•  Periyar is the longest and largest river in Kerala
• It has a length of about  244 Km
• It is known as Choorni in Artha Sasthra of Kaudilyan 
• It drains an area of  5,398 sq km. 
• It rises at Sivagiri peak of Sundara mala of Tamil Nadu
• Periyar flows through:  Idukki and Ernakulam 
• Periyar drains through Idukki, Ernakulam and Kottayam 
• It rises at an elevation of 2,438m above MSL.
• At Aluva river divides itself into two branches. Such as Mangalam Puzha and Marthandam Puzha
• The upper branch Mangalam Puzha joins with Chalakudi River at Punthenvelikara 
• Then it expands into a broadsheet of water at Munambham. 
• Marthandam Puzha takes a southernly course is broken up into a number of small channels which fall into the  Vembanad Lake as Varapuzha
• There are two Hydrological Observation Stations maintained by CWC on this river are  Neeleswaram and Vandiperiyar
• The Periyar is known as ‘The lifeline of Kerala’
• The Idukki Dam on the Periyar generates a significant proportion of Kerala’s electrical power. 
• Mullaperiyar dam was constructed across the river in 1895
• Water is diverted from the Mullaperiyar dam into Vaigai River in Tamil Nadu 
• Its largest tributaries are:

Muthirapuzha River

Mullayar River

Cheruthoni River 

Perinjankutti River 

Edamala River

• Through Mullaperiyar dam, the river serves as the major water source for five drought-prone districts in the state of Tamil Nadu, including Theni, Madurai and Ramanathapuram
• Aluva, Malayatur, Thekkady, Thatekadu etc are on the banks of the river Periyar 
• Idukki dam is the largest hydroelectric power project in Kerala 
• Other major hydroelectric power projects across Periyar are Pallivasal, Chenkulam, Panniyar, Neriyamangalam and Lower Periyar
•  The river in Kerala with the highest number of tributaries is Periyar
•  The port that was destroyed due to the flood in 1341 is Kodungaloor
•  The port that was formed due to the flood in 1341 is Kochi 
• ‘Great flood of 99’ or ‘Thonnootti Onbathile Vellapokkam’ happened in 1924
• The first monorail system in India was completely destroyed due to the Great flood of 99 was Kundala Valley Railway
• Various remnants of the old Kundala Valley Railway systems still exist at Munnar
• The first hydroelectric power project of Kerala is Pallivasal (1940)
•  Pallivasall is in the river Muthirapuzha 
• The first unit of the Pallivasal power station was commissioned on 19 March 1940
• The inauguration of Pallivasal power house was done by C.P Ramaswami Iyer
• The diverting wier constructed across Mudirapuzha river at Munnar called  ‘Ramaswamy Iyer Head Works’
• Sethuparvathipuram dam in Muthirampuzha river basin is also known as Kundala Dam 
• Sethuparvathipuram dam was completed in 1947
•  Aluva Advaitha Ashramam and Kalady is in the banks of Periyar

Idukki Hydro Electric Project (IHEP) 

• The largest hydroelectric project in Kerala is Idukki Hydro Electric Project 
• The installed capacity of this project is 780 MW 
• The project was completed with aid from Government of Canada
• The technical consultancy of IHEP was M/s Surveyor, Nenniger and Chenevert 
• The project was dedicated to the nation on12th February 1976
• The project was dedicated to country by Indira Gandhi
• The three Dams associated with this project are:  

Idukki Arch Dam

Cheruthoni Dam

Kulamavu Dam

• The first arch dam constructed in India Idukki Arch Dam 
• The height of dam is 168.91 meters
• The largest Straight gravity concrete dam in Kerala is Cheruthonni Dam 
• Cheruthonni dam is constructed across the river Cheruthoni 
• Kulamavu dam is constructed at Kulamavu across the river Kilivallithodu