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Chapter 4-Site-Spec /nd a/ Storm Water BMPs <br />I What to Consider <br />The length of the spreader depends upon the amount of water that flows through the conveyance. <br />Larger volumes of water need more space to even out. Level spreaders are generally used with <br />filter strips (see Vegetated Filter Strips). The depressions are seeded with vegetation (see <br />Permanent Seeding). <br />Level spreaders should not be used on soil that might erode easily. They should be constructed on <br />natural soils and not on fill material. The entrance to the spreader should be level so that the flow <br />can spread out evenly. <br />The spreader should be inspected after every large storm event to check for damage. Heavy <br />equipment and other traffic should be kept off the level spreader because these vehicles may <br />compact the soil or disturb the grade of the slope. If ponding or erosion channels develop, the <br />spreader should be regraded. Dense vegetation should be maintained and damaged areas reseeded <br />as needed. <br />Advantages of Level Spreaders <br />• Reduce storm water flow velocity, encourage sedimentation and infiltration <br />• Are relatively inexpensive to install <br />Disadvantages of Level Spreaders <br />• Can easily develop "short circuiting" (concentration of flows into small streams instead of <br />sheetflow over the spreader) because of erosion or other disturbance <br />• Cannot handle large quantities of sediment-laden storm water <br />E J <br />0 <br />4-1os