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Traditionally in Rotterdam, flood management has concentrated on preventing floods through technological measures, like storm surge barriers and dikes. However, there is currently an international shift towards more adaptive and integrated systems of flood risk management. (Ward et al., 2013) Rotterdam and the Netherlands have had flood management schemes in place for a long time. In the past flood management was aimed at reducing the chance of a flood by using structural measurements. For example dike construction began in 1000 AD and then water boards were created. (Borger and Ligtendag 1998). In the 18th century there was the establishment of a national water management body. (Rijkswaterstaat) (Borger and Ligtendag 1998). In the 20th century major flood events triggered the creation of a large flood management project for example the 1953 flood from a storm surge in the North Sea which led to the establishment of the delta works project which is a series of sluices, levees and storm surge barriers connecting South Holland and Zeeland. (e.g. Van Koningsveld et al. 2008). Rainfall in August 2006 led to flooding in Rotterdam which increased the awareness of Rotterdam’s vulnerability to flooding. The chance of flooding is increasing due to the sea level rise due to climate change and changing precipitation patterns. (Ward et al., 2013).

Due to the threat of climate change causing sea levels to rise in Rotterdam a climate change adaptation strategy was created. The target was to make Rotterdam adapted to climate change by 2025. It focuses on three key ideas; the maintaining and strengthening of existing infrastructure such as dikes, barriers and sewers, to adapt urban areas and work with other city projects. The aim is to combine new and existing management for flooding. The aim is to restore Rotterdam as being a place where it captures, and stores precipitation and it can cope with the increasing amount of flooding due to climate change. (O’Donnell, 2016) The aim is that Rotterdam is minimally affected by climate change flooding and it benefits from climate change by strengthening the economy improving the environment and enhancing natural rescues. The aim is to create a climate proof city for the population of Rotterdam. (Moel, Vliet and Jeroen, 2013)

One way flooding is managed in Rotterdam is the water plazas which aim to increase the amount of water urban areas can hold. During rainfall storms they retain water but at other times they are used as playing field and communal areas. (Ward et al., 2013) The aim of the plaza is to fill up with water in a controlled manner during heavy rainfall which prevents surrounding areas from flooding. Precipitation will remain in the plaza until it can be discharged into the nearest water body. In Rotterdam when it rains water is directed into the square which fills up with water. This collection of water relieves pressure on surrounding drainage. The drainage square drains the water much slower than the central point and there are filters on the square so the square won’t fill up with dirty water. The plaza is designed in a way so the rainfall adds to the aesthetic of the area and opens up ponds and rainwater features after a rainstorm event. Only a massive storm would fill the whole thing and take it out of action. During prolonged downpours, the water square will gradually fill up until it becomes a water storage basin, it is expected to hold a maximum of 1000 cubic metres of rainwater. (Mackenzie, 2010).  https://www.waterworld.com/articles/wwi/print/volume-25/issue-5/editorial-focus/rainwater-harvesting/Rotterdam-the-water-city-of-the-future.html. Water plazas are an effective way to manage the impact of flooding as the water is controlled and will not flood the landscape and ruin it, also the plaza has a large capacity for holding water so even if the flood is large, it can still prevent the water from flooding the surrounding area and no waste water is going into the surrounding area. However, the discharging of water to the nearest water body is slow which could be a problem if the flood is prolonged and a flood could occur. Moreover, if there is a large rain storm then the plaza will become out of action. However, these disadvantages are very small compared to the benefit of the waterway on flood management in Rotterdam.

The Delta Works is a project in Rotterdam used to manage flooding. Studies in 1937 by the department of public works showed that safety during times of storms and high sea levels could not be guaranteed in Rotterdam. The first solution was to close all the river mouths this is what the delta works is. This made the area safer and provided the rivers with a freshwater supply. Further plans were to build the remaining dams in following decades, but the 1953 food prevented this from happening. In the 1953 food nearly 2000 people died and more than 150,000 hectares of land were flooded which showed the population that something had to be done about flooding very quickly. After the flood the delta plan was inaugurated to increase the safety of the delta area. However, some water ways such as the De Nieuwe Waterweg and the Western Schelde would have to stay open, because of the economic importance. In 1959 a law was passed to begin the  construction of the dams. The delta works also has other advantages such as the agricultural freshwater supply is improved because the freshwater and saltwater border was moved further west so less freshwater was required to balance the freshwater-saltwater division. The excess water is transported to the north of the Netherland where freshwater was welcomed to improve the water conditions. The water balance of the delta area was also imposed because of the delta works. Because of the construction of major dams the streams were able to be manipulated more easily and freshwater was allowed in but only polluted or excess water was allowed out. The delta works have influenced new development in nature and recreation. Nature reserves were irreparably damaged but as compensation, new nature reserves have emerged from different sites. http://www.deltawerken.com/deltaworks/23.html.  

However, the project does have some environmental issues and ecological effects. The environmental effect of the project was not really taken into consideration. (d’Angremond 2003). Throughout the years of the project the environmental awarness grew but the project has caused numerous irreversible effects on the environment in the past. Blocking the estuary mouths led to changes in the water system, for example the disappearance of the tides which led to a less smooth transition from sea water into fresh water. Fauna and flora suffered from the change (de Vos, 2006). Also, rivers got polluted by sludge since there was no longer an open passage into the sea. https://en.wikipedia.org/wiki/Delta_Works

Moreover an economic problem of the project is that due to climate change and sea level rise the dikes will  eventually need to be made higher and wider, this is a long battle against the sea and will cost the government lots of money to keep on changing the dikes as the sea level rises. https://en.wikipedia.org/wiki/Delta_Works

Therefore, despite the delta works project being a great solution to managing flooding in Rotterdam, it brings about many sentimental and economic problems which could bring problems to Rotterdam. However, these problems are very minor compared the benefits of the project in protecting the area.

Another method of hard engineering flood management is a dike. A dike runs along a body of water such as a river or sea. A dike has water only on one side and the main purpose of a dike is protecting the land behind it form flooding. Dikes are walls that hold back the sea and the land would be flooded if the dikes were broken down. (https://wocatpedia.net/wiki/Dikes,_dams,_levees, 2014). Most dikes in Rotterdam are becoming ‘urban dikes’ that enable water front development because the dike itself can include shops or parking garages. (Restemeyer et al.,  2018).  Over the years the Netherlands has frequently been flooded Although the Netherlands is well protected from the water by the dike defence system today, there is always a risk of flooding. http://dutchdikes.net/dike-map/. Following the flood of 1953, Dutch engineers wanted to build a new barrier against the sea. The engineers replaced the old dike system which had been in place since medieval times and created 563km of a dike system. The dike system was strong enough to protect against a catamorphic storm that only occurs once in 10,000 years. There was a fibre optic and electronic sensors to report changes back to a central monitoring system and other systems to monitor water pressure and water level as the success of the dikes comes with maintenance and monitoring. (Brain and Lamb, no date). It is predicted that in the future with the rising threat of climate change, dikes alone will not be sufficient to keep Rotterdam protected and new ways to store water in times of high discharge needs to be found. Moreover, the heightening of dikes is expensive for the regional water authority and if more dikes are made this poses a risk to private property as there is less space for a densely populated delta. However, with the issue of cost, the costs damage from flooding if there wasn’t a dike is higher than the cost of building and maintaining a dike. (Doorn-Hoekveld and Groothuijse, 2017). therefore, it can be seen that dikes are a good way of managing the flood however the dike will have to be made higher and wider to cope with the rising sea level in the future which could bring about economic issues to the dike and there is environmental impacts of the dike as they can cause irreversible environmental damage.

Storm surge barriers are hard engineering strategies that allow water to pass through under normal propitiation conditions and have gates that can be closed during storm surges to prevent flooding. The storm surge barrier is used to protect against human settlements and infrastructure. Storm surge barriers are quite limited in Europe due to their cost. https://climate-adapt.eea.europa.eu/metadata/adaptation-options/storm-surge-gates-flood-barriers. The Maeslanktkering is a storm surge barrier on the Nieuwe Waterweg, Netherlands, controlled by computer. (Rekenkracht in macht., 2012). It was built in 1997 to protect the Rhine estuary and the city of Rotterdam from storm surges. (Zhong et al., 2012). The storm surge barrier is located in the waterway that connects Rotterdam with the north sea. This waterway is the main route to the port of Rotterdam. A barrier needed to be built that would not block the shipping route. (Rekenkracht in macht., 2012). A positive of this barrier is no vital parts of the barrier are placed underwater so maintenance is easier and there is no inconvenience for passing ships. (Rekenkracht in macht., 2012). Conclusions from studies have shown that flood frequency in Rotterdam has been reduced effectivity and will continue to do so in the future especially with climate change.(Zhong et al., 2012)

Dry proofing is used as a soft engineering flood management system in Rotterdam. Dry proofing is the process of sealing a building so no water can enter it e.g by closing the opening of doors and windows, waterproofing the outside wall and making sure water doesn’t enter the house through sewer system by installing back stop valves. (Manojlovic and Pasche 2007). By keeping the water out this reduces the damage from flooding but only up to a certain water level.  Dry proofing above a certain level is not useful as the pressure difference between the water outside and the lack of water inside the building would make the building structurally unstable and could cause failure of the outside walls. Dry proofing should only be done to an elevation of 100cm. Therefore, dry proofing is a moderately expensive flood management system but it is only beneficial if the flood is not that severe. In the past flooding in Rotterdam has been quite severe and with rising sea levels this management scheme will not be beneficial in the future. (Moel, Vliet and Jeroen, 2013)

Wet proofing is another soft engineering flood management scheme. This scheme allows water to enter the building but aims to reduce the damaging effect of water when it does enter the building. This can be done through changes to the buildings such as moving vulnerable items and precious items to higher floors and using elevated electricity sockets. It has been shown by Kreibich et al. (2005) that such adaptations reduced the damage to building structure and content by roughly 40–50 %. However, the issue with this is that if the flood exceeds a certain height then the second floor where you have possibly moved everything to, will also be flooded. (Moel, Vliet and Jeroen, 2013)

Warning, communication and response for people is a way to make sure people are properly warned in time and they have the time to prepare and move valuable items etc therefore reducing damage to their belongings. At the moment Rotterdam does not actively warn its citizen. A study found that only half of the people that live in the unembanked areas know that they live in an unembanked area (De Boer et al. 2012). Therefore, if Rotterdam did use effective warning systems then maybe their damages to belongings and properties due to flooding would be a lot lower. (Moel, Vliet and Jeroen, 2013)

One way of managing flooding is investment in underground storage. In Rotterdam there are underground car parks that double as flood storage areas that release stormwater into a piped system after the flood peak has passed, for example the Kruisplein car park with a storage capacity of 2400 m3. (O’Donnell, 2016). Whenever heavy rains cause the sewage system to overflow, rainwater will flow into the river storage and when the downpour is over the rainwater will be pumped into the sewers and discharged. These kinds of project are used in Rotterdam to increase the storage capacity of the existing sewage system and release some stress from the current sewage system which prevents the current system from overflowing into canals. (Mackenzie, 2010). https://www.waterworld.com/articles/wwi/print/volume-25/issue-5/editorial-focus/rainwater-harvesting/Rotterdam-the-water-city-of-the-future.html. Without the storage facility the city would experience an average of 10 annual overflow events and the water would be mixed with untreated sewage which would cause an increase in fish mortality. The storage will help to reduce the number of overflow events to just twice a year and improve water quality in the area. Moreover, creating a car park that doubles as water storage facility helps to optimise the use of the city scarce space. (underground water storage facility with a capacity of 10 million litres, 2011). http://www.Rotterdamclimateinitiative.nl/uk/news/underground-water-storage-facility-with-a-capacity-of-10-million-litres?news_id=743;p=5. Therefore, underground storage is a successful way to prevent flooding and reduce the probability of flooding happening, but it needs to be used along with other management and prevention strategies in order to manage flooding successful as the storage alone is not enough.

Buildings are also adapted in Rotterdam to cope with flooding for examples buildings elevated on stilts and floating buildings. The floating pavilion is an example of floating technology that can withstand rising water levels. Floating communities are planned for Rotterdam’s harbours an example of this is the Drijvend Paviljoen. The idea of floating buildings is not new to the Netherlands (O’Donnell, 2016). floating homes are a great way to manage flooding however it is quite costly so may not be ideal for the whole of Rotterdam but could be a potential strategy for the exceptionally flood prone areas. 

Another adaptation technique in Rotterdam is green roofs, green tram tracks and rain gardens. Rotterdam currently has more than 200,000 m2 green roofs which are used for rooftop farming and gardening. Rain gardens allow surface water to infiltrate. (O’Donnell, 2016). During heavy rainfall these roofs provide temporary water storage by absorbing precipitation, reducing the speed of rainwater runoff and delaying the peak discharge. This means the pressure on the sewage system is reduced. In large roofs areas it is best to collect the rainwater quickly and in a cost-effective manner e.g by using a siphonic system. Rotterdam promotes the installation of green roofs for example it is mandatory for municipal properties to be provided with a green roofing and it is encouraged in other buildings to have green roofs. Rotterdam has a subsidy scheme since July 2008 to encourage the installation of green roofs on privately owned buildings where €30 is given for every square meter of green roof installed. https://www.waterworld.com/articles/wwi/print/volume-25/issue-5/editorial-focus/rainwater-harvesting/Rotterdam-the-water-city-of-the-future.html. (Mackenzie, 2010).

The approach to flood management in Rotterdam is quite successful mainly because of the high risk of flooding due to sea level rise and a Rotterdam being a low-lying city creating a more obvious need to protect the residents and buildings from the impacts of flooding. Despite the success of the flood management, Rotterdam still faces many challenges with urban water management such as the environmental impacts of the hard engineering strategies and the cost of the strategies. Using a combination of flood prevention and management schemes would be the most successful way of managing floods in Rotterdam as each management system has advantages and disadvantages but together, they will be more successful.  Moreover, even more work needs to be done in the future in flood management due to the ever-rising threat of climate change and changing propitiation patterns.

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