Watersheds of Lewis and Clark
Watersheds of Lewis and Clark EVSC 3880
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This 16 page Class Notes was uploaded by Domingo Cruickshank on Monday September 21, 2015. The Class Notes belongs to EVSC 3880 at University of Virginia taught by Janet Herman in Fall. Since its upload, it has received 40 views. For similar materials see /class/209785/evsc-3880-university-of-virginia in Environmental Science at University of Virginia.
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Date Created: 09/21/15
EVSC 376 Spring 2009 Watershed Delineation Exercise Objective to create watershed boundaries from raster digital elevation model datasets and analyze stream networks and land cover characteristics within those boundaries The Process Watershed delineation in GIS is a multistep process 1 Set up the ArcGIS working environment 2 Delineate watershed Create a depressionless elevation layer Create flow direction Create flow accumulation Create watershed pour points Delineate watersheds DQOO39SD EVSC 376 Watershed Delineation 2 Set up the ArcGIS working environment N 0 P 01 5 All Scholars Lab machines contain the folder clocaldata We ll store files here for this exercise Go to the Scholars Lab EVSC376 class page ht9wwwibvirginiaeduscholarslabresourcesclassev50376 and download the hydrozip file to your machine Open this file in WinZip click the Extract button and navigate to clocaldata and click Extract E2 WinZip hydrozip Eie Actions gpmns elp New Open Favorites Add Extract Encrypt View chemm Wizard AUXFl 3 m i m H Xi lt selected 0 les 0 bytes Total 153 les 2902631KB This will preserve the directory structure within the Zipped data Your data sets will not work properly if the directory structure is not preserved Check the contents of clocaldatahydro to be sure you see that all your datafiles have been deposited Open ArcMap Start gt Programs gt GISgt ArcGlS 93 gt ArcMap and accept the defaults to create a new map Open the included ArcMap project File gt Open gt Navigate to hydro directory gt Hydromxd Set these environment properties Tools gt Options gt Geoprocessing gt Environments 1 Under General Settings set the Current Workspace and Scratch Workspace as below EVSC 376 Watershed Delineation 3 Environment Settings 2 General settings 7 7 Current Wnrkspace cLocaidmahydrq a t Scratch Workspace Dehulk Output Z Value l Output Coordinate system Same as Input L 3 I J tput has 2 Values lsameAsInput ll lv Cm imam 2 Under Raster Analysis Settings set the Cell Size as below 1823nn586159n86 Click OK to accept the Environment Settings changes Click OK on the Options dialog box 7 Enable the Spatial Analyst Extension Tools gt Extensions gt check mark next to Spatial Analyst EVSC 376 Watershed Delineation 4 mi Main Survey mm License not available Survey Ednarllmense nm available Tracking mam Dewmmn Spatial Analyst 9 2 cwmm sissszms ESRl in All Rights Essened Pymides spatial anamimaisiamsemn m erandieature data 4th 8 Click Close to accept the change and close the Extensions dialog box 9 Open Spatial Analyst Toolbar View gt Toolbars gt Spatial Analyst We will use this toolbar later in the exercise 100pen ArcToolbox WindowgtArcToolbox or by using the E button We will use the toolbox later in the exercise Delineate Watershed Create a depressionless DEM It is important to start with an elevation grid that has no depressions NOTE This procedure actually takes tartoo long to actually run here A file has been created and is in the hydroprocessed directory 1 Open the ArcToolbox toolset Spatial Analyst Tools gt Hydrology This is where the sun ace hydrology tools are located 2 Open the Hquot tool The input sun ace is the elevation grid Output is CLocadatahydroFiEevUTM1 EVSC 376 Watershed Delineation 5 mm surface raster lW el Dutputsurface raster 7 el 2 mm optional 7 While the grid is filling which will take a long time you might want to entertain yourself reading all the latest GIS goodness 0 After a few minutes a new layer will be added to the data frame This is identical to the original elevation raster with any areas of internal drainage filled in E Statesibordirs El F1IElevUTM1 a a High 3 30937 Low 225979 3 ElevUTMllN Value High 30937 Low 219697 H D USGS 250K Topo Maps E West p Note the difference in the lowest elevation value in the legend sink cells in the original data set have been filled in 4 Remove the original layer from the data frame right click on the layer name and select Remove The rest of the exercise will use the filled grid layer It is important to have a depressionless DEM for all subsequent hydrological analyses Areas of internal drainage can cause problems later in the watershed delineation process Create Flow Direction NOTE This procedure actually takes far too long to actually run here A file has been created and is in the hydroprocessed directory EVSC 376 Watershed Delineation 6 1 Open the Flow Direction tool ArcToolbox gt Spatial Analysis Tools gt Hydrology gt Flow Direction 1 The input surface is the filled dem grid 2 The output raster should be CLocaldatahydroFowDirFi1 3 Click OK to run the Flow Direction tool 2 Turn off display of the filled dem layer by unchecking the box to the left of the Fichar1001 layer 3 Zoom in close to look at this layer Note that the numbers refer to coded direction of flow 32 64 12B 16 1 3 4 2 Direction of flow must be known for each cell because it is direction of flow that determines the ultimate destination of waterflowing across the surface 0 Create Flow Accumulation NOTE This procedure actually takes fartoo long to actually run here A file has been created and is in the hydroprocessed directory 1 Open the Flow Accumulation tool under Hydrology 1 Set the input flow direction raster to the output of the last task CLocaldatahydroFlowDirfi1 2 Set the output raster to CLocaIdatahydroFowAccfow1 default name EVSC 376 Watershed Delineation 7 Flow Accumulation El Inputflow direminn rasLer Flowolrjlu L Dutput accumulation raster C39analdat hydrnFluWrcC7Fan Inputweight raster nprmnai um utdata penpunnal mm mm 39 CIK Cancel Envimnmems ShawHelpgtgt 2 Again this may take some time 3 When complete turn off the flow direction layer The flow accumulation layer has a value for each cell that value represents the number of cells upstream from that cell Cells with higher values will tend to be located in drainage channels rather than on hillsides or ridges 4 Alter the symbology for this new layer It will be easier to visualize high flow pathways by altering how cells are displayed 1 Change the symbology method to right click on layer name gt Properties gt Symbology Classified Use 2 classes 2 In the dialog box under the Classify button alter the break value for the first class to 5000 r Layer Properties General l Source l Exreml Display symbology lFields Joln5 amp Reialesl 5h um Values Draw raster grouplng values Into classes Impurt Classi ed Stretched Fields Classi rdtiun value ur LLlE Narmaligatiun lamp l1 gym Range o 7 2591739953 2591739953 r 92150753921 2591739954 9215075388 9215075st 1900609299 9215075399 1900509299 1900509299 7 4319566558 19005093 7 4319565508 4319555583 73432632 4319566189 73432632 lquot Show class breaks using cell values Display uData as v I Use hillshade effect 1 3 Change the symbology no color for the first class red for the second class This is accomplished by right clicking on the color swatches and selecting Properties for selected Colors EVSC 376 Watershed Delineation 8 Layer Properties iii Xi General Source Extent Display Symbulogy l Fields l Joins a Relatasl gnaw Unique Values quotquotW 39 39 3 V 1 Classified Stretched Fields Classlficah un Maine VALUE J Manual Normalization one fl gasses l2 Ll Classifyquot Color Ramw 39 Sym l Range l Label l a e Sloan n 7 5mm Simon 7 73432532 5nunanuum e 714321532 T Show class breaks using cell values Display uonata as v if Use hillshade effect 1 OK Cancel J 4 Nowthe cells that are displayed in red have the flow of at least 5000 upstream cells flowing through them You will need to zoom in before you can see the details of the flow network You should also see that the DEMgenerated drainage network looks somewhat like the vector streams although if you look at details you will see where the data sets do not line up a EVSC 376 Watershed Delineation 9 Flow accumulations are important because they allow us to locate cells with high cumulative flow Each watershed has an outlet point called a pour point Pour points must be located in cells of high cumulative flow or the resultant watersheds will be very small and worthless o Create Watershed Pour Points 1 We will create a new shapefile to store the pour points we are about to identify 1 Click the ArcCatalog icon 3 in the ArcMap toolbar In ArcCatalog browse to your CLocaldatahydro directory and highlight the directory name Open the Create New Shapefile dialog File gt New gt Shapefile then enter ppoint as the shapefile na m e 63453162M Raster Dataset 53453162m c dlnate system Q 5523107sm Raster Dataser 8523107sm Coordinate system it EoldEr EAlLRiverssh shape le a We Gagdalabase 7 clearwateLRivershp shape le E eievu 1 Raster Dacaser 3 Eersonal Gwd base ilLelEvutml owacc owl RasterDataset 0 Layerquot owdirjllll Rasteroaraser 9 group Law acumen lo eielevutl Raster Damset El hapefle mm mm 5 q Covemge Reiamngmp Class r shp shape le xxDDUZEZ4DDUbnd InfoTable El Ium Featureclass b Toolbox Eta gopy cm Er Ardnfoworkspace lvl gBAsE Table x Delete INFOlable Rename a El Coverage 2 gerresh A addresstocator New gt m xMLDocument a Search g Properties 2 Click the Edit button in the Spatial Reference section then the Import button Select yourelevation layer This defines the spatial reference for the new ppoints shapefile to be the same as your existing elevation layer EVSC 376 Watershed Delineation 10 l Spatial Reference Properties xv Cnurdrnaxe System l name NADVIEELUTMVZane llN Details lPreJemnn rensv rseiMermm V Falssjasting soauanauaaua lFalseJlunhlng aaaaaaa CentralMer1dran 4170aaana I39Scalejannr39 a qgeaaa Create New Shape le TX fLaUmdeVOLOrlgin39 aaaaoaa Name ppm 7 iLmear Unit Meter1uanaau NamrAmEnmnAl BZ Fea me Type39 Pmm lAngular UnitDegreen 1745 uz 19943299 quotF39rlme Mendlan Greenwich manuuauaoauannuuoou Spm ne e em lDutum a nanAmer sanermd mime Unknown Coordinate System germ Selma prade n Im n Descnpuun ed wordinale syeem V 7 V p n a mammals system and xv z and M damains fmm an existing gendataset 29 feature dataset feature class raster ew v create a new coordinate waem Mom Edrtthe propemes urme currently seieaed coordinate system 7 Shaw Dams gear Sets me zuerdinaxe wslem m Unknuvm l Coordinates will contain Mvalues Usedln store Sage A5 save me morainare system to a F Coordinateswill coniamZvalues Usedlo slure3D data 7 NF OK Cancel or Cancel Apply 3 Click OK to create the new ppoint layer 2 Back in ArcMap add the new point layer ppoint to your data frame by using the Add Data button l 3 Activate the editor toolbar View gt Toolbars gt Editor Editor v 39 Create New Feature I l 4 From the Editor Toolbar choose Editor gt Start Editing In the Start Editing dialog highlight the Source line with the Type of Shapefiles and click OK Suit Editing XI which faldaror database do you wanna edit dam frum7 VEnurce M p nint dearwacerjver snakejwer AlLRlv ere states borders EVSC 376 Watershed Delineation 11 If you see the following dialog click Start Editing Starting To Edit In a Different Coordinate System The layers below are in a different coordinate system than the current map s coordinate system You can edit data in a different coordinate system than the map however some editing tasks may give you unexpected alignment or accuracy problems Folder or database you have chosen to edit data from CLocaldatahydro These layers are in a different coordinate system than the map ClearwateLRiver Snakeijer ARiver5 statesborders lt l lljl T gon39t warn me again About Coordinate Systems Cancel 39 In the Editor Toolbar be sure that Task is Create New Feature and Target is ppoints tr e x l Edito v 1 I l j 39 Task Create New Feature 1 Target ppoints V l l 5 In order to better see where you are adding your pour point open a magnifier window Window gt Magnifier l D imp llflpv 1 lama AllQlt oDlRH gifts pppp MS 1 j 6 You may need to zoom in and increase the zoom factor of the magnifier before adding any points You must be able to see the individual raster cells to locate pour points EVSC 376 Watershed Delineation 12 7 Use the Identify tool o to examine the values of the Flow Accumulation layer before adding any points You will be able to tell which direction is upstream lower accumulation value and which direction is downstream higher accumulation value 8 Add a pour point by selecting the Sketch tool g from the Editor toolbar Click on the map to locate the pour point You must zoom in closely to locate a pour point otherwise your pour point may not be located within a highflow pathway Everything upstream from the pour point will define a single watershed 9 Save your newly defined pour points Editor gt Stop Editing gt Save Edits gt Yes Close the Identify and Magnifier windows 10 Select Tools gt Options gt Geoprocessing gt Environment Settings gt Environments gt General Settings gt Extent gt Same as layer FlowAccflow1 to make sure the output extent will be correct you don t want the watershed truncated Environment Settings EXIEH lsame as layer FlowAcc ow1 7v l aquot l Tap l szaaagmaszn Baht 485834D11152 7252mssuns4 annnm sn347454aaas7 cancel ShawHelpgtgt Open Spatial Analyst View gt Toolbars gt Spatial Analyst Set Spatial Analyst gt Options gt Extent gt Analysis extent Same as layer FlowAccflow1 General Extent l Cell Size Analysis extenL lAs Speci ed Eeiew g Tap 5240450 99 435034 D11 E gm 725204 55 5034746 43 snap exlenna EVSC 376 Watershed Delineation 13 Set Spatial Analyst gt Options gt Cell Size gt Analysis cell size Same as layer FowAccfow1 Generall Extent CElISIIE i Analysis cell size Cellgize Number ofrows Number ofgolumns i M Cancel If the Analysis Extent and cell size do not match an existing layer there will be problems of registration between the pour point raster and the other raster layers necessary to delineate watersheds Therefore it is always a good idea to set your cell size and analysis extent relative to an existing raster layer 11Use the Snap Pour Point tool to ensure your pour points are located on the highest flow accumulation cell within a specified radius The Snap Pour Point tool will search within a snap distance around your pour points for the cell of highest accumulated flow and move the pour point to that location Based on our datasets a snap distance of 100 searches within an approximate 3 cell radius to find a cell with higher flow accumulation The Snap Pour Point tool also converts your Pour Points into the raster format needed later in the watershed delineation step Before running the Snap Pour Point tool at the bottom of the Snap Pour Point dialog box click Environments gt Raster Analysis Settings gt Cell Size gt Same as layer FowAccfow1 cm 5mm EVSC 376 Watershed Delineation 14 Click OK to close the Environment Settings dialog I Snap Pour Point Input raster or feature pour point data l ppoint v Pour point eld optional ltd Input accumulation raster l FlOl39JACCFlOW1 v a Output raster l CLocaldatahydro5napPuuppoil Snap distance i 100 OK Cancel Environments Show Help gtgt Verify your Snap Pour Point dialog is filled in as above and click OK to run the tool 12When the tool completes the new output SnapPouppoi1 layer is automatically added to your map and contains the new snapped pour point Use the Zoom tool to see where the Snap Pour Point tool located your new pour point Your colors may vary Below the orange dot is the original pour point The green square is the snapped pour point The new SnapPouppoi1 layer cell identifies the place where the snapped pour point was added EVSC 376 Watershed Delineation 39 15 If your original pour points were already located within a highflow pathway you will find the snapped pour points are moved downstream by the size of your snap radius If it is important to your analysis to keep the exact cell location where you located the original pour points rerun the Snap Pour Point tool with a radius of 0 If the pour point raster cells are not in highflow pathways the watersheds you create will be too small If the pour point raster cells are not directly quotoverquot the flow path you will not create watersheds that represent large drainage areas Delineate Watersheds NOTE This procedure actually takes fartoo long to actually run here Afile has been created and is in the hydroprocessed directory 1 Open the Watershed tool under Toolbox gt Spatial Analysis Tools gt Hydrology Note that one of the options forthe input data is the point feature dataset ppoint Selecting a point feature dataset will work only if the pour points fall in a highflow pathway In the previous steps we used the Snap Pour Point tool to convert the pour point to rasterformat and to ensure they fall within a highflow pathway so we will use the raster layer SnapPouppoi1 as input Select the flow direction grid as the input flow direction raster 2 Select the raster version of the pour points SnapPouppoi1 as the input raster 3 Accept the other defaults and click OK Watershed g g In ut uw directinn raster lrlowoirflu mquot Input raster at feature pour paint data SnapPou ppoit a Pnur pnlnt eld nptlunaD VALLlE aster lctacaidatalwamWatarshjiaw ox l Cancel Envirnnmems Shanelpgtgt EVSC 376 Watershed Delineation 16 2 The new watershed raster will be added to the data frame Hydnmnxd ArcMap Arclnfo Ele gun Mew sookmarks Insert Selection 1001 Miami help i D aquot a Si 39 if lnz to l a cle rwaleLRiver a SnakeiRlver El D NLRivers QEEBOW E CZ XIIQ 1 19625127 32430192 Meters 3 ArcGlS automatically calculates the number of raster cells contained in this watershed and stores this value in the COUNT column of the raster attribute table Right click on the layer name Watershfow1 gt Open Attribute Table This watershed covers 73129141 cells E Attributes ofWatershFlaw1 D Rowid VALUE COUNT gtl 0 0 731291411 Record Show The geographic area covered by each raster cell is found in the metadata for layer Watershfow1 To view the metadata right click the layer name Watershfow1 gt Data gt View Metadata Set the Stylesheet to FGDC Click Spatial Data Organization Information to find the cell size in the x and y directions Click Spatial Reference Information to find the unit of measure in the Planar distance units field
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