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At least 847 records · Page 47Linked to original sources

USGS2011

An ecosystem-scale model for the spread of a host-specific forest pathogen in the Greater Yellowstone Ecosystem

The introduction of nonnative pathogens is altering the scale, magnitude, and persistence of forest disturbance regimes in the western United States. In the high-altitude whitebark pine ( Pinus albicaulis ) forests of the Greater Yellowstone Ecosystem (GYE), white pine blister rust ( Cronartium ribicola ) is an introduced fungal pathogen that is now the principal cause of tree mortality in many locations. Although blister rust eradication has failed in the past, there is nonetheless substantial interest in monitoring the disease and its rate of progression in order to predict the future impact of forest disturbances within this critical ecosystem. This study integrates data from five different field-monitoring campaigns from 1968 to 2008 to create a blister rust infection model for sites located throughout the GYE. Our model parameterizes the past rates of blister rust spread in order to project its future impact on high-altitude whitebark pine forests. Because the process of blister rust infection and mortality of individuals occurs over the time frame of many years, the model in this paper operates on a yearly time step and defines a series of whitebark pine infection classes: susceptible, slightly infected, moderately infected, and dead. In our analysis, we evaluate four different infection models that compare local vs. global density dependence on the dynamics of blister rust infection. We compare models in which blister rust infection is: (1) independent of the density of infected trees, (2) locally density-dependent, (3) locally density-dependent with a static global infection rate among all sites, and (4) both locally and globally density-dependent. Model evaluation through the predictive loss criterion for Bayesian analysis supports the model that is both locally and globally density-dependent. Using this best-fit model, we predicted the average residence times for the four stages of blister rust infection in our model, and we found that, on average, whitebark pine trees within the GYE remain susceptible for 6.7 years, take 10.9 years to transition from slightly infected to moderately infected, and take 9.4 years to transition from moderately infected to dead. Using our best-fit model, we project the future levels of blister rust infestation in the GYE at critical sites over the next 20 years.

Ecological Applications↗

USGS1999

Reference conditions for giant sequoia forest restoration: structure, process, and precision

National Park Service policy directs that more natural conditions be restored to giant sequoia groves, which have been altered by a century of fire exclusion. Efforts to find a reasonable and practical definition of “natural” have helped drive scientists and land managers to use past grove conditions as reference conditions for restoration. Extensive research aimed at determining reference conditions has demonstrated that past fire regimes can be characterized with greater precision than past grove structures. Difficulty and imprecision in determining past grove structure has helped fuel a debate between “structural restorationists,” who believe that forest structure should be restored mechanically before fire is reintroduced, and “process restorationists,” who believe that simple reintroduction of fire is appropriate. I evaluate old and new studies from sequoia groves to show that some of the arguments of both groups have been flawed. Importantly, it appears that restoration of fire without a preceding mechanical restoration may restore the pre-Euro-American structure of sequoia groves, at least within the bounds of our imprecise knowledge of past grove structure. However, the same may not be true for all forest types that have experienced lengthy fire exclusion. Our ability to draw robust generalizations about fire's role in forest restoration will depend heavily on a thorough understanding of past and present interactions among climate, fire, and forest structure. Use of reference conditions will be central to developing this understanding.

Ecological Applications↗

USGS2013

Interactive effects of wildfire, forest management, and isolation on amphibian and parasite abundance

Projected increases in wildfire and other climate-driven disturbances will affect populations and communities worldwide, including host–parasite relationships. Research in temperate forests has shown that wildfire can negatively affect amphibians, but this research has occurred primarily outside of managed landscapes where interactions with human disturbances could result in additive or synergistic effects. Furthermore, parasites represent a large component of biodiversity and can affect host fitness and population dynamics, yet they are rarely included in studies of how vertebrate hosts respond to disturbance. To determine how wildfire affects amphibians and their parasites, and whether effects differ between protected and managed landscapes, we compared abundance of two amphibians and two nematodes relative to wildfire extent and severity around wetlands in neighboring protected and managed forests (Montana, USA). Population sizes of adult, male long-toed salamanders ( Ambystoma macrodactylum ) decreased with increased burn severity, with stronger negative effects on isolated populations and in managed forests. In contrast, breeding population sizes of Columbia spotted frogs ( Rana luteiventris ) increased with burn extent in both protected and managed protected forests. Path analysis showed that the effects of wildfire on the two species of nematodes were consistent with differences in their life history and transmission strategies and the responses of their hosts. Burn severity indirectly reduced abundance of soil-transmitted Cosmocercoides variabilis through reductions in salamander abundance. Burn severity also directly reduced C. variabilis abundance, possibly though changes in soil conditions. For the aquatically transmitted nematode Gyrinicola batrachiensis , the positive effect of burn extent on density of Columbia spotted frog larvae indirectly increased parasite abundance. Our results show that effects of wildfire on amphibians depend upon burn extent and severity, isolation, and prior land use. Through subsequent effects on the parasites, our results also reveal how changes in disturbance regimes can affect communities across trophic levels.

Montana↗

USGS2015

Avian malaria in Hawaiian forest birds: Infection and population impacts across species and elevations

Wildlife diseases can present significant threats to ecological systems and biological diversity, as well as domestic animal and human health. However, determining the dynamics of wildlife diseases and understanding the impact on host populations is a significant challenge. In Hawai‘i, there is ample circumstantial evidence that introduced avian malaria ( Plasmodium relictum ) has played an important role in the decline and extinction of many native forest birds. However, few studies have attempted to estimate disease transmission and mortality, survival, and individual species impacts in this distinctive ecosystem. We combined multi-state capture-recapture (longitudinal) models with cumulative age-prevalence (cross-sectional) models to evaluate these patterns in Apapane, Hawai‘i Amakihi, and Iiwi in low-, mid-, and high-elevation forests on the island of Hawai‘i based on four longitudinal studies of 3–7 years in length. We found species-specific patterns of malaria prevalence, transmission, and mortality rates that varied among elevations, likely in response to ecological factors that drive mosquito abundance. Malaria infection was highest at low elevations, moderate at mid elevations, and limited in high-elevation forests. Infection rates were highest for Iiwi and Apapane, likely contributing to the absence of these species in low-elevation forests. Adult malaria fatality rates were highest for Iiwi, intermediate for Amakihi at mid and high elevations, and lower for Apapane; low-elevation Amakihi had the lowest malaria fatality, providing strong evidence of malaria tolerance in this low-elevation population. Our study indicates that hatch-year birds may have greater malaria infection and/or fatality rates than adults. Our study also found that mosquitoes prefer feeding on Amakihi rather than Apapane, but Apapane are likely a more important reservoir for malaria transmission to mosquitoes. Our approach, based on host abundance and infection rates, may be an effective alternative to mosquito blood meal analysis for determining vector-host contacts when mosquito densities are low and collection of blood-fed mosquitoes is impractical. Our study supports the hypothesis that avian malaria has been a primary factor influencing the elevational distribution and abundance of these three species, and likely limits other native Hawaiian species that are susceptible to malaria.

Hawai'i↗

USGS2015

Life stage influences the resistance and resilience of black mangrove forests to winter climate extremes

In subtropical coastal wetlands on multiple continents, climate change-induced reductions in the frequency and intensity of freezing temperatures are expected to lead to the expansion of woody plants (i.e., mangrove forests) at the expense of tidal grasslands (i.e., salt marshes). Since some ecosystem goods and services would be affected by mangrove range expansion, there is a need to better understand mangrove sensitivity to freezing temperatures as well as the implications of changing winter climate extremes for mangrove-salt marsh interactions. In this study, we investigated the following questions: (1) how does plant life stage (i.e., ontogeny) influence the resistance and resilience of black mangrove (Avicennia germinans) forests to freezing temperatures; and (2) how might differential life stage responses to freeze events affect the rate of mangrove expansion and salt marsh displacement due to climate change? To address these questions, we quantified freeze damage and recovery for different life stages (seedling, short tree, and tall tree) following extreme winter air temperature events that occurred near the northern range limit of A. germinans in North America. We found that life stage affects black mangrove forest resistance and resilience to winter climate extremes in a nonlinear fashion. Resistance to winter climate extremes was high for tall A. germinans trees and seedlings, but lowest for short trees. Resilience was highest for tall A. germinans trees. These results suggest the presence of positive feedbacks and indicate that climate-change induced decreases in the frequency and intensity of extreme minimum air temperatures could lead to a nonlinear increase in mangrove forest resistance and resilience. This feedback could accelerate future mangrove expansion and salt marsh loss at rates beyond what would be predicted from climate change alone. In general terms, our study highlights the importance of accounting for differential life stage responses and positive feedbacks when evaluating the ecological effects of changes in the frequency and magnitude of climate extremes.

Louisiana↗

USGS1988

Stable isotope geochemistry of sphalerite and other mineral matter in coal beds of the Illinois and Forest City basins

Cleat and clastic dikes of Middle Pennsylvanian-age coal beds of the Illinois and Forest City basins of Illinois, Iowa, Missouri, and Kansas locally contain appreciable amounts of sphalerite within a kaolinite-pyrite-sphalerite (+ or - pyrite)-calcite paragenetic sequence. The sphalerite and associated minerals are of interest as a partial record of the history of fluids in the sedimentary basin and as possible indicators of Mississippi Valley-type mineralization. Moreover, zinc from the sphalerite may represent an exploitable by-product of coal mining and combustion.Pyrite is abundant in these coals both as fine-grained disseminated framboids that formed during early diagenesis and as coarser grained cleat fillings, etc., that formed much later. The delta 34 S values of this later pyrite, the sphalerite, and the coal organic matter range from -12 to 19 per mil. Within individual samples, however, pyrite, sphalerite, and organic matter sulfur delta 34 S values are nearly identical. This similarity strongly suggests related origins. The delta 34 S values of pyrite, sphalerite, and organic matter from coals of the Illinois basin and the central and southern Forest City basin range from -12 to 0 per mil. This range is not unique to the sphalerite-bearing coals; pyrite and organic matter from sphalerite-free high sulfur coals have similar delta 34 S values (Price and Shieh, 1979). We believe that sulfur produced by the breakdown of organosulfur compounds in the coal is incorporated into the epigenetic sulfides. In the northern Forest City basin, however, many samples have delta 34 S values between 8 and 19 per mil. These are similar to the delta 34 S values of sphalerite and pyrite from the Upper Mississippi Valley Zn-Pb district which lies northeast of the Forest City basin and north of the Illinois basin. This similarity suggests input from a Mississippi Valley-type hydrothermal system.Cleat kaolinite has delta D values of -36 to -24 per mil and delta 18 O values of 19.2 to 20.2 per mil. Assuming that clearing postdated the lignite rank of coalification implies that kaolinite was deposited between 40 degrees and 100 degrees C. At the lower temperatures, the kaolinite fluid would have had an isotopic composition similar to seawater; at the higher temperatures, it would have had a composition similar to the sphalerite-depositing fluid. Sphalerite was deposited from a fluid that was chemically and isotopically similar to the fluids responsible for the main-stage ores of the Upper Mississippi Valley Zn-Pb district (75 degrees -113 degrees C, approximately 21 equiv wt % NaCl, delta D = -65 to -3ppm, and delta 18 O = -0.9-9.9ppm). The isotopic compositions (delta 13 C = -12.4 to -2.7ppm and delta 18 O = 21.1-25.8ppm) and paragenetic positions of the cleat calcite samples are similar to those of the late-stage calcite of the Upper Mississippi Valley Zn-Pb and Illinois-Kentucky fluorspar districts. Calcite inclusion fluids had delta D (sub H 2 O) values of -80 and -58 per mil, implying a meteoric water source. At probable temperatures of 15 degrees to 75 degrees C, this calcite formed from fluids having calculated delta 18 O (sub H 2 O) values of -9 to 1 per mil, implying slight to moderate exchange with sedimentary rocks. The diagenetic-epigenetic history of fluids recorded by the cleat minerals probably began with a slightly evolved seawater, followed by a metal-bearing deep basin brine, and concluded with a cooler, slightly evolved, meteoric-water fluid.

Economic Geology↗

USGS2005

Influence of thinning of Douglas-fir forests on population parameters and diet of northern flying squirrels

We investigated the effects of thinning young (35- to 45-yr-old) Douglas-fir (Pseudotsuga menziesii) forests on density, survival, body mass, movements, and diets of northern flying squirrels (Glaucomys sabrinus) in the northern coast range of Oregon. We used a repeated measures, randomized block design with 3 treatments (control, moderate thinning, and heavy thinning) and 4 replicates to study diets and population characteristics from 1994-1997. Densities of flying squirrels were variable in space and time, but they were positively correlated to biomass and frequency of fungal sporocarps, suggesting they were responding to food resources rather than forest structure. Fungal sporocarps comprised a major portion of the squirrel's diet, and other vegetative material made up the remainder of the diet. Several fungal genera including Gautieria, Geopora, Hymenogaster, Hysterangium, Melanogaster, and Rhizopogon were found more frequently in diets than on the trapping grids and therefore appeared to be selected by the squirrels. Flying squirrel movements were negatively correlated with the frequency of occurrence of fungal sporocarps at trap stations, suggesting that squirrels traveled greater distances to find fungal sporocarps where these food items were more sparsely distributed. We hypothesized that flying squirrel densities would be relatively low in these young, structurally simple forests; however, densities on some of the grids were >1.5 squirrels/ha, which was comparable to densities described for the species in late-successional forests. Our results indicated that commercial thinning did not have measurable short-term effects on density, survival, or body mass of flying squirrels.

Journal of Wildlife Management↗

USGS2006

Distribution and relative abundance of forest birds in relation to burn severity in southeastern Arizona

The frequency of wild and prescribed fires in montane forests of the southwestern United States has increased after a century of fire suppression and subsequent fuels accumulation. To assess the effects of recent fires (median time since fire = 6 yr) on the montane forest bird community, we surveyed birds in 8 Sky Island mountain ranges in southeastern Arizona, USA, and examined how the distribution (i.e., presence-absence) of 65 species and relative abundance of 16 species correlated with evidence of severe and less severe fire at >1,500 survey points. We detected associations between fire and bird presence-absence for 17% of the 65 species analyzed and between fire and bird relative abundance for 25% of the 16 species analyzed. Most species (73%) were positively associated with burned areas and displayed stronger associations (i.e., more extreme odds ratios) with survey points that had evidence of severe as opposed to less severe fire. Positive associations with severe fire were strong (>3 to 1 odds) for western wood-pewee (Contopus sordidulus) and house wren (Troglodytes aedon), and negative associations with severe fire were strong for warbling vireo (Vireo gilvus) and red-breasted nuthatch (Sitta canadensis). Although recent fires appear to have had a positive effect on the distribution and relative abundance of several montane forest bird species in the region, these species are not the open-woodland birds that we would have expected to have benefited from fire based on previous research. Nevertheless, our results confirm associations between fire and bird presence-absence and relative abundance reported previously for 7 species of birds. Our results also provide new information for Grace's warbler (Dendroica graciae) and greater pewee (C. pertinax), 2 species for which fire data were formerly lacking. Managers can use these data to make and test predictions about the effects of future fires, both severe and less severe, on montane forest birds in the southwestern United States.

Journal of Wildlife Management↗

USGS1976

The abundance and diversity of the herpetofaunas of tropical forest litters

Quantitative and qualitative samples of amphibian and lizard faunas were taken from forest litter in Costa Rica and compared with similar samples collected in Borneo, the Philippines, and Panama. Animal abundance is about ten times greater in Costa Rican lowland wet forest than in Borneo. Radically different routes and rates of energy flow are postulated to account for the difference. In a series of upland (1010-1425 m) samples in the Philippines, the number of litter lizards and frogs increases with elevation. A single upland (1200 m) Costa Rican sample contains about three times as many animals per 100 m2 as two lowland sites. This increase with altitude correlates well with hypotheses that overall tropical forest productivity is greatest at intermediate elevations. Herpetofaunal densities are greater in wet areas compared to dry sites and flat terrain compared to slopes. These observations are linked to the greater variation and lesser total litter fall in dry sites and/or slopes. The number of species of amphibians and lizards regularly inhabiting the litter is similar in all wet lowland forests studied. Increasing elevation and decreasing rainfall correlate with faunas having fewer species. The former is seen as the result of the differential ability of lowland species to invade uplands, and the latter as a decrease in the kind and duration of frog-spawning sites. Reduced equitability with increasing elevation is principally due to the much greater proportional increase of the commonest species. In the evolution of American and Bornean-Philippine wet lowland faunas, frogs with direct development (Eleutherodactylus) have radiated in the former in the same fashion that skinks have in the latter.

Biotropica↗

USGS1982

Stream-grade variation and riparian-forest ecology along Passage Creek, Virginia

Passage Creek, in northwestern Virginia, flows on relatively nonresistant shales, then cuts through a gorge underlain by resistant sandstone In the gorge, the stream gradient steepens, the size of bed material increases, a braided channel forms, and riparian-forest composition and growth form changes relative to areas outside the gorge Effects of flooding are intensified within the gorge and revealed in the pattern and deformation of streamside vegetation Increased stream gradient within the gorge provides for high stream power and coarse sediment deposition relative to the flood plain outside the gorge. A more diverse upland forest grows on the flood plain in the gorge The riparian forest in the gorge may be an example of a nonequilibrium forest, resulting from periodic disturbance by destructive floods. Recognition of vegetation patterns resulting from such disturbances may be useful in detection of potential flooding.

Virginia↗

USGS2023

Northwest Forest Plan — The first 25 years (1994–2018): Watershed condition status and trends

This report describes status and trends in watershed condition across the Northwest Forest Plan (NWFP) area over the first 25 years since its inception in 1994. The program charged with this task is the Aquatic and Riparian Effectiveness Monitoring Program (AREMP), which has assembled information from field data collection, spatial datasets, and a host of landscape models to evaluate the status and trends in aquatic resources in streams and watersheds. Field data included hydrologic measurements (stream wetted widths and temperatures), geomorphic responses (instream wood and sediment), and biological responses (macroinvertebrates and aquatic organism passage). Novel statistical models were used to estimate trends in these measured responses. A suite of complementary modeled results was also employed to describe hydrometeorological drivers (e.g., drought indices and stream discharge), forest cover (upslope and riparian vegetation), and geomorphic conditions (e.g., road-related estimates of chronic and shallow landslide sediment delivery risk). Collectively, information on these responses allowed us to rigorously evaluate instream responses and hypothesize watershed drivers of those responses across the NWFP area and over time. The majority of responses we observed indicated widespread and incremental improvements from active management of forests, forest roads, and road-stream crossings as envisioned by the aquatic conservation strategy of the NWFP. Additionally, many of the responses we observed were consistent with those expected under the influences of changing climates in the Pacific Northwest. Ultimately, the long-term, broad-scale information provided by AREMP is a critical foundation for evaluating the effectiveness of federal land management and the effects of changing climates on water resources that sustain the Pacific Northwest’s human and natural landscapes.

California, Oregon, Washington↗

USGS1997

Effects of climate change on southeastern forests

Forests of the coastal plain region of the southeastern United States are among the most productive in North America. Because they form the basis of a large timber and wood products industry, these forests are of considerable economic importance. Also, the forests are rich in plant and animal species. Because they are diverse as well as productive, they have considerable conservation importance. Therefore, understanding potential impacts of climate change on southern forests is critical.

Texas↗

USGS2002

Effects of wastewater on forested wetlands

Cycling nutrient-enriched wastewater from holding ponds through natural, forested wetlands is a practice that municipal waste treatment managers are considering as a viable option for disposing of wastewater. In this wastewater cycling process, sewer effluent that has been circulated through aerated ponds is discharged into neighboring wetland systems. To understand how wastewater cycling affects forest and species productivity, researchers at the USGS National Wetlands Research Center conducted dendroecological investigations in a swamp system and in a bog system that have been exposed to wastewater effluent for many decades. Dendroecology involves the study of forest changes over time as interpreted from tree rings. Tree-ring chronologies describe the pattern and history of growth suppression and release that can be associated with aging and disturbances such as hurricanes, floods, and fires. But because of limited monitoring, little is known about the potential for long-term effects on forested wetlands as a result of wastewater flooding. USGS researchers used tree rings to detect the effect of wastewater cycling on tree growth. Scientists expected to find that tree-ring width would be increased as a result of added nutrients.

Fact Sheet↗

USGS2002

The Cooperative Forest Ecosystem Research Program

Changes in priorities for forest management on federal and state lands in the Pacific Northwest have raised many questions about the best ways to manage young-forest stands, riparian areas, and forest landscapes. The Cooperative Forest Ecosystem Research (CFER) Program draws together scientists and managers from the U.S. Geological Survey, Bureau of Land Management, Oregon Department of Forestry, and Oregon State University to find science-based answers to these questions. Managers, researchers, and decisionmakers, working within the CFER program, are helping develop and disseminate the knowledge needed to carry out ecosystem-based management successfully in the Pacific Northwest.

Fact Sheet↗

USGS1986

Map showing slope movements in the Oak Forest Quadrangle, Greene County, southwestern Pennsylvania

This map is the first example in the eastern United States of a 1:24,000-scale 7.5– minute quadrangle map that identifies areas with slope—stability problems in detail. Such a map enables the user to make a rapid evaluation of the potential for mass movement. Furthermore, detailed slope movement inventory of this type can serve as a framework for statistical analyses of several factors that cause slope failures, such as the effects of bedrock lithology, soil and slope characteristics, and precipitation. Planners, engineers, soil scientists, geologists, and elected officials should find the map useful in the assessment of slope hazards and planning for future land use. Final evaluation of any site within the quadrangle should be based on an examination by a soils engineer or an engineering geologist. Field investigations in the springs of 1981 and 1982 and the fall of 1981 involved nearly 60 days of traverses. The foot traverses were supplemented by the interpretation of the land surface on vertical black-and-white aerial photography flown in January and February of 1973 at a scale of nearly 1:24,000. Earlier aerial photography flown in June and July 1939 at a scale of 1:20,000 and more recent but significantly smaller scale photography (1:80,000) flown in June 1977 supplied additional documentation. More than 1,200 active or recently active and 900 older slope movements were identified. The geologic map of the Oak Forest quadrangle (Roen, 1972) is one of several geologic maps at a scale of 1:24,000 in eastern and central Greene County. Stone (1932) wrote an earlier report of the geology and mineral resources of Greene County. A series of reconnaissance landslide maps at 1:24,000 scale based mainly on aerial photographic interpretation included Greene and adjacent counties (Hackman and Thomas, 1978). Selection of the Oak Forest quadrangle for a more comprehensive study of the slope movements was based on the existence of a recent geologic map (Roen, 1972), sizeable tracts of both forested and non-forested land, nearby precipitation record stations, a large number of pipelines which could offer pertinent data, and good accessibility of terrain from secondary roads. Finally, Hackman and Thomas (1978) showed that the area was representative of any quadrangle in the northern part of the Dunkard basin in its distribution and density of slope movements. The quadrangle is located about 65 km southwest of Pittsburgh, Penn. (fig. 1). Three distinct drainage systems (north, east, and south trending) are represented within the quadrangle (fig. 2).

Pennsylvania↗

USGS2002

Hurricane Mitch: Landscape Analysis of Damaged Forest Resources of the Bay Islands and Caribbean Coast of Honduras

The advent of analog and digital video has provided amateur photographers with professional-like technology to capture dynamic images with ease and clarity. Videography is also rapidly changing traditional business and scientific applications. In the natural sciences, camcorders are being used largely to record timely observations of plant and animal behavior or consequence of some catastrophic event. Spectacular video of dynamic events such as hurricanes, volcanic eruptions and wildfire document the active process and aftermath. Scientists can analyze video images to quantify aspects of a given event, behavior, or response, temporally and spatially. In this study we demonstrate the simple use of an aerial application of videography to record the spatial extent and damage expression of mangrove forest in the Bay Islands and mainland coast of northern Honduras from wind damage following Hurricane Mitch (1998). In this study, we conducted a video overflight of coastal forests of the Bay Islands and mainland coast of northern Honduras 14 months after impact by Hurricane Mitch (1998). Coastal areas were identified where damage was evident and described relative to damage extent to forest cover, windfall orientation, and height of downed trees. The variability and spatial extent of impact on coastal forest resources is related to reconstructed wind profiles based on model simulations of Mitch's path, strength, and circulation during landfall.

Open-File Report↗

USGS1984

Mapping of forested wetland: Use of seasat radar images to complement conventional sources

Distinguishing forested wetland from dry forest using aerial photographs has been handicapped because photographs often do not reveal the presence of water below the tree canopies. Images obtained during the summer months of 1978 by the Seasat satellite's L-band (23-cm) radar reveal forested wetland as patterns of high radar reflection in the Atlantic coastal plain between Maryland and Florida. Potential exists for Seasat radar images to complement aerial photographs in the compiling of maps of wetland. A test was conducted with four experienced photointerpreters which revealed that interpretation accuracy was significantly higher when the Seasat radar images were used than when only conventional sources were utilized. The bases of reference, that is, the maps made from conventional sources, were from the U.S. Geological Survey (USGS) series on Land Use and Land Cover, which shows Forested Wetland among its categories.

Florida, Georgia, Maryland, North Carolina↗

USGS1997

Level II scour analysis for Bridge 12 (SUNDFLR0030012) on Forest Land Road 3, crossing Roaring Branch Brook, Sunderland, Vermont

This report provides the results of a detailed Level II analysis of scour potential at structure SUNDFLR0030012 on Forest Land Road (FLR) 3 (FAS 114) crossing Roaring Branch Brook, Sunderland, Vermont (figures 1–8). A Level II study is a basic engineering analysis of the site, including a quantitative analysis of stream stability and scour (U.S. Department of Transportation, 1993). Results of a Level I scour investigation also are included in Appendix E of this report. A Level I investigation provides a qualitative geomorphic characterization of the study site. Information on the bridge, gleaned from Vermont Agency of Transportation (VTAOT) files, was compiled prior to conducting Level I and Level II analyses and is found in Appendix D. The site is in the Green Mountain section of the New England physiographic province in southwestern Vermont. The 4.93-mi 2 drainage area is in a predominantly rural and forested basin. In the vicinity of the study site, the surface cover is dense forest along the left bank and primarily shrubs and trees along the right bank, both upstream and downstream of the bridge. In the study area, Roaring Branch Brook has an incised, sinuous channel with a slope of approximately 0.01 ft/ft, an average channel top width of 33 ft and an average bank height of 4 ft. The channel bed material ranges from cobble to bedrock with a median grain size (D 50 ) of 139 mm (0.457 ft). The geomorphic assessment at the time of the Level I and Level II site visit on July 30, 1996, indicated that the reach was stable. Forest Land Road 3 (FAS 114) crossing of Roaring Branch Brook is a 37-ft-long, two-lane bridge consisting of one 35-foot steel-beam span (Vermont Agency of Transportation, written communication, December 14, 1995). The bridge is supported by vertical, concrete abutments with wingwalls. The channel is skewed approximately 30 degrees to the opening while the opening-skew-to-roadway is 15 degrees. The scour protection measures at the site included type-3 stone fill (less than 48 inches diameter) along the left and right abutments, along the upstream left and downstream right wing walls and along the downstream right bank. Type-4 (less than 60 inches diameter) stone fill was found along the upstream right and downstream left wingwalls and along the downstream left bank. Type-2 (less than 36 inches diameter) stone fill scour protection was found along the upstream left and right banks. 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 calculated to be 0.0 ft. Abutment scour ranged from 4.3 to 10.4 ft. The worst-case abutment scour occurred at the 500-year discharge along the right abutment. Additional information on scour depths and depths to armoring are included in the section titled “Scour Results”. Scoured-streambed elevations, based on the calculated scour depths, are presented in tables 1 and 2. A 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↗