Exercise: Erosion Mitigation on the Eighth Street Fire

By Charlla Adams, Boise State University

• Level: Intermediate to Advanced GIS skills

• Software: ArcView 3.x

• Extension: GeoProcessing extension

• Recommended: Do the Symbolize Eighth Street Fire Data exercise prior to doing this exercise.

This exercise can be adapted for ArcGIS software.

• 1. To use GIS to examine and model alternatives for mitigating erosion on the Eighth Street Fire area
• 2. To use theme-on-theme selection
• 3. To work with the Geoprocessing Wizard
• 4. To use the field calculator
• 5. To provide an example of a real world project using GIS
• 6. Create layouts showing the alternative methods for mitigating erosion

Introduction:

The following exercise uses GIS to examine the alternatives for mitigating erosion on the Eighth Street Fire area. Before proceeding read the Background document on the 8th Street Fire and the Eighth Street Data Dictionary to get an understanding of the data and its contents. Instruction for this exercise is minimal. You will be provided the criteria for the alternatives. Keep notes to turn in on the GIS process you used to produce the mitigation shapefiles.

This exercise assumes a working knowledge of the GeoProcessing extension, querying data, creating new shapefiles and theme-on-theme selection. If you need additional information concerning these skills use ArcView’s Help.

The instructor is provided with a project for possible ‘right’ answers to this exercise.

You will look for areas to mitigate erosion using the following alternatives:

• Aerial seeding
• Contour felling
• Tillage
• Straw wattles

Part I

Open ArcView and create a new project. Remember to save your project periodically.

A. To get started you will need to create a moderate-to-high erosion potential theme and a moderate-to-high burn theme. You will be using these themes in setting up the mitigation alternatives.

The high erosion potential theme is based on the soils shapefile. The areas with a high potential for erosion have slopes greater than 25% and the following soil types of basalt hills and structural basins, lake sediments, midslope batholith granitics and mountainous batholith granitics.

Create the moderate to high burn theme from the bis.shp.

Be sure and save these themes.

B. Aerial Seeding Alternative

Create and save an aerial seeding theme based on the following criteria.

The criteria for using aerial seeding are in burned areas of moderate to high burn intensity and have a moderate to high erosion potential.

C. Contour Felling Alternative

Create and save a contour felling theme based on the following criteria.

The criteria for contour felling are in burned areas of moderate to high burn intensity, previous tree cover, slopes between 35% and 70%, and have a moderate to high erosion potential.

D. Tillage Alternative

Create and save a tillage theme based on the following criteria.

The criteria for tillage areas are in burned areas of moderate to high burn intensity, slopes 20% to 35%, and have a moderate to high erosion potential.

E. Straw Wattle Alternative

Create and save a straw wattle theme based on the following criteria.

The criteria for straw wattle areas are in burned areas of moderate to high burn intensity and slopes greater than 35%.

Part II Clean Up

A. Alternative Attribute Tables

The alternative attribute tables of the alternative themes you created have information in them that is not pertinent to these themes. Go into the tables and delete the fields not pertinent to the new theme. Be sure and keep the Shape field, area field and perimeter field.

In ArcView the area and perimeter is not recalculated after geoprocessing the data. So be sure your map units are set in the View properties dialog box and then recalculate the area and perimeter using the following formulas in the field calculator:

For the area: [Shape].ReturnArea

For the perimeter : [Shape].ReturnLength

B. Calculate the number of acres for each alternative

Add a new field to the alternatives’ attribute tables called Acres. The field’s data type is numeric with three decimal places, and 25 characters wide.

To calculate the number of acres: Multiply the area (which is in square meters) by the conversion factor of 0.0002471054.

Part III Calculate mitigation acres by ownership

Objective:

• 1. To use the field calculator
• 2. To create statistics about the theme

A. Write a short report or create a spreadsheet to answer these questions.

• 1. Calculate the number of acres the BLM, the USFS, the State and private landowners would be responsible for in each of the mitigation alternatives.

Hint to start: create themes clipped by ownership. On the clipped themes recalculate the area and acres.

Part IV Layouts

A. Create four map layouts, one for each alternative. Print color 8.5” x 11” or as instructed by your instructor.

Conclusion:

This exercise has run you through the process of finding areas for the erosion mitigation alternatives. Now it is up to the team to put this information together with other evaluation criteria to come up with the mixture of mitigation measures to create alternatives for rehabilitation of the Eighth Street Fire area.

For further information on the evaluation criteria and benefit cost analysis for the Eighth Street Fire contact the Boise National Forest for the Interagency Fire Rehabilitation Report; Eighth Street Fire, September 6, 1996