首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
Two distinct types of alluvial fans occur in the Bow River Valley, Alberta, Canada: fluvially dominated and debris flow dominated. Large, gently sloping fans dominated by fluvial processes are associated with large and less rugged drainage basins, and small rugged basins have produced small, steep fans dominated by debris flow processes. Quantitative analysis demonstrates that strong fan-basin morphometric relationships occur despite a short fan history. Statistical analysis of fan area-basin area relationships indicate that debris flow fan areas do not increase in size as quickly as contributing basins. The relationship of fluvial fan area to basin area is not statistically significant. However, this relationship is probably affected by fan erosion. Examination of fan slope to basin ruggedness relationships indicates that fan slope increases more rapidly than basin ruggedness for both fan types. This is likely related to non-linear discharge and sediment size effects on fluvial fans, and reworking of larger fan surfaces by fluvial processes on debris flow fans.  相似文献   

2.
The estimation of debris‐?ow magnitude is an essential step in the assessment of debris‐?ow hazard. Although different methods have been developed for the assessment of debris‐?ow magnitude, this is still a dif?cult task because of the complexity of ?ow processes and the lack of data to test estimation procedures in many mountainous regions. Data on debris‐?ow magnitude from 127 basins in the Eastern Italian Alps have been collected from scienti?c and technical journals, technical reports, historical documents gathered from local archives, and ?eld surveys. These data were used to develop and test different predictive approaches, encompassing regression equations, geomorphological surveys and probabilistic analysis of time series. Regression techniques were used to correlate debris‐?ow magnitude to morphometric parameters and geological characteristics of the basins. Values of the channel debris yield rate (contribution per unit length of channel), proposed in the literature, were compared with data from the study area for identifying reference values for channel stretches of different morphological characteristics. Although limited to the few basins in which suf?cient data were available, the probabilistic analysis of time series of debris‐?ow magnitude provides indications about the relations between magnitude and frequency of debris ?ows. Some observations about the capability and drawbacks of considered methods are presented and the combined use of different approaches for the estimation of debris‐?ow magnitude is suggested. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

3.
The flooding susceptibility of alluvial fans in the Southern Apennines has long been neglected. To partly address this oversight, we focus on the region of Campania which contains highly urbanized piedmont areas particularly vulnerable to flooding. Our findings are based on stratigraphic analysis of the fans and morphometric analysis of the basin‐fan systems. Using geomorphological analysis we recognized active alluvial fans while stratigraphic analysis together with statistical analysis of the morphometric variables was used to classify the fans in terms of the transport process involved. The results indicate that in the geological context examined, the best discrimination between debris flow (Df) and water flood (Wf) processes is achieved by means of two related variables, one for the basin (feeder channel inclination, Cg) and one for the fan (fan length, Fl). The probability that an unclassified fan belongs to group Wf is computed by applying a logistic function in which a P value exceeding 0.5 indicates that a basin/fan system belongs to group Wf. This important result led to the classification of the entire basin/fan system data. As regards process intensity, debris flow‐dominated fans are susceptible to the occurrence of flows with high viscosity and hence subject to more severe events than water flood‐dominated fans. Bearing this in mind, the data gathered in this study allow us to detect where alluvial fan flooding might occur and give information on the different degrees of susceptibility at a regional scale. Regrettably, urban development in recent decades has failed to take the presence of such alluvial fans into account due to the long recurrence time (50–100 years) between floods. This paper outlines the distribution of such susceptibility scenarios throughout the region, thereby constituting an initial step to implementing alluvial fan flooding control and mitigation. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

4.
Coupling morphological, sedimentological, and rheological studies to numerical simulations is of primary interest in defining debris‐flow hazard on alluvial fans. In particular, numerical runout models must be carefully calibrated by morphological observations. This is particularly true in clay‐shale basins where hillslopes can provide a large quantity of poorly sorted solid materials to the torrent, and thus change both the mechanics of the debris flow and its runout distance. In this context, a study has been completed on the Faucon stream (southeastern French Alps), with the objectives of (1) defining morphological and sedimentological characteristics of torrential watersheds located in clay‐shales, and (2) evaluating through a case study the scouring potential of debris flows affecting a clay‐shale basin. Morphological surveys, grain‐size distributions and petrographic analyses of the debris‐flow deposits demonstrate the granular character of the flow during the first hectometre, and its muddy character from there to its terminus on the debris fan. These observations and laboratory tests suggest that the contributing areas along the channel have supplied the bulk of the flow material. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

5.
Hypsometry of glaciated landscapes   总被引：1，自引：0，他引：1  
Hypsometry (frequency distribution of elevations) is often used to characterize landscape morphology, traditionally in the context of the degree of ?uvial dissection. Recently, the hypsometry of glaciated regions has been used to infer how rates of glacial erosion compare with tectonic uplift rates. However, many factors other than tectonics can also exert a major in?uence on the hypsometry of a glaciated landscape, resulting in a wide variety of hypsometries. Using examples from the eastern Sierra Nevada, California, the western Sangre de Cristo Range, Colorado, and the Ben Ohau Range, New Zealand, we demonstrate that, all else being equal, the hypsometries of neighbouring basins can indicate the relative degree of glacial modi?cation in each. A selection of drainage basins from the Rocky Mountains shows that the position of the equilibrium line altitude (ELA) within the drainage basin relief is a dominant variable in determining the hypsometry of a glaciated basin. This is a non‐linear effect: once the ELA falls to some critical level, the glaciers scour deeply below the ELA, causing a noticeably different hypsometry. The hypsometry of an arbitrary region encompassing many drainage basins can disguise the variation present in the hypsometries, and thus landforms, of the individual basins. Unique local circumstances, such as the presence of a mountain ice?eld (Waiho Basin, Southern Alps), substantial hanging valleys (Avalanche Creek, Glacier National Park), a narrow outlet canyon (Sawmill Creek, Sierra Nevada), and isolated geologic structures (Baker Creek, Sierra Nevada), can have a major impact on the hypsometry of an individual basin. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

6.
Alluvial fan development in Alpine areas is often affected by catastrophic sedimentary processes associated with extreme ?oods events, causing serious risks for people living on the fans. Hazard assessment in these areas depends on proper identi?cation of the dominant sedimentary processes on the fans. Data from a set of 209 alluvial fans from the central Alps of Italy are presented in this paper and analysed with the help of various statistical techniques (linear regression, principal components analysis, cluster analysis, discriminant analysis and logistic regression). First, we used modern sedimentary facies and historical records (?ood events since 15th century), to distinguish between the two dominant sedimentary processes on alluvial fans: debris ?ows and stream?ows. Then, in order to analyse the main controls on past and present fan processes, 36 morphological, geological and land‐use variables were analysed. As with observations for arid‐environment fans, catchment morphology is the most in?uential factor in the study area, whereas geology and land use are minor controls. The role of climatic change and landsliding within the catchments also seems to be very important and is discussed. Statistical techniques also help in differentiating groups of alluvial fans by sets of controlling factors, including stage and type of evolution. Finally, by using discriminant analysis and logistic regression, we classi?ed alluvial fans according to the dominant sedimentary process, with a success rate ranging between 75 and 92 per cent. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

7.
Alluvial fans and debris cones link two zones of the fluvial system (e.g. hillslope gully systems to stream channels; mountain catchment sediment source areas to main river systems or to sedimentary basins) and therefore have important coupling or buffering roles. These roles may be both functional and preservational. The functional role includes debris‐cone coupling, which controls sediment supply from hillslope gully systems to stream channels, influencing channel morphology. Coupling through larger alluvial fans, expressed by fanhead trenching, causes a distal shift in sedimentation zones, or when expressed by through‐fan trenching, causes complete sediment by‐pass. The preservational role stems from the fact that fans and cones are temporary sediment storage zones, and may preserve a record of source–area environmental change more sensitively than would sediments preserved further downsystem. Fan coupling mechanisms include distally‐induced coupling (basal scour, ‘toe cutting’, marginal incision) and proximally‐induced coupling (fanhead and midfan trenching). These mechanisms lead initially to partial coupling, either extending the immediate sediment source area to the stream system or shifting the focus of sedimentation distally. Complete coupling involves transmission of sediment from the feeder catchment through the fan environment into the downstream drainage or a sedimentary basin. The implications of coupling relate to downstream channel response, fan morphology, sedimentation patterns and vertical sedimentary sequences. Temporal and spatial scales of coupling are related, and with increasing scales the dominant controls shift from storm events to land cover to climatic and base‐level change and ultimately to the relationships between tectonics and accommodation space. Finally, future research challenges are identified. Modern dating techniques and sophisticated analysis of remotely sensed data can greatly improve our understanding of fan dynamics, and should lead to better cross‐scale integration between short‐term process‐based approaches and long‐term sedimentological applications, while maintaining high quality field‐based observations. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

8.
Differences in lithologic erodibility and sediment storage within a drainage basin affect the relationship between alluvial fan area and drainage basin area along the western White Mountains. Large fans are produced by basins underlain by resistant rocks, which have steep and narrow trunk stream canyons with little sediment in storage. Small fans are produced by basins composed of erodible lithologic units, which have wider valley floors, lower valley-side slopes, and considerably more sediment stored along trunk stream canyons than is the case in basins underlain by resistant rocks.  相似文献   

9.
Mountain rivers can be subject to strong constraints imposed by changes in gradient and grain size supplied by processes such as glaciation and rockfall. Nonetheless, adjustments in the channel geometry and hydraulics of mountain rivers at the reach scale can produce discernible patterns analogous to those in fully alluvial rivers. Mountain rivers can differ in that imposed reach‐scale gradient is an especially important control on reach‐scale channel characteristics, as indicated by examination of North St Vrain Creek in Colorado. North St Vrain Creek drains 250 km2 of the Rocky Mountains. We used 25 study reaches within the basin to examine controls on reach‐scale channel geometry. Variables measured included channel geometry, large woody debris, grain size, and mean velocity. Drainage area at the study reaches ranged from 2·2 to 245 km2, and gradient from 0·013 to 0·147 m m?1. We examined correlations among (1) potential reach‐scale response variables describing channel bankfull dimension and shape, hydraulics, bedform wavelength and amplitude, grain size, ?ow resistance, standard deviation of hydraulic radius, and volume of large woody debris, and (2) potential control variables that change progressively downstream (drainage area, discharge) or that are likely to re?ect a reach‐speci?c control (bed gradient). We tested the hypothesis that response variables correlate most strongly with local bed gradient because of the segmented nature of mountain channels. Results from simple linear regression analyses indicate that most response variables correlate best with gradient, although channel width and width/depth ratio correlate best with discharge. Multiple regression analyses using Mallow's Cp selection criterion and log‐transformation of all variables produced similar results in that most response variables correlate strongly with gradient. These results suggest that the hypothesis is partially supported: channel bed gradient is likely to be a good predictor for many reach‐scale response variables along mountain rivers, but discharge is also an important predictor for some response variables. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

10.
Central Kentucky is characterized by a mixture of karst and ?uvial features, typically manifested as mosaic of karst‐rich/channel‐poor (KRCP) and channel‐rich/karst‐poor (CRKP) environments. At the regional scale the location and distribution of KRCP and CRKP areas are not always systematically related to structural, lithological, topographic, or other controls. This study examines the relationship of KRCP and CRKP zones along the Kentucky River gorge area, where rapid incision in the last 1·5 million years has lowered local base levels and modi?ed slopes on the edge of the inner bluegrass plateau. At the scale of detailed ?eld mapping on foot within a 4 km2 area, the development of karst and ?uvial features is controlled by highly localized structural and topographic constraints, and can be related to slope changes associated with retreat of the Kentucky River gorge escarpment. A conceptual model of karst/?uvial transitions is presented, which suggests that minor, localized variations are suf?cient to trigger a karst–?uvial or ?uvial–karst switch when critical slope thresholds are crossed. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

11.
The geochemical, mineralogical and lithological composition of modern stream bed material is examined in order to characterize sources and evaluate downstream mixing of sediments in the upper Fraser River drainage basin, British Columbia. The <63 µm fraction is emphasized for its relative mobility and ease of analysis using instrumental neutron activation. Overall, the composition of the stream sediments closely re?ects bedrock distribution. Samples dominated by limestone and dolostone, calcite and dolomite, and related elements (Ca, Mg, Sr etc.) correspond to Lower and Middle Cambrian carbonate bedrock largely con?ned to the Moose River sub‐basin. Clastic and non‐quartzite metamorphic lithologies, primary and secondary aluminosilicate minerals and related elements (Al, Cs, Rb etc.) are largely derived from Miette Group bedrock and associated with the uppermost Fraser River sub‐basin. Except in the case of the Moose River/Fraser River junction, the determination of proportional tributary contributions is complicated by variable or delayed mixing, localized ?oodplain or valley side sources, and limited contrast between source areas. At present the Moose River sub‐basin contributes a greater proportion of the total and ?ne‐grained sediment loads of the combined Fraser River than would be expected from drainage basin area alone. The imbalance is related to greater relief, precipitation and runoff in the Moose River sub‐basin; however, the spatial association of carbonate‐rich stream sediments, ice cover and carbonate bedrock exposure indicates that glaciers play a particularly important roll in generating ?ne‐grained ?uvial sediment. Since differences in glacier cover and glacier potential in the two major sub‐basins are likely to be persistent, and since relative sediment yields from the sub‐basins can be determined from sediment composition, a potential indicator of glacier variation and climate change during the Holocene is therein available. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

12.
The quantification of debris‐flow hazard requires estimates of debris‐flow frequency and magnitude. Several methods have been proposed to determine the probable volume of future debris flows from a given basin, but most have neglected to account for debris recharge rates over time, which may lead to underestimation of debris‐flow volumes in basins with rare debris flows. This paper deals with the determination of debris recharge rates in debris‐flow channels based on knowledge of debris storage and the elapsed time since the last debris flow. Data are obtained from coastal British Columbia and a relation is obtained across a sample of basins with similar terrain and climatic conditions. For Rennell Sound on the west coast of the Queen Charlotte Islands, the power‐law relation for area‐normalized recharge rate, Rt, versus elapsed time, te was Rt = 0·23te?0·58 with an explained variance of 75 per cent. A difference in recharge rates may exist between creeks in logged and unlogged forested terrain. The power function for undisturbed terrain was Rt = 0·20te?0·49, while the function for logged areas was Rt = 0·30te?0·77. This result suggests that for the same elapsed time since the last debris flow, clearcut gullies tend to recharge at a slower rate than creeks in old growth forest. This finding requires verification, particularly for longer elapsed times since debris flow, but would have important implications for forest resource management in steep coastal terrain. This study demonstrates that commonly used encounter probability equations are inappropriate for recharge‐limited debris flow channels. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

13.
The assessment of the dominant flow type on alluvial fans usually refers to two categories: debris‐flow fans (i.e. sediment gravity flows) and fluvial fans (i.e. fluid gravity flows). Here we report the results of combined morphometric, stratigraphic and sedimentological approaches which suggest that hyperconcentrated flows, a transitional process rheologically distinct from debris flows and floods and sometimes referred to as debris floods, mud floods, or transitional debris flows, are the dominant fan building process in eastern Canada. These flows produce transitional facies between those of debris flows which consist of a cohesive matrix‐supported diamicton, and those of river flows which display more distinct stratification. The size of the blocks in the channels and the abrasion scars at the base of several trees attest to the high transport capacity of these flows. The fan channels are routed according to various obstacles comprised primarily of woody debris that impede sediment transit. However, these conditions of sediment storage are combined with readily available sediment due to the friable nature of the local lithology. Tree‐ring analysis allowed the reconstruction of eight hydrogeomorphic events which are characterized by a return period of 9.25 years for the period 1934–2008, although most of the analyzed events occurred after 1970. Historical weather data analysis indicates that they were related to rare hydrometeorological events at regional and local scales. This evidence led to the elaboration of weather scenarios likely responsible for triggering flows on the fan. According to these scenarios, two distinct hydrologic regimes emerge: the torrential rainfall regime and the nival regime related to snowmelt processes. Hydrogeomorphic processes occurring in a cold‐temperate climate, and particularly on small forested alluvial fans of north‐eastern North America, should receive more attention from land managers given the hazard they represent, as well as because of their sensitivity to various meteorological parameters. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

14.
  相似文献   

15.
We present laboratory and field evidence that in mountainous catchment‐fan systems persistent alluvial fanhead aggradation and trenching may result from infrequent, large sediment inputs. We suggest that the river‐fan systems along the fault‐bounded range front of the western Southern Alps, New Zealand, are likely to be in a dynamic equilibrium on ≥103‐yr timescales, superimposed on which their fanheads undergo long‐term cumulative episodic aggradation. These fanheads are active only in rare events, do not take part in the usual behaviour of the catchment‐fan system and require much longer to exhibit dynamic equilibrium than the rest of the fan. These findings (1) increase our knowledge of the effects of extreme events on alluvial fan morphodynamics in humid climates, (2) question the general applicability of inferring past climatic or tectonic regimes from alluvial‐fan morphology and stratigraphy and (3) provide a conceptual basis for hazard zonation on alluvial fans. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

16.
Comparison of the responses of three drainage basins burned by the Dome fire of 1996 in New Mexico is used to identify the hillslope, channel and fire characteristics that indicate a susceptibility specifically to wildfire‐related debris flow. Summer thunderstorms generated three distinct erosive responses from each of three basins. The Capulin Canyon basin showed widespread erosive sheetwash and rilling from hillslopes, and severe flooding occurred in the channel; the North Tributary basin exhibited extensive erosion of the mineral soil to a depth of 5 cm and downslope movement of up to boulder‐sized material, and at least one debris flow occurred in the channel; negligible surface runoff was observed in the South Tributary basin. The negligible surface runoff observed in the South Tributary basin is attributed to the limited extent and severity of the fire in that basin. The factors that best distinguish between debris‐flow producing and flood‐producing drainages are drainage basin morphology and lithology. A rugged drainage basin morphology, an average 12 per cent channel gradient, and steep, rough hillslopes coupled with colluvium and soil weathered from volcaniclastic and volcanic rocks promoted the generation of debris flows. A less rugged basin morphology, an average gradient of 5 per cent, and long, smooth slopes mantled with pumice promoted flooding. Flood and debris‐flow responses were produced without the presence of water‐repellent soils. The continuity and severity of the burn mosaic, the condition of the riparian vegetation, the condition of the fibrous root mat, accumulations of dry ravel and colluvial material in the channel and on hillslopes, and past debris‐flow activity, appeared to have little bearing on the distinctive responses of the basins. Published in 2000 by John Wiley & Sons, Ltd.  相似文献   

17.
  相似文献   

18.
Inter‐basin differences in streamflow response to changes in regional hydroclimatology may reflect variations in storage characteristics that control the retention and release of water inputs. These aspects of storage could mediate a basin's sensitivity to climate change. The hypothesis that temporal trends in stream baseflow exhibit a more muted reaction to changes in precipitation and evapotranspiration for basins with greater storage was tested on the Oak Ridges Moraine (ORM) in Southern Ontario, Canada. Long‐term (>25 years) baseflow trends for 16 basins were compared to corresponding trends in precipitation amount and type and in potential evapotranspiration as well as shorter trends in groundwater levels for monitoring wells on the ORM. Inter‐basin differences in storage properties were characterized using physiographic, hydrogeologic, land use/land cover, and streamflow metrics. The latter included the slope of the basin's flow duration curve and basin dynamic storage. Most basins showed temporal increases in baseflow, consistent with limited evidence of increases and decreases in regional precipitation and snowfall: precipitation ratio, respectively, and recent increases in groundwater recharge along the crest of the ORM. Baseflow trend magnitude was uncorrelated to basin physiographic, hydrogeologic, land use/land cover, or flow duration curve characteristics. However, it was positively related to a basin's dynamic storage, particularly for basins with limited coverage of open water and wetlands. The dynamic storage approach assumes that a basin behaves as a first‐order dynamical system, and extensive open water and wetland areas in a basin may invalidate this assumption. Previous work suggested that smaller dynamic storage was linked to greater damping of temporal variations in water inputs and reduced interannual variability in streamflow regime. Storage and release of water inputs to a basin may assist in mediating baseflow response to temporal changes in regional hydroclimatology and may partly account for inter‐basin differences in that response. Such storage characteristics should be considered when forecasting the impacts of climate change on regional streamflow.  相似文献   

19.
The relative importance of tectonics, climate, base level and source lithology as primary factors on alluvial‐fan evolution, fan morphology and sedimentary style remain in question. This study examines the role of catchment lithology on development and evolution of alluvial megafans (>30 km in length), along the flanks of the Kohrud Mountain range, NE Esfahan, central Iran. These fans toe out at axial basin river and playa‐fringe sediments towards the centre of basin and tectonics, climatic change and base‐level fluctuations, were consistent for their development. They formed in a tectonically active basin, under arid to semiarid climate and a long term (Plio‐Pleistocene to Recent) change from wetter to drier conditions. The key differences between two of these fans, Soh and Zefreh fans, along the west and south flanks of this mountain range, is that their catchments are underlain by dissimilar bedrock types. The source‐area lithologies of the Soh and Zefreh fans are in sedimentary and igneous terrains, respectively, and these fans developed their geometry mainly in response to different weathering intensities of their catchment bedrock lithologies. Fan surface mapping (based on 1/50000 topographic maps, satellite images, and fieldwork), reveals that the geomorphic evolution of these fans differs in that the relatively large‐scale incision and through trenching of the Soh fan is absent in the Zefreh fan. Whereas the limited sediment supply of the Soh fan has resulted in a deep incised channel, the Zefreh fan has remained aggradational with little or no trenching into proximal to medial fan surface due to its catchment bedrock geology, composed mainly by physically weathered volcaniclastic lithology and characterized by high sediment supply for delivery during episodic flash floods. Sediment supply, which is mainly a function of climate and source lithology, is a dominant driver behind the development of fan sequences in alluvial megafans. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

20.
Alluvial fans at tributary junctions modulate sediment flux through river networks, by buffering the mainstem channel from disturbance in the tributaries. Buffering occurs through the storage (and release) of sediment in fans. Here, we use an extensive historic dataset to characterise the ways in which fan buffering can change as sediment supply varies. In New Zealand's East Coast region, sediment supply and fluvial transport are prolific by global standards. We reconstruct how tributary-junction fans in this region have responded to sediment generated by deforestation and extreme storms. The dynamics of five fans along the Tapuaeroa River are examined for the period 1939–2015. In response to major sediment loading, fans aggraded by up to 12 m and prograded by up to 170 m. Net sediment accumulation ranged from near zero to 1.5×106 m3. Fan size, gradient, sediment storage and buffering were influenced by both upstream and downstream controls. Key upstream (tributary) influences were sediment supply and stream power; downstream (mainstem) influences included distal confinement and, importantly, the nature of fan interaction with the mainstem, which aggraded by up to 6 m. The fans' ability to buffer the Tapuaeroa River from change in the tributaries was largely governed by this downstream interaction: as the mainstem aggraded, it increasingly curtailed fan progradation, thus limiting buffering. Previous studies of tributary-junction fans have related fan morphometry to basin characteristics. However, we find that fan slope and area can vary considerably at decadal, annual or even monthly timescales. Consequently, we suggest that such studies could benefit by examining regional histories of disturbance. © 2019 John Wiley & Sons, Ltd.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号