HURRICANE SANDY LIMITED REEVALUATION REPORT UNION BEACH, NEW JERSEY DRAFT ENGINEERING APPENDIX SUB APPENDIX E OVERTOPPING & FAILURE ANALYSIS Revised 18 Feb 2015 1
OVERTOPPING & FAILURE ANALYSIS 1.0 Introdution Overtopping was analyzed using 2013 FEMA Stage Elevations. The overtopping analysis, for the designed vertial wall and levee, used the interative omputer-based design and analysis system, ACES (whih is based on equations found in the Corps of Engineers Coastal Engineering Manual (CEM)) and the online version of EurOtop (whih is based off equations that an be found in the EurOtop Overtopping Manual) for omparison. The analysis inluded the development of peak overtopping rates for various idealized return periods ( 2 year, 5 year, 10 year, 25 year, 50 year, 100 year, 200 year, and 500 year). ACES and EurOtop used both the Probabilisti and Deterministi approah to analyze the overtopping for the design of the vertial wall and levee. Overtopping Analysis of the Dune and Beah areas will be explained briefly in this sub-appendix. More information of the Overtopping Analysis of the Dune and Beah areas an be read in Sub-Appendix D SBEACH. The projet onditions utilized the vertial wall, levee, and dune/beah dimensions and elevations formulated in the previous Feasibility Report and were referened to NGVD 29 vertial datum. In addition, the Union Beah Exeedane Interval was analyzed from Waves Overtopping Levees using HEC FDA at 90% Confidene. The risk-reduing apability of the Union Beah projet during hurrianes and northeasters is dependent upon the bay-fronting levees and floodwalls ability to resist against wave overtopping and still water overtopping flowrate fores. Wave breaking may result in water splashing over the rest onto the landward side of the protetion when the still water surfae elevation is lower that the rest elevation of the levee or floodwall. These wave flowrates have the potential of ausing sour and possibly failure of the protetive ability of the feature. Still water overtopping ours when the still water surfae elevation exeeds the rest elevation and water simply flows over the rest. The vertial distane between the elevation of the still water surfae and the rest elevation of the protetion feature is alled freeboard; large freeboard results in smaller overtopping flowrates than small freeboard. The elevation of the strutures evaluated is +15 ft. NGVD. 2.0 Probabilisti Approah versus Deterministi Approah As mentioned in the introdution, ACES and EurOtop used both the Probabilisti and Deterministi approah to analyze the overtopping for the design of the vertial wall and levee. Design onditions for major oastal and flood protetion projets are often vague and design parameters ontain large unertainties. Imposed fores, as well as the strengths and interations of the various omponents are usually not learly understood and the design proess itself is ill defined. In the past, designs were stritly based on deterministi expressions. A deterministi model is one in whih every set of variable states is uniquely determined by parameters in the model and by sets of previous states of these variables. Therefore, deterministi models perform the same way for a given set of initial onditions. More reently, probabilisti design methods have been introdued, in whih randomness is present and variable states are not desribed by unique values, but rather by probability distributions. Both approahes are typially used and ompared. 2
3.0 Overtopping Flood Wall Analysis The overtopping rates were alulated for the projet flood wall using the overtopping formulations provided in the EurOtop software and ACES. The equations, formulations used, and results from eah method are shown and explained throughout this setion and sub-setions. 3.1 ACES ACES is an interative omputer-based design and analysis system in the field of oastal engineering ontaining six funtional areas: wave predition, wave theory, wave transformation, strutural design, wave run-up, and littoral proesses. For the purpose of this analysis ACES was used to alulate wave-overtopping for the projet flood wall onditions. Below (Figure 3.1) is an image of the ACES interative interfae for solving for wave-overtopping: Figure 3.1 ACES interfae Note: Values shown in the interfae were not used in this analysis. 3
The inident signifiant wave height (Hi), peak wave period (T), COTAN of nearshore slope (ot phi), water depth at struture toe (ds), COTAN of struture slope (ot theta), struture height above toe (hs), and onshore wind veloity (U) are input into the ACES interfae. The Overtopping oeffiient (alpha) is omputed in ACES based off of the COTAN of struture slope value. The Run-up for signifiant waves (R), Deepwater signifiant wave (Ho), Relative height (ds/ho), and the Wave steepness (Ho/gT 2 ) are all alulated from the equations programmed in ACES. The Overtopping Coeffiient (Q*o) an be found by using Figures 7-24, in the Shore Protetion Manual (SPM). Results are shown in Setion 3.4 Individual Model Results of Flood Wall Overtopping Analysis. 3.2 EurOtop The overtopping rates were alulated for flood wall onditions using the more reent overtopping formulations provided in the online EurOtop software. Below (Figure 3.2) is an image of the EurOtop interative interfae for solving for wave-overtopping for a vertial wall: Figure 3.2 EurOtop interfae 4
The wave period (T), wave height at toe of the struture (Hmo), freeboard (R) and the water depth at toe of struture (hs) are all input into the alulation tool and the mean overtopping is solved for, as well as the wave type. A ritial determination for the overtopping analysis was to determine if the waves breaking against the wall were Non-Impulsive or Impulsive. This riteria was important in deiding whih speifi overtopping formula should be used for a vertial seawall overtopping situation. The formula for alulating Non-Impulsive vs. Impulsive waves has been provided below as Figure 3.3, and one again this is a snap shot taken diretly from the EurOtop Manual. Figure 3.3 - Formula for alulating Impulsive vs. Non-Impulsive waves (EurOtop Manual) One the wave breaking/overtopping onditions were determined using the above alulation the atual overtopping rate was alulated. For the projet area the waves were determined to be impulsive and this was due to the relatively shallow water and breaking wave onditions in front of and at the wall. The formula used for alulating the overtopping rates has been provided below as Figure 3.4 and it was taken as a snapshot from the EurOtop Manual. Figure 3.4 - Overtopping formula for Impulsive wave onditions (EurOtop Manual) The probabilisti and deterministi methods were both solved for in the EurOtop software. Results are shown in Setion 3.4 Individual Model Results of Flood Wall Overtopping Analysis. 5
3.3 Spreadsheet (hek) An exel spreadsheet (based on the Frano and Frano (1999)) was used as tool to ompare with other methods. Below are the equations used to solve for Wave Overtopping. One an see that equations are similar to the ones used in the EurOtop software. Figure 3.5 Print Sreen of equations used in Spreadsheet for Wall The probabilisti and deterministi methods were both solved for in the spreadsheet Results are shown in Setion 3.4 Individual Model Results of Flood Wall Overtopping Analysis. 3.4 Individual Model Results of Flood Wall Overtopping Analysis Table 3.1 and Figure 3.6 show a omparison of the results of eah method used. 6
Overtopping of Wall (ft^3/s/ft) Retur Stillwate ACES EurOTOP - EurOTOP - Spreadsheet Spreadsheet n r Level Probabilisti Deterministi - - Period in ft. Probabilisti Deterministi (yr) NGVD 2 5.7 0.0000 0.0000 0.0000 0.0000 0.0000 5 7.5 0.0000 0.0000 0.0000 0.0000 0.0000 10 8.9 0.0002 0.0008 0.0066 0.0033 0.0033 25 10.6 0.0196 0.0076 0.0299 0.0325 0.0325 50 11.9 0.5476 0.1001 0.1962 0.4640 0.4640 100 13.3 4.6590 0.6425 0.7727 3.4480 3.4480 200 14.7 Struture n/a n/a 11.0754 11.0754 Submerge d 500 16.6 Struture Submerge d n/a n/a 26.4825 24.5176 Table 3.1 Summary of eah method (for Wall) Note that ACES would not solve Overtopping if Stillwater elevation is above the struture. It states that the "Struture is Submerged. Also, EurOTOP would not solve overtopping for the 200 year and 500 year water levels, due to the negative freeboard. OVERTOPPING OF WALL 30.0000 Wave Overtopping Rate (ft^3/s/ft) 25.0000 20.0000 15.0000 10.0000 5.0000 0.0000 2 5 10 25 50 100 200 500 Return Period (yrs) ACES EurOTOP - Probabilisti EurOTOP - Deterministi Spreedshet - Probabilisti Spreadsheet - Deterministi Figure 3.6 Comparison of eah method used (for Wall) 7
4.0 Overtopping Levee Analysis The overtopping rates were alulated for the projet levee onditions using the overtopping formulations provided in the EurOtop software and ACES. The equations, formulations used, and results from eah method are shown below. 4.1 ACES The same analysis that was done for the flood wall was used for the levee; however, the only differene was that the appropriate slope (angle) was used for the levee. For the wall, 90 degrees (or COTAN of one) was used for the struture slope value to represent the slope of a vertial wall. Also, the overtopping oeffiient (Q*o) an be found by using Figures 7-25 thru 7-34 (whihever one is appropriate for this projet), in the Shore Protetion Manual (SPM). Results are shown in Setion 4.4 Individual Model Results of Levee Overtopping Analysis. 4.2 EurOtop The overtopping rates were alulated for levee onditions using the more reent overtopping formulations provided in the online EurOtop software, whih is based off equations that an be found in the EurOtop Overtopping Manual. To simulate a levee the simple slope tool was used. Below (Figure 4.1) is an image of the EurOtop interative interfae for solving for waveovertopping for a simple slope (used to simulate a levee): 8
Figure 4.1 EurOtop interfae The wave period (T), wave height at toe of the struture (Hmo), slope, freeboard (R) and material the levee will be omposed of are all inputted into the alulation tool and the mean overtopping is solved for, as well as the wave breaking type. Results are shown in Setion 4.4 Results of Overtopping of Levee Analysis. 4.3 Spreadsheet (hek) The spreadsheet was also used to solve for overtopping of a levee. Below (Figure 4.2) is an image from the spreadsheet. Subritial Flow Regime Superritial Erosion Zones 1 2 3 v h w h p h h w Hydrauli jump v 3 Figure 4.2 Print Sreen of equations used in Spreadsheet for Levee Results are shown in Setion 4.4 Individual Model Results of Levee Overtopping Analysis. 9
4.4 Individual Model Results of Levee Overtopping Analysis Table 4.1 and Figure 4.3 show a omparison of the results of eah method used. Overtopping of Levee (ft^3/s/ft) Retur Stillwate ACES EurOTOP - EurOTOP - Spreadsheet Spreadsheet n r Level Probabilisti Deterministi - - Period in ft. Probabilisti Deterministi (yr) NGVD 2 5.7 0.000 0.000 0.000 0.000 0.000 5 7.5 0.000 0.000 0.000 0.000 0.000 10 8.9 0.014 0.046 0.072 0.003 0.003 25 10.6 0.180 0.214 0.288 0.033 0.033 50 11.9 1.470 1.295 1.500 0.464 0.464 100 13.3 5.084 5.345 5.561 3.140 3.140 200 14.7 Struture 12.342 11.862 11.075 11.075 Submerge d 500 16.6 Struture Submerge d 39.199 33.769 41.873 38.766 Table 4.1 - Summary of eah method (for Levee) Note that ACES would not solve Overtopping of the levee, if the Stillwater elevation is above the struture. It states that the "Struture is Submerged. 45.00 OVERTOPPING OF LEVEE Wave Overtopping Rate (ft^3/s/ft) 40.00 35.00 30.00 25.00 20.00 15.00 10.00 5.00 CEDAS:ACES EurOTop - Probabilisti EurOTOP - Deterministi Spreedsheet- Probabilisti SpreedSheet - Deterministi 0.00 2 5 10 25 50 100 200 500 Return Period (yrs) Figure 4.3 - Comparison of eah method used (for Levee) 10
5.0 Overall Model Results of Levee/Floodwall System Overtopping Analysis To update the overall level of projet design performane, studies were examined whih have been performed to develop wave flowrate-damage relationship models. Several of these overtopping models were used to develop the overtopping flowrates for the different return intervals; inluding the Corps Automated Coastal Engineering System (ACES), two Eurotop methods, and a method by Frano and Frano relayed in the Coastal Engineering Manual (EM 1110-2-1100, alled the CEM). The results of these models were averaged, and the averages were ompared to overtopping thresholds. A wave overtopping flowrate threshold of 1.99 fs/ft. was adopted as the Non-Failure point for the soil ement-reinfored levees, based on ERDC lab tests onduted in 2013. A flowrate of 3.00 fs/ft. was adopted as the Failure point. The Non-Failure and Failure points are used in the eonomi lifeyle modeling. Mean water surfae elevations were utilized in the overtopping models, and also the 90% onfidene water surfae elevations. These water surfae elevations, valid in Year 0, are shown in Table 5.1, along with the assoiated freeboards in feet. Histori sea level rise estimates were evaluated in the models, whih added 0.7 ft. to the mean water surfae elevations and also to the 90% onfidene simulations. These water surfae elevations, valid in Year 50 are also shown in Table 5.1 along with the assoiated freeboards. Wave information, inluding wave height and wave period, at the base of the struture were developed using ACES feth-limited analyses, whih takes into aount the average depth along the wind feth, and an array of possible wind feth diretions. These wave heights were heked for appropriateness by omparing with depth-limited waves using the depth of water at the toe of the struture (whih is equal to the water surfae elevation minus the atual grade fronting the struture as determined using LIDAR topography). The feth limited waves in all ases were found to be lower than the depth limited wave height, and thus appropriate. 11
Levee Freeboard for Mean and 90% Confidene Water Surfae Elevations Year '0' & Year '50' Mean Water 90% Confidene Return Surfae Water Surfae Period Elevation in Ft. Elevation in ft. Time Years NGVD Freeboard in ft. NGVD Freeboard in ft. 2 6.1 8.9 6.5 8.5 5 7.5 7.5 8.7 6.3 10 8.9 6.1 10.6 4.4 Year '0' 25 10.6 4.4 13.0 2.0 50 11.9 3.1 14.8 0.2 100 13.3 1.7 16.7-1.7 200 15.2-0.2 19.3-4.3 500 16.6-1.6 21.3-6.3 2 6.8 8.2 7.2 7.8 5 8.2 6.8 9.4 5.6 10 9.6 5.4 11.3 3.7 Year '50' 25 11.3 3.7 13.7 1.3 50 12.6 2.4 15.5-0.5 100 14.0 1.0 17.4-2.4 200 15.9-0.9 20.0-5.0 500 17.3-2.3 22.0-7.0 Table 5.1 Summary of System Freeboard The depth of water fronting the struture, alled ds, played a more important role than initially thought. In the first series of modeling, the ds was omputed as the water surfae elevation minus the elevation of the subgrade bottom of the struture. As ds wasn t used for wave estimation, it was only believed to play a negligible role in the wave overtopping flowrate models. So the overly large ds using the subgrade toe was allowed. It was only when the first series of modeling results seemed overly onservative and every other method had been tried to yield more reasonable results that ds adjustments to aount for earth elevations fronting the strutures were tried as a last resort. Miraulously, this seond series of modeling yielded more expeted and reasonable results. The field of wave overtopping modeling is still in its infany, and has a while to go before the proess is fully understood. This effet of ds on overtopping is one area needing further researh outside of this study. Results of the individual overtopping models are ontained in tables 2.4 and 3.4 above. Results of the average wave overtopping flowrates vs freeboard height are shown below in Figure 5.1. Using Freeboard as the ordinate failitates finding failure and non-failure points for present, future and 90% water surfae elevations. Using the plotted urve, the Non-Failure Point of 1.99 fs/ft. was found to be aused by freeboard of 1.9 ft., and the Failure Point of 3.01 fs/ft. was aused by freeboard of 1.4 feet. 12
Wave Overtopping Flowrate in fs/ft. for +15 ft. Levees 7 6 Wave Overtopping Flowrate in fs/ft. 5 4 3 2 Failure Point 3.01 fs/ft orrelates to 1.4 ft. Freeboard Non-Failure Point 1.99 fs/ft orrelates to 1.9 ft. Freeboard 1 0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Freeboard in ft. Figure 5.1 - Average Wave Overtopping Flowrates vs Freeboard Height The Non-Failure Point freeboard of 1.9 ft. orrelates to a water surfae elevation of 13.1 ft. NGVD, and the Failure Point of 1.4 ft. of freeboard orrelates to 13.6 ft. NGVD. Of interest in this analysis is the return intervals orrelated with these Non-Failure and Failure Point water surfae elevations. The water surfae elevation-frequenies shown above in Table 5.1 are plotted in Figure 5.2 for Year 0, and in Figure 5.3 for Year 50. 13
Water Surfae Elevation in ft. NGVD 25 20 15 10 5 0 Year 0 Water Surfae Elevation- Frequeny 1 10 100 1000 Return Period in years Mean Water Surfae Elevation in ft. NGVD 90% Confidene Water Surfae Elevation in ft. NGVD 25 Figure 5.2 Year 0 Water Surfae Elevation Frequeny Year 50 Water Surfae Elevation- Frequeny 20 15 10 5 Mean Water Surfae Elevation in ft. NGVD 90% Confidene Water Surfae Elevation in ft. NGVD 0 1 10 100 1000 Figure 5.3 Year 50 Water Surfae Elevation Frequeny 14
Results for Year 0 and Year 50 Water Surfae Elevation Frequenies for Mean and 90% Confidene Levels follow: Year 0 Mean Water Surfae Elevations: Non-Failure Point (13.1 ft. NGVD)=94-year return period; Failure Point (13.6 ft. NGVD)=116-year return period Year 0 90% Confidene Water Surfae Elevations: Non-Failure Point (13.1 ft. NGVD)=26-year return period; Failure Point (13.6 ft. NGVD)=32-year return period Year 50 Mean Water Surfae Elevations: Non-Failure Point (13.1 ft. NGVD)=62-year return period; Failure Point (13.6 ft. NGVD)=81-year return period Year 50 90% Confidene Water Surfae Elevations: Non-Failure Point (13.1 ft. NGVD)=19- year return period; Failure Point (13.6 ft. NGVD)=32-year return period 15