Water released over the spillway to Delta Region
6.6 KM Godavari flow diversion, which is a record
Mega project completed in minimum time at maximum level
EAST GODAVARI: One of the world’s biggest multi-purpose irrigation project Polavaram Project receives its first fruit of success. On Friday, 11 June 2021, the process of discharging water from Polavaram project to Godavari Delta region commenced for the first time.
Department of Water Resource and MEIL officials performed Pooja at Polavaram on the occasion of Godavari water diversion through approach channel to spillway. Water Resources Department ENC Narayana Reddy, Polavaram CE Sudhakar Babu, SE Narasimha Murthy, Executive Engineers Mallikarjuna Rao, Adireddy, Balakrishna, MEIL Vice President Ranga Rajan, General Manager Muddukrishna Dev Mani Mishra, CGM Ravindra Reddy, AGM Rajesh, DGM Shyamala Rao, Manager Murali were present at the occasion.
As part of the project construction, the Upper Coffer Dam for the construction of the Earth Cum Rock Fill dam (ECRF) will be completed and water will be released over the spillway. Releasing water from the Godavari to the Approach Canal, the water will reach the Dhavaleswaram Cotton Barrage through the spillway and river sluice gates and from there through the Central Delta as well as the entire Godavari Delta through the eastern and western canals. The water that naturally flows into the Godavari reaches the delta from the barrage. Once the Polavaram project is completed, water will released through spillway, river sluice and power house discharges to the canals. Polavaram seems to be getting its first result as water is now reaching the Godavari delta while the project is under construction.
Along with the spillway three gaps (ECRF 1,2,3), hydropower plant and water transport works are crucial in the construction of Polavaram. In this, Megha Engineering completed the work of Spillway on brisk pace following engineering regulations, work manual, protocol. The approach channel, spillway gates, spill channel and pilot channel are almost complete to divert the flood this season itself. Due to the construction of the Upper Coffer Dam the flow of the Godavari River was completed. As a result, water from above stopped flowing and the availability of water to the Godavari Delta stopped. Under these conditions Godavari water started discharging downstream from the approach channel.
Along with East & West Godavari districts, Tadipudi, Pattissima, Pushkaram lift irrigation projects water will be received through this approach channel from now on through the diversion schemes for drinking and cultivating. Until recently, water flowed to them through the natural flow of the river.
Godavari river naturally flows from June to December. Usually in the months of August, September and October large-scale floods occur. Although there is no flood flow in the summer, the water released from the Sealeru and Machkand hydropower plants reaches the delta in minimal quantities. From now on, the water will be diverted through the approach channel throughout the year and again into the Godavari through the pilot channel.
After the construction of Upper Coffer Dam the water level in Godavari is naturally rising (upwards). This brings water to the low area villages. The government has already rehabilitated those villages. In the month of July Godavari gets flooded. But, this year heavy rains are expected earlier in the Sabari catchment area, which is considered a major tributary of the Godavari. Already monsoons have entered the country and are actively spreading. Under these conditions, heavy rains are expected along with Chhattisgarh and Orissa, especially in the Sabari and Pamuleru catchment areas. If this happens the water should be diverted over the spillway. In the event of a major flood, water should be diverted into the Godavari through the Approach Channel, River Sewage and Pilot Channel for the needs of the Godavari Delta, drinking water of both the Godavari districts and discharge of water to the Krishna Strategy through Pattisseema. This is inevitable to avoid the water problem facing the Godavari Delta Strategy in Kharif. By removing the temporary bund at the beginning of the approach channel to the Godavari River, on the right side a 6.6 KM diversion was constructed for the flow of river.
By lifting Radial gates heavy flood water will be released to the bottom and thus the water released from the spillway into the spill channel joins the Godavari natural flow back through the pilot channel.
As per the instructions and suggestions of the Chief Minister of Andhra Pradesh YS Jagan Mohan Reddy and with coordination of Water Resource Department officials, MEIL has increased pace in the construction work. For completion of work in the stipulated time, the upper coffer dam must be completed earlier and the Godavari flow is released into the spillway channel through the approach channel and re-incorporated into the natural Godavari flow through the Pilot Channel. This diversion of river will make possible for the construction of Earth Cum Rock Fill Dam works in Gap – 2. This is the main reason why MEIL has speed up the construction of Upper and Lower Coffer Dams.
River Diversion of 6.6 KM is rare achievement in engineering field
Diversion of Godavari river for 6.6 KM is completed. This is engineering great and rare achievement. Godavari is the second largest river in India. It runs across from the Western Ghats to Eastern Ghats and owes its greatness for its sanctity, picturesque scenery and utility to man. In the peak time floods it receives on average of 35 lakh to 50 lakh cusecs of water flow. And diverting this gigantic river is not an easy task. Natural flowing Godavari is diverted to the right side of project, from approach channel to the pilot channel. This flow will continue even after completion of the project. Gap 1, 2, 3 are constructed in the middle of the river. In this Earch Cum Rock Fill Dam, which is known as Gap – 2 is the largest. It is constructed to hold even of 50 lakh cusecs water pressure and for this construction water flow must be stopped. In this situation Andhra Pradesh Government decided to build the Upper Coffer dam to withstand water flow and continue the construction of the Earth Come Rock Fill Dam in the view of floods in this year also. River diversion was constructed in this part only.
Total length of this river diversion, i.e. approach channel, spill channel and pilot channel is 6.6 KM. These are built parallel on the right side of the Godavari. Approach channel was built up to 2.4 km towards the spillway. Spill channel is 3.1 km from the spillway and the pilot channel is 1.1 km from the end of the spill channel to meet the Godavari again into its natural flow. Upper coffer dam is 2480 m long and 42.5 m high with three ridges. As per the government decision MEIL recently buried gaps in Upper Coffer Dam. This made possible to continue construction of project without any hindrance, even if there is a flood up to 30 lakh cusecs, as the flow in the river passes through the approach channel.
Record level works in very short time
MEIL completed Godavari river diversion work in record time. For this digging was done to required level to reach the spillway again to the right of the Godavari stream. For this, the approach channel was excavated to the extent of 2.4 km. With that, a big river was formed. For this, 54 lakh 88 thousand cubic meters of earth excavation work was done and another 4 lakh 88 thousand cubic meters work has to be completed. Out of total 5.92 crore cubic meters of earth work till now 5.24 crore cubic meter work is completed. Total CC blocks (spillway) is 17 lakh cubic meter of which 15.17 lakh cubic meter work is completed. The spillway work is very crucial in this project, as it controls the flood water to the extent of 50 lakhs cusecs and release it to down through gates. Three Gorges dam, known as the largest flood discharge spillway in the world so far receives 47 lakh cusecs, whereas Polavaram receives 50 lakh cusecs of water flow. To withstand this heavy flow world’s largest gates are established. For this 15.17 cubic meters of concrete work has also been completed. Hydraulic gates are also arranged to operate the gates. As part of this, 22 power packs were installed at 44 gates. 28 radial gates have been raised hydraulically so that 28 gates can be released in the event of a flood this season.
Till now 76.29% headworks on the project has completed. As water is diverted through approach canal villages along with Polavaram are at risk of flood water. There is no trouble till the water flow through spillway is up to one lakh cusecs. The effect will be seen after flow reaches 12 lakh cusecs. When there is a minimum flow Water reaches into 9 habitations, but when water reaches 28 meters the number of flood-prone habitats will increases. If the water reaches the full spillway (45.72 m), 235 habitations will be flooded. Accordingly, the government is preparing a plan and rehabilitating the villages.