Discharge and Sediment Transport in the Tropical Rivers of Kerala,India and their Controlling Factors

Kerala, the southern-most State of India, is characterized by its unique physiographic setup and 44 small rivers flowing across its narrow width. Based on 15 years (1986-87 to 2000-01) of daily sediment concentration and discharge data of 16 rivers, annual, seasonal, monthly, and daily variation in the suspended sediment yield of the State was analyzed and its controlling factors are discussed herein.

There is a marked variability in sediment yield characteristics from north to south and from year to year. Sediment concentration in the rivers varies between 167 mg/l and 2944 mg/l. Chaliyar River transported the highest annual average sediment load of about 0.40 × 10 $^6$ t, whereas Meenachil River supplied the lowest of 0.04 × 10 $^6$ t. Sediment yield varied between 40 and 250 t/km $^2$ /year, with northern rivers showing larger yields. The central Kerala region, which is drained by major rivers and geologically stable, yielded lower values. Narrow land strips of northern and southern regions, characterized by steep slopes, were highly prone to erosion. Due to the variability in distribution of rainfall, the northern rivers transported major share of sediment during Southwest (SW) monsoon (75 to 95%), whereas there was a substantial amount of sediment transport (20-55%) during Northeast (NE) monsoon through the rivers from the southern region.