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(h) Due the varied widths of streams wherein a drop <br />structure may be useful in stabilizing stream banks and stream <br />beds, a specif-ic limitation on the volume of material discharged <br />is not being employed. <br />(j) As a precaution to recreational boaters and <br />rafters, a sign should be placed upstream of any drop structure <br />t.o warn of the structure's presence. The center portion of a <br />drop should be lower to concentrate flows and facilitate boat <br />pR5S8gP. <br />4. JETTIES. Jetties are structures which are placed along <br />a stream bank to direct the flow away from an eroding bank. <br />Jetties may also be used to direct flow toward an instream <br />sand/gravel bar or shoal t.o cause it to scour. Material <br />acceptable for jetties include large angular rock,. large <br />boulders, large concrete chunks without protruding rebar, rock- <br />filled gabions, and logs or trees alone or in combination with <br />the preceding fill materials. Jetties are generally not <br />effective on curves having a radius of less than 200 feet and one <br />jetty alone is usually not sufficient. River cobble, sand, <br />gravel and other erodable material are not acceptable. <br />JettiPS are authorized under this RPG provided: <br />(a) The maximum extension of any jetty into a waterway <br />shall not exceed 25% of the chehnel width. Flows shall not be <br />• directed to erode the opposite bank oP the waterway; <br />(b) Jetties shall be spaced close enough to prevent <br />scouring or scalloping between the structures; <br />(c) The angle of the jetty and bankline should not be <br />greater than 30 degrees; <br />(d) Jetties should generally be triangular in shape <br />(as viewed in a top or plan view). Single wing jetties directed <br />upstream or downstream are not prohibited but the permittee is <br />cautioned that single wing jetties, especially ones directed <br />upstream, may be more suspectible to damage from high flows and <br />require more frequent maintenance. <br />(e) Construction materials must be of sufficient size <br />t.u wit.t:~t.:,nd expected high velocities and turbulence; <br />(f) Jetties must be securely anchored into the bank <br />for severs] feet to protect against undercutting and <br />circumvention of the structure by high flows; <br />(g) Trees used for jetties should not be obtained from <br />ei riparian or riverine source; and <br /> <br />6 <br />