Flow Resistance in Open Channel Due to Vegetation at Reach Scale: A Review

Abstract

Vegetation on the banks and flooding areas of watercourses significantly affects energy losses. To take the latter into account, computational models make use of resistance coefficients based on the evaluation of bed and walls roughness besides the resistance to flow offered by vegetation. This paper, after summarizing the classical approaches based on descriptions and pictures, considers the recent advancements related to the analytical methods relative both to rigid and flexible vegetation. In particular, emergent rigid vegetation is first analyzed by focusing on the methods for determining the drag coefficient, then submerged rigid vegetation is analyzed, highlighting briefly the principles on which the different models are based and recalling the comparisons made in the literature. Then, the models used in the case of both emergent and submerged rigid vegetation are highlighted. As to flexible vegetation, the paper reminds first the flow conditions that cause the vegetation to lay on the channel bed, and then the classical resistance laws that were developed for the design of irrigation canals. The most recent developments in the case of submerged and emergent flexible vegetation are then presented. Since turbulence studies should be considered as the basis of flow resistance, even though the path toward practical use is still long, the new developments in the field of 3D numerical methods are briefly reviewed, presently used to assess the characteristics of turbulence and the transport of sediments and pollutants. The use of remote sensing to map riparian vegetation and estimating biomechanical parameters is briefly analyzed. Finally, some applications are presented, aimed at highlighting, in real cases, the influence exerted by vegetation on water depth and maintenance interventions.

Flow dynamics and sediment transport in vegetated rivers: A review

“…When C also increases with vegetation density, due to the accompanying decreased flow area and enhanced stem-wake and wake-wake interaction [10] . Based on experiments and numerical calculations and with the help of various data-driven methods, a large number of d C prediction models have been established, which were reviewed by D' Ippolito et al [24] and Liu et al [22] . In addition to the Reynolds number and vegetation density, the distribution pattern of vegeta-tion elements also affect the drag force [25][26] .…”

“…For the estimation of the bulk velocity of the entire flow section, the Chézy formula can be used in which the Chézy coefficient of submerged vegetation depends on d C , / H h , and  [37][38] as reviewed elsewhere [24] . Floating vegetation refers to aquatic plants that are suspended along the free water surface, forming a floating treatment wetlands.…”

Bulk Drag Predictions of Riparian Arundo donax Stands through UAV-Acquired Multispectral Images

“…The results of this study represent a satisfactory advance in the monitoring of riparian vegetation dimensional properties in the field, particularly in real-scale models and simulations of vegetated flows to be employed as supporting tool for the proposal of the most appropriate mitigating scenarios of flooding events in natural and urban areas surrounding vegetated water bodies [62][63][64][65][66][67].…”

Comparing the Hydrological Response of Forested Headwaters (Unregulated and Regulated with Check Dams) under Mediterranean Semi-Arid Conditions

“…It is well known how check dams impact catchment hydrology and morphology (for instance, by reducing channel profile slope, e.g., Zema et al [90], and favoring the growth of riparian vegetation, e.g., Bombino et al [11] and Zaimes et al [91]). These effects influence the flow regime by reducing the water velocity, which in turn modifies the travel time of water particles, and thus, affects the peak flow [19,92]. However, a deeper analysis highlights that the check dam action depends on structure functioning after construction [81].…”