Laserfiche WebLink
Sills are considerably less-expensive than bulkheads <br /> or groins. Each 13-foot Dura-bi-ig costs $5.0. Adding ` <br /> j $15 for the cost of pumping the bag full of sand, the <br />' average cost for erosion protection using sills would <br /> be per foot, according to Professor Jerome-Connor, <br /> who is coordinating tlie'MIT Sea Grant experiment <br /> with the sills on Cape Cod. <br /> other estimates range as high as S 12.50 per fo 6t, but <br /> that is still considerably less expensive than the typical <br />� o per foot cost of installing a v;ood n bulkhead, for <br /> example. Cance installed the Dura-bag sills have the <br /> added advantage of no maintenance requirements. <br /> r, Byrne said bags placed on hsapeake Bay four. <br /> years go show no signs of decay. Dr. Connor said the <br /> gags, while naturally'resistant to decomposition b <br /> ultra-violet light from the sun, are further r protected b <br /> a coating of slime that forms on exposed parts. <br /> Ir. Byrne said last week that the-Dura-bag sills on <br /> Chesapeake day are riot visible from the shore two- <br /> third.s of the time. Thelops tops of the bags are nearly <br /> flush with the sand filled in behind them, he said, and <br /> since they are placed toward the low-water line, they <br /> are partially submerged most of the time.. <br /> If the bags do not work, Dr. Byrne said, it is -i sim- <br /> ple matter to cut them open and remove there. fact, <br /> the only problem with the bags so far has bee%.. t fever <br /> isolated incidents of slashing by vandals, he sa!d:l <br /> Although sills may be promising erosion control <br /> devices in tinny places, they nevertheless have their <br /> limitations. Ideally they work best when used in areas <br /> without other anti-erosion structures already in place} <br /> although Dr. Byrne said experiments using sills in coil- <br /> junction with groins are now taking place. <br /> Also, the perched-beach concept can work only on <br /> sandy beaches where the wave action- is not over- <br /> owerin . They won't work on ocean beaches, Dr., <br /> , <br /> Byrne said; only on..baide beaches where most of <br /> the".wave action is.generated by wind. O.n Chespeale <br /> Bay, where the sills have proved succe sftrl, waves are <br /> generally two to three feet at most',. <br /> However, Chesapeake. Bay lura-bag sills,have suc- <br /> cessfully withstood storms with winds up to 60 miles <br /> per hour and waves four and a half feet above mean <br /> ' high water. Each bag when filled d weighs four to five <br /> (Continued_ n Next Page) <br /> The problem with groins is that by obstructing the <br /> natural drift of sand along the shore they cause it to <br /> build up on one side while sand on the other side f the <br /> _groin i eroded away at n increased rate. However, <br /> installation of a sill does riot affect the natural driftf <br /> sand parallel to a beach. <br /> Comparing sills t bulkheads or groins seems o'� - <br /> illustr ' -.how engineering iesigried to harmonize with <br /> naturaf processes is usually rnOTe effective than <br /> engineering that tries to oppose the forces of nature by <br /> brute force., <br />