Evaluating the optimal porosity of fences for reducing wind erosion   总被引：1，自引：0，他引：1  

ZhiBao Dong  WanYin Luo  GuangQiang Qian  HongTao Wang 《寒旱区科学》2011,3(1):0001-0012

Porosity is the most important parameter determining the shelter efficiency of fences. Wind measurements were made around fence models with different porosities in a wind tunnel. The optimal fence porosity is evaluated by means of Gandemer’s method that combines the effects of wind reduction and turbulence fields on the shelter efficiency for abating wind erosion. Defining the optimal porosity must take into account of its own purposes, required shelter degree and area to be sheltered. Turbulence has profound impacts on the shelter efficiency of high degree. Two concepts: absolute optimal porosity and practical optimal porosity concerning optimal porosity are proposed. Choosing the practical optimal porosity means reducing cost without significant expense of shelter efficiency. According to the evaluation in present study, the absolute optimal porosity for providing high degree of shelter to abate wind erosion is 0.20 while the practical optimal porosity is around 0.40. If a less shelter degree but over wider area is required, the absolute optimal porosity ranges from 0.05 to 0.10 and the practical optimal porosity is 0.10. For any degree of shelter for abating wind erosion effectively, the fence porosity must be less than or equal 0.40.  相似文献   

探地雷达对地下防空洞的探测研究     

谷松 《城市地质》2011,6(3):47-48

本文简述了探地雷达技术的基本原理及其在阜新高德东山探测防空洞的应用。  相似文献   

Impacts of Habitat Complexity on Physiology: Purple Shore Crabs Tolerate Osmotic Stress for Shelter     

I. J. McGaw   《Estuarine, Coastal and Shelf Science》2001,53(6):865

Purple shore crabs, Hemigrapsus nudus (Crustacea: Decapoda), can survive indefinitely in salinities of 8 (25% SW), but also tolerate short-term exposure to salinities as low as 2. In the laboratory their salinity preference range, determined from choice chamber experiments, is 22–32 and they can discriminate between pairs of salinities separated by a difference of 2. These crabs show a strong positive thigmotaxis and a weak negative phototaxis and tend to choose environments with available shelter. The presence of shelter significantly alters the behaviour of this species. When shelter is available the salinity preference range is 10–32. Even in salinities below this preference range, the presence of shelter prolongs the time spent in the lower test salinities. This change in behaviour has implications on the crab's physiology: the haemolymph osmolality falls to lower levels when crabs remain in low salinity under shelters. In the field, H. nudus is found in creeks with salinities close to freshwater and they may remain in this salinity for up to 11 h, if there are rocks under which to shelter. An increase in habitat complexity increases the number of crabs that are found within the creek. These crabs in the low salinity environment have a lower haemolymph osmolality than crabs on the nearby open shore. In H. nudus the behavioural selection of a shelter appears to outweigh the physiological costs associated with osmotic regulation of the body fluids. Therefore, the distribution of H. nudus in estuaries may depend more on the availability of suitable habitats rather than the salinity tolerance of this species.  相似文献   

Trimble影像扫描仪SX10在防空洞的应用     

刘平利  王传先  张鸿祥  刘松源  乔天荣 《测绘通报》2020,(5):158-160

7401防空洞是20世纪60—70年代建设的，主要预防战争空袭，由于年久失修，里面有部分坍塌，且在雨季时有渗水现象。本文通过对7401防空洞详细勘察，采用Trimble SX10三维扫描系统准确测量出7401防空洞的位置、空间尺寸、坡度、损毁段面积等情况，为7401防空洞修复提供了数据依据。  相似文献   

The Dynamics of an Introduced: Balanus glandula Population in the Southwestern Atlantic Rocky Shores. The Consequences on the Intertidal Community*     

E. A. Vallarino  R. Elias 《Marine Ecology》1997,18(4):319-335

Abstract. This paper deals with the population dynamics of the introduced barnacle Balanus glandula in a port shelter and a rocky shore exposed of a southwestern Atlantic area. Replicated areas in both zones were denuded monthly and censused in both the high intertidal and the upper mid intertidal zone. The settlement pattern. recruitment, mortality and growth of B. glandula and a comparative successional pattern in both areas were recorded. Recruitment began in winter, i.e., July in the port and August in the rocky shore. In the port, green algae dominate up to a final community of Balanus glandula all along the intertidal, while in rocky shores the red encrusting alga Hildenbrandia lecanellieri establishes a cover that is replaced by the mytilid Brachidontes rodriguezi in the mid intertidal and by B. glandula in the high intertidal and upper mid intertidal. B. glandula densities were greater in the upper mid intertidal 19 600 and 5050 indiv. · m^-2 in the port and rocky shore, respectively than in the high intertidal 13600 and 1100 indiv.· m^-2, respectively. Mortality was greater in the port up to 62%, but heavy settlement allows a final density 4 times greater than in eulittoral rocky shores and 10 times greater than in the high intertidal. The winter reproduction of Balanus glandula, the absence of predators, the neutral or beneficial effect of algae. with spatial and temporal partitioning of substrate allows it to successfully outcompete mussels and other barnacle species from the intertidal community of both sheltered and exposed areas.  相似文献   

Envisat ASAR数据在沿海防护林提取中的应用     

池泓  汪小钦 《测绘科学》2008,33(3):138-140

沿海防护林的建设与生态环境和经济发展密切相关。本文以福建省漳浦县沿海防护林地区为例,利用2005年多时相、多极化的ENVISATASAR(Environmental Satellite Advanced Synthetic Aperture Radar)数据,分析了典型地物后向散射极化和时间特性。沿海防护林的后向散射随时间变化较小,VV极化能较好的体现沿海防护林的表面形态和特征,VH极化可以将水体和沿海防护林很好的区分开来,植被间的差异在HH极化中得到较好的反映。针对不同的极化组合情况,采用面向对象的方法提取沿海防护林信息,并对提取结果进行了对比分析,认为多极化的数据更有利于防护林信息的提取。  相似文献   

The blown sand disaster to the Tarim Desert Highway in Xinjiang, China   总被引：1，自引：0，他引：1  

雷加强  王雪芹  王德  周长海  夏训诚 《中国科学D辑(英文版)》2002,45(Z1)

The Tarim Desert Highway in Xinjiang, China, the longest one in the world, has a lengthof 562 km, about 80% of which runs across, from north to south, the Taklimakan Desert. Obviously,the main problem of the road maintenance is the blown sand disaster. The research resultsshowed: (1) the physical environment along thedesert highway is characterized by strong winds,fine and loose ground materials, different dunes and so on, which provides the dynamical conditionand material source for the formation of blown sand disaster to the road and its shelter system.Meanwhile, the trend and cross-section of the road and the structure of the shelter system, asdamage objects, play important roles in the formation process of blown sand disaster; (2) theblown sand disaster to the shelter system is original from the intrusion of the drift sands and mobiledunes outside the shelter system, and the wind erosion and sand deposit caused by the air streamchanges on the ground in the shelter system. The main damage object in the Tarim Desert High-way is the shelter system presently. The damage forms include wind erosion, sand burying anddune covering; and (3) the damaged length of the blocking sand fences is 83.7%, 88.4%, 72.4%,72.8% and 40.3% and the damaged area of the straw checkerboard belts is 73.1%, 58.2%, 44.5%,35.4% and 36.6%, in turn, in 5 different landform units from north to south, and, the disasters tofences and the straw checkerboard belts are 79.5% and 57.6% in the compound dunes while theyare 64.6% and 37.7% in the interdunes respectively.  相似文献   

河西走廊中部农田防护林防风效应初探   总被引：3，自引：2，他引：3  

刘建勋  蔺国菊  申桂莲  李彩娟  董国 《中国沙漠》1997,(4)

单个农田林网的防风度为２８．２％，而大面积连片农田防护林体系的建成，区域性防风效应更加显著。与建设初期相比，张掖、临泽和高台３县（市）防护林网的总防风度为４２．８％，年大风日数降低６８．４％，年沙尘暴日数降低６６．１％。  相似文献   

Cyclones and storm surges in Bangladesh: Some mitigative measures   总被引：2，自引：2，他引：2  

Gazi Md. Khalil 《Natural Hazards》1992,6(1):11-24

Bangladesh, with its repeated cycle of floods, cyclones, and storm surges, has proved to be one of the most disaster-prone areas of the world. During the years from 1797 to 1991, Bangladesh has been hit by 60 severe cyclones (mostly accompanied by storm surges). This paper gives a brief account of these disasters with particular reference to the wind speed, surge height, loss of life, and damage to crops and properties, etc.In order to protect the coastal areas of Bangladesh from cyclonic storm surges and floods, a major system of embankments was constructed during the 1960s and 1970s, but this is now in need of rehabilitation. The Cyclone Protection Project, which was approved by the World Bank in 1989, would rehabilitate some of the existing embankments, build new embankments, and construct roads. Locally available materials, indigenous technology, and cheap surplus manpower should be used in this project. A variety of fruit trees should be planted along the dikes and roads.To the south-western part of Bangladesh bordering the Bay of Bengal, lies the world's largest single mangrove tract, known as the Sunderban, which covers a total area of 571 500 ha. This mangrove forest is of extreme importance since it provides efficient protection to life and property against cyclones and storm surges. But due to deforestation, the width of the mangrove belt is being rapidly diminished. The author therefore lays emphasis on coastal afforestation.Absolute security against cyclone hazard is probably out of the question, but an effective cyclone warning response can definitely reduce loss of life and damage to property. The author discusses the current conditions for cyclone forecasting and warning in Bangladesh, and then puts forward some proposals for improving the Cyclone Preparedness Programme.  相似文献   

In-service deterioration of compressed earth blocks     

A.?G.?KeraliEmail author 《Geotechnical and Geological Engineering》2005,23(4):461-468

With the increasing backlog of shelter in most of the third world, attempts are being made to evolve low-cost but durable walling units. The introduction of compressed earth blocks (CEBs) some 50 years ago was seen as a major milestone. These blocks are made by compressing a damp mix of soil (90–95%), and cement (5–10%) to form strong and dense blocks used for walling. While considerable knowledge is available regarding their initial performance characteristics, little research has so far been conducted on their long-term durability and deterioration due to prolonged exposure to environmental factors. It is now widely recognised that rapid and premature deterioration does take place when the material is used in unrendered walling in most humid tropical environments. Premature defects such as roughening, pitting, erosion, volume reduction, cracking as well as crazing, etc., have all been witnessed within periods ranging from 1 month to 5 years after completion of construction. This paper reports on recent research conducted in Uganda where in-service defects such as pitting and cracking where measured directly from existing exposed walling to quantify their nature and extent. It can be concluded that the greatest deterioration was found to occur on east–west facing facades, and on the lower wall sections. The deterioration was also found to correspond to the age of the structure.  相似文献