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. . John W. Rold Page 6. July 23, 1973 is one fairly well defined natural drainage way, which appears to have been be- headed by road construction and carries almost no drainage. Drainage is now entering in two small channels controlled by construction activity. One of these probably handles essentially the same runoff that the natural channel would have, but the second originates from seepage and runoff coming through the sewage treatment facility excavation. This source may well constitute some extra water being diverted into the active slides at this location. Most of the water drain- ing toward Carbonate Creek probably enters tension cracks of the slide area where they would have a maximum effect on slope instability. Since all of the downslope area is active landslide it would seem that at most the shifting of drainage might intensify active sliding at certain places while not greatly affecting the overall amount of sliding. Possible preventive or modifying actions Both Ski Company officials and townspeople from Marble have inquired about cor- rective actions that might be taken. A significant contribution could be made by the developers if they control and divert all upslope water in such a way that it does not flow across and into the slide terrain. This would not completely eliminate movement since a second and perhaps more important factor is rapid erosion and removal of the toe of the slides by the turbulent flow of Carbonate Creek. However, it would tend to inhibit the sliding and minimize downstream haz- ards. A second useful effort would be to periodically remove trees that have fall- en into the main channel. This should also help by reducing the debris plug effect during periodic flood flows. Summary and General Recommendations Following a comprehensive inventory of geologic conditions, past and planned con- struction, and problems that exist in the Mt. Daly portion of Marble Ski area we suggest the following program which we believe to be in the best interests of all concerned. A firm committment and schedule for accomplishing these should preceed any further development, approval of filings, or building permits. 1) A workable comprehensive drainage plan is badly needed for the entire Mt. Daly area. Such a plan should include provision for detention of storm runoff from in- tensively developed areas such as the Village site, needs of natural through-flowing drainage, modification of existing drainage patterns by roads and other construction, and special problems such as diverting surface and ground water flow from known un- stable areas. Interim and incomplete solutions of, drainage problems will only con- tribute to more unexpected "incidents" and unfav;Jrable publicity. 2) A system of interception and subdrains will be necessary in many parts of the Mt. Daly area, particularly on the west slopes. This will be essential to achieving stable road construction, building foundations, parking facilitie~, etc. over much of the tract. 3) The entire Condominium Filing No. 1 should be reappraised to determine those areas that are viable building sites. It is recommended that each site determined to be buildable have an engineeried grading,drainage,and foundation plan and that construction be required to adhere strictly to that plan. It is pointless to de- bate the geologic and engineering feasibility of a marginal site when you can't