Determination Of Flow Direction Research Articles

Influence of mobile light detecting and ranging data quality in road runoff evaluation

A mobile light detecting and ranging (LiDAR) system is used to provide point cloud datasets as a topographic base for runoff studies. The point clouds are rasterized to evaluate road runoff using the D8 algorithm. Gaussian noise is artificially induced in the point cloud to simulate inaccuracies in geopositioning and determine its influence in the evaluation of runoff direction. Accuracy in the determination of flow direction decreases with the increase of Gaussian noise. Accuracy also decreases with the decrease of the cell size of the raster dataset. Flow direction shows inaccuracies up to 47 deg with a cell resolution of 0.5 m and Gaussian noise of 0.15 m (standard deviation). On the other hand, cell resolutions of 5 m show a maximum difference of 15 deg with the same noise.

Flow direction and velocity determination of dumpsite-induced groundwater contamination in part of Delta State, Nigeria

Contaminant flow direction and velocity from dumpsite in Osubi, Okpe area of Delta State, Nigeria, have been determined. Two-dimensional resistivity imaging, employing the dipole–dipole electrical resistivity technique, and radial resistivity sounding were used for this study. Also, the Groundwater Vistas version 4 was also used for particle/contaminant tracking, to determine flow direction and velocity. The low resistivity of 52 to 130 Ω-m of the topsoil and the second layer to a depth of about 25 m may be an indication of the presence of leachate from the dumpsite. The flow direction across the study area is in the NE–SW direction, which is in agreement with the flow direction generated from the anisotropy polar diagrams from the radial sounding. The path contour lines show the model groundwater steady state head distribution of the hydrogeological system of the area. An approximate head gradient of about 0.0006 towards the south-west was then calculated using the model output head distributions for the area. Therefore, from the groundwater flow equation, the flow velocity was calculated using the head gradient, porosity and hydraulic conductivity to be 0.0169 m/day or 6.0 m/year. If advective flow is assumed, therefore the contaminant would flow at an average speed of 0.0178 m/day or 6.0 m/year.

Discharge and Nutrient Transport between Lakes in a Hydrologically Complex Area of Voyageurs National Park, Minnesota, 2010‐2012

AbstractAn acoustic Doppler velocity meter (ADVM) was deployed in the narrows between Namakan and Kabetogama Lakes in Voyageurs National Park, Minnesota, from November 3, 2010, through October 3, 2012. The ADVM can account for wind, seiche, and changing flow direction in hydrologically complex areas. The objectives were to (1) estimate discharge and document the direction of water flow, (2) assess whether specific conductance can be used to determine flow direction, and (3) document nutrient and chlorophyll a concentrations at the narrows. The discharge direction through the narrows was seasonal. Water generally flowed out of Kabetogama Lake and into Namakan Lake throughout the ice‐covered season. During spring, water flow was generally from Namakan Lake to Kabetogama Lake. During the summer and fall, the water flowed in both directions, affected in part by wind. Water flowed into Namakan Lake 70% of water year 2011 and 56% of water year 2012. Nutrient and chlorophyll a concentrations were highest during the summer months when water‐flow direction was unpredictable. The use of an ADVM was effective for assessing flow direction and provided flow direction under ice. The results indicated the eutrophic Kabetogama Lake may have a negative effect on the more pristine Namakan Lake. The results also provide data on the effects of the current water‐level management plan and may help determine if adjustments are necessary to help protect the aquatic ecosystem of Voyageurs National Park.

Determining flow directions in turbidites: An integrated sedimentological and magnetic fabric study of the Miocene Marnoso Arenacea Formation (northern Apennines, Italy)

Depositional models of turbidity flows require estimating paleocurrent directions using sedimentological indicators such as flute and ripple marks, but these are not always present in outcrop sections or drill cores. In this study, we apply the anisotropy of magnetic susceptibility (AMS) as an alternative tool to estimate paleocurrent directions in a case-study turbiditic system: the Marnoso Arenacea foredeep turbidites of Miocene age exposed in the northern Apennines of Italy. Different depositional facies have been sampled for AMS and additional rock-magnetic analyses. We observed a good agreement between paleocurrent directions from flute casts at the base of turbidite beds and mean directions of maximum magnetic susceptibility axes in organized facies such as massive and laminated sandstones, even if a relatively small but apparently consistent offset of ~15–20° seems to be present. Highly dispersed AMS fabrics were instead observed in disordered facies such as convoluted and undulated sandstones as well as debrites. This strong correlation between hydrodynamic regimes of depositional facies and AMS data represents a novel contribution and confirms the validity of the AMS method to estimate flow directions in the absence of sedimentological indicators. Finally, paleomagnetic analyses from the literature were used to reconstruct the paleogeography of the Marnoso Arenacea basin and make inferences about the origin and direction of transport of the sediments at the basin scale.

Parallel flow accumulation algorithms for graphical processing units with application to RUSLE model

Digital elevation models (DEMs) are widely used in the modeling of surface hydrology, which typically includes the determination of flow directions and flow accumulation. The use of high-resolution DEMs increases the accuracy of flow accumulation computation, but as a drawback, the computational time may become excessively long if large areas are analyzed. In this paper we investigate the use of graphical processing units (GPUs) for efficient flow accumulation calculations. We present two new parallel flow accumulation algorithms based on dependency transfer and topological sorting and compare them to previously published flow transfer and indegree-based algorithms. We benchmark the GPU implementations against industry standards, ArcGIS and SAGA. With the flow-transfer D8 flow routing model and binary input data, a speed up of 19 is achieved compared to ArcGIS and 15 compared to SAGA. We show that on GPUs the topological sort-based flow accumulation algorithm leads on average to a speedup by a factor of 7 over the flow-transfer algorithm. Thus a total speed up of the order of 100 is achieved. We test the algorithms by applying them to the Revised Universal Soil Loss Equation (RUSLE) erosion model. For this purpose we present parallel versions of the slope, LS factor and RUSLE algorithms and show that the RUSLE erosion results for an area of 12km x 24km containing 72 million cells can be calculated in less than a second. Since flow accumulation is needed in many hydrological models, the developed algorithms may find use in many other applications than RUSLE modeling. The algorithm based on topological sorting is particularly promising for dynamic hydrological models where flow accumulations are repeatedly computed over an unchanged DEM.

Direct Determination of Groundwater Direction and Velocity Using Colloidal Borescope at Jenderam Hilir, Selangor

The colloidal borescope can be used for measuring groundwater flow directions and velocity. It is an integrated high-resolution flux gate compass with a high-magnification colloid-imaging camera that can measure flow at selected depths within a well. In this study, the colloidal borescope was used to determine flow direction and measure velocity during a pumping test for the riverbank filtration study in Jenderam Hilir, Selangor. During each measurement, the instrument, which monitored the movement of the suspended particles, was inserted into a well at a particular depth (screen well). The relative flow direction was determined by plotting the trajectory and speed of colloidal particles across the screen with AquaLITE Software, which determined the horizontal speed of the particles and flow speed. The groundwater flow pattern was dtermined at four boreholes in the study area, and the groundwater flow velocities were found ranging from 0.72 to 2.45 x (10-4) m/s. The direction of the groundwater flow at boreholes monitoring well 02 (MW02) and monitoring well 19 (MW19) was moved toward borehole pumping well (PW). The groundwater flow at monitoring well 01 (MW01) was moving toward the northwest of the study site which was parallel with the Langat river. The groundwater flow in borehole monitoring well A (MWA) was toward the southern part of the study site and was not affected by the pumping test activities at borehole monitoring well 03 (MW03).

Distinctions of geomorphological properties caused by different flow-direction predictions from digital elevation models

Several algorithms for flow-path determination have been proposed to pursue a more realistic simulation for flow transmission in watersheds. However, the diversity of existing algorithms may lead to significant differences in the extraction of geomorphological properties. Therefore, preliminary knowledge about these approaches is necessary. In this study, the five most widely used methods – the D8, D, MD, D4, and MD8 algorithms – for flow-direction determination were implemented to investigate watershed extent, water mass contribution, and the track of the longest watercourse. Distinctions of these properties should affect subsequent applications of hydrological analyses, such as the time of concentration calculation and peak discharge estimation. For an example case in Taiwan, the watershed extent and the longest watercourse obtained from the multiple-direction (MD8) algorithm could reach 1.2 and 1.8 times, respectively, that derived from the single-direction (D8) algorithm; moreover, the multiple-direction (MD8) algorithm manifested the weakest ability of collecting water mass from the watershed. A simple index was developed in this study to rank the effects of flow dispersion and flow concentration among the different flow-direction algorithms.

Comparison of two different methods for determining flow direction in catchment hydrological modeling

Digital elevation models (DEMs) are widely used to define the flow direction in distributed hydrological models for simulation of streamflow. In recent decades, numerous methods for flow direction determination have been applied successfully to mountainous regions. Nevertheless, some problems still exist when those methods are used for flat or gently sloped areas. The present study reviews the conventional methods of determining flow direction for such landscapes and analyzes the problems of these methods. Two different methods of determining flow direction are discussed and were applied to the Xitiaoxi Catchment, located in the Taihu Basin in southern China, which has both mountainous and flat terrain. Both the agree method and the shortest path method use drainage networks derived from a remote sensing image to determine the correct location of the stream. The results indicate that the agree method provides a better fit with the DEM for the hilly region than the shortest path method. For the flat region where the flow has been diverted and rerouted by land managers, both methods require observation of the drainage network to determine the flow direction. In order to clarify the applicability of the two methods, both are employed in catchment hydrological models conceptually based on the Xinanjiang model and implemented with PCRaster. The simulation results show that both methods can be successfully applied in hydrological modeling. There are no evident differences in the modeled discharge when using the two methods at different spatial scales.

An efficient and comprehensive method for drainage network extraction from DEM with billions of pixels using a size-balanced binary search tree

With the increasing resolution of digital elevation models (DEMs), computational efficiency problems have been encountered when extracting the drainage network of a large river basin at billion-pixel scales. The efficiency of the most time-consuming depression-filling pretreatment has been improved by using the O(NlogN) complexity least-cost path search method, but the complete extraction steps following this method have not been proposed and tested. In this paper, an improved O(NlogN) algorithm was proposed by introducing a size-balanced binary search tree (BST) to improve the efficiency of the depression-filling pretreatment further. The following extraction steps, including the flow direction determination and the upslope area accumulation, were also redesigned to benefit from this improvement. Therefore, an efficient and comprehensive method was developed. The method was tested to extract drainage networks of 31 river basins with areas greater than 500,000km2 from the 30-m-resolution ASTER GDEM and two sub-basins with areas of approximately 1000km2 from the 1-m-resolution airborne LiDAR DEM. Complete drainage networks with both vector features and topographic parameters were obtained with time consumptions in O(NlogN) complexity. The results indicate that the developed method can be used to extract entire drainage networks from DEMs with billions of pixels with high efficiency.

The effect of streambed heterogeneity on groundwater-surface water exchange fluxes inferred from temperature time series

One-dimensional analytical heat transport equations based on temperature time series data have become popular tools to quantify groundwater-surface water interactions. The influence of nonideal field conditions on the use of these equations has been assessed for nonsinusoidal stream temperature signals, uncertainty in thermal parameters, sensor accuracy and multidimensional flow. Given that streambeds are often highly heterogeneous, the influence of streambed heterogeneity on flux estimates from temperature time series requires further investigation. Synthetic streambed temperatures were generated using two-dimensional numerical models with heterogeneous hydraulic conductivity distributions. Streambed temperatures were used to calculate fluxes using methods based on amplitude ratios (Ar), phase shifts (Δϕ) and both (ArΔϕ). Calculated fluxes were compared to known fluxes from the numerical models for flow fields analogous to losing streams. The influence of streambed structure, degree of heterogeneity, depth of the sensor pair, and location along a flow path were assessed. Errors in calculated fluxes increased with sensor pair depth, position along a flow path, and with the degree of heterogeneity. These errors were larger for streambeds with isotropic structures compared with anisotropic structures, and of the three methods tested; the Δϕ method produced the largest errors. The simultaneous estimation of strong fluxes using Δϕ, and an inability to obtain a flux estimate from Ar can suggest the presence of low hydraulic conductivity zones. Given the large errors and inability to determine flow direction from the Δϕ method, the Ar and ArΔϕ methods are recommended for downwelling fluxes.

Groundwater app to determine flow direction and gradient.

A computational program, called the groundwater flow calculator, was created to quickly and easily determine the hydraulic gradient and direction of groundwater flow. The groundwater flow calculator automates the hand-drawn process by Ralph Heath in the U.S. Geological Survey (USGS) Water Supply Paper 2220. In addition, a mobile app was developed to allow this procedure to run on a smart phone for use in the field.

Numerical investigation for the effect of the liquid film volume on thermocapillary flow direction in a thin circular liquid film

NASA Astronaut Dr. Pettit carried out a thermocapillary flow experiment onboard the International Space Station in 2003. In this experiment a thin water film containing milk powder was formed in a stainless-steel wire ring. Heating a section of the ring by a soldering iron induced in the water film a thermocapillary flow towards the heated section of the ring (outward flow: cold to hot). This flow was in the opposite direction of the usually observed thermocapillary flows (inward flow: hot to cold). To shed light on this interesting phenomenon observed in the space experiment, we have conducted a three-dimensional numerical simulation study. Simulation results showed that the film geometry of the water film is a key factor determining flow direction and flow strength. When the liquid film free surfaces are convex, i.e., the water film volume is larger than that when the free surfaces are flat, an outward flow develops in the film as observed in the space experiment. However, when the free surfaces are concave, the simulation predicts an inward flow.

Priority-flood: An optimal depression-filling and watershed-labeling algorithm for digital elevation models

Depressions (or pits) are areas within a digital elevation model that are surrounded by higher terrain, with no outlet to lower areas. Filling them so they are level, as fluid would fill them if the terrain was impermeable, is often necessary in preprocessing DEMs. The depression-filling algorithm presented here – called Priority-Flood – unifies and improves the work of a number of previous authors who have published similar algorithms. The algorithm operates by flooding DEMs inwards from their edges using a priority queue to determine the next cell to be flooded. The resultant DEM has no depressions or digital dams: every cell is guaranteed to drain. The algorithm is optimal for both integer and floating-point data, working in O(n) and O(nlog2n) time, respectively. It is shown that by using a plain queue to fill depressions once they have been found, an O(mlog2m) time-complexity can be achieved, where m does not exceed the number of cells n. This is the lowest time complexity of any known floating-point depression-filling algorithm. In testing, this improved variation of the algorithm performed up to 37% faster than the original. Additionally, a parallel version of an older, but widely used, depression-filling algorithm required six parallel processors to achieve a run-time on par with what the newer algorithm's improved variation took on a single processor. The Priority-Flood Algorithm is simple to understand and implement: the included pseudocode is only 20 lines and the included C++ reference implementation is under a hundred lines. The algorithm can work on irregular meshes as well as 4-, 6-, 8-, and n-connected grids. It can also be adapted to label watersheds and determine flow directions through either incremental elevation changes or depression carving. In the case of incremental elevation changes, the algorithm includes safety checks not present in prior works.

A preprocessing program for a distributed hydrological model: development and application

A preprocessing program for a distributed hydrological model is very important because it will greatly influence the results of runoff simulation. Runoff simulations include several procedures, such as the determination of flow directions, definition of runoff routing orders, estimation of flow accumulation areas and extraction of drainage networks, etc. In order to simplify the development work and to improve the efficiency of model development, a preprocessing program was developed that can work independently with a graphic user interface. Only digital elevation model (DEM) data are required in this program and characteristics of the program include the following components: (1) a method for the determination of flow direction without sink filling; (2) a leaf clipping method for watershed partitioning; and (3) the determination of the order of runoff routing according to a top-down method. Finally, a case study in the Lhasa River basin is presented, and three case studies in the Wei River, Zhangweinan River and Sanchuan River basins are selected to validate the program. The results show that disconnected or parallel drainage networks can be avoided by using the preprocessing program, especially in flat areas, which can significantly improve the development of distributed hydrological models.

Preliminary Study on the Effects of Surface Microtopography on Tracer Transport in a Coupled Overland and Unsaturated Flow System

AbstractSurface microtopography influences both spatial and temporal distributions of a series of hydrologic processes including infiltration, surface runoff, and unsaturated flow. Importantly, surface roughness and depressions also affect the fate and transport of pollutants throughout surface and subsurface environments. The objective of this study was to experimentally investigate the effects of surface microtopography on overland flow, infiltration, and tracer bromide (Br) runoff, and leaching into the subsurface system under simulated rainfall. Both rough and smooth surfaces were created by using sieved soil and scanned by an instantaneous-profile laser scanner to acquire high-resolution digital elevation models (DEMs) of the soil surfaces. A mold surface, featuring a number of depressions of varied sizes and relationships, was used to create the rough soil surface. The Windows-based puddle delineation (PD) software was applied to characterize surface microtopography, determine flow directions and ac...

A Preprocessing Program for Hydrologic Model—A Case Study in the Wei River Basin

Works of hydrologic model development at the preliminary stage, e.g., determination of flow direction and the order of flow concentration, extraction of drainage network, and spatial interpolation, are very important. In this paper, a preprocessing program is developed with multiple functions for data preparation in hydrologic model. The method in graph theory is used to determine the flow direction, and filling of sink is avoided in this study. A new method, the so-called leaf clipping method, is proposed for watershed division, and the order of runoff concentration is determined according to the flow direction and DEM data. This preprocessing program is developed by using Visual Basic language, detailed algorithms are presented and the program is demonstrated through a case study in the Wei River basin. It shows that this program is useful and helpful for the application of hydrologic models which only needs digital elevation data sets.

Experimental investigation of electrohydrodynamic conduction pumping of various liquids film using flush electrodes

Electrohydrodynamic conduction pumping of free surface liquid film, using flush electrodes has been investigated experimentally for various working fluids. The effective factors in determination of flow direction have been classified and investigated comprehensively. Furthermore, saliency of these factors on hydrodynamic behavior using various electrodes configurations and different fluids has been studied. Results show that the mobility difference and asymmetry of electrodes are main factors in pumping direction and performance, wherein various conditions, each of these factors becomes dominant. Also, efficiency of free surface liquid film conduction pumping has been defined and used to determine the best operating conditions.

TecDEM: A MATLAB based toolbox for tectonic geomorphology, Part 1: Drainage network preprocessing and stream profile analysis

We present TecDEM, a software shell implemented in MATLAB that applies tectonic geomorphologic tasks to digital elevation models (DEMs). The first part of this paper series describes drainage partitioning schemes and stream profile analysis. The graphical user interface of TecDEM provides several options: determining flow directions, stream vectorization, watershed delineation, Strahler order labeling, stream profile generation, knickpoints selection, Concavity, Steepness and Hack indices calculations. The knickpoints along selected streams as well as stream profile analysis, and Hack index per stream profile are computed using a semi-automatic method. TecDEM was used to extract and investigate the stream profiles in the Kaghan Valley (Northern Pakistan). Our interpretations of the TecDEM results correlate well with previous tectonic evolution models for this region. TecDEM is designed to assist geoscientists in applying complex tectonic geomorphology tasks to global DEM data.

Investigation on the determination of flow direction using two parallel cylindrical hot film sensors

Measurement of instantaneous air flow velocity with high frequency can be carried out by using a hot wire anemometer (HWA). HWA works on the basis of heat transfer rate from hot wire to the fluid flow, therefore directional identification of the air flow using hot wire anemometer is a difficult task. By using two parallel cylindrical hot film sensors a probe was built. By considering the wake and heat effect of the upstream sensor on the downstream sensor, direction of the air flow can be identified. In this work, the wake and heat effect resulting from the upstream sensor to the velocity measurement, by the downstream sensor was studied. This measured velocity is dependent of the following factors namely; air velocity, upstream sensor overheat ratio, distance between the two sensors and turbulence intensity of the flow. As a result it was found that the manufactured probe with sensor distance of 1 mm apart is capable of measuring reverse flow measurements of up to 20 m/s for a moderate turbulent flow.

Determination of surface flow paths from gridded elevation data

Surface flow paths are obtained from gridded elevation data by connecting grid cell centers along predetermined flow directions. These flow directions are commonly determined using single and multiple flow direction algorithms. It remains, however, unclear whether multiple flow direction algorithms, which introduce artificial dispersion, can be used to describe surface flow paths and gravity‐driven processes across a terrain without causing unrealistic flow dispersion. To explore this issue, a unified algorithm for the determination of flow directions has been developed, and new methods for the validation of the resulting surface flow paths are introduced. The unified algorithm makes it possible, by setting appropriate parameters, to perform local or path‐based analyses and to experiment with different combinations of single and multiple flow directions in a morphologically significant manner. The new validation methods use drainage systems delineated from contour elevation data as a reference and take into consideration the overlap between these systems and those obtained from gridded elevation data. The unified algorithm is presented, and the results are evaluated for selected case studies in order to provide guidance on the use of surface flow path algorithms based on gridded elevation data.