Credit: Laurie Honnigford
Rolled erosion control products come in various forms and styles, and should be selected based on their specific use.
Credit: Laurie Honnigford
Installing turf vegetation mats can help establish vegetation next to culverts.
ECTC works with public agencies to develop testing programs, approval processes, design procedures, and standard specifications. One example is ongoing work with the Federal Highway Administration (FHWA) in revising its documents, Standard Specifications for the Construction of Roads and Bridges on Federal Highway Projects (FP-03) and Design of Roadside Channels with Flexible Linings: Hydraulic Engineering Circular Number 15, Third Edition (HEC-15).
FP-03 governs the construction of roads and bridges on projects under the direct administration of FHWA. Section 713 contains standard specifications for temporary and permanent RECPs.
HEC-15, updated in September 2005, addresses the design of roadside channels—small open channels constructed as part of a highway drainage system. Roadside channels play an important role in the highway drainage system as the initial conveyance for highway runoff. Roadside channels often are included as part of the typical roadway section.
The geometry of roadside channels depends on available right of way flow capacity requirements, and the alignment and profile of the highway. The procedures in HEC-15 also may be used for ancillary roadside drainage features such as rundowns. Design procedures are given for four major categories of flexible lining: vegetative linings; manufactured linings (RECPs); riprap, cobble, and gravel linings; and gabion mattress linings. Design procedures for composite linings, bends, and steep slopes also are provided.
The FHWA's design procedures are based on the concept of maximum permissible tractive force. Methods for determining hydraulic resistance applied shear stress as well as permissible shear stress for individual linings and lining types are presented. This edition includes updated methodologies for vegetated and manufactured RECPdesign addressing currently available commercial products. This edition also includes a unified design approach for riprap integration, alternative methods for estimating hydraulic resistance, and steep slope procedures.
ECTC also has released a DVD on the proper installation of RECPs in channels, slopes, and shorelines. This DVD provides visual step-by-step instruction on procedures including site preparation, RECP placement, RECP stapling/staking, anchoring trench details, and shingling of RECPs.
— Deron Austin is director of marketing with Propex Fabrics in Chattanooga, Tenn., and Tony Johnson is director of the erosion lab at American Excelsior in Rice Lake, Wis.