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(f) The gabion baskets should be transitioned or keyed into the bank and securely tied to each other. 3. DROP STRUCTURES. A drop structure is a group of rocks, boulders and/or logs placed in a stream to act as a low level dam. Placement of a drop structure will raise the streambed elevation, decrease the stream gradient immediately upstream, dissipate stream energy, decrease current velocity and reduce streambank erosion while promoting streambed stability. Placement of drop structures is authorized provided: (a) Drop structures shall be constructed so that the maximum height above the existing streambed shall not exceed two feet. The majority of drop structures employed in the State of Colorado would not need to exceed this limitation to promote streambank and streambed stability; (b) Materials acceptable for drop structure construction include large boulders, large angular stone or rock- filled gabion baskets and logs in combination with any of the preceding i.e. large boulders, large angular stone or rock-filled gabion baskets; (c) Material size shall be large enough to withstand expected high flow velocities and associated turbulence; (d) Drop structures shall be constructed straight across a stream channel perpendicular to the current or more preferably, in a "V" shape with the point of the "V" directed upstream. This "V" shaped configuration will direct overtopping flows to the middle of the river and not against adjacent streambanks; (e) All drop structures shall be tied or keyed into the existing banks and protected by large rock anchored several feet into the bank. Protecting the flanks of the structure is critical to prevent extensive damage from high flows; (f) Construction equipment should access the stream only at a location immediately upstream of the proposed structure; (g) Construction or placement of rock for a drop structure shall start at both banks and proceed toward the middle of the stream. A backhoe or front-end loader, preferably with an opposing "thumb" on the bucket to manipulate the rocks, has been found most useful constructing drop structures; and (h) Due the varied widths of streams wherein a drop structure may be useful in stabilizing streambanks and streambeds, a specific limitation on the volume of material discharged is not being employed. However, the drop structure must not exceed 2 feet in height above the pre-structure stream bottom elevation. 9. JETTIES. Jetties are structures which are placed along a bankline to direct the flow away from an eroding bank. Jetties JAN c ~saa MINED LAND RECLAMATION DIVI^'^y