The 2020 Assam floods refer to the significant flood event of the Brahmaputra in the Indian north-eastern state of Assam. Initial flooding started in May 2020 due to heavy rainfall affecting 30,000 and destroying crops across 5 districts. As of October 2020, the floods affected over five million people, claiming the lives of 123 people, with an additional 26 deaths due to landslides, 5474 villages were affected and over one hundred and fifty thousand people found refuge in relief camps.
Optimizing the rainfall data:
It has been observed that the normal rainfall till mid of July of 2020 is 20 cm higher than the average rainfall. Surely one of the reasons behind this is the increment in the evaporation rate from the soil. Because of climate change and global warming, the rate of evaporation increases.
Again, as a result of deforestation, the infiltration capacity of the soil gets decreased drastically and it causes the runoff to be greater than usual. This is another reason for the occurrence of floods.
The meteorological subdivisions of Assam and Meghalaya received rainfall of 1,164mm as compared to normal rainfall of 894mm during the period, an excess of nearly 30%. The catchment areas of nearby states, Arunachal Pradesh and Sikkim also received excess rainfall nearly to the tune of 16% and 45% respectively aggravating the flood situation.
Remedies of flood control:
Using remote sensing and the Muskingum Method of routing:
The linear form of the Muskingum model has been widely applied to river flood routing. However, a nonlinear relationship between storage and discharge exists in most actual river systems, making the use of the linear model inappropriate. In this paper, a nonlinear Muskingum model is solved using the state variable modeling technique. Various curve fitting techniques are employed for the calibration of model parameters, and their performances within the model are compared. Both linear and nonlinear models are applied to an example with pronounced nonlinearity between storage and discharge. The results show that the nonlinear Muskingum model is superior to the linear one.
The solution procedure for the discrete-time state variable nonlinear Muskingum model, thus, involves the following five steps:
Step 1.—The inflow hydrograph to the channel reach is discretized into several time stages where time intervals need not be equal.
Step 2.—From the initial state of system storage, Sj, and initial inflow rate to the channel reach, Ix, the time rate of change of storage volume in the channel reach at the initial state.
Flow Chart for Discrete Time-State Variable Model for Nonlinear Muskingum Routing
Step 3.—The state of the system, i.e., channel storage, at the next time stage, S2, is estimated or approximated as S2^S1 + SxAf (9)
Step 4.—The magnitude of the outflow rate at the current stage can be calculated, using current values of inflow rate and channel storage at the same stage.
Step 5.—Using current information on inflow and channel storage, Steps 2-4 are repeated recursively until the last stage is reached.
HEC-RAS, HEC-HMS, ArcSWAT, and ArcGIS should be used for this modeling.
Assam Is Flooded Every Year But These Long-Term Solutions Can Reduce Loss Of Life And Land
Assam is the land of two mighty rivers – Brahmaputra and Barak. Each year these two rivers and their tributaries cause floods in vast areas of Assam which leads to human misery and the devastation of nature. This year, more than 30 districts including lower and upper Assam have been severely affected.
Why Assam floods every year?
Several factors including natural and artificial are responsible for the re-occurrence of floods in Assam. First and foremost, Assam lies in the heart of the monsoon belt and so gets overburdened with rainfall every rainy season. Due to this, the river along with its tributaries such as Subansiri, Manas, Kopili, Jia-Bhoroli, etc. gets flooded and their banks overflow flooding the vast plain of the state. Secondly, the existence of long ranges of mountains on its northern and eastern boundaries compels the water to flow down into the vast plain causing the rivers to swell. Thirdly, every year due to heavy natural as well as artificial land sliding, Assam loses hundreds of kilometers of its land area. This soil erosion makes the river shallow, which later helps in the creation of a heavy flood.
There are also human-induced factors like the destruction of wetlands, deforestation, and encroachment on river banks. Most cities and towns suffer due to poor urban planning. Drainage congestion due to man-made embankments is one of the crucial factors responsible for urban floods that can be visible every year in cities like Guwahati, Chennai, and Mumbai.
The havoc caused by the flood in Assam is beyond describable. The destruction of properties and loss of life is visible every passing year. Lakhs are rendered homeless, standing crops are damaged and roads and communication links are interrupted, hence affecting the economic condition of the state. Some of the worst affected areas include the MSME sector, tea industry, wildlife, and biodiversity of Assam. An increase in rhino poaching during the flood is one of the alarming factors for the decline of the rhino population in Assam. The floods also increase the spread of water-borne diseases like cholera, typhoid, dysentery, etc.
No doubt, the government has taken several flood control measures to lessen the menace and effects of floods in the state. Immediate assistance of NDRF and SDRF, flood relief measures including setting up of relief camps, free distribution of food, clothes, medicines, cash compensation for the lost property, etc. are undertaken by the government. The chief flood control measure has been the construction of embankments along the banks of rivers in the affected areas. In recent years, India signed a treaty with China in which the latter has agreed to provide hydrological data of the river Brahmaputra during the monsoon.
Although it is not possible to flood-proof all of Assam, several measures should be undertaken for a long-term solution. Increasing the water holding capacity of the Brahmaputra and its tributaries by dredging will be an effective solution to eliminating the havoc of floods from the state. It will decrease the rate of disaster by almost 70%. A flood is caused due to the riverbed rising. Today, technology has risen to great heights, so it is not impossible to mitigate the flood problem. Besides, dredging will also contribute to the development of a water highway in Brahmaputra, which will be a good option to develop our economy.
Besides, an artificial flood is a human creation. Therefore to reduce it, houses should be built scientifically along with proper urban planning. Jamming of water drains, and garbage in ponds should be mitigated by proper policies and through the imposition of strict rules.
Perhaps the best solution lies in the recently proposed plan of interlinking the rivers of India whereby the extra water of Brahmaputra and its tributaries can be diverted to dryland areas of western and southern India at the minimum cost of the marine environment and ecological degradation.
All views are expressed by the author. The pictures are from the website unsplash.com