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.

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.

Geomorphometric Features of the Alluvial Fans around the Chaka-Qinghai Lake in the Northeastern Tibetan Plateau

This article aims to study the geomorpometric features of alluvial fans since they act as a small-scale geomorphic unit response to tectonics and climate changes around the Chaka-Qinghai Lake area in the northeastern Tibetan Plateau. We quantitatively extracted geomorphic parameters, such as the surface area and slope of alluvial fans adjacent to the Qinghai Nan Shan and Ela Shan. Alluvial fans in the Chaka Lake partition area, south of the Qinghai Nan Shan, are featured by a small area and short length, but the largest slope. Geomorphic parameters of the alluvial fans in Ela Shan area are in- termediate in size, and the alluvial fans in the Qinghai Lake partition area north of Qinghai Nan Shan have the gentlest slope. Together with the regional faulting activity analysis, we suggest that the alluvial fans with the high slopes in the south of Qinghai Nan Shan are mainly controlled by the reverse faulting along the Qinghai Nan Shan faults, and the strike-slip movement of the Eia Shan fault zone plays a weak role. In contrast, due to the lack of active faults, the alluvial fans near the Qinghai Lake area north of the Qinghai Nan Shan only respond to regional erosion, transportation, and deposition proc- esses, thereby forming relatively gentle geomorphic units.

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.

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.

Initiation and Development of the Late Cenozoic Uplift of Daluo Mountains,Northeastern Margin of the Tibetan Plateau

Daluo Mountains lie at front of the arcuate tectonic belt at the northeastern margin of the Tibetan Plateau,and are the landform boundary zone between the active Tibetan Plateau and the stable North China Craton.Studying of the late Cenozoic uplift evolution of Daluo Mountains is important for understanding the expansion mechanism of the northeastern margin of the Tibetan Plateau and its influence on the western North China Craton.In this study,the late Cenozoic uplift of Daluo Mountains is constructed from the development of the late Cenozoic alluvial fan around Daluo Mountains.The entire sedimentary sequence and framework of the fan was revealed by the newly obtained drilling core data.The cosmogenic nuclide,optically stimulated luminescence,and detrital zircon U-Pb dating results provide new evidences for discussion about the initial timing of the late Cenozoic uplift of Daluo Mountains and the key stages of uplift during the Pleistocene.The late Cenozoic alluvial fan at front of Daluo Mountains overlies a set of fluvial-facies strata;therefore,development of the alluvial-fan marks the start of late Cenozoic uplift of Daluo Mountains.The timing of this event can be constrained to~4.64 Ma.Two extensive gravel layers(dated to ca.0.76–0.6 Ma and~0.05 Ma)developed during the Pleistocene,indicating two episodes of considerable uplift.This study provides a new time scale for the uplift and expansion of the arcuate tectonic belt at the northeastern margin of the Tibetan Plateau.

GIS tools for preliminary debris-flow assessment at regional scale

The assessment of the areas endangered by debris flows is a major issue in the context of mountain watershed management. Depending on the scale of analysis, different methods are required for the assessment of the areas exposed to debris flows.While 2-D numerical models are advised for detailed mapping of inundation areas on individual alluvial fans, preliminary recognition of hazard areas at the regional scale can be adequately performed by less data-demanding methods, which enable priority ranking of channels and alluvial fans at risk by debris flows. This contribution focuses on a simple and fast procedure that has been implemented for regionalscale identification of debris-flow prone channels and prioritization of the related alluvial fans. The methodology is based on the analysis of morphometric parameters derived from Digital Elevation Models(DEMs). Potential initiation sites of debris flows are identified as the DEM cells that exceed a threshold of slope-dependent contributing area. Channel reaches corresponding to debris flows propagation, deceleration and stopping conditions are derived from thresholds of local slope. An analysis of longitudinal profiles is used for the computation of the runout distance of debris flows. Information on erosion-resistant bedrock channels and sediment availability surveyed in the field are taken into account in the applications. A set of software tools was developed and made available(https://github.com/Hydrogeomorphology Tools) to facilitate the application of the procedure. This approach, which has been extensively validated by means of field checks, has been extensively applied in the eastern Italian Alps. This contribution discusses potential and limitations of the method in the frame of the management of small mountain watersheds.

Coupling within Fluvial Geomorphic Systems:Spatial and Temporal Implications

Coupling within fluvial systems relates to the connectivity between the various components of the system. It can be viewed at several scales from local scales of hillslopetochannel and reachtoreach coupling, to larger scales of zonal coupling between the major functional zones of the fluvial system, and to the scale of regional coupling. Coupling influences how the system responds to environmental change and how the effects of environmental change are propagated through the system. This paper provides a review, based largely on previously published work, of the coupling concept, and how the effective temporal scales vary with the spatial scale of coupling. Local scale coupling is considered through the hillslope to channel coupling in the Howgill Fells, northwest England, observed over a 30year monitoring period, together with examples from badlands in Spain, and reachtoreach coupling on the River Dane, northwest England. At the zonal scale the relative influence of climatic and baselevel change on coupling through dryregion alluvial fans is considered on fan systems in Spain, Nevada, and UAE/Oman. For large scale regional coupling, the response of the Tabernas basin, southeast Spain to tectonic uplift, is examined. The factors influencing coupling mechanisms vary with temporal and spatial scales. At the hillslopetochannel scale the significant factors are the magnitude and frequency characteristics of sediment generation and removal mechanisms within the context of progressive morphological change. Effective timescales range from the individual event to decadal timescales. At the zonal scale, that of alluvial fans, the significant factors are climatic change, and particularly in the appropriate morphological setting, baselevel change. Effective timescales are of the order of hundreds to thousands of years. At the regional scale, the response to tectonic uplift may take >100 ka to be transmitted through the drainage basin.

西藏拉萨河流域洪积扇的分布及其土地利用特征

In Lhasa River Basin(LRB),land suitable for settlement or living is experiencing a shortage of resources.Alluvial fans have the potential to alleviate this problem.However,basic information,such as the distribution and land use types of alluvial fans,is rarely studied.In this study,Google Earth,ArcGIS and visual interpretation were used to obtain the outlines,areas,quantities and distribution of alluvial fans.Meanwhile,to show the utilisation potential of alluvial fans,we analysed the land use,their distance from the roads,places(town and village)and rivers.The results showed 826 alluvial fans exist in LRB,with a total area of 1166.03 km2.The number of alluvial fans with areas between 0.1 and 1 km2 is 517,accounting for 62.59%of the total number of alluvial fans.Grassland is the dominant land use type,accounting for 68.70%of the total area of alluvial fans.The cropland area accounted for 2.16%of alluvial fans and accounted for 18.98%of the total cropland area in LRB.Exactly 93.70%,53.63%and 61.86%of the total number of alluvial fans were located within 5 km from the tertiary road,village,and river,respectively.To sum up,our survey results showed that alluvial fans are important land resources in LRB and may have huge utilisation potential.

基于机器学习确定青藏高原拉萨河流域洪积扇发育的主要影响因素

Alluvial fans are an important land resource in the Qinghai-Tibet Plateau with the expansion of human activities. However, the factors of alluvial fan development are poorly understood. According to our previous investigation and research, approximately 826 alluvial fans exist in the Lhasa River Basin(LRB). The main purpose of this work is to identify the main influencing factors by using machine learning. A development index(Di) of alluvial fan was created by combining its area, perimeter, height and gradient. The 72% of data, including Di, 11 types of environmental parameters of the matching catchment of alluvial fan and 10 commonly used machine learning algorithms were used to train and build models.The 18% of data were used to validate models. The remaining 10% of data were used to test the model accuracy. The feature importance of the model was used to illustrate the significance of the 11 types of environmental parameters to Di. The primary modelling results showed that the accuracy of the ensemble models, including Gradient Boost Decision Tree,Random Forest and XGBoost, are not less than 0.5(R^(2)). The accuracy of the Gradient Boost Decision Tree and XGBoost improved after grid research, and their R^(2) values are 0.782 and 0.870, respectively. The XGBoost was selected as the final model due to its optimal accuracy and generalisation ability at the sites closest to the LRB. Morphology parameters are the main factors in alluvial fan development, with a cumulative value of relative feature importance of 74.60% in XGBoost. The final model will have better accuracy and generalisation ability after adding training samples in other regions.

Stratigraphic Framework and Microfacies of the Triassic Lower Karamay Formation in Districts Ⅰ,Ⅲ, NW Junggar, China

The Triassic Lower Karamay Formation（T2k1） is one of the main oil-bearing stratigraphic units in the northwestern margin of Junggar Basin（NW Junggar）, China. Based on an integrated investigation of outcrops, well logs and seismic data of NW Junggar, the Lower Karamay Formation is subdivided into 2 sets, 6 beds and 13 layers. Also, it is considered that the alluvial fan, the braided river, the meandering river and the shore-shallow lacustrine were developed during the early period of Middle Triassic in Karamay districts Ⅰ, Ⅲ. The Lower Karamay Formation deposits the following 9 sedimentary subfacies： the lower fan, the middle fan, the upper fan, the braided channel, the overflow bank, the river flood of braided river, the meandering channel, the river flood of meandering river, the shore-shallow lacustrine. Seventeen microfacies such as the braided stream channel, the alluvial sand floodplain, the alluvial glutenite floodplain, the water channel, the channel bar etc. have been identified in subfacies as well. The thickness of strata is firstly up-thinning and then thickening upward to the top, it is a process from large-scale lacustrine transgression to partly lacustrine regression. Furthermore, the microfacies planar distributing law proves that the remaining oil may enrich along the margin of microfacies because of the planar microfacies changes. Therefore, this research is beneficial for searching remaining oil in NW Junggar and providing information to the project ＂The Secondary Exploration＂ of PetroChina.

Tectonic control on the drainage system in a piedmont region in tectonically active eastern Himalayas

The impact ofneotectonic activity on drainage system has been studied in a large alluvial fan in the eastern Himalayan piedmont area between the Mal River and the Murti River. Two distinct E-W lineaments passing through this area had been identified by Nakata （1972, 1989） as active faults. The northern lineament manifested as Matiali scarp and the southern one manifested as Chalsa scarp represent the ramp anticlines over two blind faults, probably the Main Boundary Thrust （MBT） and the Himalayan Frontal Thrust （HFT）, respectively. The fan surface is folded into two antiforms with a synform in between. These folds are interpreted as fault propagation folds over the two north dipping blind thrusts. Two lineaments trending NNE-SSW and nearly N-S, respec- tively, are identified, and parts of present day courses of the Murti and Neora Rivers follow them. These lineaments are named as Murti and Neora lineaments and are interpreted to represent a conjugate set of normal faults. The rivers have changed their courses by the influence of these normal faults along the Murti and Neora lineaments and their profiles show knick points where they cross E-W thrusts. The overall drainage pattern is changed from radial pattern in north of the Matiali scarp to a subparallel one in south due to these conjugate normal faults. The interfluve area between these two rivers is uplifted as a result of vertical movements on the above mentioned faults. Four major terraces and some minor terraces are present along the major river valleys and these are formed due to episodic upliftment of the ground and subsequent down- cutting of the rivers. The uppermost terrace shows a northerly slope north of the Chalsa scarp as a result of folding mentioned above. But rivers on this terrace form incised channels keeping their flow southerly suggestingthat they are antecedent to the folding and their downcutting kept pace with the tectonism.