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projects > evaluation of methods to determine groundwater seepage beneath levee 30 > 1998 proposal


Evaluation of Methods to Determine Groundwater Seepage Beneath Levee 30, Miami-Dade County, Florida

Project Proposal for 1998

Program: Fragile Environments
Project Title: Evaluation Of Methods To Determine Groundwater Seepage Below Levee 30 And Levee 31N, Dade County, Florida
Location of Study Area: Dade County, Florida
Project Start Date: October 1994
Project End Date: September 1999
Project Number:
Project Chief: Roy S. Sonenshein
Region/Division/Team/Section: WRD, Miami, Florida
E-mail:<sunshine@usgs.gov>
Phone: 305-526-2895
Fax: 305-526-2881
Mailing Address:
US Geological Survey
9100 NW 36th Street
Suite 107
Miami, Florida 33178
Program Element(s)/Task(s) South Florida. Element 2: Modeling and Support Studies for Southern Inland Coastal Systems of Eastern Dade County and Biscayne Bay, Task 2.4: Groundwater Seepage Beneath the Protective Levee
Panel:
Collaborators, Clients:
Clients include three regulatory/management agencies, the U.S. Army Corps of Engineers (COE), the South Florida Water Management District (SFWMD), and the Everglades National Park (ENP). Models being developed to study the effects of changing the water levels in Water Conservation Area 3B (WCA 3B) and of well field pumping on the ENP require the results of this study. The results of the study will be used by the South Florida Water Management District as part of the Lake Belt study in Dade County. The results of the study will also be used by Dade County in the management of two well fields, the Northwest Well Field, east of Levee 30, and the West Well Field, east of Levee 31N.



BACKGROUND NARRATIVES

Project Summary: The amount of water seeping under the protective levee system between the Everglades National Park and the urban and agricultural area to the east is poorly estimated. The objective of this project is to evaluate methods of determining ground-water seepage beneath Levee 30 and Levee 31N. The accounting of all significant hydrologic inflows and outflows to the Everglades ecosystem of the south Florida mainland is a key element of the South Florida Ecosystem Program.

Project Justification: Plans to restore historical hydrologic conditions in the northeast section of ENP include the raising of water levels in ENP and WCA 3B, which overlie the Biscayne aquifer, an extremely permeable aquifer. The increase in water levels is likely to cause an increase in seepage losses to the cast under Levee 30 and Levee 31N. Water supply for the urban areas to the east is dependent on well fields in these areas. Application of real time data to a model and development of empirical relationships between groundwater levels, stages in WCA3B and ENP, canal stages, and seepage will improve management of water resources in the area, including pumping at the West Well Field near Levee 31N and the Northwest Well Field near Levee 30.

Project Objectives: The objective of this project is to evaluate methods for quantifying ground- water seepage beneath Levee 30 and Levee 31N and analyze these methods with respect to data requirements and computational effort. The use of different ground-water models will be evaluated and empirical relationships between field data and ground-water seepage will be developed, where possible. The data needs to determine the empirical relationships will be evaluated. Accurate seepage data will enhance the accuracy of models of the Everglades and coastal systems.

Overall Strategy, Study Design, and Planned Major Products: The study area for this 5-year effort (FY95 to FY99) is limited to a 3-mile reach of Levee 30 in north-central Dade County and a 5-mile reach of Levee 31N in central Dade County. Hydrologic and geologic data will be collected and utilized in the development and calibration of ground-water flow models to determine seepage rates beneath Levee 30 and Levee 31N. Data collection will include ground- water levels, surface-water stages, canal discharges, vertical infiltration rates, and geologic cores. Oxygen isotope data will be used as a tracer at the Levee 31N study site. The models will include flow nets, and cross sectional and three dimensional numerical models that will be developed using the COE SEEP2D code and the USGS MODFLOW code. Empirical relationships will be developed using the results of the ground-water flow models to determine the data needs to provide real time seepage data to the regulatory and management agencies. The results for each study site will be published in a separate water resources investigation report.

WORK PLAN

Overall:
The project consists of two study areas, a 3-mile reach of Levee 30 in north-central Dade County and a 5-mile reach of Levee 31N in central Dade County. The Levee 30 study was started in FY95 and is nearing completion. Data collection has been completed. Modeling and the development of the empirical relationships will, be completed during FY97. The remainder of the work in FY98 will consist of completing and publishing the WRIR.

Work at the Levee 31N site will begin during the summer of 1997. This is required to obtain sufficient data during the wet season to complete the project by the end of FY99. The existing surface water stage, AVM discharge, and groundwater level recorder network for the West Well Field will be supplemented with additional data collection from existing or newly drilled monitor wells near the Levee 31N Canal. Additional wells are needed to determine the vertical head gradients west of the levee. Infiltration meters will be installed at selected locations to measure vertical seepage rates. Oxygen isotope data will be collected and analyzed under contract with the University of Miami. Collected data will be utilized in the development and calibration of a transient 3-dimensional groundwater/surface water model (MODBRANCH) to determine seepage rates beneath Levee 31N. The MODBRANCH code will be modified to incorporate a "reach transmissivity" leakage option between the river and groundwater. This "reach transmissivity" relationship has been successfully used for steady conditions at this site in a previous study.

Calculation of canal seepage rates and calibration of the Levee 31N flow model will be completed by March 1999. An empirical relationship between field data and seepage rates will be determined for the site. The water resources investigation report describing the results of the Levee 31N study will be completed and published by the end of FY 1999.

All time series and miscellaneous water level, discharge, and water quality data collected for the project will be stored in the USGS NWIS data base. Additional data will be published in the reports and/or made available via the internet. Any cores obtained from drilling will be stored either at the University of Miami core repository or the State of Florida core repository in Tallahassee.

Timeline:
FY98 L30 Complete and publish WRIR Sonenshein April 1998
L31N Existing data compilation Nemeth September 1998
L31N Field data collection Nemeth September 1998
L31N Oxygen isotope sampling and analysis Solo-Gabriel September 1998
L31N Flow model data modifications Nemeth January 1998
L31N Flow model data compilation Nemeth September 1998
FY99 L31N Flow model calibration Nemeth March 1999
L31N Complete and publish WRIR Sonenshein September 1999

Planned Deliverables/Products: Two water resources investigation report are planned which will document the results of the study. The first report will be ready for colleague review by April 1998 and will be available for distribution by the end of September 1998. The second report will be ready for colleague review by April 1999 and will be available for distribution by the end of September 1999. Both reports will include descriptions of the data collection and the models developed.

Planned Outreach Activities: Data will be made available to the SFWMD and Dade County, when requested, for their modeling and management needs. Data will be available in the US6S NWIS data base and via the internet. Both agencies have direct access to the NWIS data base. Committee meetings will be attended and preliminary results will be discussed prior to approval of the final reports.

Prior Accomplishments in Proposed Area of Work:

New Directions, Expansion of Continuing Project (if applicable): The project, scheduled to end in FY98, is being extended to a second site, Levee 31N. This site is more complex than the Levee 30 site because of the presence of the West Well Field and the pumping station in the canal to the south of the study site. This will require the use of a three dimensional flow model. A significant amount of data is available at this site. Sources include the USGS Miami office (West Well Field groundwater level and surface water stage and discharge monitoring network), the SFWMD, Everglades National Park, and the University of Miami. It is anticipated that personnel from the University of Miami Civil Engineering Department wilt be hired to assist with the data collection and modeling of the Levee 31N site.

ACCOMPLISHMENTS, OUTCOMES, PRODUCTS, OUTREACH

Accomplishments and Outcomes, Including Outreach: The collection of data at Levee 30 using continuous recorders from 21 wells and 2 surface water sites was discontinued in December 1996, with all sites leveled to a common datum (mean sea level). Infiltration meters were installed at two sites to measure vertical seepage rates in the Conservation Area. Discharge measurements have been made at three sites in the Levee 30 canal to determine the seepage rate between the ground-water and surface-water in the canal. The development of two models are under way, a seepage model using the COE SEEP2D model, and a 3D cross-sectional flow model using the USGS MODFLOW model. Data collection will be started for the Levee 31N site during the summer of 1997.

During FY97, data collected at the Levee 30 site was supplied to the SFWMD for use in the development of a regional ground-water flow model. This model is being used for the development of a "Lake Belt" plan for the area east of Levee 30 and Levee 31N. Data was provided to the Seepage Management technical advisory committee of the Governor's Commission for a Sustainable South Florida. Finally, data was also provided to the State Department of Environmental Protection for use in the evaluation of a permit for a rock mine in the vicinity of Levee 31N.

Deliverables, Products Completed: An abstract is being written for the 1997 annual meeting.

NEEDS

Required Expertise:
FY98, FY99 - Senior modeler. assistant modeler

Names of Key Project Staff:
FY98, FY99
Roy S. Sonenshein
Mark Nemeth (University of Miami, contract)
Dr. Helena Solo-Gabriele (University of Miami, contract)

Major Equipment/Facility Needs: None


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Last updated: 24 April, 2014 @ 01:01 PM (KP)