Experimental Analysis of River Evolution with Riparian Vegetation

Shuqing Yang,Haijue Xu,Yuchuan Bai

doi:10.3390/w10111500

Abstract

Studying the effects of different riparian vegetation densities on river channel evolution has practical significance for predicting the river channel evolution process during flood periods and ecological river engineering via the artificial planting of vegetation. In this study, we simulated the formation and evolution processes of river channels under different riparian vegetation coverage rates in laboratory conditions. The riparian vegetation coverage rates were set as 0, 20, 40 and 80%, on unilateral and bilateral sides of a river channel bank. Given the same flow and sediment boundary conditions, experiments were carried out in a 4 × 1.5 m tank. This paper focuses on the comparative analysis of main stream stability characteristics, bend migration characteristics, river bank erosion characteristics and sediment transport intensity. The results showed that different amounts of riparian vegetation cover created different characteristics of river channel evolution and strongly impacted the stability of the banks and bed. River channel evolution under unilateral vegetation cover is often accompanied by alternate development of the main stream and branch, and the bend stability under unilateral riverbank vegetation cover is worse than under bilateral cover. For a bilateral vegetation-covered river channel, a narrow and deep regime channel more easily forms with a higher vegetation coverage rate; the curvature of the stable river bend is smaller, but the adaptation period of the flow to the river channel bed increases. Planting of riparian vegetation played a positive role in the erosion resistibility, which effectively reduced the lateral migration rate of the riverbank. The higher the vegetation coverage rate, the greater the flow shear stress needed for the same river channel migration rate. While effectively reducing lateral migration, riparian vegetation coverage increased the vertical migration and led to a trend in overall scour depth along the riverbank.

Highlights

The process of river evolution is affected by many factors: flow, channel width, depth, slope, grain size and regional vegetation distribution
We found that when the vegetation was distributed on one side of the river bank, riparian vegetation increased, forming a new silting
From different riparian vegetation we found that sediment transport increased role in a flexible bank to a certain extent,coverage when therates, planting of vegetation was very dense, vegetation with increasing coverage rate, and good consistency was maintained between unilateral and bilateral revetment became a hard constraint, similar to a riparian vegetation wall

Summary

Introduction

The process of river evolution is affected by many factors: flow, channel width, depth, slope, grain size and regional vegetation distribution. In particular, plays a significant role in this process and considerably influences riverbank widening and river stability. Riparian vegetation area increases the river resistance and effectively reduces the flow velocity [1], greatly reducing the sediment carrying capacity [2], affecting the sediment transport and deposition process [3,4] and final river bed morphology. Water 2018, 10, 1500 is formed or destroyed, reducing riparian erosion, which in turn affects the channel lateral migration characteristics [8]. Many geomorphologists and engineers have long recognized the strong influence that vegetation exerts on river channel hydrodynamic characteristics and morphology. Further understanding of the influence is of great importance with respect to hydraulic and environmental engineering

Methods

Results

Discussion

Conclusion