A tributary is a river or stream that enters a larger body of water, especially a lake or river. Internationally, tributaries are vital for trade, biodiversity, providing drinking water and supplying water to large bodies. Tributaries serve as important habitats and carry various sediment, chemicals, organic matter and volumes of water that contribute to unique conditions that support various species. As tributaries merge to the mainstem, they can introduce both vital ecological components and dangerous contaminants at their confluences.
Although tributaries feed into larger water bodies, they themselves are often of substantial size and frequently named as rivers. The Feather River is the largest tributary of the Sacramento River and it acts as the main water source for the State Water Project , serving as an example of a tributary that generates a lot of water and has several tributaries of its own.
The Santa Ana River , by contrast, has flow mostly powered by smaller creeks, including Chino Creek, which while only about a dozen miles long, drains a vast watershed of more than square miles. In a separate attempt to characterize stream ecosystems, others have shown how surface and subsurface flow interactions along channel corridors are important to nutrient cycling and biotic communities Newbold et al.
A hierarchical classification of stream ecosystems was proposed to examine continuity and discontinuity of impacts on stream biota at different scales within watersheds Frissell et al. Patch dynamics, formed by microtopographic attributes, may indicate the fragmentation of habitat and community structure in stream ecosystems Pringle et al.
Disturbances e. Montgomery demonstrated that geomorphic processes set the templates of biological processes of disturbance, the river continuum, and patch dynamics in his process domain concept. Although the importance of channel network structure for material dynamics has gradually been recognized Johnson et al.
Similarly, the nutrient spiraling concept Newbold et al. However, Minshall and colleagues and Johnson and colleagues observed that landform attributes, such as tributary junctions in channel networks, affect the river continuum concept. Kirkby and Robinson and colleagues demonstrated the importance of channel networks in drainage basins for understanding and forecasting flow regimes, sediment transport processes, and landform evolution. Fisher noted that a paradigm shift from linear to network branched shape systems is necessary to understand the processes and linkages of physical and biological dynamics in stream ecosystems.
Benda and colleagues b and Rice and colleagues emphasized the importance of channel network structure to understand the longitudinal variations in sediment movement and aquatic environments. The watershed network can be partitioned into two systems, headwater and network systems, on the basis of process characteristics. Structural differences and the continuous versus discontinuous nature of processes are critical for distinguishing between headwaters and larger watershed systems.
Hydrologic, geomorphic, and biological processes in headwater systems cascade from hillslopes to streams figure 1 , and because hillslopes and streams are tightly coupled, material transport within headwater systems thus can be predicted as processes from hillslopes to stream channels.
In contrast, material routing in larger watersheds is controlled by the channel network structure, because numerous headwaters are nested within it.
Therefore, network structure must be considered in predicting material transport in larger watershed systems figure 1 ; Fisher Nevertheless, processes from headwaters to downstream systems are often discontinuous because of changes in valley width, tributary junction angle, substrate size, and channel gradient Benda and Cundy , Ward and Stanford , Bravard and Gilvear , Rice et al. Hillslopes have either divergent or straight contour lines, typically with no channelized flow.
A zero-order basin is defined as an unchannelized hollow with convergent contour lines Tsukamoto et al. Colluvial material, that is, debris transported by gravity from adjacent hillslopes, typically fills such hollows. Although saturated overland flow may be observed in zero-order basins and at the foot of hillslopes during storms, biological activity in such hillslopes and zero-order basins is terrestrial Hack and Goodlett Channels with defined banks may emanate from zero-order basins Tsukamoto et al.
Temporary channels have more or less continuous flow at least 4 to 5 months in an average year, whereas ephemeral channels flow only for several days during wet periods Dieterich and Anderson Thus, temporary and ephemeral channels emanating from zero-order basins typically cannot support the complete life cycles of the juvenile stages of aquatic macro-invertebrates, except for those species with a long diapause stage or other strategies for tolerating absence of surface flow Anderson , Meyer and Wallace Despite the inability to support macroinvertebrates, such channels are integral parts of channel networks and have distinct roles e.
Transitional channels may gradually or abruptly begin from zero-order basins, depending on concentration critical length of saturated overland flow, infiltration—excess overland flow, and seepage erosion by means of return flow.
Such channels may also contain discontinuous segments prior to entering first-order channels Montgomery and Dietrich First-order streams are the uppermost, unbranched channels with either perennial flow or sustained intermittent flow more than 4 to 5 months during an average year. First-order channels may directly emanate from the outlet of zero-order basins, depending on flow generation mechanisms e.
Second-order one branch or even higher order multiple branch streams may be considered headwater streams, depending on degree of coupling between hillslopes and channels e.
Both first- and second-order channels may have intermittent reaches dry parts , depending on groundwater level and volume of alluvium sediment deposited by flowing water. In the river continuum concept Vannote et al. However, there are potential problems with such classifications: 1 stream orders depend on scales of maps; 2 stream orders are modified by basin-scale topography e.
Meyer and Wallace noted that most detailed topographic maps did not include most headwater channels that might be found in field inventories. Processes from hillslopes to streams are important for defining the downstream limits of headwater systems. For instance, the transition from mass movement—dominated to fluvial process—dominated reaches occurs in headwater streams of Oregon for drainage areas up to 1.
The major causes for the deposition of debris flows are decreasing channel gradient, abrupt tributary junction, and flow divergence Benda and Cundy Swanson and colleagues also noted that drainage areas from 0. Using digital elevation models DEMs , Montgomery and Foufoula-Georgiou demonstrated that a shift from colluvial to alluvial geomorphic processes occurred from 0. However, digital elevation models have limitations related to identifying headwater swales.
With developments in laser altimetry, DEMs with contour intervals less than or equal to 2 meters can be developed; such precision will facilitate identification of geomorphic hollows and other features. Variation of discharge in drainages less than 1 km 2 was greater than for drainages larger than 1 km 2 , based on the representative elementary area concept figure 3B ; Woods et al.
Researchers Wood et al. Such site factors create greater variation of unit area discharge. In contrast, hydrological response in basins greater than 1 km 2 is more affected by routing processes and the structure and extent of the floodplain. The findings of such studies indicate that the largest drainage area of headwater systems is likely 1 km 2 figure 3a, 3B.
Although we suggest a relative upper size limit 1 km 2 for headwater systems, depending on the region, process-based criteria are more important for the definition of headwater systems than simply catchment area Whiting and Bradley , Montgomery Different magnitudes and frequencies of hydrologic processes occur in headwaters and large watershed systems Woods et al.
Geomorphic processes in headwaters are largely stochastic, whereas more chronic processes related to routing of sediment, water, and wood are common in channel network systems Benda and Dunne a , b. Such different hydrogeomorphic processes between headwater and network systems also modify biological community structure and distribution as well as recovery processes of stream biota from disturbances Rice et al.
Water inputs of headwater systems are unique, compared with larger watershed systems. Because headwaters occupy the highest positions in catchments, precipitation and snow accumulation in headwaters are generally greater than in lower elevation zones table 1. Rainfall inputs vary greatly among headwater systems; thus, isolated precipitation is typically observed more in headwater systems than in the overall watershed. The relative temporal fluctuation of peak flows in headwaters is greater than in larger watersheds table 1 , figure 3b ; Robinson et al.
Water inputs strongly affect hillslope and channel conditions because of the close coupling of hydrologic and geomorphic processes within confined and steep valleys of headwater systems figure 2 ; Sidle et al.
Stream temperature and water chemistry in headwater channels are closely related to soil pore structure and bedrock fractures in hillslopes and zero-order basins. Subsurface discharge from hillslopes contributes base flow and storm flow to headwater channels, initiates certain erosion processes, and is important for the development of headwater topography Dunne Storm flow responds rapidly to intense rainfall in headwaters because of their relatively small storage capacity and shorter flow paths.
Storm flow generation in headwater channels is also affected by the responses of hillslopes and zero-order basins to changing antecedent moisture conditions figure 4 ; Hewlett and Hibbert , Sidle et al. Storm flow is primarily generated by direct runoff from saturated riparian areas and channel interception during lower antecedent moisture conditions. Throughflow from the soil matrix at the foot of hillslopes and riparian areas gradually increases with increasing wetness of the basins.
During wet conditions, zero-order basins with relatively shallow soils start contributing surface runoff, and preferential flow from hillslopes augments storm flow. Zero-order basins and preferential flow paths are major contributors to storm flow during very wet conditions Sidle et al.
Transitional channels emerging from zero-order basins typically flow during such storms, when the storms are preceded by very wet conditions figure 4. During rain and rain-on-snow events, nearly saturated conditions in hydrologically responsive areas e. During the dry seasons, however, intermittent dry reaches may be found in headwater channels, depending on groundwater level and depth of alluvium.
Landslides and debris flows are dominant geomorphic processes in headwater systems table 1. Such mass movements transport sediment and woody debris from hillslopes to channels and modify stream and riparian conditions. Sediment and woody debris are routed as channelized debris flows and deposited in the downstream reaches of headwater systems Benda and Cundy Exposed bedrock and less woody debris typify scour and runout zones Gomi et al.
In contrast, massive piles of woody debris and sediment are found in deposition zones of debris flows Hogan et al. Logjams at the terminal end of debris flows often modify both longitudinal and planimetric profiles of channels e. Such geomorphic processes also alter riparian forest structure; for instance, alder Alnus spp.
Adjustment of channel morphology after landslides and debris flows largely depends on sediment and woody debris inputs. The regeneration of riparian stands in scour and deposition zones of debris flows begins to restore the recruitment of woody debris 20 to 50 years after mass movement in headwater streams Gomi et al.
Channel morphology in headwater systems can be characterized by channel obstructions such as large woody debris and boulders table 1 ; Zimmerman and Church Channel depth in headwaters tends to be shallower relative to the average diameters of such channel bed obstructions. Because substrate materials are not well sorted, interlocking boulders and cobbles modify the stability of channels, forming channel steps and creating sites for sediment storage Zimmerman and Church Woody debris pieces also store sediment and modify channel roughness, and owing to the narrow channel width, relatively small woody debris pieces and jams have similar functions in headwater channels Gomi et al.
Therefore, headwater streams may have more woody debris dams than larger watershed systems because smaller woody debris can form these dams figure 3c. The accumulation and distribution of woody debris alter the distribution of channel reach types such as cascades, step pools, and bedrock Montgomery and Buffington , Halwas and Church Observations of single headwater systems cannot be simply extrapolated to network systems where upstream contributions dominate base flow and storm flow generation.
Because of the longer routing processes of water and greater storage capacity, peak flows in downstream reaches are often attenuated, lost partly to deep percolation and desynchronized flows that buffer peaks between headwaters and downstream locations. Floodplain and riparian zones also contribute to storm flow generation in larger watershed systems. Synchronized outflows from headwaters enhance peak flow in downstream reaches, whereas desynchronized outflows from headwaters attenuate flood peaks table 1 , figure 5 ; Robinson et al.
Timing of outflows may be altered by hillslope and channel storage capacity e. More regular sediment transport, such as bedload movement, dominates sediment transport in downstream reaches table 1.
Sediment delivery from headwater to downstream is often interrupted because sediment is temporarily stored in or along the streambed, banks, terraces, and debris fans Hey , Benda and Dunne a , Nakamura et al. Sediment transport from tributaries alters patterns in the downstream fining of substrate size Rice et al.
Sediment movement may appear as sediment waves through channel networks from headwater to downstream systems figure 6 ; Benda and Dunne b. Sediment deposits and accumulations induce local aggradation with the fining processes of sediment in the downstream direction.
Such processes also modify channel reach types, sinuosity, and formation of side channels. Channels may shift laterally as banks erode and bars form in the unconfined floodplains of downstream reaches. Synchronized and desynchronized landslides and debris flows in headwater systems alter the impacts of sediment movement on geomorphic and biological conditions in downstream reaches figure 6.
Synchronized landslides and debris flow deposits aggregate extensively within confined reaches of downstream channels during relatively short periods. In contrast, desynchronized mass movements gradually aggregate in larger reaches of channels. Sediment transit time from headwaters to the main channel depends on the presence of unconstrained reaches, tributary junction angles, channel gradient, timing of various mass movements, and amount of runoff Benda and Cundy , Bravard and Gilvear , Nakamura et al.
However, sediment transport to downstream reaches is not as simple as shown in figure 6. Woody debris often forms jam structures in the transition zone between headwaters and downstream reaches because of deposits from landslides and debris flows, fluvial transport, and recruitment from riparian areas e. Logjams often store sediment for 40 to 50 years until the structures collapse or channel courses change Hogan et al.
Changing valley configurations, channel gradient, and material types also modify sediment transport from headwater to downstream systems Whiting and Bradley , Nakamura et al. Spatial distribution of mass movement occurrence influences sporadic sediment transport throughout network systems Benda and Dunne b. Because forested headwater streams are typically narrow with closed riparian canopies, biological processes terrestrial and aquatic in hillslopes and streams are closely linked figure 2.
Retention and routing of organic materials from allochthonous inputs that is, riparian and lateral input of leaf litter and woody debris are important factors affecting biological processes in headwater systems table 1. Allochthonous energy sources are larger than autochthonous energy sources e. Because of relatively small discharges and numerous roughness elements e. The dominant functional group of macroinvertebrates in headwater channels is shredders; they break larger particles into smaller sizes table 1 ; Cummins et al.
Fungi and bacteria also help to break CPOM into fine particulate organic matter 0. Terrestrially derived invertebrates that are associated with riparian vegetation are important for aquatic biota in headwater streams Wipfli Riparian canopy closure also modifies heat and solar radiation available to stream channels table 1.
Groundwater and subsurface flows from hillslopes and zero-order basins contribute nutrients e. Availability of nutrients and light as well as water temperature modify algal growth; this in turn alters rates of nutrient leaching and litter decomposition.
Headwater hyporheic zones are smaller, and their nutrient exchange is less, than in downstream reaches Stanford and Ward When identifying a left-bank or right-bank tributary, a geographer looks downstream the direction the river is flowing. The Euphrates River, the longest river in southwestern Asia, stretches 2, kilometers 1, miles. The tiny streams that feed the Euphrates originate in the mountains of eastern Turkey.
These streams become the Balikh and the Sajur Rivers, which join the Euphrates at different confluences in Syria. The Balikh is a left-bank tributary of the Euphrates, while the Sajur is a right-bank tributary.
Sometimes, tributaries have the same name as the river into which they drain. These tributaries are called fork s. Different forks are usually identified by the direction in which they flow into the mainstem.
The Shenandoah River, for example, flows through the U. The opposite of a tributary is a distributary. A distributary is a stream that branches off and flows apart from the mainstem of a stream or river. The process is called river bifurcation. At the Continental Divide in the U. The water from each of these distributaries flows into the ocean for which it is named.
There are two leading methods geographers and potamologist s people who study rivers use to classify tributaries. The first method lists a river's tributaries starting with those closest to the source , or headwater s, of the river.
The Rhine, one of the longest rivers in Europe, has its source in the Alps and its mouth in the North Sea. The second method lists a river's tributaries by their flow. Small streams are identified with low numbers, while larger tributaries have higher numbers. The Tshuapa and Kasai Rivers are both left-bank tributaries of the Congo River, the deepest river in the world. The Tshuapa is a smaller river, and has a lower tributary ranking, than the Kasai.
Human activity in tributaries is often responsible for polluting the mainstem. The river carries all the runoff and pollution from all its tributaries. Rivers with tributaries that drain land that is not used for agriculture or development are usually less polluted than rivers with tributaries in agricultural or urban area s. Development, not size, determines the pollution of rivers. The Amazon River, with the largest drainage basin in the world, is much cleaner than the Hudson River, for instance.
As the river slows and spreads out, it can no longer transport all of the sand and sediment it has picked up along its journey from the headwaters. Wetlands are lands that are soaked with water from nearby lakes, rivers, oceans, or underground springs.
Some wetlands stay soggy all year, while others dry out. Although wetlands are best known for providing habitat to a wide variety of plants and animals, they also help protect our communities by acting as natural sponges, storing and slowly releasing floodwaters.
A single acre of wetland, saturated to a depth of one foot, will retain , gallons of water — enough to flood thirteen average-sized homes thigh-deep. Wetlands also help provide clean water by naturally filtering out pollution.
First, there is the amount of water that flows in the river. Some rivers get enough water from their headwaters, tributaries, and rain to flow all year round. Others go from cold, raging rivers to small, warm streams as the snowpack runs out, or even stop flowing completely.
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