[BLANK_AUDIO] In this video we're going to explore path dependency from the 19th century sewer system infrastructure investment of the UK's water development path, looking at London. We're going to see how historical decisions, assumptions and approaches. Have steered this development path. And to some degree they have limited what can be done in the present day to adapt the UK's water and sanitation infrastructure to meet new expectations and challenges. This is the path dependency. To make sense of what we mean by path dependency, let's look at some of the main assumptions that became embedded as it were in London's 19th century pipe sewer network. These assumptions reflected the scientific knowledge of the time and related attitudes and practises. As we've just looked at in the previous video. First the huge sewer insulation program in London in the late 19th century reflected the decision to displace the problem of the presence of sewage material in the center heavily populated areas of the city. To collect it in large sewer interceptors and to send it eastward, away to the sea to less populated areas. Sewage treatment ideas were pretty basic at this time too. The science of the day was the belief that rivers and fast flowing water courses had pretty much an unlimited capacity to purify themselves. Sewage material dumped in them, if diluted enough, it was believed would decompose safely and not be a hazard to health or to the environment. Second, the sewer systems built in London were combined sewers. They took sewage from homes and businesses and mixed it in single pipes, with rainfall and storm drainage of runoff from the city streets and drains. This design was cheaper and simpler than building a separate systems that would transmit foul and burn off waste streams separately. Separate systems of what you'll see being in stall in the UK today for instance. Most of the UK sewer systems and the Dutch ones incidentally installed from the 1850s to 1880s were combined systems. Due to the appeal of being cheaper and simpler. In the United States of America, according to Professor Joel Tarr's work, up until the early 1900s about three quarters of the systems that have been built were of the combined type, like the UK. Professor Tarr also says that about 90% of the population sewage in the United States was disposed of untreated at this period. The UK would have probably been very similar. Third, the combined sewer design embodied the scientific idea that a waterborne flow of sewage would prevent the buildup of sewer gases, and would wash away foul material before it could decompose and give rise to bad air. In other words, this design choice comes from the scientifically incorrect miasma theory of disease. The combined design also involved a risk of overflowing during heavy loads on the system, say during heavy rain or storms. A series of flood gates were built and designed into the system to dump the contents of the interceptor sewers into the River Thames. And this was at many points along the interceptor sewer and it was a safety feature. This was a deliberate design choice to pollute the River Thames in such instances instead of flooding homes and businesses in the center of the city by allowing the sewers to back up into streets and properties. The pipe out force of the system were also designed to be located near specific farmers so that they could make economic use of the sewage flow. Fourth, large scale sewer systems were a new technology really. There were no agreed standards and there was a period of experimentation with various designs before the final large diameter, low pressure water bond flow approach was settled upon for London's pipe sewer network. Sir Edwin Chadwick, the poor law and public health figure we mentioned in the earlier video. Arranged for trials for small earthenware sewers that would operate at high pressure, similar to how many present high pressure water mains operate. These systems burst under trial. But if they had been used instead of the larger low pressure flow ones we ended up with in London, perhaps they would not have had the problems that have plagued the low pressure sewers ever since they were built. Small bore, higher pressure sealers that were trialed that were smoother and perhaps less likely to block the various solid waste. Such as rubbish and fat. The rough brick wide bore low pressure flow sealers that had the potential to run dry, if the water in them ran out and the roughness to catch materials flowing in through the pipes. Could and did lead to blockages and these need to be cleared. Let's take a look at some of these large bore brick sewers that I've been talking about. The photo on the left here shows an interceptor sewer. This one is from Brighton on England's south coast. I've chosen to show it just to show how large these systems could be. It's commonly said, by water utility staff in London, that there are sewers there that are large enough that you could drive one of London's iconic red buses right through them. The photo on the right is from underneath Toronto Canada, but many of the brick sewers under London would look very similar to this. In fact, there's a reason for that. Many countries from around the world drew upon British experiences and approaches. For instance, Scottish engineers went out as far as Japan to assist with water and sanitation system programs. For the North America case, Professor Joel Tarr has written that, and I'm quoting here, visits to sewage works in cities in Great Britain were almost mandatory for American engineers involved in planning new sewage systems in the second half of the 19th century. The design problem of the large bore low pressure brick sewers that I mentioned previously, that they could block if flow in them dried up, turned out to be a reality. Blocked sewers had to be cleaned. In the 19th century this was a very manual job. In the photo here, you can see so called sewer flushers in Fleet Sewer under Farrington Road, London. This is a manual job that hasn't gone away though. Here are some of Thames Water's present day sewer flushers doing a very similar job to their 19th century counterparts of checking the sewers and removing blockages. Modern ways of living mean that these low pressure sewers can also block with fats, oils and grease. These are from households tipping these down drains and also from businesses like food take aways and restaurants putting fats, oils and grease down drains. We recently had a whole national TV program made here by the BBC in the UK. Following water staff as they went around their various daily activities. Clearing out sewers blocked with fats, oils, and greases, and with non biodegradable baby wipes, seemed to be a very frequent activity even to this day. Ironically, the crews use high pressure water jets to clear out such blockages. So it's interesting to think what issues would have been faced. Perhaps they would be similar, perhaps somewhat different. If the sewers had been made to a high pressure design from the start. Incidentally, if you search online, or talk to water utilities staff, you're likely to hear all manners of story about what has been found to be blocking sewers. This can vary from shopping carts to toys, dismembered limbs, clothes, and even half an automobile in one case. That was Thames Waters Beckton Sewage Treatment Works in London. Sewer flushes also encounter other materials that have made their ways into sewers like drug related paraphernalia, sweet corn, unexploded hand grenades, false teeth, and lost jewelery. Some of which is sometime recovered when owners contact the water utility companies. Beyond blockages that trace, in part, to the low pressure design of the sewers chosen in the 19th century, another major problem that London now faces is the result of the decision to make these sewers a combined design and to take foul and run off waste flows together, and to allow them to overflow into the River Thames under conditions of high flow. This causes what are known as unsatisfactory combined sewer overflows, or UCSOs. The photo here on the left shows metal gates from the interceptor sewer that activate and opens under high flow conditions, to release the sewer contents into the river. The water company Thames Water estimates that about 39 million tons of untreated sewage overflow. Goes in the River Thames in London each year from these built in UCSO sites. Tens or hundreds of thousands of fish can also be killed by such incidents. The sewer systems of London are largely unchanged since they were built. But London now has more intense rainfall episodes, due to changing climate conditions like the ones we touched upon in the videos last week. Changing patterns of land use have also led to more land area in the center of London being paved over with impermeable surfaces. And this accelerates run off into the combined sewers. Together, these factors are part of the reason why UCSOs can now be triggered in London by as little as two millimeters of rainfall. It may seem hard to believe, but these UCSOs, as I've said, were intentional elements of the 19th century sewer systems design. They were designed to take place as a safety valve to prevent homes and businesses from experiencing foul flooding. The text is small here, but this map shows that there are not just a few of them. Here we see 54 sewer overflow points built into the system. They stretch miles along the course of the flow of the River Thames. I've also marked here in the dotted red box the approximate area of London, that it would've been when we started our UK water development path story. This would've been the area served by the great conduit that took its source from Tiber and Brook a few kilometers west or northwest of edges of the box. Nowadays, societal expectations have changed in a variety of ways. And the UK as a whole, including London, is also subject to environmental quality legislation from the European Union. Particularly, in this case, in the form of the Urban Wastewater Treatment directive. This directive was agreed in 1991 and it came into force initially in 1998. It sets standards for collection, treatment and discharge of waste water in urban areas. The European Commissioner Inspector followed legal proceedings against the UK's since 2009 for breaches of this directive in London due to the unsac, satisfactory overflows along the River Thames. The photo here is the European Parliament's hemicycle members chamber. There's been about a decade of consultation by Thames Water, the government, the water sector regulator OFWAT, and other stakeholders about possible solutions to this unsatisfactory overflow problem, and rather critically, who should be paying for the solution. The current idea is to build another large interceptor about 25 kilometers long at a cost of somewhere around 4 billion British pounds. Running 30 to 75 meters deep around the River Thames. This new interceptor will take sewage flow away from the old interceptor to five upgraded sewer works out to the east of London. The photos here show at the top. One of the five or six planned tunnel boring machines that would be used to do the tunnel. They're huge as you can see. The photo at the bottom shows a platform carrying out exploratory work on the River Thames. It should be noted that water utility company Thames Water is no stranger to large tunnel projects like this in London. In 1994, Thames Water completed a 250 million pound, 80 kilometer clean water ring main that carries over a billion liters of water a day through, two and a half meter diameter pipes that are some 10-60 meters under the ground. This ring main forms a complete ring underneath the city and connects Greater London's various water supplies. To enable more efficient water resources management. And Thames Water's ring main was the UK's longest tunnel at the time it was completed. Nevertheless, in spite of Thames' past experience, the Thames Tunnel is still a huge planned undertaking. Like the 19th century sewer system was touted to bring various benefits, now in the 21st century there are also estimates about what the new Thames interceptor sewer construction will bring. It's estimated it will create 4,000 jobs and that once the the tunnel's complete, it might increase London's competitiveness as a global city and bring various social, recreational, and environmental benefits from a cleaner River Thames. Unlike the cost benefit analysis for the 19th century investment though, there's no longer estimates of the economic benefits from human lives saved. But of course there should be benefits to aquatic life, for example, reduced fish kill incidents. Potential downsides of a construction project like this also have to be considered. The project has planned to take about 90% of the soil removed from conduction, construction activity away via the river itself. This is to avoid traffic disruption on London's roads. The economic water regulator for England and Whales, OFWAT, has estimated that the 4 billion pound Thames tunnel project could about 50% for sewage bills for Thames Water customers alone. That's if that's the way it's paid. This is a big impact from a big project. So as you might expect the project has its supporters and its detractors. In this slide I've put up a number of the videos made by the supporters of the project and the developers. These videos also show some of the proposed roots for the work as plans are changing over time. Have a look at these videos, see what you think about what the positives and the negatives of this project given what you've learned about so far in the course. And feel free to share your views on the discussion forums. As you do so you may want to recall that this 25 kilometer tunnel is about the same length as the 26 kilometer tunnel that Dale mentioned could one day supply water to Kathmandu, Nepaul. That was back in the week three videos. To wrap up this video, we've seen significant path dependency in the UK's water development path. We've seen how decisions made in the 19th century for the design and operation of the sewer system in London now necessitate significant reinvestment to redirect the development path. This is to address 21st century concerns that were beyond the scientific knowledge and outside the scope of attitudes and practices of our 19th century counterparts. They perhaps got some of the science wrong. They over estimated the purifying effects of dilution and they conceived of disease as occurring from sewage material due to miasmas. They designed their system based on their understanding at the time, just the same way that we do now. The capital intensity and scale of the investment however has limited how much can easily be changed afterwards. In the 19th century there was almost little or no understanding of the later effects that climate change would have on the combined sewer system design that was adopted. But now water supply and sanitation planners and other stakeholders in the UK are expected to address all of these issues. So these are changes to the status quo conditions in a dynamic baseline that stresses over centuries. In the next video we're going to look at some changes in the 20th century, before looking in a bit more detail at why current challenges suggest a change of course for the UK's continuing water development path. Thanks for watching this video. [BLANK_AUDIO]
