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<br />IV. PLANNING <br /> <br />CONSIDERATIONS <br /> <br />A. PLANNING PROCESS <br /> <br />Define the problem - The factors affecting streambank erosion are the orientation of the <br />streambank, the velocity and depth of the river, and the sotl composition of the <br />streambank. An I nd Iv I dua I assessment of each part leu I ar 5 ftuatfon shou I d cons I der the <br />type of erosion being dealt with, the types of protection that would best remedy the <br />situation, the value of the property in Jeopardy, and the cost of the structures needed. <br /> <br />SelectlnQ a Plan of Protection - Many alternative measures have been used with varying <br />degrees of success. Sometimes a "do-nothing" approach may be acceptable. In these cases, <br />minor relocation of the threatened faci litlas is "the apparent solution. Sometimes, a <br />channel relocation is the apparent solution. Generally, however, this causes simi lar <br />problems elsewhere. Solutions for erosion prevention fall Into two categories. One Is <br />the physical protection of the bank by use of rock referred to as rlprap, snowfence, or <br />various types of mats. The second category involves river works designed to deflect the <br />current and/or produce sediment deposits. These measures Include constructing wIng dams, <br />jetties.. permeable retards, and brush cabled to the bank. The cost of a structure, the <br />risk and consequence of failure, and the materials available wI II determine the type of <br />structure and its construction details. <br /> <br />The availability of materials will dictate the type of structure and its cost. For <br />example, the lack of stone within economic hauling distance would require the use of some <br />other mater I a I. <br /> <br />Some materials are very good, i.e., quarried stone, Interlocking steel pile and creosoted <br />wood timbers. Some materials may not be as acceptable such as junk cars, old tires, and <br />thin concrete slabs. Between these extremes Is a range of materials that can be used if <br />care.. discretion, and Ingenuity are appl ied to produce a more durable structure. <br />Materials can be used in conjunction with other materials, for instance, wire fencing and <br />stones; or quarried stone, cloth bags and grout; or steel sheet pIles and quarried stone. <br /> <br />The life of the structure also dictates Its type. Obviously, an untreated timber <br />structure should not be installed where a structure Is designed to last 50 years. <br />Converse Iy.. a permanent rubb Ie-mound structure wou I d not be requ j red I f the need for <br />protection was of an expedient nature. The durability of the structure and its abi I Ity to <br />absorb hydraul Ie forces Is also a factor. <br /> <br />The Corps prefers and recommends that permanent protective works be built, but understands <br />that private owners usually cannot afford the large cost. This means there may have to be <br />departures from the standard designs for permanent protective works to provide some degree <br />of protection against erosion. This wi I I tend to decrease the first cost of construction; <br />however, higher maintenance cost and reduced functional life wi I I fol low. The danger here <br />Is to underdeslgn the work and risk total failure. Close attention to the construction <br />and maintenance guidelines on this page are needed to minimize losses. <br /> <br />BulldlnQ Protective Works - Timeliness Is the essence of the successful construction of <br />shore protection measures. The best time to build protective work Is during low-water <br />periOdS. Adequate time Is needed for an Indepth study of the problem. <br /> <br />7 <br />