Example Application

Spatial Analysis Exercise<= /a>

GIS in Water Resources

Fall 2008

Prepared by David G. Tarboton and David R. Maidment

Goal

The goal of= this exercise is to serve as an introduction to Spatial Analysis with ArcGIS.

Objectives

· Calculate slope from a grid digital elevation model

· Apply model builder geoprocessing capability= to program a sequence of ArcGIS functions

· Use raster data and raster calculator functionality to calculate watershed attributes such as mean elevation, mean slope, mean annual precipitation and runoff ratio.

Co= mputer and Data Requirements

To carry o= ut this exercise, you need to have a computer, which runs the ArcInfo version of ArcGIS 9.3. T= he necessary data are provided in the accompanying zip file (42MB), http://www.ce.utexas.edu/prof/maidment/giswr2008= /Ex3/Ex3.zip These data have also been cop= ied to the LRC class file where they can be accessed at: <= span style=3D'mso-bookmark:_Toc479668056'>Civil5/LRC/Class/Maidment/giswr2008/Ex3/).

Part 1. Slope calculations

1.1&= nbsp; Hand Calculations

Given the f= ollowing grid of elevations. Calculate= by hand the slope and aspect (slope direction) at the grid cell labeled A usin= g

(i) The standard slope function=

(ii) The 8 direction pour point model

(iii) The D= ¥ algorithm

Refer to th= e powerpoint slides (http://www.ce.utexas.edu/prof/maidment= /giswr2008/visual/Spatial.ppt) from lecture 7 to obtain the necessary formulas for each of these methods

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Grid cell size 100m

53	52.5=	48.4=	48	49
49	64	54.2= A	50.2=	54
49.2=	49	44.7= B	42	45
48	51	39.2=	40.8=	41

Comment on = the differences and indicate which you think is a most reasonable approximation of the direction of water flow over the surface.

To turn in: Hand calculations of slope at poin= t A using each of the three methods and comments on the differences.=

1.2 Verifying calculations using ArcGI= S

Verify the calculations in (1.1) using ArcGIS Hydro and Geoprocessing functions and TauDEM.

Save the fo= llowing to a text file 'elev.txt' (This file is also included in http://www.ce.utexas.edu/prof/maidment/giswr2008/Ex3/Ex3.zip)

ncols 5

nrows 4

xllcorner = 0

yllcorner = 0

cellsize 100 <= /o:p>

NODATA_value -= 9999

53 = 52.5 48.4 48 49

49 = 64 54.2 50.2 54 =

49.2 49 44.7 42 45

48 = 51 39.2 40.8 41<= /o:p>

This shows = how raw grid data can be represented in a format that ArcGIS can import.

Open ArcMap= and ArcToolbox. Use the tool Conversion Tools à To Raster à ASCII to Ra= ster to import this grid file into ArcMap. Specify the name of the Output raster as elev and give it a disk location. Specify the Output data type = as FLOAT (It is more consistent to t= hink of elevation data as including floating point data, rather than integer, ev= en though this specific case is integer data).

You can use= the identify button on the grid created to verify that the numbers correspond to the values in the table above.

Open Tools à Extensions = and verify that the Spatial Analyst function is available and checked. This is where the spatial analyst license is accessed, so if Spatial Analyst does not appear you need to acqu= ire the appropriate license.

Select View à Toolbars à Spatial Analyst. This dis= plays the Spatial Analyst toolbar in the ArcMap interface. You may dock the toolbar somewhere convenient.<= /p>

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Select Spatial Analyst à Surface Analysis à Slope on the Spatial Analyst toolbar.<= /o:p>

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At the dial= og that appears select elev as the inp= ut surface and select whether you want the output in Degree or Percent (to be consistent with your hand calculations above).   It’s a bit easier to interpret slopes in Percent.

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Use the ide= ntify button on the slope grid that is created to verify that the numbers corresp= ond to the values you calculated by hand and resolve or reconcile any differenc= es. Record in a table the ArcGIS calcu= lated slope at grid cells A and B (B being the grid cell immediately below A as indicated on page 1)

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Select Spatial Analyst à Surface Analysis à Aspect = on the Spatial Analyst toolbar. At the dialog that appears sel= ect elev as the input surface.=

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Use the ide= ntify button on the aspect grid that is created = to verify that the numbers correspond to the values you calculated by hand and resolve or reconcile any differences. Record in a table the ArcGIS calculated aspect at grid cells A and B= .

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Open the Toolbox. Open the tool Spatial Analyst Tools à Hydrology à Flow Direct= ion

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Select elev as the input raster and spec= ify names for output rasters (e.g. FlowDir and PercDrop). Note that raster file names can not exceed 13 characters and that there should not be a space in the name or the file path leading up to the name. Also note that when you click on each field in the dialog box the he= lp part of the dialog to the right explains the content of the file. This is shown below for the Output= drop raster which from the description is really the slope expressed as a percentage.

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Use the ide= ntify button on the FlowDir and PercDrop grids that are created to verify that the numbers correspond to the values you calculated by hand and resolve or reco= ncile any differences. Record in a = table the ArcGIS calculated flow direction and hydrologic slope (Output drop) at = grid cells A and B

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The D¥ algorithm is not part of standard ArcGIS. Rather it is part of TauDEM that i= s available from http://www.engineering.usu.edu/dtarb/t= audem/. TauDEM should already be inst= alled on the university computers used for this class, however if you are working elsewhere you need to download and install the version of TauDEM for ArcGIS= .

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Open ArcMAP= and add the TauDEM toolbar. [Click on Tools à Customize à Add from fi= le and select the file c:\program files\Taudem\agtaudem.dll]

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You should = get a toolbar that looks like

This may be= docked in a convenient location.

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On the TauD= EM toolbar select Basic Grid Analysis= à Dinf Flow Directions.

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This is the function that computes slope and flow direction using the D¥ method. At the dialog box that appears click on the folder browse button nex= t to the Pit Filled Grid field and browse to the 'elev' grid. Click on the other browse buttons = to fill in output names (e.g. DinfDir and Dinfslp, remaining cognizant of the = 13 character and no space file name limitations). You do not need to fill in the Flo= w Path Grid field as we are not using an existing flow path grid. Click compute. This is the only TauDEM function n= eeded for this exercise. We will use other TauDEM functions later in the class.

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Use the ide= ntify button on the Dinfdir and Dinfslp grids that are created to verify that the numbers correspond to the values you calculated by hand and resolve or reconcile any differences. Re= cord in a table the TauDEM calculated Dinfdir and Dinfslp at grid cells A and B. Note that TauDEM does not compute values for the edges of the domain, because results there are ambig= uous due to the data outside the domain not being present, so TauDEM grids will appear smaller. This is not an error.

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To turn in: Table giving slope, aspect, hydrol= ogic slope, flow direction, D¥ slope, D¥ flow direction at grid cells A and B. Please also turn in a diagram or s= ketch that defines or indicates what each of these numbers means for the specific values obtained for cells A and B.

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1.3 Automating proc= edures using Modelbuilder.

Modelbuilder provides a convenient way to automate and combi= ne together geoprocessing tools in ArcToolbox. Here we will develop a Modelbuilde= r tool to automate the importing of the ASCII grid and calculation of Slope, Aspec= t, Hydrologic Slope and Flow direction.

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Right click= on the whitespace within the ArcToolbox window and select New Toolbox. Name the toolbox Ex3 (or something else you might like).

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The toolbox= es created in this manner are stored within the Documents and Settings folder = for the user of the computer (e.g. 'C:\Documents and Settings\dtarb\Application Data\ESRI\ArcToolbox\My Toolboxes').

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Right-click= on the new toolbox and select new model.

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The model w= indow should open. This is a window= where you can drag, drop and link tools in a visual way much like constructing a = flow chart.

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In the Tool= box window browse to Conversion Tools = à To Raster à ASCII to Ra= ster. Drag this tool onto the model wind= ow.

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Double clic= k on the ASCII to Raster rectangle to s= et this tool's properties.

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Set the Inp= ut ASCII raster file to elev.txt and Ou= tput raster to ElevM (I used ElevM = so as not to conflict with elev that already exists). Set the output data type to be FLOAT. Click OK to dismiss th= is dialog. Note that the model elements on the ModelBuilder palette are now colored indicating that their inputs are complete.

Locate the = tool Spatial Analyst Tools à Surface à Slope a= nd drag it on to your window. Yo= ur window should appear as follows.

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The output = from the ASCII to raster function needs to be taken as input to the slope function.<= span style=3D'mso-spacerun:yes'> To do this use the connection tool= and draw a line from elevm, the Output raster of ASCII to Raster, to Slope. Right click on Output Raster and s= elect 'Add to Display'.

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You could a= lso double click on Output raster or slope to change the name of the output fil= e if you wish (but this is not essential). The model is now ready to run. Run the model by clicking on the run button .

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The orange = boxes briefly flash red as each step is executed and then the Slope Output raster= is added to the Map display. The default variable calculated is the Slope in Degrees, if you want PercentRis= e, you can click on the Slope tool and change the default type in the PercentR= ise.

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Add the fol= lowing two tools

Spatial Analyst Tools à Surface à Aspect

Spatial Analyst Tools à Hydrology à Flow Direct= ion

Connect the= elevm outputs to these tools. Use t= he layout tool to organize the layout.

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Your model = should appear as follows. Notice tha= t the "output drop" oval is hollow.&nb= sp; This is because this is an optional output that has not been specified.

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Double clic= k on the Flow Direction rectangle and set the output drop file name to something suitable, e.g. pcdrop. When s= etting names you need to be careful that you do not use a name of a grid that alre= ady exists, or else you will get a yellow warning sign in the display and the m= odel will not run, as shown below:

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Set the flow direction output at the same time. Then double click on the slope and aspect rectangles to set the outp= uts to appropriate grid file names. Your final model should look something like:

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You can cli= ck run and do all the processing required to import the data, compute Slope, Aspec= t, Flow Direction and Hydrologic Slope at the click of a button. Pretty slick!

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Right click= on elev.txt and select Model Parameter.

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Right click= on each of the outputs Asp, FDir, pcdrop and slpdeg = in turn and select Model Parameter and Add to Display.

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A P now app= ears next to these elements in the diagram indicating that they are 'parameters'= of the model that may be adjusted at run time. Close your model and click Yes at the prompt to save it. Rig= ht click on the model in the Toolbox window to rename it something you like (e= .g. SlopeAspect). If you go back to your model and no= w Open it,

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you’l= l see that the input files are shown as parameters of the model just like when you execute a tool in ArcToolBox.

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If you see = a red X near one of your output files, it means that there is already a file of that name in the place where you propose to put the output, so rename the output= to another folder or another name.

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You are done creating this model. Close Ar= cMap.

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ModelBuilder is a very powerful w= ay of creating complex analyses, and documenting your “workflow” in a form that is visual and can readily be described. In this way, analyses that youR= 17;ve done can be passed on to other analysts, and you can also use the visual palette display in your term project report or thesis to document how you’ve done your analysis, so the visual aspect of the display helps = with documenting your work, as well as in organizing it.

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To turn in: A screen capture of your final mod= el builder model.

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We will now= use this model for different data. Locate the file demo.asc extracted from the zip file of data for this exercise. Reopen ArcMap. Right click wi= thin the Toolbox area and select Add To= olbox. Browse to the My Toolboxes folder = within Documents and Settings for the user of the computer (e.g. 'C:\Documents and Settings\dtarb\Application Data\ESRI\ArcToolbox\My Toolboxes') to locate and add the Toolbox Ex3 that contains the tool you just created.

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Double clic= k on the model in the Toolbox window to run it.&nbs= p; The following dialog box for the tool you created should appear.

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Select as i= nput under elev.txt the file demo.asc. Specify different names for the ou= tputs Asp, FlowDir, Percdrop and Slp to avoid the conflicts with existing data and remove the red crosses . Then click OK and the model should= run and add results for this new data to ArcMap. Examine the ArcMap table of conten= ts and record the minimum and maximum values associated with each of the outputs Aspect, Slope, Flow Direction and Hydrologic Slope (percentage drop).

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To turn in: A table giving the minimum and max= imum values of Aspect, Slope, Flow Direction and Hydrologic Slope (Percentage dr= op) for the digital elevation model in demo.asc.

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Congratulat= ions, you have just built a Model Builder geoprocessing program and used it to re= peat your work for a different (and much larger) dataset. If you would like to save this too= l to take to another computer or share with someone else you can copy the file Ex3.tbx from c:\documents and settings\<username>\application data\ESRI\ArcToolbox\My Toolboxes to a removable media to take with you.

Part 2. San Marcos Elevation and Precipitation.

The purpose= of this part of the exercise is to calculate average watershed elevation and slope = for subwatersheds of the San Marcos basin, and to calculate average precipitati= on over each of these subwatersheds using different interpolation methods.

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The followi= ng data is provided in the Ex3.zip file.

SanMarcos.g= db file Geodatabase.

The feature= classes Basin, Catchment, Flowline and MonitoringPoint are from Exercise 2. There are two additional feature c= lasses:

-&nb= sp;         PrecipStn. <= /span>PrecipStn contains mean annual precipitation data from precipitation stations in and around the San Marcos basin downloaded from NCDC following the procedures g= iven in http://www.ce.utexas.edu/prof/maidment= /gradhydro2005/docs/ncdcdata.doc. This data was prepared by download= ing all years of available precipitation data for the counties in and around the San Marcos basin, then averaging over these years, retaining only those stations with 6 or more years of annual total data reported by NCDC.=

-&nb= sp;         Subwatershed. Subwatersheds delineated to the outlet of the San Marcos Basin as we= ll as each of the stream gages in MonitoringPoint following the procedures that will be learned in a future exercise.

These new f= eature classes are in a feature dataset named BaseMapAlbers as it is more sensible= to do watershed level analysis where area is involved in a projected coordinate system.

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A digital e= levation model from the National Elevation dataset is provided in the folder smdem_raw.

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1. Loading the Data

Open ArcMap = and from the geodatabase SanMarcos.mdb = load the Basemap and BaseMapAlbers feature datasets. Check the spatial reference system= of each by right clicking and selecting properties. Check the spatial reference system= of the data frame layers and if necessary set it to be the same as the BaseMapAlbers feature dataset, "NAD_1983_Albers". We will use this specific NAD_1983= _Albers projection, which is the USA Contiguous Albers Equal Area Conic projection,= for this exercise.

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Add the grid= smdem_raw to ArcMap. This is a digital elevation model = that was downloaded from the USGS seamless data server http://seamless.usgs.gov. Your map should look similar to the following:

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The DEM grid= is skewed in this display because it was obtained in geographic coordinates. Right click on the smdem_raw layer= in the table of contents and select properties. Click on the source tab. This shows you the Cell Size and n= umber of columns and rows. If you s= croll down in the properties you also see the Extent and Spatial reference of this DEM.

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The cell siz= e is in degrees. This is not a very u= seful measure at this scale. Use wh= at you learned in the lecture on Geodesy to calculate the cell size in m in both t= he E-W and N-S directions, assuming a spherical earth with radius 6370 km.

To turn in: The numbe= r of columns and rows, cell size in the E-W and N-S directions in m, extent (in degrees) and spatial reference information for the San Marcos elevation dat= aset DEM 'smdem_raw'. <= /i>

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2. Projecting the DEM.

To perform s= lope and contributing area calculations we need to work with this DEM projected into= the Albers equal area projection (An equal area projection is most appropriate = for area calculations such as we will be performing). Open the Toolbox and open the tool= Data Management Tools à Projections and Transformations à Raster = à Project Raster. Set the i= nputs as follows:

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The output c= oordinate system should be specified using S= elect a predefined coordinate system … after clicking on the button to = the right of Output coordinate system<= /b>. Then browse to the USA Contiguous = Albers Equal Area Conic projection in the Projected Coordinate Systems\Continental= \North America folder.   =

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The cell siz= e should be specified as 100 m and CUBIC interpolation used. I have found cubic interpolation t= o be preferable to nearest neighbor interpolation for continuous datasets such as DEMs. (This NED data is at 1 = arc second spacing which is close to 30 m, so in general 30 m would be a better choice here, but 100 m is chosen to reduce the size of the resulting grid a= nd speed data processing and analysis.) CUBIC refers to the cubic convolution method that determines the new cell value by fitting a smooth curve through the surrounding points. This works best for a continuous s= urface like topography at limiting artificial "striping" that can appear= in a shaded relief map (we will construct a shaded relief map below) with the other methods. Click "OK= " to invoke the tool. After the process is complete, the projected DEM, smdem, is added to ArcMap.

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Examine the properties of the projected dataset.

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To turn in: The numbe= r of columns and rows in the projected DEM.&nbs= p; The minimum and maximum elevations in the projected DEM. Explain why the minimum and maximum elevations are different from the minimum and maximum elevations in the original DEM. =

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3. Exp= loring the DEM

The spatial infor= mation about the DEM can be found by right clicking on the smdem layer, then click= ing on PropertiesàSource. Similarly, the symbology of the DEM can be changed by right clicking on the layer, PropertiesàSymbology.

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To explore t= he highest elevation areas in your DEM Select Spatial Analyst à Raster Calculator. If you don= 217;t see the Spatial Analyst toolbar, go to View à Toolbars= and click on Spatial Analyst. Double click on the layer smdem with the DEM for San Marcos. Click on the “>= 221; symbol and select a number less than the maximum elevation. This arithmetic raster operation will select all cells with values above the defined thresh= old. In the example below a threshold of 600m was selected for the Z pixel value= of smdem.

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A new layer = called calculation appears on your map. = The majority of the map (brown color in the figure below) has a 0 value representing false (values below the threshold), and the red region has a v= alue of 1 representing true (elevations higher than 600 meters).

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Zoom in to t= he region of highest elevations (red region) and do some sampling on the smdem grid using the identify tool to select a point close to the maximum elevation. In a layout mark your point of maximum elevation and lab= el it with the elevation value for that pixel.

You can plac= e the dot using the Draw toolbar. It seems that when you zoom out the dot does not show up in zoomed out view. I= f that is the case, just show the zoomed-in view, as above.

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To turn in: A layout showing the location of the highest elevation value in the San Marcos DEM.<= o:p>

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4. Con= tours, Hillshade and Slope

Contours are= a useful way to visualize topography. This can be done by using the spatial analyst extension through the following steps:

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Select Sp= atial Analyst à Surface Analysis à Contour…

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Select the I= nput surface as smdem, leave the default parameters, and browse to your output folder. Name output features as contour.shp. If you find that you don’t have contours over your whole extent, it is because one of your Calculation grids has been chosen by default as the Input surface. M= ake sure smdem is provided as the input surface.

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A layer is g= enerated with the topographic contours for San Marcos. Notice the big difference in Terrain Relie= f to the west of the basin compared to the east. This results from the fact that= the Balcones fault zone runs through the middle of this basin, to the west of w= hich lies the rolling Texas hill country and to the east the flatter coastal plain. There is a tower located in the Ci= ty of San Marcos on which you can stand and see these differences in topography to east and west!

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Another opti= on to provide a nice visualization of topography is Hillshading.

Select Sp= atial Analyst à Surface Analysis à Hillshade… and set the factor Z to a higher value to get a dramatic effect and leave the other parameters at their defaults (the follo= wing hillshade is produced with a Z factor of 100). Click OK. You should see an illuminated hillshaded view of the topography.

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Spatial Anal= yst also provides the capability to compute slope.

Select Sp= atial Analyst à Surface Analysis à Slope… Set the inputs as follows:

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A grid of sl= ope values in percent is displayed.

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To turn in: A layout with a depiction of topog= raphy either with contours, hillshade or slope in nice colors. Include the streams from the San Marcos Basemap Flowline feature class and the outline of the SanMarcos Basin from the Basin feature class.

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5. Zonal Average Calculations<= /p>
In hydrology= it is often necessary to obtain average properties over watersheds or subwatersheds. The Zonal Stat= istics functions in Spatial Analyst are useful for this purpose.

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Select Sp= atial Analyst à Zonal Statistics… Set the inputs as follows:

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Click OK. A table with zonal statistics is displayed.

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This contains statistics of the value raster, in this case elevation from smdem over the zones defined by t= he polygon feature class Subwatershed= . The Value field in this zone table contains the HydroID from the subwatershed layer and may be used to join th= ese values with attributes of the Subwatershed feature class.

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Open the att= ribute table for Subwatershed. Note that Zoneelev has been joined to this (because the join option was checked above). Determine the= mean elevation and elevation range of each subwatershed in the SanMarcos Subwatershed feature class.

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Select Sp= atial Analyst à Zonal Statistics… Set the input raster to be smslope:

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Click OK.

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Examine the attribute table for Subwatershed which should now also have the zoneslope t= able joined to it. Determine the m= ean slope (in percent) of each subwatershed in the SanMarcos Subwatershed featu= re class.

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To turn in: A table giving the HydroID, Name, = mean elevation, elevation range and mean slope (in percent) of each subwatershed= in the SanMarcos Subwatershed feature class.&= nbsp; Which subwatershed has the highest mean elevation? Which subwatershed has the largest elevation range? Which subwat= ershed has the largest mean slope?

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6. Calculation of Area Average Precipitation using Thiessen Polygons

Now to do so= mething really useful. We will calcul= ate the area average mean annual precipitation over the watershed using Thiessen polygons. Thiessen polygons associate each point in a watershed with the nearest raingage. Select the tool Analysis Tools à Proximity <= /b>à Create Thiessen Polygons

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Specify PrecipStn as the Input Features.<= span style=3D'mso-spacerun:yes'> Set the output feature class to be= ThiessenP (saving it in the BaseMapAlbers feature dataset) and indicate that ALL fields should be output. Click OK.

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The result i= s a Thiessen polygon shapefile.

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To average precipitation values in these polygons over the subwatersheds we need to convert this to a grid. Selec= t Spatial Analyst à Convert à Features to Raster.

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Specify the = Input feature as ThiessenP, field as= AnnPrecip_in (it is the annual ra= infall that we would like to work with), output raster as thiessen and cell size as 100 m. Click OK.

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The result s= hould be a grid that gives in each cell the annual precipitation value from the corresponding Thiessen polygon.

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Select Sp= atial Analyst à Zonal Statistics… Set the inputs as follows:

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Click OK. A table with zonal statistics is displayed. This contains stat= istics of the value raster, in this case mean annual precipitation from thiessen over the zones defined b= y the polygon feature class Subwatershed= . The Value field in this zone table contains the HydroID from the subwatershed layer and may be used to join th= ese values with attributes of the Subwatershed feature class.

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Open the att= ribute table for Subwatershed. Note = that Zonetheiss has been joined to this (because the join option was checked above). Determine the mean precipitation for each subwatershed in the SanMarcos Subwatershed feature c= lass from the zonetheiss.mean column.

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To turn in: A table giving the HydroID, Name, = and mean precipitation by the Thiessen method for each subwatershed in the SanMarcos Subwatershed feature class. Which subwatershed has the highest mean precipitation?

7. Estimate basin average mean annual precipitation using Spatial Interpolation/Surface fitting.

Thiessen pol= ygons were effectively a way of defining a field based on discrete data, by associating with each point the precipitation at the nearest gage. This is probably the simplest and = least sophisticated form of spatial interpolation. ArcGIS provides other spatial interpolation capabilities under the Spatial Analyst à Interpolate to Raster functions, as well as in the Interpolation toolbo= x in Spatial Analyst Tools.

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We will not,= in this exercise, concern ourselves too much with the theory behind each of these methods. You should however be aware that there is a lot of statistical theory on the subject of interpolation, which is an active area of research. This theory should be considered b= efore practical use of these methods.

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Select Spatial Analyst à Interpolate to Raster = à Spline.= Use the input points from "Pr= ecipStn" and Z value field as " AnnPrecip_in", and set the spline type as Tension with default parameters as follows:

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The result is illustrated:

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Select Sp= atial Analyst > Zonal Statistics… Set the inputs as follows:<= /span>

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Click OK. A table with zonal statistics is displayed. This contains stat= istics of the value raster, in this case mean annual precipitation interpolated us= ing a tension spline over the zones defined by the polygon feature class Subwatershed. Determine the mean precipitation f= or each subwatershed in the SanMarcos Subwatershed feature class from the zone= spline.mean column.

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To turn in: A table giving the HydroID, Name, = and mean precipitation by the Tension Spline method for each subwatershed in the SanMarcos Subwatershed feature class. Which subwatershed has the highest mean precipitation using a Tension Spline interpolation?

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Experiment w= ith some of the other methods available (Natural Neighbor, Kriging, Inverse distance weighting) to see if you like them.

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To turn in. A layout = giving a nicely colored map of the interpolated mean annual precipitation surface = over the San Marcos Basin for one of the methods used and a table showing the me= an annual precipitation for the same method in each Subwatershed. Report what method you used.

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8. Runoff Coefficients.

Runoff ratio, defined as the fraction of precipitation that becomes streamflow at a subba= sin outlet is a useful measure in quantifying the hydrology of a watershed. Mathematically runoff ratio is def= ined as

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w =3D Q/P

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where Q is streamflow, and P is precipitation. In this formula, P and Q need to be in consistent units such as depth per unit area or volume. In exercise 2 we analyzed the average streamflow at the eight monitoring point= s in the San Marcos watershed. The= flow field in the Monitoring point dataset gives this data, in ft³/s.= To convert these to volume units (= say ft³) they should be multiplied by the number of seconds in a year (60 x 60 x 24 x 365.25). In the current exerc= ise mean annual precipitation has been evaluated for each subwatershed, in inches. To convert these to v= olume units (say ft³) these quantities should be multiplied by 1/12 ft= in^-1 and multiplied by the subwatershed area in ft². The subwatershed feature class inc= ludes subwatershed area, in the units of the spatial reference frame being used, = which are m². (Remember,= 1 ft =3D 0.3048 m). The necessary calculations are most easily performed in Excel. Use the Options/Export function to export the subwatershed featureclass attribute table that includes your Thiessen basin average subwatershed precipitation results to dbf format that can be read by Excel

<= /o:p>

<= /o:p>

<= /o:p>

Similarly ex= port the Monitoring Point featureclass attribute table that includes mean annual str= eamflow at each monitoring point. In = Excel multiply gage streamflow by 60 x 60 x 24 x 365.25 to obtain streamflow volu= me, Q, in ft³. Multipl= y subwatershed average precipitation (in inches) by subwatershed area (in m²)/(= 12 x 0.3048²) to obtain subwatershed precipitation volume, P, in ft3. On the maps you have that show subwatersheds and streams identify the subwatersheds upstream of each gauge. Add up the precipitati= on volumes over these subwatersheds then divide Q/P to obtain an estimate of runoff ratio for the watershed upstream of each stream gage.

<= /o:p>

To turn in. A table g= iving runoff ratio for the watershed upstream of each stream gage.=

Summary of Items to tu= rn in:

1. Hand calculations of slope at point= A using each of the three methods and comments on the differences.=

2. Table giving slope, aspect, hydrol= ogic slope, flow direction, D¥ slope, D¥ flow direction at grid cells A and B. Please al= so turn in a diagram or sketch that defines or indicates what each of these numbers means for the specific values obtained for cells A and B.

3. A screen capture of your final mod= el builder model.

4. A table giving the minimum and max= imum values of Aspect, Slope, Flow Direction and Hydrologic Slope (Percentage dr= op) for the digital elevation model in demo.asc.

5. The number of columns and rows, ce= ll size in the E-W and N-S directions in m, extent (in degrees) and spatial reference information for the = San Marcos elevation dataset DEM 'smdem_raw'.

6. The number of columns and rows in = the projected DEM. The minimum and maximum elevations in the projected DEM.&n= bsp; Explain why the minimum and maximum elevations are different from the minimum and maximum elevations in the original DEM.

7. A layout showing the location of t= he highest elevation value in the San Marcos DEM.

8. A layout with a depiction of topography either with contours, hillshade or sl= ope in nice colors. Include the streams from the San Marcos Basemap Flowline feature class and the outline of the SanMarcos Basin from the Basin feature class. =

9. A = table giving the HydroID, Name, mean elevation, elevation range and mean slope (in percent) of each subwatershed in the SanMarcos Subwatershed feature class.<= span style=3D'mso-spacerun:yes'> Which subwatershed has the highest= mean elevation? Which subwatershed= has the largest elevation range? = Which subwatershed has the largest mean slope?

10. A= table giving the HydroID, Name, and mean precipitation by the Thiessen method for each subwatershed in the SanMarcos Subwatershed feature class. Which subwatershed has the highest= mean precipitation?

11. A= table giving the HydroID, Name, and mean precipitation by the Tension Spline meth= od for each subwatershed in the SanMarcos Subwatershed feature class. Which subwatershed has the highest= mean precipitation using a Tension Spline interpolation?

12. A layout giving a nicely colored m= ap of the interpolated 2005 annual precipitation surface over the San Marcos Basin for one of the methods used and a table showing the 2005 annual precipitati= on for the same method in each Subwatershed.&= nbsp; Report what method you used.

13. A table giving runoff ratio for the watershed upstream of each stream gage.