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<br />Stne: :ural Prae:til~!!. <br /> <br />Roek Ripup <br /> <br />~oek rlprap i~ an effee:tlve ~ethod of eontrolling strea~ bank erosion on <br />nearly all stream.. Roek ean be plaeed on stream banks Yhieh are straIght to <br />severely ~eanderlng. Rock for rlp".ap should be material yhichis dense, <br />angula"., and du".able. Rock should be yell &".aded to ~ini~ize al". voids In the <br />riprap blanket, n,e ".ock should be sized to ylthstand the foree of the water <br />in a stream without displacing the roek, Depending on the type of soil In t~e <br />bank, a ripup bla",ket r.tay nqui".e a Hlte". of sand and/o". 6uveL. The filter <br />yiLl prevent the p:lping of soil pa".ticles f".ol1l the bank through the rlprap <br />blanket due to grc1undwater :novement. The strealll bank. t5 shaped to a !Itope no <br />steepe". than 2,1) h"".izontal to L.O vertical pdo" to placement of the rock. <br />The toe of a ripra.l' blanket ~ust be deep enough 1:0 prevent the stream fro'll <br />undercutting the blink below the ".ipup and causing the bank to fall. T;,e <br />upstreal1l and down',I:nal1l ends of the ripup blank"t must be tied Inca the bank <br />at a stable point. <br /> <br />SOllie stream banks".y not requi".e the ripup blanket to u:tend to the top of <br />the bank, An examlple of this could be if the bank on one slde of the stream <br />is significantly blghe". than the bank on the othe". side. The blanket should <br />extend up the bank to a heigh t 0 f one foot above the high ya ter eleva tion, <br />The area above the, rock should be shaped and seecled with approp".late <br />vegetation, <br /> <br />A vadation of thill practiee is to use wire-boall,1 rock. The cross section <br />yould be similar to the ".oek riprap cross seetion. Kowever, since the rock is <br />held in place yith anehored, wire-fencing materbl, the rock can be a ."aller <br />size. This will allow the thickness of the blanket to be reduced. Wire-jound <br />roek is not ncomm41nded on channels with high bal\ks or stuams with a hig;, <br />flow ve loci ty. <br /> <br />'laintenance nquir"ments for a dprap blanket indude replacing or reposi- <br />tioning rock If it. is displaced by high flows. The upstream and do",nstrea", <br />ends of the blankel: should be checked to l1Iake sure erosion is not occurrIng, <br />If scour holes hav., developed, the eroded areas :Ihould be HUed and protected <br />yith additional ".iprap. <br /> <br />32 <br />