Flood risk on arid alluvial fans:a case study in the Joghatay Mountains,Northeast Iran

Among the common hazards related to alluvial fans,flooding is one of the most important.Nonetheless,in populated alluvial fans,not only the natural processes are effective in floods,but the artificial structures and modifications can change the behavior of flooding and its potential risks.This study aims to indicate the flood-prone landforms in a set of populated alluvial fans in an arid region and investigate the role of anthropogenic activities in controlling/exacerbating flooding in alluvial fans.To achieve this goal,15 Ground Range Detected in High resolution(GRDH)SAR Sentinel-1 images,covering a total of 24 alluvial fans,were acquired.Pre-processing and post-processing steps were applied to all images to identify flood-prone sections of the studied alluvial fans.The results showed that feeder channels,spreading sites,and wide interfluves are the most flood-prone landforms of alluvial fans.In terms of anthropogenic modifications to mitigate flooding,a rampart system is distributed in the study area.Ramparts are levee like structures formed from the fan material.They aim to mitigate flood hazard on residential areas,infrastructures,and agricultural lands of the study area.Results show that the rampart system can reduce the danger of floods,but it cannot be considered a long-term solution.Therefore,a comprehensive flood protection system distributed throughout the whole alluvial fan system is needed.Results also reveal that in regions where flood monitoring is challenging,SAR images can be used as a freely available data set to monitor and identify flooding hotspots.

Upper Cretaceous alluvial fan deposits in the Jianglangshan Geopark of Southeast China:implications for bedrock control on Danxia landform evolution

The Jianglangshan Geopark in the western Zhejiang Province of Southeast China is well-known for its spectacular red-colored sandstone landforms. Little is known about the depositional processes of the conglomerate-dominated Fangyan Formation, the lithologic base of the Danxia landforms in this geopark. Based on detailed field investigation of lithology, sedimentary structures, bed thickness and geometry, five facies are recognized: facies A(matrixsupported cobble conglomerate), facies B(pebble conglomerate), facies C(pebbly sandstone), facies D(fine-grained sandstone) and facies E(mudstone). The results show that streamflow-dominated fans were the main depositional processes responsible for the accumulation of the Fangyan Formation along the mountain fronts. These fan conglomerates form the base for the evolution of the Danxia landscapes owing to the uplift and erosion of the study area. In contrast, the fine-grained sedimentary successions produced by fluvial floodplains in the distal part of the fans were thinner and more easily weathered. Such sedimentary facies distribution patterns were thought to be similar during Late Cretaceous across Southeast China. The Danxia landforms are largely the geographical expressions of the conglomerate-dominated redbeds in the proximal-middle fans.

Effects of land uses on soil physic-chemical properties and erodibility in collapsing-gully alluvial fan of Anxi County,China

the National Key Technologies R＆D Program of China during the 12th Five-Year Plan period （2011BAD31B00）

How do stream processes affect hazard exposure on alluvial fans? Insights from an experimental study

Alluvial fans are among the most privileged settlement areas in many mountain regions. These landforms are particularly dynamic being episodically affected by distributary processes generated by extreme flood events. Addressing risk assessment entails determining hazard exposure and unravelling how it might be related to process loading and to process dynamics once the flow becomes unconfined on the surface of alluvial fans. By following a ‘similarity of process concept’, rather than by attempting to scale a real-world prototype, we performed a set of 72 experimental runs on an alluvial fan model. Thereby, we considered two model layouts, one without a guiding channel and featuring a convex shape and the other one with a guiding channel, a bridge, and inclined but planar overland flow areas as to mirror an anthropic environment. Process magnitude and intensity parameters were systematically varied, and the associated biphasic distributary processes video recorded. For each experiment, the exposure was detected by mapping the exposed area in a GIS, thereby discerning between areas exposed to biphasic flows and the associated depositional phenomena or to the liquid flow phase only. Our results reveal that total event volume, sediment availability and stream power in the feeding channel, as well as depositional effects, avulsion, and channelization on the alluvial fan concur to determine the overall exposure. Stream process loading alone, even when rigorously defined in terms of its characterizing parameters, is not sufficient to exhaustively determine exposure. Hence, further developing reliable biphasic simulation models for hazard assessment on settled alluvial fans is pivotal.

A STUDY ON THRESHOLDS IN THE CHANGE OF ALLUVIAL FAN AND DELTA OF THE HUANGHE RIVER, CHINA

In the river systems, the environmental change always undergoes a process from quantitative to qualitative change. The upper limit of the qualitative change is called threshold. When the process reaches or goes beyond the limit, the original event series will be replaced by the other event series. Investigations show that the evolution of the Huanghe River alluvial fan and delta has also under gone a process from quantitative to qualitative change. The geometric forms in each process are roughly the same. This threshold of the geometric forms not only provides us a quantitative index for plotting the periodicity of the alluvial fan and delta, but also is of importance for estimation of the trend of natural environmental change.It is shown that there are three periodic alluvial fans of the Huanghe River since the middle Holocene and four periodic delta since 1855 A.D., the thresholds of their geometric forms are from 0.93 to 0.94 and from 1.2 to 1.21 respectively.The changing trend in the past and the

Alluvial Fan Facies and Their Distribution in the Lower Talang Acar Formation, Northeast Betara Oilfield, Indonesia

This paper studies the alluvial fan facies characteristics and distribution in the Lower Talang Acar Formation in the Northeast Betara Oilfield. The conglomerate sedimentary characteristics and its distribution were studied based on core data, logging interpretation and seismic property analysis. The research indicated that alluvial fan deposits of Bed F in the Lower Talang Akar Formation were characterized by coarse granularity, poor sorting and low quality. Sand-bodies accumulate longitudinally, and inter-layers are poorly developed, extending locally in the transverse orientation. Typical logging response of alluvial fan system is summarized, and conglomerate is characterized by low gamma-ray （GR） intensity, low resistance, high density and low value between DLD and LLD, which reflects poor physical reservoir properties, coarse rocks and relatively high density. Conglomerate is developed mainly in the northeast and middle-south of the studied area. The upper part of bed F is found in a small area in the middle-south, while the lower part of bed F is developed in a relatively large area in the middle-south.

Regional Mapping of Vertical Hydraulic Gradient Using Uncertain Well Data: A Case Study of the Toyohira River Alluvial Fan, Japan

Vertical hydraulic gradient (VHG) provides detailed information on 3D groundwater flows in alluvial fans, but its regional mapping is complicated by a lack of piezometer nests and uncertainty in conventional well data. Especially, determining representative depth of well screen in each well is problematic. Here, a VHG map of the Toyohira River alluvial fan, Sapporo, Japan, is constructed based on groundwater table elevation (GTE), using available well-data of various screen lengths and depths. The water-level data after 1988, when subway constructions are mostly completed in the city, are divided into those of shallow wells (≤20 m deep), and those of deep wells (>20 m deep). First, the GTE map is generated by kriging interpolation of shallow well data with topographic drift. Next, the individual VHG value of each deep well is calculated using its top, middle, and bottom elevations of the screen depths, respectively. The VHG maps of three cases are then obtained using neighborhood kriging. The VHG map of the bottom screen depths has proven most valid by cross-validation. The VHG map better visualizes that downward flows of groundwater are predominant over the fan. Positive area of VHG is mostly vanished around the fan-toe, indicating urbanization effect such as artificial withdrawals. A negative peak of VHG corresponds to recharge area, and is seen along the distinct losing section in the river. The negative peak also expands upstream to the fan-apex where a basement is suddenly depressed.

Study of Tectonic Activity in Young Eastern Alborz, Central Iran on the Basis of Alluvial Fans in the Shahrud-Bastam Area

Alluvial fans are grouped in buildings which can provide important evidence of tectonic and climatic changes [1], Shahrud-Bastam area as structure point is located between Eastern Alborz structural zones in the north and central Iran structural zone in the south. In this study, we have measured 16 indicators morphotectonic on 79 alluvial fans and 46 catchments, according to the results of the measurements of morphometric parameters of alluvial basins and watershed, we find out that Qods-Armiyan’s fault zone has the most of tectonic activity between Tazareh and Shahrud fault regions. According to the index As, the development of alluvial fans often has a direct relationship with Level rise, which has a particular importance in the study field.

Al-Batin Alluvial Fan, Southern Iraq

Al-Batin alluvial fan is one of the largest alluvial fans in Iraq, especially in the Iraqi Southern Desert. Its eastern and southern limits form parts of the Iraqi-Kuwait international borders. The fan is deposited by Wadi Al-Batin, the last apex being on the southern limits of the main wide depression formed by the active Abu Jir-Euphrates Fault Zone. The main trend of the fan is almost SW-NE. The length and the maximum width of the fan are 110.192 Km and 119.1 Km, respectively, whereas the slope along its length is 0.7°. The fan is covered by gypcrete sheet with thickness varying from (0.5 - 1.5) m. Four stages were recognized within the fan, which is dated to be Pleistocene in age. The four stages are marked by clear height differences. The deposition of the alluvial fan is highly affected by the activity of the active Abu Jir-Euphrates Fault Zone, which is represented on the surface as a wide shallow depression in which the fan is laid down by Wadi Al-Batin. The continuous deposition of the fan has affected the course of the Euphrates Formation within Hammar Marsh and also the course of Khor Al-Zubair in its upper reaches south of Al-Qurna, where the Euphrates and Tigris rivers merge together. Also there is a trace of ancient distributary of the Euphrates River that was flowing directly to the Arabian Gulf, through an estuary, which is abandoned and does not exist anymore.

Quantitative Characterization and Genesis Analysis of Complex Modals of Pore Structure in Alluvial-Fan Sandy Conglomerate Reservoirs

新疆油田冲积扇砂砾岩储层岩石类型多样,颗粒大小混杂,分选极差,储层孔隙结构具有典型的多种模态特征,即单模态、双模态与复模态等。利用铸体薄片、压汞、恒速压汞资料定量表征了七东1区砂砾岩储层复杂模态孔隙特征以及连通特征,利用多元回归分析法建立复杂模态孔隙结构储层的识别模型。以此为基础,分析了冲积扇砂砾岩储层孔隙结构复杂模态成因机制。研究表明:单模态储层主要以Ⅰ类储层为主,双模态储层以Ⅱ、Ⅲ类储层为主,复模态储层以Ⅲ类储层为主。从单模态类型到复模态孔喉组合类型,孔隙发育由好变差,由连通较好的网状到连通较差的星点状,面孔率降低,平均孔径减小,孔喉配位数减小。利用已有147块样品统计发现,七东1区下克拉玛依组储层中单模态储层占19%、双模态储层占48%、复模态储层占33%。由此提出不同模态判断标准,建立了储层孔隙结构预测模型,揭示了储层构型、成岩后作用及注水(聚)开发中后期的系列变化等多因素是导致形成复杂模态的原因。

Soil evolution along an alluvial-loess transect in the Herat Plain,western Afghanistan

Afghanistan is located in the Eurasian loess belt,however,there is little information on the soils in the area.Loess has covered the Herat Plain in western Herat City,Afghanistan.Despite the diversity of landform and parent material,there is no information on the soil and landform evolution in this area.The objectives of this study were to identify the soils along a transect of different landforms in the Herat Plain and determine the role of geomorphic processes on the soil and landform evolution.Five pedons from an alluvial fan,the depression between alluvial fan and piedmont plain,saline and non-saline piedmont plains,and the flood plain of the Hariroud River,were sampled.Then,the physical-chemical properties,mineralogy,and micromorphology of the samples were determined.Results showed that the soil parent material in the piedmont plain is loess,whereas,in the flood plain it is a combination of loess and river alluvial sediments.Calcification,lessivage,salinization,and gleization are the most important pedogenic processes.The calcification and lessivage appear to be the result of a wetter climate during the late Quaternary,whereas the present topography causes the gleization and salinization.Clay coatings on carbonate nodules and iron nodules are abundant pedofeatures in the Btk(argillic-calcic)horizon.Iron oxides nodules are common in the soils of the flood plain.The formation of palygorskite in both alluvial-and loess-derived soils implies the onset of aridity and the trend of increase in environmental aridity in the region.It seems that after the formation of a well developed paleosol on the alluvial fan in a more humid climate in the past,the piedmont plain has been covered by loess deposits,and the calcification,gleization,and salinization cause the formation of weakly developed surficial soils.This study highlights the role of the late Quaternary climatic changes on the evolution of landforms and soils in western Afghanistan.

漳河山前冲洪积扇BK02孔古地磁定量分析及第四纪地层划分

冀西南平原西缘广泛发育的山前漳河冲洪积扇磁性地层研究尚不完善,其岩性组合特征、沉积环境与平原区建组剖面存在较大差异,第四纪地层精细化划分对比未充分建立。文章通过对位于漳河冲洪积扇西缘的第四纪标准钻孔BK02的岩心观察,根据沉积物颜色、沉积环境、岩性组合、沉积构造及旋回特征,将其第四纪地层松散沉积物划分为了T1~T6六个岩性段。通过对该孔第四纪沉积物地磁极性倒转序列分析,并结合14C、光释光等年代学测量成果,建立了该孔第四纪年代学框架,确定下更新统底界埋深为201.60 m,中更新统底界埋深为97.34 m,上更新统底界暂定为39.86 m,全新统底界埋深为13.75 m。

基于冲积扇构型表征的储层分类评价研究

按照“模式指导、岩心标定、动静结合、层次分析”的研究思路,综合应用丰富的岩心、测井、动态监测等资料,开展沉积微相、构型表征及储层精细评价研究,创新应用冲积扇7级体系沉积模式,剖析干旱型冲积扇优势构型单元空间叠置样式、差异化建立双物源5种单井相模式。在此基础上开展块状砂砾岩体有效储层识别,应用交会图聚类分析法,优选14项敏感评价参数开展储层分类评价,表征储层质量差异,明确优势储层空间分布特征。

The concept, characteristics and significance of fluvial fans

The concept and characteristics of fluvial fan are elucidated through literature review and case analysis.Firstly,the concept and terminology of fluvial fan are introduced.Secondly,the progress and controversy on the formation mechanism,analysis methods and sedimentary models of fluvial fan are elaborated,and fluvial fan is compared with alluvial fan,river and lacustrine delta.Finally,ten identification signs of the fluvial fan are proposed.It is found through the study that development and scale of fluvial fan are affected by external factors such as climate,tectonic,provenance and wind field.The facies and lithofacies association inside the fan are controlled by the activity of the internal channel.It is pointed that fluvial fans are widely distributed in the world not only today but also in the geological history.The occurrence of fluvial fan will change the traditional continental deposition system dominated by alluvial fan-river-lacustrine.Meanwhile,the research of fluvial fan will be of great significance in the fields of sedimentology and oil and gas exploration.

分支河流体系分类初探

通过综述国内外分支河流体系(DFS)的研究进展,总结了DFS的地貌特征和主要类型,并探讨了DFS形成和发育的控制因素。研究结果表明:(1)DFS不是新的或者特殊的河道类型,而是多种河道有规律的集合,地貌特征表现为水系网络从一点呈放射状展布,多种河型共同发育,河道几何形态变化大,沉积环境包括河道和河道间区域,沉积体系复杂;主要类型包括冲积扇、河流扇和巨型扇。(2)以DFS半径为关键指标,面积和坡度为辅助指标将DFS分为小型(冲积扇)、大型(河流扇)和巨型(巨型扇),小型DFS扇体半径小于30 km,面积小于100 km2,坡度大于1.0°;大型DFS半径为30~100 km,面积为100~1 000 km2,坡度小于1.0°;巨型DFS扇体半径大于100 km,面积大于1 000 km2,坡度小于0.5°,3种类型的分布范围有一定的交叉和重复,还需结合DFS的沉积水动力过程和沉积特征进行判别。(3)构造背景和气候是控制DFS形成与分布的最根本因素;流域面积、母岩性质直接影响DFS中沉积物供给总量、供给速率及成分和结构;地形坡度作为间接因素,与河流流量、流速等自生因素相结合,控制河道形态以及河道的分汊和决口,进而控制了DFS表面的沉积环境和沉积相分布。

上新世以来北京平原NBT1孔记录的地层沉积及构造指示

磁性地层学结合宇宙成因核素、AMS14C测年为晚新生代可靠的长序地质年代框架建立提供了有效快捷手段。在北京平原东南部钻取的NBT1全取芯钻孔进行了详细的磁性地层学研究,400 m钻孔335块样品识别出10个正极性和9个负极性时段,记录了布容(Brunhes)、松山(Matuyama)、高斯(Gauss)、吉尔伯特(Gilbert)极性时,孔底进入到4.2 Ma的Gilbert负极性时。以岩性组合、26Al/10Be、AMS14C年代学为基础,结合测井沉积相分析,判断钻孔上新世晚期地层底界位于319.60 m,第四系下更新统、中更新统、上更新统底界分别位于214.80 m、70.60 m、59.25 m。在上新世约4.2~3.5 Ma发育了6期明显的冲洪积扇的快速沉积过程,第四纪早更新世以曲流河沉积体系为主,中更新世以湖沼沉积为主,夹分支河道沉积,沉积厚度相对较薄,晚更新世以分支河道-湖沼沉积为主,其顶部末次盛冰期浊黄橙色硬质黏土发育。钻孔包含了3个沉积速率较高(>150 m/Ma)的时期,分别为3.58~3.33 Ma、1.945~1.778 Ma和0.126~0.010 Ma,与上新世以来青藏高原隆升扩展及华北地区晚更新世构造活化在时间上具有一致性,揭示了华北地区的沉积构造演化对青藏高原隆升具有一定响应。

干旱气候下冲积扇—冲积平原曲流河沉积演化过程与展布——以新疆库车河现代沉积为例

【目的】针对近年来沉积学界研究热点冲积扇、季节性河流、分支河流体系与河流扇等不同沉积体的划分、体系归属讨论等问题。【方法】开展干旱气候下库车河现代冲积扇-冲积平原曲流河沉积演化过程分析,聚焦于不同沉积体的界限变化与控制因素研究。【结果】发现在干旱气候下受同一条河流(库车河)控制的沉积体,发育山间辫状河-冲积扇-冲积平原曲流河等多种类型沉积。由出山口至下游冲积平原内河水散失,库车河延伸100 km以上,逐一发育冲积扇扇根辫状河道、泥石流等沉积,扇中大面积的辫状分流河道带沉积,扇端单一径流河道(低弯度曲流河)沉积,并向下游演化为冲积平原上的高弯度曲流河沉积。【结论】山间辫状河-冲积扇-冲积平原上曲流河沉积体在平面上连续分布,河流形态、河道宽窄变化等与沉积坡度密切相关,砾质沉积物的砾径变化与沉积搬运距离呈负相关关系,沙质沉积物由近源-远源分布范围增大明显。各沉积体的展布范围受库车河不同类型河道展布控制并紧密关联,而河道类型的变化主要受控于沉积坡度、沉积物特征、水流量变化等。

贺兰山东麓冲积扇区不同微地形土壤理化性质及酶活性特征

【目的】以贺兰山东麓冲积扇为研究对象,分析不同微地形土壤理化性质与土壤酶活性的空间分布特征及其差异性,探讨两者间相互关系,为贺兰山东麓冲积扇发育机制研究、生态修复及农业生产等提供理论基础。【方法】以野外调查取样和实验室分析测定为基础,运用经典统计学方法对不同微地形(冲积台地、高漫滩、槽滩、沟床)和不同土层深度(0~20、20~40 cm)的土壤理化性质与土壤酶活性进行分析,同时利用地理探测器结合典范排序方法对土壤酶活性与土壤理化性质的关系进行研究。【结果】在不同微地形,土壤砾石含量、有机质、全氮和碱解氮含量表现为冲积台地>高漫滩>槽滩>沟床,速效磷和速效钾含量表现为高漫滩>冲积台地>槽滩>沟床,各元素含量随着土层厚度增大而降低;土壤pH、全磷和全钾含量在不同微地形差异不显著;土壤酶活性在不同微地形表现为碱性磷酸酶与脲酶活性为冲积台地最高,沟床最低,过氧化氢酶与过氧化物酶活性为沟床最高,冲积台地最低。碱性磷酸酶、脲酶和过氧化氢酶活性随着土层厚度增加而减少,过氧化物酶活性随着土层厚度的增加而增加。地理探测器探测结果显示:研究区不同微地形土壤酶活性空间分异是各土壤理化性质共同作用的结果,不同因子对土壤酶活性的影响程度不尽相同。通过进一步的冗余分析表明:全氮、碱解氮、土壤砾石含量和速效钾是影响贺兰山东麓冲积扇区土壤酶活性变化的主要指标,重要性大小排序为:全氮>碱解氮>土壤砾石含量>速效钾。【结论】贺兰山东麓冲积扇区不同微地形土壤理化性质与土壤酶活性分布存在显著差异,土壤各理化性质对土壤酶活性的作用强弱不尽相同,揭示了土壤理化性质与土壤酶活性关系的复杂性及酶活性空间分布变异影响因子的多样性。