Estimating impervious cover for a large (~20 square mile) watershed
Estimating impervious cover for a large (~20 square mile) watershed
(OP)
I have an opportunity to work on a large stream restoration project, of the size where TR-20 methods aren't generally applicable, so I'll be defaulting to USGS regression equations and unit hydrographs for the hydrologic analysis. Project is in central Georgia. I don't currently carry a license for any GIS software, and my experience with GIS is limited. In order to do the watershed analysis, I will need to delineate basins and estimate impervious cover. As I see it, I have two options for the analysis:
1) Clip together a bunch of USGS rasters in CAD and do the basin delineation by hand, assigning a certain imperviousness to urban areas and calling the rest pervious, or
2) Obtain free/cheap GIS software, topo coverages, and land use coverages, and learn to do the procedure that way.
I'm leaning towards (1) simply because the learning curve for (2) might not be worth it for this one job, although (2) is certainly something I've always wanted to learn if I can get away with less than a grand in software purchases. If I go with (1), what imperviousness would you folks assume for urban areas? I would rather not spend time getting down to the gnat's posterior on different land uses. (commercial/industrial/etc) If I go with (2), what software can get the job done on the cheap and where can I grab the data?
Thanks in advance.
1) Clip together a bunch of USGS rasters in CAD and do the basin delineation by hand, assigning a certain imperviousness to urban areas and calling the rest pervious, or
2) Obtain free/cheap GIS software, topo coverages, and land use coverages, and learn to do the procedure that way.
I'm leaning towards (1) simply because the learning curve for (2) might not be worth it for this one job, although (2) is certainly something I've always wanted to learn if I can get away with less than a grand in software purchases. If I go with (1), what imperviousness would you folks assume for urban areas? I would rather not spend time getting down to the gnat's posterior on different land uses. (commercial/industrial/etc) If I go with (2), what software can get the job done on the cheap and where can I grab the data?
Thanks in advance.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com





RE: Estimating impervious cover for a large (~20 square mile) watershed
Natural/Rural - 5% +/-
Accounts for minor rock outcrops, compacted soils and etc...
Suburban (2RAC) - 15% +/-
Mod Urban (3-5 RAC) 35% +/-
Highly Urban (6+ RAC)60 % +/-
Commercial 90% +/-
This is for directly connected impervious areas. Otherwise use the nat/rural unless you can delineate grouping of rock outcrop.
RE: Estimating impervious cover for a large (~20 square mile) watershed
There is also freeware available that will convert a lat-long list of points (stream gage locations) to a Google Earth KML/KMZ file for landuse/location review. EasyGPS,MN DNRGarmin to name a couple. The later will also convert shapefiles to KML that you might download from the national map, like river data, basin data, etc.
RE: Estimating impervious cover for a large (~20 square mile) watershed
You can download the contours into the Civil3D terrain modeling and hydrology programs and then you don't have to "do the basin delineation by hand."
Let me know if you need more info.
RE: Estimating impervious cover for a large (~20 square mile) watershed
http://streamstats.usgs.gov/
RE: Estimating impervious cover for a large (~20 square mile) watershed
civilman72 -
I don't use Civil3D, and I've quite often found errors in its automated basin delineation routines, so I do all mine by hand. I've also found extensive errors in automated basins done by ArcGIS as well, by the way. Don't trust them a lick. Mostly I want to use GIS (if I go with that option) to do automated watershed characterization.
That said, is there an easy way to get Google Earth contours into a regular cad platform? Where is the option in GE to simply show them on a raster export? I haven't fooled with that much.
peter246 -
Seen that. It worries me. My experience with automated hydrology is it's quite often wrong, even when someone's checking it.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Estimating impervious cover for a large (~20 square mile) watershed
Not sure if it's a Civil 3D only option, but in Civil3D I go to File-->Import-->Import Google Earth Terrain. You do this at the same time you have Google Earth up and running. Civil3D will grab all terrain information off the screen shot you are currently showing in Google Earth.
RE: Estimating impervious cover for a large (~20 square mile) watershed
I'm running BricsCAD, which I'm very pleased with both in terms of it's functionality, it's ACAD-like interface, and it's price. Wonder of someone's written a module to do this for it.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Estimating impervious cover for a large (~20 square mile) watershed
Have you tried ESRI's ArcGIS Expolorer Online: http://www.arcgis.com/explorer/? It appears to have basic ArcGIS functionality including viewing and editing shapefiles, and has USGS topo and imagery base layers built in.
Check out the freeware section at: http://www.esri.com/products. There might be something useful there.
RE: Estimating impervious cover for a large (~20 square mile) watershed
I believe that 10-ft interval USGS topography can be downloaded for free or nominal cost, as can the USGS Quad Maps. Lastly, the NAIP frequently flies 1-meter resolution natural color aerials which they also provide for free, or at nominal cost. I know for sure that the USDA provides free GIS files of their soil surveys. All of this should at least be a good basis from which to delineate basins and put together fairly comprehensive hydrograph calculations.
In Texas, the State provides a GIS clearinghouse where all this data is centralized and provided at no cost. You may check to see if Georgia has similar.
I'm currently away from the office so I'm unable to post in more detail. I'll post back in detail once I get in.
good luck.
RE: Estimating impervious cover for a large (~20 square mile) watershed
RE: Estimating impervious cover for a large (~20 square mile) watershed
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Estimating impervious cover for a large (~20 square mile) watershed
I'm not sure this will help your situation but, you can get DEM files that were used to produce USGS quad maps for free just google it. I'm not familiar with BrisCAD but I know Civil3d and Geopak can translate these to .tin files which can then be written out in CAD so you have real data to work with. You can then reference a raster for comparison. Worked for me in the past rather well if USGS quality is all that is available.
I've found that where I'm currently located Bing Maps has more recent aerial photography for determining impervious areas than Google Earth. I would use most recent aerial I could find and try to back it up with some site visits for large descripancy verification and adjustment.
Also in the past on a DOE drainage project we looked at several available possible applicable methods of runoff determination. I believe this included State DOT regression equation, USGS regression equation, and NRCS method or rational method can't remember which but I think it was rational method because it is typically meant for larger areas. I'd do some research on applicable methods size (area) limitations and use a few methods and pick a conservative method to model. We were using this for HEC-RAS input so we didn't need a hydrograph only a peak flow.
Hope something I mentioned is of value.
RE: Estimating impervious cover for a large (~20 square mile) watershed
http://www.webgis.com/terr_pages/lulcutm_ga.html or http://viewer.nationalmap.gov/viewer/ for example.
It may be worth hiring a GIS consultant to work with if you have limited GIS abilities.
RE: Estimating impervious cover for a large (~20 square mile) watershed
http://thecadgeek.com/blog/2009/03/acquiring-converting-dem-downloads/
The downside for you is that the directions are for creating surfaces in Civl3d but once you get the dem file you can figure out how to import it to BricsCAD (if you don't know already). I know nothing about BricsCAD but I'm assuming it has this capability
I also use The National Map Viewer to download hydrography and orthoimagry files that fit seamlessly in with the contours when everything is imported on the same datum. It's very important to set up your original drawing with a known coordinate system in order for all the files to import correctly. It doesn't have to be the same coordinate system as the imported files, just a known one. You can also get roads (transportation files), which helps with large basins in just knowing where you are. The hydrography and transportation files can be downloaded as shape files.
I agree with delineating by hand though - the catchment area function in Civil 3D never seems to really work for me. Maybe it works better on smaller watersheds or "designed" surfaces.
RE: Estimating impervious cover for a large (~20 square mile) watershed
They're going to make you save alot of time (money).
Plus, sometimes they got better data (ex.: LIDAR coverage might be available for your client).
There might be someone local that can do exactly what you want (e.g. telling you the median watershed slope) ?