The Bay of Bengal and the Arabian Sea drainage system are separated along a distinct divide which lies approximately along the Sahyadris, Amarkantak and Aravallis and the Satluj - Yamuna divide. The drainage of the Indian subcontinent has adjusted itself with the evolution of three main geomorphological entities , namely the Northern Mountains, the Northern Plains and the Peninsular Plateau. Nearly 77 percent of the drainage area consisting of the Ganga , the Brahmaputra , the Mahanadi , the Krishna , etc . is oriented towards the Bay of Bengal while 23 percent comprising the Indus , the Narmada , the Tapi , the Mahi and the Periyar system discharge their waters in the Arabian Sea.