V-1

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AREAS FLOODED, FLOOD DAMAGES, AND 

FLOOD DAMAGES PREVENTED

A. INTRODUCTION

The Mississippi River floods in April and May 2011 were among the largest and most damaging recorded along 

the US waterway in the past century with flows and stages that were comparable in magnitude to the major 

floods of 1927 and 1993. 

Large portions of the LMRV are subjected to significant loss and damage when the Mississippi River overflows 

its banks. During major floods, the region experiences flood damage (economic losses) to unprotected areas 

between the levees and backwater areas up the tributaries. These damages are associated with farmland, homes, 

businesses, personal property, roads, and bridges. Additionally, many people are left without shelter, utilities, 

and food and are inconvenienced by an interruption in daily activities and loss of income. The following section 

discusses flood damage impacts for the LMRV region in terms of population, number of structures impacted, 

agricultural acres flooded, flood damages, and flood damages prevented by the MR&T project.

The geographic extent for the MVD Post Flood Report includes the area encompassed by the maximum extent 

of without project flooding for the Mainline Mississippi River headwater and backwater flooding from the 

vicinity of Cairo, IL to the Gulf of Mexico, including the Atchafalaya River, as well as the maximum extent of 

without project flooding below Wappapello Dam. This maximum extent was delineated by completing a 

hydraulic model of the mainline Mississippi River and the area below Wappapello Dam using without - project 

flows and without levees to represent natural conditions. The resulting extent was used to establish a 

comprehensive and consistent geographic boundary on which a repeatable economic analysis could be 

performed. The economic analysis was performed to estimate the damages prevented by the MR&T system 

and its operation within the boundaries of the MVD during the 2011 Flood with the intent to:

(1) not include the Ohio River reservoirs as they are not officially part of the MR&T (recognize 

they have operation authority to support MR&T), these benefits are being computed by LRD and 

would be included in more comprehensive Greater Mississippi Basin System Performance 

Assessment . 

(2) include Wappapello Dam in the analysis as this project was authorized by the MR&T project 

and experienced historical flooding in the 2011 Flood. 

(3) not include the Yazoo tributary reservoirs because of the additional modeling effort and time 

required to capture local headwater flooding that had relatively no impacts or benefit to MR&T 

during this event.

The economic analyses utilized inundations generated from numerical hydraulic model output and other 

data to identify types and locations of properties impacted by the 2011 Flood and assess damages 

associated with these impacts. Three models, Hydrologic Engineering Center’s River Analysis System 

(HEC-RAS) Program, the Flood Event Simulation Model (FESM), and Hydrologic Engineering Center’s 

Flood Impact Analysis (HEC-FIA) Program were utilized in the evaluations. The models were used to 

generate predicted inundation boundaries for three scenarios to compare to the actual inundation area 

associated with the 2011 Flood. The actual 2011 Flood (Model Scenario 1) and the three other modeled 

scenarios are defined in Section V.B.
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Two major categories of damages were evaluated based on the availability of flood damage 

information captured from the flood event. These included flood damages to urban properties, or 

structures and flood damages to agricultural properties, including crops. It is worth noting that flood

impacts occurred to other damage categories, such as roads, bridges, infrastructure, navigation, etc., 

but, due to time constraints and the availability of information and feedback, these damages are not 

included in this evaluation. For similar reasons, a comprehensive scenario-based analysis was not 

done for impacts to the environment. This section later addresses the damages to the environment due 

to the 2011 Flood as it occurred.

B. MODEL SCENARIO ANALYSIS METHOD

The four scenarios were modeled to allow comparison of actual damage estimates (based on the existing 

conditions) with damages estimates based on what would have occurred if some FRM features were not 

present or utilized.

• Scenario 1 (Existing) - the existing 2011 scenario as it occurred during the 2011 Flood event 

(i.e., with levees and flood control reservoirs in place, including deviations to reservoirs’ 

Operation Plans). 

HEC-RAS was used to model this scenario because most flooding is within the levees; 

therefore, the assumption that the majority of the flow is downstream is accurate and can be 

captured with a 1D model. The flooding that is not within the levees is backwater flooding at 

major tributaries which can be accurately modeled with tributary reaches and storage areas 

within the HEC-RAS program. 

• Scenario 2 (No Levees and Cutoffs) - the scenario with no levees, but with flood control 

reservoirs (i.e. without levees and associated cutoffs but assuming all reservoirs are in place).

Between 1932 and 1942, the Mississippi River Commission executed 15 artificial cutoffs, or 

newer and shorter channels in the river that cut across bends in its course, to improve the 

carrying capacity of the channel and lower the project flood flow line. These artificial cutoffs 

reduced the length of the river by nearly 170 miles.

Because of the large amount of levees along the Mississippi River, any scenario without 

levees would have a large spreading type inundation that cannot be accurately modeled with 

HEC-RAS. This scenario was modeled using a simplified method developed and used by the 

MVD to analyze benefits of levees, cutoffs, and floodways (i.e., pre-MR&T conditions). This 

method uses stage and flow information collected in 1912; therefore this method reflects river 

conditions that existed before the MR&T project was constructed. While some local levees 

did exist prior to the MR&T project, they were generally lower and had a smaller crosssection and would have certainly been overtopped by the 2011 Flood. By using this 

information, an accurate estimate can be made of the 2011 river stages if levees were not 

present. From the calculated stages, inundation extents and depth grids were produced by 

MVK’s Flood Event Simulation Model. This model is a tool widely used by MVK to produce 

flood extents from forecasted stages. This simplified method was chosen because of its wide 

use within MVD and the time frame in which the method could be completed. If the schedule 

would have allowed for it, this scenario would have been also modeled with FLO-2D. If the 

modeling effort with FLO-2D was acceptable, the results from the simplified method could be 

verified and, if necessary, refined. 
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• Scenario 3 (No Levees, Cutoffs, and Reservoirs) - the scenario with no levees and no federal 

flood control reservoirs. A modification of the MVD simplified method was used to complete 

this scenario. The flows developed for a No Reservoirs scenario were utilized, which includes 

no Federal reservoirs on the Missouri and Ohio River basins. The same justification for using 

the simplified method is applicable for this scenario. 

• Scenario 4 (No Deviations/Directives) - the existing 2011 scenario without deviations or 

directives to flood control reservoirs’ Operation Plans Discharges without deviations at Corps 

reservoirs were calculated from the Water Control Section from each District. These 

discharges will replace the existing conditions discharges, and will be routed through the same 

HEC-RAS models created for the Existing scenario. For this scenario, an assumption was 

made that overtopping of levees would not occur; therefore, the assumption that the majority 

of the flow is downstream is accurate and can be captured with a 1D model. The only 

flooding not within the levees is backwater flooding at major tributaries, which can be 

accurately modeled with tributary reaches and storage areas within RAS.

In addition to the four scenarios above, two other scenarios, No Floodways and No Reservoirs, were 

initially included as part of the modeling effort to determine damages prevented by each of the system

components. However, due to the short timeframe to complete modeling, these two scenarios were 

not analyzed for this Report. However, they may be included in the Greater Mississippi Basin PostFlood Assessment effort being conducted by HQUSACE.

1. Model Inputs and Assumptions. The UMR contributes flow into the MR&T system that must be 

included in model study efforts. The upper boundary of the MR&T model on the Mississippi River is at the 

Chester, Illinois gage site (river mile 109.9 above the mouth of the Ohio River). The drainage area of the 

Mississippi River at Chester is 708,563 square miles. The six Corps offices providing Water Management 

within this watershed are Omaha District; Northwest Division-Omaha; Kansas City District; St. Paul 

District; Rock Island District; and St. Louis District. The first three offices provide Water Management for 

the Missouri River and tributaries while the latter three support the Mississippi River and tributaries.

2. Analysis, Data Quality, and Uncertainty. When performing the modeling for the four scenarios, it 

is important to note that two different modeling methods—HEC-RAS and FESM—were used. The HECRAS modeling produced inundation depth grids that were mainly inside levees, floodways, or natural 

backwater areas. Flows were readily available on all major rivers and tributaries; as a result, water surface 

elevations were produced at numerous points throughout the study area and used to produce the inundation 

depth grid. The FESM model produced inundation depth grids over very wide flood plains using a limited 

number of data points to produce the inundation. The methodology used to calculate the water surface 

elevations for the scenarios that utilized the FESM model is described in the following paragraphs. A more 

detailed description of the methodology used in Scenarios 2 and 3 can be found in Appendix G, Economics.

Due to the two different modeling approaches and extrapolation of existing flows for a scenario based on a 

set of curves, some uncertainty exists in the modeling results; however, the documented and scientific 

approach used to calculate the water surface elevations for the various scenarios does produce output that 

can be used to compare damages and damages prevented.

3. Modeling Environment. The hydraulic modeling of the scenarios was completed using either 

HEC-RAS, a one-dimensional numerical model, or FESM. HEC-RAS is a very common numerical model 

applied widely across the Corps. However, FESM is a flood inundation model designed to replace the 

FEAT Model used by the Corps. The required inputs to the model are the topography in which the 
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simulation will take place in the form of a georeferenced DEM, the path information of river channels, 

optional path information of sub channels connecting to the main simulation channels, and water elevation 

information for known points along the simulation channels. FESM differs from most flood inundation 

models in that it does not considerer either flow or friction, and as a result does not need information about 

these conditions. Another key difference is that FESM does not directly implement either the Naiver Stocks 

equations, the de Saint Venant equations (Shallow Water equations), or any obvious approximation, of these 

equations (any attempt to create a water surface is at some level an approximation of the de Saint Venant 

equations). Water elevations in channel are determined by the input data and linear interpolation along 

channels paths if the resolution of the simulation grid is smaller than the spacing between known water 

elevation points. Lateral propagation of water elevation is done by selecting grid locations adjacent to the 

expanding flood surface, and determining which adjacent locations are potential sources of inundation. The 

resulting water level and a grid location depend on the water levels of such sources modified by slope rules.

4. Flood Damages Analysis. The HEC-FIA model is the tool used in this investigation to evaluate 

flood damages. The HEC-FIA model provides the capability to estimate the impacts associated with flood 

events and the benefits attributed to flood risk reduction projects. The HEC-FIA is designed to assess 

disaster impacts after a flood using geo-referenced data grids with inundation, terrain, agricultural, and 

structural data. The HEC-FIA estimates the area inundated, number of structures inundated, structure 

damage, agricultural flood damage, and project benefits. The HEC-FIA also has the functionality to 

estimate life loss during a flooding event; however, life loss will not be addressed in this report. 

In FIA, the structure inventory used to calculate structure damages and project benefits can be generated 

from a HAZUS database, a shapefile, or can be manually entered from an existing source. HAZUS, the 

chosen source of structure inventories for this report, is a collection of models and databases, including an 

estimation of the general housing stock, developed by FEMA for estimating the impacts from natural 

disasters. Crop coverage used to estimate agricultural damages can be generated from the National 

Agricultural Statistics Service Cropland Data Layer (NASS CDL), a shapefile, or the HAZUS. The NASS 

CDL, the source of crop coverage for this report, is a geospatial crop-specific digital data layer used in GIS 

applications provided by the National Agricultural Statistics Service of the United States Department of 

Agriculture. 

C. MODEL RESULTS 

Figures V-1 through V-4 illustrate the inundation areas associated with each of the hydraulic numerical 

modeling scenarios described above. Additional details are provided in Appendix G, Economics.

Based on the model outputs alone, it is clear that the MR&T System prevents major damages over a 

widespread area. Furthermore, when coupling the without levees scenario along with no reservoirs, as 

expected, even more inundation and subsequently damages would be produced. The ‘reservoir without 

deviations’ scenario showed some increase in stages in the upper portion of the MR&T system, but those 

effects diminish as the floodwave progresses downstream.
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Figure V-1. Scenario 1: 2011 Existing Conditions
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Figure V-2. Scenario 2: 2011 Without Levees and Cutoffs
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Figure V-3. Scenario 3: 2011 Without Levees, Cutoffs, and Reservoirs
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Figure V-4. Scenario 4: 2011 Existing Conditions Without Reservoir Deviations
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D. AREAS INUNDATED

Flood damage impacts from the 2011 Flood were determined to impact 119 counties in portions of seven 

states along the lower Mississippi River—Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri, 

and Tennessee. These included areas in five US Army Corps of Engineer Districts in the lower MVD—

SWL, MVM, MVN, MVS and MVK. Two other districts had potential impacts, LRN and LRL. Population 

estimates for the 119 counties in these states totaled approximately 6.3 million in 2010, according to the US

Census Bureau statistics. Based on results of HEC-FIA, 43,358 people were impacted by the 2011 Flood 

was. HEC-FIA results account for the exact delineated boundary of the flood, whereas Census estimates 

account for the entire land area of each impacted county. Census data also includes metropolitan areas 

which are typically protected from catastrophic flooding from the Mississippi River.

Population impacts by Corps District are presented in table V-1 for the four hydrologic scenarios. Without 

the MR&T Project in place (i.e., Scenario 3), an estimated 3.6 million people (3,638,005) would be impacted 

by the 2011 Flood event. This compares to the 43,358 people impacted during 2011 Flood event (Scenario 

1). In other words, approximately 3,594,647 people were saved from flood impacts with the MR&T Project 

in place. Without the MR&T Project in place (i.e., Scenario 3), MVN would comprise about 72 percent of 

the population impacted, followed by MVK with 19 percent and MVM, 9 percent. 

Table V-1. Population Impacted by Scenario and District

District Scenario 1 Scenario 2 Scenario 3 Scenario 4

SWL 79 3,636 4,041 79 

MVM 19,348 312,410 346,253 19,348 

MVN 18,281 2,191,303 2,591,972 18,281 

MVS 0 0 0 0 

MVK 5,650 618,741 695,739 5,650 

Total Area 43,358 3,126,091 3,638,005 43,358 

Source: HEC-FIA output

E. FLOOD DAMAGES

1. Economic Damages. Surveys conducted during and after the 2011 Flood provided a fair insight into 

the types and number of properties impacted. Discussed below and in greater detail in the Economic 

Appendix, the two largest categories of flood damage occurred to urban structural and agricultural 

properties.

a. Damages to Urban Structures. The HEC-FIA software was used to generate a structure 

inventory for the area inundated downstream of the project during failure and non-failure flood events. US 

Census data at the census block level and other information from the FEMA Hazard US database (HAZUSMH) were utilized by HEC-FIA to create the structure inventory. The structures in each census block were 

evenly distributed over the urbanized area within the block. The urbanized areas were extracted from the 

2001 National Land Cover dataset. Structure elevations were based on an elevation grid from the USGS

with a ten meter grid size. The inventory created by HEC-FIA was compared with aerial imagery and is 

considered to be representative of the study area. HAZUS-MH data contains numbers of structures by 

occupancy type. Some structure characteristics and values are based on regional averages and other 

assumptions that cause uncertainties in input variables of the damage estimation process.
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HEC-FIA was also used for this study in the estimation of damages to property. In the computation of 

property damages, HEC-FIA assigns each structure a structure point or HAZUS node, a ground elevation 

based on its location on a digital terrain model. Flooding is computed from depth grids for each failure 

mode or flood event. Vehicle damages were also calculated using the HAZUS dataset. HAZUS provides 

estimated day and night vehicle counts and values for both new and used light trucks, heavy trucks, and cars. 

As with the structure inventory, this data is provided for every census block. The vehicle counts are totaled

for every vehicle type and evenly distributed by the HEC-FIA program between every structure in a census 

block. Estimates of the number of inundated structures, the degree of inundation, and the associated dollar 

damages, provide a profile of the system-wide impacts associated with a given scenario. While the 

aggregate system-wide estimates are constructed from estimates at the level of the individual structure, 

definitive attribution of a specific result to an individual structure in the form of inundation, depth of 

inundation, or dollar damage is not appropriate.

A more detailed discussion on the parameters and calculation of structural damages is presented in the 

Economic Appendix (Appendix G, Economics).

b. Number of Structures Flooded. Based on HEC-FIA output, the total number of structures 

affected for the existing 2011 Flood event, as it occurred during the flood (i.e., Scenario 1), resulted in 

21,203 structures. This included urban and rural residential, commercial, industrial, and public structures. 

For the same scenario, an estimated 43,358 people were impacted. 

The number of structures flooded by Corps District is presented in table V-2 for the four hydrologic 

scenarios. Without the MR&T Project in place (i.e., Scenario 3), an estimated 1.45 million structures 

(1,459,234) would be impacted by the 2011 Flood event. This compares to the 21,203 structures flooded 

during 2011 Flood event (Scenario 1). In other words, approximately 1,438,031 structures were prevented 

from flooding with the MR&T Project in place. The MVN contains 68 percent of the structures flooded 

without the MR&T Project in place (i.e., Scenario 3), followed by MVK with 19 percent and MVM with 12 

percent. 

c. Agricultural Damages. Agriculture flood damages were evaluated for the 2011 Flood based 

on the four different hydrologic scenarios, previously defined, for the five Corps Districts determined to 

potentially be impacted by the flood — SWL, MVM, MVN, MVS and MVK. To develop the database of 

agricultural acres impacted, state crop data layers were provided by the National Agriculture Statistics 

Service (NASS) based on the 2010 crop layer. Inundation shape files were reclassified against the land 

layers in ArcGIS to estimate the total acres of agriculture land impacted. Table V-3 provides the results for 

the reclassification for each scenario. The existing conditions (Scenario 1, existing MR&T Project as 

occurred during the 2011 Flood) proved to yield the least amount of land impacted, 1.23 million cleared 

acres compared to the other scenarios. As expected, Scenario 3 (no levees, no reservoirs) showed the largest 

total of land inundation (10.2 million acres) when evaluated against the other scenarios. 
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Table V-2. Number of Structures Flooded By Scenario and District

Scenario 1 Scenario 2 Scenario 3 Scenario 4

With MR&T Project

(as occurred in 2011 event, 

minor deviations to reservoirs)

Without MR&T Project

(no levees or cutoffs 

but w/ reservoirs)

Without MR&T Project

(no levees, cutoffs or reservoirs)

With MR&T Project

(as occurred in 2011 event, 

with no deviations to reservoirs)

SWL 70 3,171 3,507 70 

MVM 9,747 155,682 172,130 9,747 

MVN 6,799 849,826 999,238 6,799 

MVS 1 0 0 0 0 

MVK 4,587 253,667 284,359 4,587 

Total 21,203 1,262,346 1,459,234 21,203 

Source: HEC-FIA output

1 No site specific survey data on individual structures was available, thus it was difficult to determine damages in these areas with any degree of accuracy. Based on FEMA information,

some structures did receive flood damages during the 2011 Flood event but no damage estimates were available.

Table V-3. Total Agriculture Acres Impacted by Scenario and District

Scenario 1 Scenario 2 Scenario 3 Scenario 4

With MR&T Project

(as occurred in 2011 event, 

minor deviations to reservoirs)

Without MR&T Project

(no levees or cutoffs 

but w/ reservoirs)

Without MR&T Project

(no levees, cutoffs or reservoirs)

With MR&T Project

(as occurred in 2011 event, 

with no deviations to reservoirs)

SWL 34,800 210,500 212,200 34,800 

MVM 620,000 2,696,900 2,707,940 620,000 

MVN 52,300 1,295,500 1,310,900 52,300

MVS 92,500 675,500 681,860 92,500

MVK 433,500 5,295,200 5,322,800 433,500

Total Area 1,233,100 10,173,600 10,235,700 1,233,100 

Source: NASS and ArcGIS.

Values indicated are estimated areas of inundation calculated using hydraulic numerical modeling that required assumptions and simplifications.
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d. Crop Data. For this study damages were calculated for the following crops: corn, winter wheat, 

soybeans, grain sorghum, cotton, rice, and sugarcane. These crops constitute the majority of production in 

the impacted area. Crop budgets used to determine production costs and potential net income from lands in 

production were taken from budgets prepared by Mississippi State University’s Agriculture Extension 

Service. Crop prices were based on current market prices available in May 2012. Crop yield data was 

obtained from agronomy experts with Louisiana State and Mississippi State University Extension Services. 

Damage to farms was evaluated based on three broad categories; production losses, net returns losses, and 

non-crop damages. All monetary damages were indexed to 2012 dollars. 

e. Crop Loss Assumptions. Due to extended duration of the flood of 2011, it was assumed that 

replanting following the flood was not possible. After the flood started in April, it was assumed that no 

production costs were expended by farmers. Detailed explanations of the processes utilized to compute 

agricultural damages are provided in the economic appendix section of the document.

f. Total Economic Damages. The levees along the Mississippi River protect one of the most 

productive agricultural areas in the world, in addition to many other developments which have occurred over 

the years. Total flood damage estimates are presented by District in tables V-1, V-2, and V-3 for the four 

hydrologic scenarios and can be found in Appendix G, Economics. Total flood damage estimates from the 

2011 Flood, with all current operational features of the MR&T project in place (Scenario 4), totaled over 

$2.8 billion in urban and agricultural damages. Without a FRM system in place, total flood damages were 

estimated to exceed $237 billion (Scenario 3). This amounts to $234 billion in savings with the System in 

place. Total flood damages for Scenarios 2 and 1 were estimated at $225 billion and $2.8 billion, 

respectively. 

Flood damages of these sizes would almost certainly be accompanied by the threat of loss of life and 

would devastate millions of acres of farmland, numerous communities, homes, and businesses, and 

disrupt associated infrastructure. The possibility of a flood of this magnitude would be catastrophic to 

the economy of the region and repercussions would be felt throughout the entire US economy. 

• Scenario 1 - Flood Damages. Urban flood damages comprise 76 percent of the total 

flood damages for Scenario 1—the condition as it occurred during the 2011 event. The 

damages are distributed between in MVN, MVK and MVM (38, 21 and 37 percent, 

respectively). 

• Scenario 2 - Flood Damages. With no MR&T levees or cutoffs, but with reservoirs, 

urban flood damages would consist of 97 percent of the total flood damages. For this 

scenario, the majority of the total damages would take place in MVN (74 percent), 

followed by MVK and MVM, with 17 and 8 percent, respectively.

• Scenario 3 - Flood Damages. Without the MR&T Project, urban flood damages would 

account for 98 percent of the total flood damages. The majority of the total damages 

would happen in MVN (74 percent), followed by MVK (17 percent) and MVM (8 

percent).

• Scenario 4 - Flood Damages. For Scenario 4—with the MR&T in place, as it was 

designed—urban flood damages comprise 76 percent of the total flood damages. The 

total damages are distributed between in MVN and MVM (37 and 38 percent, 

respectively) with MVK comprising 21 percent.
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g. Damages to the MR&T System. The MR&T System consists of levees, drainage 

structures, pumping plants, channel improvement features, and various other structures. These levee 

systems are shown in Appendix G, Economics. The Immediate Risk Reduction Measures include needs 

of the MR&T System that were defined as Classification 1 projects in accordance with the Hot Spot 

Project FRAGO. These projects remediate issues identified during the 2011 event that are likely to 

cause failure prior to a 25-year flood event. The Long Term needs of the MR&T System are defined 

as Classification 2 and 3 projects in accordance with the FRAGO. These projects remediate issues 

identified during the 2011 event that range from unlikely to likely chance of failure due to a 25-year 

flood event. Further information on damages to MR&T features can be found in Section VI. C. 

Damage and Repair Needs which provides a detailed explanation and results of the MR&T damage 

assessment conducted by Corps staff.

In addition to levee structures and their features, the Channel Improvement community has identified 

approximately 240 MR&T channel improvement sites that sustained damage to revetment and/or dikes 

during the 2011 Flood on the Mississippi and Atchafalaya Rivers, 44 of which could have an impact on 

system performance if not repaired. Some of the most significant include Cache-Cairo, Third District, Chute 

of Island 8, Merriwether-Cherokee, President’s Island, and Walnut Point/Kentucky Bend. A brief discussion 

of the each of these can be found in Appendix G, Economics. Typical damage is shown in photographs V-1 

through V-4.

 Photograph V-1. Typical Damage to a Dike Photograph V-2. Typical Damage to Revetment
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 Photograph V-3. Location of Critical Scour Photograph V-4. Example of Overbank Scour

2. Environmental Damages. During the 2011 Mississippi River flood, large reaches of river channel 

and floodplain experienced high rates of soil/sediment erosion and deposition along with vegetation loss. 

While these are processes associated with natural river behavior, anthropogenic development has led to an 

intensification or spatial redistribution of the flooding impacts. For example, many of the major observed 

environmental impacts occurred in the three large engineered spillway or floodway areas that were activated 

during the flood: the BPNM Floodway, the Morganza Floodway, and the Bonnet Carré Spillway. Most 

damage resulted from the force of the initial flood wave as the spillway gates were opened, and the 

prolonged inundation of the spillway area. Further environmental effects occurred as the large volumes of 

river water were introduced into coastal estuary locations, which only receive large influxes of fresh water 

on a periodic basis. 

a. Terrestrial Resources

i. Land Resources. During the flood of 2011, the increased river stage caused the rerouting of 

relatively high velocity flow over many channel bars, islands, and point bars. In the past, the Corps 

recommended a minimum ‘tree screen’ of 300 feet perpendicular to the channel bank to inhibit the passage 

of strong river currents over inundated floodplain areas during floods. Many reaches of the river lack even 

this screen, and field evidence suggests that such scour damage is more likely with the lack of a tree screen. 

For example, sites such as the Merriwether-Cherokee Revetment site in Lake County, TN and President’s 

Island in Shelby County, TN (photographs V-5 and V-6 and figureV-5) experienced severe damage that 

may have been avoided if tree screens were present. Future implementation of tree screens or their 

beneficial functions should be considered with regard to local bank heights, overbank flow patterns, soil 

types, and vegetation types to enhance their resiliency and effectiveness. The Thompson Bend Riparian 

Corridor project, located near the confluence of the Ohio and Mississippi Rivers, has successfully 

incorporated similar concepts to limit erosion and scour

(http://mvs-wc.mvs.usace.army.mil/thompson/projectdescription.htm ).
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Photograph V-5. Aerial View of Merriwether-Cherokee Revetment Site in Lake County, TN

The photo on the left shows the area before the flood of 2011. Note the narrow band of trees along portions of 

the Mississippi River bank. The photo on the right is an aerial view of the same revetment site during the flood 

of 2011. Flow moved across areas with little riparian buffer/tree screen. Improved tree screens may have 

reduced erosion and flow velocities sufficiently to reduce the damage in the area.
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Photograph V-6. Damage Caused by Overbank Flow at Presidents Island

Figure V-5. Annotated Aerial View of the Flow Path of River Water Over President’s Island,

Shelby County, TN. The flow velocity may have been reduced if a tree screen 

had been properly installed along the upstream bank of the island.

The introduction of floodwater into the spillway areas caused some mortality to local vegetation. However, 

the spatial extent of this damage relative to the full vegetated extent in the flooded areas is small, and it is not 

expected to persist for more than a couple of years. Most terrestrial damage was due to soil scour and the 

deposition of substantial amounts of sediment along some locations of the floodplain and spillway 

topographical surface.

While the spillways were engineered for occasional inundation, many contained recreational (e.g., picnic 

areas, hiking paths, boat launches, and boardwalks) and civil (e.g., roads, culverts, and fences) infrastructure 

that was damaged by the floodwater during spillway operation. A number of recreational sites have been 

established within the greater spillway areas or in areas affected by their operation. These sites include 

approximately 1,093 acres below the BPNM Floodway (e.g., Towosahgy State Park and Big Oak Tree State 

Park), over 200,000 acres below the Morganza Water Control Structure (e.g. The Atchafalaya Delta Wildlife 
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V-17

Management Area), and 10 acres below the Bonnet Carré Spillway (e.g. St. Charles Parish Boat Launch and 

Recreation Area). Large-scale damage to these areas was not reported; however, most of these areas 

experienced closure or reduced access during and after the flood period. The river discharge introduced to 

the spillways during their activation did enhance certain recreational activities during and following the flood 

period, including fishing and crawfish trapping. 

ii. Wildlife Resources. When floodwater enters areas unaccustomed to inundation, terrestrial 

animals flee the area without established escape routes. These fleeing animals run the risk of becoming 

stranded in areas incapable of supporting their subsistence over the duration of the flood. In general, largescale flooding promotes crowding or isolating wildlife populations in unflooded regions and may degrade 

wildlife forage areas until the ecosystem and regional food chains can become re-established. Grounddwelling animals such as turkey, deer, rabbits, armadillos, feral hogs, and bobcats typically attempt to flee 

floodwaters while tree-dwelling or semi-aquatic animals often find shelter in trees or slackwater areas with 

emergent vegetation (photograph V-7).

Photograph V-7. Armadillos Seeking Refuge From Floodwaters

Under non-flash flood, natural flood conditions typical to BLHFs, floodwater rises on the order of inches per 

day. Under these conditions, animals have the ability to identify the flood risk over time and evacuate to 

higher ground. While some effort was made to slowly release water into the spillways to minimize its 

environmental impact, floodwater depths occasionally increased on the order of feet per day, which resulted 

in observed animal fatalities in a few locations. 

Deer fleeing the Morganza Floodway floodwaters were forced to inhabit narrow strips of high ground 

around levees, emergent trees, and surrounding agricultural fields during the spillway operation (photograph 

V-8). However, the period of time in which the water control structure was opened was generally not long 

enough to induce starvation in healthy animals. In the same area, there were some fatalities among interior 

swamp turkeys. Immediately before the floodway activation, multiple turkeys were fitted with remote 

tracking devices to record their movement during the floodway operation. Turkeys in areas that experienced 

rapid flood rise were all observed to methodically search for high ground, traveling along a circular route. 

Those unable to find high ground died. A concerted effort was made to provide field personnel forms to 

report black bear sightings. Few bears were seen, but one female bear was killed on the train track running 
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through the Morganza Floodway. There have also been reports that during the spring of 2012, some of the 

collared and tracked bears are reproducing again this year, suggesting that they lost their cubs last year 

during the flood, as black bear generally reproduce only after their cubs are 2 years old.

Photograph V-8. Deer Exiting Morganza Floodway During Its Activation

Flooding likely disturbed the nesting activities of the interior least tern, which typically locate their nests on 

isolated sandbars near the river channel banks, along with other birds that rely on river resources. Flooding 

inundated nearly all channel bars within the LMR during the flood period. This flooding may have 

constrained seasonal breeding but did not likely result in large-scale avian fatalities.

b. Aquatic Resources

i. Water Resources. Appendix F, Environmental and Cultural Resources of this report contains 

the results of the water quality sampling conducted by the USGS in coordination with the Corps during the 

2011 Flood. Although the sampling occurred at the routine NASQAN sampling sites, in many cases the 

sampling frequency was increased during the flood. The location of sampling areas is listed in table V-4. 

The exceptionally high floodwaters of 2011 did not significantly alter the concentration of fluvial sediment, 

nutrients, and pesticides within the flow of the LMR beyond the mean annual values typical for spring and 

summer. However, because of the extreme river discharges, the overall mass flux of these constituents did 

reach record levels. Within the Mississippi River, the transport levels of sediment, nutrients (e.g., nitrogen 

and phosphorus), and pesticides did not trend with discharge and showed a general tendency to decrease in 

time within the flood period. Within the spillways, these constituents did display a positive relationship with 

discharge, but their concentrations were less than that measured in the river at monitoring locations both 

upstream and downstream of the spillway location. Table V-4 displays averaged and maximum water 

quality values for four locations along the LMR and the three spillways estimated over the flood period. 

Also shown are values of the total mass flux for certain contaminants and sediment; however, these flux 

values were estimated over a shorter time period (as defined in the table legend). The suspended sediment 

and total nitrogen values shown for the BPNM Floodway were collected during a single time period 

following the initial activation of the spillway. 
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Table V-4. Water Quality Values Measured Within the LMR During the 2011 Flood Period

NUTRIENTS PESTICIDES

Location

Suspended

Sediment

Total

Nitrogen Phosphorus

Atrazine

and Metlachlor

Mississippi River at

MVK, MS

max - 164 mg/L

avg - 126 mg/L

18,800,0001

max - 2.8 mg/L

avg - 2.17 mg/L

262,000 1

max 0.24 mg/L

avg - 0.19 mg/L

26,200 1

max - 1.51 μg/L

avg - 0.88 μg/L

Mississippi River at 

St. Francisville, LA

max - 179 mg/L

avg - 103 mg/L

max - 2.70 mg/L

avg - 2.07 mg/L

max - 0.27 mg/L

avg - 0.19 mg/L

max - 1.43 μg/L

avg - 0.87 μg/L

Baton Rouge, LA

max - 168 mg/L

avg - 133 mg/L

max - 2.8 mg/L

avg - 2.03 mg/L

max - 0.21 mg/L

avg - 0.17 mg/L

max - 1.41 μg/L

avg - 0.70 μg/L

Mississippi River at

Belle Chase, LA

max - 206 mg/L

avg - 149 mg/L

max - 2.8 mg/L

avg - 2.13 mg/L

max - 0.27 mg/L

avg - 0.22 mg/L

max - 1.25 μg/L

avg - 0.83 μg/L

BP NM Floodway 150 mg/L 3 2.65 mg/L 3 0.6 μg/L 

4

Morganza Floodway

max - 31 mg/L

avg - 16.5 mg/L

404,000 1 9,930 1 900 1

Bonnet Carré Spillway

max - 177 mg/L

avg - 105 mg/L

2,307,294 1, 2 36,182 1, 2 3,3421, 2

1 values are total estimated flux during the month of May;

2 during 44 flood days spanning May and June in metric tons;

3 measured during the initial levee activation; 4 for Atrazine during the month of May only.

Of some interest are the results of the water quality data for the Atchafalaya Basin. Over 1,000 oil wells 

were inundated by the floodwaters introduced by the Atchafalaya River and the Morganza Floodway. 

Samples were collected for gasoline, oil and grease, and petroleum hydrocarbons upstream and downstream 

from the wells. On May 23, 2011, there was a slightly higher concentration of gasoline detected in the 

downstream waters, but by the next week, the concentration was higher in the upstream waters. Oil and 

grease levels were virtually identical upstream and downstream, and there were no detects of petroleum 

hydrocarbons, indicating that the efforts to shut down and secure the wells prior to inundation were 

successful. Also, it is interesting to note that during May, 2011, the total load of nitrate plus nitrite decreased 

slightly between the inflow at the ORCC and the Morganza Floodway, and the outflow at Wax Lake and 

Morgan City, indicating the possibility of denitrification occurring while the river waters were in contact 

with the forested wetlands in the Atchafalaya floodway; however, over the same time period, the suspended 

sediment loads and the total phosphorus loads increased, suggesting that the flood flows caused the 

resuspension of sediments and adsorbed phosphorus during the flood.

The floodwater released through the Bonnet Carré Spillway entered the coastal waters of southeastern 

Louisiana and southern Mississippi through Lake Borgne and Lake Pontchartrain. The river water was 

much colder, much less saline, and contained much higher nutrient loads than the surrounding coastal water, 

and significantly altered the regional water chemistry in Lake Pontchartrain, and through Mississippi Sound 

all the way to the area off shore from Biloxi, MS. Coastal waters that typically had salinity levels near 13.0 

parts per thousand (ppt) experienced levels as low as 1.0 ppt until mid summer 2011 (figure V-6). The high 

nutrient loads caused excess phytoplankton (i.e., algae) growth along coastal Louisiana and Mississippi. 

Freshwater algal species found the Mississippi Department of Marine Resources in Mississippi Sound 

included Pediastrum spp. and Scenedesmus spp. and a USGS contractor (The Academy of Natural Sciences 

of Philadelphia) counted bloom levels of cyanobacteria, likely Woronichinia.
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Figure V-6. USGS Plot of Measured Sea Water Salinity at Mississippi Sound During the Flood Period

Salinities were in the range of 10 to 15 ppt, dropped to only about 1 ppt during the opening of the Bonnet Carré Spillway 

(5/9/2011), then recovered back to the 15 ppt after the spillway was closed (6/20/2011). This particular gaging station 

was nearly 40 miles away from the spillway, providing some sense of the spatial extent of the effects of the 2011 Flood. 

The death and decaying process of large volumes of algae depletes the dissolved oxygen in the water in the 

vicinity of the algae bloom, which leads to hypoxic conditions and sea life mortality. It is hypothesized that 

the large, continuous discharge of river water into Lake Pontchartrain during the flood period effectively 

flushed the introduced freshwater and nutrients through the lake into Mississippi Sound (photographs V-9 

and V-10 and figure V-7). This may have caused the hypoxic conditions to form in the estuarine areas. 

Details on this sampling effort, as well as information on phytoplankton community composition and 

comparisons between the 2008 and 2011 events are presented in the paper in Appendix F.

Photograph V-9. Aerial Photo of Algae Bloom and Mississippi Department of Marine Resources Boat Collecting 

Phytoplankton Samples on June 27,2011
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Photograph V-10. Turbidity off the Coast of Mississippi Believed 

To Be Due to the Mixing of Fresh and Salt Water, June 22, 2011

Figure V-7. Survey of Bottom Water Hypoxia in August 2011 in Mississippi Sound

(Dr. Steve Howden, Department of Marine Science, University of Southern Mississippi) 

The scale bar (right hand side) shows bottom water dissolved oxygen concentrations (mg O2/L). This data would 

suggest that the nutrient rich freshwater from the river encouraged algal growth and when those algae died, their 

decomposition exhausted the available dissolved oxygen in the coastal waters.
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ii. Fisheries. Most aquatic life along the Mississippi River and side channels has evolved behavior 

to mitigate the effects of floods (e.g., seeking refuge in side channels and pools). However, some fish 

fatality occurred due to drastic drops in river water temperature due to very large rainstorms during the flood 

period. Quick changes in water temperature may inhibit the natural mixing within the water column, which 

creates temporary zones of low oxygen incapable of supporting life (i.e., hypoxia). The floodwater within 

the spillway areas disrupted the habitat of some commercially viable species that lived in the area, such as 

crawfish. However, it is unclear if any of these species’ populations were significantly affected.

One of the species of concern in the Mississippi River is the pallid sturgeon. There is little scientific 

literature describing how pallid sturgeon respond to distributary channel flows (i.e., flow diverted into 

spillways). For example, it is unknown if secondary channels are actively sought for refuge and increased 

food sources during main channel floods or if they are avoided (USFWS, 2009). Because of this, it is 

unknown if the sturgeon observed within the spillway had entered it on purpose or were entrained when 

swimming nearby. Pallid sturgeon favor turbid water and do consume floodplain food sources, such as 

macroinvertebrates, as well as invertebrates and small fish living in the main channel (USFWS, 2010). 

Recent investigations of the BPNM floodway have not identified any topographic or hydrographic features 

that would appear to attract the sturgeon to the vicinity, other than functioning as a large side channel. Prior 

floods have shown that pallid sturgeon are entrained by the Bonnet Carré Spillway. Pallids require 

freshwater, and once the spillway is closed, Lake Pontchartrain returns to a brackish salinity, which would 

limit pallid sturgeon viability. Therefore, it is necessary to attempt to “rescue” the pallid sturgeon trapped in 

the Bonnet Carré Spillway and Lake Pontchartain and return them to the Mississippi River. Pallid sturgeon 

may also be entrained by the ORCC; however, a significant population of pallids lives in a scour hole 

downstream from the ORCC. It is believed that the length of the freshwater extent of the Atchafalaya River 

is too short to allow the successful reproduction of pallid sturgeon, thus making the population living 

downstream of the structure non-viable. 

In coastal areas spanning from Lake Pontchartrain and Lake Borgne through Mississippi Sound, and beyond 

Biloxi, MS, the dissolved oxygen and salinity levels dipped below that required for many aquatic species. 

Species unable to flee the affected waters, such as sessile animals like oysters, experienced high levels of 

mortality. For example, mature oysters reefs along Mississippi Sound experienced mortality rates exceeding 

85 percent. Preliminary reports estimate that the economic cost of the flood damage (caused by spillway 

use) to the entire oyster industry as approximately $60 million. The degraded quality of the coastal waters 

was estimated to have reduced the commercial Mississippi blue crab harvest by approximately 50 percent 

for 2011 (May to August). The regional brown shrimp population appeared to have been unaffected by the 

influx of floodwater. Information was requested about the impacts to Louisiana oysters, but the Louisiana 

state resource agencies declined to comment on their situation.

The Louisiana Department of Wildlife and Fisheries has reported (R.T. Ruth, personal communication) that 

there was the movement of silver carp from the Mississippi River, through the freshened waters of Lake 

Pontchartrain, into the Pearl River system. Additional documentation of damages associated with the flood 

in the Atchafalaya Basin can be found in the report 2011 Atchafalaya Basin Inundation Data Collection and 

Damage Assessment Project authored by Carlson, Horn, Van Biersel, and Fruge.

c. Cultural Resources. Damage to archeological sites within the major spillways, during their 

activation, has largely been limited to the BPNM Floodway. Activation of the BPNM floodway 

requires detonation of explosives to remove an earthen levee between the floodplain and the spillway 

entrance. This type of sudden activation creates a near-instantaneous release of a large volume of 

floodwater into the spillway that has the potential to severely scour soil and sediment along the 

spillway surface. Scour can destroy archaeological site integrity and expose both Native American 

and Euro-American historic burials at this site. The activation of the BPNM floodway caused deep 
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scouring around the north end of Birds Point frontline levee. At this location, scouring damaged a 

previously undetected, late-Mississippian archeological site (National Register site number is 

23MI136) (photograph V-11). The flow entrained and transported prehistoric human skeletal remains 

and related artifacts (e.g., faunal material, pottery pieces) over a seven-acre area. This inadvertent 

discovery was identified during the immediate post-flood period (June 2011) during the early stages of 

the “Operation Make Safe” levee restoration. 

Photograph V-11. Large Areas of Soil Scour After Spillway Operation at the BPNM Floodway

In this area, soil erosion led to the exposure of a previously unidentified burial site (23MI136).

The Bonnet Carré Spillway contains sections of two cemeteries (i.e., Kugler cemetery and Kenner 

cemetery) but no scour was observed within their areas. Spillway maintenance activity accidently 

exposed buried bodies within the Kugler cemetery in 2008. There are no identified archeological sites 

within the Morganza Spillway.

F. DAMAGES PREVENTED

The existing MR&T Project (whether Scenario 1 or Scenario 4) prevented approximately $234

billion in urban and agricultural flood damages (compared to Scenario 3) during this single event. 

Without a FRM system in place, approximately 1.45 million residential and commercial structures 

would have been impacted. With the MR&T System, this decreases to 21,203 structures. 

In comparison, the MR&T Project (reservoirs only, Scenario 2) prevented approximately $11.8 billion 

in urban and agricultural flood damages (compared to Scenario 3) during the 2011 Flood, which 

results to only a 5 percent reduction in total flood damages. Estimates of flood damages prevented for 

the four hydrologic scenarios are presented by Corps District in Appendix G, Economics. For 

Scenarios 1 and 4, the flood damage prevented estimates are the same since the hydrographs for these 

two scenarios were the same. Flood damages prevented for Scenarios 1f and 4 reduced flood damages 

by approximately 98 percent. 
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1. Reduced Impact on Population. Estimates on the number of people protected by the MR&T 

Project during the 2011 Flood are presented in tables in Appendix G, Economics. The results of the damage 

analysis showed that 98 percent of the overall population was spared from the adverse impacts of flooding. 

The same amount of protection was afforded with Scenario 1 as 4. As shown, the majority of the reduced 

impacts occurred in MVN, MVK, and MVM. 

2. Project Effectiveness. Project effectiveness is measured by the amount of flood risk reduced by the 

project, or in terms of its percent in flood risk reduction (FRR). This also relates to the degree of protection 

(DOP) afforded by the project. The results of project effectiveness from flood damages prevented for each 

scenario are displayed in table V-5. Based on the results of the flood damage evaluation, the FRR for 

Scenarios 1 and 4 resulted in a 98 percent DOP while Scenario 2 (reservoirs only) provided only minimal 

protection in terms of FRR with a 5 percent DOP. 

3. Overview. Without the MR&T Project in place (i.e., Scenario 3) total flood damages in the sevenstate impacted area would have been over $237 billion. Furthermore, the Project provided a 98 percent flood 

risk reduction. Based on the significant influence of the Mississippi River on surrounding economies, it is 

not hard to grasp the importance of the main stem levee system to the region. Protecting approximately 

53 million acres of land in the States of Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri, and 

Tennessee of the lower Mississippi River valley, it has the task of trying to contain one of the oldest and 

most powerful natural resources in the world—the Mississippi River.
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Table V-5. Summary of Damages Prevented and Effectiveness of MR&T Project 1

Without MR&T Project

(Scenario 3) 2 With-Project Conditions

Scenario With-MR&T Project Description

Total Damages

(million $)

Total Residual Damages

(million $)

Total Damages 

Prevented Benefits (million $) FRR 3

1

As Occurred 2011

(minor deviations in reservoir operations) $237,152,397,000 $2,863,843,000 $234,288,554,000 98 %

2 With Reservoirs, But No Levees $237,152,397,000 $225,315,506,000 $11,836,891,000 5%

4

As Designed 2011

(no deviations in reservoir operations in 2011) $237,152,397,000 $2,863,843,000 $234,288,554,000 98 %

1 values expressed in 2012 prices

2

 the without-project condition 3

 percent of FRR from project implementation; also referred to as DOP