Estimating the Suspended Sediment Load by Using the Historical Hydrometric Record from the Lanyang-Hsi Watershed

The long-term hydrometric data archived by the Water Re sources Bureau (WRB) at the gauge station near the Lanyang-Hsi ri ver mouth were re-processed to derive the time-series of suspended sediment load. A bias-corrected rating-curve method was used to estimate the sedi ment load. The statistical analysis provides a criterion for the construction of adequate rating curves. In most cases, yearly data were used to establish the ra ting curves. Estimated results showed strong inter-annual variations of sediment loads, ra nging 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 Hy drological Ye arbooks. Two peaks of sediment load (> 15 Mt yr-1) occurred in the ye ars following two ro ad construction events, indicating the exacer bation of erosion in the watershed induced by human activities. This study indicates that WRB's long-term average method smoothes out the tempo ral fluctuation and, therefore, misses important information borne in the data. Hence, we suggest that historical data can be reprocessed to estimate yearly sediment load, which may lead to a better understanding of the sedi ment yielding process and its response to human disturbances.