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1.
Landslide erosion is a dominant hillslope process and the main source of stream sediment in tropical, tectonically active mountain belts. In this study, we quantified landslide erosion triggered by 24 rainfall events from 2001 to 2009 in three mountainous watersheds in Taiwan and investigated relationships between landslide erosion and rainfall variables. The results show positive power‐law relations between landslide erosion and rainfall intensity and cumulative rainfall, with scaling exponents ranging from 2·94 to 5·03. Additionally, landslide erosion caused by Typhoon Morakot is of comparable magnitude to landslide erosion caused by the Chi‐Chi Earthquake (MW = 7·6) or 22–24 years of basin‐averaged erosion. Comparison of the three watersheds indicates that deeper landslides that mobilize soil and bedrock are triggered by long‐duration rainfall, whereas shallow landslides are triggered by short‐duration rainfall. These results suggest that rainfall intensity and watershed characteristics are important controls on rainfall‐triggered landslide erosion and that severe typhoons, like high‐magnitude earthquakes, can generate high rates of landslide erosion in Taiwan. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

2.
Extreme sedimentation in Swift Creek, located in the Cascades foothills in NW Washington (48°55′N, 122°16′W), results from erosion of the oversteepened, unvegetated toe of a large (55 hectares) active landslide. Deposition of landslide‐derived sediment has necessitated costly mitigation projects in the channel including annual dredging and temporary sediment traps in an attempt to reduce the risk of flooding and damage to man‐made structures downstream. This study attempts to understand the process of sediment production along with the corresponding erosion rates of the sediment source to help with the development of mitigation plans and construction of optimal sediment reservoirs. The bedload and suspended sediment in the creek are a direct result of the weathering process of the serpentinitic bedrock underlying the landslide. The serpentinite does not weather to smectite clay, as previously thought. Instead, it weathers to asbestiform chrysotile with minor amounts of chlorite, illite and hydrotalcite, all of which occur in clay seeps on the unvegetated surface of the landslide. The chrysotile fibers average 2 µm in length and make up at least 50%, by volume, of the suspended load transported in Swift Creek. This study does not address the environmental or health implications of the asbestiform chrysotile transport or deposition. During the sampled time between February 2005 and February 2006, 127 discrete suspended sediment samples were collected and discharge was measured 66 times. The suspended sediment concentrations ranged from 0·02 g L?1 to 41·6 g L?1 and the discharge ranged from 0·0 m3 s?1 to 0·5 m3 s?1. A nonlinear functional model estimated the total suspended sediment flux from detailed precipitation records and discrete suspended sediment concentration and discharge measurements to be 910 t km?2 yr?1. When the suspended sediment flux is coupled with estimates of downstream deposition of coarse sediment, the estimated erosion rate for the entire Swift Creek landslide is 158 mm yr?1. The majority of the material entering Swift Creek is presumed to originate on the unvegetated toe of the landslide, for which the erosion rate is thus approximately 1 m yr?1. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

3.
The ongoing debate over the effects of global environmental change on Earth's cryosphere calls for detailed knowledge about process rates and their variability in cold environments. In this context, appraisals of the coupling between glacier dynamics and para‐glacial erosion rates in tectonically active mountains remain rare. We contribute to filling this knowledge gap and present an unprecedented regional‐scale inventory of supra‐glacial sediment flux and hillslope erosion rates inferred from an analysis of 123 large (> 0·1 km2) catastrophic bedrock landslides that fell onto glaciers in the Chugach Mountains, Alaska, as documented by satellite images obtained between 1972 to 2008. Assuming these supra‐glacial landslide deposits to be passive strain markers we infer minimum decadal‐scale sediment yields of 190 to 7400 t km–2 yr–1 for a given glacier‐surface cross‐section impacted by episodic rock–slope failure. These rates compare to reported fluvial sediment yields in many mountain rivers, but are an order of magnitude below the extreme sediment yields measured at the snouts of Alaskan glaciers, indicating that the bulk of debris discharged derives from en‐glacial, sub‐glacial or ice‐proximal sources. We estimate an average minimum para‐glacial erosion rate by large, episodic rock–slope failures at 0·5–0·7 mm yr–1 in the Chugach Mountains over a 50‐yr period, with earthquakes likely being responsible for up to 73% of this rate. Though ranking amongst the highest decadal landslide erosion rates for this size of study area worldwide, our inferred rates of hillslope erosion in the Chugach Mountains remain an order of magnitude below the pace of extremely rapid glacial sediment export and glacio‐isostatic surface uplift previously reported from the region. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

4.
Extreme erosion events can produce large short-term sediment fluxes. Such events complicate erosion rates estimated from cosmogenic nuclide concentrations in river sediment by providing sediment with a concentration different from the long-term basin average. We present a detrital 10Be study in southern Taiwan, with multiple samples obtained in a time sequence bracketing the 2009 Typhoon Morakot, to assess the impact of landslide sediment on 10Be concentrations (N10Be) in river sediment. Sediment samples were collected from 13 major basins, two or three times over the last decade, to observe the temporal variation of N10Be. Landslide inventories with time intervals of 5–6 years were used to quantify sediment flux changes. A negative correlation between N10Be and landslide areal density indicates dilution of N10Be by landslide sediment. Denudation rates estimated from the diluted N10Be can be up to three times higher than the lowest rate derived from the same basins. Observed increases imply that, 3 years after the passage of Typhoon Morakot, fluvial channels still contain a considerable amount of sediment provided by hillslope landslides during the event. However, higher N10Be in 2016 samples indicate that the contribution from landslide sediment at the sampled grain size has decreased with time. The correlation between changes in N10Be and landslide area and volume is not strong, likely resulting from the stochastic and complex nature of sediment transport. To simultaneously evaluate the volume of landslide-derived sediment and estimate the background denudation rate, associated with less impulsive sediment supply, we constructed a sediment-mixing model with the time series of N10Be and landslide inventories. The spatial pattern of background erosion rate in southern Taiwan is consistent with the regional tectonic framework, indicating that the landscape is evolving mainly in response to the tectonic forcing, and this signal is modified, but not obscured by impulsive sediment supply. © 2019 John Wiley & Sons, Ltd.  相似文献   

5.
This study investigates critical run‐off and sediment production sources in a forested Kasilian watershed located in northern Iran. The Water Erosion Prediction Project (WEPP) watershed model was set up to simulate the run‐off and sediment yields. WEPP was calibrated and validated against measured rainfall–run‐off–sediment data. Results showed that simulated run‐off and sediment yields of the watershed were in agreement with the measured data for the calibration and validation periods. While low and medium values of run‐off and sediment yields were adequately simulated by the WEPP model, high run‐off and sediment yield values were underestimated. Performance of the model was evaluated as very good and satisfactory during the calibration and validation stages, respectively. Total soil erosion and sediment load of the study watershed during the study period were determined to be 10 108 t yr?1 and 8735 t yr?1, respectively. The northern areas of the watershed with dry farming were identified as the critical erosion prone zones. To prioritize the subwatersheds based on their contribution to the run‐off and sediment production at the watershed's main outlet, unit response approach (URA) was applied. In this regard, subwatersheds close to the main outlet were found to have the highest contribution to sediment yield of the whole watershed. Results indicated that depending on the objective of land and water conservation practices, particularly, for controlling sediment yield at the main outlet, critical areas for implementing the best management practices may be identified through conjunctive application of WEPP and URA. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

6.
Sediments produced by landslides are crucial in the sediment yield of a catchment, debris flow forecasting, and related hazard assessment. On a regional scale, however, it is difficult and time consuming to measure the volumes of such sediment. This paper uses a LiDAR‐derived digital terrain model (DTM) taken in 2005 and 2010 (at 2 m resolution) to accurately obtain landslide‐induced sediment volumes that resulted from a single catastrophic typhoon event in a heavily forested mountainous area of Taiwan. The landslides induced by Typhoon Morakot are mapped by comparison of 25 cm resolution aerial photographs taken before and after the typhoon in an 83.6 km2 study area. Each landslide volume is calculated by subtraction of the 2005 DTM from the 2010 DTM, and the scaling relationship between landslide area and its volume are further regressed. The relationship between volume and area are also determined for all the disturbed areas (VL = 0.452AL1.242) and for the crown areas of the landslides (VL = 2.510AL1.206). The uncertainty in estimated volume caused by use of the LiDAR DTMs is discussed, and the error in absolute volume estimation for landslides with an area >105 m2 is within 20%. The volume–area relationship obtained in this study is also validated in 11 small to medium‐sized catchments located outside the study area, and there is good agreement between the calculation from DTMs and the regression formula. By comparison of debris volumes estimated in this study with previous work, it is found that a wider volume variation exists that is directly proportional to the landslide area, especially under a higher scaling exponent. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

7.
Glacier recessions caused by climate change may uncover pro‐glacial lakes that form important sedimentation basins regulating the downstream sediment delivery. The impact of modern pro‐glacial lakes on fluvial sediment transport from three different Norwegian glaciers: Nigardsbreen, Engabreen and Tunsbergdalsbreen, and their long‐term development has been studied. All of these lakes developed in modern times in overdeepened bedrock basins. The recession of Nigardsbreen uncovered a 1.8 km long and on average 15 m deep pro‐glacial lake basin during 1937 to 1968. Since then the glacier front has been situated entirely on land, and the sediment input and output of the lake has been measured. The suspended sediment transport into and out of the lake averaged 11 730 t yr?1 and 2340 t yr?1 respectively. Thus, 20% remained in suspension at the outlet. The measured mean annual bedload supplied to the lake was 11 800 t yr?1, giving a total transport of 23 530 t yr?1 which corresponds to a specific sediment yield of 561 t km?2 yr?1. A 1.9 km long and up to 90 m deep pro‐glacial lake basin downstream from Engabreen glacier was uncovered during 1890 to 1944. The average suspended sediment load delivered from the glacier during the years 1970–1981 amounted to 12 375 t yr?1and the transport out of the lake was 2021 t yr?1, giving an average of 16% remaining in suspension. The mean annual bedload was 8000 t yr?1, thus the total transport was 20 375 t yr?1, giving a specific sediment yield of 566 t km?2 yr?1. For Tunsbergdalsbreen glacier, measurements in the early 1970s indicated that the suspended sediment transport was on average 44 000 t yr?1. From 1987 to 1993 the recession of the glacier uncovered a small pro‐glacial lake, 0.3 km long and around 9 m deep. Downstream from this, the suspended sediment load measured in 2009 was 28 000 t yr?1, indicating that as much as 64% remained in suspension. Flow velocity, grain size of sediment, and morphology of the lake are important factors controlling the sedimentation rate in the pro‐glacial lakes. A survey of the sub‐glacial morphology of Tunsbergdalsbreen revealed that there are several overdeepened basins beneath the glacier. The largest is 4 km long and 100 m deep. When the glacier melts back they will become lakes and act as sedimentation basins. Despite an expected increase in sediment yield from the glacier, little sediment will pass these lakes and downstream sediment delivery will be reduced markedly. Beneath Nigardsbreen there was only a small depression that may form a lake and the sediment delivery will not be significantly affected. © 2014 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

8.
Changes in floodplain sediment dynamics have profound effects on riverine habitats and riparian biodiversity. Depopulation due to socio‐economic changes in the Dragonja catchment (91 km2) in southwestern Slovenia resulted in the abandonment of agricultural fields, followed by natural reforestation since 1945. This profoundly changed the water and sediment supply to the streams, as well as floodplain sediment deposition. This paper presents a reconstruction of the development of the Dragonja floodplain due to these land use changes during the last 60 years. The reconstruction is based on dating of floodplain sediments using 137Cs profiles, measurement of actual sedimentation rates using artificial grass sedimentation mats, and linking this information to the present‐day hydrological behaviour of the river. The sedimentation mats showed that floodplain sedimentation was restricted to peak flows of considerable magnitude. Due to the reforestation, the return period of such high flows increased from 0·31 year in the period 1960–1985 to 0·81 year between 1986 and 2003, with commensurate changes in sedimentation rates. At the 1·5 m river terrace (formed about 60 years ago), 137Cs‐based sedimentation rates (1960–1986) were roughly twice the rates inferred from the artificial grass mats (2001–2003). This finding matches the increase in the return period for larger peak events during the 1986–2003 period, which caused fewer major inundations at this level. Conversely, sedimentation rates determined for the lowest terrace at 0·5 m were similar for both techniques (and periods) because the return periods of the peak events responsible for sediment deposition at this lower level did not change much over the period 1986–2003. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

9.
The primary objective of this study was to compute a detailed budget for a small semiarid tropical drainage basin in Kenya. Results indicated that transfer of sediments (‘inputs’) from primary source areas was minor in comparison to changes in storage. The major sediment source area within the Katiorin drainage basin was the colluvial hillslope zone. The net change in storage within this zone was approximately 2100 Mg yr?1. Surface wash and rilling were the dominant transport processes responsible for the remobilization of colluvial sediments. Sediment storage within the in-channel reservoir increased by 60 Mg yr?1, which was minor when compared to the total store of sediment in this reservoir. During 1986, the channel network stored only a small fraction ( < 3 per cent) of the sediment delivered from the hillslope subsystem. Therefore, the in-channel reservoir had limited influence on sediment conveyance to the basin outlet. These data indicate that a static equilibrium condition cannot be assumed within the Katiorin drainage basin. Such an assumption would result in erosion estimates of approximately 5.5 mm yr?1 for the entire basin (based on a sediment output of 7430 Mg km?2 yr?1 and a measured bulk density of 1.35 Mg m?3). However, this masked the actual rates of 1.2 to 7.1 mm yr?1 in subbasin primary source areas, and rates of 0.6 to 17 mm yr?1 for colluvial material in the various subbasins. The extreme accelerated erosion rates resulted from minimal ground vegetation, steep slopes, soil crust formation, an erodible substrate, and a well-integrated drainage network for rapid conveyance of sediments from the hillslope subsystem to the basin outlet.  相似文献   

10.
This study proposes a sediment‐budget model to predict the temporal variation of debris volume stored in a debris‐flow prone watershed. The sediment‐budget is dominated by shallow landslides and debris outflow. The basin topography and the debris volume stored in the source area of the debris‐flow prone watershed help evaluating its debris‐flow susceptibility. The susceptibility model is applied to the Tungshih area of central western Taiwan. The importance of the debris volume in predicting debris‐flow susceptibility is reflected in the standardized coefficients of the proposed statistical discriminant model. The high prediction rate (0·874) for the occurrence of debris flows justifies the capability of the proposed susceptibility models to predict the occurrence of debris flows. This model is then used to evaluate the temporal evolution of the debris‐flow susceptibility index. The analysis results show that the numbers of watershed which are classified as a debris‐flow group correspond well to storage of sediment at different time periods. These numbers are 10 before the occurrence of Chi‐Chi earthquake, 13 after the occurrence of Chi‐Chi earthquake, 16 after the occurrence of landslides induced by Typhoon Mindulle (Typhoon M), and 14 after the occurrence of debris flows induced by Typhoon M. It indicates that the occurrence of 7·6 Chi‐Chi earthquake had significant impact on the debris flow occurrence during subsequent typhoons. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

11.
The Stavropol region of southern Russia is severely affected by human‐induced gully erosion. A lack of detailed information on the different stages of gully formation resulting from major agricultural expansion c. 100 years ago, is an obstacle for management and containment of these systems. In this study we combine measurements of particle‐bound radionuclides (137Cs, 210Pbex, 226Ra, 232Th and 40K) and classical geomorphology to investigate and reconstruct the different phases of development of a gully during the last c. 100 years. We believe the ?rst phase (1) involved an initial incision into the bottom of a small valley (catchment area c. 1 km2) about 100 years ago. A short period of rapid growth was followed by a longer stage of gully stabilization. Subsequent phases were: (2) the period 1954–1960 – re‐incision in the lower gully reach was initiated by a high‐magnitude rainfall event, and a substantial amount of sediment was delivered to the gully fan; (3) c. 1960–1986 – the knickpoint retreated slowly, sediment was redeposited nearby, and the fan surface became stable; (4) 1986–1987 – a dam was built in the gully mouth and breached shortly after construction following 2 days of high rainfall, and substantial sediment accumulated in the gully above the dam and below the spillway channel on the fan surface; (5) 1987–1993 – the knickpoint retreat continued and the lower fan surface was stable until 1993 when the last signi?cant runoff event overlayed it with c. 10 cm of fresh sediment. These detailed reconstructions of gully development stages allow the contribution of high‐magnitude events to gully growth and regional sediment delivery to be assessed. They further guide management actions to prevent such dam failures in the future. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

12.
Two landsliding episodes between late 1973 and early 1975 delivered about 60000 m3 of sediment to six small deeply incised streams draining a 2·7 km2 area. About 4700 m3 of logs in the landslide debris formed major log jams in five streams, which impounded large volumes of landslide-derived sediment. Five years after the landsliding, 42 per cent (25000 m3) of sediment was still in storage behind 35 log jams ranging from 1·4–8·2 m high. The landsliding episodes have produced multi-stepped stream profiles, aggradation of channel reaches up to 150 m long to mean depths between 1·2 and 4·1 m, reductions in gradient, fining of bed material size, and related changes in bedforms and channel width:depth ratios that seem likely to persist for at least several decades. Sediment presently stored behind log jams is equivalent to between 50 and 220 years normal supply of sediment from hillslopes to stream channels. Long-delayed, large magnitude impacts on higher-order channels may occur if sudden failure of log jams is induced by a large storm at some future date.  相似文献   

13.
Fluvial sediment delivery is the main form of sediment transfer from the land to the sea, but this process is currently undergoing significant variations due to the alteration of catchment and base level controls related to climate change and human activities, especially the widespread construction of dams. Using the lower Wei River as an example and an integrated approach, this study investigates the variation of fluvial sediment delivery, as well as the connectivity under the effects of both controls. Based on hydrological records and channel cross‐section surveys, sediment budgets were constructed for two periods (1960–1970, 1970–1990) after the dam was closed in 1960. In the period 1960–1969, due to the elevated base level (327.2 ± 1.62 m) caused by the dam, the aggradation rate was 0.451 × 108 t yr‐1 in the channel and 0.716 × 108 t yr‐1 on the floodplain, indicating that the positive lateral connectivity between these locations was enhanced. As a consequence, serious sediment storage resulted in a sediment delivery ratio (SDR) that was smaller than that occurring before 1960. In the period 1970–1990, sweeping soil and water conservation (SWC) measures were implemented, resulting in a reduction of the connectivity between the trunk and tributaries, and a decrease of ~31% in the mean sediment input. In addition, together with the base level fluctuation in the range of 327.47 ± 0.49 m, the annual variation in sediment storage was primarily dependent on the water–sediment regime affected by the SWC. The negative lateral connectivity was enhanced between the channel and floodplain via bank erosion. Consequently, the aggradation rate was reduced by 89% on the floodplain and by 96% in the channel. Sediment output continued to decrease primarily due to the SWC practices and climate changes in this period, whereas the SDR increased due to the enhanced longitudinal connectivity between the upstream and downstream. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

14.
Catchment‐scale analyzes of spatial and temporal variability in landscape connectivity are critical considerations in appraisals of landscape evolution and disaster mitigation in tectonically active mountain belts such as Taiwan. This study uses historical aerial photographs, flow discharge and seismic data to analyze landslide changes and channel adjustments over a 30 year period in the Liwu Basin. Recurrent earthquakes and typhoon events trigger frequent landslide activity, channel adjustment and sediment reworking in this system. Spatial variability in magnitude–frequency relations of hillslope‐valley floor (lateral) and upstream–downstream (longitudinal) connectivity during the study period are shown to reflect annual reworking in source and accumulation zones, while partly‐confined valleys in the mid‐catchment area trap sediment behind landslide‐induced dams that are formed and breached on an approximately decadal basis. This promotes partial longitudinal connectivity in these areas. Landscape responses to disturbance events were especially pronounced following combinations of seismic and typhoon events prior to the 1998 and 2005 images. Although single high magnitude events and series of moderate events affect patterns of landscape connectivity in the Liwu Basin, residence times for sediment storage are very short in this highly‐connected river system, where confined valley settings extend virtually to the coast. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

15.
River deltas are the major repositories of terrestrial sediment flux into the world's oceans. Reduction in riverine inputs into the deltas due to upstream damming might lead to a relative dominance of waves, tides and currents that are especially exacerbated by coastal subsidence and sea‐level rise ultimately affecting the delta environment. Analysis of multi‐date satellite imagery and maps covering the Krishna and Godavari deltas along the east coast of India revealed a net erosion of 76 km2 area along the entire 336‐km‐long twin delta coast during the past 43 years (1965–2008) with a progressively increasing rate from 1·39 km2 yr?1 between 1965 and 1990, to 2·32 km2 yr?1 during 1990–2000 and more or less sustained at 2·25 km2 yr?1 during 2000–2008. At present the Krishna has almost become a closed basin with decreased water discharges into the delta from 61·88 km3 during 1951–1959 to 11·82 km3 by 2000–2008; and the suspended sediment loads from 9 million tons during 1966–1969 to as low as 0·4 million tons by 2000–2005. In the case of the Godavari delta, although the water discharge data do not show any major change, there was almost a three‐fold reduction in its suspended sediment loads from 150·2 million tons during 1970–1979 to 57·2 million tons by 2000–2006. A comparison of data on annual sediment loads recorded along the Krishna and Godavari Rivers showed consistently lower sediment quantities at the locations downstream of dams than at their upstream counterparts. Reports based on bathymetric surveys revealed considerable reduction in the storage capacities of reservoirs behind such dams. Apparently sediment retention at the dams is the main reason for the pronounced coastal erosion along the Krishna and Godavari deltas during the past four decades, which is coeval to the hectic dam construction activity in these river basins. Copyright © 2010 John Wiley and Sons, Ltd.  相似文献   

16.
A sediment budget for an upland catchment–reservoir system at Burnhope Reservoir, North Pennines, UK has been developed. This provides a framework for quantifying historic and contemporary sediment yields and drainage basin response to disturbance from climate change and human activities in the recent past. Bathymetric survey, core sampling, 137Cs dating and aerial photographs have been used to assess sediment accumulation in the reservoir. The average reservoir sedimentation rate is 1·24 cm yr?1 (annual sediment yield 33·3 t km?2 yr?1 ± 10%, trap efficiency 92%). Mean annual reservoir sedimentation over the 67 year period has been estimated at 592 t ± 10%. Inputs of suspended sediment from direct catchwater streams account for 54% of sediment supply to the budget (best estimate yield of 318 t yr?1 ± 129%), while those from actively eroding reservoir shorelines contribute 328 t yr?1 ± 92%. Sediment yield estimates from stream monitoring and reservoir sedimentation are an order of magnitude lower than those reported from South Pennine reservoirs of comparable drainage basin area. Analysis of historical rainfall series for the catchment shows fluctuations in winter and summer rainfall patterns over the past 62 years. From 1976 to 1998 there has been a diverging trend between winter and summer rainfall, with a large increase in winter and a gradual decrease in summer totals. Periods of maximum variation occur during the summer drought events of the late 1970s, early 1980s and mid‐1990s. Analysis of the particle size of core sediments highlights abrupt increases in sand‐sized particles in the top 20 cm of the core. Based on the 137Cs chronology, these layers were deposited from the late 1970s onwards and relate to these diverging rainfall records and rapidly fluctuating reservoir levels. This provides evidence of potential sediment reworking within the reservoir by rapid water‐level rise after drought. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

17.
Pikes Peak Highway is a partially paved road between Cascade, Colorado and the summit of Pikes Peak. Significant gully erosion is occurring on the hillslopes due to the concentration of surface runoff, the rearrangement of drainage pathways along the road surface and adjacent drainage ditches, and the high erodibility of weathered Pikes Peak granite that underlies the area. As a result, large quantities of sediment are transported to surrounding valley networks causing significant damage to water quality and aquatic, wetland, and riparian ecosystems. This study establishes the slope/drainage area threshold for gullying along Pikes Peak Highway and a cesium‐137 based sediment budget highlighting rates of gully erosion and subsequent valley deposition for a small headwater basin. The threshold for gullying along the road is Scr = 0 · 21A–0·45 and the road surface reduces the critical slope requirement for gullying compared to natural drainages in the area. Total gully volume for the 20 gullies along the road is estimated at 5974 m3, with an erosion rate of 64 m3 yr–1 to 101 m3 yr–1. Net valley deposition is estimated at 162 m3 yr–1 with 120 m3 yr–1 unaccounted for by gullying. The hillslope–channel interface is decoupled with minimal downstream sediment transport which results in significant local gully‐derived sedimentation. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

18.
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19.
A model‐based method is proposed for improving upon existing threshold relationships which define the rainfall conditions for triggering shallow landslides but do not allow the magnitude of landsliding (i.e. the number of landslides) to be determined. The SHETRAN catchment‐scale shallow landslide model is used to quantify the magnitude of landsliding as a function of rainfall return period, for focus sites of 180 and 45 km2 in the Italian Southern Alps and the central Spanish Pyrenees. Rainfall events with intensities of different return period are generated for a range of durations (1‐day to 5‐day) and applied to the model to give the number of landslides triggered and the resulting sediment yield for each event. For a given event duration, simulated numbers of landslides become progressively less sensitive to return period as return period increases. Similarly, for an event of given return period, landslide magnitude becomes less sensitive to event duration as duration increases. The temporal distribution of rainfall within an event is shown to have a significant impact on the number of landslides and the timing of their occurrence. The contribution of shallow landsliding to catchment sediment yield is similarly quantified as a function of the rainfall characteristics. Rainfall intensity–duration curves are presented which define different levels of landsliding magnitude and which advance our predictive capability beyond, but are generally consistent with, published threshold curves. The magnitude curves are relevant to the development of guidelines for landslide hazard assessment and forecasting. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

20.
Sediment yields were calculated on the ?anks of Merapi and Semeru volcanoes in Java, Indonesia, using two different methods. During the ?rst year following the 22 November 1994 eruption of Merapi, a sediment yield in excess of 1·5 × 105 m3 km?2 yr?1 was calculated in the Boyong River drainage basin, based on the volumes of sediment that were trapped by ?ve check dams. At Semeru, sediment discharges were assessed in the Curah Lengkong River from direct measurements on the lahars in motion and on the most signi?cant stream?ows. The calculated rate of sediment yield during one year of data in 2000 was 2·7 × 105 m3 km?2 yr?1. Sediment yields are dominated by rain‐triggered lahars, which occur every rainy season in several drainage basins of Merapi and Semeru volcanoes, mostly during the rainy season extending from October to April. The return period of lahars carrying sediment in excess of 5 × 105 m3 is about one year in the Curah Lengkong River at Semeru. At Merapi, the volume of sediments transported by a lahar did not exceed 2·8 × 105 m3 in the Boyong River during the rainy season 1994–95. On both volcanoes, the sediments are derived from similar sources: pyroclastic‐?ow/surges deposits, rockfalls from the lava domes, and old material from the riverbed and banks. However, daily explosions of vulcanian type at Semeru provide a more continuous sediment supply than at Merapi. Therefore, sediment yields are larger at Semeru. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

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