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M. Gordon Wolman

Publications and source records attributed to M. Gordon Wolman.

11 recordsLinked to original sources
USGS2014

Reconnaissance study of erosion and deposition produced by the flood of August 1955 in Connecticut

A large area in the valley bottoms in Connecticut was inundated by the flood of August 1955. Relative to the total area flooded that part permanently modified by the flow was surprisingly small. Although great in some places, the distribution of these permanent modifications of channel and flood plain was spotty. Erosion of the channel and valley bottom appears to have been most severe in narrow, steep valleys. Environments of deposition were diverse. They appeared to be related to rate and direction of flow, quantity and size of sediments locally available, and in some cases to the presence of vegetation. Most of the coarse sediment deposited in the valley appears to have been derived from local sources such as valley walls and terraces composed of glacial outwash and till and flood plains containing considerable gravel. Fine sand predominated in most of the sediment deposited. Considering the magnitude of the runoff, the quantity of fine sediment transported or deposited by the flood was small. The maximum observed concentration was 473 parts per million in Scantic River at Broad Brook. Newly deposited fine sediments are thin or absent on the flood plains of many valleys which were beneath 20 ft of slow‐moving flood waters. The paucity of deposition in such ideal depositional environments also indicates that the flow did not have a high concentration of fine sediments. A number of boulders five to seven feet in diameter were moved by flood waters in reaches in which smaller gravels were undisturbed. Severe erosion in the uplands was minor. In this reconnaissance we saw little evidence of newly formed gullies and no areas of severe sheet erosion. This was the case in both woodland and pasture land. Large amounts of subsurface flow and relatively unerodible ground are presumed to be responsible for the absence of erosion.

Connecticut↗
USGS1987

Analysis and interpretation of water-quality trends in major U.S. rivers, 1974-81

Water-quality records from two nationwide sampling networks are now of sufficient length to permit nationally consistent analysis of long-term water-quality trends at more than 300 locations on major U.S. rivers. Observed trends in 24 water-quality measures for the period 1974--81 provide evidence of both improvement and deterioration in stream quality during a time of major changes in atmospheric and terrestrial influences on surface waters. Particularly noteworthy are widespread decreases in lead and fecal bacteria concentrations and widespread increases in nitrate, arsenic, and cadmium concentrations. Changes in municipal waste treatment, leaded-gasoline consumption, highway-salt use, and nitrogen-fertilizer application, and regionally variable trends in coal production and combustion during the period, appear to be reflected in water-quality changes. There is evidence that atmospheric deposition of a variety of substances has played a surprisingly large role in water-quality changes.

Water Supply Paper↗
USGS1964

Fluvial processes in geomorphology

This excellent text is a pioneering work in the study of landform development under processes associated with running water. Its primary emphasis is on subjects that were the focus of the authors' studies in both field and laboratory. Part I deals with the process of change in the evolving landscape. Part II explores process and form, and Part III, the effects of time. In Part I, the relation of geomorphology to field problems is analyzed in studies of a mountain block in a semiarid climate, a meandering river cut into bedrock, and benches along a sea coast. Part Two contains studies of weathering, climate, and such denudational processes as flooding and erosion. Here, too, are examinations of the drainage basin as a geomorphic unit, water and sediment in channels, channel form and process, and hillslope characteristics and processes. In Part III, the authors cover geochronology, drainage pattern evolution, channel changes with time, and the evolution of hillslopes. Two appendixes will help readers convert units and equivalents, and identify symbols and nomenclature.

Book↗
USGS1961

Factors controlling the size and shape of stream channels in coarse noncohesive sands

The size and shape of equilibrium channels in uniform, noncohesive sands, 0.67 mm and 2.0 mm in diameter, were studied experimentally in a laboratory flume 52 feet long in which discharge, slope, sediment load, and bed and bank material could be varied independently. For each run a straight trapezoidal channel was molded in the sand and the flume set at a predetermined slope. Introduction of the discharge was accompanied by widening and aggradation until a stable channel was established. By definition a stable equilibrium existed when channel width, water surface slope, and rate of transport became constant. The duration of individual runs ranged from 2 to 52 hours depending upon the time required for establishing equilibrium. Stability of the banks determined channel shape. In the 2.0 mm sand at a given slope and discharge, only one depth was stable. At this depth the flow was just competent to move particles along the bed of the channel. An increase in discharge produced a wider channel of the same depth and thus transport per unit width remained at a minimum. Channels in the 0.67 mm sand were somewhat more stable and permitted a 1.5 fold increase in depth above that required to start movement of the bed material. An increased transport was associated with the increase in depth. The rate of transport is adequately described in terms of the total shear or in terms of the difference between the total shear and the critical shear required to begin movement. In these experiments the finer, or 0.67 mm, sand, began to move along the bed of the channel at a constant shear stress. Incipient movement of the coarser, or 2.0 mm, sand, varied with the shear stress as well as the mean velocity. At the initiation of movement a lower shear was associated with a higher velocity and vice versa. Anabranches of braided rivers and some natural river channels formed in relatively noncohesive materials resemble the essential characteristics of the flume channels. For a given slope and size of bed material the discharge per unit width in the laboratory channels was similar to that computed for anabranches and river channels measured in the field. Unlike most natural channels, despite impressive bank erosion, the channels in the laboratory only meandered at supercritical flows associated with very steep slopes. These conditions involving shallow depths, high velocity, and steep slopes are uncommon in most natural rivers.

Professional Paper↗
USGS1960

River meanders

Most river curves have nearly the same value of the ratio of curvature radius to channel width, in the range of 2 to 3. Meanders formed by meltwater on the surface of glaciers, and by the main current of the Gulf Stream, have a relation of meander length to channel width similar to rivers. Because such meanders carry no sediment, the shapes of curves in rivers are evidently determined primarily by the dynamics of flow rather than by relation to debris load. Velocity distributions along river curves provide a generalized picture of flow characteristics. Evidence on flow resistance in curved channels suggests that a basic aspect of meander mechanics may be related to the distribution of energy loss provided by a particular configuration or curvature. No general theory of meanders is as yet satisfactory, however; in fact, present evidence suggests that no single theory will explain the formation and characteristics of all meanders and that few of the physical principles involved have yet been clearly identified.

Geological Society of America Bulletin↗
USGS1960

Flow resistance in sinuous or irregular channels

The resistance to fully developed turbulent flow at constant depth in an open channel increases as the square of the mean velocity as long as the boundary conditions remain completely unchanged. The presence of the free water surface allows the possibility of departure from the relationship of resistance to the square of the velocity. Experimental evidence is given, which is in quantitative agreement with fluid dynamic theory, that such departure may be abrupt, with a marked increase of resistance. These departures are observed under conditions of boundary and flow which occur commonly in natural rivers. It is shown that the condition under which this discontinuous increase in resistance occurs is definable by the mean Froude number for the whole flow which may be as small as 0.4. At this initial state, the rate of resistance increase with the square of the velocity may be more than double. The phenomenon, which is absent in straight uniform channels, is associated with excessive deformations of the free surface due to transverse deflections of the whole or a part of the flow by changes along the channel in the curvature of the flow boundary. In the simple cases examined the critical Froude number at which the sudden jump occurs depends mainly on the ratio of channel width to mean radius of channel curvature, though the inclination of the banks appears also to have a minor effect Over the range of values of the above ratio usually to be found in natural rivers, the critical Froude number ranges between 0.4 and 0.55. The possible significance is discussed of the remarkable correspondence between this range of critical Froude number and the range of Froude number within which river flow at bankfull stage appears to be restricted.

Professional Paper↗
USGS1957

River channel patterns: Braided, meandering, and straight

Channel pattern is used to describe the plan view of a reach of river as seen from an airplane, and includes meandering, braiding, or relatively straight channels. Natural channels characteristically exhibit alternating pools or deep reaches and riffles or shallow reaches, regardless of the type of pattern. The length of the pool or distance between riffles in a straight channel equals the straight line distance between successive points of inflection in the wave pattern of a meandering river of the same width. The points of inflection are also shallow points and correspond to riffles in the straight channel. This distance, which is half the wavelength of the meander, varies approximately as a linear function of channel width. In the data we analysed the meander wavelength, or twice the distance between successive riffles, is from 7 to 12 times the channel width. It is concluded that the mechanics which may lead to meandering operate in straight channels. River braiding is characterized by channel division around alluvial islands. The growth of an island begins as the deposition of a central bar which results from sorting and deposition of the coarser fractions of the load which locally cannot be transported. The bar grows downstream and in height by continued deposition on its surface, forcing the water into the flanking channels, which, to carry the flow, deepen and cut laterally into the original banks. Such deepening locally lowers the water surface and the central bar emerges as an island which becomes stabilized by vegetation. Braiding was observed in a small river in a laboratory. Measurements of the adjustments of velocity, depth, width, and slope associated with island development lead to the conclusion that braiding is one of the many patterns which can maintain quasi-equilibrium among discharge, load, and transporting ability. Braiding does not necessarily indicate an excess of total load. Channel cross section and pattern are ultimately controlled by the discharge and load provided by the drainage basin. It is important, therefore, to develop a picture of how the several variables involved in channel shape interact to result in observed channel characteristics. Such a rationale is summarized as follows: Channel width appears to be primarily a function of near-bankfull discharge, in conjunction with the inherent resistance of bed and bank to scour. Excessive width increases the shear on the bed at the expense of that on the bank and the reverse is true for very narrow widths. Because at high stages width adjustment can take place rapidly and with the evacuation or deposition of relatively small volumes of debris, achievement of a ,relatively stable width at high flow is a primary adjustment to which the further interadjustments between depth, velocity, slope, and roughness tend to accommodate. Channel roughness, to the extent that it is determined by particle size, is an independent factor related to the drainage basin rather than to the channel. Roughness in streams carrying fine material, however, is also a function of the dunes or other characteristics of bed configuration. Where roughness is independently determined as well as discharge and load, these studies indicate that a particular slope is associated with the roughness. At the width determined by the discharge, velocity and depth must be adjusted to satisfy quasi-equilibrium in accord with the particular slope. But if roughness also is variable, depending on the transitory configuration of the bed, then a number of combinations of velocity, depth, and slope will satisfy equilibrium. An increase in load at constant discharge, width, and caliber of load tends to be associated with an increasing slope if the roughness (dune or bed configuration) changes with the load. In the laboratory river an increase of load at constant discharge, width, and caliber resulted in progressive aggradation of long reaches of channel at constant slope. The adjustments of several variables tending toward the establishment of quasi-equilibrium in river channels lead to the different channel patterns observed in nature. For example, the data indicate that at a given discharge, meanders occur at smaller values of slope than do’ braids. Further, at the same slope braided channels are associated with higher bankfull discharges than are meanders. An additional example is provided by the division of discharge around islands in braided rivers which produces numerous small channels. The changes in slope, roughness, and channel shape which accompany this division are in accord with quasi-equilibrium adjustments observed in the comparison of large and small rivers.

Professional Paper↗
USGS1957

River flood plains: Some observations on their formation

On many small rivers and most great rivers, the flood plain consists of channel and overbank deposits. The proportion of the latter is generally very small. Frequency studies indicate that the flood plains of many streams of different sizes flowing in diverse physiographic and climatic regions are subject to flooding about once a year. The uniform frequency of flooding of the flood-plain surface and the small amount of deposition observed in great floods (average 0.07 foot) support the conclusion that overbank deposition contributes only a minor part of the material constituting the flood plain. The relatively high velocities (1 to 4 fps) which can occur in overbank flows and the reduction in sediment concentration which often accompanies large floods may also help account for this. Although lateral migration of channels is important in controlling the elevation of the flood plain, rates of migration are extremely variable and alone cannot account for the uniform relation the flood-plain surface bears to the channel. Detailed studies of flood plains in Maryland and in North Carolina indicate that it is difficult to differentiate between channel and overbank deposits in a stratigraphic section alone. Because deposition on the flood plain does not continue indefinitely, the flood-plain surface can only be transformed into a terrace surface by some tectonic or climatic change which alters the regimen of the river and causes it to entrench itself below its established bed and associated flood plain. A terrace, then, is distinguished from a flood plain by the frequency with which each is overflowed.

Professional Paper↗
USGS1956

Floods in relation to the river channel

Among the rivers studied by us two broad types may be distinguished. Channels in the semi-arid areas scour at high discharges so that the bed lowers nearly as much as the water surface rises. Detailed data on the middle reaches of the Rio Grande in New Mexico during the spring floods of 1948 and 1952 indicate that the bed aggrades to nearly its pre-flood level as the flood recedes. Channel banks may move rapidly by undercutting during periods of scour and levees are liable to failure not from overtopping but by undercutting. In Connecticut, a sub-humid area, the repetitive processes of scour and fill in the semi-arid region were not demonstrated by the great floods of 1955. In a few reaches fresh sand was deposited over gravel beds subsequently to be removed by lower flows. Boulders four to six feet in diameter were moved in places over undisturbed beds of one-inch gravel. Channel widening occurred primarily in rivers in narrow valleys which confined the flow within the channel. Scour and deposition on flood plains adjacent to the rivers was irregular. Most deposits could be traced to local sources. In general, flood waters modified but did not vastly alter the prevailing configuration of the channel and structure of the flood plain.

Proceedings of the International Association of Hy↗