Rainwater harvesting vs flood in Manipur valley

Dr N Irabanta Singh *

Flood in Imphal on June 14 2017 :: Pix - Shankar Khangembam

Introduction :

The Manipur state lies at a latitude of 23083'N-25068'N and a longitude of 930 03' E-94078'E. the total area covered by the state is 22,347 km2 (8628 miles2). Imphal, the capital of the state lies in an oval shaped valley of 700sq. miles (approx). (2000km2) surrounded by the blue mountain and is at an elevation of 790 metres (2,590 feet) above the sea level. The slope of the valley is from north to south.

The mountain ranges create a moderate climate, preventing the cold winds from reaching the valley and barring cyclone storms originating from the Bay of Bengal. Almost all the rivers in the valley area are in the mature stage and therefore deposit their sediment load in the Loktak Lake.

The rivers draining the Manipur hills are comparatively young due to the hilly terrain through which they flow. These rivers are corrosive and assume turbulent form in the rainy season. The state is drenched in rains from May until mid October. It receives an average annual rainfall of 1,467.5mm (57.78 inches). Rain distribution in Imphal is around 933mm (36.7 inches) in Imphal.

The precipitation ranges from light drizzle to heavy downpour. In the article, the author wished to express his views regarding rainwater harvesting and how it will lessened burden of flood in Manipur valley in the coming years.

Rainwater harvesting :

Rainwater harvesting is the accumulation and deposition of rainwater for reuse on site, rather than allowing it to run off. Rainwater can be collected from rivers or roofs, and in many places, the water collected is redirected to a deep pit (well, shaft, or borehole), a reservoir with percolation, or collected from dew or fog with nets or other tools. Its uses include water for gardens, livestock, irrigation, domestic uses with proper treatment, indoor heating for houses, etc. The harvested water can also be used as drinking water, longer term storage, and for other purpose such as ground water recharge.

Case study in North East India :

Rainwater harvesting is one of the simplest and oldest method of self supply of water for household uses usually financed by the users. Such technique is usually seen in all the household in Aizawl (Mizoram state). Here, one can see installation of big sintex water reservoir according to the financial position of the individual house owner. This help a lot to tide over water scarcity in Aizwal area during winter season.

The directorate of Geology and Mining, Government of Nagaland had implanted a pilot project on rainwater harvesting with funding from the Ministry of Water Resources, Department of Central Groundwater Board, Government of India. The project has immensely benefited to the Institutions/ hospitals/ communities in and around Kohima town. The project has created awareness to the public at large on rainwater harvesting with up-graded equipments and accessories.

The project had been implemented with the participation of the local people. Conservation and enhancing ground water through artificially recharging the ground water from rainwater was a new scheme which was appreciated by the beneficiaries.

Causes of flood in Manipur Valley :

There are several factors responsible for causing flood in Manipur Valley. Slash and burn in the hills – Shifting cultivation in the hills of Manipur is the main cause for slash and burn of the forest in the hills. As a result, woods and bamboos have been cut down and cleaned after burn for shifting cultivation. As a result, sufficient rainwater could not be absorbed by the barren land. So, for 2 hour torrensic rainfall, the water will flow down to the gorges and rivers in the hills causing flood in Manipur valley after 3/4 days continuous rain in the hills.

Status of some important rivers in Manipur valley :

The condition of Imphal river which flows in the Manipur valley is horrible. There are uncontrolled construction on either side of the river banks specially in Imphal river areas. Apart from that plantation of rabi crops during the winter season resulted the soil in the river bed loosened. This made it easy to carried away by the flowing river water during the rainy season.

In addition to this, many uncompleted construction works in the river banks left siltation. As a result causes siltation on river bed and weakened the river banks. The soil carried down from the hills during the rainy season plus alluvial soil in the river bed resulted in 3/4 inches thick siltation once the river water recedes. Such conditions are found in other rivers( The Nambul, Iril, and Thoubal) flowing through the Manipur valley.

Further, the Imphal river bed starting from Kangpokpi content stones, pebbles and sand that reaches upto Pheidingga. Even small pebbles reaches upto Minuthong. It may be reminded that the Government of India had already launched the “Branhe putra Project”, construction near the river had been prohibited.

Non-mitigation of flood water in Manipur valley through Loktak Lake :

Loktak Lake multipurpose Project was conceived in the later part of sixties and the execution of the project started during the 4th plan period (1969-1974), after experiencing one of the worst flood in the history of Manipur during July 1966. Flood level recorded on 6 July, 1966 was 771.63 meters at Loktak Lake (near Minuthong). The union Government of India taking serious note of the prevailing situation had sent the then Minister of Irrigation and Power, Eng. Dr. K.L. Rao and his team for stock of the situation.

Eng. K.L. Rao along with the then CM/Manipur, Shri M. Koireng paid an inspection visit to all the affected area of Manipur Valley on 28 and 29 Sept, 1966. Under his supervision, the detailed project report (DPR) was prepared and the central Govt. approved the DPR, the main purpose of the Loktak Lake multipurpose project was to mitigate the flood in Manipur valley by utilizing data available from several observation and readings to provide better irrigation facilities in the area; to generate about 450 M.W. of energy annually, from 105 MW. Loktak Power Station ( bank of Leimatak river) and reclaim about 57,000 acres of new land to be made available for agriculture purpose around the peripheral area of the lake ( Imphal Times, 25 January, 2015).

Discussion :

The importance of rainwater harvesting with advance equipments and materials as well as conservation of ground water through artificially recharging which was the objective of Kohima Town ( Nagaland) rain water harvesting project Frequent flash flood in the Khwairamband bazaar can be averted if the rainwater harvesting project is installed and utilized the Kangla Pat for rain water storage. The concerned Department should approach the Ministry of Water Resources, Government of India, New Delhi for funding.

Manipur faces flood situation when rainfall rate in the catchment areas reaches 30mm but the rainfall rate recorded this year (2017) in catchment areas of Imphal river reached 788mm. Further rivers of Manipur cannot drawn out water from Imphal river as the water levels of both Khuga river and Chakpi river remain quite high which too fall in Manipur rivers.

Further, stone and sand carried down by the Thongjao river during the flood later on deposited at the Loktak Lake. In addition to this, the Wangjing and Sekmai river too gave a lot of trouble during the rainy season. The Ikok pat, Kharung pat, Pumlen pat are important pats(lakes) of Manipur valley that gave important hardships to the inhabitants of the pats during the rainy season.

Due to unplanned constructions of roads and human habitation, water in the Lake fail to mitigate properly. This needs proper attention of the Government to address this problems in order to solve flood problem in the Manipur valley.

Conclusion and recommendation :

Rainwater harvesting project in the Imphal City need submission for funding from the Ministry of water resources, Government of India, New Delhi for curing flash flood in the Khwairamband bazaar. Due to subsequent Governments insincerity to implement Loktak multipurpose project successfully, the Manipur valley will remain flooded during the rainy season in the coming years too.

It is also recommended for
(i) Alternative to Jhuming in the hill regions of Manipur by plantation of medicinal plants for commercial production. The models for implementation could be (a) Paddy, cinnamom and Sarpagandha plantation model, (b) Medicinal trees combined with Ashok, Cinnamon, Sandal wood and Agarwood model, and (c) Alder, Paddy, rosemary plantation model.

(ii) Plantation of deep rooted trees on the bank of rivers – Plantation of deep rooted trees such as S cared Fig (sana khongnang), Mango (Heinou), Grevillea (Kaubilia),etc are recommended. These plants will resist soil erosion in the river banks.

(iii) Installation of suitable surface water resources near the main rivers of Manipur valley-The flood in Manipur valley could be reduced if the authority made surface water harvesting reservoirs at suitable river basins for future use of water during winter season.