Jorge D. Abad

RVR Meander: A toolbox for re-meandering of channelized streams

RVR Meander was developed as a toolbox for modeling restoration and naturalization processes in rivers. This model includes Windows-based and Geographical Information System-based programs for analyzing and modeling planform migration of streams. In the past, several rivers have been channelized causing environmental and ecological problems. Restoration techniques evolve as natural solutions to channelization, therefore, the prediction of planform migration in rivers is indispensable for economic and social reasons such as development of urban areas close to rivers, prevention of damages to infrastructure, reduction of agricultural land losses, and for the maintenance of biological diversity in rivers. Abad and Garcia [2004, Conceptual and mathematical model for evolution of meandering rivers in naturalization processes. On CD-ROM of Proceedings of Joint Conference on Water Resources Engineering and Water Resources Planning and Management, ASCE, June 27-July 1, Salt Lake City, Utah, 10pp.] presented a conceptual and mathematical model for evolution of meandering rivers that can be used in restoration and naturalization processes. In this work, the description of RVR Meander is based on the computational characteristics and applicability rather than presenting its theoretical basis. RVR Meander is an object oriented user-friendly model for restoration purposes. Two modules are included: statistical analysis and planform migration of rivers. This model has been successfully tested on Microsoft Windows NT 4.0/2000/XP and on ArcMap 8.1/8.2/8.3.

Modification of meander migration by bank failures

Meander migration and planform evolution depend on the resistance to erosion of the floodplain materials. To date, research to quantify meandering river adjustment has largely focused on resistance to erosion properties that vary horizontally. This paper evaluates the combined effect of horizontal and vertical floodplain material heterogeneity on meander migration by simulating fluvial erosion and cantilever and planar bank mass failure processes responsible for bank retreat. The impact of stream bank failures on meander migration is conceptualized in our RVR Meander model through a bank armoring factor associated with the dynamics of slump blocks produced by cantilever and planar failures. Simulation periods smaller than the time to cutoff are considered, such that all planform complexity is caused by bank erosion processes and floodplain heterogeneity and not by cutoff dynamics. Cantilever failure continuously affects meander migration, because it is primarily controlled by the fluvial erosion at the bank toe. Hence, it impacts migration rates and meander shapes through the horizontal and vertical distribution of erodibility of floodplain materials. Planar failures are more episodic. However, in floodplain areas characterized by less cohesive materials, they can affect meander evolution in a sustained way and produce preferential migration patterns. Model results show that besides the hydrodynamics, bed morphology and horizontal floodplain heterogeneity, floodplain stratigraphy can significantly affect meander evolution, both in terms of migration rates and planform shapes. Specifically, downstream meander migration can either increase or decrease with respect to the case of a homogeneous floodplain; lateral migration generally decreases as result of bank protection due to slump blocks; and the effect on bend skewness depends on the location and volumes of failed bank material caused by cantilever and planar failures along the bends, with possible achievement of downstream bend skewness under certain conditions.

Modeling Framework for Organic Sediment Resuspension and Oxygen Demand: Case of Bubbly Creek in Chicago

A modeling framework that combines both two-dimensional (2D) and one-dimensional (1D) numerical models for the evaluation of organic-matter transport across the bed-water interface is presented. Emphasis is placed on capturing oxygen demand in the water column associated with the resuspension of organic sediments from the bottom. The proposed numerical approach solves the hydrodynamics coupled with sediment transport and water quality dynamics and represents a substantial improvement to the state of the art of water quality modeling methodologies available in the literature. A biochemical oxygen demand (BOD)–dissolved oxygen (DO) water quality module is incorporated into the 2D depth-averaged numerical model STREMR-HySedWq. The model is applied to the South Fork of the South Branch of the Chicago River, known as Bubbly Creek, with the goal of modeling combined sewer overflow (CSO) events and their impact on DO levels in the short-term (hours or days). Given the intermittent nature of this kind of events, ...

On the analysis of the medium term planform dynamics of meandering rivers

The continuous wavelet transform is applied to the analysis of curvature signals from both synthetic meanders and 52 realizations from 16 natural meanders ranging from class B to class G (Brice classification), thus providing information on the spatial distribution of their arc-wavelength spectrum, and therefore, representing an objective characterization of meanders. Past research has studied the meander dynamics by using the centerline (short-term frame) and the valley centerline (long-term frame). The present study introduces a medium term frame, termed the mean center (MC), which is defined as the medium term coherent wave being present in the meander planimetry for a period that is strongly governed by the occurrence of cutoff events; although in the absence of them, it is present for ∼10 to ∼30 years. The MC is obtained by using a methodology that combines the capabilities of the principal component analysis and the discrete wavelet transforms. The application of wavelet cross correlation shows that peaks in the centerline curvature are strongly correlated with those of the MC suggesting that (1) a linear relationship between them may be associated to bank processes and, (2) in all other cases, a higher nonlinear relationship may be induced by autogenic hydrodynamic processes. In freely meandering rivers, compound bends, multiple loops, and cutoff events are associated to peaks in the MC local curvature. We define the planform amplitudes as the orthogonal distance of the centerline from mean center. Planform amplitudes (orthogonal distance of the centerline from mean center) are normally distributed and ranges from 2 to 20 river mean widths.

Planform evolution of two anabranching structures in the Upper Peruvian Amazon River

We present a study to relate the sinuosity of the main channel and its effect on the dynamics of the secondary channels of anabranching structures. For this purpose, two locations of the Peruvian Amazon River were selected: (1) a site with a medium to high-sinuosity main channel (MS site: Muyuy, Peru) and (2) a site with a low-sinuosity main channel (LS site: at the triple boundary between Brazil, Colombia, and Peru). The main channels for both the MS and LS anabranching structures have freedom to migrate in the lateral direction, while at least one of their secondary channels is adjacent to the geological valley. For MS and LS sites, temporal analysis of planform evolution was carried out using 30 years of satellite imagery from which metrics such as width, sinuosity, and annual maximum migration rates of main and secondary channels were calculated. Additionally, detailed hydrodynamic and bed morphology field measurements were carried out, and a two-dimensional shallow water numerical model was developed. For a medium to high-sinuosity main channel anabranching structure, the secondary channels present a dominant mechanism for reworking the floodplain, while for the low-sinuosity anabranching structure, the main channel planform dynamics is dominant. Flow velocities along the main and secondary channels for low, transition, and high-flow discharges describe that for MS (LS) site, the velocities are much higher along the secondary (main) channels.

Exploratory study of the influence of the wake produced by acoustic doppler velocimeter probes on the water velocities within measurement volume

Acoustic doppler technique is widely used in both fields and laboratory facilities to compute the mean water velocity and to characterize the turbulence of a flow. In general they provide the three dimensional components of flow velocity in a measurement volume in the water body with fairly good spatial and temporal resolution for engineering applications. The most sophisticated devices can even gauge a velocity profile measuring the water velocity in several measurement volumes along a line. However, these devices are semi int rusive which might have, depending on the experimental setup, substantial consequences in the measurements obtained due the flow perturbation created by the probe. The goal of this paper is to explore experimentally and numerically the wake effect of the p robe on the measurement volume in order to validate the measurements provided by this kind of instruments or incorporate some corrections if needed. A computational fluid dynamic (CFD) model is used to simulate an open channel flow where the model was validated with previous experimental results. In the other hand, the laboratory measurements were conducted in an open channel flume located in the Ven Te Chow Hydrosystems Laboratory of the University of Illinois. The measurements were done using particle image velocimetry technique (PIV) producing two dimensional velocity fields around the acoustic probe measurement volume with and without the presence of the probe. The numerical and experimental ranges of Reynolds numbers (Re) tested were 3x10 6 to 1x10 7 and 1x10 4 to 5x10 4 respectively. Non dimensional contour plots showing the difference between the flow velocity and turbulent quantities with and without the probe are built. Both results show that the errors are less than 10 percent around the probe. This methodology is still under development, however it provides more insight for experimental setups and it could be applied to other acoustic doppler instruments such as the ADV (Acoustic Doppler Velocimeter) and ADCP (Acoustic Doppler Current Profiler) among others.

Effect of Sediment Transport Boundary Conditions on the Numerical Modeling of Bed Morphodynamics

AbstractExperimental sediment transport and river morphologic studies in laboratory flumes can use two sediment-supply methods: an imposed feed at the upstream end, or a recirculation of sediment f...

Two-dimensional BOD and DO water quality model for engineering applications: the case of Bubbly Creek in Chicago, Illinois

Bubbly Creek was historically used as a drainage channel for the waste resulting from Chicago’s stockyards. Nowadays there is flow in the creek only during rainfall events resulting in Combined Sewer Overflows (CSO) and water quality is a very important issue, particularly during the summer months, when the dissolved oxygen levels are extremely low and sediment oxygen demand is expected to be large. Due to the particular flow regimes of the creek and the conditions of the benthic sediments in the bed, a special BOD-DO (Biochemical Oxygen Demand Dissolved Oxygen) water quality module was developed and implemented into the two-dimensional depth-averaged numerical model STREMR-HySedWq. The approach illustrated represents a substantial improvement to the state-of-the-art of water quality modeling methodologies. The model was able to capture the key processes and provide useful preliminary results for the two following scenarios: [1] CSO events, for which the model was coupled to a one-dimensional cross-section-averaged BOD-DO water quality model, and [2] potential “purification” solutions, such as flow augmentation and supplemental aeration, with the goal of increasing the DO levels in the creek during dry weather periods. DESCRIPTION OF BUBBLY CREEK

Three-dimensional flow structure and bed morphology in large elongate meander loops with different outer bank roughness characteristics

Few studies have examined the three-dimensional flow structure and bed morphology within elongate loops of large meandering channels. The present study focuses on the spatial patterns of three-dimensional flow structure and bed morphology within two elongate meander loops and examines how differences in outer bank roughness influence near-bank flow characteristics. Three-dimensional velocities were measured during two different events – a near-bankfull flow and an overbank event. Detailed data on channel bathymetry and bedform geometry were obtained during a near-bankfull event. Flow structure within the loops is characterized by strong topographic steering by the point bar, by the development of helical motion associated with flow curvature, and by acceleration of flow where bedrock is exposed along the outer bank. Near-bank velocities during the overbank event are less than those for the near-bankfull flow, highlighting the strong influence of the point bar on redistribution of mass and momentum of the flow at sub-bankfull stages. Multiple outer bank pools are evident within the elongate meander loop with low outer bank roughness, but are not present in the loop with high outer bank roughness, which may reflect the influence of abundant large woody debris on near-bank velocity characteristics. The positions of pools within both loops can be linked to spatial variations in planform curvature. The findings indicate that flow structure and bed morphology in these large elongate loops is similar to that in small elongate loops, but differs somewhat from flow structure and bed morphology reported for experimental elongate loops. This article is protected by copyright. All rights reserved.

Workshop discusses database for Marcellus water issues

ShaleNetwork 2012 Workshop; State College, Pennsylvania, 23–24 April 2012 The largest source of natural gas in the United States, the Marcellus shale, underlies a 95,000-square-mile area from Virginia to New York and from Ohio to Pennsylvania. Since 2005, about 5000 wells have been drilled in Pennsylvania alone, and about 2500 of these are now producing gas. While many welcome the shale gas jobs, others worry about environmental impacts. A workshop was convened at Pennsylvania State University to coordinate the collection of data for water quality and quantity in regions of hydrofracturing. The purpose of the event was to encourage participants to use and contribute data to a growing database of water quality and quantity for regions of shale gas development (www.shalenetwork.org).