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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />CENTRAL CITY MASTER DRAINAGE STUDY <br /> <br />28 <br /> <br />Spring Gulch, flattening the slopes would increase the size of <br />the tailing "foot print." In either case, unless an effective <br />slope stabilization program is designed and constructed <br />flattening the slopes will destroy the "armoring" of the existing <br />slope without preventing newly exposed material from being <br />eroded. <br /> <br />An alternative to flattening the slopes to 3:1 and application of <br />standard revegetation is to flatten them to 2:1 and apply erosion <br />blankets to aid in establishing vegetation. Installation of <br />erosion blankets increases the unit cost of revegetation six- <br />fold. Structural alternatives for slope stabilization are <br />several times more expensive than installation of erosion <br />blankets. <br /> <br />Stabilizing tailing piles is as important in protecting downtown <br />Central City as drainage improvement for Nevada and Spring <br />Gulches. Design of proper remediation requires more information <br />than that available at the writing of this report. Information <br />such as suitability of tailings to support plant life, gradation <br />of surface soils, establishment of vegetation or slopes steeper <br />,than 2:1, availability of topsoil, etc. are necessary for design. <br /> <br />5.5 <br /> <br />Maintenance Practices <br /> <br />Stabilization of the Free parking lot tailing slopes can be <br />enhanced by changing grading practices. Presently, local runoff <br />that accumulates on the parking lot drains over the crest of the <br />slopes or to roadside swales on Nevada and Spring Streets. Large <br />gullies have formed on the slopes. The direction of flow should <br />be changed back to the south to the entrance of the Nevada Gulch <br />flume by grading the parking lot surface. An on-going program of <br />grading will be required to maintain this direction of flow. <br /> <br />~ <br /> <br />~ <br /> <br />HydroDynamics Incorporated <br />