Veligonda Project

The Veligonda Project is an irrigation project located in Markapur, Prakasam district in Andhra Pradesh, India. When completed, the project will provide irrigational facilities to 447,000 acres and drinking water to 1.5 million people in 30 Mandals of fluoride and drought affected areas in Prakasam district, Nellore district and Kadapa district by diverting 43.5 TMC of floodwater from the Krishna River from foreshore of Srisailam Reservoir near Kollamvagu and proposed to store in Nallamalasagar Reservoir. The water for the project is drawn through two 18.8 km long tunnels across Nallamala hills. The project has been renamed to the "Poola Subbaiah Irrigation Project". It displaces around 20,946 families. The oustees have protested for enhanced compensation over the years and many have not received the compensation promised to them.

Design
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The design includes two parallel tunnels of 18.8 km with 7 m (tunnel 1) and 9.2 m (tunnel 2) internal diameter and 21.6 km and a flood flow canal for the water transmission system linking Srisailam reservoir to a reservoir called 'Nallamala Sagar'. Nallamala Sagar is planned to have 43.5 Tmcft live storage at 244 m msl full reservoir level and 214.3 m msl minimum draw down level. Full supply level to the tunnels from the Srisailam reservoir is 857 ft msl (261.2 m msl) and the sill level at tunnels water inlet is 840 ft msl (256.03 m msl).

Irrigation to 1.19 lakh acres and drinking water to 4 lakh population in Prakasam district is planned as part of the first stage. In the second stage, irrigation to 3.28 lakh acres and drinking water to 11.25 lakh population in 30 mandals of Prakasam, Nellore and Kadapa districts is planned. Velagalapalle lift irrigation scheme, Papinenipalli lift irrigation scheme are also part of the project. About 2.58 TMC water to the mega industrial hub  at Donakonda in Prakasam district  and another 1.27 TMC water  National Investment and Manufacturing Zone (NIMZ) in Pamuru and Pedacherlopalle mandals of Prakasam district are also parts of the expanded scope of the project.

Construction
The project was commissioned by YS Rajasekhara Reddy when he was the CM of the undivided AP in 2005. The project works were completed by more than 50 per cent by time of his sudden death in 2009. With successive governments not giving required funds, the progress hit the roadblock. The contractors who bagged the project were also vexed due to difficulties in making the tunnels in the toughest terrain. The tunnel-I which was 18.787 km long was completed for a length of 13.6 km by 2014. Although digging of just around 5 km is left to commission the project, the irrigation department could complete only around 2 kms between 2014-19.

The project is being implemented by a double shielded tunnel boring machine to make the tunnel without disturbing wildlife in the Nagarjunsagar-Srisailam Tiger Reserve.

18.2 km of the first tunnel, and 11.02 km of the second tunnel digging were completed by January 2020. The first tunnel completed as of 14 January 2021. The remaining length of second tunnel is completed using drilling and blasting method by January 2024 albeit with 5 m diameter instead of 9.2 m paving the way to fill the project reservoir.