Load Reduction Efficiency Research Articles

Rapid nutrient load reduction during infiltration of managed aquifer recharge in an agricultural groundwater basin: Pajaro Valley, California

AbstractArtificial recharge of groundwater is an increasingly important method for augmenting groundwater supply and can have a positive or negative influence on the quality of water resources. We instrumented a managed aquifer recharge (MAR) pond in central coastal California to assess how patterns of infiltration and recharge affect the load of nitrate delivered to the underlying aquifer. The concentration of nitrate in infiltrating water consistently decreased during passage through the first metre of subsurface soils. Enrichment of 18O and 15 N in the residual nitrate in infiltrating water proceeded in a ratio of 1:2, indicating that denitrification plays a significant role in the quantitative reduction of nutrients exported during infiltration through shallow soils. The extent and rate of nitrate removal was spatially and temporally variable across the bottom of the recharge pond, with 30% to 60% of the nitrate load being removed over the first 6 weeks of managed aquifer recharge operation. During the period of highest N loading to the system, when the average infiltration rate was > 1 m/day, the recharge pond achieved a load reduction efficiency of 7 kg NO3−‐N/day/ha, which compares favourably to nitrate load reductions achieved by treatment wetlands. Groundwater mounding and water composition below the recharge pond suggest that recharge and subsequent lateral transport occur heterogeneously in the underlying aquifer. Nitrate concentrations in the aquifer following infiltration were lowered primarily by dilution, with little evidence for additional denitrification occurring in the aquifer in comparison to high rates documented during shallow infiltration. Copyright © 2011 John Wiley & Sons, Ltd.

Numerical Analysis of Slab Culvert Beneath Imperfect Ditch Covered with Geogrid Layers

The overburden of high embankment culvert is over 10 m, such high fill always leads large earth pressure on the slab of the culvert. The imperfect ditch covered with geogrid method was employed to reduce the vertical earth pressure on the slab. A series of numerical analyses were performed to investigate the load reduction effect of the imperfect ditch. In the simulation, the number of geogrid layers, the geometry of the load reduction ditches, as well as the location and the stiffness of the geogrid are investigated to analyse the influences on the vertical earth pressures. The results show that the slope angle and the height of the ditch, the plane stiffness of the geogrid have great effect on the load reduction efficiency, ditches with higher height and a slope of 90°lead to a significantly reduction on vertical earth pressures on the crown of culverts. The width of load reduction ditch, number of geogrid layers, the location and spacing of the geogrids have little effect on load reduction, the results can provide references for load reduction of slab culvert.

Assessing Best Management Practice Implementation Strategies under Climate Change Scenarios

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.

Performance of a Bioretention Area and a Level Spreader-Grass Filter Strip at Two Highway Sites in North Carolina

The pollutant removal efficiency of a bioretention area and a level spreader-grass filter strip implemented at North Carolina highway facilities was assessed. The assessment consisted of monitoring inflow, outflow, and on-site rainfall for at least 13 storm events. Monitoring included continuous discharge measurement and collecting and analyzing flow-proportional samples for each event. All samples were analyzed for solids, turbidity, and nitrogen and phosphorus forms and selected samples were analyzed for metals. The level spreader-grass filter strip had the best overall efficiency with load reduction efficiencies in all pollutants ranging from 24 to 83% and the highest reduction for total suspended solids (TSS). Much of the efficiency of this best management practice can be attributed to the 49% reduction in runoff volume from inflow to outflow. Pollutant reduction efficiencies for the bioretention area ranged from −254 to 76% with the highest reduction for TSS. The lowest or large negative efficiency w...

How to Include Economic Analysis in TMDL Allocation

The total maximum daily load approach currently used by the USEPA to restore an impaired stream by allocating allowable loads to the polluters does not mandate any economic consideration. The need for a cost-effective allocation process has long been identified but no single best way to accomplish this has yet been developed. This paper describes how the most economical load allocation scenario may be determined through an optimal placement of control measures within an agricultural watershed. The proposed optimization approach is applied to the bacterially impaired Roses Creek watershed located in the Commonwealth of Virginia. The cost-effectiveness relationships were established for vegetative buffer strips, streamside fencing, pet waste management, and septic system repair and installation to illustrate the methodology. Similar relationships may be established for other control measures provided their load reduction efficiencies are known.

Evaluating the Effectiveness of Two Stormwater Wetlands in North Carolina

Two constructed stormwater wetlands in North Carolina were monitored to document their efficiencies at reducing nitrogen, phosphorus, and sediment loads in runoff from urban areas. Inflow to and outflow from the two wetlands were monitored during at least ten storm events, and flow-proportional samples of each were collected and analyzed. The first wetland (CMS), located in the Piedmont region, had a relatively low wetland surface to drainage area ratio of 2.2%, while the second (UNC), located in the mountains region, had less storage and a wetland surface to drainage area ratio of 4.7%. The UNC wetland had a much more diverse and extensive plant community. For the CMS wetland, the median load reduction efficiencies of nitrogen forms ranged from 47% to 54%, while the corresponding reductions for the UNC wetland ranged from 57% to 71%. The median reduction efficiencies for phosphorus forms for the CMS wetland ranged from 59% to 76%, while those for the UNC wetland ranged from -95% to 70%. The median reduction efficiencies for TSS were 72% and 88% for the CMS and UNC wetlands, respectively. The median load reduction efficiencies of nitrogen forms, total phosphorus, and sediment for the UNC wetland were greater than for the CMS wetland and were considerably greater than corresponding median efficiencies of other completed studies. These results indicate that both of these wetlands were, in general, more efficient at reducing pollutant loading than many others reported in the literature. The greater efficiencies may be the result of a relatively high surface area to drainage area ratio and a diverse plant community in the UNC wetland and a considerable storage capacity of the CMS wetland.

Effects of Inland Nitrogen Transport and Attenuation Modeling on Coastal Nitrogen Load Abatement

Modeling of the spatial distribution of nitrogen transport and attenuation from various inland sources and along different hydrological pathways to coastal waters is needed for relevant decisions on effective allocation of measures for coastal nitrogen load abatement. We identify, classify, and quantify uncertainties associated with main discrepancies between spatial process representations in different catchment-scale nitrogen transport-attenuation models. The results show important model differences, indicating scientific disagreement on the realistic spatial process understanding, representation, and quantification in nitrogen transport-attenuation modeling. By further developing solutions for economic optimization of spatially differentiated nitrogen source abatement in coastal catchments, we find this disagreement to considerably affect the economic efficiency of coastal nitrogen load reduction. It may also lead to stakeholder mistrust and conflict and needs to be recognized and handled in environmental policy.

Impact of air leakages and short circuits in ventilation units with heat recovery on ventilation efficiency and energy requirements for heating

The impact of unintentional air flows on the performance of ventilation units with heat recovery is discussed on the basis of single room ventilation units. Assuming an external short circuit (outdoor) and internal (inside the ventilation unit) air leakages, which lead to internal short circuits, a model is developed and characteristic numbers for ventilation efficiency, efficiency of heating load reduction and effectiveness of electrical energy use are derived. Differences between supply and extract air flow rates, resulting in increased air flows through cracks in the building envelope, are taken into consideration too. The use of tracer gas techniques to measure air leakage rates from ventilation units is described briefly. It is shown by numerical examples that unintentional air flows can considerably reduce the performance of ventilation units in terms of ventilation efficiency and, in combination with unintentional heat flows through the casing, energy savings. Therefore, these flows should be avoided or at least reduced to an acceptable level by an appropriate construction, manufacturing process and installation of the units.

LAKE CHAMPLAIN BASIN NONPOINT SOURCE PHOSPHORUS ASSESSMENT1

ABSTRACT: Existing land use data were used to estimate nonpoint source phosphorus loads to Lake Champlain (Vermont/New York/Quebec) in a loading function model that combined P concentration coefficients with regional hydrologic data. The estimates were verified against monitored loading data, then used to assess the relative magnitudes of contributions from major land uses and regions of the Lake Champlain Basin. The Basin is comprised of 62 percent forest, 28 percent agricultural land, 3 percent urban land, and 7 percent water. The best‐fit model estimated an annual total P load of 457 mt/year, which did not differ significantly from the 458 metric tons/year measured for an average hydrologic year, and accurately predicted loads from major tributaries. Agriculture contributes 66 percent of the annual nonpoint source P load to Lake Champlain; urban and forest land contribute 18 percent and 16 percent, respectively. Because agricultural land contributes most nonpoint source P to Lake Champlain, load reduction effort must deal with agricultural sources. However, because the urban 3 percent of the basin contributes 18 percent of the estimated load, high load reduction efficiencies might be achieved by addressing urban sources. This assessment clearly demonstrated the relationship between land use and P loads in the Lake Champlain Basin, a prerequisite for policy‐makers to endorse a P management strategy requiring changes in land use and management.

Wind-tunnel tests on a model antenna rotating in a cross flow

Aerodynamic loads acting on a rotating antenna depend essentially on its speed of rotation. Due to the complexity of wind-tunnel tests on a rotating model, the evaluation of these loads is usually obtained through tests carried out on a non-rotating model, suitably modifying the results with theoretical or semi-empirical methods to account for rotation. In order to investigate the accuracy of this methodology, wind-tunnel tests on a rotating antenna placed in a cross flow were carried out and the experimental results were compared with those obtained from tests on a static model with subsequent application of the quasi-steady theory to determine the loads whilst in rotation. Differences emerged from the comparison between the two procedures, some of which were quite significant; an attempt has been made to determine the reasons leading to these differences. Furthermore, the tests on the rotating model were used to verify the efficiency of load reduction of a new fin configuration previously analysed with tests on a static model. Tests showed that significant reductions in torque can be obtained with the new fin configuration, confirming the possibility of its use in practical applications.