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William W. Emmett

Publications and source records attributed to William W. Emmett.

15 recordsLinked to original sources
USGS2005

Channel and hillslope processes revisited in the Arroyo de los Frijoles watershed near Santa Fe, New Mexico

Detailed documentation of geomorphic changes in the landscape of more than a few years is rarely possible. Channel cross sections, channel profiles, sediment deposition behind dams, and hillslope-erosion plots, originally benchmarked within several watersheds outside Santa Fe, New Mexico, in the 1950’s and 1960’s, for a 1966 report that documented processes and rates of arid-region sediment production and deposition, were resurveyed in the mid-1990’s. Many of the original study sites were relocated and surveyed in the mid-1990’s to determine subsequent channel and hillslope changes and to determine whether trends of channel and hillslope aggradation and degradation that were evident in the 1950’s and 1960’s have continued. In general, the net change in channel geometry has been small over the last 30–40 years. The average change in cross-sectional area of 32 resurveyed cross sections was erosion of 0.27 square meter, which equates to a 4-percent increase in cross-sectional area. The average net change in thalweg elevation for 51 resurveyed cross sections was degradation of 0.04 meter. Unpublished data (1964–68) from the scour chains showed that 371 chains had an average scour of 0.14 ± 0.14 meter and that 372 chains showed an average fill of 0.13 + 0.11 meter. Scour, found in the original study (1958–64) to be proportional to the square root of discharge, was confirmed with the addition of unpublished data (1964–68). The observed channel changes have no consistent trend, compared either to results observed in the original 1966 study or to distance from the watershed divide. The conclusion drawn in the original study was that most channels were aggrading; the resurvey showed that aggradation did not continue. An increase in housing and population in the Arroyo de los Frijoles watershed since the 1950’s has led to more roads. Channel degradation is most noticeable at road crossings. The greatest degradation of the main channel Arroyo de los Frijoles, 1.53 meters, and the greatest aggradation, 0.38 meter, occur downstream and upstream, respectively, from a culvert in a dirt road. Periods of high average annual rainfall intensity reported for Santa Fe for 1853–80 immediately preceded late 19th century arroyo incision, and another period of high-intensity rainfall began in 1967. This may indicate that climatic factors are again favorable for arroyo incision in this part of New Mexico; data from this resurvey, however, do not provide evidence of a renewed cycle of erosion. At a 1930’s Civilian Conservation Corps-constructed dam on Coyote C. Arroyo, the measured sediment yield from 1966 to 1993 was 139 metric tonnes per square kilometer per year. Sediment yields have decreased through time because of either a decrease in the trap efficiency of the reservoir over time or a decrease in sediment delivery to the reservoir because of upstream channel storage. The effects of base-level rise on the channel profile were documented in 1993 through resurveys of sediment deposits behind two small dams, Big Sweat Dam and Little Sweat Dam. Both dams, built in 1960, showed sediment deposition that extends 20 and 9.3 meters upstream, respectively, and the 1993 sediment gradient was nearly the same as the unaffected channel upstream. Big Sweat Dam showed fluctuations in channel gradient within 5.3 meters of the dam, which may be a result of local scour following complete filling of the dam, scour from increased sinuosity, or differences in the location of surveying stations over time. The sinuosity of the channel has increased over time, presumably from a reduction in slope. Channel gradients 0 to 11.0 meters upstream from Little Sweat Dam have remained constant at about 0.028 from 1964 to 1993. Measurement of erosion or hillslope-erosion plots show that average values of surface erosion range from 0.019 to 0.096 centimeters per year and are within values reported for regional erosion and denudation studies. Sediment yield from the Slopewash Tributary erosion plot was 307 metric tonnes per square kilometer per year. The reproducibility and accuracy of the resurveys from the 1950’s to the 1990’s attest to the concepts used to quantify geomorphic features established in the Vigil Network. With relatively simple techniques, more than 30 years of geomorphic change were observed in this study.

New Mexico↗
USGS1997

Bedload and river hydraulics - Inferences from the East Fork River, Wyoming

During 1973-79, bedload data were collected in a sophisticated trap on a river of moderate size, the East Fork. The transport rate was measured most days through a full snowmelt season, and the rate was determined separately for eight zones across the channel width. The quantitative data are unique and unlikely to be repeated. Nor need they be, because as a result of this effort a practical bedload sampler was adequately tested against full river measurement. It was shown that bedload moves sporadically and randomly on the river bed. Therefore, transport rate is highly variable in short periods of time. There is also a wide variance from day to day. Yet, different rivers have transport rates, which are functions of discharge, depth, and sediment size, that are clearly distinct. Comparison of computed and measured transport rates indicates that a major problem remains: What grain size is representative of the bedload when there is a wide or heterogeneous particle-size distribution? Size of the bedload in motion may be very different from the size of bed material obtained from samples of the streambed. For general computation, the river channel slope may be averaged, and it may be assumed that water-surface slope does not change materially with changing discharge. Indeed, this generality is correct, in that, compared with depth, velocity, and width, slope is conservative at-a-station. However, in more detail, slope changes importantly with discharge in short reaches of channel, and those changes are very different in pool and riffle. These local changes in slope are not merely an aspect of a detailed longitudinal profile but involve cross-channel as well as down-channel components. The pool and riffle sequence involves not only undulation of bed elevation and bar formation on alternate sides of the channel, but alternation of the zone of superovulation of the water surface, and changing relation of watersurface slope to discharge. These details can be seen only in the full topography of the water surface. Riffles fill during high flow and scour at low flow. Changes in local water-surface slope illustrate this process. Pools are a storage zone for sediment in the low-flow season. Even though large volumes of sediment move, the distance moved is not large—in the East Fork River, sand of size 0.5-1 millimeter moved 650 meters during the 1979 snowmelt runoff season. Bedload transport is greatest over or near bars and not in the deepest part of the channel. Direct observation of the locus of sediment transport indicates that this locus moves from one side of the channel to the other in concert with the occurrence of alternate bars. Separately, data indicate that at constant stream power, transport rate increases as depth decreases.

Wyoming↗
USGS1980

Field data describing the movement and storage of sediment in the East Fork River, Wyoming; Part I, River hydraulics and sediment transport, 1979

Bed-material gradation and water-surface slope were determined for a 3.3-kilometer reach of East Fork River, Wyo. During peak snowmelt runoff, frequent measurements of water discharge and sediment-transport rate provided data describing the inflow and outflow of water and sediment. In spring 1979, bankfull stage was exceeded on 8 days. Maximum discharge was about 32 cubic meters per second, which has a recurrence interval of about 2 years. The median particle size of bed material is 1.28 millimeters; the 35 and 65 percentiles are represented by diameters of 0.50 and 2.88 millimeters, respectively. The average water-surface slope in the reach is 0.0007 and varies little with river stage. Bedload-transport rates ranged from a little less than 0.001 to a little more than 0.1 kilograms per meter of channel width per second. Median bedload grain size, with several exceptions, ranged from 0.4 to 1.5 millimeters. Gravel-size particles generally constituted 10 to 40% of the bedload. Suspended-sediment concentrations ranged from 6 to 95 milligrams per liter. Suspended sediment smaller than sand constited about half the measured suspended sediment, ranging from 17 to 81%. (USGS)

Open-File Report↗
USGS1980

A field calibration of the sediment-trapping characteristics of the Helley-Smith bed-load sampler

For sediment particle sizes between 0.50 mm and 16 mm, the Helley-Smith bedload sampler has a near perfect sediment-trapping efficiency. For particles sizes smaller than 0.50 mm, the Helley-Smith sampler has a high bedload sediment-trapping efficiency because part of the sediement retained by the sampler has been transported in suspension and it cannot be quantified separately from the bedload. For particle sizes larger than about 16 mm, the Helley-Smith sampler has low sediment-trapping efficiency but this may be related to the paucity of coarse particles in transport in the calibration tests rather than reflecting an actual low trap efficiency for large-size particles. (USGS)

Professional Paper↗
USGS1979

Sediment transport in the Tanana River in the vicinity of Fairbanks, Alaska, 1977-78

Measurements of the sediment load of the Tanana River in the vicinity of Fairbanks, Alaska, show that suspended-sediment transport rate in tons per day, relates to water discharge, in cubic feet per second, as: Suspended-sediment transport rate (tons/day) = 5.717 x 10 to the minus 8th power x water discharge (cubic feet/second) to the 2.713 power, (where the correlation coefficient squared = 0.967). The bedload-transport rate is approximately 1 to 2 prcent of the suspended-sediment transport rate. Data collected at Fairbanks and upstream from Fairbanks near North Pole, Alaska, show little difference in size distribution of suspended sediment between the two locations. The median particle size distribution of suspended sediment is generally in the silt range, but at some low-water discharges, the median particle size is in the very fine sand range. The median particle size is in the very fine sand range. The median particle size of bedload near Noth Pole is generally in the gravel range, but at some low transport rates, the median particle size is in the medium sand range. At Fairbanks, data collected in 1977 indicate median particle sizes of bedload comparable to those of the upstream location, whereas data collected in 1978 indicate a marked decrease in median particle size of bedload between the two locations. For both locations and at all water discharges and sediment transport rates, particles constituting the suspended load are significantly smaller than particles constituting the bedload.

Alaska↗
USGS1976

Data for calibrating unsteady-flow sediment-transport models, East Fork River, Wyoming, 1975

In 1975, data to calibrate a one-dimensional unsteady-flow and sediment-transport routing model were collected on a reach of the East Fork River of western Wyoming. The reach, 3.1 miles (5 kilometers) in length, wan immediately upstream from a previously established bedload sampling station. Nineteen channel cross sections were sounded at regular intervals during the spring-runoff period. Four stage recorders provided continuous records of water-surface elevations. Samples of bed material at most of the cross sections were obtained prior to high water. Streamflow and sediment-discharge measurements were collected at four of the sections. The physiography and hydrology of the contributing watershed, the study reach, and the equipment and techniques used in data collection are described briefly. The bulk of the report is a presentation of data for the several-week period of late May to early June 1975, for which concurrent water discharge data, bedload transport and size data, and cross-section depth measurements were collected. In addition, some data collected in 1973 and 1974 and before and after the calibration period in 1975 are included for completeness.

Wyoming↗
USGS1974

Channel changes

Environmental impacts may alter the quantities of water and sediment carried in a stream and thus may increase or diminish naturally occurring rates of channel changes and the pre-impact frequency of flows. Repetitive cross-channel surveys to determine changes in channel size or location are a measure of the response of stream to environmental impact and may provide data necessary before corrective measures can be taken to minimize the effects of the impact. One effect on stream channels from the impact of urbanization can be shown, by example from one stream, to be a loss in channel size due to deposition of sediment. After 17 years of urbanization encroaching on the area, the channel was only 66 percent of the size it was at the beginning of that period.

Geology↗
USGS1972

The hydraulic geometry of some Alaskan streams south of the Yukon River

Channel geometry surveys were conducted to determine bankfull stage, discharge, and other hydraulic parameters at 22 locations along the proposed route of the trans-Alaska pipeline corridor south of the Yukon River. Combined with the records from gaging stations located at some of the sites, the data are sufficient to describe some of the channel and flow characteristics typical of each of two major hydrologic areas, the Yukon River Region and the South-Central Region. Although each region follows general hydrologic trends, least squares relations indicate each exhibits its own particular deviations. Average values of the hydraulic and geometric properties of rivers were used to illustrate their application to practical engineering problems, namely the computation of depth of channel scour and of bedload discharge. For design purposes, caution is recommended when making computations based on average values. In the absence of other data, however, the average data become useful predictive tools.

Alaska↗
USGS1972

Some rates of geomorphological processes

This brief report summarizes three sets of measurement data on certain processes. The first concerns the rate of movement of soil on hillslopes, especially by mass movement or slow gravitational creep. The results are abstracted from an unpublished manuscript by the junior author who reports on the measurements which Leopold began 10 or more years ago and to which in more recent years Emmett has added new sites and has carried on the annual remeasurement. The results are those from "mass-movement lines", which consist of a series of pins or iron rods, 10 inches (25 cm) long driven vertically into the ground along a straight line-of-sight, secured at each end with stiff iron posts. The Survey consists of setting a theodolite over one of the end bench marks and orienting on the other. The distance of each individual pin from the line of sight is recorded. Resurveys are usually made annually.

Geographia Polonica↗
USGS1966

Channel and hillslope processes in a semiarid area, New Mexico

Ephemeral washes having drainage areas from a few acres to 5 square miles are shown by actual measurement to be accumulating sediment on the streambed. This aggradation is not apparent to the eye but is clearly shown in 7 years of annual remeasurement. A similar aggradation was in progress in the same area some 3000 years ago as evidenced by an alluvial terrace later dissected by the present channel system. At that time as well as at present, aggradation occurred even in tributary areas draining a few acres. Colluvial accumulations merge with channel deposits and blanket the valleys and tributary basins even up to a few hundred feet of the drainage divides. The present study concerned the amounts of sediment produced by different erosion processes in various physiographic positions in the drainage basins. Measurements show that by far the largest sediment source is sheet erosion operating on the small percentage of basin area near the basin divides. Mass movement, gully head extension, and channel enlargement are presently small contributors of sediment compared with sheet erosion on unrilled slopes. As in previous studies, not all of the erosion products could be accounted for by accumulations on colluvial slopes and on beds of channels. The discrepancies are attributed primarily to sediment carried completely out of the basins studied and presumably deposited somewhere downstream. Aggradation of alluvial valleys of 5 square miles area and smaller both in the present epicycle, and in prehistorical but post-glacial times in this locality, cannot be attributed to gullying or rill extension in the headwater tributaries but to sheet erosion of the most upstream margins of the basins. Studies of rainfall characteristics of the 7 years of measurement compared with previous years in the 100-year record do not provide a clear-out difference which would account for the presently observed aggradation of channels. Longer period of measurement of erosion and sedimentation will be necessary to identify what precipitation parameters govern whether the channels aggrade or degrade.

Professional Paper↗
USGS1965

Vigil Network sites: A sample of data for permanent filing

The Vigil Network consists of places where observations are made through time to record changes in landscape features over a long period. Resurveys will usually be made once each year or every few years and the period of observation, hopefully, will extend through and beyond the International Hydrological Decade. Vigil Network sites will usually be chosen to represent some typical feature of a given landscape. In the example shown here, the feature is a small ephemeral channel in a basin of moderate relief underlain by silty sandstone typical of the surrounding area. Vigil sites are not protected from man's influence and indeed may be selected because of the possible or portending cultural influences. In this respect they differ from the Bench Mark Network whose purpose is to make precise observations of hydrologic factors in areas uninfluenced by and protected from man's use. The factors which might be observed are many and varied. A few might be mentioned here, others are explained at length elsewhere (Miller and Leopold, 1963; Leopold, 1962). Streamchannel position, form, depth, and profile; vegetation in form of transects or quadrats; soil movement on slopes; rock movement on slopes or in channels. These and many more would yield valuable information on changes with time. To assure permanence of initial field observations, including reference points, bench marks, and cross sections, brief descriptions, maps, and initial data should be filed identically in designated repositories where the data will be made available for inspection by any interested scientist. It is recommended that the designation of two such locations where records of the type here attached will be filed be taken up by the Coordinating Council of the International Hydrological Decade. In designating such repositories it should be recognized that there is no need for elaborate indexing. The main requirement is merely the maintenance of a simple file where the data are stored and can be inspected or copied by any scientist. There need be no special provision for lending or reproduction services. The present document is an example showing what data, maps, and descriptions should be included in those permanent files at the two repositories. The material in these repositories should be sufficient to permit someone in the indefinite future to find and remeasure the same features described now. Thus the scientific value of the original surveys increases with time, - provided that the descriptions are sufficient to allow a person to find with assurance the original feature in the field. It must be visualized that a permanent repository must economize in space. Thus, as the example here shows, the filed material is not all of the original field notes but a summary, brief but descriptive.

International Association of Scientific Hydrology ↗
USGS1964

Geometry of river channels: Discussion by William W. Emmett and Luna B. Leopold

For many years river engineers and geomorphologists have sought a rationale for the general similarity that can be observed among river channels from various environments. Some aspects of this general comparability were noted a century ago by Playfair, and other aspects were examined in a more quantitative way approximately 10 yr ago by R. E. Horton. Such similarities with respect to the channel cross section and the associated hydraulic parameters and their changes downstream were studied by some of the engineers who attained prominence for their work on the self-adjusting irrigation canals of India, especially G. Lacy, 15 C. Inglis, 16 and T. Blench. 17 Among these men, canal characteristics were the principal objects of investigation, although natural river channels assumed an increasing share of the attention of the students of "regime analysis," especially Blench. L. B. Leopold and T. Maddock 18 developed a scheme by which the average relationships among form and hydraulic parameters could be easily described, this description being the one on which the author chose to elaborate.

Conference Paper↗
USGS1963

Downstream patterns of riverbed scour and fill

Progress has been made in describing riverbed scour and fill at a given stream section. One needs only the data routinely collected at a stream-gaging station to observe scour and fill at that station. However, similar progress has not been made to determine whether or not the scour and fill observed at a given section extends over a relatively long reach of the channel. Gaging stations are generally located too far apart to draw any conclusions as to scour processes between stations. It remains necessary then to establish a sufficient number of cross sections along a channel to describe the downstream pattern of riverbed scour.

Conference Paper↗