The Ulhas River is one of the West Flowing Rivers in Maharashtra falling into the Arabian Sea. The boundary of the basin consists of the main Sahyadri hills on the East, Westerly off shoots on the North and South and on the West, a narrow opening at the end leading to the sea. The Ulhas basin lies between North latitudes of 18º 44’ to 19º 42’ and East longitudes of 72º 45' to 73º 48’. The CWC Hydrological Observation Station is located at Badlapur.
The Ulhas drains an area of 4,637 sq km which lies completely in Maharashtra. The Thane, Raigad and Pune districts fall in the basin. The Ulhas rises from Sahyadri hill ranges in the Raigad district of Maharashtra at an elevation of 600 meter above M.S.L. The total length of this West flowing river from its origin to its outfall in to the Arabian Sea is 122 km.
The important tributaries of the Ulhas River are Pej, Barvi, Bhivapuri, Murbari, Kalu, Shari, Bhasta, Salpe, Poshir and Shilar. The Kalu and Bhasta are the major right bank tributaries which together accounts for 55.7% of the total catchment area of Ulhas.
The average rainfall in the Ulhas basin is 2,943mm. The basin receives most of the rainfall from the South-West monsoon during June to October. Almost 99% of the total rainfall in the basin is received during this period. The average maximum and minimum temperatures are 38.90 C and 12.40C respectively. May is the hottest month of the year and January is the coldest month of the year.