What are the causes of Flood and Drought cycles in the Mahanadi basin?
The Mahanadi Basin, the largest river basin in Odisha, is characterized by a peculiar paradox: it frequently oscillates between devastating floods and severe droughts. This "cycle of extremes" is driven by a combination of geographical, climatic, and man-made factors.
1. Causes of Frequent Floods
Floods in the Mahanadi basin are primarily monsoonal and are concentrated in the Delta region (Cuttack, Puri, Jagatsinghpur, Kendrapara):
- Concentrated Rainfall: About 80% to 90% of the annual rainfall occurs within the four monsoon months (June–September). Low-pressure systems in the Bay of Bengal often lead to heavy downpours in the upper catchment of Chhattisgarh and Western Odisha simultaneously.
- Bottle-neck Topography: As the massive volume of water from the upper basin reaches Naraj (Cuttack), the river enters the flat deltaic plains. The carrying capacity of the river channels decreases, causing the water to overtop embankments.
- Siltation of Riverbeds: Years of soil erosion in the Eastern Ghats have led to the deposition of sediment on the riverbeds. This reduces the depth of the river, meaning even a moderate increase in water volume leads to spillage.
- Synchronization of Peaks: Sometimes, the peak discharge from the upper Mahanadi coincides with high rainfall in the tributaries like the Tel and Ib, creating a super-flood situation that the Hirakud Dam cannot fully contain.
2. Causes of Recurring Droughts
Despite being a high-rainfall zone, the Western and Southern parts of the basin (like Bolangir, Nuapada, and Bargah) frequently face meteorological and hydrological droughts:
- Erratic Monsoon Distribution: While the total rainfall may seem adequate, its spatial and temporal distribution is highly uneven. Dry spells of more than 15–20 days during the paddy transplanting season lead to agricultural drought.
- High Evapotranspiration: The Western Highlands experience very high temperatures. The red and laterite soils in these areas have low water-holding capacity, causing the soil to dry up quickly after the rain stops.
- Inter-State Water Conflicts: The construction of barrages and dams in the upper reaches of the Mahanadi in Chhattisgarh has reduced the non-monsoon flow into Odisha. This leads to water scarcity for Rabi crops and drinking water in the downstream districts.
- Deforestation: Loss of forest cover in the catchment area has reduced the natural sponge effect, leading to high surface runoff during rains and very little groundwater recharge for the summer months.
3. The Role of Climate Change
In recent years, Climate Change has intensified these cycles:
- Intensity vs. Frequency: The number of rainy days is decreasing, but the intensity of rainfall is increasing. This means more flash floods followed by longer dry periods.
- Sea Level Rise: Rising sea levels prevent floodwaters from draining quickly into the Bay of Bengal, a phenomenon known as the backwater effect, which prolongs the duration of floods in the delta.
Conclusion
In conclusion, the Mahanadi basin suffers from a mismatch between water availability and demand. While floods are a result of topographic constraints and extreme weather, droughts are caused by distributional gaps and inter-state issues. A holistic Integrated Basin Management approach, focusing on Climate-Resilient infrastructure and water-use efficiency, is essential to break this cycle of flood and famine in Odisha.