Late quaternary sediment budget in alluvial-fan–source-basin systems in Japan

Sediment budgets since the Late-glacial were constructed for five alluvial-fan–source-basin systems in Japan. The Late-glacial and Holocene sediment yield from each source area was estimated based on digital elevation data and the morphometric analyses of geomorphological maps, in which all hillslopes and fluvial surfaces were classified. Late-glacial and Holocene sediment storage in each fan was calculated from stratigraphical data. The results have revealed that the ratio of sediment storage in a fan to sediment supply is between ca. 0.3 and 0.8. Such high ratios of sediment storage over long time periods cast doubt on the previously proposed steady-state theory of alluvial fan development. The storage ratio decreases if fan sediments are removed by neighbouring large rivers. The maximum storage ratio of 0.8 reflects the ratio of washload to total load for Japanese mountain rivers. © 1997 John Wiley & Sons, Ltd.     

CHANNEL RESPONSE TO SEDIMENT WAVE PROPAGATION AND MOVEMENT,REDWOOD CREEK,CALIFORNIA, USA

Redwood Creek, north coastal California, USA, has experienced dramatic changes in channel configuration since the 1950s. A series of large floods (in 1955, 1964, 1972 and 1975) combined with the advent of widespread commercial timber harvest and road building resulted in extensive erosion in the basin and contributed high sediment loads to Redwood Creek. Since 1975, no peak flows have exceeded a 5 year recurrence interval. Twenty years of cross-sectional survey data document the downstream movement of a ‘sediment wave’ in the lower 26 km of this gravel-bedded river at a rate of 800 to 1600 m a⁻¹ during this period of moderately low flows. Higher transit rates are associated with reaches of higher unit stream power. The wave was initially deposited at a site with an abrupt decrease in channel gradient and increase in channel width. The amplitude of the wave has attenuated more than 1 m as it moved downstream, and the duration of the wave increased from eight years upstream to more than 20 years downstream. Channel aggradation and subsequent degradation have been accommodated across the entire channel bed. Channel width has not decreased significantly after initial channel widening from large (>25 year recurrence interval) floods. Three sets of longitudinal surveys of the streambed showed the highest increase in pool depths and frequency in a degrading reach, but even the aggrading reach exhibited some pool development through time. The aggraded channel bed switched from functioning as a sediment sink to a significant sediment source as the channel adjusted to high sediment loads. From 1980 to 1990, sediment eroded from temporary channel storage represented about 25 per cent of the total sediment load and 95 per cent of the bedload exported from the basin.     

频率域线源大地电磁法有限元正演模拟

本文介绍了频率域线源大地电磁法有限元正演模拟的研究结果. 在外边界上统一应用适合于人工源的一阶吸收边界条件来形成边值问题,可减小基于平面波假设造成的人为截断边界的影响. 程序编辑中设计了两个二维数组分别存储总体系数矩阵的非零元素和在总体结点编号中的位置,使内存占用量减少,且物理意义明确,方便用高斯-赛德尔等迭代法解有限元方程时调用. 采用视δ函数模拟线源,提高了解方程组的稳定性. 最后通过对1个简单模型和1个复杂模型的模拟,证明所用的方法对异常体能够有明显的反映,说明了该方法的可靠性和有效性.     

SPATIAL AND TEMPORAL VARIABILITY OF SOIL SURFACE ROUGHNESS AND THE APPLICATION IN HYDROLOGICAL AND SOIL EROSION MODELLING

Accurate estimations of water retention and detention are needed to simulate surface runoff and soil erosion following a rainfall event in a catchment. Several equations to estimate the amount of surface depressional storage, the fraction of the soil surface covered by water and the amount of rainfall excess needed to start surface runoff have been developed by Onstad (1984). The random roughness and slope gradient are needed for those estimations. Surface micro-elevation data have been gathered by a photographic method. The random roughness was determined from those elevation measurements. Several factors which have an impact on the soil surface roughness were taken into account. The main sources of influence are the type of land use, the crop stage within the growing period and tillage direction. Analyses of variance indicated that the variation in the RR-index could be explained mainly by type of land use, orientation and field type. The temporal variation was relatively small. Gradient data have been determined from a digital elevation model, constructed by digitizing contours. Combining the random roughness and the steepness of slope, the amounts of surface water retention and detention could be estimated. Knowledge of water retention and detention will improve the estimations of runoff and soil erosion modelling in catchments, such as those made with the LISEM model. The agricultural systems examined in this study have similar random roughness values in summer. Different soil erosion rates for several types of land use can not therefore be explained by the random roughness.     

基于降雨的昆明水库蓄水模式分析及风险研究

根据昆明国家基准气候站1988~2017年的降雨资料,以昆明松华坝水库为例,运用统计、比较等方法,通过分析降雨时空分布特征、蓄水地理环境特征等因素,将昆明水库蓄水模式分为雨季降雨最佳蓄水模式、干旱背景蓄水模式、局地强降雨蓄水模式、秋季连阴雨降雨蓄水模式和冬季降雨降雪蓄水模式5种;从降雨强度、降雨历时、降雨范围3个方面对降雨蓄水风险进行评估,得出昆明由于降雨引发的蓄水风险相对小,蓄水较为安全;昆明可通过开展常态化人工增雨,增加库塘蓄水,同时加强生态环境建设,保护蓄水环境。     

气候变化和人类活动对长江流域水储量变化的影响研究

利用2002-08～2016-12 GRACE数据扣除泄漏影响得到的长江流域陆地水储量（TWS）变化,分析其时空变化特征和趋势。结果表明,在此期间长江流域TWS增速为0.13±0.12 cm/a;TWS变化大的区域,如泄漏改正后三峡库区TWS变化由约10 mm/a变为15~20 mm/a,并呈现更大的空间异质性。利用多种气象数据,从气候变化和人类活动角度深入研究长江流域水循环变化。结果表明,降水量与TWS变化在时间和空间上都具有较高的相关性,TWS变化延迟1~2个月;上游源头处温度是影响TWS变化的主导因素,温度升高加速了上游高山冰川融化,使TWS具有增长趋势;三峡工程的蓄水也导致TWS变化;ENSO是长江流域TWS变化的主要影响因素。     

Increased soil organic carbon storage in Chinese terrestrial ecosystems from the 1980s to the 2010s

Journal of Geographical Sciences - Soil stores a large amount of the terrestrial ecosystem carbon (C) and plays an important role in maintaining global C balance. However, very few studies have...     

基于Paxos的强一致性复制在天文数据存储中的应用研究

随着新一代天文观测技术的快速发展,观测设备所获得的科学数据迅猛增长,传统的外挂式存储设备已经难以满足海量观测数据的近实时存储和同步数据处理的需求。基于廉价硬件的分布式存储系统是解决当前天文观测数据存储的有效手段。由于廉价硬件节点发生故障的概率相对较高,为了确保科学观测和数据的可靠存储,提出了一种基于Paxos的改进的分布式软件多副本复制算法。实验表明,在针对大于1 MB的天文FITS图像文件存储过程中,算法虽然增加少量的存储延迟,但能够容忍多种软硬件异常下多个副本的强一致性,较好地解决当前海量天文数据存储中的多副本数据存储的一致性问题。     

利用预测型线性规划评价矿区地下水开采量

建立了某矿区水源地当前和未来不同时期地下水开采量评价的预测型线性规划模型,得到了不同时期的最大开采量及相应的最优运行方案,为矿区发展规划提供了决策依据。      

水库库容变化对蓟县地震台DSQ型水管倾斜仪观测的影响

对比于桥水库库容变化与蓟县地震台DSQ型水管仪观测数据表明,水库容量对水管仪长周期趋势性变化影响不大,蓄水和泄水过程中库容量变化与水管仪观测数据不存在相关关系。根据近场三维不规则形状荷载模型,对于于桥水库3次蓄水和3次泄水过程,定量计算库容变化对蓟县地震台DSQ型水管倾斜仪观测影响的理论值,结果表明,库容变化引起的水管仪倾斜值与实际观测数据变化幅度相比小得多,库容改变不足以对水管仪倾斜观测造成显著干扰。该分析结果可在观测资料异常判定中提供参考。