Distribution of Initial Vegetation Recruitment on Bare Bar in Sand Bed River

Yuexia Zhou,Eijiro Kubo,Yuji Toda

doi:10.4236/jwarp.2018.104024

Abstract

Riparian vegetation is known to affect the flood flow and the riparian environment, and it is important for river engineers to know the vegetation dynamics in river. Despite a number of researches have been performed for vegetation dynamics, the mechanism of initial vegetation recruitment is still not clear. In this study, two field surveys by using Unmanned Aerial Vehicle (UAV) remote sensing, UAV aerial photographs analysis and a numerical simulation were conducted to detect the location of initial vegetation recruitment and explore its relationship with hydrology and river morphology. The initial vegetation recruitment was identified by comparing vegetation distributions before and after vegetation germination. Most of the initial vegetation recruitment locations were found either along dunes on sandbar or along the wet/dry rotational area of shore bank. Results of the aerial photographs analysis showed that the initial vegetation recruitment occurred at the downstream side of crest of dunes. As for the vegetation recruitment zone located along shore bank, the relative elevation of different recruitment zones is almost same, and the mean value of the relative elevation is around 0.33 m. With the comparison of the contour map of river morphology and the initial vegetation recruitment zone, the shape of initial vegetation recruitment zone is positively consistent with the shape of river morphology distribution. The results of numerical analysis show that the initial vegetation recruitment zone located along shore bank experienced intermediate flood pulse. The inundation frequencies during seed dispersal and germination period for the internal and external boundaries of vegetation recruitment zone are 23.87% and 6.2%, respectively.

Highlights

Riparian vegetation zone is a complex ecotone, which connects water body to upland vegetation, and this ecotone can be affected by high water table and soil water retention ability [1]
The zones at Position-S1 to Position-S6 are the zones of initial vegetation recruitment distributed along shore bank, and the zones at Position-D1 to Position-D3 are the zones of initial vegetation recruitment far away from shore bank, and they distributed along dunes on bare bar
Our conclusion is similar to the previous studies, this study provides the possibility of using Unmanned Aerial Vehicle (UAV) remote sensing

Summary

Introduction

Riparian vegetation zone is a complex ecotone, which connects water body to upland vegetation, and this ecotone can be affected by high water table and soil water retention ability [1]. Once the riparian vegetation was established, it has been known to affect river hydrology, such as river flow velocity and water depth, by changing flow resistance [7] [8], and river morphology, such as river bed elevation and transaction, by changing sediment deposition and degradation [4] [9]. Bank vegetation can resist the erosion of river bank during floods, which resulted in deeper river channel depth and narrower water channel width [10] [11] [12]. The decrease of water channel width provide much more stable habitat for riparian vegetation, and this means vegetation recruitment and river morphology are interacted [5]. Study on the effect of hydrology and morphology to vegetation recruitment was proposed by many researchers

Methods

Results

Conclusion