The Kalakadu Mundandurai reserve is the watershed for 14 major rivers and streams, the Jambunadhi, Karunaiar, Karayar, Thamirabarani, Servalar, Keela Manimuthar, Nambiar, Kodumudiar and Ramanadi in Tirunelveli District and Kodaiyar of Kanyakumari District being the life lines of these districts.

THAMIRABARANI: This river (Now people call Tambaraparani as Thamirabarani) originates on the eastern slopes of Western Ghats in the Tirunelveli district of TamilNadu. The origins of Thamirabarani and its tributaries are situated at the peaks called ADUPPUKKAL MOTTAI, AGATHIMALAI and CHERUMUNJI MOTTAI at an altitude of about +2000 M from the Mean Sea Level. The Thamirabarani basin is situated between latitudes 8. 21' N and 9. 13' N and between longitudes 77. 10' E. It passes through kannikatti (700m), there located a famous falls, VANATHEERTHAM water falls (40 m deep) is located close to the origin of the main river. This river joins the Papanasam Reservoir at its 16th km.

The Kariyar river joins with the Thamirabarani river at Kattlai hills, there exists the Kariyar dam. The river has 4 tributaries called PEYAR, ULLAR, KARIYAR and PAMBAR upstream of Papanasam Reservoir. Kariyar river turned to be poisonous in the summer season till 18th century. People avoided to drink that water. Three miles away from kariyar dam, there located Mundandurai where another tributory, Servalar, joins, there exists the Lower dam where the crocodiles are grown. Thamirabarani serves the wet lands on both sides enroute before it confluences with GULF OF MANNAR. Many tributaries join the river course in the plains both on the right and left flanks. From the SRIVAIKUNDAM ANICUT it runs eastwards for 30 km and enters the Gulf of Mannar near PALAYAKAYAL.

SERVALAR: The River SERVALAR, a main tributary of Thamirabarani joins the main river at a running distance of 22 km. The DIVERSION WEIR marks the confluence of SERVALAR and THAMIRABARANI. The weir diverts water through power tunnels to the PAPANASAM POWER HOUSE. The Servalar reservoir across Servalar has a POWER HOUSE. The tail race water from Papanasam Power House joins the main river.

GADANA: The GADANA River joins at its 43rd km on the left. The Gadana river has two tributaries namely JAMBUNADHI and RAMANADHI. There are six anicuts across Gadana and 7 across Ramanadhi.

MANIMUTHAR: Another tributary the Manimuthar originates in the AGATHIMALAI ranges at an altitude of about +2000 m above M.S.L. It joins the Thamirabarani at its 36th km near Ambasamudram.