bluuebunny/crossref_metadata_2025_split huggingface dataset:
Coupling of runoff processes and sediment transport in mountainous watersheds underlain by different sedimentary rocks
Authors: Hattanji Tsuyoshi , Onda Yuichi 
Published: March 2004

AbstractRunoff and sediment transport were observed in two mountainous watersheds with different lithologies. One watershed is underlain by chert and the other by sandstone and shale. The chert watershed consists of bedrock cliffs and shallow regolith (0–2 m), whereas the sandstone–shale watershed is covered with a deeper regolith (1–5 m). In the sandstone–shale watershed, a large spring located in the channel head contributed to storm runoff. Tensiometric response in regolith above the spring showed negative pressure head throughout storm runoff, thus implying that the subsurface flow in bedrock predominated even during storm runoff. In the chert watershed, the runoff coefficient was larger than in the sandstone–shale watershed. Tensiometric response in regolith showed positive pressure head during storm runoff, indicating generation of rapid subsurface stormflow. Concentration of subsurface flow from side slopes increased peak streamflow in the downstream direction. In these two watersheds, different subsurface flowpaths, including bedrock fractures, facilitated different modes of sediment transport. Groundwater outflow at the spring caused seepage erosion in the sandstone–shale watershed, whereas peak streamflow transported bedload supplied by rockfall in the chert watershed. Copyright © 2004 John Wiley & Sons, Ltd.
Sources of suspended sediment within a tropical catchment recovering from selective logging
Authors: Chappell Nick A. , Douglas Ian , Hanapi Jamal Mohd , Tych Wlodek 
Published: March 2004

AbstractQuantification of the source of suspended sediments generated by selective forestry activities is central to the development of sustainable forestry guidelines. This assessment is hampered by a dearth of available studies, particularly from the tropics. This study involved the monitoring (at 10 s intervals) of surface discharge and turbidity from 15 contributory areas of a 44 ha catchment. The catchment is located within lowland dipterocarp rain forest on Borneo Island, in a region recovering from the first episode of selective timber removal that took place some 5 years previously. Both the within‐storm dynamics of the sediment flux and the time‐integrated sediment yields were analysed to link the source landforms to the catchment behaviour.A 10 year rainfall event of 167 mm occurred during the monitoring period and triggered a debris slide and several log‐culvert collapses along the area's main timber haulage road. The sampling design captured this event's dynamics and allowed lumped catchment response to be traced to the new landforms. During the 1 day period of the 10 year event, some 33 t of suspended sediment were transported from one debris slide, comprising a significant proportion of the 105 t discharging from the whole catchment, which itself constituted 40% of the annual yield of 592 t km−2. The contributory areas with only ephemeral waterflows, including former haulage roads and tracks, generated relatively little sediment during this 10 year event or in other storms. This work suggests that though some sediment sources recover from the impacts of forest road construction and harvesting, collapse of roadfill materials or more local log‐culvert failure persists for several years after harvesting. Sustainable forestry guidelines that do not focus on ameliorating these persistent instabilities may not significantly mitigate the geomorphic impacts of conventional, selective harvesting. Copyright © 2004 John Wiley & Sons, Ltd.
Theoretical research on the relationship between return period of rainfall and shallow landslides
Authors: Iida Tomoyuki 
Published: March 2004

AbstractA hydrogeomorphological model for shallow landslide prediction that considers both the stochastic character of rainfall intensity and duration and the deterministic aspects controlling slope stability is presented. The probability of shallow subsurface flow (i.e. the process triggering shallow landsliding) is expressed by a lognormal distribution. The short‐term probability of landsliding is defined as the probability that the saturated depth exceeds a critical value. The average recurrence interval of landsliding Tav can be defined as the expected value of the recurrence interval of landsliding. This model was applied to a field site in Japan where extensive shallow landsliding occurred as a consequence of a heavy rainstorm in 1988. A digital elevation model was utilized to calculate Tav for every grid cell. It was found that Tav is a useful index to correlate to the susceptibility to shallow landsliding. A time series of landsliding was then simulated using this model. A series of values of return periods of rainfall (and, consequently, of saturated throughflow) were randomly generated for 10 000 years (one rainstorm event per year). It was found that the spatial extent of landsliding (expressed as a percentage of scar area) associated with each rainstorm event was strongly influenced not only by rainfall, but also by the historical sequence of landsliding. The effective return period of rainfall for shallow landsliding was then estimated using the same model. It was found that rainfall events with return periods <500 years and <1000 years trigger about 50% and 65% respectively of the total number of landslides over the long term. Copyright © 2004 John Wiley & Sons, Ltd.
Hydrogeomorphology: overview of an emerging science
Authors: Sidle Roy C. , Onda Yuichi 
Published: March 2004

AbstractHere, we introduce a series of 14 papers generated from a symposium related to hydrogeomorphology that was part of the Fifth International Conference on Geomorphology. Additionally, recent developments in hydrogeomorphology are highlighted, particularly with respect to research in Japan. Linkages are drawn between natural hazards and the necessity to focus on hydrogeomorphic processes. Future research needs are discussed in the areas of temporal and spatial patterns of water and sediment dynamics, including the effects of distributed land management practices and interactions with natural hazards. Copyright © 2004 John Wiley & Sons, Ltd.
Suspended solids discharge from a small forested basin in the humid tropics
Authors: Sammori Toshiaki , Yusop Zulkifli , Kasran Baharuddin , Noguchi Shoji , Tani Makoto 
Published: March 2004

AbstractSuspended solids (SS) discharge from a tropical rain forest was observed at the Bukit Tarek Experimental Watershed in Peninsular Malaysia in order to elucidate mechanisms of SS production and transport. Peaks of water discharge and electrical conductivity (EC) lagged further behind rainfall peaks than did dissolved oxygen (DO), indicating that the discharge in the early stage of a storm is mainly formed by rain water with high DO. Stream water showing a high value of EC originating from subsurface water formed the main storm flow and lagged behind the rainfall. SS concentrations rose to a peak quickly and, like DO, the peak preceded that of water discharge. A clockwise hysteresis loop in the relationship between SS and water discharge exists, and the magnitude of hysteresis loop is in proportion to storm size. The values of SS concentration correlate positively with the values of rainfall intensity on logarithmic axes. The time intervals between peaks of rainfall and SS concentrations are assumed to be a delivery term expressing distance from sediment source to measuring point. Immediate transport of SS from the source to the sampling site, the short time gap between the peaks of rainfall and SS concentrations, and the high rate of infiltration on the hillslope suggest that the sources of high SS concentrations are located close to the stream. The calculated source area is located at a gentler part of the stream, where wet riparian areas exist. The strong relationship between water discharge and SS concentration during the small storm proves that the source areas of SS and water were the same. In contrast, the source area of SS disappeared when rainfall ceased, whereas the source area of water discharge was still expanding in the larger storm. These phenomena may produce clockwise loops in the SS concentration–water discharge relationship. Copyright © 2004 John Wiley & Sons, Ltd.
The role of subsurface water flow paths on hillslope hydrological processes, landslides and landform development in steep mountains of Japan
Authors: Onda Yuichi , Tsujimura Maki , Tabuchi Hidekazu 
Published: March 2004

AbstractHydrological monitoring was conducted in high‐relief watersheds in the Japan Alps to investigate the relationship between hillslope hydrological processes and landform evolution in steep granite and shale mountains. In the Koshibu watershed, underlain by Mesozoic shale, the drainage density and frequency was significantly lower than in the Yotagiri watershed underlain by granite. Drainage micro‐morphology analysis showed that hillslopes in the watersheds K1 and K6 (Koshibu basin) are mostly combinations of talus and bedrock exposures. In contrast, watershed Y1 (Yotagiri basin) is composed of several zero‐order streams with hollows. Infinite slope stability analysis indicates that the regolith shear strength in the K6 watershed (Koshibu basin) is lower than that of the Y1 hillslope, but groundwater levels were higher in the Y1 hillslope than in the K6 hillslope during storm events. These data suggest that, although the shear strength of the soil is stronger in the Yotagiri watershed, the slopes are unstable because of the groundwater conditions, whereas deep‐seated landslides may occur episodically in the Koshibu watershed associated with extreme storms and very high antecedent soil moisture. These differences would strongly contribute to the different observed hillslope processes and drainage characteristics. Copyright © 2004 John Wiley & Sons, Ltd.
Landslides in Rio de Janeiro: The role played by variations in soil hydraulic conductivity
Authors: Vieira Bianca Carvalho , Fernandes Nelson Ferreira 
Published: March 2004

AbstractLandslides are natural processes triggered by complex relationships between many conditioning factors. In Rio de Janeiro city, intense rainstorms combined with steep slopes, usually occupied by slums, create favourable conditions for landslide generation. In general, slope failures are related to high positive pore‐pressures inside soil mantles, which are associated with topographic hollows and hydraulic discontinuities inside the deep weathered profile.This study aims to characterize the role played by spatial variations in saturated soil hydraulic conductivity Ksat on landsliding in the Papagaio Basin (2·5 km2), triggered by intense rainstorms (250 mm in less than 2 days) in February 1996. Field measurements, using the Guelph permeameter, were conducted along soil profiles (up to 5·0 m depth), around and inside landslide scars representing different geomorphological domains. Also, soil physical properties (grain size, total porosity, macroporosity, microporosity, etc.) were evaluated at the 87 sites where Ksat was measured.Despite the many geological and pedological variations inside the basin, including changes in lithology, fracture density, vegetation type and succession stage, soil characteristics and weathering stage, and human activities, 94% of the Ksat values varied by only two orders of magnitude (1·0 × 10−6–9·0 × 10−5 m s−1). However, abrupt changes in Ksat were observed along some of the soil profiles studied, e.g. an increase of two orders of magnitude in only 0·30 m. These hydraulic discontinuities may contribute locally to the development of high pore pressures during intense rainstorms, leading to landsliding. The results also suggest that different Ksat variation patterns coexist inside the basin, which should be considered in mathematical models of landslide prediction. Copyright © 2004 John Wiley & Sons, Ltd.
Sediment pathways in a tropical forest: effects of logging roads and skid trails
Authors: Sidle Roy C. , Sasaki Shozo , Otsuki Mieko , Noguchi Shoji , Rahim Nik Abdul 
Published: March 2004

AbstractSignificant erosion occurred from recently constructed forest logging roads and skid trails in a small headwater catchment in Peninsular Malaysia. Soil loss was estimated by measuring dimensions of all significant rills and gullies along the road, as well as by measuring height of preserved soil pedestals in sidecast and fill material and on skid trails. Estimates of surface erosion from logging roads and skid trails were 272 ± 20 t ha−1year−1and 275 ± 20 t ha−1year−1respectively. However, owing to lack of connectivity of skid trails to the stream, much of the sediment mobilized on skid trails was stored either on adjacent hillslopes or the trails themselves, rather than being transported to the stream system, as was the case for the road. Steeper skid trails (>20% gradient) had slightly higher erosion rates (320 ± 24 t ha−1year−1) than trails with gentler gradients (245–264 t ha−1year−1). Some 60% of the soil loss on logging roads comes from erosion of the running surface. Disturbed cut and fill material along the road supplied the remaining 40% of the soil loss from roads. Roads and skid trails had no designed drainage systems; runoff discharged onto the hillslope at 25 major discharge nodes from the logging road (690 m total length) and at 34 nodes from skid trails (2300 m). Sediment pathways were either fully or moderately connected to headwater channels at 64% of the logging road nodes, but at only 26% of the nodes emanating from skid trails. A detailed sediment budget revealed that 78% of the soil loss from the road system (including log landings) was delivered to the stream in the first 16 months after logging began. Most (90%) of the deposition from skid trails occurred below just three discharge nodes. Runoff from and onto skid trails often exacerbated the sediment connectivity to channels. Clearly, sediment discharge from logging roads was more highly connected to the stream than discharge from skid trails. Once in the channel, much of this sediment was temporarily stored in the floodplain and behind woody debris. Copyright © 2004 John Wiley & Sons, Ltd.
Distributed simulations of landslides for different rainfall conditions
Authors: Dhakal Amod S. , Sidle Roy C. 
Published: March 2004

AbstractA physically based distributed slope stability model is described that utilizes a combined surface–subsurface kinematic wave module to assess groundwater fluctuations related to slope stability. A total of 82 major rainstorms from 1972 to 1990 in Carnation Creek, British Columbia, were examined to determine the influence of different characteristics of rainstorms (such as mean and maximum hourly intensity, duration, and rainfall amount) on the slope stability. These rainstorms vary in mean intensity from 1·6 to 11·2 mm h−1, storm duration from 11 to 93 h, and maximum hourly intensity from 3·4 to 35 mm h−1. Four synthetic ‘uniform intensity’ rainstorms were also tested against real storms to assess the effect of short‐term hourly rainfall intensity peaks on landslide occurrence. Altogether, 602 simulations were conducted. The combined influence of mean and maximum hourly intensity, duration, and total rainfall amount of rainstorms were important in generating landslides. The temporal distribution of short‐term intensity also influenced the landslide occurrence. When saturated hydraulic conductivity of the soil was lowered or soil depth was raised, most rainstorms produced larger numbers of landslides. For the most part, actual rainstorms produced less stable conditions than their synthetic ‘uniform intensity’ counterparts. For all landslide‐producing storms, slope failure usually occurred after some threshold of cumulative rainfall and maximum hourly rainfall intensity. These simulations provide insights into the distributed behaviour of landslide occurrence during large rainstorms with varying characteristics. Copyright © 2004 John Wiley & Sons, Ltd.
Hydrogeomorphic linkages of sediment transport in headwater streams, Maybeso Experimental Forest, southeast Alaska
Authors: Gomi Takashi , Sidle Roy C. , Swanston Douglas N. 
Published: March 2004

AbstractHydrogemorphic linkages related to sediment transport in headwater streams following basin wide clear‐cut logging on Prince of Wales Island, southeast Alaska, were investigated. Landslides and debris flows transported sediment and woody debris in headwater tributaries in 1961, 1979, and 1993. Widespread landsliding in 1961 and 1993 was triggered by rainstorms with recurrence intervals (24 h precipitation) of 7·0 years and 4·2 years respectively. Occurrence, distribution, and downstream effects of these mass movements were controlled by landform characteristics such as channel gradient and valley configuration. Landslides and channelized debris flows created exposed bedrock reaches, log jams, fans, and abandoned channels. The terminus of the deposits did not enter main channels because debris flows spread and thinned on the unconfined bottom of the U‐shaped glaciated valley. Chronic sediment input to channels included surface erosion of exposed till (rain splash, sheet erosion, and freeze–thaw action) and bank failures. Bedload sediment transport in a channel impacted by 1993 landslides and debris flows was two to ten times greater and relatively finer compared with bedload transport in a young alder riparian channel that had last experienced a landslide and debris flow in 1961. Sediment transport and storage were influenced by regeneration of riparian vegetation, storage behind recruited woody debris, development of a streambed armour layer, and the decoupling of hillslopes and channels. Both spatial and temporal variations of sediment movement and riparian condition are important factors in understanding material transport within headwaters and through channel networks. Copyright © 2004 John Wiley & Sons, Ltd.
Numerical calculation of soil pipe flow and its effect on water dynamics in a slope
Authors: Kosugi Ken'ichirou , Uchida Taro , Mizuyama Takahisa 
Published: March 2004

AbstractA chain of connected macropores, which develops nearly parallel to the impermeable subsurface layer, is commonly found in hillslopes and referred to as a soil pipe. Field observations have revealed that water flow in such a pipe (pipe flow) has large hydrogeomorphic effects, since it contributes to rapid transfer of storm water and subsurface soil erosion. This study proposed a simple simulation method to describe water dynamics in a piped hillslope. The applicability of the method was examined using data obtained from a bench‐scale experiment using pseudo soil pipes. Results of the experiment showed that (1) the flume‐bed pore water pressure became small around the upper ends of the pipes; (2) when pipe outlets were connected to a stream channel (the open pipe condition), the flume‐bed pore water pressures in the whole slope were much lower than those under the ‘no pipe’ condition; (3) when pipe outlets were not connected to a stream channel (the closed pipe condition), the flume‐bed pore water pressure at the pipe outlets was higher than that under the ‘no pipe’ condition. These results were reproduced by solving the two‐dimensional Richards equation assuming an equivalent soil matrix layer for the original ‘pipes plus soil matrix’ part, which had a larger saturated hydraulic conductivity than the surrounding soil matrix. This simple simulation method has an advantage over previous pipe flow models: both the pipe flow and the interaction between the soil pipes and the surrounding soil matrix can be computed by solving the Richards equation without using any further assumptions for the boundary conditions between the soil pipes and the soil matrix. Results of numerical experiments using the simple method showed that (1) under the closed pipe condition, the flume‐bed pore water pressure at the pipe outlets increased as the pipe length increased, and (2) once the open pipes clogged, flume‐bed pore water pressures in the whole slope increased, and the greatest increase occurred at the boundary between the clogging and non‐clogging parts. Copyright © 2004 John Wiley & Sons, Ltd.
A geomorphological explanation of the unit hydrograph concept
Authors: Cudennec C. , Fouad Y. , Sumarjo Gatot I. , Duchesne J. 
Published: March 2004

AbstractThe water path from any point of a basin to the outlet through the self‐similar river network was considered. This hydraulic path was split into components within the Strahler ordering scheme. For the entire basin, we assumed the probability density functions of the lengths of these components, reduced by the scaling factor, to be independent and isotropic. As with these assumptions, we propose a statistical physics reasoning (similar to Maxwell's reasoning) that considers a hydraulic length symbolic space, built on the self‐similar lengths of the components. Theoretical expressions of the probability density functions of the hydraulic length and of the lengths of all the components were derived. These expressions are gamma laws expressed in terms of simple geomorphological parameters. We validated our theory with experimental observations from two French basins, which are different in terms of size and relief. From the comparisons, we discuss the relevance of the assumptions and show how a gamma law structure underlies the river network organization, but under the influence of a strong hierarchy constraint. These geomorphological results have been translated into travel time probability density functions, through the hydraulic linear hypothesis. This translation provides deterministic explanations of some famous a priori assumptions of the unit hydrograph and the geomorphological unit hydrograph theories, such as the gamma law general shape and the exponential distribution of residence time in Strahler states. Copyright © 2004 John Wiley & Sons, Ltd.
Explaining the internal behaviour of artificial neural network river flow models
Authors: Sudheer K. P. , Jain Ashu 
Published: March 2004

AbstractA novel method of visualizing and understanding the internal functional behaviour of an artificial neural network (ANN) river flow model is presented. The method hypothesizes that an ANN is able to map a function similar to the flow duration curve while modelling the river flow. A mathematical analysis of the hypothesis is presented, and a case study of an ANN river flow model confirms its significance. The proposed approach is also useful within other models that improve the performance of an ANN. The reasons why these models improve a raw ANN can be clearly understood using this approach. While the field of ANN knowledge‐extraction is one that continues to attract considerable interest, it is anticipated that the current approach will initiate further research and make ANNs more useful to the hydrologic community. Copyright © 2004 John Wiley & Sons, Ltd.