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1.
Regional analysis of slope stability is often constrained by availability of data. Model requirements for input data cannot be met at the desired spatial resolution because data are either site‐speci?c or non‐existent. Faced with these dif?culties it has often been the practice to assume that certain parameters are uniform throughout the area of interest. An alternative approach proposed here allows a more detailed discrimination of slope stability conditions. Based on the principles of hillslope hydrology, hydrologic information can be generated at suf?cient resolution to allow higher resolution slope stability analysis. Measurements from an instrumented network in a small area have been used to establish index‐based models for topographic and climate‐related controls of piezometric response. The ability to relate groundwater levels to rainfall and topographic parameters provides a means of up‐scaling to larger catchments and ultimately the opportunity to generate a catchment‐wide prediction of the distribution, magnitude and frequency of rainstorm‐generated groundwater levels. The example provided in this study uses the topography index of TOPMODEL in GIS to predict the spatial patterns of groundwater elevation for seasonal soil moisture conditions and given rainfall inputs. This allows modelling of catchment‐wide response of soil water to rainstorms with different return periods (representing different magnitudes), and is an essential prerequisite for a probabilistic regional slope stability analysis. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

2.
This paper describes an extension to the Combined Hydrology And Stability Model (CHASM) to fully include the effects of vegetation and slope plan topography on slope stability. The resultant physically based numerical model is designed to be applied to site‐specific slopes in which a detailed assessment of unsaturated and saturated hydrology is required in relation to vegetation, topography and slope stability. Applications are made to the Hawke's Bay region in New Zealand where shallow‐seated instability is strongly associated with spatial and temporal trends in vegetation cover types, and the Mid‐Levels region in Hong Kong, an area subject to a variety of landslide mechanisms, some of which may be subject to strong topographic control. An improved understanding of process mechanism, afforded by the model, is critical for reliable and appropriate design of slope stabilization and remedial measures. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

3.
The growing availability of digital topographic data and the increased reliability of precipitation forecasts invite modelling efforts to predict the timing and location of shallow landslides in hilly and mountainous areas in order to reduce risk to an ever‐expanding human population. Here, we exploit a rare data set to develop and test such a model. In a 1·7 km2 catchment a near‐annual aerial photographic coverage records just three single storm events over a 45 year period that produced multiple landslides. Such data enable us to test model performance by running the entire rainfall time series and determine whether just those three storms are correctly detected. To do this, we link a dynamic and spatially distributed shallow subsurface runoff model (similar to TOPMODEL) to an in?nite slope model to predict the spatial distribution of shallow landsliding. The spatial distribution of soil depth, a strong control on local landsliding, is predicted from a process‐based model. Because of its common availability, daily rainfall data were used to drive the model. Topographic data were derived from digitized 1 : 24 000 US Geological Survey contour maps. Analysis of the landslides shows that 97 occurred in 1955, 37 in 1982 and ?ve in 1998, although the heaviest rainfall was in 1982. Furthermore, intensity–duration analysis of available daily and hourly rainfall from the closest raingauges does not discriminate those three storms from others that did not generate failures. We explore the question of whether a mechanistic modelling approach is better able to identify landslide‐producing storms. Landslide and soil production parameters were ?xed from studies elsewhere. Four hydrologic parameters characterizing the saturated hydraulic conductivity of the soil and underlying bedrock and its decline with depth were ?rst calibrated on the 1955 landslide record. Success was characterized as the most number of actual landslides predicted with the least amount of total area predicted to be unstable. Because landslide area was consistently overpredicted, a threshold catchment area of predicted slope instability was used to de?ne whether a rainstorm was a signi?cant landslide producer. Many combinations of the four hydrological parameters performed equally well for the 1955 event, but only one combination successfully identi?ed the 1982 storm as the only landslide‐producing storm during the period 1980–86. Application of this parameter combination to the entire 45 year record successfully identi?ed the three events, but also predicted that two other landslide‐producing events should have occurred. This performance is signi?cantly better than the empirical intensity–duration threshold approach, but requires considerable calibration effort. Overprediction of instability, both for storms that produced landslides and for non‐producing storms, appears to arise from at least four causes: (1) coarse rainfall data time scale and inability to document short rainfall bursts and predict pressure wave response; (2) absence of local rainfall data; (3) legacy effect of previous landslides; and (4) inaccurate topographic and soil property data. Greater resolution of spatial and rainfall data, as well as topographic data, coupled with systematic documentation of landslides to create time series to test models, should lead to signi?cant improvements in shallow landslides forecasting. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

4.
It is critical to understand and quantify the temporal and spatial variability in hillslope hydrological data in order to advance hillslope hydrological studies, evaluate distributed parameter hydrological models, analyse variability in hydrological response of slopes and design efficient field data sampling networks. The spatial and temporal variability of field‐measured pore‐water pressures in three residual soil slopes in Singapore was investigated using geostatistical methods. Parameters of the semivariograms, namely the range, sill and nugget effect, revealed interesting insights into the spatial structure of the temporal situation of pore‐water pressures in the slopes. While informative, mean estimates have been shown to be inadequate for modelling purposes, indicator semivariograms together with mean prediction by kriging provide a better form of model input. Results also indicate that significant temporal and spatial variability in pore‐water pressures exists in the slope profile and thereby induces variability in hydrological response of the slope. Spatial and temporal variability in pore‐water pressure decreases with increasing soil depth. The variability decreases during wet conditions as the slope approaches near saturation and the variability increases with high matric suction development following rainfall periods. Variability in pore‐water pressures is greatest at shallow depths and near the slope crest and is strongly influenced by the combined action of microclimate, vegetation and soil properties. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

5.
Field observations of shoreline conditions at Hyrum Reservoir, Utah, were conducted during the summers of 1991 to 1993. A process of bluff retreat is described for a multiple-layered bluff environment of sand and clay layers. Failure is initiated by wetting and drying of clay sediments, which produces horizontal cracks within bluff material. These cracks appear to penetrate to a depth of approximately 100-150 mm before initiating vertical cracking in the sediments. The vertical cracks are propagated by continued drying of the surface sediment, ultimately leading to failure of the bluff material. The physical dimensions of sediment blocks succumbing to this mechanism range from a few hundred millimetres up to 3 m on a side, with a depth of approximately 100-150 mm. The mechanism described here appears to operate optimally when the supply of subsurface moisture is abundant and nearly continuous throughout the spring and early summer. Reservoir draw-down, large capillary fringe effects in the bluff and periodic wetting from upslope undrained hollows are the dominant moisture controls at this site. Moisture delivery to the face is strongly influenced by anisotropy of saturated hydraulic conductivity in the alternating clay and sand layers and related differences in sediment texture.  相似文献   

6.
Rainfall thresholds for shallow landslide initiation were determined for hillslopes with two types of bedrock, permeable sandstone and impermeable mudstone, in the Boso Peninsula, Japan. The pressure‐head response to rainfall was monitored above a slip scarp due to earlier landslides. Multiple regression analysis estimated the rainfall thresholds for landsliding from the relation between the magnitude of the rainfall event and slope instability caused by the increased pressure heads. The thresholds were expressed as critical combinations of rainfall intensity and duration, incorporating the geotechnical properties of the hillslope materials and also the slope hydrological processes. The permeable sandstone hillslope has a greater critical rainfall and hence a longer recurrence interval than the impermeable mudstone hillslope. This implies a lower potential for landsliding in sandstone hillslopes, corresponding to lower landslide activity. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

7.
Describing the spatial variability of heterogeneous snowpacks at a watershed or mountain‐front scale is important for improvements in large‐scale snowmelt modelling. Snowmelt depletion curves, which relate fractional decreases in snow‐covered area (SCA) against normalized decreases in snow water equivalent (SWE), are a common approach to scale‐up snowmelt models. Unfortunately, the kinds of ground‐based observations that are used to develop depletion curves are expensive to gather and impractical for large areas. We describe an approach incorporating remotely sensed fractional SCA (FSCA) data with coinciding daily snowmelt SWE outputs during ablation to quantify the shape of a depletion curve. We joined melt estimates from the Utah Energy Balance Snow Accumulation and Melt Model (UEB) with FSCA data calculated from a normalized difference snow index snow algorithm using NASA's moderate resolution imaging spectroradiometer (MODIS) visible (0·545–0·565 µm) and shortwave infrared (1·628–1·652 µm) reflectance data. We tested the approach at three 500 m2 study sites, one in central Idaho and the other two on the North Slope in the Alaskan arctic. The UEB‐MODIS‐derived depletion curves were evaluated against depletion curves derived from ground‐based snow surveys. Comparisons showed strong agreement between the independent estimates. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

8.
Understanding flow pathways and mechanisms that generate streamflow is important to understanding agrochemical contamination in surface waters in agricultural watersheds. Two environmental tracers, δ18O and electrical conductivity (EC), were monitored in tile drainage (draining 12 ha) and stream water (draining nested catchments of 6‐5700 ha) from 2000 to 2008 in the semi‐arid agricultural Missouri Flat Creek (MFC) watershed, near Pullman Washington, USA. Tile drainage and streamflow generated in the watershed were found to have baseline δ18O value of ?14·7‰ (VSMOW) year round. Winter precipitation accounted for 67% of total annual precipitation and was found to dominate streamflow, tile drainage, and groundwater recharge. ‘Old’ and ‘new’ water partitioning in streamflow were not identifiable using δ18O, but seasonal shifts of nitrate‐corrected EC suggest that deep soil pathways primarily generated summer streamflow (mean EC 250 µS/cm) while shallow soil pathways dominated streamflow generation during winter (EC declining as low as 100 µS/cm). Using summer isotopic and EC excursions from tile drainage in larger catchment (4700‐5700 ha) stream waters, summer in‐stream evaporation fractions were estimated to be from 20% to 40%, with the greatest evaporation occurring from August to October. Seasonal watershed and environmental tracer dynamics in the MFC watershed appeared to be similar to those at larger watershed scales in the Palouse River basin. A 0·9‰ enrichment, in shallow groundwater drained to streams (tile drainage and soil seepage), of δ18O values from 2000 to 2008 may be evidence of altered precipitation conditions due to the Pacific Decadal Oscillation (PDO) in the Inland Northwest. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

9.
We propose a novel technique for improving a long‐term multi‐step‐ahead streamflow forecast. A model based on wavelet decomposition and a multivariate Bayesian machine learning approach is developed for forecasting the streamflow 3, 6, 9, and 12 months ahead simultaneously. The inputs of the model utilize only the past monthly streamflow records. They are decomposed into components formulated in terms of wavelet multiresolution analysis. It is shown that the model accuracy can be increased by using the wavelet boundary rule introduced in this study. A simulation study is performed to evaluate the effects of different wavelet boundary rules using synthetic and real streamflow data from the Yellowstone River in the Uinta Basin in Utah. The model based on the combination of wavelet and Bayesian machine learning regression techniques is compared with that of the wavelet and artificial neural networks‐based model. The robustness of the models is evaluated. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

10.
Over a period of 12 months, soil moisture content and potential was monitored in an annual‐grass‐dominated 20 ha catchment in order to determine flow paths leading to exfiltration at the catchment outlet. Water was found to enter the catchment valley either through flow originating in the slopes or through surface infiltration during rainfall events. Although subsurface flow from the slopes to the catchment outlet occurred throughout the year, surface recharge was restricted to a few events during the wet season. In the deeper saturated profile of the valley, flow was directed upwards along the valley edges and gradually became horizontal towards the central axis of the valley. During the peak of the rainfall season, horizontal flow close to the catchment outlet intercepted the gradually sloping surface, resulting in exfiltration. Plants influenced the hydrology of the catchment by removing moisture from the root zone during spring and early summer, resulting in evapotranspiration losses from the vadose zone. Heterogeneities within the valley soil were evident as variable‐permeability layers that resulted in a seasonally confined water table within the valley. This investigation shows that the vadose zone plays an important role in redistributing surface recharge and emphasizes the importance of accounting for effective moisture in low‐yielding catchments with ephemeral surface runoff. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

11.
Rain‐on‐snow events have generated major floods around the world, particularly in coastal, mountainous regions. Most previous studies focused on a limited number of major rain‐on‐snow events or were based primarily on model results, largely due to a lack of long‐term records from lysimeters or other instrumentation for quantifying event water balances. In this analysis, we used records from five automated snow pillow sites in south coastal British Columbia, Canada, to reconstruct event water balances for 286 rain‐on‐snow events over a 10‐year period. For large rain‐on‐snow events (event rainfall >40 mm), snowmelt enhanced the production of water available for run‐off (WAR) by approximately 25% over rainfall alone. For smaller events, a range of antecedent and meteorological factors influenced WAR generation, particularly the antecedent liquid water content of the snowpack. Most large events were associated with atmospheric rivers. Rainfall dominated WAR generation during autumn and winter events, whereas snowmelt dominated during spring and summer events. In the majority of events, the sensible heat of rain contributed less than 10% of the total energy consumed by snowmelt. This analysis illustrated the importance of understanding the amount of rainfall occurring at high elevations during rain‐on‐snow events in mountainous regions.  相似文献   

12.
The processes of hillslope runoff and erosion are typically represented at coarse spatial resolution in catchment‐scale models due to computational limitations. Such representation typically fails to incorporate the important effects of topographic heterogeneity on runoff generation, overland flow, and soil erosion. These limitations currently undermine the application of distributed catchment models to understand the importance of thresholds and connectivity on hillslope and catchment‐scale runoff and erosion, particularly in semi‐arid environments. This paper presents a method for incorporating high‐resolution topographic data to improve sub‐grid scale parameterization of hillslope overland flow and erosion models. Results derived from simulations conducted using a kinematic wave overland flow model at 0.5 m spatial resolution are used to parameterize the depth–discharge relationship in the overland flow model when applied at 16 m resolution. The high‐resolution simulations are also used to derive a more realistic parameterization of excess flow shear stress for use in the 16 m resolution erosion model. Incorporating the sub‐grid scale parameterization in the coarse‐resolution model (16 m) leads to improved predictions of overland flow and erosion when evaluated using results derived from high‐resolution (0.5 m) model simulations. The improvement in performance is observed for a range of event magnitudes and is most notable for erosion estimates due to the non‐linear dependency between the rates of erosion and overland flow. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

13.
Reports of abruptly declining flows of Canada's Athabasca River have prompted concern because this large, free‐flowing river could be representative for northern North America, provides water for the massive Athabasca oil‐sands projects and flows to the extensive and biodiverse Peace–Athabasca, Slave and Mackenzie River deltas. To investigate historic hydrology along the river and its major tributaries, we expanded the time series with interpolations for short data gaps; calculations of annual discharges from early, summer‐only records; and by splicing records across sequential hydrometric gauges. These produced composite, century‐long records (1913–2011) and trend detection with linear Pearson correlation provided similar outcomes to nonparametric Kendall τ‐b tests. These revealed that the mountain and foothills reaches displayed slight increases in winter discharges versus larger declines in summer discharges and consequently declining annual flows (~0.16% per year at Hinton; p < 0.01). Conversely, with contrasting boreal contributions, the Athabasca River at Athabasca displayed no overall trend in monthly or annual flows, but there was correspondence with the Pacific Decadal Oscillation that contributed to a temporary flow decline from 1970 to 2000. These findings from century‐long records contrast with interpretations from numerous shorter‐term studies and emphasize the need for sufficient time series for hydrologic trend analyses. For Northern Hemisphere rivers, the study interval should be at least 80 years to span two Pacific Decadal Oscillation cycles and dampen the influence from phase transitions. Most prior trend analyses considered only a few decades, and this weakens interpretations of the hydrologic consequences of climate change. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

14.
High‐resolution, spatially extensive climate grids can be useful in regional hydrologic applications. However, in regions where precipitation is dominated by snow, snowmelt models are often used to account for timing and magnitude of water delivery. We developed an empirical, nonlinear model to estimate 30‐year means of monthly snowpack and snowmelt throughout Oregon. Precipitation and temperature for the period 1971–2000, derived from 400‐m resolution PRISM data, and potential evapotranspiration (estimated from temperature and day length) drive the model. The model was calibrated using mean monthly data from 45 SNOTEL sites and accurately estimated snowpack at 25 validation sites: R2 = 0·76, Nash‐Sutcliffe Efficiency (NSE) = 0·80. Calibrating it with data from all 70 SNOTEL sites gave somewhat better results (R2 = 0·84, NSE = 0·85). We separately applied the model to SNOTEL stations located < 200 and ≥ 200 km from the Oregon coast, since they have different climatic conditions. The model performed equally well for both areas. We used the model to modify moisture surplus (precipitation minus potential evapotranspiration) to account for snowpack accumulation and snowmelt. The resulting values accurately reflect the shape and magnitude of runoff at a snow‐dominated basin, with low winter values and a June peak. Our findings suggest that the model is robust with respect to different climatic conditions, and that it can be used to estimate potential runoff in snow‐dominated basins. The model may allow high‐resolution, regional hydrologic comparisons to be made across basins that are differentially affected by snowpack, and may prove useful for investigating regional hydrologic response to climate change. Published in 2011 by John Wiley & Sons, Ltd.  相似文献   

15.
Interaction between groundwater and surface water in watersheds has significant impacts on water management and water rights, nutrient loading from aquifers to streams, and in‐stream flow requirements for aquatic species. Of particular importance are the spatial patterns of these interactions. This study explores the spatio‐temporal patterns of groundwater discharge to a river system in a semi‐arid region, with methods applied to the Sprague River Watershed (4100 km2) within the Upper Klamath Basin in Oregon, USA. Patterns of groundwater–surface water interaction are explored throughout the watershed during the 1970–2003 time period using a coupled SWAT‐MODFLOW model tested against streamflow, groundwater level and field‐estimated reach‐specific groundwater discharge rates. Daily time steps and coupling are used, with groundwater discharge rates calculated for each model computational point along the stream. Model results also are averaged by month and by year to determine seasonal and decadal trends in groundwater discharge rates. Results show high spatial variability in groundwater discharge, with several locations showing no groundwater/surface water interaction. Average annual groundwater discharge is 20.5 m3/s, with maximum and minimum rates occurring in September–October and March–April, respectively. Annual average rates increase by approximately 0.02 m3/s per year over the 34‐year period, negligible compared with the average annual rate, although 70% of the stream network experiences an increase in groundwater discharge rate between 1970 and 2003. Results can assist with water management, identifying potential locations of heavy nutrient mass loading from the aquifer to streams and ecological assessment and planning focused on locations of high groundwater discharge. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

16.
In North American Land Data Assimilation System Phase 2 (NLDAS‐2) Noah simulation, the NLDAS team introduced an intermediate ‘fix’ to constrain the surface exchange coefficient when the atmospheric boundary layer is stable. In the current NLDAS‐2 Noah version, this fix is used for all stable cases including snow‐free grid cells. In this study, we simply apply this fix to the grid cells in which both stable atmospheric boundary layer and snow exist simultaneously, excluding the snow‐free grid cells as we recognize that the fix in NLDAS‐2 is too strong. We conduct a 31‐year (1979–2009) NLDAS‐2 Noah interim (Noah‐I) run and use observed streamflow, evapotranspiration, land surface temperature, soil temperature, and ground heat flux to evaluate the results, including comparisons with the original NLDAS‐2 Noah run. The results show that Noah‐I has the same performance as NLDAS‐2 Noah for snow water equivalent; however, Noah‐I significantly improved the simulation of other hydrometeorological products as noted earlier when compared with NLDAS‐2 Noah and the observations. This simple modification is being included in the next Noah version used in NLDAS. The hydrometeorological products from the improved NLDAS‐2 Noah‐I are being staged on the National Centers for Environmental Prediction public server. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

17.
Prior to hydrologic modelling, topographic features of a surface are derived, and the surface is divided into sub‐basins. Surface delineation can be described as a procedure, which leads to the quantitative rendition of surface topography. Different approaches have been developed for surface delineation, but most of them may not be applicable to depression‐dominated surfaces. The main objective of this study is to introduce a new depression‐dominated delineation (D‐cubed) method and highlight its unique features by applying it to different topographic surfaces. The D‐cubed method accounts for the hierarchical relationships of depressions and channels by introducing the concept of channel‐based unit (CBU) and its connection with the concept of puddle‐based unit (PBU). This new delineation method implements a set of new algorithms to determine flow directions and accumulations for puddle‐related flats. The D‐cubed method creates a unique cascaded channel‐puddle drainage system based on the channel segmentation algorithm. To demonstrate the capabilities of the D‐cubed method, a small laboratory‐scale surface and 2 natural surfaces in North Dakota were delineated. The results indicated that the new method delineated different surfaces with and without the presence of depressional areas. Stepwise changes in depression storage and ponding area were observed for the 3 selected surfaces. These stepwise changes highlighted the dynamic filling, spilling, and merging processes of depressions, which need to be considered in hydrologic modelling for depression‐dominated areas. Comparisons between the D‐cubed method and other methods emphasized the potential consequences of use of artificial channels through the flats created by the depression‐filling process in the traditional approaches. In contrast, in the D‐cubed method, sub‐basins were further divided into a number of smaller CBUs and PBUs, creating a channel‐puddle drainage network. The testing of the D‐cubed method also demonstrated its applicability to a wide range of digital elevation model resolutions. Consideration of CBUs, PBUs, and their connection provides the opportunity to incorporate the D‐cubed method into different hydrologic models and improve their simulation of topography‐controlled runoff processes, especially for depression‐dominated areas.  相似文献   

18.
Two distributed parameter models, a one‐dimensional (1D) model and a two‐dimensional (2D) model, are developed to simulate overland flow in two small semiarid shrubland watersheds in the Jornada basin, southern New Mexico. The models are event‐based and represent each watershed by an array of 1‐m2 cells, in which the cell size is approximately equal to the average area of the shrubs. Each model uses only six parameters, for which values are obtained from field surveys and rainfall simulation experiments. In the 1D model, flow volumes through a fixed network are computed by a simple finite‐difference solution to the 1D kinematic wave equation. In the 2D model, flow directions and volumes are computed by a second‐order predictor–corrector finite‐difference solution to the 2D kinematic wave equation, in which flow routing is implicit and may vary in response to flow conditions. The models are compared in terms of the runoff hydrograph and the spatial distribution of runoff. The simulation results suggest that both the 1D and the 2D models have much to offer as tools for the large‐scale study of overland flow. Because it is based on a fixed flow network, the 1D model is better suited to the study of runoff due to individual rainfall events, whereas the 2D model may, with further development, be used to study both runoff and erosion during multiple rainfall events in which the dynamic nature of the terrain becomes an important consideration. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

19.
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20.
Within a landform, the channelized water path from any point to the corresponding outlet is split into successive components within the Strahler ordering scheme. The probability density functions (pdf) of the length L of the whole channelized path and of the lengths of the components are studied as multi‐level structural functions. We have considered a granitic area and studied both its main basin and the set of its 48 constituent basins. With respect to the main basin, the pdf of the component lengths exhibit a strong scaling property, except for the highest orders, due to a hierarchical constraint; hence, the pdf of sum L has no particular shape. We have nevertheless identified an underlying structural pattern at particular infra‐ and supra‐basin levels, where the hierarchical constraint is weaker. This identification process entails noting structurally emerging patterns based on multi‐level variables and distributions, which satisfy the general self‐similarity of networks. The fairly good fit of an analytical gamma law with most of these emerging patterns can prove to be a positive step towards both a general modelling approach to the geomorphometric functions and a stronger geomorphological basement of hydrological transfer functions. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

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