长江上游土地利用变化与冲沟发生和演变

冲沟侵蚀是中国西部山区一个重要的环境问题。小流域研究表明，黄河和长江中的泥沙主要是冲沟侵蚀引起的。目前，长江上游80%的冲沟因被幼林草植被覆盖而处于非活跃期。到底这些冲沟系统是什么时候形成的？未来的暴雨和径流是否会激活这些冲沟系统？土地利用与景观结构对冲沟系统的发生、演变有何关系？基于这些问题，近几年来在中科院山地环境学“百人计划”和“国外引进杰出人才”项目及德国洪堡基金的资助下，中德科学工作者进行了合作研究。本文介绍了长江上游地区土地利用变化与冲沟发生、演变的部分研究成果。我们在西昌安宁河干暖河谷选择了两个冲沟系统一个位于西溪乡长山岭，一个位于大青梁子。为了定量评价土地利用对冲沟发育的影响，我们对研究小流域的航片、土壤剖面、泥沙堆积与土地利用历史等进行了详尽的综合对比分析。同时，对两个冲沟系统的大小和土壤流失的体积进行了详细的野外调查、测定和计算。据此，获得了研究流域的冲沟侵蚀速率。研究结果表明，长江上游数百年的持续景观演变，尤其是20世纪中期人为强烈的不合理农业垦殖和利用土地，造成了四川西南部大量冲沟系统的形成和发展，研究流域的冲沟侵蚀速率高达375t/hm2*a-1。采取成功的水土保持措施以控制冲沟侵蚀，对中国西南山地退化环境的生态修复具有重大实践意义。     

The value of a physically based model versus an empirical approach in the prediction of ephemeral gully erosion for loess-derived soils

A data set on soil losses and controlling factors for 58 ephemeral gullies has been collected in the Belgian loess belt from March 1997 to March 1999. Of the observed ephemeral gullies, 32 developed at the end of winter or in early spring (winter gullies) and 26 ephemeral gullies developed during summer (summer gullies). The assessed data have been used to test the physically based Ephemeral Gully Erosion Model (EGEM) and to compare its performance with the value of simple topographical and morphological indices in the prediction of ephemeral gully erosion.Analysis shows that EGEM is not capable of predicting ephemeral gully cross-sections well. Although conditions for input parameter assessment were ideal, some parameters such as channel erodibility, critical flow shear stress and local rainfall depth showed great uncertainty. Rather than revealing EGEM's inability of predicting ephemeral gully erosion, this analysis stresses the problematic nature of physically based models, since they often require input parameters that are not available or can hardly be obtained.With respect to the value of simple topographical and morphological indices in predicting ephemeral gully erosion, this study shows that for winter gullies and summer gullies, respectively, over 80% and about 75% of the variation in ephemeral gully volume can be explained when ephemeral gully length is known. Moreover, when previously collected data for ephemeral gullies in two Mediterranean study areas and the data for summer gullies formed in the Belgian loess belt are pooled, it appears that one single length (L)–volume (V) relation exists (V=0.048 L^1.29; R²=0.91). These findings imply that predicting ephemeral gully length is a valuable alternative for the prediction of ephemeral gully volume. A simple procedure to predict ephemeral gully length based on topographical thresholds is presented here. Secondly, the empirical length–volume relation can also be used to convert ephemeral gully length data extracted from aerial photos into ephemeral gully volumes.     

新疆北天山晚古生代洋盆演化与推覆构造

通过实地考察并综合区域及深部物探资料,研究了北天山逆冲推覆系统的构造样式、结构特征和组合方式;认为北天山晚古代洋盆为板内地壳扩张活动形成的裂陷构造产物,存在时限短暂、对生物群迁移基本没有阻隔作用,不应具有分隔岩石圈板块的大地构造意义。     

Gullying and erosion control at archaeological sites in Grand Canyon,Arizona

Gully erosion of cultural sites in Grand Canyon National Park is an urgent management problem that has intensified in recent decades, potentially related to the effects of Glen Canyon Dam. We studied 25 gullies at nine sites in Grand Canyon over the 2002 monsoon–erosion season to better understand the geomorphology of the gully erosion and the effectiveness of erosion‐control structures (ECS) installed by the park under the direction of the Zuni Conservation Program. Field results indicate that Hortonian overland flow leads to concentrated flow in gullies and erosion focused at knickpoints along channels as well as at gully heads. Though groundcover type, soil shear strength and permeability vary systemat‐ically across catchments, gradient and, to a lesser degree, contributing drainage area seem to be the first‐order controls on gully extent, location of new knickpoints, and ECS damage. The installed ECS do reduce erosion relative to reaches without them and initial data suggest woody checkdams are preferable to rock linings, but maintenance is essential because damaged structures can exacerbate erosion. Topographic data from intensive field surveys and detailed photogrammetry provide slope–contributing area data for gully heads that have a trend consistent with previous empirical and theoretical formulations from a variety of landscapes. The same scaling holds below gully heads for knickpoint and ECS topographic data, with threshold coefficients the lowest for gully heads, slightly higher for knickpoints, and notably higher for damaged ECS. These topographic thresholds were used with 10‐cm digital elevation models to create simple predictive models for gully extent and structure damage. The model predictions accounted for the observed gullies but there are also many false‐positives. Purely topographical models are probably inadequate at this scale and application, but models that also parameterize the variable soil properties across sites would be useful for predicting erosion problems and ECS failure. Copyright © 2006 John Wiley & Sons, Ltd.     

Assessment of gully erosion rates through interviews and measurements: a case study from northern Ethiopia

Gullying has been widespread in the Ethiopian Highlands during the 20th century. It threatens the soil resource, lowers crop yields in intergully areas through enhanced drainage and desiccation, and aggravates flooding and reservoir siltation. Knowing the age and rates of gully development during the last few decades will help explain the reasons for current land degradation. In the absence of historical written or photographic documentation, the AGERTIM method (Assessment of Gully Erosion Rates Through Interviews and Measurements) has been developed. It comprises measurements of contemporary gully volumes, monitoring of gully evolution over several years and semi‐structured interview techniques. Gully erosion rates in the Dogu'a Tembien District, Tigray, Ethiopia, were estimated in three representative case‐study areas. In Dingilet, gullying started around 1965 after gradual environmental changes (removal of vegetation from cropland in the catchment and eucalyptus plantation in the valley bottom); rill‐like incisions grew into a gully, which increased rapidly in the drier period between 1977 and 1990. The estimated evolution of the total gully volume in the other areas show patterns similar to those of the Dingilet gully. Average gully erosion rate over the last 50 years is 6·2 t ha^?1 a^?1. Since 1995, no new gullies have developed in the study area. Area‐specific short‐term gully erosion rates are now on average 1·1 t ha^?1 a^?1. The successful application of the AGERTIM method requires an understanding of the geomorphology of the study area and an integration of the researchers with the rural society. It reveals that rapid gully development in the study area is some 50 years old and is mainly caused by human‐induced environmental degradation. Under the present‐day conditions of ‘normal’ rain and catchment‐wide soil and water conservation, gully erosion rates are decreasing. Copyright © 2006 John Wiley & Sons, Ltd.     

Enhancing RUSLE to include runoff‐driven phenomena

RUSLE2 (Revised Universal Soil Loss Equation) is the most recent in the family of Universal Soil Loss Equation (USLE)/RUSLE/RUSLE2 models proven to provide robust estimates of average annual sheet and rill erosion from a wide range of land use, soil, and climatic conditions. RUSLE2's capabilities have been expanded over earlier versions using methods of estimating time‐varying runoff and process‐based sediment transport routines so that it can estimate sediment transport/deposition/delivery on complex hillslopes. In this report we propose and evaluate a method of predicting a series of representative runoff events whose sizes, durations, and timings are estimated from information already in the RUSLE2 database. The methods were derived from analysis of 30‐year simulations using a widely accepted climate generator and runoff model and were validated against additional independent simulations not used in developing the index events, as well as against long‐term measured monthly rainfall/runoff sets. Comparison of measured and RUSLE2‐predicted monthly runoff suggested that the procedures outlined may underestimate plot‐scale runoff during periods of the year with greater than average rainfall intensity, and a modification to improve predictions was developed. In order to illustrate the potential of coupling RUSLE2 with a process‐based channel erosion model, the resulting set of representative storms was used as an input to the channel routines used in Chemicals, Runoff, and Erosion from Agricultural Management Systems (CREAMS) to calculate ephemeral gully erosion. The method was applied to a hypothetical 5‐ha field cropped to cotton in Marshall County, MS, bisected by a potential ephemeral gully having channel slopes ranging from 0·5 to 5% and with hillslopes on both sides of the channel with 5% steepness and 22·1 m length. Results showed the representative storm sequence produced reasonable results in CREAMS indicating that ephemeral gully erosion may be of the same order of magnitude as sheet and rill erosion. Copyright © 2010 John Wiley & Sons, Ltd.     

基于RTK-GPS技术的干热河谷冲沟沟头形态特征

采用高精度实时动态差分GPS(以下简称RTK-GPS)技术对干热河谷冲沟进行野外调查,获取36个不同活跃度类型沟头的形态参数,研究不同活跃度类型之间沟头的形态特征差异,并分析集水区、沟床植被盖度与形态特征之间的关系。结果表明:1.沟头不同活跃度类型之间,其跌坎高差、沟床比降差异最为显著,可作为沟头活跃度类型野外判别的主要参考指标;沟壁坡度、宽-深比等的差异较为显著,亦可在一定程度上表征沟头活跃程度。2.沟床植被盖度与各形态特征参数的相关性显著,表明沟床植被盖度可作为形态参数的综合替代性指标。同一活跃度类型的沟头,其跌坎高差、沟床比降等与沟床植被盖度呈极显著负相关关系,说明随着沟床植被盖度的增加(或减小),跌坎高差、沟床比降均呈减小(或增加)趋势。3.集水区植被盖度与各形态特征参数的关系不显著,表明干热河谷集水区植被盖度对沟头发育的贡献有限。     

自然泥石流与矿渣泥石流复合效应与防治对策

石棉县后沟是一条典型的自然泥石流和矿渣泥石流并存的泥石流沟。本文以石棉后沟为例,结合早期自然泥石流、矿产开采以来矿渣泥石流、以及2013年7 4复合型泥石流,总结了自然泥石流和矿渣泥石流的复合效应,包括泥石流物源补给的多元效应、泥石流发展演化的逆转效应、泥石流起动发生的复杂效应、泥石流动力沿程的放大效应、泥石流致灾破坏的链式效应。对照泥石流对已建防治工程的破坏,提出了自然泥石流和矿渣泥石流复合型泥石流沟防治对策,建议充分利用起动位置和物源集中补给位置的差异,加强对中上游及支沟自然泥石流起动和运动的拦挡防治,最大限度减小自然泥石流对下游矿渣防护工程的基底侵蚀和冲击破坏,从而保障综合防治工程的有效性。     

Analysis of the Grain Size Properties and Flow Body Classes of the Mud Sand Flow: An Example of Liantanggang Collapsing Hill and Gully in Wuhua County of Guangdong

Mud sand flow is a kind of solid-liquid two-phase flow formed in collapsing hill and gully basin during rainfall. It is the main way to export erosion product. The discrimination of its fluid type is one of the collapsing hill and gully control theoretical basis. This paper analyzed the basic characteristics of mud sand flow like grain size and so on through fieldwork and sampling. The results show that the density of mud sand flow is between 1.16~1.60 t/m³ and the solids content is between 257.03~960.55 kg/m³, both of which decrease from the upper to the lower channel. The slurry of mud sand flow is composed mainly of silt and clay. As the density increases, the particle size distribution curve transforms from a single peak to the bimodal distribution similar to the weathering crust with no sorting, and the grain size of mud sand flow becomes coarser which shows a well positive linear correlation between the sediment median particle diameter and density of mud sand flow. The comparison during mud sand flow, hyperconcentrated flow and debris flow shows that collapsing hill and gully mud sand flow, which belongs to an intermediate class between hyperconcentrated flow and debris flow, has a closer link with debris flow. Therefore, mud sand flow can be considered as a sub-class of generalized debris flow that may be called as collapsing hill and gully type debris flow.     

Factors and processes of permanent gully evolution in a Mediterranean marly environment (Cape Bon,Tunisia)

Abstract

Gully erosion is considered to be one of the most important soil erosion processes in Mediterranean marly environments, but its actual contribution to total soil loss is still under discussion. The objectives of this paper are: (a) to acquire the distributed value of erosion rate in a permanent gully developed on a marly substratum in a Mediterranean environment; and (b) to quantify the key factors responsible for the spatial and temporal differences in erosion rates observed within the gully. A permanent gully located in Cap Bon (northeastern Tunisia) has been intensively and regularly monitored over a 7-year period with electronic survey equipment (total station) to give five field topographic surveys, as well as hydrological measurements at the gully outlet. The net soil loss for the 7-year period comprised a denudation of 51 m³ of sediment on the gully bank slopes, which corresponds to a mean soil loss of 61 m³ ha^?1 year^?1 or 6.1 mm year^?1. Denudation was observed on bed units with a slope gradient greater than 20%, while the remainder showed deposition. By confirming the factors involved in gully evolution, and by refining the statistical link between factors and erosion rates within the gully, the results provide important information to predict gully erosion rates in Mediterranean marly environments.

Editor Z.W. Kundzewicz; Associate editor G. Mahé

Citation El Khalili, A., Raclot, D., Habaieb, H., and Lamachère, J.M., 2013. Factors and processes of permanent gully evolution in a Mediterranean marly environment (Cape Bon, Tunisia). Hydrological Sciences Journal, 58 (7), 1519–1531.