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 437 毫秒
1.
A catalogue of historical landslides, 1951–2002, for three provinces in the Emilia‐Romagna region of northern Italy is presented and its statistical properties studied. The catalogue consists of 2255 reported landslides and is based on historical archives and chronicles. We use two measures for the intensity of landsliding over time: (i) the number of reported landslides in a day (DL) and (ii) the number of reported landslides in an event (Sevent), where an event is one or more consecutive days with landsliding. From 1951–2002 in our study area there were 1057 days with 1 ≤ DL ≤?45 landslides per day, and 596 events with 1 ≤ Sevent ≤ 129 landslides per event. In the first set of analyses, we find that the probability density of landslide intensities in the time series are power‐law distributed over at least two‐orders of magnitude, with exponent of about ?2·0. Although our data is a proxy for landsliding built from newspaper reports, it is the first tentative evidence that the frequency‐size of triggered landslide events over time (not just the landslides in a given triggered event), like earthquakes, scale as a power‐law or other heavy‐tailed distributions. If confirmed, this could have important implications for risk assessment and erosion modelling in a given area. In our second set of analyses, we find that for short antecedent rainfall periods, the minimum amount of rainfall necessary to trigger landslides varies considerably with the intensity of the landsliding (DL and Sevent); whereas for long antecedent periods the magnitude is largely independent of the cumulative amount of rainfall, and the largest values of landslide intensity are always preceded by abundant rainfall. Further, the analysis of the rainfall trend suggests that the trigger of landslides in the study area is related to seasonal rainfall. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

2.
The analysis of the positive feedback between landslides and erosion requires determination of the precise temporal and spatial relations between events of colluvium delivery and fluvial erosion. In our study we use decennial datasets on the occurrence of landsliding and erosion achieved through dendrochronological methods. Four sites covering areas of landslide slopes and adjacent valley floors with stream channels were studied. Landsliding on slopes was dated from the tree‐ring eccentricity developed in stems tilted due to bedrock instability. Erosion in channels was dated using the wood anatomy of roots exposed by erosion of the soil cover. Analysis of the temporal relations between dated landsliding, erosion and precipitation record has revealed that two types of repeating sequences can be observed: (1) rainfall → landsliding → erosion; (2) rainfall → erosion → landsliding. These sequences are an indication of the occurrence of slope‐channel positive feedback in the sites studied. In the first type, landsliding triggered by rainfall delivers colluvia into the valley floor and causes its narrowing, which in turn causes increased erosion. In the second type erosion triggered by rainfall disturbs the slope equilibrium and causes landsliding. Landsliding and erosion, once triggered by precipitation, can occur alternately in years with average precipitation and reinforce one another. Bidirectional coupling between landsliding and channel erosion was shown notably through the effects of channel shifting and forced sinuosity and by increased erosion of the slopes opposite the active landslides. Observations also suggest that the repetition of sequences described over longer periods of time can lead to a general widening of the valley floor at the expense of slopes and to a gradual change of the valley cross‐profile from narrow, V‐shaped into a wide flat‐bottomed. Thus landsliding–erosion coupling/positive feedback was recognized as an important factor shaping hillslope–valley topography of the mid‐mountain areas studied. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

3.
Resistance to flow at low to moderate stream discharge was examined in five small (12–77 km2 drainage area) tributaries of Chilliwack River, British Columbia, more than half of which exhibit planar bed morphology. The resulting data set is composed of eight to 12 individual estimates of the total resistance to flow at 61 cross sections located in 13 separate reaches of five tributaries to the main river. This new data set includes 625 individual estimates of resistance to flow at low to moderate river stage. Resistance to flow in these conditions is high, highly variable and strongly dependent on stage. The Darcy–Weisbach resistance factor (ff) varies over six orders of magnitude (0·29–12 700) and Manning's n varies over three orders of magnitude (0·047–7·95). Despite this extreme range, both power equations at the individual cross sections and Keulegan equations for reach‐averaged values describe the hydraulic relations well. Roughness is divided into grain and form (considered as all non‐grain sources) components. Form roughness is the dominant component, accounting for about 90% of the total roughness of the system (i.e., form roughness is on average 8.6 times as great as grain roughness). Of the various quantitative and qualitative form‐roughness indicators observed, only the sorting coefficient (σ = D84/D50) correlates well with form roughness. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

4.
This study examined the temporal dynamics and longitudinal distribution of wood over a multi‐decadal timescale at the river reach scale (36 km) and a meander bend scale (300–600 m) in the Ain River, a large gravel‐bed river flowing through a forested corridor, and adjusting to regulation and floodplain land‐use change. At the 36 km scale, more wood was recruited by bank erosion in 1991–2000 than since the 1950s. The longitudinal distribution of accumulations was similar between 1989 and 1999, but in both years individual pieces occurred homogeneously throughout the reach, while jam distribution was localized, associated with large concave banks. A relationship between the mean number of pieces and the volume recruited by bank erosion (r2 = 0·97) indicated a spatial relationship between areas of wood production and storage. Wood mass stored and produced and channel sinuosity increased from 1993 to 2004 at three meander bends. Sinuosity was related to wood mass recruited by bank erosion during the previous decade (r2 = 0·73) and both of these parameters were correlated to the mean mass of wood/plot (r2 = 0·98 and 0·69 respectively), appearing to control wood storage and delivery at the bend scale. This suggests a local origin of wood stored in channel, not input from upstream trapped by preferential sites. The increase in wood since 1950 is a response to floodplain afforestation, to a change from braided to meandering channel pattern in response to regulation, and to recent large floods. We observed temporal stability of supply and depositional sectors over a decade (on a reach scale). Meander bends were major storage sites, trapping wood with concave banks, also delivering wood. These results, and the link between sinuosity and wood frequency, establish geomorphology as a dominant wood storage and recruitment control in large gravel‐bed rivers. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

5.
The sediment budget of the small research catchment of Cal Parisa (Vallcebre, Eastern Pyrenees) was studied by hydrological monitoring and assessment of the erosion rates in the major sediment sources. This area is characterized by clayey mudrock prone to landsliding and badland erosion, but the catchment was selected in an area free of major badland features, as a representative of middle mountain regions where a system of terraces and drainage ditches had been built for agricultural use but is now abandoned. Streamwater chemistry is dominated by Ca2+ and HCO3− at concentrations close to calcite saturation. Total dissolved solids show dilution during runoff peaks and positive hysteresis loops that support a slow contribution of subsurface water. Relative dissolved ion concentrations are different for each event analysed. Particulate sediment yield is very low and represents only about 1 per cent of gross erosion in the catchment. Mineralogical analysis of suspended sediments shows an enrichment in calcite because of precipitation. Chemical analysis of suspended sediments, using common one-litre water samples, shows higher contents of Ca, P and Mn in transported sediment than in sediment source areas, attributed to the precipitation of calcite, and enrichment in organic particulate matter during events respectively for the two first elements, whereas enrichment in Mn remains uncertain. Solid matter yield is therefore clearly dominated by dissolved transport as a result of both high calcium bicarbonate concentrations in runoff waters and strong suspended sediment conveyance discontinuities. Land conservation structures are very effective because they are in good condition whereas the soil is covered by dense permanent vegetation. Nevertheless, this state is unstable because the network of drainage ditches needs maintenance; its spontaneous breakdown after abandonment may result in the rearrangement of the elementary stream network and gullying of old fields in hollows. © 1997 John Wiley & Sons, Ltd.  相似文献   

6.
Erosion rates surveyed using 230 erosion pins on 24 occasions over eight years (1994–2001) on forested stream banks, tributaries and forest ditches in the 0·89 km2 Nant Tanllwyth catchment, part of the Hafren Forest on Plynlimon, mid‐Wales, showed statistically significant increases of up to 40 mm a?1 in mean erosion rates during the two‐year period in which environmentally sensitive plot‐scale timber harvesting operations took place (1996–97). In the four years following timber harvesting mean erosion rates at all sites recovered to levels that were lower than before the harvesting operations began. This is attributed to increased light levels, following canopy removal, allowing vegetation to colonize exposed banks. There was a statistically significant relationship (p < 0·05) between mean erosion rate in 2000–01 (four years after harvesting) and percentage vegetation cover at erosion monitoring sites in the clearfelled (south tributaries) area though the same relationship did not hold for sites on the mainstream banks or for sites on the north (mature forest) ditch sites. The implications of natural vegetation colonization for management of such streams are discussed. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

7.
Debris flows are among the most destructive and hazardous mass movements on steep mountains. An understanding of debris-flow erosion, entrainment and resulting volumes is a key requirement for modelling debris-flow propagation and impact, as well as analysing the associated risks. As quantitative controls of erosion and entrainment are not well understood, total volume, runout and impact energies of debris flows are often significantly underestimated. Here, we present an analysis of geomorphic change induced by an erosive debris-flow event in the German Alps in June 2015. More than 50 terrestrial laser scans of a 1.2 km long mountain torrent recorded geomorphic change in comparison to an airborne laser scan performed in 2007. Errors were calculated using a spatial variable threshold based on the point density of airborne laser scanning and terrestrial laser scanning and the slope of the digital elevation models. Highest erosion rates approach 5.0 m3/m2 (mean 0.6 m3/m2). During the event 9550 ± 1550 m3 was eroded whereas only 650 ± 150 m3 was deposited in the channel. Velocity, flow pressure, momentum and shear stress were calculated using a carefully calibrated RAMMS Debris Flow model including material entrainment. Here we present a linear regression model relating debris-flow erosion rates to momentum and shear stress with an R2 up to 68%. Channel transitions from bedrock to loose debris sections cause excessive erosion up to 1 m3/m2 due to previously unreleased random kinetic energy now available for erosion. © 2019 John Wiley & Sons, Ltd.  相似文献   

8.
In the last decade, sediment replenishment forming cohesionless sandy banks below dams has become an increasingly common practice in Japan to compensate for sediment deficits downstream. The erosion process of the placed cohesionless sediment is a combination of lateral toe-erosion and the following mass failure. To explore cohesionless bank failure mechanisms, a series of experiments was done in a soil tank using a compacted sandy soil mass exposed to an increasing water level. Two types of uniform sand(D_(50) = 0.40 mm and 0.17 mm) and two bank heights(50 cm and 25 cm) were used under the condition of a constant bank slope of 75°. The three dimensional(3D) geometry of the bank after failure was measured using a handheld 3D scanner. The motion of bank failure was captured using the particle image velocimetry(PIV) technique, and the matric suction was measured by tensiometers. The compacted sandy soil was eroded by loss of matric suction accompanying the rise in water level which subsequently caused rotational slide and cantilever toppling failure due to destabilization of the bank. The effect of erosion protection resulting from the slumped blocks after these failures is discussed in the light of different failure mechanisms. Tensile strength is analyzed by inverse calculation of cantilever toppling failure events. The tensile strength had non-linear relation with degree of saturation and showed a peak.The findings of the study show that it is important to incorporate the non-linear relation of tensile strength into stability analysis of cantilever toppling failure and prediction of tension crack depth within unsaturated cohesionless banks.  相似文献   

9.
River banks are important sources of sediment and phosphorus to fluvial systems, and the erosion processes operating on the banks are complex and change over time. This study explores the magnitude of bank erosion on a cohesive streambank within a small channelized stream and studies the various types of erosion processes taking place. Repeat field surveys of erosion pin plots were carried out during a 4‐year period and observations were supplemented by continuous monitoring of volumetric soil water content, soil temperature, ground water level and exposure of a PEEP sensor. Bank erosion rates (17·6–30·1 mm year?1) and total P content on the banks were relatively high, which makes the bank an important source of sediment and phosphorus to the stream, and it was estimated that 0·27 kg Ptot year?1 ha?1 may potentially be supplied to the stream from the banks. Yearly pin erosion rates exceeding 5 cm year?1 were mainly found at the lower parts of the bank and were associated with fluvial erosion. Negative erosion pin readings were widespread with a net advance of the bank during the monitoring period mainly attributed to subaerial processes and bank failure. It was found that dry periods characterized by low soil water content and freeze–thaw cycles during winter triggered bank failures. The great spatial variability, in combination with the temporal interaction of processes operating at different scales, requires new tools such as 3‐D topographical surveying to better capture bank erosion rates. An understanding of the processes governing bank erosion is required for riparian management using vegetational measures as root size and structure play different roles when it comes to controlling bank erosion processes. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

10.
A combination of numerical analysis and 10Be concentrations measured in sediment samples from the high‐relief Torrente catchment, southern Spain, allows us to investigate the sampling requirements for determining erosion rates using cosmogenic nuclides in high‐relief, landslide‐dominated terrain. We use simple modelling to quantify the effect of particle spalling and/or landsliding on erosion rates determined using a cosmogenic in‐situ produced isotope. Analytical results show that the cosmogenic nuclide concentration of a surface experiencing regular detachment of a grain or block may be considered to be in steady state, and ‘in‐situ’ erosion rates estimated, when an appropriate number of spatially independent samples are amalgamated. We present equations that enable calculation of the number of bedrock samples that must be amalgamated for the estimation of mean erosion rates on an outcrop experiencing regular detachment of a grain or chip of thickness L every T years. Our findings confirm that mean catchment erosion rates may be reliably estimated from 10Be concentrations in fluvial sediment in high‐relief rapidly eroding terrain. These catchment‐wide integrated erosion rates can be calculated where erosion is primarily accomplished through shallow (<3 m) spalling processes; where deep‐seated (>3 m) landslides are the dominant mode of erosion only minimum erosion rates can be determined. Lastly, we present erosion rate measurements from the Torrente catchment that reveal variation of two orders of magnitude (0·03–1·6 m ka?1) quantifying the high degree of spatial variation in erosion rates expected within rapidly uplifting catchments. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

11.
Pan evaporation (Ep) is an important indicator of water and energy and the decline of Ep has been reported in many regions over the last decades. The climate and Ep are dependent on each other. In this study, the temporal trends of Ep and main Ep drivers, namely mean air temperature (Ta), wind speed (u), global solar radiation (Rs), net long‐wave radiation(Rnl) and vapour pressure deficit (D) from 1970 to 2012, were calculated on the basis of 26 meteorological stations on the Tibetan Plateau. The arithmetic average of Ep from 26 stations decreased with the rate of ?11.91 mm a?2; the trends of Rs, Rnl, Ta, u and D were ?1.434 w m?2 decade?1, 0.2511 w m?2 decade?1, 0.3590°C decade?1, ?0.2376 m s?1 decade?1 and 9.523 Pa decade?1, respectively. The diffuse irradiance is an essential parameter to model Ep and quantify the contribution of climatic factors to changing Ep. 60 724 observations of Rs and diffuse solar irradiance (Rd) from seven of the 26 stations were used to develop the correlation between the diffuse fraction (Rd/Rs), and the clearness index (Rs/Ro). On the basis of the estimation of the diffuse component of Rs and climatic data, we modified the PenPan model to estimate Chinese micro‐pan evaporation (Ep) and assess the attribution of Ep dynamics using partial derivatives. The results showed that there was a good agreement between the observed and calculated daily Ep values. The observed decrease in Ep was mostly due to declining wind speed (?13.7 mm a?2) with some contributions from decreasing solar irradiance (?3.1 mm a?2); and the increase of temperature had a large positive effect (4.55 mm a?2) in total whilst the increase of Rnl had insignificant effect (0.35 mm a?2) on Ep rates. The change of Ep is the net result of all the climatic variables. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

12.
Topography evolves under the coupled effect of exogenic and endogenic governing factors, and their scale-(in)variant dynamics. This results in a self-affine topography across a finite range, with a characteristic fractal dimension. Fractal analysis has been used to classify geological terrains having distinct litho-tectonic settings. However, process-based understanding of the fractal behaviour of a natural landscape is still limited. The current study aims to substantiate and expand upon the present knowledge of topographic response to the complex actions of the governing factors using fractal characteristics. We examined the association between the litho-tectonic, climatic settings and the fractal characteristics of the topography in the tectonically active Northwest Himalaya. Our analysis was carried out in three separate sectors having diverse litho-tectonic settings. We used the roughness–length method to calculate the fractal parameters (fractal dimension, D; ordinate intercept, q). The Higher and the Lesser Himalaya were found to be characterized by low D and high q, while the tectonically active Sub Himalaya was found to have moderate D and low q. The southernmost foreland alluvial plains were characterized by high D and low q. Clusters of the fractal parameters were found to be consistent in spatial pattern across the three sectors. Our results showed that the geological–geomorphological settings and the associated processes (e.g. uplift, erosion and diffusion) can be well inferred using the fractal characteristics of the topography. Further, our results implied first-order control of lithology in sustaining and shaping the topographic geometry (both its amplitude and texture) in the tectonically active Northwest Himalaya. The spatial distribution of the fractal parameters also suggested the secondary control of tectonic uplift and, to a much lesser extent, mean annual rainfall on the topographic geometry. These results collectively point to the role of complex actions of the governing factors in the landscape evolution process. © 2020 John Wiley & Sons, Ltd.  相似文献   

13.
The use of drainage ditches on farmland has an impact on erosion processes both on‐site and off‐site, though their environmental impacts are not unequivocal. Here we study the runoff response and related rill erosion after installing drainage ditches and assess the effects of stone bunds in north Ethiopia. Three different land management systems were studied in 10 cropland catchments around Wanzaye during the rainy season of 2013: (1) the exclusive use of drainage ditches (locally called feses), (2) the exclusive use of stone bunds, and (3) a mixture of both systems. Stone bunds are an effective soil and water conservation technique, making the land more resistant against on‐site erosion, and allowing feses to be installed at a larger angle with the contour. The mean rill volumes for the 10 studied cropland catchments during the rainy season of 2013 was 3.73 ± 4.20 m3 ha?1 corresponding to a soil loss of 5.72 ± 6.30 ton ha?1. The establishment of feses causes larger rill volumes (R = 0.59, N = 10), although feses are perceived as the best way to avoid soil erosion when no stone bunds are present. The use of feses increases event‐based runoff coefficients (RCs) on cropland from c. 5% to values up to 39%. Also, a combination of low stone bund density and high feses density results in a higher RC, whereas catchments with a high stone bund density and low feses density have a lower RC. Peak runoff discharges decrease when stone bund density increases, whereas feses density is positively related to the peak runoff discharge. A multiple linear relation in which both feses and stone bund densities are used as explanatory variable, performs best in explaining runoff hydrograph peakedness (R2 = 83%). Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

14.
The estimation of evapotranspiration (E) in forested areas is required for various practical purposes (e.g. evaluation of drought risks) in Japan. This study developed a model that estimates monthly forest E in Japan with the input of monthly temperature (T). The model is based on the assumptions that E equals the equilibrium evaporation rate (Eeq) and that Eeq is approximated by a function of T. The model formulates E as E (mm month−1) = 3·48 T ( °C) + 32·3. The accuracy of the model was examined using monthly E data derived using short‐term water balance (WB) and micrometeorological (M) methods for 15 forest sites in Japan. The model estimated monthly E more accurately than did the Thornthwaite and Hamon equations according to regression analysis of the estimated E and E derived using the WB and M methods. Although the model tended to overestimate monthly E, the overestimation could be reduced by considering the effect of precipitation on E. As T data are commonly available all over Japan, the model would be a useful tool to estimate forest E in Japan. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

15.
The C factor, representing the impact of plant and ground cover on soil loss, is one of the important factors of the Modified Universal Soil Loss Equation (MUSLE) in the Soil and Water Assessment Tool (SWAT) to model sediment yield. The daily update of C factors in SWAT was originally determined by land use types and plant growth cycles. This does not reflect the spatial variation of C values that exists within a large land use area. We present a new approach to integrate remotely sensed C factors into SWAT for highlighting the effect of detailed vegetative cover data on soil erosion and sediment yield. First, the C factor was estimated using the abundance of ground components extracted from remote sensing images. Then, the gridding data of the C factor were aggregated to hydrological response units (HRUs), instead of to land use units of SWAT. In the end, the C factor values in HRUs were integrated into SWAT to predict sediment yield by modifying the ysed subroutine. This substitution work not only increases the spatial variation of the C factor in SWAT, but also makes it possible to utilize other sources of C databases rather than those from the United States. The demonstration in the Dage basin shows that the modified SWAT produces reasonable results in water flow simulation and sediment yield prediction using remotely sensed C values. The Nash–Sutcliffe efficiency coefficient (ENS) and R2 for surface runoff range from 0·69 to 0·77 and 0·73 to 0·87, respectively. The coefficients ENS and R2 for sediment yield were generally above 0·70 and 0·60, respectively. The soil erosion risk map based on sediment yield prediction at the HRU level illustrates instructive details on spatial distribution of soil loss. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

16.
The factors influencing soil erosion may vary with scale. It remains unclear whether the spatial variation in soil erosion resistance is controlled by regional variables (e.g. precipitation, temperature, and vegetation zone) or by local specific variables (e.g. soil properties, root traits, land use, and farming operations) when the study area enlarges from a hillslope or catchment to the regional scale. This study was performed to quantify the spatial variations in soil erosion resistance to flowing water under three typical land uses along a regional transect on the Loess Plateau and to identify whether regional or local specific variables are responsible for these changes. The results indicated that the measured soil detachment capacities (Dc) of cropland exhibited an irregular trend along the regional transect. The Dc of grassland increased with mean annual precipitation, except for two sites (Yijun and Erdos). The measured Dc of woodland displayed an inverted ‘U’ shape. The changes in rill erodibility (Kr) of three land uses were similar to Dc, whereas no distinguishable trend was found for critical shear stress (τc). No significant correlation was detected between Dc, Kr and τc, and the regional variables. The spatial variation in soil erosion resistance could be explained reasonably by changes in soil properties, root traits, land use, and farming operations, rather than regional variables. The adjustment coefficient of Kr for grassland and woodland could be well simulated by soil cohesion and root mass density (R2 = 0.70, P < 0.01), and the adjustment coefficient of critical shear stress could be estimated with aggregate stability (R2 = 0.57, P < 0.01). The results are helpful for quantifying the spatial variation in soil detachment processes by overland flow and to develop process‐based erosion model at a regional scale. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

17.
Ditch cleaning in drained peatland forests increases sediment loads and degrades water quality in headwater streams and lakes. A better understanding of the processes controlling ditch erosion and sediment transport in such systems is a prerequisite for proper peatland management. In order to relate hydrological observations to key erosion processes in headwater peatlands drained for forestry, a two‐year study was conducted in a nested sub‐catchment system (treated with ditch cleaning) and at two reference sites. The treated catchment was instrumented for continuous discharge and turbidity monitoring, erosion pin measurements of changes in ditch bed and banks and time‐integrated sampling of suspended sediment (SS) composition. The results showed that ditch cleaning clearly increased transient suspended sediment concentrations (SSCs) and suspended sediment yields (SSYs), and resulted in temporary storage of loosely deposited organic sediment in the ditch network. After exhaustion of this sediment storage, subaerial processes and erosion from ditch banks became dominant in producing sediment for transport. Recorded SSCs were higher on the rising limbs of event hydrographs throughout the study period, indicating that SS transport was limited by availability of erosion‐prone sediment. A strong positive correlation (R2 = 0.84, p < 0.001) between rainfall intensity (above a threshold of 1 mm h?1) and average SSC obtained on the rising limb of hydrographs for the sub‐catchment showed that soil detachment from ditch banks by raindrop impact can directly increase SSC in runoff. At the main catchment outlet, variation in SSC was best explained (R2 = 0.67, p < 0.05) by the linear combination of initial discharge (?), peak discharge (+) and the lag time from initial to peak discharge (?). Based on these factors, ditch cleaning slightly increased peak discharges and decreased transit times in the study catchment. The implications of the results for water pollution management in peatland forests are discussed. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

18.
Factors affecting rill erosion of unpaved loess roads in China   总被引：1，自引：0，他引：1       下载免费PDF全文
This study explores factors that affect road surface erosion in a small watershed on the Loess Plateau. Global positioning system (GPS)‐assisted field surveys and geographical information system methods were applied. The results show that road surface rills in the watershed are more easily formed on main roads, which are disturbed by intensive human activities. Secondary unpaved road networks occupied the largest road surface area and contributed 49% of the total road surface rill volumes. Spatial analysis reveals that roads near residential areas or leading to other human‐disturbed land‐use types are at high risk of soil loss. In each road segment, slope gradient, road segment length and drainage area have impacts on surface rill formation and development. Among these factors, slope gradients have been verified as a controlling factor of rill erosion intensification. Both road segment length (R = 0.83, N = 82) and drainage area (R = 0.72 for road segment and 0.76 for upslope drainage areas, N = 82) significantly influence total road surface rill volumes. The interaction variable of road segment length multiplied by slope is more closely correlated with road segment soil loss than that of the independent variables alone. Linear equations composed of slope gradient, road segment length and upslope drainage area are proposed. The new equation performs much better at predicting surface soil loss from secondary road segments compared with the previous models, which have not considered upslope drainage areas. The relationships and equations from this study will be helpful for road erosion evaluation in a small watershed of the study area. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

19.
Historic land use in the Chesapeake Bay drainage basin induced large fluxes of fluvial sediment to subestuarine tributaries. Stratigraphic and palaeoecologic analyses of deltaic deposits may be used to infer changes on the landscape, but are not sufficient to quantify past sediment supply. When viewed as an inverse boundary‐value problem, reconstruction of the sediment supply function may be achieved by combining deltaic sedimentation chronologies with an equation governing delta progradation. We propose that the diffusion equation is appropriate for simulating delta progradation and obtaining the sediment supply function provided a suitable diffusion constant (D) can be determined. Three new methods for estimating D are presented for the case of estuarine deltas. When the inverse boundary‐value technique was applied to Otter Point Creek, a tidal freshwater delta at the head of Bush River in upper Chesapeake Bay, D values ranged from 3763 to 6199 m2 a?1. Delta growth simulations showed a 1740–1760 initial pulse, a 1760–1780 erosive/redistributive interval, a 1780–1920 growth period, and a 1920‐present erosive/redistributive era. Coupling of simulated delta elevations with an empirical plant habitat predictive equation allowed for comparison of predicted versus actual relative habitat areas. Also, the model yielded reconstructed watershed erosion rates and stream suspended sediment concentrations that could be useful for development of water quality regulations. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

20.
Rainfall erosivity represents the primary driver for particle detachment in splash soil erosion. Several raindrop erosivity indices have been developed in order to quantify the potential of rainfall to cause soil erosion. Different types of rainfall simulators have been used to relate rainfall characteristics to soil detachment. However, rainfall produced by different rainfall simulators has different characteristics, specifically different relationships between rainfall intensity and rainfall erosivity. For this reason, the effect of rainfall characteristics produced by a dripper‐type rainfall simulator on splash soil erosion (Ds) has been investigated. The simulated rainfall kinetic energy (KE) and drop size distribution (DSD) were measured using piezoelectric transducers, modified from the Vaisala RAINCAP® rain sensor. The soil splash was evaluated under various simulated rainfall intensities ranging from 10 to 100 mm h?1 using the splash‐cup method. The simulated rainfall intensity (I) and kinetic energy relationship (I–KE) was found to be different from natural rainfall. The simulated rainfall intensity and splash soil erosion relationship (I–Ds) also followed this same trend. The I–KE relationship was found to follow the natural rainfall trend until the rainfall intensity reached 30 mm h?1 and above this limit the KE started to decrease. This emphasizes the importance of the I–KE relationship in determining the I‐Ds relationship, which can differ from one rainfall simulator to another. Ds was found to be highly correlated with KE (r = 0·85, P < 0·001), when data produced by the rainfall intensity ranged from 10 to 100 mm h?1. However, when the threshold rainfall intensity (30 mm h?1) was considered, the correlation coefficient further improved (r = 0·89, P = 0·001). Accordingly, to improve the soil splash estimation of simulated rainfall under various rainfall intensities the I–KE characterization relationship for rainfall simulators has to be taken into account. Copyright © 2010 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