Riparian Vegetation Density Mapping of an Extremely Densely Vegetated Confined Floodplain

István Fehérváry,Tímea Kiss

doi:10.3390/hydrology8040176

Abstract

The most crucial function of lowland-confined floodplains with low slopes is to support flood conveyance and fasten floods; however, obstacles can hinder it. The management of riparian vegetation is often neglected, though woody species increase the vegetation roughness of floodplains and increase flood levels. The aims are (1) to determine the branch density of various riparian vegetation types in the flood conveyance zone up to the level of artificial levees (up to 5 m), and (2) to assess the spatial distribution of densely vegetated patches. Applying a decision tree and machine learning, six vegetation types were identified with an accuracy of 83%. The vegetation density was determined within each type by applying the normalized relative point density (NRD) method. Besides, vegetation density was calculated in each submerged vegetation zone (1–2 m, 2–3 m, etc.). Thus, the obstacles for floods with various frequencies were mapped. In the study area, young poplar plantations offer the most favorable flood conveyance conditions, whereas invasive Amorpha thickets and the dense stands of native willow forests provide the worst conditions for flood conveyance. Dense and very dense vegetation patches are common in all submerged vegetation zones; thus, vegetation could heavily influence floods.

Highlights

In Europe, floodplains cover ca. 7% of the continent’s area, and they exhibit unique morphological, hydrological, ecological and pedological characteristics [1]
The objectives of the research are (1) to identify the riparian vegetation types using automatic classification; (2) to determine the vertical branch density of vegetation in the active floodplain in the flood conveyance zone (i.e., 1–5 m, up to the level of the artificial levees); and (3) to assess the horizontal and vertical spatial distribution of densely vegetated patches, which might influence the propagation of the flood wave
The young poplar plantation was identified based on its canopy relief ratio (CRR ≤ 0.039), which separates well the young trees with low and undeveloped canopy from trees with higher and developed canopy, and from open surfaces (Figure 3, Table 2)

Summary

Introduction

In Europe, floodplains cover ca. 7% of the continent’s area, and they exhibit unique morphological, hydrological, ecological and pedological characteristics [1]. 7% of the continent’s area, and they exhibit unique morphological, hydrological, ecological and pedological characteristics [1]. Very often, they are artificially confined; the flood conveyance is restricted to a narrow zone. In lowland floodplain areas where the rivers have low slopes and low velocities, the main aim of flood management is to fasten the flow and decrease the flood duration. Floods last for months; the main aim of flood mitigation is to shorten the floods instead of their retention, increasing the flood conveyance of the artificial floodplain. In case of declining flood conveyance capacity of confined floodplains, the probability of an artificial levee overtopping or breaching increases, endangering citizens, settlements or infrastructure built on the flood-protected side of the floodplain [2]

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Discussion

Conclusion