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Assessment of downstream trends in channel gradient, total and specific stream power: a GIS approach
Geographic Information Systems (GIS) analyses of Digital Elevation Models (DEMs) coupled with catchment area based discharge estimation techniques provide a relatively simple means of modelling contiguous downstream trends in channel gradient, total stream power, and in riverscapes conducive to regime analysis, also specific stream power. For a small, high relief, coastal catchment in SE Australia, good agreement was obtained between channel gradients derived from a 25 m cell-size DEM and field survey equivalents over distances of several kilometres, indicating that channel gradients derived from DEMs can have a reasonable degree of absolute as well as relative accuracy over multi-kilometre reach scales. Assessment of downstream rates of change in channel gradient and specific stream power across four river systems suggests that some of the river reaches most responsive to high magnitude floods occur in zones where these variables rapidly decrease downstream. Modelling of downstream trends in channel gradient, total and specific stream power from catchment-wide DEMs has potential to provide a framework with which to investigate conceptual and empirical models between channel gradient, stream power and the form and dynamics of river systems. 相似文献
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城市化进程中平原河网地区河流结构特征及其分类方法探讨 总被引：15，自引：0，他引：15
平原河网地区河流结构发育受到自然条件和城市化的双重影响。依据遥感解译数据,围绕城市化水平、河流形态、河流结构和河流调蓄功能四个维度,就建成区面积比例、河流长宽分布、河系分维、河流调蓄能力等具体指标,分析了城市化水平和土地利用特征不同区域的河流空间形态、结构特征和功能状态,探讨了城市化进程中平原河网地区河流结构的可能演化轨迹,尝试建立了城市化影响下平原河网地区河流结构分类方法,提出了城市河流综合整治过程中应充分重视保护自然河流结构,注重发挥河流综合功能等观点。 相似文献
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基于地理处理建模的珍稀特有植物空间分布识别方法 总被引：2，自引：0，他引：2
基于ArcGIS地理处理建模与模型集成技术,提出一种在生态环境GIS中整合植物生境建模的实现方法.依据提取经验知识中的生境因子建立模型,提供交互工具在电子地图上勾画调查范围,再由系统驱动生境模型完成植物空间分布识别.最后,对珠峰自然保护区3种珍稀特有树种分布进行了模型识别应用实验.结果表明:基于地理处理的生境建模在大量基础资料匮乏的情况下,可对物种保护规划、资源量调查和估算、巡护路线制定等提供辅助和参考.同时,结合GIS实现建模工具集成,在模型运行效率、模型的交互性与可扩展性、模型集成的灵活度等方面都具有一定优势,在实地调研条件有限的情况下具备较强的可操作性和实用性. 相似文献
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The vegetation of riparian habitats is often distinct from that of the surrounding landscape, thus representing unique habitat for a variety of biota. Although highly mobile, birds often exhibit distinct species assemblages associated with habitat. Therefore, degradation or removal of riparian habitat, particularly in arid environments, may threaten bird diversity. Along the Vaal River, South Africa, mining and agriculture have reduced natural riparian habitat to ca. 9% of its former extent in the Northern Cape Province. We surveyed bird assemblages within intact riparian, savanna and bush-thickened habitats along the Vaal River to ascertain their importance to bird diversity. Avian abundance and species richness did not differ between the three habitats. Species composition of riparian bird assemblages was significantly different to that of savanna and bush-thickened habitats, however, which were not significantly different from each other, and more species were characteristic of riparian habitat (17 species) than bush-thickened (seven species) or savanna (one species) habitats. Of three species reaching the south-western limit of their African distribution, all occurred in riparian habitat. Thus, despite its fragmented nature, the riparian vegetation on the Vaal still supports an important component of avian diversity, and a landscape-level approach is required to manage this relatively rich, arid-land, river. 相似文献
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Ben J. Kefford 《International Journal of Salt Lake Research》1998,7(2):153-170
In order to relate macroinvertebrate fauna to electrical conductivity (EC), a survey of selected orders of macroinvertebrates
was conducted in the Glenelg, Hopkins, Merri and Barwon River Catchments in south-west Victoria, Australia. The survey consisted
of sampling 21 paired sites at confluences of streams. There was little difference between the in-stream habitat but there
was a range of differences in EC between each of the paired sites. The dissimilarity of macroinvertebrate fauna between the
paired sites was compared to the proportional difference in EC and other water quality variables (dissolved oxygen, water
temperature, pH, NO2−N, NO3−N, PO4 and turbidity). This allowed the elimination of EC being confounded with geographical scale parameters and took into account
other water quality parameters that may be confounded with EC. A positive relationship was found between the dissimilarity
of the fauna at each of the two paired sites and the proportional difference in EC. No such relationship was found for any
other measured water quality variable. The results of this survey show that macroinvertebrate community structure is associated
with EC of the river systems investigated after eliminating large scale geographical patterns, in-stream habitat and the measured
water quality parameters. 相似文献
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平原河网地区河流结构特征及其对调蓄能力的影响 总被引：19，自引：2，他引：17
平原河网地区是河流高度发育并受到城市化深刻影响的区域。本文以上海为例,基于上海及周边城市普遍采用的河流分类和水利片管理系统,分析不同城市化水平地区河流结构的共同特征及其差异性,探讨河流结构对河网调蓄能力的可能影响,提出估算河网调蓄能力的方法。研究表明,平原河网地区河流结构指标反映了该地区河流数量、长度以及低等级河流高度发育的自然地理特征,城市化在达到一定程度后即会干扰河流结构的自身发育规律,并表现为河流发育能力的下降;河流结构在城市化影响下表现出由复杂到简单、由多元到单一的变化趋势;河网调蓄能力受低等级河流数量及结构的影响更大,并随着城市化水平的提高而下降;就整体而言,城市化对河网调蓄能力的影响大于对河流结构的影响;以水面数量和河流结构两项指标作为参数能够更准确地估算河网调蓄能力。 相似文献
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Floodplain lakes are rarely analysed for fossil chironomids and usually not incorporated in modern chironomid-climate calibration
datasets because of the potential complex hydrological processes that could result from flooding of the lakes. In order to
investigate this potential influence of river inundations on fossil chironomid assemblages, 13 regularly inundated lakes and
20 lakes isolated from riverine influence were sampled and their surface sediments analysed for subfossil chironomid assemblages.
The physical and chemical settings of all lakes were similar, although the variation in the environmental variables was higher
in the lakes isolated from riverine influence. Chironomid concentration and taxon richness show significant differences between
the two classes of lakes, and the variation in these variables is best explained by loss-on-ignition of the sediments (LOI).
Relative chironomid abundances show some differences between the two groups of lakes, with several chironomid taxa occurring
preferentially in one of the two lake-types. The variability in chironomid assemblages is also best explained by LOI. Application
of a chironomid-temperature inference model shows that both types of lakes reconstruct July air temperatures that are equal
to, or slightly underestimating, the measured temperature of the region. We conclude that, although there are some differences
between the chironomid assemblages of floodplain lakes and of isolated lakes, these differences do not have a major effect
on chironomid-based temperature reconstruction. 相似文献
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Paul Swagemakers Damian Copena Rodríguez María Dolores Domínguez García Xavier Simón Fernández 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):109-118
Modification and channelization of streams and rivers have been conducted extensively throughout the world during the past century. Subsequently, much effort has been directed at re-creating the lost habitats and thereby improving living conditions for aquatic organisms. However, as restoration methods are plentiful, it is difficult to determine which one to use to get the anticipated result. The aim of this study was to compare two commonly used methods in small Danish streams to improve the physical condition: re-meandering and passive restoration through cease of maintenance. Our investigation included measurement of the physical conditions in 29 stream reaches covering four different groups: (1) re-meandered streams, (2) LDC streams (the least disturbed streams available), (3) passively restored streams (>10?years stop of maintenance) and (4) channelized and non-restored streams. The in-stream habitats were compared through analysis of the measured physical parameters and by applying a habitat model. We found that re-meandering is a more effective way of re-creating near-natural physical conditions in small streams compared to passive restoration. This is probably due to the limited energy in small streams which restricts re-shaping of the stream channel. However, based on habitat suitability modelling, the change to the physical condition did not translate into improved habitat suitability for young of the year brown trout highlighting the value of using several methods when evaluating restoration success. 相似文献
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Diatom assemblages of surface sediments in 46 billabongs from four river floodplains in the southeast Murray-Darling Basin,
Australia were sampled to investigate drivers of species distribution. The principal purpose of the study was to derive information
to aid interpretation of diatom-based palaeoecological studies of these systems and of floodplain lakes more generally. Patterns
in billabong diatom assemblages in relation to river reach, hydrology and farming intensity on surrounding land were examined,
as were correlations with water quality variables. Seasonal variation in billabong water quality was high relative to spatial
variation, and spatial patterns in billabong water quality were weak. In contrast, strong patterns were evident in diatom
assemblages. Three main patterns were observed: (1) a distinction between billabongs dominated by planktonic diatoms from
those dominated by benthic and attached forms; (2) differences in diatom assemblages in billabongs on different river reaches;
and (3) differences in assemblages in billabongs with different hydrology. Of all water quality variables tested, total phosphorus
(TP), total nitrogen (TN) and pH exerted the strongest independent influence on diatom distribution; however, only TP remained
an important variable when species variation due to river reach, hydrology, and aquatic plant cover was taken into account.
The weak influence of water quality on diatom distribution is interpreted as reflecting the dichotomy between plankton and
non-plankton-dominated billabongs, the influence of hydrology and biogeography, the lack of strong spatial water quality gradients
and the high degree of temporal variability in water quality. The findings show that diatom records from billabong sediments
can provide evidence of long-term changes in the abundance of aquatic macrophytes and hydrology. They also suggest that merging
calibration data sets across regions for the purpose of improving diatom transfer functions for water quality reconstruction
is of limited value for floodplain lakes, and that performance is more likely to be gained by boosting site numbers within
regions. 相似文献
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STEPHEN T. ENGLE 《New Zealand geographer》2001,57(1):27-35
Geographic Information Systems (GIS) have been increasingly touted for their ability to help empower indigenous peoples. The opportunity to discuss the development of an iwi‐based GIS with Te Ruunanga O Raukawa provides a platform for reflecting critically on issues that impact the effective use of GIS by indigenous groups. The dialectical context of GIS is explored by (re)considering the opportunities and challenges of applying GIS as a cross‐cultural communication device. A position is negotiated which interprets GIS as conditionally empowering provided that indigenous peoples consider their symbolic representation in, and physical access to GIS before making an initial investment in the technology. 相似文献
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As saline streams are geographically widespread in arid and semiarid regions, flow intermittence frequently occurs as another stressor factor apart from salinity. Rambla Salada is a temporary naturally saline stream with an intermittent reach upstream. This stream is an ideal scenario to study the effects of intermittent stream flow on macroinvertebrate community composition and biological traits in a naturally saline Mediterranean stream. This study analysed three sites with different hydrological regimes (one intermittent and two perennials). Flow intermittence exerted low pressure on the macroinvertebrate composition and biological traits which led to the loss of drought-intolerant species and taxa rather than acting as a selective force to promote desiccation-resistant taxa. Macroinvertebrate community at the intermittent site was a subset of the community found in perennial sites, and the presence of flier taxa at this site helped avoid flow cessation. These minor changes have consequences to assess the ecological quality of these saline temporary streams in the context of the Water Framework Directive, given the major differences revealed by some indices between the intermittent and perennial sites as the former obtained lower values due to the presence of few desiccation-intolerant species, which significantly increased the value of those biological indices. 相似文献
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Railroads, roads and lateral disconnection in the river landscapes of the continental United States 总被引：1，自引：0，他引：1
Railroads and roads are ubiquitous features in the river corridors of the United States. However, their impact on hydrologic, geomorphic, and ecological processes in fluvial and riparian landscapes has not been systematically explored at regional or continental extents. This study documents the geographic distribution of roads and railroads in the alluvial floodplains of the continental United States and the regional variability of their potential impacts on lateral connectivity and resultant channel and floodplain structure and function. We use national scale data sets and GIS analysis to derive data on stream–transportation network interactions in two broad categories: (1) crossing impacts, such as bridges and culverts, and (2) impacts where transportation infrastructure acts as a longitudinal dam along the stream channel, causing lateral floodplain disconnection. Potential stream crossing impacts are greatest in regions with long histories of road and railroad development and relatively low relief, such as the Mid-Atlantic, New England, and the Lower Mississippi and Ohio Valleys. Potential lateral disconnections are more prevalent in rugged regions such as the Western U.S. and Appalachians where transportation routes follow river corridors along valley bottoms. Based on these results, we develop a conceptual model that suggests that the area of lateral disconnection due to transportation infrastructure should be most extensive in mid-sized alluvial valleys in relatively rugged settings. The result of this disconnection is the disruption of the long-term, cut-and-fill alluviation and of the shorter-term flood and flow pulse processes that create and maintain ecosystem function in river landscapes. The tremendous extent of transportation infrastructure in alluvial valleys documented in this study suggests a revision to H.B.N. Hynes' statement that the valley rules the stream. Instead, it appears that in modern landscapes of the U.S. the valley rules the transportation network — and the transportation network rules the stream. 相似文献
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The principles and the algorithm of order classification of river watershed divides are outlined. It is shown that a formal application of any available order classification procedures for river watershed divides is not theoretically grounded as well as being impractical, because the physical mechanisms for formation of watershed divide network are different from those operating in the river network. We have formulated the basic principle of determining the watershed divides order on the basis of a serial sequence of sections constituting the travel path of an arbitrary water drop from the watershed divide to the outlet section of the basin. It is suggested that the order N should be assigned to the section of the watershed divide belonging to the full divide line of the N-order basin only if the travel path from it to the N-order stream is “full” in the topological sense, i.e. includes sections of all orders, from 1 to N. Also, we present a variant of determining the order on the basis of so-called higher-order triplets, incomplete sequences of sections of three neighboring orders along the travel path, with the higher of them determining the watershed divide order. The use of triplets is a subjective procedure of generalization that eliminates the influence of recent random erosional incisions on the forms of stable high-order watersheds. We outline the variants of the technique for identifying the network of watershed divides and calculating their orders, based on processing the digital elevation models (DEM) through the use of standard GIS ArcMap tools. Results are obtained in the form of a correlated classification of river and watershed networks which are rationally interpreted and hold promise for investigating the structure, functioning and evolution of river systems. The study revealed the existence of formation “cores” of river systems, i.e. regions within which the system reaches a higher stream order and which are bounded by watersheds of the same order. 相似文献
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Flow and form in rehabilitation of large-river ecosystems: An example from the Lower Missouri River 总被引：2，自引：0，他引：2
On large, intensively engineered rivers like the Lower Missouri, the template of the physical habitat is determined by the nearly independent interaction of channel form and flow regime. We evaluated the interaction between flow and form by modeling four combinations of modern and historical channel form and modern and historical flow regimes. The analysis used shallow, slow water (shallow-water habitat, SWH, defined as depths between 0 and 1.5 m, and current velocities between 0 and 0.75 m/s) as an indicator of habitat that has been lost on many intensively engineered rivers and one that is thought to be especially important in rearing of young fishes. Two-dimensional hydrodynamic models for modern and historical channels of the Lower Missouri River at Hermann, Missouri, indicate substantial differences between the two channels in total availability and spatial characteristics of SWH. In the modern channel, SWH is maximized at extremely low flows and in overbank flows, whereas the historical channel had substantially more SWH at all discharges and SWH increased with increasing discharge. The historical channel form produced 3–7 times the SWH area of the modern channel regardless of flow regime. The effect of flow regime is evident in increased within-year SWH variability with the natural flow regime, including significant seasonal peaks of SWH associated with spring flooding. Comparison with other reaches along the Lower Missouri River indicates that a) channel form is the dominant control of the availability of habitat even in reaches where the hydrograph is more intensively altered, and b) rehabilitation projects that move toward the historical condition can be successful in increasing topographic diversity and thereby decreasing sensitivity of the availability of habitat to flow regime. The relative efficacy of managing flow and form in creating SWH is useful information toward achieving socially acceptable rehabilitation of the ecosystem in large river systems. 相似文献
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Expressing the rate of energy dissipation either within a basin or in a downstream manner is important in understanding occurrence and association between various morphological variables. This study focuses on the downstream variation in stream power and its relationship with morphological variates along the main channel of River Ona, Ibadan, Nigeria. River Ona stretches for 20.5 km downstream of Eleyele Dam. Twenty‐seven (27) points were sampled along this stretch. The 27 points were averaged into nine (9) reaches. At each cross‐section, channel characteristics were observed and measured. These include: width (W), depth (D), velocity (V), slope (S), Cross‐sectional area (A), discharge (Q), total stream power (TSP), specific stream power (SSP), width‐depth ratio (W/D), hydraulic radius (R) and wetted perimeter (P). This study confirmed that the influence of a dam present upstream of a river channel significantly alters the behaviour of slope and this in essence affects the distribution of energy along the river channel. Slope produces a logarithmic relationship with increasing distance downstream (Y = ‐32.79‐0.70InS, r = 0.70, r2 = 0.49, p < 0.05) while there was no significant relationship between Q and distance downstream. 相似文献
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Jonathan P. Fleming John D. MadsenEric D. Dibble 《Applied geography (Sevenoaks, England)》2012,32(2):629-635
Diverse native aquatic macrophytes serve a number of physical and biological functions in the aquatic environment and provide essential habitat for several fish species. In systems that lack submersed macrophytes, native macrophyte re-establishment can be used to revitalize the aquatic community. Planning re-establishment projects requires knowledge of the system along with the growth requirements of macrophytes. Prior studies have identified factors that are important for macrophyte colonization, persistence, and dispersal. However, deductive approaches to identify macrophyte habitat that is suitable for management application have not been developed. A potential solution to this problem is the incorporation of waterscape-wide variables into a Geographic Information System (GIS) and the use of spatial modeling techniques to identify suitable macrophyte habitat. This provides a scientifically based approach to macrophyte re-establishment planning to make efforts more efficient and to recognize potential coverage. The flexibility, scalability, and topological advantages of using a GIS to identify and visualize habitat allow integration with other spatial ecological variables to improve the management of aquatic resources from plants to fish, including invasive species mitigation. Using Little Bear Creek Reservoir, Alabama, as an example system, we illustrate a GIS modeling process that can be applied to any system where the identification of macrophyte habitat is relevant to aquatic resource management goals. 相似文献
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在sRTM-DEM数据的基础上,运用GIS空间分析技术,系统提取了格尔木河三级流域及部分二级流域地形参数和面积-高程积分值,探讨了面积-高程积分值的面积及空间依赖性,并对面积-高程积分值(HI)对构造活动性、岩性变化、冰川作用强度的指示意义进行了研究.研究表明:HI值具有面积依赖及空间依赖性;东昆南断裂(F4)-西大滩断裂(F3)以昆仑山口为界可以分为东西两部分,各自的活动性都是中间强往两边依次减小,东昆中断裂(F1)的活动性变化不大;岩性对HI影响表现出,侵入岩的抗侵蚀力最大,片岩的抗侵蚀力最小,碳酸盐岩组合的抗侵蚀力居中;冰川作用对地貌发育和侵蚀程度有改造作用,与只有古冰川发育或无古冰川流域比较,有现代冰川发育,古冰川作用遗迹广泛的流域,HI值较大并会出现U型谷. 相似文献