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Vegetative Resistance to Flow in the Everglades

Project Proposal for 1999

Project number: 4384-16300
USGS Geologic Division

Continuing Project Work Plan - FY 1999

IDENTIFYING INFORMATION
Project title: Vegetative Resistance to Flow in the Everglades
Geographic area: (1) Taylor Slough Basin, (2) Sites P33, NESRS3, Everglades National Park
Project start date: October 1994
Project end date: March 2000

Project chief: Jonathan K. Lee
Region/Division/Team/Section: Northeast Region, Water Resources Division, National
Research Program
Email:jklee@usgs.gov
Phone: (703) 648-4033
Fax: (703) 648-5484
Mail address: U.S. Geological Survey, 430 National Center, 12201 Sunrise Valley Drive,
Reston, VA 20192

Program(s): Fragile Environments

Program element(s)/task(s): 1.5

BACKGROUND NARRATIVES
Project summary: Surface-water flow models are needed to evaluate restoration and management alternatives for the south Florida ecosystem. Model results are sensitive to expressions used to represent flow resistance due to vegetation. The project seeks to develop methods for representing flow resistance due to vegetation types typically found in the Everglades. The project also seeks an understanding of the effect of vegetation on surface-water flow and improved techniques for measuring flow velocities and water-surface slopes in wetlands.

Project objectives and strategy: Restoration and management decisions about the south Florida ecosystem are based in part on the results of numerical surface-water models. Model results are sensitive to the expressions used for vegetative flow resistance and to the values of the coefficients that appear in these expressions. The objectives of the project are to identify the most appropriate parameters for representing resistance due to vegetation types typically found in the Everglades, develop empirical expressions for flow resistance, and evaluate the coefficients that appear in these expressions.

The overall strategy has four parts:

  • A study of flow resistance in a uniform stand of sawgrass in a flume to determine how flow resistance depends on flow characteristics and the vegetation.
  • Evaluation of flow resistance in the field to determine how factors not represented in the flume affect flow resistance. The collection of field data depends on the development of improved techniques for measuring flow velocities and water-surface slopes. Field measurements will also lead to an understanding of the effect of vegetation on flow structure.
  • Development of empirical relations for flow resistance within model-grid-scale areas of mixed vegetation of nonuniform density by using computer models, remote-sensing techniques, and geographical-information-system (GIS) tools.
  • Assessment of methods developed in the flume and aggregation efforts for expressing vegetative resistance to flow. This will be done with hydrodynamic surface-water models of the Everglades Nutrient Removal (ENR) Project and a small part of the Taylor Slough basin.

Potential impacts and major products: The project will identify the most appropriate parameters for representing resistance due to vegetation types typically found in the Everglades, develop empirical expressions for vegetative flow resistance, and evaluate the coefficients that appear in these expressions. The project will also lead to an understanding of the effect of vegetation on surface-water flow. Improved techniques will be developed for measuring flow velocities and water-surface slopes in wetlands.

Among the scientific questions that this project will help answer are:

  • What are the most appropriate parameters for representing flow resistance in the Everglades?
  • Can empirical expressions using these parameters be developed for vegetative flow resistance?
  • Can the coefficients that appear in these expressions be determined?
  • How does vegetation affect the flow structure, both vertically and horizontally?
  • How can flow velocities and water-surface slope be best measured?

The development of improved expressions for vegetative flow resistance will enhance numerical models used by federal and state agencies that are evaluating restoration and management alternatives for the south Florida ecosystem. Because the models are sensitive to the expressions used for flow resistance and the coefficients that appear in these expressions, the project will result in improved model results, which in turn will improve management and restoration decisions based on the model results. For this reason, the project is important to program priorities.

Planned major products include a report and paper on modeling Cell 1 of the Everglades Nutrient Removal Project, a series of reports and papers on flow-resistance results from flume and field measurements, and a report and journal article on parameter aggregation and field validation of methods for representing vegetative flow resistance.

Collaborators, clients: Flow-resistance information and the models that require this information are used by the South Florida Water Management District (SFWMD), the Corps of Engineers (COE), and the National Park Service (NPS). The design and operation of stormwater treatment areas (STAs), such as the prototype ENR Project, for the removal of phosphorus from agricultural runoff will be improved when the hydraulic models used to design and plan the operation of STAs incorporate improved expressions for vegetative resistance to flow. Restoration and management decisions based on models such as the South Florida Water Management Regional Model and the U.S. Geological Survey (USGS) Southern Inland and Coastal Systems (SICS) Model will be based on more realistic simulations when the improved expressions are incorporated in these models.

Because of the urgent need for flow-resistance information for the ENR Project and the need to answer specific hydraulic questions, considerable effort has gone into modeling and field data collection there. This work was partly funded under a separate project with the SFWMD through the USGS Florida District. I have worked closely with Mariano Guardo of the SFWMD to obtain data for the development and application of a hydraulic model of Cell 1 of the ENR Project. The Cell 1 model has been used to determine the effects of plugs placed in north-south canals in the ENR Project and will be used in the future to test methods of representing vegetative flow resistance. In particular, the SFWMD, with assistance from the USGS, has provided the following data for Cell 1 of the ENR Project: ground-surface elevations, maps of vegetation type and density, information on the structures used to control inflows and outflows, and experimental data, including boundary-condition, wind, precipitation, evapotranspiration, levee-seepage, point-velocity, and water-surface-elevation data.

Vegetation maps developed by the former National Biological Survey (now the Biological Resources Division of the USGS) and the University of Florida are being used by the vegetative-resistance project in developing methods for defining flow resistance as a function of vegetation type and characteristics. Vegetation-map data are being manipulated by the SICS GIS model interface (Dave Stewart, WRD). Techniques for obtaining vegetation information are also being developed by the project Multi-Sensor Fusion and Exploitation of Remotely Sensed Imagery for Developing Land Characteristics and Land Cover (Greg Desmond, NMD). In return, the vegetative-resistance project has provided ground information for use by the remote-sensing project. Field sites in the Shark River Slough were established jointly with those of the evapotranspiration (ET) project (Ed German, WRD), and I will use data collected by the ET project. The ET project will develop an improved process-oriented description of ET, which will be used in the modeling efforts. The vegetative-resistance project will use ground-surface-elevation data collected by the project High-Accuracy Elevation Data Collection (Greg Desmond, NMD) in modeling part of the Taylor Slough basin. The expressions and coefficients developed by the flow-resistance project will be used by the project Southern Inland and Coastal Systems Model Development (Eric Swain, WRD), which is developing a surface-water model of the Taylor Slough basin, and a project developing a model for canal/wetland interactions (Schaffranek, WRD). Ed German and the Florida District are providing airboat support.

WORK PLAN
Time line (FY 1999 to project end): The major tasks and deliverables and the key staff responsible are:

  • Complete a draft journal article on the pipe manometer (Lee), October 1998.
  • Complete the analysis of hydraulic (Lee) and vegetation (Carter) data from sites P33 and NESRS3 and complete a draft report (Lee and Carter) on these data, December 1998.
  • Complete the analysis of hydraulic (Lee) and vegetation (Carter) data from the flume and complete a draft report (Lee and Carter) on these data, March 1999.
  • Complete a draft journal article on the effect of Everglades vegetation on horizontal and vertical flow structure (Lee and Carter), March 1999.
  • Complete the analysis of hydraulic (Lee) and vegetation (Carter) data from Taylor Slough and complete a draft report (Lee and Carter), March 1999.
  • Complete the draft of a journal article on the results of the flume and field studies (Lee and Carter), June 1999.
  • Complete the parameter-aggregation study (Lee), September 1999.
  • Complete the Taylor Slough modeling study (Lee), November 1999.
  • Complete the drafts of a report and journal article on parameter aggregation and field validation of methods for representing vegetative flow resistance (Lee), January 2000.
  • Obtain Director's approval for all reports and papers (Lee and Carter), March 2000.

FY 1999 activities: FY 1999 activities will focus on completing the analysis of already collected flow-resistance data from the Stennis Space Center flume and the field; developing methods for representing flow resistance as a function of the flow and the vegetation characteristics; developing a model of a part of the Taylor Slough basin to test flow-resistance and parameter-aggregation concepts; and writing reports and papers.

Analysis of the flume and field data (from Taylor Slough and sites P33 and NESRS3 in the Everglades National Park) collected in FY 1996 through FY 1998 will continue. These data will be published in FY 1999. The relation between flow resistance and vegetation characteristics and the usefulness of possible expressions for representing vegetative flow resistance will be studied. Basic data will be published in data reports in FY 1999 and made available on the World Wide Web. Analysis of the data will be summarized in a journal article.

A 1-week field trip is planned to the ENR Project and Water Conservation Area 2 to collect additional data on flow resistance in cattails. The data-collection team consists of five people. Data will be collected at several locations dominated by cattails or submersed aquatic vegetation. Measurement of flow depth, flow velocity, and water-surface slope is necessary to evaluate flow resistance. An acoustic Doppler velocimeter (ADV) will used to measure flow-velocity profiles in flows where the mean velocity is often less than 1 centimeter per second. A unique manometer developed by the project for the local measurement in the field of water-surface slopes on the order of 1 centimeter per kilometer will be used to obtain water-surface slopes. Vegetation will be sampled wherever hydraulic measurements are made. At each measurement site, biomass per unit area, number of stems and leaves per unit area, and leaf and stem width as a function of distance from the bed will be measured. These flow and vegetation data will be used to study the relation between flow resistance and vegetation characteristics. Data will be published in a data report and made available on the World Wide Web.

Empirical relations will be developed for flow resistance within model-grid-scale areas of mixed vegetation of nonuniform density by using computer models, remote-sensing techniques, and GIS tools. This work will be carried out in close cooperation with the project Multi-Sensor Fusion and Exploitation of Remotely Sensed Imagery for Developing Land Characteristics and Land Cover (Greg Desmond, NMD).

Surface-water flow models of Cell 1 of the ENR Project (developed under a separate project with the USGS Florida District and the SFWMD) and a small part of Taylor Slough basin will be used to develop ways of representing flow resistance in model-grid-scale areas of mixed vegetation of nonuniform density (parameter aggregation) and validate the selected methods for representing vegetative flow resistance.

FY 1999 deliverables/products:

  • A journal article on the unique pipe manometer developed for this project and used to obtain water-surface slopes in wetlands.
  • A report on the hydraulic and vegetation data obtained at sites P33 and NESRS3 in the Everglades National Park.
  • A report on the hydraulic and vegetation data from the flume.
  • A journal article on the effect of Everglades vegetation on horizontal and vertical flow structure.
  • A report on the hydraulic and vegetation data from Taylor Slough.
  • A journal article on the results of the flume and field studies.

FY 1999 outreach: Results will be communicated to the SFWMD, the NPS, the COE, and the public at informal meetings throughout the year. The vegetative resistance project has worked closely with Mariano Guardo of the SFWMD in development of the hydraulic model of Cell 1 of the ENR Project. This collaboration will continue during testing of new methods of representing flow resistance in the model. Talks and posters will be presented at American Geophysical Union and American Society of Civil Engineers conferences.

New directions or major changes for FY 1999: Because of the illness of the project chief, several products planned for delivery in FY 1998 will not be completed until FY 1999. For the same reason, it will not be possible to complete all the remaining work during FY 1999. Several tasks and deliverables will not be finished until FY 2000

ACCOMPLISHMENTS, OUTCOMES, PRODUCTS, OUTREACH
FY 1998 accomplishments and outcomes, including outreach: Velocity-profile and vegetation data collected in the flume in FY 1996 and FY 1997 were analyzed. Water-surface-elevation and pipe-flow data collected in the flume in FY 1996 were analyzed and used to calibrate a unique pipe manometer used to obtain water-surface slopes in wetlands. A 2.4-meter-long, 7.6-centimeter-diameter plastic pipe with a short elbow at one end is positioned horizontally just below the water surface and parallel to the flow direction with the elbow at the upstream end and pointing down. The velocity of water in the pipe is a function of the characteristics of the pipe and the difference in water-surface elevation at the entrance and exit. The centerline flow velocity in the pipe is measured by inserting an ADV that is equipped with a side-looking probe into the downstream end of the pipe. The pipe was calibrated in the flume at the hydraulics laboratory at Stennis Space Center and has proven to be an efficient, accurate method for the local measurement of water-surface slopes for the low-velocity, small-gradient flows of the Everglades.

Velocity-profile and vegetation data collected in the field in FY 1996 and FY 1997 at sites P33 and NESRS3 in the Everglades National Park were analyzed. Pipe-flow data collected at these sites in FY 1997 were analyzed, and water-surface slopes were obtained from the pipe-flow data. Field measurements were made in November 1997 in the Taylor Slough basin in the Everglades National Park to obtain information on the relation between flow and vegetation characteristics. Measurement of flow depth, flow velocity, and water-surface slope was necessary to evaluate flow resistance. Vegetation was sampled wherever hydraulic measurements were made. Approximately 20 hydraulic and 20 vegetation measurements were made during this field trip. An ADV was used to measure flow velocities, and the pipe manometer was used to obtain water-surface slopes.

Outreach during FY 1998 included the following talks and posters:

Carter, V. P., Reel, J. T., Lee, J. K., and Rybicki, N. B., 1998, The relation between vegetation and water-flow velocity profiles in an emergent wetland, Everglades National Park, Florida, in Spilhaus, A. F., Jr., ed., Spring Meeting, Boston, 1998, Supplement to Eos, Transactions, American Geophysical Union: Washington, D.C., American Geophysical Union, p. S93 (abstract, poster).

Lee, J. K., and Carter, V. P., 1997, Vegetative resistance to flow in the Florida Everglades, in Gerould, S., ed., U.S. Geological Survey program on the south Florida ecosystem: Technical Symposium, Ft. Lauderdale, Fla., 1997, Proceedings: U.S. Geological Survey Open-File Report 97-385, p. 49-50 (abstract).

Lee, J. K., and Carter, V. P., 1998, Field measurement of flow resistance due to vegetation in the Florida Everglades, in Spilhaus, A. F., Jr., ed., Spring Meeting, Boston, 1998, Supplement to Eos, Transactions, American Geophysical Union: Washington, D.C., American Geophysical Union, p. S87 (abstract, talk).

Reel, J. T., and Lee, J. K., 1997, The relation between vegetation and water-flow velocity profiles in a sawgrass marsh, Everglades National Park, Florida, in Gerould, S., ed., U.S. Geological Survey program on the south Florida ecosystem: Technical Symposium, Ft. Lauderdale, Fla., 1997, Proceedings: U.S. Geological Survey Open-File Report 97-385, p. 74 (abstract, poster).

FY 1998 deliverables, products completed: A modified version of the finite-element surface-water model FESWMS-2DH for use in modeling wetlands was completed in FY 1998. A report describing the new features that were added to FESWMS-2DH was approved by the Director. A report describing the application of the improved model to Cell 1 of the ENR Project was approved by the Director. The model and data sets for Cell 1 were delivered to the SFWMD. The citations follow:

Lee, J. K., 1998, Finite-element surface-water modeling system: Two-dimensional flow in the horizontal plane--Addendum to the users manual: U.S. Geological Survey Open-File Report 97-410, 80 p.

Lee, J. K., and Guardo, Mariano, 1998, A finite-element surface-water model of Flow-Way Cell I of the Everglades Nutrient Removal Project: U.S. Geological Survey Water-Resources Investigations Report 97-4159, 70 p.

PROJECT SUPPORT REQUIREMENTS
Names and expertise of key project staff: FY 1999:  J.K. Lee, hydrologist; V. P. Carter, biologist; N. B. Rybicki, biologist; J. Reel, biological technician; H. Ruhl, biological technician; Pat Gammon, botanist; P. M. Shackelford, hydrologic technician.

FY 2000: J. K. Lee, hydrologist; N. B. Rybicki, biologist; J. Reel, biological technician; H. Ruhi, biological technician.

Other required expertise for which no individual has been identified: FY 1999:
Hydrologist, GS-12; Computer Specialist (summer student), GS-4.

FY 2000: Hydrologist, GS-12; Computer Specialist (summer student), GS-4.

Major equipment/facility needs: None.
 


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