From headwaters to mouth, the physical variables within a river system present a continuous gradient of physical conditions. This gradient should elicit a series of responses within the constituent...

The River Continuum Concept

H umans have long been fascinated by the dynamism of free-flowing waters. Yet we have expended great effort to tame rivers for transportation, water supply, flood control, agriculture, and power generation. It is now recognized that harnessing of streams and rivers comes at great cost: Many rivers no longer support socially valued native species or sustain healthy ecosystems that provide important goods and services (Naiman et al. 1995, NRC 1992).

/pdf/the-natural-flow-regime-3j2upj9j41.pdf

The Natural Flow Regime

Publisher Summary This chapter reviews the rates at which Coarse Woody Debris (CWD) is added and removed from ecosystems, the biomass found in streams and forests, and many functions that CWD serves. CWD is an important component of temperate stream and forest ecosystems and is added to the ecosystem by numerous mechanisms, including wind, fire, insect attack, pathogens, competition, and geomorphic processes. Many factors control the rate at which CWD decomposes, including temperature, moisture, the internal gas composition of CWD, substrate quality, the size of the CWD, and the types of organisms involved. The mass of CWD in an ecosystem ideally represents the balance between addition and loss. In reality, slow decomposition rates and erratic variations in input of CWD cause the CWD mass to deviate markedly from steady-state projections. Many differences correspond to forest type, with deciduous-dominated systems having generally lower biomass than conifer-dominated systems. Stream size also influences CWD mass in lotic ecosystems, while successional stage dramatically influences CWD mass in boat aquatic and terrestrial settings. This chapter reviews many of these functions and concludes that CWD is an important functional component of stream and forest ecosystems. Better scientific understanding of these functions and the natural factors influencing CWD dynamics should lead to more enlightened management practices.

Ecology of Coarse Woody Debris in Temperate Ecosystems

Because freshwater covers such a small fraction of the Earth’s surface area, inland freshwater ecosystems (particularly lakes, rivers, and reservoirs) have rarely been considered as potentially important quantitative components of the carbon cycle at either global or regional scales. By taking published estimates of gas exchange, sediment accumulation, and carbon transport for a variety of aquatic systems, we have constructed a budget for the role of inland water ecosystems in the global carbon cycle. Our analysis conservatively estimates that inland waters annually receive, from a combination of background and anthropogenically altered sources, on the order of 1.9 Pg C y−1 from the terrestrial landscape, of which about 0.2 is buried in aquatic sediments, at least 0.8 (possibly much more) is returned to the atmosphere as gas exchange while the remaining 0.9 Pg y−1 is delivered to the oceans, roughly equally as inorganic and organic carbon. Thus, roughly twice as much C enters inland aquatic systems from land as is exported from land to the sea. Over prolonged time net carbon fluxes in aquatic systems tend to be greater per unit area than in much of the surrounding land. Although their area is small, these freshwater aquatic systems can affect regional C balances. Further, the inclusion of inland, freshwater ecosystems provides useful insight about the storage, oxidation and transport of terrestrial C, and may warrant a revision of how the modern net C sink on land is described.

/pdf/plumbing-the-global-carbon-cycle-integrating-inland-waters-1enndt5kqx.pdf

Plumbing the Global Carbon Cycle: Integrating Inland Waters into the Terrestrial Carbon Budget

The Intergovernmental Panel on Climate Change (IPCC) Technical Paper Climate Change and Water draws together and evaluates the information in IPCC Assessment and Special Reports concerning the impacts of climate change on hydrological processes and regimes, and on freshwater resources – their availability, quality, use and management. It takes into account current and projected regional key vulnerabilities, prospects for adaptation, and the relationships between climate change mitigation and water. Its objectives are:

/pdf/climate-change-and-water-2dpc0zbpsj.pdf

Climate change and water.

Fluvial Processes in Geomorphology

The relative importance in geomorphic processes of extreme or catastrophic events and more frequent events of smaller magnitude can be measured in terms of (1) the relative amounts of "work" done on the landscape and (2) in terms of the formation of specific features of the landscape. For many processes, above the level of competence, the rate of movement of material can be expressed as a power function of some stress, as for example, shear stress. Because the frequency distributions of the magnitudes of many natural events, such as floods, rainfall, and wind speeds, approximate log-normal distributions, the product of frequency and rate, a measure of the work performed by events having different frequencies and magnitudes will attain a maximum. The frequency at which this maximum occurs provides a measure of the level at which the largest portion of the total work is accomplished. Analysis of records of sediment transported by rivers indicates that the largest portion of the total load is carried by flow...

https://www.jstor.org/stable/info/30058255

Magnitude and Frequency of Forces in Geomorphic Processes

Fluvial processes in geomorphology , Fluvial processes in geomorphology , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

http://www.gbv.de/dms/goettingen/185614760.pdf

The hydraulic factors of width, depth, velocity, and suspendedsediment load of ephemeral streams near Santa Fe, N. Mex., were measured during flood flow. Later, channel slope was measured. These flood-flow data, in conjunction with an analysis of drainage-basin configuration by the methods proposed by Horton, are used to determine the generalized interrelation of stream order and hydraulic variables. The method developed for determining this interrelation allows an integration of the geographic and physiographic characteristics of a drainage basin with the channel characteristics; specifically, the interrelation of the length, number, and drainage area of streams of various sizes with their respective discharge, width, depth, velocity, slope, channel roughness, and suspended-sediment load. These interrelations show that stream order is related to stream length, number of streams, drainage area, and discharge by simple exponential functions. The relation of discharge to width, depth, velocity, slope, and other hydraulic factors can be approximated by simple power functions. Thus, any pair of these factors is related by exponential or power functions. The data indicate that suspended-load measurements made during various stages of a few individual floods provide a close approximation to the suspended-load rating curve obtained from periodic measurements taken at a sediment station over a period of years. The analysis of the hydraulic data shows that in the ephemeral streams studied, velocity increases downstream at a faster rate than in perennial rivers. This appears to be associated with an increase in suspended-load concentration downstream in these ephemeral channels. The tendency for stream channels to maintain a quasiequilibrium with imposed discharge and load is shown to be characteristic of ephemeral channels in the headwaters of the drainage basin, even to the most headward rill. The formation of a discontinuous gully is analyzed in terms of this tendency. This type of gully is characterized by a gradient of the channel bed flatter than the gradient of the valley floor in which the gully is cut. The low gradient is explained as a hydraulic adaptation of channel slope to quasiequilibrium with the narrow gully width. Examples indicate that as a discontinuous gully widens, its gradient steepens and its length consequently increases. Thus a series of discontinuous gullies tends to coalesce into a continuous trench having a bed gradient nearly equal to the slope of the original valley floor. INTRODUCTION AND ACKNOWLEDGMENTS The flow of water in natural channels may be described as perennial, intermittent, or ephemeral. A perennial stream carries some flow at all times. An intermittent stream is one in which, at low flow, dry reaches alternate with flowing ones along the stream length. Those which carry water only during storms, and are therefore called ephemeral, are generally smaller but are much more numerous than perennial ones. From the divide to the mouth of a drainage basin, the increase in channel size is accompanied by a decrease in the number of channels. Drainage channels are more apparent and more abundant in arid than in humid regions where vegetation hides small rills. Vegetation also tends to increase the length of overland flow, thereby decreasing channel density. For both kinds of areas, however, the land presents to the eye a contrast depending on the perspective one assumes. In arid areas there is the panorama of broad, apparently smooth surfaces sweeping up to the abrupt fronts of mountain ranges or mesa escarpments. A closer examination may show that the whole countryside is actually cut into a myriad of rills, gullies, and arroyos. Humid regions, on the other hand, are typically characterized by rounded, rolling topography which is covered by natural or cultivated vegetation. Although many details of drainage nets are commonly concealed beneath vegetation, careful search discloses the presence of many more channels than can be inferred from a distant view. Despite the fact that the channels of ephemeral streams are generally recognized to have an important part in the erosion of the land and resultant production of fluvial landforms, they have not received careful or concentrated investigation.. The present report is devoted to a preliminary quantitative description of flow characteristics, channel properties, and configuration of the drainage net in arid regions only. However, PHYSIOGRAPHIC AND HYDRAULIC STUDIES OF RIVERS it is believed that the principles established may be applicable to humid regions as well. Practical considerations, along with personal bent, dictated that channels of arid rather than humid regions should receive our attention first. "Accelerated erosion" in the West is a problem of great social and economic importance. The arroyos that trenched alluvial valleys of the Southwest beginning in the latter part of the 19th century, some of which even now are eroding apace, are spectacular examples of ephemeral streams. Conservationists, range managers, geologists, and a host of others have debated the cause of gullying, have experimented with methods of gully control, and have tried to prognosticate the eventual status of the channel system. But in all such efforts practically no attempt has been made, to study the process of gully erosion itself, to describe the hydraulic conditions in the eroding channels, or to understand the nature of the equilibrium which was upset by grazing and climatic change. It seems bootless to spend large sums on the control of gullies and arroyos without concomitant attempts to increase knowledge of their hydraulic characteristics. The present study provides new data that are pertinent to a fuller understanding of ephemeral streams. Specifically, geometric and hydraulic properties of channels are related to the drainage-net .configuration. The plan of presentation is as follows: First, the channels in the area studied are described and the methods of investigation outlined. Next, the measurements of hydraulic variables, including channel shape, discharge, and sediment load are presented. A method of integrating hydraulic characteristics with properties of the drainage net is shown to increase markedly the utility of available data. Finally, the role of equilibrium in ephemeral channels, as related to the accelerated erosion problem, is discussed. Many colleagues and friends gave us continuing advice and assistance in the study, and particular thanks are due M. Gordon Wolman, Thomas Maddock, Jr., John T. Hack, and Walter B. Langbein. The field work was made considerably easier in many ways by the cooperation of Paul C. Benedict and Berkeley Johnson. Charles E. Stearns visited us in the field and later discussed the manuscript with us. We are indebted to John T. Hack and Stanley Schumm for permission to include in this report some of their unpublished data. GEOGRAPHIC SETTING AND BASIC MEASUREMENTS Nearly all the data included in this report were collected in the basins of the Rio Galisteo and Rio Santa Fe, tributaries to the Rio Grande in semiarid central New Mexico (see fig. 1).

/pdf/ephemeral-streams-hydraulic-factors-and-their-relation-to-4eahncgfyx.pdf

Ephemeral streams; hydraulic factors and their relation to the drainage net

Alluvial terraces were studied in several major river basins in eastern Wyoming. Three terraces are present along nearly all the streams and large tributaries. There are several extensive dissected erosion surfaces in the area, but these are much older than, and stand well above, the recent alluvial terraces with which this report is concerned. The three alluvial terraces stand respectively about 40, 10, and 5 feet above the present streams. The uppermost and oldest is a fill terrace comprised of three stratigraphic units of varying age. The oldest unit is Pleistocene and the youngest unit postdates the development of a soil zone, or paleosol, which is characterized by strong accumulation of calcium carbonate and gypsum. This paleosol is an important stratigraphic marker. The middle terrace is generally a cut terrace and is developed on the material making up the youngest alluvium of the high terrace. The lowest is a fill terrace, the surface of which is only slightly higher than the present flood plain. The oldest terrace can tentatively be traced into mountain valleys of the Bighorn Range on the basis of discontinuous remnants. The terrace remnants occur far upstream from the youngest moraine in the valleys studied. On this basis, the terrace sequence is considered to postdate the last Wisconsin ice in the Bighorn Mountains. The paleosol is tentatively correlated with Altithermal time, called in Europe the Climatic Optimum. The terrace sequence is very similar to that suggested by various workers in the southwestern United States. Two streams, Clear Creek and the Powder River, deposited comparable silty alluvium, the surface of which now comprises the highest alluvial terrace. The gradients of these former flood plains differed markedly between the two streams despite the comparability in size of material deposited. This difference in gradient is believed to have required different relative contributions of water from mountain and plain areas than now exist. Knowledge of Recent physiographic history of the area is the basis of determining the relative ages of some gully features. Certain vertical-walled channels or arroyos that might appear to be attributable to postsettlement grazing or other man-induced influences are shown to be Recent but pre-Columbian in age. Such differentiation in age of erosion features is necessary for proper understanding of present-day soil erosion problems.

/pdf/a-postglacial-chronology-for-some-alluvial-valleys-in-571qahne1c.pdf

John P. Miller

Papers

Fluvial Processes in Geomorphology

Magnitude and Frequency of Forces in Geomorphic Processes

Fluvial Processes in Geomorphology

Ephemeral streams; hydraulic factors and their relation to the drainage net

A postglacial chronology for some alluvial valleys in Wyoming