末次间冰期以来黄河中游黄土高原沟谷侵蚀-堆积过程初探

以陕西洛川北汉寨小流域为基础，建立末次间冰期以来黄河中游黄土高原的沟谷侵蚀－堆积模式，并定量计算流域不同时期侵蚀模数或堆积速率，初步恢复了末次间冰期以来黄土高原中部地区的沟谷侵蚀－堆积过程。计算结果表明，末次间冰期公来，黄土高原中部地区的自然侵蚀作用可能在逐渐加剧。侵蚀－堆积是黄土区沟谷发育的基本过程，并与气候变化密切相关。侵蚀期相当于湿润期，也就是降雨量大的时期；沉积黄土层的时期沟谷发育大大减缓甚至停止，并且在原来的谷底、谷坡上还可堆积黄土。     

海岸带滩涂地貌演变遥感方法研究

遥感技术是进行海岸带资源调查的有效技术手段,对水利工程规划、防灾减灾、滩涂开发利用等方面有较大的实用价值。在海岸带资源调查中,传统的地面调查方法不仅工作量大,而且实施起来非常困难;遥感技术由于具有感测范围大、获取信息快、更新周期短的特点,为海岸带资源调查和地貌演变的分析和研究提供了较好的方法和手段。文章探讨了遥感技术在江苏省安台线(海安、东台之间海域界线)勘界工作中的运用,采用较新的卫星遥感影像作为工作底图,同时利用1988—2003年之间不同时相的七景影像监测滩涂的演变,在提供了准确的滩涂地形、地貌资料的基础上,通过监测潮沟的变化推断出滩涂的演变,为海域勘界工作提供了有力而可靠的依据。     

Implications of palæo- and neotectonics in gully erosion-prone areas of southeastern Nigeria

Incidences of landsliding and gullying are prevalent in parts of southeastern Nigeria. It is proposed here that the apparent susceptibility of the geologic formations to landsliding and gullying may indeed derive substantially from the effects of palæo- and neotectonic features. Tertiary palæotectonics created regional cuestas, joints and faults that now determine the pace of gully erosion. Recent tectonics and seismic effects cause ground vibrations that initiate movement on the marginally stable slopes. It is observed that southeastern Nigeria has climatic and land-use characteristics which are very similar to those of southwestern Nigeria, as well as being underlain by similar Tertiary formations, yet gully erosion and landslides are much less common in the latter. This is ascribed to the differences in the palæotectonic setting. Recent case incidences of tectonics-related disasters are presented.     

Gully erosion in the Siwalik Hills,Nepal: estimation of sediment production from active ephemeral gullies

A simple field‐based monitoring programme was established in a small catchment (area 4·6 km²) to find the rates of gully erosion in the Siwalik Hills, Nepal. The rates are used to estimate the amount of sediment produced by gully erosion in the catchment. Three large and active gullies were selected with areas ranging from 0·44 to 0·78 ha. Aerial photographs taken in 1964, 1978 and 1992 were ortho‐rectified and used to study the dynamics of gully heads. The same gullies were also monitored manually using an orthogonal reference system fixed by erosion pins around the gully heads. Results from the aerial photos indicated that the gullies expanded remarkably over the period from 1964 to 1992, by 34 to 58 per cent. Head‐retreat rates during that period were 0·48, 0·55 and 0·73 m a^?1 and average annual sediment evacuation was estimated as 2534 ± 171, 959 ± 60 and 2783 ± 118 m³ a^?1 for the three gullies respectively. From the field measurement, estimated volumes were found to vary from 731 ± 57 to 2793 ± 201 m³ a^?1 over the monitoring period of two years. It was also found that the gullies produce sediment which accounts for up to 59 per cent of the sediment produced from surface erosion in the headwater catchment. The findings are useful for planning and executing appropriate control measures and constructing a sediment hazard map at the catchment scale. Copyright © 2006 John Wiley & Sons, Ltd.     

Sediment production in large gullies of the Mediterranean area (NE Spain) from high‐resolution digital elevation models and geographical information systems analysis

Recent studies in the Mediterranean area have shown gully erosion to have a very significant contribution to total soil loss. In the Penedès vineyard region (NE Spain), between 15 and 27% of the land is affected by large gullies and gully‐wall retreat seems to be an ongoing process. Multi‐date digital elevation model (DEM) analysis has allowed computation of sediment production by gully erosion, showing that the sediment production rates are very high by the, up‐to‐date, usual global standards. Here, we present a study carried out using large‐scale multi‐date (1975 and 1995) aerial photographs (1 : 5000 and 1 : 7000) to monitor sediment yield caused by large gullies in the Penedès region (NE Spain). High‐resolution DEMs (1 m grid) were derived and analysed by means of geographical information systems techniques to determine the gully erosion rates. Rainfall characteristics within the same study period were also analysed in order to correlate with the soil loss produced. Mass movement was the main process contributing to total sediment production. This process could have been favoured by rainfalls recorded during the period: 58% of the events were of an erosive character and showed high kinetic energy and erosivity. A sediment production rate of 846 ± 40 Mg ha^?1 year^?1, a sediment deposition rate of 270 ± 18 Mg ha^?1 year^?1 and a sediment delivery ratio of 68·1% were computed for a gully area of 0·10 km². The average net erosion within the study period (1975–95) was 576 ± 58 Mg ha^?1 year^?1. In comparison with other methods, the proposed method also includes sediment produced by processes other than only overland flow, i.e. downcutting, headcutting, and mass movements and bank erosion. Copyright © 2003 John Wiley & Sons, Ltd.     

Tunnel development over a 12 year period in a semi‐arid catchment of the Loess Plateau,China

The tunnel systems in a semi‐arid catchment of the Loess Plateau of China were repeatedly surveyed prior to the rainy seasons of 1989, 1999 and 2001. The surveys aimed to: (1) measure tunnel development over the 12 year period 1989–2001; (2) explore how the physiographical conditions affect the spatio‐temporal variability of tunnel development; and (3) to identify the geomorphic processes associated with tunnel development. The ultimate goal was to quantify the geomorphic significance of tunnel systems in the catchment. Over the 12 year period, the number of tunnel inlets was more than doubled and most of the newly increased inlets were initiated in the few catastrophic storm events. However, tunnel enlargement can occur in storm or inter‐storm periods, mainly through earth falls and slumps in inlets, and water erosion and roof cave‐in collapses in tunnel paths. Tunnel development varied with material properties, land uses and topographic conditions. Net tunnel erosion may contribute at least 25–30% of the catchment sediment yield and was mainly produced by the initiation and enlargement of tunnel inlets rather than tunnel paths. To protect the areas against tunnel erosion, terracing of the upper slopes seems to be more effective than planting vegetation on the lower slopes. Copyright © 2003 John Wiley & Sons, Ltd.     

中国西北地区陆内前陆盆地的鉴别标志

讨论了中国西北地区陆内前陆盆地的主要鉴别标志 :(1)不对称山前坳陷的构造几何形态 ;(2 )先缓后陡的两段式沉降曲线 ;(3)反沉积旋回上部磨拉石堆积、强烈构造运动和层内递进型构造角度不整合类型。认为在鉴别陆内前陆盆地中必须进行多项标志的综合分析     

元代以来黄土塬区沟谷发育与土壤侵蚀

以洛川旧县镇南沟小流域为研究对象，用实地考察和史料考证相结合的方法，恢复了元代(1267年)以来洛川黄土塬区沟谷发育与土壤侵蚀过程，计算出了不同时段沟谷发育速度、土壤侵蚀强度，分析了黄土塬区沟谷形态的演变。自元代以来黄土塬区沟谷发育、土壤侵蚀呈加剧态势，其变化一方面与降水量变化关系密切，降水量较丰富时沟谷发育、土壤侵蚀较强；另一方面人为加速侵蚀与自然侵蚀相叠加是近现代沟谷发育、土壤侵蚀剧烈的主要原因。黄土塬区沟谷形态由巷形谷、V形谷向U形谷演变，沟头段巷形谷和上游段V形谷是土壤侵蚀与治理的重点。     

Reconstructing the development of a gully in the Upper Kalaus basin,Stavropol region (southern Russia)

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

Long‐term growth of a valley‐bottom gully,western Iowa

Growth of a permanent, valley‐bottom gully from 1964 to 2000 was determined annually from survey and sediment‐discharge data and compared with runoff and base?ow discharges. Data were analysed to test the hypothesis that rates of gully growth decay exponentially with time in response to shrinking catchment area caused by gully enlargement. Also, monthly values of growth rates and runoff, averaged over the 36‐year record, were analysed with mass‐wasting data to determine the extent to which colluvium availability affected growth rates seasonally. From 1964 to 2000, the gully volume increased by 9200 m³, accounting for 34 per cent of sediment yield from the watershed. There were tight power‐law relationships between annual growth rates and annual runoff, with runoff exponents of 1·57 and 1·30 for headward and volumetric growth, respectively. Increases in gully length, area, and volume were ?tted successfully assuming an exponential decay in growth rate with time. Rather than being due to a decrease in catchment area, however, the decline in growth rate was caused by a 77 per cent decrease in the ratio of runoff to base?ow, which also widened the gully and reduced the mean slope of its banks. Order‐of‐magnitude seasonal changes in erosion ef?ciency, de?ned as the fraction of stream power used to evacuate sediment from the gully, were roughly correlated with colluvium availability, as indicated by seasonal changes in the number of bank mass‐wasting events. No more than 2·2 per cent of stream power was used to evacuate sediment during any month. This study demonstrates the danger of attributing declining rates of gully growth to a shrinking catchment area if corroborative runoff and base?ow data are not available. Moreover, it illustrates that stream power alone provides only a rough and physically indirect measure of erosion potential. Copyright © 2004 John Wiley & Sons, Ltd.