The Purna River is a river is the principal tributary of Tapi River in Western India. It rises in the Betul district in Gawaligarh hills of the eastern Satpura range at an elevation of 900 m at north latitude of 21°38' and an east longitude of 77°36' in southern Madhya Pradesh state, and flows westward, draining Maharashtra's Marathwada, Vidarbha region before emptying into the Tapi River. The Purna River starts in Amaravati district of Maharashtra and flows across Akola, Buldhana and Jalgaon district. The river finally flows into the Gulf of Khambhat near the city of Navsari in Southern Gujarat. The total drainage area of Purna River is 18,929 sq. km and it joins Tapi at 282 km of Tapi’s run.

The sub basin can be divided into three prominent physiographic regions :

• Eastern parts,

• Middle reaches and

• Coastal zones.

The eastern parts of the basin cover a chain of rugged mountain ranges of the Western Ghats running at an elevation of above 1300 m and descending to an elevation of about 100 m at the edges of uplands of the Surat district. The middle reaches of the basin area marked by high relief zone with ridges and valleys. The hilly zone then merges into the plains through an undulating piedmont coastal zone running parallel to the sea.

Rain fall

The basin receives most of the rainfall from the South-West monsoon during June to September. The weighted mean maximum, minimum and average annual rainfall of the basin for the period 1903 to 1989 are 2599 mm, 654 mm and 1431 mm respectively.

Temperature

There climatological data the Valsad and Surat IMD observatories which are situated in the vicinity of the basin have been considered. The mean monthly temperature varies from 12.7 ^o C during December to 37.3 ^o C in April.

Humidity

The humidity during winter season is as low as 42% in the month of February and as high as 89% in the month of August as observed at Valsad IMD observatory.

Wind speed