green alternatives to rock rip rap for streambank...

Presented by Michael Close, PE, CPESC, Engineering Solutions Specialist – Erosion ControlNorth American Green, a Tensar International Company

Green Alternatives To Rock Rip Rap For Streambank Protection And Shoreline Stabilization

Why use a Turf Reinforcement Mat (TRM)?

• Used when grass/vegetation is not enough

• TRMs reinforce turf/vegetation to limit erosion• ASTM D6460 Determination of Rolled Erosion Control Product (RECP) Performance in Protecting Earthen Channelsfrom Stormwater-Induced Erosion•ASTM D6459 Determination of RECP Performance in Protecting Hillslopes from Rainfall-Induced Erosion

• A TRM is a permanent RECP

• An Erosion Control Blanket (ECB) is a temporaryRECP

Shear Stress Comparison, Channels

Material Shear Stress (lbs/ft2)ECBs & TRMs un-vegetated 1.5 to 3Transition Mat/TRM un-vegetated 7 to 9 Most Grasses 3 to 8TRMs vegetated 8 to 151 ft avg. dia. Riprap (12” dia.) 4.8

Shear stress approximation (lbs/ft2)= D(50)*4.8See HEC-15 [D(50) in feet]

Does 4.8 lbs/ft2 seem too conservative for 1ft dia.?

How do Engineers Design Riprap?

• “… the way we’ve always done it”

• Which method applies?• Technical Supplement 14C, National Engineering Handbook titled Stone Sizing Criteria by USDA/NRCShttp://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=17812.wba

• Background to Rock Sizing Equations by Catchments & Creeks Pty Ltd http://www.catchmentsandcreeks.com.au/docs/Background-To-

Rock-Sizing-Equations.pdf

• Riprap Design Criteria, Recommended Specifications, and Quality Control http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_568.pdf

(Riprap Design Software descriptions on page 135)

Resources for Riprap Design?

How are TRMs different? Are they all installed the same way?

• Stitch Bonded TRMs•Can be laid over seed (New vegetation grows up thru TRM)•Some can be placed 1st then covered with sod•Some include mulch aiding vegetation establishment

•High Performance TRMs •Typically placed 1st then covered with sod or soil & seed•Traditionally used for most challenging conditions•High tensile strength, high UV stability, high quality control standards

What new in TRMs?

•Next Generation TRMs• High Tensile Strength at Low Strain – Presently HPTRMs do not reach ultimate tensile strength until elongations reach 25% to 40%

•Place Hydraulic Erosion Control Products (HECP) before or after placing a TRM

• New TRMs are available to use with hydraulically applied mulch or hydroseeding

FHWA Standard Specification

Riprap Cost

• Alabama DOT, Class 2 Riprap = 50% > 80 lbs• D(50) of about 9.5”, Range from bid tabulations

from $25 to $50/ton = $17.40/syd to $34.80/syd

Riprap vs. TRM w/Reinforced Vegetation

• Installed Cost of 12” Riprap from 3 State DOTs• For small areas of 1000 to 2000 square yards =

$30 to $40 per square yard • For large areas of an acre or larger (>4840 syds) =

$15 to $20 per square yard

• Installed Cost of TRM, seed, fertilizer, & lime• $5 to $12 per square yard

Proposal To Reissue and Modify Nationwide Permits

• Proposed Rule by the US Army Corps of Engineers• Available for viewing on the Federal Register• Comment period from June 1, 2016 to August 1, 2016• Existing NWPs expire March 17, 2017

• “As discussed elsewhere in this notice, we are proposing to develop a standard form for use in submitting PCNs. The proposed PCN form will include two questions for PCNs involving bank stabilization activities. The first question will ask whether the applicant has considered the use of living shorelines, if he or she is submitting a PCN for a bank stabilization activity. The second question will ask if there are consultants and contractors in the area that are qualified to design and construct living shorelines.”

Turf Reinforcement Mat ApplicationsDesigning Erosion Control Solutions

Channels

Vanderburgh Co Fairgrounds, Evansville IN

Vanderburgh Co Fairgrounds, Evansville IN

MSE and other Retaining Walls

Transition Mats over TRMs

• ASTM subcommittee D18.25.12 draft definition for transition mats

• Immediate un-vegetated permissible shear stress > 6 psfwhen placed over an RECP

• Vegetated permissible shear stress > 12 psf when placed over an RECP

Projects with combination Slope Stability and Erosion Control needs

• TRMs with Soil Anchors – No full scale tests to determine erosion control benefit to date.

• Geogrid in fill sections• Slope Failure Repairs• Mechanically Stabilized Earth (MSE) wire-faced retaining walls • MSE Steepened Slopes

• Plate Piles (e.g. Geopier SRT system)

TRMs with Soil Anchors

GeogridLayers

Remove slide mass Excavate benches. Place engineered fill.

Slope Failure Repair Solution with Geogrid

Plate Piles resist movement by “pinning” failing or unstable slope

Unstable Layer

Competent Layer

Slope increment supported by Plate Pile

Erosion Control Material Design Software (ECMDS)

Login at: http://www.tensarnagreen.com/ or

http://www.ecmds.com/

•ECMDS designs for the following applications• Channels• Slopes• Vegetation Selection• Spillways• User-Defined Channels• Outlet • Drop Structure• Mattress Channel

ECMDS 5.0 Features

Assists in selection of:• Temporary Erosion Protection

• Rolled Erosion Control Products (RECPs)• Hydraulic Erosion Control Products (HECPs)

• Permanent Erosion Protection• Vegetation• Reinforced Vegetation• (TRMs, Transitions mats)• Hard Armor• (Marine Mattresses, rock riprap, concrete)

ECMDS 5.0 Features

ECMDS Slope Module Features

RUSLE methodology

•Outlined in USDA Agriculture Handbook 703, 1997

•RUSLE factors rainfall, slope length and grade, soil types, and cover type

•Failure based on tolerable soil loss limits

Federal Highway Administration’s Hydraulic Engineering Circular #15

• “Design of Roadside Channels with Flexible Linings”

• Based on permissible shear stress procedures

• More concise design methodology than permissible velocity

ECMDS Channel Module Features

Refining Vegetative Channel Liner Design

•USDA’s Agriculture Handbook 667•Improved definition of vegetative cover (e.g. growth habit and density)

• enhanced definition of effective roughness• better definition of cover provided by vegetation

•Determination of shear force penetrating vegetation•Calculates shear stress acting on underlying soil

ECMDS Channel Module Features