Tripura, basically a hilly state, has 16 rivers and 1138 rivulets that have rainwater. In fact, numerous rivulets originated from upland of hills feed water flows on rivers. However, Gomati, Haora, Manu, Muhuri, Khowai, etc., rivers are burdened with mid channel bar, point bar, etc., with sediment deposits barring heavy rainy season. Conditions of rivulets are much more awful for lack of water flow. Shenaihani Chhera and Bangeswar Chhera near Agartala, Rangapania Chhera, Chikon Chhera, Latia Chhera of Bishramganj, Harinmara Chhera of Kulai etc are just few of a long list of rivulets which are in appalling conditions presently.
An almost dried up spring located at ‘42 Mile’ village in Atharamurah hill range would catch one’s eyes instantly. Once lively flowing, the spring at present has very little to offer to local tribal people. One elderly tribal woman was found bathing in spring by collecting water from a small pit using a bowl. Leaking through the sandy soil of the hill, water drops get accumulated in the pit and the woman was having bath from that pit. The lady lamented, even 20 years ago, we would bath under this lively spring.
Shri Baishampayan Chakraborty, an official of the State Water Resource department opined that there were at least eight springs in Atharamurah hills along the National Highway 44, all of which have completely dried up sans the one at 42 Mile village. But why are surface water sources in such miserable conditions?
According to the experts, such terrible conditions have emerged due to some genuine reasons that included deficit rainfall, massive de-forestation and above all human intervention in form of illegal lifting of sands from the bed of river or rivulets.
Rainfall being primary source of water for the rivers and rivulets of the state, deficit in rainfall is promptly reflected in surface water table. According to a study report of Shri Mrinmoy Dutta, Joint Director of ICAR and Shri Dhiman Das Chaudhury, Technical Officer of the Agromet Services, ICAR, long period average (LPA) of monsoon rainfall for Tripura is 1416 mm. However, in 2012 precipitation was 1211 mm, which accounts 85% of LPA. During the year deficit in total rainfall was also noticed as it accounted at 77% of LPA. Barring Khowai and Unakoti district, all other 6 districts experienced deficit rainfall during 2012. North and Dhalai districts were worst affected, the report said.
According to a study by Sheilaja Devi of Rubber Board, Tripura generally experienced heavy showers in two phases, in May-June and September-October during the period 1984 to 1995. The scenario changed since 1996 from when the state is experiencing heavy showers in June-July instead of May-June while heavy rain in September-October has become uncertain and erratic. Sheilaja Devi’s study observed that amount of rainfall during SW Monsoon in Tripura is receding at a rate of 0.4 days per year. Another significant factor responsible for decaying condition of rivers and rivulets is mindless lifting of sand in huge quantity using pumps from the river bed.
Locals of Champaknagar in West District informed Haora river is badly affected due to lifting of huge sand in 20 Km stretch of the river lying between Champaknagar and Chandrapur of suburban Agartala. Their view was substantiated by the study of Nibedita Das and Sudatta Wadadar of Department of Geography and Disaster Management of Tripura University. The study concludes that sand-lifting activities using pumps are weakening the bank of Haora river and as a result instances of river bank failure is rising. Coupled with bank failure, sediment inputs in the river bed is causing formation of sand bar in the river leading to decrease in channel depth, changing channel characteristics and normal course of the river.
Explaining reasons behind present condition of rivers etc.,, Manik Chandra Debnath, technical expert of the state nodal watershed project said, decrease in channel depth owing to soil erosion is causing decline in the tidal flow of the rivers while the primary reason behind stagnation of water in rivers etc is de-forestation.
The experts found the correlation between drying up of rivers and deficit in rainfall as well as de-forestation. They explained this way: roots of trees and bushes of a forest hold the soil preventing soil erosion. Moreover, the bushes, grass and biomass help rain water get soaked onto the soil/ground. That is how water is accumulated under the top soil in the ground. However, de-forestation is a major hindrance to such natural process of water storage.
This has resulted in depletion of water level under top soil; simultaneously seepage water is also fast disappearing. Importantly, seepage water is a major source of water to rivers/ cropping fields, particularly during dry season. Moreover, absence of cover in the form of canopy of trees and bushes is leading to soil erosion during rainy season. Thus, the result of de-forestation is pushing the rivers into the brink of extinction.
According to a report of Geological Survey of India, soil of Tripura is erosion prone by nature and formation. Due to this stress exerted by rain or other means cause erosion of soil. To this end, a statistics bears significance. The total geographical area of Tripura is 10,49,169 hectare. Out of this, catchments area of rivers and rivulets covers 10,47,000 hectare.
Moreover, the scale of soil erosion is of very severe nature in 4,89,623 hectare while severe nature in 1,13,250 hectare. In other words, more than 50% of the total area is erosion prone. According to the State Agriculture Department sources, currently in lands with 3 to 15% slope or more, soil erosion rate is 68.17 ton per hectare to 79.84 ton per hectare. Thus, erratic rainfall coupled with de-forestation led soil erosion is causing gradual drying up of rivers and rivulets of Tripura.
Meanwhile, Department dealing with State Watershed Project has identified all the rivulets numbering 1134 as decaying or in critical condition. Out of all such oddities, a ray of hope seems emerging, for, the Department, entrusted with restoring surface water bodies and catchments areas, has mooted a comprehensive plan to the end. Under the plan, the department has begun works centering 45 such rivulets during the last two years.
(Written as part of fellowship programme of Centre for Science and Environment, New Delhi)