We used cosmogenic 10 Be to measure erosion rates over 10 k.y. time scales at 32 Idaho mountain catchments, ranging from small experimental watersheds (0.2 km 2) to large river basins (35 000 km 2). These long-term sediment yields are, on average, 17 times higher than stream sediment fluxes measured over 10-84 yr, but are consistent with 10 m.y. erosion rates measured by apatite fission tracks. Our results imply that conventional sediment-yield measurements-even those made over decades-can greatly underestimate long-term average rates of sediment delivery and thus overestimate the life spans of engineered reservoirs. Our observations also suggest that sediment delivery from mountainous terrain is extremely episodic, sporadically subjecting mountain stream ecosystems to extensive disturbance.

IntermountainForest and Range rirnent Station m, UT 84401 General TechnicaiReport May 1983 This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain. Eliminate the last parenthesis Equation 17The first and i&t brackets in the denominator are backwards Line 52, 1st Column 28.3 instead of 20.3 - Most stream habitat evaluation techniques currently in use today have not been tested to determine their validity in describing conditions and have been designed to optimize time rather than accuracy. The purpose of this report is to further standardize the way physical and biological attributes are measured and quantified and to shed light on the strengths and weaknesses of those attributes. This report discusses some of the environmental parameters that best measure and describe conditions existing in aquatic ecosystems. The precision and an estimation of the accuracy that can be expected when measuring many of these conditions are given.We are grateful to the Library Executor of the late Sir Ronald A. Fisher, to Dr. Frank Yates, and the Longman Group Ltd., London, for permission to reprint our table -19 from their book Statistical Tables for Biologicaf, Agriculture, and Medical Research (6th ed., 1974) The past decade has seen an increase in the number of studies evaluating the status and potential of streams as habitats for aquatic organisms. Stream inventories, monitoring, habitat research studies, assessments, channel and flow condition evaluations, and classification are used to evaluate this potential. The success or failure of these stream studies depends on the suitability, comprehensiveness, precision, and accuracy of measurements used to obtain the data upon which final interpretations are based. These interpretations have been used by planners and decisionmakers on the assumption that they were derived from measurements that truly described stream habitat conditions and the resulting biotic community.Within the past decade measurements of stream habitat conditions, such as velocity, depth, and cover, have been incorporated into models designed to indicate fish standing crops and to assist in evaluating impacts from land management activities. Binns (1979) developed a Habitat Quality Index to predict trout standing crops in Wyoming streams. The USDI Fish and Wildlife Service (Cooperative In-stream Flow Group) uses a cluster of aquatic habitat descriptors in a predictive model to quantify the effects of change in streamflow on fish survival. Their Aquatic Habitat Evaluation Team also has developed an Aquatic Habitat Evaluation Procedures model (HEP) and Habitat Suitability Index model (HSI) for obtaining data and interpretation for use in decisionmaking. Wesche (1974) developed a cover rating mode1 that is used on Wyoming streams to determine aquatic habitat conditions and fish standing crops. Cooper (1976) employed an aquatic habitat survey model to measure stream channel conditions for information needed for land us...

Abstract. In this paper, we conduct a reanalysis of methods and data used by Jones and Grant [1996]. Data from three small watersheds (60-101 ha) and three pairs of large basins (60-600 km 2) in Oregon's western Cascades were used to evaluate effects of timber harvest and road construction on peak flows. We could not detect any effect of cutting on peak flows in one of the large basin pairs, and results were inconclusive in the other two large basin pairs. One small watershed was 100% clear-cut, a second was 31% patch-cut with 6% of the area affected by road construction, and a third was held as a long-term control. Peak flows were increased up to 90% for the smallest peak events on the clear-cut watershed and up to 40% for the smallest peak flows on the patch-cut and roaded watershed. Percentage treatment effects decreased as flow event size increased and were not detectable for flows with 2-year return intervals or greater on either treated watershed. Treatment effects decreased over time but were still found after 20 years on the clear-cut watershed but for only 10 years on the patch-cut and roaded watershed. The results reported by Jones and Grant [1996] suggest much greater effects of forest practices on peak flows than reported elsewhere on both small watersheds and large basins. In this paper, we review the analytical methods used by Jones and Grant (hereafter J and G) and report on a reanalysis of their data. Small Watershed StudiesThe small watershed studies consisted of three drainages ranging in size from 60 to 101 ha on the H. J. Andrews Experimental Forest near Blue River in the western Cascades of Oregon. One watershed was maintained as a long-term control throughout the life of the study. After a calibration period (Table 1) the second watershed was 100% clear-cut and burned. Roads, comprising 6% of the watershed area, were constructed on the third watershed, followed by patch-cut logging and burning on three units covering an additional 25 % of the watershed for a total clear-cut area of 31%. J and G used hydrographs from control and treated watersheds paired by the same climatic event in both basins to assess treatment effects. Peak discharges were of primary interest, but storm volume, time of peak, and begin time were also 3393

A series of 75 non-bordered plots was used to measure surface erosion on granitic road cuts on forest roads in the mountains of Idaho. Erosion data were collected for four years following road construction. Erosion rates for the first winter period after construction averaged about five times greater than the average of erosion rates for subsequent seasons. Both mass and surface erosion processes were observed on road cuts with mass erosion particularly important during the first season after construction. Regression analysis showed slope gradient, slope aspect, ground cover density and snow-free period rainfall erosivity had statistically significant effects on erosion. Slope gradient was by far the most influential site factor affecting erosion but slope length had no affect. Three erosion control treatments -dry seeding, hydroseeding plus mulch, and terracing with hydroseeding plus mulch -were evaluated. Two treatments -dry seeding and hydroseeding plus mulchcaused statistically significant reductions in erosion. Dry seeding was the most cost-effective treatment on sites with deep alluvial soil. Elsewhere, hydromulching was the most cost-effective treatment. Further testing is needed to evaluate the effectiveness of erosion control treatments during the first period after construction. We were unable to discriminate between erosion rates on the moderately to highly weathered granitic rock included in this study. A discussion of the application of the study results is presented.

A study was conducted on two small watersheds in the Boise National Forest to determine the role of forest vegetation in maintaining more secure slopes in shallow, coarse-textured soils typical of the Idaho batholith. Both soil water piezometry and soil shear strength measurements were made in the watersheds. Results of the field studies and supporting analyses indicate that forest vegetation often provides a critical margin of safety. Woody vegetation growing on slopes of the batholith contributes to stability by root reinforcement, by soil moisture depletion from interception and transpiration, by regulation of snow accumulation and melt rates, and by soil arching restraint between tree stems. Conversely, removal of vegetation from a slope by timber harvesting or wildfire results in a loss or reduction of effectiveness of these stabilizing mechanisms. Loss of vegetative stabilization in turn can le^d to increased frequency of landslides as documented in this study. Management implications of the study are discussed. Suggested measures and approaches include more stringent controls on size and location of clearcut units, greater use of "vegetation leave areas" or buffer zones particularly along haul roads and next to streams, and construction of hydraulic structures that divert water away from critical areas.