Numerical Investigation on Downstream Increase in Peak Discharge of Hyperconcentrated Floods in the Lower Yellow River

Zhijing Li,Zhongwu Jin

doi:10.4236/jamp.2016.44073

Abstract

Hyperconcentrated floods in the Yellow River usually accompanied with some peculiar phenomena that cannot be explained by general conceptions of ordinary sediment-laden flow (e.g., downstream increase in peak discharge, instability flow, ripping up the bottom). Up to date, the mechanisms for the abnormal phenomena are not well understood. The aim of this paper is to facilitate a new insight into the abnormal downstream increase in peak discharge of hyperconcentrated floods in the lower Yellow River. Numerical model experiments have been conducted on a typical flood occurred in August 1992 in the Lower Yellow River during which the peak discharge at Huayuankou station was 1690 m 3 /s larger than the value at Xiaolangdi station at upstream. It is found that a fully coupled model that incorporates the contribution of bed evolution to the mass conservation of the water-sediment mixture, can reasonably well capture the characteristics of peak discharge rise and severe bed scour, while separate numerical experiment using a decoupled model, which ignores the feedback effects of bed evolution, shows no rise in the peak discharge. This leads us to comment, if only briefly, that the entrainment of sediment due to bed erosion is the main reason for causing peak discharge increase along downstream course.

Highlights

Hyperconcentrated flow is identified as a kind of complex sediment laden flow carrying a large amount of sediments with high concentration and certain fine particles, which is a typical solid and liquid two-phase flow [1]
This paper has made a numerical investigation of hyperconcentrated floods, the typical flood (“92.8”) occurred in the Lower Yellow River is studied with a series of numerical experiments
When hyperconcentrated flood propagates through braided channel like the Yellow River and its tributaries on the Loess Plateau, extremely rapid fluvial process happens, in turn, the fluvial process changes the propagation of flood waves and induces peculiar phenomena

Summary

Introduction

Hyperconcentrated flow is identified as a kind of complex sediment laden flow carrying a large amount of sediments with high concentration and certain fine particles, which is a typical solid and liquid two-phase flow [1]. (2016) Numerical Investigation on Downstream Increase in Peak Discharge of Hyperconcentrated Floods in the Lower Yellow River. Without flow input from regions between, the peak discharge at Huayuankou station was measured as 6260 m3/s which was 1,690 m3/s larger than the value at Xiaolangdi station (4570 m3/s) at upstream with a length of 128 km This phenomenon was observed during hyperconcentrated flood occurred in August 1973 (“73.8”) and August 2004 (“04.8”). A lot of field investigations of the hyperconcentrated flood in the rivers on the Loess Plateau have been carried out by Chinese hydraulic engineers and sediment measurements have been done over a long time period by more than 10,000 people working at 122 hydrological stations on the river and its tributaries [7]. Computed results and theoretical analysis indicate that the entrainment of sediment due to bed erosion is the main reason for causing peak discharge increase along downstream course

Governing Equations

Auxiliary Relationships

Numerical Algorithm

Numerical Case Study

Results and Discussion

Conclusion