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Chapter - Best Management Practices for Erosion and Sediment Control <br /> 4.05 S T RAVV BP,C E BARRIER <br /> (ES BMP 1 , 05) <br /> Definition <br /> " A temporary sediment barrier consisting of a row of entrenched and anchored straw bales . <br /> Purposes <br /> • 1 . To intercept and detain small amounts of sediment from disturbed areas of limited <br /> extent. <br /> 2 . To decrease the velocity of sheet flows and low-to-moderate level channel flows . <br /> " ' Conditions Where Practice Applies <br /> 1 . Below disturbed areas subject to sheet and rill erosion . <br /> r <br /> 2 . Where the size of the drainage area is no greater than 1 /4 acre per 100 feet ( 1 .3 <br /> ha/100 m) of barrier length ; the maximum slope length behind the barrier is 100 feet <br /> (30 m) ; and the maximum slope gradient behind the barrier is 50 percent (2: 1 ) . <br /> 3 . In minor swales or ditch lines where the maximum contributing drainage area is no <br /> greater than 2 acres(0. 8 ha) . <br /> 4. Where effectiveness is required for less than 3 months . <br /> ` 5 . Under no circumstances should straw bale barriers be constructed in streams or in <br /> swales where there is a possibility of a washout. <br /> r <br /> Planning Considerations <br /> Improper use of straw bale barriers has been a major problem. Straw bale barriers have <br /> been used in streams and drainageways where high water velocities and volumes have <br /> destroyed or impaired their effectiveness . Improper placement and installation of the <br /> barriers, such as staking the bales directly to the ground with no soil seal or entrenchment, <br /> has alloyed undercutting and end flow. This has resulted in additions instead of removal <br /> of sediment from runoff waters. Finally, inadequate maintenance lowers the effectiveness <br /> of these barriers . Trapping efficiencies of carefully installed straw bale barriers on one <br /> project in Virginia dropped from 57 percent to 16 percent in one month due to lack of <br /> • <br /> maintenance. <br /> There are serious questions about the continued use of straw bale barriers as they are <br /> presently installed and maintained. Averaging approximately $3 to $6 per linear foot <br /> installed ($10 to $20 / m) the thousands of straw bale barriers used annually in Florida <br /> represent sufficient expense that optimum installation procedures should be emphasized . <br /> If such procedures are carefully followed , straw bale barriers can be quite effective . <br /> 4-1 .3 <br />