Water quality and quantity effects from clearcutting
o Increased sedimentation, nutrient loading
o Increased stream temperature
o Injury to fish, amphibian and other wildlife population
o Water yield changes:
o Increased high flows from storms and spring run-off
o Decreased low flows in summer, negatively affecting riparian & aquatic habitat
Supporting quotes from experts:
"Water quality characteristics most affected by timber harvesting are: (1) sediment (2) dissolved nutrients . . . and (3) water temperature."(20) Undisturbed forests are generally low in dissolved or suspended matter (except during floods); sediment loads and dissolved nutrients generally increase with the level of disturbance to the forest. Timber harvesting adjacent to stream channels increases sediment flows into streams, and can affect the temperature of the stream, because it removes the streamside vegetation that buffers the stream. (Backiel and Gorte, Report to Congress on Clearcutting)
Logging and related activities such as road building, skidding, slash burning, and others have the potential to produce erosion that can deliver sediment and nutrients to streams. (Foster Wheeler, 69)
Use of the soil resource for timber harvest has altered some characteristics of the soil and made it more susceptible to erosion (Poff 1996). (Foster Wheeler , 21)
Bates and Henry conducted a 15-year study on the effects of clearcutting in Colorado snow-zone watersheds. Their results were similar to many other studies, from the Paulini brothers [in 1607] to the present-cutting increases peak flows and increases sedimentation [in] watersheds. (Euphrat, 14)
Harr et al. found that clearcutting increased storm runoff in coastal Oregon watersheds. (Euphrat, 56)
Clear cutting has devastating impacts on salamander populations. This has been documented in the scientific literature, in particular by Professor James Petranka and co-workers. There is also unpublished data existing in forest service reports concerning the effects of clear cutting on salamander and other vertebrate populations in New Mexico forests. There is extensive information available from Forest Service scientists in Arcata, Ca about clear cutting in the Pacific Northwest. (Dr. Wake, personal email)
The effect of riparian zone trees on stream temperature has been documented in the Pacific Northwest (Meehan et al. 1977). There is very little information about the specific function of shade in the Sierra Nevada, although several authors have extrapolated the results of studies from the Pacific Northwest. For this analysis, we assume that temperature can be affected by lack of shade during the summer. (Foster Wheeler, 38)
Effects as Documented by ERA [Equivalent Roaded Area] Assessment Levels:
Significant effect: Impact scores will be high in basins that receive a concentration of clearcutting and have a higher than average road concentration.
o No effect: Areas with low road density or dominated by selective harvesting will continue to have low scores. (Euphrat, 97)
Bare ground and equipment-operated ground:
Bare ground is a potential source area for stream sedimentation, because machine-operated ground creates surfaces of relatively lower permeability over which overland flow is more likely to carry sediment. (Euphrat, 69)
Significant differences were found between the clearcut and selectively harvested sites All of the sites had been tractor-harvested Most notably, clearcut sites had significantly more equipment-operated ground than selective-harvest sites .[T]ransects of harvest areas showed a difference in the amount of bare ground between selection and clearcut sites, significant at the 90% level indicative of probable source areas for sediment transport. (Euphrat, 70)
[Study of harvest method and amount of bare ground] suggests that, per unit of ground, the potential for stream channel effects from surface soil erosion is greater on clearcuts. (Euphrat, 100)
Change in water yield in the Mokelumne watershed (Calaveras County, CA):
Increases in Peak flow and heteroscedasticity
Peak flows were seen to increase in response to extreme events over time; low flows decreased over the same period.
From EBMUD's Protecting the Mokelumne
The impacts of high flow volume include:
o River basin and shoreline scouring
o Sediment transport to Pardee Reservoir, displacing water supply storage and adversely impacting water quality (turbidity, copper compounds)
o Increased plant by product (nitrogen and phosphorus) volumes entering Pardee Reservoir, accelerating eutrophication
o Higher water temperatures in flows to Pardee, compromising programs to enhance fish habitat conditions in Pardee, Camanche, and the Lower Mokelumne River. (EBMUD, 11)
For the Middle Fork of the Mokelumne, Blanchard has already suggested that, for the period 1930 to 1960, total water yield increased. He attributed this to the removal of vegetation by timber harvesting, and anticipated an increased water yield of 4 to 6 inches, or 20%. (Euphrat, 45)
Euphrat found that the 20% increased yield that had occurred, according to Blanchard, continues still. What is notable, however, is the increased spread (heteroscedasticity) of the data; lows are lower and highs are higher The increase in variation over time appears to be most marked beginning at water year 1971 [current Forest Practice Rules began in 1972] [O]ver this period of time, the streams are producing both more water in wet years, and less water in dry years. Interestingly, this effect of timber harvesting was a principal argument for conservation at the turn of the century, and a reason for which the reservation of forest area was justified by the fledgling Forest Service. (Euphrat, 46-47)
Euphrat's analysis of residuals from the rainfall-runoff relationship for large storms in the Middle and South Forks of the Mokelumne indicates that runoff is getting greater over time, with a significance at the 99% level or higher These data indicate that, over time, these streams are increasing their total flows per storm by many percent
It has been shown that timber harvesting has occurred during this time span, and that the cumulative timber harvesting acreage tracks with time. Road density also increased to present levels between 1930 and 1975, and road maintenance and rebuilding have also paralleled timber harvesting. It is tempting to attribute the increase in large-storm runoff to other factors that track with time, but little else has occurred in these watersheds of such significance to the hydrologic environment. Thus, time serves as a useful proxy variable for the suite of activities that is road-based logging.
Euphrat's data show that runoff from large storms in the Mokelumne watershed has significantly increased over the period 1930-1980, the period in which these basins experienced timber harvesting and roadbuilding activities. Because the effect does not appear to be flattening over time, the change in runoff characteristics may well be tied to timber harvesting as well as road densities. Timber harvesting affects runoff by its reduction of vegetation cover and subsequent impacts on the snow pack. It may be fair to say that more recent timber harvesting, affecting annually and cumulatively greater and greater areas, combined with roads, skid trails, and tree removal, is creating progressively greater runoffs from large storms, with the largest storms displaying the greatest increase of runoff.
Hewlett and Helvey found similar results on a 108 acre watershed in North Carolina, and attributed the increase in quickflow to increased runoff from saturated surfaces. Harr et al. found that clearcutting increased storm runoff in coastal Oregon watersheds. (Euphrat, 56)
The increased runoff and high significance in the extreme portions of this storm population show that peak flow changes in the mid-elevation Mokelumne are greatest during extreme events. This could be due to sediment additions from roads, from the change in runoff created by forest openings, or from the road surfaces themselves. The warm rain-on-snow storms, the topography, and the dense road network all make the Sierra different from other regions. Clearly, more research is needed in this region, on both control and treated watersheds, to determine the relative contribution of each of these variables to peak runoff events and sediment transport. (Euphrat, 57)
The weekly low-flow data from Forest Creek and the South Fork Mokelumne showed decreases over time significant at the 95% level. (Euphrat, 60)
The lowering of the lowest weekly flows, significant on Forest Creek at the 95% level, and on the South Fork at the 99.99% level, is important in terms of the riparian and aquatic habitats available in the streams of the lower Mokelumne watersheds. For fish and other aquatic species, decreased low-flows reduce available living area and increase temperatures through lack of dilution. For riparian species, low-flows change habitat close to stream channels and allow more species that cannot tolerate perennial flooding to live adjacent to the stream. For people and animals, it restricts the amount of water available for consumption and lowers its quality, through heat and associated eutrophication. (Euphrat, 60)
Small streams appear to be most affected by and the least able to recover from this phenomenon. (Euphrat, 101)
Observation of stream channels, as was conducted in the watershed survey, suggested that low summer flows in smaller channels are more discontinuous now than under original conditions It appeared that a small stream, unprotected, would rapidly move from perennial to ephemeral, or from Class I to Class III under California Department of Forestry definitions. (Euphrat, 60-61)
-Large Storms: Total quick runoff from storms has gotten larger over the period 1941-1990 (the period of record for this study), with significance at the 99% level or greater. Storm temperature and rainfall intensity are not correlated with this time period, although road mileage and harvested area are. Increased peak flows may decrease streambank stability, and are a serious geomorphic concern in linear, unstable alluvial basins such as Forest Creek.
Long-term fishery effects: Low flows are becoming lower, leading to elevated water temperatures Compound effects on Forest Creek and parts of the Middle Fork are also significantly changing the shape of the stream channel and its banks
Significant effect: Elimination of anadromous fishery; severe reduction of local cold water fishery. (Euphrat, 95)
Recommendations to SPI in the Foster Wheeler report
Over time, develop a monitoring plan that integrates implementation monitoring, effectiveness monitoring, and adaptive management This monitoring plan can also address any potential future issues related to use of the clearcut silvicultural system. There are two items resulting from this assessment that could be addressed in a monitoring plan. These items are:
o The use of the clearcut silvicultural method would likely result in greater water runoff from individual timber harvest units. While this greater area of clearcuts would be unlikely to affect significant peak flows or rain-on-snow events, there is some potential for increased sediment delivery from some units either to roads or across WLPZs. The management recommendations for roads in this watershed assessment should minimize potential sediment delivery from that source . The monitoring plan should address the continued effectiveness of WLPZs under the clearcut silvicultural prescription.
o Though the Upper Mokelumne watershed is considered to be relatively stable, there is some potential for localized increases in mass wasting when the clearcut silvicultural treatment is used in areas of steepest slopes . The monitoring plan should assess whether the implemented screening and measures are effective at minimizing mass wasting. Adaptive management will provide the opportunity to address the effectiveness of implemented mitigation measures. Monitoring may identify problems with implementation or it may identify that certain measures are unnecessary to protect watershed resources. (Foster Wheeler, 111)
From EBMUD's Protecting the Mokelumne
Poor timberland management and maintenance practices could send sediments and nutrients to the lower river, harming water quality and fish. (EBMUD, 2)
from CCWD and CPUD's. UPPER MOKELUMNE RIVER SANITARY SURVEY. December 2000:
o Logging activities pose a potential threat to surface water quality because it promotes erosional transport of sediment into the waterbodies as well as animal wastes. Increased sedimentation and turbidity impedes the effectiveness of disinfection processes. (Tetra Tech, 5-9)
Cumulative Environmental Impact of Road Logging:
As we appreciate the suite of impacts that affect the land, recall that one set of impacts may begin before a previous set has finished, and that road systems and large tree removal are essentially permanent changes. Recall also that water-driven sediment transport tends to occur watershed-wide at virtually a single instant; the largest storms will entrain most of the material that can move. Following storm driven removal of unstable landings and fills, human actions move still more material from stable areas into inherently less stable areas, as they rebuild the road and landing system. The action of flushing sediment, via precipitation, and re-destabilizing the landscape, through human agency, is part of the road logging system. (Euphrat, 24-25)
Cumulative watershed impacts are the result of disturbance, first, and the interplay of sediment and water, second. (Euphrat, 26)
Major sources cited:
o Backiel, Adela and Gorte, Ross W. Congressional Research Service Report for Congress: Clearcutting in the National Forests. July 29,1992. http://forestry.about.com/science/forestry/gi/dynamic/offsite.htm?site=http://www.cnie.org/nle/for%2D2.html
o East Bay Municipal Utility District. Protecting the Mokelumne River: A District's Response to the Proposed Divestiture of PG&E's Mokelumne River Project. Available through the East Bay Municipal Utility District website
o Euphrat, Frederick D. Cumulative Impact Assessment and Mitigation for the Middle Fork of the Mokelumne River, Calaveras County, California. A dissertation submitted in partial satisfaction for the degree of Doctor of Philosophy in Wildland Resource Science in the Graduate Division of the University of California at Berkeley, 1992.
o Foster Wheeler Environmental Corporation. Watershed Assessment Upper Mokelumne River, Volume I-Watershed Assessment; Prepared for Sierra Pacific Industries. August 2000
o Sierra Business Council. Sierra Nevada Wealth Index: Understanding and Tracking our Region's Wealth;. 1999-2000 Edition. 1999
o Sierra Nevada Forest Plan Amendment - FEIS Volume 2, Chapter 3, part 5.2. Affected Environment and Environmental Consequences
o Tetra Tech, Inc. UPPER MOKELUMNE RIVER SANITARY SURVEY, Final REPORT. Prepared for Calaveras County Water District and Calaveras Public Utilities District. December 2000.