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At least 325 records · Page 18Linked to original sources
USGS1997

Level II scour analysis for Bridge 49 (BENNCYHUNT0049) on Hunt Street, crossing the Walloomsac River, Bennington, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BENNCYHUNT0049 on the Hunt Street crossing of the Walloomsac River, Bennington, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in southwestern Vermont. The 34.1-mi 2 drainage area is a predominantly rural and forested basin. The bridge site is located within an urban setting in the Town of Bennington with buildings and parking lots on overbanks except for the downstream left bank which is covered by trees and brush. In the study area, the Walloomsac River has a straight, incised channel. The confluence of the Walloomsac River and Roaring Branch is 140 feet downstream. The channel has a slope of approximately 0.01 ft/ft, an average channel top width of 54 ft and an average bank height of 6 ft. The predominant channel bed material is cobble with a median grain size (D 50 ) of 76.8 mm (0.252 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 31, 1996, indicated that the reach was stable. The Hunt Street crossing of the Walloomsac River is a 51-ft-long, two-lane bridge consisting of one 49-foot steel span (Vermont Agency of Transportation, written communication, December 13, 1995). The bridge is supported by vertical, concrete abutments. The right abutment has a spill-through slope along its face. The channel is skewed approximately 25 degrees to the opening and the opening-skew-to-roadway is 20 degrees. Scour countermeasures at the site include type-2 stone fill (less than 36 inches diameter) on the spill through slope on the right abutment and along the base of the left abutment. Type- 2 stone fill also protects the channel banks upstream and downstream of the bridge for a minimum distance of 17 feet from the respective bridge faces. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour computed for all modelled flows ranged from 0.9 to 5.0 ft. The worst-case contraction scour occurred at the 500-year discharge. Computed left abutment scour ranged from 15.3 to 16.5 ft. with the worst-case scour occurring at the incipient roadway-overtopping discharge. Computed right abutment scour ranged from 6.0 to 8.7 ft. with the worst-case scour occurring at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1997

Level II scour analysis for Bridge 10 (BENNUS00070010) on U.S. Route 7, crossing the Walloomsac River, Bennington, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BENNUS00070010 on U.S. Route 7, also known as North Street, crossing of the Walloomsac River, Bennington, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in southwestern Vermont. The 30.1-mi 2 drainage area is a predominantly rural and forested basin. The bridge site is located within an urban setting in the Town of Bennington with buildings, parking lots, lawns, and a playground on the overbank areas. In the study area, the Walloomsac River has a straight channel with constructed channel banks through much of the reach. The channel is located on a delta and has a slope of approximately 0.02 ft/ft, an average channel top width of 37 ft and an average bank height of 5 ft. The predominant channel bed material is cobble with a median grain size (D 50 ) of 96.0 mm (0.315 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 5, 1996, indicated that the constructed reach was stable. The U.S. Route 7 crossing of the Walloomsac River is a 53-ft-long, two-lane bridge consisting of one 50-foot steel span (Vermont Agency of Transportation, written communication, September 27, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The wingwalls are angled in toward the channel because the widths of the upstream and downstream constructed channel banks are narrower than the bridge opening. The channel is skewed approximately 5 degrees to the opening and the opening-skew-to-roadway is 10 degrees. Scour countermeasures at the site include masonry and stone walls on both the upstream and downstream banks. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour computed for all modelled flows ranged from 0.0 to 0.1 ft. The worstcase contraction scour occurred at the 500-year discharge. Computed left abutment scour ranged from 5.9 to 6.8 ft. with the worst-case scour occurring at the 500-year discharge. Computed right abutment scour for all modelled flows was 6.8 ft. Total scour depths for all modelled flows did not exceed the depth of the abutment footings. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1998

Level II scour analysis for Bridge 42 (NEWFTH00350042) on Town Highway 35, crossing Stratton Hill Brook, Newfane, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure NEWFTH00350042 on Town Highway 35 crossing Stratton Hill Brook, Newfane, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (FHWA, 1993). Results of a Level I scour investigation also are included in appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in appendix D. The site is in the New England Upland section of the New England physiographic province in southeastern Vermont. The 1.16-mi2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forested. In the study area, Stratton Hill Brook has an incised, striaght channel with a slope of approximately 0.1 ft/ft, an average channel top width of 36 ft and an average bank height of 8 ft. The channel bed material ranges from gravel to boulders with a median grain size (D50) of 121 mm (0.396 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 20, 1996, indicated that the reach was stable. The Town Highway 34 crossing of Stratton Hill Brook is a 34-ft-long, one-lane bridge consisting of a 32-foot steel-beam span (Vermont Agency of Transportation, written communication, April 6, 1995). The opening length of the structure parallel to the bridge face is 30.8 ft. The bridge is supported by vertical, concrete abutments with upstream wingwalls. The channel is skewed approximately 20 degrees to the opening while the computed opening-skew-to-roadway is 15 degrees. During the Level I assessment, it was observed that the right abutment footing was exposed 1.5 feet. The only scour protection measure at the site was type-1 stone fill (less than 12 inches diameter) along the downstream left bank. Additional details describing conditions at the site are included in the Level II Summary and appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and Davis, 1995) for the 100- and 500-year discharges. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows was zero ft. Abutment scour ranged from 2.3 to 3.3 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and Davis, 1995, p. 46). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1998

Level II scour analysis for brigde 5 (STOCTH00360005) on Town Highway 36, crossing Stony Brook, Stockridge, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure STOCTH00360005 on Town Highway 36 crossing Stony Brook, Stockbridge, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in appendix D. The site is in the Green Mountain section of the New England physiographic province in central Vermont. The 23.0-mi2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest on the left and right banks downstream and left bank upstream, while the right bank upstream is pasture with some shrubs and brush. In the study area, Stony Brook has an incised, sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 109 ft and an average bank height of 11 ft. The channel bed material is predominantly gravel with a median grain size (D50) of 71.7 mm (0.235 ft). The geomorphic assessment at the time of the Level I site visit on April 12, 1995, and Level II site visit on July 9, 1996, indicated that the reach was stable. The Town Highway 36 crossing of Stony Brook is a 50-ft-long, one-lane bridge consisting of one 48-foot steel-beam span (Vermont Agency of Transportation, written communication, March 23, 1995). The opening length of the structure parallel to the bridge face is 46.3 ft. The bridge is supported by a vertical, concrete abutment on the left and a vertical, concrete abutment with wingwalls on the right. The channel is skewed approximately 5 degrees to the opening while the opening-skew-to-roadway is 0 degrees. A scour hole 2.0 ft deeper than the mean thalweg depth was observed during the Level I assessment along the left side of the channel at the downstream bridge face where the flow impacts a bedrock outcrop. Scour protection measures at the site included type-1 stone fill (less than 12 inches diameter) along the right bank upstream and at the upstream and downstream ends of the left abutment, type-2 stone fill (less than 36 inches diameter) at the upstream end of the upstream right wingwall, and type-3 stone fill (less than 48 inches diameter) at the downstream end of the downstream right wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and recommended rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and Davis, 1995) for the 100- and 500-year discharges. Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 2.0 to 3.2 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 9.7 to 22.2 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and Davis, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS2011

TOPMODEL simulations of streamflow and depth to water table in Fishing Brook Watershed, New York, 2007-09

TOPMODEL, a physically based, variable-source area rainfall-runoff model, was used to simulate streamflow and depth to water table for the period January 2007-September 2009 in the 65.6 square kilometers of Fishing Brook Watershed in northern New York. The Fishing Brook Watershed is located in the headwaters of the Hudson River and is predominantly forested with a humid, cool continental climate. The motivation for applying this model at Fishing Brook was to provide a simulation that would be effective later at this site in modeling the interaction of hydrologic processes with mercury dynamics. TOPMODEL uses a topographic wetness index computed from surface-elevation data to simulate streamflow and subsurface-saturation state, represented by the saturation deficit. Depth to water table was computed from simulated saturation-deficit values using computed soil properties. In the Fishing Brook Watershed, TOPMODEL was calibrated to the natural logarithm of streamflow at the study area outlet and depth to water table at Sixmile Wetland using a combined multiple-objective function. Runoff and depth to water table responded differently to some of the model parameters, and the combined multiple-objective function balanced the goodness-of-fit of the model realizations with respect to these parameters. Results show that TOPMODEL reasonably simulated runoff and depth to water table during the study period. The simulated runoff had a Nash-Sutcliffe efficiency of 0.738, but the model underpredicted total runoff by 14 percent. Depth to water table computed from simulated saturation-deficit values matched observed water-table depth moderately well; the root mean squared error of absolute depth to water table was 91 millimeters (mm), compared to the mean observed depth to water table of 205 mm. The correlation coefficient for temporal depth-to-water-table fluctuations was 0.624. The variability of the TOPMODEL simulations was assessed using prediction intervals grouped using the combined multiple-objective function. The calibrated TOPMODEL results for the entire study area were applied to several subwatersheds within the study area using computed hydrogeomorphic properties of the subwatersheds.

Scientific Investigations Report↗
USGS2004

Estimation of Total Nitrogen and Phosphorus in New England Streams Using Spatially Referenced Regression Models

The U.S. Geological Survey (USGS), in cooperation with the U.S. Environmental Protection Agency (USEPA) and the New England Interstate Water Pollution Control Commission (NEIWPCC), has developed a water-quality model, called SPARROW (Spatially Referenced Regressions on Watershed Attributes), to assist in regional total maximum daily load (TMDL) and nutrient-criteria activities in New England. SPARROW is a spatially detailed, statistical model that uses regression equations to relate total nitrogen and phosphorus (nutrient) stream loads to nutrient sources and watershed characteristics. The statistical relations in these equations are then used to predict nutrient loads in unmonitored streams. The New England SPARROW models are built using a hydrologic network of 42,000 stream reaches and associated watersheds. Watershed boundaries are defined for each stream reach in the network through the use of a digital elevation model and existing digitized watershed divides. Nutrient source data is from permitted wastewater discharge data from USEPA's Permit Compliance System (PCS), various land-use sources, and atmospheric deposition. Physical watershed characteristics include drainage area, land use, streamflow, time-of-travel, stream density, percent wetlands, slope of the land surface, and soil permeability. The New England SPARROW models for total nitrogen and total phosphorus have R-squared values of 0.95 and 0.94, with mean square errors of 0.16 and 0.23, respectively. Variables that were statistically significant in the total nitrogen model include permitted municipal-wastewater discharges, atmospheric deposition, agricultural area, and developed land area. Total nitrogen stream-loss rates were significant only in streams with average annual flows less than or equal to 2.83 cubic meters per second. In streams larger than this, there is nondetectable in-stream loss of annual total nitrogen in New England. Variables that were statistically significant in the total phosphorus model include discharges for municipal wastewater-treatment facilities and pulp and paper facilities, developed land area, agricultural area, and forested area. For total phosphorus, loss rates were significant for reservoirs with surface areas of 10 square kilometers or less, and in streams with flows less than or equal to 2.83 cubic meters per second. Applications of SPARROW for evaluating nutrient loading in New England waters include estimates of the spatial distributions of total nitrogen and phosphorus yields, sources of the nutrients, and the potential for delivery of those yields to receiving waters. This information can be used to (1) predict ranges in nutrient levels in surface waters, (2) identify the environmental variables that are statistically significant predictors of nutrient levels in streams, (3) evaluate monitoring efforts for better determination of nutrient loads, and (4) evaluate management options for reducing nutrient loads to achieve water-quality goals.

Scientific Investigations Report↗
USGS2011

Variation in spring harvest rates of male wild turkeys in New York, Ohio, and Pennsylvania

Spring harvest rates of male wild turkeys ( Meleagris gallapavo ) influence the number and proportion of adult males in the population and turkey population models have treated harvest as additive to other sources of mortality. Therefore, hunting regulations and their effect on spring harvest rates have direct implications for hunter satisfaction. We used tag recovery models to estimate survival rates, investigate spatial, temporal, and demographic variability in harvest rates, and assess how harvest rates may be related to management strategies and landscape characteristics. We banded 3,266 male wild turkeys throughout New York, Ohio, and Pennsylvania during 2006–2009. We found little evidence that harvest rates varied by year or management zone. The proportion of the landscape that was forested within 6.5 km of the capture location was negatively related to harvest rates; however, even though the proportion forested ranged from 0.008 to 0.96 across our study area, this corresponded to differences in harvest rates of only 2–5%. Annual survival was approximately twice as high for juveniles as adults . In turn, spring harvest rates for adult turkeys were greater for adults than juveniles . We estimated the population of male turkeys in New York and Pennsylvania ranged from 104,000 to 132,000 in all years and ranged from 63,000 to 75,000 in Ohio. Because of greater harvest rates for adult males, the proportion of adult males in the population was less than in the harvest and ranged from 0.40 to 0.81 among all states and years. The high harvest rates observed for adults may be offset by greater recruitment of juveniles into the adult age class the following year such that these states can sustain high harvest rates yet still maintain a relative high proportion of adult males in the harvest and population.

New York, Ohio, Pennsylvania↗
USGS2017

Validation of NEXRAD data and models of bird migration stopover sites in the Northeast U.S.

The national network of weather surveillance radars (NEXRAD) detects birds in flight, and has proven to be a useful remote-sensing tool for ornithological study. We used data collected during Fall 2008 to 2014 by 16 NEXRAD and four terminal Doppler weather radars (TDWR) in the northeastern U.S. to map and study the spatial distribution of landbirds shortly after they leave daytime stopover sites to embark on nocturnal migratory flights. Given observed variability in the precise timing of migratory exodus, we developed a new method to sample the onset of migration at the point of maximum rate of increase in bird densities aloft to consistently sample exodus across radars and days. The mean linear trend in aggregate stopover densities of migrants indicated a 4% decline per year from the 2008 baseline density (29% decline over the seven years). Regionally, coastal Virginia and Maine had the steepest declines. The steepest increases in migrant densities across years occurred within the Delmarva Peninsula and in coastal Connecticut. We used NEXRAD observations to develop models to predict potentially important stopover sites throughout USFWS Region 5. Observed NEXRAD data were positively correlated to observations from TDWR and NASA’s S-Band Dual-Polarimetric Radar (NPOL), though not strongly. Predicted densities increased with increasing hardwood cover across multiple scales and with vegetation productivity. Contrastingly, predicted densities decreased with increasing agricultural, emergent marsh and coniferous land cover, but did not change with fraction of urban cover. Stopover density increased closer to bright areas and the Atlantic coast. Moreover, interactive effects indicated that migrants were more concentrated in forested areas that were both brightly lit and near the Atlantic coast. Large areas of predicted regionally important stopover sites were located along the coastlines of Maine, Long Island Sound, New Jersey, the lower Delmarva Peninsula, within the Adirondack Mountains, Catskill Mountains, and eastern Virginia. We also created maps of classified stopover use during bimonthly periods and at multiple-scales. Migrant densities peaked along the Adirondack Mountains early in September, and along the Atlantic coast in late September with the passage of Neotropical migrants. Stopover densities peaked in the most northern extent of Maine and New England States in late October with the departure of temperate migrants. Ground surveys conducted at 48 forested sites within the Delmarva Peninsula and Tidewater Virginia during Fall 2013 and 2014 revealed that nocturnal migrant densities pooled across species and for 14 individual species, after accounting for temporal phenology in their passage timing, were related to factors operating at multiple scales including food resources (primarily arthropod abundance in understory) and understory shrub density at a patch scale, and latitude and proximity to the Atlantic coast at a regional scale. We integrated field survey and radar data to estimate relative stopover duration and to identify stopover functional types among 45 sites that included data from a past study near the Gulf of Mexico. We identified four functional types spanning the gradient of short rest stops to refueling stops with variable duration of stopover in relation to food abundance. The Mid-Atlantic sites were dominated by rest stops near coastal areas and lacked quick refueling stops due to low overall food abundance. The maps and ecological understanding produced can help inform conservation planning to protect and enhance stopover sites for migratory landbirds in the future.

Report↗
USGS2016

Forest disturbance interactions and successional pathways in the Southern Rocky Mountains

The pine forests in the southern portion of the Rocky Mountains are a heterogeneous mosaic of disturbance and recovery. The most extensive and intensive stress and mortality are received from human activity, fire, and mountain pine beetles (MPB; Dendroctonus ponderosae ). Understanding disturbance interactions and disturbance-succession pathways are crucial for adapting management strategies to mitigate their impacts and anticipate future ecosystem change. Driven by this goal, we assessed the forest disturbance and recovery history in the Southern Rocky Mountains Ecoregion using a 13-year time series of Landsat image stacks. An automated classification workflow that integrates temporal segmentation techniques and a random forest classifier was used to examine disturbance patterns. To enhance efficiency in selecting representative samples at the ecoregion scale, a new sampling strategy that takes advantage of the scene-overlap among adjacent Landsat images was designed. The segment-based assessment revealed that the overall accuracy for all 14 scenes varied from 73.6% to 92.5%, with a mean of 83.1%. A design-based inference indicated the average producer’s and user’s accuracies for MPB mortality were 85.4% and 82.5% respectively. We found that burn severity was largely unrelated to the severity of pre-fire beetle outbreaks in this region, where the severity of post-fire beetle outbreaks generally decreased in relation to burn severity. Approximately half the clear-cut and burned areas were in various stages of recovery, but the regeneration rate was much slower for MPB-disturbed sites. Pre-fire beetle outbreaks and subsequent fire produced positive compound effects on seedling reestablishment in this ecoregion. Taken together, these results emphasize that although multiple disturbances do play a role in the resilience mechanism of the serotinous lodgepole pine, the overall recovery could be slow due to the vast area of beetle mortality.

Colorado, New Mexico, Wyoming↗
USGS2011

Spatial patterns of mercury in macroinvertebrates and fishes from streams of contrasting forested landscapes in the eastern United States

Controls on mercury bioaccumulation in lotic ecosystems are not well understood. During 2007&ndash;2009, we studied mercury and stable isotope spatial patterns of macroinvertebrates and fishes from two medium-sized (<80 km 2 ) forested basins in contrasting settings. Samples were collected seasonally from multiple sites across the Fishing Brook basin (FBNY), in New York's Adirondack Mountains, and the McTier Creek basin (MCSC), in South Carolina's Coastal Plain. Mean methylmercury (MeHg) concentrations within macroinvertebrate feeding groups, and mean total mercury (THg) concentrations within most fish feeding groups were similar between the two regions. However, mean THg concentrations in game fish and forage fish, overall, were much lower in FBNY (1300 and 590 ng/g dw, respectively) than in MCSC (2300 and 780 ng/g dw, respectively), due to lower trophic positions of these groups from FBNY (means 3.3 and 2.7, respectively) than MCSC (means 3.7 and 3.3, respectively). Much larger spatial variation in topography and water chemistry across FBNY contributed to greater spatial variation in biotic Hg and positive correlations with dissolved MeHg and organic carbon in streamwater. Hydrologic transport distance (HTD) was negatively correlated with biotic Hg across FBNY, and was a better predictor than wetland density. The small range of landscape conditions across MCSC resulted in no consistent spatial patterns, and no discernable correspondence with local-scale environmental factors. This study demonstrates the importance of local-scale environmental factors to mercury bioaccumulation in topographically heterogeneous landscapes, and provides evidence that food-chain length can be an important predictor of broad-scale differences in Hg bioaccumulation among streams.

New York, South Carolina↗
USGS2021

Clustering supported classification of ChemCam data from Gale crater, Mars

The Chemistry and Camera (ChemCam) instrument on board the MSL rover Curiosity has collected a very large and unique dataset of in-situ spectra and images of Mars since landing in August 2012. More than 800,000 single shot LIBS (laser-induced breakdown spectroscopy) spectra measured on more than 2,500 individual targets were returned so far by ChemCam. Such a dataset is ideally suited for the application of statistical methods for the recognition of patterns that are difficult to observe by humans. In this work, we develop an approach relying on the feature extraction method non-negative matrix factorization (NMF) and the repetition of k-means clustering to classify ChemCam spectra. A strong consistency of the clustering results among the repetitions were found, which allowed us to identify six clusters representing the dominant compositions measured by ChemCam in Gale crater so far. By tracking clusters across the rover traverse from landing to sol 2756, we are able to provide a chemostratigraphic overview of Gale crater from the ChemCam perspective. Transitions between major geologic groups (such as the Bradbury and the Mt. Sharp groups) are identifiable demonstrating that they are compositionally distinct, consistent with previous work. Compositional differences between their members also appear in the results. Furthermore, a first approach in which a random forest classifier was trained and validated with the obtained cluster assignments, reveals promising results for predicting cluster memberships of new ChemCam LIBS data acquired after sol 2756.

Earth and Space Science↗
USGS2001

Acidic deposition in the northeastern United States: Sources and inputs, ecosystem effects, and management strategies: The effects of acidic deposition in the northeastern United States include the acidification of soil and water, which stresses terrestrial and aquatic biota

Acidic deposition is the transfer of strong acids and acid-forming substances from the atmosphere to the surface of the Earth. The composition of acidic deposition includes ions, gases, and particles derived from the following: gaseous emissions of sulfur dioxide (SO 2 ), nitrogen oxides (NO x ), ammonia (NH 3 ), and particulate emissions of acidifying and neutralizing compounds. Over the past quarter century of study, acidic deposition has emerged as a critical environmental stress that affects forested landscapes and aquatic ecosystems in North America, Europe, and Asia. This complex problem is an example of a new class of environmental issues that are multiregional in scale and are not amenable to simple resolution by policymakers. Acidic deposition can originate from transboundary air pollution and can affect large geographic areas. It is highly variable across space and time, links air pollution to diverse terrestrial and aquatic ecosystems, and alters the interactions of many elements (e.g., sulfur [S], nitrogen [N], hydrogen ion [H + ], calcium [Ca 2+ ], magnesium [Mg 2+ ], and aluminum [Al]). It also contributes directly and indirectly to biological stress and to the degradation of ecosystems. Despite the complexity of the effects of acidic deposition, North American and European management actions directed toward the recovery of damaged natural resources have resulted in recent decreases in both emissions and deposition of acidic S compounds. Accordingly, acidic deposition presents an instructive case study for coordinating science and policy efforts aimed at resolving large-scale environmental problems.

northeastern United States↗
USGS1996

Level II scour analysis for Bridge 45b (BRIDTH00040045b) on Town Highway 4, crossing an unnamed Dailey Hollow Branch Tributary, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH0004045B on town highway 4 crossing an unnamed Dailey Hollow Branch Tributary, Bridgewater, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in central Vermont. The 2.47-mi 2 drainage area is in a predominantly rural and forested basin. Surface cover in the vicinity of the study site is variable. A gravel road is adjacent to the left bank with the immediate upstream left bank covered by grass and the immediate downstream left bank covered by shrubs and brush. The upstream right bank is densely forested; the downstream right overbank is covered by grass with trees and brush on the immediate channel bank. In the study area, this unnamed Dailey Hollow Branch Tributary has an incised channel with a slope of approximately 0.04 ft/ft, an average channel top width of 29 ft and an average channel depth of 4 ft. The predominant channel bed material is gravel with a median grain size (D 50 ) of 47.0 mm (0.154 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 15, 1994, indicated that the reach was stable. The town highway 4 crossing of the unnamed Dailey Hollow Branch Tributary is a 62-ft-long, corrugated steel multi-plate arch structure. It is supported by concrete footings leaving natural stream bed exposed (Vermont Agency of Transportation, written communication, January, 1996). The road embankments are protected by stone fill, however, the size is unknown due to sand and grass covering the fill except for the upstream left embankment which has type-2 stone fill (less than 36 inches diameter). The downstream left bank is protected by type-3 stone fill (less than 48 inches diameter) extending 25 feet downstream of the culvert. The channel approach to the culvert has a mild s-curve bend with the opening skewed ten degrees to flow. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1993). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 1.1 to 1.8 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 7.7 to 11.7 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1993, p. 48). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 10 (HANCTH00010010) on Town Highway 1, crossing the White River, Hancock, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure HANCTH00010010 on town highway 1 crossing the White River, Hancock, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province of central Vermont. The 59.8-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is primarily grass with trees and brush on the immediate channel banks. In the study area, the White River has a sinuous channel with a slope of approximately 0.005 ft/ft, an average channel top width of 104 ft and an average channel depth of 6 ft. The predominant channel bed materials are gravel and cobble with a median grain size (D50) of 98.9 mm (0.325 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 15, 1994, indicated that the reach was stable. The town highway 1 crossing of the White River is a 91-ft-long, two-lane bridge consisting of one 89-foot steel-beam span (Vermont Agency of Transportation, written communication, August 26, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 15 degrees to the opening while the opening-skew-to-roadway is 0 degrees. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows was 0.0 feet. Abutment scour ranged from 13.1 to 17.1 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 99 (LUDLVT01000099) on State Highway 99, crossing Branch Brook, Ludlow, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure LUDLVT01000099 on State Highway 100 crossing Branch Brook, Ludlow, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in central Vermont. The 15.7-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the channel banks are densely covered by trees and brush. The overbanks are primarily covered by field grasses. In the study area, Branch Brook has an incised, straight channel with a slope of approximately 0.003 ft/ft, an average channel top width of 73 ft and an average channel depth of 5 ft. The predominant channel bed materials are cobble and gravel with a median grain size (D 50 ) of 60.5 mm (0.198 ft). The geomorphic assessment at the time of the Level I and Level II site visit on October 13, 1995, indicated that the reach was stable. The State Highway 100 crossing of Branch Brook is a 84-ft-long, two-lane bridge consisting of one 82-foot steel-beam span (Vermont Agency of Transportation, written communication, March 13, 1995). The bridge is supported by vertical, concrete abutments. The abutments are set back from the channel edge and have a spill-through slope consisting of type-4 stone fill (median size less than 60 inches in diameter). The channel skew and the opening-skew-to-roadway is zero degrees. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 1.5 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 1.0 to 7.4 ft. The worst-case abutment scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 32 (CONCTH00030032) on Town Highway 3, crossing the Moose River, Concord, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CONCTH00030032 on Town Highway 3 crossing the Moose River, Concord, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. Approximately 85 percent of the drainage above the site is in the White Mountain section and 15 percent is in the New England Upland section of the New England physiographic province in northeastern Vermont. The 98.7-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is primarily grass with several houses and other buildings while the immediate channel banks have dense woody vegetation. In the study area, the Moose River has an incised, sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 83 ft and an average channel depth of 3 ft. The predominant channel bed material is cobble with a median grain size (D 50 ) of 86.2 mm (0.283 ft). There are bedrock exposures downstream of the bridge. The geomorphic assessment at the time of the Level I and Level II site visit on August 17, 1995, indicated that the reach was stable. The Town Highway 3 crossing of the Moose River is a 96-ft-long, two-lane bridge consisting of two steel-beam spans (Vermont Agency of Transportation, written communication, March 24, 1995). The bridge is supported by vertical, concrete abutments with wingwalls and a concrete pier. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is 0 degrees. The right upstream end of the pier is undermined by 1.3 feet. The footing of the right abutment is exposed by as much as 4.0 feet vertically. The footing of the downstream right wingwall is exposed 3.5 feet and the end of the wingwall has broken and fallen into the river. Type-3 stone fill (less than 48 inches diameter) has been placed at the end of the existing wingwall. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 0.0 to 0.7 ft. Abutment scour ranged from 9.9 to 16.4 ft. Pier scour ranged from 14.4 to 16.2 ft. The worst-case contraction, abutment, and pier scour occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 94 (FERDVT01050094) on State Route 105, crossing the Nulhegan River, Ferdinand, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure FERDVT01050094 on State Route 105 crossing the Nulhegan River, Ferdinand, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the White Mountain section of the New England physiographic province in northeastern Vermont. The 38.4-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is grass and brush with wetlands immediately adjacent to the stream channel. In the study area, the Nulhegan River has a meandering channel with a slope of approximately 0.002 ft/ft, an average channel top width of 60 ft and an average channel depth of 6 ft. The predominant channel bed material is sand with a median grain size (D 50 ) of 0.465 mm (0.00153 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 5, 1995, indicated that the reach was laterally unstable. The State Route 105 crossing of the Nulhegan Riveris a 44-ft-long, two-lane bridge consisting of one 42-foot steel-beam span (Vermont Agency of Transportation, written communication, March 6, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is zero degrees. Scour protection measures at the site were type-2 stone fill (less than 36 inches diameter) on the upstream right bank, the upstream right wingwall, the right abutment, the downstream end of the left abutment and the downstream wingwalls. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 1.2 to 1.9 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 6.6 to 11.0 ft. The worst-case abutment scour also occurred at the 500-year discharge. Total scour depths computed for this site were not below the bottom of the footings, except for the 500- year discharge model at the left abutment. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A crosssection of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗
USGS1996

Level II scour analysis for Bridge 38 (RANDTH00640038) on Town Highway 64, crossing the Second Branch of the White River, Randolph, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure RANDTH00640038 on town highway 64 crossing the Second Branch of the White River, Randolph, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province of central Vermont. The 46.5-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the The upstream left bank is forested, the upstream right bank is covered primarily by brush, the surface cover is pasture on the downstream left and row crops on the downstream right. In the study area, the Second Branch of the White River has an incised, sinuous channel with a slope of approximately 0.0015 ft/ft, an average channel top width of 71 ft and an average channel depth of 8 ft. The predominant channel bed material is gravel with a median grain size (D 50 ) of 32.0 mm (0.105 ft). The geomorphic assessment at the time of the Level I site visits on August 10, 1994 and December 5, 1994 indicated that the reach was laterally unstable. The town highway 64 crossing of the Second Branch of the White Riveris a 43-ft-long, one-lane covered bridge consisting of one 35-foot steel-beam span (Vermont Agency of Transportation, written communication, August 1, 1994). The bridge is supported by vertical, stone abutments with upstream wingwalls. The channel bends sharply at it’s approach to the bridge, however, at the bridge face, the channel is skewed approximately 0 degrees to the opening. The opening-skew-to-roadway is also 0 degrees. A scour hole 2 ft deeper than the mean thalweg depth was observed upstream of the bridge along the outside of the channel bend. Other scour problems at this site included undermining of the right abutment at it’s upstream and downstream ends. Additional details describing conditions at the site are included in the Level II Summary and Appendices D and E. Scour depths and rock rip-rap sizes were computed using the general guidelines described in Hydraulic Engineering Circular 18 (Richardson and others, 1995). Total scour at a highway crossing is comprised of three components: 1) long-term streambed degradation; 2) contraction scour (due to accelerated flow caused by a reduction in flow area at a bridge) and; 3) local scour (caused by accelerated flow around piers and abutments). Total scour is the sum of the three components. Equations are available to compute depths for contraction and local scour and a summary of the results of these computations follows. Contraction scour for all modelled flows ranged from 1.7 to 2.6 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 7.2 to 24.2 ft. The worst-case abutment scour also occurred at the 500-year discharge. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A cross-section of the scour computed at the bridge is presented in figure 8. Scour depths were calculated assuming an infinite depth of erosive material and a homogeneous particle-size distribution. It is generally accepted that the Froehlich equation (abutment scour) gives “excessively conservative estimates of scour depths” (Richardson and others, 1995, p. 47). Usually, computed scour depths are evaluated in combination with other information including (but not limited to) historical performance during flood events, the geomorphic stability assessment, existing scour protection measures, and the results of the hydraulic analyses. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein.

Vermont↗