Modelling the effects of emergent vegetation on an open‐channel flow using a lattice model

A two‐dimensional lattice model has been developed to describe the influence of vegetation on the turbulent flow structure in an open channel. The model includes the influence of vegetation density on the frictional effect of the channel bed and walls. For the walls, a semi‐slip boundary condition has been considered as an alternative to overcome the no‐slip boundary condition limitations in turbulent flows. The drag stress exerted by the flow on the vegetation as well as the gravity effect has also been taken into account. The proposed lattice model has been used to simulate the experimental results reported from the study of the influence of alternate vegetated zones on the open‐channel flow. The results show that the lattice model approach is a valid tool for describing these kinds of flows. Copyright © 2007 John Wiley & Sons, Ltd.     

乐安江漫滩区稗草中重金属污染和来源分析

2005年10月,采集了乐安江及其支流漫滩区表层土中的优势植物--稗草,并测定了其中6种重金属(Cd、Cr、N i、Cu、Pb、Zn)的含量。流经亚洲最大露天铜矿(德兴铜矿)的乐安江,其三条支流由于被德兴铜矿的酸性矿山废水(AMD)和一个活性炭厂排出的废液所污染,以至其漫滩区表层土中的稗草含有高浓度的Cd、Cu、Pb、Zn。稗草中6种金属的生物体内累积性按下列次序退减:Cd>Zn>Cu>Pb>N i>Cr,这与它们在环境中的迁移性相一致。     

Modeling Floodplain Filtration for the Improvement of River Water Quality

A mathematical model was developed to describe a treatment method of floodplain filtration for the improvement of river water quality. The process consists of spraying poor quality river water onto the river floodplains and thus allowing soil filtration to treat water before it gets back again into the main river stream. This technique can be readily employed in Korea because it exploits the characteristics of the climate and rivers in the country, as described in an experimental study of Chung et al. The model was analyzed by numerical methods and validated by comparing the simulated values with experimental data. A scenario analysis of the model was also performed in order to have a better understanding of the floodplain filtration process. Our results show that the model was able to predict the reduction in organic matter and NO₃^– in river water through the floodplain filtration. Furthermore, it was found that only a few decimeters of top soil profile were enough to degrade most of the organic matter under wider operational conditions than those reported in the literature. Also, it was found that significant infiltration of atmospheric oxygen took place near the soil surface. The N₂O emission and the NO₃^– leaching increased with the increase in the influent NO₃^– concentration. However, the N₂O emission due to floodplain filtration was not expected to exceed 0.1 mL/m²-day.     

Flow characteristics of rectangular open channels with compound vegetation roughness

An idealized parallel flow caused by a lateral bed roughness difference due to the partial vegetation across a channel is investigated. Similar to the flow in a compound channel, there are mixing layers adjacent to the interface between the vegetation and the non-vegetation lanes, and a lateral momentum exchange occurs between the slow-moving water in the former lane and the fast-moving water in the latter lane. Under a uniform flow condition, the three-dimensional (3D) instantaneous velocities of two cases with different discharges and water depths are measured with a 16MHz acoustic Doppler velocimeter (micro ADV). The longitudinal variation of the streamwise velocity and the vertical variation of the Reynolds stress are analyzed. A quadrant analysis is carried out to investigate the outward and inward interaction, ejection, and sweep phenomenon caused by the vegetation variation across the channel. The results show that the flow characteristics in the vegetation lane are similar to those in an open channel fully covered with submerged vegetation, and the flow characteristics in the smooth non-vegetation lane are similar to those in a free open channel. For the cases studied here, the width of the mixing region is about 10% of the channel width, and the mixing region is mainly on the non-vegetation half.     

Integrated numerical model for vegetated surface and saturated subsurface flow interaction

The construction of an integrated numerical model is presented in this paper to deal with the interactions between vegetated surface and saturated subsurface flows. A numerical model is built by integrating the previously developed quasi-three-dimensional (Q3D) vegetated surface flow model with a two-dimensional (2D) saturated groundwater flow model. The vegetated surface flow model is constructed by coupling the explicit finite volume solution of 2D shallow water equations (SWEs) with the implicit finite difference solution of Navier-Stokes equations (NSEs) for vertical velocity distribution. The subsurface model is based on the explicit finite volume solution of 2D saturated groundwater flow equations (SGFEs). The ground and vegetated surface water interaction is achieved by introducing source-sink terms into the continuity equations. Two solutions are tightly coupled in a single code. The integrated model is applied to four test cases, and the results are satisfactory.     

Evaluating flood extent mapping of two hydraulic models, 1D HEC‐RAS and 2D LISFLOOD‐FP in comparison with aerial imagery observations in Gorgan flood plain,Iran

We compared flood mapping techniques using a one‐dimensional (1D) hydraulic model HEC‐RAS and two‐dimensional (2D) LISFLOOD‐FP for a 10‐km reach of Gorgan River in Iran. Both models were run using the same hydrologic input data. The input into the models was a steady discharge of 90 cm, corresponds to a flood peak occurred on March 25, 2012. Flood maps generated using these two models were compared with an observed flood inundation map, using F‐statistic. The roughness coefficients of the models were calibrated by maximizing the value of the F‐statistic. Based on the F‐statistic, LISFLOOD‐FP gives a slightly better result (F = 0.69) than HEC‐RAS (F = 0.67). Visual comparison of the flood extents generated by the two models showed reasonably good agreement. Validation was done using a flood event occurred on May 31, 2014. The LISFLOOD‐FP model gave a better result for validation as well. The 2D model showed more consistency in comparison with the 1D model.     

植被作用下的复式河槽流速分布特性

通过水槽试验，探讨了不同滩地植物 (乔木、灌木和野草) 对复式河槽流速分布的影响. 详细地介绍试验过程及三维流速仪ADV的测量原理. 试验时， 选塑料吸管、鸭毛和塑料大草分别模拟乔木、灌木和野草. 同时，考虑了流量、床面底坡对 流速分布的影响. 试验结果表明，滩地未种树的复式河槽在大的相对水深时，流速满足对数 分布；滩地种树后，主槽流速增大，流速分布复杂，滩地流速减小，呈 S 形分布，不同植物的S 形分布是不同的. 这种S 型分布将水流划分为3个区的复杂行为，每区的范围与水深，垂线位置和植物类型有关. 床面坡度对流速分布的影响非常明显     

汉江下游武汉段河漫滩沉积物吸附磷的特征

研究了汉江下游武汉段河漫滩7个沉积物的吸附特征及温度和扰动强度对磷吸附等温线的影响，用改进的Langmuir模型和Freundlish模型对实验吸附数据进行拟合，可得到最大吸附容量（Qmax）、原有吸附可交换态磷（NAP）、临界磷平衡浓度（EPC0）和固-液分配系数（Kp）的值．结果表明，改进的Langmuir模型更适用于描述汉江河漫滩沉积物的吸附特征，其物理意义更明确；Kp与Qmax呈较好的线性关系；沉积物吸附和解吸磷能力与温度变化一致；沉积物在等温吸附磷过程中，固体浓度效应在强扰动强度（200r／min）时最强。弱扰动强度（150r／min）时次之，中扰动强度（100r／min）时最弱．