Gengxin Ou

Determination of the anisotropy of an upper streambed layer in east-central Nebraska, USA

Information on the anisotropy of streambed hydraulic conductivity (K) is a necessity for analyses of water exchange and solute transport in the hyporheic zone. An approach is proposed for the determination of K, developed from existing in-situ permeameter test methods. The approach is based on determination of vertical and horizontal hydraulic conductivity of streambed sediments on-site and eliminates the effects of vertical flow in the hyporheic zone and stream-stage fluctuation, which normally influence in situ permeameter tests. The approach was applied to seven study sites on four tributaries of the Platte River in east-central Nebraska, USA. On-site permeameter tests conducted on about 172 streambed cores for the determination of vertical hydraulic conductivity (Kv) and horizontal hydraulic conductivity (Kh) at the study sites indicate that the study sites have relatively small anisotropic ratios, ranging from 0.74 to 2.40. The ratios of Kh to Kv from individual locations within a study site show greater variation than the anisotropic ratios from the mean or median K at each of the study sites.RésuméL’information sur l’anisotropie de la conductivité hydraulique (K) est nécessaire pour les analyses d’échange d’eau et de transport de soluté dans la zone hyporhéique. Une démarche est proposée pour la détermination de K, dérivée de méthodes existantes de test au perméamètre in situ. La démarche est basée sur la détermination sur site des conductivités hydrauliques verticale et horizontale des sédiments du lit et élimine les effets du flux vertical dans la zone hyporhéique et de la fluctuation du niveau d’eau, qui influencent normalement les tests perméamètre in situ. La démarche a été menée sur sept sites d’étude sur quatre tributaires de la Platte River, Centre-Est Nebraska, USA. Des tests de perméabilité sur site réalisés sur environ 172 carottes pour la détermination des conductivités hydrauliques verticale (Kv) et horizontale (Kh) indiquent des ratios d’anisotropie relativement petits, s’échelonnant de 0.74 à 2.40. Les ratios de Kh sur Kv mesurés sur différents emplacements d’un même site montrent une plus grande variabilité que les ratios d’anisotropie de la moyenne ou de la médiane de K sur chacun de ces sites d’étude.ResumenLa información sobre la anisotropía de la conductividad hidráulica de un cauce (K) es una necesidad para los análisis del intercambio de agua y transporte de solutos en una zona hiporreica. Se propone un método para la determinación de K, desarrollado a partir de métodos de prueba in situ en permeámetros existentes. El método está basado en la determinación de la conductividad hidráulica vertical y horizontal de los sedimentos del cauce en el sitio y elimina los efectos del flujo vertical en la zona hiporreica y las fluctuaciones del estado de la corriente, la cual normalmente influye en las pruebas in situ con los permeámetros. El método fue aplicado en siete sitios de estudio en cuatro tributarios del Platte River en el centro este de Nebraska, EEUU. En los lugares de las pruebas en los permeámetros se llevaron a cabo 172 testigos en el cauce para la determinación de la conductividad hidráulica vertical (Kv) y la conductividad hidráulica horizontal (Kh) en los sitios de estudios indican que los sitios de estudio tienen un cociente de anisotropía relativamente pequeña, oscilando de 0.74 a 2.40. Los cocientes de Kh a Kv a partir de lugares individuales dentro del sitio de estudio muestran mayores variaciones que los cocientes de anisotropía a partir de la K media o mediana en cada uno de los sitios estudiados.摘要河床渗透系数的各向异性比是进行河流潜流带水量交换和溶质运移分析时必不可少的重要信息。本文提出一种测定河床渗透系数的改进渗透方法,该方法是基于原位渗透试验的改进。改进试验中采用非原位操作方法,避免了河水位波动和河流潜流带垂向流对原位试验的影响。本研究采用改进的非原位渗透试验方法分别应用在美国内布拉斯加州中东部普拉特河的四条支流上的七个试验场地。非原位渗透试验共计测定172组河床砂样的垂向渗透系数(Kv)和水平渗透系数(Kh)。结果表明这些试验场地具有较弱的各向异性特征,各向异性比介于0.74和2.40之间。在任意试验场地内,每个试验位置上的Kh/Kv值与使用该场地的Kh与Kv的平均值(或中位数)得到的各向异性比相比,具有更大的变异性。ResumoA informação acerca da anisotropia da condutividade hidráulica (K) do sedimento do leito de rios é uma necessidade para as análises de trocas de água e transporte de solutos na zona hiporreica. Propõe-se uma metodologia para determinar K, desenvolvida a partir de métodos existentes de ensaios de permeâmetro in situ. A metodologia é baseada na determinação, no local, da condutividade hidráulica vertical e horizontal de sedimentos do leito de rios e elimina os efeitos do fluxo vertical na zona hiporreica e da flutuação do nível do rio, que normalmente influenciam os ensaios de permeâmetro in situ. A metodologia foi aplicada a sete casos de estudo em quatro afluentes do rio Platte no Centro-este de Nebraska, nos EUA. Os ensaios de permeâmetro in situ, feitos em cerca de 172 sondagens em sedimentos dos leitos de rios, para a determinação da condutividade hidráulica vertical (Kv) e condutividade hidráulica horizontal (Kh) indicam que as zonas de estudo têm rácios de anisotropia relativamente baixos, variando entre 0.74 e 2.40. Os rácios entre Kh e Kv de locais individuais dentro de uma zona de estudo mostram uma variação maior do que os rácios de anisotropia da K média ou mediana em cada uma das zonas de estudo.

Evaluating Hydrologically Connected Surface Water and Groundwater Using a Groundwater Model

Determination of the nature and extent of the connection between groundwater and surface water is of paramount importance to managing water supplies. The development of analyses that detail the surface water-groundwater system may lead to more effective utilization of available water. A tool was developed to help determine the effects of groundwater and surface water interactions. The software tool includes two graphic user interfaces to allow full compatibility with numerical MODFLOW groundwater models. This case study shows the tool, in conjunction with MODFLOW groundwater models and carefully designed scenarios, can successfully calculate the rates of stream-groundwater interactions, thereby providing the basis for designating management areas with the most significant hydrologic impact. This tool can be applied in other regions with similar settings and needs for integrated water management.

SMPP: The Spreadsheet-Based MODFLOW Pre-Processor

Several packages in MODFLOW 2000 (or a later version), such as the Farm Process package (FMP), were developed to better simulate the groundwater flow system and its related water and nonwater components. These newly developed packages are more data demanding because they use more sophisticated algorithms to closely represent real hydrological processes. Substantial analysis of the spatial and temporal data sets is required to generate the correct model files. The Spreadsheet-Based MODFLOW Pre-Processor (SMPP) was developed to support efficient handling of data in the FMP and other MODFLOW packages. The final results from SMPP are input files for the MODFLOW packages. SMPP was developed in Microsoft Excel using Visual Basic Application (VBA) scripts and is therefore intended to be used in Microsoft Excel 2010 or later with other GIS tools. It gathers all the needed data for model establishment in the embedded spreadsheets. The spreadsheet format was chosen because (1) this data processing tool is familiar to groundwater modelers; (2) the formulas are flexible and the results are calculated instantly; and (3) it provides prompt graphical or visual representations. Therefore, modelers can readily perform complicated analyses of large amounts of groundwater data with spreadsheets (Hunt 2005). The need for spatial information is increasing in MODFLOW models because the new packages involve more sophisticated algorithms and higher precision in representing hydrologic elements in spatial scales. However, carrying out complicated spatial analysis tasks using the groundwater modeling GUI software could be more challenging than using GIS tools. SMPP is designed to adopt