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1.
Horton's hierarchical and fractal analysis of channel circumference reveals that tidal-channel systems in the Dutch Wadden Sea have similar branching patterns. Channel systems have the same characteristics as three- to four-times branching networks. The branch lengths of these channels decrease logarithmically. The channel systems can be regarded as statistical self-similar fractal networks, considering the natural variability in branch lengths and channel positions. Branching of channels does not continue below the 500 m scale. The channel-system circumference length is logarithmically related to the tidal prism and drainage area. The similarity of the channel systems, regardless of their size, relative amount of intertidal flats, and tidal amplitude, points to a self-organising nature. All processes depend on the feedback between morphology and hydrodynamics. At first sight, the channel systems can be regarded as an ebb-driven drainage network, governed by erosion. However, flood-dominated net sedimentation occurs in large parts of the drainage basins and modifies the ebb-driven network. The complex interaction of hydrodynamic and morphodynamic processes in tidal basins limits the applicability of process-based models. Behaviour-oriented modelling has a wide applicability and can be improved using the fractal geometry as the dynamical equilibrium morphology. The fractal-network geometry can also be used for stochastic reconstructions of fossil tidal-channel systems, when only limited observations are available. 相似文献
2.
Yasuo Shimano 《Environmental Geology》1992,20(1):5-14
This research is to analyze the composition of stream networks of drainage basins in Japan and to discuss the characteristics of drainage basins in the Japanese Islands. Study areas were selected for 180 drainage basins in the entire country. In this study, a topographic map with a scale of 1:50,000 was used and inserted into the valley line by V-shaped-contour methods in each drainage basin. The streams are ordered according to Strahler's system and measured by the stream number, stream length, stream slope, drainage area, and stream fall in each drainage basin. Horton's law of drainage network composition holds good in most drainage basins in Japan. The average values of the bifurcation ratio, stream length ratio, stream slope ratio, drainage area ratio, and stream fall ratio are 4.24, 1.91, 1.98, 4.52, and 1.04, respectively. The mean bifurcation ratio of drainage basins in Japan is 4.24, and this ratio is slightly greater than in other countries. It is also greater than the theoretical value of 4.0. This implies that the slope of drainage basins in Japan is so steep and the relief energy so large that excess streams have developed to a rather marked degree. The average stream fall ratio is 1.04 for drainage basins in Japan. It suggests that drainage basins are generally considered to be in a stage of maturity in stream channel development for the Japanese Islands. The stream fall ratio, however, is slightly greater than 1.0. Although, the stream beds are nearly in dynamic equilibrium in most cases, it tends to be in a slightly aggrading state. 相似文献
3.
Small blue crabs (Callinectes sapidus Rathbun, 43–70 mm carapace width) can influence the size-distribution of the gastropod,Bittium varium, strongly reducing the contribution of snails >3 mm shell length in field enclosures. We test the hypothesis that these size-dependent effects are due to size-selective predation rather than size-dependent emigration from the field enclosures. In laboratory feeding trials, blue crabs showed negative selectivity for snails <2.5 mm and positive selectivity for snails >3.3 mm. When feeding, blue crabs crushBittium shells, but the opercula are deposited undamaged in the sediment. Sediment from a field enclosure experiment contained 6.5× moreBittium opercula from enclosures with blue crabs than from enclosures without blue crabs. We reconstructed the size distribution ofBittium killed by blue crabs from the opercula recovered from sediment. This distribution qualitatively matched those “missing” from the size frequency distribution of surviving snails. Estimates of selectivity from laboratory feeding trials predicted the pattern of size-selection fromBittium killed in the enclosures. We also estimated Strauss's linear index of selectivity and Chesson's α based on the size distribution of snails available during the field enclosure experiment. These indices predicted both the pattern of selectivity and the size distribution ofBittium killed in enclosures with blue crabs. We conclude that size-selective predation by blue crabs can explain the observed shifts inBittium size distributions. 相似文献
4.
Evaluation of morphometric parameters of drainage networks derived from topographic maps and DEM in point of floods 总被引：4，自引：0，他引：4
An evaluation of morphometric parameters of two drainage networks derived from different sources was done to determine the
influence of sub-basins to flooding on the main channel in the Havran River basin (Balıkesir-Turkey). Drainage networks for
the sub-basins were derived from both topographic maps scaled 1:25.000 and a 10-m resolution digital elevation model (DEM)
using geographic information systems (GIS). Blue lines, representing fluvial channels on the topographic maps were accepted
as a drainage network, which does not depict all exterior links in the basin. The second drainage network was extracted from
the DEM using minimum accumulation area threshold to include all exterior links. Morphometric parameters were applied to the
two types of drainage networks at sub-basin levels. These parameters were used to assess the influence of the sub-basins on
the main channel with respect to flooding. The results show that the drainage network of sub-basin 4—where a dam was constructed
on its outlet to mitigate potential floods—has a lower influence morphometrically to produce probable floods on the main channel
than that of sub-basins 1, 3, and 5. The construction of the dam will help reduce flooding on the main channel from sub-basin
4 but it will not prevent potential flooding from sub-basin 1, 3 and 5, which join the main channel downstream of sub-basin
4. Therefore, flood mitigation efforts should be considered in order to protect the settlement and agricultural lands on the
floodplain downstream of the dam. In order to increase our understanding of flood hazards, and to determine appropriate mitigation
solutions, drainage morphometry research should be included as an essential component to hydrologic studies. 相似文献
5.
This study evaluated the use by fish of restored tidal wetlands and identified links between fish species composition and habitat characteristics. We compared the attributes of natural and constructed channel habitats in Sweetwater Marsh National Wildlife Refuge, San Diego Bay, California, by using fish monitoring data to explore the relationships between channel environmental characteristics and fish species composition. Fishes were sampled annually for 8 yr (1989–1996) at eight sampling sites, four in constructed marshes and four in natural marshes, using beach seines and blocking nets. We also measured channel habitat characteristics, including channel hydrology (stream order), width and maximum depth, bank slope, water quality (DO, temperature, salinity), and sediment composition. Fish colonization was rapid in constructed channels, and there was no obvious relationship between channel age and species richness or density. Total richness and total density did not differ significantly between constructed and natural channels, although California killifish (Fundulus parvipinnis) were found in significantly higher densities in constructed channels. Multivariate analyses showed fish assemblage composition was related to channel habitat characteristics, suggesting a channel’s physical properties were more important in determining fish use than its restoration status. This relationship highlights the importance of designing restoration projects with natural hydrologic features and choosing proper assessment criteria in order to avoid misleading interpretations of constructed channel success. We recommend that future projects be designed to mimic natural marsh hydrogeomorphology and diversity more closely, the assessment process utilize better estimates of fish habitat function (e.g., individual and community-based species trends, residence time, feeding, growth) and reference site choice, and experimental research be further incorporated into the restoration process. 相似文献
6.
Marek Kacewicz 《Mathematical Geology》1994,26(8):985-994
The feedforward backpropagation technique provides a model-free estimation with neural networks. The algorithm was used to estimate fracture aperture of natural fractures in three dimensional space. A three-layer neural network with at least 5 nodes in a hidden layer was trained on a data set consisting of formation imaging microscanner logs (FMS)from horizontal boreholes. Sensitivity studies were performed to account for the rate of learning convergence, convergence to local error minima, etc. Among the factors contributing mostly to the overall good or bad performance of the network, the following are worth mentioning: number of data points, data spacing, and data variability. It is shown that a smoothing operation applied to aperture data along the wellbore often helps to reduce disorientation of the network and to switch from oscillations or chaotic jumps to convergence. 相似文献
7.
Drainage morphometry and its influence on hydrology in an semi arid region: using SRTM data and GIS 总被引：3，自引：0，他引：3
An attempt has been made to study drainage morphometry and its influence on hydrology of Peddavanka watershed, South India. Drainage networks for the sub-basins were derived from topographical map (1:50,000) and Shuttle Radar Topographic Mission (SRTM) Digital Elevation Model (DEM) data used for preparing elevation, slope and aspects maps. Geographical information system (GIS) was used in evaluation of linear, areal and relief aspects of morphometric parameters. The study reveals that SRTM DEM and GIS-based approach in evaluation of drainage morphometric parameters and their influence on hydrological characteristics at watershed level is more appropriate than the conventional methods. The mean Bifurcation ratio (R b) of the entire basin is 3.88 which indicate that the drainage pattern is not much influenced by geological structures. VIII sub-basin have high elongation ratio (R e), basin relief (B h), Ruggedness number (Rn) and time of concentration (T c). It indicates that the erosion and peak discharges are high in these basins. Therefore, the construction of the check dams and earth dams will help in reducing peak discharge on the main channel. These studies are very useful for implementing rainwater harvesting and watershed management. 相似文献
8.
Shreerup Goswami Kamal Jeet Singh Shaila Chandra 《Journal of Asian Earth Sciences》2006,28(4-6):218-233
Gondwana basins of Orissa State constitute a major part of the Mahanadi Master Basin. These Gondwana sediments, ranging from Asselian to Albian in age, contain remnants of three basic floral assemblages i.e. Glossopteris Assemblage, Dicroidium Assemblage and Ptilophyllum Assemblage which can be recognized through the Permian, Triassic and Early Cretaceous, respectively. The megafloral assemblages of different basins of this state are discussed briefly. This report mainly deals with the plant species diversification in different lithological formations and the development of flora in the Gondwana basins of Orissa. A number of successive megafloras are recognized. Among those, leaves are the dominant part of the preserved flora, followed by fruits and roots. No wood parts are preserved in the major basins. These pre-angiospermic floras have been systematically analyzed to depict the evolutionary trends, and palaeofloristics of these basins. The distribution of plant fossils in different formations of these basins depicts provincialism in Gondwana flora within the Orissa. 相似文献
9.
Graham K. MacDonald Paula E. Noel Danika van Proosdij Gail L. Chmura 《Estuaries and Coasts》2010,33(1):151-160
We assess the status of channel networks and pools of two tidal salt marshes recovering from more than a century of agricultural
reclamation on the Bay of Fundy, Canada. A process of largely unmanaged restoration occurred at these sites since abandonment
of agricultural activities during the first half of the twentieth century. Each recovering marsh was compared to a reference
marsh that was never drained or ditched. We field mapped channel networks at all marshes and used aerial photographs to map
the pre-abandonment channel network at one of the sites. The recovering marshes have hybrid channel networks that feature
highly variable channel morphologies, loss of original channels, and incorporation of drainage ditches. Although channel networks
in recovering marshes integrate agricultural ditches, the recovering marsh networks may not be substantially increased in
length or density. Our aerial photograph analysis shows that channel density at one of the recovering marshes is comparable
to the pre-abandonment density, but with reduced sinuosity. Field mapping of permanent tidal pools on the lower Bay marshes
revealed that pools cover 13% of the recovering marsh, compared to ∼5% of the reference marsh. This study demonstrates that
these essential marsh features can be regained through restoration or simple abandonment of drainage infrastructure. 相似文献
10.
S.B. Kelly 《地学学报》1992,4(5):578-584
Hydrographically closed basins are sensitive to environmental change at all scales, the influence of climate being particularly strong. Some Devonian basins contain non-marine successions which appear to represent the deposits of such basins. Climatic fluctuations may be recorded by sediments in the form of Milankovitch band cyclicity. Two novel records of climatically related cyclicity are discussed. Well 12/13-1 in the North Sea penetrates a fine-grained Old Red Sandstone succession which is thought to be comparable to the largely lacustrine Middle Devonian deposits of the Orcadian Basin which outcrop onshore. The gamma ray log through the Devonian interval reveals periodic large peaks which correlate with U-rich, fine-grained intervals deposited during periods of greatest lake expansion. The peaks are cyclical; power spectrum of the gamma ray data reveal periodicities of c. 8 and 40 m, which are thought to correlate with the 21,000 yr (precession) and 100,000 yr (eccentricity) Milankovitch cycles. The Sherkin Sandstone Formation of the Munster Basin, SW Ireland, is a thick (> 1000 m) succession of largely alluvial deposits which were deposited by a terminal fan network. Detailed analysis of channel body sandstones and sedimentary structures contained within them reveals a cyclical variation in the dimensions of the bedforms camed by the channels. The same cyclicity is evident in the proportion of channel deposits. This variation reflects fluctuations in palaeodischarge, probably related to climatic variation. The main cycles are approximately 130 m thick; spectral analysis reveals two further strong periodicities at approximately 36 and 55 m. Estimated sediment accumulation rates suggest that the cycles represent periods of the order of lo4 years. It is proposed that the longer cycles reflect the 412,000 yr orbital eccentricity cycle and that the shorter cycles are either harmonics or components of the 100,000 yr eccentricity cycle. 相似文献
11.
Victor R. Baker 《Environmental Geology》1976,1(5):261-281
The “upstream” approach to flood hazard evaluation involves the estimation of hydrologic response in small drainage basins.
This study demonstrates the application of geomorphology to such studies in a region of unusually intense flooding in central
Texas. One approach to flood hazard evaluation in this area is a parametric model relating flood hydrograph characteristics
to quantitative geomorphic properties of the drainage basins. A preliminary model uses multiple regression techniques to predict
potential peak flood discharge from basin magnitude, drainage density, and ruggedness number. After mapping small catchment
networks (4 to 20 km2) from remote sensing imagery, input data for the model are generated by network digitization and analysis by a computer-assisted
routine of watershed analysis.
The study evaluated the network resolution capabilities of the following data formats: (1) large-scale (1:24,000) topographic
maps, employing Strahler's “method of v's”, (2) low altitude black-and-white aerial photography (1:13,000 and 1:20,000 scales),
(3) NASA-generated aerial infrared photography at scales ranging from 1:48,000 to 1:123,000, and (4) Skylab Earth Resources
Experiment Package S-190A and S-190B sensors (1:750,000 and 1:500,000 respectively). Measured as the number of first order
streams or as the total channel length identified in small drainage areas, resolution is strongly dependent on basin relief.
High-density basins on the Edwards Plateau were poorly depicted on orbital imagery. However, the orbital network definition
of low-relief basins on the inner Texas Coastal Plain is nearly as accurate as results from large-scale topographic maps.
Geomorphic methods are also useful for flood hazard zonation in “downstream” flood plain areas. Studies of the Colorado River
valley near Austin, Texas, easily distinguished infrequent (100- to 500-year recurrence interval), intermediate (10- to 30-year),
and frequent (1- to 4-year) hazard zones. These mapping techniques are especially applicable to the rapid regional evaluation
of flood hazards in areas for which there is a lack of time and money to generate more accurate engineering-hydraulic flood
hazard maps. 相似文献
12.
Driss Khattach Pierre Keating El Mostafa Mili Touria Chennouf Pierre Andrieux Abdellah Milhi 《Comptes Rendus Geoscience》2004,336(16):1427-1432
Various techniques (horizontal and vertical derivatives, upward continuation, Euler deconvolution) have been applied to the gravity data from the Triffa's plain and the north flank of the Beni-Snassen massif to delineate various major geological structures such as faults and basins. These results allow the production of a structural map showing the fault systems for the survey area. This map forms the basis for planning future hydrogeological research in this region. To cite this article: D. Khattach et al., C. R. Geoscience 336 (2004). 相似文献
13.
Estimating concentrations or flow rates along a stream network requires specific models. Two classes of models, recently proposed in the literature, are generalized, to the intrinsic case in particular. We present a global construction by ‘streams’, i.e. on the whole set of paths between sources and outlet. Combining stationary or intrinsic one-dimensional random functions leads to stationary or intrinsic models on segments, with discontinuities at the forks. A construction from outlet to sources, leads to stationary or intrinsic models on each stream, without any discontinuity at the forks. The linear variogram is found as a particular case. The extension to the linear model of coregionalization is immediate, allowing a multivariate modelling of concentrations. To cite this article: C. de Fouquet, C. Bernard-Michel, C. R. Geoscience 338 (2006). 相似文献
14.
15.
Steven I. Usdansky 《Mathematical Geology》1987,19(8):793-805
Multisystem nets are topological analogs of real and potentially real phase diagrams which can be constructed given only the chemography of phases of interest. Combinatorial analysis of c-component (c + 4)-phase multisystems suggests the existence of [(c + 4)!/2] [2(c +4) – 2 (c + 4)] distinct nets. (c + 4)-phase multisystem nets are characterized by three different invariant point stability levels, four different reaction stability levels, and three invariant points along each univariant reaction. Invariant points at the intermediate stability level occur in two disjoint networks. Unlike (c + 3)-phase multisystems, in which all nets are related by transposition, (c + 4)-phase nets form distinct equivalence classes under transposition based on identities of those invariant points at the intermediate stability level. A position matrix is introduced to denote adjacency/connectivity relationships, and a relationship is suggested between the number of nets in each equivalence class under transposition and the number of ways of assigning stability levels to invariant points of an arbitrary position matrix. 相似文献
16.
Jorge P. Castello Luis Poersch Marcelo C. Vasconcellos Ronaldo Cavalli Wilson Wasielesky 《Estuaries and Coasts》2008,31(1):215-222
A predictive model for impact assessment of shrimp (Farfantepenaeus paulensis) culture in pen enclosures was developed. Experiments were carried out at Saco da Mangueira, a small embayment at the Patos
Lagoon estuarine area (southern Brazil). Nitrogen budget was assessed considering inputs and outputs from the culture system.
The measured parameters were water flow, shrimp density, pen mesh size and clogging effect, artificial diet quality, and food
conversion rates. Shrimp excretion was estimated from literature available. A N-NT concentration of 0.07 mg L−1 of was assumed as a conservative critical reference value to assess environmental impact and water deterioration. Trials
showed that for Saco da Mangueira conditions, a total number of 70 pen enclosures of 0.3 ha (i.e., a total production of 32.2 ton)
is recommended as a maximal number. This model is a useful tool for impact assessment and coastal management and may be applied
to other estuarine areas. 相似文献
17.
Qing Wang Yuanyuan Kong Wen Zhang Jianping Chen Peihua Xu Huizhong Li Yiguo Xue Xiaoqing Yuan Jiewei Zhan Yujie Zhu 《Arabian Journal of Geosciences》2016,9(18):718
A method was developed to analyze the susceptibilities of 541 regional basins affected by debris flows at the Wudongde Dam site in southwest China. Determining susceptibility requires information on source material quantity and occurrence frequency. However, the large number of debris flows can hinder the individual field investigation in a each small basin. Factors that may trigger debris flows can be identified using remotely sensed interpretation information. Susceptibility analysis can then be conducted based on these factors. In this study, SPOT5 satellite imagery, digital elevation models (DEM), a lithology distribution map, and rainfall monitoring data were used to identify 12 debris flow trigger factors: basin relief ratio, slope gradient in the initiation zone, drainage density, downslope curvature of the main channel, vegetation coverage, main channel aspect, topographic wetness index, Melton’s ruggedness number, lithology, annual rainfall, form factor, and cross-slope curvature of the transportation zone. Principal component analysis was used to obtain the eight principal components of these factors that contribute to susceptibility results. Then, a self-organizing map method was adopted to analyze the principal components, which resulted in a debris flow susceptibility classification. Field validation of 26 debris flow basins was used to evaluate the errors of the susceptibility classification, as well as assess the causes of such errors. The study found that principle component analysis and self-organizing map methodologies are good predictors of basin susceptibility to debris flows. 相似文献
18.
Stephen E. Davis Daniel L. Childers John W. Day David T. Rudnick Fred H. Sklar 《Estuaries and Coasts》2001,24(4):610-622
We used enclosures to quantify wetland-water column nutrient exchanges in a dwarf red mangrove, (Rhizophora mangle L.) system near Taylor River, an important hydraulic linkage between the southern Everglades and eastern Florida Bay, Florida, USA. Circular enclosures were constructed around small (2.5–4 m diam) mangrove islands (n=3) and sampled quarterly from August 1996 to May 1998 to quantify net exchanges of carbon, nitrogen, and phosphorus. The dwarf mangrove wetland was a net nitrifying environment with consistent uptake of ammonium (6.6–31.4 μmol m−2 h−1) and release of nitrite +nitrate (7.1–139.5 μmol m−2 h−1) to the water column. Significant flux of soluble reactive phosphorus was rarely detected in this nutrient-poor, P-limited environment. We did observe recurrent uptake of total phosphorus and nitrogen (2.1–8.3 and 98–502 μmol m−2 h−1, respectively), as well as dissolved organic carbon (1.8–6.9 μmol m−2 h−1) from the water column. Total organic carbon flux shifted unexplainably from uptake, during Year 1, to export, during Year 2. The use of unvegetated (control) enclosures during the second year allowed us to distinguish the influence of mangrove vegetation from soil-water column processes on these fluxes. Nutrient fluxes in control chambers typically paralleled the direction (uptake or release) of mangrove enclosure fluxes, but not the magnitude. In several instances, nutrient fluxes were more than twofold greater in the absence of mangroves, suggesting an influence of the vegetation on wetland-water column processes. Our findings characterize wetland nutrient exchanges, in a mangrove forest type that has received such little attention in the past, and serve as baseline data for a system undergoing hydrologic restoration. 相似文献
19.
The Sample Catchment Basin (SCB) mapping technique extends the representativeness of the geochemical features of stream sediments to the surface of the whole upstream drainage basin. SCB boundaries clash with the water divides traced from each sampling point and are limited upstream by the presence of further SCBs. They are also assumed to represent the elementary map unit. The rank of SCBs can be defined counting the number of upstream SCBs along the branches of a fluvial network. The presence of low rank SCBs minimizes the statistical redundancy of measures. The SCB technique is particularly suitable for the geochemical mapping of mountainous or hilly areas and to correctly display the information into a morphological context. This approach can be also valuable in the case of low sampling density, inhomogeneous sampling schemes, and especially when very accurate evaluations of the spatial distribution of chemicals (with natural or anthropogenic origin) are required. 相似文献
20.
U. Santosuosso A. Papini 《International Journal of Environmental Science and Technology》2016,13(8):2037-2044
Geographic profiling is a method that proved to be useful also in order to investigate the point of origin of a biological invasion. K-means clustering and Voronoi diagrams can partition a data set of geographic positions of populations invading a defined area and are, therefore, useful in cases in which an invasion had more introduction events as points of origin. One critical point of the method is to identify the right number of clusters in which to divide the starting data set formed by groups of points on a map. The Silhouette method proved to be capable of identifying the best number of subsets (clusters) of the general set of observations by providing different values for different subdivisions of the set of observations in clusters. For each cluster, the corresponding Voronoi tessellation was built on the starting map. To test the method, we did a simulation of clusters of data (points) on a map and we verified whether the proposed methods worked efficiently with the simulated data set with hundred repeats and using a varying number of clusters on the same map. The used techniques revealed to be efficient in finding the highest probability area of the map that would include the starting points for each cluster. A case study consisted in a known data set, that is, the spreading pattern of Caulerpa racemosa var. cylindracea (sea grapes), that was compatible (highest probability) with an original point of introduction in southern Italy and long distance (thousands of kilometers) secondary spreads via anthropic dispersal. The proposed techniques may also be applied to other kinds of data sets of biological data distributed on a map or in general on a geometrical surface. 相似文献