Application of 137Cs fingerprinting technique to interpreting sediment production records from reservoir deposits in a small catchment of the Hilly Loess Plateau, China

According to variations of 137Cs and clay contents, 44 flood couplets were identified in a profile of reservoir deposit with a vertical length of 28.12 m in the Yuntaishan Gully. Couplet 27 at the middle of the profile had the highest average 137Cs content of 12.65 Bq·kg−1, which indicated the 1963s’ deposits, then 137Cs content decreased both downward and upward in the profile. The second top and bottom couplets had average 137Cs contents of 2.15 Bq·kg−1 and 0.92 Bq·kg−1, respectively. By integrated analysis of reservoir construction and management history, variations of 137Cs contents over the profile, sediment yields of flood couplets and rainfall data during the period of 1958–1970, individual storms related to the flood couplets were identified. 44 floods with a total sediment yield of 2.36×104 m3 occurred and flood events in a year varied between 1 and 10 times during the period of 1960–1970. 7–10 flood events occurred during the wet period of 1961–1964 with very wet autumn, while only 1–2 events during the dry period of 1965–1969. Average annual specific sediment yield was 1.29×104 t·km−2·a−1 for the Yuntaishan Gully during the period of 1960–1970, which was slightly higher than 1.11×104t·km−2·a−1 for the Upper Yanhe River Basin above the Ganguyi Hydrological Station and slightly lower than 1.40×104t·km−2·a−1 for the nearby Zhifang Gully during the same period. Annual specific sediment yields for the Yuntaishan Gully were correlated to the wet season’s rainfalls well.