1 00:00:01,371 --> 00:00:04,338 ♪ ♪ 2 00:00:07,105 --> 00:00:11,171 NARRATOR: Venice, Italy, is in peril. 3 00:00:11,871 --> 00:00:13,238 MAN (speaking Italian): 4 00:00:13,238 --> 00:00:15,338 NARRATOR: The sea level rising. 5 00:00:15,338 --> 00:00:18,005 ♪ ♪ 6 00:00:18,005 --> 00:00:20,638 Extreme floods inundating the city. 7 00:00:20,638 --> 00:00:22,538 ♪ ♪ 8 00:00:22,538 --> 00:00:23,771 ROSA SALZBERG: It's really alarming 9 00:00:23,771 --> 00:00:25,438 to see what happens to Venice when it floods. 10 00:00:25,438 --> 00:00:30,571 NARRATOR: The city itself crumbling. 11 00:00:30,571 --> 00:00:32,438 Salt is the enemy of Venice. 12 00:00:32,438 --> 00:00:36,771 NARRATOR: There may not be much time left to act. 13 00:00:38,138 --> 00:00:42,071 GEORG UMGIESSER: There's a lot of responsibility on us. 14 00:00:42,071 --> 00:00:45,238 Because if you make it wrong, people will feel it. 15 00:00:45,238 --> 00:00:48,938 NARRATOR: Scientists and engineers are deploying 16 00:00:48,938 --> 00:00:53,138 new solutions to defend against the rising water. 17 00:00:53,138 --> 00:00:56,105 From allying with nature... 18 00:00:56,105 --> 00:00:59,938 GIOVANNI CECCONI: This is the brick of life, the mud. 19 00:00:59,938 --> 00:01:02,071 DAVIDE SERNAGLIA (speaking Italian): 20 00:01:02,071 --> 00:01:06,538 NARRATOR: ...to a multibillion-dollar flood defense system. 21 00:01:06,538 --> 00:01:08,538 ♪ ♪ 22 00:01:08,538 --> 00:01:13,238 A moonshot to save Venice from the next inundation. 23 00:01:14,438 --> 00:01:18,071 Can they succeed and protect this ancient city? 24 00:01:18,071 --> 00:01:21,171 ♪ ♪ 25 00:01:21,171 --> 00:01:23,305 "Saving Venice." 26 00:01:23,305 --> 00:01:26,105 Right now, on "NOVA." 27 00:01:27,971 --> 00:01:32,738 ♪ ♪ 28 00:01:49,505 --> 00:01:51,371 ♪ ♪ 29 00:01:51,371 --> 00:01:54,038 NARRATOR: Venice, Italy, 30 00:01:54,038 --> 00:01:57,805 an ancient city of tradition, arts, and culture. 31 00:01:57,805 --> 00:01:59,571 ♪ ♪ 32 00:01:59,571 --> 00:02:01,905 Home to iconic sights, 33 00:02:01,905 --> 00:02:04,305 like the Rialto Bridge, 34 00:02:04,305 --> 00:02:08,105 the Doge's Palace, 35 00:02:08,105 --> 00:02:11,771 and the Basilica San Marco. 36 00:02:11,771 --> 00:02:13,771 ♪ ♪ 37 00:02:13,771 --> 00:02:18,738 But it is perhaps most famous as the city of water, 38 00:02:18,738 --> 00:02:23,305 where people and goods travel by gondolas and boats 39 00:02:23,305 --> 00:02:25,738 along a network of canals. 40 00:02:25,738 --> 00:02:29,971 ♪ ♪ 41 00:02:29,971 --> 00:02:32,271 These waterways connect the city 42 00:02:32,271 --> 00:02:37,838 to a shallow, 210-square-mile tidal lagoon, 43 00:02:37,838 --> 00:02:40,271 separated from the Adriatic Sea 44 00:02:40,271 --> 00:02:43,071 by a string of spits and barrier islands 45 00:02:43,071 --> 00:02:47,638 that shelter this natural harbor. 46 00:02:47,638 --> 00:02:52,838 Only at narrow inlets can ships pass in and out of the lagoon. 47 00:02:54,905 --> 00:02:57,205 Over the centuries, 48 00:02:57,205 --> 00:02:59,771 the Venetians reinforced these natural barriers 49 00:02:59,771 --> 00:03:03,205 with sea walls and jetties. 50 00:03:06,071 --> 00:03:09,238 But in the era of climate change, these defenses 51 00:03:09,238 --> 00:03:11,271 are no longer enough. 52 00:03:18,105 --> 00:03:19,838 MAN (speaking Italian): 53 00:03:19,838 --> 00:03:22,405 NARRATOR: Venice experiences sudden floods, 54 00:03:22,405 --> 00:03:24,838 known as acqua alta, 55 00:03:24,838 --> 00:03:27,971 caused by the sea surging through the inlets. 56 00:03:27,971 --> 00:03:31,371 ♪ ♪ 57 00:03:31,371 --> 00:03:38,038 These can inundate over 80% of the city in a matter of hours 58 00:03:38,038 --> 00:03:39,871 and leave the lowest-lying areas 59 00:03:39,871 --> 00:03:43,538 under more than three feet of seawater. 60 00:03:45,605 --> 00:03:48,705 In the entire 20th century, 61 00:03:48,705 --> 00:03:53,171 there were only nine of these extreme floods. 62 00:03:53,171 --> 00:03:58,771 In just the first two decades of the 21st century, 63 00:03:58,771 --> 00:04:01,471 there were 16. 64 00:04:03,271 --> 00:04:07,305 Venice is facing the reality of climate change. 65 00:04:07,305 --> 00:04:09,971 MAN (speaking Italian): 66 00:04:09,971 --> 00:04:13,838 NARRATOR: A stark warning of what may be to come 67 00:04:13,838 --> 00:04:16,338 for other coastal cities. 68 00:04:17,905 --> 00:04:21,838 ED BLAKELY: Over a hundred of our largest cities are built on coastlines. 69 00:04:21,838 --> 00:04:27,605 40% of the world's population is on those coastlines. 70 00:04:27,605 --> 00:04:33,638 So Venice is kind of the canary in this coal mine. 71 00:04:33,638 --> 00:04:37,805 As Venice floods, undergoes these changes, 72 00:04:37,805 --> 00:04:41,438 all the world's cities can see what's going to happen to them. 73 00:04:41,438 --> 00:04:42,938 ♪ ♪ 74 00:04:42,938 --> 00:04:46,005 NARRATOR: Now the eyes of the world are watching 75 00:04:46,005 --> 00:04:50,571 as Venice puts a new flood barrier to the test. 76 00:04:51,705 --> 00:04:55,671 SERNAGLIA (speaking Italian): 77 00:04:58,371 --> 00:05:00,038 NARRATOR: A multibillion-dollar system 78 00:05:00,038 --> 00:05:03,038 of gates designed to protect the city 79 00:05:03,038 --> 00:05:05,371 when the next flood threatens. 80 00:05:05,371 --> 00:05:08,938 ♪ ♪ 81 00:05:08,938 --> 00:05:11,038 SERNAGLIA: 82 00:05:15,805 --> 00:05:19,371 NARRATOR: But this barrier system is just the latest 83 00:05:19,371 --> 00:05:24,505 in a long line of Venetian engineering solutions. 84 00:05:24,505 --> 00:05:27,305 ♪ ♪ 85 00:05:27,305 --> 00:05:30,638 Living on a lagoon has posed problems 86 00:05:30,638 --> 00:05:34,905 since the first settlers arrived 1,600 years ago. 87 00:05:38,138 --> 00:05:40,071 (bells ringing) 88 00:05:40,071 --> 00:05:45,538 The city of Venice wasn't the original settlement. 89 00:05:45,538 --> 00:05:48,271 ♪ ♪ 90 00:05:48,271 --> 00:05:50,438 Six miles northeast of the city, 91 00:05:50,438 --> 00:05:56,105 the first homes were built on the island of Torcello. 92 00:05:56,105 --> 00:05:59,538 It is an area dominated by a network 93 00:05:59,538 --> 00:06:01,738 of shallow tidal creeks 94 00:06:01,738 --> 00:06:04,605 and low-lying salt marsh islands, 95 00:06:04,605 --> 00:06:07,338 which offered food and shelter to the first settlers. 96 00:06:07,338 --> 00:06:10,371 ♪ ♪ 97 00:06:10,371 --> 00:06:12,071 (speaking softly) 98 00:06:12,071 --> 00:06:14,738 ALBERTO BARAUSSE: Venice was born in the lagoon 99 00:06:14,738 --> 00:06:16,771 because the lagoon was useful to Venice. 100 00:06:16,771 --> 00:06:20,071 So Venetians shaped the lagoon the way they wanted. 101 00:06:21,638 --> 00:06:25,805 NARRATOR: But this environment posed a problem. 102 00:06:25,805 --> 00:06:32,071 How could they build on such soft ground? 103 00:06:32,071 --> 00:06:35,871 This is actually the, the kind of landscape they, 104 00:06:35,871 --> 00:06:37,971 they saw back then. 105 00:06:37,971 --> 00:06:40,905 Uh, so very low-lying land, marshes, 106 00:06:40,905 --> 00:06:44,138 some islands, but in general very wet, 107 00:06:44,138 --> 00:06:49,605 swampy soil, such as this one. 108 00:06:49,605 --> 00:06:52,738 I just want to show you how soft this mud is 109 00:06:52,738 --> 00:06:56,605 by trying and walk here. 110 00:06:56,605 --> 00:06:59,071 I'm not that heavy weight. 111 00:06:59,071 --> 00:07:02,138 I weigh 65 kilos. 112 00:07:02,138 --> 00:07:04,371 But I'm sinking like this. 113 00:07:06,571 --> 00:07:10,905 NARRATOR: 65 kilos is around 140 pounds. 114 00:07:13,105 --> 00:07:15,238 If the mud can't support this, 115 00:07:15,238 --> 00:07:19,405 how could it bear the weight of a wooden house, 116 00:07:19,405 --> 00:07:24,371 let alone one of Venice's grand stone buildings? 117 00:07:24,371 --> 00:07:28,005 ♪ ♪ 118 00:07:28,005 --> 00:07:29,238 The solution? 119 00:07:29,238 --> 00:07:32,571 Forcing wooden poles into the soft mud. 120 00:07:34,205 --> 00:07:37,071 These poles don't support the weight. 121 00:07:37,071 --> 00:07:38,305 (speaking Italian): 122 00:07:38,305 --> 00:07:42,671 NARRATOR: They transform the mud around them. 123 00:07:42,671 --> 00:07:44,538 The idea is to do a little experiment. 124 00:07:44,538 --> 00:07:47,905 When you plant many poles, 125 00:07:47,905 --> 00:07:50,205 they compact the mud between them. 126 00:07:50,205 --> 00:07:53,971 The water is pushed out, 127 00:07:53,971 --> 00:07:55,805 and the compaction of the mud itself 128 00:07:55,805 --> 00:08:00,138 make the mud more capable of supporting weight. 129 00:08:03,038 --> 00:08:06,938 NARRATOR: Modern-day excavations under the city reveal 130 00:08:06,938 --> 00:08:10,305 that Venetians maximized the compaction of the mud 131 00:08:10,305 --> 00:08:15,938 by using a large number of poles packed tightly together. 132 00:08:17,538 --> 00:08:22,905 Directly on top, they placed wooden planks, 133 00:08:22,905 --> 00:08:25,171 then impermeable limestone. 134 00:08:25,171 --> 00:08:29,571 And, above the waterline, bricks. 135 00:08:29,571 --> 00:08:31,505 BARAUSSE (speaking Italian): 136 00:08:38,538 --> 00:08:41,971 There you see, I'm lightweight, more than him. 137 00:08:41,971 --> 00:08:44,271 He can also try. 138 00:08:48,005 --> 00:08:49,805 Okay, you see Omar is not sinking, 139 00:08:49,805 --> 00:08:52,738 because the effect of the poles 140 00:08:52,738 --> 00:08:54,871 that compacts the mud between them. 141 00:08:54,871 --> 00:08:57,638 So it changes from more, I would say, 142 00:08:57,638 --> 00:08:59,671 fluid-like to more solid-like. 143 00:08:59,671 --> 00:09:04,805 And the proof of this is when we put the plank over there 144 00:09:04,805 --> 00:09:09,338 and do the same thing on the mud without the poles underneath, 145 00:09:09,338 --> 00:09:13,738 you see? There's a difference. 146 00:09:13,738 --> 00:09:15,771 ♪ ♪ 147 00:09:15,771 --> 00:09:18,138 NARRATOR: This technology is the secret 148 00:09:18,138 --> 00:09:20,605 of Venice's construction and longevity. 149 00:09:22,205 --> 00:09:25,671 It allowed the first settlers to adapt the environment 150 00:09:25,671 --> 00:09:29,871 and build the first houses. 151 00:09:32,138 --> 00:09:35,338 The Venetians used wooden piles to build on a cluster 152 00:09:35,338 --> 00:09:39,671 of 118 marshy islands. 153 00:09:41,505 --> 00:09:48,471 And over the centuries, they created the city we see today. 154 00:09:48,471 --> 00:09:49,938 BARAUSSE: Venice is standing on mud, 155 00:09:49,938 --> 00:09:53,071 it was built on mud, and it will stand 156 00:09:53,071 --> 00:09:56,371 for many, many years onwards. 157 00:09:57,538 --> 00:10:00,071 NARRATOR: But building on low-lying islands 158 00:10:00,071 --> 00:10:03,471 does have a drawback. 159 00:10:03,471 --> 00:10:05,505 ♪ ♪ 160 00:10:05,505 --> 00:10:09,271 Venice sits barely above the level of the waves, 161 00:10:09,271 --> 00:10:14,705 and this has always made the city vulnerable. 162 00:10:17,571 --> 00:10:20,438 SALZBERG: Marin Sanudo was a Venetian nobleman 163 00:10:20,438 --> 00:10:23,605 who, for about the first three decades of the 16th century, 164 00:10:23,605 --> 00:10:25,705 kept an almost daily diary of 165 00:10:25,705 --> 00:10:28,505 all kinds of things that were happening in the city. 166 00:10:28,505 --> 00:10:32,105 So it's a kind of gold mine for Venetian historians. 167 00:10:34,338 --> 00:10:37,038 NARRATOR: On November 16, 1517, 168 00:10:37,038 --> 00:10:41,371 he noted an event in the lowest part of Venice, 169 00:10:41,371 --> 00:10:44,271 the historic Piazza San Marco. 170 00:10:44,271 --> 00:10:47,938 SALZBERG: He writes that "on Monday morning, 171 00:10:47,938 --> 00:10:50,038 "as it had rained a lot, both during the night 172 00:10:50,038 --> 00:10:52,371 "and in the morning, the water rose very much. 173 00:10:52,371 --> 00:10:54,638 "So much so that St. Mark's Square, 174 00:10:54,638 --> 00:10:56,105 "from the Grand Canal to the Rialto, 175 00:10:56,105 --> 00:10:59,238 "and all the streets were full of water. 176 00:10:59,238 --> 00:11:01,338 "And it was neither possible to travel 177 00:11:01,338 --> 00:11:04,038 "nor by land nor with boats. 178 00:11:04,038 --> 00:11:05,605 "And it was terrible to see the water, which also 179 00:11:05,605 --> 00:11:07,405 "continued to rise. 180 00:11:07,405 --> 00:11:10,738 "So much so that nobody remembers anything similar. 181 00:11:10,738 --> 00:11:12,471 "It destroyed many goods in the shops, 182 00:11:12,471 --> 00:11:15,105 "and in many poor houses on the ground floor, 183 00:11:15,105 --> 00:11:19,471 it flooded all they had, causing them great hardship." 184 00:11:20,871 --> 00:11:23,038 It's an extraordinary passage to read now, 185 00:11:23,038 --> 00:11:25,605 because it's, it's very evocative of what it's like, 186 00:11:25,605 --> 00:11:27,771 it's like to be in the city when there's an acqua alta, 187 00:11:27,771 --> 00:11:29,038 when there's a high water. 188 00:11:33,005 --> 00:11:36,571 NARRATOR: For hundreds of years, 189 00:11:36,571 --> 00:11:40,205 floods have swept through the city. 190 00:11:40,205 --> 00:11:43,771 And the cumulative effect of these inundations 191 00:11:43,771 --> 00:11:49,738 is placing the survival of Venice's buildings in doubt. 192 00:11:49,738 --> 00:11:52,271 ELISABETTA ZENDRI (speaking Italian): 193 00:11:55,205 --> 00:11:57,805 NARRATOR: Scientists led by Elisabetta Zendri 194 00:11:57,805 --> 00:12:01,038 are monitoring the damage these floods inflict on the city. 195 00:12:01,038 --> 00:12:04,338 ♪ ♪ 196 00:12:04,338 --> 00:12:09,305 Venice is known as the city of canals. 197 00:12:09,305 --> 00:12:12,038 And most of the historical buildings 198 00:12:12,038 --> 00:12:14,671 are in direct contact with seawater. 199 00:12:14,671 --> 00:12:18,905 ♪ ♪ 200 00:12:18,905 --> 00:12:22,305 The building materials are porous. 201 00:12:22,305 --> 00:12:25,305 And seawater rises up the walls. 202 00:12:25,305 --> 00:12:30,105 But this is not only water, this is salty water. 203 00:12:30,105 --> 00:12:36,338 And when the water evaporates from the walls, 204 00:12:36,338 --> 00:12:41,105 the salt, uh, can crystallize into the pores. 205 00:12:41,105 --> 00:12:44,505 ♪ ♪ 206 00:12:44,505 --> 00:12:47,938 The crystallization pressure causes 207 00:12:47,938 --> 00:12:50,105 cracks of the pores. 208 00:12:50,105 --> 00:12:55,205 And this is the final consequence. 209 00:12:55,205 --> 00:12:58,771 All the façade is compromised. 210 00:13:00,005 --> 00:13:06,705 This problem is present in all the buildings in the city. 211 00:13:09,138 --> 00:13:11,071 Salt is the enemy of Venice. 212 00:13:12,738 --> 00:13:18,738 NARRATOR: As climate change raises sea level, flooding is increasing. 213 00:13:20,105 --> 00:13:25,238 More salt is getting into the porous brickwork. 214 00:13:25,238 --> 00:13:28,871 And the problem is only going to get worse. 215 00:13:33,205 --> 00:13:36,305 Models suggest the sea level here could rise 216 00:13:36,305 --> 00:13:42,405 more than 40 inches by the end of the century. 217 00:13:44,005 --> 00:13:48,671 It would seem the future of this remarkable city is bleak. 218 00:13:53,771 --> 00:13:56,471 But now there is hope. 219 00:13:56,471 --> 00:13:58,871 ♪ ♪ 220 00:13:58,871 --> 00:14:01,538 After nearly 20 years of construction 221 00:14:01,538 --> 00:14:06,771 and some $8 billion, a network of enormous flood barriers, 222 00:14:06,771 --> 00:14:08,971 called the MOSE, is in place. 223 00:14:08,971 --> 00:14:11,805 It is designed to block the floodwaters 224 00:14:11,805 --> 00:14:14,305 before they reach the city. 225 00:14:14,305 --> 00:14:18,805 In charge is Elisabetta Spitz. 226 00:14:18,805 --> 00:14:22,338 ♪ ♪ 227 00:14:22,338 --> 00:14:26,005 SPITZ (translated): The MOSE is a masterpiece of Italian engineering. 228 00:14:26,005 --> 00:14:28,905 It has required so much labor, 229 00:14:28,905 --> 00:14:31,371 so much research, so much testing. 230 00:14:32,905 --> 00:14:36,938 NARRATOR: The scale of this project is immense. 231 00:14:36,938 --> 00:14:42,071 78 individual gates are arranged in four barriers 232 00:14:42,071 --> 00:14:45,838 that each stretch over 1,100 feet 233 00:14:45,838 --> 00:14:49,605 across the inlets to the lagoon. 234 00:14:49,605 --> 00:14:52,305 At Chioggia, 235 00:14:52,305 --> 00:14:54,838 Malamocco, 236 00:14:54,838 --> 00:14:59,505 and two barriers separated by an artificial island at Lido, 237 00:14:59,505 --> 00:15:02,371 the widest entrance. 238 00:15:02,371 --> 00:15:05,705 (ship horn blows) 239 00:15:05,705 --> 00:15:08,738 These inlets are the only way 240 00:15:08,738 --> 00:15:12,905 for commercial ships to access the lagoon. 241 00:15:12,905 --> 00:15:15,571 ♪ ♪ 242 00:15:15,571 --> 00:15:21,638 So the barriers are only lifted when a flood endangers Venice. 243 00:15:25,638 --> 00:15:29,938 Each gate is colossal, approximately the size 244 00:15:29,938 --> 00:15:33,005 of two tennis courts. 245 00:15:34,771 --> 00:15:39,471 (translated): These gates are fixed to concrete beds 246 00:15:39,471 --> 00:15:43,705 sitting on the bottom of the sea. 247 00:15:43,705 --> 00:15:47,671 NARRATOR: During construction, each gate was connected to these beds 248 00:15:47,671 --> 00:15:52,138 by two immense hinges, which allow them to pivot. 249 00:15:53,538 --> 00:15:55,605 The gates are full of water, 250 00:15:55,605 --> 00:15:57,671 which weighs them down and keeps them 251 00:15:57,671 --> 00:16:00,805 lying flat on the sea floor. 252 00:16:00,805 --> 00:16:03,271 Until the team injects compressed air 253 00:16:03,271 --> 00:16:07,138 through a system of valves. 254 00:16:07,138 --> 00:16:09,271 SPITZ (translated): Air is pumped into the gates, 255 00:16:09,271 --> 00:16:11,838 and they slowly rise. 256 00:16:13,438 --> 00:16:16,538 And emerge from the sea. 257 00:16:18,838 --> 00:16:22,171 Then they join together, 258 00:16:22,171 --> 00:16:25,271 and hold back the high tide. 259 00:16:25,271 --> 00:16:28,671 NARRATOR: Most floods last fewer 260 00:16:28,671 --> 00:16:31,805 than four hours. 261 00:16:31,805 --> 00:16:36,071 So once the threat has passed, the team can lower the barriers. 262 00:16:38,738 --> 00:16:41,471 The MOSE is still 263 00:16:41,471 --> 00:16:44,238 in its testing phase. 264 00:16:44,238 --> 00:16:48,138 The team is perfecting how to operate the barriers 265 00:16:48,138 --> 00:16:51,571 when an acqua alta threatens the city. 266 00:16:53,338 --> 00:16:55,105 SPITZ (translated): This project needs to work perfectly. 267 00:16:55,105 --> 00:16:57,571 Water cannot pass through. 268 00:17:00,871 --> 00:17:06,238 (crowd cheering and applauding) 269 00:17:06,238 --> 00:17:08,305 NARRATOR: But deploying the barriers 270 00:17:08,305 --> 00:17:11,571 is far from straightforward. 271 00:17:11,571 --> 00:17:15,605 An acqua alta arrives incredibly quickly. 272 00:17:15,605 --> 00:17:18,705 The water can rise as much as 12 inches 273 00:17:18,705 --> 00:17:21,071 in just one hour. 274 00:17:21,071 --> 00:17:27,005 And it takes over an hour to raise all the gates. 275 00:17:27,005 --> 00:17:29,471 ♪ ♪ 276 00:17:29,471 --> 00:17:31,871 Venice needs an early warning system 277 00:17:31,871 --> 00:17:35,871 that predicts exactly when the floods will arrive. 278 00:17:38,838 --> 00:17:44,805 One factor is easy to forecast-- the tides. 279 00:17:46,771 --> 00:17:48,938 The highest tides occur when the sun 280 00:17:48,938 --> 00:17:52,538 and the moon align, and their gravitational pull 281 00:17:52,538 --> 00:17:56,505 on the Earth's water combines. 282 00:17:56,505 --> 00:17:59,505 Known as spring tides, 283 00:17:59,505 --> 00:18:02,105 they happen twice a month, 284 00:18:02,105 --> 00:18:06,005 and their timings can be calculated years in advance. 285 00:18:07,471 --> 00:18:12,305 But Venice doesn't flood whenever there is a spring tide. 286 00:18:12,305 --> 00:18:15,738 Another factor must combine with the high water 287 00:18:15,738 --> 00:18:19,605 to cause these inundations. 288 00:18:19,605 --> 00:18:23,205 Understanding this is the key 289 00:18:23,205 --> 00:18:27,905 to predicting an acqua alta. 290 00:18:32,138 --> 00:18:35,971 It is an issue that oceanographer Georg Umgiesser 291 00:18:35,971 --> 00:18:39,605 has been studying for almost 40 years. 292 00:18:39,605 --> 00:18:43,271 UMGIESSER: Venice is a special city. 293 00:18:43,271 --> 00:18:45,271 We have to protect it, because otherwise, 294 00:18:45,271 --> 00:18:49,338 generations will lose their history. 295 00:18:51,238 --> 00:18:52,305 NARRATOR: To investigate, 296 00:18:52,305 --> 00:18:56,005 he ventures far beyond the city limits. 297 00:18:57,005 --> 00:18:59,171 UMGIESSER: It's a special environment. 298 00:18:59,171 --> 00:19:02,405 It's just out of the world. 299 00:19:02,405 --> 00:19:07,638 NARRATOR: Georg's destination is a scientific monitoring platform. 300 00:19:08,905 --> 00:19:11,138 UMGIESSER: I like to go out there. 301 00:19:11,138 --> 00:19:13,505 It's very beautiful. 302 00:19:13,505 --> 00:19:17,805 ♪ ♪ 303 00:19:19,405 --> 00:19:22,438 NARRATOR: Ten miles from Venice, 304 00:19:22,438 --> 00:19:26,138 the monitoring platform sits in a strategic position 305 00:19:26,138 --> 00:19:29,038 at the northern end of the Adriatic Sea, 306 00:19:29,038 --> 00:19:33,238 a branch of the Mediterranean. 307 00:19:33,238 --> 00:19:37,305 Here it detects any changes in sea conditions 308 00:19:37,305 --> 00:19:43,171 heading up this narrow body of water before they reach Venice. 309 00:19:43,171 --> 00:19:47,238 ♪ ♪ 310 00:19:47,238 --> 00:19:49,805 Measurements from the platform, 311 00:19:49,805 --> 00:19:53,005 along with data from across the Mediterranean, 312 00:19:53,005 --> 00:19:58,005 show that most of Venice's acqua alta have something in common. 313 00:20:01,005 --> 00:20:02,005 A specific type 314 00:20:02,005 --> 00:20:06,171 of storm system in the Mediterranean. 315 00:20:06,171 --> 00:20:08,938 When you have a low-pressure system, then you always have 316 00:20:08,938 --> 00:20:13,005 a wind circulation which is anti-clockwise. 317 00:20:13,005 --> 00:20:14,438 The closer you get 318 00:20:14,438 --> 00:20:18,538 to the low-pressure system, the stronger the winds are. 319 00:20:18,538 --> 00:20:20,671 And so once this is moving now closer to, to Italy, 320 00:20:20,671 --> 00:20:23,671 the winds also in the Adriatic Sea 321 00:20:23,671 --> 00:20:26,771 get stronger and stronger. 322 00:20:26,771 --> 00:20:30,205 NARRATOR: Known as the sirocco, 323 00:20:30,205 --> 00:20:33,738 these winds are a major threat to Venice. 324 00:20:33,738 --> 00:20:39,405 ♪ ♪ 325 00:20:39,405 --> 00:20:42,171 UMGIESSER: Basically, they push the water 326 00:20:42,171 --> 00:20:44,371 against the northern part, 327 00:20:44,371 --> 00:20:47,505 and they push the water against the lagoon. 328 00:20:47,505 --> 00:20:49,838 Then you have, also, the atmospheric pressure. 329 00:20:49,838 --> 00:20:51,938 If you have lower pressure, 330 00:20:51,938 --> 00:20:53,771 the water raises up. 331 00:20:53,771 --> 00:20:57,405 ♪ ♪ 332 00:20:57,405 --> 00:21:01,871 NARRATOR: The twin effects of low pressure and wind 333 00:21:01,871 --> 00:21:05,271 can dramatically increase the water level in Venice. 334 00:21:05,271 --> 00:21:08,505 And if these coincide with a spring tide, 335 00:21:08,505 --> 00:21:13,771 an acqua alta can hit. 336 00:21:13,771 --> 00:21:16,471 ♪ ♪ 337 00:21:16,471 --> 00:21:21,838 This combination is known as a surge tide. 338 00:21:21,838 --> 00:21:25,405 As weather patterns change around the planet, 339 00:21:25,405 --> 00:21:26,605 the storm systems that drive 340 00:21:26,605 --> 00:21:32,238 these inundations have become more frequent. 341 00:21:32,238 --> 00:21:35,805 ♪ ♪ 342 00:21:35,805 --> 00:21:38,671 UMGIESSER: Exceptional high tides in Venice 343 00:21:38,671 --> 00:21:44,105 are classified as water level higher than 140 centimeters. 344 00:21:44,105 --> 00:21:48,405 We saw in the last 150 years 18 events. 345 00:21:48,405 --> 00:21:50,938 In the last three years, we saw seven. 346 00:21:50,938 --> 00:21:54,171 So something is changing, clearly. 347 00:21:54,171 --> 00:21:59,505 And the only reason why that could be is climate change. 348 00:21:59,505 --> 00:22:01,771 ♪ ♪ 349 00:22:01,771 --> 00:22:05,871 NARRATOR: But now Georg has an early warning system. 350 00:22:05,871 --> 00:22:08,371 ♪ ♪ 351 00:22:08,371 --> 00:22:13,538 If a spring tide is due, and a low-pressure system is forming, 352 00:22:13,538 --> 00:22:17,071 Georg will see changes in the water level at the platform 353 00:22:17,071 --> 00:22:21,405 up to a week before the surge tide arrives, 354 00:22:21,405 --> 00:22:22,505 giving him a way 355 00:22:22,505 --> 00:22:29,238 to alert Venice that a flood is on the way. 356 00:22:29,238 --> 00:22:33,838 UMGIESSER: There's a lot of responsibility on us. 357 00:22:33,838 --> 00:22:37,271 It's a burden, it's a burden, because if, 358 00:22:37,271 --> 00:22:40,171 if you make it wrong, uh, people will feel it. 359 00:22:42,105 --> 00:22:43,738 NARRATOR: Georg has detected 360 00:22:43,738 --> 00:22:49,305 that water around the platform is rising. 361 00:22:49,305 --> 00:22:53,205 This is a forecast we issued at the 30th of October. 362 00:22:53,205 --> 00:22:58,938 Based on what we have here, we can see that at a certain point, 363 00:22:58,938 --> 00:23:01,605 just before the second of November, 364 00:23:01,605 --> 00:23:04,371 we should expect an event. 365 00:23:04,371 --> 00:23:09,971 We are sure that something will happen here. 366 00:23:09,971 --> 00:23:14,305 ♪ ♪ 367 00:23:19,238 --> 00:23:20,905 NARRATOR: Georg is forecasting 368 00:23:20,905 --> 00:23:23,538 that at 8:45 p.m., 369 00:23:23,538 --> 00:23:25,171 a flood will hit the city 370 00:23:25,171 --> 00:23:28,071 that could cover the lowest-lying areas 371 00:23:28,071 --> 00:23:33,938 in almost 20 inches of seawater. 372 00:23:33,938 --> 00:23:36,038 ♪ ♪ 373 00:23:36,038 --> 00:23:37,338 At the MOSE, 374 00:23:37,338 --> 00:23:41,471 Davide Sernaglia is in charge 375 00:23:41,471 --> 00:23:44,871 of raising the barriers. 376 00:23:46,738 --> 00:23:49,105 SERNAGLIA: We have 70 guys 377 00:23:49,105 --> 00:23:51,805 that work together here. 378 00:23:51,805 --> 00:23:55,005 MARCELLO (speaking Italian): 379 00:23:55,005 --> 00:23:57,538 SERNAGLIA (speaking English): And all have to work 380 00:23:57,538 --> 00:23:58,638 like an orchestra. 381 00:23:58,638 --> 00:24:02,471 ♪ ♪ 382 00:24:08,338 --> 00:24:11,205 (speaking Italian): 383 00:24:11,205 --> 00:24:13,405 (speaking English): We have to check the compressor, the valve, 384 00:24:13,405 --> 00:24:16,105 the transmission system. 385 00:24:16,105 --> 00:24:19,571 It's not possible to lost time. 386 00:24:19,571 --> 00:24:23,705 But it's not simple. (chuckles) 387 00:24:30,338 --> 00:24:34,805 NARRATOR: It's 7:45 a.m., and in the city, 388 00:24:34,805 --> 00:24:36,471 workers are inserting a backup plan 389 00:24:36,471 --> 00:24:41,705 in case the MOSE fails to lift. 390 00:24:41,705 --> 00:24:43,771 MAURIZIO SCARPA (translated): We're positioning the raised walkways 391 00:24:43,771 --> 00:24:46,938 for the high-water event. 392 00:24:48,471 --> 00:24:50,038 Tonight, this will all be flooded. 393 00:24:50,038 --> 00:24:53,038 If the MOSE isn't put up, it will be flooded. 394 00:24:53,038 --> 00:24:58,205 ♪ ♪ 395 00:24:58,205 --> 00:25:02,071 They say it will be raised up, but we can't say for certain. 396 00:25:02,071 --> 00:25:07,605 ♪ ♪ 397 00:25:07,605 --> 00:25:08,905 NARRATOR: The approaching flood 398 00:25:08,905 --> 00:25:13,405 is predicted to inundate nearly half the city. 399 00:25:13,405 --> 00:25:19,271 ♪ ♪ 400 00:25:19,271 --> 00:25:22,338 Kiosk owner Walter Mutti 401 00:25:22,338 --> 00:25:25,105 remembers the havoc when an acqua alta hit 402 00:25:25,105 --> 00:25:29,505 on November 12, 2019. 403 00:25:29,505 --> 00:25:33,605 (water splashing) 404 00:25:33,605 --> 00:25:37,171 MUTTI (translated): At 9:30, suddenly the wind changed. 405 00:25:37,171 --> 00:25:39,038 (sirens blaring) 406 00:25:39,038 --> 00:25:42,271 The flood sirens began to sound. 407 00:25:42,271 --> 00:25:45,371 The wind suddenly became merciless, extremely strong. 408 00:25:45,371 --> 00:25:50,405 The tide was increasing out of all proportion. 409 00:25:50,405 --> 00:25:53,205 In 20 minutes, it had grown by 410 00:25:53,205 --> 00:25:57,471 eight to 12 inches, which is unheard of. 411 00:25:57,471 --> 00:26:02,905 I was inside and I felt the newsstand shaking. 412 00:26:02,905 --> 00:26:09,205 I came out and the water was already this high. 413 00:26:13,471 --> 00:26:16,238 I went home, and when I came back at 2:00 a.m. 414 00:26:16,238 --> 00:26:18,805 to try and save the papers and so on, 415 00:26:18,805 --> 00:26:20,938 I couldn't see my kiosk anymore. 416 00:26:28,571 --> 00:26:31,338 NARRATOR: Walter had to wait three weeks 417 00:26:31,338 --> 00:26:33,038 before he could solve the mystery 418 00:26:33,038 --> 00:26:37,338 of what had happened to his kiosk. 419 00:26:37,338 --> 00:26:42,271 MUTTI: The fire department came and they searched the canal. 420 00:26:45,705 --> 00:26:49,638 They found a newsstand, but it was full of mud. 421 00:26:52,071 --> 00:26:56,471 I understood that I lost everything. 422 00:26:56,471 --> 00:26:59,405 ♪ ♪ 423 00:26:59,405 --> 00:27:04,071 NARRATOR: It cost $30,000 to restore his kiosk. 424 00:27:04,071 --> 00:27:09,471 And Walter knows another flood could spell financial ruin. 425 00:27:11,405 --> 00:27:14,438 MUTTI: I hope it never happens again. 426 00:27:16,505 --> 00:27:19,005 I hope my fears are not realized 427 00:27:19,005 --> 00:27:21,405 and that the MOSE will work. 428 00:27:21,405 --> 00:27:25,438 ♪ ♪ 429 00:27:25,438 --> 00:27:29,638 NARRATOR: It's 5:45 p.m. 430 00:27:29,638 --> 00:27:33,171 Davide and his team need to raise 431 00:27:33,171 --> 00:27:37,005 all the gates before the surge tide arrives in three hours. 432 00:27:37,005 --> 00:27:40,471 ♪ ♪ 433 00:27:40,471 --> 00:27:45,305 But there is bad news. 434 00:27:45,305 --> 00:27:50,071 SERNAGLIA (speaking Italian): 435 00:27:54,671 --> 00:27:57,171 ♪ ♪ 436 00:27:57,171 --> 00:27:59,471 NARRATOR: The wind has changed direction, 437 00:27:59,471 --> 00:28:02,138 pushing the storm towards Venice 438 00:28:02,138 --> 00:28:06,805 and causing the tide to rise far faster than expected. 439 00:28:06,805 --> 00:28:10,171 SERNAGLIA: 440 00:28:10,171 --> 00:28:15,205 NARRATOR: Davide orders the immediate lifting of Treporti, 441 00:28:15,205 --> 00:28:17,805 the northernmost set of gates. 442 00:28:19,338 --> 00:28:21,005 SERNAGLIA: 443 00:28:21,005 --> 00:28:24,305 MARCELLO (speaking Italian): 444 00:28:25,438 --> 00:28:28,938 SERNAGLIA: 445 00:28:34,205 --> 00:28:37,038 MARCELLO: 446 00:28:37,038 --> 00:28:38,738 SERNAGLIA: 447 00:28:38,738 --> 00:28:41,771 ♪ ♪ 448 00:28:41,771 --> 00:28:44,505 MARCELLO: 449 00:28:44,505 --> 00:28:50,005 ♪ ♪ 450 00:29:01,671 --> 00:29:05,438 NARRATOR: But outside, the storm intensifies. 451 00:29:05,438 --> 00:29:07,305 (wind roaring) 452 00:29:12,638 --> 00:29:15,838 MARCELLO: 453 00:29:22,171 --> 00:29:25,105 SERNAGLIA: 454 00:29:25,105 --> 00:29:27,838 ♪ ♪ 455 00:29:27,838 --> 00:29:31,138 NARRATOR: With all the Treporti gates safely deployed, 456 00:29:31,138 --> 00:29:35,071 Davide orders the lifting of the other barriers. 457 00:29:35,071 --> 00:29:40,005 SERNAGLIA: 458 00:29:40,005 --> 00:29:45,038 ♪ ♪ 459 00:29:48,371 --> 00:29:53,771 NARRATOR: But two of the San Nicolò gates aren't rising. 460 00:29:53,771 --> 00:29:59,205 SERNAGLIA: 461 00:30:00,371 --> 00:30:02,838 NARRATOR: Each gate has safety valves 462 00:30:02,838 --> 00:30:05,771 to prevent it from accidentally rising up. 463 00:30:07,671 --> 00:30:10,771 They have to be open to allow air into the gate. 464 00:30:10,771 --> 00:30:13,338 Otherwise, it won't lift. 465 00:30:15,005 --> 00:30:19,105 SERNAGLIA: 466 00:30:22,038 --> 00:30:24,605 MAN (on radio, speaking Italian): 467 00:30:24,605 --> 00:30:27,805 SERNAGLIA: 468 00:30:33,405 --> 00:30:35,805 ♪ ♪ 469 00:30:35,805 --> 00:30:38,238 NARRATOR: Davide suspects that the safety valves 470 00:30:38,238 --> 00:30:40,571 haven't opened on these two gates, 471 00:30:40,571 --> 00:30:44,138 and they can't rise into position. 472 00:30:44,138 --> 00:30:46,605 And the storm is driving the water 473 00:30:46,605 --> 00:30:50,271 over three inches higher than expected. 474 00:30:53,271 --> 00:30:56,205 SERNAGLIA: 475 00:31:05,505 --> 00:31:07,471 STEFANO (speaking Italian): 476 00:31:07,471 --> 00:31:09,671 ♪ ♪ 477 00:31:09,671 --> 00:31:11,905 NARRATOR: Davide decides the only option 478 00:31:11,905 --> 00:31:14,771 is to risk rebooting the system. 479 00:31:14,771 --> 00:31:18,138 SERNAGLIA: 480 00:31:21,805 --> 00:31:25,705 ♪ ♪ 481 00:31:36,605 --> 00:31:40,338 FRANCESCO (speaking Italian): 482 00:31:44,171 --> 00:31:48,505 SERNAGLIA: 483 00:31:50,238 --> 00:31:53,371 (man speaks on radio) 484 00:31:53,371 --> 00:31:57,938 ♪ ♪ 485 00:31:57,938 --> 00:32:02,205 FRANCESCO: 486 00:32:05,638 --> 00:32:09,471 MAN (on radio, speaking Italian): 487 00:32:11,505 --> 00:32:15,105 SERNAGLIA: 488 00:32:15,105 --> 00:32:17,071 MAN (on radio): 489 00:32:17,071 --> 00:32:18,205 SERNAGLIA: 490 00:32:20,005 --> 00:32:24,071 SERNAGLIA: 491 00:32:26,771 --> 00:32:29,571 ♪ ♪ 492 00:32:29,571 --> 00:32:32,105 NARRATOR: The lowest parts of Venice had been 493 00:32:32,105 --> 00:32:34,638 forecast to be under almost 20 inches 494 00:32:34,638 --> 00:32:38,271 of damaging seawater. 495 00:32:40,238 --> 00:32:42,705 But in the Piazza San Marco, 496 00:32:42,705 --> 00:32:45,705 the only water is rain. 497 00:32:45,705 --> 00:32:47,338 (people talking and laughing) 498 00:32:47,338 --> 00:32:49,871 The MOSE has kept the acqua alta 499 00:32:49,871 --> 00:32:53,105 out of Venice. 500 00:32:55,271 --> 00:32:57,638 SERNAGLIA (speaking Italian): 501 00:33:05,538 --> 00:33:10,638 ♪ ♪ 502 00:33:12,471 --> 00:33:13,905 NARRATOR: The following morning, 503 00:33:13,905 --> 00:33:17,671 one Venetian in particular is feeling positive. 504 00:33:17,671 --> 00:33:22,971 (humming) 505 00:33:22,971 --> 00:33:26,005 MUTTI (translated): In the end, everything was fine. 506 00:33:27,638 --> 00:33:30,238 Luckily, they lifted the MOSE. 507 00:33:30,238 --> 00:33:32,705 And so personally, I, like the rest of the city, 508 00:33:32,705 --> 00:33:34,505 breathe a sigh of relief. 509 00:33:34,505 --> 00:33:38,905 It gives you more faith, definitely. 510 00:33:38,905 --> 00:33:43,471 (chuckles): However, tomorrow is another battle. 511 00:33:43,471 --> 00:33:46,038 (bell tolls) 512 00:33:46,038 --> 00:33:49,605 NARRATOR: Just 36 hours later, 513 00:33:49,605 --> 00:33:52,705 Walter is proved right. 514 00:33:52,705 --> 00:33:55,105 ♪ ♪ 515 00:33:55,105 --> 00:33:58,471 The Piazza San Marco is flooding. 516 00:33:58,471 --> 00:34:00,838 ♪ ♪ 517 00:34:00,838 --> 00:34:05,538 A surge tide is forcing seawater up through the drains, 518 00:34:05,538 --> 00:34:10,238 and a torrent is pouring into the basilica. 519 00:34:10,238 --> 00:34:14,971 ♪ ♪ 520 00:34:14,971 --> 00:34:19,038 Inside, seawater is coming up through the floor. 521 00:34:19,038 --> 00:34:23,638 (water gurgling) 522 00:34:25,838 --> 00:34:28,571 The reason is, three miles away, 523 00:34:28,571 --> 00:34:34,705 the MOSE hasn't been deployed. 524 00:34:34,705 --> 00:34:40,138 This isn't because of mechanical failure. 525 00:34:40,138 --> 00:34:42,371 For now, the barriers are only raised for 526 00:34:42,371 --> 00:34:45,671 the most extreme high waters. 527 00:34:45,671 --> 00:34:50,071 ♪ ♪ 528 00:34:50,071 --> 00:34:54,305 But smaller acqua alta aren't blocked 529 00:34:54,305 --> 00:34:57,538 and can still inundate the lowest-lying parts of the city. 530 00:34:57,538 --> 00:35:02,605 ♪ ♪ 531 00:35:03,871 --> 00:35:08,938 There is a good explanation for this decision. 532 00:35:08,938 --> 00:35:11,971 Raising the flood barriers too often also poses 533 00:35:11,971 --> 00:35:15,171 a threat to the city and its people. 534 00:35:15,171 --> 00:35:17,471 ♪ ♪ 535 00:35:17,471 --> 00:35:21,838 Giovanni Cecconi has studied the lagoon for over 40 years. 536 00:35:23,405 --> 00:35:29,471 Including almost 20 years working on the MOSE. 537 00:35:29,471 --> 00:35:31,505 ♪ ♪ 538 00:35:31,505 --> 00:35:33,405 CECCONI: If we stop the tide, 539 00:35:33,405 --> 00:35:37,205 if we use the MOSE too much, 540 00:35:37,205 --> 00:35:40,371 then the lagoon will die. 541 00:35:42,471 --> 00:35:45,038 A healthy lagoon make 542 00:35:45,038 --> 00:35:48,505 the Venice city healthier. 543 00:35:48,505 --> 00:35:50,705 ♪ ♪ 544 00:35:50,705 --> 00:35:53,205 NARRATOR: And the key to a healthy lagoon 545 00:35:53,205 --> 00:35:55,738 is the tide. 546 00:35:55,738 --> 00:35:57,438 CECCONI: Twice a day, 547 00:35:57,438 --> 00:36:00,671 we have a cycle of inflow and outflow. 548 00:36:00,671 --> 00:36:05,505 Because of the tide, this water is mixed. 549 00:36:05,505 --> 00:36:07,605 If you don't have the stirring, 550 00:36:07,605 --> 00:36:13,705 the same old water will get more and more polluted. 551 00:36:13,705 --> 00:36:17,771 NARRATOR: And Venetians rely on the lagoon's tides for one 552 00:36:17,771 --> 00:36:22,905 of the most basic pieces of the city's infrastructure. 553 00:36:22,905 --> 00:36:26,705 CECCONI: In Venice, you don't have a septic sewage system. 554 00:36:26,705 --> 00:36:30,638 So the waste is discharged into the inner canal. 555 00:36:30,638 --> 00:36:34,071 ♪ ♪ 556 00:36:34,071 --> 00:36:37,838 NARRATOR: When the MOSE is closed, there is no tide, 557 00:36:37,838 --> 00:36:40,371 and human waste accumulates. 558 00:36:40,371 --> 00:36:44,238 ♪ ♪ 559 00:36:44,238 --> 00:36:47,471 CECCONI: It is very important that 560 00:36:47,471 --> 00:36:50,338 the sewage system is flushed 561 00:36:50,338 --> 00:36:52,505 by the tide. 562 00:36:52,505 --> 00:36:55,805 ♪ ♪ 563 00:36:55,805 --> 00:36:58,205 Because without the tide, 564 00:36:58,205 --> 00:37:02,271 the, Venice will die in its own, uh, 565 00:37:02,271 --> 00:37:05,005 waste. (chuckles) 566 00:37:06,905 --> 00:37:09,371 NARRATOR: Because of climate change, 567 00:37:09,371 --> 00:37:12,138 Venice will need to deploy the MOSE more 568 00:37:12,138 --> 00:37:15,171 and more often. 569 00:37:15,171 --> 00:37:16,971 But doing so will jeopardize 570 00:37:16,971 --> 00:37:19,771 the city and its people. 571 00:37:19,771 --> 00:37:22,438 ♪ ♪ 572 00:37:22,438 --> 00:37:24,638 Scientists need to find 573 00:37:24,638 --> 00:37:27,105 more ways to protect Venice 574 00:37:27,105 --> 00:37:31,338 that work alongside the MOSE. 575 00:37:31,338 --> 00:37:36,105 And the answer could be hiding in plain sight: 576 00:37:36,105 --> 00:37:40,471 the salt marshes. 577 00:37:40,471 --> 00:37:43,471 This network of islands 578 00:37:43,471 --> 00:37:46,405 acts as a natural flood barrier, 579 00:37:46,405 --> 00:37:52,371 channeling water and reducing the power of waves. 580 00:37:52,371 --> 00:37:54,638 And salt marshes have another advantage. 581 00:37:54,638 --> 00:37:58,805 They can keep pace with sea level rise 582 00:37:58,805 --> 00:38:02,071 because of the way that they grow. 583 00:38:02,071 --> 00:38:06,038 ♪ ♪ 584 00:38:06,038 --> 00:38:09,905 These two plants are cooperating to keep the soil higher. 585 00:38:09,905 --> 00:38:13,571 The roots are very important because 586 00:38:13,571 --> 00:38:16,071 they hold the soil together. 587 00:38:16,071 --> 00:38:17,805 At the same time, 588 00:38:17,805 --> 00:38:21,705 they push the plant a little higher. 589 00:38:21,705 --> 00:38:25,271 This is the first mechanism of counteracting 590 00:38:25,271 --> 00:38:29,971 sea level rise, producing more volume below. 591 00:38:29,971 --> 00:38:33,171 ♪ ♪ 592 00:38:33,171 --> 00:38:36,338 NARRATOR: In summer, these plants grow rapidly, 593 00:38:36,338 --> 00:38:39,205 forming a thick carpet of vegetation. 594 00:38:39,205 --> 00:38:42,871 As high tides flow over the salt marsh, 595 00:38:42,871 --> 00:38:45,071 this web of branches and stems 596 00:38:45,071 --> 00:38:48,038 acts like a giant fishing net, 597 00:38:48,038 --> 00:38:51,771 trapping mud and debris that then settle on top 598 00:38:51,771 --> 00:38:56,205 of the salt marsh, causing it to gain height 599 00:38:56,205 --> 00:38:59,971 and providing a mechanism for the marshes 600 00:38:59,971 --> 00:39:04,405 to keep pace with sea level rise. 601 00:39:04,405 --> 00:39:08,471 CECCONI: The more it is flooded, the more it grows. 602 00:39:08,471 --> 00:39:11,705 Each year, it is growing now 603 00:39:11,705 --> 00:39:14,638 more than one or two centimeter. 604 00:39:14,638 --> 00:39:17,538 ♪ ♪ 605 00:39:17,538 --> 00:39:22,305 NARRATOR: These low-lying marshes have yet another benefit. 606 00:39:22,305 --> 00:39:25,138 They offer one of the most potent ways 607 00:39:25,138 --> 00:39:28,538 of fighting climate change on the planet. 608 00:39:28,538 --> 00:39:33,438 ♪ ♪ 609 00:39:33,438 --> 00:39:37,405 Acre for acre, they can lock up carbon 50 times faster 610 00:39:37,405 --> 00:39:40,805 than the Amazon rain forest. 611 00:39:42,971 --> 00:39:45,538 ♪ ♪ 612 00:39:45,538 --> 00:39:47,638 But in Venice's lagoon, 613 00:39:47,638 --> 00:39:51,105 salt marshes are in decline. 614 00:39:51,105 --> 00:39:56,205 200 years ago, there were nearly 70 square miles. 615 00:39:56,205 --> 00:40:00,505 Now there are just 16. 616 00:40:00,505 --> 00:40:02,038 ♪ ♪ 617 00:40:02,038 --> 00:40:07,771 This decrease is linked largely to one factor: 618 00:40:07,771 --> 00:40:10,705 erosion from ships. 619 00:40:10,705 --> 00:40:14,471 All cargo ships access the lagoon 620 00:40:14,471 --> 00:40:17,438 via the Malamocco Inlet. 621 00:40:17,438 --> 00:40:20,138 They follow a narrow channel 622 00:40:20,138 --> 00:40:23,205 to reach Porto Marghera. 623 00:40:23,205 --> 00:40:26,471 ♪ ♪ 624 00:40:28,505 --> 00:40:32,038 Just two miles from Venice, this is one of the busiest 625 00:40:32,038 --> 00:40:34,805 ports in Italy, 626 00:40:34,805 --> 00:40:37,438 processing over 25 million tons 627 00:40:37,438 --> 00:40:40,005 of cargo every year. 628 00:40:40,005 --> 00:40:45,105 ♪ ♪ 629 00:40:45,105 --> 00:40:47,905 Coastal researcher Luca Zaggia 630 00:40:47,905 --> 00:40:49,871 is worried the city and its lagoon 631 00:40:49,871 --> 00:40:53,371 are at risk from all these large cargo vessels. 632 00:40:53,371 --> 00:40:57,671 ♪ ♪ 633 00:40:57,671 --> 00:41:00,438 ZAGGIA: The ships are getting bigger. 634 00:41:00,438 --> 00:41:05,171 So starting from the '60s, they doubled the size. 635 00:41:05,171 --> 00:41:08,871 Today, we have ships as long as 300 meters, 636 00:41:08,871 --> 00:41:12,838 which is, uh, quite a lot for this channel. 637 00:41:12,838 --> 00:41:16,805 NARRATOR: 300 meters is the length 638 00:41:16,805 --> 00:41:20,338 of six Olympic-size swimming pools-- 639 00:41:20,338 --> 00:41:23,271 nearly 1,000 feet. 640 00:41:23,271 --> 00:41:27,271 And when it comes to ships, size matters. 641 00:41:27,271 --> 00:41:29,838 ♪ ♪ 642 00:41:29,838 --> 00:41:32,471 ZAGGIA: This is a big wake. 643 00:41:34,505 --> 00:41:37,605 Well, that was not bad. 644 00:41:37,605 --> 00:41:42,238 So now, on the, on the side, 645 00:41:42,238 --> 00:41:44,871 you see the water bounces back and forth 646 00:41:44,871 --> 00:41:49,138 for about 15, 20 minutes. 647 00:41:49,138 --> 00:41:51,638 And the erosion created by the ships, 648 00:41:51,638 --> 00:41:54,105 it's undercutting the shore. 649 00:41:54,105 --> 00:41:56,838 And we lost here essentially 150 meters. 650 00:41:56,838 --> 00:41:59,971 ♪ ♪ 651 00:41:59,971 --> 00:42:03,338 NARRATOR: The larger the ship and the quicker it is moving, 652 00:42:03,338 --> 00:42:05,905 the faster the erosion 653 00:42:05,905 --> 00:42:10,905 due to the size of the waves. 654 00:42:12,238 --> 00:42:14,771 ZAGGIA (speaking Italian): 655 00:42:14,771 --> 00:42:17,005 NARRATOR: A ship's momentum generates 656 00:42:17,005 --> 00:42:20,671 two different destructive waves. 657 00:42:20,671 --> 00:42:26,838 ZAGGIA: 658 00:42:26,838 --> 00:42:32,405 NARRATOR: First, a depression wave that sucks water towards the vessel. 659 00:42:32,405 --> 00:42:36,838 ZAGGIA: 660 00:42:38,638 --> 00:42:42,971 NARRATOR: And then a displacement wave generated by the hull, 661 00:42:42,971 --> 00:42:47,438 pushing water out of the way as the vessel powers forward. 662 00:42:47,438 --> 00:42:49,738 ♪ ♪ 663 00:42:49,738 --> 00:42:54,905 The power of these two waves combines to destroy the land 664 00:42:54,905 --> 00:43:00,238 close to the channel. 665 00:43:00,238 --> 00:43:03,605 The ship wakes, they arrive until this point. 666 00:43:03,605 --> 00:43:06,071 They undercut the cliff. 667 00:43:06,071 --> 00:43:09,438 And finally, slabs of soil will collapse. 668 00:43:09,438 --> 00:43:12,105 Over a year, you can lose about 669 00:43:12,105 --> 00:43:14,805 four meters of shoreline. 670 00:43:14,805 --> 00:43:17,971 ♪ ♪ 671 00:43:17,971 --> 00:43:20,105 NARRATOR: And on the other side of the channel, 672 00:43:20,105 --> 00:43:22,205 the waves from large ships 673 00:43:22,205 --> 00:43:25,405 are scouring mud from the sea floor. 674 00:43:25,405 --> 00:43:27,771 Since the 1970s, 675 00:43:27,771 --> 00:43:30,405 erosion has caused the lagoon to become 676 00:43:30,405 --> 00:43:32,238 over three feet deeper. 677 00:43:32,238 --> 00:43:34,071 ♪ ♪ 678 00:43:34,071 --> 00:43:36,738 And when the lagoon gets deeper, it increases 679 00:43:36,738 --> 00:43:39,838 the risk of Venice flooding. 680 00:43:39,838 --> 00:43:43,471 ZAGGIA: This is a buffer between the land and the ocean. 681 00:43:43,471 --> 00:43:46,905 You have no idea of how many problems you can have 682 00:43:46,905 --> 00:43:49,438 on the coast without this buffer. 683 00:43:49,438 --> 00:43:51,938 So we need to limit the erosion 684 00:43:51,938 --> 00:43:55,338 if we want to save Venice. 685 00:43:55,338 --> 00:43:59,271 NARRATOR: But that's becoming more difficult. 686 00:44:01,305 --> 00:44:05,305 Traffic in this channel is increasing. 687 00:44:05,305 --> 00:44:07,805 (ship horn blows) 688 00:44:07,805 --> 00:44:10,238 Cruise ships used to sail right through the center 689 00:44:10,238 --> 00:44:13,405 of Venice. 690 00:44:13,405 --> 00:44:16,638 Here, they traveled very slowly 691 00:44:16,638 --> 00:44:20,371 and produced only very small wakes. 692 00:44:20,371 --> 00:44:23,238 (ship horn blaring) 693 00:44:23,238 --> 00:44:25,505 But in 2019, 694 00:44:25,505 --> 00:44:28,838 a cruise ship plowed into a dock in the city. 695 00:44:28,838 --> 00:44:32,671 ♪ ♪ 696 00:44:32,671 --> 00:44:37,071 (people shouting) 697 00:44:37,071 --> 00:44:42,338 (hull scraping) 698 00:44:42,338 --> 00:44:47,105 NARRATOR: Luckily, there were only minor injuries. 699 00:44:47,105 --> 00:44:51,105 But now the authorities only allow cruise ships 700 00:44:51,105 --> 00:44:54,805 in the Malamocco Canal, where they are free to travel 701 00:44:54,805 --> 00:44:59,171 at much higher speeds. 702 00:44:59,171 --> 00:45:02,671 Luca believes this will increase the erosion. 703 00:45:02,671 --> 00:45:05,905 ♪ ♪ 704 00:45:05,905 --> 00:45:09,105 ZAGGIA: My opinion is, the lagoon, 705 00:45:09,105 --> 00:45:12,505 it's not suitable for large vessels. 706 00:45:12,505 --> 00:45:15,438 We must be correct with the environment, because, uh, 707 00:45:15,438 --> 00:45:17,571 we inherited it from the past. 708 00:45:17,571 --> 00:45:19,505 And we are in charge of it. 709 00:45:19,505 --> 00:45:21,571 And this is what protects Venice from, 710 00:45:21,571 --> 00:45:23,805 from further damages. 711 00:45:23,805 --> 00:45:27,538 ♪ ♪ 712 00:45:27,538 --> 00:45:30,138 NARRATOR: Protecting the natural flood defense systems 713 00:45:30,138 --> 00:45:34,771 in the lagoon is key to the survival of Venice. 714 00:45:34,771 --> 00:45:37,005 ♪ ♪ 715 00:45:37,005 --> 00:45:39,605 And around the globe, the idea of using nature 716 00:45:39,605 --> 00:45:44,805 to counteract rising sea levels is gaining traction. 717 00:45:48,638 --> 00:45:50,938 Ed Blakely directed the recovery effort 718 00:45:50,938 --> 00:45:53,805 in New Orleans after Hurricane Katrina. 719 00:45:53,805 --> 00:45:58,438 ♪ ♪ 720 00:45:58,438 --> 00:46:01,205 We've been removing salt marshes 721 00:46:01,205 --> 00:46:04,571 and these kinds of things that act as filters 722 00:46:04,571 --> 00:46:07,138 for the water that will come into a city. 723 00:46:07,138 --> 00:46:09,538 ♪ ♪ 724 00:46:09,538 --> 00:46:12,038 The floods that came in Katrina, 725 00:46:12,038 --> 00:46:15,771 the surge that was coming up the Gulf, the Mississippi, 726 00:46:15,771 --> 00:46:18,871 the lack of the trees meant it reached the city. 727 00:46:18,871 --> 00:46:21,505 Had those trees still been there, 728 00:46:21,505 --> 00:46:24,438 New Orleans would have been saved. 729 00:46:24,438 --> 00:46:27,771 ♪ ♪ 730 00:46:27,771 --> 00:46:29,338 In my view, natural solutions 731 00:46:29,338 --> 00:46:32,071 are the best way to protect populations. 732 00:46:32,071 --> 00:46:36,505 Basically putting nature back where it should be. 733 00:46:36,505 --> 00:46:39,205 Mangroves are particularly effective in dealing 734 00:46:39,205 --> 00:46:42,005 with surges, because as the river rises, 735 00:46:42,005 --> 00:46:43,605 they absorb that, 736 00:46:43,605 --> 00:46:47,405 and they dampen the sea rise effect. 737 00:46:47,405 --> 00:46:51,505 You can also start replanting. 738 00:46:51,505 --> 00:46:54,405 Restoring the cypress trees and things that were 739 00:46:54,405 --> 00:46:59,071 in the canal systems that contain the water and hold it. 740 00:46:59,071 --> 00:47:03,705 And building barrier islands that once were there. 741 00:47:03,705 --> 00:47:06,938 Replacing them makes a lot of sense. 742 00:47:08,771 --> 00:47:12,271 I think nature is our only ally in the future. 743 00:47:12,271 --> 00:47:15,138 If we don't restore nature, we have little hope 744 00:47:15,138 --> 00:47:18,305 of restoring and keeping our cities. 745 00:47:18,305 --> 00:47:22,138 ♪ ♪ 746 00:47:22,138 --> 00:47:25,271 NARRATOR: But could Venice take the idea 747 00:47:25,271 --> 00:47:28,838 of working with nature one step further? 748 00:47:28,838 --> 00:47:31,438 ♪ ♪ 749 00:47:31,438 --> 00:47:34,671 Could the key to saving Venice 750 00:47:34,671 --> 00:47:37,871 be the geology beneath the city? 751 00:47:37,871 --> 00:47:42,838 ♪ ♪ 752 00:47:42,838 --> 00:47:48,005 It's an idea that engineer Pietro Teatini is exploring. 753 00:47:48,005 --> 00:47:51,071 ♪ ♪ 754 00:47:51,071 --> 00:47:54,105 TEATINI: The idea is, by injecting 755 00:47:54,105 --> 00:47:56,938 seawater into deep aquifers 756 00:47:56,938 --> 00:47:59,905 or deep reservoir below the lagoon bottom, 757 00:47:59,905 --> 00:48:03,505 to try to uplift the city of Venice 758 00:48:03,505 --> 00:48:06,538 around 25 centimeter. 759 00:48:08,138 --> 00:48:11,138 This is something that can really be, be done, 760 00:48:11,138 --> 00:48:14,005 and in practice, it works. 761 00:48:14,005 --> 00:48:16,471 ♪ ♪ 762 00:48:16,471 --> 00:48:18,271 NARRATOR: Beneath Venice's lagoon, 763 00:48:18,271 --> 00:48:22,171 there are layers with different geological properties. 764 00:48:22,171 --> 00:48:25,238 Some are impermeable clay. 765 00:48:25,238 --> 00:48:27,771 These surround aquifers, 766 00:48:27,771 --> 00:48:31,705 strata of highly absorbent sandy deposits. 767 00:48:31,705 --> 00:48:36,238 Injecting seawater directly into these aquifers 768 00:48:36,238 --> 00:48:38,738 would cause them to swell 769 00:48:38,738 --> 00:48:41,805 and push up on the layers above, 770 00:48:41,805 --> 00:48:44,938 lifting the whole of Venice. 771 00:48:49,271 --> 00:48:51,338 It's an ambitious plan. 772 00:48:51,338 --> 00:48:54,138 But lifting land by injecting water 773 00:48:54,138 --> 00:48:57,738 is a proven technology. 774 00:48:57,738 --> 00:48:59,405 ♪ ♪ 775 00:48:59,405 --> 00:49:01,971 In the 1930s, oil was pumped 776 00:49:01,971 --> 00:49:04,571 from the Wilmington Oil Field in California 777 00:49:04,571 --> 00:49:06,805 in such vast quantities 778 00:49:06,805 --> 00:49:09,538 that the land began to sink. 779 00:49:09,538 --> 00:49:12,171 ♪ ♪ 780 00:49:12,171 --> 00:49:14,805 By the late 1950s, 781 00:49:14,805 --> 00:49:18,505 it affected an area of 20 square miles. 782 00:49:18,505 --> 00:49:20,405 And in some places, 783 00:49:20,405 --> 00:49:24,138 the ground had dropped 29 feet. 784 00:49:24,138 --> 00:49:27,038 Engineers began injecting 785 00:49:27,038 --> 00:49:30,005 seawater under the ground, 786 00:49:30,005 --> 00:49:33,271 which lifted the land up 787 00:49:33,271 --> 00:49:37,038 and back to its previous level. 788 00:49:37,038 --> 00:49:39,805 ♪ ♪ 789 00:49:39,805 --> 00:49:41,905 Pietro and his team have calculated 790 00:49:41,905 --> 00:49:46,138 they could lift Venice for $100 million, 791 00:49:46,138 --> 00:49:50,105 a fraction of the cost of the MOSE. 792 00:49:54,938 --> 00:50:00,138 TEATINI: The idea that we have is to put ten wells around Venice, 793 00:50:00,138 --> 00:50:03,138 centered on the Bridge of Rialto. 794 00:50:03,138 --> 00:50:06,038 We inject different amount 795 00:50:06,038 --> 00:50:09,405 of water into each well. 796 00:50:09,405 --> 00:50:13,438 And we adjust the pumping rate 797 00:50:13,438 --> 00:50:17,505 in order to have as uniform as possible 798 00:50:17,505 --> 00:50:20,371 uplifting of the city, 799 00:50:20,371 --> 00:50:25,638 but without generating any kind of cracks or fracture. 800 00:50:25,638 --> 00:50:29,338 We reach this maximum uplift 801 00:50:29,338 --> 00:50:32,071 of about 20, 25 centimeter 802 00:50:32,071 --> 00:50:35,138 in ten years. 803 00:50:36,571 --> 00:50:40,338 NARRATOR: Raising Venice nearly ten inches would decrease 804 00:50:40,338 --> 00:50:42,405 the impact of future surge tides 805 00:50:42,405 --> 00:50:45,505 and sea level rise in the city. 806 00:50:48,638 --> 00:50:52,938 Working alongside the MOSE and the lagoon's salt marshes, 807 00:50:52,938 --> 00:50:56,405 it could reduce the risk of Venice flooding 808 00:50:56,405 --> 00:50:58,838 and help protect 809 00:50:58,838 --> 00:51:02,338 the city's centuries-old buildings. 810 00:51:05,271 --> 00:51:08,671 ♪ ♪ 811 00:51:08,671 --> 00:51:12,205 Venice was born out of its natural 812 00:51:12,205 --> 00:51:15,338 environment and clever engineering. 813 00:51:15,338 --> 00:51:18,871 Adapting the lagoon's muddy islands 814 00:51:18,871 --> 00:51:22,405 offered Venetians a way to build their first homes. 815 00:51:22,405 --> 00:51:25,638 Now, 1,600 years later, 816 00:51:25,638 --> 00:51:29,171 they have come full circle. 817 00:51:29,171 --> 00:51:32,871 Faced with losing their city to climate change, 818 00:51:32,871 --> 00:51:35,638 once again, they are innovating 819 00:51:35,638 --> 00:51:37,971 with large-scale engineering 820 00:51:37,971 --> 00:51:43,105 and the restoration of their ancient lagoon. 821 00:51:43,105 --> 00:51:48,171 Only by using multiple approaches can they hope 822 00:51:48,171 --> 00:51:52,105 to save Venice. 823 00:51:52,105 --> 00:51:53,638 BLAKELY: My view of the future of Venice 824 00:51:53,638 --> 00:51:56,338 is that if it keeps going the way it's going, 825 00:51:56,338 --> 00:52:00,038 there will be no Venice in less than 50 years. 826 00:52:00,038 --> 00:52:02,438 But if it changes its course, 827 00:52:02,438 --> 00:52:05,005 it can last another thousand years. 828 00:52:05,005 --> 00:52:07,605 That's up to Venice. 829 00:52:07,605 --> 00:52:10,505 ♪ ♪ 830 00:52:32,538 --> 00:52:40,071 ♪ ♪ 831 00:52:47,305 --> 00:52:52,171 ANNOUNCER: To order this program on DVD, visit ShopPBS. 832 00:52:52,171 --> 00:52:54,905 Or call 1-800-PLAY-PBS. 833 00:52:54,905 --> 00:52:57,771 Episodes of "NOVA" are available with Passport. 834 00:52:57,771 --> 00:53:01,571 "NOVA" is also available on Amazon Prime Video. 835 00:53:01,571 --> 00:53:06,771 ♪ ♪ 836 00:53:15,571 --> 00:53:22,738 ♪ ♪