Case Study: Model Test on the Effects of Grade Control Datum Drop on the Upstream Bed Morphology in Shiting River

Ma Ma,Liu Liu,Wang Wang,Yang Yang,Nie Nie

doi:10.3390/w11091898

Abstract

This paper conducted an undistorted scaled model test (geometric scale λL = 1:80; the others are derived scales based on Froude similitude) of a 1.3 km-long river reach in Shiting River, China, investigating the impacts of the grade control datum (GCD, defined as the crest elevation of the grade control structure) drop on the upstream bed morphology. Three GCDs and six flood events (occurrence probability 1–50%, discharge = 600–4039 m3/s) were tested on the model. Experimental results indicate that, for a constant GCD, the increase in discharge deepens and widens the upstream river bed. For a lower GCD, the increase in channel depth and width caused by the increasing discharge is greater. For each discharge, the decrease in GCD induces a lower and steeper upstream river bed, widening the upstream main channel. For lower discharge, the GCD drop induces a head cut erosion area upstream of the grade control structure and the head cut erosion area is filled by the upstream sediment when the flow discharge is high. Experimental data also indicate that the maximum general scour depth at the 105th Provincial Highway Bridge is approximately independent of discharge for a constant GCD. For a lower GCD, the general scour depth at the 105th Provincial Highway Bridge increases slightly with discharge.

Highlights

Scour is a main design concern for hydraulic structures such as bridge or wind turbine foundations [1,2,3,4], buried pipelines [5,6,7], weirs and sills [8,9,10,11,12], etc
The scour at instream structures can be classified into three types: general scour, constriction scour and local scour [13,14,15]
Designed Grade control structures (GCSs) play a role as a grade control datum (GCD) for the upstream river reach [16,20]

Summary

Introduction

Scour is a main design concern for hydraulic structures such as bridge or wind turbine foundations [1,2,3,4], buried pipelines [5,6,7], weirs and sills [8,9,10,11,12], etc. Bed degradation usually occurs when the bed erosion rate is greater than the upstream sediment replenishment rate It can induce general scour at the foundations of instream structures and destabilize riverbanks, threatening the security of both the public and private properties [16]. Grade control structures (GCSs) such as submerged weirs, bed sills and check dams are common countermeasures for bed degradation [9,10,11,17,18,19]. They can raise the upstream water level and reduce the flow capacity for sediment transport, preventing the upstream river bed from being excessively degraded. Grade control structures (GCSs) were extensively used in this river reach as countermeasures for bed degradation

Methods

Results

Conclusion