# raster flow accumulation

If your computer has multiple processors or processors with multiple cores, better performance may be achieved, particularly on larger datasets. The mapping platform for your organization, Free template maps and apps for your industry. When using parallel processing, temporary data will be written to manage the data chunks being processed. This study gives an overview of the existing algorithms for flow accumulation calculations for single-flow direction matrices. The Flow Accumulation output raster will allow the delineation of the draining area to any specified point. DOUBLE —The output raster will be double type. Output cells with a flow accumulation of zero are local topographic highs and can be used to identify ridges. The Parallel processing with Spatial Analyst help topic has more details on this capability and how to configure it. The input and output of each command is a GeoTiff raster file. This is the default. The output from the tool would then represent the amount of rain that would flow through each cell, assuming that all rain became runoff and there was no interception, evapotranspiration, or loss to groundwater. These are D8, Multiple Flow Direction (MFD) and D-Infinity (DINF) flow methods. The output raster map uses the same georeference as the input raster map. Raster data sets can represent drainage networks (e.g., the flow accumulation cells that have at least 5000 upstream cells). If flow accumulation of a cell is larger than this value, then the flow of this cell is routed to its neighbors using the SFD (D8) model. In particular, you can … - Selection from Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition [Book] This method of deriving accumulated flow from a DEM is presented in Jenson and Domingue (1988). out_dem: Output raster DEM file. This example creates a raster of accumulated flow into each cell of an input flow direction Grid raster. (1991). If no weight raster is provided, a weight of 1 is applied to each cell, and the value of cells in the output raster is the number of cells that flow into each cell. By default, this tool will use 50 percent of the available cores. Creates a raster of accumulated flow into each cell. Generally speaking, cells with a high value of flow accumulation represent stream channels, while cells with low flow accumulation represent uplands. With this in mind, a network of rasterized stream segments is created. This tool supports parallel processing. The input raster that shows the direction of flow out of each cell. The Flow Accumulation tool supports three flow modeling algorithms while computing accumulated flow. A sample usage of the Flow Accumulation tool with an input weight raster might be to determine how much rain has fallen within a given watershed. Use the flow_direction_type parameter to specify which method was used when the flow direction raster was created. The result of Flow Accumulation is a raster of accumulated flow to each cell, as determined by accumulating the weight for all cells that flow into each downslope cell. The result of Flow Accumulation is a raster of accumulated flow to each cell, as determined by accumulating the weight for all cells that flow into each downslope cell. if the -s flag is not used); If this option is used for SFD flow it is ignored. If no weight raster is specified, a default weight of 1 will be applied to each cell. The results of Flow Accumulation can be used to create a stream network by applying a threshold value to select cells with a high accumulated flow. Flow accumulation means add all the flow entering into the particular cell. Flow Accumulation: Drainage Delineation and Rainfall Volume Once you have a raster that indicates flow direction, a number of other interesting and useful calculations are possible. Flow direction is measured in radians, counter clockwise from east. Jenson, S. K., and J. O. Domingue. Flow accumulation grids are generated from a 8 point flow direction grid. An optional input raster for applying a weight to each cell. Note: This workflow requires a license for the Spatial Analyst extension. The output raster that shows the accumulated flow to each cell. Output cells with a high flow accumulation are areas of concentrated flow and can be used to identify stream channels. 1988. The result of Flow Accumulation is a raster of accumulated flow to each cell, as determined by accumulating the weight for all cells that flow into each downslope cell. If the input flow direction raster is not created with the Flow Direction tool, there is a chance that the defined flow could loop. Input raster DEM or D8 pointer file. Run the Flow Accumulation tool. Output cells with a high flow accumulation are areas of concentrated flow and can be used to identify stream channels. out_accum: Output raster flow accumulation file. This study gives an overview of the existing algorithms for flow accumulation calculations for single-flow direction matrices. Flow Accumulation . Usage. Input raster DEM file. FLOAT — The output raster will be floating point type. 8 In comparison to the RUSLE, the USPED is a physically based model that incorporates # Requirements: Spatial Analyst Extension, # Check out the ArcGIS Spatial Analyst extension license, "C:/sapyexamples/output/outflowacc02.img", Analysis environments and Spatial Analyst. Raster Analysis Raster cells store data (nominal, ordinal, interval/ratio) •Complex constructs built from raster data Connected cells can be formed in to networks ... Flow Accumulation • Primary attribute representing the drainage area of any given cell • Indicates overland flow paths INTEGER — The output raster will be integer type. Supply Grid [raster] A grid giving the supply (loading) of material to a transport limited accumulation function. If you have admin privileges on your machine, you can also use a registry key (for example, [HKEY_CURRENT_USER\SOFTWARE\ESRI\Desktop10.6\Raster]). Cells of undefined flow direction will only receive flow; they will not contribute to any downstream flow. This is discussed in Identifying stream networks. Cells with a flow accumulation of 0 are local topographic highs and may be used to identify ridges. Starting from the East, the values for the flow direction grid should be 1, 2, 4, 8, 16, 32, 64 and 128. # Description: Creates a raster of accumulated flow to each cell. Flow direction is measured in radians, counter clockwise from east. Cells of undefined flow direction will only receive flow; they will not contribute to any downstream flow. A weight factor can optionally be applied. log: Optional flag to request the output be log-transformed. Specify the location of the Output accumulation raster. Use the output from Step 2 as the 'Input flow direction raster'. The current processing cell is not considered in this accumulation. D-Infinity Flow Direction Grid [raster] A grid giving flow direction by the D-infinity method. This example creates a raster of accumulated flow into each cell of an input flow direction IMG raster. This is the default. The Flow Accumulationtool calculates accumulated flow as the accumulated weight of all cells flowing into each downslope cell in the output raster. The Flow Accumulation tool is contained in the Spatial Analyst Tools tool box. Note: Flow Accumulation. The Flow Accumulation tool does not honour the Compression environment setting. The result of Flow Accumulation is a raster of accumulated flow to each cell, as determined by accumulating the weight for all cells that flow into each downslope cell.. Photogrammetric Engineering and Remote Sensing. Tarboton, D. G., R. L. Bras, and I. Rodriguez–Iturbe. Calculating the flow accumulation matrix is an essential step for many hydrological and topographical analyses. The output raster will always be uncompressed. DINF —The input flow direction raster is of type D-Infinity (DINF). In the process of simulating runoffs, the flow accumulation is created by calculating the flow direction. Tips: When displaying an output Flow accumulation map, you can use Logarithmic Stretching in the Display Options dialog box of the raster map. If no weight raster is provided, a weight of 1 is applied to each cell, and the value of cells in the output raster is the number of cells that flow into each cell. The Flow Accumulation tool calculates accumulated flow as the accumulated weight of all cells flowing into each downslope cell in the output raster. out_pntr: Output raster flow pointer file. A fast and simple algorithm for calculating flow accumulation matrices is proposed in this study. The result of Flow Accumulation is a raster of accumulated flow to each cell, as determined by accumulating the weight for all cells that flow into each downslope cell. Cells of undefined flow direction will only receive flow; they will not contribute to any downstream flow. The current processing cell is not considered in this accumulation. Input flow direction can be created using the D8, Multiple Flow Direction (MFD) or D-Infinity (DINF) methods. Flow accumulation - the number of cells that drain through each cell in an elevation raster - can represent the flow of water across a landscape. The output Flow accumulation map is by default displayed using system representation Pseudo. The result of Flow Accumulation is a raster of accumulated flow to each cell, as determined by accumulating the weight for all cells that flow into each downslope cell. out_type: Output type; one of 'cells', 'sca' (default), and 'ca'. The flow accumulation algorithm typically used is the D8 algorithm, although if you look into the literature there are lots of versions and variations on determining flow accumulation. 1991. The accumulated flow is based on the number of total or a fraction of cells flowing into each cell in the output raster. The default temp folder location will be on your local C drive. D-Infinity Flow Direction Grid [raster] A grid giving flow direction by the D-infinity method. The threshold raster defines the cell values that are determined to have enough accumulation to be classified as a stream, and the threshold raster is generated from a raster created by the Flow Accumulation GP tool. The flow direction raster can be created using D8, Multiple Flow Direction (MFD) and D-Infinity methods. Cells of undefined flow direction will only receive flow; they will not contribute to any downstream flow. Use the Input flow direction type to specify which method was used when the flow direction raster was created. The result of Flow Accumulation is a raster of accumulated flow to each cell, as determined by accumulating the weight for all cells that flow into each downslope cell. In the graphic below, the top left image shows the direction of travel from each cell and the top right the number of cells that flow into each cell. I have downloaded one of your rasters and I see that the values range from 1 to 255. "On the Extraction of Channel Networks from Digital Elevation Data." The flow accumulation lines are displayed in the map. Learn more about how Flow Accumulation works. This option affects only the flow accumulation raster and is meaningfull only for MFD flow (i.e. Compute watershed grids: fill, flow direction, and flow accumulation in ArcMap The Flow Accumulation tool supports three flow modeling algorithms while computing accumulated flow. The flow direction raster can be created using the Flow Direction tool. For future processing, it is important that the stream network, a set of raster linear features, be represented as values on a background of NoData. Click OK. A fast and simple algorithm for calculating flow accumulation matrices is proposed in this study. These are D8, Multiple Flow Direction (MFD) and D-Infinity (DINF) flow methods. This tutorial demonstrates how to reproject a DEM raster in QGIS, how to fill the sinks of a DEM, to calculate flow accumulation, to obtain the channel network and the basin limits with SAGA GIS based on the DEM using the Upslope Area interactive tool. Compute flow accumulation with the module r.watershed. You can control the location of this folder by setting up a system environment variable named TempFolders and specifying the path to a folder to use (for example, E:\RasterCache). out_type: Output type; one of 'cells' (default), 'catchment area', and 'specific contributing area'. Hydrological Processes 5: 81–100. This can be created by the tool “D-Infinity Flow Directions”. See Analysis environments and Spatial Analyst for additional details on the geoprocessing environments that apply to this tool. This could also be viewed as the amount of rain that fell on the surface, upslope from each cell. log: Optional flag to request the output be log-transformed. Navigate to Spatial Analyst Tools > Hydrology > Flow Accumulation. MFD —The input flow direction raster is of type Multi Flow Direction (MFD).The MFD option is available in the drop-down list only when an input flow direction raster of type MFD is provided to the tool. For each cell in the output raster, the result will be the number of cells that flow into it. Deposition) method, which is using the raster calculation between flow accumulation and slope of watershed, because it is obvious that it can be done with the tools included in a normal GIS ArcMap installation [5]. For example, the procedure to create a raster where the value 1 represents the stream network on a background of NoData could use one of the following: In both examples, all cells that have more than 100 cells flowing into them are assigned 1; all other cells are assigned NoData. For an input D8 flow direction raster, a cell is considered to have an undefined flow direction if its value in the flow direction raster is anything other than 1, 2, 4, 8, 16, 32, 64, or 128. These are D8, Multiple Flow Direction (MFD) and D-Infinity (DINF) flow methods. To each cell, the flow accumulation is determined by how many cells that flows through that cell; if the flow accumulation value is greater, the area will be easier to form a runoff. D8 —The input flow direction raster is of type D8. It's a set of command-line .exe files (you run them in the Windows Command Prompt) for calculating flow direction, flow accumulation, and stream thresholds. The results of Flow Accumulation can be used to create a stream network by applying a threshold value to select cells with a high accumulated flow. TauDEM can be installed stand-alone without ArcGIS. Cells of undefined flow direction will only receive flow; they will not contribute to any downstream flow. If the flow direction contains a loop, Flow Accumulation will go into an endless cycle and never finish. ArcGIS Desktop Basic: Requires Spatial Analyst, ArcGIS Desktop Standard: Requires Spatial Analyst, ArcGIS Desktop Advanced: Requires Spatial Analyst. The output accumulation raster can be integer, floating point, or double type. The Flow Accumulation tool calculates accumulated flow as the accumulated weight of all cells flowing into each downslope cell in the output raster. Calculating the flow accumulation matrix is an essential step for many hydrological and topographical analyses. Preferably the points we wish to use as input for the delimitation of a contributing area should be located along the stream definition (drainage network) determined by the flow accumulation raster output. clip: Optional flag to request clipping the display max by 1 percent. Cells with a high flow accumulation are areas of concentrated flow and may be used to identify stream channels. output: Output raster file. "Extracting Topographic Structure from Digital Elevation Data for Geographic Information System Analysis." The type of input flow direction raster between these three influences how the Flow Accumulation tool partitions and accumulates flow in each cell. Photogrammetric Engineering and Remote Sensing 54 (11): 1593–1600. You can control the number of cores the tool uses with the Parallel processing factor environment. In such a case, the weight raster may be a continuous raster representing average rainfall during a given storm. The accumulated flow is based on the number of total or a fraction of cells flowing into each cell in the output raster. If the input data is smaller than 5,000 by 5,000 cells in size, fewer cores may be used. The Flow Accumulation tool supports three flow modeling algorithms while computing accumulated flow. Then use r.shade to drape the flow accumulation map over the relief map. This video is about understanding the concept behind flow accumulation. See Also: Other flow modelling tools; D8 flow pointer (direction) Rho8 flow … An analytic method for determining an appropriate threshold value for stream network delineation is presented in Tarboton et al. When making maps that present the results of watershed delineation you may want to show the grid-based flow network instead of, or in addition to, the vector stream network, especially if the two flow networks do not agree. This can be created by the tool “D-Infinity Flow Directions”. Supply Grid [raster] A grid giving the supply (loading) of material to a transport limited accumulation function. Grid cells possessing the NoData value in the input flow-pointer grid are assigned the NoData value in the output flow-accumulation image. From the flow direction information, a flow accumulation raster calculates the number of cells that contribute flow to each cell. Usage tips: The result of Flow Accumulation is a raster of accumulated flow to each cell, as determined by accumulating the weight for all cells that flow into each downslope cell. Cells of undefined flow direction will only receive flow; they will not contribute to any downstream flow. Recommended workflow: The result of Flow Accumulation is a raster of accumulated flow to each cell, as determined by accumulating the weight for all cells that flow into each downslope cell. If no weight raster is provided, a weight of 1 is applied to each cell, and the value of cells in the output raster is the number of cells that flow into each cell. For example, the procedure to create a raster where the value one represents the stream network on a background of NoData could use one of the following: The input flow direction raster can be of type D8, Multi Flow Direction (MFD) or D-Infinity (DINF). 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