Floods & Structures : How can we build structures flood-resilient ?


Nebu Abraham

How can we build structures that are flood-resilient? How can we make room for water on our costs and hinterlands so that the impact of floods get neutralised to a large extent? Here are a few examples from different corners of the world.

Periodic flooding is necessary to increase soil fertility and supplement nutrients in the soil. But floods can prove a challenge for built-up spaces. Construction challenges in flood-prone areas are unique. But, at a time when every other place gets battered by heavy rains, triggered by unpredictable cloudbursts, there is need to make built up spaces even in non-flood prone areas flood-resilient.
The massive disruption caused by the recent floods in Bengaluru is illuminative. For several days, citizens of the premier IT hub of India had to battle flood waters; some ultimately fleeing to safer localities, leaving their valuable belongings behind. The damage to infrastructure, public utilities and productivity caused by the flooding was quite substantive.
Floods could result from cloudbursts, rapidly melting snow, wind gusts over water, unusually high tides, tsunamis, failure of dams, levees, dikes, retention basins or other water-retentive structures. The construction challenges in many of these contexts are known. It is just that enough intellectual and resource investments have not been made to build flood-resilience when constructing public and private structures.
Numerous strategies are prevalent across the world to manage floods. All structural formations, including roadways and external yards of buildings, should be at the right levels to prevent water stagnation. Given the high-water levels, building plinths and road levels need to be adjusted. This can be determined by using data from the previous years or by estimating the flood damage to existing structures. The importance of a good drainage system cannot be overstated. In addition to all this, landslides need to be averted to prevent catastrophe.
The frequency of landslides has risen significantly, particularly in the Himalayas and the Western Ghats. The same should apply for several other little reported locales where the water-bearing capacity of the top soil comes under severe pressure owing to rampant deforestation and other many human interventions. In Uttarakhand, for instance, it is the grossly irrational construction spree that has been cited as the reason for the devastating floods on the Ganga.
Regrettably, nothing has been done to right the wrongs so far. Nor has compensation been paid to the families who have suffered heavy damage to their homes and belongings owing to flooding. The less said the better about the flood relief strategies that are in place in the country.
River encroachments and river depth decline are two major causes of flooding. The river always tends to veer off course when there is a barrier to its flow. Siltation results in rise of the river bed which, in turn, results in the water carrying capacity of the river. Attempts have been made to deepen river beds by dredging excess sand and silt deposits.
In some States, this has been proposed, but implementation of such proposals have been haphazard. Wherever it has been attempted, it has resulted in massive corruption and smuggling in river sand, aggravating an already serious problem. Still, ideally, this is an option which could be considered for implementation under stringent oversight to prevent corruption and irregularities.
All the bridges and culverts that impede the flow of rivers must be removed, and any developments built over the waterway must be designed in such a way that they do not restrict the river’s free flow. Encroachments should be dealt with sternly, and squatters and encroachers should face severe consequences. According to the Indian Constitution, the river has its own basic right, which must be upheld.
It is necessary to examine every dam and determine its storage capacity. The inability of the dams to hold enough water is currently our main problem. However, until we are ready to switch to more contemporary methods of energy production, we may have to rely on these structures to meet our energy demands. Due to silt deposits, mostly every reservoir has had to limit its capacity. Unfortunately, the technology we have today make it difficult to remove silt inexpensively. This forces us to dump extra water into the stream, which finally results in a flood, as happened in 2018 in Kerala.
Another factor that contributes to the damage along the coastline is high tide. This problem has not been managed appropriately. The politician-bureaucrat nexus has always gone for the easy option of building seawalls. But seawalls are no answer to coastal erosion, which takes away with it the homes and equipment of the fishers. Coastal defences including sea walls, beach replenishment, and barrier islands have been used to combat coastal floods in Europe and the Americas. But, in India, such efforts have at best been half-hearted.
To lessen the effects of flooding, we might use a variety of strategies. One of the biggest issues is managing the water, and how do we manage the high pressure? Rivers that are prone to flooding are frequently carefully maintained in various nations. Levees, bunds, reservoirs, and weirs are utilised as defences to stop rivers from overflowing their banks. Sandbags and other emergency measures are used. Emergency measures like sandbags or transportable inflatable tubes are utilised in case these defences fail.
Let’s examine various flood control strategies utilised around the world. Each nation has its unique method for managing floods, while some fall short under extreme circumstances.

The Dutch model

With a dam by the name of Oosterchelde serving as its crowning achievement, the Netherlands possesses the most complex flood defence system. Including dams, sluice gates, storm surge barriers, dikes, and other structures, the Delta Works programme is a comprehensive system for the Netherlands’ flood risk control. Along with the involvement of water professionals, this approach involves civil society and government officials at all levels.
The 1953 North Sea flood in the Netherlands’ southwest necessitated the development of an efficient flood management strategy. The Netherlands has frequently experienced floods that have negatively impacted the country’s standard of living, and the Dutch have continuously looked for novel flood management strategies. 50% of the land in the Netherlands is below sea level.
Due to its low height and location at the confluence of the sea and three major rivers, the city of Dordrecht has experienced the worst flood in recorded history. Due to the city’s history of flooding, particularly the storm in 1421 that wrecked numerous dikes and inundated 23 villages within the city, as well as its ongoing vulnerability to floods, it has become the national epicentre for valuing water initiatives. The project’s main objective is to alter how flooding are viewed in order to promote sustainable urban planning.
Due to the heightened risk of flooding brought on by climate change, the city required a multi-layered approach that incorporates preparedness and prevention measures. Prevention is key to the success, thus as part of it, approvals for constructions in high-risk flood zones were withheld, and laws were enacted to limit reconstruction in these regions. Dikes were erected in the city to keep the water away from the homes by creating embankments, and stop-logs were put in place on the streets and highways.
Constant inspections are performed to ensure that this system operates properly, particularly during floods. As a part of the Delta programme, the wide green dike was reintroduced as a natural remedy, and this allows for the integration of flood protection and climate adaptation goals with nature conservation objectives.
The wide green dike is a natural structure made of clay and grass, with a little slope at the seaward face, that seamlessly blends into the nearby salt marsh. Under normal circumstances, the salt marsh dampens incoming waves, and even when the salt marsh is submerged, waves only reach the dikes during strong storms. The salt marsh has the ability to dampen waves. This feature, along with the minor slope at the seaward face that lessens the effect of the waves, makes the grass-covered clay layer sufficient to prevent erosion of the structure even during intense events.
Across the past century, traditional water retention structures have been built across the nation. They are covered in concrete, asphalt, or stones and are made to withstand wave loads. However, modern water retention structures are far more wave resistant.
The fourth component of the Valuing Water Initiative comprises establishment of a strategy to tackle actual flooding. Among other things, the city has created an evacuation plan for residents to move to higher ground.
A great location for an evacuation is the De Staart district, which is located at a higher elevation than the rest of the city. To assist in evacuation, particularly for the most vulnerable residents of the community, the city has constructed sustainable housing, adaptable areas, and a public transit system.

Russian Initiative

Over 300 floods of varying magnitude have hit Russia at some point in its history. One of Russia’s longest-running building projects was the Saint Petersburg Dam, a flood control system that was started there in 1978. Even though the facility’s construction was put on hold for a while, it was resumed in 2005 and commissioned in 2011.
A 25-km long network of dams, the Saint Petersburg Dam, is used to control flooding. It stretches from Lomonosov to Kotlin Island before turning east toward Cape Lisiv Nos. By separating Neva bay from the rest of the Gulf of Finland, the Dam complex protects Saint Petersburg from storm surge. The dam can protect the city even if the water level rises by up to five metres.

British initiative
Like in Venice, a mechanical barrier has been erected across the Thames River in London to keep the city safe from flooding. However, if the sea level continues to rise, it may not be able to prevent the water from causing damage.

Canadian example
The Canadian province of Manitoba has seen disastrous floods as a result of excessive snowmelt. The Red River and Lake Winnipeg combine as they travel north from the United States as is the case with all north-flowing rivers in the northern hemisphere’s temperate zone. Snowmelt in the southern regions causes the river levels to rise before the northern section has entirely thawed. This could result in a disastrous flood comparable to what happened in the spring of 1950 within Winnipeg.
To protect the city from floods, the government of Manitoba built a sizeable diversion system, dikes and floodway. When floods decimated several communities in 1997, Winnipeg was safeguarded by this method.

American model
In the US’ New Orleans Metropolitan Area, 35% of the land is below sea level. This area is protected from flooding by hundreds of miles of levees and flood gates. This system failed during Hurricane Katrina because of multiple failures, flooding about 50% of the urban regions with water up to 20 feet deep in coastal communities. The federal government proposed purchasing the flood-prone properties in order to facilitate successful flood management and prevent further disasters. This land was changed into wet land, which ultimately served as a sponge during floods.

European Model
Countries on the European continent have portions of their territory that are below sea level, making them vulnerable to flooding as a result of rising sea levels driven by a constantly changing climate. The flood management concepts developed by the Netherlands, such as Zuiderzee and Delta Works, are important examples for other member countries with comparable terrains and altitudes.
They have shown to be homogeneous projects, and they may hold the key to fending off the growing danger posed by rising water levels as well as other recurrent natural disasters like the lengthened or shortened rainy seasons and droughts. Since they have been at war with the sea for centuries, the Netherlands has emerged as the global leader in the fight against floods.
They are still looking into novel strategies to mitigate the effects of flooding. The destruction that Katrina caused might have been largely avoided if Louisiana had a system like the Netherlands had. The Netherlands is aggressively attempting to mitigate the threat posed by rising sea levels, as evidenced by projects like the underground storage of water, storing water in reservoirs as in vast parking garages, etc. During floods, they even transform a playground into a miniature lake. In Rotterdam, there is a plan to build floating homes.

Bengaluru floods
Urban infra comes apart

The recent flooding in Bengaluru has exposed the many deficiencies of urban infrastructure in the country in the face of such devastating events.
Torrential rain inundated many low-lying areas across the city and several luxury villas on the so-called Billionaire Street near Yemalur in east Bengaluru were submerged in waist-deep water after two days of incessant rain.
Residents of Epsilon and Divyasree 77, where corporate honchos live in villas, had to be evacuated by boats after they were flooded. Suddenly, it became clear that none of the constructions had mechanisms to evacuate such a huge quantity of water.
At the Epsilon, each villa cost Rs. 8 to 15 crore and at Divyasree 77 Villas, value of the apartments ranged from Rs 3.5 to Rs 8 crore. In Yemalur, property prices has been estimated to be between Rs 5,000 and Rs 6,000 per sq ft. and in places around Outer Ring Road, from Rs 5,500 to Rs 6,000 per sq ft.
With rainwater gushing in, residents in several housing complexed had to move to higher levels, with whatever they could pick up. Those living in low-lying areas and in single-storey structures were not so fortunate. They had to simply abandon their homes. And, those who were caught by the sudden flooding, had to leave their vehicles where they were. Many of those vehicles have lost a sizeable part of their value having remained submerged in water and slush for days.
Those living at the ground level could not use their toilets and drinking water suddenly became a far too precious commodity. The slush that had flown into homes had caused devastation beyond description for many, especially for those living in low-lying areas.
Builders in the city say that the floods have put them on a learning curve. They do expect property prices to get hit in the short term, but are confident that the people would forget it all very soon. They cite the example of Mumbai and Chennai, which had experienced devastating floods a few years ago, to buttress their argument.
However, with sudden flooding a reality, builders must look at rainfall patterns, waterlogging possibilities, emergency water evacuation measures, etc. when they begin work on new projects. Experts have pointed out that flooding in areas like Bellandur and Outer Ring Road area took place predominantly because buildings encroached into the stormwater drains.
Home buyers also may have some homework to do before they venture out to buy a property and seek answers to questions such as how prepared a project is to tackle sudden flooding, what evacuation processes have been conceived and how the residents can remain safe in the event of the apartment getting cut off due to flooding.