flooding performance indicator: methodology and

FLOODING PERFORMANCE INDICATOR: METHODOLOGY AND SHARED VISION MODEL APPLICATION

Prepared for:

I.J.C. PLAN FORMULATION AND EVALUATION GROUP

Prepared by:

W.F. BAIRD & ASSOCIATES COASTAL ENGINEERS LTD. OAKVILLE, ONTARIO

FEBRUARY 2005

Flooding Performance Indicator:

Methodology and Shared Vision Model Application

Baird & Associates

This report has been prepared for PFEG by:

W.F. BAIRD & ASSOCIATES COASTAL ENGINEERS LTD. 627 LYONS LANE OAKVILLE, ON L6J 5Z7

For further information please contact Pete Zuzek (905)845-5385 ext. 425



Baird & Associates

TABLE OF CONTENTS

1.0 INTRODUCTION ......................................................................................1

1.1 Shared Vision Model Goals .......................................................................................................1 1.1.1 Flooding Performance Indicator ...........................................................................................1

2.0 DATA .......................................................................................................4

2.1 Water Level Database...............................................................................................................4 2.2 County/Regional Municipality Database .................................................................................4 2.3 Township Database ....................................................................................................................4 2.3 Normal Wave Height Database.................................................................................................4 2.5 Reach Database ..........................................................................................................................5 2.6 Parcel Database ..........................................................................................................................5 2.7 Attenuation Tables .....................................................................................................................5

3.0 METHODOLOGY FOR FLOODING P.I.......................................................6

3.1 WAVAD Modeling .....................................................................................................................6 3.1.1 WAVAD Site Selection ...........................................................................................................6

3.2 COSMOS Modeling to Predict Wave Attenuation..................................................................8 3.2.1 Calculating Wave Attenuation ...............................................................................................9

3.3 Damage to Structures...............................................................................................................10 3.3.1 Definition of a Structure ......................................................................................................10 3.3.2 Damages to Structures Caused by Inundation ....................................................................11 3.3.3 Damages to Structures Caused by Wave Impacts................................................................12 3.3.4 Calculating Damages to a Structure caused by Inundation ...............................................14 3.3.5 Calculating Damages to a Structure Caused by Wave Attack ............................................14

3.4 Damages to the Contents of a Structure.................................................................................15 3.4.1 Damages to Structure Contents Caused by Inundation ......................................................15 3.4.2 Calculating Damages to Structure Contents caused by Inundation...................................17

3.5 Long-term Effects of Inundation and Wave attack ..............................................................17 3.6 Impacts of a Flooding Event....................................................................................................18 3.7 Combining the Percent Damages............................................................................................18

4.0 ECONOMICS..........................................................................................20

4.1 Resolution of Economic Damages to Existing Shore Protection ..........................................20 4.2 Economic Value of Buildings and their Contents in the Flooding Hazard Zone................20 4.3 Methods for Estimating Economic Damages due to Flooding .............................................21

Flooding Performance Indicator: Methodology and Shared Vision

Model Application

Baird & Associates

Table of Contents

4.3.1 Method I – No Repairs .........................................................................................................21 4.3.2 Method II – Complete Repair without Mitigation ...............................................................22 4.3.3 Method III - Repair with Mitigation ....................................................................................22

4.4 Economic Damages caused by flooding in Niagara County .................................................23 4.5 Economic Costs of Flooding for Lake Ontario ......................................................................25

5.0 SUMMARY.............................................................................................28

5.1 Required Data...........................................................................................................................28 5.2 Fields and flags for Parcel Database.......................................................................................29 5.3 Recommended Programming Algorithm...............................................................................29

6.0 REFERENCES ........................................................................................30

APPENDIX A – RECOMMENDED PROGRAMMING ALGORITHM


Model Application

Baird & Associates

Table of Contents

1.0 INTRODUCTION

This report outlines the methods that will be used to evaluate criteria for the Flooding Performance Indicators for Lake Ontario and discusses how the predicted flooding damages may be represented economically. The process of incorporating these two aspects into the Shared Vision Model is also described using Niagara County as an example.

1.1 Shared Vision Model Goals

The Shared Vision Model (SVM) is being developed to connect all of the research completed by the Technical Working Groups (TWG) to the decisions that the Study Board has to make on criteria and regulation. The model will determine how different plans affect the economics and the environment around Lake Ontario, and will gage these results against set criteria and performance indicator goals from each TWG. The SVM is transparent and takes an integrated process approach that will help to make informed decisions that are connected to the research.

1.1.1 Flooding Performance Indicator

A visual summary of the Flooding Performance Indicator and the various scales of resolution for the calculations in the SVM is provided in Figure 1.1. It is a hypothetical diagram that uses the western end of Lake Ontario to illustrate the methods being developed for the SVM.

• Flooding Damages are calculated for all reaches with elevations below 77.2 m (3.0 m above Chart Datum). Damages are calculated at individual parcels depending upon whether or not the parcel is subjected to wave actions from the open lake. Three types of damages are possible: inundation damage to contents, inundation damage to the structures themselves, and damage to the structures caused by wave attack.

• Waves are the driving force for damage to the structure caused by wave attack. The application of the WAVAD wave modelling results has been critical to the development of these methods.

• Normalised weekly maximum wave heights are calculated and collected at one or more WAVAD locations per county, depending on the regional variability in the wave climate. The presence of ice is included in the calculation for the maximum wave height. In Figure 1.1, wave heights will be calculated at three locations (WE1, WE2, and WE3.) for County A.



Baird & Associates 1

• COSMOS modelling was undertaken to assess wave attenuation magnitudes and distances for impacts to structures located at some known distance from the top of the bluff. The model results are summarized in a series of attenuation matrices (CSM). With the matrices, the SVM will be able to simulate the complex wave attenuation calculations for each parcel where the land elevation is low enough to support wave propagation across the parcel (i.e. the backyard between the lake and house). There is one set of matrices for the entire lake. The COSMOS modeling was undertaken using a program originally developed by Nairn and Southgate (1993), and since modified by Baird & Associates.

• Lake levels are modified to include for storm surge. Storm surge has been determined at a county-by-county basis.

• Information specific to each parcel, such as the elevation of the land surrounding the structure, and the distance from the structure to the top of the bluff was integrated in the database using GIS datasets.

• Field observations and measurements were used to develop an offset from the surrounding land elevation to the main floor elevation of each house in the flood hazard zone. The results were aggregated to the reach level.

• There is an allowance for temporal considerations. When a structure is inundated for extended periods of time significantly more damage may occur due to long-term effects of inundation, such as rot, corrosion of structural members, etc. versus a short term flood event (i.e. less than 24 hours).

• It is often not physically or economically possible to implement repairs immediately,

and thus a repair-buffer has been implemented.

• The economics are calculated in three different ways in order to provide the study board with the flexibility and option of which to include. Method I includes applying economic damages to a structure and its contents continuously over a simulation, and not repairing the damages (i.e. the structure is left to degrade). The second method (II) involves repairing/replacing the home and contents to full value after each damaging event, and the third method (III) repairs the damages only while it is less expensive than mitigating the problem to prevent future flooding damages. While the FEPS is capable of calculating all three methods of damages, we fee; it is most appropriate to implement Method III which includes mitigation. Home owners will not sustain damages indefinitely without taking action, especially when realistic mitigation alternatives, such as coastal engineering structures, are available.




Figure 1.1 Visual Summary of the Flooding Performance Indicator in the SVM




2.0 DATA

Databases are being developed to manage all of the data components in the FEPS that will be integrated in the SVM. A general description of each database is provided below along with the general requirements for the Flooding Performance Indicator.

2.1 Water Level Database

The SVM generates a lake-wide water level database that will hold the quarter-monthly water level elevation data, in IGLD 1985, for each Regulation Plan. The flooding equations use the quarter-monthly lake levels as defined by the SVM, adjusted to depths below Chart Datum (74.2m, IGLD’85 for Lake Ontario).

2.2 County/Regional Municipality Database

Attributes that are significant in the assessment of existing shore protection, the prediction of erosion and flooding hazards, and the calculation of sediment budget variables, vary around Lake Ontario and the Upper St. Lawrence River. Baird & Associates has assessed these attributes. The findings have been summarized on a county/regional municipality-wide basis in this database. Constants are applied at this database level, including those used in the inundation and wave damage calculations. The system wide County database is provided in the file COUNTY.xls.

2.3 Township Database

The township database is a subset of the County database. The township database summarizes the attributes that are important for assessing the proximity of existing buildings to shore protection and the calculation of assessment values for parcels with missing data. To date, the township database contains the county it is located in and the distance to protection field (the distance from the lakeside of a house to where riparians have built existing shore protection). The system wide Township Database is provided in TOWNSHIP.xls.

2.3 Normal Wave Height Database

After a county/regional municipality-wide analysis of normal wave energy, Baird & Associates selected a number of specific WAVAD points to represent the wave climate around the perimeter of the lake. The wave damage calculations, which are being developed by Baird & Associates based on the COSMOS modeling results and empirical methods, require normalised quarter-monthly maximum wave heights as an input. The




normal wave height database will store these quarter-monthly wave height values for each selected WAVAD point around the lake. The wave height in the database is normal to the general shoreline azimuth. The Normal average and maximum quarter-monthly Wave Height Database for Niagara County is included. See WAVAD_HEIGHTS.xls.

2.5 Reach Database

The reach database classifies the shoreline on a 1 km basis and links the to the appropriate township and county. For example, this database will list the township associated with each reach, the level of exposure to the open lake for onshore waves, the approximate land to main-floor elevation offsets, and the specific WAVAD site that each reach corresponds to and the reach specific historical Average Annual Recession Rate (AARR). A value of –9985 present in the WAVAD ID field indicates that no WAVAD Pt. has been assigned to that reach (this may occur for reaches on the St. Lawrence River, tributaries and embayments). Niagara County’s Reach Database is provided. See REACH.xls.

2.6 Parcel Database

The parcel database contains detailed information for each lot along the shoreline, is identified by a unique parcel ID number, and is associated with a 1 kilometer Reach on Lake Ontario. Assessments of the land value both with and without a building, classification of shore protection type and quality, as well as measurements of distance to bluff, the length of exposed and protected shoreline, and land elevations on each flood susceptible parcel are just some of the variables included in the parcel database. Refer to the Parcel Database (PARCEL.xls) for the data at every lot contained within Niagara County.

2.7 Attenuation Tables

Attenuation tables have been developed in COSMOS and included as a database within the FEPS. The flood tool calls on these specific tables based on variables such as the offshore wave height, and water level.




3.0 METHODOLOGY FOR FLOODING P.I.

There are two distinct types of direct damages considered for flooding events. First, there is damage to the exterior of a structure due to wave forces, such as a residential house or commercial building. Second, regardless of the structure type, damage to the internal structure and contents will occur if flood waters exceed the main floor elevation. In the FEPS algorithm, the calculations are performed for each damage type within any given parcel. For example, structure and contents damage can occur simultaneously when waves propagate across the parcel at high lake levels and strike the structure with force. In the absence of waves or for second row homes not exposed to waves, the structural integrity of the walls and value of the internal contents can be damaged by flood inundation due to high lake levels and storm surge (without the impact of waves).

3.1 WAVAD Modeling

Before the equations can be applied, WAVAD points need to be selected, as the data is required for the wave damage calculations.

3.1.1 WAVAD Site Selection

An analysis of 40-year normal wave energy has been performed at each county/regional municipality along the shores of Lake Ontario. Figure 3.1 illustrates all of the possible WAVAD site locations in Niagara County, NY.

Figure 3.1 Niagara County: WAVAD Locations




Five WAVAD sites were selected in Niagara County for a normal wave energy comparison (ID numbers: 1021, 1165, 1310, 1457, and 1601, taken normal to the general shoreline azimuth). Figure 3.2 and 3.3 illustrate the yearly normal wave energies and average monthly normal wave energies at each WAVAD point respectively. WAVAD points 1457 and 1021 were selected to represent the wave climate for the entire County. WAVAD point 1457’s waves will represent the wave climate for the mid to east reaches of the county since its normal wave energies were between those of point 1601 and 1310. WAVAD point 1021 will represent the wave climate for the reaches on the west side of the county since it has similar normal wave energies to those of point 1165. These sites are the locations where the quarter-monthly average and maximum wave heights will be determined and populated in the database.

Figure 3.2 Niagara County: Yearly Normal Wave Energy (1961-1980)




Figure 3.3 Niagara County: Average Monthly Normal Wave Energy (1961-2000)

3.2 COSMOS Modeling to Predict Wave Attenuation

The COSMOS model was used to predict wave attenuation across the parcel in order to determine the wave heights that may actually strike the structure during a flood event. The COSMOS code is too complicated to include in the SVM and it is proprietary model. Therefore, a methodology was developed to simplify the detailed COSMOS model calculations for inclusion in the FEPS and the SVM, while still maintaining the integrity of the predictions.

The COSMOS model was run for a large number of distinct wave height and water level combinations at the same profile. Curves were fit to the resulting distribution of points. The mathematical definition of these curves for specific wave height, periods and water depth conditions, which are 5th order polynomials, can be used to calculate the wave height at a known distance from the top of bank. To make the runs non-site specific, the results were correlated to freeboard (i.e. elevation above the backyard). A visual sample plot of the results can be seen below in Figure 3.4.




Figure 3.4 COSMOS attenuation results for various wave heights at freeboards of –1.50 m.

The wave attenuation tables present the coefficients for the various curves. Below in Table 3.1 is a sample wave attenuation table. There are tables available for the x5 term through to the constant (x0) term. These tables are applicable for all reaches exposed to the open lake, and located in the Velocity zone (first row parcels).

Table 3.1 Wave Attenuation Coefficients for the x2 term.

Freeboard 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 52 0 0 0 0 0 0 0 0 0 0 01.5 0 0 0 0 0 0 0 0 0 0 01 0 0 0 0 0 0 0 0 0 0 00.5 0 0 0 0 0 0 0 0 0 0 00 0 0 1.00E-06 2.00E-06 3.00E-06 8.00E-06 1.00E-05 2.00E-05 2.00E-05 3.00E-05 5.00E-05-0.5 0 5.00E-05 5.00E-05 6.00E-05 6.00E-05 6.00E-05 7.00E-05 7.00E-05 7.00E-05 8.00E-05 1.00E-04-1 0 3.00E-05 1.00E-04 1.00E-04 1.00E-04 1.00E-04 1.00E-04 1.00E-04 1.00E-04 1.00E-04 0.0002-1.5 0 1.00E-07 1.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04-2 0 4.00E-08 3.00E-05 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 3.00E-04-2.5 0 2.00E-08 1.00E-06 1.00E-04 2.00E-04 3.00E-04 3.00E-04 3.00E-04 3.00E-04 3.00E-04 3.00E-04-3 0 7.00E-09 3.00E-08 4.00E-05 2.00E-04 2.00E-04 3.00E-04 3.00E-04 3.00E-04 3.00E-04 4.00E-04

Offshore Height

3.2.1 Calculating Wave Attenuation

012345__ 2345 AAAAAAmHouseHs +×+×+×+×+×= χχχχχ




Where:

Hs_House_m represents the wave height in meters at the structure.

A5 through A0 represent the constants from the wave attenuation tables. Selected using Freeboard_m and the Hmax.

Where:

Hmax represents the maximum wave height in each ¼-month for the reach-specific WAVAD _Id, from the Wave Heights database.

Freeboard_m represents the freeboard on the bank (negative for flooding events). ( )yrSurgeLakelevelionLandElevatmFreeboard 2_ +−=

Where:

LandElevation represents the average of the land elevation values for a particular parcel, as sourced from the Parcel database.

Lakelevel represents the ¼-monthly lake level as sourced from the Water Level database.

2yrSurge represents the 2 year return-period storm surge for the relevant county, as sourced from the County database.

3.3 Damage to Structures

Damages to structures as a result of flooding can be caused by several different mechanisms; these include wave impacts, inundation damages, and long-term factors such as rot and corrosion if the flood event is of sufficient duration. Unless otherwise stated, damages are stated in percent damage of the structure itself.

3.3.1 Definition of a Structure

The focus was primarily on privately-owned riparian properties and public parkland facilities. There may be further flooding damages to marinas and municipal/industrial infrastructure, however other Technical Working Groups represent those interests. For the flooding performance indicator, only permanent structures and mobile homes were considered. Although there may be impacts to garden sheds, greenhouses, docks, etc. the damages are far less significant, and data regarding the economic value of such structures is non-existent.




From extensive fieldwork, and review of the oblique aerial photography, it was determined by Baird & Associates that the most common and appropriate structure type for damage calculations was a single story residential structure.

3.3.2 Damages to Structures Caused by Inundation

A structure may be damaged simply by a high lake level. When a structure becomes inundated, the water has risen above the lowest opening and damage to gypsum/plaster wallboards, insulation, electrical components, etc. begins. The damage is calculated using stage damage curves. The stage-damage curves that are used for the Flooding Performance Indicator were originally developed by FEMA. (pers comm., Dr. John Hoehn). A sample is shown below in Figure 3.5. If the lake level reaches 3 ft above the main floor, 23% of the structure value is lost.

Figure 3.5 FEMA stage damage curve used in the flooding performance indicator.

Figure 3.6 presents an example of a structure that has been damaged by inundation only, as it was sheltered from direct inundation. The home is located in Monroe County, NY.




Figure 3.6 A home in Monroe County, NY subject to inundation damages

3.3.3 Damages to Structures Caused by Wave Impacts

A structure may be damaged by waves striking the exterior sides of the structure. This is only possible when the lake level is above the land elevation surrounding the building. Waves generated offshore generally dissipate before striking the structure, but some may make contact. Waves contain incredibly large amounts of energy; and therefore relatively small waves can cause significant damage. Structural components such as cladding/siding, porch stairs, basement windows, screened-in porches and doors are particularly susceptible to this type of damage. In a joint publication, the Ontario Ministry of Natural Resources (MNR) and Environment Canada (1981) presented survey results with data from Great Lakes property owners about damages to structures during the 1973 high lake-level period where some buildings were subjected directly to wave forces. The results, as seen below in Figure 3.7, were used to provide a relationship between the wave power at the house and percent damage. Also seen below in figure 3.8 is a photograph displaying a home in Monroe County being damaged by wave forces during a storm.




Figure 3.7 Percent damage to single-story wood-frame residences when subjected to wave attack.

Figure 3.8 A home in Monroe County, NY subjected to wave forces




3.3.4 Calculating Damages to a Structure caused by Inundation

All structures within the flooding hazard zone may be damaged by inundation.

( )TypeStructuremmfaboveHeightfStructureInunDamage _,_____ =

Where:

Damage_Inun_Structure represents the percent damage to a structure caused by inundation in the current quarter-month.

Structure_Type represents the equation to be used, based upon the preferred structure type.

Height_above_mf_m represents the lake level relative to the main floor elevation. Above the main floor elevation is positive.

mElevFloorMainmFloodWLmmfaboveHeight ________ −=

Where:

WL_Flood_m is as calculated

Main_Floor_Elev_m is sourced from the REACH database.

3.3.5 Calculating Damages to a Structure Caused by Wave Attack

Damage to a structure caused by wave attack should only be calculated if a structure is exposed to the open lake and if it is in the velocity zone:

Exposure = 981 AND Velocity_Zone = -9987.

Where:

Exposure is sourced from the Reach database

Velocity_Zone is sourced from the Parcel database.

If these two conditions are not both met, the structure can only be damaged by inundation.

WavePowerWavePowerWavePowerWavePowerStructureWavesDamage

×+×+

×−×=

2652.00797.00053.00001.0__

2

34




Where:

Damage_Waves_Structure represents the percent damage to a structure caused by wave attack in the current quarter-month.

WavePower represents the wave power (or energy flux) in Watts/m.

mFreeboardgmHouseHsg

WavePower w _8

__ 2

×××

=ρ

If WavePower is greater than 45, then Damage_Waves_Structure = 100.

Where:

Hs_House_m is as calculated

Freeboard_m is as calculated

g represents acceleration due to gravity, in m/s.

wρ represents the density of water in kg/m3

3.4 Damages to the Contents of a Structure

Damages to the contents of a structure as a result of flooding can be caused by inundation damages, and long-term factors such as rot and corrosion. Unlike the structure itself, wave forces cannot directly damage the contents of the structure, as the walls of structure generally protect the contents from wave impacts. Unless otherwise stated, damages are stated in percent damage of the structure contents themselves.

3.4.1 Damages to Structure Contents Caused by Inundation

A high lake level may damage the contents of a structure; as the interior of the building gets flooded, the furniture, appliance, electronics, artwork, finishing-work, etc. begin to get wet and experience damage. The estimated damage is calculated using stage damage curves. The stage damage curves that are used for the Flooding Performance Indicator were originally developed by FEMA. A sample is shown below in Figure 3.9. It can be seen in the figure, that as the lake level increases, the damage increases.




Figure 3.9 FEMA stage damage curve used in the flooding performance indicator

Figure 3.10 Damage to contents caused by inundation (Photo Courtesy Mr. J. Schultz)




3.4.2 Calculating Damages to Structure Contents caused by Inundation.

All structures within the flooding hazard zone may be damaged by inundation.

( )TypeStructuremmfaboveHeightfContentsInunDamage _,_____ =

Where:

Damage_Inun_Contents represents the percent damage to the contents of a structure caused by inundation in the current quarter-month.

Structure_Type represents the equation to be used, based upon the preferred structure type.

Height_above_mf_m represents the lake level relative to the main floor elevation. Above the main floor elevation is positive.

mElevFloorMainmFloodWLmmfaboveHeight ________ −=

Where:

WL_Flood_m is as calculated.

Main_Floor_Elev_m is sourced from the REACH database.

3.5 Long-term Effects of Inundation and Wave attack

The curves provided by FEMA were developed from observed and recorded data following short duration events, such as river flooding or extra-tropical events, such as hurricanes. These flood waters may prevail for several hours to days, but generally not longer than one week. The extreme high water levels on Lake Ontario are quite different. For example, high levels may develop in the spring and remain high for weeks or even months.

During prolonged inundation, the effects of long-term flooding damage such as the onset of mold, mildew, bacterial growth, permanent electrical damage, wood rot, steel corrosion, etc. are very difficult, if not impossible to model. However, if left unchecked, eventually the structure would deteriorate beyond repair due to these processes. For this reason, if a flood event contains more than 12 quarter-months of inundation (~3 calendar months), then the structure and its contents are predicted to be damaged beyond repair, and thus the flood lose is 100 percent damaged.




3.6 Impacts of a Flooding Event

It is important to recognize that the calculated damage based on the algorithms described above may occur in any given quarter-month or consecutive quarter-months. However, additional programming was required to ensure the function was predicting logical impacts. For example, if there are two consecutive quarter-months where the calculated flood damages are 20% and 10% (respectively), it is unlikely that the total damages caused in those two quarter-months is 30%. Realistically, the damage is done in the first quarter-month, and cannot be re-damaged in the second quarter-month, as repairs are not completed immediately. Therefore, the flood damage associated with the second 10% event have already occurred during the first 20% event.

For the above reasons, only the maximum predicted damage during an individual flooding event that extends across multiple quarter-months is considered. Furthermore, it was decided that an event should be defined as follows: The first quarter-month of an event occurs when the lake level exceeds the land elevation such that water reaches the foundation and damage can occur. The final quarter-month in an event occurs when waters recede past the foundation and it is followed immediately by a quarter-month without any damage. Once the flooding event is defined, economic damages are calculated based on the highest lake.

During the defined ‘storm period’, we assume the structure owner does not undertake repairs as there is still damage occurring; rather, the owner waits until the damage is complete and the lake levels have subsided, and show no signs of imminent return to the damage levels. A Buffer Window of 12 quarter-months is then assigned during which repairs are completed. After a simulated repair, the structure can then be damaged again by a flood event.

Should the simulation end during a defined storm, the repairs and related economic calculations will be completed after the final quarter-month time step.

3.7 Combining the Percent Damages

While the three different types of damage (structure caused by waves, structure caused by inundation, and contents caused by inundation) are unique in how they are calculated, it must be recognized that these events are all interconnected, as they are most often happening simultaneously with one or more other events.

Since waves on the side of a structure are capable of causing far more significant damage than simply inundation alone, there is a point where the waves “take over”. Or rather the damage expressed in the wave calculations is including the damage created by the inundation calculations. Through a series of calibrations, and professional judgment, Baird & Associates determined the following threshold:




When Damage_Waves_Structure > 50, Damage_Inun_Structure = 0.

When a structure is completely lost due to wave forces, it must be assumed that the contents are also lost, as there is no longer any structure to protect the contents from complete damage or removal. For this reason, Baird & Associates determined the following threshold:

When Damage_Structure ≥ 100, Damage_Inun_Contents = 100.

Where:

Damage_Structure is the maximum damage caused to a structure in an event, caused by either wave attack OR inundation.




4.0 ECONOMICS

The basis for comparison between different regulation plans is economic damages or costs and benefits. This section will address the issues involved with assessing economic damage to existing buildings, based on the assumption of future-inclusion to the Shared Vision Model.

There are several methods available for estimating economic damages caused by flooding. Three of them are presented in this report.

4.1 Resolution of Economic Damages to Existing Shore Protection

While a very comprehensive database has been compiled at a parcel level, it is not appropriate to interpret the economic damages to particular buildings from a simulation. The lack of available data on shore protection structure details, building details, etc. prohibits this approach. However, on a reach basis or over a stretch of many reaches, the function will predict the correct order of magnitude for the flood damages. For this reason, it is recommended that the results not be interpolated to a resolution finer than one reach.

For the Coastal PIs, the Shared Vision Model is calculating impacts for a buffer of approximately 100 m., which generally includes the first two parcel rows in residential areas. Second row parcels are included in the analysis, but are not subjected to damages from wave impacts.

4.2 Economic Value of Buildings and their Contents in the Flooding Hazard Zone

The economic value of structures is extracted from the assessment field in the parcel database. It should be recognized that allowances for future land development has not been incorporated, as this component of “the future” will be discussed in the contextual narratives. In addition, it was assumed that modern flood-proofing standards will be adhered to for new development and homes will not be at risk in the future. Finally, with close to 20,000 existing digital property parcels in the database, there is sufficient information to accurately rank and compare new alternative regulation plans.

Since the value of a homes contents (i.e. furniture) is not included in the assessment records, Insurance Industry recordss were consulted to determine the general ratio of building value versus contents value. The standard value for contents is 50% of the homes assessed value. This percentage is used in the function but also included on the user interface in the FEPS to test the sensitivity of different percentages.




Calculating the building values is done as follows:

LandCumulativeTotalCumulativeCostStructure −=_

Where:

Structure_Cost represents the cost of the structure(s) only, in dollars.

CumulativeTotal represents the total cost of the parcel in dollars. Includes both structure(s) and land value.

CumulativeLand represents the total cost of the land in dollars. It includes only the land value.

4.3 Methods for Estimating Economic Damages due to Flooding

The economics of flood damage are calculated in three different ways in order to provide the study board with the three methods of analyzing damages. As discussed previously, Method I applies economic damages to a structure and its contents after ever flood event, with no repairs/replacements during the simulation, or mitigation of the hazard. Method II assumes repairs are made after every damaging flood event and the building and contents are restored to full value (only to be damaged again). In Method III repairs are completed until the economic cost is more expensive than mitigating the problem (i.e. preventing future flooding damages). While all three techniques are functional in the FEPS, we believe Method III provides the most realistic and appropriate economic values.

4.3.1 Method I – No Repairs

Method I allows a building to sustain damage. After the flood event, it is assumed the owner does not repair the building damage or replace the contents to the previous full value. The building and contents are assigned a new reduced value. Subsequent flooding events and the associated economic damage is calculated against the new reduced value.

For example: If a structure value is $100,000, and it sustains 20% damage during a flooding event, the new structure value is $80,000. The economic impact of the first event is $20,000. Should a subsequent event cause 50% damage, the new structure value would become $40,000. The economic impact of the second event would be $40,000 and the total economic impact of all the flooding events would be $60,000.

The structure is said to have been completely damaged when the structure value goes below $1000.




4.3.2 Method II – Complete Repair without Mitigation

In Method II, following damage to a building and contents, the algorithm calculates the economic cost to restore the structure to its original condition at the end of the buffer window. The method does not incorporate adaptation, and assumes the owner repairs the structure and contents to full value after each flood event, regardless of the number of events, or the total costs of those events.

For example: If a structure value is $100,000 and it sustains 20% damage during a flooding event, we assume $20,000 is “spent” to repair the structure and restore it to its original value of $100,000. The economic impact of the first event is $20,000. Should a subsequent event cause 50% damage, the economic cost of this event is $50,000 to repair/replace the structure/contents to its original value of $100,000. The total economic cost of all the flooding events for the simulation would be $70,000.

4.3.3 Method III - Repair with Mitigation

Method III calculates damage to buildings and contents during a flood. After the building is damaged, the method applies the cost to restore the structure to its original condition at the end of the buffer window. However, this method builds in adaptation, and the property owner is expected to make the repairs each time a damage event occurs, provided the cumulative cost of those events does not exceed a threshold. Should this value be exceeded for a flood event, the cost to restore the building and contents is calculated, and a mitigation cost is included that will prevent all future flood risks. The threshold is calculated as follows:

Mitigation_Threshold = 0.4 × Structure_Cost (damage ration before mitigation in Fig. 4.1)

Where:

Mitigation_Threshold represents the damages that must be incurred (in dollars) before the flood risk is mitigated. In the example above, damage is sustained and repaired until is totals 40% of the structure cost.

The concept of mitigation costs was included in Method III to build in adaptation, which is a realistic human reaction to excessive or repeated flooding events. This value represents the owners cost to move the building, raise the building above the flood hazard, or build appropriate shore protection. While it is impossible to know exactly what a riparian would do, this algorithm assumes the owner would do something to prevent future damages. As such, once a mitigation cost is applied, the parcel is no longer subject to flood damage. The cost of this mitigation is calculated as follows:

Mitigation_Cost = 0.2 × Structure_Cost (mitigation ration in Fig. 4.1)




For example (using Mitigation Threshold and Costs from above): If a structure value is $100,000, and it sustains 45% damage during a flooding event, $45,000 is “spent” to repair the structure and restore it to its original value of $100,000. The economic impact of the first event is $45,000. Since the mitigation threshold has been exceeded (Mitigation_Threshold = $40,000), a mitigation cost of $20,000 is applied, and no subsequent damages will occur during the simulation. The total economic impact of flooding for the simulation would be $65,000.

4.4 Economic Damages caused by flooding in Niagara County

The full 101 year simulation of damages caused by flooding has been run for Niagara County, NY using the four base hydrographs and Method III (with mitigation). The input menu for the FEPS tool is presented below in Figure 4.1. The user selects the parcel limits in the upper left (i.e. Niagara Co.), calculation method, and driving forces (i.e. existing regulation plan selected – 1958D with Deviations). Economic variables are specified in the upper right corner and damage variables/ratios in the lower right. For example, the damage ratio before mitigation is 40% of initial structure value.

Figure 4.1 Input menu for the FEPS Flooding Algorithm (Method III variables)




The results for structure and contents damage, plus mitigation (Method III) are summarized in Table 4.1 below for the 101 year simulations. 1958D with deviations resulted in 48 homes flooded for a total of 2.5 M in damages. The damages for Plan 1998 were slightly more at 3.2 M. The 101 year simulation for Pre-Project water levels featured almost twice as many homes flooded (111) and 7.1 M in economic damages. The damages for 1958D without deviations were orders of magnitude greater at 267 houses flooded and 23.7 M in economic damages.

Table 4.1 Niagara county flooding damages by regulation plan for Repairs with Mitigation – Method III (all values in millions of dollars).

Structure Contents Mitigation Total

Plan Present ($x106)

Damages ($x106)

Present ($x106)

Damages ($x106) ($x106) Homes

Flooded Damages ($x106)

1958D w Deviation

s 1.5 0.5 0.5 58 2.5

1958D wout dev 13.8 6.2 3.7 267 23.7

1998 1.9 0.7 0.6 61 3.2 Pre-

project

14.14

4.2

7.07

1.7 1.2 111 7.1

Table 4.2 summarizes the results for Method II, which assumes all flooding damages are repaired 100% and no actions are taken to mitigate the hazard. Homes in low lying areas could be repeatedly flooded throughout the simulation and are always repaired.

Table 4.2 Niagara county flooding damages for Method II, Repairs without Mitigation (all values in millions of dollars).

Structure Contents Mitigation Total

Plan Present ($x106)

Damages ($x106)

Present ($x106)

Damages ($x106) ($x106) Homes

Flooded Damages ($x106)

1958D w Deviation

s 68.9 33.0 786 101.90

1958D wout dev 96.6 46.0 1,337 142.6

1998 73.0 34.9 820 107.9 Pre-

project

14.14

68.1

7.07

31.4 1163 99.5




For the existing regulation plan (1958D with deviations), damages increased by 40 times for Method II (no mitigation) versus Method III (with mitigation). For mitigation costs of 0.5 M, almost 100 M in economic damages associated with flooding were avoided. There are several important observations based on findings for Method II and III:

• It is less expensive to mitigate coastal flood hazards than to continuous sustain the damages and repair a home to full value (structure and contents). Method II damages for 1958D with deviations are 102 M, while the Method III damages were only 2.5 M.

• The results from Table 4.2 Method II closely approximate the results that would be generated from a traditional “Stage Damage Curve”. When economic impacts of flooding for a reach of shoreline are calculated simply by relating dollar damage to a lake level, it is impossible to integrate mitigation techniques or even keep track of the number of flooding events at a particular parcel. These limitations were highlighted by the Yoe 1992 report prepared for Environment Canada during the Levels Reference Study and it would be unacceptable to follow this approach again in the current investigation.

• The parcel by parcel analysis in the FEPS algorithm provides a much more realistic representative of human behavior and generates plausible economic damages. A riparian land owner would not sustain flood damage year after year and continue to repair the home to full value. However, this unrealistic approach is precisely the type of economic damages calculated by a traditional Stage Damage curve.

4.5 Economic Costs of Flooding for Lake Ontario

The examples in Section 4.4 provided details of the calculations for Method II and III in Niagara County, NY. Section 4.5 summarizes the results of the lakewide calculations for the Flooding Performance Indicator.

Recall that all parcels with land elevations equal to or less than 77.2 m IGLD’85 (3.0 m above CD) at the building foundation were considered susceptible to flooding for the range of alternative regulation plans under consideration. Therefore, the surrounding land elevation(s) and main floor offset was included for the these parcels in the database. In total, there are 3,143 riparian properties within this zone.

Figure 4.2 summarizes the spatial distribution of these parcels by County in NY State and Regional Municipality in Ontario. Monroe County has the highest concentration of flood parcels, with over 1,000 homes in the hazard zone. Hamilton, Orleans and Oswego County have between 400 to 500 parcels. Several counties have very few, including Cayuga, Halton, Peel and Toronto. It is also important to note that some of the Canadian Regional Municipalities did not have digital parcel data and thus were not included in the analysis (i.e. Bay of Quinte).




Figure 4.2 Number of Parcels in the Flood Hazard Zone of Lake Ontario (note, some regions not covered by digital parcel database, such as Bay of Quinte)

As discussed earlier, our recommendation for the Plan Formulation and Evaluation Group is to utilize Method III, which integrates mitigation in the methodology. Figure 4.3 summarizes the economic costs of flooding for a 101 year simulation. The analysis was completed on four regulation plans and hydrographs, including: 1958D with and without deviations, Plan 1998 and the Pre-Project condition.

Total damages for 1958D with deviations over the 101 years are $103 million. The damages associated with Plan 1998 are slightly higher, at $110 million. Under the simulated Pre-project lake levels, damages increase dramatically to $236 million. When 1958D is simulated without deviations, the high lake levels in the 1980’s cause significant damages, and the total economic impact is $678 million.

There are two principal observations for this PI. First, the operation of the St. Lawrence Seaway has significantly reduced the potential for flooding impacts on Lake Ontario. Second, this PI is very sensitive to high lake levels. For example, in most years, Plan




1998 features lake levels lower than 1958D with deviations. However, for a few years, such as 1947, 1974, and 1976, Plan 1998 features higher peak summer water levels. These years also represent some of the highest lake levels from 1900 to 2000 and consequently the economic damages associated with Plan 1998 are slightly higher than Plan 1958D with deviations.

Figure 4.3 Economic Costs of Flooding for 101 Year Simulation (damages in real dollars, no discounting)




5.0 SUMMARY

5.1 Required Data

In order to evaluate the flooding impacts to existing buildings with the SVM, certain data will be required from all of the databases. Table 5.1 lists all of the required variables necessary for shore protection impact analysis and the databases they are found in.

Table 5.1 Required Data for the Evaluation of Flooding Impacts

Database Variable Unit

WAVE_ATTEN.xls Wave Attenuation coefficients No Units

COUNTY.xls 2 year surge Meters

WAVAD_HEIGHTS.xls The Maximum wave height occurring in a quarter-month

Meters

WAVAD_HEIGHTS.xls The average wave height occurring in a quarter-month

Meters

PARCEL.xls Land Elevation Values Meters

PARCEL.xls Distance to Bluff Meters

PARCEL.xls Velocity Zone No Units

REACH.xls WAVAD_Id – the WAVAD point to use

No Units

REACH.xls Main Floor Elevation Meters

REACH.xls Exposure to the Open Lake No Units




5.2 Fields and flags for Parcel Database

All of the parcels present on Lake Ontario will been included in the parcel database. The parcels that qualify for flooding damages will have to be selected from the parcel database with the SVM. Only parcels with a land elevation greater than 0 should be included in the flooding damages calculations.

5.3 Recommended Programming Algorithm

Baird & Associates has programmed the Flooding Performance Indicator functionality into the FEPS application. The algorithm used is included as a flowchart in Appendix A.

We look forward to your comments. Please call or e-mail if you have any questions or concerns.




6.0 REFERENCES

Dewberry and Davis, 1986. Design Manual for Retrofitting Flood-prone Residential Structures. Prepared for the Office of Loss Reduction, Federal Emergency Management Agency under Contract Number EMU-84-R-1749.

Environment Canada (Fisheries and Oceans) and Ontario Ministry of Natural Resources, 1981. Great Lakes Shore Management Guide.

Nairn, R.B., and Southgate, H.N. 1993. Deterministic profile modelling of near shore processes. Part 1. Waves and Currents. Coastal Engineering., 19, pp 27–56., Part 2. Sediment transport and beach profile development. Coastal Engineering, 19, pp 57– 96.

Schultz, J. Personal Communications, 30 March 2004, data downloaded from http://www.law.uh.edu/librarians/jschultz/TheBigOne.html

USACE, 2002. DRAFT Coastal Storm Damage Relationships: A Workshop to Elicit Expert Opinion. USACE Institute for Water Resources.

Yoe, C., 1992. A Critical Review of Existing and Updated U.S. and Canadian Stage-Damage Curves. Prepared for Environment Canada.




http://www.law.uh.edu/librarians/jschultz/TheBigOne.html

APPENDIX A Recommended Programming Algorithm


Model Application

Baird & Associates

Appendix

Start of Flooding Routine

Obtain or define the following variables:

Flood_calc_method (from user input)

Geographic_extents (from user input)

Plan (WL plan from user input)

Sig_Damage_mult (from user input)

Time_to_repair (from user input)

Wave_dam_thresh (from user input)

Time_fail_threshold (from user input)

Mitigation_cost_ratio (from user input)

For each Reach in Geographic_extents, GET:

County (from REACH DB)

WAVAD_pt (from REACH DB)

Exposure (from REACH DB)

Flow Chart for IJC Flooding AlgorithmPage 1 of 3

From County, GET:

2yr_storm_surge (from COUNTY DB)

MainFloorOffset (from COUNTY DB)

Start of Parcel Loop

DO for each parcel in Reach

Start of Reach Loop

DO for each reach in Geographic_extents

From Parcel, GET:

DistToBluff_m (from PARCEL DB)

LandElevation (from PARCEL DB)

CumulativeTotal (from PARCEL DB)

CumulativeLand (from PARCEL DB)

CALCULATE:

Main_Floor_Elev_m = LandElevation + MainFloorOffset

Structure_Cost_USD = CumulativeTotal –CumulativeLand

Total_Cost = 0

Count_since_last_repair = 0

Number_fails_since_repair = 0

Determine Structure_Type by Structure_Cost_USD Ranges

Start of Week Loop

DO for each ¼-Month in Plan

For Each 1/4 –month time-step, GET:

WaterLevel_m_IGLD85 (from WLS DB)

Hs_max (from WAVE_HTS_USA DB)

CALCULATE:

WL_Flood_m = WaterLevel_m_IGLD85 + 2yr_storm_surge

Freeboard_m = LandElevation -WL_Flood_m

Height_above_mf_m = WL_Flood_m –Main_Floor_Elev_m

Using Freeboard_m, Hs_max, GET:

A5 (from FLD_ATTEN_X5 DB)






Is the reach exposed?

IS Exposure = 981 ANDVelocity_Zone = -9987 ?

YES

NO

CALCULATE Attenuation Hs_House_m:

Hs_House_m = A5 x DistToBluff_m5+…+ A1x DistToBluff_m1 + A0

CALCULATE Power:

Power = (1000*9.81*Hs_House_m2)/8 * (9.81*Freeboard)0.5

CALCULATE Wave Damage:

Damage_Waves_Structure = 0.0001*Power4

– 0.0053*Power3 + 0.0797*Power2+ 0.2652*Power

IS Power < 45

YES

NO


Damage_Waves_Structure = 0


Damage_Waves_Structure = 100

CALCULATE Inundation Contents Damage:

Damage_Inun_Contents =

Use equation selected by Structure_Type

CALCULATE Inundation Structure Damage:

Damage_Inun_Structure =

Use equation selected by Structure_Type

Combine Damage?

IS Damage_Waves_Structure > Wave_dam_thresh

YES

NO

CALCULATE Damages:

Damage_Structure = Damage_Waves_Structure

Damage_Contents = Damage_Inun_Contents

CALCULATE Damages:

Damage_Structure = Damage_Waves_Structure + Damage_Inun_Structure

Damage_Contents = Damage_Inun_Contents

1C

1B

1A

GOTO

2A

Is the lot wet?

IS Freeboard <= 0?

YES

NO


Damage_Structure = 0

Damage_Contents = 0

GOTO

2A

Is parcel Flood-prone?

IS LandElevation > 0

YES

NO

GOTO

1BDO NEXT PARCEL

Should skip parcel?

IS Dist2Bluff = -9997, -9994, or –9987 ?

YES

NO


2A

Fully Damaged Contents?

IS Max_Damage_Contents >=100 NO

YES

CALCULATE Maximum Damages:

Max_Damage_Contents = 100

Fully Damaged Contents?

IS Max_Damage_Structure >=100 NO

YES


Max_Damage_Structure = 100


GOTO

1BDO NEXT PARCEL

CALCULATE Economic Damage:

Total_Cost = Total_Cost + (Max_damage_structure / 100 * Structure_Cost_USD) +(Max_Damage_Contents / 100 * Structure_Cost_USD * 0.5)

Total_Building_Cost = Total_Building_Cost + (Max_damage_structure / 100 * Structure_Cost_USD)

Total_Contents_Cost = Total_Contents + (Max_Damage_Contents / 100 * Structure_Cost_USD * 0.5)

Reset Cumulative Variables



Counter_since_last_repair = 0

Number_fails_since_repair = 0

Is it time to repair?

IS Counter_since_last_repair > Time_to_repair

NO

YES

GOTO

1CDO NEXT ¼-Month

Should resolve problem?

IS Total_Building_Cost >= Sig_damage_mult * Structure_Cost_USD ?

YES

NO

CALCULATE ResolveCost:

Total_Cost = Total_Cost + Mitigation_Cost_Ratio * Structure_Cost_USD + 5000

Is it the last week?

NO

YES


NO

YES

GOTO

1BDO NEXT PARCEL

GOTO

1CDO NEXT ¼-Month

Does Method do repairs?NO

YES

GOTO

3A

CALCULATE Maximum Structure Damages:

Max_Damage_Structure = Damage_Structure

Is it safe?

IS Damage_Structure = 0

AND Damage_Contents= 0 ?YES

NO

BUFFER Counter :

Counter_since_last_repair = Counter_since_last_repair + 1

BUFFER Counter :

Counter_since_last_repair = 0

Number_fails_since_repair = Number_fails_since_repair + 1

Maximum in event?

IS Damage_Structure > Max_Damage_Structure? YES

NO

Maximum in event?

IS Damage_Contents > Max_Damage_Contents?YES

NO

CALCULATE Maximum Contents Damages:

Max_Damage_Contents = Damage_Contents

Has it been flooded for too long?

IS Number_fails_since_repair > Time_fail_threshold

NO

YES





3A CALCULATE Economic Damage:

Total_Cost = Total_Cost + (Damage_structure / 100 * Structure_Cost_USD) +(Damage_Contents / 100 * Structure_Cost_USD * 0.5)

Completely Damaged?

IS Total_Cost >= Structure_Cost_USD

NO

YES


NO

YES

GOTO

1BDO NEXT PARCEL

GOTO

1CDO NEXT ¼-Month

CALCULATE Total Cost :

Total_Cost = Structure-Cost_USD

GOTO

1BDO NEXT PARCEL

flooding performance indicator: methodology and

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