VTechWorks Repository :: Browsing by Author "Mostaghimi, Saied"

Browsing by Author "Mostaghimi, Saied"

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Agricultural BMPs applicable to Virginia
Heatwole, Conrad D.; Dillaha, Theo A. III; Mostaghimi, Saied (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1991-03)
Agronomic and Nitrate Leaching Impacts of Pelletized versus Granular Urea
Shah, Sanjay Bikram (Virginia Tech, 2000-08-02)
Agronomic and water quality impacts of urea particle size were evaluated through field and laboratory experiments and mathematical modeling. In a two-year field study, corn silage yield, corn nitrogen (N) removal, and nitrate-N (NO₃⁻-N) leaching from urea pellets (1.5 g each) and granules (0.01-0.02 g each) applied at 184 kg-N/ha were compared. A control treatment (no N) and two other N application rates (110 and 258 kg-N/ha) were also included. Urea particle size impact on dissolution rate, dissolved urea movement, mineralization, and N0³-N leaching were evaluated in the laboratory. A two-dimensional (2-D) mathematical model was developed to simulate the fate of subsurface-banded urea and its transformation products, ammonium (NH₄⁺)and NO₃⁻. With 184 kg-N/ha, corn silage yield was 15% higher (p = 0.02) and corn N removal was 19% higher (p = 0.07) with pellets than granules in the second year of the field study. In the absence of yield response at 110 kg-N/ha, reason for higher yield at 184 kg-N/ha with pellets was unclear. Greater N removal reduced NO₃⁻-N leaching potential from pellets compared to granules during the over-winter period. No urea form response to yield or corn N removal was observed in the first year. In 23 of 27 sampling events, granules had higher NO₃⁻-N concentration in the root zone than pellets, with average nitrate-N concentrations of 2.6 and 2.2 mg-N/L, respectively. However, statistically, NO₃⁻-N leaching from the root zone was unaffected by urea form, probably due to high variability within treatments masking the treatment effects. In October 1997, pellets retained 16% more (p = 0.04) inorganic-N in the top half of the root zone than granules, due to slower nitrification in pellets as was determined in the mineralization study. Slower NO₃⁻-N leaching allowed for greater N extraction by plants. Pellets had lower dissolution, urea hydrolysis, and nitrification rates than granules; however, nitrification inhibition was the dominant mechanism controlling N fate. The model took into account high substrate concentration effects on N transformations, important for simulating the fate of band-applied N. The model exhibited good mass conservative properties, robustness, and expected moisture and N distribution profiles. Differences in measured field data and model outputs were likely due to uncertainties and errors in measured data and input parameters. Model calibration results indicated that moisture-related parameters greatly affected N fate simulation. Sensitivity analyses indicated the importance of nitrification-related parameters in N simulation, particularly, their possible multiplicative effects. Need for extensive model testing and validation was recognized. The validated 2-D N model could be incorporated into a management model for better management of subsurface-banded granular N. However, the 2-D model is not appropriate for simulating the three dimensional N movement from pellets.
Applying Probabilistic Risk Assessment to Agricultural Nonpoint Source Pollution
Buck, Sharon Perkins (Virginia Tech, 1997-01-30)
A probabilistic risk assessment (PRA) for the discharge of excessive nitrogen from nonpoint sources (NPSs) to a stream was performed for a small agricultural watershed in northern Virginia. Risk, by definition, is the product of the frequency of occurrence of an event and the consequences of that event. The purpose of this research was to determine the probability of occurrence of a nitrogen discharge event (i.e., frequency). The consequences of such a discharge event were not explicitly determined but were implicitly assumed to be negative in nature. An event tree was developed to show the basic hydrologic processes at work in a small watershed. However, the event tree could not be used to discover the causes for nitrogen loss from the watershed. Therefore, a fault tree was developed for excessive nitrogen discharge in surface runoff on any day from agricultural sources. The development of the fault tree was found to be a useful exercise in understanding the intricate cause and effect relationships between agricultural practices and NPS pollution. Based on the results, the fault tree methodology might be used as an effective teaching or communication tool. The fault tree was also evaluated quantitatively to determine a probability of occurrence for excessive nitrogen discharge to the stream on any day. Land use, fertilization, monitoring, and long-term weather records were used in conjunction with scientific judgment and expert opinion to establish the probabilities within the fault tree and to calculate the overall probability of nitrogen discharge to the stream on any day. The results obtained from the fault tree calculations tend to underestimate the importance of cropland best management practices (BMPs) over the long term, because the fault tree was developed on a daily basis (i.e., every day in a year has the same probability of a discharge event occurring). A more accurate depiction of the NPS pollution control problem was achieved by assuming the occurrence of a runoff event. A second fault tree was presented for the discharge of excessive nitrogen to the stream during a runoff event. The quantitative assessment of the new fault tree showed more clearly the impact of BMPs on reducing the likelihood of nitrogen discharge. A 0.15 decrease in the probability of nitrogen discharge during a runoff event was calculated for the Owl Run watershed from 1987 to 1993 due to the effects of BMPs installed during that time period. A 0.20 decrease was calculated for an Owl Run subwatershed for the same time period. This subwatershed isolated two major dairy operations and the effects of the BMPs installed for those dairies. Despite the success of the fault tree in mirroring changes within the watershed, the amount of data and time required to perform the quantitative assessment may limit its use in the NPS pollution control field. The basic nature of the fault tree technique also limits its usefulness in the field. One such limitation is that degrees of events cannot be expressed. For example, a BMP is either present or not present on a fault tree. There can be no indication of how effective the BMP is in preventing NPS pollution without substantially increasing the level of detail displayed by the tree. Another limitation is that the ultimate result of the fault tree calculations is a probability of occurrence. This value is not as easily understood as the output of NPS pollution computer models, for example, where the output has specific meaning and units (e.g., milligrams of nitrogen per liter of runoff). The qualitative fault tree, however, has the advantage over computer models when it comes to understanding the concepts behind the technique and being able to see the cause and effect relationships at work in the watershed. Laypersons can understand the fault tree more easily than the complex computer code and intricate equations of models.
Areal Modeling of Erosion for Environmental Nonpoint Applications (AMEENA)
Al-Smadi, Mohammad Ahmed (Virginia Tech, 2007-08-10)
Erosion and sediment delivery from upland areas to waterbodies is a major problem impacting water quality in the United States and elsewhere. Measures to reduce these impacts are either targeted at reducing erosion on-site or at reducing delivery of sediment to waterbodies. AMEENA (Areal Modeling of Erosion for Environmental Nonpoint Applications) is a spatially distributed model that estimates erosion and deposition on a watershed scale by predicting erosion and transport over the landscape surface. Erosion is predicted based on the Revised Universal Soil Loss Equation (RUSLE), and sediment transport capacity is estimated as a function of upslope flow volume, local gradient, and land use. Gross erosion is routed to edge-of-stream with a routing algorithm that iteratively compares available sediment with transport capacity on a cell by cell basis from ridge cells to stream cells. The model is implemented completely within a raster GIS to facilitate use of the model as a tool to readily evaluate impact of land use practices on sediment delivery to streams. AMEENA was validated using field data of net erosion and sediment deposition from three field studies. AMEENA predicted the spatial distribution of net erosion and deposition better than WaTEM/SEDEM which is a distributed parameter erosion model based on a similar modeling approach. AMEENA's suitability to simulate the impact of management practices such as filter strips and critical area planting was evaluated on plot (profile) scale and catchment scale simulations. Results of plot scale simulations were intuitive and the model proved more reasonable for these scenarios than did RUSLE2 and WEPP. The catchment scale study highlighted features of AMEENA that are not available in RUSLE2 and WEPP in terms of identifying erosion “hot spots” and the ability to utilize the explicit sediment flow path identification in locating best placement of off-site sediment control measures. Since AMEENA does not account for in-stream erosion processes, it is not suitable for simulating areas dominated by channel or gully erosion.
Assessing the Contamination Risk of Private Well Water Supplies in Virginia
Bourne, Amanda C. (Virginia Tech, 2001-07-18)
When well water becomes contaminated to the extent that is does not meet EPA drinking water quality standards, it is considered unsafe for consumption. Nitrate and total coliform bacteria are both health contaminants and are both regulated in public water systems. A nitrate concentration of 10 mg/L or higher is considered unsafe, as is the presence of total coliform bacteria. Well degradation, inadequate well construction, and aquifer contamination can all result in contamination of well water. Factors such as well type, well age, well depth, treatment devices, population density, household plumbing pipe materials, and nearby pollution sources may affect household water quality. The specific objective of this study was to determine which factors influence nitrate levels and total coliform presence/absence of household well water. If possible, these influencing factors would be used to develop a relationship that would allow household residents to predict the nitrate level and total coliform presence/absence of their well water. As a result, a means of predicting the contamination risk to a specific well water supply under a given set of conditions, in addition to increasing awareness, could provide the homeowner with a rationale for further investigating the possibility of contamination. Existing data from the Virginia Cooperative Extension Household Water Quality Testing and Information Program were assembled for analyses in this project. The data consisted of 9,697 private household water supplies sampled from 1989-1999 in 65 Virginia counties. Initially, the entire state of Virginia was analyzed, followed by the five physiographic provinces of Virginia: the Blue Ridge, Coastal Plain, Cumberland Plateau, Ridge & Valley, and Piedmont. Ultimately, Louisa County was investigated to evaluate the possibility that better models could be developed using smaller land areas and, consequently, less geological variation. Least squares regression, both parametrically and non-parametrically, was used to determine the influence of various factors on nitrate levels. Similarly, logistic regression was used to determine the influence of the same parameters on nitrate categories, presence/absence of total coliform, and risk categories. Using stepwise model-building techniques, based primarily on statistical significance (p-values) and partial coefficient of determination (partial-R2), first and second-order linear models were evaluated. The best-fitting model only explained 58.5% of the variation in nitrate and none of the models fit well enough to be used for prediction purposes. However, the models did identify which factors were, in a statistical sense, significantly related to nitrate levels and total coliform presence/absence and quantified the strength of these relationships in terms of the percent of variation explained.
Assessing the Nonpoint Source Pollutant Removal Efficiencies of a Two-Basin Stormwater Management System in an Urbanizing Watershed
Lovern, Sharla Benjamin (Virginia Tech, 2000-05-15)
Monitoring of a regional stormwater management facility, located on the Virginia Tech campus in Blacksburg VA, was conducted in order to assess its efficacy in reducing nonpoint source pollutant losses downstream. The facility design includes both an upper water quality (wet) pond and a lower 100-yr-event quantity (dry) pond. These on-stream ponds capture both baseflow and storm runoff from the southern portion of the Virginia Tech campus and surrounding lands, and release the water back to the unnamed stream shortly above its conjunction with Stroubles Creek, a tributary of the New River. Monitoring sites for flow measurement, water quality sampling, and biotic assessments (habitat evaluation and rapid bioassessment of benthic macroinvertebrates) were located above and below each of the ponds. Both grab samples and automated samples were collected at these stations. Between 1997 and 1999, water quality grab samples included 35 baseflow samples and 22 stormflow samples. The grab samples were analyzed for concentrations of total suspended solids (TSS), metals, bacteria, and nutrients as well as temperature, pH, dissolved oxygen, conductivity, total organic carbon (TOC), and chemical oxygen demand (COD). Automated flow-weighted sampling was initiated in February of 1999 and results are reported through the end of October 1999. Thirty-three storms in 1999 were monitored for flow and various water quality parameters (TSS, TOC, COD, and nutrients). Pollutant loads and pollutant removal estimates were calculated with regard to the wet pond, dry pond, and the combined facility. Two types of pollutant removal efficiencies were calculated: (1) the EMC efficiency, based on pollutant concentrations from individual storms; and (2) the SOL efficiency, based on pollutant loads, to estimate long-term performance over the study period. Benthic macroinvertebrate sampling and habitat assessment were performed in both 1997 and 1999. In addition, a preliminary investigation of pond characteristics was conducted, including measurements of water quality and composition, sediment deposition and composition, and residence time. As a system, the stormwater management facility appears to have minimum impact on improving the downstream water quality. Pollutant concentrations and loads both appear to increase downstream of the facility as compared to upstream, during both storm event and baseflow periods. Monitoring results of the benthic assemblages showed evidence of moderate to high impairment at all sampling locations, and habitat assessments showed evidence of high sedimentation levels within the stream, even after installation of the stormwater management facility. Total suspended solids (TSS) concentration removal efficiency was 10% for the combined wet pond and dry pond system, much lower than the 80 to 90% TSS removal expected for properly functioning stormwater management facilities (Hartigan, 1989). There is some evidence of sedimentation within the ponds because of a slight reduction in sediment-bound constituent export, but the dissolved nutrient constituents had either very low and most often negative (indicating pollutant export) removal efficiencies. Concentrations of metals measured in the stream often exceeded their respective acute and chronic water quality criteria at all sampling locations. Pollutant removal efficiencies measured in the wet pond are atypical of those reported in the literature (Schueler, 1993). Insufficient residence time (two days compared to the optimal two weeks), and wet pond embankment failure are likely the principal causes of the wet pond's inadequate performance and thus, the inadequate performance of the overall facility. TSS removal efficiencies were low in the wet pond (19% for concentrations and 33% for loads) compared to the 80 to 90% expected for similar ponds. Nevertheless, the wet pond reduced the concentrations of several pollutants typically associated with TSS and not likely to be associated with the fill material for the wet pond embankment. Zinc concentrations in sediment cores were highest near the pond inlet, where the majority of sedimentation occurs. During storm events, the following results were noted. Copper and zinc concentrations in 1998 were lower at the pond outlet as compared to the pond inlet, and TOC concentrations and loads were also reduced by the wet pond (13% for concentrations and 12% for loads). However, sedimentation is also expected to remove phosphorusl, and wet pond phosphorus loads were only reduced by 10% and 3% for orthophosphorus and total phosphorus, respectively. Because the wet pond is undersized with respect to the watershed it serves (surface area less than 1% of the watershed area (0.87 ha), as compared to the 3% ratio often recommended for optimal pollutant removal (Athanas, 1988)), higher removal efficiencies were found during baseflow periods. The greatest reductions in baseflow concentrations were for ammonia (67%), nitrate (57%), total nitrogen (54%), and COD (45%). However, the residence time of two days appears to be insufficient to reduce fecal coliform concentrations in the stream, and over 40% of the fecal coliform samples collected exceeded the water quality standard for contact recreation (DEQ-WQS, 1997). Furthermore, the wet pond did not appear to reduce TSS or TOC during baseflow periods. Export of TSS (-29% EMC efficiency) and TOC (-44% EMC efficiency) from the wet pond during baseflow periods is likely due to the wet pond embankment failure as well as pond eutrophication. Eutrophication processes are favored by the water temperature increase as flow passes through the shallow wet pond. The wet pond increased downstream temperatures by approximately 8°C above inflow temperatures during the summer, and to levels above 21°C which cannot be tolerated by sensitive coldwater species (Schueler, 1987). The dry pond did not remove dissolved nutrient constituents or other pollutants during baseflow periods, but there is some evidence of sedimentation within the dry pond during storm events. During storm events, the dry pond was effective in removing TSS, with a concentration removal efficiency of 69% (EMC efficiency) and loading removal efficiency of 43% (SOL Efficiency). Removal of TKN and total phosphorus (36% and 37% respectively for concentrations) within the dry pond is further evidence of sedimentation within the dry pond. The wet pond embankment was built in 1997, and monitoring occurred during a potential stabilization period when evidence of water quality benefits are slow to appear, especially with respect to downstream habitat and aquatic communities. Some benefits which could have been observed more immediately may have been negated or masked by the progressive erosion of the wet pond embankment as a result of a design flaw. Further complicating the results is the appearance; based on observations of extended drawdown time and results from a water budget analysis in the wet pond (where inflow substantially exceeds inflow); that groundwater interacts with the pond in a complicated fashion, possibly including both recharge and discharge. To fully understand the impact of the stormwater management facility on the water quantity and quality within this tributary of Stroubles Creek, monitoring efforts should continue after the wet pond embankment is repaired and is fully operational. If biotic community improvement is desired, the stabilization period could be defined by the time necessary to flush out accumulated sediment within the channel. Monitoring efforts should also expand to include the investigation of the groundwater regime and water level fluctuations within the wet pond. Further measurements of pollutant removal processes and influences upon those processes within the wet pond should also be considered. Last, the influence of the stormwater management facility on downstream flow regimes should be investigated to assess the adequacy of its performance with regard to flow control and prevention of stream channel degradation.
Assessing Urban Non-Point Source pollutants at the Virginia Tech Extended Dry Detention Pond
Hodges, Kimberly Jean (Virginia Tech, 1997-05-23)
With a growing concern for the environment and increasing urbanization of rural areas, understanding the characteristics of urban non-point source pollution has become a focus for water quality investigators. Once thought to be a small contributor to the pollution problem, urban non-point sources are now responsible for transporting over 50% of all pollutants into natural waterways. Assessing non-point source pollution is the key to future water quality improvements in natural receiving waters. The purpose of this research was to investigate the water quality of an urbanized watershed, analyze current prediction methods and to investigate the effectiveness of an extended dry detention basin as a pollutant removal management practice on a 21.68-acre urban watershed on the Virginia Tech Campus. This research included extensive stormwater monitoring and sampling to characterize the runoff and water quality from an urban watershed. The resulting analysis included comparing well-known desktop prediction methods with pollutant removal rates using an extended dry detention basin and comparison with different literature values. Finally, the study team calibrated the PSRM-QUAL model for watershed prediction of non-point source runoff and pollution. The results of the stormwater monitoring process show that water quality prediction methods are not very successful on a storm by storm basis, but can be fairly accurate over longer periods of time with little or no storm water quality sampling. The extended dry detention basin is a simple yet effective management practice for the removal of sediments and sediment bound pollutants.
Auxiliary Procedures for the AGNPS Model in Urban Fringe Watersheds
Yagow, Eugene R. (Virginia Tech, 1997-02-28)
The Agricultural Nonpoint Source model (AGNPS) is a single-event grid-based model used for simulating runoff, sediment and nutrients from agricultural areas. This study involved using geographic information system (GIS) spatial data and functionality to improve the spatial and temporal assignment of parameter values for the AGNPS 5.0 model and incorporated methods for representing urban fringe land uses and their nonpoint source (NPS) pollution contributions in model inputs. Auxiliary procedures for modeling with AGNPS were developed both for enhancing input into the model and for enhancing modeled output. On an event basis, one procedure automated the creation of complex-formatted AGNPS 5.0 model input files using GIS as a spatial data manager. One pair of alternative procedures were developed to automate the assignment of parameter values on an event basis. One procedure used typical average annual parameter values, and the second assigned parameter values using adaptations of existing time-dependent relationships. On a monthly basis, a sequencing procedure was created to perform multiple runs with the model for a list of storms while updating parameters for each event and aggregating monthly modeled spatial output. Another pair of alternative procedures were developed to facilitate the simulation of monthly output from AGNPS modeled events. The first of these aggregated event output for all storms in each month, while the second supplemented the aggregated output with baseflow and septic system loads. The study area was the 6,500 ha urbanizing Bull Run watershed in northern Virginia, which was modeled as 14,621 cells. Databases were assembled and 109 selected storm events within a 16-year period were modeled using the above procedures. Event data were added together, where necessary, to correspond with observed data from composite-sampled intervals. Output from the two event parameterization procedures were compared with monitored loads calculated for 89 composite periods, while output from the two monthly simulation procedures were compared with monthly monitored data for 23 complete months. The monitored-modeled comparisons were considered inconclusive. Evidence strongly suggested that the rainfall records from a rain gauge outside the watershed did not correspond well with monitored runoff. The average runoff produced with the AGNPS model from the 109 selected storms amounted to 40.7% of rainfall, consistent with the calculated long-term average of 38% for the Bull Run watershed. A nonpoint source pollution index was developed to utilize monthly modeled total nitrogen, total phosphorus, and suspended sediment. Individual rating curves were developed to separately transform loads and concentrations of each pollutant into sub-index values. The maximum sub-index from each parameter was added together and averaged for the index. The index was calculated at the watershed outlet from monitored data, and in a spatially-distributed fashion along all streams from simulated output.
Bacteria Total Maximum Daily Load Issues: Report of the Bacteria TMDL Subcommittee of the Water Quality Academic Advisory Committee
Dillaha, Theo A. III; Hershner, Carl H.; Kator, Howard I.; Mostaghimi, Saied; Shabman, Leonard A.; Smith, Eric P.; Younos, Tamim M.; Zipper, Carl E. (Virginia Water Resources Research Center, 2002-10)
BMP impacts on sediment and nutrient yields from an agricultural watershed in the coastal plain region
Inamdar, S. P.; Mostaghimi, Saied; McClellan, P. W.; Brannan, Kevin M. (American Society of Agricultural and Biological Engineers, 2001)
The goal of the Nomini Creek watershed monitoring study was to quantify the effectiveness of BMPs at the watershed scale and to determine if the improvements in water quality could be sustained over a long-term period. Information on the long-term effectiveness of BMPs is critical since BMPs are being implemented under the state cost-share program to reduce nonpoint source pollution (NPS) to the Chesapeake Bay. The Nomini Creek project started in 1985 and was completed in 1997. A pre- versus post-BMP design was used. A combination of managerial and structural BMPs was implemented. Major BMPs implemented in the Nomini Creek watershed included no-tillage, filter strips, and nutrient management. The data collected at the 1463 ha Nomini Creek watershed consisted of land use, hydrologic, water quality, soils, and geographical information. The BMPs implemented at Nomini Creek reduced average annual loads and flow-weighted concentrations of nitrogen (N) by 26% and 41%, respectively. Average annual total-N loads discharged from the watershed were reduced from 9.57 kg/ha during the pre-BMP period to 7.05 kg/ha for the post-BMP period. Largest reductions were observed for dissolved ammonium-N, soluble organic-N, and particulate-N. In contrast, nitrate-N loads increased after BMP implementation. Increase in nitrate exports was likely due to ammonfication and nitrification, and subsequent leaching of particulate-N species that were conserved on the field. In comparison to N, reductions in phosphorus (P) loads and concentrations were not significant. BMP implementation resulted in a mere 4% reduction for total-P with a corresponding 24% reduction in flow-weighted concentration. The average annual total-P loads exported from the watershed were 1.31 and 1.26 kg/ha for the pre- and post-BMP periods, respectively. Reductions in total-P loads were due to decreases in particulate-P. Exports of ortho-P and dissolved organic-P increased after BMP implementation. It is likely that some of this post-BMP increase in dissolved P fractions was associated with dissolution and leaching of particulate-P, and higher rainfall-runoff activity in the watershed during the post-BMP period. In comparison to nutrients, there was no significant change in suspended solids discharged from the watershed. Overall, the findings of this study indicate that the BMPs were effective in reducing the losses of some forms of nutrients, such as ammonium-N and particulate-P, from the Nomini Creek watershed, but additional BMIs are necessary to achieve significant reductions in all forms of N and P.
Characterization of palmer drought index as a precursor for drought mitigation
Lohani, Vinod K. (Virginia Tech, 1995-08-15)
Coping with droughts involves two phases. In the first phase drought susceptibility of a region should be assessed for developing proper additional sources of supply which will be exploited during the course of a drought. The second phase focuses on the issuance of drought warnings and exercising mitigation measures during a drought . These kinds of information are extremely valuable to decision making authorities. In this dissertation three broad schemes i) time series modeling, ii) Markov chain analysis, and iii) dynamical systems approach are put forward for computing the drought parameters necessary for understanding the scope of the drought. These parameters include drought occurrence probabilities, duration of various drought severity classes which describe a region's drought susceptibility, and first times of arrival for non drought classes which signify times of relief for a drought-affected region. These schemes also predict drought based on given current conditions. In the time series analysis two classes of models; the fixed parameter and the time varying models are formulated. To overcome the bimodal behavior of the Pallner Drought Severity Index (PDSI), primarily due to the backtracking scheme to reset the temporary index values as the PDSI values, the models are fitted to the Z index in addition to the PDSI for the forecasting of the PDSI.
A Comparative Study of Stream-Gaging Methods Employed in Nonpoint Source Pollution Studies in Small Streams
Mitchem, Charles E. Jr. (Virginia Tech, 1998-04-09)
The U.S. Geological Survey started measuring stream flow in 1888 as part of a public land irrigation study. The demand for accurate stream flow measurement has increased with the rising concern about nonpoint source (NPS) pollution. NPS pollution studies, such as TMDL development, often involve quantification of flow in small first and second order streams. This application of technology intended for use in larger streams presents special problems that must be addressed by the user. The goal of this study was to conduct a comparative analysis of the current technologies used to measure flow in small streams with respect to accuracy and cost. The analyses involved field investigations, laboratory experiments, and a cost analysis. The specific study objectives were: 1) Compare the accuracy of various methods for estimating stream discharge in small first and second order streams, 2) Compare the accuracy of various methods for estimating stream discharge in a controlled laboratory environment, and 3) Evaluate the costs associated with installation, operation, and maintenance of each of the systems investigated. Ten stream-gaging methods were evaluated for their field performance, laboratory performance, and costs. Analysis of the field investigation data indicated that the Marsh McBirney current meter and the One-orange method were the most accurate among the methods studied. The results of the laboratory experiments imply that the Starflow acoustic Doppler and Valeport BFM001 current meter performed best among the ten methods. The Starflow acoustic Doppler device also proved to be the most cost-effective method. Overall, the Marsh McBirney and Valeport BFM001 current meters exhibited the best performance for both field and laboratory situations among the methods evaluated.
Comparison of 1-D and 2-D modeling approaches for simulating runoff and sediment transport in overload areas
Hong, Seonggu (Virginia Tech, 1995-10-26)
One-dimensional and two-dimensional modeling approaches were compared for their abilities in predicting overland runoff and sediment transport. Both the I-D and 2-D models were developed to test the hypothesis that the 2-0 modeling approach could improve the model predictions over the 1-0 approach, based on the same mathematical representations of physical processes for runoff and sediment transport. Runoff processes were described based on the St. Venant equations and the sediment transport was based on the continuity relationship. The finite element method was employed to solve the governing equations. The nonlinear, time-dependent system of equations obtained by the finite element formulation was solved by the substitution method and the implicit method. The models were verified by comparing the analytical solutions presented by Singh and Regl (1983) and the solution by the Izzard method (Chow, 1959). The comparison showed that both the 1-0 and 2-D models provided reasonable estimations of runoff and sediment loadings. Evaluation of the models was based on four different hypothetical case studies and two experimental studies. The hypothetical case studies investigated the effects of the discretization level, cross slopes, and the size of the field area on the model predictions. The two experimental studies provided a comparison of model predictions with observed data. The results of the hypothetical case studies indicated that the maximum differences in the model predictions at the outlet were about 30% between the two modeling approaches. When the discretization level was sufficient to reasonably describe the shape of the surface, the 1-0 model prediction were almost the same as the 2-D model predictions. Even though cross slopes existed in the field, the differences in the model predictions at the outlet were not significant between the 1-0 and 2-0 models. The differences in the model predictions of runoff and sediment loading were not affected by the changes in the size of the field. Since the 2-D model resulted in 10 to 20% differences in model predictions when different boundary conditions were used and the 1-D model predictions were also affected by the choice of element length, the differences in model predictions at the outlet, shown in model application results, which were less than 30% in most cases, could not be considered significant. The model applications to the experimental studies also showed that no substantial differences existed in the model predictions between the I-D and 2-D models. Even though the spatial distributions of the flow depth and sediment concentration were significantly different, runoff volumes and sediment yields at the outlet showed less than 10% differences. Compared with the I-D model, the 2-D model required much more computational time and effort to simulate the same problems. In addition, convergence problems due to negative flow depths limited the 2-D model applications. The 2-D simulations required more than twice the computational time needed for the I-D simulations. As long as the model predictions at the outlet are concerned, the much greater computational costs and efforts could not justify the use of the 2-D approach. Based on the simulation results from the selected hypothetical case and experimental studies, the 2-D model provided better representations of spatial distribution of flow depths and sediment concentrations than the I-D model. However, no substantial differences in predictions of total runoff volume and sediment yield at the outlet area were found between the I-D and 2-D models.
Comparison of two hydrological models on a Virginia Piedmont watershed
Fu, Youtong (Virginia Tech, 1994-12-05)
KINEROS and PSRM-QUAL:J two distributed parameter event-based hydrologic models, were applied to Foster Creek Watershed, Louisa County, Virginia. The simulations of the two models were conducted using published data and a ten year database from the Foster Creek Watershed, Louisa County, Virginia. Data management and analysis was supported through the use of PC-VirGIS, a DOS based GIS package developed by the Information Support Systems Laboratory, Virginia Tech. The performance of the two models were based on the criteria established to compare the simulated and recorded peak discharge rates , total runoff volumes and time to peak. Goodness of fit criteria were based on graphic comparison relative error, model efficiency, linear regression, hypothesis testing and variance. Based on these measurements, the simulated results by both models were acceptable. KINEROS generally made better predictions of peak discharge rate and time to peak. Hydrograph shapes also generally matched the recorded sequence more closely. PSRM-QUAL simulated the total runoff volume slightly better than KINEROS. The sensitivity of KINER OS and PSRM-QUAL to the model input parameters was evaluated. For KINEROS, peak discharge rate and runoff volume were very sensitive to changes in rainfall amount, saturated hydraulic conductivity and effective capillary drive. For PSRM-QUAL, peak discharge rate and total runoff volume were very sensitive to changes in SCS CN, initial abstraction coefficient and rainfall amount.
A comprehensive modeling approach for BMP impact assessment considering surface and ground water interaction
Cho, Jae-Pil (Virginia Tech, 2007-04-04)
The overall goal of this study was to develop a comprehensive tool for assessing the effectiveness of selected BMPs on both hydrology and water quality and to demonstrate the applicability of the system by considering 1) temporally and spatially changing land use management practice in an agricultural watershed and 2) interaction between surface and ground water over the entire system. A user interface and Dynamic Agricultural Non-point Source Assessment Tool (DANSAT) were developed to achieve this goal. DANSAT is the only distributed-parameter, physically-base, continuous-simulation, and multi-soil layer model for simulating impacts of agricultural BMPs on hydrology and water qulality in small agricultural watersheds. DANSAT was applied to QNB plot (18m Ã 27m) and two agricultural watersheds in Virginia, including Owl Run watershed (1140 ha) and QN2 in the Nomini Creek watershed (216 ha), to evaluate the model components and its performance in predicting runoff, sediment yield, and pesticide load. DANSAT performed well in predicting total runoff and temporal variations in surface runoff for both field-scale and watershed-scale applications. Total percent errors between the measured and predicted results were less than 10% except for one case (39.8% within a subwatershed of Owl Run watershed), while the daily Nash-Sutcliffe model efficiencies were greater than 0.5 in all applications. Predicted total sediment yields were within ±35% of observed values in all applications. However, the performance of DANSAT in predicting temporal trend and spatial distribution of sediment loads was acceptable only within Owl Run watershed, where high correlations between flow rates and sediment loads exist. The predicted total pesticide loads were within ±100% of observed values. DANSAT failed to simulate the temporal occurrence of pesticide loads with a 0.42 daily Nash-Sutcliffe efficiency value. The Dual-Simulation (DS) was developed within the linked ground water approach to resolve problems encountered due to the existence of different temporal scales between DANSAT and the existing ground water models such as MODFLOW and MT3D. The linked approach performed better in predicting the seasonal trend of total runoff compared to the integrated approach by showing an increase in monthly Nash-Sutcliffe efficiency value from 0.53 to 0.60. Surface and subsurface output variables were sensitive to the changes in spatially distributed soil parameters such as total porosity and field capacity. A maximum grid size of 100 m was recommended to be appropriate for representing spatial distribution of topographic, land use, and soil characteristics based on accuracy analysis during the GIS manipulation processes. Larger time-step based on predefined acceptable maximum grid size, decreased the computational time dramatically. Overall sensitivity to different grid sizes and time-steps was smallest for hydrology components followed by sediment and pesticide components. Dynamic crop rotation was considered by DANSAT, and the model successfully simulated the impacts of temporal and spatial changes in crop rotations on hydrology and water quality for both surface and subsurface areas. DANSAT could prove to be a useful tool for non-point source pollution managers to assess the relative effectiveness of temporally and spatially changing BMPs on both surface and ground water quantity and quality.
A computer simulation model for investigating the effect of land application of sludge on runoff water quality
Deizman, Marcia McCutchan (Virginia Tech, 1989-04-22)
CREAMS-NT, a modified version of the field-scale model for Chemicals, Runoff, and Erosion from Agricultural Management Systems (CREAMS) model, was developed to simulate the nitrogen (N) transformations and subsequent nutrient transport processes which occur in the soil following organic waste applications. CREAMS-NT accounts for nutrient addition through fertilization and rainfall and losses of N by volatilization, denitrification, plant uptake, leaching, and overland flow. Data required by CREAMS-NT includes runoff volume, sediment yield, percolation, and soil environmental conditions which is generated by the hydrologic and erosion components of the original CREAMS model. The mineralization, nitrification, denitrification, ar1d volatilization processes are simulated using firstâ order knetic equations adjusted for the effects of soil environmental conditions including temperature, moisture, pH, soil/sludge contact, and soil cation exchange capacity. Prior to a runoff event, soil ammnonium-N (NH4 â N) is partitioned between adsorbed and desorbed phases. CREAMS-NT predicts the transport of organic-N, NH4 â N, and sediment=bound phosphorus (P3b) in runoff using enrichment ratios. The transport of soluble nutrients, nitrate-N (NO3 â N), NH4 â N, and soluble P (PTF), is estimated using extraction coefficients.
A computer simulation model for predicting pesticide losses from agricultural lands
Kenimer, Ann Lee (Virginia Tech, 1987-08-05)
A field scale model for predicting the surface losses of pesticides (Pesticide Losses In Erosion and Runoff Simulator, PLIERS) was developed. PLIERS accounts for pesticide losses by degradation and volatilization, the washoff of pesticides from plant canopy and surface residue, the adsorption and desorption of pesticides to and from soil particles, and the movement of pesticides in the dissolved and adsorbed phases. Hydrologic data are generated by the comprehensive watershed model, FESHM; which contains an extended sediment detachment and transport algorithm. PLIERS uses first order rate equations to describe degradation and volatilization, and pesticide washoff. The adsorption of pesticides to individual particle size classes is estimated using the Freundlich equation. Movement of atrazine and 2,4-D in runoff and sediment was measured on twelve field plots under simulated rainfall. The plots were treated with conventional or no-tillage in combination with one of three residue levels (0, 750, and 1500 kg/ha). Runoff and sediment losses were found to increase with decreasing residue cover for both tillage systems. No-till reduced sediment loss and total runoff volume by 98 and 92 percent, respectively, compared to conventional tillage. Concentrations of atrazine and 2,4-D ir1 runoff and sediment were greater from the no-till plots than from the conventional plots but the total losses were less. Both pesticides were carried predominately in the dissolved phase. Averaged over all plots, the atrazine losses were 2.9 percent of applied amount for conventional tillage and 0.3 percent for no-tillage. The corresponding values for 2,4-D were 0.3 percent and 0.02 percent. PLIERS was validated using data from the rainfall simulator field plot studies. Agreement between predicted and observed data was very good for dissolved pesticide losses and satisfactory for adsorbed pesticide losses. In addition, the effects of tillage type and residue level were reflected in PLIERS predictions. PLIERS shows great potential as a flexible planning tool since it could be used with any comprehensive hydrologic model and is able to predict the losses of pesticides under various field conditions.
Cyberbiosecurity: A New Perspective on Protecting US Food and Agricultural System
Duncan, Susan E.; Reinhard, Robert; Williams, Robert C.; Ramsey, A. Ford; Thomason, Wade E.; Lee, Kiho; Dudek, Nancy; Mostaghimi, Saied; Colbert, Edward; Murch, Randall Steven (Frontiers, 2019-03-29)
Our national data and infrastructure security issues affecting the "bioeconomy" are evolving rapidly. Simultaneously, the conversation about cyber security of the U.S. food and agricultural system (cyber biosecurity) is incomplete and disjointed. The food and agricultural production sectors influence over 20% of the nation's economy ($ 6.7T) and 15% of U.S. employment (43.3M jobs). The food and agricultural sectors are immensely diverse and they require advanced technologies and efficiencies that rely on computer technologies, big data, cloud-based data storage, and internet accessibility. There is a critical need to safeguard the cyber biosecurity of our bio economy, but currently protections are minimal and do not broadly exist across the food and agricultural system. Using the food safetymanagement Hazard Analysis Critical Control Point systemconcept as an introductory point of reference, we identify important features in broad food and agricultural production and food systems: dairy, food animals, row crops, fruits and vegetables, and environmental resources (water). This analysis explores the relevant concepts of cyber biosecurity from food production to the end product user (such as the consumer) and considers the integration of diverse transportation, supplier, and retailer networks. We describe common challenges and unique barriers across these systems and recommend solutions to advance the role of cyber biosecurity in the food and agricultural sectors.
Describing and Predicting Breakthrough Curves for non-Reactive Solute Transport in Statistically Homogeneous Porous Media
Wang, Huaguo (Virginia Tech, 2002-11-18)
The applicability and adequacy of three modeling approaches to describe and predict breakthough curves (BTCs) for non-reactive solutes in statistically homogeneous porous media were numerically and experimentally investigated. Modeling approaches were: the convection-dispersion equation (CDE) with scale-dependent dispersivity, mobile-immobile model (MIM), and the fractional convection-dispersion equation (FCDE). In order to test these modeling approaches, a prototype laboratory column system was designed for conducting miscible displacement experiments with a free-inlet boundary. Its performance and operating conditions were rigorously evaluated. When the CDE with scale-dependent dispersivity is solved numerically for generating a BTC at a given location, the scale-dependent dispersivity can be specified in several ways namely, local time-dependent dispersivity, average time-dependent dispersivity, apparent time-dependent dispersivity, apparent distance-dependent dispersivity, and local distance-dependent dispersivity. Theoretical analysis showed that, when dispersion was assumed to be a diffusion-like process, the scale-dependent dispersivity was locally time-dependent. In this case, definitions of the other dispersivities and relationships between them were directly or indirectly derived from local time-dependent dispersivity. Making choice between these dispersivities and relationships depended on the solute transport problem, solute transport conditions, level of accuracy of the calculated BTC, and computational efficiency The distribution of these scale-dependent dispersivities over scales could be described as either as a power-law function, hyperbolic function, log-power function, or as a new scale-dependent dispersivity function (termed as the LIC). The hyperbolic function and the LIC were two potentially applicable functions to adequately describe the scale dependent dispersivity distribution in statistically homogeneous porous media. All of the three modeling approaches described observed BTCs very well. The MIM was the only model that could explain the tailing phenomenon in the experimental BTCs. However, all of them could not accurately predict BTCs at other scales using parameters determined at one observed scale. For the MIM and the FCDE, the predictions might be acceptable only when the scale for prediction was very close to the observed scale. When the distribution of the dispersivity over a range of scales could be reasonably well-defined by observations, the CDE might be the best choice for predicting non-reactive solute transport in statistically homogeneous porous media.
Development and Evaluation of a Gis-Based Spatially Distributed Unit Hydrograph Model
Kilgore, Jennifer Leigh (Virginia Tech, 1997-12-10)
Synthetic unit hydrographs, which assume uniform rainfall excess distribution and static watershed conditions, are frequently used to estimate hydrograph characteristics when observed data are unavailable. The objective of this research was to develop a spatially distributed unit hydrograph (SDUH) model that directly reflects spatial variation in the watershed in generating runoff hydrographs. The SDUH model is a time-area unit hydrograph technique that uses a geographic information system (GIS) to develop a cumulative travel time map of the watershed based on cell by cell estimates of overland and channel flow velocities. The model considers slope, land use, watershed position, channel characteristics, and rainfall excess intensity in determining flow velocities. The cumulative travel time map is divided into isochrones which are used to generate a time-area curve and the resulting unit hydrograph. Predictions of the SDUH model along with the Snyder, SCS, and Clark synthetic unit hydrographs were compared with forty observed storm events from an 1153-ha Virginia Piedmont watershed. The SDUH model predictions were comparable or slightly better than those from the other models, with the lowest relative error in the peak flow rate prediction for 12 of the 40 storms, and a model efficiency of at least 0.90 for 21 of the storms. Despite the good predictions of the hydrograph peak flow rate and shape, the time to peak was underpredicted for 34 of the 40 storms. Runoff from the 40 storms was also generated for two subwatersheds (C: 462 ha; D: 328 ha) in Owl Run to assess the effect of scale on the SDUH model. Peak flow rate predictions were more accurate for the entire watershed than for either subwatershed. The time to peak prediction and model efficiency statistics were comparable for the entire watershed and subwatershed D. Subwatershed C had poorer predictions, which were attributed to a large pond in the main channel, rather than to scale effects. The SDUH model provides a framework for predicting runoff hydrographs for ungauged watersheds that can reflect the spatially distributed nature of the rainfall-runoff process. Predictions were comparable to the other synthetic unit hydrograph techniques. Because the time to peak and model efficiency statistics were similar for the 1153-ha watershed and a 328-ha subwatershed, scale does not have a major impact on the accuracy of the SDUH model.

Browsing by Author "Mostaghimi, Saied"

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