利用DEM提取流域水系时洼地与平地的处理方法

在利用数字高程模型(DEM)模拟坡面流提取流域水系特征过程中,对洼地和平地的处理是首先需要解决的关键问题。针对现有方法对复杂地形DEM中平地、洼地及其复合情形处理效率和效果的不佳,提出了洼地的分类与归并、有效填洼、平地的分类、基于出流代价的河谷平地排水流向构建等新的处理方法,并在开发的软件系统中得到实现。实验结果表明:采用该方法可对复杂洼地进行有效处理,构建的河谷平地水流流向在顾及周边地形的同时向可能形成的河道收敛,避免了平行河道、伪河道等奇异河道的产生,由此提取的流域水系与实际自然水系基本一致。     

水流分配策略随下坡坡度变化的多流向算法

提出了一种新的多流向算法方法(MFD-fg),其基本思想是水流分配策略应在空间上随着与下坡坡度相关的地形参数而变,从而地形对水流分配的影响可以得到合理、有效的建模。比较分析表明,MFD-fg采用以最大下坡坡度的线性函数对水流分配进行加权,是较好的水流分配策略。应用实验表明,与目前具代表性的单流向算法与多流向算法相比,MFD-fg方法的结果可获得更合理的汇流面积。     

An improved buffer analysis technique for model-based 3D mineral potential mapping and its application

Buffer zones in bo\th two-dimensional (2D) and three-dimensional (3D) spaces are commonly used in prospectivity mapping. The method completes a modelling that starts with a real example and progresses to the development of a virtual model. This includes the consideration of lithological or structural contacts at depth, which is a theoretical concept based on extrapolation of data collected in the field, rather than an empirical observation of the feature based on physical samples. This contribution documents an improved buffer analysis method for the study of 3D-space that is implicit (rapid), precise (smooth) and based on triangulated characteristics, which can be used to construct influence domains of geological models. As traditional 2D GIS-based mineral potential mapping is gradually becoming limited with time, mineral potential mapping in three dimensions (3D) is increasingly becoming an important tool in finding concealed economic mineralization. This contribution documents an improved methodology of buffer analysis for prospectivity mapping processing mineralized favourable models rather than describing an advance in the geometry of surface rendering of “geological complexity”. Measures used in this buffer analysis include the: (1) voxelization of geological objects (i.e. assigning numerical values of features on a regular cube in 3D-space); (2) revision of the 3D Euclidean distance transform and the calculation of signed distance field; (3) extracting surfaces from the field; and (4) construction of a buffer-surface based on a “discrete smooth interpolation” (DSI) algorithm. Furthermore, this contribution constructs 3D models using a buffer analysis algorithm and prospectivity mapping introduced here, which is based on real data from the Jiama Cu-polymetallic deposit in Tibet and Daye Fe deposit in the Hubei Province, China. This contribution also presents a comparison between voxel and irregular triangle models, which illustrate that irregular triangle mesh buffer analysis (ITB) can improve modelling techniques for GIS-based 3D mineral potential mapping. The outcome is an increase in the accuracy of prospectivity mapping.     

复杂条件下湍流通量的观测与分析

随着气候与环境问题的突出，地球生态系统与大气间的CO2、水汽和能量交换引起更大关注。全球通量网和其它研究计划已在不同地区建立了大量通量站；并主要利用涡动相关方法进行通量的观测与分析。许多通量站设在地形起伏、斑块植被地区，且由于长期连续运转，不可避免地会遇到许多不利气象条件。国内各部门应用的涡动相关方法通量观测系统已有数百套。此方法似乎简单，而较准确的有代表性的通量取得却涉及许多问题。国外近10年来有关研究很活跃，国内则显得相对薄弱。仪器和台站很多，却缺乏合乎国际规范的处理程序和质量控制体系，影响到资料共享和合作研究。应根据国际最新进展和部分台站资料，在做成较规范的湍流资料处理程序的基础上，建立包括通量源区分析的质量控制与保证系统。对地形和植被都较复杂的情况，结合国际上几个较典型的通量站和国内祁连山大野口等通量站特点，做了简要介绍。      

Simultaneous Estimation of Geologic and Reservoir State Variables Within an Ensemble-Based Multiple-Point Statistic Framework

Assessment of uncertainty due to inadequate data and imperfect geological knowledge is an essential aspect of the subsurface model building process. In this work, a novel methodology for characterizing complex geological structures is presented that integrates dynamic data. The procedure results in the assessment of uncertainty associated with the predictions of flow and transport. The methodology is an extension of a previously developed pattern search-based inverse method that models the spatial variation in flow parameters by searching for patterns in an ensemble of reservoir models. More specifically, the pattern-searching algorithm is extended in two directions: (1) state values (such as piezometric head) and parameters (such as conductivities) are simultaneously and sequentially estimated, which implies that real-time assimilation of dynamic data is possible as in ensemble filtering approaches; and (2) both the estimated parameter and state variables are considered when pattern searching is implemented. The new scheme results in two main advantages—better characterization of parameters, especially for delineating small scale features, and an ensemble of head states that can be used to update the parameter field using the dynamic data at the next instant, without running expensive flow simulations. An efficient algorithm for pattern search is developed, which works with a flexible search radius and can be optimized for the estimation of either large- or small-scale structures. Synthetic examples are employed to demonstrate the effectiveness and robustness of the proposed approach.     

基于栅格DEM的多流向算法述评

基于栅格DEM的流向算法是数字地形分析的重要研究内容之一。在分布式水文模型、土壤侵蚀等领域中,当需要获取与流向直接相关的水文参数(如汇流面积、地形指数等)的详细空间分布时,多流向算法(MFD)明显优于单流向算法(SFD)。根据所采用的水流分配策略,将现有MFD分为四类:(1)固定水流分配权重的MFD;(2)水流分配权重随汇流面积变化的MFD;(3)水流分配权重随局域地形特征变化的MFD;(4)基于局域形态单元的MFD。从模型合理性、算法复杂度和易用性、对DEM误差的敏感性等方面进行的分析表明,水流分配权重随局域地形特征变化的MFD优于其他三类MFD。目前对MFD采用人造DEM数据集的直接定量评价研究还十分不足,文章以一个例子来体现直接定量评价MFD的可行性及有效性,同时也定量反映出水流分配权重随局域地形特征变化的MFD具有更低的计算误差。目前通用的针对流向算法的DEM洼地平区预处理算法多针对SFD而设计,不适合MFD的实际应用,本文对适用于MFD的DEM预处理算法所应具有的特征也进行了讨论。     

Stochastic groundwater modeling of a sedimentary aquifer: evaluation of the impacts of abstraction scenarios under conditions of reduced recharge

A transient finite difference groundwater flow model has been calibrated for the Nasia sub-catchment of the White Volta Basin. This model has been validated through a stochastic parameter randomization process and used to evaluate the impacts of groundwater abstraction scenarios on resource sustainability in the basin. A total of 1500 equally likely model realizations of the same terrain based on 1500 equally likely combinations of the data of the key aquifer input parameters were calibrated and used for the scenario analysis. This was done to evaluate model non-uniqueness arising from uncertainties in the key aquifer parameters especially hydraulic conductivity and recharge by comparing the realizations and statistically determining the degree to which they differ from each other. Parameter standard deviations, computed from the calibrated data of the key parameters of hydraulic conductivity and recharge, were used as a yardstick for evaluating model non-uniqueness. All model realizations suggest horizontal hydraulic conductivity estimates in the range of 0.03–78.4 m/day, although over 70 % of the area has values in the range of 0.03–14 m/day. Low standard deviations of the horizontal hydraulic conductivity estimates from the 1500 solutions suggest that this range adequately reflects the properties of the material in the terrain. Lateral groundwater inflows and outflows appear to constitute significant components of the groundwater budgets in the terrain, although estimated direct vertical recharge from precipitation amounts to about 7 % of annual precipitation. High potential for groundwater development has been suggested in the simulations, corroborating earlier estimates of groundwater recharge. Simulation of groundwater abstraction scenarios suggests that the domain can sustain abstraction rates of up to 200 % of the current estimated abstraction rates of 12,960 m³/day under the current recharge rates. Decreasing groundwater recharge by 10 % over a 20-year period will not significantly alter the results of this abstraction scenario. However, increasing abstraction rates by 300 % over the period with decreasing recharge by 10 % will lead to drastic drawdowns in the hydraulic head over the entire terrain by up to 6 m and could cause reversals of flow in most parts of the terrain.     

Inter-comparison of Aermod and ISC3 modeling results to the Alaska tracer field experiment

AERMOD is an advanced plume model that incorporates updated treatments of the boundary layer theory, understanding of turbulence and dispersion, and includes handling of terrain interactions as well as the PRIME downwash algorithm. It was reported that the US EPA approved AERMOD for short-range dispersion modeling. It was the high time that AERMOD would replace ISC3. ISC3 is a traditional Gaussian plume model regarded as the regulatory model of US EPA with the capacity of building downwash similar to that of AERMOD. In this paper, the authors describe the advantages of AERMOD over the regulatory model of ISC3 by comparing their predicted ground level concentrations (GLC) along downwind distance to the Alaska tracer field data. The field experiment features buoyant release of effluent at elevated height over a flat terrain and local flows influenced by building downwash. Three measures to compare the observed and simulated concentration data, such as linear regression, quantile-quantile (QQ) and residual box are utilized. To sum up, AERMOD shows significantly better space-time correlation and probability distribution than the ISC3, which frequently overestimates the GLC for effluent released with significant plume rise under stable atmospheric conditions. The performance of AERMOD is greatly enhanced by introducing the state-of-the-art knowledge of boundary layer meteorology as well as the turbulence parameterization method. In particular, AERMOD takes into account the meander effect on coherent plume in stable condition with current state-of-the-art Planetary Boundary Layer (PBL) parameterizations, while ISC3 is not capable of producing such important effect. Generally speaking, 1.17 is the overall predicted-to-observed ratio for short-term averages using AERMOD. 1.94 is the overall predicted-to-observed ratio for short-term averages using ISC3.     

Assessment of dynamic impact force of debris flow in mountain torrent based on characteristics of debris flow

Landslides and debris flows that occur around residential areas are considered, globally, as significant disasters that cause damage to human life and property. With terrain slope defining the flow characteristics of debris flows, flow depth, flow velocity, and impact force vary by time and distance. In particular, when a structure is located in the flow path of debris flows, the flow characteristics of debris flows vary by terrain slope and direction angle. To simulate the flow characteristics of these debris flows, the simulation results obtained by FLO-2D were analyzed with six-stage conditions for the research area. In the analysis, the flow depth, flow velocity, and impact force were estimated on the basis of the outlet of the research area in the presence and absence of structure(s) at certain distances. With this, the variation of the impact force in accordance with the variation of the flow depth of the debris flows was highly similar to the simulation results obtained by FLO-2D, when the correction index (α) of the suggested dynamic impact force equation was 0.3–0.4. There were sections where the estimated value of the impact force was overestimated near the outlet, and it was judged that the fixed values of the terrain factors (width, roughness coefficient, slope, etc.) caused the impact force to be overestimated. However, the correlation analysis showed that the correlation index was above the normal ranges in the suggested dynamic impact force equation for debris flows with the application of the terrain factors.     

地形起伏对高密度电法探测地下岩溶管道的影响试验研究

高密度电阻率法在岩溶区找水具有较好的效果,但岩溶区地形复杂,高密度电法受地形起伏影响较大。为了提高岩溶区高密度电法找水的勘探效果,掌握地形起伏对高密度电法影响的规律,本文采用高密度电阻率法微测系统,利用铜柱体模拟地下岩溶管道,研究地形起伏对高密度电法探测岩溶管道的影响。研究结果表明:高密度联合剖面法及高密度α₂装置受谷地地形影响较大,容易在谷地中间产生虚假的低阻异常,矩形AMN和滚动MNB装置受地形影响较小;受谷地地形影响,高密度电法能勘探的有效异常体深度减小;同一电极距下,平地模型及谷地模型反演异常体顶部埋深均小于真实异常,横向宽度均大于真实异常,平地模型反演异常体的顶部埋深大于谷地模型反演异常体,横向宽度小于谷地模型反演异常体。     

Analysing laser‐scanned digital terrain models of gravel bed surfaces: linking morphology to sediment transport processes and hydraulics

The grain‐scale topography of a sediment surface is a key component of a fluvial system, affecting aspects including sediment transport, flow resistance and ecology. However, its effect is hard to quantify because of the need for grain‐scale elevation data from in situ fluvial gravel surfaces which are difficult to collect. The sediment surface properties are, therefore, commonly estimated as a function of the sediment grain‐size distribution; however, because of additional factors, such as grain packing and shape, there is not necessarily a unique relationship between the two. A new methodology has been developed that uses terrestrial laser scanning to collect grain‐scale topographic data from in situ fluvial gravel surfaces, from which digital terrain models are created. This paper investigates methods of analysing such digital terrain models, and possible sedimentological interpretations that can be drawn from the analysis. Eleven digital terrain models from exposed gravel surfaces in two contrasting rivers (the River Feshie and Bury Green Brook) were analysed by calculating: the distribution of surface elevations, semivariograms, surface inclinations, surface slopes and aspects and grain orientation. The distribution of surface elevations and surface slope and aspect analysis were found to be most informative. In the River Feshie, grain‐size was interpreted as being a dominant control on sediment surface structure and gravel imbrication was identified. In Bury Green Brook, the location of the digital terrain models within the riffle–pool sequence was the dominant control on surface structure and grain orientation. Such digital terrain models therefore provide a new approach to measuring and quantifying the topography of fluvial sediment surfaces.     

Gravel fabric in a sub-Himalayan braided stream

Data on the fabric properties of gravels have been collected at 10 locations over a distance of 27 km from the Chakki River — a braided channel of the Beas River system. The imbrication of AB-planes reveals a close correspondence with the channel direction; the deviations seldom exceed 30°. Increase in sinuosity and the existence of subsidiary channels contribute, at some locations, to larger deviations. Imbrication directions tend to be modified because of the influence of local channels which develop temporarily on the bar surfaces.A current-normal mode exists for the A-axis orientation data. Bimodal distributions are recognised and attributed to shifting flow conditions. Variance values are low for both the imbrication and A-axis data. The range in mean values of the dip of AB-planes is between 22.6° and 37.6° with s = 8° to 14°. The mean values of plunge of the A-axis vary from 2.9° to 13.2° with s = 3.4° to 12.69°. There is a marked decrease in plunge of the A-axis in the downstream direction in the Chakki River.A particle size versus orientation approach indicates that, irrespective of size, there is a strong upcurrent imbrication. Longitudinal alignment of particles in the smaller size intervals is not supported by the data obtained in this study. A particle shape versus orientation approach reveals that the A-axis orientation is not dependent on particle shape. The A-axis fabric patterns of both tabular and bladed clasts show a peripheral circular arrangement of the maxima, the bisectrix of which points in a current-normal direction. Orientation patterns do not reflect any control in terms of the lithic composition of clasts.     

The importance of digital elevation model resolution on granular flow simulations: a test case for Colima volcano using TITAN2D computational routine

The mobility of gravity-driven granular flows such as debris flows or pyroclastic density currents are extremely sensitive to topographic changes, such as break in slopes, obstacles, or ravine deviations. In hazard assessment, computer codes can reproduce past events and evaluate hazard zonation based on inundation limits of simulated flows over a natural terrain. Digital Elevation Model (DEM) is a common input for the simulation algorithm and its accuracy to reproduce past flows is crucial. In this work, we use TITAN2D code to reproduce past block-and-ash flows at Colima volcano (Mexico) over DEMs with different cell size (5, 10, 30, 50, and 90 m) in order to illustrate the influences of the resolution on the numeric simulations. Our results show that topographic resolution significantly affects the flow path and runout. Also, we found that simulations of past flows with the same input parameters (such as the basal friction angle) over topography with different resolutions resulted in different flow paths, areas, and thickness of the simulated flows. In particular, the simulations performed with the 5- and 10-m DEMs produced similar results. Also, we obtained consistent simulation results for the 30- and 50-m DEMs. However, for the coarser 90-m DEM results are largely different and inaccurate. We recommend generating a benchmark table in order to acquire characteristic values for the basal friction angle of studied events. In case of rugged topographies, a DEM with high resolution should be used for more confident results.     

新安江产流模型与改进的BP汇流模型耦合应用

为提高新安江模型的汇流计算精度并减少经验因素对参数率定的影响,将新安江产流模型与改进的BP汇流模型相耦合,建立XBK(XAJ-BP-KNN)模型。该模型以前期模拟流量和新安江产流模型计算的产流量作为BP网络的输入,出口断面流量作为网络输出,拟合汇流的非线性关系,代替新安江模型的分水源、线性水库及河道马斯京根法的汇流计算;采用相似原理和K-最近邻算法,基于历史样本的模拟误差及相应影响要素对网络输出进行误差修正,实现了无前期实测流量的连续模拟;模型使用SCE-UA算法与遗传早停止LM算法相结合的全局优化方法进行参数优选。在呈村流域的验证表明XBK模型的模拟精度高于新安江模型,全局优化方法能找到最优参数,降低了模型的使用难度。     

基于LiDAR点云数据的低矮植被分类方法

基于LiDAR点云数据进行小区域低矮植被分类方法的研究,利用渐进加密三角网算法分离地面点与低矮植被点,通过分析调整阈值对分离效果的影响验证该算法的适用程度。本文研究表明渐进加密三角网算法适用于低矮植被分布多的地势平坦地区,不适用于地形起伏较大的山区与城市地区。     

A comparison of the RCM and ISC3 dispersion models against the Alaska data set

1IntroductionThe USEPA approved to promulgate ISC3(USE-PA,2002)in replacement of ISC(USEPA1995a,b),which has been the workhorse of air dispersionmodel for decades in the United States.Both ISC andISC3utilize the PRIME building downwash algorithm(Schulman …     

Tectonic architecture through Landsat-7 ETM+/SRTM DEM-derived lineaments and relationship to the hydrogeologic setting in Siwa region, NW Egypt

Fracture zones on the Earth’s surface are important elements in the understanding of plate motion forces, the dynamics of the subsurface fluid flow, and earthquake distributions. However, good exposures of these features are always lacking in arid regions, characterized by flat topography and where sand dunes extensively cover the terrain. During field surveys these conditions, in many cases, hinder the proper characterization of such features. Therefore, an approach that identifies the regional fractures as lineaments on remotely-sensed images or shaded digital terrain models, with its large scale synoptic coverage, could be promising.In the present work, a segment tracing algorithm (STA), for lineament detection from Landsat-7 Enhanced Thematic Mapper Plus (ETM+) imagery, and the data from the Shuttle Radar Topographic Mission (SRTM) 30 m digital elevation model (DEM), has been applied in the Siwa region, located in the northwest of the Western Desert of Egypt. The objectives are to analyze the spatial variation in orientation of the detected linear features and its relation to the hydrogeologic setting in the area and the underlying geology, and to evaluate the performance of the algorithm applied to the ETM+ and the DEM data.Detailed structural analysis and better understanding of the tectonic evolution of the area could provide useful tools for hydrologists for reliable groundwater management and development planning. The results obtained have been evaluated by the structural analysis of the area and field observations. Four major vertical fracture zones were detected corresponding to two conjugate sets of strike-slip faults that governed the surface, and subsurface environments of the lakes in the region, and these correlate well with the regional tectonics.     

西藏波密县天摩沟“9·4”特大泥石流灾害成因初步分析

从地貌地质环境、地面气象要素、大气环流背景、T213数值预报产品和卫星资料等方面,着重分析诱发灾害的气象条件,对2007年9月4日西藏波密县古乡天摩沟发生的一次特大泥石流地质灾害事件成因进行初步分析。结果表明：由于前期气温持续偏高,加剧冰川融水,加上9月4日凌晨出现强降水,天摩沟地形高度落差大、松散固体物质丰富,水源、能量转化和物源三种条件同时满足^[1],是造成这次特大泥石流地质灾害的直接原因。     

基于地图代数的数字地表流线模拟研究

降雨在地表上随地形流动自然形成沟谷线、汇流区、分水岭等流域形态,研究地表流水线的数字模拟对数字流域水文分析具有重要意义.提出数字地表流线模型的概念,只考虑地形因素,利用等高线图建立一个能获得区域内每滴雨水沿地表流动的轨迹模型.并运用地图代数的距离变换对等高线及所在空间进行全方位的距离度量,研究了数字地表流线模型的建立方法.实验表明,该模型利用距离变换信息而不是高程计算流向,可避免DEM高程误差对流向、流线的影响,且不需要在DEM上进行复杂的洼地、平地的识别与处理.该模型对原始数据要求不高,能有效应用于沟谷线的自动提取、汇流区自动分割和分水线网络的自动提取.     

Computational models for dune time-lag: Population structures and the effects of discharge pattern and coefficient of change

An earlier model for dune time-lag in periodically varying unidirectional flows (J.R.L. Allen, 1976) is modified so as to treat more realistically the stochastic behaviour of dunes and the ability of the individual to change in height during its life-span.The improved model shows that hydrograph shape could substantially influence dune behaviour in unsteady flows. For the same flow period and extreme discharge values, a reduction in the relative duration of the high-water stages causes an increase in the phase differences between dune dimensions and flow, and an increase in the dimensions averaged over the flow cycle as compared with the similarly averaged dimensions given no lag. The relative range of dimensions over the flow cycle is little affected.The time-dependent structure of the dune populations is explored using histograms of the instantaneous values of dune wavelength, height and age. At small values of the time ratio (ratio of characteristic dune life-span to flow period), the dunes invariably are unimodally distributed in wavelength, height and age, and the relative dispersion of these properties is small. At intermediate ratios, dune properties are bimodally distributed and moderately to highly dispersed over much of each flow cycle, usually the later part and sometimes the whole of the low-water phase. Dune properties are at all times highly dispersed and, broadly, unimodally distributed when the time ratio is large. There is a close correlation between the patterns in time of dune creation rate, population structure, the average values and relative dispersions of dune dimensions, and the phase difference evaluated for each instant.An increase of the coefficient of change of dune height decreases the equivalent phase difference for height, diminishes the calculated wavelength and height averaged over the flow cycle, but increases the ranges of height and wavelength. Increasing the coefficient has no apparent effect on the equivalent phase difference for wavelength.