A Model to Simulate Pumping Tests in Wells with High Loss and Backflow

Traditional methods of analyzing pumping tests in single wells fail when the well loss is very high due to a low transmissivity skin. Because of the restricted rate at which water can enter a high loss well from the aquifer, well casing storage becomes a significant factor. Additionally, if a slug of water enters the well from the pump column immediately after the pump is switched off, it has a long‐lasting significant effect on the recovering water level in the well because it cannot be absorbed rapidly by the aquifer. A theoretical model is derived here that simulates the water level in a well in these circumstances. In the model, the continuously changing rate of water inflow from the aquifer to the well is approximated by a step function with a finite difference time step. It is demonstrated by a real example that the model can be applied easily to analyze pumping tests, including tests with a varying pumping rate. The analysis confirms suspected high well loss, calculates the unknown rate of backflow, and determines the aquifer's transmissivity.     

现浇生态混凝土应用于边坡灾害治理及生态恢复的研究

通过研究生态混凝土的微观结构与孔隙率、透水性、强度三者的耦合关系,对生态混凝土的孔隙结构特征进行了分析,提出孔隙结构分布值R是影响生态混凝土的重要指标。通过对生态混凝土护坡的防冲刷机理分析和试验验证,提出了边坡生态恢复和灾害治理相结合的方法,即采用生态混凝土和预应力锚索框架格护坡。对河南洛阳段高速公路一侧的土质高陡边坡,在进行稳定性分析的基础上应用该方法,并且对后续的生态恢复效果进行了研究。研究结果表明：该方法适宜于坡度较大的边坡,结合预应力锚索框架格能对滑坡起到防治作用;降雨条件下抗;中刷能力强,植物覆盖率较高,对周围的生态恢复起到了一定的作用。     

Mangrove Forests: a Tough System to Invade but an Easy one to Rehabilitate

Mangrove forests are tough ecosystems to invade because few species can tolerate the hydrological and edaphic conditions that prevail in mangrove habitats. The small pantropical mangrove species pool is also the basis for asserting that mangrove forests are easy to rehabilitate, at least in terms of tree species composition. The high complexity of the animal and microbial component of mangrove ecosystems is not addressed in this article. The following questions are useful as a guide for evaluating the invasion of plant species into mangrove habitats: (1) Is the invading species a halophyte? (2) What conditions of the environment is the invading species occupying and how long will those conditions last? (3) What is the geographic location of the invasion, does it penetrate the forest or is it only at the edge? (4) Is the invasion a short-term response to changes in microsite conditions? (5) Is the invasion the result of a long-term shift in the mangrove habitat?     

Quantifying Threshold Water Tables for Ecological Restoration in Arid Northwestern China

In arid northwestern China, as many inland areas around the world with arid or semi-arid climate, inland river flow recharges groundwater; vegetation pattern depends on the water table, which characterizes the landscapes of oasis, transition zone and desert, within different distances from an inland river. The water table conditions play an important role in water and land management—a high water table causes salinization within the oasis while a low water table causes desertification around the oasis. This study applies a theoretical-empirical method to calculating critical groundwater depths including the depth of critical groundwater level causing salinization (DCGS) and the depth of critical groundwater level causing desertification (DCGD); the calculations are validated with field observations in the Luocheng Irrigation District located in the middle reach of the Heihe River, an inland river of the northwestern China. Specifically, the calculated DCGS is 1.29 m for the case study area and the range of water table depth at the locations with saline soil is 0.5-1.2 m. The calculated DCGD for three vegetation communities, Nitraria tangutorum + Glycyrrhiza uralensis Fisch community, Tamarix chinensis + Phragmites australis community, and Alhagi sparsifolia + Phragmites communis, are 8.26, 11.26, and 13.26 m, respectively, basically within an observed range of 6.0-13.0 m in the study area. The critical depths can be used to design an engineering approach to control water tables and mitigate salinization and desertification problem for ecosystem restoration in the study region.     

A Dynamic Model to Simulate Spills of Fuel and Diesel Oil in the Terrestrial Environment during Extreme Fluvial Floods

Extreme fluvial floods may cause severe contamination with fuel oil and diesel, originating from gasoline pipes and tanks in private households and industrial areas, respectively. Geo‐referenced oil spills in the region of Bitterfeld (Germany) after extreme flood events, such as in August 2002, were simulated using the two‐dimensional (2D) Finite Element model system Telemac2D, which is subdivided into a hydrodynamic (Telemac‐2D) and a transport module (Subief2D). Fuel oil settled via adhesion showed a thickness of less than 1.0 mm. Fuel oil concentrations on the flood wave amounted up to 80 g m^–3 in the vicinity of the point sources. At a distance of several hundred meters downstream of the point sources, the fuel oil concentrations were calculated to be zero. Settled areas were only partially contaminated with fuel oil. While one village experienced severe oil contamination, the town of Bitterfeld was almost unaffected by oil spills. It was demonstrated that the 2D transport model applied is capable of simulating fuel oil spills during extreme high waters in the terrestrial environment. Such simulations of fuel oil spills will feed into a GIS‐based decision support system of flood protection.     

The Ecological Restoration of Heavily Degraded Saline Wetland in the Yellow River Delta

As a result of discontinuous water flow, agriculture, and increasing urban use of fresh water affecting the natural wetlands of the Yellow River Delta, these areas have experienced significant degradation in the past two decades, ultimately diminishing the overall natural wetland land area in the region. This study aimed to address the issue of decreasing fresh water in the Yellow River Delta by studying the effects of three different approaches to restoration on long‐term wetland recovery. The results of the study demonstrated that soil salt and available Na contents significantly decreased in response to all three restoration treatments. Impacts of the restoration treatments were more significant in 2009 than in 2010, as shown by the high rate of activity in the reed debris group. The highest phosphatase activity of the experimental period was also observed in the reed debris group. Meanwhile, a marked variation in soil nutrient elements (total carbon (TC), total nitrogen (TN), available phosphorus, and available potassium) was observed in the restoration treatment plots throughout the experimental period. TC and TN contents were generally higher in the restoration treatment groups than in the control group. Moreover, urease and phosphatase activity levels were highly correlated with one another, as well as with soil nutrient elements. In 2009, the yield of the Suaeda salsa plant was highest in the reed debris treatment group and lowest in the ploughing treatment group. The S. salsa plant did show a positive response to all of the different restoration treatments. Taken together, these results suggest that restoration approaches that implement ploughing techniques aided in the restoration of degraded saline wetlands.     

太湖污染控制及水生态系统的恢复对策

Taihu Lake is a mutiple-function fresh water lake situated in the delta of Yangtze River. Nowadays, the serious pollution mainly created by industry and residents'' life has made the water quality of the lake decline continuously. Eutrophication is the main characteristic of the water pollution. The water pollution not only affect the several functions of the lake, but also cause the changes of the aquatic biological community.The pollution control strategies to be adopted include the treatment of the industrial waste water and residents'' life sewage, as well as the agricultural non-point polluting source. Ecological engineering is the useful measure for diminishing the nutrition salts in water. On the basis of pollution control, the ecological restoration methods include the transplanting of the emerged and/loading anchored aquatic plants at first and the restoration of the submerged plants in the next.     

A Dynamic Model to Simulate Arsenic,Lead, and Mercury Contamination in the Terrestrial Environment During Extreme Floods of Rivers

Beside damages of infrastructure in industrial regions, extreme floods can cause contamination with particle‐bound pollutants, e. g., due to erosion of soils and sediments. In order to predict contamination with inorganic pollutants, the transport and fate of arsenic, lead, and mercury during a fictive flood event of River Vereinigte Mulde in the region of Bitterfeld (Germany) with 200 years recurrence time was modeled. The finite element model system Telemac2D, which is subdivided into a hydrodynamic (Telemac‐2D), a transport (Subief‐2D), and a water quality module (wq2subief) was applied. The transport and water quality model models were calibrated using results of sediment trap exposures in the floodplain of River Vereinigte Mulde. Model results exhibited that the spatial patterns of particle‐associated arsenic and lead concentrations significantly changed. Extended, mostly agriculturally used areas showed arsenic and lead concentrations between 150 and 200 mg kg^–1 and 250 and 300 mg kg^–1, respectively, while urban areas were to a great extent spared from high contamination with arsenic and lead. Concentrations of particle‐associated mercury showed a pattern distinct from those of arsenic and lead. Outside of small patches with concentrations up to 63 mg kg^–1, concentrations of particle‐associated mercury remained close to zero. Differences in the spatial patterns of the three pollutants regarded mainly arise from significantly different initial and boundary conditions. Sensitivity analyses of initial and boundary conditions revealed a high sensitivity of particle‐bound pollutant concentrations, whereas the sensitivities of concentrations of suspended sediments and soluble pollutants were mediocre to negligible.     

A New Package in MODFLOW to Simulate Unconfined Groundwater Flow in Sloping Aquifers

The nonhorizontal‐model‐layer (NHML) grid system is more accurate than the horizontal‐model‐layer grid system to describe groundwater flow in an unconfined sloping aquifer on the basis of MODFLOW‐2000. However, the finite‐difference scheme of NHML was based on the Dupuit‐Forchheimer assumption that the streamlines were horizontal, which was acceptable for slope less than 0.10. In this study, we presented a new finite‐difference scheme of NHML based on the Boussinesq assumption and developed a new package SLOPE which was incorporated into MODFLOW‐2000 to become the MODFLOW‐SP model. The accuracy of MODFLOW‐SP was tested against solution of Mac Cormack (1969). The differences between the solutions of MODFLOW‐2000 and MODFLOW‐SP were nearly negligible when the slope was less than 0.27, and they were noticeable during the transient flow stage and vanished in steady state when the slope increased above 0.27. We established a model considering the vertical flow using COMSOL Multiphysics to test the robustness of constrains used in MODFLOW‐SP. The results showed that streamlines quickly became parallel with the aquifer base except in the narrow regions near the boundaries when the initial flow was not parallel to the aquifer base. MODFLOW‐SP can be used to predict the hydraulic head of an unconfined aquifer along the profile perpendicular to the aquifer base when the slope was smaller than 0.50. The errors associated with constrains used in MODFLOW‐SP were small but noticeable when the slope increased to 0.75, and became significant for the slope of 1.0.     

武汉东湖水生植被的恢复试验研究

本文报道了在武汉东湖所作的水生植被恢复的研究结果,分别在东湖水果湖、汤林湖和后湖等三个湖建立水生植被恢复示范区。     

Leaky Aquifer Models to Simulate the Well Flow in Fractured Aquifers with Linear Interporosity Flow

Following Hemker and Maas (1987) the models of two or three leaky aquifers are applied to simulate the flow to vertical wells operating in the fractured or dual porosity aquifers. The software WellTest (WT) (Székely 2015) is used for calculating the drawdown and discharge rate variation. The comparative analysis with the independent analytical solutions by Boulton and Streltsova-Adams (1978), Warren and Root (1963), Kazemi et al. (1969) concluded with acceptable agreement between the WT simulation and the alternate calculation methods. The selected field tests have been conducted in fractured limestone aquifers. The pumping test west of Copenhagen shows an example of fractured aquifer with considerable negative skin effect at the well face. The flowing well Wafra W1 in Kuwait operates in the two-zone aquifer exhibiting sufficient vertical recharge via leakage beyond a circular domain of estimated radius of 2460 m.     

滇池东北部沿岸带生态修复技术研究及工程示范--环境恶化、生态退化现状及其成因

本文作为“滇池沿岸带生态修复技术研究及工程示范”系列研究论文之一,主要研究了滇池东北部沿岸带环境恶化与生态退化现状、成因及妨碍自然生态恢复的主要限制因素．风浪强烈侵蚀、湖底坚硬贫瘠、水质严重污染、大型水生植物和底栖动物消失,滇池东北部沿岸带已经蜕变成了“水域荒漠”．湖滩湿地围垦、人工岸堤修建和水质污染是导致沿岸带环境恶化、生态退化的主要原因,强烈的风浪冲刷和严重的水质污染是阻碍沿岸带自然生态恢复的主要限制因素．生态恢复必须从基础环境改造入手,实施生态修复．     

Efficient Methods to Simulate Planar Free Surface in the 3D 4th-Order Staggered-Grid Finite-Difference Schemes

We numerically tested accuracy of two formulations of Levander's (1988) stress-imaging technique for simulating a planar free surface in the 4^th-order staggered-grid finite-difference schemes. We have found that both formulations (one with normal stress-tensor components at the surface, the other with shear stress-tensor components at the surface) require at least 10 grid spacings per minimum wavelength ( _min÷h = 10) if Rayleigh waves are to be propagated without significant grid dispersion in the range of epicentral distances up to 15 _dom ^S.Because interior 4^th-order staggered-grid schemes usually do not require more than 6 grid spacings per minimum wavelength, in the considered range of epicentral distances, it was desirable to find alternative techniques to simulate a planar free surface, which would not require denser spatial sampling than _min÷h = 6. Therefore, we have developed and tested new techniques: 1. Combination of the stress imaging (with the shear stress-tensor components at the surface) with Rodrigues' (1993) vertically refined grid near the free surface. 2. Application of the adjusted finite-difference approximations to the z-derivatives at the grid points at and below the surface that uses no virtual values above the surface and no stress imaging. The normal stress-tensor components are at the surface in one formulation, while the shear stress-tensor components are at the surface in the other formulation.The three developed formulations give for the spatial sampling _min÷h = 6 results very close to those obtained by the discrete-wavenumber method. Because, however, the technique with the vertically refined grid near the free surface requires 3 times smaller time step (due to the refined grid), the technique with adjusted finite-difference approximations is the most accurate and efficient technique from the examined formulations in the homogeneous halfspace.     

滇池东北部沿岸带生态修复技术研究及工程示范——生态修复目标的确定及其可行性分析

连续6年对星湖仙女湖区水生植被种类、分布、生物量、水体状况进行了调查研究;共采集到水生植物24种,隶属于18科23属,可分为挺水植被、漂浮植被、浮叶植被和沉水植被4种生活型和8个植物群丛,其中苦草群丛占水生植被生物量70％以上,密齿苦草为绝对优势种;2004年与1999年比较,星湖仙女湖水体叶绿素a增加142％,透明度下降54％,水生植被盖度和生物量减少99％,水生植被群落结构趋于简化、多样性下降;星湖仙女湖水生植被发生逆向演替的主要原因是水体污染负荷增加和渔业生产的影响,削减污染负荷和控制渔业生产是促进星湖仙女湖水生植被恢复的重要途径．     

富营养化湖泊围隔中重建水生植被及其生态效应

水体富营养化导致水生植被衰退、蓝藻水华暴发、水质恶化和水生生态系统崩溃.恢复水生植被被认为是改善受损水体水质和提高其生态系统稳定性的重要手段.本研究通过构建大型围隔,根据水生植物的耐污程度及其对水质和底质等条件的需求,选取几种适宜的水生植物在围隔内进行移栽与群落构建,并以不移栽水生植物的围隔和围隔外水体作为对照.实验期间(2011年4月至2012年6月),围隔内移栽的几种水生植物全部存活,并建立了相对稳定的群落.同时还跟踪监测了3个处理组的水质情况,结果显示,移栽水生植物的围隔内水质明显优于围隔外,与未移栽水生植物围隔相比,也有很大程度的改善,其中移栽水生植物围隔内水体的总氮、铵态氮、总磷、水下消光系数相比于围隔外水体分别低30.55%、44.09%、36.04%和42.13%,相比于未移栽水生植物围隔内水体分别低5.96%、13.40%、6.70%和7.60%,透明度分别比围隔外水体和未移栽水生植物围隔水体高74.59%和8.70%,浮游植物生物量也大大低于围隔外,而浮游动物生物量却明显高于后者.此外,实验后移栽水生植物围隔内沉积物氮、磷含量及其间隙水总氮、总磷、铵态氮浓度明显低于围隔外和未移栽水生植物围隔.研究表明,在富营养化浅水湖泊中通过建立围隔进行合理的群落配置,进而逐步恢复水生植物是完全可行的,而水生植物恢复后加强对其管理和维护至关重要.     

Linking MODFLOW with an Agent-Based Land-Use Model to Support Decision Making

The U.S. Geological Survey numerical groundwater flow model, MODFLOW, was integrated with an agent-based land-use model to yield a simulator for environmental planning studies. Ultimately, this integrated simulator will be used as a means to organize information, illustrate potential system responses, and facilitate communication within a participatory modeling framework. Initial results show the potential system response to different zoning policy scenarios in terms of the spatial patterns of development, which is referred to as urban form, and consequent impacts on groundwater levels. These results illustrate how the integrated simulator is capable of representing the complexity of the system. From a groundwater modeling perspective, the most important aspect of the integration is that the simulator generates stresses on the groundwater system within the simulation in contrast to the traditional approach that requires the user to specify the stresses through time.     

北京什刹海生态修复试验工程

什刹海是北京市一个小型浅水城市风景游览的富营养湖泊.生态恢复试验工程以物理除藻为前提,通过实施基底修复而后开展水体充氧等手段,达到恢复水生植被的根本目的.应用的修复技术有:(1)臭氧/超声波除藻;(2)基底修复;(3)水下曝气充氧及冬季冰下底部充氧;(4)上游区复合生物浮床;(5)水下光补偿技术;(6)高等水生植物栽植与优化配置;(7)水生植物调控与机械割草;(8)水质净化与保洁管理.工程实施近1年(2001年8月-2002年6月)后效果明显,总氮、总磷分别下降了4.74mg/L和0.45mg/L,去除率达到79%和91%,什刹海的水质也由Ⅴ类上升为Ⅳ类.     

A Nonlinear Model of Contaminant Transformations in an Aquatic Environment

A nonlinear model of the decomposition of a multicomponent contaminant is developed with allowance made for the distribution of components over their reactivity. Model application is illustrated by the analysis of published empirical data on organic matter biodegradation in water column and bottom sediments, in an activated-sludge bioreactor, and the biological absorption and enzymatic destruction of organic matter by macrophytes. Photodestruction, chemical destruction, and sedimentation are also considered. The nonlinear model is compared with a first-order reaction equation.__________Translated from Vodnye Resursy, Vol. 32, No. 3, 2005, pp. 322–336.Original Russian Text Copyright © 2005 by Dolgonosov, Gubernatorova.