Example Application

The purpose of this exercise is to illustrate, step-by-step, how to use the major functionality available in the Arc Hydro tools for Raster Analysis. This is a hands-on document focusing on how, not why. There is little discussion on implementation or internal operation of a tool. This document is targeted to an experienced water resources ArcGIS user who wants to learn how to use the tools. The online help provides more detail on the tools operation.

In this exercise, the user will perform drainage analysis on a terrain model for the San Marcos Basin. The Arc Hydro tools are used to derive several data sets that collectively describe the drainage patterns of the catchment. Raster analysis is performed to generate data on flow direction, flow accumulation, stream definition, stream segmentation, and watershed delineation. These data are then used to develop a vector representation of catchments and drainage lines from selected points. The utility of the Arc Hydro tools is demonstrated by applying them to develop attributes that can be useful in hydrologic modeling. To accomplish these objectives, the user is exposed to important features and functionality of the Arc Hydro tools, both in the raster and the vector environments.

Computer and Data Requirements

To carry out this exercise, you need to have a computer, which runs ArcInfo version of ArcGIS with the Spatial Analyst extension. The data are provided in the accompanying zip file, Ex5data.zip, For UT Austin students, the files are located on the LRC NT network in the directory class\maidment\giswr\Ex5\. The data files used in the exercise consist of a shapefile from the Arc Hydro Network for this basin and the National Elevation dataset DEM grid generated from the NED archive for the San Marcos Basin.

All of the data being used is in the Texas State Mapping System (TSMS) Albers projection. The following files are required for this exercise and are stored in the file Ex5data.zip

Smdem grid file: the National Elevation dataset DEM grid generated from the NED archive for the San Marcos Basin .

A SanMarcos geodatabase containing the HydroEdge and Streamgage feature classes.

ArcHydrosetup folder: A folder with the needed executables to install the Arc Hydro tools. This folder contains the Setup.exe, the msxml.msi, and a readme file with the instructions to install.

Getting Started

Setting up the Arc Hydro Tools

Make sure the Arc Hydro tools are installed on the system. If not, run the Arc Hydro tools setup program. The first step is to see if the Arc Hydro toolbar is loaded. If the toolbar has already been added to the normal.mxd, it will be available to any new ArcGIS project, and this step is not be necessary.

1. Run the setup

The complete setup must perform 2 installations:

Arc Hydro Tools (Setup.exe)
XML Parser (msxml.msi)

Run the setup, setup.exe, by double-clicking on the file or using Add/Remove Programs.

Note: if a previous version of the Arc Hydro tools is already installed, the following window will be displayed.

To uninstall the previous version, use the function Add/Remove Programs in the Control Panel, select Arc Hydro Tools and click Change/Remove. Then follow the instructions from the Wizard to uninstall the tools.

Check the location where the tools were installed and make sure it is empty (note the directory will not be deleted). If some of the Arc Hydro tools dlls are still in the bin directory (ArcHydroTools.dll, ApUtilities.dll, ApFramework.dll or TimeSeriesManager.dll), unregister and delete these files before proceeding with the installation of the new version.

After double-clicking the setup, browse to the desired installation location (use default location): the files will be installed in the bin directory under the destination folder. Follow the instructions to complete the setup.

After installing the Arc Hydro Tools, the install prompts whether to install the XML Parser, that is required to run the tools. (That is, when prompted to install MSXML 3.0, say no).

· Select No

· Install MSXML 4.0 by running msxml.msi. Follow the instructions to complete the setup.

2. Open ArcMap and load Arc Hydro tools

· Open ArcMap. Create a new empty map, and save it as Ex5.mxd (or any other name).

· Right click on the menu bar to pop up the context menu showing available tools.

· If the Arc Hydro Tools menu does not appear in the list, click on “Customize”.

· In the Customize dialog that appears, check the Arc Hydro Tools box.

· You should now see the Arc Hydro tools added to ArcMap. You can leave it floating or you may dock it in ArcMap.

Note

It is not necessary to load the Spatial Analyst, Utility Network Analyst, or Editor tools because Arc Hydro Tools will automatically use their functionality on as needed basis. These toolbars need to be loaded though if you want to use any general functionality that they provide (such as general editing functionality or network tracing).

However, the Spatial Analyst Extension needs to be activated, by clicking Tools>Extensions…, and checking the box next to Spatial Analyst.

Dataset Setup

The existing data to be used in an Arc Hydro project can be stored in any geodatabase and loaded in the map. All vector data created with the Arc Hydro tools will be stored in a new geodatabase that has the same name as the stored project or ArcMap document (unless pointed to an existing geodatabase) and in the same directory where the project has been saved (your folder for Ex5). By default, the new raster data are stored in a subdirectory with the same name as the dataset or Data Frame in the ArcMap document (called Layers by default and under the directory where the project is stored). The location of the vector, raster, and time series data can be explicitly specified using the function ApUtilities>Set Target Locations.

Load the terrain data

· Click on the icon to add the raster data.

Note: raster data cannot yet be stored in a personal geodatabase: they must be stored in a directory.

· In the dialog box, navigate to the location of the data; select the raster file smdem containing the DEM for San Marcos and click on the “Add” button.

· The added file is listed in the Arc Map Table of contents. You can recolor the raster by going to the theme’s Properties/Symbology and choosing a new color ramp

· Save your ArcMap document where you want your results files to appear as SanMarcosBasin.mxd

Exploring your DEM

· Click on the icon to add the linear feature class data.

· In the dialog box, navigate to the data folder for this exercise; select the HydroEdge feature class containing the stream network for San Marcos and click on the “Add” button.

· The added file is listed in the Arc Map Table of contents.

In this exercise, we are going to use an integer elevation grid with values stored in centimeters. The original National Elevation Dataset has floating point grids with values in meters but it turns out that the San Marcos DEM as a floating point grid takes five times as much disk storage (42MB compared to 8.5 MB!) to store as a floating point grid rather than an integer grid, so we’re going to work in centimeters. If you want to convert the grid to floating point meters, you can use the Spatial Analyst Raster Calculator to convert it (use the >> button on the bottom right hand side corner of the menu to get the option for a floating point grid).

To explore the highest elevation areas in your DEM Select Spatial Analyst/Raster Calculator. If you don’t see the Spatial Analyst toolbar, go to View/Toolbars and click on Spatial Analyst. Double click on the layer smdem with the DEM for San Marcos. Click on the > symbol and select a number less than the maximum elevation (61599 centimeters). This arithmetic raster operation will select all cells with values above the defined threshold. In the example below a threshold of 55000 centimeters was selected for the Z pixel value of smdem.

A new layer called calculation appears on your map. The majority of the map (brown color) has a 0 value representing false (values below the threshold), and the red region has a value of 1 representing true (elevations higher than 55,000 centimeters).

Zoom in to the 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 label it with the elevation value for that pixel.

You can place the dot using the Draw toolbar. It seems that when you zoom out the dot does not show up in zoomed out view. If that is the case, just show the zoomed in view, as above.

Contours

Contours are a useful way to visualize topography. This can be done by using the Spatial analyst extension tool by doing the following:

Select Spatial Analyst > Surface Analysis > Contour…

Select the Input surface as smdem, leave the default parameters, and browse to your output folder. 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.

A layer is generated with de topographic contours for San Marcos. Notice the big difference in Terrain Relief 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 which lies the rolling Texas hill country and to the east the flatter coastal plain. There is even a tower located in the City of San Marcos on which you can stand and see these differences in topography to east and west!

Other option to provide a nice visualization of topography is Hillshading.

Select Spatial Analyst > Surface Analysis > Hillshade… and set the factor Z to a higher value to get a dramatic effect and leave the other parameters at their defaults. Click OK. You should see and illuminated hillshaded view of the topography.

To be turned in: A layout with a depiction of topography either with contours or hillshade in nice colors. Include the streams from NHD. Mark your point of highest elevation and indicate its elevation.

Terrain Preprocessing

Terrain Preprocessing uses DEM to identify the surface drainage pattern. Once preprocessed, the DEM and its derivatives can be used for efficient watershed delineation and stream network generation.

All the steps in the Terrain Preprocessing menu should be performed in sequential order, from top to bottom. All of the preprocessing must be completed before Watershed Processing functions can be used. DEM reconditioning and filling sinks might not be required, depending on the quality of the initial DEM. By doing the DEM reconditioning you can be sure any point on the NHD stream network will represent a cell (stream cell) for which you can process and compute attributes.

Be aware, some of the terrain processes may take some time to finish. Process like Filling Sinks and Flow accumulation took about 10 minutes to process on one of our computers, so please be patient!

1. DEM Reconditioning

This function modifies a DEM by imposing linear features onto it (burning/fencing). It is an implementation of the AGREE method developed at the University of Texas at Austin in 1997. For a full reference to the procedure refer to the web link http://www.ce.utexas.edu/prof/maidment/GISHYDRO/ferdi/research/agree/agree.html.

The function needs as input a raw dem and a linear feature class (like the river network) that both have to be present in the map document.

· Select Terrain Preprocessing | DEM Reconditioning.

· Select the appropriate dem (smdem) and linear feature (HydroEdge). The output is a reconditioned Agree DEM (default name AgreeDEM).

Click OK if you get the warning shown below.

This process takes about 5 minutes!

2. Fill Sinks

This function fills the sinks in a grid. If cells with higher elevation surround a cell, the water is trapped in that cell and cannot flow. The Fill Sinks function modifies the elevation value to eliminate these problems.

· Select Terrain Preprocessing | Fill Sinks.

· Confirm that the input for DEM is “AgreeDEM” (or your original DEM if Reconditioning was not implemented). The output is the Hydro DEM layer, named by default “Fil”. This default name can be overwritten.

· Press OK. Upon successful completion of the process, the “Fil” layer is added to the map.

This process takes about 10 minutes!

3. Flow Direction

This function computes the flow direction for a given grid. The values in the cells of the flow direction grid indicate the direction of the steepest descent from that cell.

· Select Terrain Preprocessing | Flow Direction.

· Confirm that the input for Hydro DEM is “Fil”. The output is the Flow Direction Grid, named by default “Fdr”. This default name can be overwritten.

·&nb