6 - STORM SURGES IN PUERTO RICO_Power Plants-Aguirre. Aguirre

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1 1 6 - STORM SURGES IN PUERTO RICO_Power Plants-Aguirre Aguirre Figure 1 shows a GE image of the Aguirre Electric Power Plant inside Jobos Bay. Figure 2 shows a picture of the plant looking at base level from the sea. This gives an estimate of the available freeboard (vertical distance between the sea surface and the terrain elevation). Figure 3 shows the FEMA map for just the area power plant area. Figure 4 shows the nodes of the computational mesh superimposed on the image. The distance between nodes varies between 55 to 86 meters. The images show that the power plant looks to be relatively well protected by Cayos Caribe (easternmost) and Cayos de Barca (westernmost), with an opening (Boca del Infierno) separating them (an opening about 435 meters wide). Figure 1 GE image of the Aguirre Electric Power Plant, located inside Jobos Bay. The FEMA map (Figure 3; the 100- and 500-year event) shows a very narrow coastal strip that gets flooded (see 5 - STORM SURGES IN PUERTO RICO_San_Juan_airport.pdf for the accompanying Legend to all the FEMA maps). Recall that the elevation values listed in the map are relative to MSL. So, for example, for a Base Flood Elevation listed as AE (EL 2.4) one needs to subtract the land elevation in order to estimate the flood depth once you are on land. We can see that the BFE in the VE zone is 4.0 m above MSL. That is, the crest elevation of the highest wave propagating towards the power plant lies, according to the FEMA map, 4 meters above MSL, which puts the crest elevation above most of the terrain elevation where the power plant is located, according to Figure 6 (see Construccion en Zona Costanera.pdf). Figure 4 shows that only three WHAFIS/RUNUP transects (# 146, 147 and 148) were

2 2 Figure 2 Photo of the Aguirre power plant looking at sea level from the sea. Figure 3 FEMA map (tile 2105) for the Aguirre power plant.

3 3 Figure 4 Transect locations where WHAFIS/RUNUP studies were carried out in the preparation of the FEMA maps. located inside the Bay (see 5 - STORM SURGES IN PUERTO RICO_San_Juan_airport.pdf report for an explanation of the WHAFIS/RUNUP transects). The table labelled Table 8 TRANSECT DATA (appearing in the Coastal Technical Report Data Notebook for Puerto Rico Flood Insurance Study) states that the 100-year SWE (including the three storm surge setups) along transects 147 and 148 (inside the Bay) vary between 2.5 and 2.9 meters above MSL. This gives as the maximum wave height inside the Bay along transect 147, according to the FEMA map, values varying between ( )/0.7 = 2.1 m to ( )/0.7 = 1.6 m (see document titled Construccion en Zona Costanera.pdf I will explain how this is estimated). Below we will see the values given by the SWAN model for the different hurricane categories under different sea level rise scenarios (see Figures 25 to 39). Before continuing with showing the flood maps for the Aguirre power plant, there is an issue that needs to be mentioned. Figure 5 shows the bathymetric coverage of the Lidar surveys carried out in the early 2000s as a result of a proposal submitted to FEMA back then (see section titled 4 - CRITICAL INFRASTRUCTURE, SEA LEVEL RISE, AND COASTAL FLOODING IN PUERTO RICO.pdf ). It happens that for some unknown reasons the bathymetric Lidar signal could not penetrate the water column more or less between Guanica and just eastward of Jobos Bay (see cyan color). As shown in the same figure, NOS ship-based data was used to fill up the Lidar gap (while inland elevations were based on Lidar). Ships cannot go close to land. So there must have been a coastal bathymetry gap with no data whatsoever,

4 4 Figure 5 - Bathymetric coverage used in the preparation of the DEMs used for the modeling (NOAA Technical Memorandum NESDIS NGDC- 13; DIGITAL ELEVATION MODELS OF PUERTO RICO: PROCEDURES, DATA SOURCES AND ANALYSIS. L.A.Taylor, B.W. Eakins, K.S. Carignan, R.R. Warnken, T. Sazonova, D.C. Schoolcraft. 2007) that must have been interpolated on the sea side of the output DEM. This could explain the fact that, in contradistinction to the north coast, the DEMs shoreline and Google Earth s shoreline do not, even approximately, coincide. They are shifted by some tens of meters. This is noticeable in the inundation maps for the south coast. This raises a flag in that the GE images will tend to underestimate the inland extent of the flooding. For example, Figure 6 below shows a GE image of the Malecón of Santa Isabel ( Malecón stands for seawall). When you superimpose on the image the shoreline of the Ponce 1/3 arc-seconds DEM shown

5 5 by the red curve (taken as the elevation z = 0 m contour; and after changing the DEM datum from MHW - which is the way they are made - to MSL, one can see the shift that the DEM shoreline has relative to the GE shoreline. The figure also shows the tracks of a jet ski instrumented with a depth sounder and a kinematic GPS. The north-south shift between the red curve and the Malecón varies between 21 and 41 meters for this site. Along the north coast, although the shorelines fit between the NGDC DEMs and GE is not perfect, it is much better. This merits further discussion so as not to be confused. Figure 6 GE image for the Malecóon de Santa Isabel. The (thin) red curve shows the location of the z = 0 m elevation of the Ponce 1/3 arc-seconds (approximately 10 m resolution) prepared by NGDC/NOAA. The multicolor curves show tracks of a fully equipped jet ski used to obtain bathymetry for the site. Note how close the jet ski could come close to the seawall, trying to estimate the shoreline location. The image shows the shift between the DEM shoreline and the GE shoreline. What the computer model sees is the shoreline at the location of the red curve. And inland of the shoreline position it sees the topographic elevations, which being Lidar-derived and bare earth, one assumes that those elevations are good within a certain margin of error. Flooding will occur at those dry computational cells for which, at some moment in the simulation, the sea surface elevation becomes higher. Within the margin of error of the topography elevation measurements, flooding will be correctly computed, and represented. The only handicap is that, when the image of the flooding is overlaid on top of the GE image, it will be displaced south when seen from the GE point of view. If we move the flood image north so that shorelines approximately match, then we will have a better idea of the inland extent of the flooding. This is what I mean when I state above that This raises a flag in that the GE images will tend to underestimate the inland extent of the flooding. Having clarified this, we can then continue by showing the storm surge maps for the Aguirre power plant. Figure 7 shows topographic contours for the Aguirre plant based on the Guayama 1/3 arc-seconds (10 m) DEM created by NGDC/NOAA for tsunami flood mapping. They are superimposed on top of a GE

6 6 image of the plant. We can immediately see the shift in the topography mentioned above. This DEM topography is what the Computer models see. Therefore, to have a better idea of the flood Figure 7 - Topographic contours based on the Guayama 1/3 arc-seconds (10 m) DEM created by NGDC/NOAA for tsunami flood mapping. They are superimposed on top of a GE image of the plant. See the shift in the topography mentioned above. penetration into the Aguirre power plant one should displace landwards the model results until the shoreline of the model approximately follows the GE shoreline with as small shift as possible. We can then conclude that the flood maps to be shown below underestimate the inland flood penetration by the amount of the shift shown in Figure 7. If it is ever desired to have more accurate flood maps for the Aguirre plant then the plant s topography supplied to the models should be improved. Using Figure 7, and also using bathtub-type sea level rise flooding, all areas below the 1 meter contour would be flooded due to a sea level rise of 1 meter. We can see flooding inside the power plant at this level of sea level rise. Or even for a +0.5 m rise, highlighting the exposure to sea level rise of this very important power plant. And if you add the yearly possibility of storm surges, the situation is direr. Figure 8 shows the computational grid nodes superimposed on a GE image of the Aguirre power plant. It shows the relatively high density of nodes, but that in hindsight, should be increased for such an important player as the Aguirre power plant. Figure 9 shows a zoom of the power plant area, showing the location of the computational nodes. As a comparison, the tsunami flood maps for the island were prepared with a regular grid of 30 meters resolution all over the island.

7 7 Figure 8 - GE image of the Aguirre Electric Power Plant, located inside Jobos Bay, with the nodes of the computational mesh overlaid on top in order to present a view of the size of the computational triangles inside the Bay and around the periphery of the power plant. Figure 9 Zoom of Figure 7 on the Aguirre power plant location. The white crosses represent the locations of the nodes of the unstructured mesh used by ADCIRC+SWAN.

8 8 Figures show the inundation maps for Category 1 to 5, under present sea level conditions. The figures show that the freeboard (distance between the sea surface elevation under fairweather conditions and the terrain elevation; as seen in Figure 2) is not sufficient to avoid flooding by the stillwater, even for a category 1 hurricane (passing through the most critical trajectory for the Aguirre power plant). This mere fact should allow wind forced waves to propagate inland, even without including wave runup/overtopping. It is to be expected that, at least, some broken waves might reach some of the fuel tanks seen in the images. This is the type of result that only computer modeling can forecast. If Hurricane Matthew (October 2016) had turned north south of the longitude of Ponce, its highest winds would have been approximately at Jobos Bay, and the consequences would have been catastrophic, just by sea water flooding and high energy wind waves propagating inshore. Figures show the same results for an initial sea surface elevation of +0.5 m. Figures show the results for an initial sea surface elevation of +1.0 m. In Figures 23 and 24 the location of the nodes in the computational mesh has also been drawn in order to show how the extent of the inland flooding has approached the inland limit of the mesh. In hindsight the mesh should have been extended further inland. As stated at the beginning of this section on the Aguirre power plant, it is relatively well protected from fair-weather ocean wind waves due its location inside Jobos Bay. But it begs to answer the question of how well protected the power plant is from hurricane forced waves entering through Boca del Infierno, or propagating landward above Cayos Barca and Caribe (when the storm surge overtops them). As stated at the beginning, the modeling included running the spectral wind model, SWAN, a widely used model. This model supplied information to the circulation model, ADCIRC, which allowed it to estimate the very important storm surge component of wave setup. In the process, SWAN estimates the so-called Significant Wave Height, Hs, which is the average of the highest one-third of the waves. It is images of Hs, which we will show next, that will show the level of exposure of the power plant to hurricane forced waves. It should be stated that although SWAN is a well-tested wave model, there are other, more sophisticated models that should be used if one wants to make a more accurate estimate of the wave heights capable of reaching the location of the power plant. But these more sophisticated wave models are too computationally heavy and do not lend themselves for coupling with ADCIRC. In another project we will simulate the inland propagation of storm waves moving on top of the storm surge by means of a Boussinesq wave model. The Hs images will cover a large percentage of Jobos Bay in order to better ascertain how well the offshore keys protect the power plant. And since an offshore gas port is being planned in the vicinity, the images give a bird s eye view of what could be expected sometime during the lifetime of the offshore port. Again we must recall that these are Maximum of Maximum values, and do not represent the maximum Hs values for a given specific hurricane.

9 9 Figure 10 - Inundation Depth for Category 1 hurricane for SLR = 0 m. See metadata at the top for hurricane characteristics. In this image, and others along the south coast, we can notice that color filling starts seaward of the GE shoreline, a problem mentioned above. This implies that the wetted areas extend farther inland than shown in the images. Figure 11 - Inundation Depth for Category 2 hurricane for SLR = 0 m. See metadata at the top for hurricane characteristics.

10 10 Figure 12 - Inundation Depth for Category 3 hurricane for SLR = 0 m. See metadata at the top for hurricane characteristics. Figure 13 - Inundation Depth for Category 4 hurricane for SLR = 0 m. See metadata at the top for hurricane characteristics.

11 11 Figure 14 - Inundation Depth for Category 5 hurricane for SLR = 0 m. See metadata at the top for hurricane characteristics. Figure 15 Inundation Depth for Category 1 hurricane for SLR = +0.5 m. See metadata at the top for hurricane characteristics.

12 12 Figure 16 Inundation Depth for Category 2 hurricane for SLR =+ 0.5 m. See metadata at the top for hurricane characteristics. Figure 17 Inundation Depth for Category 3 hurricane for SLR = +0.5 m. See metadata at the top for hurricane characteristics.

13 13 Figure 18 - Inundation Depth for Category 4 hurricane for SLR = +0.5 m. See metadata at the top for hurricane characteristics. Figure 19 - Inundation Depth for Category 5 hurricane for SLR = +0.5 m. See metadata at the top for hurricane characteristics.

14 14 Figure 20 - Inundation Depth for Category 1 hurricane for SLR = +1.0 m. See metadata at the top for hurricane characteristics. Figure 21 - Inundation Depth for Category 2 hurricane for SLR = +1.0 m. See metadata at the top for hurricane characteristics.

15 15 Figure 22 - Inundation Depth for Category 3 hurricane for SLR = +1.0 m. See metadata at the top for hurricane characteristics. Figure 23 - Inundation Depth for Category 4 hurricane for SLR = +1.0 m. See metadata at the top for hurricane characteristics. The location of the nodes of the computational mesh (white crosses) are shown to show that the inland limit of the mesh is being approached.

16 16 Figure 24 - Inundation Depth for Category 5 hurricane for SLR = +1.0 m. See metadata at the top for hurricane characteristics. The location of the nodes of the computational mesh (white crosses) are shown to show that the inland limit of the mesh is being approached. Figures 25 to 29 show Hs for a Sea Level Rise (SLR) equal to zero meters. Figures 30 to 34 show Hs for a Sea Level Rise (SLR) equal to +0.5 meters. And Figures 35 to 39 show the case for SLR = +1.0 m. Notice:. Since Jobos Bay lies in a part of the island where there is deep water close to shore, large waves are capable of reaching the keys. Less than half a kilometer offshore of Boca del Infierno we can see waves with Hs = 8 to 9 meters, or higher. As the storm surge elevation increases, the keys offer less protection, thus allowing higher waves to reach the location of the power plant. Even for SLR = 0 m we can see waves higher than 3 m inside the Bay. Right in front of the power plant. As expected, as sea level increases we can see larger waves penetrating the Bay. Now for a Category 1 hurricane we can see wave heights on the order of 1.5 m reaching the location of the power plant. At some storm surge level the SWE overtops the land elevation and waves can then propagate inland and crash directly against the infrastructure.

17 17 Figure 25 Hs (m) for a category 1 hurricane. SLR = 0 m. Figure 26 - Hs (m) for a category 2 hurricane. SLR = 0 m.

18 18 Figure 27 - Hs (m) for a category 3 hurricane. SLR = 0 m. Figure 28 - Hs (m) for a category 4 hurricane. SLR = 0 m.

19 19 Figure 29 - Hs (m) for a category 5 hurricane. SLR = 0 m Figure 30 - Hs (m) for a category 1 hurricane. SLR = +0.5 m.

20 20 Figure 31 - Hs (m) for a category 2 hurricane. SLR = +0.5 m. Figure 32 - Hs (m) for a category 3 hurricane. SLR = +0.5 m.

21 21 Figure 33 - Hs (m) for a category 4 hurricane. SLR = +0.5 m. Figure 34 - Hs (m) for a category 5 hurricane. SLR = +0.5 m.

22 22 Figure 35 - Hs (m) for a category 1 hurricane. SLR = +1.0 m. Figure 36 - Hs (m) for a category 2 hurricane. SLR = +1.0 m.

23 23 Figure 37 - Hs (m) for a category 3 hurricane. SLR = +1.0 m. Figure 38 - Hs (m) for a category 4 hurricane. SLR = +1.0 m.

24 24 Figure 39 - Hs (m) for a category 5 hurricane. SLR = +1.0 m. Overall Conclusions These conclusions need to be seen from the perspective that the modeling done does not include, yet, the effect of wave runup/overtopping. This effect has been shown here in the island, and elsewhere, that it is capable of increasing the inland extent of flooding by an order of 2, or higher. Henceforth, these should be seen as minimum value scenarios. Since Jobos Bay lies in a part of the island where there is deep water close to shore, large waves are capable of reaching the keys. Less than half a kilometer offshore of Boca del Infierno we can see waves with Hs = 8 to 9 meters, or higher. As the storm surge elevation increases, the offshore keys offer less protection, thus allowing higher waves to reach the location of the power plant. Large wind waves can propagate into Jobos Bay through Boca del Infierno, and also be regenerated inside the Bay by hurricane force winds. These waves can, if the conditions are adequate, crash directly against the infrastructure that lies inland. Even for SLR = 0 m we can see waves higher than Hs = 3 m inside the Bay for the more intense hurricanes; right in front of the power plant. The breaking of these waves right in front of the power plant should produce a large wave setup. This large wave setup could explain the higher storm surge (SWE) than what the FEMA map shows. And the higher wave setup near the Boca del Infierno entrance could also help push water to the inside the Bay, thus further increasing the SWE at the power plant shore.

25 As expected, as sea level increases we can see larger waves penetrating into the Bay. Now for a Category 1 hurricane we can see wave heights on the order of 1.5 m reaching the location of the power plant. At some storm surge level the SWE overtops the land elevation and waves can then propagate inland and crash directly against the infrastructure. It can be seen that the Aguirre power plant, although inside Jobos Bay, can be flooded by the anomalous stillwater generated by even a category 1 hurricane whose trajectory is the most critical for the plant. A Matthew-like hurricane making landfall in Ponce will be catastrophic for the Aguirre power plant, just from seawater flooding effects. And in 1928 an even stronger hurricane, the 1928 category 5 San Felipe, made landfall in the vicinity. This stillwater flooding is worse than what the FEMA map shows. This could be due to a larger wave setup estimated by ADCIRC+SWAN than the one assumed in the preparation of the FEMA map for the site. This is in agreement with the fact that waves estimated by SWAN inside Jobos Bay are larger than what the WHAFIS/RUNUP models give (maximum heights of 1.6 to 2.1 m). As should be expected, the potential for flooding by seawater during a hurricane increases as sea level increases. Not only the base sea surface elevation increases, making inland flooding easier, but also because the protective effect of the offshore keys diminishes as sea level increases. Outside the Bay very large wind-forced waves can crash close to the Bay entrance. This is due to the fact that large water depths lie close to land. This should be taken care of in the design of the Aguirre gas port. At some point in time during the rest of this century, the Aguirre power plant will have to be relocated inland. Once wave runup/overtopping is carried out by a Boussinesq wave model, a final vulnerability assessment can be made of the exposure of the Aguirre power plant to storm surges. In a different section we will assess the tsunami vulnerability. 25