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<br />. <br /> <br />. <br /> <br />. <br /> <br />Grouted RiDrap <br />Grouted riprap consists of loose riprap that is stabilized with pwnped concrete grout once the <br />rock is placed. It requires less maintenance than loose riprap and may be advantageous to reduce <br />vandalism and trash accumulation. It also works well on flat or steep banks. Grouted riprap <br />should meet all of the requirements for loose riprap, including bedding, except that the smallest <br />size rock should be eliminated from the gradation. Unfortunately, grouted riprap is significantly <br />more expensive than loose riprap and will therefore be eliminated from consideration for this <br />project. <br /> <br />Wire Enclosed Rock (Gab ion) <br />Gabion refer to wire enclosed rock that are bound together in a wire basket so that they act as a <br />single unit. One advantage of wire enclosed rock is that it provides an alternative in situations <br />where available rock sizes are too small for ordinary riprap. Another advantage is the versatility <br />of the rectangular configuration of the gabions that allow for diverse installations. However, the <br />durability and life span of the wire enclosed rock is severely limited by the life of the galvanized <br />binding wire. Under normal conditions the life may be 10-15 years, but under harsh conditions <br />the life could be much less. Gabion installations require routine maintenance and inspection. It <br />is the opinion of the engineer that wire enclosed rock is not the best choice for this project, and is <br />therefore eliminated from consideration. <br /> <br />Bendwav Weirs <br />Bendway weirs are a form of rock jetties that are unique compared to traditional methods of bank <br />stabilization. Bendway weirs represent a fairly new concept that has been developed and field <br />tested for a number of applications in Colorado, the midwest, and other parts of the nation. In a <br />typical stream bend, surface water currents tend to move toward the outside ofthe bend along the <br />outer bank. The flow concentration along the bank edge can result in severe erosion. The <br />traditional riprap revetment resists the streampower and the increased bank velocities. However, <br />the bendway weir method involves redirecting the bank velocity away from the bank towards the <br />middle of the stream. With a series of weirs angled uDstream along the outside of the stream <br />bend, the current is redirected through the bend and into the downstream crossing. The jetties, or <br />bendway weirs, consist of well graded rock material shaped into berms that are keyed into the <br />bank, and then project into the stream at an angle (usually 5 to 15 degrees). The cost for the <br />bendway weir method is similar to, but usually less than, the cost of placing loose riprap along <br />the bank. This approach proves to be very promising, but it may also be considered by some <br />engineers to be in the experimental phase. The bendway weir approach, although similar to the <br />spur dike approach (discussed below), is not recommended for this project. <br /> <br />Spur Dikes <br />Spur dikes are nearly identical to bendway weirs, except that the jetties are constructed at an <br />angle facing downstream rather than upstream. Spur dikes have been successfully implemented <br />in Colorado and other parts of the nation. Spur dikes were originally developed by the U.S. <br />Army Corps of Engineers to stabilize large rivers such as the Mississippi and the Missouri in <br />order to maintain a navigable waterway for barges and boats. Many spur dikes, on those rivers, <br />were constructed over 30 years ago are still functioning quite well today. The spur dike approach <br /> <br />6 <br />