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Relative Slope Stability and Land-Use Planning in the San Francisco Bay Region, California by TOR H

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Relative Slope Stability and Land-Use Planning in the San Francisco Bay Region, California by TOR H Relative Slope Stability And Land-use Planning In The San Francisco Bay Region, California By TOR H. NILSEN and ROBERT H. WRIGHT, U.S. GEOLOGICAL SURVEY, and THOMAS. C. VLASIC and WILLIAM E. SPANGLE, WILLIAM SPANGLE AND ASSOCIATES, CITY AND REGIONAL PLANNERS GEOLOGICAL SURVEY PROFESSIONAL PAPER 944 jointly supported by the U.S. Geological Survey and the Department of Housing and Urban Development) Office of Policy Development and Research as a part of a program to develop and apply earth-science information in support of land-use planning and decisionmaking UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1979 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress catalog-card No. 79-600059 For sale by the Superintendent of Documents, U. S. Government Printing Office Washington, D. C. 20402 Stock Number 024-001-03165-5 FOREWORD This report is a product of the San Francisco Bay water resources management, solid and liquid waste Region Environment and Resources Planning Study, disposal, erosion and sedimentation problems, bay an experimental study designed to facilitate the use of water circulation patterns, and others. The methods earth-science information in regional planning and used in the study and the results that have been pro­ decisionmaking. The study is jointly supported by the duced have elicited great interest and have been U.S. Geological Survey and the Office of Policy Devel­ widely applied by planners, government officials, in­ opment and Research, Department of Housing and dustry, universities, and by the general public. Urban Development. The Association of Bay Area In this report, the results of several years of research Governments participates in the study and provides on problems of slope stability are interpreted and liaison with other regional planning agencies and with summarized. Some of these results, derived chiefly county and local governments. from research and experience in the San Francisco Although the study focuses on the nine-county, Bay region, will be useful wherever the threat of slope 2 7 ,400-square-mile (19,100 km ) San Francisco Bay re­ failure complicates decisions on land use. For exam­ gion, it bears on a complex issue that is of national ple, the report describes a method of evaluating slope concern: how best to accommodate orderly develop­ stability. Based on a knowledge of geology, slope, and ment and growth while conserving our natural re­ the incidence of landslide deposits, this method can source base, insuring public health and safety, and help planners, elected officials, and developers antici­ minimizing degradation of our natural and manmade pate and avoid problems where development is immi­ environment. The complexity of the problem can be nent. Maps that accompany the report illustrate the greatly reduced if we understand the natural charac­ method as it has been used in the San Francisco Bay teristics of the land, the processes that shape it, its re­ region. The maps also show a relation that is particu­ source potential, and its natural hazards. These larly important in planning for land use: slope stabil­ subjects are chiefly within the domain of the earth sci­ ity varies throughout the region, but some large areas ences: geology, geophysics, hydrology, and the soil sci­ are relatively stable and others, equally large, are po­ ences. Appropriate earth-science information, if tentially unstable. Finally, the report discusses how a available, can be rationally applied in guiding growth regionwide knowledge of relative slope stability may and development, but the existence of the information be used to improve both planning and day-to-day de­ does not assure its effective use in the day-to-day de­ cisions on land use. cisions that shape development. Planners, elected of­ The maps that accompany the report are at ,a scale ficials, and the public rarely have the training or of 1:125,000 (1 inch = about 2 miles). This scale is a experience needed to recognize the significance of ba­ compromise between the need for abundant detail sic earth -science information, and many of the con­ and precision, which are attainable on maps at large vention~;il methods of communicating earth-science scales, and the need for regionwide coverage on map information are ill suited to their needs. sheets of manageable size. Furthermore, at this scale, The study is intended to aid the planning and deci­ the maps provide uniform coverage of the entire nine­ sionmaking community by (1) identifying important county region. They show that all nine counties and problems that are rooted in the earth sciences andre­ many of the 91 cities in the region contain potentially lated to growth and development in the bay region; (2) unstable slopes and that most slope-stability prob­ providing the earth-science information that is need­ lems are not confined by political boundaries. The ed to solve these problems; (3) interpreting and pub­ nonpolitical nature of landslides and other kinds of lishing findings in forms understandable to and slope failure suggest a need for coordinated planning, usable by nonscientists; (4) establishing new avenues whether it be regionwide or by the joint efforts of ju­ of communication between scientists and users, and risdictions with common boundaries or agencies with (5) exploring alternate ways of applying earth-science overlapping responsibilities. information in planning and decisionmaking. Since the study was started in 1970, more than one hundred reports and maps have been completed. These cover a wide range of topics: flood and earth­ AJ~Ro~~D~~· quak~ hazards, unstable slopes, engineering charac­ Project Director teristics of hillside and lowland areas, mineral and San Francisco Bay Region Study III CONTENTS Page Page Foreword _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ III Use of slope stability information in land-use planning-Con. Definitions of terms ________________________ VII Application to land-use planning-Continued Abstract_______________________________ 1 Basic guidelines _____________________ 60 Introduction by T. H. Nilsen, T. C. Vlasic, and W. E. Spangle 1 Application in plan formulation _ _ _ _ _ _ _ _ _ _ _ 60 Planning for slope stability-an overview _ _ _ _ _ _ _ _ 2 Federal level ____________________ 61 The landslide problem _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3 Required land-use element of the Compre­ Costs of landslide disasters _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 9 hensive Planning Assistance Program __ 61 Actions to reduce "risk" _________________ 10 HUD Housing production and mortgage cre- Land-use planning and regulation in the San dit/minimum property standards _____ 61 Francisco Bay region _ _ _ _ _ _ _ _ _ _ _ _ _ _ 11 Federal disaster-assistance program ____ 61 Federal level ____________ ..... _ _ _ _ _ _ _ 11 State level _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 62 State level _____________________ 11 Office of Planning and Research _ _ _ _ _ _ 62 Regional level ____________________ 12 California Resources Agency _ _ _ _ _ _ _ _ _ 62 Local level---------------------- 13 State Lands Commission _ _ _ _ _ _ _ _ _ _ _ 63 Slope stability considerations in land-use planning _ _ _ 13 Business and transportation agencies _ _ _ _ 63 Relative slope stability of the San Francisco Bay region, Regional level _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 63 by T. H. Nilsen and R. H. Wright _ _ _ _ _ _ _ _ _ _ _ 16 Association of Bay Area Governments _ _ _ 63 Previous work _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 16 Metropolitan Transportation Commission _ 65 Landslides _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 20 San Francisco Bay Conservation and Devel- General classification __________________ 20 opment Commission ------------ 65 Falls ____________________________ 21 California Coastal Zone Conservation Com- Slides ___________________________ 22 mission _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 66 Lateral spreading _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 24 City and county general plans _ _ _ _ _ _ _ _ _ _ 67 Flows _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 26 Portola Valley general plan _ _ _ _ _ _ _ _ _ _ _ 68 Soil slips _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 28 Hayward general plan _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 69 Complex landslides _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 28 Sonoma County general plan ________ .:_ _ _ 71 Creep _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 28 Land-capability studies ______________ 75 SummMy ------------------------ 30 Application in plan implementation _ _ _ _ _ _ _ _ _ _ 79 Factors causing landslides _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 30 Early warning system _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 79 Photointerpretive mapping of landslides _ _ _ _ _ _ _ _ _ 33 Regulations _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 79 Slope-stability maps _____________________ 34 Zoning ordinance _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 79 Preparation of slope stability maps of the San Francisco Slope-density provisions _ _ _ _ _ _ _ _ 80 Bay region _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 37 Resource management zoning _ _ _ _ _ 81 Slope maps _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 37 Cluster zoning _ _ _ _ _ _ _ _ _ _ _ _ _ _ 82 Maps of landslide deposits _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 37 Subdivision ordinance _ _ _ _ _ _ _ _ _ _ _ _ 82 Surficial and bedrock geology maps _ _ _ _ _ _ _ _ _ _ _ _ 39 Site development ordinance _ _ _ _ _ _ _ _ _ 83 Derivation of the slope-stability maps __________ 41
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