Structure and pattern of plant community richness in the riparian forests were studied in diverse and important lower (<300 m MSL) riparian zones of the Chalakkudy River. The vegetation were distributed to very low altitudes (50 MSL). Such low altitude riparian forest vegetation is a rare phenomenon in the entire Western Ghats. The analysis and comparison of the community structure of the riparian forests reveals that altered flow and availability of water mainly by damming has serious impact on the community composition of the riparian forest vegetation. The ecosystem analysis shows that the remaining highly rich zone is the Vazhachal area (200-250 MSL, 26.4ha) and is under threat of submergence by the proposed Athirappilly Hydroelectric Project. The Riparian forests in the upstream and downstream to this zone were found to be highly disturbed and alteration in the quantum and the flow of water by the construction of this dam will also affect the remaining vegetation in the downstream. The role of riparian forests in conservation of biodiversity is very significant. The richness of this river for its riparian forests may account for the richness in fish diversity.