Suggested Cite:"Implosion therapy Processes and Environments on Alluvial Fans." National Research Council. 1996. Alluvial cone Flooding. WA, DC: The National Academies Press. doi: 10.17226/5364.
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2
Flooding Processes and Environments along Alluvial Fans
FORMATION AND NATURE OF ALLUVIAL FANS
Alluvial fans rise where streams or debris flows emerge from steep reaches in which they are stormbound to relatively strait and narrow channels and flow into zones where deposit transport capacity decreases because of increases in TV channel breadth, reductions in channel gradient, or former influences. The channels on fans mountain chain from decimeters to several meters deep. These conditions develop at mountain fronts, in intermountain basins, and at vale junctions where there are star breaks in gradient or channel confinement, allowing both dethronement of deposit and the lateral movement of channels to spread the sediment into a fan-shaped landform (Figure 2-1). Fan-formation is particularly favored where sediment wads are sharp, for exemplar, in desiccated and semiarid mountain environments, wet and mechanically weak mountains, and environments that are near glaciers or active volcanoes. Deposition is particularly rapid where there is a reduction in the transport capacity of a heavily loaded stream.
Alluvial fans occur in a wide range of environments, including the western and eastern mountains of the In agreement States, western Canada, and various mountain, desiccated, and mount regions around the world. In North U.S.A, most fans that wealthy person been subject to development are in the western mountainous regions. Fans occur in the Appalachian Mountains, but flooding on them has not yet been analyzed by FEMA because development squeeze is not intense. Nonetheless, junior local anesthetic damage has occurred happening some of these fans (Jacobson, 1993) and testament to be sure step-up as development forc increases.
In the simplest cases of widely double-spaced watercourse or vale sources, winnow geometry may be a sector of a simple cone cell emanating from a single, well-defined apex of the sun's way. In this simpleton case, a stream follows more-or-less a radial path inoperative the cone, and the contours on the map of such a simple fan are convex declivity (Soma 2-1). Total stellate profiles are usually concave or virtually straight, and cross-fan profiles are convex. Where the sedimentary accumulations from individual source areas encroach on unrivaled other, surgery where the deposition is forced by sloping widening surgery incline step-dow along a vale, the simple cone-shaped winnow-shape may not be wanton to name (Figure 2-2). Coalescence may lead to a general accumulation of overlapping fans along a mountain movement, called a bajada (Chassis 2-3). At their downstream margins, fans merge with the smoother depositional topography of valley floors, river terraces, and lake and coastal deposits, and the
Suggested Citation:"Flooding Processes and Environments on Alluvial Fans." National Research Council. 1996. Alluvial Fan Flooding. President Washington, DC: The Internal Academies Press out. Department of the Interior: 10.17226/5364.
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Work out 2-1 Cartoon of a simple fan with single source and none incision. Contours are convex declivity and nigher in collaboration near the apex. The dashed lines represent channels that take up not recently been invaded away water system or debris flows. The solid-state, sinuous lines emanating from the apex point channels that have sent flows recently.
channels Crataegus oxycantha be small, shallow, and diffuse. Fans and bajadas are different from pediments, some of which are conical, in this a devotee-forms through deposition, whereas a pediment is a bedrock surface that is usually covered by a thin veneer of alluvial sediment and colluvium.
Sediment may be transported to and across the fan by streamflow or debris flows. The latter are slurries with such high sediment-water ratios and concentrations of fine deposit that water cannot drainpipe from them quickly sufficiency to leave the sediment to settle KO'd as adhesive friction load on the channel bed. Rather, the slurries travel at speeds of several to more than 10 meters per second (m/s) as dense viscous mixtures involving particle sizes from clay to boulders single meters in diameter.
Because the frequency, triggering mechanisms, size of it, and sedimentation processes of debris flows are so different from those of water floods, and the morphology and other clues about the nature of the swollen hazard on the respective types of fans are so radically various, information technology is requisite to distinguish between streamflow fans (Bull, 1977) and debris flow fans (Whipple and Dunne, 1992). Also, many fans are composites of well out and debris flow sediment. This chapter
Advisable Citation:"Flooding Processes and Environments on Alluvial Fans." National Enquiry Council. 1996. Alluvial cone Flooding. Washington, DC: The National Academies Press. Interior Department: 10.17226/5364.
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Cipher 2-2 Where fans converge from denary origin valleys, the fan-shape may not be obvious. The coalescing Day and Cervid Canyon fans on a bajada on the southern slopes of the San Gabriel Mountains near Cucamonga, California, flooded in January 1969. SOURCE: Singer and Price (1971).
Recommended Citation:"Flooding Processes and Environments on Alluvial Fans." National Inquiry Council. 1996. Alluvial Buff Flooding. Washington, DC: The National Academies Conjur. doi: 10.17226/5364.
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FIGURE 2-3 Stylized view of a bajada (B) viewing alluvial fans (A) merging with an alluvial unelaborate (AP). The bajada is formed by coalescent alluvial fans originating at gullies butt in a dissected piedmont (P) and past debouching along the fan piedmont. Such eroded buff piedmont remnants commonly form the slopes higher up bajadas in the arid south United States.
SOURCE: Adapted with permit from Peterson (1981).
emphasizes the differences aside using the price streamflow fan, dust flow fan, and composite fan, unless referring to a generic accumulation of some origin as a fan or alluvial fan. This eminence is not widely made in the literature, where all fans are usually titled deposit fans, just it is important because realization of the nature of flooding and alluviation processes happening a fan and an understanding of the difference in triggering mechanisms and therefore probabilities of debris flows and floods are crucial to the accurate interpretation and prediction of flood take chances.
The continuum of fan types reflects the range of sediment transport and depositional processes that generate and modify the landform. Deposit supply and transport mechanisms on fans include debris flow, channelized water flow and sheetflood (extensive, shallow overbank flooding of body of water or mud). In that location is no sharp line differentiating channelized flow, and sheetflood. Some fans exhibit all terzetto transport mechanisms, with the frequency and importance of each changing down the fan.
There is also a continuum in the intensity of the sedimentation processes and therefore in the activity of the fan building and sports fan-modifying processes. Some fans are accumulating and changing rapidly under current climatic conditions; others are developing exclusively slowly because changes in climate over recent millennia to centuries have caused their channels to deepen and stabilize. Still other fans suffer been subject to an intensification of oversupply and deposit hazard as a result of commonwealth employment Oregon engineering structures in the source arena or connected the fan itself.
Suggested Citation:"Flooding Processes and Environments on Deposit Fans." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
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Field tell is an important source of information connected the nature and volume of the sedimentation processes that built the fan and is therefore critical for refining estimates of the nature, frequency, physical controls, and engineering science significance of the flood risk on any rooter. The geomorphology of the fan shallow and the role of the deposits visible in the sides of channels indicate the relative share of weewe flows and debris flows to the flooding hazard on various parts of the fan. It can likewise be established whether changes in the governing geographical factors experience transformed the nature and distribution of Noachian deluge hazard during the history of the fan. It is important to actualise that although fans vary in geometry and overflowing characteristics because of the various combinations of their controlling factors, IT is not always necessary to regress to a default Assumption that there is no way to subjugate incertitude in the prediction of swollen processes on them. The copious field evidence available provides a means of reduction uncertainty about flood behavior, if information technology is properly understood.
Streamflow Fans
On fans that are actively forming from water-borne sediment alone, channels are unremarkably braided, Oregon multithreaded, from the apex. Deposition occurs connected the channel bed in the form of parallel bars on the margins or in the centers of channels. Rapid erosion of channelize bed and Banks is possible because of the loose, unconsolidated nature of the sediments. Thus, fast wearing away operating theater deposition along a canalise reach can alter the run conveyance capacity during a single flood.
Bank erosion and lateral bar formation can force the channel to shift, spell some bed aggradation and mid-channel bar organisation canful force water overbank and into newfangled paths, soh that channels divide and streams episodically unconstraint one surgery both channels. Channels may shift dominantly atomic number 3 a result of the assemblage of sidelong bars, in which case they do not build prepared their bon or Banks to a higher place the level of the surrounding surface. In addition to this gradual canal migration, sudden changes in flow path (avulsions) hind end occur due to overbank flooding. Flush quite large and well-defined channels can be abandoned if a flood breaches one of the channel banks and piddle flows overbank in depressions between old bar deposits on the rooter surface, often eroding a unsounded line headward prepared to the source channel, which is then entertained. Particularly astronomic, klick-scale changes in the positions of flow paths and active alluviation zones can occur without the transmit occupying or shifting across medium positions if the channelized and the overbank hang cause sediment to be deposited within and close to the channel, fosterage the bed and the line margins above the surrounding winnow surface (Figure 2-4). Breaching of the elevated Sir Joseph Banks in a large flood can allow the menses to travel toward the lower areas between channels or along the fan margins. Small shifts approximate the fanhead can cause dramatic changes in channel position further go through the fan.
As one and only proceeds down the fan, the channels break up more frequently than they join, so that on average the channels diverge and lessen in width, depth, and discharge along a general menses thread during any one and only flood event. Despite the lessening in discharge, the reduction in breadth, profoundness, and gradient butt force water overbank in many floods, and thin, unchannelized, relatively uniform expanses of water can cut through large areas (sheetflood). Sufficiently far down much fans, most of the runoff occurs As a sheetflood, either generated locally on the sports fan or forced overbank by the diminishing conveyance capacity of the channels. The sheetflood itself is guerrilla with zones of accumulated feed giving way downslope to divergences and shallowing at which small
Suggested Quotation:"Flooding Processes and Environments along Alluvial Fans." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The Status Academies Press. doi: 10.17226/5364.
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FIGURE 2-4 Oblique aerial photograph of an sediment fan of the western slopes of the McDowell Mountains in halfway Arizona display recent interval and braiding of channels downfan. The topographic apex is at the lower edge of the conniption. Floodflow can submerge much of the area in the view except for a few ridges of old lover remnants. Courtesy of H. W. Hjalmarson.
fans of sediment are deposited. At the toe of most fans, sheetflood that has a relatively low sediment compactness because of deposit on vegetated surfaces can over again gain an erosive capacity if it is concentrated into a number of swales and small channels before ingress trunk streams that drain the entire mountain front.
Along streamflow fans where the sediment balance has turned blackbal, either at present or for some period in the recent past, the channels are deeper because alluviation on their floors and margins is replaced aside incision. The flow and deposit conveyance capacity increase because form roughness is to a lesser extent in the petit mal epilepsy of offensive block growth. Thus, many of these channels are incised below the surrounding lover surface, and avulsion occurs less frequently or non at beat the current climatic and hydrologic regime. The separation of the current into diverging, smaller channels is converse, and one or a few trunk streams convey the floodflow to the toed of the fan. Because these major conduits are incised they are not so oftentimes diverted by mid-channel exclude deposits and they do non brea across the fan every bit quickly As those on actively accumulating fans. Instead, they tend to assemble local runoff generated happening the rooter come on because the rills and small channels produced by such runoff repeatedly fret toward the stable trunk channel. The channel network is slenderly convergent downfan, and mapped contours show upfan re-entrants that reflect
Advisable Citation:"Flooding Processes and Environments on Alluvial Fans." National Research Council. 1996. Alluvial cone Flooding. Washington, DC: The Political entity Academies Press. doi: 10.17226/5364.
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the incision. Around channel banks may be colonized by trees and bushes, adding another stabilizing regulate. Because their surfaces are none thirster accumulating sediment, such fans Oregon parts of fans are said to be inactive.
Incised streamflow fans are peculiarly well-matured in regions where a major climatic change has emended the conditions that favored sediment collection (e.g., the transition from glaciation to interglacial period in parts of the Sierra Nevada and the Cascade Range of Washington state, Oregon from wetter to drier periods in the mountains of Arizona). They are also well-developed in areas where fans have been steepened tectonically as in parts of southerly California. In these cases, in that location is a strong isolation of deeply incised channels from the surrounding ''remains" fan surface. Thence the job of recognition is complicated because all degrees of isolation occur, ranging from aggressive accumulation to rich incision. Chapter 3 describes field methods for identifying and mapping degrees of activity and for dating the metre of stylish activity along various parts of fans.
Middle cases of channel stability and childbed are particularly widespread and important to tell apart and evaluate. They go on, for instance, in radiating channel systems (distributaries) where the sediment balance of a reach is near-steady state. So much channels may gradually get over shallower downfan until their floodwaters simply sprinkle American Samoa sheetflood, repeatedly spreading thin layers of sediment and water and edifice an apron of comparatively fortunate watered and delicately sediment that supports thick vegetation. In some years, there is accumulation of sediment, and in others there is net removal, so the bed may rise Oregon flow away a a few decimeters, but neither the scour nor the filling veer persists for long enough to raise or lower the channel bed significantly in relation to the fan shallow.
Alternatively, on that point Crataegus laevigata be a persistent but very gradual trend that causes the distribution channel to acclivity, lower, or teddy laterally at a rate that is problematic to detect with normally available information (e.g., sequences of maps or aerial photographs, anecdotal reports, dating of Recent epoch sediments with buried artifacts). In other cases, a reach that has stabilized may be perturbed by runoff or sediment that enters it from an unstable reaching upstream. Thus analysis of the stability of a reach requires taking a broad view of the potential for change in channels upfan. Spatial context is important in any analysis of flooding and sedimentation hazards on a streamflow fan. Hjalmarson (1994) provides an illustrated account of individual distributary-flow from channels with a range of flow path stability and strength of flood pretend.
Debris Flow Fans
Debris course fans occur where strongly impermanent sediment transport is triggered by collapse of an accruement of weathered rock, soil, or deposit in a steep source region or by concentration of flow onto a steep accumulation of sediment that is then trenched rapidly in such a style that a high sediment concentration is industrial with a mixture of sizes, including a significant proportion of fine deposit. The sediment-water ratio of the mixture must be and then high that the flowing junk has a low permeability and water cannot drain forbidden (upward) speedily enough to allow the water to branch out from the deposit and the sediment to settle onto the bed.
The resulting badly sorted slurry is dense and highly gluey and travels as a bedded flow except where agitated away waterfalls and cascades, by bigger rocks in the make out, or by engineering structures. Observers often describe much flows as looking like wet concrete. Flows with
Advisable Citation:"Flooding Processes and Environments on Alluvial Fans." National Enquiry Council. 1996. Alluvial Fan In flood. Washington, DC: The National Academies Compress. doi: 10.17226/5364.
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intermediate deposit-water ratios and characteristics between those of debris flows and turbid water flows are sometimes referred to as hyperconcentrated flows.
Rubble flows lie of the full vagabon of sediment sizes supplied from the source field, and flows generated from rocks of different types within the source basin may contain different proportions of clay. The greater the proportion of fines, the greater is the inner strength of the flow because of "cohesive" soldering caused past electrical charges shared 'tween clays and water films. Some flows are sufficiently dense and viscous to transport boulders; others farewell the largest boulders behind. Every bit the sediment-urine ratio decreases (i.e., in more dilute flows), progressively smaller boulders go down to the bed and are deposited Beaver State transported as traction load up in a troubled flow.
The flow properties of the slurries determine the circumstances of the debris flows when they emerge onto the winnow, the nature of sediment deposition, and the sequent sound structure of the deposit. These properties depend on the order of magnitude of the discharge and the rheological properties of the debris, which in turn are controlled by its sediment-water ratio and remains message. Discharge rate, clay content, and sediment-water ratio of each debris flow are set by the generating mechanism and the particular combination of circumstances that trigger the flow. For example, a super rainstorm or snowmelt may generate landslides that fall into stream channels containing meaningful discharge, and the resulting mixture may produce a dilute debris flow. Collapse of drippy debris into a steep channel network that already contains a large volume of fallen rubble from centuries of slow mass-wasting on adjacent hillslopes may result in scour of that accumulation into a particularly dense and viscous, boulder-charged debris flow from. The volumes and peak flow rates of detritus flows devolve on (1) the order of magnitude of the water supplied from a rainstorm, snowmelt, lake outburst, Beaver State eruption, and (2) the volume of loose debris that is in stock to be liquefied by this water during the initial break, undermining and acculturation, or scour from the valley floor on the steep portion of the detritus flow cart track. Therefore, the debris flows that ply and molding any one lover have a probability distribution of discharges and rheological properties, which shape the nature and magnitude of flood risk. Fortunately, these aspects of flood out risk fundament be read from the sound structure of the fan and its source basin.
The range of rheological properties among debris flows emanating from the source valley usually accounts for differences in word structure along different parts of a single debris perio fan. Flows with the highest sediment-water ratios and therefore the greatest strength come to repose on relatively steep gradients (typically 6 to 8 degrees) on the upper parts of the fan in the form of bouldery snouts and levees. These deposits occlusion channels worn by piss floods between debris flow episodes and divert ulterior flows of water operating room debris into new channels. The result is a topographically rough surface of berms, lobes, and bouldery channel blockages along the high parts of junk run over fans (Figure 2-5).
Somewhat Sir Thomas More dilute and weaker flows travel through with the steepest channel reaches, only deposit stony levees as their margins are slowed. If the peak discharge value of a rubble flow exceeds the conveyance capacity of the channel, its upper part is partially decanted overbank and it travels whatever distance crossways the devotee surface until it becomes slow enough and thin adequate to occlusive as a bouldery or gravelly sheet with a sharp edge. Stranding of boulders in levees and overbank sheets causes a progressive downfan step-dow in the boulder content of flow deposits. The near dilute and weakest debris flows remain channelized as far as the lower parts of the fans, where gradients may be as low A 2 to 3 degrees. Some of these flows stay within the channel, raising its bed and lowering its depth, spell others cover the Sir Joseph Banks onto the surface of the
Suggested Citation:"Flooding Processes and Environments along Alluvial Fans." National Enquiry Council. 1996. Sediment Fan Flooding. Washington, DC: The Political entity Academies Press. doi: 10.17226/5364.
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FIGURE 2-5 The upper part of this debris flow fan in Jesse Owens Valley, California, shows a classical cracked, bouldery rise. Courtesy of T. Dunne.
fan as the declining gradient reduces the transferral capacity of the channel, forcing run overbank. The result is a smooth surface with sole an episodic boulder on the lower parts of a debris flow fan. On debris run over fans, streams are a great deal pent to nondiverging, boulder-lined channels left aside the dust flows, and therefore they neither shift across the lover nor overtop the banks in most cases, leave out connected the depress parts of the fan where shallow channels were to begin with formed by the stretch, low-viscosity flows described above. Course, if the debris liner the channels is beachy rather than bouldery, the capacity for canal unfirm and eventual realignment aside water floods is greater.
Umpteen channels on junk flow fans are single-train of thought depressions blocked at their upper ends by bouldery accumulations, soh they are ne'er invaded by stream floods or junk flows. Like-minded alluvial fans, debris flow fans are subject to varying amounts of deposition and parts or even much of the fan May be inactive low the present climate. For example, the debris flow rate fans emanating from the east side of the Sierra Nevada Mountains in the northwestern part of Owens Valley take over more surgery less ceased to accumulate since the oddment of the last glaciation in the mountains, and the oldest parts of the fans date from early glaciations. Parts of fans debouching from the unglaciated grey Sierra and from the White Mountains on the western side of Owens Valley continue to receive
Suggested Citation:"Flooding Processes and Environments along Sediment Fans." Status Research Council. 1996. Alluvial Fan Swollen. Washington, DC: The National Academies Press. doi: 10.17226/5364.
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debris flows in the modern climate. Descriptions of large debris flow fans in Jesse Owens Vale, California, are provided by Whipple and Dunne (1992), and smaller debris flow fans in a surface-active agent environment are described by Kellerhals and Church (1990).
One approach to flood risk on debris run fans concludes that even on active fans the probability of a junk menses is little than 1 pct in any matchless year, and therefore the "100-class flood" is non a debris flow but a runoff event. This is a generalization that fails to prize an important aspect of debris rate of flow initiation, namely, that it is not an self-sufficing, random event in the same way of life that overflow floods are assumed to be. Debris accumulates in reservoir localities and on stream channels over timescales from decades to centuries betwixt failures that evacuate the debris (Benda and Dunne, 1987; Dunne, 1991; Reneau and Dietrich, 1991). Thus, a frequency reckoning of dated detritus flows in a region mightiness indicate that the average frequency of happening is, enunciat, 200 years per rooter (with a probability of occurrence in any combined year of 0.5 per centum). However, if a geologist were to walk up any one of the source basins, helium or she mightiness discovery many potential bankruptcy sites and the channels below them to beryllium filled aside thick layers of deposit that induce collected since the late debris current occurred centuries sooner. In a neighboring vale, Holocene epoch debris flows may have stripped so much sediment from the valley and reset the clock thusly that the probability of debris flow is virtually zero for the foreseeable future. Thus floodlight put on the line estimates can be refined by first recognizing from playing area evidence that debris flows are the dominant sediment transporting factor along a particular fan and and so examining the source basin to determine whether debris availability favors an enhanced risk of a debris flow in the event of a large rainstorm operating room snowmelt.
Composite Fans
Many another fans are federal official by both water floods and debris flows. Others were formed by debris flows under a different climatic regime and are now the sites of stream sedimentation and flooding only. Gum olibanum, both streamflow sediments and debris flow sediments and their associated morphologies attest to the nature of the inundation risk along different parts of the identical fan. The rubble flow sediments are usually amassed connected the upper, steeper parts of the fans, producing a surface laced with berms, lobes, and channel plugs. The frown, streamflow part of the sports fan has the characteristics of an alluvial fan described above, although there may also be a contribution of debase rubble flow deposition on these distal areas. An reading of the relative contributions of debris flows and water floods can cost obtained through systematic identification and mapping of the distribution of the two types of sediments on the fan surface and in vertical sections along the sides of channels.
Incised Channels happening Fans
At the heads of just about alluvial fans, channels are powerfully incised in a fanhead trench, from which they egress at any length downfan to take on the fibre of a diverging braided channel net Oregon a linear, Boulder-leveed channel characteristic of debris menses fans, as delineated above. This report card calls this point the hydrographical apex. Various reasons for the transition are acknowledgeable in the field. The simplest subject arises on a composite fan where episodic debris flow
Suggested Citation:"Flooding Processes and Environments on Alluvial Fans." Political entity Search Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. Interior Department: 10.17226/5364.
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deposition produces a slope that is steeper than that required by intervening floods to deligh the sediment load supplied by the source basin or produces enough transport bank forte to throttle water system flows to depths sufficient to transport the sediment render. In that case, the water floods will scour aside some of the debris flow deposit, establishing a lower-gradient canalize cut within the debris flow deposits. At some distance down the devotee, where the gradient of the debris run over sediment surface has diminished, the required teem gradient intersects the fan surface and a single-thread operating theatre braided channel or a swath of sheetflooding emerges from the fanhead encroach at what Hooke (1967) called an intersection point in time, that is, a transition between flow and sediment transport process regimes.
In unusual cases, trenching at the fanhead operating theatre still over the entire fan may pass atomic number 3 a solvent of channel scratch of older fan deposits, either because the deposit supply has vitiated or because the transport electrical capacity has augmented outstanding to climate or vegetation changes within the source basin, operating room to tectonism. The roles of climatic change and tectonism in trenching the heads of fans are reviewed thoroughly by Bull (1991).
High PROCESSES ON ALLUVIAL FANS
Flooding along Streamflow Fans
Since streamflow deposit fans typically occur in arid and mountainous environments, one and only of the introductory difficulties encountered in the quantification of sediment rooter flooding processes is the order of magnitude-frequency relationship for flows supplied to the apex. The sparseness of hydrologic monitoring stations in such regions and the shortness of most records render most estimates of probable flood discharges highly hesitant. Fans receive high water discharges from hurricanes or typhoons on the subtropical eastern sides of continents, and from more localized rainstorms or from intense, lasting snowmelt in mountainous western North America. In rebel Europe, particularly in southeastern Spain, the most destructive discharges are again generated by rainstorms. In each of these regions, the history of hydrologic depth psychology and prediction has been one of surprises.
Stream overflowing along alluvial fans differs from well-nig riverine flooding in that the hazard not only derives from the alluvion itself, but also is intimately contiguous with sedimentation processes. These latter have immediate touch on during Noah's flood itself, and they have long-run geomorphic influence through with the rearrangement of sediment on the fan. High-topped flood stages in channels are accompanied by shrill rate of flow velocities, and by heavy loads of floating wood, and other debris in some environments. High-top velocities are promoted by the relatively steep, hydraulically peltate nature of the channels. The flood hazard is markedly increased, however, by the potential for canalize change during the flood itself. The loose bed material may be worn several meters deep-water. Happening some fans the loose, loose nature of the sediments allows rapid channel broadening past bank collapse if the flood persists for several hours or days. On others, the deposition of parallel bars along a canalize margin causes the channel to shift against the opposite, concave bank at rates of astir to tens of meters per flood. Thus, rapid scour and filling of the transmission channel drive changes in the channel conveyance capacity between and during floods.
The largest and about widespread threat arises, however, through the process of avulsion ("tearing away") in which water escapes from a channel by scrubbing a new itinerary through the bank.
Advisable Citation:"Overflowing Processes and Environments along Alluvial Fans." National Research Council. 1996. Deposit Fan Flooding. Washington, DC: The Status Academies Press. doi: 10.17226/5364.
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This process may begin by sudden swear collapse or by inclined overflow of irrigate from the rising flood. As the relatively thin surface water flows overbank, it often travels down a gradient that is steeper than the transmission channel (because of the convex shape of the winnow cross section and the perched nature of some channels above the general fan surface) and so is able to pick up deposit and scour a new path. The water may too take advantage of a former channel, or a series of abandoned channel segments. In the squabby-full term, this process English hawthorn Be easily predicted if there are obvious low sections of swear or narrow levees separating the channel from much lower parts of the fan. However, it is difficult to anticipate all such weak sections of the Sir Joseph Banks and to predict the strict flow track that the diversion is likely to follow across the illegal fan surface, especially since the diverted flow has the transport capacity to modify that superficial. Connected the timescale of decades, IT is virtually intolerable, with either field inspection or mathematical modelling of sediment channelize, to anticipate the locations of in channel deposition and bank erosion that might provoke avulsion. The problem is aggravated past the fact that a digression happening the upper part of the fan may alter flow paths on the lower role of the fan in shipway that are independent of local anesthetic fan morphology. Topographic changes in the channel network far upstream of a channel reach have the superior potential for radically fixing the risk of inundation, overtopping channel banks, Oregon undermining a site downfan, but are probably the about difficult threat to anticipate and quantify.
Sheetfloods spread extensively on low relief depress parts of fan, and as they decelerate they oftentimes deposit sheets and low bars of sand or get. Even though velocities and depths are low, alluvion by muddy water can be very ruinous.
Flooding on Debris Flow Fans
Debris flows are heavy (approximately 1.8 to 2.0 times the density of water), mucilaginous (approximately 10,000 times the viscosity of water), and tight (3 to 10 m/s (9 to 30 feet/s)). They can transport boulders up to several meters in diam, either as individuals supported in the matrix of the flow or as dams of boulders pushed along at the front. Some debris flows consist of waves of slurry behind rough dams (Sharp and Nobles, 1953; Suwa and Okuda, 1983). Large woody debris, technology artifacts, and vehicles are also transported by debris flows and can because stoppage, fall diversion, and additional damage to houses and other structures downfan. As they approach their final deposition point, debris flow sediments take on a finite yield strength that prevents them from debilitating aside like water. They remain as permanent covers on fan surfaces, and are expensive to remove from urban areas or channels. (On the other hand, still, they are less verisimilar than water flows to undermine and destroy a touring, sol erst cleared the road is generally silence useful.) In extreme cases, such as after particularly large debris flows along fans unreal active volcanoes, deposits may be so stringy and extensive that they permanently bury settlements. The deposits also block drainage in valley floors and at tributary junctions.
Some aspects of the prediction of debris flow-frequence and magnitude at the lover apex are more than arduous than is the case for water floods, but other characteristics of debris flow occurrence simplify the job. Within the United States government, there are no monitoring stations with records unsound enough to offer a representative sample of debris flow occurrence on which a probability depth psychology power be founded. A procedure commonly used by photoflood control agencies involves using records of runoff for anticipation of a water flood peak with a 1 percent probability of occurrence,
Advisable Citation:"Flooding Processes and Environments on Alluvial Fans." National Research Council. 1996. Alluvial Fan Flooding. WA, DC: The National Academies Press. doi: 10.17226/5364.
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and then increasing the book of that predicted flood prime to account for the observed sediment-water ratio in a recent debris flow (which normally triggered the business concern by surprising the agency in the first place) (Brunner, 1992). Although so much a procedure might give a reasonable respond for those hyperconcentrated flows generated away overflow processes, it is wrong to mix a probability analysis the results of runoff processes (gauging station records of floods) with rubble flows, which are the usually triggered by whatsoever physical body of mass failure.
A especially misleading situation arises when the assumption of interannual independence that has been found to be a useful approximation for rainfall-generated and snowmelt floods is applied to debris course occurrence. This is because the occurrence of a debris flow in one year substantially reduces the chance of future debris flows by removing the sedimentary accumulations necessary for their generation and growth (Benda and Dunne, 1987; Keaton, 1988; Keaton et al., 1988). Fortunately, it is often practicable to identify through and through field observations those conditions that favor the contemporaries and growth of debris flows. For model, deep accumulations of colluvium on bedrock indicate a relatively highschool chance of detritus flow happening in comparison to that in a washstand in which most of the colluvium was evacuated in a relatively recent meteorologic event, after a forest fire, or after a climatical change. Thick accumulations of sediment along channels upstream of a fan argue that nary debris flow has passed for a considerable amount of time and therefore that the conditions are evolving toward a failure that could convey prodigious quantities of sediment from canyon floors to the fan. Such observations combined with a probability analysis of rainfall or snowmelt required to set off a mass nonstarter are required for estimating the debris flow risk at the vertex. Estimating the probable order of magnitude is to a greater extent time-consuming, since it requires documenting volumes of sediment in old debris flow deposits or in the valleys above the fan.
Avulsions of debris flows take plac on bowlder-rich fans and are particularly effortful to forecast because of the uncertainty close to the magnitude and rheology of the next dust flow. However, some clues to the likelihood of an avulsion occurring can be obtained from field inspection of the morphology and sedimentology of the fan itself. In particular, utilizable indications of the avulsion potential might be provided by (1) the volumes of sediment susceptible to liquefaction in the informant area (Joseph Francis Keaton, 1988; Keaton et al., 1988) and therefore the likelihood of a peak discharge peachy enough to overtax the conveyance capability of the carry for such a debris flow; (2) previous blockage of the primary channelise by bouldery berms; (3) relatively scurvy convey Sir Joseph Banks near the apex of the sun's way or in the vicinity of any blockage in the main channel; and (4) the topography of the fan surface at these locations. Calculations of the channel conveying content for debris flows with a range of rheology can be made for various channel cross sections down the lover to approximate the potential for overbank flow and spreading (Whipple, 1992; Whipple and Dunne, 1992). At the distal margins of debris flow fans, low-strength flows much bedcover widely in a manner similar to sheetflooding on streamflow alluvial fans (Figure 2-6).
A peculiarly hazardous situation arises on debris run fans roughly active volcanoes because of the huge volumes of sediment that force out be molten and the persistence of the liquefaction. For instance, the October 1994 lahar (volcanic debris flux) generated by a typhoon from the slopes of Mt. Pinatubo in the Philippine Islands deposited approximately 50 billion cubiform meters (1.8 billion cubic feet) on an urban and genteel sediment rooter. The North Crotch Toutle River lahar generated by the Mt. St. Helens eruption of May 18, 1990, deposited approximately 100 million cubic meters (3.5 billion box-shaped feet) of debris (Fairchild, 1985). Such volumes
Suggested Acknowledgment:"Flooding Processes and Environments on Alluvial Fans." Internal Research Council. 1996. Alluvial cone Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
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FIGURE 2-6 A 1952 rubble flow flood on Cottonwood Canon Fan, California. Reference: Reprinted with permission from Beaty (1963).
entirely overwhelm the pre-existing channel organisation and topography of fans and create new pathways that are impossible to omen in detail.
Overflowing on Composite Fans
Composite fans are dependent to both streamflow and debris flow flooding. The relation importance of each varies 'tween fans, between positions on each fan, between individual
Suggested Citation:"Flooding Processes and Environments on Alluvial Fans." Status Research Council. 1996. Alluvial Fan Overflowing. Capital of the United States, DC: The People Academies Press. doi: 10.17226/5364.
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meteorologic events, and between episodes as climate fluctuates or as debris accumulates slowly for centuries subsequently a period of debris menses natural process.
Generally, debris flow activity is most shop happening the high parts of a asterid dicot family fan, but a large, dilute, and therefore weak debris flow Crataegus laevigata remain channelized and mobile for tens of kilometers, and consequently traverse the zone that is dominated by streamflow activity. However, through geologic mapping of distinct rubble flux and alluvial deposits it is normally mathematical to delimitate and map the probable nature of the various types of dethronement (bouldery, lobate detritus flow deposits; channelized debris flow deposits with bouldered levees; tabular sheets of debris hang deposits; bars of streamflow raspy; and sheets of gravely or sandy streamflow deposits) and thus the maximum extent of debris flows along a complex rooter. After examining the debris flow generation potential of the origin area, it is likewise possible to make an approximate calculation of the maximum thinkable transmit of debris flows downfan. It is too possible through with geologic mapping and dating of deposits and exam of source areas to determine whether the dust flow activity that may have built most of a fan is still active or will yield much smaller debris flows than during the full point of utmost fan construction.
An important issue for the prediction of flood risk connected fans affected by debris stream is that the rearrangement of the channel arrangement by a detritus flow buttocks cause a weeklong-full term change in the flooding hazard during swarm flooding. Furthermore, after a detritus flow has deposited large volumes of sediment happening the upper parts of a fan, streamflow in the same operating theatre later events will spread the sediment far downfan, causing channel instability and sedimentation that cut back Noah and the Flood transport capability of channels.
CHANGE OVER TIME
Fans form over thousands to millions of years, during which time environmental conditions affecting their formation change much or less continuously. For this reason, they are always evolving, although parts (reaches) of them May temporarily discove a steady State in which their channel gradients can make it the supplied sediment and no further deposition occurs in that reach. Even in that state, the channels can shift crosswise the fan and retread its surface by erosion and dethronement.
However, part or the whole of the sports fan whitethorn become a zone of greatly diminished collection or in the extremum vitrine Crataegus oxycantha become a zone of net eating away with the entire channel system entrenched. The fan opencast may thus be weathering and wearing away, Beaver State it may have attained a steady state after a period of incision. However, some runoff and canal patterns develop along the fan afterward it ceases to be a zona of net collection.
Changes in the deposit Balance and its spacial distribution can occur because of (1) externally imposed changes (e.g., of climate operating theatre land cover influencing deposit supply and transmit capacity or of tectonism influencing channel slope and therefore transport capacity); (2) long-run phylogenesis of the fan-shape (especially its gradient) as IT evolves over time in reception to the sediment accumulation; and (3) shorter-term changes in form due to sediment accumulation (e.g., convey shifting incidental to bar accumulation, channel avulsion, raising of channel above the surrounding surface, deposition and channel filling by a uniform dust flow, runs of wet years caused by upwind fluctuations, which may reason accelerated channel turnout Beaver State shifty or reactivation of sediment sources producing debris flows that have been dormant for a age).
Suggested Citation:"Flooding Processes and Environments on Sediment Fans." National Research Council. 1996. Deposit Fan Flooding. American capital, D.C.: The National Academies Press. doi: 10.17226/5364.
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True if the fan is smooth a zone of active assemblage, the venue of that deposition may vary between fans or on the same fan during its lifetime. Distributaries break through most frequently where aggradation is intense and thus may shift the centers of active sedimentation across operating room along the fan. Deposition as wel may shift down the fan if the uplift rank in the scores rootage exceeds the deposition order at the fanhead. This can lawsuit trenching of the informant canyon and the upper fan surgery intense episodes of debris stream and well out transport associated with increased runoff. In the latter cases, the channel may represent entrenched below the upriver part of the fan surface and all deposition and related channel shifting or deepen occurs on the get down portions of the devotee. Discernment of such changes is remarkable for understanding flood hazards on fans because (1) more or less of the changes occur sufficiently quickly to bear upon channels connected timescales relevant to engineering analyses, so that information technology is important to sleep with whether a special fan is undergoing a change at the present time, and (2) geologically recent, but no-longer active, processes may leave a morphologic signal on the winnow or in the source basin that mustiness exist interpreted in order to refine estimates of Holocene changes in flood hazard.
Fans grow in a motle of ways and the thickness generally increases at the slope transition drum-shaped at the fan toe as it is increasingly buried (Hooke and Dorn, 1992). Deposits near the apex commonly are remobilized and redeposited far down the fan on and below the fan toe. French (1995) gives a method of estimating the depth of sediment deposit at these side transitions on fans. The all but unceasing dethronement typically begins at the toed and propagates both up the fan and below the toe where the slope typically diminishes.
The phylogeny of the fan surface causes a difficult problem for the reading of field evidence concerning sediment fan flooding and for the forecasting of future flood risk. For instance, if a part of a fan surface has not been disturbed past flooding or erosion for 15,000 years, its surface will have become weathered and covered aside a soil-visibility and vegetation (described in Chapter 3). The surface of such a fan will be very other from the surface of a nigh channelized and actively evolving area. An important geophysics and hydrologic interrogation for flood risk analysis is whether the sr. surface has evolved kayoed of the flood zone surgery whether IT simply has non been flooded for 15,000 years because random channel migration across the winnow took the locus of swollen and sedimentation farthest from the site for that distance of time.
If, for example, the active alluviation zone is at once migrating into the older surface through lateral bank erosion, or lies at an elevation sole a couple of meters below that surface (i.e., within the place of flood leg), operating theater if upstream of the site there is an opportunity for avulsions that could moderate channels or sheetfloods across the older surface, then the experienced surface lies within the zone subject to alluvial fan flooding.
If, aside contrast, channels have become constituted during the past 15,000 years for matchless of the reasons given above, the elevation difference betwixt the recently active sedimentation zone and the elder surface may be greater than any flood operating room debris flow stage thinkable in the current regime of climate, hydrology, surgery land usage in the source area. In this case, "overbank" flooding is not possible. Maximal conceivable flood high, albeit approximate because of the assumptions that must be made about potential changes of bed elevation, are predictable through methods delineate away Burkham (1988) for floods and Whipple (1992) for debris flows. If field review reveals that the margin 'tween the older and the latterly proactive surfaces is armour-clad with bouldery surgery cohesive sediment, and if the ages of trees along this edge equally well as the aerial exact register (now close to 50 years former) indicate little OR no migration of that boundary, then one's confidence is increased that lateral pass bank erosion does non threaten the site.
Advisable Credit:"Flooding Processes and Environments connected Alluvial Fans." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. Interior Department: 10.17226/5364.
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Such evidence is found, for example, along many channelized sediment fans that have been entrenched and rendered less active by changes of climate and hydrology. Former debris hang activity, or large meltwater or monsoonal Pleistocene floods, have a great deal built fans of coarse deposit that were trenched by littler floods soon after the mood change and now have channels that privy contain all the stream discharges conceivable under current state of affairs conditions and are rough with sediment likewise resistant to Be eroded rapidly. More than equivocal conditions occur along channels that have undergone less extreme changes, but photographic and dendrochronological prove indicates that channels along some, even mulct-grained, fans do not aggressively undermine their root-reinforced banks, presumably because camber scrub is not required by the combination of flood lows and sediment counterpoise in the reach. Finally, even if the sr. surface is judged to be free from the risk of overbank inundation and undermining, the channel scheme upfan needs to be systematically surveyed for the potential of an avulsion that would lead flows across the older surface. This would require a combining of geomorphologic survey (for low banks, elevated channels, zones of sediment accumulation, bank erosion and canalize shifting, and topographic lows on the sports fan opencut) and calculations of the high of conceivable floods and dust flows. On many alluvial fans, however, there is a relatively clear detachment between older, higher, stable parts of fans, and channels or narrow inset floors trenched into the fan deposits.
The kinds of airfield evidence that can beryllium used for making such determinations are reviewed in Chapter 3, and valuable sources of information are listed in Appendix B. It is unfortunate that the problem of interpreting the significance of different ages of sports fan surface for alluvial fan flooding risk is ofttimes not reduced away a simple indicator or quantitative indicator. However, with a systematic approach much as the example given above (identify the risk of exposure of overbank inundation, lateral bank eroding, and inundation by avulsion from upstream), most field situations can be classified as a basis for some regularisation and choice of a method for estimating flood adventure, Eastern Samoa required by Federal Emergency Management Agency. Complex situations, however, will tax whatsoever approach.
REPORTS OF FLOODING Along ALLUVIAL FANS
Documented accounts of flooding confirm that active fans mathematical function primarily as a terminus for water and debris, while relict fans and streams function to convey water and sediment. Vermiform appendix A summarizes accounts of flooding at 29 individual or groups of alluvial fans to illustrate a wide variety of flood conditions on streamflow, detritus flow, and composite fans. Most of the alluvial fans are in the arid southwesterly United States, and a few are in wet areas throughout the world. The accounts are for ascertained floods and consist of direct and asquint measurements and observations of floodlight characteristics and geomorphological interpretation of flood remnants. Only a some maps of the extent of flooding are available, and direct measurements of course depths and velocities on fans are infrequent. Opportunities for systematic appeal of flood information on alluvial fans are also rarified.
These accounts demonstrate the complex nature of flooding along alluvial fans, ranging from flooding in constant channels to massive deposition of debris in urbanized areas. Accounts past different observers of a particular flood on a particular fan can depict divergent characteristics. This is because (1) observations from a undivided advantage point of the widespread and variable nature of sports fan flooding are limited and not in demand and (2) local conditions change during a flood
Suggested Commendation:"High Processes and Environments on Alluvial Fans." National Research Council. 1996. Alluvial Devotee Flooding. Washington, District of Columbia: The National Academies Press. Interior: 10.17226/5364.
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because of the rearrangement of the channel system of rules by remobilization of deposited debris, as described in the previous section. Also, the flood characteristics on adjacent or nearby fans resulting from the same storm commonly are other because of localised differences in rainstorm intensiveness, sediment availability in the source areas, and the respective differences in Recent epoch flow path history.
Although flooding accounts depict varicoloured properties in clock and space, they prove certain identifiable properties when considered collectively. High floodflow velocities were reported for some half of the sites traded in Appendix A. Critical flow velocities for water floods are besides recommended at other sites by the steep fan slopes and low hydraulic disorderliness associated with fine-textured surface sediments and simple canal geometries. Show off floods (impermanent floods with a short time to eyeshade) are reported at Eight sites, including accounts of translatory waves at the Chicago Creek, British Columbia; Shoe Parkland, Colorado; and Montrose, CA, alluvial fans. At the Cottonwood Canyon, Magnesia Spring Canon, and Montrose deposit fans in California the reported combination of high flow velocities, flashy menses, unstable channels, and movement of flow paths produced an especially serious hazard that resulted in loss of life at deuce of the fans.
Sheetflooding and distributary-flow likewise are typical of alluvial fan overflowing. Unstable channel boundaries are common, piece stabile channel beds Beaver State banks are less common, as suggested by accounts at only 5 of the sites deliberate. Menses path movement was reported for 8 sites, nobelium drift for 13 sites, and either none mention of movement or absence of movement at the unexhausted 8 sites. A possible reason for the lack of menstruate path movement and disruption of the surface of some of the active fans is the short duration of the floods in concert with a controlled supply of loose medium to coarse material from the drainage basin. Typical distributary channels appear to scour and fill; however, stable flow paths do occur during individual floods.
The Carefree and Raging Burro alluvial fans in Arizona are examples of inferior active or inactive fans with extraordinary channel dent and a limited supply of cooked-to-unrefined deposit from the drainage washbowl. Well-nig of the deposit delivered to the fans is carried by streamflow and is coarse sand and fine grating. The basins are non very steep. For example, the basin of the Irresponsible fan is a pediment. On these fans the channels are slightly trenched below the circumferent fan surface and are silk-lined with desolate trees and shrubs. During recent prima floods, there was zero movement of the many distributary channels on either of these fans.
Deluge hazards on the to the lowest degree active fan surfaces, such as the Carefree (see Chapter 4) and Wild Burro deposit fans, posterior be deceptively small because of the small size of distributary channels and the rather eternal distances from highland drainage basins. E.g., shallow floodflow unexpectedly entered several small delimited channels during a major flood on the Saddle Mountain, AZ, alluvial cone (USACE, 1993). A subsequent field investigation revealed no bran-new channel formation on the fan. Rather, small distributary channels that in places appeared to be spatula-shaped topographic lows conveyed overrun from the larger distributary channels or carried runoff from high-intensity rainfall directly on the fan surface. Many a inferior active alluvial fans in the arid south United States have developed soils with small, slightly incised stable flow paths that conduct shallow high-speed floodflow during major floods.
Rising tide hold in plant such as levees and debris dams at single of the sites were part or totally inefficacious during major floods. For example, at Daytime and Deer creeks (Figure 2-2), Henderson Canon (see Chapter 4), and Magnesia Take form Canyon alluvial fans in CA, the flood control structures were overwhelmed, and floodwater followed original flow paths and fan
Recommended Citation:"Flooding Processes and Environments on Alluvial Fans." National Research Council. 1996. Alluvial Fan Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
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topography at and below sites of structural failure. This suggests that (1) major flood control works are necessary to mitigate flood out hazards on active alluvial fans, (2) predevelopment fan topography influences the emplacemen of prima flooding even afterwards fans are urbanized and underage flood control structures are in place, and (3) flood control works must be designed to treat circumstantial types of hazards and exceptional design consideration should be minded for areas where water give notice still reach after flood hold in structures are installed.
The small Glendora alluvial cone is extremely urban, and the paths of floodwater for a flood in Jan 1969 were significantly controlled by the network of streets that crossing the fan antiparallel and at good angles to the general direction of rooter slope (Figure 2-7). The alluvial fans of Cottonwood Creek and Stuart and Crane Gulches are also highly urban, and the paths of floodwater are significantly controlled past the conveying capacity and location of many streets. A FIRM showing alluvial fan flooding hazards based on the assumption of single risk, thereby ignoring the channels created by the streets, would be inappropriate for these municipality areas.
The Horseshoe Park and Wadi Mikeimin alluvial fans each were formed during a single flood. The Horseshoe Park alluvial cone was formed aside a catastrophic flood from a dam failure. The fan-botuliform at a topographic break at the mouth of the Roaring River. Wadi Mikeimin also formed at a put in floodflow confinement at the speak up of a river. The Yow and Mikeimin River fans were significantly modified by erosion following the winnow construction floods.
Abnormally large volumes of sediment were produced by storm runoff from recently burned basins of the Montrose, Cottonwood Creek, and Wasatch front alluvial fans. The close proximity of these devotee basins to urbanizing areas may result in a greater incidence of wildfires with associated debris flows and alluviation connected urbanized fan surfaces.
Reported flood characteristics of the sampling of fans admit high-velocity water flows, debris flows, translatory waves, sheetflood, distributary-course, unstable and stable channelise boundaries, apparent movement of flow paths, stable flux paths, and deposit along the unchanneled buff coat. The composite of these accounts of flooding shows a wide variability of processes and flood hazard in time and space, which places a premium on battlefield inspection and interpretation of concrete evidence from each alluvial lover before a determination is made of flood risk.
REFERENCES
Beaty, C. B. 1963. Origin of alluvial fans, White Mountains, California and Silver State. Annals of the Association of American Geographers 53:516–535.
Benda, L., and T. Dunne. 1987. Sediment Routing by Debris Perio. Publication. 165. Oxford University, England: International Association of Hydrological Sciences.
Brunner, G. W. 1992. Numerical simulation of mudflows from suppositious failures of the Rook Lake debris block near Mount St. Helens, Washington, Appendix A: Derivation of the equation to deliberate the ultimate bulking factor. In Program for Perpendicular Streams Workshop, Seattle, Washington, Oct 27–29, 1992. Portland, Ore.: U.S. Army Corps of Engineers.
Bull, W. B. 1977. The alluvial cone environment. Progress in Physical Geography 1(2):222–270.
Bull, W. B. 1991. Geomorphic Responses to Climate Change. New York: Oxford University Pressing.
Suggested Citation:"Swollen Processes and Environments connected Alluvial Fans." Political entity Research Council. 1996. Deposit Devotee Flooding. Washington, DC: The National Academies Press. doi: 10.17226/5364.
×
FIGURE 2-7 In urban settings, such American Samoa on the Glendora fan in California, streets can regulate the path of floods. This area flooded in January 1969. SOURCE: Giessner and Mary Leontyne Pric (1971).
Suggested Citation:"Flooding Processes and Environments on Alluvial Fans." National Research Council. 1996. Sediment Fan Flooding. Washington, DC: The General Academies Press. doi: 10.17226/5364.
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Burkham, D. E. 1988. Methods for delineating flood-prone areas in the Great Basin of Nevada and adjacent states. U.S. Geological Survey Water-Issue Paper 2316. Reston, Va.: U.S. Earth science Survey.
Dunne, T. 1991. Stochastic aspects of the relations between climate, hydrology, and landform evolution. Minutes, Japanese Geomorphological Unionised 12:1–24.
Fairchild, L. H. 1985. Lahars at Mount St. Helens. Ph.D. dissertation, University of Washington, Seattle.
French, R. H. 1995. Estimating the profoundness and length of sediment deposition at incline transitions on alluvial fans during outpouring events. Journal of Soil and Water Preservation 50(5):521–522.
Geissner, F. W., and M. Price. 1971. Flood tide of January 1969 Near Azusa and Glendora, California. U.S. Geological Survey Hydrologic Atlas HA 424. Reston, Va.: U.S. Geological Go over.
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Hooke, R. L. 1967. Processes on arid-neighborhood alluvial fans. Journal of Geology 75:438–460.
Hooke, R. L., and R. I. Dorn. 1992. Partition of alluvial fans in Death Valley, California, new insights from rise exposure geological dating. Earth Control surface Processes and Landforms 17:557–574
Jacobson, R. B. 1993. Geomorphic studies of the storm and torrent of November 3–5, 1985 in the Upper Potomac River and Cheat River basins in Westerly Virginia and Virginia. U.S. Geological Survey Bulletin 1981. Reston, Va.: U.S. Geological Survey.
Keaton, J. R. 1988. A probabilistic model for hazards-related sedimentation processes on alluvial fans in Davis County. PH scale.D. thesis. Texas A&M University, College Station.
Keaton, J. R., L. R. Anderson, and C. C. Mathewson. 1988. Assessing debris flow hazards connected alluvial fans in Davis County, Utah. Final report for U.S. Geological View Landslide Hazard Reduction. Correspondence Atomic number 102. 14-08-0001-A0507. Reston, Va.: U.S. Geological Survey.
Kellerhals, R., and M. Church. 1990. Hazard direction of fans, with examples from British Capital of South Carolina. Pp. 335–354 in Alluvial Fans: A Field Approach, A. H. Rachocki and M. Christian church, eds. New York: John Wiley & Sons.
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Sharp, R. P., and Nobles, L. H. 1953. Mudflow of 1941 at Wrightwood, Southern CA. Geologic Society of U.S.A Bulletin 64:547–560.
Singer, J. A., and M. Cost. 1971. Flood of January 1969 Come near Cucamonga, Calif.. U.S. Geological Survey Hydrologic Atlas vertebra HA-425. Reston, Va.: U.S. Earth science Survey.
Suwa, H., and S. Okuda. 1983. Deposition of debris flows happening a buff surface, Mt. Yakedake, Japan. Zeitschrift fur Geomorphologie Affix Banding 46:79–101.
U.S. Corps of Engineers (USACE). 1993. Judgement of Structural Flood Control Measures on Alluvial Fans. Davis, Calif.: Hydrologic Engineering Center.
Suggested Citation:"Flooding Processes and Environments connected Alluvial Fans." Domestic Research Council. 1996. Alluvial cone Flooding. Washington, DC: The National Academies Press. Interior Department: 10.17226/5364.
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Whipple, K. X. 1992. Predicting debris flow runout and deposition happening fans: the grandness of the perio hydrograph, erosion, debris flow and environment in mountain regions. Pp. 337–345 in Proceedings of the International Association of Hydrologic Sciences Symposium, D. Walling, T. H. Davies, and B. Hasholt, EDS. IAHS Publication 209. Oxford, England: IAHS Press.
Whipple, K. X., and T. Dunne. 1992. The influence of debris flow rheology connected winnow geomorphology, Owens Vale, California. Geological Society of America Bulletin 104:887–900.
What Is Formed by the Coalescing of Alluvial Fans?
Source: https://www.nap.edu/read/5364/chapter/4