FLOOD06541 - Laserfiche WebLink

Home Browse Search

. . John W. Rold Page 3. July 23, 1973 of the fill material to aid compaction, and perhaps most serious of all; fill was being placed on the natural steep slope rather than being benched, and fill was being placed on colluvium instead of being keyed into bedrock. Evaluation and Recommendations In our initial report entitled "Engineering Geologic Factors of the Marble Area, Colorado", we showed a large portion of the south exposure of this ridge (in- cluding the slide area) as a generalized hazard area. This included the area downslope from the upper boundaries of lots 49, 34, 33, 32, and 26 as now shown on plats. In a more detailed evaluation by our office (JWR letter to Gunnison County Commissioners on Feb. 1, 1973), most of these and several additional lots were indicated as being doubtful as viable building sites. At the time of this evaluation, the more detailed Engineering Geologic mapping by Chas. Robinson was available for our reference. The slide of May 14th shows that our concerns about the stability of this area were justified and reinforced our conviction that de- tails of construction and drainage can make the difference between workable de- velopment and disaster. . Press reports we read of this incident ran the gamut from greatly exaggerated, to factual, to whitewash. One report gave the impression that half of Mt. Daly had slid into Beaver Lake, and a report quoting the developer said that only 35 feet of a temporary road had failed. One of these reports was about as mislead- ing as the other. The facts are that a large portion of at least one condominium lot failed suddenly by landsliding. If the area had been developed, there would have been danger not only to that lot but to at least three upslope lots. Anyone familiar with the development plans should have found it a sobering and education- al experience. After additional field study of the area and in light of the recent slide, I be- lieve (as we have stated .twice before) that much of this portion of the Condominium Filing No. 1 is too steep and unstable for development, particularly of the density proposed. The existing roads (it is immaterial'whether they are permanent or other- wise) pose a continuing threat of similar future failures. There are two reasons for these, as explained earlier, many of the fills are poorly placed and the switch- backs intercept both seepage and surface water and concentrate the runoff in areas of already marginal stability. As an example, the large fill at the switchback turn immediately above lot No. 27 showed large tension cracks and downward dis- placement indicating incipient landsliding when I inspected it the day of the slide on lot 53. Drainage from the upward leg of the switchback was flowing off the end of the switchback and disappearing into tention cracks in the colluvium near the toe of the fill. At this time the Engineering Geologic constraints of this area are well known. However, existing road construction and platting predate that information. If the area is to be safely developed both the platting and road construction will have to be reviewed and brought into harmony with natural constraints. I am con- vinced that anything less will result in additional incidents such as the recent slide. Neither the environment, the developer nor the general publiC will be served by repeat performances.