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TECHNICAL MEMORANDUM <br /> July 13, 1995 <br /> Page 17 <br /> The development of an erosion control manual or guidelines for Medford must include <br /> consideration of the quantity of rainfall received in the Medford area. Erosion control <br /> practices for northwest Oregon and the Puget Sound area are based upon receiving over <br /> 40 inches of rain per year Some techniques developed for these areas may not be <br /> appropriate for a dry climate as that experienced in Medford. The experience of <br /> municipalities with drier climates should be emphasized. <br /> Standard methods for preventing, reducing, or treating erosion are well documented in a <br /> number of references including the references attached to this technical memorandum. The <br /> general types of controls that are described in these documents are listed in Table 3 -8. <br /> Table 3 -8 Standard Erosion Control Measures <br /> Type of Control Discussion <br /> Vegetative Erosion Controls <br /> Undisturbed vegetative buffers Natural vegetated areas left undisturbed to filter sediment from <br /> runoff. <br /> Manmade vegetative buffers Temporary or permanent vegetated areas in place to prevent <br /> erosion and filter sediment from runoff. <br /> Mulches Used to protect disturbed or reseeded soils. Often used when <br /> construction is outside of normal growing season. <br /> Structural Control Measures — Diversions and Rundowns <br /> Diversion structures: dikes and swales Used to reduce runoff velocities, particularly down or across a <br /> slope. Can be used in conjunction with sediment traps or ponds <br /> to direct runoff directly to those facilities. <br /> • <br /> Rundowns Structures used to collect concentrated flows and direct them <br /> down slopes. Pipe systems or open systems such as concrete <br /> flumes are used to protect the slope. <br /> Structural Control Measures — Filter Structures <br /> Inlet filters Gravel and filter fabric can be placed around an inlet to provide a <br /> sediment filter. Straw bales can_also be used to provide this <br /> function. <br /> Permeable berms Berms constructed in drainage ditches or the downstream slope of <br /> construction sites are used to trap sediment. Berms may be <br /> constructed with gravel, straw bales or earthen structures with <br /> outlet pipes. <br /> Silt fences Used near the perimeter of the construction area to intercept and <br /> detain sediment from erodible surfaces. Fence may be <br /> constructed from filter fabric or straw bales. <br /> DRAFT <br /> J:\21 I'M'rsk3Wn31.cug <br />