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Varra Companies, Inc. <br />Office of Special Projects <br />8120 Gaee Street Frederick Colorado 80516 Telephone (970) 353-8310 Fax(970)353-4047 <br />Should flood waters encounter an active face or unfinished basin slope, some <br />erosion may initially occur during a flood event; but will be dependent in part on <br />the extent and duration of the flood waters face to wall contact. Since the <br />waters will largely be sheet flows, back-cutting of the basin wall will be of <br />comparatively short duration and minimal reach. Where the point of entry is <br />more channelized, back-cutting will be more pronounced, but the reach will be <br />of comparatively narrow extent, making repair of back cut areas less <br />problematic. If back cutting reaches an existing oil and gas line or structure, we <br />trust the attending owner will have made the necessary protection to their <br />facilities. If floodwaters enter an active cut on the basin wall or advancing wall, <br />it is generally not a smooth drop, and the staggered cuts made during active <br />extraction will act to dissipate velocities of the initial waters, thereby reducing <br />potentials for erosion into the active basin, or back-cutting into the walls, as the <br />initial flood waters front is replaced by sheet waters overflowing the feature <br />until the basin is quickly filled by increasing sheet flows, whose velocities are <br />minimal and predominantly depositional. <br />The previously well understood use of a 100 foot buffer between extraction and <br />active tributaries was determined in the early 1980's forward, based upon <br />forestry practices. When operations during this period were actively operating <br />to within 25± feet of active tributaries, a 100 foot buffer was proposed and <br />supported by the Mined Land Reclamation Board, to maintain a filter strip of <br />vegetation, preserve streamside vegetation, stream temperatures and <br />consistency of riparian habitat; and somewhat mistakenly, to minimize risks of <br />intrusion. <br />It was later determined that elevation of streamside berms, and stream bed <br />cutting during flooding, not buffer distances, were the major influences of <br />intrusion. Braided streams meander and sediment load can influence flood and <br />flood impacts dramatically and may vary significantly depending upon the storm <br />event and upstream conditions. When sediment load is low in flood flows, the <br />waters will attempt to balance their energy by cutting the stream bed and <br />subsequently undercutting adjacent streamside banks or berms. When culverts, <br />pipes, other cavities are present forming a weakness in the streamside berm, or <br />where elevations facilitate the flow of flood waters, floodwaters will pursue the <br />path of least resistance. Regardless, all structures placed within a floodplain <br />without any attending protection are placed there at their own risk, and one <br />owner should not be called upon or forced to carry the cost of the protection of <br />Varra Companies, Inc. correspondence of 23 February 2011 to the Colorado Office of Mined Land Reclamation 10 <br />(OMLR) in reply to OMLR correspondence of 4 October 2010 - Western Sugar Reclamation Land <br />Development Project - M-2010-049.