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6

The method that I've implemented in a couple of languages and believe that ESRI uses (sorry, no references other than Jenson and Domingue cited elsewhere in this page) is to start at a user-supplied "pour-point" cell or a cell at the edge of the flow direction grid (fdr), examine its eight neighbors to find which of those direct flow into the current cell, ...


5

ESRI has a good support section on hydrologic analysis. Also, there is a pretty good video tutorial here on how to create drainage networks in ArcMap. The attached image from ESRI shows a stream network created using ArcMap's hydrologic tools and a digital elevation model (DEM) available from USGS Earth Explorer.


3

The ArcGIS help says: Watersheds can be delineated from a DEM by computing the flow direction and using it in the Watershed tool. To determine the contributing area, a raster representing the direction of flow must first be created with the Flow Direction tool. The Flow Direction is calculated from the DEM using the D8 method, Where the flow is ...


3

This has been asked before, though perhaps in a slightly different context. All of the geoprocessing tools in the Hydrological toolset of Spatial Analyst use the D8 flow direction model, as stated in the How Flow Direction Works page: There are eight valid output directions relating to the eight adjacent cells into which flow could travel. This approach ...


3

The solution to your problem may be to use Infrastructure Network Editing, specifically the Flow Accumulation tool on the Infrastructure Reporting Toolbar. You'll need at least a Standard (Editor) license to build a geometric network. You'll also need to specify a weight. At each point or line, Calculate Accumulation will add up all your upstream weights ...


3

Assuming that each withdrawal point is related to the closest stream segment, we can do the following: Use the split line at point tool to split the stream line into segments based on outlet points (depending on your data you may already have this). Make sure that each point has an ID, which should relate to stream order (see one method below for an ...


3

The areas you are looking to create are called "subwatersheds" or subsheds. You can use the "Batch Subwatershed Delineation" tool in ArcHydro under the "Watershed Processing" menu. This will calculate subsheds from a set of points you define. The other input is a flow direction grid. This is a raster where the value of each pixel represents the direction ...


3

You will need to define your lakes as sinks (Create sink structures), and then use the ArcHydro function Adjust flow in lakes/streams/sinks. (These functions are only available in ArcHydro for ArcGIS 10.1, I have made a function that, with some modifications, might help you on the way if you are in 10.0.) You can also erase (Extract by mask) the lakes from ...


3

Have you tried to create a mosaic out of the rasters and doing one watershed computation? This link is helpful for raster mosaics in qgis. Trying to make separate basins and putting them together probably won't work due to edge contamination.


3

You can calculate Flow Length from a Flow Direction raster, but you need your original DEM to do that. Your watersheds are just "areas that drain into a point" and don't retain the necessary flow direction information. Since your stream gauge is in the middle of the larger watershed, calculate the downstream flow length and then use the identify tool (or ...


2

The default for the watershed tool is to limit the output extent to the same as your input pour points. You can change this in the Output Extent (Environment setting) to the maximum of inputs or same as the original DEM. For more info see The analysis environment of Spatial Analyst. Try the Snap Pour Point tool to see if this helps ensure that your crater ...


2

I am not sure that following the boundary will be more efficient than expanding the area. With raster data, you need to account for the number of times that you "go through" the entire image. With a region growing method, each pass will process an increasing number of pixels until you reach the boundary. If you look at the contour only, you might end up with ...


2

There are a number of stages required to get the required output, all of the tools are well documented in the arcgis online help and the page on stream ordering is very useful. The first stage in any hydrology processing is to fill any pits in the DEM using the fill tool to ensure that water can flow over the surface without becoming 'stuck' in an erroneous ...


2

In some cases you will be computing and others you simply need to obtain the data. Rainfall: you will need these as input rasters by month. Do you have this data? You could check out NOAA http://www.cpc.ncep.noaa.gov/products/GIS/GIS_DATA/ Flow Accumulation: This should be calculated off of a flow direction grid using Spatial Analyst. Flow direction is ...


2

You will definitely need an elevation raster (DEM) to do what you want. With the DEM you can use two GRASS modules to get individual drainage areas for points along the river network as follows: First calculate a flow direction grid from the DEM with r.watershed: r.watershed elev=DEM thresh=<your threshold> drain=flow_dir_grid See the r.watershed ...


2

When you start getting into hydrograph routing (flow rate vs time), you are leaving the GIS realm and get into specialized hydraulic modeling software. HEC-RAS is great for open channels, and can handle pipe flow, but needs hydrology (how much runoff are you getting) input (often from HEC-HMS). The mix of hydrologic and hydraulic modeling required to ...


1

Going back to basics: I don't see a region setting in your script. You should first do a g.run_comand('g.region',rast='dra'). Next, are you sure that the points in the csv file fall exactly on the streams? If an outlet point is even slightly off the stream channel, you will get very tiny basins.


1

It looks like you're running GRASS using the default Windows shell. The loop code you posted is for a UNIX-like shell, and the Windows shell doesn't understand it. You have two options: Use the Windows shell commands for all of your batch processing. This question/answer might help (although I've not done it myself): ...


1

If you can create polylines representing your stream networks (essentially a map of flow accumulation), then you can use the sample tool to extract raster values along a line and export these values (for example) into excel. You can do this with slope values to get a profile of slope along the river and with elevation values to get standard elevation ...


1

This would be the largest flow accumulation point . (you could have several lowest points due to your DEM resolution). use zonal statistics to identify the maximum flow accumulation inside your basin use "Con" to find the pixel of your basin that is equal to this maximum value convert the result to point


1

Have you worked in the GRASS environment in QGIS before? If you want to perform a watershed analysis this is the place you will need to start. The second part of this tutorial on creating heatmaps is useful for learning how to work in GRASS: ...


1

Please do not use sink-filling for r.watershed, it is nor needed nor desired. r.watershed takes care by itself due to its internal least cost routing algorithm. A minimalistic example: r.watershed elev=dem basin=catchments thresh=10000 For a tutorial, see http://grasswiki.osgeo.org/wiki/Creating_watersheds


1

Yes, take a look at the Processing framework searching for catchment or watershed in the toolbox. Also check the Processing manual: https://github.com/volaya/Processing-manual/blob/foss4g_ws/sphinx/source/modeler_hydro.rst https://github.com/volaya/Processing-manual/tree/foss4g_ws/sphinx/source


1

It's a SAGA module, which appears to be undocumented. There's a discussion here about the issue, with some potential leads you could follow up with.


1

If you want to calculate rainfall rasters for yourself you should have enough point-sample data and profound knowledge of interpolation techniques like spline interpolation or kriging. Therefore I would use data from NOAA instead as they are more reliable. If the resolution of these rasters is too coarse you may want to try a hybrid between interpolation ...


1

If by Basin Length, you mean the maximum distance from the watershed boundary to the pour point, you need to use the Hydrology tools from the Spatial Analyst Toolbox. First fill the sinks of your DEM using the Fill Tool. Then calculate the Flow Direction, using the Flow Direction Tool Finally Use the Flow Length Tool. The value of the output at the pour ...


1

Are you talking about a line or a polygon? You could go to the attribute table and then right-click on top of a column and select 'calculate geometry' (or something similar unfortunately I can't access ArcMap at the moment to check this). In the pop-up you can select length, I believe. Hope this helps.



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