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NOTES: Construe-tlon materials are usually from quarry-run stone wIth specified limItations on the maximum sIze of stone and amount of fInes. The hardpotnts are built with crowns of various widths up to 10 feet or more depending on the severity of the expected attack, the method of construct Ion, and the requ I rements for ma I ntenance. The spacing between any two hardpolnts has generally been related to the average of their lengths IllUltlplled by a spacing-length ratio. The spacing-length ratio Is derived from the experience of the designer. The final selection of spacing and length may be an economic one, but for bank protection purposes, the length of the dikes should be just sufficient to move the eroding current away from the bank. Of course, there Is a I imitation on length since It must not be such that the dike will unduly restrict the navigation channel or increase the current velocity to an unacceptable value. Short rock jetties are effective In deflecting the current away from the eroding bank and tend to create a foreshore between the project i ng dikes of rock. Use of broken concrete, If available, would eliminate some of the Initial cost. COSTS: Approximately $18,OOO/hardpolnt. Assuming a lO-foot top, 46-foot length, and 12-foot height with spacing at about 11 times the length of the hardpolnt, the cost would equal $37/bank-foot. MAINTENANCE REQUIREMENTS: If constructed properly, little maintenance. ENVIRONMENTAL ASPECT: In this teChnique, stone Is extended from the bank and spaced at po I nts a long an erod I ng bank I f ne. The stone fill shou I d be covered with tbpso II and p I anted with nat I ve p I ants. The structures red i rect the current f I ow and cause some sediment bui Idup. The spacing of the structures depends on flow rates and river morphology. Short hardpoints should be used over long ones. Long hardpolnts, If used, should be notched to permit some flow to maintain the aquatic ecosystem. The aquatic portion of the structure would Improve the habitat diversity and provide a substrata for estab Ii shment of invertebrates. The above-water port I on of the structure, J f proper I y planted, would provide wi Idllfe cover and food. Vegetated hardpoints are not as aesthetically pleasing as some erosion control structures, but may be lOClre visually acceptable than steel jacks, timber jetties, bulkheads, and old tires. Many hardpoints are constructed entirely of stone with no vegetation and would be less I ikely to blend Into the riverine environment. 18