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Aoocndix D - Porrntia! Hvdrola¢ic Srrucrurrt ra Minimise fmaactt and Minin¢ Merhodt Frequently a biorevetement will include willow plantings. These consist of willow stakes or fascines, that are approximately 5 to 8 foot wands of dormant willows cut in the spring before they have leafed out. Store in water with a root promotion solution until planted. Do not allow them to dry out. Fascines are bundles of willows that have been planted horizontally in shallow trenches at benched heights ranging from several inches to 2 to 3 feet above the low flow water surface elevation. Willow plantings are most successful when planted in sites with adequate moisture in well-drained conditions such as silty sand. They should not be planted below the perennial waterline (base flow elevation of stream), or success will be tempered. Gabion Baskets Gabion baskets are sized rock enclosed in a wire mesh basket. It is recommended that a type of galvanized wire be used to promote a longer life of the installation. Size of the basket and rock can vary with the type of installation and the objectives of the control measure. Gabion baskets provide a durable and lon; lasting erosion control measure and rock materials aze usually available a[ the mining site. Figure D-10 shows photographs of two types of gabion baskets. Jetties Jetties consist of dike-type strucmres that may be used for bank protection (Figure D-11). Jetties project from the toe of a graded 4:1(H:V) channel bank to no more than one-third the stream's width, and optimally 15 to 25 feet. Jenies aze installed in a series along a straight reach or outside bank. Their orientation should be either perpendicular to a stream's centerline or at a 4~ degree angle downstream. Jetty spacing should be placed at a ratio of centerline spacing to jetty projection less than or equal to three. Thus, if the jetty extends 25 feet from the toe of the bank, jetty installation should occur every 75 feet or less. Jetties should be toed in at least 5 feet deep, and wing wails should extend at least 25 feet. Jetties should be constructed of Type Hrip-rap. The core of the jetties may be constructed with a mixture of concrete rubble. Banks between jetties should be stabilized with vegetation. Fiawre D-12 contains photographs of jetties installed in river channels. Vegetation Stabilization Vegetation is often used in a variety of methods to stabilize and protect stream banks from erosion. A combination of species are used, including willows and grasses. Vegetation is often used in conjunction with other stabilization methods such as rock armoring, bioreve[emenrs, and vegetated zones between jetties. Fierrre D-13 shows revegetated stream banks following mining operations. GRADE CONTROL STRUCTURES In-stream grade control structures, if used, should be installed on the upstream end of [he in- stream pi[. Examples of these structures are described below. .i me~n~e~n ~. iwa D-5