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At least 307 records · Page 17Linked to original sources
USGS1997

Level II scour analysis for Bridge 37, (BRNETH00740037) on Town Highway 74, crossing South Peacham Brook, Barnet, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRNETH00740037 on Town Highway 74 crossing South Peacham Brook, Barnet, 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 New England Upland section of the New England physiographic province in northeastern Vermont. The 12.1-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture upstream of the bridge and on the downstream left bank while the immediate banks have sparse shrubs and trees. Downstream of the bridge, the surface cover is shrub and brushland. In the study area, South Peacham Brook has an incised, sinuous channel with a slope of approximately 0.004 ft/ft, an average channel top width of 33 ft and an average bank height of 3 ft. The channel bed material ranges from sand to cobble with a median grain size (D 50 ) of 0.914 mm (0.003 ft). The geomorphic assessment at the time of the Level I and Level II site visit on August 24, 1995, indicated that the reach was laterally unstable. There are cutbanks upstream and downstream of the bridge. The Town Highway 74 crossing of South Peacham Brook is a 30-ft-long, two-lane bridge consisting of one 28-foot concrete slab span (Vermont Agency of Transportation, written communication, March 16, 1995). The opening length of the structure parallel to the bridge face is 25.7 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 30 degrees to the opening while the computed openingskew-to-roadway is 5 degrees. A channel scour hole 2.0 ft deeper than the mean thalweg depth was observed at the upstream bridge face, along the upstream right wingwall protection, during the Level I assessment. The scour protection measures at the site included type-1 stone fill (less than 12 inches diameter) along the downstream left and right wingwalls, downstream banks, and at the downstream end of the left and right abutments. There is also type-2 stone fill (less than 36 inches diameter) along the upstream right bank and upstream 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 others, 1995) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge was determined and analyzed as another potential worst-case scour scenario. 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 15.8 to 22.5 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 6.7 to 11.1 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. 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 30 (MNTGTH00410030) on Town Highway 41, crossing the Trout River, Montgomery, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure MNTGTH00410030 on Town Highway 41 crossing the Trout River, Montgomery, 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 northern Vermont. The 46.1-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover on the left bank is pasture upstream and downstream of the bridge with dense woody vegetation along the immediate banks. The upstream and downstream right bank surface cover is brush. In the study area, the Trout River has an incised, meandering channel with a slope of approximately 0.005 ft/ft, an average channel top width of 130 ft and an average bank height of 6 ft. The channel bed material ranges from sand to cobble with a median grain size (D 50 ) of 68.3 mm (0.224 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 27, 1995, indicated that the reach was laterally unstable. At this site there is visible lateral channel movement upstream and downstream of the bridge with meanders and cut banks. The Town Highway 41 crossing of the Trout River is a 90-ft-long, one-lane bridge consisting of one 87-foot steel-beam span (Vermont Agency of Transportation, written communication, August 3, 1994). The opening length of the structure parallel to the bridge face is 86.7 ft.The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 10 degrees to the opening while the opening-skew-toroadway is 0 degrees. A scour hole 4.5 ft deeper than the mean thalweg depth, was observed 35 ft downstream of the bridge during the Level I assessment. The scour counter-measures at the site included type-1 stone fill (less than 12 inches diameter) at the upstream left wingwall, at the left abutment, along the upstream right bank, and at the upstream end of the downstream left wingwall. There was also type-2 stone fill (less than 36 inches diameter) along the downstream right 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 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 ft. Abutment scour ranged from 2.5 to 8.9 ft. The worst-case abutment scour occurred at the 500-year discharge. The computed scour depths are well above the pile depths set in bedrock. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scouredstreambed 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 particlesize 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 34 (WWINTH00370034) on Town Highway 37, crossing Mill Brook, West Windsor, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure WWINTH00370034 on Town Highway 37 crossing Mill Brook, West Windsor, 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 east-central Vermont. The 16.6-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is pasture except for the upstream left bank where there is mostly shrubs and brush. In the study area, Mill Brook has a sinuous channel with a slope of approximately 0.003 ft/ ft, an average channel top width of 52 ft and an average bank height of 5 ft. The channel bed material ranges from sand to cobbles with a median grain size (D 50 ) of 43.4 mm (0.142 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 5, 1996, indicated that the reach was laterally unstable. Point bars were observed upstream and downstream of this site. Furthermore, slip failure of the bank material was noted downstream at a cut-bank on the left side of the channel across from a point bar. The Town Highway 37 crossing of Mill Brook is a 37-ft-long, one-lane covered bridge consisting of one 32-foot wood thru-truss span (Vermont Agency of Transportation, written communication, March 23, 1995). The opening length of the structure parallel to the bridge face is 29.6 ft. The bridge is supported by vertical, laid-up stone abutment walls with concrete facing and laid-up stone wingwalls. The channel is skewed approximately 10 degrees to the opening while the opening-skew-to-roadway is zero degrees. A scour hole 1.5 ft deeper than the mean thalweg depth was observed along the right abutment during the Level I assessment. Scour protection measures at the site included type-3 (less than 48 inches diameter) and type-4 (less than 60 inches diameter) stone fill. Type-3 stone fill was observed along the upstream right bank and along the right abutments. Type-4 stone fill was observed at the upstream end of the upstream 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. In addition, the incipient roadway-overtopping discharge was determined and analyzed as another potential worst-case scour scenario. 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. There was no contraction scour predicted for any of the modeled flows. Abutment scour at the left abutment ranged from 5.7 to 7.3 ft, while that at the right abutment ranged from 11.6 to 17.7 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 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↗
USGS2014

Hydrogeologic aspects of the Knippa Gap area in eastern Uvalde and western Medina counties, Texas

The Edwards aquifer is the primary source of potable water for the San Antonio area in south-central Texas. The Knippa Gap area is a structural low (trough) postulated to channel or restrict flow in the Edwards aquifer in eastern Uvalde and western Medina Counties, Tex. To better understand the function of the Knippa Gap, the U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, developed the first detailed surficial geologic map of the Knippa Gap area with data and information obtained from previous investigations and field observations. A simplified version of the detailed geologic map depicting the hydrologic units, faulting, and structural dips of the Knippa Gap area is provided in this fact sheet. The map shows that groundwater flow in the Edwards aquifer is influenced by the Balcones Fault Zone, a structurally complex area of the aquifer that contains relay ramps that have formed in extensional fault systems and allowed for deformational changes along fault blocks. Faulting in southeast Uvalde and southwest Medina Counties has produced relay-ramp structures that dip downgradient to the structural low (trough) of the Knippa Gap.

Texas↗
USGS2001

Integrated surface and borehole strong-motion, soil-response arrays in San Francisco, California

An integrated set of four borehole arrays and ten surface installations is installed in the city of San Francisco, California to measure the response of soft-soil deposits to strong earthquake ground motions. The borehole arrays extend through thick layers of softwater-saturated soils of Holocene age and older more consolidated soils of Pleistocene age into bedrock at depths up to 100 m. The surface installations are configured in pairs to provide simultaneous comparative surface measurements of soft soils and nearby rock. The rock locations also permit comparative measurements of rock as observed at the surface and in nearby boreholes. Complementary structural response arrays alsoare installed near each array. The arrays are designed to address a wide variety of scientific and engineering issues, and especially the issue of anelastic and nonlinear soil response at high strain levels. Exact anelastic models have been developed to account for contrasts in anelastic properties at boundaries and the resultant inhomogeneity of propagating wave fields. These models predict that significant amounts of energy may be trapped in soil basins with resultant larger amplifications than can be predicted using conventional homogeneous wave-field models with damping. Results of these models are discussed.

California↗
USGS2012

Quaternary geologic map of the Havre 1° x 2° quadrangle

The Havre quadrangle encompasses approximately 16,084 km 2 (6,210 mi 2 ). The northern boundary is the Montana/Saskatchewan (U.S./Canada) boundary. The quadrangle is in the Northern Plains physiographic province and it includes parts of the Bearpaw Mountains, the Little Rocky Mountains, and the Boundary Plateau. The primary river is the Milk River. The ancestral Missouri River was diverted south of the Bearpaw Mountains by a Laurentide ice sheet. The fill in the buried ancestral valley at and southwest of Havre contains a complex stratigraphy of fluvial, glaciofluvial, ice-contact, glacial, lacustrine, and eolian deposits. The old valley east of Havre now is occupied by the Milk River. The map units are surficial deposits and materials, not landforms. Deposits that comprise some constructional landforms (e.g., ground-moraine deposits, end-moraine deposits, stagnation-moraine deposits, all composed of till) are distinguished for purposes of reconstruction of glacial history. Surficial deposits and materials are assigned to 24 map units on the basis of genesis, age, lithology or composition, texture or particle size, and other physical, chemical, and engineering characteristics. It is not a map of soils that are recognized in engineering geology, or of substrata or parent materials in which pedologic or agronomic soils are formed. Glaciotectonic (ice-thrust) structures and deposits are mapped separately, represented by a symbol. On the glaciated plains and on the Boundary Plateau the surficial deposits are glacial, ice-contact, glaciofluvial, catastrophic flood, alluvial, lacustrine, eolian, and colluvial deposits. In the Bearpaw Mountains and Little Rocky Mountains beyond the limit of Quaternary glaciation they are fluvial, colluvial, and mass-wasting deposits and residual materials. Tills of late Wisconsin and Illinoian ages are represented by map units. Tills of two pre-Illinoian glaciations are not mapped but are widespread in the subsurface and are identified in stratigraphic sections. Thirteen stratigraphic sections document a complex glacial and interglacial history in the quadrangle. Pliocene continental glaciation possibly is represented by erratic blocks of garnet gneiss and pegmatite from the Canadian Shield, perched high on drainage divides in the western Bearpaw Mountains. Glacial striations on bedrock, two boulder trains, and linear ice-molded landforms (primarily drumlins) indicate the possible presence of an east-southeast flowing ice stream in the Havre glacial lobe during late Wisconsin glaciation.

Montana↗
USGS2013

Quaternary geologic map of the Shelby 1° x 2° quadrangle, Montana

The Shelby quadrangle encompasses approximately 16,084 km 2 (6,210 mi 2 ). The northern boundary is the Montana/Saskatchewan (U.S./Canada) boundary. The quadrangle is in the Northern Plains physiographic province and it includes the Sweet Grass Hills. The primary river is the Marias River. The ancestral Missouri River was diverted south of the Bearpaw Mountains by a Laurentide ice sheet. The fill in the buried ancestral valleys of the Missouri River and Marias River in the southeast quarter of the quadrangle contains a complex stratigraphy of fluvial, glaciofluvial, ice-contact, glacial, lacustrine, and eolian deposits. The map units are surficial deposits and materials, not landforms. Deposits that comprise some constructional landforms (for example, ground-moraine deposits, end-moraine deposits, stagnation-moraine deposits, all composed of till) are distinguished for purposes of reconstruction of glacial history. Surficial deposits and materials are assigned to 21 map units on the basis of genesis, age, lithology or composition, texture or particle size, and other physical, chemical, and engineering characteristics. It is not a map of soils that are recognized in pedology or agronomy. Rather, it is a generalized map of soils recognized in engineering geology, or of substrata or parent materials in which pedologic or agronomic soils are formed. Glaciotectonic (ice-thrust) structures and deposits are mapped separately, represented by a symbol. On the glaciated plains, the surficial deposits are glacial, ice-contact, glaciofluvial, alluvial, lacustrine, eolian, colluvial, and mass-movement deposits. In the Sweet Grass Hills, beyond the limit of Quaternary glaciation they are fluvial, colluvial, and mass-movement deposits. Till of late Wisconsin age is represented by three map units. Tills of Illinoian and pre-Illinoian glaciations are not mapped, but are widespread in the subsurface. Linear ice-molded landforms (primarily drumlins) indicate directions of ice flow during late Wisconsin glaciation.

Montana↗
USGS2012

Quaternary geologic map of the Glasgow 1° x 2° quadrangle, Montana

The Glasgow quadrangle encompasses approximately 16,084 km 2 (6,210 mi 2 ). The northern boundary is the Montana/Saskatchewan (U.S./Canada) boundary. The quadrangle is in the Northern Plains physiographic province and it includes the Boundary Plateau, Peerless Plateau, and Larb Hills. The primary river is the Milk River. The map units are surficial deposits and materials, not landforms. Deposits that comprise some constructional landforms (for example, ground-moraine deposits, end-moraine deposits, and stagnation-moraine deposits, all composed of till) are distinguished for purposes of reconstruction of glacial history. Surficial deposits and materials are assigned to 23 map units on the basis of genesis, age, lithology or composition, texture or particle size, and other physical, chemical, and engineering characteristics. It is not a map of soils that are recognized in pedology or agronomy. Rather, it is a generalized map of soils recognized in engineering geology, or of substrata or parent materials in which pedologic or agronomic soils are formed. Glaciotectonic (ice-thrust) structures and deposits are mapped separately, represented by a symbol. The surficial deposits are glacial, ice-contact, glaciofluvial, alluvial, lacustrine, eolian, colluvial, and mass-movement deposits. Residuum, a surficial material, also is mapped. Till of late Wisconsin age is represented by three map units. Till of Illinoian age is also represented locally but is widespread in the subsurface. This map was prepared to serve as a database for compilation of a Quaternary geologic map of the United States and Canada (scale 1:1,000,000). Letter symbols for the map units are those used for the same units in the Quaternary Geologic Atlas of the United States map series.

Montana↗
USGS2016

Quaternary geologic map of the Wolf Point 1° × 2° quadrangle, Montana and North Dakota

The Wolf Point quadrangle encompasses approximately 16,084 km 2 (6,210 mi 2 ). The northern boundary is the Montana/Saskatchewan (U.S.-Canada) boundary. The quadrangle is in the Northern Plains physiographic province and it includes the Peerless Plateau and Flaxville Plain. The primary river is the Missouri River. The map units are surficial deposits and materials, not landforms. Deposits that comprise some constructional landforms (for example, ground-moraine deposits, end-moraine deposits, and stagnation-moraine deposits, all composed of till) are distinguished for purposes of reconstruction of glacial history. Surficial deposits and materials are assigned to 23 map units on the basis of genesis, age, lithology or composition, texture or particle size, and other physical, chemical, and engineering characteristics. It is not a map of soils that are recognized in pedology or agronomy. Rather, it is a generalized map of soils recognized in engineering geology, or of substrata or parent materials in which pedologic or agronomic soils are formed. Glaciotectonic (ice-thrust) structures and deposits are mapped separately, represented by a symbol. The surficial deposits are glacial, ice-contact, glaciofluvial, alluvial, lacustrine, eolian, colluvial, and mass-movement deposits. Till of late Wisconsin age is represented by three map units. Till of Illinoian age also is mapped. Till deposited during pre-Illinoian glaciations is not mapped, but is widespread in the subsurface. Linear ice-molded landforms (primarily drumlins), shown by symbol, indicate directions of ice flow during late Wisconsin and Illinoian glaciations. The Quaternary geologic map of the Wolf Point quadrangle, northeastern Montana and North Dakota, was prepared to provide a database for compilation of a Quaternary geologic map of the Regina 4° × 6° quadrangle, United States and Canada, at scale 1:1,000,000, for the U.S. Geological Survey Quaternary Geologic Atlas of the United States map series. This map was compiled from data from many sources, at several different map scales. That information was generalized and simplified, and then transferred to a base map at 1:250,000 scale to serve as the base for final reduction to 1:1,000,000, the nominal reading scale of maps in the Quaternary Geologic Atlas of the United States map series. This map is the generalized and simplified 1:250,000 scale compilation. Letter symbols for the map units are those used for the same units in the Quaternary Geologic Atlas of the United States map series. The map summarizes new, and selected published and unpublished, geologic information for public use and for use by Federal, State, and local governmental agencies for land use planning, including assessment of natural resources, natural hazards, recreation potential, and land use management. It also is a base from which a variety of maps relating to earth surface processes and Quaternary geologic history can be derived.

Montana, North Dakota↗
USGS1996

Level II scour analysis for Bridge 51 (RANDTH00SC0051) on School Street, crossing Thayer Brook, Randolph, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure RANDTH00SC0051 on School Street crossing Thayer Brook, 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). A Level I study is included in Appendix E of this report. A Level I study provides a qualitative geomorphic characterization of the study site. Information on the bridge available from VTAOT files was compiled prior to conducting Level I and Level II analyses and can be found in Appendix D. The site is in the Green Mountain physiographic division of central Vermont in the town of Randolph. The 5.30-mi 2 drainage area is a predominantly rural basin. In the vicinity of the study site, the left and right banks are forested with residences on the left overbanks. In the study area, Thayer Brook has a sinuous channel with a slope of approximately 0.03 ft/ ft, an average channel top width of 36 ft and an average channel depth of 3 ft. The predominant channel bed materials are gravel and cobble (D 50 is 58.2 mm or 0.191 ft). The geomorphic assessment at the time of the Level I site visits on August 4, 1994 and December 8, 1994, indicated that the reach was stable. The School Street crossing of Thayer Brook is a 39-ft-long, two-lane bridge consisting of one 35-foot concrete span (Vermont Agency of Transportation, written commun., August 2, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. Type-2 stone fill (less than 36 inches diameter) along the downstream left bank was the only existing protection. The approach channel is skewed approximately 45 degrees to the bridge face; the opening-skew-to-roadway is also 45 degrees. Additional details describing conditions at the site are included in the Level II Summary, Appendix D, and Appendix 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 1.0 to 2.2 ft. with the worst-case scenario occurring at the 500-year discharge. Abutment scour ranged from 6.2 to 12.0 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, 1993, p. 48). Many factors, including historical performance during flood events, the geomorphic assessment, scour protection measures, and the results of the hydraulic analyses, must be considered to properly assess the validity of abutment scour results. Therefore, scour depths adopted by VTAOT may differ from the computed values documented herein, based on the consideration of additional contributing factors and experienced engineering judgement.

Vermont↗
USGS1996

Estimation of flood-frequency characteristics of small urban streams in North Carolina

A statewide study was conducted to develop methods for estimating the magnitude and frequency of floods of small urban streams in North Carolina. This type of information is critical in the design of bridges, culverts and water-control structures, establishment of flood-insurance rates and flood-plain regulation, and for other uses by urban planners and engineers. Concurrent records of rainfall and runoff data collected in small urban basins were used to calibrate rainfall-runoff models. Historic rain- fall records were used with the calibrated models to synthesize a long- term record of annual peak discharges. The synthesized record of annual peak discharges were used in a statistical analysis to determine flood- frequency distributions. These frequency distributions were used with distributions from previous investigations to develop a database for 32 small urban basins in the Blue Ridge-Piedmont, Sand Hills, and Coastal Plain hydrologic areas. The study basins ranged in size from 0.04 to 41.0 square miles. Data describing the size and shape of the basin, level of urban development, and climate and rural flood charac- teristics also were included in the database. Estimation equations were developed by relating flood-frequency char- acteristics to basin characteristics in a generalized least-squares regression analysis. The most significant basin characteristics are drainage area, impervious area, and rural flood discharge. The model error and prediction errors for the estimating equations were less than those for the national flood-frequency equations previously reported. Resulting equations, which have prediction errors generally less than 40 percent, can be used to estimate flood-peak discharges for 2-, 5-, 10-, 25-, 50-, and 100-year recurrence intervals for small urban basins across the State assuming negligible, sustainable, in- channel detention or basin storage.

North Carolina↗
USGS1997

Level II scour analysis for Bridge 22 (JAY-TH00400022) on Town Highway 40, crossing Jay Branch, Jay, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure JAY-TH00400022 on Town Highway 40 crossing Jay Tributary, Jay, 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 northern Vermont. The 2.15-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is primarily pasture on the upstream and downstream left overbank while the immediate banks have dense woody vegetation. The downstream right overbank of the bridge is forested. In the study area, Jay Branch Tributary has an incised, sinuous channel with a slope of approximately 0.02 ft/ft, an average channel top width of 26 ft and an average bank height of 3 ft. The channel bed material ranges from gravel to cobble with a median grain size (D 50 ) of 40.5 mm (0.133 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 7, 1995, indicated that the reach was stable. The Town Highway 40 crossing of Jay Branch Tributary is a 27-ft-long, two-lane bridge consisting of one 25-foot steel-beam span (Vermont Agency of Transportation, written communication, March 6, 1995). The opening length of the structure parallel to the bridge face is 23.5 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel skew and the opening-skew-to-roadway are zero degrees. The scour counter-measures at the site included type-2 stone fill (less than 36 inches diameter) at the upstream end of the left and right abutments, at the upstream right wingwall, and at the downstream left wingwall. There was also type-3 stone fill (less than 48 inches diameter) at the upstream left and 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 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 0.7 to 1.1 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 4.6 to 4.9 ft. The worst-case left abutment scour occurred at the 100-year discharge. Right abutment scour ranged from 4.0 to 5.0 ft. The worst-case right 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↗
USGS1997

Level II scour analysis for Bridge 4 (MAIDTH00070004) on Town Highway 7, crossing Cutler Mill Brook, Maidstone, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure MAIDTH00070004 on Town Highway 7 crossing the Cutler Mill Brook, Maidstone, 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 18.1-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is predominantly shrub and brushland. In the study area, the Cutler Mill Brook has a non-incised, meandering channel with local braiding and a slope of approximately 0.004 ft/ft, an average channel top width of 43 ft and an average bank height of 2 ft. The channel bed material ranges from sand to cobble with a median grain size (D 50 ) of 27.6 mm (0.091 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 19, 1995, indicated that the reach was laterally unstable due to large meanders in the channel. The Town Highway 7 crossing of the Cutler Mill Brook is a 25-ft-long, one-lane bridge consisting of one 22-foot concrete span (Vermont Agency of Transportation, written communication, August 5, 1994). The opening length of the structure parallel to the bridge face is 21.7 ft. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 20 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 along the left abutment during the Level I assessment. The only scour protection measure at the site was type-2 stone fill (less than 36 inches diameter) along both banks upstream, along the entire base length of the upstream left wingwall, and along the upstream end of the upstream 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 others, 1995) for the 100- and 500-year discharges. In addition, the incipient roadway-overtopping discharge was determined and analyzed as another potential worst-case scour scenario. 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 2.2 to 4.2 ft. The worst-case contraction scour occurred at the 500-year discharge. Abutment scour ranged from 5.7 to 12.4 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↗
USGS1998

Level II scour analysis for Bridge 46 (LINCTH00060046) on Town Highway 6, crossing the New Haven River, Lincoln, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure LINCTH00060046 on Town Highway 6 crossing the New Haven River, Lincoln, 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 Green Mountain section of the New England physiographic province in west-central Vermont. The 45.9-mi 2 drainage area is in a predominantly suburban and forested basin. In the vicinity of the study site, the surface cover is forest upstream of the bridge. The downstream right overbank near the bridge is suburban with buildings, homes, lawns, and pavement (less than fifty percent). The downstream left overbank is brushland while the immediate banks have dense woody vegetation. In the study area, the New Haven River has an incised, sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 95 ft and an average bank height of 7 ft. The channel bed material ranges from sand to bedrock with a median grain size (D 50 ) of 120.7 mm (0.396 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 13, 1996, indicated that the reach was stable. The Town Highway 34 crossing of the New Haven River is a 85-ft-long, two-lane bridge consisting of an 80-foot steel arch truss (Vermont Agency of Transportation, written communication, December 14, 1995). The opening length of the structure parallel to the bridge face is 69 feet. The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 25 degrees to the opening while the opening-skew-to-roadway is 5 degrees. A scour hole 2.0 ft deeper than the mean thalweg depth was observed in the downstream channel during the Level I assessment. Protection measures at the site include type-1 stone fill (less than 12 inches diameter) at the upstream left wingwall, type-2 stone fill (less than 36 inches diameter) at the downstream end of the downstream left wingwall, and type-3 stone fill (less than 48 inches diameter) at the upstream right wingwall and 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). 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 1.7 ft. The worst-case contraction scour occurred at the incipient roadway-overtopping discharge. Left abutment scour ranged from 12.9 to 17.8 ft. Right abutment scour ranged from 5.9 to 11.9 ft. The worst-case abutment scour occurred at the incipient roadway-overtopping 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↗
USGS1998

Level II scour analysis for Bridge 17 (NEWHTH00200017) on Town Highway 20, crossing Little Otter Creek, New Haven, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure NEWHTH00200017 on Town Highway 20 crossing Little Otter Creek, New Haven, 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 Champlain section of the St. Lawrence Valley physiographic province in west-central Vermont. The 10.8-mi 2 drainage area is in a predominantly rural and wetland basin. In the vicinity of the study site, the surface cover is shrubland on the downstream right overbank. The surface cover of the downstream left overbank, the upstream right overbank and the upstream left overbank is wetland and pasture. In the study area, Little Otter Creek has a meandering channel with a slope of approximately 0.0007 ft/ft, an average channel top width of 97 ft and an average bank height of 5 ft. The channel bed material ranges from silt and clay to cobble. Medium sized silt and clay is the channel material upstream of the approach cross-section and downstream of the exit cross-section. The median grain size (D 50 ) of the silt and clay channel bed material is 1.52 mm (0.005 ft), which was used for contraction and abutment scour computations. From the approach cross-section, under the bridge, and to the exit cross-section, stone fill is the channel bed material. The median grain size (D 50 ) of the stone fill channel bed material is 95.7 mm (0.314 ft). The stone fill median grain size was used solely for armoring computations. The geomorphic assessment at the time of the Level I and Level II site visit on June 11, 1996, indicated that the reach was stable. The Town Highway 20 crossing of Little Otter Creek is a 32-ft-long, two-lane bridge consisting of a 28-ft steel-beam span (Vermont Agency of Transportation, written communication, December 15, 1995). The opening length of the structure parallel to the bridge face is 24.9 ft. The bridge is supported by almost vertical, concrete abutments. The channel is skewed approximately 15 degrees to the opening while the opening-skew-toroadway is zero degrees. The scour countermeasures at the site consisted of type-1 stone fill (less than 12 inches diameter) along the left and right abutments, as well as along the upstream left and right banks. Type-2 stone fill (less than 36 inches diameter) was present along the downstream right 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. In addition, the incipient roadway-overtopping discharge was determined and analyzed as another potential worst-case scour scenario. 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 9.7 to 13.8 ft. The worst-case contraction scour occurred at the 500-year discharge. Left abutment scour ranged from 6.9 to 7.9 ft. Right abutment scour ranged from 10.5 to 11.8 ft. The worst-case left and right 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↗
USGS2015

Curiosity’s robotic arm-mounted Mars Hand Lens Imager (MAHLI): Characterization and calibration status

MAHLI (Mars Hand Lens Imager) is a 2-megapixel, Bayer pattern color CCD camera with a macro lens mounted on a rotatable turret at the end of the 2-meters-long robotic arm aboard the Mars Science Laboratory rover, Curiosity. The camera includes white and longwave ultraviolet LEDs to illuminate targets at night. Onboard data processing services include focus stack merging and data compression. Here we report on the results and status of MAHLI characterization and calibration, covering the pre-launch period from August 2008 through the early months of the extended surface mission through February 2015. Since landing in Gale crater in August 2012, MAHLI has been used for a wide range of science and engineering applications, including distinction among a variety of mafic, siliciclastic sedimentary rocks; investigation of grain-scale rock, regolith, and eolian sediment textures and structures; imaging of the landscape; inspection and monitoring of rover and science instrument hardware concerns; and supporting geologic sample selection, extraction, analysis, delivery, and documentation. The camera has a dust cover and focus mechanism actuated by a single stepper motor. The transparent cover was coated with a thin film of dust during landing, thus MAHLI is usually operated with the cover open. The camera focuses over a range from a working distance of 2.04 cm to infinity; the highest resolution images are at 13.9 µm per pixel; images acquired from 6.9 cm show features at the same scale as the Mars Exploration Rover Microscopic Imagers at 31 µm/pixel; and 100 µm/pixel is achieved at a working distance of ~26.5 cm. The very highest resolution images returned from Mars permit distinction of high contrast silt grains in the 30–40 µm size range. MAHLI has performed well; the images need no calibration in order to achieve most of the investigation’s science and engineering goals. The positioning and repeatability of robotic arm placement of the MAHLI camera head have been excellent on Mars, often with the hardware arriving within millimeters of expectation. Stability while imaging is usually such that the images are sharply focused; some exceptions—thought to result from motion induced by wind—have occurred during longer exposure LED-illuminated night imaging. Image calibration includes relative radiometric correction by removal of dark current and application of a flat field. Dark current is negligible to minor for typical daytime exposure durations and temperatures at the Gale field site. A pre-launch flat field product is usually applied to the data but new products created from images acquired by MAHLI of the Martian sky are superior and can provide a relative radiometric accuracy of ~6%. The camera lens imparts negligible distortion to its images; camera models derived from pre-launch data, with CAHV and CAHVOR parameters captured in their archived labels, can be applied to the images for analysis. MAHLI data and derived products, including pre-launch images, are archived with the NASA Planetary Data System (PDS). This report includes supplementary calibration and characterization data that are not available in the PDS archive (see supplement file MAHLITechRept0001_Supplement.zip).

MSL MAHLI Technical Report↗
USGS1989

Structures associated with strike-slip faults that bound landslide elements

Large landslides are bounded on their flanks and on elements within the landslides by structures analogous to strike-slip faults. We observed the formation of thwse strike-slip faults and associated structures at two large landslides in central Utah during 1983-1985. The strike-slip faults in landslides are nearly vertical but locally may dip a few degrees toward or away from the moving ground. Fault surfaces are slickensided, and striations are subparallel to the ground surface. Displacement along strike-slip faults commonly produces scarps; scarps occur where local relief of the failure surface or ground surface is displaced and becomes adjacent to higher or lower ground, or where the landslide is thickening or thinning as a result of internal deformation. Several types of structures are formed at the ground surface as a strike-slip fault, which is fully developed at some depth below the ground surface, propagates upward in response to displacement. The simplest structure is a tension crack oriented at 45?? clockwise or counterclockwise from the trend of an underlying right- or left-lateral strike-slip fault, respectively. The tension cracks are typically arranged en echelon with the row of cracks parallel to the trace of the underlying strike-slip fault. Another common structure that forms above a developing strike-slip fault is a fault segment. Fault segments are discontinuous strike-slip faults that contain the same sense of slip but are turned clockwise or counterclockwise from a few to perhaps 20?? from the underlying strike-slip fault. The fault segments are slickensided and striated a few centimeters below the ground surface; continued displacement of the landslide causes the fault segments to open and a short tension crack propagates out of one or both ends of the fault segments. These structures, open fault segments containing a short tension crack, are termed compound cracks; and the short tension crack that propagates from the tip of the fault segment is typically oriented 45?? to the trend of the underlying fault. Fault segments are also typically arranged en echelon above the upward-propagating strike-slip fault. Continued displacement of the landslide causes the ground to buckle between the tension crack portions of the compound cracks. Still more displacement produces a thrust fault on one or both limbs of the buckle fold. These compressional structures form at right angles to the short tension cracks at the tips of the fault segments. Thus, the compressional structures are bounded on their ends by one face of a tension crack and detached from underlying material by thrusting or buckling. The tension cracks, fault segments, compound cracks, folds, and thrusts are ephemeral; they are created and destroyed with continuing displacement of the landslide. Ultimately, the structures are replaced by a throughgoing strike-slip fault. At one landslide, we observed the creation and destruction of the ephemeral structures as the landslide enlarged. Displacement of a few centimeters to about a decimeter was sufficient to produce scattered tension cracks and fault segments. Sets of compound cracks with associated folds and thrusts were produced by displacements of up to 1 m, and 1 to 2 m of displacement was required to produce a throughgoing strike-slip fault. The type of first-formed structure above an upward-propagating strike-slip fault is apparently controlled by the rheology of the material. Brittle material such as dry topsoil or the compact surface of a gravel road produces echelon tension cracks and sets of tension cracks and compressional structures, wherein the cracks and compressional structures are normal to each other and 45?? to the strike-slip fault at depth. First-formed structures in more ductile material such as moist cohesive soil are fault segments. In very ductile material such as soft clay and very wet soil in swampy areas, the first-formed structure is a throughgoing strike-slip fault.

Engineering Geology↗
USGS1998

Level II scour analysis for bridge 42 (BAKETH00060042) on Town Highway 6, crossing The Branch, Bakersfield, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BAKETH00060042 on Town Highway 6 crossing The Branch, Bakersfield, 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.

Vermont↗