Rethinking embankments: Natural design versus human interventions

Globally, though unacceptable, it is quite common to pay little attention to environmental degradation during the rapid industrialisation and urbanisation phase. Once a country becomes resourceful, it starts looking after the damages done to nature. Sometimes, nature kicks back and ecosystems heal, sometimes it's too late.

In Bangladesh, for the last few decades, we have been doing immense harms to our rivers. Apparently, the government has finally gathered some political willpower to attempt at repairing its rivers, at least domestically.

Bangladesh Inland Water Transport Authority (BIWTA) has been conducting eviction drives on the banks of Buriganga, Turag, Balu and Shitalakkhya rivers since last year. It has removed thousands of illegal structures and recovered hundreds of acres of land along the rivers.

The soothing sight of small silted up rivers being re-excavated at different parts of the country compares to nothing. The government has formulated a long term scheme, Delta Plan 2100, with a stated objective to take care of the water resources. Tens of billions of dollars will be spent over the period in many "hard" engineering solutions- dredging, building higher embankments, river training etc.

Letting the rivers flow naturally

Globally, we are at a crossroads. Environmental degradation, biodiversity loss and climate change has pushed us against the wall. It's time we gathered more courage when it comes to conservation of nature.

In 2017, New Zealand recognized The Whanganui River as a living entity with the legal status of a person. Bangladesh followed suit and the high court last year granted all the rivers of the country the rights and status of living entities.

An innocent living person cannot be shackled, or poisoned. Rivers used to be wild and free. Modernity put them in chains, also known as dams, barrages and embankments.

In the pre-colonial era, people of subcontinent considered floods a duality of calamity and benefits. Overflowed rivers brought nutrient-rich sediment to farmlands. Floods are indeed a natural part of the hydrology of the delta and serve essential ecosystem functions such as groundwater recharge, soil nutrient replenishment, and fish stock renewal.

But the British colonisers did not like this 'uncontrolled' flood inundation. Instead, they believed nature could and should be mastered through science and technology, and wanted to manage rivers to boost agricultural production.

Consequently, "Water resources lost their mystery, being seen merely as a commodity. Rivers were to be engineered, controlled, tamed and made into a source of water for artificial 'rivers' (canals)" (Hardiman, D 2008, 'The Politics of Water in Colonial India: The Emergence of Control' in K Lahiri-Dutt, & RJ Wasson (eds), Water First: Issues and Challenges for Nations and Communities in South Asia, Sage, New Delhi).

This 'command and control' approach to water management led to the construction of numerous embankments, dams and barrages along the rivers.

Manmade problem

Ironically, built to stop flooding, embankments sometimes increase the extent of it. Two thousand miles of embankments had been built along the Kosi River in Bihar, India to control the annual monsoonal floods. The consequences have reportedly been exactly the opposite. A study shows, "Where there were six million acres of flood-prone area in 1952, now there are seventeen million. And where there was inconvenience there is now a yearly disaster" (Colopy, C 2012, Dirty, Sacred Rivers; Confronting South Asia's Water Crisis, Oxford University Press, New York).

More often than not, embankments breach, and sudden onrush of water causes more damage than slowly rising flood level. And when they do, the calamity is doubled by waterlogging, as the flood water is trapped outside the embankment.

Yet, the above-mentioned are the least of concerns regarding embankments. At least, for Bangladesh.

Rivers do not only drain water, they also bring nutrient-rich sediment. Geologically speaking, Bangladesh came into being with the sediment from the Himalayas. As flood water inundates the banks during the monsoon, the sediment deposits on the land.

Every year, about a billion ton of sediment is deposited in the alluvial fan of Bangladesh. When embankments prevent sediment-laden water from flooding the adjacent land, the riverbed gets silted, which chokes the river, increasing the flood risk even further.

Of course, dams and barrages built upstream initiate the situation by holding water that would prevent the alluvium from settling onto the riverbed. Rivers actually need "breathing" space. And they need to flow freely.

The impact of embankments has been well studied in the coastal region of Bangladesh.

In the coastal belt of the country, there are 139 polders with 5700-kilometre embankments. Polders- a name borrowed from the Dutch which refers to low-lying land surrounded by mud walls- were created by the Dutch in the 1960s with a view to protect farmlands from saline water intrusion.

Steven Goodbred, a professor of earth and environmental sciences at Vanderbilt University, and his colleagues, conducted a study at Polder 32. They discovered that the daily high tide water level was 1 to 1.5 meters higher than the land inside the polder, while it was 10 cm below the land just outside the embankment. Even the elevation of the Sundarbans mangrove forest, on the other side of the river, was higher than the polder.

In 2009, cyclone Aila devastated and breached the dykes of the polders on many points. All the people living in polder 32 lost their homes and had to live on the remaining parts of the dyke until the breaches got repaired two years later. During the spring high tides in this repair time, most of the polder remained under water for almost 10 hours every day while the patch of the adjacent forest only inundated for two hours.

The finding suggests that the polder would be higher without human intervention, and free-flowing rivers would keep the land above average high tides through natural sediment deposition.

According to the study, these embankments caused 2-3 cm of elevation loss every year over a 50-year span: five times faster than the rate of sea-level rise.

Nature-based solution

In the context of climate change, rising sea is slowly devouring Bangladesh. Bangladesh's only chance of survival stands in letting the process of sedimentation continue.

There are some countries that are trying this approach. Vietnam devised plans to allow more flooding in the upper sections of the Mekong delta. The Netherlands is also opting for controlled river flooding.

Interestingly, the concept of using tidal flow to raise land is not only familiar to the local communities in Bangladesh, some of them have actually been practicing it since 1990s. This involves the periodic breaching and closing of dykes to facilitate land accretion.

According to a policy paper published in 2011 by Uttaran, a local NGO working in the coastal region, about 31 square kilometres of land had been raised by local communities in Beel Bhayna and Beel Dakatiya using techniques that later came to known as tidal river management (TRM). The paper titled "Tidal River Management: Community Based River Basin Management and Climate Change Adaptation in Southwest Coastal Region of Bangladesh" says that local communities raised land by more than one and half metre in one year in Beel Jethua, an area sized 250 acres, using the same method.

TRM was practiced by Bangladesh Water Development Board (BWDB) in other places like Beel Khukshiya on the Hari River basin. Several local and international institutions have recognised the concept to be effective. It should be scaled up and replicated across the coastal areas to mitigate waterlogging, promote land accretion, and increase navigability of rivers.

People affected by such planned flooding would need to be compensated for their agricultural losses for a couple of years in the coastal regions. However, fisheries can be developed during this period.

In non-coastal areas, natural flooding is likely to affect only a specific crop during the monsoon. However, there are natural and native solutions to that problem too. There are paddy varieties that grow taller with rising water. Although these varieties are in the face of being lost due to the promotion of high-yield and hybrid varieties, they can still be reintroduced in flood affected areas. Agriculture ministry does not promote these varieties because of lower rice yield, but it does not consider the higher straw production, which is used as livestock feed.

Housing in these areas will need to be redesigned too. Raised houses on steel pilings would be perfect in this case, with a growing steel industry in the country. A public funded project to provide such houses to the poor living in the floodplains will create an opportunity to improve housing in the country as well. Disaster management experts have been advocating for better built houses instead of shelters for a long time now. The idea is to concede to the superiority of nature's design, and readjusting our lifestyle in an accommodative way.

Being courageous enough to allow the rivers to flow and flood freely may require us to expand our social safety net programmes in the short run. That will cost us money.

But consider the never ending projects of Bangladesh Water Development Board (BWDB) costing thousands of crores of Taka every year, aimed at stopping erosion and controlling flood. Yet, river erosion and flooding never stop. This money can go to those above-mentioned adaptive strategies.

Keeping a door open for spending a good amount of money is a must for any project to look lucrative in the eyes of financiers, developers and many other stakeholders including the GDP-loving governments. Thus, a project with the afore-mentioned public spending opportunities should be a win-win for all the parties involved, nature included.

Upper riparian countries, especially India has been building not dozens, but hundreds of dams and barrages on the trans-boundary rivers to withdraw water unilaterally. While we attempt to resolve this issue politically (and fail), we should also promote the idea of adapting to natural processes instead of trying to control it.

There are movements against big dams and barrages in India. We should support them not only with words, but also by proving that we mean it. If we can strengthen the bond among the peoples in this region through this process, promote natural means as a panacea for many manmade problems, may be in the future, we will be ashamed that once we shackled the rivers.