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Streamflow hydrographs summarize the behavior of watersheds. Their separation into quick and slow components requires hydrological knowledge of the specific drainage area. To better understand the hydrological response of 14 small agricultural watersheds in Québec, Canada, covering different physiographic attributes ranging from lowlands to hilly and steep landscapes, streamflow electrical conductivity was used as a geochemical tracer. These agricultural watersheds have undergone significant management practices, including artificial drainage. The objective of this research was to evaluate the performance of existing automated filter methods for hydrograph separation (BFLOW, UKIH, PART, FIXED, SLIDE, LOCMIN, and Eckhardt). The geochemical method was used as a reference for comparison with the filter methods. Comparison of the slow flow estimates from non-calibrated filters, using a MANOVA model, showed that the filter performance increased under conditions with high contributions of quick runoff to the stream, such as during snowmelt (spring season), during heavy precipitation, and in subwatersheds with landscape conditions more prone to quick runoff. However, filter performance decreased as hydrological processes predisposed more flow to slower pathways, typically in summer and fall, as well as in lowland landscapes generally associated with high rates of tile drainage rather than in hilly and steep relief. Underlying the filter assumptions is the classic concept of a rainfall event with quick runoff as the main source of the drainage area response. Thus, slow flow is associated with a low threshold response. Eckhardt filter simulations were in good agreement with the geochemical method after calibration, based on model statistical measures (R, NSE, and PBIAS). However, larger errors were associated with higher flow values. The slow flow overestimations were more pronounced during periods of extreme events, i.e., spring runoff and heavy precipitation. The linear concept of the Eckhardt filter yields no information on slow flow response behavior that could be useful in capturing its temporal variability. Because the routing of water has been managed to improve agricultural productivity, these hydrological modifications resulted in a more complex slow flow response. The performance of filtering methods is thus affected. Therefore, simplifications of filter assumptions are less likely to provide more effective estimates of slow flow. Furthermore, given the heterogeneity of hydrological processes due to seasonal climatic characteristics, the routine application of basic filter concepts is not sufficient to address the variable nature of the hydrological response. The variability scale of geochemical separation, from regional (agro-climatic) to local (adjacent watersheds), proved that it is always relevant to have adequate separation. However, the validation of filters without a tracer is limited and almost unsuitable for these agricultural watersheds. [ABSTRACT FROM AUTHOR]

Controlled drainage is a best management practice that decreases nitrate loads from subsurface drainage, but questions remain about optimal operation strategies. One unanswered question is whether the outlet should be lowered prior to or directly after a rainfall event to reduce the amount of time that the water table is at a level that would be detrimental to either trafficability or crop yield. The objective of this study was to determine how much controlled drainage lengthens the time needed for the water table to fall after a rainfall event, to inform possible improvement in the management of controlled drainage systems. This objective was addressed using water table recession rates from two pairs of controlled and free-draining fields located at the Davis Purdue Agricultural Center in Indiana over a period of nine years (2006-2014). At each pair, comparison of mean recession rates from the two fields indicated that controlled drainage reduced recession rate. The significance of the relationship between paired observations and the effect of controlled drainage was determined by a paired watershed approach using analysis of variance (ANOVA) and covariance (ANCOVA). Raising the outlet of the subsurface drainage system decreased the mean rate of water table recession by 29% to 62%, increasing the time needed for the water table level to fall from the surface to 30 and 60 cm depths by approximately 12 to 26 h and 24 to 53 h, respectively. Based on these results, it can be concluded that lowering the outlet before storm events would reduce the amount of time that the water table is at a detrimental level for either crop growth or trafficability. However, the trade-off between costs and benefits of active management depends on the sensitivity of the crop and probability of a severe storm. [ABSTRACT FROM AUTHOR]

The potential impacts of climate change on BMP effectiveness were investigated using SWAT simulations for an agricultural watershed that drains into the Chesapeake Bay in the U.S. Northeast climate region. Critical source areas (CSAs) for sediments, nitrogen, and phosphorus, identified for current and future climate (SRES scenarios A1B and A2), were classified by density to support BMP prioritization schemes. BMPs were designed for these CSAs and tested against current and future climate using SWAT simulations to evaluate their robustness. A second set of BMPs was designed by optimization for all agricultural and urban lands in the study watershed and was similarly tested for robustness. In both cases, the design goal was for the watershed's water quality response to meet the bay TMDLs once BMPs were implemented. Results indicated that density 2 and 3 CSAs (hotspots exporting excess amounts of 2 or 3 constituents) may be good prioritization targets, but reaching the bay TMDLs would still require targeting all CSAs. BMPs designed for CSAs under current climate were effective to reach bay TMDLs under current climate but not under scenarios A1B and A2. BMPs designed for CSAs under scenario A2 were effective to reach the bay TMDLs under all climates, except for nitrogen under A2. Similarly, BMPs optimized for agricultural and urban lands, when designed for current climate, were effective in meeting TMDLs for current climate only. Optimizing these BMPs for future climate produced a design that met TMDLs under both current and future climates, except for nitrogen with future climate. However, in this case, the nitrogen TMDL was exceeded by a smaller amount than in the CSA design. It was concluded that, in the U.S. Northeast, BMPs designed to remediate water quality problems under current climate will be insufficient to maintain water quality with climate change. Increased annual rainfall and storm intensity will increase the proportion of watershed area needing BMPs, and current hotspots will generate excess amounts of new constituents that will require re-design of existing BMPs. Community-based participatory strategies will likely be required to foster BMP adoption and sustain water quality gains in the Chesapeake Bay region. [ABSTRACT FROM AUTHOR]

Suspended sediment is the primary pollutant prevalent in runoff waters exiting construction sites with exposed and disturbed land. In this research, the effectiveness of a chemical stabilizer, known as anionic polyacrylamide (PAM), to prevent erosion and promote sedimentation was examined using different application methods (i.e., dry granular vs. semi-dissolved solution). In this study, the effectiveness of Silt Stop 712, a proprietary PAM product, was tested using different application methods at three different rates, i.e., 16.8, 28, and 39.2 kg ha-1 (15, 25, and 35 lbs acre-1), on bare, unseeded, unprotected 1.2 m x 0.6 m x 0.08 m (4 ft x 2 ft x 0.25 ft) laboratory-scale soil test plots. Laboratory-scale testing procedures using simulated rainfall were applied to mimic interrill erosion and sediment detachment scenarios similar to a highway embankment with a compacted 3H: 1V fill slope. Our results showed that dry PAM treatments applied at the recommended rate of 39.2 kg ha-1 (35 lbs acre-1) were capable of reducing turbidity by 97% and net soil loss by approximately 50% in comparison to the bare soil control Conversely, semi-dissolved PAM treatments applied at the same rate, i.e., 39.2 kg ha-1 (35 lbs acre-1), followed by a drying period of 48 h prior to the experiment, reduced turbidity by approximately 69% and soil loss by 76%. The lower application rates, i.e., 16.8 and28 kg ha-1 (15 and25 lbs acre-1), of semi-dissolved PAM without a drying time were observed to lose effectiveness after about 40 min; however, the higher application rate of 39.2 kg ha-1 (35 lbs acre-1) of semi-dissolved PAM provided consistent turbidity reductions throughout the entire experiment. Based on these results: (1) dry PAM applied directly to the surface at the manufacturer's recommended rate was more effective as a sediment control (i.e., turbidity reduction) measure, and (2) semi-dissolved PAM applied directly to the surface at the manufacturer's recommended rate and allowed to dry for 48 h prior to rainfall was a more effective erosion control (i.e., soil loss reduction) measure. [ABSTRACT FROM AUTHOR]

In recent years, riparian buffers have become known as one of the most effective best management practices for nonpoint-source pollution. However, establishment of riparian buffer systems with respect to plant species and their position in the buffer zone has not been investigated due to lack of efficient evaluation methods for the analysis of water quality improvement with established riparian buffers. To solve this problem, the SWAT-REMM prototype version was developed by researchers in Canada. In the SWAT-REMM prototype version, many riparian-related input parameters are not directly read from the local input data. Thus, a SWAT-REMM enhancement was developed by improving three major limitations of the prototype version of SWAT-REMM: (1) riparian buffers at designated reaches in the watersheds, (2) riparian buffers using local soil properties at the riparian buffer zone along reaches, and (3) multiple weather stations in a larger-scale watershed. The enhanced SWAT-REMM version was applied to the Bonggok watershed in Korea. This study investigated riparian buffers with different widths (10 m, 5 m, and 1 m) along the slope. Total nitrogen reduction ranged from 14.8% to 54.0% in each catchment for 10 m widths. Total nitrogen reduction ranged from 6.9% to 31.6% in each catchment for 1 m widths. The reduction efficiency was not simply proportional to the width of buffers. This study evaluated the enhanced SWAT-REMM simulation of water quality improvement. Based on this research, the enhanced SWAT-REMM can be used to evaluate water quality improvement by riparian buffers at various watersheds worldwide using local data. In particular, simulation of riparian buffers at user-designated reaches in a watershed enables simulation of riparian buffers in watersheds experiencing frequent flooding where no riparian buffers can be established. It is expected that the enhanced SWAT-REMM can be used to determine economical and environmentally optimum riparian buffer scenarios. [ABSTRACT FROM AUTHOR]

New Soil and Water Assessment Tool (SWAT) algorithms for simulation of stormwater best management practices (BMPs) such as detention basins, wet ponds, sedimentation filtration ponds, and retention irrigation systems are under development for modeling small/urban watersheds. Modeling stormwater BMPs often requires time steps as small as minutes to realistically capture the instantaneous flow and sediment load coming from upland areas. SWAT2005 uses the Modified Universal Soil Loss Equation (MUSLE) for modeling upland erosion and sediment load. The MUSLE model is an empirical soil loss equation, which was formulated based on field observations rather than theoretically derived relationships to predict long-term average soil loss. This article presents modified physically based erosion models in SWAT for seamless modeling of erosion processes with the recently developed sub-hourly flow models. In the new algorithms, splash erosion is calculated based . on the kinetic energy delivered by raindrops, adapted from the European Soil Erosion Model, and overland flow erosion is estimated using a physically based equation adapted from the Areal Nonpoint-Source Watershed Environment Response Simulation (ANSWERS) model. The Yang model and the Brownlie model were also modified for in-stream sediment routing. The SWAT model with the modified sub-daily sediment algorithms was calibrated and validated each for a one-year period at 15 min intervals with measured data from the USDA-ARS Riesel watersheds in Texas. Results show that SWAT with the sub-daily algorithms performed as well or better in terms of sediment yield prediction than SWAT with the current daily output structure. In addition, SWAT (sub-daily) was able to adequately represent the timing, peak, and duration of sediment transport events. Thus, this initial evaluation indicates that the new sub-daily flow and sediment structure in SWAT is a promising tool for water quality assessment studies in small watersheds or urban watersheds where sub-daily process are so important to quantify. [ABSTRACT FROM AUTHOR]

As climate changes, the uncertainty of water availability, changing magnitudes of nonpoint-source pollution, and uncertainty of best management practice (BMPs) effectiveness are issues that watershed managers and stakeholders must consider and plan for. The objective of this study was to determine how BMP effectiveness will be affected by climate change using the Soil and Water Assessment Tool (SWAT). Using downscaled monthly precipitation and temperature data output from the Community Climate System Model (CCSM), daily precipitation and temperature data were produced based on observed weather station data for the Tuttle Creek Lake watershed in Kansas and Nebraska. The A1B, A2, and B1 SRES emissions scenarios were compared to historical CCSM model output. Eight agricultural BMPs were physically represented within SWAT and compared across climate scenarios. Water yield, surface runoff, baseflow, sediment load, nitrogen load, and phosphorus load increased in all three future climate scenarios. Terraces, contour farming, and native grass were determined to be the most effective in pollution load reduction and percent efficiency at the field and watershed scales in future scenarios. Porous gully plugs and filter strips showed no significant changes in pollution load or percent reduction. Grazing management, no-tillage, conservation tillage, and grazing management percent and load reduction in future scenarios varied at the field and watershed scales. This study demonstrates that BMP performance in terms of sediment, nitrogen, and phosphorus reduction significantly changes in future climate scenarios at the field scale, while performance generally does not change significantly at the watershed scale. [ABSTRACT FROM AUTHOR]

The assessment of BMP (best management practice) impacts using a watershed model has helped to establish a watershed conservation and protection plan that is projected to be required by government and decision makers. Cedar Creek watershed, located southeast of Dallas, Texas, was included in the 303(d) list as an impaired watershed due to high pH values. A number of efforts have been made to develop watershed protection plans by the North Central Texas Water Quality (NCTXWQ) project team. Tarrant Region Water District (TRWD) has monitored the water quality in the reservoir and found that chlorophyll-a has been increasing at an annual rate of 3.85%. Chlorophyll-a is a good indicator of algae growth, and TRWD, with 18 years of monitoring, revealed that the increase of chlorophyll-a needs to be a primary focus of the watershed protection plats. A stakeholder group and the project team suggested that total phosphorous (TP) reduction from the watershed should be targeted at 35% of current loading in order to preserve the water quality in the reservoir. In previous studies, flow and nutrients in the watershed were calibrated using SWAT (Soil and Water Assessment Tool). In addition, sensitivity analyses for each BMP were conducted such that each BMP was simulated in the model at a 100% adoption rate. The cost-effectiveness of each BMP was estimated and ranked by TP reduction. In this study, using the calibrated model and the cost-effectiveness analyses of the BMPs, the initially selected BMPs were simulated in SWAT to identify the reduction rate at the watershed outlet (reservoir) using a marginal adoption rate and to illustrate the spatially distributed impacts' of each BMP at the subbasin scale. The results show that simulation of the eight selected BMPs in subbasins with higher TP loading cats achieve the 35% reduction goal at the reservoir. [ABSTRACT FROM AUTHOR]

Cropland best management practice recommendations often combine tillage and nutrient application improvements to reduce nutrient losses with surface runoff. This study used the Soil and Water Assessment Tool (SWAT) model to evaluate nutrient runoff yields from conventional-till and no-till management practices with surface and deep-banded fertilizer application in a sorghum-soybean rotation. The model was calibrated for three field plots (0.39 to 1.46 ha) with different combinations of practices and validated for three field plots (0.40 to 0.56 ha) during 2001 to 2004. Daily performance of the calibrated SWAT model in simulating total N for all treatments was satisfactory for median-based Nash-Sutcliffe model efficiency (Ef* of 0.54 to 0.64), good to very good for percent bias (PBIAS of 31% to 7%), and satisfactory to good for median-based root mean square error to observations standard deviation ratio (RSR* of 0.72 to 0.62). Performance was slightly lower and more variable for total P calibration (Ef* of 0.42 to 0.62, PBIAS of-48% to 2%, and RSR* of 0.76 to 0.62). Monthly statistics improved for total P runoff yield compared to daily performance, but changed little for total N runoff yields, probably due to the stronger influence of outliers in the N data. Based on validation results, SWAT was more robust in simulating total N runoff yields from the treatment with less soil disturbance (NT/SB) and total P for the two treatments with more soil disturbance (NT/DB and TILL). A major concern was that SWAT predicted greater annual average total N runoff yields for no-till treatments than for tilled treatments, which was contrary to measured values at the study site. This reinforces a fundamental research issue that tillage system effects on nutrient losses are still very much uncertain and thus may not be properly modeled. The SWAT model generally underpredicted monthly total N yields for all treatments in the higher-precipitation months of May and June and overpredicted total N and total P yields from September through November. Calibration for N and P resulted in identical calibration parameters for NPERCO (1.0), RSDCO (0.05), BIOMIX (0.2), PPERCO (10), PHOSKD (175), and UBP (50) regardless of tillage practice or fertilizer application method. Together with results that calibrated parameters for runoff (CN, Ksat, AWC) and erosion (Cmin) differed among the treatments, this study found that differences in nutrient yields among tillage and fertilizer management may be adequately modeled with SWAT by calibrating runoff and sediment yields only, and that further calibration of nutrient parameters may not improve model results. [ABSTRACT FROM AUTHOR]

In 2006, bacterial pathogens were the leading cause of water quality concerns in the U.S. With more than 300 water bodies in the state of Texas failing to meet water quality standards because of bacteria, managing bacteria pollution commanded the attention of regulatory agencies, researchers, and stakeholders across Texas. In order to assess, monitor, and manage water quality, it was necessary to characterize the sources of pathogens within the watershed. The objective of this study was to develop a spatially explicit method to estimate potential E. coli loads in Plum Creek watershed in east central Texas. Locations of contributing non-point and point sources in the watershed were defined using Geographic Information Systems (GIS). By distributing livestock, wildlife, wastewater treatment plants, septic systems, and pet sources, the bacterial load in the watershed was spatially characterized. Contributions from each source were quantified by applying source specific bacterial production rates, and ranking of each contributing source was assessed for the entire watershed. Cluster and discriminant analyses were used to identify similar regions within the watershed for selecting appropriate best management practices. Based on the statistical analysis and the spatially explicit method, four clusters of subwatersheds were found and characterized. The analysis provided a basis for development of spatially explicit identification of best management practices (BMPs) to be applied within the Watershed Protection Plan (WPP). [ABSTRACT FROM AUTHOR]

Best management practices (BMPs) have been implemented on a farm-by-farm basis within the Cannonsville Reservoir watershed (CRW) as part of a New York City watershed-wide BMP implementation effort to reduce phosphorus (P) loads to the water supply reservoirs. Monitoring studies have been conducted at selected locations and at the watershed outlet on one of the farms, which spans an entire subwatershed within the CRW, with the aim of quantifying effectiveness of the BMPs installed on the farm. This study applied the Soil and Water Assessment Tool (SWAT) and a recently developed BMP characterization tool to the farm over pre- and post-BMP installation periods with the object of determining the extent to which model results incorporating all installed BMPs match observed data, and the individual impact of each of the BMPs installed on the farm. The SWAT model generally performed well at the watershed level for flow, sediment, and phosphorus simulations. Annual Nash-Sutcliffe (NS) coefficients for the components ranged between 0.56 and 0.80, while monthly NS coefficients ranged between 0.45 and 0.78. The model also performed well at the field level, with simulated in-field P loads closely matching observed data. Because the fields had various combinations of BMPs installed on them, it was difficult to separate out individual BMP impacts based on SWAT simulations. It was, however, possible to determine the effects of BMP combinations such as nutrient management plans and rotations (31% dissolved P; 25% total P). For dissolved P, integration of BMP tool efficiencies allowed individual BMP impacts to be incorporated while still maintaining the same level of representation as was obtained using model simulations. As the SWAT model is often used with little or no post-BMP data to verify simulation results, this study served to validate SWAT model suitability for evaluating BMP impacts. The BMP tool was found to suitably complement the model by providing insights into individual BMP impacts, and providing BMP efficiency data where the model was lacking. [ABSTRACT FROM AUTHOR]

Soil erosion from agricultural lands and the subsequent transport of sediment and sediment-bound nutrients (particularly P) are serious problems contributing to surface water pollution and threatening agricultural sustainability. Raindrop impact on bare soil destabilizes soil aggregates and leads to surface sealing, increasing runoff volumes and soil loss. Surface-applied polyacrylamide (PAM) decreases soil erosion by stabilizing the soil structure and reducing surface sealing. Previous research has shown that surface-applied PAM reduces erosion at relatively high application rates (20 to 80 kg ha-l). The purpose of this study was to evaluate the effectiveness and longevity of a new liquid/emulsion PAM formulation to reduce runoff, sediment, and P loss from rainfed agricultural fields. The formulation was applied using a hand sprayer at a low PAM rate of 5 kg ha-1 (13,333 L of solution ha-1). Plot-scale field rainfall simulations (75 mm ha-1) were conducted on individual test plots at three test intervals (rainfall simulated 2 days, 3 weeks, and 10 weeks after DAM application) on two soil types (Ashdale silt loam and Plano silt loam). The new polymer formulation, Soil Net EM-1000-50, reduced runoff volumes an average of 100% at the 2-day test interval, 59% at the 3-week test interval, and 55% at the 10-week test interval. Overall, larger rainfall depths were applied to treatment plots prior to runoff generation compared to controls. The most significant differences were observed at the 2-day test interval, when an average of 141 mm of rainfall was applied to the PAM-treated plots before runoff started, compared to 82 mm for the controls. These runoff reductions are not only important in terms of erosion but may also enhance water supply through increased infiltration. Sediment loss was reduced an average of 100% at the 2-day test interval, 80% at the 3-week test interval, and 74% at the 10-week test interval. Phosphorus loss was reduced an average of 100% at the 2-day test interval, 75% at the 3-week test interval, and 83% at the 10-week test interval. The polymer treatment was more effective on the Ashdale silt loam, which had received manure during the two years preceding the rainfall simulations. Manure application was the primary difference between the two soils (manure was not applied to the Plano silt loam), suggesting that the PAM treatment reacts more favorably to manured soils. The low cost of this new PAM technology (approx. $25 ha-1) coupled with its success in reducing runoff, sediment, and P loss over a 10-week period, make EM-1000-50 an attractive and economically feasible management practice for agricultural producers in rainfed regions. [ABSTRACT FROM AUTHOR]

Nitrate nitrogen (NO3-N) enriched water originates from subsurface drains or "tiles" that underlay many fields in the Corn Belt and is the primary source of NO3-N to surface waters in this region. To better assess the fate and transport of nutrients, such as NO3-N, the tile drain and pothole components of SWAT (Soil and Water Assessment Tool) were enhanced and modified in the previous component of this study. In this study, the environmental and economic impacts of various best management practice (BMP) scenarios often adopted by local farmers to reduce sediment and nutrient loadings (in particular NO3-N) were evaluated using the modified SWAT (SWAT-M) and FEM (Farm-level Economic Model) models. Measured values of water quality indicators from the Walnut Creek watershed (WCW) located in central Iowa were used to verify the capability of SWAT-M to predict the impact of late-spring nitrate test (LSNT) and rye cover crop management on NO3-N reduction at the subbasin level. The results obtained from SWAT-M simulation results, similar to field measurement data, indicated a 25% reduction in NO3-N under the LSNT scenario. FEM results indicated a corresponding increased annual cost of $6/ha across all farms in the watershed. Simulation of other scenarios, including winter cover cropping and a combination of LSNT and cover cropping at different adoption rates within WCW, resulted in a progressive reduction in sediment and nutrient losses as adoption rates increased. Use of the rye cover crop added about $25/ha to $35/ha to the annual cost of the average farm, indicating that some cost-share support may be necessary to encourage farmers to use winter cover crops. [ABSTRACT FROM AUTHOR]

Surface water impairments for pathogens are a major problem in waterways throughout the United States, especially in New Jersey. Fecal coliform (FC) counts are commonly used as an indicator of pathogens. In this study, bioretention systems, which are stormwater best management practices, were modeled with columns. Unlike traditional detention basins, bioretention systems are meant to manage water quality in addition to quantity and peak flow rates. Typical rainfall conditions for New Jersey were mimicked in the laboratory with regard to rainfall intensity and stormwater composition (bacterial colony counts) using a diluted manure slurry. The applied influent flow rate was 77.0 mL/min, while the average leachate flow rate observed in the bottom spout was 20.8 mL/min. The hydraulic performance of the columns was adequate in that the influent completely infiltrated well before the New Jersey Department of Environmental Protection (NJDEP) performance standard of 72 h. However, ponding of more than 30.5 cm (the NJDEP performance standard for ponding) was observed in some of the simulations. The mean, median, and range of reduction coefficients for fecal coliform (FC) were 91.6%, 98.6%, and 54.5% to 99.8%, respectively, for 13 simulations. The mean, median, and range of reduction coefficients for total suspended solids (TSS) were 91.5%, 91.9%, and 81.0% to 99.4%, respectively, for 15 simulations. The average pH of the influent water was 6.87, while the average leachate pH was 4.61. It is likely that both adsorption and filtration were responsible for the FC and TSS reductions. Die-off factors that may have influenced FC reduction in addition to adsorption and filtration are discussed. Reduction coefficients were observed to not necessarily be the ultimate indicator of system performance or effectiveness, as they are conditional upon the leachate concentration. [ABSTRACT FROM AUTHOR]

Environmental models are used to assess and evaluate various best management practices (BMPs) at field (e.g., Agricultural Policy/Environmental eXtender, APEX) and watershed (e.g., Soil and Water Assessment Tool, SWAT) levels. However, models such as SWAT and APEX are only capable of simulating, mechanistically, a limited number of BMP scenarios individually. Therefore, this study was conducted to: (1) develop an automated program referred to as SWAPP to convert SWAT files to and from APEX format and simulate SWAT and APEX simultaneously, and (2) to evaluate this program using measured data from the upper North Bosque River watershed in central Texas. In this study, SWAT (version 2000) and APEX (version 2110) were utilized within SWAPP. Simulations from SWAT alone (SWAT-A) and the combined SWAT and APEX models in SWAPP were compared with the historical measured data collected in the upper North Bosque River (UNBR) watershed. In the first phase of this study, SWAT-A was applied to simulate all land uses in the UNBR watershed. In the second phase, stream flow and losses of sediment and nutrients from all crop and pasture lands within the UNBR watershed were simulated by APEX. The results obtained from APEX, and remaining land uses in the UNBR watershed (e.g., urban) simulated by SWAT, were then routed to the outlet of the watershed using the SWAT routing function. The measured flow, sediment, and nutrients at three sites within the UNBR watershed were simulated by SWAT-A and the combined SWAT and APEX within SWAPP for the period of January 1994 through July 1999. The results obtained from the three sites within the UNBR watershed indicate that the pattern (Nash-Sutcliffe efficiencies, E) and average monthly values of flow and loadings predicted by the combined SWAT and APEX within SWAPP were similar, and in some cases (mainly for sediment and nutrients loadings) closer to the measured values, as compared to SWAT-A. For instance, the E values for flow obtained from SWAPP ranged from 0.65 to O. 74, while those from SWAT-A ranged from 0.55 to O. 75. The E value for sediment loading at three sampling sites ranged from 0.55 to O. 74 for SWAPP, as compared to 0.41 to O. 72 for SWAT-A, and the E values for nutrient loadings ranged from -0.04 to 0.88 for SWAPP, compared to -0.74 to 0.82 for SWAT-A. The results obtained from this study indicated that the SWAPP program not only improved the modeling results, but also provides an opportunity to utilize APEX within the SWAPP program for simulating management practices, such as multicropping or filter strips, at the field level, whereas SWAT alone currently has limited capability to simulate these practices. In addition, SWAPP can be used to rapidly convert SWAT data files, generated from Geographical Information System (GIS) layers, to APEX data file format. [ABSTRACT FROM AUTHOR]

Growing urbanization has led to increasing concern and emphasis on better construction site stormwater management. The objectives of this study were to determine the effectiveness of using compost rather than conventional hydroseeding or topsoil to reduce erosion from disturbed soils. The runoff rates, interrill erosion rates, and interrill erodibility factors from five compost and two control treatments (hydroseeding and topsoil) were compared. Compost treatments followed Texas Department of Transportation (TxDOT) specifications for compost applied as an erosion control at 1.3 and 5 cm depths. Rainfall simulation was used to apply a storm of 92 mm h-1. Surface runoff was collected after 5 min of rainfall (first-flush) and during the last 30 min of rainfall (steady-state). The first-flush mean runoff from the 5 cm depth general-use compost treatment was significantly higher than that of all other treatments. The other treatments (50% woodchips and 50% compost blend at 1.3 and 5 cm depths) and hydroseeding had significantly lower runoff and erosion rates compared to topsoil and compost manufactured topsoil at first-flush and steady-state. Furthermore, there were no performance differences between 1.3 and 5 cm compost applications at first-flush or steady-state. The TxDOT specification for erosion control compost depth might be able to be reduced from 5 to 1.3 cm. [ABSTRACT FROM AUTHOR]

Structural best management practices (BMPs) that reduce soil erosion and nutrient losses have been recommended and installed on agricultural land for years. A structural BMP is expected to be fully functional only for a limited period after installation, after which degradation of the BMP is likely to lead to a reduction in the water quality improvement provided by the BMP. Assessing the impact of BMPs on water quality is of widespread interest, but no standard methods exist to determine the water quality impact of structural BMPs, particularly as the impact changes through time. The objective of this study was to determine the long-term (∼20 year) impact of structural BMPs in two subwatersheds of Black Creek on sediment and phosphorus loads using the Soil and Water Assessment Tool (SWAT) model The BMPs were represented by modifying SWAT parameters to reflect the impact the practice has on the processes simulated within SWAT, both when practices are fully functional and as their condition deteriorates. The current condition of the BMPs was determined using field evaluation results from a previously developed BMP condition evaluation tool. Based on simulations in the two subwatersheds, BMPs in good condition reduced the average annual sediment yield by 16% to 32% and the average annual phosphorus yield by 10% to 24%. BMPs in their current condition reduced sediment yield by only 7% to 10% and phosphorus yield by 7% to 17%. [ABSTRACT FROM AUTHOR]

This article introduces a collection of papers from the fourth biennial ASABE 21st Century Watershed Technology Conference and Workshop: Improving Water Quality and the Environment, held in Hamilton, New Zealand, on November 3-6, 2014. This Special Collection consists of three articles selected from the 47 meeting papers. The technical presentations at the conference focused on solving spatial and temporal water quality and quantity problems and addressed topics such as watershed management in developing countries, water quality standards, agricultural best management practice (BMP) effectiveness, emerging problems, impact of extreme weather conditions, biological monitoring, increasing stakeholder involvement, political and economic implications, watershed implementation planning, forest and rangeland water quality issues, and water resources education. At first glance, these topics seem quite diverse. A more detailed look suggested that the "big data" and data mining themes of the last conference in Bari, Italy, continued to develop. [ABSTRACT FROM AUTHOR]