Keywords: 
• bottom-block scour /
• cross section /
• flood level /
• flow state /
• Yellow River

Abstract: The paper is intended to show the patterns of the changes both in the cross section and the local flow due to a peculiar kind of scour, bottom-block scour, or named as bottom tearing scour and bottom ripping up, which is often found to occur in the forms of bottom-block uplifting and moving on the Yellow River, instead of commonly seen sediment particles' transport. Based on the data measured at the Longmen and Tongguan hydrometric stations and the lab experiments by the authors, the bottom-block scour is found to follow a four-staged pattern: Starting from pre-scour, to channel bed elevation keeping relatively stable, bed rapid declining due to mud-layered block uplift, and continual scour followed by back-silting. The bottom-block scour is found to tend to make a steeper and clockwise rating curve loop while non-bottom-block scour tends to make a mild-sloped and anticlockwise one. When the bottom-block scour starts, the local water level begins with a sudden rising and is followed by a rapid fall. Intensively turbulent flow is found not at the place where the bottom-block scour happens, but downstream of it. The paper is of significance in predicting and handling the risk of river training works failure due to the bottom-block scour.