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)ter4 - Best. Management Practices for Erosion and <br />4.05 S T RAVV BP,C E BARRIER <br />(ES BMP 4.05) <br />Definition <br />No 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 />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 />°n 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 />