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3
Key Scientific, Engineering, and Other
Technical Topics
SUSTAINABILITY OF THE COASTLINE
Trends in and Causes of Coastal Erosion
An important assumption underlying the LACPR draft final technical
report is that the current configuration of the Louisiana coastline is sus-
tainable:
Extensive coastal landscapes in Louisiana can be con-
structed and maintained at a pace sufficient to offset ex-
pected future landscape degradation (USACE, 2009, p.
43, main report).
Any program or assessment regarding the future sustainability of
Louisiana’s coastline must consider historical and future trends in ero-
sion and sea level rise. For instance, Louisiana has lost 1,900 square
miles of land since the 1930s (Barras et al., 1994; Barras et al., 2003;
Dunbar et al., 1992). Between 1990 and 2000, wetland loss was ap-
proximately 24 square miles per year. The projected loss over the next
50 years, with current restoration efforts accounted for, is estimated to be
approximately 500 square miles (Barras et al., 2003). As the late coastal
expert Shea Penland stated, and as noted in this committee’s 2008 report,
“The state is rapidly disappearing into the Gulf of Mexico” (Penland,
2005). The Science Board of the Louisiana Coastal Area (LCA) ecosys-
tem restoration program made a similar observation, stating “It is obvi-
ous that not all of the coastline can be maintained, much less restored,
and not all coastal communities can be adequately protected” (Science
Board of the LCA, 2009). Figure 2 illustrates the impact of these rates of
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14 Second Review of LACPR Draft Report
land loss and how much additional land is forecasted to be submerged by
the year 2050.
Several factors have contributed to these losses, including:
• A reduction in sediment delivery volumes from the Mississippi
River as compared to historical rates. The construction of sev-
eral large dams on the Missouri River in the 1950s and 1960, and
the construction of the Missouri River Bank Stabilization and
Navigation Project (authorized in 1945) have greatly reduced
sediment deliveries from the Missouri River. Prior to those ac-
tions, the Missouri River had been the largest contributor of
sediment to the Mississippi River of all its tributaries (see Figure
3).
• Construction of flood control structures along the mainstem Mis-
sissippi River in Louisiana that prevent the flooding of wetlands
by sediment-laden waters, a process that previously helped build
and replenish wetlands. Rather, the sediment-laden waters have
been confined to move through the lower Mississippi delta to the
edge of the continental shelf and then to the deep waters of the
Gulf of Mexico permanently removing this sediment from the
littoral zone.
• Wetland edge erosion by storms that likely are exacerbated by
the larger open water fetch in ever-enlarging interdistributary
bays (e.g., Barataria, Terrebonne, Atchafalaya).
• Natural consolidation of soils in Louisiana’s coastal wetlands.
• Navigation and pipeline canals cut through the wetlands by the
oil and gas industry.
• Offshore disposal of clean dredged materials by the Corps of
Engineers.
Treatment of Coastal Erosion Issues in the LACPR Report
An assumption that “extensive coastal landscapes in Louisiana can
be constructed and maintained” (USACE, 2009; main report, p. 43) in
the face of these erosion trends will require that the State of Louisiana be
provided annual volumes of sediment comparable to a significant frac-
tion of the Mississippi River’s historical sediment load. That is, millions
of cubic of yards of sediment will have to be provided annually to the
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FIGURE 2: 100+ years of land change for coastal Louisiana.
SOURCE: U.S. Geological Survey (2003).
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FIGURE 3: Mississippi River suspended sediment discharge, around 1700 (esti-
mated) and 1980-1990. Values in millions of metric tons per year. Widths of the
river and its tributaries are exaggerated to reflect relative sediment loads.
SOURCE: Meade (1995).
coast, whether from the Mississippi River or from other sources. Fur-
thermore, these required amounts will increase over time because of the
increasing rate of sea level rise. These materials will have to be placed
in a way that fosters marsh growth with its attendant organic contribution
to wetlands accretion.
The LACPR draft final technical report suggests, but does not con-
vincingly demonstrate, that wetlands losses can be countered and the cur-
rent Louisiana coastline sustained. The LACPR draft final technical re-
port proposes a dredging program with six dredges working around the
clock, 365 days per year (USACE, 2009, p. 44, main report). Each
dredge was assumed to produce 900 acres of land per year, with the six
dredges thus producing 5,400 acres. This is equivalent to 8.4 square
miles—an amount less than rate of annual erosion losses of roughly 24
square miles. Moreover, although this dredging program may be theo-
retically possible, the question is whether it is economically feasible or
environmentally acceptable, particularly since
offshore sources and lake bottoms are identified as the source of some of
the dredge materials (and therefore would entail long and costly transport
of sediment).
There is no existing sediment budget that accounts for the amounts
and the locations of sediment sources and sediment losses to erosion
each year in coastal Louisiana. Results from this sediment budgeting can
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Key Scientific, Engineering, and Other Technical Topics 17
be used to provide a best estimate of the amount of material necessary to
maintain the coast. The LACPR team currently is developing a regional
sediment budget for coastal Louisiana, which is explained as:
The USACE is currently developing a Regional Sedi-
ment Budget for coastal Louisiana; however, the final
budget is not expected to be completed until July 2010.
Based on rough calculations, the LACPR team con-
cluded that adequate sediment sources are available to
implement proposed no net loss coastal restoration plans
but acquiring those resources involves trade-offs (e.g.
costs and environmental impacts) (USACE, 2009, p. 10,
main report).
Without a credible sediment budget, a goal to achieve “no net loss”
(USACE, 2009; main report, p. 43) seems questionable, even with exten-
sive dredging. It is worth noting that a sediment budget is not simply a
calculation of inflows vs. outflows but also would consider the distribu-
tion and character of wetlands and barrier shorelines being considered for
future maintenance.
A previous report from the National Research Council entitled
Drawing Louisiana’s New Map (NRC, 2006) reviewed the Corps of En-
gineers’ 2004 Louisiana Coastal Area (LCA), Louisiana—Ecosystem
Restoration Study. That NRC report concluded that it is not feasible to
maintain coastal Louisiana in its current form and that the Corps should
modify its plans and educate stakeholders about other approaches that
will need to be taken:
The Mississippi River delta is inherently dynamic and
large. Even maintenance of the status quo would require
unreasonable quantities of sediment to travel great dis-
tances at unreasonable cost. No reasonably scoped effort
will bring back the Mississippi River delta of historical
times. Those responsible for restoration efforts in Lou-
isiana will have to clarify that if these projects are exe-
cuted successfully, the future delta will contain all of the
landform types that exist today; however, those land-
forms will be smaller in size, and some will be located in
different places than today. To conserve resources and
focus effort where it will be most beneficial, some pres-
ently inhabited regions may have to be abandoned or re-
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located. If this is undertaken in a carefully planned
manner that view processes on the scales of decades
rather than years, the impacts to individuals and com-
munities can be minimized (NRC, 2006. p. 41).
That report also found that:
Achieving no net loss is not a feasible objective because
the social, political, and economic impediments are ex-
tensive; the sediment supply is limited; and the affected
area is large. . . These facts have to be broadly appreci-
ated to avoid widespread disappointment with the LCA
projects (NRC, 2006, p. 162-163).
The LACPR team maintains that the goal of achieving no net loss of
the coastal landscape of south Louisiana is technically feasible. This
NRC committee, however, is skeptical whether such an effort is achiev-
able or economically sustainable in the long run and whether it can be
accomplished without substantial adverse environmental impacts. Fur-
ther, the pursuit of this goal would consume considerable levels of finan-
cial resources for restoration and protection efforts, some of which might
be better spent on other high-priority projects as determined by the
LACPR and the State of Louisiana.
The LACPR team should complete a sediment budget for coastal
Louisiana. They also should provide a better explanation of poten-
tial costs and environmental impacts of dredging alternatives.
Rather than focusing energy and resources into trying to main-
tain the current configuration of southern Louisiana’s eroding coast-
line, the LACPR team is encouraged to focus its protection and res-
toration plans on high-priority projects.
ADDRESSING SCIENTIFIC UNCERTAINTIES IN
RESTORATION
Restoration efforts in ecosystems as large and complex as those in
coastal Louisiana entail many scientific uncertainties and unknowns.
The mean and the oscillating water levels required to sustain various
types of habitat are not known to a great level of precision. Sedimenta-
tion rates necessary to establish specific ecosystems are not well known.
Most importantly, the prediction of the location and extent of coastal
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Key Scientific, Engineering, and Other Technical Topics 19
wetlands that can provide a given level of storm surge reduction involves
processes and parameters that are not fully understood or quantified.
This section addresses some examples of scientific uncertainties that re-
quire more detailed consideration in the LACPR planning study.
There are many contributions to uncertainty in the modeling of
waves and surge and in the modeling of marsh creation by diversion.
With modeling efforts of this magnitude, the level of uncertainty is un-
derstandably high. Therefore, it is important for model uncertainty to be
quantified and to be propagated through the decision process. With re-
gard to marsh creation, the uncertainty must acknowledge and reflect the
lack of validated predictive models. The existing models, as applied
within the LACPR study, contain unsupported assumptions (see below),
and the lack of validation needs to be recognized and accounted for when
utilizing model results.
Uncertainty in surge/wave models
Most of the LACPR evaluations regarding both structural and non-
structural alternatives are based on the estimations of water levels along
the Louisiana coastal area. These water levels are obtained from numeri-
cal models. It thus is important that these models represent all important
physical processes in trying to emulate natural conditions.
The LACPR team used reasonably well-tested numerical models for
tide and storm surge modeling and for modeling short waves in deep and
shallow environments. The ADCIRC model was used to calculate water
level associated with storm surge and the WAM and STWAVE models
were used to calculate wave heights. The LACPR study does not con-
sider the frictional dissipation due to bottom and vegetation interaction in
STWAVE simulations. The LACPR report justifies this decision by stat-
ing that the STWAVE results that include friction have been known to
underestimate wave heights at “some locations inshore of coastal marsh
areas.” This argument suggests that STWAVE does not properly model
the physical processes in these areas. Because waves are important fac-
tors in structural performance and also contribute to hurricane surge,
modeling them accurately is important to the LACPR study and its re-
sults. Further analysis of the sensitivity of both surge and wave model
friction would provide additional insight into the role of wetlands and
associated nearshore areas in attenuating waves and surge.
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Marsh Modeling
A significant portion of the LACPR coastal restoration plans relies
on the use of diversions of sediment-laden flows from the Mississippi
River channel into adjacent wetlands. Although such diversions may
ultimately be efficient in helping create and restore wetlands ecosystems,
the efficacy of such diversions has not been demonstrated clearly in the
LACPR report, either through a study of existing diversions or via mod-
eling analyses. Given that restoration activities are affected by nutrient
reintroduction, water quality issues are of great importance and also
should be accounted for and tracked in restoration planning, projects, and
monitoring (Twilley and Rivera-Monroy, 2009).
The modeling of marsh-creation contains several poorly supported
assumptions. First, the estimation of the areal footprint impacted by a
given diversion is chosen by subjective consideration only (USACE,
2009, p. 59, Summary). These estimates would be more reliable if they
had a strong quantitative basis for estimating the area of a footprint of a
given project, based either on derived estimates or on observations of
existing marsh-building diversions. Second, the sedimentation model
assumes a turbulence structure that is identical to open channel flow.
This is inappropriate in a vegetated system, and will likely produce sig-
nificant errors in the estimation of how marsh-building sediment is dis-
tributed from a diversion. Third, the total amount of river water diver-
sion—525,000 cubic feet/second—is over 40 percent of the total channel
flow. Because of the obviously large impact on main channel flow, the
extent to which upstream diversions impact downstream diversions and
promote sedimentation within the main channel should be considered;
that is, the presence of upstream diversion creates greater uncertainty
regarding the potential success of downstream diversions and may affect
river sedimentation.
Finally, the success of diversions will be predicated on the impact of
future sea level rise, as newly created wetlands will need to keep pace
with rising sea levels. Increased sedimentation as a result of diverting
water from the river already is a concern to maritime interests. For ex-
ample, the construction of the West Bay diversion, near Head of Passes,
has been blamed by some for increased shoaling near the Pilottown An-
chorage.
The LACPR report should provide a better and more
quantitative explanation of the scientific uncertainty associated with
projections of marsh and wetlands restoration (including diversions),
surge attenuation by wetlands, numerical modeling efforts, and the
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Key Scientific, Engineering, and Other Technical Topics 21
implications of Mississippi River diversions.
The high level of uncertainty of the effects of proposed river di-
versions suggests the need for careful monitoring and evaluation of
existing diversions. It also suggests the importance of an adaptive
strategy that can adjust to and build upon new information as more
is learned about the responses of these coastal wetlands systems to
human interventions.
ENGINEERING CONCEPTS
Levels of Protection
The Corps of Engineers has been authorized by Congress to make
repairs to the New Orleans hurricane protection system. Repairs and
strengthening of the system are being carried out by the Corps of Engi-
neers’ “Task Force Hope” team with a goal to provide protection against
hurricane storm surge with a 100-year recurrence interval, or the surge
associated with a hurricane expected to occur on average once in 100
years, for New Orleans by 2011. The term "100-year recurrence inter-
val" is a frequently used term to describe an event that has a one per cent
chance of occurring in any given year. Similarly, a 500-year recurrence
interval refers to an event that has a 0.2 percent chance of occurring in a
given year, while a 20-year recurrence interval refers to an event that has
a 5 per cent chance of occurring in a given year. These are average
measures and a storm surge with a 100-year return period may occur
more, or less than, once in a given 100-year period.
The probabilistic nature of hurricane statistics is complicated by
long-term changes in climate and other environmental variables.
Changes and variability in the behavior of the climate system imply that
long-term averages and extreme values may shift over time—a concept
referred to as ‘nonstationarity’ (for further discussion of hydrologic non-
stationarity and its implications for water management, see Milly et al.,
2008).
The standard of providing protection against the 100-year flood is an
important one within the National Flood Insurance Program. It has been
applied both in New Orleans and widely across the nation as a de facto
safety standard. In areas in which storm surges that exceed the capacity
of the hurricane protection system (e.g., levees) do not pose a major pub-
lic safety concern, cause extraordinary property damage, or imperil
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22 Second Review of LACPR Draft Report
evacuation routes, this 100-year standard may be reasonable. However,
for heavily populated cities such as New Orleans, where hurricane pro-
tection system failure has been shown to be catastrophic—this level of
protection is insufficient.
The Association of State Floodplain Managers (ASFPM) 2007 re-
port, Levees: The Double-edged Sword, provides helpful guidance on
this subject. That report explains, for example:
In those cases in which a levee is found to be an appro-
priate measure to protect urban areas or to be credited
for protection, the levee should be constructed to a high
level of protection. As described in various reports, the
level of the 500-year flood, plus freeboard, is considered
an appropriate minimum protection standard with urban
areas. . .
There is now widespread misunderstanding of the true
risks associated with levees. This in turn has helped lead
to the current over-reliance on structural solutions to re-
duce the impact of flooding, and to the creation of a false
sense of security among those living, working, or seek-
ing to build in areas behind levees. …. Communication
of the residual risk associated with any levee is key to
public understanding and acceptance of appropriate pub-
lic safety and flood risk reduction policies in the nation
(ASFPM, 2007; italics added).
In addition to the ASFPM report, the National Research Council re-
cently issued a report on the New Orleans hurricane protection system,
including the presentation of key lessons learned during Hurricane
Katrina (NRC, 2009). That report considered the issue of flood protec-
tion criteria for New Orleans, concluding that:
The 100-year level of flood protection is a crucial flood
insurance standard. . . For areas in which catastrophic
levee failure is not a major public safety concern, and
where large floods would not imperil evacuation routes,
the 100-year standard may be appropriate. For heavily-
populated urban areas, where the failure of protective
structures would be catastrophic—such as New Or-
leans—this standard is inadequate (NRC, 2009).
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Key Scientific, Engineering, and Other Technical Topics 23
This committee agrees that providing protection from storm surge
with an expected recurrence interval of 100 years is inadequate for New
Orleans. In its first report (NRC, 2008), this committee noted that the
LACPR draft technical reports defined ‘Category 5’ protection as falling
in the range of a 400-year to a 1,000-year event, a point that the LACPR
reiterated in its 2009 draft technical report:
USACE policy guidance memorandums directed that a
set of measures be presented that could reduce risk
across a range of storm surge events including 100-year
risk reduction, a “low Category 5” event or Hurricane
Katrina-like event (estimated as a 400-year surge event)
and a “high Category 5” event (estimated as a 1000-year
event) (USACE, 2009; p. 3, main report.).
In its 2008 report this committee recommended that the LACPR
team focus on producing designs and plans based on storms with return
intervals associated with Category 5 storms. As defined by the LACPR,
this would encompass storm surges from 400 to 1,000-year recurrence
intervals, consistent with the authorizing 2006 legislation. This design
standard would provide New Orleans with protection from storm surge
that is comparable to the level of protection provided to the city from the
levees along the Mississippi River, which provide protection against riv-
erine floods with a 700- to 800-year recurrence interval.
The first priority of comprehensive hurricane protection and coastal
restoration for southern Louisiana should be to ensure protection against
storm surges with 400- to 1,000-year recurrence intervals in the City of
New Orleans, where the population density and the property at risk are
the highest. This level of protection could be provided by raising and
strengthening levees alone or by a combination of levee repair and ele-
vating structures behind them.
Storm surge protection for the City of New Orleans should be
designed for a hurricane storm surge event with an expected return
interval of 400 to 1,000 years. The 2007 report from the Dutch engi-
neers found that even higher levels of protection are economically
justifiable.
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Limited Consideration of System Failure
The low-lying, and in many areas subsiding, topography of southern
Louisiana makes the region particularly vulnerable to flooding. Al-
though low-lying areas above sea level may flood during severe storms,
many areas in southern Louisiana lie below the average level of the adja-
cent waterbodies of Lake Pontchartrain, Lake Borgne, and the Missis-
sippi River. There is an elaborate system of flood control structures,
such as levees and floodwalls, in the region to help protect against storms
and high water.
A breach of the hurricane protection system will have very different
consequences for land areas above sea level as compared to those below
sea level. In the former case, inundation will occur only during the event
itself with water receding thereafter; flood depths will depend on the du-
ration of the storm, the size of the breach, and the surge elevation outside
the protection system. However, in areas below sea level, inundation
will continue until the breach is repaired and the water is pumped out;
flood depths will depend primarily on the water level in the adjoining
waterbody. The flooding of New Orleans after Hurricane Katrina—via
waters from Lake Pontchartrain that flowed through breaches in flood-
walls that line the city’s outfall and navigation canals—is a poignant ex-
ample of this and a sobering reminder that failure of the hurricane protec-
tion system is a key component of the residual risks that attend hurricane
and flood protection systems.
The LACPR draft final technical report does not consider the possi-
bility of failure when evaluating water levels and flooding associated
with storm surge. Rather, all analyses presented in this report, whether
to determine system configurations that meet 100-, 400-, and 1,000-year
water levels, or to evaluate these system configurations for different
storm occurrence frequencies, assume perfect system performance. Al-
though well-designed protective structures together with diligent mainte-
nance and repair efforts will reduce the likelihood of failure, assuming
zero probability of failure is unrealistic and unacceptable, especially for
areas where such failure would subject lands to unabated filling from an
adjacent waterbody.
A significant portion of the hurricane protection plans within the
LACPR draft final technical report call for the construction of levees
protecting different cities and municipalities. New Orleans is one of the
nation’s largest metropolitan areas protected by levees and many of the
structures within its hurricane protection system are being raised and
strengthened in the wake of Hurricane Katrina. In addition to levees (or
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Key Scientific, Engineering, and Other Technical Topics 25
ring levees) being proposed for Houma and Morgan City, costly levees
are proposed for even smaller communities such Delcambre and Erath.
In assessing flood risks for coastal Louisiana, the LACPR draft final
technical report does not incorporate the probability of system failure as
part of the risk assessment. The current approach highlights the use of a
“qualitative” assessment of failure potential based on the total levee
length, number and size of hydraulic structures, and overtopping. More-
over, the LACPR draft final technical report assumes that structural
measures can be built to perform reliably to specified risk reduction lev-
els; therefore, hydrologic stages assume no possibility of structural fail-
ure or breaching of levees. Abundant historical experience shows, how-
ever, that structural failure can occur, with an increasing likelihood in
larger storms. This has been recognized in the work of the Interagency
Performance Evaluation Task Force (IPET), which conducted an exten-
sive evaluation of the performance of the New Orleans hurricane protec-
tion system during Hurricane Katrina and under future storm conditions
(IPET, 2008).
It is likely that any conclusions regarding overall system perform-
ance of the proposed protection systems will be grossly misleading with-
out appropriately (and quantitatively) accounting for the probability of
failure of the structural protection systems. By not accounting for the
possibility of structural failure in its analysis, the LACPR draft final
technical report underestimates the residual risk in the hurricane protec-
tion options that have been presented. Depending on the significance of
this underestimate, it may discourage supplemental nonstructural mitiga-
tion efforts such as voluntary relocation and the elevation of structures,
and may enhance a false sense of security for those living behind these
structures.
The LACPR team should perform a quantitative risk assessment
of the structural protection systems that includes the probability of
system failure of the various components including floodwalls, lev-
ees, ring levees, and floodgates. These probabilities of failure should
be performed for a range of hazard levels and a range of structural
designs.
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OTHER TECHNICAL ISSUES
Formulation and Evaluation of Alternatives
The LACPR planning area is divided into five planning units (PU1,
PU2, PU3a, PU3b, PU4; see Figure 4) based on geographic areas and
delineated such that there is minimal interaction between units. Within
each planning unit, numerous potential plan components were identified.
These potential components were combined into a large number of alter-
native plans. The best-performing alternative plans were then identified
on the basis of analysis, experience, and judgment. The result was a total
of 111 alternative planning unit-level plans, ranging from 33 alternative
plans in PU2 to 13 alternative plans in PU3a.
The alternative plans fall into five categories:
• No-action alternatives, which assume continued loss of coastal
lands.
FIGURE 4: LACPR planning area and planning units.
SOURCE: USACE (2009).
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Key Scientific, Engineering, and Other Technical Topics 27
Coastal restoration alternatives, where the only actions taken
are preservation and restoration of coastal lands.
Nonstructural alternatives, which combine nonstructural
measures with coastal restoration. The nonstructural measures
considered consist of buyouts and/or raise-in-place measures for
structures that meet certain criteria.
Structural alternatives, which combine levees, floodwalls,
flood gates, etc., with coastal restoration.
Comprehensive alternatives, which combine coastal
restoration, structural measures, and complementary non-
structural measures.
Alternative plans are further differentiated by the level of protection
provided. Plans assume protection from storm surges having recurrence
intervals of 100 years, 400 years, or 1,000 years. As the level of protec-
tion rises, implementation costs increase but expected residual damages
decrease.
The result of the evaluation phase should be to identify the preferred
alternative plan for each planning unit. The LACPR team elected to stop
short of this outcome. Instead, the report narrows the list to five or six
alternative plans for each planning unit (27 in all). This is followed by
some discussion of the tradeoffs existing among these plans. Finally, the
27 alternative planning unit-level plans are assembled into seven coast-
wide plans.
Evaluation
As a basis for evaluation, the LACPR team characterized each of the
alternative plans in terms of ten metrics. Five of these are relatively di-
rect cardinal measures of plan impact, such as the average number of
people impacted per year, lifecycle cost of the plan (annualized $/year),
or residual damages (annualized $/year). Four metrics are cardinal prox-
ies for actual impact, such as number of archeological sites protected or
acres of wetland impacted. One metric (indirect environmental impact)
is measured on an arbitrary ordinal scale, ranging from -8 to +8. An or-
dinal scale differs from a cardinal scale in that ordinal measures reveal
only rank (1st, 2nd, 3rd, etc.) and provide no information on the difference
between alternative measures. For example, a horse might win a race by
a nose or by ten lengths; the ordinal measures for the first two horses are
still 1st and 2nd.
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The LACPR team first attempted to identify preferable alternative
plans through the use of Multi-Criteria Decision Analysis (MCDA). It
was intended that stakeholder workshops could be used to assign weights
to the ten metrics and that these weights could then be applied to the ac-
tual values of the metrics for each alternative plan. The weighted sums
of the metric scores would then be used to rank the alternatives. This
committee's prior 2008 report addressed the first estimates of metric
weights, noting flaws in the process of obtaining these weights through
direct elicitation. The Corps subsequently employed, in a single set of
workshops, a swing weighting approach that produced somewhat better
results.
Swing weighting is considered preferable to direct elicitation be-
cause it provides respondents with an understanding of the possible range
of each of the metrics. To determine swing weights, respondents are
asked to rank metrics based on the relative desirability of “swinging” the
value of each metric from its least preferred to its most preferred level,
compared to the swing from least to most preferred for each of the other
metrics. The metric which is judged to have the most desirable “swing”
is assigned a weight of 100. Then the respondent is asked to compare the
importance of the range (“swing”) of the next most important metric and
to state the relative desirability of this range as a fraction of the desirabil-
ity of the most favored metric. The weight for the second metric is 100
times this fraction. This process continues until weights have been de-
rived for all metrics. Swing weighting is considered to be a reasonable
compromise between the need for rigor and ease of use (Edwards and
von Winterfeldt, 1986)
In retrospect, the resulting stakeholder weights exhibit a number of
inconsistencies. The implied tradeoffs between cost and benefit are sus-
pect because of the low priority that stakeholders gave to life cycle costs.
Application of the same weights to nonstructural and structural projects
may be inappropriate since the metrics do not reflect plan characteristics
such as political and social acceptability, visual amenity, or other factors
that may diverge significantly between the two kinds of approaches.
There is also some concern that respondents may have been confused by
some metric definitions, especially where signs reversed (some metrics
were to be minimized while others were to be maximized). Finally, the
number of stakeholders that participated in this process was very low—
there were 114 stakeholder participants (USACE, 2009, p. 12, Sum-
mary). The fundamental issue of how adequately a group of 114 stake-
holders represent the interests of the roughly 2.3 million people that in-
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Key Scientific, Engineering, and Other Technical Topics 29
habit the coastal Louisiana study area was not addressed in the draft final
technical report.
As a result of these and other shortcomings, the LACPR-defined
metrics combined with the stakeholder weights did not produce a ranking
of alternative plans that the LACPR team had confidence in, or that
seems reasonable (USACE, 2009, p. 12, Summary). The LACPR team
noted that further iterations of the MCDA process could improve the re-
sult, but that available time and resources did not permit that option.
This committee is more skeptical, believing that substantial redesign of
the MCDA process is needed, including extensive use of focus groups to
redefine and refine metrics, not just additional iterations of the existing
process.
Nevertheless, the LACPR team attempted to make use of the MCDA
results by combining them with other scoring and ranking approaches.
Nine additional decision criteria were defined, including direct and indi-
rect environmental impacts, various measures of cost and cost effective-
ness, and various measures of residual risk. These criteria are measured
in various ways, including dollars, risk/cost ratios, wetland acres, and
ordinal rankings (MCDA results, indirect environmental impact).
All of the measures, both cardinal and ordinal, are normalized to a 0-
1 scale. Note that the MCDA results are already the result of rescaled
metric measures, which are then weighted and summed, and rescaled
again in this exercise. Armed with these additional criteria and rescaled
results, the LACPR team performed 13 different rankings of the alterna-
tive projects in each planning unit. All these rankings included the
MCDA results, but with a relatively minor weight. Four rankings were
performed on the basis of weighted ordinal ranks; the number of in-
cluded criteria and the weights applied differed from one to the other.
Next, nine more rankings were performed where weights were applied,
not to ordinal ranks, but to the normalized scores (in some cases derived
from ordinal ranks). Again, these rankings differed in that they included
different sets of criteria and applied different weights. The final choice
of the preferred projects was based on observed consensus among the 13
rankings. Those projects (usually five) were chosen that appeared most
often at the top of the individual rankings. The effect of this is to reduce
the number of planning-unit level projects from 111 to 27. Unsurpris-
ingly, given the method used, the rankings were quite consistent.
The deficiencies in the application of MCDA have been noted above
and are acknowledged by the LACPR study team. Unfortunately, the
attempt to salvage the results of this flawed exercise has introduced more
problems, rendering the end result even less useful. One problem that
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30 Second Review of LACPR Draft Report
runs through this process is the repeated weighting of ordinal numbers.
Since an ordinal number reveals only order (1st, 2nd, etc.) it is, strictly
speaking, not possible to perform arithmetic operations on such a meas-
ure. To do so is to treat the ordinal number as though it were cardinal.
This may be acceptable in limited circumstances. For example, an
MCDA approach may use an ordinal metric measure that is roughly pro-
portionate to the true cardinal value, so that treating it as cardinal number
does not significantly bias the result. But the LACPR report rankings
begin with a weighted ordinal measure, combine it into another ordinal
measure, then weight it again before combining it into still another ordi-
nal measure. Whatever information was revealed by the first measure is
likely to be significantly distorted, if not lost altogether.
The 13 rankings produced in the LACPR report contain no useful in-
formation regarding the relative desirability of the alternative plans. The
apparent consensus among the rankings simply reflects the commonality
of the metric definitions and underlying assumptions. It does not provide
any corroborating evidence for the rankings. Accordingly, the 27 alter-
native plans presented in Table 15-1 of the Technical Report may not
necessarily be preferable to the 111 alternatives from which they have
been chosen.
Multi-Criteria Decision Analysis is a potentially useful approach
to evaluate projects with important environmental, social, and cul-
tural impacts; however, flaws in the application of these methods to
the LACPR study have prevented any convincing results. As ap-
plied, the methods do not support the identification of a preferred
alternative for any of the planning areas. Furthermore, they do not
support the rankings of alternative plans as presented in the LACPR
report.
Nonstructural Measures
The draft final technical report lacks specificity with regard to a
number of the alternatives it proposes for further consideration. For ex-
ample, many of the alternatives suggested for further consideration in-
volve nonstructural protection. Simply announcing that a nonstructural
measure—such as elevating buildings—can reduce flood damages will
not necessarily result in buildings being elevated. The LACPR report
does not deal with actions needed to actually persuade households to
voluntarily take part in such a nonstructural protection program, such as
informing households of the risks they face, formulating standards for
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Key Scientific, Engineering, and Other Technical Topics 31
cost-effective elevation and other nonstructural mitigation measures,
training and certifying contractors/inspectors to conducting on-site audits
to identify appropriate actions households might take to reduce risk, pro-
viding financial assistance to households to undertake cost-effective ac-
tions, and so forth. The report also lacks clarity as to who should under-
take such a program (i.e., the state, local governments, nonprofit entities,
or the Corps).
The LACPR draft final technical report acknowledges many of the
recommendations offered in this committee’s previous, 2008 report—
such as the need for measures to counter induced development behind
levees and to prevent new and more intensive development from occur-
ring in the future in high hazard areas whether or not protected by levees.
However, recognition of a problem does not necessarily solve it. These
problems are also not solved by stating that the issues of induced devel-
opment and prevention of development in high hazard areas are a state,
not federal, responsibility. Since the State of Louisiana lacks state regu-
lations that address either issue, they likely will not be addressed without
more direct federal action.
The previous, 2008 report from this committee noted that there was
precedent to employ many different nonstructural measures to help re-
duce development in areas subject to frequent flooding:
The LACPR draft technical report would be stronger if it
proposed an integrated set of measures for limiting fu-
ture increases in vulnerability. These would include
comprehensive plans prepared by parishes and munici-
palities that assess the suitability of land for develop-
ment and propose policies for limiting development in
areas deemed unsuitable due to the risk of flooding. Po-
tential policies that are regularly used for this purpose
throughout the United States include: (1) zoning regula-
tions that limit the intensity of development to a level
appropriate for the degree of flood risk; (2) subdivision
regulations with flood-hazard mitigation provisions; (3)
building regulations that require additional freeboard be-
yond that mandated by the National Flood Insurance
Program; (4) public acquisition of land for open space,
habitat protection, and outdoor recreation; (5) public ac-
quisition of easements that limit the amount of develop-
ment possible in the future; and (6) location of new pub-
lic infrastructure (e.g., roads and water and sewer lines)
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32 Second Review of LACPR Draft Report
such that it does not induce or support unsafe new de-
velopment in flood-hazard areas (NRC, 2008).
There is ample precedent for federal requirements of state and local
land-use planning and regulation to limit induced development and pre-
vent development of high hazard areas as a condition for federal partici-
pation in the construction of hurricane protection levees (see ASFPM,
2004 for case studies of contemporary flood risk management actions in
several U.S. communities). This would be similar to the National Flood
Insurance Program’s requirement of local regulations to prevent devel-
opment in floodways and to elevate buildings to the 100-year base flood
level as a condition for offering flood insurance to the residents of a
community.
Implementation of a variety of nonstructural measures will be
essential in better managing and reducing flood risks in southern
Louisiana. The LACPR team and the Corps of Engineers should
take a more aggressive leadership role in a variety of nonstructural
measures that are important to reducing flood risks in coastal Lou-
isiana. Examples of these nonstructural measures include limiting
development in vulnerable areas and stronger public education ef-
forts regarding flooding risk in different sections of New Orleans.
