Numerical simulation on sand sedimentation and erosion characteristics around HDPE sheet sand barrier under different wind angles

For the safety of railroad operations,sand barriers are utilized to mitigate wind-sand disaster effects.These disasters,characterized by multi-directional wind patterns,result in diverse angles among the barriers.In this study,using numerical simulations,we examined the behavior of High Density Polyethylene(HDPE)sheet sand barriers under different wind angles,focusing on flow field distribution,windproof efficiency,and sedimentation erosion dynamics.This study discovered that at a steady wind speed,airflow velocity varies as the angle between the airflow and the HDPE barrier changes.Specifically,a 90°angle results in the widest low-speed airflow area on the barrier’s downwind side.If the airflow is not perpendicular to the barrier,it prompts a lateral airflow movement which decreases as the angle expands.The windproof efficiency correlates directly with this angle but inversely with the wind’s speed.Notably,with a wind angle of 90°,wind speed drops by 81%.The minimum wind speed is found at 5.1H(the sand barrier height)on the barrier’s downwind side.As the angle grows,the barrier’s windproof efficiency improves,extending its protective reach.Sedimentation is most prominent on the barrier’s downwind side,as the wind angle shifts from 30°to 90°,the sand sedimentation area on the barrier’s downwind side enlarges by 14.8H.As the angle grows,sedimentation intensifies,eventually overtakes the forward erosion and enlarges the sedimentation area.

Cost analysis of sand barriers in desertified regions based on the land grid division model

Sand barriers are the most widely used mechanical implements for wind-blown sand control and desertification prevention.However,there is no standard quantitative cost analysis of the sizes and materials required for sand barriers.In this study,based on the original land grid division model for optimal resource utilization,we calculated the total side lengths of square and regular hexagonal sand barriers with the sizes of 1.0 m×1.0 m,2.0 m×2.0 m,and 3.0 m×3.0 m in a desertified region of the Shapotou area on the southeastern edge of the Tengger Desert,China.Then,through literature review and social survey,we obtained the material cost and material utilization amount of sand barriers with different materials and sizes.Finally,we calculated the costs of square and regular hexagonal sand barriers comprised of wheat straw,corn stalk,Salix mongolica,poly lactic acid,magnesium cement,and high-density polyethylene,with the sizes of 1.0 m×1.0 m,2.0 m×2.0 m,and 3.0 m×3.0 m.The results show that the material cost of regular hexagonal corn stalk sand barriers with the size of 3.0 m×3.0 m is the lowest,while the material cost of square magnesium cement sand barriers with the size of 1.0 m×1.0 m is the highest.When using the same material,the cost of regular hexagonal sand barriers is lower than that of square sand barriers with the same size.When using the same size,the cost of sand barriers with corn stalk material is lower than that of sand barriers with other materials.Based on the above analysis,we can conclude that the economic benefits of regular hexagonal sand barriers are greater than those of square sand barriers.This study provides a theoretical basis for accurately calculating the material cost of sand barriers,particularly for the estimated cost of mechanized sand barrier engineering projects.

Progress and Problems of Development Research and Application of Sand Barriers

Due to the restrictions on the conditions for afforestation and sand control,the development research,and application of sand barriers have accelerated in recent years,but some problems that cannot be ignored have emerged in practice. In this paper,the functions of wind prevention,sand blocking and fixation,improving soil physical and chemical properties and increasing plant diversity of sand barriers,accretion coefficient and capacity between sand barriers,and mobile sand barriers were analyzed firstly,and then several issues that should be noted in the development and application of sand barriers were proposed. The results show that sand barriers can fix sand on the spot and maintain the stability of sand surface. As an auxiliary measure before afforestation on a mobile sand surface,they are practical and feasible. The biggest drawback of sand barriers is that they are easy to be saturated. Although they can increase plant diversity and surface roughness,they lose the function of blocking sand flow after being saturated,and their function of in-situ sand fixation also rapidly decreases with the degradation of sand barriers. Mobile sand barriers overcome the disadvantage of sand barriers being easy to be saturated to some extent,but the cost greatly increases. In terms of desertification prevention and control by plants,plants are used as sand barriers to study their functions of sand blocking and sand fixation in many researches and practices,but the more important ecological functions of adjusting temperature on sand surface and achieving surface thermodynamic equilibrium of plants are ignored.

Sand barrier morphological evolution based on time series remote sensing images:a case study of Anhaiao,Pingtan

The morphological evolution of the sand barrier in the Anhaiao coastal zone of Pingtan from 1996 to 2018 was studied.Tidal correction was used to refine the location of the coastline.A standard deviation ellipse method was applied to further analyze the movement of the barrier head with the axis and rotation angle.A natural neighbor interpolation(NNI)method was carried out to calculate the terrain of the intertidal area,and the erosion and deposition characteristics were illustrated based on the terrain.The results showed that the northern part of the sand barrier facing the lagoon area was deposited over the whole studied period,while erosion has always occurred in the southern part of the sand barrier facing the open sea.The erosion and deposition were slightly different on both sides of the barrier head due to hydrodynamic turbulence.The middle sand barrier moved 102.60 m away from its original location in 1996,and the end of the barrier moved 65.45 m.The head of the sand barrier continued moving 379 m to the northwest.Consequently,the preliminary morphological evolution of the sand barrier corresponding to the distance and direction of movement was detected.

Damage by wind-blown sand and its control measures along the Taklimakan Desert Highway in China

Desertification is one of the most serious environmental problems in the world,especially in the arid desert regions.Combating desertification,therefore,is an urgent task on a regional or even global scale.The Taklimakan Desert in China is the second largest mobile desert in the world and has been called the''Dead Sea''due to few organisms can exist in such a harsh environment.The Taklimakan Desert Highway,the longest desert highway(a total length of 446 km)across the mobile desert in the world,was built in the 1990s within the Taklimakan Desert.It has an important strategic significance regarding oil and gas resources exploration and plays a vital role in the socio-economic development of southern Xinjiang,China.However,wind-blow sand seriously damages the smoothness of the desert highway and,in this case,mechanical sand control system(including sand barrier fences and straw checkerboards)was used early in the life of the desert highway to protect the road.Unfortunately,more than 70%of the sand barrier fences and straw checkerboards have lost their functions,and the desert highway has often been buried and frequently blocked since 1999.To solve this problem,a long artificial shelterbelt with the length of 437 km was built along the desert highway since 2000.However,some potential problems still exist for the sustainable development of the desert highway,such as water shortage,strong sandstorms,extreme environmental characteristics and large maintenance costs.The study aims to provide an overview of the damages caused by wind-blown sand and the effects of sand control measures along the Taklimakan Desert Highway.Ultimately,we provide some suggestions for the biological sand control system to ensure the sustainable development of the Taklimakan Desert Highway,such as screening drought-resistant species to reduce the irrigation requirement and ensure the sound development of groundwater,screening halophytes to restore vegetation in the case of soil salinization,and planting cash crops,such as Cistanche,Wolfberry,Apocynum and other cash crops to decrease the high cost of maintenance on highways and shelterbelts.

Sand control effect of HDPE sandbreak nets with different porosity structure

Straw checkerboard sand barriers with a porous structure that consists of a pervious upper portion and a dense lower portion are widely used to achieve great sand control effect.Considering this,and resolving the serious earth surface undercutting problem after HDPE sandbreak net checkboard barriers setting,the authors used HDPE(high-density polyethylene)materials to prepare new sandbreak materials with a similar porous structure.Through wind tunnel simulations and field sand control monitoring,we compared the sand control effect of three HDPE sandbreak nets with different porosity structure.Compared to the sandbreak net with uniform porosity structure,the three types of HDPE sandbreak nets with different porosity structure had poorer effect on reducing sand transport rates,but had longer effective protection distance before sandbreak nets at low wind velocity conditions(<12 m/s),longer effective protection distance at high wind velocity(>14 m/s)and longer effective protection distance between sandbreak nets at all experimental wind velocity conditions.Wind and sand control effect characteristics of HDPE sandbreak nets with different porosity structure provide an ideal material on semiburied checkerboard sand barriers for sand stabilization.By contrast,uniform-type sandbreak nets are used as materials on high upright sand fences for sand blocking.These HDPE sandbreak nets can be used to replace traditional sandbreak materials and have a very high potential for widespread and popular application in aeolian sand disaster control.

Evolution Characteristics and Development Trends of Sand Barriers

Sand barriers are one of the main measures used to prevent desertification and have been widely used in desertification control. Here, we use bibliometric methods and content analysis to summarize sand barrier type, applications and research. Existing problems in research are pointed out and revolution characteristics and development trends of sand barriers are discussed. We conclude that three main driving factors have stimulated sand barrier study： demand, technology and development concept. Developing environmentally friendly technology and promoting industrialization of sand area economies are future directions for sand barrier research.

潮汕地区全新世障壁海岸三角洲沉积演化与砂体展布

全新世我国华南沿海广泛发育障壁海岸,此环境下发育独特的障壁海岸三角洲沉积。基于对潮汕地区的现代地质考察,并总结前人的研究认识,得出该地区韩江三角洲形成演化的主要控制因素为海平面变化、障壁—潟湖体系、河流搬运能力;明确了不同时期三角洲演化的特征及砂体的展布规律;然后,结合螺河三角洲和万宁小海的发育特点,划分出障壁海岸三角洲演化的三大阶段,即形成期:障壁—潟湖体系形成,潟湖内开始形成三角洲;发展期:潟湖内水体稳定,三角洲前积较快,障壁沙坝向海迁移;改造期:潟湖逐渐消失,沉积物开始在障壁沙坝外侧沉积,三角洲向海推进;最后,建立了潮汕地区早期潟湖内河流作用为主、后期障壁外多种动力共同作用下的障壁海岸三角洲的沉积模式。

土福湾赤岭岸线沙滩修复技术探讨

针对拦沙结构物优化问题,以土福湾赤岭岸线修复工程为例,分析了缩短拦沙堤长度而不影响航道的可行性。岸滩采用滩肩补沙方式,缩短拦沙堤长度至150 m,允许沙子绕过拦沙堤进入备用蓄沙池。实地检验近2年,期间遭受多场台风侵袭,尤其是2020年下半年台风组团影响,方案经受住了考验,证明设计效果良好。旁通输沙方案也节省了投资。研究表明,适当缩短拦沙构筑物也有可能达到预期成果,为类似沙滩养护工程带来新的启示。

太中银铁路典型路段防沙体系及其防护效果试验研究

针对太中银铁路受风沙危害日益严重的情况,根据因地制宜、因害设防等原则,以其中沙害最严重的定银线上K1 563＋500—K1 566＋850区段为试验段,在该区段内开展先设立复式阻沙栅栏、草方格及尼龙格状固沙网等工程治沙措施,后种植树（草）的防沙体系及其防护效果的试验研究.结果表明：阻沙栅栏的阻沙率随风速的增大而降低,平均阻沙率为81.1％;采取阻沙栅栏与尼龙格状固沙网相结合的综合阻沙固沙措施,不但能进一步提高阻沙率（平均为92.8％）,还能扩大积沙沉积的范围,且延长阻沙栅栏的使用寿命;采用草方格沙障措施可使地表粗糙度增加109倍,近地表风速降低45％～60％,流动沙面被固定;在工程治沙措施的保护下,区段内植被覆盖度提高了10～15倍,形成植物防沙体系,有效治理了铁路沙害.

古尔班通古特沙漠工程防护体系内的蚀积变化与植被的自然恢复

通过两年的实地监测和研究表明 ,古尔班通古特沙漠工程行为扰动地表后 ,草方格能有效固定沙面 ,并在初始两年形成稳定凹曲面。无人工辅助条件下 ,在草方格设置当年草本植物即可侵入 ,但小乔木和灌木的定居尚需近一步观测研究。线形工程的走向和风况影响植物种的传播 。

机械防沙体系防沙功能的衰退过程

作为一种十分有效的防治流沙的方法,机械防沙体系在防止风沙前移显示出很大的优越性,其目的就是要把流沙滞留在体系内,体系在发挥其功能的同时也是逐步丧失其功能的过程。在平坦地形条件下,草方格沙障积沙是从前沿向纵深发展的。在复杂地形地貌条件下,流沙的堆积具有不平衡性,且积沙形式多样。无论积沙形式如何,都有整体向前推进的趋势。阻沙栅栏的积沙形式因材料及孔隙度的大小而异,阻沙栅栏在初期时,可以拦截较多的沙量(75%),草方格固沙带只承担25%的积沙量,随着时间推移,阻沙栅栏的效益逐渐降低,草方格固沙带则要承担较多的积沙量。从阻滞的沙量来看,一道栅栏阻拦的沙量至少等于40行草方格滞留的沙量,在工程实践中应优先考虑栅栏的应用。

滦河口北部七里海地区中晚全新世沉积演化过程

滦河口北部七里海地区全新世演化过程是划分滦河三角洲范围的依据,也是认识陆海相互作用的有益补充。通过对七里海地区6个钻孔进行详细的沉积学、微体古生物研究和年代测定,分析了中晚全新世以来的沉积环境演化过程。滦河口北部七里海地区发育中晚全新世冲积扇-湖相三角洲、晚全新世砂坝-潟湖和海相三角洲及近现代砂坝-潟湖地貌沉积体系。6~5 ka B.P.,七里海西部发育冲积扇湖相三角洲沉积体系,东部为湖相三角洲前缘。5~1 ka B.P.,七里海南部形成潟湖,推断现今海岸线外侧发育一道滨海砂坝,区域形成第一期砂坝-潟湖地貌沉积体系。10~19世纪,区域受滦河泛滥的影响,逐渐成陆,发育潟湖-潮上带-分支河道的三角洲沉积组合。19世纪,第一期砂坝-潟湖地貌沉积体系中砂坝不断向陆迁移至翡翠岛,七里海地区形成浅水湖沼。1883年,滦河洪水在七里海新开口冲破海岸沙丘,形成七里海潟湖,区域形成现今砂坝-潟湖地貌沉积体系。1915年,滦河冲开翡翠岛南部沙丘入海,发育现代三角洲。

Seedling germination technique of Carex brunnescens and its application in restoration of Maqu degraded alpine grasslands in northwestern China

Carex brunnescens(Pers.)Poir.is considered to be the only clonal herb found to date that can develop and form fixed dunes in Maqu alpine degraded grasslands of northwestern China.However,due to strong dormant characteristics of C.brunnescens seeds,the sand-fixing effect of the plant is severely limited.This study explores a technique that can rapidly promote the seed germination of C.brunnescens,and also investigates the adaptation and sand-fixing effect by cultivating C.brunnescens seedlings to establish living sand barriers in the sand ridges of moving sand dunes.Results show that the seed germination rate obtained a maximum of 63.7%or 65.1%when seeds were treated with 150 mg/L gibberellic acid(GA3)for 24 h followed by soaking in sulfuric acid(98%H2SO4)for 2.5 min or sodium hydroxide(10%NaOH)for 3.5 h,and then germinated(25°C in daytime and 5°C at nighttime)in darkness for 10 d.After breaking seed dormancy of C.brunnescens,the living sand barrier of C.brunnescens(plant spacing 15−20 cm;sand barrier spacing 10−20 m)was established in the perpendicular direction to the main wind in the middle and lower parts of the sand ridges on both sides of the moving sand dunes.When the sand ridges were leveled by wind erosion,the living sand barrier(plant spacing 15−20 cm;sand barrier spacing 0.5−1.0 m)of C.brunnescens was reestablished on the wind-eroded flat ground.Finally,a stable sand-fixing surface can be formed after connecting the living sand barriers on both sides,thus achieving a good sand-fixing effect.These findings suggest that rapid seed germination technology combined with the sand−fixing method of C.brunnescens can shorten the seed germination period and make the seedling establishment become much easier which may be an effective strategy to restore and reconstruct Maqu degraded grasslands.

里下河古潟湖相软土基本工程特性与形成机理的关系

淮盐高速公路穿越的里下河地区,广泛分布有高含水量、高压缩性古潟湖相软土,工程性质很差,该层软土的工程性质与里下河古潟湖的形成机理密切相关。本文在对潟湖形成一般模式总结的基础上,结合苏北地区第四纪以来沉积环境及区域地质地貌变化情况,得出里下河古潟湖相软土的形成机理,并对淮沿高速公路盐线典型地段土样工程性质进行分析,根据土的工程性质的垂直变化,判断古潟湖相软土的分布情况,进而寻找古潟湖相软土工程性质与其形成机理之间的关系。

我国沙障的研究进展与应用综述

在总结我国沙障材料、沙障布设技术、沙障防沙治沙技术模式及其效益评价的研究进展基础上,指出目前沙障研究与应用存在沙障新材料较缺乏、防风固沙技术模式需进一步优化、沙障防护效益评价指标较单一等问题。随着人工智能技术与新材料的兴起,今后我国沙障领域的研究方向为:开发与研制长效、环保、经济的沙障新材料,发展智能化的沙障铺设机械,对沙障防护效益和沙障新材料降解过程进行长期连续性观测研究。

Coastal plain evolution in southern Hainan Island,China

The coast of southern Hainan Island is characterized by wide sandy embayments, which consist of ( i) drowned valleys bounded by steep bedrock hills and only locally receiving sediments, and embayments of various dimensions covered either by (ii) alluvial-deltaic deposits or by (iii) sands of coastal beach ridges/barriers and associated elongated lagoons. During the late Tertiary-Pleistocene the area has experienced isostatic and eustatic movements associated with neotectonics and climatic changes. Such history isrecorded in terraces at various altitudes (SO, 40, 20 m asl) and sequences of coastal sand ridges/baymouth bars. The Holocene variations in sea level and climate are recorded in the dated coastal ridges, coral reef and beachrock. Conditions suitable for reef development started about 8000 a BP. The GPR profiles also show that the internal structures of the sand ridges have composite nature being formed by several superimposed secondary ridges.

Coastal evolution of Yancheng, northern Jiangsu, China since the mid-Holocene based on the Landsat MSS imagery

Since the 1970s, remote sensing images have provided new information for the delineation and analysis of coastline changes, especially focusing on the short timescale changes. This paper, based on the Landsat MSS imagery, focuses on the coastline evolution of Yancheng, northern Jiangsu, China since the mid-Holocene. A zebra stripe image, which could reveal the ancient coastal evolution of Yancheng, was extracted from a Landsat MSS image. Based on the extracted black-white stripes, 19 surface sediment samples were recovered and analyzed to recognize the sedimentary characteristics of these stripes. It shows that most sand and silty sand samples appear on the white stripes, while silt and silty clay samples are on the black stripes. Sandy and muddy sediments present an alternating distri- bution pattern on the Yancheng coastal plain. A historical coastline map was drawn according to the previous research achievements of the paleo-coastal sand barriers and paleo-coastlines, and was superimposed on the zebra stripe image. The trend of the extracted zebra stripes is consistent with the historical coastlines, and it should be the symbol of the Yancheng coastline evolution. On the basis of ten sets of black-white stripes and previous research results, we divided the progression of Yancheng coastal evolution into three stages （i.e., the early stable stage （6500 a BP-AD 1128）, the rapid deposition stage （AD 1128-1855） and the adjustment stage （AD 1855-present））. Ten sets of black-white stripes were identified as the characteristic pattern of the coastline evolution on the Yancheng coastal plain.