砒砂岩分布及其治理.doc

砒砂岩分布及其治理吴永红 金剑 慕志龙 云殿智(黄委会西峰水土保持科学试验站，甘肃 庆阳 745000)摘要:在地理信息系统支持下，以TM影像为主要信息源，采用计算机辅助下的人工解译，对以晋陕蒙接壤地区为中心的砒砂岩分布范围进行全面界定，并将其划分为裸露区、覆土区、覆沙区三个类型区，确定了每一类型区的分布范围及面积大小。通过对砒砂岩区治理水土流失的生物措施及工程措施进行调研，本文提出了砒砂岩区综合治理的总体思路。提出在大面积封禁治理，充分发挥生态系统的自我修复功能的前提下，将沙棘作为砒砂岩区生物措施治理的突破口，采用混交造林方式，在立地条件较好的地方栽种油松、柠条；在工程措施方面结合沙棘植物“柔性坝”技术，以大、中型拦泥库为骨架，以淤地坝为主体，建设支流坝系。实现淤粗排细，改善进入下游河道的水沙条件及泥沙组成。关键词:砒砂岩 分布范围 治理 遥感The Soft Rock Borderline Defining and Its treatmentsWu Yonghong Jin Jian Mu Zhilong Yun Dianzhi(Xifeng Soil and Water Conservation Experimental Station under Yellow River Water Conservancy Committee, 745000, Qingyang, Gansu)Abstract: Take the tm remote sensing data as the main information source, with the supportting of geographic information system, by the meathod of computer assistanted artificial translation, we defined the bordline of the soft rock which mainly takes Shanxi, Shaanxi and Inner Mongolia contiguous area as its distribution center, and divided it into such three types areas as the exposed area, the loess covered area and the sand covered area. The distributive scope and the area size of each type have been determined. By inveresting biological and engineering measures for soil erosion in soft rock area, this paper gives some advices and general ideas on vegetation construction and comprehensive treatment in these areas, under the premise of large area closing treatment and the ecological recovering of ecosystem, takes seabuckthorn as the breakthrough for biological treatment, Chinese pine, ningtiao can be planted on places with good site condition. Mixed forestation is the most suitable forestation structure. For engineering measures, we should consider seabuckthorn vegetation flexible dam technology, take large and medium-sized dams as its framework, silt dams as it principal part, contruct branch dam system, in order to deposit coarse silt and exclude fine silt, and reform the runoff and sediment condition and sediment composition in lower reaches of the yellow river.Key words: soft rock board line distribution type remote sensing 1 前言在黄河流域的晋陕蒙接壤地区，分布着被当地人俗称为“砒砂岩”的松散岩层，它具体指古生代二叠纪、中生代三叠纪、侏罗纪和白垩纪的厚层砂岩、砂页岩和泥质砂岩组成的岩石互层。该地层为陆相碎屑岩系，由于其上覆岩层厚度小、压力低，造成其成岩程度低、沙粒间胶结程度差、结构强度低。它无水坚硬如石，遇水则松软如烂泥。由于这种岩层自身物理、化学性质和当地特殊的自然、人文环境，使得该岩层极易发生风化剥蚀，群众深受其水土流失危害，视其危害毒如砒霜，故称其为“砒砂岩”。砒砂岩区土壤侵蚀模数高达34万/km2.，多年平均输沙量为1.61亿t，其中大于0.05mm的粗沙量为0.982亿t，占河龙区间北部八条粗沙来源支流总输沙量的39%，是黄土高原侵蚀最剧烈的区域，被中外专家称为“世界水土流失之最”和“环境癌症”。国家非常重视砒砂岩区的治理，在该地区先后开展实施了许多研究和治理项目，这些项目对于揭示砒砂岩地区水土流失的复杂机理和实施科学防治起到了积极作用。但多年来人们只知道晋陕蒙接壤地区是砒砂岩的分布中心，砒砂岩的分布范围究竟有多大，学术界尚未有全面准确的数据。因此，准确划分砒砂岩区的范围和类型对全面治理砒砂岩区水土流失极为重要，同时也可为治理黄河粗泥沙来源区提供科学依据。为了能够快速、准确地查清砒砂岩分布范围，我们采用遥感技术进行砒砂岩分布范围界定。我们选择TM卫星遥感影像作为信息源，运用地理信息系统作为数据采集平台，通过野外实地调查建立TM影像解译标志，进行机助人工图像解译，由计算机进行面积自动量算。2 范围界定与类型区划分的标准2.1 砒砂岩范围界定标准顾名思义，凡是存在砒砂岩的地方就应该确定为砒砂岩分布区，但是以此划定的范围对于研究黄河泥沙和进行砒砂岩治理并无实际意义。我们界定范围的目的就是要为今后砒砂岩区的治理提供依据，因此，我们所说的砒砂岩分布区指的是砒砂岩在地表出露并已造成水土流失危害或潜在水土流失危害的地区。即使从地质图或钻探资料上看，某些地方的下覆基岩与砒砂岩有着同样的岩性，但在这些地方地表没有砒砂岩露头，即没有砒砂岩影像特征，砒砂岩在这些地方没有形成水土流失危害，就不把这些地方划为砒砂岩分布区。因此，砒砂岩分布范围的界定标准是：如果砒砂岩在某一地区的侵蚀沟中有大面积出露，即影像上具有砒砂岩的影像特征，则该区为砒砂岩分布区。当然，在黄土高原的其它地方也有与砒砂岩具有相同的岩性，同时也有水土流失现象，但这些岩层不叫砒砂岩，这些地方也不属于我们这次范围界定的工作区，这次范围界定的工作区是：以晋陕蒙接壤区为中心的砒砂岩集中、连片出露的地方。1998年，黄委会绥德水保站利用当时的Mss卫片进行了晋陕蒙接壤区砒砂岩范围界定和类型区划分。按照地表覆盖物的不同，砒砂岩地区可分为裸露砒砂岩区、盖沙区、盖土区三个类型区。这种划分方法基本上能够反映不同类型砒砂岩的特征。因此，这次调研仍沿用这种划分方法和命名方法，以免产生概念混淆，引起误解。但具体边界主要依据TM影像特征和野外调查结果进行确定。绥德水保站所界定的砒砂岩分布范围限定在晋陕蒙接壤区，这次调研将砒砂岩范围向西扩展至杭锦旗境内的毛布拉孔兑，所确定的砒砂岩分布范围较绥德水保站所确定的范围大。2.2 砒砂岩类型区划分标准裸露砒砂岩区：砒砂岩直接见于地表，上面无黄土、风沙土覆盖或覆土（沙）极薄（0.1-1.5m）。凡是此类砒砂岩出露面积占总面积70%以上的区域，即为裸露砒砂岩区。裸露砒砂岩区地貌多呈岗状丘陵，沟壑密度平均为57km/km2，植被稀少，覆盖度极低，上覆薄层的黄土或浮沙，一般为10150cm，基岩大面积裸露。侵蚀模数2.1万t/km2.a左右，以水蚀为主，复合侵蚀严重。砒砂岩不仅在沟谷中出露，而且在坡面上出露。岩性为砾岩、砂岩及泥岩，交错层理发育，颜色混杂，有棕红色、紫红色、黄绿色、白色、灰白色，风蚀与水蚀都很严重。其影像特征是沟谷水系发育，沟谷阴影不明显，影像色调较浅，缺乏植被的颜色（绿色），大部分地区呈现肉红色、浅紫色。盖土区：砒砂岩掩埋于各种黄土地貌之下。砒砂岩作为黄土沉积前的一种凸凹不平的古地形，代表了黄土沉积前的整个沉积间断，其本身就是一种风化剥蚀面，呈波状面分布。在沟谷中表现为黄土戴帽，砒砂岩穿裙的特殊的地貌景观。黄土覆盖一般大于1.5m，凡是此类砒砂岩分布且砒砂岩出露面积达30%以上的区域，称为盖土砒砂岩区。盖土砒砂岩区地貌多呈黄土丘陵沟壑，植被覆盖较裸露区好，上覆黄土或浮沙，黄土层从几米到几十米不等，梁峁顶部分布较厚，沿坡从上到下逐渐变薄。沟壑密度在36km/km2之间。除部分梁峁和缓坡地为耕地外，多为天然草场，植被覆盖度为20%左右，侵蚀模数1.5万t/km2.a，属剧烈侵蚀区，以水蚀为主，水蚀、风蚀和重力侵蚀交替发生。砒砂岩主要在沟缘线以下的沟谷中出露，而且切割很深，呈典型的“V”字形沟道，坡度在35以上。岩性为砂岩及泥岩，层理发育，但每一种颜色的砒砂岩分布厚度较大，颜色有紫红色、黄绿色、灰白色。与裸露区相比，盖土区植被较好，因此影像特征表现为整体绿色较多，沟谷水系发育。由于沟道切割很深，因此沟谷阴影明显，影像色调较深。盖沙区：由于受库布齐沙漠和毛乌素沙地风沙的影响，鄂尔多斯高原上的丘陵及梁地砒砂岩掩埋于风沙之下，或形成部分沙丘及薄层（1030m）沙和砒砂岩相间分布，或形成风沙戴帽，砒砂岩穿裙的地貌景观，凡有此类砒砂岩分布且出露面积达30%以上的区域，称为盖沙砒砂岩区。平均沟壑密度为13km/km2，地表沙化严重，侵蚀模数0.8万t/km2.a，以风蚀为主，呈现出风、水蚀复合侵蚀的景观。盖沙区与裸露区及覆土区的区别就是地表黄土覆盖薄且有浮沙覆盖，地表水系不发育。因此，它的影像特征是纹理不明显，水系不发育，沟道阴影较轻，有明显沙地的影像特征。岩性为泥岩、含砾砂岩、页岩、及长石砂岩，胶结疏松，颜色有紫红色、咖啡色、灰白色、姜黄色，风化剥蚀严重。3 砒砂岩分布范围根据砒砂岩分布范围界定结果，砒砂岩分布区总面积1.67万km2，集中分布在内蒙古自治区鄂尔多斯市的东胜区、准格尔旗、伊金霍洛旗、达拉特旗、杭锦旗，在陕西省的神木、府谷两县，山西省的河曲、保德两县，内蒙古的清水河县有零星分布；其中：裸露砒砂岩区面积4543.89km2，盖沙砒砂岩区面积3709.18km2，盖土砒砂岩区面积8432.41km2，分别占总面积16685.48 km2的27.2%、22.2%、50.6%。分布范围东至黄河，西达杭锦旗境内的毛布拉孔兑，从西北向东南沿毛乌素沙地西北缘分布，南抵陕西省神木县城，北到库布齐沙漠南缘，介于北纬38104010，东经1084511131之间，大致分布在由杭锦旗、清水河县、神木县城三点组成的三角形区域内（见图1）。砒砂岩在各主要直接入黄支流的分布面积以窟野河和皇甫川面积最大，其次为孤山川、清水川、浑河。皇甫川、孤山川、清水川几乎全流域都分布在砒砂岩区，窟野河在神木以上基本全部分布在砒砂岩区。还约有三图1 砒砂岩分布区地图fig.1 Map of soft rock distribution分之一面积的砒砂岩分布在内蒙古十大孔兑及其它直接入黄支沟。4 砒砂岩区的综合治理4.1 综合治理开发的总体思路针对砒砂岩区的具体情况和经济发展的需求，本区治理开发的总体思路是：实行大面积封禁治理，充分发挥生态系统的自我修复功能，在这个前提下，因地制宜，积极推进林草植被建设、退耕还林还草，以沟道坝系建设为切入点，加大以治沟骨干工程为主的沟道坝系建设力度。4.2 植物措施治理思路（1）实施生态修复和植被建设砒砂岩区地广人稀，荒地资源丰富，加之能源重化工基地建设和城镇化进程加快，广大农村人口增长趋势已渐和缓。尽管降雨时空分布不均，但多年平均降雨量约400mm。在该区域实施生态修复将是生态建设中速度最快、效益最好、成本最低的措施之一。（2）以沙棘作为砒砂岩区生物措施治理的突破口根据现有沙棘的生长表现来看，沙棘可作为砒砂岩区生物治理的突破口，尤其适宜在水土流失严重的裸露砒砂岩上推广种植，以充分发挥其优良的防护效能。从长远来看，栽种沙棘应结合本区特点，对于平缓区应尽量采用宽带状种植，株行距以124610m为宜，以利于放牧。大力提倡营造沙棘混交林，在发挥沙棘保水保土效益及改良土壤功能的同时，为其它植物的生长发育创造适宜的环境，促进该区植被向良性演替方向发展。另外，还要加强沙棘优良品种的开发研究，以提高其经济价值。（3）在盖沙砒砂岩上种植柠条柠条耐干旱瘠薄，适应广泛，在砒砂岩区的各种土地条件下生长良好，尤其适合生长在松散的沙质土上。因此，宜在盖沙砒砂岩区应推广种植。为了充分利用柠条的放牧价值，应提倡轮封轮牧，适时平茬，合理利用。对低产沙地草场，可通过补植或补播柠条加以改造，提高草场的利用价值。（4）油松、沙棘可作为砒砂岩区造林的主要树种从调查结果可以看出，油松能在砒砂岩坡面上正常生长，年平均高生长20-30cm，沙棘无论在坡面还是沟道，均能很好生长，年均高生长量20-50cm。因此，油松、沙棘是砒砂岩区造林的主要树种，但油松只适宜在砒砂岩缓坡上造林。（5）其它可推广种植的植物种经典型调查分析，在砒砂岩区具有推广价值的优良饲草植物有：羊草、冰草、无芒雀麦、紫花苜蓿、沙打旺、扁蓄豆、野豌豆、驼绒藜等；优良灌木树种有：花棒、羊柴、乌柳、沙柳、柽柳、黄刺玫、蒙古莸花、芨芨草等；优良乔木树种有：侧柏、樟子松、河北杨、旱柳、刺槐等。（6）根据不同草树种的生物学特性和造林立地条件，砒砂岩区宜采用混交类型进行植被建设4.3 工程措施治理思路（1）以大中型拦泥库为骨架，淤地坝为主体，建设支流坝系根据坝系工程布局研究成果，在一般情况下，骨干坝与淤地坝的比例在1：2到1：5之间，而砒砂岩坝系均存在骨干坝比例偏大，中、小型淤地坝比例偏小的问题。当然，这种情况的出现与坝系的发展阶段有关，这些坝系都才从第一阶段向成熟的坝系发展，中、小型淤地坝尚处于起步阶段，是今后进行坝系建设的主体。在流域面积小于3km2的支毛沟内，建设以拦泥淤地、发展基本农田为主的中小型淤地坝；在流域面积大于3km2的支沟内，兴建蓄水、拦沙、防洪、淤地为一体的治沟骨干工程，保证下游坝地的安全生产；在治沟骨干工程难以控制、条件好的大支沟或干流兴建大中型拦泥库；在有水源的沟道布设水库、池塘，为城镇生活和工业用水以及农业灌溉提供水源。（2）采用植物“柔性坝”和淤地坝集成技术，实现淤粗排细在靠近淤地坝坝体部位、上游尾端和溢洪道进口上部布设沙棘植物“柔性坝”。以植物“柔性坝”拦沙工程为主体，以沟道淤地坝、“人工湿地”、“人工滩地”为沟底基本农田的主要组成部分。以骨干坝为依托，以微型水库为保证，形成支毛沟拦截粗沙，“人工滩地”、沟道坝地拦截细沙，坝与坝之间形成“人工湿地”、沟道坝地，增加天然径流入渗量。微型水库拦蓄全部剩余径流，达到缓洪、拦蓄粗泥沙、泄洪入河，实现淤粗排细，改善进入下游河道的水沙条件及泥沙组成，维护河流生态功能。参 考 文 献 毕慈芬，邰源林，王富贵，李贵，,乔旺林，胡存胜：防止砒砂岩地区土壤侵蚀的水土保持综合技术探讨，泥沙研究，2003年6月第3期，p6365；2 姚文艺，时明立，崔长江：黄河泥沙问题研究综述，黄河水利职业技术学院学报，2004年1月第16卷1期，p14；The Soft Rock Borderline Defining and Its Treatments Wu Yonghong, Jin Jian,Mu Zhilong and Yun Dianzhi（Xifeng Soil and Water Conservation Experimental Station under Yellow River Water Conservancy Committee, , Qingyang, Gansu745000）Abstract: Take the tm remote sensing data as the main information source, with the supporting of geographic information system, by the method of computer assistant artificial translation, we defined the board line of the soft rock which mainly takes Shanxi, Shaanxi and Inner Mongolia contiguous area as its distribution center, and divided it into such three types areas as the exposed area, the loess covered area and the sand covered area. The distributive scope and the area size of each type have been determined. By investigating biological and engineering measures for soil erosion in soft rock area, this paper gives some advices and general ideas on vegetation construction and comprehensive treatment in these areas, under the premise of large area closing treatment and the ecological recovering of ecosystem, takes sea buckthorn as the breakthrough for biological treatment, Chinese pine, caragana intermedia can be planted on places with good site condition. Mixed forestation is the most suitable forestation structure. For engineering measures, we should consider sea buckthorn vegetation flexible dam technology, take large and medium-sized dams as its framework, silt dams as it principal part, constructs branch dam system, in order to deposit coarse silt and exclude fine silt, and reform the runoff and sediment condition and sediment composition in lower reaches of the yellow river.Key words: soft rock board line distribution type remote sensing1 PrefaceIn the Shanxi, Shaanxi and Inner Mongolia contiguous area of Yellow River Basin, Distributed a loose rock commonly known as Soft Rock by the local people (Soft Rock is a local name, some people translate it as Feldspathic Sandstone), it specifically refers to the thick interbed rock layers which is composed of sandstone, sand shale and mud sandstone of Paleozoic Permian, Mesozoic Triassic, Jurassic and Cretaceous. This formation belongs to continental clastic rock series. Because of its thin overlying rocks and low pressure, it has characteristics of lower degree diagenesis, poor levels of cementation between sands, and lower structural strength. It is hard as stone when it is dry, but soft as mud when it is wet. As a result of its natural physical, chemical characters and the special local natural and cultural environment, weathering denudation is often occurred on soft rock. The local people was deeply endured the hazards of its severe soil erosion, regards it as arsenic poisoning, so called it Soft Rock.The soil erosion modulus in soft rock area is as high as 30000 40000 t/km2.a. The annual sediment discharge is 161 million tons. Among them, the yield of coarse sediment which diameter greater than 0.05 mm is 098.2 million tons, account for 39% of the total volume of sediment discharge of the eight northern coarse sediment tributaries in the territorial of Hekou town to Longmen. It is the severest erosion region in Loess Plateau, it was called the highest erosion of the world and environmental cancer by Chinese and foreign experts. Our central government attaches great importance to the controlling soft rock erosion in this area, and have launched a number of research and treatment projects in the region. It has played a positive role for revealing the complex mechanism of soil loss and the implementing scientific control. But for many years people only know that Shanxi, Shaanxi and Inner Mongolia contiguous area is the soft rock distribution center, but how far on earth is the range of the Soft Rock? No one knows. Therefore, that how to draw the line and make a division to the soft rock distribution is not only very important to control the soil and water loss in soft rock areas, but also provide the scientific basis for the coarse silt areas of the Yellow River.In order to identify the distribution of the Soft Rock quickly and accurately, we use remote sensing technology to define the scope of Soft Rock, chose satellite remote sensing image TM as a source of information, use geographic information systems as the platform for data acquisition. Through the wild-spot investigations to establish TM image interpretation signs, a computer-aided interpretation of images is used. The area of each map spot is automatically calculated by computer.2 Standards for board line definition and types division2.1 Standards for soft rock board line definition As the name suggests, all place where exists soft rock should be identified as soft rock area, but this delineation has no practical significance in Soft Rock management and the sediment research work of the Yellow River. The purpose that we define the scope of Soft Rock area is to provide the basis for the future management, therefore, what we call the Soft Rock area refer to the region that Soft Rock is exposed on the surface land and severe soil erosion has caused or potential erosion will occur. That is to say , Even if the sandstone bedrock of certain areas have the same lithology from drilling data or geological map, but there isnt Soft Rock outcrop in these areas, or we cant find Soft Rock from satellite image, and severe soil erosion hasnt occurred in these areas, we dont identify these areas as Soft Rock area. Therefore, the standards for soft rock board line definition are: areas that there are large Soft Rock outcrop or we can distinguish Soft Rock from satellite image. These areas are Soft Rock area. Indeed, in some places on loess plateau, the lithology is the same with Soft Rock, and soil erosion has occurred in these areas, but we dont call it Soft Rock area, it doesnt belong to our workaround. The workaround is places mainly take Shanxi, Shaanxi and Inner Mongolia contiguous area as its distribution center and have large areas of Soft Rock outcrop.In 1998, researchers of Suide soil and water conservation station drew the line and made a division to the Soft Rock distribution in Shanxi, Shaanxi and Inner Mongolia contiguous area by Mss Satellite image. According to the different surface cover, they divided whole Soft Rock area into exposed, sand covered and loess covered Soft Rock partitions. This division method can basically represent the characteristics in Soft Rock area. Therefore, our investigation is still in use of such division methods and its name in order to avoid confusion and misunderstanding. But the exact border is based on specific image features of TM and field survey. Previous research drew the scope line in Shanxi, Shaanxi and Inner Mongolia contiguous area. Our research work extends the range west to Maobula gully in Hangjin Country. The area is larger than before.2.2 Standards for type areas divisionExposed area: Soft Rock can be seen at the surface land, there isnt loess, Aeolian sandy soil covered on it or covered with thin loess or Aeolian sandy soil (0.1-1.5 m).All such regions that account for more than 70 percent of the total area are exposed Soft Rock area. Exposed Soft Rock areas are hilly topography, with average gully density of 5 7 km/km2,Scarce vegetation, low coverage degree, covered with thin layer of loess or floating sand (usually 10 150 cm), large areas bedrock are exposed. Erosion modulus is about 21,000t/km2.a, mainly by water erosion, with serious composite erosion. Soft Rock not only exposed in valley but also on slope, with lithology of conglomerate, sandstone and mudstone, across bedding, mixed colors, as reddish brown, purple, yellow-green, white, gray, serious water and wind erosion. Its image features is characterized by developed valley and drainage network. The valley shadow is not obvious. Image tone is light. It is lack of vegetation in color (green). Most parts present red meat, light purple.Loess covered area: Soft Rock is covered with loess on slop and exposed in gully. The average thickness is more than 1.5m. All such regions that bare Soft Rock takes more than 30 percent of the total area are loess covered Soft Rock area. Its landform is loess hilly and gully. Vegetation coverage degree is high than exposed area. Loess thickness range differs from a few meters to tens of meters. Loess is thick on top hill and gradually become thin from top to bottom. Average gully density between 3 6 km/km2. Most slop land is natural pasture except some cultivated land on mild slope land of top hill. Vegetation coverage degree is about 20%. Soil erosion modulus is 1,5000t/km2.a, belong to severe soil erosion region. Water erosion is the major erosion type, with wind erosion and gravity erosion alternative occurred. Soft Rock exposed in the gully which below the shoulder line of valleys, and deeply cut, appears typical V shape gully; its slope is steeper than 35 degree. With Horizontal beddings, lithology of Soft Rock is sandstone, mudstone. Rock colors are purple, yellow-green and gray. Compared with exposed area, loess covered area is well covered with vegetation. Its image features is characterized by developed valley and drainage network and green in color, with deeply cut gully, obvious gully shadow and dark image tone.Sand covered area: By the impact of sandstorms from the Kubuqi Desert and the Mu Us Sandy Land, the Soft rock on hills of Ordos plateau buried under the sand, or dunes alternate with Soft Rock, formed the landscape that Soft Rock is covered with loess on slop and exposed in gully. All such regions that bare Soft Rock takes more than 30 percent of the total area are sand covered Soft Rock area. Its average gully density is between 1 3 km/km2. The desertification of surface land is serious. Soil erosion modulus is 8000t/km2.a. Wind erosion is the major erosion type, compound with serious water erosion. The difference between loess covered area and sand covered area is the material that covered on Soft rock. The surface of sand covered area is covered by sand and drainage network is not developed. Therefore, its image features are characterized by no obvious texture, not developed drainage network, light gully shadow, obvious sandy features. The Soft Rock lithology is mudstone, pebbled sandstone, shale and arkose, with loose cementation and severe weathering denudation. Rock colors are purple, brown, gray, yellow ginger.3 oft Rock distributive scopesFig.1 Map of soft rock distributionThe result shows that the total area of Soft Rock is 16,700 km2, located in Dongsheng district, Zhungeer, Yijinhuoluo, Dalate, Hangjin country of Ordos City in the Inner Mongolia Autonomous Region ; Shenmu, Fugu County of Shaanxi Province; other small areas of Soft Rock scattered in Hequ and Baode County of Shanxi Province and Qingshuihe County of Inner Mongolia, among the total area of 16685.48 km2, bare Soft Rock area is 4543.89 km2, sand covered Soft Rock is 3709.18 km2, loess covered Soft Rock is 8432.41 km2, accounts for