Performance of small-scale irrigation schemes in Lake Tana Basin of Ethiopia: technical and socio-political attributes     

Abebech Abera  Niko E.C. Verhoest  Seifu A. Tilahun  Tena Alamirew  Enyew Adgo  Michael M. Moges 《自然地理学》2019,40(3):227-251

This study was conducted to investigate technical and socio-political attributes that lead to the underperformance of two selected irrigation schemes (Shina and Bebeks) in the Lake Tana floodplains, Ethiopia. Irrigation application efficiency (AE) at nine experimental fields showed a wide range, from 20 to 80%, but was mostly between 40 and 60%. Irrigation water-use efficiency (IWUE) varied from 1.9 to 7.2 kg m^?3 for onion and 0.9 to 1.2 kg m^?3 for maize. The lined and earthen canal conveyance losses in Bebeks were 0.037 and 0.047 l s^?1 m^?1, whereas in Shina they were 0.033 and 0.044 l s^?1 m^?1, respectively. The overall consumed ratio (OCR) of water was 0.58 for Bebeks and varied from 0.73 to 1.2 in Shina. Both schemes are performing below the standard based on technical performance indicators. Irrigation water user associations (WUAs) were not implemented, but irrigation committees (ICs), composed of local political leaders, are managing both schemes. Canal and reservoir sedimentation from erosion of upstream catchment areas during the rainy season was the major problem.  相似文献   

Regional subglacial quarrying and abrasion below hard-bedded palaeo-ice streams crossing the Shield–Palaeozoic boundary of central Canada: the importance of substrate control     

Syed Bukhari  Nick Eyles  Shane Sookhan  Riley Mulligan  Roger Paulen  Maarten Krabbendam  Niko Putkinen 《Boreas: An International Journal of Quaternary Research》2021,50(3):781-805

Three-dimensional surface visualization models derived from high-resolution LiDAR data provide new information about the type and scale of erosional processes below Late Wisconsin palaeo-ice streams traversing the boundary between Canadian Shield crystalline rocks with offlapping Palaeozoic limestones in central Ontario. The hard bed is directly analogous to that found below ice streams in East Antarctica and East Greenland and provides insight into the effects of abrupt changes in substrate type on subglacial processes. Erosion of hard crystalline Canadian Shield rock was largely ineffectual consisting of areal abrasion of rounded whalebacks and local lee side plucking. In contrast, fast flow over the strike of gently dipping well-bedded and jointed Palaeozoic limestones cut large flow-parallel grooves and ridges akin to mega-scale glacial lineations reflecting intense abrasion below narrow streams of subglacial debris dominated by hard crystalline Shield clasts (erodents). Regionally extensive plucking of structurally weak, well-jointed and bedded limestone produced large volumes of rubbly carbonate debris leaving a 25-km-wide belt of uncontrolled hummocky rubble terrain (long known as the Dummer Moraine in Southern Ontario) some 350 km long and locally as much as 10 m thick. Subglacial plucking and abrasion under fast flowing ice were highly effective in stripping limestone cover rocks from Precambrian basement, and over many glacial cycles, may have played a role in the location and excavation of numerous large and deep lake basins around the Shield–Palaeozoic boundary zone in North America.  相似文献   

Neoglacial (<3000 years) till and flutes at Saskatchewan Glacier,Canadian Rocky Mountains,formed by subglacial deformation of a soft bed          下载免费PDF全文

Nick Eyles  Joe. I. Boyce  Niko Putkinen 《Sedimentology》2015,62(1):182-203

Understanding the processes that deposit till below modern glaciers provides fundamental information for interpreting ancient subglacial deposits. A process‐deposit‐landform model is developed for the till bed of Saskatchewan Glacier in the Canadian Rocky Mountains. The glacier is predominantly hard bedded in its upper reaches and flows through a deep valley carved into resistant Palaeozoic carbonates but the ice margin rests on a thick (<6 m) soft bed of silt‐rich deformation till that has been exposed as the glacier retreats from its Little Ice Age limit reached in 1854. In situ tree stumps rooted in a palaeosol under the till are dated between ca 2900 and 2700 yr bp and record initial glacier expansion during the Neoglacial. Sedimentological and stratigraphic observations underscore the importance of subglacial deformation of glaciofluvial outwash deposited in front of the advancing glacier and mixing with glaciolacustrine carbonate‐rich silt to form a soft bed. The exposed till plain has a rolling drumlinoid topography inherited from overridden end moraines and is corrugated by more than 400 longitudinal flute ridges which record deformation of the soft bed and fall into three genetically related types: those developed in propagating incipient cavities in the lee of large subglacial boulders embedded in deformation till, and those lacking any originating boulder and formed by pressing of wet till up into radial crevasses under stagnant ice. A third type consists of U‐shaped flutes akin to barchan dunes; these wrap around large boulders at the downglacier ends of longitudinal scours formed by the bulldozing of boulders by the ice front during brief winter readvances across soft till. Pervasive subglacial deformation during glacier expansion was probably facilitated by large boulders rotating within the soft bed (‘glacioturbation’).  相似文献   

双船双方位角地震探测技术方法及应用效果     

杨蜀冀  韦成龙  伍忠良  刘协来  杨册  王聪 《热带海洋学报》2018,37(1):98-104

南海东沙海域的陆坡台地区, 浅表断裂及生物礁发育众多, 浅层新生界多为碳酸盐岩层, 中深层的中生界内部构造复杂, 断裂较多, 常规单船窄方位地震剖面显示中深层反射品质较差。利用双船可以设计灵活的观测系统, 形成双方位角地震探测方式, 对于地下同一反射点的照明, 可以获得比窄方位角探测更好的效果, 也可以改善高速屏蔽层下方、高陡倾角斜层等区域的成像质量。文章通过重点技术的攻关研发, 进行了单源激发、双缆接收的双方位角采集试验, 成功实现该方法在南海海域中深层地震勘探中的应用。  相似文献   

红外相机CASCAM光学设计   总被引：1，自引：1，他引：0  

季春宏  姚永强  长岛千惠  佐藤修二 《天文学报》2003,44(4):390-404

介绍紫金山天文台研制的光学-近红外相机CASCAM（Chinese Academy of Science，CAMera)的光学系统设计．CASCAM相机以红外列阵HAWAII-1和光学CCD为探测器，配备国家天文台兴隆观测站2．16米和1．26米望远镜进行0．4—2．5μm波长范围的成像和偏振成像观测．相机的光学系统由F／9→F／6缩焦系统和Offner反射成像系统构成．优化设计结果表明，光学设计方案已满足天文观测的要求．CASCAM相机在设计上实现了光学-近红外很宽波段的消色差变焦，并在楔形分柬片、常温滤光片轮和折射式焦面摆动技术等方面进行了新的尝试．  相似文献   

在可控制的相对湿度下矿物表面上多环芳烃的降解     

Shuji TAMAMURA  Tsutomu SATO  Yukie OTA  Kazuichi HAYAKAWA 《地质学报》2006,80(4):616

多环芳香烃由于诱发突变和致癌的性质威胁着人类的健康,近年来,其降解问题得到了广泛的关注。笔者研究了在没有光照的条件下,改变相对湿度(5%至30%之间),苯并芘(一种典型的多环芳烃物质)在石英,矾土,蒙脱石,高岭石,腐殖酸和吸附了腐殖酸的石英上的稳定性,继而可以检测出矿物表面催化多环芳烃降解的效果。苯并芘的稳定性主要是由吸附剂的物化性质决定的。石英表现出很好的催化效果,即便其表面被腐殖酸所包覆。在整个实验过程中(3天)吸附在蒙脱石和腐殖酸表面的苯并芘依然很稳定。实验装置中的湿度影响在某些特定的矿物中的苯并芘的稳定性。特…  相似文献   

“探宝号”船可变阵列震源的实现及应用     

赵庆献王立明  杨蜀冀罗文造 《南海地质研究》2005,(1):92-100

2001年，广州海洋地质调查局对“探宝号”船原有震源更新升级为阵列可变的BOLT震源系统。随着更新改造工程的成功，该船已成为具备承担高分辨率、常规、低频深水油气地震勘探的多功能地震调查船。本文介绍了地震勘探震源的基本工作原理以及三种阵列的分布、波形、频谱等特性。  相似文献   

Polymetallic Mineralization at the Suttsu Vein-type Deposit, Southwestern Hokkaido, Japan   总被引：1，自引：0，他引：1  

Shuji Ono  Koji Hirai    Hiroharu Matsueda  Taro Kabashima 《Resource Geology》2004,54(4):453-464

Abstract. The Suttsu polymetallic vein-type deposit, hosted by tuff, tuff breccia and shale of the Miocene Kunnui Formation and propylitized hornblende-augite andesite, is located in southwestern Hokkaido, Japan. It has been exploited and explored for Cu, Pb, Zn and Ag until 1962.
In this study, we examined K-Ar ages, ore mineralogical characteristics and fluid inclusions to obtain new data for the deposit.
The K-Ar ages on sericite indicate that the polymetallic mineralization occurred in Late Miocene (8.1–5.7 Ma). The polymetallic banded ore from the Ohkubo vein is characterized by an abundance of Au, Ag, Sn, Bi, in, Se and Te. These metals are mainly ascribed to electrum (30.3–37.8 atom% Ag), Se-bearing pavonite (8.5–9.5 wt% Se), gustavite-lillianite solid solution, Se-bearing bismuthinite (5.0–5.3 wt% Se), kawazulite, cassiterite, Sn-bearing chalcopyrite (3.3–4.2 wt% Sn), In-bearing stannite, stannite-chalcopyrite solid solution, and In- and Sn-bearing sphalerite (2.6–8.4 wt% In and 1.8–4.3 wt% Sn), occurring in narrow bands of the ore. The In- and Sn-bearing sphalerite likely forms a sphalerite-roquesite-stannite solid solution with the contents of roquesite and stannite being about 2–9 and 2-A mole%, respectively. Temperatures and salinities (in wt% NaCl equiv.) of the ore fluids are estimated to be 180-250C and 3–4 wt%, respectively. The Sn-bearing chalcopyrite therefore probably precipitated metastably. The geologic and mineralogical features suggest that pre-Tertiary basement rocks rich in organic material underlie the Miocene Kunnui Formation nearby the deposit and that they contributed to local and temporary reduction of magnetite-series magmas favorable for the early stage tin-polymetallic mineralization.  相似文献   

Observation of Pore Spaces and Microcracks Using a Fluorescent Technique in Some Reservoir Rocks of Oil, Gas and Geothermal Fields in the Green Tuff Region, Japan     

Takaaki WAJIMA  Shuji OKUDA  Youqing CHEN  Masahiko BESSHO  Takashi NISHIYAMA 《Resource Geology》2000,50(3):191-200

Abstract: Pore spaces and microcracks in representative oil, gas and geothermal reservoir rocks from the Green Tuff region, Japan, were examined using a fluorescent technique. This technique was developed to visualize microscopically pore spaces and microcracks filled with synthetic resin mixed with fluorescent paint under ultraviolet light. Various morphology of pore spaces and microcracks was clearly identified. Spaces in studied reservoir rocks are classified into following three types: pore spaces in matrix, pore spaces in particles, and microcracks. It is observed that valuable oil and gas reservoir rocks relatively include many pore spaces, while microcracks are important for geothermal rocks. Correlation between textural characteristics and porosity or permeability was found in the oil reservoir rocks. Effective permeability depends upon pore spaces in matrix more than upon other components such as pore spaces in particles and microcracks. Looseness in matrix caused by larger grain size of particles is strongly correlated with permeability. Pore spaces play an important role as a reservoir in oil and gas fields, but are less important in geothermal field. Instead, microcracks are important for geothermal reservoir system.  相似文献   

Wide-Field Camera for Gravitational Microlensing Survey: MOA-cam2     

Toshifumi Yanagisawa  Yasushi Muraki  Yutaka Matsubara  Fumio Abe  Kimiaki Masuda  Sachiyo Noda  Takahiro Sumi  Yuji Kato  Mitsuaki Fujimoto  Shuji Sato  Ian Bond  Nicholas Rattenbury  Philip Yock  Pam Kilmartin  John Hearnshaw  Micheal Reid  Denis Sullivan  Brian Carter  Richard Dodd  Garry Nankivell  Noiman Rumsey  Morihiro Honda  Maki Sekiguchi  Masanori Yoshizawa  Takashi Nakamura  Humitaka Sato  Seiji Kabe  Makoto Kobayashi  Yoshiyuki Watase  Jun Jugaku  Toshiharu Saito  Barbel Koribalsky 《Experimental Astronomy》2000,10(4):519-535

We have constructed a large, mosaic CCD camera called MOA-cam2 which has 4096 × 6144-pixelsto search for gravitational microlensing events. MOA-cam2 has three4096 × 2048-pixel SITe CCD chips, which have a very high quantum efficiency (nearly 80% in the wave region 500 to 800 nm),and three buttable sides. We have placed the threechips side by side with 100 m dead space. MOA-cam2 has been installed on the 61 cm Boller and Chivens telescope of the MOA collaboration at the Mt. John University Observatory (MJUO) in NewZealand since July 1998. The field coverage is 0.92° × 1.38° per exposure. The technical details of MOA-cam2 and the first images obtained with the Boller and Chivens telescope are presented. MOA-cam2 introduces a second phase of research on gravitational microlensing by the MOA collaboration.  相似文献