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Hi Mark, I've been wondering if I should have an elevation for offshore or not, that is good advice, I will give it a shot and see how it goes. What is your advice for dealing with a stream network that is interrupted by small ponds and lakes? Should I edit the stream layer to bisect the water body and delete the lines which make up the edges of these water bodies? (See image below). Or should I create polygons for the water bodies, delete the lines that go around the edges, and Level the DEM to lower the elevation of the water bodies? (and if I do Level DEM, should Fill Sinks be performed before or after?) The green shows the original stream network with lines outlining the water body. Red shows an edited stream network which goes through the water body, deleting the coastline. Also, the only available DEM appears to have some errors that were created when the tiles were added together, resulting in some striations that run throughout in a gridded pattern. Some areas are worse than others and it seems to not have a huge effect on the large watersheds but does affect the subwatershed scale. Have you ever come across this or have any ideas of how to deal with it? I read in one tutorial that perhaps setting the resampling technique to Cubic would help alleviate, but it hasn't worked in this case. Any help is much appreciated!
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07-18-2015
08:17 AM
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Hi Mark, Thank you, that all makes a lot of sense, understanding that AdjointCatchments are "pre-delineated" watersheds has cleared up a lot. I have a few more questions if you don't mind. 1. Is there anyway to automate the delineation of watersheds, without going in and setting individual points? And is this possible for sub-watershed delineation as well? I am working in an area that does not have gage stations, which is the example that is used for watershed delineation in most of the tutorials I have read. Additionally, the subwatersheds are going to be used as the boundaries for local area environmental plans. It would be ideal if these could be of similar sizes to aid in the planning process. Since there is some flexibility in size of subwatershed, depending on where I place the point, some mechanism to outline the general size in an automation process would be great, although maybe I'm hoping for two much! 2. I am working in an area with a lot of coastline. I would like the watersheds to extend all the way to the coast to cover the entire study area. By experimenting I found that the smaller the threshold used when defining streams the more catchments that are generated, with many of them coming to the coast, leaving just a few gaps. Is there a better way to force delineation along a coastline or am I doing the correct thing? 3. Since I have defined streams/drainage lines quite small in order to get them all the way to the coast you can see that there are many small streams flowing into the ocean (see image). Technically, each one of these is their own watershed if I were to delineate them. However this seems odd to me, do you know what is generally done in this situation? I hope that question makes sense. Thank you!
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07-16-2015
08:18 AM
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Hi Malcolm, I am wondering what your final solution was. Did you end up doing what you've outlined in the above comment? I have the exact same assignment and was also stuck on the functional difference between catchments and watersheds. It appears that adjointcatchments are the largest drainage basins in my study area, thereby acting as the largest possible watersheds, and the catchments within the adjointcatchments would be subwatersheds. This is my first time using archydro though so any guidance is much appreciated. Thanks!
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07-15-2015
12:20 PM
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