Soil erosion and sediment interception by check dams in a watershed for an extreme rainstorm on the Loess Plateau,China

The magnitude of soil erosion and sediment load reduction efficiency of check dams under extreme rainstorms is a long-standing concern.The current paper aims to use check dams to deduce the amount of soil erosion under extreme rainstorms in a watershed and to identify the difference in sediment interception efficiency of different types of check dams.Based on the sediment deposition at 12 check dams with 100% sediment interception efficiency and sub-catchment clustering by taking 12 damcontrolled catchments as clustering criteria,the amount of soil erosion resulting from an extreme rainstorm event on July 26,2017(named "7·26" extreme rainstorm) was estimated in the Chabagou watershed in the hill and gully region of the Loess Plateau.The differences in the sediment interception efficiency among the check dams in the watershed were analyzed according to field observations at 17 check dams.The results show that the average erosion intensity under the "7-26" extreme rainstorm was approximately 2.03×104t/km2,which was 5 times that in the second largest erosive rainfall in 2017(4.15×103t/km2) and 11-384 times that for storms in 2018(0.53×102t/km2-1.81×103t/km2).Under the "7-26" extreme rainstorm,the amount of soil erosion in the Chabagou watershed above the Caoping hydrological station was 4.20 × 106 t.The sediment interception efficiency of the check dams with drainage canals(including the destroyed check dams) and with drainage culverts was 6.48 and 39.49%,respectively.The total actual sediment amount trapped by the check dams was 1.11 × 106 t,accounting for 26.36% of the total amount of soil erosion.In contrast,3.09×106 t of sediment were input to the downstream channel,and the sediment deposition in the channel was 2.23×106t,accounting for 53.15%of the total amount of soil erosion.The amount of sediment transport at the hydrological station was8.60×105t.The Sediment Delivery Ratio(SDR) under the "7·26" extreme rainstorm was 0.21.The results indicated that the amount of soil erosion was huge,and the sediment interception efficiency of the check dams was greatly reduced under extreme rainstorms.It is necessary to strengthen the management and construction technology standards of check dams to improve the sediment interception efficiency and flood safety in the watershed.