Estimating the suspended sediment load by using the historical hydrometricrecord from the Lanyang-Hsi watershed

The long-term (1950-94) hydrometric data archived by the Water Resources Bu reau (WRB) at the gauge station near the Lanyang-Hsi river mouth were re-pr ocessed to derive the time-series of suspended sediment load. A bias-correc ted rating-curve method was used to estimate the sediment load. The statist ical analysis provides a criterion for the construction of adequate rating curves, In most cases, yearly data were used to establish the rating curves . Estimated results showed strong inter-annual variations of sediment loads , ranging from 0.05 to 37 Mt yr(-1), which differs from the narrow range (7 .9-8.1 Mt yr(-1)) of long-term averages reported in the Hydrological Yearbo oks. Two peaks of sediment load (> 15 Mt yr(-1)) occurred in the years foll owing two road construction events, indicating the exacerbation of erosion in the watershed induced by human activities. This study indicates that WRB 's long-term average method smoothes out the temporal fluctuation and, ther efore, misses important information borne in the data. Hence, we suggest th at historical data can be reprocessed to estimate yearly sediment load, whi ch map lead to a better understanding of the sediment yielding process and its response to human disturbances.