Flow Direction Data Research Articles

Fast parallel algorithms for finding the longest flow paths in flow direction grids

In hydrological modeling, the longest flow path is an important feature used to characterize a catchment. Many existing GIS platforms offer dedicated software tools for its identification and delineation, generally implementing methods based on searching through the flow direction data. Unfortunately, currently available algorithms for this task often turn out to be inefficient, especially when working with modern large datasets. Moreover, existing methods often rely on incorrect assumptions or perform calculations in a way that can lead to precision issues. In this work, new parallel algorithms were developed, tested and presented. Measurements show that two of the newly proposed implementations are able to identify the longest flow paths in significantly less time compared with other existing methods.

Hydrological Object‐Based Flow Direction Model for Constructing a Lake‐Stream Topological System

AbstractThe topological system of lakes and streams is the basis for deriving a multitude of patterns and processes in hydrology, geomorphology and ecology. Flow direction is key to constructing a lake‐stream topological system. However, lakes and streams are important hydrological objects that should be considered since they are linked during the process of material and energy transportation. Therefore, a flow direction algorithm that can clearly express the topological relationship of lakes and streams, was proposed here. Lakes and streams were taken as the hydrological objects in stream networks and coupled into a flow direction algorithm. A topological system was established based on the proposed algorithms. Six areas on the Tibetan Plateau were chosen as sample areas with the MERIT digital elevation model (DEM) as the DEM data source. Streams derived from flow direction data in the HydroSHEDS data set (HYDROSTREAMS) and MERIT hydro data set (MERITSTREAMS), as well as streams derived from flow direction results of the D‐infinity algorithm and priority‐flood algorithm were compared with streams derived from the proposed algorithm. The topological relationship between streams and lakes was clearly expressed by the proposed algorithm. In lake areas, the proposed algorithm showed better performance, and no parallel streams were found. In nonlake areas, the stream networks derived from these algorithms were stable. The proposed algorithm offers an opportunity to treat lakes and streams differently during simulation, thus adding to the authenticity of the simulation.

Measurement of Unsteady Aerodynamic Data in Turbomachi-nery Periodic Flows

The objective of this work is to demonstrate the feasibility and advantage of an alternative approach to aerodynamic data acquisition in high-speed highly-loaded turbine engine rotating components. Two methodologies of data acquisition using fast sensing pressure probes are described here. The conventional approach is based on using separate probes for detection of unsteady total and static pressures and the flow direction. This method is labor intensive, requiring either multiple access ports on the investigated engine or repetitive test runs for each individual probe if only one access port is available. An alternative method, using only one Pitot-cylinder probe, can be used to acquire total pressure and flow direction data. The Pitot-cylinder probe basically functions like a controlled flow direction follower. The data reduction procedure for this probe relies on strict periodicity of the investigated flow during a test run. A detailed explanation of data reduction procedure and examples of achieved results are presented.

A hydrography upscaling method for scale-invariant parametrization of distributed hydrological models

Abstract. Distributed hydrological models rely on hydrography data such as flow direction, river length, slope and width. For large-scale applications, many of these models still rely on a few flow direction datasets, which are often manually derived. We propose the Iterative Hydrography Upscaling (IHU) method to upscale high-resolution flow direction data to the typically coarser resolutions of distributed hydrological models. The IHU aims to preserve the upstream–downstream relationship of river structure, including basin boundaries, river meanders and confluences, in the D8 format, which is commonly used to describe river networks in models. Additionally, it derives representative sub-grid river length and slope parameters, which are required for resolution-independent model results. We derived the multi-resolution MERIT Hydro IHU dataset at resolutions of 30 arcsec (∼ 1 km), 5 arcmin (∼ 10 km) and 15 arcmin (∼ 30 km) by applying IHU to the recently published 3 arcsec MERIT Hydro data. Results indicate improved accuracy of IHU at all resolutions studied compared to other often-applied upscaling methods. Furthermore, we show that MERIT Hydro IHU minimizes the errors made in the timing and magnitude of simulated peak discharge throughout the Rhine basin compared to simulations at the native data resolutions. As the method is open source and fully automated, it can be applied to other high-resolution hydrography datasets to increase the accuracy and enhance the uptake of new datasets in distributed hydrological models in the future.

Analysis of current direction in a tropical fluvial system: A study of Ajay river basin within West Bengal, India

The Ajay is an ephemeral, monsoon influenced river, originated from the Chhotanagpur plateau at Batpar of Jamui, Bihar, flowing through heterogeneous lithology and merge with the river Bhagirathi in West Bengal. Here, an attempt has been made to study the directional relationship between paleo-flow and the present flow direction of the Ajay river in West Bengal. Paleocurrent data help to reconstruct the details of paleo-fluvial system, especially the sedimentary environment of the past. The present work was carried out on the basis of detailed field work at different river segments. In this work, paleo-directional data were obtained from the primary sedimentary structure. Present flow direction data were collected using floats, microform developed on active channel bed and also from sediment grain orientation. By using collected directional data, vector mean of paleo and present flow direction were computed. Analytical results reveal that difference is minimum between present and paleo flow direction in studied segments. The directional relationship between the paleo and the present flow direction was divergent in two segments, convergent in four segments and parallel in three segments. The results help us to understand the sedimentary environment and changing flow regimes of the studied segments.

Methodology of Sub-Catchment Division Considering Land Uses and Flow Directions

Catchment division constitutes the foundation for urban water flood forecasting but represents a technically challenging task. The accurate division of catchments is significant for precisely forecasting urban waterlogging. However, existing catchment division methods usually lead to produce results that do not accurately reflect the actual land-use distributions. In recent years, most research has been performed in smaller study areas (less than 10 km2), in residential areas, parks and campuses, and usually focused on a single landscape type. However, for large highly urbanized areas with complex land uses, due to the spatial heterogeneity and complexity of such areas in terms of building, traffic network and hydrology, etc., there is few studies on sub-catchment division. Moreover, the division results by using existing method usually have deviate with the actual land-type distributions. To address the above-mentioned issues, a sub-catchment division method was here proposed that accounts for land-use types and flow directions, and it is suitable for large urban areas by introducing an auto-adaptive threshold adjustment in a novel algorithm. First, the study area is divided into first- and second-level (FL and SL, respectively) catchments according to the macroscale features such as natural landforms, canals, and pipe network. Second, an amended DEM (Digital Elevation Model) and flow direction data are used to divide the SL catchments into third-level direction-based (D-B) catchments. Finally, a novel land use-based algorithm is proposed to divide the D-B catchments into the “smallest” catchments (S-catchments). A large-scale area (44 km2) in Dongying City of China was employed to validate the proposed method. The experiment showed that the proposed method is suitable for subcatchment divisions in large regions and can ensure that the subcatchments are consistent with the actual distribution of land uses and runoff directions.

The study of single station inverting the sea surface current by HF ground wave radar based on adjoint assimilation technology

This paper introduces the assimilation technology in an ocean dynamics model and discusses the feasibility of inverting the sea surface current in the detection zone by assimilating the sea current radial velocity detected by single station HF ground wave radar in ocean dynamics model. Based on the adjoint assimilation and POM model, the paper successfully inverts the sea surface current through single station HF ground wave radar in the Zhoushan sea area. The single station HF radar inversion results are also compared with the bistatic HF radar composite results and the fixed point measured results by Annderaa current meter. The error analysis shows that acquisition of flow velocity and flow direction data from the single station HF radar based on adjoint assimilation and POM model is viable and the data obtained have a high correlation and consistency with the flow field observed by HF radar.

Modelling water quality in drinking water distribution networks from real-time direction data

Abstract. Modelling of contamination spread and location of a contamination source in a water distribution network is an important task. There are several simulation tools developed, however the significant part of them is based on hydraulic models that need node demands as input data that sometimes may result in false negative results and put users at risk. The paper considers applicability of a real-time flow direction data based model for contaminant transport in a distribution network of a city and evaluates the optimal number of flow direction sensors. Simulation data suggest that the model is applicable for the distribution network of the city of Riga and that the optimal number of sensors in this case is around 200.

Assessment of methods for extracting low-resolution river networks from high-resolution digital data

A range of methods for deriving lower-resolution river networks from higher-resolution Digital Terrain Model (DTM) data are assessed at various spatial scales. Derived flow networks are compared to fine-scale hydrologically corrected rivers using a range of performance criteria. These include a measure of spatial distance between fine-scale and derived rivers, and criteria which assess errors in derived catchment area. The Network Tracing Method (NTM), a vector-based network scheme, and the COTAT+ method, a raster-based scheme, are shown to produce river networks that most closely resemble the base fine-scale river networks. COTAT+ is better at preserving catchment areas while the NTM method is often spatially closer to the base river network, especially when applied at lower resolutions, due to a higher percentage of diagonal flow paths. Automatically derived river flow networks will only ever be as good as the base DTM or flow direction data set from which they are derived.

A methodology for aligning raster flow direction data with photogrammetrically mapped hydrology

The requirement to digitally delineate accurate watershed boundaries is a routine task necessary in numerous natural science disciplines. The base topographic data necessary for watershed analysis in many jurisdictions is typically contained within two primary photogrammetrically interpreted base topographic layers: the hydrology (streams, rivers, wetlands, lakes, etc.), and the elevation (contours, spots, digital terrain model points, etc.). From these two data sources, a flow direction corrected, single line, vector hydrology network and a raster digital elevation model can be developed. There are numerous approaches to watershed delineation, but the most accurate implementations employ both these enhanced data sets in extracting watershed divides. A popular method to increase the accuracy of extracted watershed boundaries is to utilize that hydrology network to post-condition the digital elevation model, thus ensuring the local topography honours the stream network. This process is known as stream burning. This paper outlines an alternative approach to accomplish a similar objective. The outlined approach unambiguously translates the topological relationships within the vector hydrology layers directly into a raster flow direction grid. Initial testing of this methodology has shown several accuracy and processing advantages for extracting watershed boundaries.

Implementation of a large‐scale variable velocity river flow routing algorithm in the Canadian Regional Climate Model (CRCM)

Implementation and validation of a flow routing scheme for the North American domain of the Canadian Regional Climate Model (CRCM) is described. A variable velocity flow routing algorithm is used to transport runoff from the land surface to the continental edges and provide freshwater flux forcing for the oceans. The flow routing scheme uses Manning's equation to estimate flow velocities for river channels whose cross‐sections are assumed to be rectangular. Discretization of major North American river basins and their flow directions are obtained at the polar stereographic resolution of the CRCM using 5‐minute global river flow direction data as a template. In the absence of observation‐based gridded estimates of runoff, model runoff estimates from a global simulation of the Variable Infiltration Capacity (VIC) hydrological model (forced with observationbased meteorological data) are used to validate the flow routing scheme. Model results show that the inclusion of flow routing improves the comparison with observation‐based streamflow estimates when compared to the unrouted runoff. Monthly comparison of simulated streamflow with observation‐based estimates, and basin‐wide averaged flow velocities, suggests that the flow routing scheme performs satisfactorily.

A phenomenon-based approach to upslope contributing area and depressions in DEMs

Description of the terrain surface through digital elevation models (DEMs) strongly depends on data collection methods and DEM data structures. For efficiency and availability reasons regular point distributions are most common, which yield artefacts such as depressions and preferential flow directions. These facts need to be considered when natural phenomena are modelled, as is shown for handling depressions and for estimation of flow paths and upslope contributing areas. Analysis of the main reasons for the occurrence of depressions shows that they usually better reflect the terrain than their surroundings. Thus, the most common remedial method of raising depressions is rejected. Algorithms that ‘cut’ a flow path from the depression through its bounding barrier are favoured instead. Several flow routing algorithms are evaluated for their behaviour in regular grids. It is shown that the multiple flow direction (mfd) algorithm that distributes water from a grid cell to the lower of its eight neighbours proportionally to their elevation differences (slope) exhibits correct flow directions and the best rotation invariance. It is suggested that the estimation of upslope contributing areas (TCAs) is undertaken in two steps: first, a high quality flow direction data set is derived by a well-behaved mfd algorithm or by subgrid modelling of flow paths; secondly, the upslope contributing areas are obtained by counting the upslope elements. © 1998 John Wiley & Sons, Ltd.

Late Quaternary turbidity current pathways to the Madeira Abyssal Plain and some constraints on turbidity current mechanisms

AbstractTurbidites deposited in the Madeira Abyssal Plain during the last 200 000 yr originated mainly from the flanks of the Canary Islands and from the Northwest African continental margin north of the Canaries. Derivation of these turbidites from sources to the east of the abyssal plain apparently contradicts flow direction indicators derived from the sediments on the plain, which indicate derivation from the north‐east. However, two systems of shallow channels, mapped using side‐scan sonar and 3.5‐kHz data, link the easterly sediment sources to the north‐eastern edge of the abyssal plain, reconciling the apparently contradictory flow direction data. A northern system originates in the area between Madeira and the Canary Islands and follows a westerly and then north‐westerly path, in part cutting obliquely across regional bathymetric trends. It carries sediment from the African continental margin north of the Canary Islands, and from the eastern Canaries, to the north‐eastern abyssal plain. The southern channel system carries material from the western Canary Islands more directly westward to the central part of the plain. The pathways of individual turbidites can be reconstructed in some detail, by combining channel mapping with published information on turbidite provenance and flow directions on the Madeira Abyssal Plain. Interaction between turbidity currents and channel morphology controls turbidite depositional patterns. Small turbidites are completely contained within channels 20 m deep and 2 km wide. It is proposed that these are relatively high‐density flows which have evolved in crossing the almost flat floor of a basin south‐east of Madeira before entering the channel system. Larger turbidites show evidence of flow stripping where they interact with channels, with the result that their coarse and fine fractions follow different paths to and across the abyssal plain.

Stratigraphy, paleomagnetism, and magnetic fabric of the Toba Tuffs: Constraints on the sources and eruptive styles

The Toba depression in north central Sumatra is a complex of several overlapping calderas resulting from three major ignimbrite‐forming eruptions. Within the depression, the upland masses of Samosir and northern Uluan consist of welded ignimbrite capped by coarse breccia and lacustrine sediment, hitherto interpreted to be two parts of a single resurgent dome. This study has demonstrated that the welded tuffs of Samosir and Uluan have different magnetic polarities and therefore at least two different ignimbrites are present; the Samosir/Uluan massif may consist of parts of two resurgent domes. The first ignimbrite eruption occurred at 0.84 Ma and produced a very thick (>400 m), densely welded unit having a reversed polarity. Anisotropy of magnetic susceptibility (AMS) flow direction and lithic size data indicate that the source lies in the southern part of the Toba depression, and the thick deposit of Uluan is thought to have ponded in a 40‐km‐wide caldera. The second ignimbrite is normally magnetized. AMS flow direction data indicate two separate source vents, one to the north in the Haranggaol caldera, and another to the south. The thick deposit at Samosir is thought to have ponded in the southern caldera. Coarse sediments then accumulated over Samosir and northern Uluan and were capped by lacustrine deposits. A renewed episode of resurgence then uplifted Samosir Island and possibly the northern part of Uluan. At approximately 0.075 Ma the last and apparently largest ignimbrite eruption occurred from calderas in the north and south parts of the Toba depression. This ignimbrite is mostly nonwelded and normally magnetized. Part of the Uluan dome was destroyed by collapse of the Sibandung caldera and Latung graben and concomitant with renewed subsidence of the Haranggaol and Porsea calderas.

The thick, turbulent boundary layer on a cylinder: Mean and fluctuating velocities

The mean and fluctuating velocities in a turbulent boundary layer on a cylinder have been experimentally characterized for the case where the boundary layer is thick compared to the radius of transverse curvature. The mean velocity measurements suggest a mixed scaling for the ‘‘log law of the wall’’ using the wall coordinate yUτ/ν and the ratio of the local boundary layer thickness to the radius of the cylinder δ/a. A relation for the slope and intercept of the log law of the wall as functions of δ/a based on empirical results and simple analysis is presented. Measurements of the Reynolds stress for δ/a of order 10 show that the Reynolds stress drops off much more quickly with distance from the wall than for a turbulent boundary layer on a flat plate. Both the Reynolds stress data and the turbulent intensity in the mean flow direction data are functions of the inverse radial distance from the center of the cylinder.

Flow Direction Determination of Lava Flows

The flow direction technique, previously applied to ash-flow sheets, can be used to determine direction of movement and locate eruptive centers for lava flows. The method provides statistically stronger and more consistent flow direction data for lava than ash-flow tuff. The accuracy and reliability of the technique was established on the porphyritic basaltic andesite of Mount Taylor, New Mexico, which erupted from a known center, the Mount Taylor Amphitheater. The technique was then applied to volcanic units with unknown sources: the John Kerr Peak Quartz Latite and mid-Tertiary andesite flows in the Mogollon Mountains, both in southwestern New Mexico. The flow direction technique indicated flow patterns and suggested source areas for each rock unit. In the Mogollon Mountains flow direction measurements were supported by independent directional criteria such as dips of cross beds, stratigraphic thickening, facies changes, and megascopic textures.-