Watershed. Topography. Soil. Hydrology

Transcription

1 Watershed Topography The Egley Complex occurred within the Silver Creek watershed and Silvies River watershed both of which drain into the Oregon closed basins of Harney and Malheur Lakes. Most of the Egley Complex is on a dipping plateau region that generally tilts to the south. The plateau landscape is undulating to rolling with numerous broad, open flats streaked by gently sloping draws of timber. This general topography is broken occasionally by deeper drainages and isolated mountain peaks and buttes. Elevation ranges from almost 6,000 feet at Green Butte to approximately 4,200 feet where Gove Canyon exits the burn area at the far southeast corner. Slope gradients range from 0 to above 90 percent. Slope gradients are mainly in the 10 to 20 percent range with only about 5 percent of the burn area on slopes of 35 percent or greater. About 425 miles of streams occur within the Fire perimeter and have been classified by Inland Native Fish Strategy (INFISH). Refer to the Fisheries section for more information on streams. To better assess the effects of the Egley Complex fire, 7th level subwatersheds were delineated for: Blue Creek, Stinger Creek, an unnamed tributary to Stinger Creek, Spring Creek, Delintment Creek, the upper reaches of Mutton Creek, and the upper reaches of Dodson Creek. These watersheds are of particular concern due to high burn severity. Soil Soil resources are described in Chapter 3 under Issue 2, Soils. Hydrology Hydrology in the Silvies River basin is dominated by snowmelt runoff in early spring and precipitation in the form of convective storm cells during the summer (May-Aug). Average total annual precipitation at Burns is about 11 inches per year, both as rain and snow. The recovery for non-woody vegetation on the Egley Complex is estimated at approximately 1 year for low severity burn areas, 2 to 3 years in moderate severity burn areas and at the earliest 3 years (more likely 5 to 10 years) in high severity burn areas. Vegetative recovery rates would depend upon precipitation rates and timing, existing seed banks, and topsoil condition. Flood potential would decrease as vegetation reestablishes, providing ground cover, increasing surface roughness, and stabilizing and improving the infiltration and water storage capacity of the soils. Woody material was observed in stream channels and is an important natural component stream system in the Egley fire area. Despite the presence of woody material, the channels can efficiently and rapidly transport sediment and water during rainfall and snowmelt events. Fire Severity Ratings were categorized from Debano, et al. 1998: Low - Low and unburned fire severity areas are characterized by incomplete consumption of both canopy and ground fuels and contain adequate effective 3-69

2 Environmental Assessment ground cover to protect the site from accelerated levels of soil erosion. The overstory is mostly green with limited scorch, the litter layer is scorched with black ash retaining the structure of needles and leaves; depth of ash was 1 2 inches with the litter intact below it. Woody debris is partially consumed or charred. Mineral soil is not changed. Fire severity in forest ecosystems is low if the litter and duff layers are scorched but not altered over the entire depth. The surface is mostly black in a shrubland or grassland ecosystem, although gray ash is present for short times. Low soil heating, or light ground char, occurs where litter is scorched, charred, or consumed, but the duff is left largely intact, although it can be charred on the surface. Soils are typically only hydrophobic at the mineral soil surface in unburned soils and soils burned at low severity. Soil temperatures at 1cm are less than 50C. Lethal temperatures for soil organisms occur down to depths of about 1 cm. Moderate - Moderate fire severity areas are characterized by partial consumption of both canopy and ground fuels. The tree needles were scorched and have turned brown. These needles will eventually fall off the trees and provide some ground cover after the fire. Ash color is mostly gray to black, depth is 2 3 inches, and some effective ground over remaining. Woody debris is mostly consumed, except for logs, which are deeply charred. On shrubland or grassland sites, gray or white ash is present and char can be visible in the upper 1cm of mineral soil, but the soil is not altered. Moderate soil heating, or moderate ground char, occurs where the litter on forest sites is consumed and the duff is deeply charred or consumed, but the underlying mineral soil surface is not visible altered. Some hydrophobic soils were found in these areas but were less than in the high areas. Light colored ash is present. Soil temperatures at the 1cm depth can reach 100 to 200 C. Lethal temperatures for soil organisms occur down to depths of 3 to 5 cm. High - High severity areas are characterized by complete consumption of canopy and ground fuels, black to white ash 1 3 inches thick and minimal effective ground cover remaining. All shrub stems are consumed and only the charred remains of large stubs may be visible. Logs can be consumed completely or deeply charred and deep ground char can occur under slash concentrations or burned logs. High soil heating, or deep ground char, occurs, where the duff is completely consumed and the top of the mineral soils is visible reddish or range on severely burned sites. Color of the soil below 1 cm is darker or charred from organic material. The char layer can extend to a depth of 10cm or more. Soil textures in the surface layers are changed and fusion evidenced by clinkers can be observed locally. Soil temperatures at 1cm are greater than 250 C. Lethal temperatures for soil organisms occur down to depths of 9 to 16 cm. Estimated Runoff It is anticipated the there would be an increase in surface runoff due to the Egley Fire, particularly in severely burned watersheds. Burn severity within each of the delineated watersheds was overlain on the soil resource inventory using GIS. The hydrologic soil group-burn severity combination was determined for each watershed and each combination was assigned a corresponding runoff curve number. The curve numbers were determined using tables in Urban Hydrology for Small Watersheds (USDA-NRCS 3-70

3 1986) for unburned areas assuming antecedent moisture condition II or average soil moisture conditions. Hydrologic changes from the loss of soil cover (forest floor) were adjusted by increasing the curve number. Initial erosion of ash and surface soil during the first storm events would reduce slope roughness by filling depressions above rocks, logs, and remaining vegetation. The ability of the burned slopes to detain water and sediment would be reduced accordingly. This would increase the potential for flash floods and would increase the distance that eroded materials are transported. Overall water infiltration would be reduced. There are several factors that would expedite a quick recovery in terms of normal hydrologic response on some hill slopes. Absence of extremely steep slopes lessens the potential energy for erosion. Needle cast beneath forest canopies on low and moderate burn severity sites would provide some soil cover and promote water infiltration. The existence of unburned fine roots from grasses and forbs in the low and moderate severity burn areas just below the surface would likely aid plant recovery, and suggests there still might be a seed source for natural vegetation recovery. The major concern for vegetative and hydrologic recovery is in the high severity burn areas. Post-fire conditions have been assessed to determine how fire-induced changes to slope hydrology and soil conditions would impact the values at risk. Key to this assessment is the burn severity mapping. The analysis watersheds were in the most severely burned area. There was no significant hydrophobic development in the soils (see soil section for more information about water-repellency). The runoff curve number (RCN) model WILDCAT4 (Hawkins and Greenberg, 1990) was used to estimate pre- and post-fire runoff by small watersheds. The model uses NRCS Curve Numbers to predict runoff in a timed pattern from design rainstorms, and uses triangular unit hydrographs to route the rainfall excess to make hydrographs. There is no channel routing involved (Hawkins and Greenberg, 1990). The model utilizes the curve number information for each watershed along with the design storm information and the time of concentration information to estimate runoff from the watersheds. The model predicted pre- and post-fire estimates of peak flood flows for the design storm of 0.6 inches in 30 minutes with a return interval of 10 years. These results are most applicable during the first year of recovery, as hydrologic response would decrease in subsequent years as vegetation recovers. Based on the Wildcat4 model, post-fire flow increases range from approximately 4.5 times greater than pre-fire flows to more than 30 times greater than pre-fire flows. Only the most severely burned watersheds were analyzed. Water Quality Elevated water temperatures lead to lower dissolved oxygen concentrations and can be harmful to aquatic life. The Oregon Department of Environmental Quality has determined that the seven-day-average maximum temperature of a stream identified as having Lahontan cutthroat trout or redband trout use in the Malhuer Lake subbasin may not exceed 20.0 degrees Celsius (68.0 degrees Fahrenheit). Table 3-9 below summarizes the water quality limited creeks within the Egley Fire perimeter, their status, and the year action was taken. Currently, there is insufficient data to determine whether Emigrant 3-71

4 Environmental Assessment Creek requires a TMDL (Total Maximum Daily Load) or is eligible for 303(d) listing due to exceeding temperature. USGS 4th Field HUC Record ID SILVER SILVIES SILVIES Table 3-9 Water Quality Limited Creeks in Egley Fire Perimeter Name LLID Parameter Status River Mile Dodson Creek to 8.4 Emigrant Creek to 17.2 Emigrant Creek to 17.2 Flow Modification Flow Modification Temperature limited; not needing a TMDL limited; not needing a TMDL Insufficient Data Assessment: Year and Action 2002 Delisted - limited, not a pollutant 2002 Delisted - limited, not a pollutant 1998 added to database Source: Oregon Department of Environmental Quality 2004/2006 Integrated Report Database, March 10, Effects to Watershed Effects to soil resources as it relates to compaction and displacement are described in Chapter 3 under Issue 2 Soils. This section describes effects to soil resources as it relates to hydrology, runoff and water quality. Overlap of effects is inevitable and the reader should be familiar with this section as well as the soils section to get a full understanding of the effects. Direct and Indirect Effects of the Proposed Action Alternative Existing postfire logging studies conclude that site characteristics would generally have a profound influence on whether significant sediment is produced by logging operations. For example, fire salvage logging impacts to soil resources largely depend on the logging system, site characteristics such as soil texture, rock and gravel content, infiltration rates, ash content, slope, spring runoff, and postfire storm intensities. In the Summit fire in Eastern Oregon, despite high wildfire severity, a combination of several factors probably contributed to relatively low levels of soil disturbance and sediment transport observed in the harvest areas. These factors included: 1) low slopes; 2) low to moderate risk soils; 3) no new roads; (McIver, 2003). These factors are very similar to the Egley Fire site conditions and logging methods, with the exception that machinery would primarily remain on existing roads, only leaving the road when all other options have been exhausted. Additionally, vegetation will have one growing season to improve soil cover. In another study, soil erosion in burned areas was more strongly correlated with slope, ground litter and herbs, and surface rock fragments rather than with the actual logging activities (Stabenow, et al, 2006).Overall, the current literature suggests that the primary 3-72

5 factors affecting detrimental soil disturbance in postfire salvage harvest are existing site characteristics, harvest season, harvest area slope, and harvest method. The site characteristics, slope, and harvest method in the Egley project area would not have significant impacts on soil resources. Existing conditions are primarily the result of the fire with some lingering effects of past activities. Because machinery would remain on the roads, roadside harvest would not significantly change or impact existing soil conditions. Soils information for erosion associated with salvage activities was taken from the two National Forest soil resource inventories and field data collection. The information on these soils was used to help model skid trail erosion rates using the Forest Service Watershed Erosion Prediction Project s (FS WEPP) Disturbed WEPP Interface. This interface utilizes the power of a large physically based erosion model, but simplifies the data requirements to make using the model easy and relatively quick. The data requirements are climate station, soil texture, rock fragments, gross vegetation type, percent ground cover, slope gradients, slope horizontal length and land treatment. Average pre-fire or unburned erosion rates were less than tons per acre per year. A ten-year recurrence interval was modeled for runoff for annual erosion rates and was used to indicate post-salvage changes. Even though model inputs anticipated a worst-case scenario for disturbance, there would be no significant increase in erosion due to harvest activities. Although the vast majority of harvest area occurs on slopes of 10% or less, there are occasional opportunities to cable logs on steeper slopes. Therefore, the WEPP Disturbed Interface was also used to estimate slopes with a 35% grade, the maximum harvest grade. It is unlikely any harvest would actually occur on slopes this steep, however it was deemed prudent to anticipate a worst case scenario. Some erosion would occur, but would be due to fire effects, not harvest activities because no skidding would take place on these slopes. Average pre-fire or unburned erosion rates were less than tons per acre per year. A 3 year recurrence interval was modeled for runoff for annual erosion rates and was used to indicate post-salvage changes. It is assumed that 3 years is sufficient for ground covering vegetation to recover. Results indicate a 1.46 ton/acre/year erosion rate, all due to fire effects. Cabling logs that have been limbed would not have significant impact on soil resources. Even though model inputs anticipated a worst case scenario for disturbance, there would be no significant increase in erosion due to harvest activities. Due to the low gradient slopes in the proposed harvest areas and mitigation measures in the project design, erosion due to salvage activities would not exceed forest standards or become an issue. The high rock and gravel content common to the soils within the Egley Fire boundary resist erosive energy. However, erosion due to the fire would likely occur, especially in areas of high burn severity, steep slopes, and where vegetative ground cover was consumed. Erosion would be a direct result of the hydrologic response to the fire described above in the hydrology section. Although the fire would increase erosion rates, there would be no significant increase in erosion rates due to skid trails or other associated harvest activities. In the rare event machinery does leave the road, primary concerns would be compaction and displacement, not erosion. 3-73

6 Environmental Assessment Direct and Indirect Effects of the No Action Alternative Impacts to soil resources would be only from the fire, as no equipment would traverse the landscape adjacent to roads where hazard trees would be felled. These impacts are the same as was described above. The only detrimental land disturbance would be from the existing roads, as described above in the Proposed Action alternative. The No Action alternative would not directly affect current existing conditions or the ecological processes that naturally occur following wildfire. Direct and Indirect Effects of Alternative Two Impacts to soil resources would be only from the fire, as no equipment would traverse the landscape adjacent to roads where hazard trees would be felled. These impacts are the same as was described above. The only detrimental land disturbance would be from the existing roads, as described above in the Proposed Action alternative. Hazard trees that are felled and left on the ground would remain there for decades, unless another large fire consumes them similarly to the way the 2007 Egley Fire burned the downed logs of the 1990 Pine Springs Fire. The climatic conditions in the Egley Fire area are cold and dry, inhibiting the decomposition of the downed logs. The downed logs would not contribute significantly to soil organic matter, soil productivity, or soil structure within a human time frame. Cumulative Effects Common to All Alternatives The primary and most extensive impacts to soil and water resources in the Egley Fire area would be from the fire itself as described above in the Proposed Action alternative. Overall effects to soil and water resources from project activities would not be significant or exceed forest plan standards. Furthermore, it would be difficult to differentiate cumulative impacts between the fire and project activities due to: Large fire area Small project area No new road construction Low gradient slopes Machinery would rarely leave the road prism Some limited restoration work was completed under the Burned Area Emergency Response (BAER) protocol in an attempt to mitigate some of the fire damage to soil and water resources (See Appendix B for a full listing of potential cumulative actions). The work was done from August 2007 through November This BAER work included: Installation of in-stream structures (temporary hay bale dams) to slow water velocity and catch sediment. In-channel tree felling to slow water velocity and catch sediment. Aerially seeding more than 2,000 acres to establish vegetative ground cover in severely burned, high-risk erosion areas. Repairing a headcut to prevent further upstream erosion through a severely burned meadow. 3-74

7 Heli-mulching a high risk erosion area that could potentially deliver sediment directly to redband trout habitat. Road maintenance and repair to improve drainage. Combined with mitigation measures integral in the project design, the BAER restoration work would further mitigate fire effects to soil and water resources. There would be no significant effects that result from postfire project activities. Future commercial harvesting within the Green Ant project area in Emigrant Creek Watershed is not expected to significantly contribute to soil and water impacts because INFISH RHCA buffers would be utilized and all activities are designed to meet Forest Plan standards. Photo Blue Creek 3-75