The purpose of these guidelines for investigating geologic hazards and preparing engineering-geology reports, is to provide recommendations for appropriate, minimum investigative techniques, standards, and report content to ensure adequate geologic site characterization and geologic-hazard investigations to protect public safety and facilitate risk reduction. Such investigations provide important information on site geologic conditions that may affect or be affected by development, as well as the type and severity of geologic hazards at a site, and recommend solutions to mitigate the effects and the cost of the hazards, both at the time of construction and over the life of the development. The accompanying suggested approach to geologic-hazard ordinances and school-site investigation guidelines are intended as an aid for land-use planning and regulation by local Utah jurisdictions and school districts, respectively. Geologic hazards that are not accounted for in project planning and design often result in additional unforeseen construction and/or future maintenance costs, and possible injury or death.
This photographic journal chronicles the history and construction of the high Sierra check dams from the first one at Yellowhammer Lake in 1920 through the last one constructed at High Emigrant Lake in 1951, past the establishment of the Emigrant Wilderness in 1975, and through various stages of support and opposition which are on-going to this day. Each major period in either check dam construction or the period after is divided into separate chapters, with each check dam described in detail with historical and recent photographs, many that have never been published. In addition, available historical writings and records of Fred Leighton and others were utilized to provide a more in depth perspective on the check dams from those directly involved in construction and/or maintenance. Outdoor enthusiasts discovering the Emigrant Wilderness of the high Sierra for the first time might easily consider it a pristine wilderness, rich in wildlife, streams, lakes, and scenic views. And yet, this is one area where the hand of man has worked to enrich the natural landscape. One of the most notable changes man has made in this area is the construction of small rock dams at the outlet of selected lakes and meadows. These dams were called check dams by Fred W. Leighton, who developed the concept of raising the water level of natural lakes and meadows for fishery and riparian enhancement. These check dams provide an enhanced habitat for mountain fish by providing additional water flow in the late summer months when natural streams typically run very low or completely dry.
On the afternoon of December 12, 2013, a large, joint-controlled block of the Shinarump Conglomerate Member of the Chinle Formation, with an estimated volume of almost 1400 cubic yards and weighing about 2700 tons, detached from the cliff face at the top of the Rockville Bench in Rockville, Utah. The block fell on to the steep Moenkopi Formation slope below the cliff, and shattered into numerous cobble- to very large boulder-sized fragments. The fragments moved rapidly downslope before striking and destroying a house, detached garage, and car at 368 West Main Street in Rockville. The two occupants in the house were killed. The purpose of this 20-page investigation wast to document the characteristics of the fatal rock fall; evaluate future rock-fall hazard at and near the site; and provide recommendations for homeowners, the Town of Rockville, and other officials to consider in managing rock-fall risk. Although the first fatal event, this rock fall is the sixth large rock fall within the Town of Rockville in the 35 years prior to December 12, 2013. Five of those events occurred within the past nine years, and at least three of those struck and damaged structures at the base of the Rockville Bench.
This 116-page report presents the results of an investigation by the Utah Geological Survey of land subsidence and earth fissures in Cedar Valley, Iron County, Utah. Basin-fill sediments of the Cedar Valley Aquifer contain a high percentage of fine-grained material susceptible to compaction upon dewatering. Groundwater discharge in excess of recharge (groundwater mining) has lowered the potentiometric surface in Cedar Valley as much as 114 feet since 1939. Groundwater mining has caused permanent compaction of fine-grained sediments of the Cedar Valley aquifer, which has caused the land surface to subside, and a minimum of 8.3 miles of earth fissures to form. Recently acquired interferometric synthetic aperture radar imagery shows that land subsidence has affected approximately 100 mi² in Cedar Valley, but a lack of accurate historical benchmark elevation data over much of the valley prevents its detailed quantification. Continued groundwater mining and resultant subsidence will likely cause existing fissures to lengthen and new fissures to form which may eventually impact developed areas in Cedar Valley. This report also includes possible aquifer management options to help mitigate subsidence and fissure formation, and recommended guidelines for conducting subsidence-related hazard investigations prior to development.
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