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San Diego Water Damage and Flood

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The Mississippi River acts as the drain for around 40 percent of the continental U.S. and portions of Ontario and Manitoba provinces in Canada. Ten years ago a confluence of events occurred that resulted in the most expensive flood in the history of the United States. It remains one of the greatest natural disasters to ever hit the U.S.1

This flood was soon dubbed “The Great Flood of 1993”. The factors leading up to this flood included two high pressure systems that blocked any movement of thunderstorms brought about by the collision of warm air moving north up from the gulf stream and a jet stream of cold, dry air moving south down from Canada. This caused sustained torrential rain to fall into the Mississippi Basin from May through the end of July. These rains came on top of the normal spring rains and runoff from snowmelt that already saturated the soil.2

In addition to these atmospheric conditions there were also several human causes that contributed to this great flooding event.3 Poorly built, poorly functioning federal levees created problems for the control and management of all the rivers that empty into the Mississippi Basin. During the same period the Flood Plain was being urbanized with many unsuitable areas receiving approval for development. This urbanization resulted in reduced infiltration rates and the St. Louis river was being channelized. Ordinarily channeling is used as a way to control and manage a river but with the sustained heavy rains, the channeling of the St. Louis river created greater flooding downstream because the water traveled down the wider channel faster.4

Hundreds of levees along the Mississippi and Missouri rivers failed back in 1993 causing the deaths of 50 people and damages between $15 and $20 billion dollars. To understand why the levees failed it is important to remember that the rains lasted from May through September causing major flooding all along North Dakota, South Dakota, Nebraska, Kansas, Minnesota, Iowa, Missouri, Wisconsin and Illinois leaving 75 towns “totally and completely under flood waters” according to Lee W. Larson, Chief of the Hydrologic Research Laboratory at NOAA’s National Weather Service. Some locations along the Mississippi River continually flooded for a period of six months.5

According to the National Weather Service 600 river forecast points exceeded flood stage simultaneously and almost 150 major rivers and tributaries were affected by the flooding. The areas flooded within the hydrographic basin totaled around 30,000 square miles.6

Destruction and Damage

The Great flood resulted in extensive damage and included hundreds of broken levees and 75 towns that were covered with flood waters, several of which were never rebuilt. There was extensive damage to agricultural lands with a 70% loss of crops. Over 12.7 million acres of corn and soybeans over nine Midwestern states were never harvested.7 Transportation systems experienced nearly $2 billion dollars of damage and lost revenues. Transportation was severely affected because many railroads, highways and airports are normally built on flat floodplain terrain that lies close to urban centers.8

Commercial barge traffic along the river was closed down for more than a month although the effects with delays and backups played havoc with river transportation well into November of 1993. Losses to the barge industry included $600 million in direct damage costs and $320 million in business losses.9

Railroads were hit with $241 million in damages and rerouting fees due to 800 miles of track being damaged or submerged under water for months as well as $169 million in lost revenue.10

Flooded highways and bridge approaches were a problem throughout the many affected states. Highway damages totaled $434 million while lost revenues were estimated at $150 million. 33 airports were also affected and experienced $5 million in damages. The Spirit of St. Louis airport was most heavily hit and accounted for $1.2 of the $5 million.11

Over 54,000 people had to be evacuated from flooded areas, some for more than 6 months and 50,000 homes were damaged or destroyed by the great flood.12

Wetlands and the Flood

Wetlands play an important role in mitigating floods. They often are filled and store floodwaters so that the effects of a flood on agricultural lands and residential areas are minimized. Unfortunately, wetlands have decreased and disappeared with these areas being converted or urbanized over the past two centuries. These wetlands include river flood plains and upland prairie potholes. Many of the prairie pothole wetlands are of the closed flow variety. They fill with rain and melting snow and then the waters slowly evaporate or drain through the ground water system. Normally, they provide a perfect retention basin during and after intensive rains because they do not normally add to stream flow runoff. In the flood of 1993 however, the rains were intense and prolonged. All of the wetlands storage capacity was exceeded and these areas began to add to the runoff.13

The effects of the flooding on the wetlands and environment varied over the short term as well as the long term. Prolonged exposure to flood waters over the 14-week flooding period to the hardwood forests and the backwater wetlands resulted in a lot of tree tip-overs, scoured out ground cover, island erosion, the destruction of emerging vegetation, damaged project dikes and destroyed most of the moist soil plants. Wildlife populations also suffered. Many bird species failed to reproduce due to flooded foraging areas, mussel populations were affected by the severe disturbances to the substrate and sedimentation movement and mammals showed a higher than average mortality rate on adjacent roads and railroad tracks because they were displaced from the flood plain. Fish that rely upon their sight to locate food were also affected by the increased haziness and sediment in the water.14

Water quality was also negatively affected by the large amounts of agricultural chemicals, sewage, livestock waste and industrial and household chemicals that ended up in the water supply.15

Not all of the effects on the wetlands were negative. The flooding brought about some short term benefits. The lower Missouri River flood plain shoed that both the extent and timing of the great flood provided both ideal temperatures and discharge cues for spawning river and floodplain fishes.16

Lessons Learned from the Great Flood

After the great flood there were many lessons to be learned. Perhaps one of the most important was the realization that some land needed to be surrendered back to the river rather than built up again. Cities are forcing residents back up into the bluffs away from the river and away from the flood plains. Newer, higher, better functioning levees have failed or destroyed and much more land has been set aside for conservation.17

A better understanding of river-floodplain ecology , river geomorphology and basin hydrology are by-products of the flood experience. Developing rapid-response plans to gather data to refine hydraulic models and confirm ecological theories has received strong consideration in light of this extreme flooding event.18

Policy changes have also come about as a result of this flood. One of the things that surfaced during the review were the numbers of agencies, relief organizations and programs, and building codes that developed in an uncoordinated fashion because of the many different local, state and federal agencies in charge of floodplain management. Requests to develop sounder policies for floodplain management resulted in the creation of the Interagency Floodplain Management review Committee in 1994. This committee evaluated the impacts of flooding from different policy perspectives including economic, environmental and social with a goal to develop coordinated, unified policies that reduce future risk and share the flood response burdens more equitably.19

Changes were made to disaster response assistance programs and establishing a protocol whereby all levels of the government, all businesses and all citizens understand they have a responsibility and stake in properly managing the floodplain. Anyone that supports any direct or indirect high risk behavior with regard to the management of the floodplains has to share in floodplain management and the costs to reduce that additional risk. The committee proposed a policy to support a floodplain management strategy that first and foremost:

  • Avoids the inappropriate use of the floodplain
  • Minimizes vulnerability to damage through both structural and nonstructural means
  • Mitigates flood damages when they do occur20


Despite the policy changes and recommendations that came about as a result of the great 1993 flood more recent events like the flooding of New Orleans, in the wake of Hurricane Katrina, it is clear that the implementation of these policies has been less than fully effective. Continuing concerns about global warming and climate change add to the urgency to educate and force people to respect nature, to respect floodplain boundaries and to be mindful of how we expand and build out cities and the effects of population on the environment. The time has come to take our floodplain and river management system seriously and implement strong, possibly unpopular policies that will allow for stronger, better flood mitigation. A study of the Great Flood of 1993came to much the same conclusionstating that "thoughtful past recommendations of how to attain flood mitigation have not been adequately implemented."21

Author: Robert Riggs

1 http://il.water.usgs.gov/pubs/fs2004-3024.pdf
2 http://www.sln.org.uk/geography/schools/blythebridge/GCSEMississippi.htm
3 http://www.sln.org.uk/geography/schools/blythebridge/GCSEMississippi.htm
4 http://www.bbc.co.uk/schools/gcsebitesize/geography/water_rivers/river_flooding_management_rev5.shtml
5 http://www.livescience.com/7508-history-repeats-great-flood-1993.html
6 http://en.wikipedia.org/wiki/Great_Flood_of_1993
7 http://www.umesc.usgs.gov/documents/reports/1999/status_and_trends/99t001_ch15lr.pdf
8 http://www.umesc.usgs.gov/documents/reports/1999/status_and_trends/99t001_ch15lr.pdf
9 http://www.umesc.usgs.gov/documents/reports/1999/status_and_trends/99t001_ch15lr.pdf
10 http://www.umesc.usgs.gov/documents/reports/1999/status_and_trends/99t001_ch15lr.pdf
11 http://www.umesc.usgs.gov/documents/reports/1999/status_and_trends/99t001_ch15lr.pdf
12 http://mo.water.usgs.gov/Reports/1993-Flood/
13 http://water.usgs.gov/nwsum/WSP2425/flood.html
14 http://water.usgs.gov/nwsum/WSP2425/flood.html
15 http://www.umesc.usgs.gov/documents/reports/1999/status_and_trends/99t001_ch15lr.pdfhttp://www.umesc.usgs.gov/documents/reports/1999/status_and_trends/99t001_ch15lr.pdf
16 http://water.usgs.gov/nwsum/WSP2425/flood.html
17 http://www.stltoday.com/news/local/metro/lessons-from-the-great-flood-some-defenses-strengthened-other-land/article_cabf7844-1042-556b-925e-f3defcab4a20.html
18 http://www.umesc.usgs.gov/documents/reports/1999/status_and_trends/99t001_ch15lr.pdf
19 http://www.umesc.usgs.gov/documents/reports/1999/status_and_trends/99t001_ch15lr.pdf
20 http://www.umesc.usgs.gov/documents/reports/1999/status_and_trends/99t001_ch15lr.pdf
21 S. Changnon, ed., The Great Flood of 1993: Causes, Impacts, and Responses, Westview Press, Boulder, CO

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