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<br />NOTES: Construction materials are usually from quarry-run stone with specified <br />'Imitations on the maximum size of stone and amount of fines. The hardpolnts are built <br />with crowns of various widths up to 10 feet or roore depending on the severity of the <br />expected attack~ the methoc of construct Ion, and the requ I rements for ma i ntenance. The <br />spacing between any two herdpolnts has generally been related to the average of their <br />lengths multiplied by a sp<lcing-Iength ratio. The spacing-length ratio is derived from <br />the experience of the designer. The final selection of spacing and length may be an <br />economic one, but for bank protection purposes~ the length of the dikes should be just <br />sufficient to move the erJdlng current away from the bank. Of course~ there Is a <br />limitation on length since It must not be such that the dike wi II unduly restrict the <br />navigation channel or incre3se the current velocity to an unacceptable value. Short rock <br />jetties are effective In deflecting the current away from the eroding bank and tend to <br />create a foreshore between the projecting dikes of rock. Use of broken concrete~ if <br />available, would eliminate !.ome of the Initial cost. <br /> <br />COSTS: Approximately $18,OOO/hardpoint. Assuming a IO-loot top, 46-loot length, and <br />12-loot height with spacing at about 11 times the length 01 the hardpolnt, the cost would <br />equai $37/bank-Ioot. <br /> <br />MAINTENANCE REQUIREMENTS: II constructed properly, little maintenance. <br /> <br />ENViRONMENTAL ASPECT: In 1his technique, stone is extended Irom the bank and spaced at <br />points along an eroding b,nkline. The stone IIII should be covered with tbpsoll and <br />planted with native plants. The structures redirect the current flow and cause some <br />sediment but ldup. The spacing of the structures depends on flow rates and river <br />morpho logy. Short hardpo I n ts shou I d be used over long ones. Long hardpo I nts, I fused, <br />should be notched to perml" some flow to maintain the aquatic ecosystem. The aquatic <br />portion of the structure WOJld improve the habitat diversity and provide a substrata for <br />establishment of Invertebrates. The above-water portion of the structure, If properly <br />p I anted, wou I d prov I de wi I d II fe cover and food. Vegetated hardpo t nts are not as <br />aesthetically pleasing as some erosion control structures~ but may be more visually <br />acceptable than steel jacks. timber jetties, bu Ikheads, and old tires. Many hardpolnts <br />are constructed entirely of stone with no vegetation and would be less likely to blend <br />Into the riverine environment. <br /> <br />18 <br />