Tutorial VII - Running LAHARZ

The LAHARZ program is used in ArcInfo which is a command-based GIS. We will use ArcInfo only for the execution of the model we will view the data in ArcMap.

From your PC, navigate to the network workgroup computer, "slush." Click on "gis." Click on Nicaragua. Click on LAHARZ. Copy all of the files to your workspace using ArcCatalog.

1. "Click on the Start Menu" on the Windows task bar. "Select: Programs à ArcGIS à ArcInfo Workstation àArc." ArcInfo will immediately load with a command prompt.

2. Type the following: "w workspace" with a space between w and workspace. "Press the return key." This will assign the directory to work with.

3. Type "&amlpath c:\workspace\laharzbeta" and "Press the return key." Type "&menupath c:\workspace\laharzbeta" and "Press the return key." These commands direct ArcInfo to the LAHARZ program.

4. Type "&r laharz" with a space between r and laharz. The first menu for LAHARZ will then load.

5. "Select Pick Stream" from the LAHARZ main menu. "Click Intersection of Stream and H/L Cone." "Click Continue." "Select hl400_g" under the Choose H/L Grid heading. "Select condir" under the Choose Flow Direction Grid heading. "Select confill" under the Choose Elevation Grid heading. "Select constr" under the Choose a Stream Grid heading.

6. A stream grid network will load on the screen. "Zoom into an area that has a stream crossing the H/L cone using the Zoom Window button". "Zoom in until you can select the stream cell just inside of the H/L cone boundary." "Select the Query Cell Button." "Click on the stream cell just inside of H/L boundary." "Click Take as Upstream Cell Value." "Click the Full View Button."

7. "Zoom in on the downstream end of the stream you chose." "Select the Query Cell Button." "Click on your stream cell near the boundary of the map." "Click Take as Downstream Cell Value." "Click the Full View Button." "Click the Continue Button".

8. "Select Create Lahar Inundation Zones" "Choose confill" under the Choose Elevation Grid heading. "Select condir" under the Choose Flow Direction Grid heading. "Enter a name for the drainage you selected." "Enter volumes into the last four white boxes" Use the following values: "62500, 125000, 250000, 500000" DO NOT USE COMMAS. If we were to actually run the model, the next step would be selecting continue. However, DO NOT SELECT CONTINUE. "Select the Quit Button." "Select the Quit Button again." The LAHARZ model takes more than an hour to run for this DEM. For the purpose of this tutorial, you will not need to run the model.

9. Type "q" at the ArcInfo command prompt. This will exit ArcInfo.

Hazard Zone Discussion

A hazard map is constructed based on probabilities. In practice, it is impossible to predict when a lahar will occur, and equally important, how big that lahar will be. Therefore, maximum and minimum values must be chosen to encompass all possible events. The maximum event represents the highest hazard to people and infrastructure, but has a low probability of occurring (i.e. these events happen, but very rarely). The smallest event has a very high probability of occurring (i.e. once every year or more), but they represent less of a hazard to people and infrastructure than the larger lahars. Thus, the hazards that lie between the minimum and maximum hazards represent the degree of hazard (Low to High).