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7

Assuming your stream polylines do not already have an attribute that states which watershed they belong to, you can run Identity (Advanced license only) or Intersect to get that attribute assigned in a new feature class. This also makes sure your streams actually break at the boundary rather than continuing through multiple areas. Then you can open the ...


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, ...


6

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.


5

I can think of a few ways to do this: Symbolize the lines so they have direction indicated, and manually Flip those in the wrong direction. Use an attribute if available or a calculation (such as end z > start z) to select segments going the wrong direction and Flip (GP) them. Create a geometric network of the lines and use the Flow Direction tools, ...


5

it looks like there's a wee bit of confusion on what's greater/smaller than what but I'll leave that for you to manipulate. This solution will iterate ONLY ONCE through each table which will not confuse the cursors and will save you 10 million iterations(from loop in a loop iteration). Using a dictionary lookup is so fast it's considered 'free'. So populate ...


4

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 ...


4

You need to nest your search cursor loops to iterate through both at the same time, while relating the rows in some way (so arcpy knows when it is at the right one, and will stop looping to compare the value). Luckily you've got those matching ID fields already. This should get you started comparing the area values. Let me know if it doesn't run or I've ...


3

It may seem like laziness on the part of Watershed tool developers to stick with the simplest and oldest flow algorithm, D8, but there is a very sound reason for doing so. The difference between the D8/Rho8 flow algorithm and the more advanced algorithms that you mention (e.g. D-infinity) is mainly in their inability to represent the dispersion of overland ...


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

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 ...


3

First you need to make sure that your watershed are polygons. If not : feature to polygon. Then you can make the intersection (intersect_analysis) between your watershed and your lines. You'll end up with lines that have the fields of the waershed as an attribute table. You can then use summary statstics to have the total length for each watershed. Note ...


3

Here are the general steps involved in creating a watershed boundary. You need to work with a raster DEM, not vector contours. This means that you have two options; you can either try to interpolate your contours or you can look for an existing raster DEM of the study area. Most of the interpolation methods contained within ArcGIS's interpolation toolbox ...


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

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

Please check out http://data.freshwaterbiodiversity.eu/shapefiles.html it may help. This contains lot of shape files for research.


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

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

You can achieve this with a simple model. This question was asked here, for which I give a model showing how it can be done.


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 ...


2

Can I clarify, did you extract the basin for a specific point that you digitized? If so, did you use the Snap Pour Point tool to reposition your digitized point onto the 'digital' stream (i.e. the path of high flow accumulation derived from the DEM) as per the instructions given by ESRI? If so, this is likely your problem. The extraction of a watershed (or ...


2

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 ...


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 ...



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