Associate Professor Jose Rodriguez

The vulnerability of coastal wetlands to future sea-level rise (SLR) has been extensively studied in recent years, and models of coastal wetland evolution have been developed to assess and quantify the expected impacts. Coastal wetlands respond to SLR by vertical accretion and landward migration. Wetlands accrete due to their capacity to trap sediments and to incorporate dead leaves, branches, stems and roots into the soil, and they migrate driven by the preferred inundation conditions in terms of salinity and oxygen availability. Accretion and migration strongly interact, and they both depend on water flow and sediment distribution within the wetland, so wetlands under the same external flow and sediment forcing but with different configurations will respond differently to SLR. Analyses of wetland response to SLR that do not incorporate realistic consideration of flow and sediment distribution, like the bathtub approach, are likely to result in poor estimates of wetland resilience. Here, we investigate how accretion and migration processes affect wetland response to SLR using a computational framework that includes all relevant hydrodynamic and sediment transport mechanisms that affect vegetation and landscape dynamics, and it is efficient enough computationally to allow the simulation of long time periods. Our framework incorporates two vegetation species, mangrove and saltmarsh, and accounts for the effects of natural and manmade features like inner channels, embankments and flow constrictions due to culverts. We apply our model to simplified domains that represent four different settings found in coastal wetlands, including a case of a tidal flat free from obstructions or drainage features and three other cases incorporating an inner channel, an embankment with a culvert, and a combination of inner channel, embankment and culvert. We use conditions typical of south-eastern Australia in terms of vegetation, tidal range and sediment load, but we also analyse situations with 3 times the sediment load to assess the potential of biophysical feedbacks to produce increased accretion rates. We find that all wetland settings are unable to cope with SLR and disappear by the end of the century, even for the case of increased sediment load. Wetlands with good drainage that improves tidal flushing are more resilient than wetlands with obstacles that result in tidal attenuation and can delay wetland submergence by 20 years. Results from a bathtub model reveal systematic overprediction of wetland resilience to SLR: by the end of the century, half of the wetland survives with a typical sediment load, while the entire wetland survives with increased sediment load.

A quasi-2D unsteady flow and sediment transport model suitable for the simulation of large lowland river systems, including their floodplains, is presented. The water flow and sediment equations are discretised using an interconnected irregular cells scheme, in which different simplifications of the 1D de Saint Venant equations are used to define the discharge laws between cells. Spatially-distributed transport and deposition of fine sediments throughout the river-floodplain system are simulated. The model is applied over a 208-km reach of the Paraná River between the cities of Diamante and Ramallo (Argentina) comprising a river-floodplain area of 8100. km². After calibration and validation, the model is applied to predict water and sediment dynamics during synthetically generated extraordinary floods of 100, 1000, and 10,000 years return period. The potential impact of a 56-km long road embankment constructed across the entire floodplain is simulated and compared to model results without the embankment. The embankment results in increases in upstream water levels, inundation extent, flow duration, and sediment deposition.

A movable bed model was designed in a laboratory flume to simulate a mixed load sand-bed stream. The modelling objectives were to reproduce bedload and suspended sediment transport as well as downstream and transverse sediment fluxes in ratios similar to the field site. To meet these objectives the model contained an exact geometric scale and graded lightweight sediments to simulate migrating dunes and suspended load transport. The experiments are somewhat novel in that most mobile bed models have vertical exaggeration, whereas in these experiments exact geometric similitude of channel dimensions was maintained. The goal of this paper is to review the scaling strategy and the level of similarity among dimensionless parameters between model and field. Similarity in dimensionless bed shear stress and the particle Reynolds number enabled the experiments to replicate the dominant sediment dynamics present in the stream during a bankfull flow. There was a conflict in the strategy, in that grain roughness was exaggerated with respect to nature. However, the paper shows that geometric similarity of bedforms and the resulting drag is much closer to what is predicted for nature. In addition, measurements of sediment transport are compared to values computed from well-supported formulations, which is shown to reinforce the validity of the scaling strategy. Lastly, criteria for movable bed equilibrium are defined and it is shown that lightweight sediments contributed to the rapid development of near-equilibrium conditions. Overall, the paper shows a methodology that can be used to model mixed load streams at an exact geometric scale. © 2014 International Association for Hydro-environment Engineering and Research, Asia Pacific Division.

Mangrove and salt marsh vertical accretion and surface elevation change was measured at Kooragang Island within the Ramsar-listed Lower Hunter estuarine wetlands in New South Wales, Australia, using surface elevation tables and marker horizons over a ten-year period. We surveyed mangrove, salt marsh and a zone of mangrove encroachment into salt marsh. The period of analysis was dominated by El Niño (drought) climatic conditions, though included a series of east coast low pressure systems and associated storms over the central coast of NSW in June 2007. The storms may have initially caused scouring of sediments in the mangrove zone, followed by significant accretion within both the mangrove and salt marsh during the six months following the storms, with most of this accretion corresponding to spring tides several months after the storms. These accretion events were not accompanied by an equivalent elevation change, and robust elevation trends over the study period in mangrove and salt marsh indicate that the storms may have had little impact on the longer-term elevation dynamics within both the mangrove and salt marsh at Kooragang Island. Elevation dynamics in these zones appear to be regulated by vertical accretion over longer time periods and modulated by hydrology at shorter temporal scales. Elevation declined in the mangrove encroachment zone despite continued vertical accretion and we propose that this discrepancy may be associated with expansion of tidal creeks near the zone of mangrove encroachment or loss of salt marsh vegetation. This pattern of encroachment is consistent with observations from sites throughout the region and may be related to climatic perturbations (El Niño Southern Oscillation) rather than directly attributed to the storms. © 2013 Elsevier Ltd.

Time-dependent bed shear stresses induced by the passage of a barge tow have been measured with hot film shear stress sensors in a 1:25 scale model. Conditions typical of those observed for Upper Mississippi River navigation traffic were simulated in the experimental facility. Two sets of experiments were carried out: the first set consisted of simultaneous shear stress measurements at different locations for a variety of flow depths and boat operating conditions, providing space-time distributions of ensemble averaged wall shear stresses. The second set included a large number of realizations gathered for one particular flow condition at a single position, allowing analysis of the time evolution of the turbulence characteristics (i.e., standard deviation) of the bed shear stresses. The results of the first set of experiments show that for all the experimental conditions the basic patterns of the shear stress are similar, with two regions of high shear stress associated with the passage of the bow and the stern of the barge tow, respectively. Analysis of the second set of experiments showed that, as a result of the passage of the barge tow, the bed-shear stress standard deviation departs from the values commonly observed under steady, uniform, open-channel flow conditions. This behavior has important implications for sediment transport.

Many urban and suburban communities in the Midwest are seeking to establish sustainable, morphologically and hydraulically varied, yet dynamically stable fluvial systems that are capable of supporting healthy, biologically diverse aquatic ecosystems - a process known as stream naturalization. This paper describes an integrated research program that seeks to develop a scientific and technological framework to support two stream naturalization projects near Chicago, Illinois. The research program integrates theory and methods in fluvial geomorphology, aquatic ecology, hydraulic engineering and social theory. Both the conceptual and the practical challenges of that integration are discussed. Scientific and technical support emphasize the development of predictive tools to evaluate the performance of possible naturalization designs at scales most appropriate to community based projects. Social analysis focuses on place based evaluations of how communities formulate an environmental vision and then, through decision making, translate this vision into specific stream naturalization strategies. Integration of scientific and technical with social components occurs in the context of community based decision making as the predictive tools are employed by project scientists to help local communities translate their environmental visions into concrete environmental designs. Social analysis of this decision making process reveals how the interplay between the community's vision of what they want the watershed to become, and the scientific perspective on what the watershed can become to achieve the community's environmental goals, leads to the implementation of specific stream naturalization practices.

In order to compute the total amount and vertical distribution of suspended sediment, a reference concentration near the bed or entrainment function is needed, and considerable research effort has been dedicated to obtain such formulae. Several entrainment functions are available in the literature, but all of them have been developed for steady, uniform flow conditions. The ability of such relationships to predict entrainment rates in unsteady flows has not been demonstrated, nor has there been any attempt to develop a general formulation that works for both steady and unsteady flow conditions. The traditional approach relates the entrainment of sediment to the wall shear stress associated with skin friction in a deterministic way, providing only a relation between mean values. An alternative is to consider both the shear stress and the entrainment as stochastic turbulent quantities and to express them in terms of their probability density functions (PDFs). In this way, statistics of the entrainment can be obtained from measured shear stress PDFs, either in steady or unsteady situations, since the effect of unsteadiness is embedded in the PDF. This new methodology was used to estimate sediment entrainment produced by the passage of vessels in the Mississippi River and the Illinois River. Using a low order cumulant expansion to describe the PDF of the shear stress and a generalized version of García and Parker's entrainment relationship, an expression for the average of the entrainment as a function of the average, variance, skewness and flatness of the shear stress distribution was obtained. Predictions compared favorably with values reported in the literature.

Unsteady flows are ubiquitous in nature. In order to understand the behavior of sediment when subjected to unsteady flows, a set of experiments was performed in a rectangular duct with a mobile bed. A computer-operated valve governed the velocity of the water in the duct, and the flow velocity, wall shear stress, and vertical distribution of suspended sediment were simultaneously measured. Beds composed of 120 µm and 580 µm diameter sand were investigated. Both quasi-steady flows and pulse flows were simulated in the duct. For the pulse flows the water was accelerated at a constant rate to a peak velocity and then decelerated at a constant rate to zero velocity. Phase lags were observed between the bed shear stress and the upward flux (entrainment) of sand from the bed. The phase lags were larger for tests with fine sand than for tests with coarse sand. Differences were attributed to differences in bed roughness and flow Reynolds numbers. Relations based on flow acceleration and sediment size were developed for predicting the entrainment phase lag. Large phase lags can have a considerable impact on the amount of sediment transported by boat wakes, waves, and other unsteady flows.

This study investigated the potential to simulate a river basin with significant wetland hydrodynamics within a network flow programming (NFP) framework. The Macquarie River Catchment, which encompasses the Macquarie Marshes, was selected as a case study to test the approach. The Marshes support water-dependent ecological communities which require flooding events, triggered through natural and environmental flows, to inundate wetland areas for ecologically sufficient periods of time. Ecological responses of the Macquarie Marshes with respect to inundation are currently simulated using the Macquarie Valley Integrated Quantity and Quality Model (IQQM). This model represents the Marshes hydraulics using a rules-based algorithm informed by detailed hydrodynamic modelling of the Marshes. However, the model does not have the potential to optimise water resource and ecological management. The primary objective of this study was to use NFP to emulate the Macquarie Marshes hydrodynamics in a manner consistent with the Macquarie Valley IQQM model. This paper presents and evaluates several NFP techniques to emulate the Marshes hydraulics. It was found that iterative use of NFP with side constraints almost exactly matched the emulator rules and implemented them more accurately than the IQQM model. This successful outcome will enable multi-criterion optimisation of the basin operation to deal directly with the ecological responses of water sensitive communities.

The configuration of the Macquarie Marshes is a mosaic-like collection of swamps, marshes and lagoons. The Macquarie Marshes is also one of the most ecologically important wetland systems in Australia. It contains unique plant communities that serve as a sanctuary for many species of waterbirds and other fauna such as frogs and mammals. A significant deterioration of the ecological features of the Macquarie Marshes has been recorded in the past decades. This fact is mostly attributed to reductions of the input discharges to the marshes due to water allocations for industrial, agricultural and domestic usage. Reduction of water supply translates into changes of the hydraulic regime which has a direct impact on the flood dependent vegetation species of the marshes. The complexity of the system and its ecological significance requires the use of an adequate computational tool that would allow for a realistic assessment of the site. In this paper we present initial work regarding the development of a vegetation dynamics model that can integrate vegetation establishment with time aggregated characteristics of the flow. We simulate floods on a fictional wetland by implementing a quasi-2D hydrodynamic model (VHHMM 1.0) over a rectangular cell grid. This same grid constitutes the basis for a cellular vegetation model that can calculate changes in the vegetation for each element inside the domain. The work presented here for a fictional site was developed in order to test the capability of our model to recreate consistent vegetation gradients by using deterministic transitional rules. These rules relate time aggregated characteristics of the flow such as flood period and depth of water to water requirements of different vegetation communities. We found that a well calibrated set of deterministic transitional rules based on water preferences can recreate consistent vegetation distributions; however, succession and critical conditions for succession rules will have to be defined for a specific site application. Further development of this model will result in a strategic tool for managing environmental water allocations and water sharing plans in the Macquarie Marshes.

Pool-riffle sequences are one of the most common geomorphological features in many streams and provide important habitat diversity both in terms of flow and substrate. The conditions for their formation and self-maintenance are still the subject of active research, but it has become clear in later years that a combination of three mechanisms: 1) stage-dependent flow conditions, 2) three-dimensional flow patterns and 3) selective sediment transport over a mobile bed, can explain the resilience and ubiquity of pool-riffle sequences observed in the field. In this paper, we analyze the importance of these three mechanisms using different combinations of stage-dependent three-dimensional flow patterns in pool-riffle sequences and sediment size distributions obtained in both pools and riffles. Self-maintenance mechanisms are identified by evaluating erosional or depositional tendencies in pools and riffles for different flow conditions using local values of bed shear stress and their corresponding fractional sediment transport volumes. Self-maintenance is directly linked to episodes of pool erosion and riffle deposition and we use the term sediment transport reversal rates to indicate this situation, rather than velocity reversal or shear stress reversal that only consider flow variables. This approach allows us to compare, for the first time, the relative importance of each of the mechanisms and their role in the self-maintenance of these bedforms, which can vary from site to site. Computations are performed using existing field, laboratory and numerical simulation data from several study sites. We discuss the limitations of our approach and the extensions to more complex field cases.

This work presents preliminary results of implementing a quasi-2D hydrodynamic module (VMMHH 1.0) to simulate flows and flooding patterns throughout the Macquarie Marshes, south east Australia, in order to assess habitat requirements. The model uses an interconnected cell scheme that solves mass conservation and uses simplified versions of the momentum equations to represent flow between cells. This model has been used before to assess geomorphological changes in large river floodplains and vegetation evolution in estuarine wetlands, showing results consistent with cases of gradual floodplain inundation following overbank flow. The simplified characteristics of the quasi-2D model allow for an adequate representation of hydrodynamic processes with similar performance of other higher dimensional models. Model results and computational times are compared with outputs from a conventional 1D/2D model (MIKE FLOOD) applied to the same domain showing that the VMMHH 1.0 is adequate for representation of floods in the Macquarie Marshes.

Coastal salt marsh provides important roost habitat for migratory shorebirds. In Australia, its distribution appears to be following a global trend of decline, as it is squeezed between landward encroachment of mangrove forest and urban/industrial development of foreshore land. Efforts to maintain and rehabilitate salt marsh are hampered by an incomplete understanding of the complex ecological processes that govern estuarine vegetation distribution. Our research is focused on the hydraulic and geomorphologic conditions required to sustain salt marsh in a rehabilitated wetland in the Hunter estuary. The effect of culvert removal on habitat availability for migratory shorebirds is examined through high resolution mapping of tidal inundation, topographic elevation and habitat distribution, and measurement of the flow field at discrete locations using acoustic Doppler velocimeters. This analysis has allowed development of habitat zonation curves for areas of attenuated and unattenuated tidal flow in the study area, which support the landward migration of mangroves following culvert removal. Characterisation of the hydraulic flow field has identified significant differences in velocity and turbulent kinetic energy that have wider implications for rates of sediment accretion in estuarine wetlands.

Channelization limits the geomorphological and biological diversity of many urban streams. This paper presents a pool-riffle design for straight urban streams where existing infrastructure prevents re-alignment of channel planform. The design of the pool-riffle units is the result of a multi-disciplinary approach, which includes ecological, geomorphological and engineering aspects. The proposed structures fulfill four main requirements: they increase flow variability during low and moderate flows; they produce minimal increase in the water levels during high flows; they self-maintain in terms of bed erosion and sediment deposition, and they provide in-stream habitat for fish. The hydraulic performance of the design was tested at two different scales using two existing models: FLOW-3D® at the pool-riffle unit scale and HEC-RAS at the reach scale. Copyright ASCE 2004.

In the present paper, two different models of bank erosion are analyzed. The first model consists of a linear relation between bank erosion rate and near-bank excess velocity that is used by most planform evolution models. The second formulation is a bank failure model that consider in more detail the dynamics of bank erosion, but has been applied mainly for the case of straight reaches. Using the bank failure model, an analytical expression for the erosion coefficient is obtained, which depends explicitly on resistive properties of the banks, on the near bank perturbation velocity and on the streamwise cross sectional averaged velocity. The present analysis also considers bank retreat as a stepwise phenomenon triggered by a critical value of the localized erosion. Copyright ASCE 2004.

In many urban watersheds, physical habitat degradation rather than water quality degradation has reduced fish community abundance and diversity. Engineering methods are needed to restore degraded stream habitat under conditions of modified hydrologic regimes and land-use constraints on channel planform. Habitat improvement can then be considered an essential component of stormwater management programs. We implemented a design methodology, known as stream naturalization, with the Village of Northbrook, Illinois to improve stream habitat as part of a city-center 0.8-km riverwalk development. Habitat improvement focused on design of pool-riffle structures. Pool-riffle structures were proposed because geomorphic/habitat and bioassessment surveys found irregular pool spacing and lack of deep pools greater than a depth of 0.8 m, limited habitat quality and fish abundance. Simulation of the hydraulic performance of the proposed pool-riffle structures was completed using FLOW3D®, a three-dimensional hydrodynamics model. Velocities from simulations provided data to size bed material, ensuring a stable structure while allowing transport of small particles through pools. The model predicted a natural flow field with lateral convergence-divergence rotating cells providing habitat diversity both hydraulically and morphologically. Pool-riffle structures were constructed in the fall 2001 and winter 2002.

Channelization limits the geomorphological and biological diversity of many urban streams. Whenever the existing infrastructure prevents re-alignment of the channel planform, in-channel structures of the pool-riffle type offer an alternative means to provide some degree of variability in the flow pattern. This paper presents mean flow and turbulence measurements obtained on a physical model of pool-riffle structures designed to restore low gradient streams in heavily urbanized areas. The data collected include high-resolution 3D velocities as well as water surface elevations for different flow conditions. The results show that the flow is highly three-dimensional, and that the effect of the structures is more important for low flow conditions. Also, flow patterns resemble that of natural pool-riffle sequences. Implications for sediment transport, bed and bank morphology and aquatic habitat are analyzed.