Travertine crystal growth ripples record the hydraulic history of ancient Rome's Anio Novus aqueduct.

Travertine crystal growth ripples are used to reconstruct the early hydraulic history of the Anio Novus aqueduct of ancient Rome. These crystalline morphologies deposited within the aqueduct channel record the hydraulic history of gravity-driven turbulent flow at the time of Roman operation. The wavelength, amplitude, and steepness of these travertine crystal growth ripples indicate that large-scale sustained aqueduct flows scaled directly with the thickness of the aqueous viscous sublayer. Resulting critical shear Reynolds numbers are comparable with those reconstructed from heat/mass transfer crystalline ripples formed in other natural and engineered environments. This includes sediment transport in rivers, lakes, and oceans, chemical precipitation and dissolution in caves, and melting and freezing in ice. Where flow depth and perimeter could be reconstructed from the distribution and stratigraphy of the travertine within the Anio Novus aqueduct, flow velocity and rate have been quantified by deriving roughness-flow relationships that are independent of water temperature. More generally, under conditions of near-constant water temperature and kinematic viscosity within the Anio Novus aqueduct channel, the travertine crystal growth ripple wavelengths increased with decreasing flow velocity, indicating that systematic changes took place in flow rate during travertine deposition. This study establishes that travertine crystal growth ripples such as those preserved in the Anio Novus provide a sensitive record of past hydraulic conditions, which can be similarly reconstructed from travertine deposited in other ancient water conveyance and storage systems around the world.

Three-dimensional model to capture the fate and transport of combined sewer overflow discharges: A case study in the Chicago Area Waterway System.

We used a numerical model to analyze the impact of combined sewer overflows (CSOs) in the hydrodynamics and water quality of the Chicago Area Waterway System (CAWS). We coupled the Environmental Fluid Dynamics Code (EFDC) with the Water Quality Analysis Simulation Program (WASP) to perform three-dimensional simulations of the hydrodynamics and water quality in CAWS. The analysis was performed for two different storms: (i) May 6, 2009 representing a 6-hour duration 4-month return period, and (ii) September 12, 2008 representing a 48-hour duration 100-year return period. Results from the simulations show distinct differences between the two storms. During the May 2009 storm there was only one major CSO pumping event with negligible impact on the water quality of CAWS. During the September 2008 storm there were several CSOs that impacted the hydrodynamics and water quality of CAWS. In particular, CSOs during the September 2008 event induced a reversal flow in CAWS, with a plume of constituents that traveled in the opposite direction as water does under normal conditions. However, the simulation results show that CSOs events in CAWS take place during periods of high rainfall, thus the discharge of CSOs is significantly diluted along the CAWS. As a result, the concentrations of organic matter and inorganic nutrients observed at the downstream boundary in CAWS were significantly lower than those recorded at the CSOs outfalls and are within the limits established in the regulation for regular effluents. These results suggest that even during storms events with significant CSOs into the CAWS there is a significant dilution that reduce the impact in the water quality at the system boundaries.

Implications of Climate Change on the Heat Budget of Lentic Systems Used for Power Station Cooling: Case Study Clinton Lake, Illinois.

We use a numerical model to analyze the impact of climate change-in particular higher air temperatures-on a nuclear power station that recirculates the water from a reservoir for cooling. The model solves the hydrodynamics, the transfer of heat in the reservoir, and the energy balance at the surface. We use the numerical model to (i) quantify the heat budget in the reservoir and determine how this budget is affected by the combined effect of the power station and climate change and (ii) quantify the impact of climate change on both the downstream thermal pollution and the power station capacity. We consider four different scenarios of climate change. Results of simulations show that climate change will reduce the ability to dissipate heat to the atmosphere and therefore the cooling capacity of the reservoir. We observed an increase of 25% in the thermal load downstream of the reservoir, and a reduction in the capacity of the power station of 18% during the summer months for the worst-case climate change scenario tested. These results suggest that climate change is an important threat for both the downstream thermal pollution and the generation of electricity by power stations that use lentic systems for cooling.

A Laboratory Investigation of the Suspension, Transport, and Settling of Silver Carp Eggs Using Synthetic Surrogates.

Asian carp eggs are semi-buoyant and must remain suspended in the water to survive, supported by the turbulence of the flow, until they hatch and develop the ability to swim. Analysis of the transport and dispersal patterns of Asian carp eggs will facilitate the development and implementation of control strategies to target the early life stages. Experimenting with Asian carp eggs is complicated due to practical issues of obtaining eggs in close proximity to experimental facilities and extensive handling of eggs tends to damage them. Herein, we describe laboratory experiments using styrene beads (4.85 mm diameter) as synthetic surrogate eggs to mimic the physical properties of water-hardened silver carp eggs. The first set of experiments was completed in a rectangular vertical column filled with salt water. The salinity of the water was adjusted in an iterative fashion to obtain a close approximation of the fall velocity of the styrene beads to the mean fall velocity of silver carp water-hardened eggs. The terminal fall velocity of synthetic eggs was measured using an image processing method. The second set of experiments was performed in a temperature-controlled recirculatory flume with a sediment bed. The flume was filled with salt water, and synthetic eggs were allowed to drift under different flow conditions. Drifting behavior, suspension conditions, and settling characteristics of synthetic eggs were observed. At high velocities, eggs were suspended and distributed through the water column. Eggs that touched the sediment bed were re-entrained by the flow. Eggs saltated when they touched the bed, especially at moderate velocities and with a relatively flat bed. At lower velocities, some settling of the eggs was observed. With lower velocities and a flat bed, eggs were trapped near the walls of the flume. When bedforms were present, eggs were trapped in the lee of the bedforms in addition to being trapped near the flume walls. Results of this research study provide insights about transport, suspension, and dispersion of silver carp eggs. The knowledge gained from this study is useful to characterize the critical hydrodynamic conditions of the flow at which surrogates for silver carp water-hardened eggs settle out of suspension, and provides insight into how eggs may interact with riverbed sediments and morphology.

Assessment of floodplain vulnerability during extreme Mississippi River flood 2011.

Regional change in the variability and magnitude of flooding could be a major consequence of future global climate change. Extreme floods have the capacity to rapidly transform landscapes and expose landscape vulnerabilities through highly variable spatial patterns of inundation, erosion, and deposition. We use the historic activation of the Birds Point-New Madrid Floodway during the Mississippi and Ohio River Flooding of 2011 as a scientifically unique stress experiment to analyze indicators of floodplain vulnerability. We use pre- and postflood airborne Light Detection and Ranging data sets to locate erosional and depositional hotspots over the 540 km(2) agricultural Floodway. While riparian vegetation between the river and the main levee breach likely prevented widespread deposition, localized scour and deposition occurred near the levee breaches. Eroded gullies nearly 1 km in length were observed at a low ridge of a relict meander scar of the Mississippi River. Our flow modeling and spatial mapping analysis attributes this vulnerability to a combination of erodible soils, flow acceleration associated with legacy fluvial landforms, and a lack of woody vegetation to anchor soil and enhance flow resistance. Results from this study could guide future mitigation and adaptation measures in cases of extreme flooding.

Density currents in the Chicago River: characterization, effects on water quality, and potential sources.

Bidirectional flows in a river system can occur under stratified flow conditions and in addition to creating significant errors in discharge estimates, the upstream propagating currents are capable of transporting contaminants and affecting water quality. Detailed field observations of bidirectional flows were made in the Chicago River in Chicago, Illinois in the winter of 2005-06. Using multiple acoustic Doppler current profilers simultaneously with a water-quality profiler, the formation of upstream propagating density currents within the Chicago River both as an underflow and an overflow was observed on three occasions. Density differences driving the flow primarily arise from salinity differences between intersecting branches of the Chicago River, whereas water temperature is secondary in the creation of these currents. Deicing salts appear to be the primary source of salinity in the North Branch of the Chicago River, entering the waterway through direct runoff and effluent from a wastewater-treatment plant in a large metropolitan area primarily served by combined sewers. Water-quality assessments of the Chicago River may underestimate (or overestimate) the impairment of the river because standard water-quality monitoring practices do not account for density-driven underflows (or overflows). Chloride concentrations near the riverbed can significantly exceed concentrations at the river surface during underflows indicating that full-depth parameter profiles are necessary for accurate water-quality assessments in urban environments where application of deicing salt is common.

Noise-resolution trade-off in projection algorithms for laser diffraction particle sizing.

The size distribution of a particle suspension can be inferred from studying the diffracted light pattern produced by a laser beam that passes through the suspension. This involves solving an ill-posed linear system. Two previous versions of projection algorithms were tested by use of computer simulations and experiments. Both algorithms showed limitations in restoring the size distribution, because of either the shape of the size distribution or the presence of noise in the scattered light signal. The generalized projection algorithm presented in this work solves these difficulties by introducing a parameter that allows the user to adjust the noise-resolution trade-off, making it suitable for the analysis of natural suspensions.