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2000 Progress Report: Source Load Modeling for Sediment in Mountainous Watersheds
EPA Grant Number: R825433C027Subproject: this is subproject number 027 , established and managed by the Center Director under grant R825433
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: EERC - Center for Ecological Health Research (Cal Davis)
Center Director: Rolston, Dennis E.
Title: Source Load Modeling for Sediment in Mountainous Watersheds
Investigators: Kavvas, M. Levant , Goldman, Charles R. , Reuter, John E.
Institution: University of California - Davis
EPA Project Officer: Levinson, Barbara
Project Period: October 1, 1996 through September 30, 2000
Project Period Covered by this Report: October 1, 1999 through September 30, 2000
RFA: Exploratory Environmental Research Centers (1992)
Research Category: Center for Ecological Health Research , Targeted Research
Description:
Objective:Develops a model to accurately and effectively predict sediment transport and load in mountainous Sierra Nevada watersheds.
This project has the following objectives:
· Application of newly-developed spatially-averaged, non-point source
pollution model for the simulation and prediction of sediment and phosphorus
dislocation at the watershed and subwatershed scale in the Lake Tahoe Basin,
· Linking terrestrial ecosystem parameters with aquatic ecosystem parameters,
· Development of decision guidelines considering ecological as well as
economic aspects
This subproject will focus on the natural and anthropogenic factors operating within the watershed which control erosion and the transport of sediment and nutrients to the lake's tributaries. The primary objective is to develop a model which allows us to more accurately and effectively predict sediment transport and load in mountainous Sierra Nevada watersheds. In Sections C.2b and C.2c we will assess the impact of this load on the lake. Considering the hydrologic and geomorphologic features characteristic of mountain watersheds, ecological health will be assessed as a response to changes and/or disturbances in the spatial distribution of terrestrial parameters. The results of this work will provide invaluable tools for watershed managers to assess cost/benefits of various policy scenarios.
The following will be the direct benefits of this modeling work: (1) application of a newly-developed methodology to describe the flow dynamics of non-point source pollution over complex landscape surfaces, (2) improve our understanding of the major sources of sediment and associated pollutants in Sierra Nevada watersheds, distinguishing between natural and anthropogenic sources; (3) enable agencies to set management priorities to reduce sediment and associated pollutants; (4) provide advice for soil conservation strategies and provide a framework for testing the efficiency of erosion control techniques at local and regional levels and; (5) development of approaches/tools which can be used for environmentally-based watershed management.
The Lake Tahoe Basin is characterized by a very small ratio of watershed area (800 km2) to lake surface (499 km2) as well as low annual precipitation and nutrient poor soils. This, combined with the characteristics of the natural alpine/subalpine landscape, makes the environment highly sensitive to perturbation in the watershed--easily damaged but extremely slow to recover. Accelerated erosion from natural and disturbed watersheds is considered one of the major factors contributing to the decline in ecological health in the Basin. Each of the 63 individual watersheds within the Basin has a unique composition of geology, geomorphic features, precipitation and degree/type of urbanization and land disturbance. Only 8 to 10 watersheds account for approximately 40% of the channelized surface runoff. These tributaries have been well monitored by the Lake Tahoe Interagency Monitoring Program under the direction of the Tahoe Research Group (TRG) since the late seventies. An excellent hydrologic data base on flow as well as water quality data is available. Detailed meteorological information is also available for the same time period, and a comprehensive limnological study of the lake has been continuing since 1967. From the results of these research activities, we have concluded that erosive surface transport processes is the major source of sediment and phosphorus to the Lake. Phosphorus has become the primary nutrient limiting phytoplankton growth in the lake and therefore has an immense impact on the aquatic ecosystem. Therefore, controlling the delivery of sediment and its associated phosphorus is critical for the protection of the aquatic resource(s).
In an attempt to develop a watershed hydrology model component hydrologic process models were combined into one computer program. This watershed hydrology model is made up of the following components: (a) an overland flow model which describes both the rill flow and the interrill-area sheet flow; (b) a land surface hydrology model which describes the interception, evapotranspiration and soil unsaturated flow processes; (c) a snowmelt model; (d) a subsurface stormflow model which describes the fast saturated flow that forms above an impeding soil layer below the plant root zone; (e) a deep unconfined groundwater aquifer flow model; and (f) a stream network flow routing model based upon diffusion wave approximation. All of these component flow process models, except the streamflow routing component, are based upon areally-averaged conservation equations. Calibration and validation of this new watershed hydrology model were recently completed, and are discussed next.
In an effort to calibrate the model two major steps have been taken: 1) the collection of observed data and 2) development of a topographic and soils database. Within the Ward Creek watershed there are five USGS streamflow gauging stations and two NRCS snow sites. Streamflow data are available in daily format, but finer temporal resolution data can be obtained through contact with USGS office in Sacramento. Snow site has information such as snow water content, snow depth, and temperature. In order to estimate required parameters by the model, topographic and soils database have been collected from different sources. USGS 7.5 minute quadrangle digital elevation models (DEM) were acquired from the Sierra Nevada Ecosystem Project. Using the DEM as a base map, many important topographic features were derived such as channel network, watershed boundaries, and its subbasins. DEM is also used to derive topographic parameters such as slope and aspect. In addition to these topographic parameters, soil parameters were derived to provide necessary input to unsaturated flow and subsurface flow components of the model. These parameters were derived based upon the soil map unit coverage provided by Tahoe Environmental GIS. With this map unit coverage combined with the map unit interpretation database (NRCS), parameters such as saturated hydraulic conductivity, porosity, and Brooks-Corey parameters can be derived. The calibration of the hydrology component of the model is very important since the subsequent sediment transport component will heavily depend upon the performance of the hydrology component. In other words, good prediction of sediment transport component cannot be achieved without the valid hydrology component.
Based upon the recent calibration of model parameters the validation of the proposed hydrology model has been performed during 1998-1999 project year. The model was applied to the Ward Creek watershed where the sediment and associated phosphorous loading is identified to be significant. Three consecutive rainfall events during the month of September in 1998 were used to verify the performance of the model. It is important to note that our calibration is different from the traditional one used with many conceptual models in that all parameters are estimated physically based upon available base maps such as digital elevation model, soils map, and vegetation map rather than the model fitting. This particular aspect of the model is a clear advantage especially when the model needs to be applied to an ungaged basin. Another important asset of the model is that individual contribution from each hydrologic component can be realistically identified by activating only the corresponding component. Meanwhile, it would be difficult to see this contribution in traditional conceptual models as their hydrologic components are not modeling the processes physically. The result from the model was compared to its observed counterpart and showed good resemblance, thus verifying the performance of the model. With the diagnostic approach mentioned above the model was found to be very effective in identifying the important hydrologic mechanism of the basin of interest. In the case of Ward Creek watershed the saturation overland flow mechanisms turned out to be the most significant in matching the observed hydrograph due to the existence of shallow root zone and high permeability of the soils.
With the completion of the hydrology model the foundation for the modeling sediment/nutrient transport was built and the development of the transport models was the new focus for the current project year. The erosion process is modeled mainly in two types, which are upland and in-stream erosion. The upland erosion model is built directly on the developed surface runoff component. Development of upland erosion component has been completed and the model is now being calibrated using the experimental data found in the literature. For the development of an in-stream erosion model, a 2-D channel flow model was developed since it allows us to identify the source of erosion in a stream by distinguishing the main and bank portion of the stream separately. Further effort will be made to develop the in-stream erosion component during the upcoming project year. Another important task of collecting the sediment and nutrient-related data will continue to go hand in hand with our modeling effort for the model calibration/validation purposes.
Along with the modeling of the watershed processes, there have been efforts to set up an experimental site to provide valuable data for the validation of the model at a field scale. A site in the upper reaches of the Ward Valley was selected for the study of subsurface and overland flow contributions to a stream. The source area is approximately 4000 square feet with a mild, concave, downward slope to the stream bank. In winter and spring, this area is often covered with as much as 15 feet of snow. The area is clear of snow by early May to late June.
In October of 1997, a trench was dug along the stream. Polyethylene sheets and drainage pipe were installed to separate and capture subsurface flow within the root zone and impeding layer. A gutter was installed along the uphill side of the trench to capture overland flow. End of pipe weirs were modified and calibrated during the winter and spring of 1998. By June, useful subsurface flow data was being recorded.
During the fall of 1998, a micrometeorology station was installed and two piezometers were drilled in the concave section of the source area. The station includes air temperature and humidity probes, a pyranometer, net radiometer, wind anemometer, rain gage, and soil and snow temperature probes. The information gathered with these instruments will be used to determine energy and rain fluxes into the snowpack for the purpose of calculating snowmelt. Hydraulic heads within the root zone will be monitored with the piezometers.
Data from the spring melt of 1999 was successfully obtained. This data is presently being analyzed and will be used to test the field scale model. While much useful information has already been obtained, there is still room for improvement. First, the two piezometers must be deepened to capture more of the baseflow during the dry season. Second, more piezometers must be added to obtain a more accurate, dynamic picture of the water surface profile within the subsurface. Lastly, the methods of obtaining the snow temperature profile must be improved so that changes in the snowpack and the relative locations of the temperature probes can be accounted for between site visits.
Planned improvements on the experimental site were completed during the summer and fall of 1999 for the winter snowfall and spring melt of 2000. Existing piezometers were deepened and three additional piezometers were installed to better capture the dynamics of subsurface water profile. Also added is the stream weir near the beginning of the trench, which will capture the inflow from the source area that drains to the stream bordering upon the experimental hillslope for water budget analysis. Overland flow gutter is newly installed to capture the saturation overland flow occurring near the stream. Sediment samples were taken from both stream weir and monitoring tank that collects subsurface flows. These samples will be analyzed to determine if any significant amount of nutrients are transported into the stream by sediment particles carried by surface and subsurface flows.
Future Activities:Quantitative simulation or modeling of surface runoff, erosion, and non-point source pollution transport is a necessary approach in performing useful ecological assessment studies. In particular, decisions faced by watershed management groups often focus on the relative benefit and cost/benefit relationships between a variety of design scenarios. Despite the recent availability of models intended to predict watershed response to management strategies, the high degree of uncertainty and general lack of verification outside their calibration systems, casts scientific doubt on their utility in environmental planning. This is especially true in mountainous ecosystems such as the Sierra Nevada. Consideration of the complexity of regional landscapes in the subalpine-alpine environment at a multitude of scales (i.e. < 50 m x 50 m, 100's of hectares, many square kilometers) becomes fundamental in evaluating alternative strategies for improved land management with an integrated watershed approach.
To overcome these deficiencies and to be able to incorporate complex subalpine/alpine landscape surfaces, the newly developed methodology will be used as the basis for a watershed-scale model to describe the transport of sediment and pollutants. Following the principles of conservation of mass and linear momentum, the relevant point equations for rill and interrill transport are integrated. In the second step, the areal averaging of the sediment transport hydrodynamics considers the transect of a hillslope. Consequently, features of the hillslope/landscape are correctly incorporated into the physical-based process formulation without the need for reducing assumptions. This methodology has significantly less parameters to deal with than the ordinary point-equation approach. The new spatially-averaged conservation/ transport equations technology will perform well despite using significantly less information about the land surface microtopography than common physically-based models. Hence, the new methodology will be superior to the existing methods that are based only on point-scale conservation equations.
In our applied physically-based erosion/watershed model, the hillslope component as well as the channel component of the erosion model consider the continuity as well as the momentum equations to describe the downslope movement of sediments under varying flow characteristics. On the upland areas, sediment is transported from interrill areas into rills and then carried off the hillslopes from where it is washed into the overall catchment channel network. The calculation of particle detachment, transport and deposition based on hydraulic principles is the major goal of the channel phase within a meso- or macro-scale erosion model. Consequently, a hydrologic flow and erosion/sediment and nutrient transport model will be developed and tested by field experimental data at the hillslope scale, and by means of the historical watershed-scale and Lake Tahoe-scale data (which has been collected and is being collected by Lake Tahoe Research Group) at those larger scales.
Supplemental Keywords:Ecosystem Protection/Environmental Exposure & Risk, Water, INTERNATIONAL COOPERATION, Scientific Discipline, Waste, RFA, ECOSYSTEMS, Water & Watershed, Aquatic Ecosystem Restoration, Aquatic Ecosystems & Estuarine Research, Terrestrial Ecosystems, Aquatic Ecosystem, Biochemistry, Environmental Microbiology, Fate & Transport, Watersheds, Monitoring/Modeling, Ecology and Ecosystems, ecological impact, fate and transport, watershed management, watershed restoration, ecological research, ecology assessment models, aquatic habitat protection , land use, wetland restoration, aquatic ecosystems, environmental stress, sediment transport, watershed sustainablility, hydrology, Sierra Nevada, watershed influences, restoration strategies, ecosystem stress, integrated watershed model
Progress and Final Reports:
1999 Progress Report
Original Abstract
Final Report
Main Center Abstract and Reports:
R825433 EERC - Center for Ecological Health Research (Cal Davis)
Subprojects under this Center:
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R825433C001 Potential for Long-Term Degradation of Wetland Water Quality Due to Natural Discharge of Polluted Groundwater
R825433C002 Sacramento River Watershed
R825433C003 Endocrine Disruption in Fish and Birds
R825433C004 Biomarkers of Exposure and Deleterious Effect: A Laboratory and Field Investigation
R825433C005 Fish Developmental Toxicity/Recruitment
R825433C006 Resolving Multiple Stressors by Biochemical Indicator Patterns and their Linkages to Adverse Effects on Benthic Invertebrate Patterns
R825433C007 Environmental Chemistry of Bioavailability in Sediments and Water Column
R825433C008 Reproduction of Birds and mammals in a terrestrial-aquatic interface
R825433C009 Modeling Ecosystems Under Combined Stress
R825433C010 Mercury Uptake by Fish
R825433C011 Clear Lake Watershed
R825433C012 The Role of Fishes as Transporters of Mercury
R825433C013 Wetlands Restoration
R825433C014 Wildlife Bioaccumulation and Effects
R825433C015 Microbiology of Mercury Methylation in Sediments
R825433C016 Hg and Fe Biogeochemistry
R825433C017 Water Motions and Material Transport
R825433C018 Economic Impacts of Multiple Stresses
R825433C019 The History of Anthropogenic Effects
R825433C020 Wetland Restoration
R825433C021 Sierra Nevada Watershed Project
R825433C022 Regional Transport of Air Pollutants and Exposure of Sierra Nevada Forests to Ozone
R825433C023 Biomarkers of Ozone Damage to Sierra Nevada Vegetation
R825433C024 Effects of Air Pollution on Water Quality: Emission of MTBE and Other Pollutants From Motorized Watercraft
R825433C025 Regional Movement of Toxics
R825433C026 Effect of Photochemical Reactions in Fog Drops and Aerosol Particles on the Fate of Atmospheric Chemicals in the Central Valley
R825433C027 Source Load Modeling for Sediment in Mountainous Watersheds
R825433C028 Stress of Increased Sediment Loading on Lake and Stream Function
R825433C029 Watershed Response to Natural and Anthropogenic Stress: Lake Tahoe Nutrient Budget
R825433C030 Mercury Distribution and Cycling in Sierra Nevada Waterbodies
R825433C031 Pre-contact Forest Structure
R825433C032 Identification and distribution of pest complexes in relation to late seral/old growth forest structure in the Lake Tahoe watershed
R825433C033 Subalpine Marsh Plant Communities as Early Indicators of Ecosystem Stress
R825433C034 Regional Hydrogeology and Contaminant Transport in a Sierra Nevada Ecosystem
R825433C035 Border Rivers Watershed
R825433C036 Toxicity Studies
R825433C037 Watershed Assessment
R825433C038 Microbiological Processes in Sediments
R825433C039 Analytical and Biomarkers Core
R825433C040 Organic Analysis
R825433C041 Inorganic Analysis
R825433C042 Immunoassay and Serum Markers
R825433C043 Sensitive Biomarkers to Detect Biochemical Changes Indicating Multiple Stresses Including Chemically Induced Stresses
R825433C044 Molecular, Cellular and Animal Biomarkers of Exposure and Effect
R825433C045 Microbial Community Assays
R825433C046 Cumulative and Integrative Biochemical Indicators
R825433C047 Mercury and Iron Biogeochemistry
R825433C048 Transport and Fate Core
R825433C049 Role of Hydrogeologic Processes in Alpine Ecosystem Health
R825433C050 Regional Hydrologic Modeling With Emphasis on Watershed-Scale Environmental Stresses
R825433C051 Development of Pollutant Fate and Transport Models for Use in Terrestrial Ecosystem Exposure Assessment
R825433C052 Pesticide Transport in Subsurface and Surface Water Systems
R825433C053 Currents in Clear Lake
R825433C054 Data Integration and Decision Support Core
R825433C055 Spatial Patterns and Biodiversity
R825433C056 Modeling Transport in Aquatic Systems
R825433C057 Spatial and Temporal Trends in Water Quality
R825433C058 Time Series Analysis and Modeling Ecological Risk
R825433C059 WWW/Outreach
R825433C060 Economic Effects of Multiple Stresses
R825433C061 Effects of Nutrients on Algal Growth
R825433C062 Nutrient Loading
R825433C063 Subalpine Wetlands as Early Indicators of Ecosystem Stress
R825433C064 Chlorinated Hydrocarbons
R825433C065 Sierra Ozone Studies
R825433C066 Assessment of Multiple Stresses on Soil Microbial Communities
R825433C067 Terrestrial - Agriculture
R825433C069 Molecular Epidemiology Core
R825433C070 Serum Markers of Environmental Stress
R825433C071 Development of Sensitive Biomarkers Based on Chemically Induced Changes in Expressions of Oncogenes
R825433C072 Molecular Monitoring of Microbial Populations
R825433C073 Aquatic - Rivers and Estuaries
R825433C074 Border Rivers - Toxicity Studies