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<br />IV. PLANNING CONSIDERATIONS <br /> <br />A. PLANNING PROCESS <br /> <br />Define the broblem - The factors affecting streambank erosion are the orientation of the <br />streambank, the velocity and depth Of the river, and the 5011 cOOlpositlon of the <br />streambank. An Individual assessment of each particular situation should consider 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 />Selectl"!:! a Plan of Protection - Many alternative measures have b$en used with varying <br />degrees of success. Sometimes a lido-nothing" approach may be acceptable. In these cases, <br />minor reloc::ation of the threatened facilities Is the apparent solution. Sometimes, a <br />channel relocation Is the apparent solution. Generally, however, this causes similar <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 cat~gory Involves river works designed to deflect the <br />current an~/or produce sediment deposits. These measures include cQnstructing wing dams, <br />jetties, p<lrmeable retards, and brush cabled to the bank. The cost of a structure, the <br />risk and consequence of failure, and the materials available will determine the type of <br />structure and Its construction detai Is. <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., qUqrrled 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 applied 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 plies and quarried stone. <br /> <br />The life of the structure also dictates Its type. Obviously, an untreated timber <br />structure should not be Instal ied where a structure is designed to last 50 years. <br />Converse Iy, a permanent rubb Ie-mound structure wou I d not be requ I red if the need for <br />protection was of an expedient nature. The durability of the structure and 1ts ability to <br />absorb hydraulic 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 loss&s. <br /> <br />BulldlnQ Protective Works - Timeliness Is the essence of the successful construction of <br />shore protection measures. The bast 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 />