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Rationale for Approval Recommendation May 20, 2002 <br />Four Corners Materials, Inc. <br />AM-01. Thomas Pit, Permit No. M-1976-020 <br />As part of DMG's routine review process, DMG informs the applicant of all adequacy <br />issues identified during the review period. Issues raised by the objecting parties and <br />specifically addressed by the Act and Rules were addressed in DMG's adequacy review <br />process for AM-01. The applicant responded to DMG adequacy issues by submitting <br />additional information which demonstrated compliance with the requirements of the Act <br />and Rules. Therefore, DMG found the application for AM-01 adequate and recommended <br />approval of the application on the decision date, as required by C.R.S. 34-32.5-115(4-. <br />5. Comments regarding the /ong-term stabi/ity of the proposed river bank <br />modifications. /Rau, D & L James, Dan James, Pierce, Ritz, Mayo, Whee/ing/ <br />The pond construction and its associated river bank modification proposed in AM-01, <br />have been designed and certified by a Registered Professional Engineer to safely <br />withstand flood events up to and including the 100 year storm. The plans proposed in <br />AM-01 have been reviewed by a team of DMG staff members, one of which is also a <br />Registered Professional Engineer. DMG staff conducted an independent engineering <br />evaluation of the plans submitted with AM-01 and determined that the proposed plans <br />provide an appropriate safety factor to be able to resist effects of the 100 year event on <br />the river channel. <br />The jetty structure proposed in AM-01, is designed to absorb and deflect flood flow <br />energy, thereby reducing the potential for erosion for the west bank area downstream of <br />the jetty. The jetty is to be constructed with angular durable rock, 5 foot minimum <br />diameter, and imbedded approximately 3 feet deep in the channel bed. The jetty <br />structure will rise to a maximum height of 8.5 feet above the channel bed. Although the <br />jetty structure is 103 feet long, it will extend only 69 feet into the channel due to the 42 <br />degree downstream orientation of the jetty from the channel bank. At the location of the <br />proposed jetty structure, the river channel is approximately 350 feet wide. The 100 year <br />floodplain at the location of the jetty structure is approximately 2,270 feet wide. <br />The steep slopes of the west bank area immediately downstream of the jetty will be <br />reduced to 2H:1 V slope and reinforced with concrete block, Superior Excelsior S-2 <br />erosion control blanket and appropriate vegetative cover. The concrete block, each <br />measuring 4 feet by 4 feet by 3 feet, are to be imbedded 3 feet deep so that the exposed <br />surface of the block are flush with the surface of the channel bank. Two rows of <br />concrete block will be placed with 2 foot spacing between the blocks and will be tied <br />together with 0.75 inch rebar, to form a continuous solid rib along approximately 480 feet <br />of the embankment. The rib of imbedded concrete block will extend approximately 10 <br />feet up from the toe of the slope. The application indicates that the ordinary high water <br />line will extend approximately 2.5 feet up from the toe of the slope. Embankment areas <br />located above the concrete block rib will be covered with 12 - 14 inch depth of topsoil <br />and seeded with a variety of native and introduced species of grasses and sedges. <br />Revegetation efforts also include transplanting approximately 360 willow shrubs and 75 <br />5 <br />