Hydraulic Jet Control for River Junction Design of Yuen Long Bypass Floodway, Hong Kong

The Yuen Long Bypass Floodway (YLBF) was designed to collect flows from the Sham Chung River (SCR) and the San Hui Nullah (SHN) and to serve as a diversion channel of the Yuen Long Main Nullah (YLMN). Under a 200-year return period design condition, the floodway was designed (1) to divert a flow of approximately 38?m3/s from the supercritical YLMN flow and (2) to convey a total combined flow of 278?m3/s to downstream within acceptable flood levels. The success of the design depends critically on complicated junction flow interactions that cannot be resolved by 1D unsteady flow models. These features include the supercritical-subcritical flow transition at the San Hui-Floodway (SHN-YLBF) junction and the diversion of part of the supercritical flow from the Main Nullah (YLMN). A laboratory Froude scale physical model was constructed to study water stages and flow characteristics in the floodway and to investigate optimal design arrangements at channel junctions and transitions. This paper summarizes the main features of the unique river junction network, in particular the use of the hydraulic jet principle at the SHN-YLBF junction to lower flood levels. In addition, a numerical flow model is employed to study flow details at the river junctions. The model is based on the general 2D shallow water equations in strong conservation form. The equations are discretized using the total variation diminishing finite-volume method which captures the discontinuity in hydraulic jumps. The numerical model predictions are well supported by the laboratory data, and the theoretical and experimental results offer useful insights for the design of urban flood control schemes under tight space constraints.     

Prediction of Future Uniform Milk Prices in Florida Federal Milk Marketing Order 6 from Milk Futures Markets

This study assessed the accuracy of 3 methods that predict the uniform milk price in Federal Milk Marketing Order 6 (Florida). Predictions were made for 1 to 12 mo into the future. Data were from January 2003 to May 2007. The CURRENT method assumed that future uniform milk prices were equal to the last announced uniform milk price. The F+BASIS and F+UTIL methods were based on the milk futures markets because the futures prices reflect the market's expectation of the class III and class IV cash prices that are announced monthly by USDA. The F+BASIS method added an exponentially weighted moving average of the difference between the class III cash price and the historical uniform milk price (also known as basis) to the class III futures price. The F+UTIL method used the class III and class IV futures prices, the most recently announced butter price, and historical utilizations to predict the skim milk prices, butterfat prices, and utilizations in all 4 classes. Predictions of future utilizations were made with a Holt-Winters smoothing method. Federal Milk Marketing Order 6 had high class I utilization (85 ± 4.8%). Mean and standard deviation of the class III and class IV cash prices were $13.39 ± 2.40/cwt (1 cwt = 45.36 kg) and $12.06 ± 1.80/cwt, respectively. The actual uniform price in Tampa, Florida, was $16.62 ± 2.16/cwt. The basis was $3.23 ± 1.23/cwt. The F+BASIS and F+UTIL predictions were generally too low during the period considered because the class III cash prices were greater than the corresponding class III futures prices. For the 1- to 6-mo-ahead predictions, the root of the mean squared prediction errors from the F+BASIS method were $1.12, $1.20, $1.55, $1.91, $2.16, and $2.34/cwt, respectively. The root of the mean squared prediction errors ranged from $2.50 to $2.73/cwt for predictions up to 12 mo ahead. Results from the F+UTIL method were similar. The accuracies of the F+BASIS and F+UTIL methods for all 12 fore-cast horizons were not significantly different. Application of the modified Mariano-Diebold tests showed that no method included all the information contained in the other methods. In conclusion, both F+BASIS and F+UTIL methods tended to more accurately predict the future uniform milk prices than the CURRENT method, but prediction errors could be substantial even a few months into the future. The majority of the prediction error was caused by the inefficiency of the futures markets to predict the class III cash prices.     

Dispersion Model for Tidal Wetlands

Tidal wetlands in California are mostly estuarine salt marshes characterized by tidal channels and mudflats that are flooded and drained on a semidiurnal basis. Depths are rarely greater than 2 or 3 m, except where dredging occurs for harbor operations, and lengths from head to mouth are usually in the range of 1–10 km. This paper presents a coupled set of models for prediction of flow, solute transport, and particle transport in these systems. The flow and solute transport models are based upon depth-integrated conservation equations while the particle transport model is quasi-three-dimensional. Common to these models is an assumption that a turbulent boundary layer extends vertically from the bed and can be described by the law of the wall. This feature of the model accounts for: (1) momentum transfer to the bed, (2) longitudinal dispersion of dissolved material based on the work of Elder (1959), and (3) advection and turbulent diffusion of particles in three dimensions. A total variation diminishing finite volume scheme is used to solve the depth-integrated equations. Using this model, we show that dispersion can be accurately modeled using physically meaningful mixing coefficients. Calibration is therefore directed at modifying bed roughness, which scales both the rate of advection and dispersion.     

A bio-electrochemical reactor coupled with adsorber for the removal of nitrate and inhibitory pesticide

In this study, the treatment characteristics of nitrate and toxic pesticide by a combined bioelectrochemical reactor (BER)/adsorption process was investigated. Experimental results showed that the disappearance of NO3- in BER was in accordance with the applied current. NO2- was not detected in the effluent, but the production of N2O was increased with increasing IPT loading. In the presence of IPT, up to 30% of the nitrate nitrogen consumed was converted to N2O, while more than 95% converted to N2 in the absence of IPT. In adsorption column, IPT was efficiently removed onto either granular activated carbon or silicone resin so as to meet the guideline value (40 microg/I) and to reduce the N2O accumulation. A simplified kinetic model that considers the sequential reduction of nitrate and inhibition of the N2O reduction step by pesticide as well as Langmuir adsorption isotherm was developed and used to evaluate the process performance. Theoretically predicted effluent concentrations were in good agreement with the observed results for nitrate, nitrite, N2O, N2 and IPT. It was considered that high removal performance of nitrate and pesticide by the combined process is attributable to high affinity of adsorbates for IPT in comparison with relatively large inhibition constant (Ki).     

Hydrodynamic modeling and characterizing of Lagrangian flows in the West Scott Creek wetlands system,South Carolina

With increased recognition of the value of tidal wetlands and their defining hydrology, the need for better understanding of tidal flow and mixing characteristics is vital to any wetland restoration and enhancement projects and studies. A numerical modeling study was carried out to study the mixing and transport processes in the tide dominated West Scott Creek Estuary, South Carolina. The West Scott Creek estuary is a system of meandering tidal creeks and salt marsh between Edisto Island and the Edisto Beach barrier island. A coupled, depth-integrated hydrodynamic and particle transport model was developed. The model was calibrated and verified against a set of field-measured hydrodynamic data and the model-predicted water elevations, velocities and discharges were in good agreement with the field measurements. The hydrodynamically calibrated model was coupled with a particle tracking module to quantify the residence time distribution and associated transport mechanisms in a spatially varying situation. Computed residence time distribution, under tidal forcing, indicates a strong spatial variation and a non-monotonic distribution along the thalweg of the creek. The model computed a residence time of 4.92 days at the head of the creek. Numerical analysis of the Lagrangian flow field indicated varying mixing regions (strong and weak) within the wetland and the result is anticipated to provide useful information to assess the impact of coastal development in and around the West Scott Creek estuary including the restoration of tidal hydrology.     

Characteristics and quality of gum arabic from naturally grown Acacia senegal (Linne) Willd. trees in the Central Rift Valley of Ethiopia

Drylands of Ethiopia, including those in the Rift Valley, host good potential for commercial production of natural gums such as gum arabic. However, little researches have assessed the qualities of these gums for their commercial and industrial promotions. The objectives of this study were to assess the (i) quality of gum arabic collected from naturally grown Acacia senegal trees in the Central Rift Valley of Ethiopia and (ii) evaluate these quality characteristics against reported quality attributes of the same kind of gum from known destinations such as the Sudan and with international specifications. Gum samples were collected from randomly identified 10 trees of A. senegal in the study area and composited into one big sample by putting all in one plastic bag. The characteristics analyzed included: color, odor, moisture content, ash content, viscosity, pH, specific rotation, N and tannin contents, and concentration of several metals using standard laboratory procedures. The results yielded moisture content of 15%, ash content of 3.56%, intrinsic viscosity of 1.19 ml g⁻¹, pH on 25% solution of 4.04, specific rotation of −32.5, nitrogen content of 0.35%, protein content of 2.31% and with no tannin content. Mineral contents of the gum arabic (g/100 g) are Ca 0.7, Mg 0.2, Na 0.01, K 0.95, Fe 0.001, P 0.6 and non-detectable traces of Pb, Co, Cu, Zn, Ni, Cd, Cr and Mn. These values agree well with values of same quality characteristics of gum arabic reported from Sudan and other exporting countries, and also conform well to international standards in all aspects. Indeed, it is possible to utilize the gum arabic resource of the Central Rift Valley of Ethiopia for commercial and/or industrial purposes.     

Diffusional Mass Transfer at Sediment–Water Interface of Cylindrical Sediment Oxygen Demand Chamber

Diffusional mass transfer of dissolved substances across the sediment–water interface in coastal waters is an important factor for realistic determination of sediment oxygen demand (SOD) and nutrient recycle. The benthic diffusive boundary layer inside a cylindrical chamber commonly deployed for in situ measurements of sediment oxygen demand is studied. In a series of laboratory experiments, the SOD is measured with the chamber operated in both continuous flow and batch modes, and a microelectrode is employed to measure the near bed dissolved oxygen (DO) profile for different chamber flows and sediment types. The dependence of the diffusive boundary layer thickness and the sediment–water mass transfer coefficient on the hydraulic parameters are quantified. Using the derived mass transfer coefficient, it is shown that for a given sediment type, the SOD is a function of the bulk DO concentration and chamber flowrate. The theoretical predictions are validated by both laboratory and field SOD data.