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USGS1968

Stratigraphy and structure of the tatum salt dome area, southeastern Mississippi and northeastern Washington Parish, Louisiana

In the 3000-square-mile area of southeastern Mississippi and northeastern Washington Parish , Louisiana , which has Tatum dome in its center, rocks of known Jurassic to Recent age are more than 20,000 feet thick. They are underlain by an unknown thickness of Louann Salt of Jurassic (?) age. The age, thickness, and nature of the sedimentary rocks between the salt and the basement, as well as the character of the basement, are unknown. The salt in the northern half of the area has moved upward to shallow depths as diapirs in overlying rocks. Outside of the area of shallow-piercement domes there are more deeply seated domes, ridges, and anticlines that may be the result of vertical movement of the salt . The Wiggins anticline in the south and, southwest of it, an area dipping more steeply to the southwest probably were not affected by salt movement. Structural maps of four horizons and isopach maps of rocks in the three intervals between them give information about the sedimentary and structural history of the region since the end of Early Cretaceous time. The horizons contoured mark either unconformities or the upper boundaries of zones of fairly uniform structural history. The top of the Lower Cretaceous rocks dips generally to the west. Upper Cretaceous rocks dip to the west-southwest and thicken to the northeast. Pre-Miocene Tertiary rocks dip to the southwest and thicken to the northwest. Miocene and later rocks dip and thicken to the south-southwest. The structure of the older formations is considerably more irregular than that of the younger ones; domes, ridges, and basins that were conspicuous in the Early Cretaceous became less pronounced as younger sediments progressively covered them. Of the eight shallow-piercement domes with which the author is familiar, three are known to have penetrated Oligocene rocks; two, middle Eocene; one, lower Eocene; one, Upper Cretaceous; and one, Lower Cretaceous. Some movement has taken place at Tatum dome since the sandy, gravelly Citronelle Formation was laid down.

Louisiana, Mississippi↗

USGS1990

Bird specimens and documentation: Critical data for a critical resource

As governments impose increasingly stringent regulations on the collection of bird specimens and as man alters ever greater areas of habitat with the loss of many of their contained species, museum specimens increase immeasurably in importance. Yet at present, museum collections do not contain an adequate representation of the world's avifauna and, unfortunately, are not likely to do so. Thus, it is imperative that data associated with specimens that are obtained be as complete as possible. To this end, we describe categories of information with wide application to many types of studies, outline character states, and recommend standard forms of data notation. We recognize that under certain circumstances, it may be appropriate to record more limited data. However, we encourage at least those engaged in general collecting to record as many of these standard data as possible.

Condor↗

USGS2010

Power to detect trends in Missouri River fish populations within the Habitat Assessment Monitoring Program

As with all large rivers in the United States, the Missouri River has been altered, with approximately one-third of the mainstem length impounded and one-third channelized. These physical alterations to the environment have affected the fish populations, but studies examining the effects of alterations have been localized and for short periods of time, thereby preventing generalization. In response to the U.S. Fish and Wildlife Service Biological Opinion, the U.S. Army Corps of Engineers (USACE) initiated monitoring of habitat improvements of the Missouri River in 2005. The goal of the Habitat Assessment Monitoring Program (HAMP) is to provide information on the response of target fish species to the USACE habitat creation on the Lower Missouri River. To determine the statistical power of the HAMP and in cooperation with USACE, a power analysis was conducted using a normal linear mixed model with variance component estimates based on the first complete year of data. At a level of 20/16 (20 bends with 16 subsamples in each bend), at least one species/month/gear model has the power to determine differences between treated and untreated bends. The trammel net in September had the most species models with adequate power at the 20/16 level and overall, the trammel net had the most species/month models with adequate power at the 20/16 level. However, using only one gear or gear/month combination would eliminate other species of interest, such as three chub species (Macrhybopsis meeki, Macrhybopsis aestivalis, and Macrhybopsis gelida), sand shiners (Notropis stramineus), pallid sturgeon (Scaphirhynchus albus), and juvenile sauger (Sander canadensis). Since gear types are selective in their species efficiency, the strength of the HAMP approach is using multiple gears that have statistical power to differentiate habitat treatment differences in different fish species within the Missouri River. As is often the case with sampling rare species like the pallid sturgeon, the data used to conduct the analyses exhibit some departures from the parametric model assumptions. However, preliminary simulations indicate that the results of this study are appropriate for application to the HAMP study design.

Open-File Report↗

USGS1955

Ground-water conditions between Oracle and Oracle Junction, Pinal County, Arizona

The development of the San Manuel copper prospect has greatly increased traffic along State Highway 77. Considerable interest in commercial possibilities along that road has resulted in a request by the Arizona State Land Department for information about the ground-water conditions between Oracle and Oracle Junction. This request came too late for information to be included in a recently completed memorandum report on the occurrence of ground water in the vicinity of Oracle, released in February 1955. These data are presented as a supplement to that report to minimized duplication of statements about the general geologic and hydrologic conditions. The necessary well data and sample descriptions that were not included in the Oracle report are shown in tables 3 and 4. The area discussed in this supplement comprises parts of Tps. 9 and 10 S., Rs. 13, 14, and 15 E., and includes about 90 square miles (fig. 3). The eastern portion overlaps part of the area covered by the earlier report.

Arizona↗

USGS1979

Notes on the acquisition of high resolution seismic reflection profiles, side-scanning sonar records, and sediment samples from lower Cook Inlet and Kodiak Shelf, R/V Sea Sounder Cruise S8-78-WG, August 1978

The third U.S. Geological Survey geo-environmental cruise in lower Cook Inlet and on the Kodiak shelf and adjacent continental slope, Gulf of Alaska, was conducted aboard the R/V SEA SOUNDER from 2 August to 22 August, 1978 (Fig. 1, 2, and 3). The objectives of the cruise were to study in detail specific potentially hazardous environmental conditions identified as a result of the first reconnaissance cruise conducted in June and July of 1976 and from work by other investigators, and to initiate reconnaissance characterization studies on the continental slope. High-resolution seismic reflection profiling (sparker, Uniboam: 3.5 kHz, 12 kHz) and side-scanning sonar surveys formed the basis for selecting stations for observation with bottom television and 70 mm bottom camera as well as for sampling of surficial sediments (gravity corer, grab sampler), Generalized trackline charts are given in Figures 2 and 3. Detailed shot-point charts could not be constructed clearly, because of the overlap and coincidence of many of the lines. Station locations are shown in Figure 4 and 5, and sampling information is given in Table 4. Table 5 contains the navigation records from the cruise. The results of our investigations to date can be found in the references listed at the end of this text, Background information in lower Cook Inlet with several references is given in Open-File Report 75-429 (Magoon and others, 1975), and on the Kodiak shelf in Open-File Report 76-325 (von Huene and others, 1976). In addition, this report accompanies the basic seismic-reflection and side-scanning sonar records acquired on the cruise. The seismic-reflection records are publicly available from the National Geophysical and Solar Terrestrial Data Center EDS/NOAA, Boulder, Colorado 80302. These records can be inspected at U.S. Geological Survey offices at Rm B-164, Deer Creek Facility, 3475 Deer Creek Road, Palo Alto, California 94303.

Alaska↗

USGS1995

Reference manual for data base on Nevada water-rights permits

The U.S. Geological Survey and Nevada Division of Water Resources have cooperatively developed and implemented a data-base system for managing water-rights permit information for the State of Nevada. The Water-Rights Permit data base is part of an integrated system of computer data bases using the Ingres Relational Data-Base Manage-ment System, which allows efficient storage and access to water information from the State Engineer's office. The data base contains a main table, three ancillary tables, and five lookup tables, as well as a menu-driven system for entering, updating, and reporting on the data. This reference guide outlines the general functions of the system and provides a brief description of data tables and data-entry screens.

Open-File Report↗

USGS1995

Reference manual for data base on Nevada well logs

The U.S. Geological Survey and Nevada Division of Water Resources are cooperatively using a data base for are cooperatively using a data base for managing well-log information for the State of Nevada. The Well-Log Data Base is part of an integrated system of computer data bases using the Ingres Relational Data-Base Management System, which allows efficient storage and access to water information from the State Engineer's office. The data base contains a main table, two ancillary tables, and nine lookup tables, as well as a menu-driven system for entering, updating, and reporting on the data. This reference guide outlines the general functions of the system and provides a brief description of data tables and data-entry screens.

Open-File Report↗

USGS1997

Preliminary geologic map of the Mint Canyon 7.5' quadrangle, southern California: A digital database

This Open-File report is a digital geologic map database. This pamphlet serves to introduce and describe the digital data. There is no paper map included in the Open-File report. This digital map database is compiled from previously published sources combined with some new mapping and modifications in nomenclature. The geologic map database delineates map units that are identified by general age and lithology following the stratigraphic nomenclature of the U. S. Geological Survey. For detailed descriptions of the units, their stratigraphic relations, sources of geologic mapping, and data on exploratory wells consult Yerkes (1996), and Yerkes and Showalter (1990). More specific information about the units may be available in the original sources.

California↗

USGS1997

Preliminary geologic map of the Burbank 7.5' quadrangle, southern California: A digital database

California↗

USGS1997

Preliminary geologic map of the Hollywood 7.5' quadrangle, Southern California: A digital database

This Open-File report is a digital geologic map database. This pamphlet serves to introduce and describe the digital data. There is no paper map included in the Open-File report. This digital map database is compiled from previously published sources combined with some new mapping and modifications in nomenclature. The geologic map database delineates map units that are identified by general age and lithology following the stratigraphic nomenclature of the U. S. Geological Survey. For detailed descriptions of the units, their stratigraphic relations, sources of geologic mapping, and data on exploratory wells consult Yerkes (1997), and Yerkes and Showalter (1990). More specific information about the units may be available in the original sources.

California↗

USGS2000

Geologic studies in Alaska by the U.S. Geological Survey, 1997

The eight papers that follow continue the series of U.S. Geological Survey (USGS) reports on investigations in the geologic sciences in Alaska. The series presents new and sometimes preliminary findings that are of interest to earth scientists in academia, government, and industry; to land and resource managers; and to the general public. Reports presented in Geologic Studies in Alaska cover a broad spectrum of topics from all parts of the State (fig. 1), which serves to emphasize the diversity of USGS efforts to meet the Nation's needs for earth-science information in Alaska. The papers in this volume are organized under the topics Resources, Geologic Framework, and Environment and Climate. Such an organization is intended to reflect the scope and objectives of USGS programs currently active in Alaska. Resource papers include one that presents detailed observations from a Mississippian Zn-Pb-Cu-Ag occurrence in the Brooks Range (Werdon). Mineralogic, chemical, and isotopic data provide the basis for a proposed relationship between this vein-breccia deposit and the shale-hosted massive sulfide deposit type, which includes the active Red Dog mine in the western Brooks Range. Also included under the topic of Resources is a paper that presents geochemical and isotopic data from the Greens Creek and Woewodski Island volcanogenic massive sulfide deposits in southeastern Alaska (Newberry and Brew). The depositional environment and sedimentological setting of Tertiary coal beds in the Matanuska and Susitna Valleys is the focus of a third paper under the topic of Resources (Flores and others). Geologic Framework studies provide background information that is the scientific basis for present and future studies of the environment, mineral and energy resources, paleoclimate, and hazards in Alaska. One paper presents the results of sedimentologic and paleontologic comparisons of lower Paleozoic, deep-water-facies rock units in central Alaska (Dumoulin and others). The authors show which of these units are likely to correlate with one another, suggest likely source regions, and provide a structural restoration of units that have been fragmented by large fault motions. A second framework paper provides a map, rock descriptions, and chemical compositions of volcanic rocks in a newly recognized, geologically young volcanic center in the Aleutian volcanic arc (Hildreth and others). A third paper presents an interesting summary of gravity changes that occurred in south-central Alaska during the great earthquake of 1964 and for the following 25 years (Barnes). Gravity changes correlate with land-elevation changes in some cases, but not in others, which means that different processes are responsible for the gravity changes.

Alaska↗

USGS2000

Geologic studies in Alaska by the U.S. Geological Survey, 1998

The 14 papers that follows continue the series of U.S. Geological Survey (USGS) reports on investigations in the geologic sciences in Alaska. The series presents new and sometimes preliminary findings that are of interest to earth scientists in academia, government, and industry; to land and resource managers; and to the general public. Reports presented in Geologic Studies in Alaska cover a broad spectrum of topics from all parts of the State (fig. 1), which serves to emphasize the diversity of USGS efforts to meet the Nation’s needs for earth-science information in Alaska.

Alaska↗

USGS2009

Groundwater/surface-water interactions in the Tunk, Bonaparte, Antoine, and Tonasket Creek Subbasins, Okanogan River Basin, North-Central Washington, 2008

An investigation into groundwater/surface-water interactions in four tributary subbasins of the Okanogan River determined that streamflows and shallow groundwater levels beneath the streams varied seasonally and by location. Streamflows measured in June 2008 indicated net losses of streamflow along 10 of 17 reaches, and hydraulic gradients measured between streams and shallow groundwater indicated potential recharge of surface water to groundwater at 11 of 21 measurement sites. In September 2008, net losses of streamflow were indicated along 9 of 17 reaches, and potential recharge of surface water to groundwater was indicated at 18 of 21 measurement sites. The greatest losses of streamflow occurred near the confluences with the Okanogan River, likely due to the presence of thick layers of unconsolidated deposits in the flood plain of the Okanogan River. Based on available geologic information compiled from drillers' logs, a surficial geologic map, and streamflow records, the extensive and thick deposits of unconsolidated material in the Tunk and Bonaparte Creek subbasins are factors in sustaining the almost perennial streamflow in those creeks. The less extensive and generally thinner unconsolidated deposits in the Tonasket and Antoine subbasins are contributing factors to the occasional extended periods of zero flow (a dry stream channel) in those creeks. Even though groundwater withdrawals would affect streamflows, relatively low precipitation in the area, along with limited groundwater storage capacity and the presence of permeable, unconsolidated deposits underlying the stream channels, would likely lead to loss of surface water to the groundwater system without any withdrawals.

Scientific Investigations Report↗

USGS1980

Physical environment and hydrologic characteristics of coal-mining areas in Missouri

Hydrologic information for the north-central and western coal-mining regions of Missouri is needed to define the hydrologic system in these areas of major historic and planned coal development. This report describes the physical setting, climate, coal-mining practices, general hydrologic system, and the current (1980) hydrologie data base in these two coal-mining regions. Streamflow in both mining regions is poorly sustained. Stream water quality generally varies with location and the magnitude of coal-mining activity in a watershed. Streams in non coal-mining areas generally have dissolved-solids concentrations less than 400 milligrams per liter. Acid-mine drainage has seriously affected some streams by reducing the pH to less than 4.0 and increasing the dissolved-solids concentrations to greater than 1,000 milligrams per liter. This has resulted in fish kills in some instances. Ground-water movement is impeded both laterally and vertically in both mining regions, especially in western Missouri, because of the low hydraulic conductivity of the rocks of Pennsylvanian age. The quality of ground water varies widely depending on location and depth. Ground water commonly contains high concentrations of iron and sulfate, and dissolved-solids concentrations generally are greater than 1,000 milligrams per liter.

Missouri↗

USGS1990

Distribution of wells in the central part of the western San Joaquin Valley, California

Information from 5,860 wells in the central part of the western San Joaquin Valley, California, was collected from several sources and compiled into a common data base. Only 2,547 wells had sufficient information for classification into four categories based on the hydrogeology: wells perforated in the semiconfined zone at depths less than or equal to 50 ft, wells perforated in the semiconfined zone at depths greater than 50 ft , wells perforated in the semiconfined and confined zones, and wells perforated only in the confined zone. Additionally, wells perforated in the semiconfined zone at depths greater than 50 ft were classified by the type of deposits in which they were perforated (Coast Range alluvium or Sierran sand). A computerized data base system was developed to manage well information, and to facilitate characterizing the nature and distribution of the wells. Wells perforated in the semiconfined zone at depths less than or equal to 50 ft are evenly distributed over part of the study area underlain by shallow groundwater. These wells generally are used as observation wells. Most wells perforated in the semiconfined zone at depths greater than 50 ft are perforated in the Sierran sand. This concentration of wells indicates a tendency for using the Sierran sand, where it exists, as a source of water. There are 533 wells perforated in both the semiconfined and confined zones and 410 wells perforated only in the confined zone. Most of these wells are upslope of the valley trough in areas where the Sierran sand is not present. Wells perforated only in the confined zone are concentrated near the creeks. (USGS)

Water-Resources Investigations Report↗

USGS1996

Level II scour analysis for Bridge 5 (CHELTH00030005) on Town Highway 3, crossing Jenkins Brook, Chelsea, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure CHELTH00030005 on town highway 3 crossing Jenkins Brook, Chelsea, 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 study 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 of central Vermont in the town of Chelsea. The 6.97-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest. In the study area, Jenkins Brook has an incised, sinuous channel with a slope of approximately 0.04 ft/ft, an average channel top width of 48 ft and an average channel depth of 3 ft. The predominant channel bed material is cobble with a median grain size (D 50 ) of 154 mm (0.506 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 17, 1994, indicated that the reach was stable. The town highway 3 crossing of Jenkins Brook is a 23-ft-long bridge consisting of one 20- foot concrete span (Vermont Agency of Transportation, written communication, August 25, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The upstream wingwalls are protected by type-3 stone fill (less than 48 inches diameter) and the downstream wingwalls have type-2 stone fill (less than 36 inches diameter). The footings of both abutments are exposed. The channel is skewed approximately 25 degrees to the opening while the opening-skew-to-roadway is 15 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 ft. Abutment scour ranged from 7.6 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↗

USGS1996

Level II scour analysis for Bridge 36 (BRIDTH00050036) on Town Highway 5, crossing Bridgewater Hollow Brook, Bridgewater, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure BRIDTH00050036 on town highway 5 crossing Bridgewater Hollow Brook, 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 of central Vermont. The 3.60-mi 2 drainage area is in a predominantly forested basin. In the vicinity of the study site, the banks have dense woody vegetation coverage. In the study area, Bridgewater Hollow Brook has an incised, sinuous channel with a slope of approximately 0.028 ft/ft, an average channel top width of 24 ft and an average channel depth of 4 ft. The predominant channel bed material is cobble (D 50 is 196 mm or 0.644 ft). The geomorphic assessment at the time of the Level I and Level II site visit on November 2, 1994, indicated that the reach was stable. The town highway 5 crossing of Bridgewater Hollow Brook is a 30-ft-long, one-lane bridge consisting of one 27-foot steel-beam span (Vermont Agency of Transportation, written communication, August 25, 1994). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 30 degrees to the opening and the opening-skew-to-roadway is also 30 degrees. The scour protection measures at this site were sparse type-2 stone fill (less than 36 inches diameter) along both abutments, upstream wingwalls, and the downstream left wingwall and type-1 stone fill (less than 12 inches diameter) along 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 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. There was no contraction scour for all modelled flows. Abutment scour ranged from 4.9 to 7.0 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↗

USGS1997

Level II scour analysis for Bridge 30, (HUNTTH00220030), on Town Highway 22, crossing Brush Brook, Huntington, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure HUNTTH00220030 on Town Highway 22 crossing Brush Brook, Huntington, 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 4.98-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is forest. In the study area, Brush Brook has an incised, straight channel with a slope of approximately 0.06 ft/ft, an average channel top width of 49 ft and an average bank height of 9 ft. The channel bed material ranges from sand to boulders with a median grain size (D 50 ) of 206 mm (0.675 ft). The geomorphic assessment at the time of the Level I and Level II site visit on June 25, 1996, indicated that the reach was stable. The Town Highway 22 crossing of Brush Brook is a 30-ft-long, one-lane bridge consisting of one 27-foot steel-beam span (Vermont Agency of Transportation, written communication, December 12, 1995). The opening length of the structure parallel to the bridge face is 25.6 ft. The bridge is supported by vertical, concrete abutments. The channel is skewed approximately zero degrees to the opening while the computed opening-skew-toroadway is 15 degrees. A scour hole 1 ft deeper than the mean thalweg was observed along the left abutment during the Level I assessment. The left abutment footing is exposed and undermined. The only scour countermeasure noted at the site was type-2 stone fill (less than 36 inches diameter) along the downstream left road approach embankment. 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 zero. Abutment scour ranged from 7.8 to 10.1 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↗

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