A new depression‐dominated delineation (D‐cubed) method for improved watershed modelling

Prior to hydrologic modelling, topographic features of a surface are derived, and the surface is divided into sub‐basins. Surface delineation can be described as a procedure, which leads to the quantitative rendition of surface topography. Different approaches have been developed for surface delineation, but most of them may not be applicable to depression‐dominated surfaces. The main objective of this study is to introduce a new depression‐dominated delineation (D‐cubed) method and highlight its unique features by applying it to different topographic surfaces. The D‐cubed method accounts for the hierarchical relationships of depressions and channels by introducing the concept of channel‐based unit (CBU) and its connection with the concept of puddle‐based unit (PBU). This new delineation method implements a set of new algorithms to determine flow directions and accumulations for puddle‐related flats. The D‐cubed method creates a unique cascaded channel‐puddle drainage system based on the channel segmentation algorithm. To demonstrate the capabilities of the D‐cubed method, a small laboratory‐scale surface and 2 natural surfaces in North Dakota were delineated. The results indicated that the new method delineated different surfaces with and without the presence of depressional areas. Stepwise changes in depression storage and ponding area were observed for the 3 selected surfaces. These stepwise changes highlighted the dynamic filling, spilling, and merging processes of depressions, which need to be considered in hydrologic modelling for depression‐dominated areas. Comparisons between the D‐cubed method and other methods emphasized the potential consequences of use of artificial channels through the flats created by the depression‐filling process in the traditional approaches. In contrast, in the D‐cubed method, sub‐basins were further divided into a number of smaller CBUs and PBUs, creating a channel‐puddle drainage network. The testing of the D‐cubed method also demonstrated its applicability to a wide range of digital elevation model resolutions. Consideration of CBUs, PBUs, and their connection provides the opportunity to incorporate the D‐cubed method into different hydrologic models and improve their simulation of topography‐controlled runoff processes, especially for depression‐dominated areas.     

地形条件约束下的区域发展模式选择

实践已经证明,资源环境是人类社会生存和发展的基础所在。而区域发展是人类经济社会活动发展在空间上的表现形式,所以资源环境也是区域发展的基础所在,地形条件则是制约区域资源开发广度和深度的重要因素。为此,在假定区域其他投入要素不变的前提下,深入分析了地形条件和区域发展之间的机理关系,并选择具有较强代表性的京九铁路和陇海铁路作为实例,利用图形分析和相关分析方法,实证研究了沿线地形条件与经济社会发展之间的关系。通过研究发现地形条件能够通过交通运输负担影响区域发展,地形条件简单的地区,经济社会活动承担的交通运输负担较轻,经济社会发展水平较高。因此,不同地区应根据自身的资源环境基础和地形条件,选择适宜于自身发展的区域发展模式,避免发展模式的雷同,尤其山地丘陵地区应该选择物质流动负担较小的经济活动。     

测量工作在土地整理类项目中的应用体会

本文介绍了测量工作在土地整理类项目中的应用并简述了点滴作业体会.     

基于多重分形的Karst流域地貌信息挖掘

本文利用多重分形理论揭示出了DEM不同尺度下的地貌多重分形谱的变化规律。基于多重分形理论研究表明:多重分形理论构建的高程多重分形谱模型能挖掘出更全面、更精细Karst流域地貌形态信息,其中高程多重分形谱模型中的宽度定量表征出了Karst流域地貌的起伏程度,多重分形谱最大、最小子集维数的差值定量表征了地貌形态的差异性,而且根据多重分形谱的参数随DEM分辨率变化关系并结合广义熵理论,确定了Karst地貌形态研究的数据的空间分辨率最优范围在(0-15]之间。     

Plant community patterns in a gypsum area of NE Spain. II. Effects of ion washing on topographic distribution of vegetation

A model, based on the physico-chemical properties of gypsum, is postulated in order to interpret the regular distribution of plant communities associated with the topography and the main environmental stresses to which each vegetation type is subjected in a landscape unit.The leaf chemical composition of 28 representative plant species supports the main predictions of the model: species from low areas present large concentrations of Na, N and ash but low contents of Ca. It is demonstrated that the strong nutrient and salt downwashing in the hilly terrain is an important cause of the vegetation segregation observed on a large spatial scale.     

Controlling factors of recent clastic coastal sediments (Viransehir,Mersin bay,S Turkey)

The Plio-Quaternary conglomeratic sets within the marine environment of the Viranşehir coast (W Mersin, S Turkey) are responsible for the evolution of sandy and gravely beaches due to their control on various factors such as sea floor irregularity, wave energy, and organic activity. The conglomeratic sets close to the shoreline (50–150 cm) act as wave breakers, creating hard substratum and high energy, well-oxygenated environment for organisms like Patella sp., Phoronida worms and Brachidontes pharaonis (Fischer P. 1870). The boring activities of these organisms have disintegrated the sandy matrix of these sets. Finer-grained matrix sediments have been transported to the interset and open sea, while cobble–pebbles have been carried landwards and have created imbricated gravely beach deposits without matrix. Sandy beach is evolving where the conglomeratic sets away from the shoreline (5.0–10.0 m). In this example, sets form a bar; causing fivefold division as backshore, berm, surf zone, bar and offshore from land to sea. Poorly sorted, cobbles-pebbles cobbles and pebbles are found associated with the high-energy environments of bars, whilst well-sorted sands are observed in low energetic environments on shore. The sets and recent shell fragments are the main sources of coastal sediments in Viranşehir. However, the amount of shell fragments decrease towards the active river mouth. This is due to sediment and fresh water influx from the river causing deteriorated temperature, salinity and light penetration of the marine environment resulting in less organic diversity. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

“05.4.8”四川冰雹个例定量降水的预报技巧研究

从集合预报的角度研究了"05.4.8"四川冰雹个例的定量降水的预报技巧随水平尺度以及地形的变化。初步结论为当水平尺度小于100km时,预报技巧随着水平尺度的增加而迅速增加,当水平尺度达到200km及以上时,预报技巧增加地非常缓慢,基本维持不变;在不同的地理位置,预报技巧的差别很大。总体而言,预报技巧在山地要较平原地区来得高。     

Rapid formation of taylor columns: Obstacles against sidewalls

Abstract

The problem of topographic forcing by an obstacle against the boundary of a rotating flow is considered in various parameter regimes. The timescale for the motion is the topographic vortex-stretching time, which is inversely proportional to the background rotation rate and the fractional height of the obstacle. For slow flows this time is short compared with the advection time and the governing equation of conservation of potential vorticity is linear. The final state satisfies the non-linear equation for the advection of potential vorticity, however, and so time dependence has given a specific solution to a non-linear problem. The presence of the sidewall causes a stagnant Taylor column to be set up far more rapidly than cases with no sidewall. It is shown that viscosity and mixing arrests the inviscid evolution at some stage, thus some fluid still crosses the obstacle in the steady state. These solutions suggest that experimental results on separation obtained by Griffiths and Linden (1983) can tentatively be ascribed to entrainment and expulsion of fluid through vertical shear layers at the edge of the topography.     

Some relationships between lithology,basin form and hydrology: a case study from the Thames basin,UK

The role of lithology in influencing basin form and function is explored empirically by investigating correlations between a range of catchment variables, where the spatial unit of analysis is not surface catchments but lithologically coherent groundwater units. Using the Thames basin, UK, as a case study, nine groundwater units have been identified. Values for 11 hydrological and geomorphological variables, including rainfall, drainage density, Baseflow Index, aquifer porosity, storage coefficient and log‐hydraulic conductivity, aquifer and drainage elevation, river incision, and hypsometric integral have been estimated for each of the groundwater units in the basin, and Pearson correlation coefficients calculated for all pairs of variables. Seven of the correlation coefficients are found to be significant at a confidence level of > 99%. Negative correlations between drainage density and log aquifer hydraulic conductivity, and between drainage density and river incision, and positive correlations between log‐hydraulic conductivity and river incision, log‐hydraulic conductivity and Baseflow Index, and between Baseflow Index and river incision are inferred to have consistent causal explanations. For example, incision of rivers into aquifers leads to relative increases in hydraulic gradients in the vicinity of rivers which, in turn, promotes the development of secondary porosity increasing both aquifer hydraulic conductivity and, hence, Baseflow Index. The implication of this interpretation is that the geomorphological evolution of basins is intimately linked to the evolution of hydraulic conductivity of the underlying aquifers. This is consistent with, and supports the notion of a coupled complexly evolving surface water‐groundwater system. Copyright © 2011 John Wiley & Sons, Ltd.