9

In spatial hydrology, DEM-based flow accumulation operations are typically static. That is, they represent a steady-state condition of the discharge of surface and near surface water passing through a point. Flow accumulation grids are actually accumulating contributing area downslope, i.e. areas not volumes. The accumulated cells that you described is ...


9

From Esri's support site : HowTo: Create points representing the highest or lowest elevations within polygon features Just replace the elevation raster by the Flow Accumulation raster. Identify the value of the highest elevation within each polygon feature using the Zonal Statistics tool: Open ArcMap and navigate to ArcToolbox > Spatial Analyst ...


8

It's a good question, so let's be rigorous with a solution. Regardless of the algorithm involved, the flow direction is ultimately determined by fitting planes to the surface at each point. (Theoretically, these planes are the derivative of the surface; in practice they are often computed as least-squares fits to the values in the immediate 3X3 ...


7

These are common problems, typically resolved by stream burning, but that relies on you having a vector network to enforce drainage. I recommend you check out the free GIS software Whitebox GAT it has several alternative methods to fill and compute flow accumulation.


6

The following is a step-by-step process for how to take an ArcGIS D8 flow direction raster and use it to perform a D8 flow accumulation operation in Whitebox Geospatial Analysis Tools. I will preface this by saying that it would obviously be much easier if you had the original DEM from which the flow direction raster was derived. Also, I'm making the ...


6

It is an error. Your link and presumably image source is the 10.0 help. The error is still present in the 10.1 help. However in the 10.2 help, it has been corrected to show only a 1. It's also worth noting that if you work through the math matrix as whuber has done at Arcmap 10 restrict Flow Accumulation, that error is apparent as well as the adjacent 35 ...


6

I'm guessing you mean CPU activity, and not GPU? ArcGIS doesn't use the GPU for number-crunching, unfortunately. If your machine has more than 4GB of RAM, make sure you have the 64-bit Geoprocessing addon installed. Without it, ArcGIS will be limited to using 4GB of RAM for a geoprocessing task. Also, ArcGIS can't use more than one CPU core on a ...


5

I have a tremendous respect for GRASS and the r.tarraflow algorithm and I'm sure that given enough effort, you would be able to make it work for this application. But as an alternative, I develop a cross-platform free and open-source GIS called Whitebox Geospatial Analysis Tools (download here). Here is an example for how to use it for hydrological ...


5

All flow algorithms are based on the assumption that surface and near-surface flow paths are determined by local topographic gradients. Flow algorithms calculate flow paths by comparing the elevation drops between grid cells in a DEM and their eight neighbouring cells. The difference between non-dispersive (D8, Rho8, D8-LTD) and dispersive (D-infinity, FD8) ...


4

This brings up an interesting theoretical question regarding slope process in relation to scale. The TWI/CTI is a slope/flow accumulation interaction. However, once must question the exact process that is being represented when deriving slope at very fine grains (eg., <1m) and how it affects this interaction. I would imagine that, without increasing the ...


3

This from the flow direction tool help in ArcGIS 10.4: If a cell has the same change in z-value in multiple directions and that cell is part of a sink, the flow direction is referred to as undefined. In such cases, the value for that cell in the output flow direction raster will be the sum of those directions. For example, if the change in z-...


3

I think that I found a solution for this. The r.watersheds function that calculates flow accumulation, have a parameter (flow) to integrate a raster indicating values to sum. Parameter: flow=name Name of input raster representing amount of overland flow per cell Raster flow map specifies amount of overland flow per cell. This map indicates the ...


3

It looks like your issues may in large part be caused by the large flat in the NE portion of your basin. Different pit filling and flow direction algorithms will handle this area differently, and it looks like the one you are using is forcing the flow out of your basin instead of into your expected network. First, Bill Chappell's answer provides some good ...


3

Watershed delineation is tricky, I usually include a larger area then my study area so I don't have anything weird at the edges. i.e. like the edges are cliffs or walls. With that being said, I also include a background stream layer to check that my calculated stream fits the background stream. This stream layer could be a topo map, just to confirm my data ...


3

David Tarboton does a good job of breaking it down at http://hydrology.usu.edu/taudem/taudem5/help53/D8FlowDirections.html basically as does Jenson. Jenson, S. K., and J. O. Domingue. 1988. "Extracting Topographic Structure from Digital Elevation Data for Geographic Information System Analysis." Photogrammetric Engineering and Remote Sensing 54 (11): 1593–...


3

You might want to have a look at these Matlab functions http://www.mathworks.com/matlabcentral/fileexchange/50124-topotoolbox More specificaly, you can generate a flow accumulation matrix using DEM = GRIDobj('YourRaster.tif'); FD = FLOWobj(DEM,'preprocess','carve'); A = flowacc(FD);


3

The image should be 1 bit/pixel (0/1 values doesn't guarantee that). Use gdal_translate to change (tiff or png format will fit). gdal_translate -co "NBITS=1" image.tif bit_image.tif Change the background color to null r.null map=image setnull=1 After r.thin should work.


3

This quickly becomes a very complicated problem if you're trying to compute true flood extents. You can estimate flow through an open channel using Manning's Equation, but flow velocities over different land cover types complicate the equation and therefore the flood extent. The folks associated with the National Water Model have been working towards this ...


2

You can perform raster algebra using the Raster Calculator (Spatial Analyst). The syntax would be like the following: Float(Ln("flowAccumulation.img"))


2

Try the flow length tool in Spatial Analyst - http://pro.arcgis.com/en/pro-app/tool-reference/spatial-analyst/flow-length.htm . If you are interested in vertical height above the water surface try Topography Tools, which has two algorithms HAND and HAR for estimating height above the water surface.


2

To understand why, have a look at your flow direction raster. In a flat filled area such as this, the flow direction is limited to the flat filled surface regardless of whatever topography may have been present there before filling. There are alternatives to this that either apply a downstream trend to the filled surface (helps a bit) or better yet, you ...


2

Faced the same problem in GRASS 7. After some deliberation, the following steps did the work If the data type of the raster is FLOAT32, convert the raster using gdal.translate to Int32.This should also solve the error "Input must be of the type CELL. Now run r.null on the raster. The raster layer with non-null values is now ready to be thinned using r.thin


2

A new GRASS addon r.accumulate is available. This module only requires a flow direction map to calculate weighted flow accumulation. If you have a drainage map from r.watershed, r.accumulate direction=drain_directions accumulation=flow_accum or using its GUI, In this example, the yellow arrows and color-coded numbers show flow directions and accumulation,...


2

Both statements are correct. In watershed delineation you essentially need an “all or nothing” delineation of flow direction to create a watershed divide as referenced in your initial statement, which precludes the use of divergent flow For overland flow direction in general however, a multiple-flow direction algorithm is generally more forgiving of DEM ...


2

The NHD distributes all of the elevation processing products along with the stream lines and catchments (Example for PNW). Note that these products are the "hydro corrected" products that are used to build the catchments, so they should essentially match flow boundaries and flow lines that are present in the NHD+v2 catchments. It is at the native 30m ...


2

You may want to check out this thread. It's a method for deriving the centerline of polygons, and to me the product does look like rooftops.


2

These workflow: arcpy.InterpolateShape_3d(in_surface="dem", in_feature_class="STREAMS", out_feature_class="C:/SCRATCH/streams3d.shp", sample_distance="", z_factor="1", method="BILINEAR", vertices_only="DENSIFY", pyramid_level_resolution="0") arcpy.SplitLine_management(in_features="streams3d", out_feature_class="C:/SCRATCH/bits3d.shp") arcpy....


1

This kind of flat flow accumulation is very common where the DEM is flat (e.g., water bodies, LiDAR doesn't penetrate water!) or there are downstream structures that convey water through the ground surface (e.g., culverts, again LiDAR doesn't penetrate the ground, but most of the time, pier bridges are OK). You can try hydro enforcing (or DEM burning) ...


1

Note that it's important to fill sinks before computing flow direction. Sometimes this issue can occur after filling the sinks, but as there are visibly man-made features in this raster (e.g, the road), this might not be so unrealistic. Other times, this occurs from over interpolation of a raster (creating highly refined flowpaths for the courseness of your ...


1

r.watershed assumes a flow of 1 when the flow parameter is omitted, resulting in the number of accumulated upstream raster cells. So the unit of the final output will be the same as that of the flow raster map. For example, depth flow results in depth output; volume flow results in volume output.


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