1 00:00:06,995 --> 00:00:08,995 Welcome to urban engineering. 2 00:00:09,800 --> 00:00:11,280 My name is Marie-Claire ten Veldhuis, 3 00:00:11,640 --> 00:00:16,120 and I work as an assistant professor for urban watersystems at Delft University of Technology. 4 00:00:17,220 --> 00:00:21,960 In this submodule we will see what interventions have been developed to protect cities from 5 00:00:21,960 --> 00:00:25,079 flooding and dirty waters. 6 00:00:25,079 --> 00:00:31,000 The Romans were great engineers: they built impressive structures strong enough so we 7 00:00:31,000 --> 00:00:34,780 can still see the remains of some of them today. 8 00:00:36,260 --> 00:00:43,700 One of their great works started around 600 BC: they built a gigantic underground tunnel 9 00:00:44,010 --> 00:00:46,180 to collect stormwater from the streets of Rome, 10 00:00:46,980 --> 00:00:50,580 to protect Roman citizens from stormwater flooding. 11 00:00:51,390 --> 00:00:55,339 The so-called Cloaca Maxima, or “Greatest Sewer”, 12 00:00:55,339 --> 00:01:02,339 is still in place and its sewer mouth can be seen on the borders of the Tevere River. 13 00:01:02,400 --> 00:01:08,259 The design principle of the Cloaca Maxima was simple: a channel that naturally received 14 00:01:08,259 --> 00:01:13,970 much of the stormwater from the city was gradually covered and transformed into an underground 15 00:01:13,970 --> 00:01:16,920 tunnel, a gigantic sewer. 16 00:01:17,560 --> 00:01:22,080 The sewer proved to be a convenient solution to drain stormwater from the city’s roofs 17 00:01:22,080 --> 00:01:26,320 and streets, while life above ground could continue undisturbed. 18 00:01:27,460 --> 00:01:30,860 Perhaps too convenient, because not only stormwater flowed into the 19 00:01:30,860 --> 00:01:32,300 underground sewer. 20 00:01:32,500 --> 00:01:37,340 Wastewater from public toilets, bathhouses and workshops was dumped into the 21 00:01:37,350 --> 00:01:39,229 underground tunnel, too, 22 00:01:39,229 --> 00:01:44,209 and a smelly mixture flowed out through the sewer system into the Tevere river. 23 00:01:45,710 --> 00:01:50,170 We call sewers like the Cloaca Maxima combined sewers. 24 00:01:50,170 --> 00:01:55,170 They collect wastewater during dry weather and fill up with stormwater when it rains. 25 00:01:55,760 --> 00:02:01,440 Combined sewer systems have been constructed in many cities worldwide as a robust engineering 26 00:02:01,440 --> 00:02:07,440 solution: they prevent flooding of the streets and dispose of dirty, 27 00:02:07,450 --> 00:02:11,030 smelly wastewaters from the city’s households and businesses. 28 00:02:12,530 --> 00:02:15,159 In many cities including large cities like Paris, 29 00:02:15,159 --> 00:02:17,200 London, New York and Tokyo, 30 00:02:17,200 --> 00:02:22,519 sewers have been constructed under almost street connecting every house and every road 31 00:02:22,519 --> 00:02:24,340 to the sewer system. 32 00:02:24,340 --> 00:02:31,340 This amounts to thousands of kilometres of sewers underlying our city’s streets. 33 00:02:32,250 --> 00:02:35,880 But large combined sewer systems are not always the most convenient solution. 34 00:02:35,880 --> 00:02:40,950 In some areas of the world, stormwater is collected by open channels instead 35 00:02:40,950 --> 00:02:42,870 of underground sewers. 36 00:02:43,140 --> 00:02:47,680 In areas where rainfall can be really intense, think for instance of heavy storms in the tropics, 37 00:02:48,000 --> 00:02:51,280 very large amounts of stormwater need to be transported. 38 00:02:52,200 --> 00:02:56,420 In that case, building underground pipes of such large sizes 39 00:02:56,420 --> 00:03:02,239 is simply too expensive and open channels are often a more feasible solution. 40 00:03:03,060 --> 00:03:08,780 When stormwater is collected in open channels, a separate solution needs to be found for 41 00:03:08,790 --> 00:03:11,230 wastewater collection. 42 00:03:11,230 --> 00:03:15,060 Dumping wastewater into the open channels is undesirable because the channels would 43 00:03:15,060 --> 00:03:22,060 get contaminated and foul-smelling and pose a health risk to the citizens. 44 00:03:22,450 --> 00:03:27,069 We call such systems separate sewer systems: they collect wastewater in a pipe, 45 00:03:27,069 --> 00:03:28,529 separate from stormwater. 46 00:03:29,540 --> 00:03:32,720 Stormwater can easily be collected in open channels. 47 00:03:33,080 --> 00:03:35,220 But channels take up a lot of space, 48 00:03:35,440 --> 00:03:39,050 and this is why in large, densely built cities, 49 00:03:39,050 --> 00:03:43,810 underground stormwater pipes are still preferred instead of open channels. 50 00:03:43,810 --> 00:03:50,130 Japan is a typical example where high amounts of rainfall coincide with very high population density. 51 00:03:50,920 --> 00:03:55,959 It would be a lot easier and cheaper to collect large amounts of rainfall in open channels, 52 00:03:55,959 --> 00:04:01,510 but many Japanese cities are so densely populated that there is not enough space and large stormwater 53 00:04:01,510 --> 00:04:04,200 pipes are built instead. 54 00:04:04,200 --> 00:04:06,800 For instance in Sataima, a city in Japan, 55 00:04:06,800 --> 00:04:11,760 a gigantic underground stormwater system has been built that consists of five large storage 56 00:04:11,760 --> 00:04:18,519 basins connected by 6km of tunnels, 50 m beneath the surface. 57 00:04:18,519 --> 00:04:22,270 Eventually, stormwater is pumped into the Edo river by 58 00:04:22,270 --> 00:04:27,300 a series of 10 MW pumps that can pump up to 200 tons of water, 59 00:04:27,300 --> 00:04:32,040 the approximate volume of a standard 25 meter pool, per second. 60 00:04:33,710 --> 00:04:37,850 In most cities in moderate climates such as in Europe and the US, 61 00:04:37,850 --> 00:04:41,930 underground, combined sewer systems have been the rule for decades. 62 00:04:41,930 --> 00:04:47,650 Gradually, this is changing and cities are converting their combined systems to separate systems. 63 00:04:48,090 --> 00:04:50,230 Now the question is, why? 64 00:04:51,440 --> 00:04:55,750 When it rains really hard, the capacity of combined sewers is not sufficient 65 00:04:55,750 --> 00:04:57,410 to cope with all stormwater. 66 00:04:58,080 --> 00:05:01,800 When a combined sewer fills up and it continues to rain, 67 00:05:01,800 --> 00:05:05,250 the sewer gets overloaded and a mixture of wastewater and stormwater spills from the 68 00:05:05,250 --> 00:05:06,430 combined sewer. 69 00:05:07,650 --> 00:05:10,430 To prevent the water from spilling onto the street, 70 00:05:10,430 --> 00:05:14,919 combined sewer overflow locations are created where water from the combined sewer flows 71 00:05:14,919 --> 00:05:17,539 out to rivers, streams or lakes. 72 00:05:18,320 --> 00:05:21,660 Combined sewer overflows cause pollution of our surface waters. 73 00:05:21,669 --> 00:05:26,880 They may harm natural water ecosystems and even pose a threat to citizens’ health. 74 00:05:26,880 --> 00:05:29,930 Nowadays, we prefer to prevent such pollution and get 75 00:05:29,930 --> 00:05:33,460 rid of combined sewer overflows. 76 00:05:33,460 --> 00:05:37,500 One way to do this, is by changing combined sewers into separate 77 00:05:37,500 --> 00:05:42,460 systems by taking stormwater apart, creating alternative solutions for stormwater collection. 78 00:05:43,540 --> 00:05:48,060 Instead of leading stormwater flowing from streets and roofs towards a combined sewer, 79 00:05:48,060 --> 00:05:51,800 stormwater can be collected in separate channels, gutters, 80 00:05:51,880 --> 00:05:54,360 infiltration beds and swales. 81 00:05:55,770 --> 00:05:59,690 In these facilities, stormwater is stored and filtered. 82 00:06:00,400 --> 00:06:04,700 It can infiltrate to groundwater or, in case of high ground water tables, 83 00:06:04,710 --> 00:06:07,650 slowly flow towards a natural stream or river. 84 00:06:08,660 --> 00:06:13,220 Stormwater is then no longer mixed with wastewater, creating dirty spills; instead it becomes 85 00:06:13,220 --> 00:06:15,560 an attractive part of the urban landscape. 86 00:06:15,800 --> 00:06:18,860 Many creative solutions have been invented in the past decades, 87 00:06:18,870 --> 00:06:22,870 often referred to as Sustainable Urban Drainage Solutions. 88 00:06:24,100 --> 00:06:26,660 Most have been implemented in newly built areas, 89 00:06:26,669 --> 00:06:31,069 where they have become an integrated part of urban design. 90 00:06:31,840 --> 00:06:35,680 More and more solutions are created for existing urban areas as well. 91 00:06:36,060 --> 00:06:41,980 Examples of such solutions are permeable pavements, green roofs and water squares. 92 00:06:41,990 --> 00:06:44,520 Surely, examples of sustainable urban drainage can 93 00:06:44,520 --> 00:06:46,410 be found in your city as well. 94 00:06:46,410 --> 00:06:49,550 Try and locate some examples and next time when it rains, 95 00:06:49,550 --> 00:06:56,550 go out to take a photo or movie of sustainable urban drainage and upload it 96 00:07:10,340 --> 00:07:13,660 Here, we are in Breda city, under one of its main roads. 97 00:07:14,520 --> 00:07:18,200 We are about 5 meters below street level in the cities oldest sewer. 98 00:07:18,960 --> 00:07:22,000 It was constructed in 1863 and still functions today. 99 00:07:22,300 --> 00:07:26,160 and originally this was not a sewer, but a moat, running along the city walls. 100 00:07:26,660 --> 00:07:30,120 the moat collected water from many creeks running through the city center. 101 00:07:30,740 --> 00:07:35,300 These creeks collect not only storm water, but were also used to dump waste water 102 00:07:35,355 --> 00:07:37,355 from the cities households and factories. 103 00:07:37,740 --> 00:07:40,380 Gradually, these creeks became so polluted and smelly, 104 00:07:40,380 --> 00:07:44,280 that they were filled up or covered over, and so was this cities moat, 105 00:07:44,280 --> 00:07:46,920 creating this brickwork tunnel, we can still see today. 106 00:07:48,240 --> 00:07:53,520 It's a combined sewer system collecting waste water from the cities households, shops and restaurants 107 00:07:53,520 --> 00:07:57,700 as well as storm water from the streets, the roofs and the central market place. 108 00:08:15,500 --> 00:08:18,020 This shows that the sewer is popular with rats. 109 00:08:18,560 --> 00:08:23,760 Citizens used these bowls to feed the rats, in order to make sure that the rats would stay inside the sewer. 110 00:08:23,940 --> 00:08:27,960 Nowadays the sewer is closed, and the rats will stay inside anyway. 111 00:08:34,680 --> 00:08:37,460 Here we see a really greasy household connection, 112 00:08:37,460 --> 00:08:40,780 probably one of the restaurants that throws its kitchen oil into the sewer. 113 00:08:41,400 --> 00:08:46,620 This is not supposed to happen, the grease will stick on to pipes and pumps and eventually clog the system. 114 00:08:53,860 --> 00:08:57,280 Imagine what would happen if this wastewater is no longer transported, 115 00:08:57,280 --> 00:08:59,046 and flows back onto the streets. 116 00:08:59,840 --> 00:09:04,220 The wastewater is full of pathogens, and the citizens could easily pick up water born deceases, 117 00:09:04,220 --> 00:09:06,460 like happend frequently in the middle ages. 118 00:09:06,860 --> 00:09:10,060 Back then, sewers for waste water collection were rare. 119 00:09:11,060 --> 00:09:13,100 Look at these lines on the sewer walls. 120 00:09:13,400 --> 00:09:15,420 This shows us we are in a combined sewer. 121 00:09:15,784 --> 00:09:17,784 Right now the water level is really low, 122 00:09:18,200 --> 00:09:20,400 because the sewer only transports wastewater. 123 00:09:20,400 --> 00:09:22,620 But when it rains, the water level quickly rises, 124 00:09:22,960 --> 00:09:29,080 and from these deposits on the wall we can tell that during recent rainfall, the water must have been at this level. 125 00:09:31,300 --> 00:09:35,660 In case of very heavy rainfall, the water level might even rise up to the ceiling. 126 00:09:36,340 --> 00:09:40,480 In that case we need a solution to prevent the water level from rising onto the streets. 127 00:09:40,900 --> 00:09:45,200 Especially because then, the stormwater is mixed with the wastewater from the sewer. 128 00:09:45,420 --> 00:09:49,600 Causing the citizens not only to get their feet wet, but it would also pose a threat to their health. 129 00:09:51,680 --> 00:09:54,460 This is a combined sewer overflow weir. 130 00:09:54,700 --> 00:09:58,160 To prevent combined sewer water from flowing out onto the streets, 131 00:09:58,160 --> 00:10:02,700 combined sewer overflows are constructed to release the system from excess water. 132 00:10:03,240 --> 00:10:07,540 This means that a mixture of stormwater and wastewater flows out of the system. 133 00:10:08,140 --> 00:10:12,860 Therefore, combined sewer overflows need to be constructed in non-vulnerable areas. 134 00:10:13,260 --> 00:10:17,500 Preferrably, at large surface waters or away from the people. 135 00:10:17,960 --> 00:10:21,660 However, in densely populated areas, such locations are hard to find. 136 00:10:21,920 --> 00:10:24,940 And therefore, if you live in a city with a combined sewer system, 137 00:10:24,940 --> 00:10:29,720 it is probably not a good idea to go fishing, or take a boat trip after a heavy storm. 138 00:10:31,240 --> 00:10:33,640 Fortunately, this happens only sporadically. 139 00:10:33,640 --> 00:10:38,600 under normal conditions, waste water and storm water flow through the sewer to a pumping station. 140 00:10:42,400 --> 00:10:43,920 Here we see sewer pumps, 141 00:10:43,920 --> 00:10:48,780 that pump the waste water and storm water to a sewer treatment plant several kilometers away. 142 00:10:49,240 --> 00:10:53,480 The capacity of one pump is enough to transport the wastewater flow. 143 00:10:53,480 --> 00:10:55,940 Additional pumps are available when it rains. 144 00:10:56,500 --> 00:11:01,720 In total, these pumps can transport four times the average wastewater flow from the city center. 145 00:11:02,140 --> 00:11:05,720 That is about the volume of a swimming pool pumped away, every hour. 146 00:11:07,560 --> 00:11:13,420 All together, twelve hundred kilometers of sewers in combination with the pumping station and overflow weirs, 147 00:11:13,420 --> 00:11:16,420 make sure the citizens of Breda can go about their business 148 00:11:16,420 --> 00:11:19,460 without being bothered by dirty smells or flooded roads. 149 00:11:20,140 --> 00:11:23,840 Thanks to an invisible but indispensable feat of urban engineering.