Period Covered by the Report: 9-10-03 to 12-9-03
Date of Report: 1-10-04
EPA Grant Number: R83-0633-010
Title: Effective Stormwater and Sediment Control During Pipeline Construction Using a New Filter Fence Concept
Investigators: Billy J. Barfield, Khaled A.M. Gasem, Marty Matlock
Institution: Oklahoma State University, University of Arkansas
EPA Project Officer: Bala Krishnan
Project Period: 9-10-03 to 9-9-04
Project Amount: $159,734
Research Category: Pollution Prevention
Description:
Objective(s) of the Research Project Specified for Current Project Period:
Develop an analysis of the regulatory criteria for implementing the improved silt fence Prepare and present a workshop at the IPEC meeting Develop and calibrate a physical process-based model to predict the performance of FAESF and use that model to select alternative designs that would work under a wider variety of conditions than could be tested in this project Prove the new silt fence design and implementation under laboratory and field conditions where the current silt fence fails due to: Flow concentrations that result from current installation technology Failure to trap clays and fines
Objective(s) Proposed for Year 2 Project Period to be Addressed in Current Project Period:
Prove the new silt fence design and implementation under laboratory and field conditions where the current silt fence fails due to: Excessive stretching of the filter fabric Insufficient stability of the support posts Develop design requirements for machine systems to install fences
Progress Summary/ Accomplishments:
A preliminary assessment of regulatory criteria for Oklahoma, Texas, Arkansas, Kansas and Missouri has been completed. The results were presented at the IPEC workshop in November 2003. The regulatory implications of the Phase II regulations of the Clean Water Act Stormwater Permit Program are still evolving. The regional states are adopting and implementing policies this year. Those policies and their implications to the pipeline construction industry will be summarized in a report at the end of 2004.
A workshop was conducted November 12, 2003 at the IPEC meeting in Houston, Texas. The PIs on this project and additional researchers presented the current status of design research, field monitoring, and regulatory issues. The attendees, representing regulatory, industry, and academic/research constituencies then participated in a discussion to establish consensus on state of the art in fence design, criteria for successful BMP performance, and technical, economic, and regulatory issues.
Significant progress has been achieved in the development of the mathematical model. The overall framework for the hydrology and overland sediment routing component has been established, and the selected algorithms have been programmed into a spreadsheet-based model. Assessment based on the limited rainfall simulation data collected to date shows that the hydrology portion of the model gives reasonable predictions, deviating from measured data by approximately 13 percent. For silt fence laid on a slope allowing concentrated flow along the toe, algorithms to divide the flows between through and along the fence have been developed based on flume test data. For cases where impoundment upstream of the fence occurs, relationships between static head and flow through the fence will be used. The rill detachment/deposition algorithms implemented in SEDIMOT III were programmed into the spreadsheet-based model to predict the scour along the toe of the fence. Work is in progress to convert the spreadsheet-based model to a visual basic version.
To address the objective of trapping fines, an investigation is currently underway to identify various formulations of polyacrilimide (PAM) that would have the best potential to enhance the flocculation of clay particles under the anticipated field conditions. We are currently assembling the laboratory supplies that will be needed for preliminary lab tests of the selected compounds.
Preliminary analysis of the effectiveness of reinforcing the fence to prevent excessive stretching is also in progress. The approaches considered include use of conventional silt fence with a fused-on backing or use of other geotextiles with better tensile strength. Use of non-woven geotextile is considered promising because its hydraulic properties stay more consistent under deformation from ponded or flowing water upstream of the fence. In addition, these fabrics have significantly greater tensile strength and resistance to puncturing and tearing, so a fused-on backing would not be required. A potential disadvantage is that the standard ASTM test for flow rate indicates that water will flow through the fence significantly faster than it does through the woven fences, theoretically reducing the detention time and trapping efficiency. However, our experience with the woven fabrics indicates that that particular test result is not very representative of the hydraulic performance of a geotextile when placed vertically and functioning as a silt fence.
A 3-D Pro-E model has been developed that simulates the material properties, height of the fence, and post spacing. We are in the process of obtaining the finite element analysis module (Pro-Mechanica) that will be used to assess the ability of materials with different properties to withstand the loading of impounded and flowing water. An optimum post spacing for each type of material can then be determined, and the relative costs and benefits with respect to installation and material costs of using a cheaper, weaker material requiring more post support versus using a stronger, more expensive material and fewer posts can be completed.
Finally, the objective of developing a machine that installs the fences is being addressed by an OSU Biosystems and Agricultural Engineering senior design team, in cooperation with the industry partner Charles Machine Works. Their project focus is to develop an implement that will bury the silt fence sufficiently deep and with minimal disturbance, such that flow along or across the soil-fabric interface cannot result in undercutting. During the past fall semester, the group completed a preliminary design report.
Publications/ Presentations: We have had abstracts accepted for the ASCE Environment and Water Resources Institute annual meeting, June 27 to July 1, 2004; the 6th International Conference On Hydroscience and Engineering, May 30 to June 1, 2004; and the American Society of Agricultural Engineers International Meeting, August 1-4, 2004. All of these will include a paper to be in a published proceedings and an oral presentation to be given at the meeting.
Future activities: The principal efforts for the next quarterly reporting period will be preparation for field testing, continued development of the mathematical model, and laboratory analysis of selected PAM formulations. Prototype fences with various configurations of aprons and lateral flow barriers will be fabricated using the materials identified as suitable based on the finite element modeling. The field plot and rainfall simulator are already in place and ready for use. We also plan to do a series of flume tests to confirm that, as long as the apron stays intact, no significant erosion will occur under the apron as a result of flow along the top of the apron. Routines to simulate impoundment upstream of the fence, flow through the fence, and settling of settleable solids will be added into the mathematical model.
Activities for subsequent reporting periods in the current project year include completing the field testing of the hydraulic properties of the apron and lateral flow barriers, assessment of the strength of the selected fabrics or fabric/backing combinations, and incorporating the remaining elements into the mathematical model, particularly the sediment trapping components. Development of that part of model will require collection of a portion of the field test data, with validation to be accomplished using the remainder. Data collected as part of our project dealing with current silt fence technology will also contribute to this effort.
The senior design team will complete prototype testing of their fence installation system during the spring semester, and those results will be available to assist in satisfying Objective 6.
Supplemental Keywords: Soil, sediments, pollution prevention, sustainable development, engineering, hydrology, south central, Oklahoma, EPA Region 6, petroleum industry, construction industry.
Relevant Web Sites: We have obtained the services of a computer specialist who will be creating and maintaining a web site that will display information and photos from project activities. Links to this web site will be provided through the following OSU Biosystems and Agricultural Engineering pages: