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Methods For Controlling Erosion e Fence Revetments - Fence revetments are used to solve a variety of bank protection problems. They are constructed parallel to the bank and to the flow at, or riverward of, the toe or the bank slope. Fences are constructed of wood or wire and are pervious. Stream vdocity behind the structure is significantly reduced, thereby reducing erosion. Because fences stop erosion by reducing secondary cwrents and circulation, no bank sloping 01 treatment is necessary. Aquatic features are not destroyed, and once vegeta- tion becomes re-established on the eroding bank, riparian habitat and aesthetic benefits are improved. Fences have been used successfully on many rivers. They are prone to damage fi om ice and debris, and must be regularly maintained. 4.7 Vegetallon. Vegetatiw treatments to prevent streambank erosion are perhaps the oldest form of bank protectiorl. Vegetation has been used extensively throughout North America and Europe. It is commonly incorporated into most contrul techniques, and is often used alone to provide comprehensive protection from erosion. Vegetation is an economical method of limited streambank erosion protection. The principal functions are to keep fast-moviDg water and transported coarse materials away from the surface of a streambaJlk slope, while improving the structural integrity of the bank by providing soil stability \lith root mass. Vegetation may be used in conjunction with other stabilization methods, or as a singular method. The types of vegetative treatments used for streambaJlk erosion control include direct seeding, mu1cbing, sod planting, reed rolls, sprigging, fascines, barriers. and root pads. Vegetative treatments can have some effect on the hydraulic properties of the river. A very slight increase in stage during high water periods may occur when woody vegetatioll is used below the splash zone. Sediment inputs to the system from the stream bank decrease, so there may be a slight increase in bed sediment movement. If excessive bed sediment movement occurs, the potential for headcutting upstream of the area incmases. This could result in higher channel velocities and a lower stage for a given di$:harge. The vegetation will provide additional haJ)itat to wildlife and provides organic input to the river. The success of vegetative protection depends largely upon a well formulated plan, taking iUo account the following factors: (a) bank slope; (b) topsoil; (c) slope protection; and (d) vegetation type. The type of vegetation selected is possibly the single most critical factor in designing for vegetative protection. Vegetation must be suited to the bank zone it is placed upon. Bank zones include splash, bank and terrace, and each has conditions for which only certain types of vegetation are suitable. Followin g is a discussion of a few types of techniques which employ vegetation as a component. It is very limited presentation and is intended to give the reader a sense of the divemity of vegetation use in erosion control. Chapter 6 presents more details about the use 0' vegetation. Brush Mattresses - Brush mattresses are constructed by placing a layer of brush, arranged with stems parallel, and securing it with wire that is attached to live and dead e 48 Colorad,o Erosion Control Manual