Civil Engineering

. In addition, bactericides, Current vegetable production systems use polyethylene (plastic) insecticides, and fungicides required to protect vegetamulch and require multiple applications of agrochemicals. During rain events, runoff from vegetable production is enhanced because 50 to ble crops are known to have adverse effects on finfish, 75% of the field is covered with an impervious surface. This study shellfish, and other aquatic organisms at environmenwas conducted to quantify off-site movement of soil and pesticides tally relevant levels with runoff from tomato (Lycopersicon esculentum Mill.) plots con- Pait et al., 1992; Hetzer et al., 1999 Hetzer et al., , 2000. taining polyethylene mulch and a vegetative mulch, hairy vetch (Vicia Tomatoes are one of the most economically important villosa Roth). Side-by-side field plots were instrumented with autovegetables grown in the USA. The U.S. tomato industry mated flow meters and samplers to measure and collect runoff, which includes both the fresh market and processing tomato was filtered, extracted, and analyzed to determine soil and pesticide industries, which have average annual yields of 3.5 billoss. Seasonal losses of two to four times more water and at least lion pounds (ca. 1.6 billion kg) and 9.8 million tons (ca. 8.9 three times as much sediment were observed from plots with polyethylene mulch (55.4 to 146 L m Ϫ2 and 247 to 535 g m Ϫ2 , respectively) versus million Mg) valued at $1.1 billion and $529 million, plots with hairy vetch residue (13.7 to 75.7 L m Ϫ2 and 32.8 to 118 g respectively (Davis et al., 1998). Fresh-market vegetable m Ϫ2 , respectively). Geometric means (Ϯstandard deviation) of total production generally requires polyethylene (plastic) pesticide loads for chlorothalonil (tetrachloroisophthalonitrile) and mulch to primarily control weeds and to preserve soil ␣and ␤-endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydromoisture. Use of this impervious mulch on 50 to 75% 6,9-methano-2,4,3-benzodioxathiepin 3-oxide) for a runoff event were of the field may cause large amounts of water to run 19, 6, and 9 times greater from polyethylene (800 Ϯ 4.6, 17.6 Ϯ 3.9, off the fields with an intense pulse of agrochemicals and and 39.1 Ϯ 4.9 g m Ϫ2 , respectively) than from hairy vetch mulch plots sediments during rain events. Research from McCall et (42 Ϯ 6.0, 2.8 Ϯ 5.0, and 4.3 Ϯ 4.6 g m Ϫ2 , respectively) due to greater al. (1988) and Wan and El-Swaify (1999) have shown concentrations and larger runoff volumes. The increased runoff volume, soil loss, and off-site loading of pesticides measured in runoff

Climate and soil conditions in South Florida along with an extensive canal system facilitate movement of agricultural pesticides into surface waters. In a two-year study (2002)(2003)(2004) of the currently used pesticides in South Florida, atrazine, endosulfan, metolachlor, chlorpyrifos, and chlorothalonil were the most frequently detected in the canals and in Biscayne Bay, with average concentrations of 16, 11, 9.0, 2.6, and 6.0 ng/L, respectively. Concentrations of atrazine and chlorpyrifos were highest near corn production. Chlorothalonil and endosulfan concentrations were highest near vegetable production, with no clear trend for metolachlor, which is used on multiple crops. Concentration data were used to calculate an aquatic life hazard potential for the planting period (November) versus the harvest period (March). This analysis indicated that a higher hazard potential occurs during harvest, primarily from the use of endosulfan. These data will also serve to document canal conditions prior to implementation of the Comprehensive Everglades Restoration Plan (CERP).

This study was conducted to evaluate the eect of hairy vetch cover crop residue on runo losses of atrazine and metolachlor under both no-till corn ®eld plots and from a laboratory runo system. A 2-year ®eld study was conducted in which losses of atrazine and metolachlor from vetch and non-vetch ®eld plots were determined from the ®rst runo event after application (5 and 25 days after application in 1997 and 1998, respectively). A laboratory study was conducted using soil chambers, designed to simulate ®eld soil, water, vegetation, and herbicide treatment conditions, subjected to simulated rain events of 5, 6, 20 and 21 days after application, similar to the rainfall pattern observed in the ®eld study. Atrazine losses ranged from 1.2 to 7.2% and 0.01 to 0.08% and metolachlor losses ranged from 0.7 to 3.1% and 0.01 to 0.1% of the amount applied for the 1997 and 1998 runo events, respectively. In the laboratory study, atrazine runo losses ranged from 6.7 to 22.7% and 4.2 to 8.5% and metolachlor losses ranged from 3.6 to 9.8% and 1.1 to 4.7% of the amount applied for the 5±6 and 20±21 day events, respectively. The lower losses from the ®eld study were due to smaller rainfall amounts and a series of small rains prior to the runo event that likely washed herbicides o crop residue and into soil where adsorption could occur. Runo losses of both herbicides were slightly higher from non-vetch than vetch ®eld plots. Losses from the laboratory study were related to runo volume rather than vegetation type. Ó

Two long-term no-till corn production studies, representing dierent soil texture, consistently showed higher leaching of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] to groundwater in a silt loam soil than in a sandy loam soil. A laboratory leaching study was initiated using intact soil cores from the two sites to determine whether the soil texture could account for the observed dierences. Six intact soil cores (16 cm dia by 20 cm high) were collected from a four-year old no-till corn plots at each of the two locations (ca. 25 km apart). All cores were mounted in funnels and the saturated hydraulic conductivity K sat was measured. Three cores (from each soil texture) with the lowest K sat were mixed and repacked. All cores were surface treated with 1X7 kgaiha À1 [ringÀ 14 C] atrazine, subjected to simulated rainfall at a constant 12 mm h À1 intensity until nearly 3 pore volume of leachate was collected and analyzed for a total of 14 C. On an average, nearly 40% more of atrazine was leached through the intact silt loam than the sandy loam soil cores. For both the intact and repacked cores, the initial atrazine leaching rates were higher in the silt loam than the sandy loam soils, indicating that macropore¯ow was a more prominent mechanism for atrazine leaching in the silt loam soil. A predominance of macropore¯ow in the silt loam soil, possibly due to greater aggregate stability, may account for the observed leaching patterns for both ®eld and laboratory studies. Ó

By coupling numerical wave model (NWM) and artificial neural networks (ANNs), a new procedure for wave prediction is proposed. In many situations, numerical wave modeling is not justified due to economical consideration. Although incorporation of an ANN model is inexpensive, such a model needs a long time period of wave data for training, which is generally inconvenient to achieve. A proper combination of these two methods could carry the potentials of both. Based on the proposed approach, wave data are generated by a NWM by means of a short period of assumed winds at a concerned point. Then, an ANN is designed and trained using the abovementioned generated wind-wave data. This ANN model is capable of mapping wind-velocity time series to wave height and period time series with low cost and acceptable accuracy. The method was applied for wave hindcasting to two different sites; Lake Superior and the Pacific Ocean. Simulation results show the superiority of the proposed approach.

The earth-fill dam leakage is studied in this paper by applying the seepage flow and thermal simulation. The mass balance and convection-diffusion equations are discretized based on the finite element method to solve the phenomena in saturated and unsaturated zones. The Shamil embankment dam is used for verification of the proposed model. Different conductivity cases are analyzed and compared against measured data. Results show that investigation of temperature variations can magnify the effect of leakage more clearly than the inspection of seepage piezometric levels.

This paper describes a numerical model developed to simulate flow and bed deformation around hydraulic structures. The model uses an improved formula for the bed shear stress by applying vorticity effect and solves the full three-dimensional Reynolds-averaged Navier-Stokes equations to calculate the flow field. The capability for numerical models to predict local scour is severely restricted by the sediment transport formula. Up to now, the scour computations were developed based on general sedimentation formula through a straight unobstructed flow path. The new sedimentation formula introduced in this paper can take into account vortices that affect the local scour process. To verify the model, a bridge pier and a groyne, which are considered as typical river-engineering structures, were simulated in different hydraulic conditions by applying both the ordinary bed shear stress equation and the new one. Comparisons show that the new equation could predict the scour more accurately than the ordinary one.

Mangroves are one of the main important species which have critical function in ecological processes in the coastal habitats. Recent studies have focused on long term effects such as biological and chemical responses and reactions of ecosystems. In this research, short term response of Avicennia marina's pneumatophores as one of substantial parts of mangroves has been considered while facing the oil slick in tidal waves. Factorial experimental design was conducted considering three factors, each one in two levels in both spring and winter seasons, separately. Experiments were carried out in the north coastline of the Persian Gulf where one of the mentioned species habitat in the Nayband Natural National Park of Iran is located. Experimental evidences on the studied blocks were investigated by experimental analysis, accurately. Results revealed the main effective factors which can raise the damages of oil spill in the mangroves habitat through oil adsorption on the pneumatophores. Investigations showed the concentration level of the main significant factors that can affect the adsorption process. The second significant factor on physical adsorption is retention time, also known as contact time. Tests results indicated that adsorption in winter is generally more than that in spring. No significant effect of day or night time on the physical oil adsorption by pneumatophores was traced.

This paper presents the results of simulating oil spillage trajectory in the Persian Gulf by using the GH limiter. The GH limiter has been used for the first time with unique formulation. All the numerical solution dispersion errors (typical of second-order methods and above) can be diminished by limiters. GH limiter minimizes all the dispersion errors, even the under-shoots. A distinguished difference of this new limiter with other limiters is diminishing the errors without altering or reducing the maximum value of pollution. It is tested against other limiters to show the high precision of GH. The model has been applied to simulate the oil spill accident in the Al-Ahmadi located south of Kuwait in Persian Gulf and its performance were further validated against documented events of Al-Ahmadi historical oil spill crisis in the Gulf. A comparison of numerical results with the observed data shows good conformity.

A three-dimensional cell-centred boundary-fitted finite volume model is developed to solve shallow water equations in open channels. An explicit finite volume method is used to discretize the governing equations in a structured and collocated grid system. A special coupling scheme is applied in some cross-section, based on differences of averaged free surface elevation and flow discharge in 3D model and 1D flow data. The proposed scheme can decrease numerical oscillation and increase the accuracy of the model. The model was applied to simulate 3D flow parameters variation in the developing region of a laboratory flume. Computed 3D velocity profiles were drawn and compared in several cross-sections and layers. Comparing the model results with available experimental data confirmed the efficiency of the scheme.

A hybrid numerical scheme has been presented in this paper for channel flow simulation by coupling one-dimensional and two-dimensional models. Both 1D and 2D differential equations have been discretized by applying the finite volume cell-centered method in a collocated grid system and solved along channel axis for all sections and elements. Due to truncation, dissipation and round off errors, using numerical methods for domains with great number of elements that require huge computations may lead to some sort of divergence. This problem is highlighted, when a collocated grid system is dealt with. To reduce divergence and instability, 2D results of water level and cross section discharge have been compared with those of the 1D results where needed and adjusted properly. Double simulation provides some other advantages as described in the paper. In order to simulate a 2D flow in a channel network, a new sequential implicit scheme has been also suggested and applied. In addition to the above, 2D advection-diffusion equation has been discretized based on general finite volume method to simulate pollution. Three test cases are discussed for proving the mentioned techniques: (a) 2D flow modeling in a meandering channel with 90° bends by applying 1D-2D hybrid model, (b) 2D flow simulation at a 90° open-channel junction by applying both 1D-2D hybrid model and sequential implicit scheme at the junction and (c) tracer test in the S-curved Channel. The comparisons show the advantages of the proposed hybrid scheme for 2D flow and pollution simulation. Also the results show the ability and accuracy of sequential implicit scheme for channel network simulation.

Application of temperature simulation for seepage inspection in earth-fill dams The earth-fill dam leakage is studied in this paper by applying the seepage flow and thermal simulation. The mass balance and convection-diffusion equations are discretized based on the finite element method to solve the phenomena in saturated and unsaturated zones. The Shamil embankment dam is used for verification of the proposed model. Different conductivity cases are analyzed and compared against measured data. Results show that investigation of temperature variations can magnify the effect of leakage more clearly than the inspection of seepage piezometric levels.

This paper presents the results of oil spill simulation in the northwest of the Persian Gulf, next to Al-Ahmadi oil wells. A two-dimensional depth averaged flow and oil pollution model is developed for coastal water simulation. To increase accuracy advective terms in transport equation were discretized by applying third-order upwind scheme and modified by using GH limiter. The oil spill is considered in two different layers: surface smudge layer and depth emulsion part. The model takes into account the major physiochemical phenomena of oil spill including wind and current speed, oil evaporation, dissolution and coastline deposition. Average monthly wind speed has been used for long-term prediction in the Persian Gulf. Comparing the model result with the actual measured data in the incident sight revealed good agreement for predicting oil spill behavior and model accuracy.

Computational fluid dynamics using the Reynolds-averaged Navier–Stokes (RANS) remains the most cost-effective approach to study wake flows and power losses in wind farms. The underlying assumptions associated with turbulence closures are the biggest sources of errors and uncertainties in the model predictions. This work aims to quantify model-form uncertainties in RANS simulations of wind farms at high Reynolds numbers under neutrally stratified conditions by perturbing the Reynolds stress tensor through a data-driven machine-learning technique. To this end, a two-step feature-selection method is applied to determine key features of the model. Then, the extreme gradient boosting algorithm is validated and employed to predict the perturbation amount and direction of the modeled Reynolds stress toward the limiting states of turbulence on the barycentric map. This procedure leads to a more accurate representation of the Reynolds stress anisotropy. The data-driven model is trained on hi...

In this research, a new numerical seepage model is introduced. The computational domain is discretized by an irregular hexahedron element and the equations system is solved using an ADI iterative method. The proposed model is able to analyze any non-homogeneous and non-isotropic domain in steady state with natural boundary conditions for seepage flow. Miscellaneous examples are analyzed by the model and the results are compared with their existing analytical or other numerical solutions. The necessity of three-dimensional modeling has been showo through examples.

ايران در منطقه لرزه‌خيز واقع شده ‌است و ساخت پل ‌ها در نزديک گسل در اين شرايط اجتناب ‌ناپذير مي‌باشد، در نتيجه تعدادي از پل‌ هاي ايران در هنگام زلزله تحت اثر ميدان نزديک قرار مي‌گيرند. زلزله ‌هاي ثبت شده در سال‌هاي گذشته نشان مي‌دهد که رکورد‌هاي زلزله ‌هايي که در فاصله نزديکي از گسل ثبت شده‌اند تفاوت زيادي با زلزله‌هاي ثبت شده دور از گسل دارند. مطالعات کم صورت گرفته بر روي زلزله ‌هاي ميدان نزديک و هم‌چنين اثرات آن بر روي سازه‌ها نياز به بررسي بيشتر بر روي اين زلزله‌ها را بيان مي‌دارد. در این مقاله ابتدا با روش شبیه سازی تصادفی برای فرکانس‌ های بالا و  همین‌ طور مدلسازی تعدادی از گسلها برای فرکانس ‌های پایین و سپس با ترکیب این دو قسمت، رکورد نهایی سناریو سازی شده بدست می اید و رکورد ها ی حاصل در بررسی پل مستقیم سه دهانه بتنی به کار میرود. در این مطالعه  اثر بزرگای زلزله، دوری یا نزدیکی ایستگاه به مرکز زلزله و اثر لایه بندی محیط در این مدلسازی بررسی شده است.