The effect of some watershed,soil characteristics and morphometric factors on the relationship between the gully volume and length in Fars Province,Iran

A survey consisting of 146 first order gullies selected from five sites with different land use, soil and watershed properties was carried out to estimate the parameters of the empirical power function in order to describe the relationship between the gully volume and length in Fars province, Iran. Subsequently, the gullies were clustered into seven groups (“A” to “G”) based on nine morphometric factors. The linearized functions were fitted to the natural logarithms of the volume and length in each group and the parameters “a” and “b” were determined. The obtained “a” and “b” parameters are in the ranges of 1.0–10.8 and 0.8–1.4, respectively. Comparison of “a” and “b” parameters in each group with the mean of nine factors and the mean soil, watershed and land use characteristics in each group showed that the gully volume and average cross section are correlated with the gully depths in different sections and the gully head slopes. Also it was shown that the parameters of fitted functions to the plots of gully volumes versus gully lengths are proportional to width at the gully heads. The gully widths at the top and bottom of the five meter sections are correlated with the average upstream watershed area of the gullies.     

陕北黄土区切沟内陷穴发育特征研究

通过对陕北黄土区六道沟流域切沟内陷穴进行调查和统计分析,探讨陷穴的发育形态、分布特征及其影响因素。结果表明:陷穴主要形态类型有浅碟形、漏斗形、竖井状以及葫芦状,其断面形态接近于圆形或椭圆形,陷穴形态规模相对偏小,处于成熟期的比例达72.8%;陷穴长轴、短轴和深度之间均具有显著的正相关关系,其中长轴和短轴之间具有较好的线性关系;陷穴主要发育位置为沟道中上游及支沟沟头处,多与黄土桥和跌水相伴而生;切沟为陷穴的形成和发育提供了条件,陷穴亦可促进切沟进一步发展。上述结果完善了切沟内陷穴的发生发育特点和空间分布特征,为深入认识陷穴侵蚀机理,进一步研究陷穴侵蚀状况、陷穴与切沟发育关系以及区域水土流失治理等提供了基础。     

Short-term gully retreat rates over rolling hill areas in black soil of Northeast China

Soil loss has become one severe problem in black soil areas of Northeast China after several decades of cultivation. Gully erosion is one of its main components. In this study, short-term gully retreat was monitored from 5 active gullies selected in representative black soil area during April 2002 to June 2004, using differential global positioning system (GPS). With the support of geographic information system (GIS), multitemporal digital elevation models (DEM) were constructed from the data collected by GPS and then used for further analysis. This presents a new method to compute the retreat rate of gully heads and the rate of soil losses caused by gully erosion. The results indicate that the average volumetric retreat rate was 729.1 m³ year^− 1, corresponding with an average linear retreat rate of 6.2 m year^− 1 in gully head and planimetric changes of 323.6 m² year^− 1 during the two monitored years, but more erosion took place during the second and third monitored period compared to the first. The erosion by freeze thawing and snowmelt accounts for a large percent. And this will be emphasized when rainfall is added in spring. If only considering the third monitored period, the conservatively estimated retreat rate by freeze thawing and snowmelt (i.e. before rainy season) may even reach 8.6 m year^− 1 in gully head, with a volumetric rate of 120.9 m³ year^− 1 and planimetric changes of 173.6 m² year^− 1. These results reveal that gully erosion is a great threat in the study area and conservation measures are urgently needed. Based on the analysis of multi-temporal DEM, one conceptual model for gully developing in black soil of Northeast China is proposed, which is supported by the data.     

不同土层复配方案对土壤水稳性团聚体及有机质的影响

为探究“治沟造地”重大工程项目（GLCP）中新增耕地快速改良的方法,达到营造良好土壤、提升新增耕地生产能力的目的,以延安羊圈沟流域的GLCP为背景,利用马兰黄土（ML）和红黏土（RC）对新造耕地0~30 cm土层进行复配试验。结果表明：当RC为20 cm、ML为10 cm（T3处理）时,复配层土壤孔隙度较对照处理增加了16.7%,容重下降了11.1%。与对照组相比,T3处理0~10、10~20、20~30 cm土层中>0.25 mm水稳性团聚体含量（W_0.25）显著增加,分别增加了11.8、12.3倍和27.9倍;T2（RC为25 cm、ML为5 cm）、T3处理更利于大团聚体的形成,较对照组除在0.25~0.5、0.5~1 mm的粒级有较大增加外,在2~5 mm和>5 mm粒径范围也有明显增加。0~20 cm土层中,即使在考虑对照组前期土壤有机质积累的情况下,T3处理的土壤有机质也与对照组相近甚至更高,且高于其他试验组,表现出更好的有机质赋存能力。T3处理的玉米生长状况较好,其地上生物量最高,较对照组提高了23.9%。研究表明,当复配土壤RC为20 cm、ML为10 cm时,土壤具有最佳的性状和生产力。试验初步证明土层复配是一种可行的快速营造高质量土壤的方法,该方法可为GLCP新造地的改良及类似土地整治工程的实施提供实践参考。     

黄土高原沟壑区小麦品种演替过程中籽粒灌浆特性研究

为了解黄土高原沟壑区小麦品种演替过程中的籽粒灌浆特性,以此地区20世纪50年代至今的主栽小麦品种为供试材料,研究了不同小麦品种演替过程中籽粒干物质积累量及灌浆速率的变化。结果表明,黄土高原沟壑区小麦演替过程中,小麦籽粒千粒重呈现逐渐增加的趋势。平均灌浆速率逐渐增加,小麦籽粒的干物质积累随之增加,长旱58的W0最大,达50.53 g。灌浆三阶段中,各阶段的灌浆速率表现为,V2>V1>V3。从灌浆持续时间看,T1和T2持续的时间较长且变异系数较大,而T3和T相对稳定。从灌浆速率来看,V1、V2、V3、Vm、Va变异系数较大,灌浆速率易受环境因素影响而波动。     

黄土丘陵沟壑区坡体稳定性影响因素分析

选取黄土丘陵沟壑区纸坊沟小流域为研究区,利用高精度遥感影像(分辨率0.068 m)和DEM (分辨率0.34 m)数据,结合野外调查,对崩塌、滑塌、滑坡、脱落和陷穴等失稳体进行识别,通过统计学、敏感系数方法,利用识别失稳体数据,分析不同类型失稳体空间分布状况,定量研究不同类型失稳体的影响因子敏感程度,揭示不同类型失稳体的主控因子,进一步阐明流域坡体失稳体的空间分布规律和影响坡体稳定性的主控因子。结果表明:(1)利用高精度遥感影像,获取流域失稳体,主要是以小规模和浅层的脱落、崩塌和滑塌为主,三者面积合计为0.417 km²,占流域总面积的5.04%。(2)评价因子内部中,土壤母质的红黏土、土地利用的天然灌木林地和草地、地貌部位的沟坡、坡度＞35°、地形起伏度为0.74~3.34 m是坡体失稳发生的高敏感区域,也是崩塌、滑塌、脱落和陷穴发育共有的敏感区域。(3)影响坡体稳定性主控因子权重由大到小为土壤母质、地形起伏度、坡度、土地利用和坡向。崩塌、滑塌和脱落的主控因子与整体坡体稳定性的主控因子相同,但因子内部权重存在差异。崩塌与整体坡体稳定性影响因子顺序分布一致。滑塌主控因子权重由大到小为土壤母质＞地形起伏度＝坡度＞土地利用＞坡向＞地貌部位。脱落主控因子权重由大到小为土壤母质＞土地利用＞地形起伏度＞坡度＝坡向＞地貌部位。滑坡的主控因子为坡度和地形起伏度。陷穴的主控因子权重由大到小为土壤母质＞地形起伏度＞坡度＞坡向。     

Gully erosion and environmental change: importance and research needs

Assessing the impacts of climatic and, in particular, land use changes on rates of soil erosion by water is the objective of many national and international research projects. However, over the last decades, most research dealing with soil erosion by water has concentrated on sheet (interrill) and rill erosion processes operating at the (runoff) plot scale. Relatively few studies have been conducted on gully erosion operating at larger spatial scales.Recent studies indicate that (1) gully erosion represents an important sediment source in a range of environments and (2) gullies are effective links for transferring runoff and sediment from uplands to valley bottoms and permanent channels where they aggravate off site effects of water erosion. In other words, once gullies develop, they increase the connectivity in the landscape. Many cases of damage (sediment and chemical) to watercourses and properties by runoff from agricultural land relate to (ephemeral) gullying. Consequently, there is a need for monitoring, experimental and modelling studies of gully erosion as a basis for predicting the effects of environmental change (climatic and land use changes) on gully erosion rates.In this respect, various research questions can be identified. The most important ones are:

What is the contribution of gully erosion to overall soil loss and sediment production at various temporal and spatial scales and under different climatic and land use conditions?

What are appropriate measuring techniques for monitoring and experimental studies of the initiation and development of various gully types at various temporal and spatial scales?

Can we identify critical thresholds for the initiation, development and infilling of gullies in different environments in terms of flow hydraulics, rain, topography, soils and land use?

How does gully erosion interact with hydrological processes as well as with other soil degradation processes?

What are appropriate models of gully erosion, capable of predicting (a) erosion rates at various temporal and spatial scales and (b) the impact of gully development on hydrology, sediment yield and landscape evolution?

What are efficient gully prevention and gully control measures? What can be learned from failures and successes of gully erosion control programmes?

These questions need to be answered first if we want to improve our insights into the impacts of environmental change on gully erosion. This paper highlights some of these issues by reviewing recent examples taken from various environments.     

黄土高原丘陵沟壑区放牧林草地团聚体水稳性的研究

以黄土高原丘陵沟壑区——山西偏关县为例,对不同放牧植被类型、不同放牧强度、不同放牧畜种条件下表层土(0-10cm)的团聚体水稳性进行分析研究。结果表明,放牧草地较之放牧林地的土壤结构及结构稳定性要好;重度放牧下土壤团聚体含量最小,其结构稳定性亦最差;从畜牧羊种选择来看,绵羊相对于山羊来说对土壤结构破坏较小,土壤中团聚体含量较多、团聚体水稳性也较好。     

放牧对黄土高原丘陵沟壑区林草地土壤特性的影响

在黄土高原丘陵沟壑区——山西偏关县通过放牧试验研究了草地和柠条林地在不同放牧强度、不同放牧畜种条件下表层土(0~10 cm)的物理和化学性质。结果表明,放牧强度直接影响着草地和柠条林地土壤的物理结构。随放牧强度的增加,牲畜对土壤的践踏加剧,导致土壤紧实度增加,容重上升,含水量下降。草地和柠条林地的水解氮含量都随放牧强度的增加而增加,速效钾含量则都表现为中度放牧>重度放牧>轻度放牧;速效磷的含量草地随放牧强度的增加而减少,柠条林地的速效磷含量则随放牧强度的增加而增加。从畜牧羊种选择来看,绵羊相对于山羊来说对放牧地践踏较轻,土壤容重较小,土壤含水量、水解氮、速效磷和速效钾含量则较高。     

李家大沟泥石流与三峡库区奉节县新城建设

三峡库区奉节县新城建设大大改变了李家大沟中下游的地质环境,泥石流将直接威胁到新城区的建设和人民财产的安全。从工程地质角度出发,对李家大沟泥石流的形成环境(地层岩性条件、构造条件、地貌条件、气象条件、植被发育及人类工程活动)、基本特征(形成区和流通区特征)和形成机制进行了详细的系统研究,对泥石流的危害性和发展趋势做了预测评价,并提出了合理科学的建议。