado to
northern Wisconsin created a weather-front convergence zone across the
upper Midwest. Moist, warm air originating over the Gulf of Mexico
collided along this jet stream with cooler air masses from central
Canada. The cool air, being heavier, forced the warm, wet air to rise,
and in the process, increased the air\'s relative humidity to the point
of producing precipitation. This pattern brought almost continuous
precipitation to the region throughout the spring and summer of 1993. In
addition, several major rainstorms occurred in mid-June and July. In
southern Minnesota and northern Iowa, 2 to 7 inches (5.08-17.78
centimeters) of rain fell on June 17-18. In central Iowa, 2 to 5 inches
(5.08-12.7 centimeters) came down during July 4-5, followed by another 2
15-16, 2 to 7 inches (5.08-17.78 centimeters) dropped over western
Minnesota and eastern North Dakota and on July 22-24, 2 to 13 inches
(5.08-33.02 centimeters) of rain fell across the area reaching from
Nebraska to Illinois. The combination of persistent rain over a seven
month period and major storms brought about the flood. Flood-control
reservoirs within the region were at or near capacity and the ground was
saturated.

In addition to the persistent and heavy rainfall, the region
experienced, especially during June, frequent storms with gusty winds
and quarter-size and larger hailstones. A large number of funnels and
tornadoes were spotted. The three month period of April, May, and June
in the Upper Mid West generally exhibits an even frequency of tornadoes.
Preliminary reports indicate only 11 tornadoes or funnels where sighted
during April within the region with another 12 in May. However, in June,
54 funnels or tornadoes were spotted, more than twice the number
recorded in the previous two months. Floods are often accompanied by
other severe weather conditions adding to the problems faced by people
residing in the flooded region.

HUMAN AND ECONOMIC IMPACTS

The human and economic impacts from a flood of this magnitude are
difficult to measure. The flood crested from five to sixteen feet above
flood stage. At Des Moines, Iowa, the Des Moines River reached 34.3 feet
(10.45 meters) on July 11, 11.3 feet (3.44 meters) above the official
flood level. On July 13, at Quincy, Illinois, the Mississippi peaked at
32.2 feet (9.81 meters), almost twice the flood level of 17 feet (5.18
meters). At St. Louis on August 1, the river topped 49 feet (14.93
meters), 6 feet above the previous highest recorded level and 16 feet
above the official flood level. At that time, 7.5 million gallons (28
million liters) of water flowed past the city\'s landmark Gateway Arch
every second, six times the normal amount for that time of the year. As
of July 19, at least 40,000 homes and businesses had been damaged or
destroyed and some 70,000 people were homeless. Some 40 blocks of
downtown Davenport were under water and nearly every river town between
St. Paul and St. Louis on the upper Mississippi experienced major
flooding which lasted for days. Ironically, these river communities,
surrounded by water, found themselves without drinking water as well as
without water for cleaning, cooking, and sanitation. Wells were
polluted, and septic and sewage systems backed up creating major health
problems. In Des Moines alone, a community of 250,000 people, 18 sewage
plants were breached by the flood, causing microbes to enter nearly 800
miles (1287 kilometers) of piping throughout the city. It took about a
month to disinfect the system once the water had receded. Streets and
buildings were laminated with a brown stew consisting of raw sewage,
industrial waste, and agricultural pesticides, an excellent growing
environment for bacteria.

Farming, the major economic activity throughout the region, was
especially hard hit since some of the best cropland is situated on the
floodplains. On August 9, near the end of the flood, the estimated cost
of flood damage had reached \$12 billion, \$8 billion of which had been
suffered by farmers. Also, on August 9, the U.S. Department of
Agriculture announced that an estimated 8 million acres (3.25 million
hectares) of farmland had been flooded and another 12 million acres
(4.88 million hectares) were too soaked to yield crops, a total area
greater in size than the entire state of South Carolina. Corn and
soybean yields were well below normal. By July 12, the U.S. Department
of Agriculture had cut its 1993 forecast of corn production by 7.6
percent and soybeans by 3.4 percent. Even though other sections of the
country made up some of the loss in the production of these crops, the
economic impact spread throughout the businesses within the region. All
of the activities which normally support and depend on farming were hard
hit. A tremendous amount of soil was washed away, and in 1994, many
farmers with floodplain fields faced the huge task of removing tons of
debris and reshaping the land in order to remove drainage problems
within fields. Some fields were not worth salvaging.

ST.CHARLES

The satellite imagery associated with this instructional activity
centers on the Missouri River as it flows by the community of St.
Charles and the northwestern portion of St. Louis. St. Charles is the
political seat of St. Charles County and is situated on some bluffs
about 100 feet (30.7 meters) above the Missouri River. In 1769, the
French established the first trading post in the region and named it
\"Les Petites Cotes\" or \"The Little Hills.\" It was later renamed St.
Charles and was incorporated as a city by the French in 1795. In 1803,
along with the other areas under the Louisiana Purchase, St. Charles
became part of the United States. When Missouri became a state, St.
Charles was the first state capital from 1821 to 1825. Throughout its
history, the city has been linked to the Missouri River, initially as a
shipping center of items being brought down the river, and more recently
as a fast growing suburban community requiring land transportation lines
across the river to St. Louis.

St. Charles County covers 586 square miles (1518 sq. km.) which includes
an eastward triangular shaped extension bordered on the north by the
Mississippi River and the south by the Missouri River. Figure 4, which
is a three-band composite image acquired by the Spaceborne Imaging
Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) on April 17, 1994,
onboard the space shuttle Endeavour, shows St Charles County outlined in
red. The eastern end of this extension is the point at which these two
large rivers merge, and this entire section of the county forms one
large floodplain. In fact, the township which covers this section is
appropriately named, River. The dark blue areas in Figure 4 represent
very flat surfaces such as floodplains; whereas, the brown areas
identify rough surfaces such as hills. According to the 1990 census, the
county had a population of 212,907 but River township which covers a
major portion of the county had a population of only 7,298. The city of
St. Charles with a population of 53,000 is the largest incorporated
community in the county and most of the larger communities are clustered
together on the highlands.

On the morning of July 16, 1993, two days before one of the satellite
images was taken, the flood waters poured over the top of an abandoned
railroad embankment being used as a levee just north of St. Charles and
linked the Missouri and Mississippi rivers to form a 20 mile long body
of water. Studying Figure 1 in conjunction with Figure 4 will show that
the flood waters on the Missouri River had spread out to cover a portion
of Boone township and adjacent areas across the river. At St. Charles,
the combination of bluffs on the north side of the river and levees on
the south side had created a narrow neck through which the flood waters
had to flow. Once beyond this neck, the waters had expanded again
covering large sections of River township and small portions of St.
Louis County. This entire flood water pattern is in the shape of an hour
glass and represents the classic problem associated with levee
construction. See the next section on floodplain management, especially
the portion on levees. As the water flows through the stem, it gets
higher and moves faster. It comes out of the stem moving at a very fast
speed, particularly in the main channel. The Missouri River, just
downstream from St. Charles, makes a ninety degree turn to the
southeast. The railroad embankment which formed a portion of the levee
on the north side of the river runs adjacent to the river and turns with
the river. Although it is not known why the railroad embankment
collapsed, the sequence of conditions just described could have placed
considerable pressure on the embankment, especially in the curved
section where the embankment was perpendicular to the water shooting out
of the stem. This flood has created a heated debate between
environmentalists and engineers as to the value of levees. The
Mississippi basin has over 7,000 miles (11479 kilometers) of levees. The
environmentalists want the flooding rivers to spread across their
natural floodplains and not be blocked; the engineers are under a great
amount of pressure to protect the property of those people living on or
near the floodplains, and levees are viewed as one way to accomplish
this task. In working through this lesson module consider the pros and
cons of trying to control a flood.

ANALYSIS:

In establishing an approach to determine the geographic extent and
location of the flooded area, this analysis is based on understanding
and employing the spectral characteristics of the various bands in the
Landsat data sets. Also, simple mathematical operations are applied
rather than using sophisticated statistical techniques which often
create problems for local government decision makers who are generally
not trained in the use of quantitative methods.

This mathematical approach deals with first identifying which image
bands relate best toward solving the environmental hazards problem and
secondly determining how mathematically to merge spectral bands into one
final image from which the needed information can be obtained. Starting
with the 1988 data set as the base year, the initial step was to find
one band which clearly separated water areas from land surfaces. The
visible bands, as often is the case, showed variation within water
bodies but did not provide sharp differentiation between water and other
surfaces. The three reflected infrared bands did detect water areas as
solid bodies with little reflective variation which is the normal
condition when working in the near and middle infrared portions of the
spectrum. Comparing these three bands to the St. Charles United States
Geological Survey 7.5 minute topographic map, band 4 related extremely
well to the water features displayed on the map. The map was originally
prepared in 1954 and photorevised in 1968 and 1974. Even though the U.S.
Midwest suffered through a severe drought during the 1988 summer, the
water level of the Missouri River and adjacent smaller water bodies
within the study area did not vary significantly between what was
indicated on the map and the band 4 image. The data ranges for bands 5
and 7, the other two infrared bands, were too clustered making it
difficult to separate water from a variety of other surfaces. Band 4 did
possess a problem in that its lower data values, which indicate water
areas, were also identifying the tops of commercial and industrial
buildings. This problem will be addressed later. In general band 4
represented the best spectral band for the base year image. Band 6, the
thermal band, was not considered due to its low spatial resolution.

Basically, for the same considerations used in choosing band 4 from the
1988 image, band 4 from the 1993 data set was the best in identifying
the flood conditions. To enhance both bands, they were stretched to make
full use of the absolute data range (0-255). The dynamic ranges for band
4, 1988 and band 4, 1993 were 12-200 and 15-173, respectively. Rather
than automatically using the minimum and maximum values associated with
the bJands to stretch the data, the bands\' histograms were examined to
select values that reduce the effect of the extreme conditions within
the data. The PEDAGeOG software provided the ability to display the
statistics and histograms for images. In this analysis the minimum and
maximum values used to stretch the data generally grouped the lower and
upper .05 percent of the dynamic data range at the lower and upper
levels of the absolute data range respectively. In other words, the
minimum and maximum values used for band 4, 1988 and band 4, 1993 were
14-140 and 22-141, respectively. These values were converted to 0 and
255 and all of the other band values in between were adjusted to the new
scale. Figure 5 demonstrates the difference between the regular bands
and the stretched bands. The stretched bands provide more visual detail.
In addition, the stretched bands are based on the same scale.

The two stretched images were added together and scaled between 0-255 to
produce a new image. Water had low reflectance values in both of the
stretched bands. By adding the permanent (river channels and ponds)
water surfaces as shown in the 1988 band to the same areas in the 1993
band, low values were generated which made it possible to separate the
permanent water areas from the flooded areas. The flooded areas in the
1993 band also had low reflectance values but when added to the high
values associated with the land condition in the 1988 band, the flooded
areas had higher values than the permanent water areas. The high land
reflectance values in both images created values higher than those
related to the permanent water or flooded areas. Figure 6 shows the
results of this mathematical process. The permanent water conditions
appear as very dark areas, the flooded surfaces as dark areas but not as
dark as the permanent water surfaces, and the areas not covered by water
as light surfaces.

This approach worked well except for certain commercial/industrial areas
which were being identified as permanent water or flooded areas in the
new image. This condition can be seen in the lower right corner of
Figure 6. To correct this problem a third band, band 7 of the 1993 data,
was added to the new image. An examination of this band, Figure 7, shows
little reflectance confusion between permanent water areas and
commercial/industrial areas. Like the other two bands, this band was
also stretched and then added to the combined images of the two band 4s.
Figure 8 is the final image scaled between values of 1 and 255. The
commercial/industrial areas materialized as bright surfaces and were not
confused with dark, wet surfaces.

A density slice of the Figure 8 image enabled a separation between
permanent water, flooded areas, and dry land surfaces. To determine the
density slice ranges for these three classes, a histogram for this image
was generated which showed three distinct clusters. The density slice
ranges were: 1-20 (permanent water), 21-100 (flooded areas), and 101-255
(dry land). The density slice function under PEDAGeOG allows an
investigator to create a classified image and provides a pixel count for
each class. Table 1 shows a numerical break down of the three classes.
Knowing the number of pixels associated with each class and the size of
a pixel (25m x 25m), it was possible to calculate the amount of area
covered under each class.

  ------------------------ --------------- ----------- -------------- ------------
  **Surface\               **Pixels^\*^\   **Acres**   **Hectares**   **KM^2^**
  **                       **                                         

  **Permanent Water**      **14578**       **2251**    **911**        **9.11**

  **Flooded Land**         **80813**       **12480**   **5050**       **50.50**

  **Dry Land**             **166753**      **25753**   **10422**      **104.22**
  ------------------------ --------------- ----------- -------------- ------------

Figure 9 is the classified image with permanent water as dark blue,
flooded land as light blue, and dry land as brown. The numerical values
associated with this image vary between 1 and 3, corresponding to the
three classes. This image can become a theme layer in a raster-based
geographic information system (GIS). An examination of the image
revealed dry land adjacent to the river in several areas. These areas
related to the one- to five-year flood plain which had been left unused
and had become covered by trees. Most likely, the satellite\'s scanner
was detecting the reflectance from the crowns of these trees and found
it hard to record the flood water under the trees. A natural
continuation of this lesson module would be to explore the use of other
bands for the purpose of separating these flooded areas from other dry
lands.

This mathematical approach was compared to the results from a principal
component test based on using 8 spectral bands (1,3,4, and 7 from the
1988 data set and 1,3,4, and 7 from the 1993 data set). The results from
the two approaches were almost identical with respect to geographic
location and amount of area covered by the three classes. However, few
people dealing with the problems created by a flood will have a
background to understand principal components; they are more likely to
comprehend the logic associated with the mathematical approach. As an
environmental hazard, annual flooding impacts hundreds of communities
throughout the world. For government relief efforts to be effective the
rapid location and extent of flooding must be determined. Through a
relatively simple digital image processing approach, with Landsat
thematic mapper data sets, the extent of flooding in the St. Charles,
Missouri area was effectively and accurately mapped. Such approaches
offer local communities opportunities for gathering such information in
a rapid and inexpensive manner.

MATERIALS AND REFERENCES:

1\. The two Landsat Thematic Mapper data sets used in this module are
available through the EOSAT Scholar Series. They can be acquired from
the Earth Observation Satellite Company, 4300 Forbes Boulevard, Lanham,
Maryland 20706, USA. (800) 344-9933. The two sets together are priced at
\$100.

2\. The software package employed on this project is entitled PEDAGeOG
(Pictures of Earth - Display and Analysis for GeOGraphy). PEDAGeOG and
user\'s manual is distributed by Eidetic Digital Imaging Ltd., 1210
Marin Park Drive, Brentwood Bay, B.C. V8M 1G7, Canada. Both a DOS and
Windows version are available. The software is simple to use and is
designed for high school and undergraduate students. A site license is
\$150.

3\. A teacher\'s manual based on the 1993 Mississippi Flood and the two
data sets used in this lesson module and the PEDAGeOG software are
available. The lessons presented in this manual are different from one
introduced in this module. The manual can be acquired from Eidetic
Digital Imaging Ltd., 1210 Marin Park Drive, Brentwood Bay, B.C. V8M
1G7, Canada for \$20 plus shipping costs.

4\. St. Charles, Missouri, United States Geological Survey 7.5 Minute
Topographic Quadrangle (Map) corresponds directly with the data sets in
area and clearly helps in identifying various physical and cultural
features.

5\. NOVA produced an excellent 60 minute video on the 1993 Flood,
entitled Flood! which covers St. Charles County and the various problems
produced by a flood. The video has some very nice oblique aerial images
of the flood and some GIS animation. It can be acquired from WGBH, 19
Gregory Drive, South Burlington, VT 05403, USA. (800) 255- 9424. The
price is \$19.95 plus shipping and tax.

6\. General References:

-   *\"Mississippi Rising,\"* Time, Vol. 142, No. 2, pp. 36-37, July 12,
    1993.

-   *\"A Season In Hell,\"* Time, Vol. 142, No. 3, pp. 22-25, July 19,
    1993.

-   *\"Flood, Sweat and Tears,\"* Time, Vol. 142, No. 4, pp. 22-33, July
    26, 1993.

-   *\"Showing No Mercy,\"* Time, Vol. 142, No. 5, pp. 34-36, Aug. 2,
    1993.

-   *\"A Broken Heartland,\"* Time, Vol. 142, No. 6, pp. 28-29, Aug. 9,
    1993.

-   *\"The \'Billion-Dollar Flood\' Keeps on Rolling Along,\"* Newsweek,
    Vol. 122, No. 3, pp. 22-23, July 19, 1993.

-   *\"Come Hell or High Water,\"* Newsweek, Vol. 122, No. 4, pp. 16-26,
    July 26, 1993.

-   *\"On the Disaster Dole,\"* Newsweek, Vol. 122, No. 5, pp. 24-25,
    Aug. 2, 1993.

-   *\"To the Emotional Rescus,\"* Newsweek, Vol. 122, No. 7, pp. 29,
    Aug. 16, 1993.

-   Alan Mairson, *\"The Great Flood of \'93,\"* National Geographic
    Magazine, Vol. 185, No. 1, pp. 42-81, January 1994.