GE 4150- Natural HazardsLab 7: Model mudflows and rainfall for Forest Falls California (Data taken from Spatial Analysis of Geohazards Using ArcGIS8 by William Harbert)Synopsis: We will be analyzing the Forest Falls mudslide which occurred in California. The mudflow killed one person, destroyed 15 houses, and damaged numerous houses andautomobiles. Mud and debris blocked the only road out of town for 18 hours. We are going to analyze the many factors contributing to this mud slide, including slope and barren slopes. In addition we are going to use Doppler radar to estimate water runoff and create a precipitation map. Points: This lab will be worth 20 points: 10 for the maps, 10 for the reportExercise Steps:1. Copy the exercise data from the Lab 7 folder on the class drive to your h: 2. Right click in the white space in ArcToolbox. Choose Environments, put in the following information: General Settings- Set the working directory to your h: (class folder)General Settings- Output Extent: Same as Layer “Elevation”Raster Analysis Settings- Cell Size: Same as Layer “ElevationRaster Analysis Settings - Mask: NoneClick Ok. Now your working directory has been set, and any new raster dataset we createwill have the same extent and cell size as the Elevation DEM. 3. Create a hillshade from the Elevation DEM and name hillshade in your h: (class folder).4. Steep slopes are a major factor for landslides. In this region slopes of 15 degrees or less are considered buildable. Stable material could begin to move between 33-35 degrees. We are going to calculate slope angles from the DEM. From the Spatial Analystmenu choose Surface Analysis>Slope. Select Elevation as your input surface and make sure the output measurement is specified in degrees. Name the output raster Slope and save in your h: (classfolder). Accept all other default settings and click Ok. Notice much of the area has very steep sleeps as high as 80 degrees which is almost vertical. Turn slope off when you are finished. 5. We would like to isolate the dangerous slopes, those equal to or above 35 degrees. Use the raster calculator and type in the following expression:SteepSlope = con(([Slope] >= 35),1) Again use all of the symbols and layers by clickingon them in the Raster Calculator. Symbolize the SteepSlope using a red color (or anothercolor you want) and set the transparency to 40%. In the expression ‘con’ means condition. The expression states that if the value is greater than or equal to 35 for Slope,then assign 1 to the output grid. For more information on the con function open the ArcMap help and search for con. 6. Zoom to the extent of the Study Area. The northern part of the study area shows roads in Forest Falls. The lower part of the study area shows the three creeks involved in the Forest Falls mudflow event: Bridal Veil, Slide Creek, and Snow Creek. Snow Creek is the watershed most affected by the mudflow. 7. Turn on the parcels layer. This shows residential parcels which were damaged by the mudflow. Parcels are symbolized from low (green) to high (red) damage. Notice the terrain upslope from the damage parcels has steep slopes greater than 35 degrees. 8. Turn off SteepSlope and turn on and expand Vegetation. Barren soils are very susceptible to erosion and landslide. We want to map these barren areas. Using select by attributes select barren areas from the vegetation layer. Choose the COVERTYPE field, choose unique values and choose BAR and create the expression. Create a layer from selected features and name the layer Barren. Turn off Vegetation and Barren. Turn on theFire Perimeters and note the proximity of previous fires to the town. When finished turn off the layer. 9. Turn off the hillshade. Turn on and expand the Rainfall layer. During the disastrous storm, the study area received more than 3 inches of rain in less than 2 hours. The Rainfall group layer contains Radar Summary and isohyets which are lines connecting points that receive equal amounts of rainfall (similar to contour lines representing topography). The Radar Summary raster shows rainfall in cubic inches that fell on each cell during the two-hour storm. We are going to convert the Radar Summary to represent volume in gallons. Open the raster calculator and type the following expression: RainVol = ([Radar Summary] / 12) * 0.3048 * 30 * 30 * 264.172Dividing the Radar Summary by 12 converts from cubic inches to feet. Multiplying the raster in feet by 0.348 converts it into meters. We then multiply by the cell size which is 30 by 30 meters. Multiplying by 264.172 converts cubic meters into gallons. Now RainVol shows the volume of rain in gallons that the area received during the 2-hour storm. Turn off RainVol and Rainfall. 10. Next we want to determine flow direction and accumulation, which will be determined from the DEM. First we want to ensure the DEM has no sinks, so we are going to fill it. Sinks and peaks are created in the DEM from errors due to the resolution or the rounding of elevation values. Essentially a pixel may have an elevation value which is very different from the surrounding pixels. In ArcToolbox expand Spatial Analyst Tools, and choose Hydrology tools. Open the fill tool. Choose Elevation as the input surface and save the output raster as FillElev. Leave other defaults and press Ok. Turn off FillElev and turn on Drainage. Drainage shows the three watersheds for each river. Turn off Drainage. 11. We now need to calculate flow direction for the Snow Creek watershed. Right click inthe white portion of ArcToolbox and choose Environments. Expand Raster AnalysisSettings and for the mask use SnowCreek. This step will allow all of our analysis to onlybe calculated for the extent of the Snow Creek watershed. Press OK. Now open the FlowDirection tool in the hydrology tools in ArcToolbox. Choose the FillElev as the input raster. Save the output raster as DirSnCrk. Leave other defaults and click OK. 12. A raster is created off flow direction from each cell to its steepest downslope neighbor. The numbers represent the direction water would flow from a pixel; the direction is represented by colors and number shown below:Therefore you can see ridges which display flow direction in the west (violet) and to the east (black). The flow direction tool observes each pixel and the elevation of the pixels around it to determine the flow direction. Essentially a drop of water will move from the highest elevation to