This project is based on the Interagency Fire Rehabilitation Report on the Eighth Street Fire.
The Eighth Street Fire began August 26, 1996 in Military Reserve Park north of Boise. The fire quickly spread to several thousand acres pushed by strong southerly winds and record-breaking heat. The fire raced through brush and grassland on steep slopes, eventually burning into timberlands along the Boise Ridge. The Eighth Street Fire was contained on August 30 and controlled on September 2. By then 15, 300 acres adjacent to the city of Boise had been burned.
The fire burned through land owned or managed by the Bureau of Land Management, State of Idaho, Boise National Forest, Boise City, Ada County and private entities.
Teams of specialists from the different agencies surveyed and mapped the burned area, ground conditions and identified hazards to structures, property and life. Most of the slopes within the burned area had lost all vegetation cover and were at high risk for accelerated erosion. Some of the slopes were burned so severely that water-repellent soils developed.
The major concern from the fire was large debris flows and flooding into Boise’s north end and downtown corridor. Also at risk was the invasion of exotic weeds on slopes that lost vegetation. This change would increase the chance of future fires, decrease biodiversity and alter many ecosystem functions.
In an effort to begin immediate rehabilitation of the affected watershed four alternatives were recommended based in part on GIS (Geographic Information Systems). All the treatments were limited to the hill slopes. None of the alternatives would completely eliminate the risks to the City of Boise.
Alternative 1 was the “no action” alternative. Under this alternative no treatments would be undertaken on the burned area. Recovery would occur naturally.
Alternative 2 was a “Low Level of Rehabilitation”. Some of the measures to reduce erosion and sedimentation would include contour-felling, straw bale check dams, constructing drains, putting in culverts, aerial seeding with grass/forb/shrub mixture and planting bitterbrush. Additional measures were suggested to provide for recreational opportunities.
Alternative 3 was a “Moderate Level of Rehabilitation” and included all of the activities in Alternative 2 plus the following additional measures. Tillage on areas burned at a moderate to high intensity where slopes were between 25 and 35 percent. Addition of slope structures, straw wattles or straw bales, on slopes between 35 and 70 percent and a moderate to high burn intensity,
Alternative 4, “High Level of Rehabilitation”, would include the measures from Alternatives 2 & 3 plus contour trenching/terracing on areas burned at a high intensity.
The descriptions of the treatment measures include only the measures being mapped for the exercises.
Description: Logs, 8” to 14” diameter, terraced along the contour and used as barriers to overland runoff. They serve as sink to infiltrate overland flow back into the subsurface. Hand trenches are also constructed among the felled logs.
Purpose: The contour felled log barriers are an effective treatment for water repellent soils and in high intensity burned areas. They minimize soil erosion, stabilize the slope, capture sediments, and disperse concentrated water flow.
Description: Straw wattles are pre-manufactured rice or hay straw bundles. They are 25’ long, 8” in diameter and weigh 35 pounds. The straw wattles are spaced 25’ apart, checkerboard fashion along the contour of hillsides and approximately 150’ slope distance apart. They are held in place with wooden stakes.
Purpose: Straw wattles are used as a soil erosion and runoff control measure on granitic side slopes with a high degree of water repellency. They stabilize the slope, minimize soil erosion and capture sediment. The objective is to reduce the loss of soil productivity.
Description: Aerial seeding would be done in late fall early winter with a seed mixture know for erosion control.
Purpose: The objective of aerial seeding is to reduce erosion by increasing ground cover. The root systems of the plants assist in soil stabilization.
Description: Tillage practices are mechanical earthwork following the slope contours. The practices include discing, harrowing, drill seeding, ripping, anchor chaining and contour furrowing.
Purpose: Tillage practices mechanically breakup water repellant soil, prepares a seedbed, increases hill slope storage component and improves soil infiltration rates. This allows for better re-vegetation rates and reduces soil erosion and overland water flow.
This was a brief overview of the Eighth Street Fire. Detailed information concerning the affected environment, the effects of the alternatives and the Cost/Risk analysis can be found in the Interagency Rehabilitation Report Eighth Street Fire, September 6, 1996. Contact the Boise National Forest office for details on obtaining this report.
The data is provided courtesy of the Boise National Forest and Boise State University GeoSpatial Research Facility. They have been modified and simplified for use in this exercise. The reliability or suitability of this data cannot be guaranteed. Original data was compiled from various sources and the spatial information may not be accurate. This information may be modified without notification.