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9

First, you need to calculate at least the slope. F.ex I have the following data: Then put the correct data as variables to the module: And at last you should get the result: UPDATE With Catchment Area as input the results are:


8

If you use GRASS GIS as backend in QGIS (via QGIS-GRASS toolbox or Sextante plugin), you can use a range of hydrological tools. See http://grass.osgeo.org/wiki/Hydrological_Sciences for options.


7

The GRASS recommendation from @markusN is a good one. Another option, although it's not integrated into QGIS, is the Gerris Flow Solver. GFS is a tremendously powerful hydraulic and hydrological modeling tool. From the site: Gerris is a Free Software program for the solution of the partial differential equations describing fluid flow. The source code is ...


7

The Flow Direction tool in Spatial Analyst only supports 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 is commonly referred to as an eight-direction (D8) flow model and follows an approach presented in ...


7

Choosing the right algorithm for hydrologically correcting a DEM really depends on your particular application. DEM size is certainly an issue, as you discovered. If you have a massive DEM, there are only a few algorithms that will work for your application. Another important consideration is whether or not all of the topographic depressions in your DEM are ...


7

You can classify the streams using, among others, the Strahler Stream Ordering method. In the Strahler method, all links without any tributaries are assigned an order of 1 and are referred to as first order. The stream order increases when streams of the same order intersect. Therefore, the intersection of two first-order links will create a ...


6

Have a look at Crayfish for QGIS http://plugins.qgis.org/plugins/crayfish/ "Crayfish is a plugin (extension) developed by Lutra Consulting for the free and open source GIS platform Quantum GIS (QGIS). The Crayfish plugin aspires to be a complete set of pre and post-processing tools for hydraulic modellers using TUFLOW, ISIS 2D and other modelling ...


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

This looks like a valid workflow for this task. However, depending on the level of accuracy that you work with, you will miss out on things like pipes under roads allowing for ditches and small creeks to flow past the road. These would probably require some field work to identify though. You don't mention which software you use, but for ArcMap point (6) ...


6

While Jacub is correct that a stream ordering technique is your best bet for being able to represent stream magnitude or discharge, since the position in the network is a surrogate for these two stream characteristics, I would argue that you want to avoid using Horton-Strahler stream order for this purpose. It is seriously deficient in these applications, ...


5

It will work as a rule of thumb, what you have to consider is the method used by arcmap to calculate flow accumulation. It is based off the D8 method, which assumes that 100% of a cell's input flows out to one of the 8 surrounding cells at the compass points: N, NE, E, SE etc. This works as an approximation but you can't say that such a model would reflect ...


5

I would do this (relies on network analysis and PostGIS, but should be doable in ArcGIS, too): relocate the villages and cities to the closest point on the river network line (or create a temporary table for that). In PostGIS, the select query would be something like this: SELECT DISTINCT ON (v.gid) v.gid, v.village_id, ...


5

When converting a LiDAR dataset to a DEM, you are taking a set of discrete data points and converting them into a single, continuous dataset. Let's say that your .las file contains X (latitude), Y (longitude) and Z (elevation) values with an average resolution of ~1 meters. The resolution here is really important- we're only talking about an average and so ...


5

If you run an intersection between the 2 different line feature classes, and specify the output type to be Point, then you should be able to do a count of the ids in the point table of the input lines.


5

Ok here is the image Blue are the bridges from OSM. The DEM is in grey-scale with buildings (I want buildings) I selected the intersect roads that cross the bridges. Buffered the selected roads by the approximate width of a road. Ran 'Zonal Minimum' on the buffer. Now you have the zonal minimum raster (red) with the low values. The I just used CON to ...


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

As someone who did feature capture from imagery for a while, I would caution you against expecting a pool at a spring. The majority of the ones I've encountered (both in capture and on the ground in person) don't have one. We often referred to ancillary sources to suggest/confirm a spring. Depending on your purposes, USGS quad sheets or hydrography datasets ...


5

This is a good question, and one that I tend to get asked from time to time. First, as you've pointed out, the equation for TWI = ln(a / tan(B)), where a is the 'specific' catchment area (i.e. the upslope inflowing area normalized for a measure of contour length) and B is the slope gradient, in radians, at the grid cell. As you correctly pointed out TWI will ...


4

To expand on my comment: use a combination of Flow Direction and Flow Length to calculate this value. Flow Direction (illustrated below) calculates the direction water would immediately flow from a given pixel. Either north, northeast, east, southeast, south, southwest, west, or northwest. Flow length uses the precalculated flow direction raster to ...


4

With regard to generating hydrologicaly correct elevation models, also called drainage enforced, ANUDEM, remains best of breed to my knowledge. It's the program used to generate the Canadian national elevation dataset (CDED, ironically stored as integer-metres). Also the TopoToRaster tool in ArcGIS uses Anudem under the hood (a revision or three behind ...


4

Check out the NVS Vector Stream Tool which ... is a user-friendly ArcCatalog (9.3.x) Toolbox geoprocessing tool which simply assigns a numeric order to segments of a poly line feature class. Unlike the Spatial Analyst Tools for Hydrography, this tool solely uses vector stream data instead of raster stream data accompanied by a flow direction ...


4

Thanks for the reply. I actually figured it out yesterday and hadn't had a chance to mark this as "solved." I had been interpreting the advice on the ESRI forums as the following steps: Create a slope raster, then run the flow accumulation tool on it. Create a raster with a constant value, then run the flow accumulation tool on it. Divide result from ...


4

Yes, I would use ArcHydro. I found a document on this page (updated link thanks to @Polygeo) a while ago, that outlines some possible workflows (from the ArcHydro Team). There have been some changes compared to ArcMap 10.0 so for me it was quite useful.


4

I made a port of part of this fortran code: function hrap(lon,lat){ var deg2rad = function (deg) { return deg * (Math.PI / 180); }; var stlat = 60.0; var clon = 15.0; var rad = 6371.2; with (Math){ var sfactor = (1+sin(deg2rad(stlat)))/(1+sin(deg2rad(lat))); var R = rad*cos(deg2rad(lat))*sfactor; var x = R*cos(deg2rad(lon+clon)); var y = ...


4

Martin is correct that while your workflow will do well for a specific user case, it doesn't account for many of the issues that road embankments create for flowpath modelling using fine-resolution LiDAR data, such as the problems with discontinuous flow in roadside ditches and the effects of minor unmapped culverts (which can alter flowpaths considerably). ...


4

You can download hydrology shapefiles from here for a number of countries around the world. Select your country of choice and Inland water as your subject. You should receive 2 types of shapefiles: A line shapefile depicting line features for rivers, canals and basins A polygon shapefile depicting area features for rivers, canals and basins I believe ...


3

Since the continental divide is determined hydrographically, I would use data from the National Hydrography Dataset (NHD), or the analagous Watershed Boundary Dataset (WBD). Based on this geodatabase of HUC8 boundaries from WBD, the results look pretty good at 1:24,000 scale: This shows Triple Divide Peak in Montana.


3

Sue Greenlee's original code - that Esri's and many other watershed codes are based on - was published in FORTRAN in 1988. I'd go looking for that - don't see it on the web - but you could always email her! Kind of surprised it's not in GitHub, it's pretty neat code. Jenson S. K. and J. O. Domingue. 1988. Extracting Topographic Structure from Digital ...


3

In a conversation following the question, we refined the objective. It is to obtain the watershed area of each point. Some of these points are close to each other, but they are all unique and we would like to determine the watershed area for each point. We will use the watershed area in a predictive model to distinguish a score for each point. The ...


3

If you have ArcGIS 10 and the 3D Analyst, you could use the "Add Surface Information Tool". It populates the attribute table of the Polyline Feature Class/Shapefile with basic elevation and slope statistics.



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