Improving Road Erosion Modeling for the Lake Tahoe Basin and
Evaluating BMP Strategies for Fine Sediment Reduction at
Watershed Scales
Randy B. Foltz, William J. Elliot, Woodam Chung and Hakjun Rhee
I.
Project Team and Contact Information
Principal Investigator:
Institution:
Address:
Phone:
Fax:
Email:
Co-Principal Investigator:
Institution:
Address:
Phone:
Fax:
Email:
Co-Principal Investigator:
Institution:
Address:
Phone:
Fax:
Email:
Co-Principal Investigator:
Institution:
Address:
Phone:
Fax:
Email:
Point of Contact:
Request for Proposals and
task statement this proposal is
responding to:
Randy B. Foltz
USDA Forest Service, Rocky Mountain Research Station
1221 S. Main St., Moscow, ID 83843
208-883-2312
208-883-2318
rfoltz@fs.fed.us
William J. Elliot
USDA Forest Service, Rocky Mountain Research Station
1221 S. Main St., Moscow, ID 83843
208-883-2338
208-883-2318
welliot@fs.fed.us
Woodam Chung
Department of Forest Management, College of Forestry and
Conservation, University of Montana
Missoula, MT 59812
406-243-6606
406-243-4845
woodam.chung@umontana.edu
Hakjun Rhee
Biological Systems Engineering, Washington State University
Pullman, WA 99164-6120
208-883-2396
208-883-2318
jrhee@fs.fed.us
Randy B. Foltz
USDA Forest Service, Rocky Mountain Research Station
1221 S. Main St., Moscow, ID 83843
Email: rfoltz@fs.fed.us
Phone: 208-883-2312
Fax: 208-883-2318
PSW Research Station, USDA Forest Service RFP 2007 Theme 2,
Sub-theme A, Proposals are sought that gain a more detailed
understanding of the specific sources, transport, and treatability and/or
management of fine sediments from watershed sources.
II. Justification Statement
Lake Tahoe is well known for its beauty and exceptionally clear waters. However, there has been a
decreasing trend in water clarity of the lake caused by an increased influx of fine sediments and nutrients
into the lake (TRPA; Tahoe Regional Planning Agency, 2004). A key strategy for protecting water
quality in the Lake Tahoe Basin is to reduce pollutants entering stream channels (Tallac Applied Ecology
& Design, 2006). Proper implementation of this strategy has been challenging because it requires
Foltz, Elliot, Chung & Rhee, PSW 2007-2-A, Page 1 of 22
accurately identifying the non-point pollution sources (e.g., erosional “hot spots”), and the adequate
BMPs (Best Management Practices) that reduce sediment and nutrient transport to stream channels.
Roads, especially with native surfaces, can be the greatest single source of sediment delivered to stream
systems (Megahan, 1972; King and Gonsior, 1980). The Forest Service Lake Tahoe Basin Management
Unit (LTBMU) evaluated 134 miles of road decommissioning and BMP upgrades between 2003 and
2005 (USDA Forest Service LTBMU, 2006), focusing on the road segments that were hydrologically
connected to streams (USDA Forest Service LTBMU, 2005). Their road BMP upgrades were to protect
soil and water resources and included upgrades of surfacing (e.g., pavement), drainage (e.g., rocked
ditch), and slope stabilization (e.g., rocked fillslope and revegetation).
One of the evaluation methods used by LTBMU was WEPP: Road, an interface developed by the Rocky
Mountain Research Station (RMRS) using the Water Erosion Prediction Project (WEPP) model (Elliot et.
al, 1999). WEPP: Road allows the users to quantify the sediment load and assess the effectiveness of
BMPs on soil erosion. For this reason, WEPP: Road will be used as a future planning and designing tool
in the basin (USDA Forest Service LTBMU, 2006). WEPP estimates usually range between -50% and
+50% of observed values (Elliot et. al, 1999). In order for WEPP: Road to produce more accurate results,
the model parameters need to be refined for a specific region. For the current version of WEPP:Road, the
decomposed granite parent material simulation was performed in the Zena Creek watershed in Idaho. The
volcanic parent material simulation was performed in the Tee Meadow watershed in Idaho. While these
sites provide reasonable WEPP estimates, an improvement in the mean sediment production estimate
would result from parameterization on Lake Tahoe soils. Rainfall simulation data collected in 2006
indicates that one can significantly improve the accuracy of WEPP sediment prediction estimates when
using site-specific parameterization. Additionally, the WEPP:Road model interface is not able to
simulate erosion under some road conditions (e.g., armored/rocked fillslopes and non-forested buffers, i.e.
the area between the road and the stream channel). The WEPP: Road validation and limitations have
been well-known issues for the applications within LTBMU (USDA Forest Service LTBMU, 2005;
Breibart, 2007). Such improvements will ensure that the WEPP model serves as a reliable tool that helps
to 1) better understand the non-point pollution sources and accurately identify them, and 2) select the
adequate BMPs and properly assess their effectiveness.
A Geographic Information System (GIS)-based quantitative approach is being developed to effectively
estimate sediment loading not only from hydrologically connected road segments, but also from the entire
road network within the basin. This automated approach can be incorporated into a road network
planning optimization model, such as NETWORK 2000™, in order to analyze the economic and
sediment reduction trade-offs of implementing alternative BMPs and management plans (e.g.,
decommissioning, road relocation, etc.). NETWORK 2000™ is a proprietary program developed by
Oregon State University (Chung and Session, 2003) and widely used within USDA Forest Service. It has
been recently modified to incorporate sediment delivery from WEPP: Road (Rackley and Chung, 2007).
This entire system (WEPP: Road incorporated into NETWORK 2000™) will provide an analytical tool
for road management to reduce sediment entering stream channels.
We propose to fill this critical need by 1) parameterizing the WEPP model specifically for the Lake
Tahoe Basin, 2) improving the current WEPP: Road interface, 3) validating the WEPP model for the Lake
Tahoe Basin and 4) developing a quantitative approach to identify erosional “hot spots” and the adequate
BMPs to efficiently reduce the sediment transport to stream channels.
III. Background
The Environmental Improvement Program (EIP) is a cooperative effort to preserve, restore and enhance
the unique natural and human environment of the Lake Tahoe Region (Tallac Applied Ecology & Design,
2006). The EIP program defines restoration needs for attaining environmental goals or “thresholds” and,
through a substantial investment of resources, increases the pace at which the thresholds will be attained
(TRPA, 2001). The 2001 Threshold Evaluation (TRPA, 2002) showed that only 40% of the threshold
indicators were meeting or nearly meeting the standard. Water quality is one of the threshold categories
that has not been successfully attained. The primary causes for the degradation of water quality are
Foltz, Elliot, Chung & Rhee, PSW 2007-2-A, Page 2 of 22
thought to be an increased flux of sediments and nutrients into the lake. Sources of nutrients and
sediments have been identified including atmospheric deposition, stream loading, direct runoff, ground
water, and shore zone erosion (Murphy and Knopp, 2000).
A key strategy is to reduce non-point source pollution (nutrients and sediments) at the source by the
application of BMPs. One of the twelve programs within the federal EIP focus areas is the Road, Trail
and Facility Water Quality Retrofit Program (RTFP) developed for the applications of Water Quality
BMPs to USFS roads, trails and recreation facilities within the Lake Tahoe Region (Tallac Applied
Ecology & Design, 2006). Forest Service LTBMU has been evaluating the effectiveness of such BMP
projects under the Forest Road BMP Retrofit Program (USDA Forest Service LTBMU, 2005). To
monitor and evaluate decommissioning, converting to trails and upgrading roads with appropriate BMPs
to protect soil and water resources, LTBMU used three methods: the Water Quality Risk Assessment
Protocols (WQRAP; developed by LTBMU Engineering staff, USDA, 1998), the Region 5 Best
Management Practices Evaluation Program (BMPEP; USDA Forest Service, 2002), and the Water
Erosion Prediction Project (WEPP) model. During the WQRAP analysis, road segments were assigned a
hazard score and risk-rated high, moderate or low. For BMPEP evaluation various questions were asked;
answers scored; and road segments risk-rated high, moderate or low. On the other hand, the WEPP model
provided a quantitative estimate of potential impacts of roads on water quality. After finding that the
WEPP outputs were consistent with risk rates from WQRAP and BMPEP, LTBMU has been using the
WEPP model in monitoring and evaluating road decommissioning and BMP upgrades since 2003 (USDA
Forest Service LTBMU, 2005).
WEPP is a physically-based soil erosion model that can provide estimates of soil erosion, sediment yield,
and sediment particle size distribution of the runoff for various combinations of soil, climate, ground
cover and topographic conditions (Elliot et. al, 1999). The WEPP model contains an interface, WEPP:
Road, which helps users to model various road conditions with different drainage spacing, road design
and ditch conditions. LTBMU has been using WEPP: Road to estimate sediment delivery from stream
crossings and hydrologically connected road segments. However, the current WEPP: Road interface has
limitations when modeling some road conditions that exist in the Lake Tahoe Basin, such as
armored/rocked fillslopes and non-forested buffers (USDA Forest Service LTBMU, 2005). Our recent
conversation with a former LTBMU employee also identified a need to improve and validate the current
WEPP: Road interface for the Lake Tahoe Basin as indicated below (Breibart, personal communication,
2007; used with his permission and included as an attachment):
1. WEPP: Road should allow the users to change the type of fill materials and cover;
2. WEPP: Road needs to better handle paved roads because it tends to overestimate erosion and
sedimentation from such roads;
3. WEPP: Road currently has only four road designs available (insloped, bare ditch; insloped,
vegetated or rocked ditch; outsloped, rutted; unrutted), but it should also be able to model
crowned and/or entrenched roads; and
4. WEPP: Road results need to be validated against field measurements of road erosion and
sedimentation within the Lake Tahoe Region.
In addition, cutslope erosion needs to be addressed for the application of the WEPP model to the Lake
Tahoe Basin since cutslopes often become a major source of sediment (Arnáez, et. al, 2004). There are
several cutslope processes that contribute sediments to road erosion, and different processes require
different modeling approaches. The cutslope processes include freeze-thaw, overland flow, mass wasting
(Arnáez, et. al, 2004), wetting-drying, dry ravel (Sidle et. al, 1993), subsurface flow interception
(Megahan, 1983) and rilling (Sidle et. al, 2004). Once the dominant cutslope erosion process is known
within the Lake Tahoe Basin, the WEPP model can be improved for modeling cutslope erosion.
The current WEPP: Road allows the users to model different road designs, road surface, traffic levels and
soils. Even though some road BMPs used by LTMBU can be evaluated using the current WEPP: Road,
such as rocked/vegetated ditch, outsloping, surfacing upgrade, road closure and decommissioning, the
model improvement will allow the users to evaluate additional road BMPs including cutslope and
fillslope revegetation, fillslope armoring (rip-rap), and road design changes (crowned and entrenched
roads). Comparing the effectiveness of different road BMPs needs further refinement of the model
Foltz, Elliot, Chung & Rhee, PSW 2007-2-A, Page 3 of 22
parameters since less difference is expected among the BMPs than the difference between a BMP and no
practices.
Parameterizing the WEPP model requires simulated rainfall experiments which control precipitation rate
and duration, and contributing area. Foltz (PI) and Elliot (Co-PI) together parameterized WEPP for forest
road conditions over the past 15 years. Our past parameterization experience indicates that infiltration
rate on the road running surface is the most critical model parameter since it affects runoff and erosion on
the road running surface and buffer. Within the Lake Tahoe Basin there have been rainfall simulation
studies (Grisomer and Hogan, 2004, 2005a and 2005b) on disturbed hillslopes such as road cuts and ski
runs, but not on road running surfaces. These studies are useful for the parameter determination in road
cutslopes. However, further rainfall simulations should be conducted for infiltration rates and erodibility
parameters on road running surfaces in the Lake Tahoe Basin.
Once parameterized, improved, and validated, WEPP: Road should be applied to the basin with
reasonable time and efforts. Rackley and Chung (2007) have developed a methodology to estimate
sediment delivery from individual road segments using WEPP: Road, GIS layers, high-resolution DEMs
(Digital Elevation Models), GPS and simple road survey data. They applied WEPP: Road to an entire
road network in a watershed and identified erosionally problematic road segments (Figure 1). Their study
indicates that once combined with an extensive transportation planning and optimization tool, the WEPP
results can be used to identify problematic road segments and select cost and erosion effective BMPs to
mitigate the problem.
IV. Project Objectives
The overall objective of this study is to reduce sediment entering Lake Tahoe by improving and validating
the WEPP model applications for road management in the Lake Tahoe Basin. Specifically, we propose
to:
1. Parameterize the WEPP model for the Lake Tahoe Basin. We will parameterize the WEPP model
with simulated rainfall experiment data from the road running surface;
2. Improve WEPP: Road interface for the Lake Tahoe Basin. Improving WEPP: Road will include
additional abilities to (a) change fillslope and buffer material type and cover, (b) model crowned
and entrenched roads and (c) model cutslope erosion;
3. Validate the WEPP model for the Lake Tahoe Basin. We will validate the WEPP model against
field observation data for both paved and unpaved roads;
4. Develop a GIS-based quantitative approach to (a) predict the sediment loading using WEPP:
Road, (b) identify erosional “hot spots” from a watershed-scale road network and (c) determine
the optimal road network design that minimizes sediment production through BMP application
and road decommissioning while ensuring the required access.
V. Approach, Methodology, and Geographic Location of Research
1. Parameterization of the WEPP Model
To parameterize the WEPP model, rainfall simulations on unpaved road running surfaces will be
conducted on 1 m × 1 m plots on two dominant soil types (decomposed granite and volcanic ash),
resulting in a total of 12 plots. We will select the plots with moderate road gradient between 5 to 10
percent. Detailed rainfall simulation and analysis methodology can be found in Foltz and Maillard
(2003).
After consultation with the LTBMU hydrologists and road engineers and field reconnaissance in June
2007, specific locations of the plots will be determined among 63 watersheds within the Lake Tahoe
Basin. Ward Creek, Blackwood Creek and Edgewood Creek will be potential study sites because of
USGS monitoring stations and previous studies (Grismer and Hogan, 2004, 2005a and 2005b; USDA
Forest Service LTBMU, 2005).
Foltz, Elliot, Chung & Rhee, PSW 2007-2-A, Page 4 of 22
2. Improvements to WEPP: Road
A wealth of scientific data exists on the Lake Tahoe Basin, including climatic and hydrologic data from
past monitoring programs. We will acquire pre-existing data and collected data as part of this study, and
develop the model templates for the Lake Tahoe Basin. WEPP: Road currently uses NOAA climate
station data for its climate template supplemented by the PRISM data base (Daly, 2006). We will include
climate data from seven nearby NRCS (Natural Resources Conservation Service) SNOTEL (SNOwpack
TELemetry) sites (USDA NRCS, 2007a) within the basin. Soil templates will be developed using NRCS
web soil survey (USDA NRCS, 2007b), erosion studies such as Grismer and Hogan (2005a) and the
rainfall simulation results above (Parameterization of the WEPP Model). Once the model templates are
developed for the Lake Tahoe Basin, our information technology specialist will modify the WEPP: Road
interface.
Modeling cutslope erosion requires identifying the dominant cutslope erosion process. Field surveys will
be conducted after the spring snow-melt season (May – Jun) and before winter snow season (October –
November) for 2007 and 2008, resulting in a total of four cutslope survey data sets. A statistically
significant number of cutslopes (about 20) will be surveyed. To identify the dominant process,
parameters of cutslope height, steepness, aspect, vegetation, ground cover, seepage, and existence of
cutslope materials inside of ditch will be measured. Photos will be taken; soil samples will be collected
from middle and bottom of the cutslopes, and analyzed in the RMRS Moscow laboratory for particle size
and organic matter. Once the dominant cutslope contribution process to sediment is identified, we will
modify WEPP: Road accordingly to model cutslope erosion.
3. Validation of the WEPP Model
WEPP model will be validated with data from summer thunderstorms by using automatic sediment
samplers located at culvert outlets of paved and unpaved roads. Two soil parent materials of decomposed
granite and volcanic ash combined with the paved and unpaved road sections will result in a total of four
road segments. The automatic sediment samplers at each location will consist of an ISCO 3700 portable
sampler (Teledyne ISCO, Inc., 2007), an ISCO 4230 flow meter (Teledyne ISCO, Inc., 2006) and a small
(two cubic feet) settling tank with a modified 22.5-degree V-notch weir at the outlet (Foltz and Truebe,
1995). The settling tank is designed so that the heavier sizes settle in the first section and the fine sizes
pass to the second section where the sampler intake is located. The flow meter allows flow rates to be
determined and will be set to trigger the sampler when flows exceed a predetermined rate. Sediment
samples will have particle size analysis performed at RMRS, Moscow, ID. Equipment installation and
daily maintenance will be performed by RMRS employees on-location. Selection of the sites will be in
consultation with LTBMU hydrologists and road engineers in July 2007. At the completion of the two
month summer thunderstorm season, the equipment will be removed and the sites mitigated in accordance
with applicable local regulations.
Flow rates, sediment concentrations, and the particle size distribution of the sediment in the runoff will
allow validation of the WEPP model on a storm-by-storm basis. With four sites and a collection period of
two months, a sufficient number of thunderstorms should occur to allow model validation.
4. “Hot Spots” Identification
WEPP: Road requires considerable field data on roads and topography to analyze a large watershed. To
minimize field data collection, we will utilize GIS and the existing spatial dataset (http://tahoe.usgs.gov/)
as suggested in Rackley and Chung (2007). For the data that cannot be obtained from GIS, such as
delivery point locations, road design, surface type and soil texture, we will develop a field data collection
protocol so that all the necessary WEPP input data can be cost-effectively collected for a large road
network. A University of Montana employee will collect this field data.
We will also develop an analytical system by incorporating the WEPP results into NETWORK 2000™, a
transportation planning and optimization tool. This system will be designed to (a) identify erosional “hot
spots” using the WEPP results, (b) analyze cost and sediment reduction trade-offs of various BMPs and
Foltz, Elliot, Chung & Rhee, PSW 2007-2-A, Page 5 of 22
alternative road management practices through a network analysis (Chung and Sessions, 2003), and (c)
find the most effective management practices that minimize both project costs and sediment delivery
through optimizing BMP strategies and road networks (Rackley and Chung, 2007). To validate the
system, we will apply it to the watersheds (study sites) described above (Parameterization of the WEPP
Model). The erosional “hot spots” identified by the system will be field checked, and the suggested road
practices will be reviewed with the LTBMU hydrologists and road engineers.
VI. Deliverables/Products
This project will provide an improved WEPP: Road interface, including the specifically designed and
validated WEPP model templates for the Lake Tahoe Basin and the NETWORK 2000™ templates for the
Lake Tahoe road network. A practical application guideline will be published in the form of a user
manual. Results will be communicated directly to hydrologists, road engineers and managers via a
workshop presentation. Also the authors will disseminate the research findings through publication of
two peer-reviewed articles. Annual progress reports and a final report will be provided to the Pacific
Southwest Research Station, USDA Forest Service.
Table 1. Description and delivery dates of project deliverables
Deliverable
Description
User manual
Guideline to apply WEPP: Road and NETWORK 2000™
for the Lake Tahoe Basin
NETWORK 2000™
Sediment and road network maps for at least two
maps, input and output watersheds with supporting files such as input and output
files
templates of WEPP: Road and NETWORK 2000™
Improved WEPP: Road Online interface with supplementary online documents at
the Rocky Mountain Research Station Moscow Lab.
website
Workshop
Presentation on the improved WEPP: Road and
NETWORK 2000™ analyses
Peer-reviewed article
Technical article on the parameterization and validation of
the WEPP model for the Lake Tahoe Basin
Peer-reviewed article
Technical article on the evaluation of the sediment loading
and road BMPs within the Lake Tahoe Basin
Delivery Dates
October 2008
March 2009
March 2009
March 2009
April 2009
April 2009
VII. Schedule of Events/Reporting and Deliverables
A two-year (three fiscal years) period is required because a half year is needed for field survey and
running WEPP: Road with NETWORK 2000™, one full year for field data collection, and a half year for
data analysis and publishing the results.
May 2007 – September 2007
• Conduct field reconnaissance.
• Conduct cutslope survey after snow-melt (June) and before snow-fall (September).
• Conduct field survey for the application of NETWROK2000™.
• Install and maintain automatic sediment samplers.
• Conduct rainfall simulation on road running surfaces.
October 2007 – September 2008
• Remove automatic sediment samplers.
• Conduct cutslope survey after snow-melt (June) and before snow-fall (September).
• Identify the dominant cutslope erosion process.
• Parameterize the WEPP model for the Lake Tahoe Basin
• Develop a guideline to apply WEPP: Road and NETWORK 2000™ for the Lake Tahoe Basin.
Foltz, Elliot, Chung & Rhee, PSW 2007-2-A, Page 6 of 22
October 2008 – April 2009
• Develop the WEPP templates and improve WEPP: Road interface.
• Validate the WEPP model for the Lake Tahoe Basin.
• Identify erosional hot spots and evaluate road management practices using the improved WEPP:
Road interface.
• Analyze trade-offs of alternative road management practices using NETWORK 2000™.
• Summarize and publish field experiments, and WEPP: Road and NETWORK 2000™ results.
• Conduct technology transfer workshop and presentations.
Foltz, Elliot, Chung & Rhee, PSW 2007-2-A, Page 7 of 22
X. A List of References
Arnáez, J., V. Larrea and L. Ortigosa. 2004. Surface runoff and soil erosion on unpaved forest roads
from rainfall simulation tests in northeastern Spain. Catena 57(1):1-14.
Breibart, Andrew. 2007. Personal communication.
Chung, W. and J. Sessions. 2003. NETWORK 2000, a program for optimizing large fixed and variable
cost transportation problems. In: System Analysis in Forest Resources, 109-120. Arthaud, G. J. and
T. M. Barrett, ed. Netherlands: Kluwer Academic Publishers
Daly, C. 2006. PRISM Group. Available at: http://www.ocs.oregonstate.edu/prism/index.phtml.
Accesses 16 January 2007.
Elliot, W. J., D. E. Hall and D. L. Scheele. 1999. WEPP: Road WEPP interface for predicting forest road
runoff, erosion and sediment delivery. USDA Forest Service Rocky Mountain Research Station and
San Dimas Technology and Development Center. Available at:
http://forest.moscowfsl.wsu.edu/fswepp/docs/wepproaddoc.html. Accessed 12 January 2007.
Foltz, R. B. and E. Maillard. 2003. Infiltration rates on abandoned road – stream crossings. ASAE Paper
No. 035009. St. Joseph, Mich.: ASAE.
Foltz, R. B. and M. A. Trube. 1995. Effect of aggregate quality on sediment production from a forest
road. In Proc. the Sixth International Conference on Low-Volume Roads, 1:49-57, Minneapolis, MN,
June 25-29, 1995. Washington, DC: Transportation Research Board, National Academy Press.
Grismer M. E. and M. P. Hogan. 2004. Simulated rainfall evaluation of revegetation/mulch erosion in
the Lake Tahoe Basin – 1: Method assessment. Land Degradation & Development 13:573-588.
Grismer M. E. and M. P. Hogan. 2005a. Simulated rainfall evaluation of revegetation/mulch erosion in
the Lake Tahoe Basin – 2: Bare soil assessment. Land Degradation & Development 16:397-404.
Grismer M. E. and M. P. Hogan. 2005b. Simulated rainfall evaluation of revegetation/mulch erosion in
the Lake Tahoe Basin – 3: Soil treatment effects. Land Degradation & Development 16:489-501.
King, J. and M. Gonsior. 1980. Effects of forest roads on stream sediment. In Symposium on Watershed
Management, Boise, Idaho, July 21-23, 1980. New York, NY: ASCE.
Megahan, W. F. 1972. Logging, erosion, sedimentation – are they dirty words? Journal of Forestry
70(7):403-407.
Megahan, W. F. 1983. Hydrological effects of clearcutting and wildfire on steep granite slopes in Idaho.
Water Resources Research 19(3):811-819.
Murphy, D. D. and Knopp, C. M. 2000. Lake Tahoe watershed assessment. USDA Forest Service
Pacific Southwest Station, General Technology Report PSW-GTR-175.
Rackley, J. and W. Chung. 2007. Incorporating forest road erosion into forest resource transportation
planning: a case study in the Mica Creek watershed in Northern Idaho. Journal of Environmental
Management (in review).
Sidle, R. C., R. W. Brown and B. D. Williams. 1993 Erosion processes on arid minespoil slopes. Soil
Science Society of America Journal 57(5):1341-1347.
Sidle, R. C., S. Sasaki, M. Otsuki, S. Noguchi and A. R. Nik. 2004. Sediment pathways in a tropical
forest: effects of logging roads and skid trails. Hydrological Processes 18(4):703-720.
Tallac Applied Ecology & Design. 2006. A federal vision for the Environmental Improvement Program
at Lake Tahoe. Lake Tahoe, CA: USDA Forest Service LTBMU.
Teledyne ISCO, Inc., 2006. 4230 flow meter installation and operation guide. Available at
http://www.isco.com/pcfiles/PartPDF4/UP000XPF.pdf. Accesses 22 January 2007.
Teledyne ISCO, Inc., 2007. 3700 portable sampler installation and operation guide. Available at
http://www.isco.com/pcfiles/PartPDF4/UP000Z8A.pdf. Accesses 22 January 2007.
TRPA. 2001. Environmental Impact Program: the cooperative effort to preserve, restore, and enhance
the unique natural and human environment of the Lake Tahoe Region. Stateline, NV: TRPA.
TRPA. 2002. 2001 threshold evaluation report. Stateline, NV: TRPA.
TRPA. 2004. Annual water quality report. Stateline, NV: TRPA.
USDA Forest Service LTBMU. 2005. 2004 Forest road BMP upgrade monitoring program. Lake
Tahoe, CA: USDA Forest Service LTBMU.
USDA Forest Service LTBMU. 2006. 2005/2006 Monitoring program annual report. Lake Tahoe, CA:
USDA Forest Service LTBMU.
Foltz, Elliot, Chung & Rhee, PSW 2007-2-A, Page 18 of 22
USDA Forest Service. 2002. Investigating water quality in the Pacific Southwest Region: Best
Management Practices Evaluation Program (BMPEP User’s Guide). Vallejo, CA: Pacific Southwest
Region.
USDA NRCS. 2007a. SNOTEL data and & products. Available at:
http://www.wcc.nrcs.usda.gov/snotel/. Accessed 12 January 2007.
USDA NRCS. 2007b. The NCSS (National Cooperative Soil Survey) web soil survey. Available at:
http://websoilsurvey.nrcs.usda.gov/app/. Accesses 24 January 2007.
Foltz, Elliot, Chung & Rhee, PSW 2007-2-A, Page 19 of 22
XI. Figures
Figure 1. Annual sediment yields delivered to stream channels was quantified using WEPP: Road.
WEPP: Road successfully identified erosional “hot spots”, which are red and orange road
segments.
Foltz, Elliot, Chung & Rhee, PSW 2007-2-A, Page 20 of 22