627.4 P : ,= (7946) ; i;v- \ WU i ! i k.-; v
- P • . •• ■««. : . * . ,; «*#„**?'- IN* :::' *
;. M 1, 1 r-3 ; OTMU?ok am m ■ r !MM0I0MM3KB m'. ’ta'-r- ' •'; '■
8&u — • •; .yaj; - ■ 4:#T*- ■-. V*»- . • -r. •£>—- -- -• - . ■' - ■ -V"i. i. . ■ - ■ •. flat....: Q " i ...... ■ 5 ' ill : ***** ! 1
! , .-r -• /iv •; :.... -•: - ■ / i ; vT. . \ , - ife I -J* <*-V ■a* ■rSZ— - «. ..v- > '.'J ■ ■v -Vp* -...... v ... ! • '3 •* •. - - • >rt. ■'• ; '-y- 4; ' •• •/. .-•*• - :• ,v •: ■ >s-^y t"’-- .,**** w/ * -■ - v? - ' ■• “ rkt N P ' :;ppr ' -Tv j. v. ► - -.&£> .f'V
i>
. 5.% VJk. . ' -• i.. ^v-.r P ■ i j s*r< . ' "-'•;-v-,v..:; ••;.:•■• *v\ ■ -r '-: • ^
•- ■■ ■■:••"■
■ . -■■■;••■" - «, ft. :o. ' > V ■ ■. • ■ ...^ ■ P.X- .N - «***■'♦.'-:-*^-. ■ 'M 9- r-3&m ■ .*■ . . -'-■?».« y* •■• *•. r. ■ :‘w,^": ■■:.■■■ v:: p*. :^f ’ •■ • ■ £' ^ ' / 1 , ■"V; ' ■ • ->• :* V>k k; - . :. . -' P*-yv- x 'iy . ,»# «*? Ss.V
, m, u vJ“- 5g • ■ " •-+ ;y*
-• • ■'• ••'- 'r' ■ : :p‘;.v i ^■v;v.; - ••; v...
mmmi, mmmmm V--iWsS5^ t. 1
: :
i Flood-prone areas and land-use planning— Selected examples from the San Francisco Bay Region, California
By A. O. WAANANEN, J. T. LIMERINOS, and W. J. KOCKELMAN,
U.S. GEOLOGICAL SURVEY, and
W. E. SPANGLE and M. L. BLAIR, WILLIAM SPANGLE & ASSOCIATES
GEOLOGICAL SURVEY PROFESSIONAL PAPER 942 !
Jointly supported by the U.S. Geological Survey and the Department of Housing and Urban ; Development, Office of Policy Development and Research, as part of a program to develop and apply earth-science COVER PHOTOGRAPH of San Francisco Bay Region taken April 14, 1972, ' information in support of land-use planning and decisionmaking at altitude of 65,000 feet from U-2 aircraft. Courtesy National Aeronautics and Space Administration (Ames Research Center, Moffett Field, Calif.) Front shows city of San Francisco and Golden Gate at bottom, San Francisco Bay and city of Oakland in middle, Sacramento-San Joaquin Delta and crest of Sierra Nevada at top. Back shows Bolinas Lagoon and trace of San Andreas fault at bottom, San Pablo Bay in middle, Sacramento valley and crest of Sierra Nevada at top.
i i
j
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1977 I
I
FOREWORD
This report is a product of the San Francisco Bay Region nonscientists; (5) establishing new avenues of communication Environment and Resources Planning Study, an experimental between scientists and users; and (6) exploring alternate ways of UNITED STATES DEPARTMENT OF THE INTERIOR program designed to facilitate the use of earth-science infor applying earth-science information in planning and decision mation in regional planning and decisionmaking. The study is making. CECIL D. ANDRUS, Secretary supported jointly by the U.S. Geological Survey, Department of Since the study was started in 1970, it has produced more than the Interior, and the Office of Policy Development and Research, 100 reports and maps. These cover a wide range of topics: flood Department of Housing and Urban Development. The Associa and earthquake hazard reduction, unstable slopes, engineering tion of Bay Area Governments participates in the study and characteristics of hillside and lowland areas, mineral and water- provides a liaison and communication link with other regional resources management, solid and liquid waste disposal, erosion GEOLOGICAL SURVEY planning agencies and with county and local governments. and sedimentation problems, bay water circulation patterns, and Although the study focuses on the 9-county 7,400-square- others. The methods used in the study and the results it has V. E. McKelvey, Director mile San Francisco Bay region, it bears on an issue that is of produced have elicited broad interest in a wide range of appli national concern. This issue—how best to accommodate orderly cations from planners, government officials, industry, univer development and growth while conserving our natural resource sities, and the general public. base, insuring public health and safety, and minimizing degra The present report, “Flood-Prone Areas and Land-Use Plan dation of our natural and manmade environment—is difficult and ning—Selected Examples from the San Francisco Bay Region, complex. The complexity, however, can be greatly reduced if we California,” examines the problem of flooding in the San Fran understand the natural characteristics of the land, the processes cisco Bay region, describes the preparation and use of various that shape it, its resource potential, and its natural hazards. These types of flood maps and flood information reports, lists sources of subjects are chiefly within the domain of the earth sciences: information on flooding and flood plains, discusses flood-loss Library of Congress catalog-card No. 77-77832 geology, geophysics, hydrology, and the soil sciences. Appropriate prevention and reduction measures, and discusses the role of com earth-science information, if available, can be applied rationally prehensive planning in flood-plain management. in guiding growth and development, but the existence of the infor Adequate information on flood-prone areas and flood hazards mation does not assure its effective use in the day-to-day decisions is essential to effective planning and management. Many sources that shape development. Planners, elected officials, and the public of such information are available, and representative samples of rarely have the training or experience needed to recognize the importance in planning are discussed in this report. How this significance of basic earth-science information, and many of the information is used by agencies involved in managing flood conventional methods of communicating earth-science informa plains is shown by a case study involving Napa County. The tion are ill-suited to their needs. section also shows the interplay among these agencies. It was hoped that the study would aid the planning and The methods of gathering and using flood-plain information decisionmaking community by (1) identifying important prob for planning in the San Francisco Bay region are applicable in lems that are rooted in the earth sciences and related to growth other parts of the country. The examples given in this report are and development in the bay region; (2) understanding the rela selected to show both the wide range of tools available to the tionships between the problems; (3) providing the earth-science planner, and how those tools may be applied to deal most information that is needed to solve these problems; (4) interpreting effectively with flood hazards. and publishing findings in forms understandable to and usable by
Project Director San Francisco Bay Region Study
in
For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock Number 024-001-02970-7
: !
CONTENTS
Page Page 1 Foreword ...... III Planning for flood-loss reduction—Continued I Conversion factors ...... VI Implementation of land-use plans for flood-loss reduction 35 Definition of terms ...... VII Land-use and development regulation ...... 36 Abstract ...... 1 Program development and execution...... 37 Introduction ...... 1 Project review ...... 38 The San Francisco Bay region...... 2 Governmental organization for flood-loss reduction in the San Acknowledgments...... 6 Francisco Bay region, by M. L. Blair and W. E. Spangle 38 Floods and the flood plain, by A. O. Waananen ...... 7 Federal programs ...... 39 Major floods in the region ...... 7 National Flood Insurance Program ...... 39 Characteristics of floodflows ...... 8 Federal Disaster Assistance Program ...... 41 Flood frequency ...... 8 U.S. Army Corps of Engineers...... -...... 42 Stage-discharge relation ...... 9 Comprehensive Planning Assistance Program . 42 Characteristics of the flood plain ...... 9 Community Development Block Grant Program 43 Manmade influences on potential flooding ...... 11 U.S. Soil Conservation Service and resource Influence of urbanization on potential flooding — 12 conservation districts ...... 43 Watershed management ...... 13 Regional and local programs —...... 44 Structural measures ...... 13 Flood control districts ...... -...... 44 Obstructions ...... 14 Regional agencies —...... 45 Delineation of flood plains, by J„ T. Limerinos ...... 14 Planning for flood-loss reduction in the Napa Valley, by Flood-plain inundation maps ...... 14 M. L. Blair ...... -...... 46 Maps of flood-prone areas ...... 15 Description ...... — 46 Flood-hazard maps ...... ~...... 17 Flooding problems in the Napa Valley...... -...... 48 Flood-plain information reports...... 19 Planning for Napa Valley—Regional perspective 50 Flood insurance studies ...... 21 Plan formulation ...... 50 Other flood-plain mapping ...... 21 Plan implementation ...... 53 Interpretation of flood-plain maps and information for Planning for flood-prone areas—Napa County ... 54 site evaluation ...... 22 Plan formulation ...... -...... 54 Sources of flood-plain maps and information...... 23 Plan implementation ...... — 55 Flood-loss prevention and reduction measures, by The Napa County Flood Control and Water W. J. Kockelman ...... 23 Conservation District ...... 58 Protection of existing development ...... 24 Planning for flood-prone areas—City of Napa — 58 Removal or conversion of existing development — .... 26 Plan formulation ...... 59 Discouragement of development ...... 27 Plan implementation ...... —...... ___ 59 Regulation of flood-plain uses ...... -...... 28 Significance of the Napa Valley experience ------63 Planning for flood-loss reduction, by W. E. Spangle and Summary ------65 M. L. Blair ...... -...... —..... 30 References cited ------______68 The planning process ...... 31 Selected readings...... 70 Flood-prone areas—Planning for appropriate land uses 32 Sources of flood-plain maps and information 70 Role of land capability studies 34
ILLUSTRATIONS
P*«e 3 Figure 1. Map showing principal streams and drainage basins in the San Francisco Bay region ------2. Map showing mean annual precipitation in the San Francisco Bay region ------5 3. Diagram showing the hydrologic cycle ...... —...... ------7 t 4. Graph showing flood-frequency curve for a hypothetical basin in the San Francisco Bay region ------...... ---- 9 5. Diagram showing typical sections and profiles in an unobstructed reach of stream valley ...... ——..—... 10 6. Diagram showing riverine flood-hazard areas of a regulatory flood plain ...... •...... 11 Graph showing ratios of peak flows for the 50- and 100-year floods in urbanized and unurbanized basins in the ' 7. San Francisco Bay region ...... - — ...... —-----~—*—-—« 8. Map showing part of the flood-prone area map for the Napa area ...... — ..... - 16 ! 9. Diagram showing areas encompassed by the regional flood-prone area map sheets for the San Francisco Boy 17 v CONTENTS VI CONTENTS VII Pane Figure 10. Regional flood-prone area map for the Napa area...... 18 DEFINITION OF TERMS 11. Flood-hazard map for the Napa area ...... ^ '7n Tr^lr...... 20 23 1113. £5 S3 *=ilKiSE 23 Physiographic, hydrologic, hydraulic, and selected adminis damage, including but not limited to emergency proparedness 14. Flow diagram showing the planning process ...... r*...... ;•*...... 31 trative terms used in this report are defined as follows: plans, flood-control works, and land-use and control measures. 15. Map showing resource conservation districts and U.S. Soil Conservation Service field offices, San Francisco Bay Acre-foot is the quantity of water required to cover 1 acre to a Flood profile is a graph of elevation of the water surface of a depth of 1 foot, and is equivalent to 43,560 cubic feet, 325,871 river in flood in relation to the distance along the stream. A flood region...... -...... 43 \ 16. Map showing Napa County and Napa Valley planning area...... -...... 47 gallons, or 1,233 cubic metres. profile may be drawn to show elevation at a given time, crests 17. Aerial photograph showing Napa River, city of Napa ...... --...... -...... ;...... 48 Area plan establishes policy, expanding upon and consistent during a particular flood, or stages for floods of any designated 18. Graph showing annual floods above 47-foot elevation, 1900-1967, Napa River near Napa, California ...... 49 with a comprehensive plan, for a part of a planning jurisdiction, frequency. 19-22. Maps showing- such as a watershed or a central business district. Flood-prone area map, as used in this report, is a map 19. Flood plains in Napa County...... 50 [ Channel is an open conduit either naturally or artificially based on limited studies that indicates areas likely to be flooded by virtue of their location adjoining a river, stream, bay, or other 20. Prime agricultural lands in Napa County...... -...... -...... 51 created which periodically or continuously contains moving 21. Urban areas and areas with slopes less than 15 percent in Napa County ...... 51 water, or which forms a connecting link between two bodies of watercourse or water body. Floodproofing is any combination of structural and non- 22. Association of Bay Area Governments regional plan for Napa County ...... 52 water. River, creek, run, branch, and tributary are some of the structural measures, changes, or adjustments to properties and 23. Diagram showing Napa Valley Area Plan...... 55 terms used to describe natural channels. 24. Diagram showing proposed land-use plan for city of Napa ...... Comprehensive plan is a document setting forth official structures which reduce or eliminate flood loss of lands, water and 60 sanitary facilities, structures, and contents of buildings. 25. Map showing U.S. Army Corps of Engineers flood-control project and related projects in the city of Napa ...... 61 governmental policy for the long-term future development of an area considering all major determinants ofgrowth and change— Flood stage is the stage at which overflow of the natural 26. Map showing Parkway Plaza Redevelopment Project in the city of Napa ...... ;...... 64 economic, political, social, and physical. banks of a stream begins to cause damage in the reach in which 27. Photographs showing part of Parkway Plaza during and after redevelopment...... „...... 66 28. Index map showing the topographic map sheets and the flood-prone area maps available in the San Francisco Bay Cubic foot per second is the rate of discharge representing a the elevation is measured. region ...... volume of 1 cubic foot passing a given point during 1 second, and is Flood wave is a distinct rise in stage culminating in a crest 71 equivalent to 7.48 gallons per second, 448.8 gallons per minute, or and followed by recession to lower stages. A flood wave may move 0.02832 cubic metres per second. downstream at a velocity greater than the average velocity of flow Discharge is the volume of water (or more broadly, total in a stream. TABLES fluids) that passes a given point within a given period of time. Flood way is the channel of a river or other watercourse and Drainage area of a stream at a specified location is that the adjacent land areas required to carry and discharge a flood of a area, measured in a horizontal plane, which is enclosed by a given magnitude. drainage divide. ' Functional plan describes facilities and operations for a Page Flood, or flooding, is the general and temporary condition specific function of government such as transportation, flood Table 1. Flood-loss prevention methods and devices...... 1...... 24 of partial or complete inundation of normal dry land areas from control, or flood-plain management; it is more specific and usually 2. Expected costs associated with stream flooding ...... ~...... 35 (a) the overflow of streams, rivers, and other inland water, or is shorter in range than a comprehensive plan. 3. Primary functions of flood control districts in the San Francisco Bay region ...... 44 (b) abnormally high tidal water or rising coastal waters resulting Gage height is the water-surface elevation referred to some 4. Major floods at the U.S. Geological Survey gaging station Napa River near Napa, California, 1900-1967 49 arbitrary gage datum. Gage height is often used interchangeably 5. Estimated damage from three floods on the Napa River...... from sf- -.'ere storms, hurricanes, or tsunamis. Also, any relatively . 50 with the more general term “stage” although gage height is more 6. Categories of land serving open-space purposes ...... high Bt.reamflow overtopping the natural or artificial banks in any 52 appropriate when used with a reading on a gage. 7. Recommended acreage for each open-space category in Napa County...... reach of a stream; or a relatively high flow as measured by either 52 Gaging station is a particular site on a stream, canal, lake, 8. Population and land-use projections for the Napa basin, 1960-2060 ...... gage height or discharge quantity. 62 Flood discharge is a quantitative measure of the rate of flow or reservoir where systematic observations of gage height or 9. Sources of maps and flood information ...... measurements of discharge are obtained. 10. Flood-plain maps and information available for areas in the San Francisco Bay region...... 70 ni a point during a flood event; it is usually expressed in cubic feet 72 per second or cubic metres per second. General plan is another term for a comprehensive plan. Flood frequency is the average interval of time between Infiltration is the flow of a fluid into a substance through floods equal to or greater than a specified discharge or stage; it is pores or small openings, as the infiltration of water from precipi generally expressed in years (see recurrence interval). tation or overland flow into the underlying soil. CONVERSION FACTORS Flood-frequency curve is a graph which shows the pro Land-use plan is a key component of a comprehensive plan bability of any given discharge being exceeded in any year, or including objectives, policies, and proposals for the type, pattern, which shows the recurrence interval, or return period, within and intensity of land use in a planning area; it is also called a land- [Factor, for converting English unit, to nielnc unit, are shown to four significant figure.. However, in the text the metric equivalent, are .hewn only to the number r ■ ■* . which, on the average, a given discharge will be exceeded once by use element. figures consistent with the values for the English units] y to uie number of significant the annual peak discharge. Mudslide is the general and temporary movement down a slope of a mass of rock or soil, artificial fill, or a combination of English Multiply by— Flood-hazard map is a map, based on a thorough technical Metric these materials, caused or precipitated by the accumulation of acres study of waterways in a given locality, of sufficient scale and 4.047 x 10’3 water on or under the ground. km2 (square kilometres) clarity to permit ready identification of individual sites as being acre-ft (acre-feet) 1.233 x 10*3 National Flood Insurance Program is the Federally hm3 (cubic hectometres) either within or outside an area having special flood hazards. 1.233 * 10* subsidized program established by the National Flood Insurance m3 (cubic metres) Flood insurance is the insurance coverage for both floods ft (feet) 3.048 x io-» m (metres) and mudslides obtained under the National Flood Insurance Act of 1968 (U.S. Congress, 1968) that provides previously un ft-'/s (cubic feet per second) 2.832 x 10-* available flood-insurance protection to property owners in flood- m3/s (cubic metres per second) Program. in. (inches) 2.540 x 10* prone areas.Insurance protectionisprovided onlyin returnforthe mm (millimetres) Flood peak is the highest value of the stage or discharge mi (miles) 1.609 man km (kilometres) attained by a flood; thus, peak stage or peak discharge. participating communities’ implementation of a flood-plain mi2 (square miles) 2.590 km2 (square kilometres) Flood plain is the land area adjoining a river, stream, agement program. watercourse, ocean, bay, or lake that has been or may be covered One-hundred-year flood (100-year flood) is the level of by floodwater. (This definition of flood plain may differ from that flooding that will be equaled or exceeded once in 100 years and has used in geologic and geomorphic writing.) a 1-percent chance of occurring each year, on the average. Flood-plain management is the operation of an overall Peak discharge_ is the highest rate of streamflow at a point program of corrective and preventive measures for reducing flood I during a rise in the stream. Peak discharge is usually expressed in ! I cubic feet per second or cubic metres per second. A peak discharge i f
i VIII CONTENTS that is the greatest in a 12-month period—usually October stream channels. Stage is the height of a water surface above an established through September—is an annual peak discharge; a peak dis datum plane; also see gage height. charge that causes flooding is a flood discharge. Stage-discharge relation is the relation between gage Peak stage is the maximum water-surface elevation during a height and the quantity of water flowing in a channel. rise in a stream and generally is coincident with the peak Storm runoffis that portion of the total runoffthat reaches discharge. FLOOD-PRONE AREAS AND LAND-USE PLANNING- the point of measurement within a relatively short period of time Recurrence interval, or return period, of a flood of a given SELECTED EXAMPLES FROM THE SAN FRANCISCO BAY REGION, magnitude is the average interval of time within which the given after the occurrence of precipitation. Also called direct runoff. flood will be exceeded once by the annual maximum discharge. Storm water is the excess water running off from the surface 1 CALIFORNIA Regulatory flood discharge is the flood discharge selected of a drainage area during and immediately after a period of rain or snowmelt. It is that portion of the rainfall and resulting surface to provide the basis for delineating that part of the flood plain that ■ is to be managed or regulated to reduce flood damage (often the flow that is in excess of that which can be absorbed through the ' By A. O. Waananen, J. T. Limerinos, and W. J. Kockelman 100-year flood). infiltration capacity of the surface of the basin. See storm runoff. U. S. Geological Survey Regulatory flood fringe is the shoreward part of the Streamflow is the discharge that occurs in a natural regulatory flood plain that would carry shallow slow-moving channel. Although the term “discharge” can be applied to the flow and water when inundated by the regulatory flood discharge. of a canal, the word “streamflow” uniquely describes the dis W. E. Spangle and M. L. Blair Regulatory flood level or profile is the stage along the charge in a surface stream course. The term “streamflow” is more stream that corresponds to the regulatory flood discharge. general than “runoff’ as streamflow may be applied to discharge William Spangle & Associates Regulatory flood plain is that part of the flood plain that whether or not it is affected by diversion or regulation. would be inupdated by the regulatory, or 100-year, flood discharge Stream valley includes both the incised stream channel and and consists of a regulatory floodway and a regulatory flood its flood plain. fringe. Watershed management is the analysis, protection, devel ABSTRACT Full flood control often is not possible or feasible; yet, Regulatory flood profile; see regulatory flood level. opment, operation, or maintenance of the land, vegeteivm. and ■ abandonment of the flood plain may not be reason Regulatory floodway includes the incised stream channel water resources of a drainage basin for the conservation «>•■' all its , Flood-plain occupance and use is often based on the economic able because the flood plain is a valuable resource and the unobstructed part of the flood plain that would carry deep resources for the benefit of man and other living cream*’US. : advantages of level ground, fertile soils, ease of access, and and, in many areas, will continue to be occupied. The fast-moving water when inundated by the regulatory flood dis Water-surface elevation is the height in relation c-an available water supplies, without full consideration of flood risk. charge. nature and extent of flood-plain use should be com sea level expected to be reached by floods of various mo. :> >,udes 1 Structural measures have provided substantial protection in Runoff is that part of the precipitation that appears in and frequencies at pertinent points in the flood plains ofo: -lor many areas, but full protection of flood plains from all floods is patible with the risk involved and the degree of surface streams. It is the same as “streamflow” unaffected by riverine areas. economically infeasible, and flood losses have been increasing. protection that would be practicable. artificial diversions, storage, or other works of man in or on the Thus, planning for flood-plain use to minimize flood damage is The alleviation or reduction of flood loss has urgently needed. Flood-prone area maps and other flood infor been achieved traditionally through construction of mation facilitate effective land-use planning by providing a protective works such as dams, dikes, levees, chan regional overview of the potential flood hazard or detailed in formation for local planning. Various measures are available for nel improvements, and seawalls. These structural reducing flood losses through protection, removal, or conversion measures have partially reduced hazards. But in of existing development, discouragement of development in high- creasing development of urban flood plains, as re risk areas, and regulation of uses on flood plains. ported by White (1960, 1975), has resulted in the Many Federal, State, and local governmental agencies are paradox of continuing expenditures for flood control involved in flood-plain management and regulation, but often and rising flood losses. without coordinated authority and scope. The common goal of flood-plain regulation and use is protecting life, minimizing public Recognition of the mounting flood losses despite expenditures, and reducing flood loss. A comprehensive program flood-control efforts in the United States was con combining structural and nonstructural measures can yield sub tained in the report “A Unified National Program stantial benefits and may present a practical approach for for Managing Flood Losses” prepared by a special managing a flood plain. Task Force on Federal Flood Control Policy (U.S. A review of flood-plain planning, management, and regula tion in the San Francisco Bay region, as shown by a study of Napa Congress, 1966a). The President, in his letter trans County, demonstrates complex multi jurisdictional involvements. mitting the report to the Speaker of the House of Yet, need exists for more adequate comprehensive planning and Representatives, observed that: coordination to provide for sound development and use of flood Nature will always extract some price for use of her flood plains. plains. However, this Nation’s annual flood damage bill *** is excessive ***. Beyond the dollar loss the accompanying toll in personal INTRODUCTION ! hardship cannot be calculated. In addition, opportunities are Floods are natural and recurrent events. They being lost to use flood plain lands effectively for recreation and wildlife purposes. become a problem when man competes with rivers The Federal interest in this matter is beyond doubt. The Federal for the use of the flood plains—the high-water effort to cope with the problem will be unsparing. But I cannot channels of rivers. overemphasize that very great responsibility for success of the Flood plains are occupied by man because they program rests upon State and local governments, and upon are usually accessible and profitable to develop. But individual property owners in hazard areas. The key to resolving continued use may be possible only at a price—to the problem lies, above all else, in the intelligent planning for and State and local regulation of use of lands exposed to flood hazard. sustain flood loss or provide flood-control facilities. l f
FLOOD-PRONE AREAS AND LAND-USE PLANNING INTRODUCTION 3 2 The purpose of this report is to describe the The Task Force report cited the increasing development and use of flood-prone area maps for damage potential under existing policies through the San Francisco Bay region, the. application of inadvertent encouragement of uneconomic use of these maps and other flood-plain information in flood plains. It presented recommendations for modi regional and local land-use planning and in the use, fying and broadening policies and programs for flood regulation, and management of flood plains, and the control and flood-plain management so that any measures which can prevent or reduce flood loss future flood-plain development would yield benefits through control of flood-plain use and protective in excess of costs. Executive Order 11296 (U.S. measures. The maps and related materials described President, 1966), issued in response to these recom are intended to serve as tools useful to regional and mendations, directed the heads of the Federal exec utive agencies to provide leadership in preventing local planning and decisionmaking agencies. Part of uneconomic uses and development of the Nation’s the information and techniques. presented, ,. canr „also , flood plains. This order further instructed Federal be used by those involved in the reduction of flood agencies to evaluate flood hazards associated with losses in communities throughout the nation. The Federal development proposals and instructed Fed- section “Planning for Flood-Loss Reduction in the eral grant, loan, and mortgage insurance agencies to Napa Valley” describes how earth-science informa evaluate flood hazards insofar as practical to pre tion has been used in one area of the Bay region and clude the uneconomic, hazardous, and unnecessary shows the practical benefits and difficulties of apply use of flood plains. ing such information. Federal and State policies on flood management are now shifting from protective measures to a THE SAN FRANCISCO BAY REGION balance between structural and regulatory controls. Flood-plain management, including land-use regu The San Francisco Bay region is comp* of lation, can effectively reduce flood losses. Land-use nine counties contiguous to San Francisc-. ■*~y regulations can be used alone or in combination with (fig. 1). It includes all stream basins draining protective works. Information on the extent of the San Francisco, San Pablo, and Suisun Bays w ■ n flood hazard, land use, and development is essential these counties, and coastal basins draining ink. he for effective application of regulatory controls. Pacific Ocean along about 150 mi (241 km) of co- st The move toward flood-plain management and from about Pigeon Point on the south to the no h the need for flood-plain information has been inten boundary of Sonoma County. The region ene? i- sified by Federal legislation such as the National passes an area of 7,416 mi2 (19,207 km2). Flood Insurance Act of 1968 (U.S.. Congress, 1968) The population of the region was more than 4.8 and the Flood Disaster Protection Act of 1973 (U.S. million in 1975. Major urban centers include the Congress, 1973). Oakland, San Francisco, and San Jose metropolitan The delineation on suitable maps of areas sus areas. Highly developed manufacturing, industrial, ceptible to flooding can provide a means for iden and service activities dominate the economy. Agri tifying and evaluating flood risk. Such information culture and related activities, shipping, and distri can be helpful to elected officials, administrators, bution are also major segments of the economy of the planners, designers, engineers, and developers con area. cerned with the effective and wise management and Transportation facilities are extensive. A highly use of flood plains. developed Federal, State, and county highway and Comprehensive discussions of the management road system provides access to all parts of the region and regulation of flood plains, including legal as and adjacent areas. Three major railroads serve the pects, are presented in the reports “Regulations for region. Airlines provide passenger and cargo service Flood Plains,” by Kusler and Lee (1972), and “Regu t roughout the world. Seven major seaports permit lation of Flood Hazard Areas to Reduce Flood ocean-going vessels to serve important industrial Losses,” by the U.S. Water Resources Council (1971, and agricultural centers and transport commercial 1972). White (1975) presents a comprehensive dis cargoes. cussion of the state of the art in flood-hazard reduc Drainage from the Sacramento and San Joaquin tion, with emphasis on research needs. Further, Rivers flows through the region. The eastern part of consideration of nonstructural alternatives to reduce the region includes part of the Sacramento-San flood losses is required by Section 73 of the Water Joaquin delta area east of Suisun Bay and part of the Resources Development Act of 1974 (U.S. Congress, lower Sacramento River basin south of Putah Creek. 1974c). The Gualala, Russian, and Napa Rivers and Ala-
] r
land-use planning INTRODUCTION 5 4 FLOOD-PRONE AREAS AND 11 narts of the region, but the storm centers usually meda and Coyote Creeks are the principal streams in a V , the north of the region, and the result is pass to the region; their combined drainage area is about 42 ai tendency for precipitation to decrease from percent of the land area of the region. Other streams a gener include the Petaluma River and Sonoma and Suisun north to south. Elevation has a strong local influence. on the Creeks in the north, San Ramon-Walnut, San depth of precipitation and, because elevations range Lorenzo, and San Pablo Creeks in the east, and Los from sea level to more than 4,300 ft (1,300 m), Gatos Creek, through Guadalupe River, in the south; there is a wide range in mean annual precipitation all are tributary to Suisun Bay, San Pablo Bay, and -from 10 in. (250 mm) in low-lying valley areas San Francisco Bay. Coastal streams that flow di in the east to 80 in. (2,000 mm) in some mountain rectly into the Pacific Ocean include the Gualala and areas in the north. The distribution of mean annual Russian Rivers and Lagunitas Creek north of San precipitation in the San Francisco Bay region is Francisco and Pilarcitos, San Gregorio, and Pesca- shown in figure 2. Temperatures are generally mild, dero Creeks south of San Francisco. Topography.—The San Francisco Bay region notably through the winter season, reflecting the lies completely within the Coast Ranges geomorphic moderating influence of the Pacific Ocean. Thus province of California, and in part has moderate to precipitation in the region occurs principally as rain. high relief with peaks ranging up to more than 4,300 However, at elevations above 2,000 ft (610 m), the ft (1,300 m) in elevation. The Coast Ranges extend winter precipitation sometimes occurs as snow; but, from Santa Barbara County on the south to Hum the snowfalls are generally light, and the snow does boldt County on the north and form a nearly contin not remain on the ground for more than a few days. uous barrier between the Pacific Ocean and the Snow thus does not have a significant role in the Great Central Valley. The only significant break in hydrology of the region. Intense local convective this barrier is in the San Francisco Bay region where storms are almost unknown in the region. Sustained the Carquinez Strait between San Pablo and Suisun heavy rains during general storms are the principal Bays and the Golden Gate at San Francisco provide cause of riverine flooding in the San Franc sco Bay gaps through which the Sacramento and San Joa region. quin River flows are discharges (fig. 1). Mountains Flooding problems.—The San Franc: c o Bay are present on the peninsulas north and south of the region periodically experiences damag-. / Hoods. Golden Gate at San Francisco and along the east These floods usually are of riverine origin affect side of San Francisco Bay. The region also contains flood-plain lands adjacent to the streams. asion- several alluviated valleys of moderately large size. ally extreme high tides in the bay and coastal areas, Owing to the hilly and mountainous character of or combinations of high tides, winds, and floods in many parts of the San Francisco Bay region settle the streams, cause coastal flooding and inundation ment and development has tended to concentrate in of lands adjacent to San Francisco Bay. The result the foothills, river valleys, and coastal areas. Urban ing annual flood loss in the region is estimated to and suburban development has been extensive in the average more than $22 million (1965 prices), based areas bordering San Francisco Bay, the Santa Clara on studies by the California Region Framework Valley south of the bay, the San Ramon-Walnut Study Committee (1971). These losses occur even Creek Valley east of the bay, and stream valleys in though millions of dollars have been expended on the north bay area, as well as in the adjacent flood-loss reduction measures. On a National basis, foothills. despite a Federal investment of more than $9 billion Climate.—The climate of the San Francisco Bay region is marked by wide contrasts within short iQQc°+k^'Protection and prevention measures since distances. The Pacific Ocean and the topography are o, the annual flood loss was estimated to average more than $1.7 billion, as of 1966 (U.S. Water Re- the two major features that influence the climate. 8ources °uncil, 1968, p. 5-2-6), and as much as $2 Precipitation in the region is highly seasonal; almost Hydrology from S. E. Rantz (1971) 90 percent of the annual precipitation occurs during ne8s°ni972 \ ^U'S‘ ^ffice of Emergency Prepared ness, j.y/2, v. 1, p. 15). the 6-month period November through April, and the Figure 2.—Mean annual precipitation in the San Francisco Bay region. surh^»a ^-control and flood-management measures summer months are dry. Concentration of rainfall in wet months can result in serious floods from inter mentu n res^rv®lrs» levees, and channel improve- mittent streams which seem to be of small conse- flood Protection for many areas. But quence during the dry season. Most of the precipi alwava a C .??n se^om be complete. There is tation occurs in a series of general storms that reach than has Pr°bablllty that a greater flood will occur s been experienced in recorded history. Par- p
FLOOD-PRONE AREAS AND IAND-USE PLANNING 6 The San Francisco Bay region study of flood- tial protection from flooding may encourage greater nrone areas and land-use planning should provide City of Napa Planning Department. use and development of the flood plain. Then, when a an example to other metropolitan areas throughout Thoughtful review comments on a preliminary flood exceeds that for which protection is provided, the Nation of potential uses of flood information and report draft led to significant improvements in the losses may be greater than if no protection had been inundation maps in regional and local land-use final report. Appreciation is extended to the follow ing individuals who participated in the review pro provided. Further, average annual flood loss from planning and decisionmaking. The section “Plan cess: James H. Hickey, Director, Napa County Con lesser floods has not been reduced as the continuing ning for Flood-Loss Reduction in the Napa Valley” demands for land development have brought about servation, Development and Planning Department; shows the practical application of this information. further encroachment on and more intensive use of Christopher Hartzell, Land Resources Division, and Similar applications can be made in other areas the flood plains. Annual flood loss has increased in Yvonne San Jule, Senior Regional Planner, Associa throughout the Nation. Techniques for developing the San Francisco Bay region and throughout the tion of Bay Area Governments; William H. Fraley, Nation (U.S. Congress, 1966a) as a result of increases the maps may vary, however, depending on the Director, Alameda County Planning Department; in property values, in the magnitude of floods, and in hydrologic and hydraulic data available. and Charles E. Murphy, Flood Control Engineer, building and other uses on flood-plain lands. Marin County Department of Public Works. The ACKNOWLEDGMENTS Extensive flooding occurred throughout the San description of the National Flood Insurance Pro Figure 3.—The hydrologic cycle. Francisco Bay region inl955 and 1958 and in parts of This report was prepared by the U.S. Geological gram was provided by Nicholas Lally, Director, Typically, a stream will overflow its normal the region in 1940,1952,1963, and 1964. Losses from Survey in cooperation with the U.S. Department of Flood Plain Management Division, Federal Insur channel about once in 2 or 3 years and invade low the four later floods were about $23 million in 1955, Housing and Urban Development. Counsel and ad ance Administration, U.S. Department of Housing places on its flood plain. The overflow occurs when $14 million in 1958, $4 million in 1963, and $17 and Urban Development. vice in the initial phases of the study were provided the volume of water entering a stream channel million in 1964, estimated at the time of occurrence, by a multidisciplinary review committee that in exceeds the hydraulic capacity of the channel. or reported by the California Region Framework FLOODS AND THE FLOOD PLAIN cluded the following members: Dan Coleman, Dan Greater floods occur at less frequent intervals, with Study Committee (1971, p. SF-2). These floods in Coleman Associates; Arnold B. Jonas, Alameda By A. O. Waananen concomitant increase in the area affected; but, only clude some of the greatest in the region since the turn County Planning Department; Bruce Kivrof, Ala about once in a century or longer, a great flood will of the century. On an areawide basis, they have a The occurrence of floods is a part of a natural meda County Flood Control and Water Cor* ovation pattern of water circulation from the seas to the submerge all the alluvial deposits in the stream probability of being exceeded once in 50 years, on the District; Ray Laird, Association of Bay Ax rovern- average (2 percent chance of being exceeded in any atmosphere, to the ground, and back to the seas valley. Floods vary in size, area inundated, duration, ments; Jack A. Lindley, Alameda Co? • Flood again called the hydrologic cycle (fig. 3). In this cycle and frequency depending on natural and certain one year). An appreciation of the flood hazard in the Control and Water Conservation District, vies E. region may be gained from the realization that water from the surface of the oceans and other water manmade conditions. The natural conditions in Murphy, Marin County Department of P u 1 Vorks; planning for flood-plain management is usually bodies evaporates into the atmosphere. This vapor is clude the total quantity, intensity, and geographical and Romaine F. Repair, U.S. Army Cor: Engi- based on the flood level that would be exceeded once condensed by various processes and falls to the earth distribution of rainfall and snowmelt, storm pat neers, San Francisco District. as precipitation. Part of the precipitation that falls terns, antecedent moisture conditions, temperature, t, ' in 100 years, on the average. The 100-year floodflows Acknowledgment is made of the exte >. data, on. the land surface is retained temporarily in the and season of the year, as well as the physical would be about 20 percent greater than the maxi maps, and reports on floods and flood dan*, flood- mum flows that have occurred in this century. soil, in surface depressions, and on vegetation and features of the watershed, such as topography, soils, control projects, flood-plain information. ,nd-use other objects until it is returned to the atmosphere by geology, and drainage pattern. The manmade con Potential losses from the 100-year flood in all streams and watershed planning, and flood-plain manage in the region would exceed $200 million (1965 prices), evaporation and transpiration. The remainder ditions include the various rural and urban land ment, prepared by Federal, State, county, arid local based on estimates by the California Region Frame moves through surface and underground channels to uses, storage, diversion, and regulation of stream- work Study Committee (1971). agencies and by numerous public and private agen rivers, lakes, and eventually the sea, and is likewise flows, as well as changes in drainage and other cies and organizations, that were used in the prepar Relationships and benefits of study.—The delin subject to evaporation and transpiration. Precipi factors that affect storm-water runoff. ation of maps of flood-prone areas and the studies eation of flood-prone areas represents an interpre tation in its various forms is the source of freshwater leading to this report. The cooperation of regional tation of water-resources data useful in land-use on the earth’s surface. Through the hydrologic cycle MAJOR FLOODS IN THE REGION and local agencies in the San Francisco Bay region planning and decisionmaking. This study is part of freshwater thus becomes a renewable resource. The San Francisco Bay region is rarely subjected sue as the Association of Bay Area Governments, the San Francisco Bay Region Environment and Floods are natural and normal events. Streams to areawide floods. The mountains and bays sub and agencies of the city of Napa and Napa County, Resources Planning Study, and is directed toward divide the region into relatively small and indepen are gratefully acknowledged. S. E. Rantz, U.S. Geolo have, from time immemorial, periodically overflowed minimizing flood losses. The identification of areas dent valleys thus eliminating the cumulative effect gical Survey, provided helpful guidance in the initia their banks and inundated their natural flood plains that may be subject to flooding from either riverine that might be found in a single-stream system. tion of the report and in earlier studies related to the and floodways. In many areas the rich fertile soils or tidal sources, as shown by flood-prone area maps deposited by such overflows, and the replenishment Floods on the various streams in the region are preparation of maps of flood-prone areas, and flood-inundation studies, is important to the of soil moisture by the floodflows, have sustained an caused by intense rains and usually are of short fniw partlcular the authors want to thank the wise use and development of such areas. Awareness abundant agriculture. In semiarid areas such over duration. Runoff is derived almost entirely from u„ rng officials of Napa County for of potential flooding can lead to a more complete flows may constitute the only source of enrichment rain, as the snow that does fall is not extensive. vervhp°Wdi information and materials that were appraisal of the extent of possible flooding at specific and irrigation. Prior to intensive development per Outstanding floods have occurred. Records ex Joseoh VRif°riT^SCUSsion of the NaPa Valley: sites and to improved decisions on site selection, iodic flooding was accepted as a natural, if at times tending back to 1787 mention storms during the design, and protection. Further, in flood-prone areas’ Flood d J District Engineer, Napa County winter 1798-99 that were reported to have lasted for Antho °0n£°\?n* Water Conservation District; frightening, event. After the floods the streams regional and local administrators and planners usually would revert to their normal channels, leav 28 days, and rains in January and February 1819 Countv Cnn McC.imans> Senior Planner, Napa would be alerted to the desirability of considering ing the flood plains suitable again for agriculture caused floods that changed the courses of many and evaluating alternative uses of flood plains. DepartmentDevelopment and Planning and other compatible uses. streams. ’ and Michael Joell, Principal Planner,
' LAND-USE planning FLOOD-PRONE AREAS AND FLOODS AND THE FLOOD PLAIN 9 8 approached the 1889-90 flood in magnitude and Floods in 1861-62 affected extensive areas in peak discharge. Thus, a peak discharge that has a 2 STAGE- DISCHA RG E RE LATION California, and in many areas they were °^su^“ areaManTsevere floods of limited extent have percent (1 in 50) chance, or probability, of being For every peak discharge there is a correspond magnitude that they represent the greatest floods occurred in different parts of the region. Conserva exceeded in any year is a 50-year flood peak, while known. In the San Francisco Bay region consider the peak discharge that has a 1 percent (1 in 100) ing peak stage, or water-surface elevation. The stage tion and flood-control reservoirs in many of the depends not only on the magnitude of the discharge, able damage was caused in the towns of Napa, basins in the region have reduced the peak chance is a 100-year flood peak. Alvarado, and San Leandro and in San Mateo and A flood-frequency curve is illustrated in figure 4, but also on the physical features of the stream valley. discharges that otherwise would have occurred. Pertinent physical features include ground or Santa Clara Counties (fig. 1). Floods on the Napa Floodwaters from many storms have been retained which shows a typical curve for a basin in the San River and Petaluma Creek in January 1881 exceeded Francisco Bay region that has a drainage area of 5 streambed slope in the direction of flow, cross- in reservoirs operated by the Santa Clara Valley sectional size and shape of the stream channel and any other known flood. During the 1889-90 season Water District (formerly Santa Clara County Flood mi2 (13 km2) and mean annual precipitation of 40 in. record precipitation occurred at many points in the the valley, and the roughness and alinement of the Control and Water District) since about 1935 for (1,000 mm), Figure 4 shows the 50-year flood dis region. The flood of January 1890 near San Jose was charge at the hypothetical site to be 1,740 ft3/s (49.3 streambed, banks, and overflow area. The slope of subsequent release at controlled rates to percolation the greatest since 1862 and may not have been m3/s). Thus, a flood discharge of 1,740 ft3/s (49.3 the water-surface profile during periods of high basins for replenishment of ground-water supplies. equaled since. The 1890 flood in Napa River at Napa m3/s) has a 2 percent chance of being exceeded in water usually is approximately parallel to the aver But most of the streams in the region have insuf was reported to be only a foot lower than the record any year; or it may recur at intervals of 50 years, on age slope of the channel, with no abrupt changes in ficient storage or no storage for the control or height set in 1881. Flows in the Russian River in 1890 the average. Similarly, the magnitude of the 100-year elevation in the water-surface profile if the flow is not exceeded the levels set in 1861 and approached those attenuation of major floods. flood discharge is 2,090 ft3/s (59.2 m3/s). These obstructed or constricted. However, some pro of the great flood of 1879 in this basin; the basin values show the ratio of the 100-year to the 50-year nounced changes in cross-sectional size and shape experienced another great flood in 1895. In March CHARACTERISTICS OF FLOODFLOWS flood discharge to be 1.2, rather than 2, the relation of are common in a reach or length of stream valley. 1907 floods in Los Gatos Creek and other streams in Two characteristics of floodflows—the frequency the time intervals. The ratios between flood dis Stream valleys, for example, may range from wide, flat flood plains to steep-sided canyons. Such the Santa Clara Valley were especially severe, and of occurrence and the relation between the quantity charges of various recurrence intervals depend pri pronounced differences in shape and ground lands near San Jose were flooded. Alameda Creek of flow and the water-surface elevation—are of par marily on the regimen of storm precipitation and elevation, combined with the relatively uniform reached levels as high as those in 1895. Flooding was ticular significance to the use of flood-plain lands. thus vary from region to region. The average ratio water-surface levels, may cause wide variations in also severe in the Russian River basin. In addition, These characteristics are described in the following between the 100- and 50-year flood discharges in the the extent of flooding and the depth of flow in the many other floods of moderate extent have been sections. San Francisco Bay region is 1.20, but it ranges from experienced and reported in some part of the San 1.25 for basins with a mean annual precipitation of main channel and on the flood plain. This is Francisco Bay region since 1849, as reported in U.S. 10 in. (250 mm) to 1.10 for basins with a mean annual illustrated in figure 5, which shows two valley FLOOD FREQUENCY sections and the profiles of the streambed and of the Geological Survey Water-Supply Paper 843, “Floods precipitation of 80 in. (2,000 mm). In any evaluation of flood hazard or flood poten of December 1937 in Northern California,” Recurrence intervals are average periods based water surface for the 10- and 100-year flood (McGlashan and Briggs, 1939, p. 434-437), and in tial the probability of recurrence of floods oCa given on historical data; because the occurrence of floods is discharges in a reach. The sections show that the channel is more deeply incised at section A than at reports on floods subsequent to 1937. magnitude must be estimated. The proba ’ *,y of erratic the 50-year floodflow may not necessarily section B. Flow velocities in an unobstructed The floods of December 1955 generally were the occurrence of floods of various magnitudes at a site occur in any given 50-year period, or floods of this waterway are usually greater in the part of the greatest floodflows of the present century over the may be determined by statistical analysis oi annual magnitude may occur several times during that San Francisco Bay region except for those in San peak discharges for all years of record at the site, period. A similar relation is true for a peak discharge section with the greater depths. The relation between stage and discharge is Lorenzo Creek at Hayward in 1962 and Coyote Creek whether or not all of these events caused inundation. of any given recurrence interval. at Madrone in 1911. Other notable recent floods Peak discharge is the highest rate of flow in a stream normally used as a basis for computing #or occurred in 1952, 1958, 1963, 1964, and 1969 and and generally occurs coincident with the greatest determining streamflows. Conversely, this relation affected different parts of the region. The December water-surface elevation during a rise in the stream. 60 provides a means for determining the water-surface 2090 59 1964 and January-February 1963 floods were severe The annual peak discharge, by conventional usage 2000 elevation at a site or in a reach corresponding to Q principally in the northern part of the region, while in most areas, is the greatest flow in a 12-month Z floodflows of designated frequency, such as the 10- or o the January 1969 floods were limited to the southern period—usually October through September (the so- mO 1740 the 100-year flood. part. called water year). < £ 1500 The flood of December 23, 1955, was the highest x w CHARACTERISTICS OF THE FLOOD PLAIN The magnitude of the annual peak discharge at a o °- in Alameda Creek in the record of peak discharge site vanes from year to year, and it is customary to Q HI that started in 1916, and probably the highest since HI compare hose magnitudes in terms of their proba- Y u. the flood of November 1892. The four highest floods Calaveras Reservoir which was Z o these lands results from the overflow of streams and completed in 1925. a npaV rT m,any year- A common practice is to refer to z rivers or from abnormally high tidal water or rising recurren°f a given magnitude in terms of its 500 coastal water resulting from severe storms, hurri- Precipitation records and historical accounts 10 appear to indicate that the San Francisco Bay region occurrence *Th ^ the inYerse of the probability of canes or tsunamis (seismic sea waves). Along 2 5 10 20 30 50 100 has not experienced a major or area wide flood since is the avera ^ recurrence interval, or return period, streams the flood plain may include the full width of RECURRENCE INTERVAL, IN YEARS 1889-90. Only the flood of December 1955 has peak discha^ *** °^^me within which a given narrow stream valleys or broad areas along the discharge will be exceeded once by the annual Figure 4.—Flood-frequency curve for a hypothetical basin in the streams in wide, flat valleys. The hydrologist and the San Francisco Bay region. hydraulic engineer often use the term flood to de- I '
FLOOD-PRONE AREAS AND LAND-USE PLANNING FLOODS AND THE FLOOD PLAIN 10 11
SECTIONS measures include reservoirs, levees, floodways, and Rav reeion some overflow generally occurs at inter channel improvements; nonstructural measures (flood-plain management practices) generally in SECTION vals averaging from 3-81 years in streams not mark- I A clude flood-plain regulation or control of land use. // i - , ? r 1 !l edlyAny encroachment on the flood plain interferes The purpose of flood-plain regulation is to promote / beneficial use of flood plains with a minimum of / • i\ with the natural flow pattern during high stages. / flood damage and expense for flood protection. Non mm The areal extent of inundation of the flood plain is y / : L, 7 ; structural measures may be used effectively in com / , ! I * therefore related to the magnitude of the flood dis / bination with structural measures to achieve maxi / / charge and the physical characteristics—both nat * / mum benefits. The development and application of / A i ural and manmade or man-influenced—of the flood-plain regulations are described in the section $ *c:- stream valley, which includes both the incised / & . > “Planning for Flood-Loss Reduction.’1 / */ stream channel and its flood plain. Uses of the flood A basic feature of flood-plain regulation is the / •f/ / plain, such as for agriculture and recreation, that i establishment of a regulatory flood discharge, com / t/. i involve little physical change have minor effects on 7/ 4 monly the 100-year flood. The topography of the / i I \ / I the stage and the extent of inundation. But the I flood plain, the magnitude of the floodflow, and the >.7*. v: •' modification of natural drainage systems and the corresponding water-surface elevation and profile . • vV: SECTION »«••• Alluvium '‘. vfr B concentration of various structures that are part of would determine the areal extent of the inundation. the pattern of urban, suburban, industrial, and The part of the flood plain affected by this discharge Channel commercial development present obstructions to or can be described as the regulatory flood plain. It Flood plain Flood plairf-J alterations of flow that may affect the stage, depth, would include the channel, flood way, and fringe area ----- Flood plain for 100-year flood ------Stream valley------and extent of flooding. required to transport the regulatory flood discharge. Occupance of the flood plain can thus result in Figure 6 shows the flood-hazard areas of a regulatory SECTION A two kinds of flood losses. An individual who >tses the flood plain along a river. A regulatory floodway PROFILES flood plain for any development invites floo losses would include the channel of a stream and the to himself; the potential for loss depend.-v :-n the unobstructed adjacent land areas necessary to con Channel SECTION B ,00-vs vulnerability of his specific use. But, me mpor- vey floodflows for a selected flood discharge without tantly, his entry on the flood plain n . : reate substantially increasing flood heights above un ...... problems and costs to others by causing h/ - — flood restricted levels. The width of a regulatory floodway stages through impedance or obstruct).' of the could be reduced for the same size flood, if some back Regulatory Flood Plain > normal pattern of floodflow and reduction flood- water effects are permissible, through channeliza «------Flood Plain (SPF)- Figure 5.—Typical sections and profiles in an unobstructed reach of stream valley. plain storage capacity. The increased floe-" depths tion or installation of dikes, levees, or other con would affect not only his flood-plain neighbors but strictive embankments or fill. EXPLANATION scribe a relatively high streamflow that overtops the could also affect residents outside the area who Coastal areas may be subject to high hazard from high energy winds and wave action, in addition REGULATORY FLOODWAY — Kept open to carry banks of a stream or channel or a relatively high flow would otherwise not be flooded. Hillside develop floodwater—no building or fill. as measured by either the elevation of the water to inundation, with resultant possible destruction of ments may also affect flood-loss potential as a result REGULATORY FLOODWAY FRINGE - Use permitted surface or the volume of flow (see “Definition of of accelerated runoff discharged to flood-plain areas structures and facilities or severe erosion. if protected by fill, flood proofed, or otherwise Terms”). downstream. Comprehensive discussion of the regulation of protected. flood plains and flood-hazard areas is presented in REGULATORY FLOOD LIMIT - Based on technical The principal characteristics of a stream valley The periodic inundation of flood-plain lands study—outer limit of the floodway fringe. are shown in figure 5. The channel and flood-plain reports by Kusler and Lee (1972) and the U.S. Water may result in losses to occupants including loss of STANDARD PROJECT FLOOD (SPF) LIMIT - Area sections are integral parts of the natural conveyance ife and property, hazards to health and safety, dis Resources Council (1971, 1972). subject to possible flooding by very large floods. system of a stream. The erosive power of a stream ruption of commerce and governmental services, and MANMADE INFLUENCES ON POTENTIAL FLOODING Figure 6.—Riverine flood-hazard areas of a regulatory flood carves a channel large enough to carry the most expenditures for flood protection and relief. These plain. (Adapted from U.S. Water Resources Council, 1971.) frequent flow. Occasionally heavy rains or melting osses may be caused by both the cumulative effect of The use of the flood plain by man has been the water course—that govern the stage-discharge snow contribute a flow greater than the capacity of fi 8 plains that cause increased accompanied by a variety of changes in the charac relation and the consequent peak (flood) stage. These the channel. Then the flood plain carries the flow in tlood heights and velocities and uses of areas that teristics of the flood plain and floodflows. Under nat manmade influences thus affect the potential for excess of channel capacity. Flows that occur at are vulnerable to floods or present health and safety ural conditions the flood stage, or level of flooding, flooding and damage. Some changes, such as those intervals of 3-5 years may overtop the natural banks nt* T ,b®cause th«y are inadequately elevated or depends on both the peak discharge and the physical resulting from urban development, may be inadver and occupy low-lying sections adjacent to the stream protected from flood damage. features of the stream valley. Under the changed tent and have adverse effects. Others, such as reser that constitute part of a natural floodway. Greater nanJph! ?roble,ms resulting from flood-plain occu- voirs and channel improvements, are intentional floods, which occur at less frequent intervals, extend conditions resulting from manmade influences the pance and use have led to the development of plans and are directed toward alleviating the flood hazard. over the remainder of the flood plain. During these nature and extent of developments on the flood plain and upstream affect both the peak discharge and the Some projects reduce flood hazards in addition to greater floods the floodway may transport the princi serving the primary or multiple-purpose uses for pal part of the floodflows. In fringe areas on the flood three pertinent physical features—slope, cross- structural and nonstructural. Structural sectional area, and the roughness and alinement of which they were constructed. LAND-USE planning FLOODS AND THE FLOOD PLAIN 13 12 FLOOD-PRONE AREAS AND
INFLUENCE OF URBANIZATION ON POTENTIAL FLOODING Urban development also has other effects in servation, developing and operating watershed- addition to the impact on peak flows. Total yield and management programs, and constructing channel A characteristic of urban growth is the continu W 3 annual runoff usually increase as the shortened time improvements for flood control and navigation all ing increase in the extent and intensity of flood-plain w use. The level and fertile lands and the ease of access < of surface runoff reduces infiltration opportunity. have an influence on flood discharge and stage. The and transportation initially made the flood plain D Low flows increase as a result of the discharge of general impact of these operations and measures is a attractive. With continued growth an increasingly wastewater from lawn irrigation and industrial and reduction in the magnitude of floodflows. oz i greater part of the flood plain and adjacent foothill municipal operations, and effluent from sewage Reservoirs.—Operating storage reservoirs that LL CQ treatment plants and septic tanks. In contrast, have gates to control the release of water will reduce areas was used for homes, industry, and associated *5 recharge to the underlying ground-water basins, downstream peak discharge when storage space is commercial and municipal purposes. Such resulting
flood-prone areas and land-use planning delineation of flood plains 15 14 delineation of flood plains a short distance upstream from the improved reach cies. Inundation maps are an integral part of compre poses such as structural design, economic studies, or formulation of land-use plans and regulations. A of channel, but will have little effect downstream. hensive flood-plain information reports prepared by By J. T. Limerinos part of the flood-prone area map prepared for the In some instances improving the channel may the U.S. Army Corps of Engineers and of watershed Napa Quadrangle is shown in figure 8. have adverse effects. Straightening an alluvial Areas subject to flooding are commonly identi work plans and water- and land-management re The maps of flood-prone areas in the San Fran channel by removing bends, and possibly increasing fied in reports on floods and in studies of measures ports prepared by soil conservation agencies. Flood plains of many streams have been mapped by local cisco Bay region are listed in table 10. flow velocities, for example, may result in erosion for the alleviation or control of flooding. Reports on agencies and special districts. A regional map of flood-prone areas in the San and sedimentation problems. Paved channels could major floods prepared by various governmental Francisco Bay region in California, prepared by provide the ultimate in eliminating flow-retarding agencies may include maps showing the extent of MAPS OF FLOOD-PRONE AREAS Limerinos, Lee, and Lugo (1973) as part of the San influences, but the measure may not be fully accept inundation from the floods. Studies of flood-control able because of esthetic, ecological, and other envi Francisco Bay Region Study, provides an overview or flood-management projects similarly include ap of areas subject to the 100-year flood. The map was ronmental considerations, such as interference with praisals of the probable extent of the areas subject to A report by the Task Force on Federal Flood Con natural alluvial deposition and ground-water re trol Policy (U.S. Congress, 1966a), included a recom prepared at a scale of 1:125,000, or 1 in. equals inundation from floods of designated recurrence approximately 2 mi (10 mm equals 1,250 m), by trans- charge. Although channel modifications may bene intervals before and after installation of the pro mendation that flood-prone area maps be prepared to fit lands adjacent to the treated reach, they will tend assist in minimizing flood losses by quickly identi fering and compositing information from the posed measures. to pass the flood problems on downstream. 1:24,000-scale flood-prone area maps available for Flood-plain information in more detail is also fying areas of potential flood hazards. As part of a Levees.— Levees are embankments along national program the U.S. Geological Survey in 1969 the entire area. The three-sheet map covers the 7,400 available for many areas in several series of maps streams or on flood plains that confine river and began compiling a series of maps for California to mi2 (19,000 km2) in the nine-county region, as shown and information reports prepared by Federal, State, overbank flows to a definite width for the protection identify flood-prone areas and to alert owners, plan in figure 9. A section of the map, for the Napa area in and local agencies. These maps generally provide of lands that are landward from the levee. The major ners, public agencies, and developers to the areal Napa County, is shown in figure 10. The topographic sufficient information for identifying areas of poten contour interval for this map is large—40 ft (12 m) or principal levees are usually designed to provide extent of flood hazards. The maps prepared in 1969 tial flood hazards; for some areas the data in the protection from the 100-year and greater floods. showed areas “occasionally flooded,” the delineated in the flatlands and 200 ft (61 m) elsewhere—but the flood-plain information reports may permit detailed small map scale precludes greater refinement. The Levees reduce the cross-sectional area of flow and areas generally being those inundated by the great increase the velocity of flow within the constricted evaluation of the hazards. This information is useful est recent floods. Maps prepared since 1969 show the small scale of the map, however, permits coverage of extensive areas on a few map sheets of manageable (leveed) reach of channel and flood plain. The stage to planners, developers, public agencies, and private approximate limits of flooding for the 100-year flood. size, thus furnishing a convenient and illuminating of the flood discharge may be raised in and upstream citizens concerned with future land development and Through 1974 nearly 500 map sheets had been pre appraisal of the areas in the region that are vul from the leveed reach, but it will be little affected use. pared for California; 119 of these are for the San downstream. Flood-plain inundation maps provide ;ic in Francisco Bay region (see table 10 and fig. 28). nerable to flooding. A regional flood-prone area map provides the formation useful in developing land-use p. ::*ts and The flood-prone area maps were prepared on regional and county-level planners and decision OBSTRUCTIONS policies for flood plains and adjacent are ;d in topographic quadrangle maps which include con makers with information useful in formulating formulating regulations for managing floo nains. tour lines—imaginary lines connecting points on the ■ broad policies to guide the future development of Some of the principal types of maps aiv . •ports ground surface that have the same elevation—show The stages reached in streams and on the flood flood plains. The inundation map may be used, for that identify and delineate areas subject tv- unda- ing the configuration and elevation of the land sur plain during major floods may be affected by several example, in conjunction with a regional map of pre | ti°n fr°m floods and the sources of this information face. Each quadrangle covers an area encompassed factors. Bridges that have limited waterway open sent land use and other information in developing a are described in the following sections. by 7 1/2 minutes of latitude and longitude, or ap ings and raised approach embankments present regional land-use plan. The map may also serve to proximately 57 mi2 (148 km2). The scale of these impediments to flow that raise stream stages at the FLOOD-PLAIN INUNDATION MAPS identify problem areas where detailed study of the maps is 1:24,000, or 1 in. equals 2,000 ft (10 mm equals bridge. The effects sometimes extend for some dis Two general types of flood-plain inundation flood hazard would be desirable; thus, the map may tance upstream. Obstructions in the flood way and on 240 m). The areas subject to flooding were delineated maps—flood-prone area and flood-hazard maps— also be an aid in local planning. the flood plain such as commercial and industrial ave been issued by the U.S. Geological Survey. from readily available information for quick ap buildings and residences may also cause substantial praisal rather than by detailed field surveys. The The small scale of a regional map and the Maps of flood-prone areas show the areas likely to be generalized delineation of the areas subject to inun reductions in cross-sectional area and raise the flood ooded by virtue of their proximity to a river, stream, information included data on flood inundation, flood stage. Flow velocities may be reduced immediately frequency, peak stage and discharge, and the results dation may not permit sufficient identification of ay, ocean, or other watercourse or water body, as de flood problems at specific sites to be helpful for direct downstream from such obstructions but may be ac termined from readily available information. Flood- of some hydrologic and hydraulic studies. Estimated celerated in the intervening flow paths. An obstruc 100-year flood levels were used to identify flood limits use in local land-use planning and decisionmaking. hazard maps show the extent of inundation as tion in the floodway such as an isolated building at specific points along the margin of the flood plain. Thus, when construction or occupancy is planned on determmed from a thorough technical study of flood- may cause a local rise in water level immediately Lines denoting the limit of inundation were then or adjacent to the flood-prone areas shown on the Lp glven locality- The detail and accuracy may map, a more rigorous description of the flood hazard upstream. Concentrated development in urban areas snepLffl16^ l°* ^^.identifying the relation of drawn in general conformance with the stream slope may cause sufficient resistance to flow to cause a and the topographic contours of the land surface. should be established through comprehensive flood substantial increase in flood stage and associated FlnnH°°i • az?r(*s to individual building sites. More detailed information than is shown on the studies. The regional and the standard quadrangle greater damage from inundation. prepared lnundation maps have also been flood-prone area maps usually is required for pur- maps of flood-prone areas may be helpful, however, y o her governmental and private agen- f
LAND-USE planning 17 16 FLOOD-PRONE AREAS AND DELINEATION OF FLOOD PLAINS to the local planner in instances when time and FLOOD-HAZARD MAPS funding restrictions preclude the more rigorous flood-hazard mapping studies. A flood-hazard map, as prepared by the Geo . The flood-prone areas delineated on the regional logical Survey, generally is a detailed map based on and quadrangle maps for the San Francisco Bay a thorough technical study that shows the extent of region included areas contiguous to the ocean and areas subject to potential hazard from severe floods. the bay that have a potential flood hazard associated Map scales may range from 1:1200 (1 in. equals 100 ft with high tides. The tidal elevations, in relation to or 10 mm equals 12 m) to 1:24,000 (1 in. equals 2,000 ft sea level, were based on data compiled by the U.S. or 10 mm equals 240 m), and contour intervals from 1 1 Coast and Geodetic Survey, as interpreted and re to 20 ft (0.3 to 6 m), depending on the type and density ported by the U.S. Army Engineer District, San of the existing or planned flood-plain development. Francisco, Corps of Engineers. (Tide data for San The large scale maps generally are helpful for de Francisco Bay are usually reported locally in rela veloping plans and programs for flood-plain man- tion to datum at mean lower low water, MLLW.) In agement. undation resulting from tsunamis, or earthquake The cost of a flood-hazard map and the asso generated ocean waves, was not considered in the ciated study increases greatly with increase in map study of flood-prone areas. Although no devastating scale and corresponding refinement of the study. tsunami has been recorded in the San Francisco Bay Thus, cost may preclude preparing maps at large region, and the likelihood of one is small, the pos scale for all the flood plains in a large area. The sibility still exists. Ritter and Dupre (1972) have larger-scale maps may be essential, however, for evaluated the impact of a possible damaging tsu areas where the existing or potential development on nami, as shown on two maps entitled “Maps Show the flood plain is significant. Where little structural ing Areas of Potential Inundation by Tsunamis in development exists or is planned the smaller map the San Francisco Bay Region, California.” A tsu scales, such as 1:24,000 and contour intervals of 5 ft nami having a wave height of 20 ft (6 m) with a runup (1.5 m), may be adequate. Then, individual sites or of 10 ft (3 m) could be disastrous to people partici local areas can be studied and mapped in greater pating in shoreline-recreational activities. Shore, detail for definition of the potential hazard with dock, and harbor facilities, marinas, and boats also respect to depth and duration of inundation and flow might suffer extensive damage from inundation and velocity. from swift currents in the bay generated by tsu In 1954 the Geological Survey began publishing namis. A 20-ft (6-m) tsunami also could inundate a series of hydrologic investigations atlases for the many inhabited areas—suburban, commercial, and presentation of hydrologic information. This series industrial—around the perimeter of the bay, with has been used extensively for documenting floods attendant potential hazard and damage. and flooding in urban areas, river basins, and coastal areas (Bue, 1967). The maps presented are useful in evaluating flood potential and hazard. The atlases generally use topographic quad rangle maps or aerial photomosaics as bases. The extent of inundation from floods of record is usually 2 delineated on the basis of detailed surveys and investigations. Photomosaics permit ready identifi cation of specific sites, structures, properties, and extent of inundation but lack technical data on land- surface elevations and depth relations. Topographic COUNTIES A. MARIN maps provide the specific data on land elevations 38°17'30" B. SONOMA C. NAPA and location basic to engineering studies and de D. SOLANO termination of the depths of flooding. The extent of E CONTRA COSTA F. ALAMEDA inundation may be determined from aerial photo G SANTA CLARA H. SAN MATEO graphs taken during major flood or from field and I SAN FRANCISCO office studies of peak stages and water-surface pro files. The atlases usually include, in addition to the map, a brief test that presents information on peak stages and discharges, floods frequency, water- * Figure 9.—Areas encompassed by the regional flood-prone area 1213 map sheets for the San Francisco Bay region. surface profiles, depth of flooding, and the extent of Figure 8.—Part of the flood-prone area map for the Napa area •(Area of fig. 24 not shown on original map.) LAND-USE planning 18 FLOOD-PRONE AREAS AND DELINEATION OF FLOOD PLAINS 19 122° 15* regulation. Some also include data on flood history tions, or other land-use changes in the basin, may and flow velocity. Illustrations may include flood- affect the streamflow, water-surface elevations, and
38622'30" flow hydrographs or stage-duration curves, dis flow velocities. The usual effect is a change in the charge-frequency curves, graphs of annual peak flood profile. In some instances, recomputation of the discharges, and suitable photographs. 100-year flood profile may be appropriate. Maps showing areas subject to flooding at se 1 lected frequencies are most meaningful in evalu FLOOD-PLAIN INFORMATION REPORTS ating flood-protection proposals, establishing flood- A series of flood-plain information reports pre insurance rate zones, and developing flood-plain pared by the U.S. Army Corps of Engineers presents management programs. The extent of areas subject a comprehensive appraisal of the flood hazard in the to inundation by the 100-year flood is sometimes areas studied. The studies were authorized initially delineated in the atlases by extending the flood- in the Flood Control Act of 1960 (U.S. Congress, depth relations shown by the stage- and discharge- 1960) to provide technical information to local plan frequency curves and the water-surface profiles. ning agencies. The authorization was amended and Depth of flooding may be estimated from the water- extended by the Flood Control Act of 1966 (U.S. surface profiles and ground elevation or from the Congress, 1966b) in response to recommendations by spot water-surface elevations and depth to the gen the Task Force on Federal Flood Control Policy (U.S. eral ground surface shown on some atlases. Congress, 1966a). Under the 1966 Act the Corps of Seven hydrologic atlases related to floods have Engineers is authorized to compile and disseminate been published for areas in California, including two information on floods and flood damages, including in the San Francisco Bay region (table 10). Hydro- identification of areas subject to inundation by logic Investigations Atlas HA-54, “Floods at Fre floods of various magnitudes and frequencies, and mont, California,” by Young (1962), delineates the general criteria for guiding Federal and non-Federal flooding in 1955 and 1958 in Alameda Creek in the interests and agencies in the use of flood-plain areas. vicinity of Fremont in Alameda County. Atlas HA- The principal purpose of the studies, guides, and 348, “Floods on Napa River at Napa, California,” by flood-plain management services provided by the Limerinos (1970), delineates the flooding in 1940 and Corps of Engineers is to furnish local agencies appro <955 in Napa River in Napa County. priate information and guidance for development of A section of the map in the Napa River atlas plans and regulations for improved management 'HA-348) is reproduced in figure 11. The area en and use of flood-plain lands. The surveys and studies compassed by figure 11 (same as fig. 8), is indicated, are made and guides are prepared in response to for comparison, on the section of the regional flood- approved requests. prone area map shown in figure 10. The inundation A flood-plain information report typically in by the floods of 1940 (recurrence interval, 40 years) cludes maps or aerial photomosaics, flood profiles, and 1955 (recurrence interval, 8 years) is shown in charts, tables, photographs, narrative material on. figure 11. The map was prepared on the basis of the extent, depth, and duration of past floods, and detailed field surveys, inspection, and hydraulic similar data on floods that may reasonably be studies. Circled figures at points along the main expected in the future. The maps generally are of stream denote river miles measured from Dutton sufficient detail and scale for ready identification of Landing (Brazos). The map (1:24,000; contour in areas subject to hazard from the 100-year flood (inter terval, 5 ft or 1.5 m) is generally adequate to identify mediate regional flood) and a possible greater flood the hazards in the lightly developed areas upstream (standard project flood). Depths of flooding may be from river mile 9.5, if little structural development is determined from flood profiles and ground eleva planned for those areas. More detail at a larger scale tions. The reports may cover small or large basins or may be desirable for planning and design in the parts of basins. highly developed areas downstream from river mile Ten flood-plain information studies have been 9.5. completed for selected streams in the San Francisco Flood-hazard maps require updating when Bay region, as shown in table 10; studies on other changes have occurred in the channel, on the flood streams are in progress. 6 MILES plain, and in upstream areas. These changes may Some flood reports published by the Corps of 0 Engineers for specific floods, such as the floods of 2 6 include structural modifications in the channel and 8 kilometres in upstream areas such as deepening, widening, or December 1955 (U.S. Army Corps of Engineers, 1956) Figure 10.—Regional flood-prone area map for the N and December 1964 (U.S. Army Corps of Engineers, apa area. (Prom Limerinos, L«e, and Lugo, 1973.) realining. Development on the flood plain, obstruc ■
FLOOD-PRONE AREAS AND LAND-USE PLANNING 20 DELINEATION OF FLOOD PLAINS 21
122° 17'30'' 1965a), include generalized maps of the extent of tion then furnishes flood-insurance rate maps to flooding or maps showing elevations and location of insuring agencies and the local communities. These high-water marks. Similarly, survey reports of the usually delineate areas of special flood hazard (inun ^ ■ j. 0 v V O • *\ • A Corps of Engineers for flood control and allied dation by the 100-year flood) and elevations of the w purposes frequently contain maps giving general 100-year flood levels within these areas. HoJ Aim. A ■ • ized information on areas subject to inundation The flood-insurance rate maps and topographic (table 10). Data from these reports and maps were maps define the extent of the flood-hazard area and Hold 's. iP utilized in the preparation of the maps of flood-prone the depths of flooding on the flood plain. The reports \ EXPLANATION areas issued by the Geological Survey; the individual on the detailed studies are filed in each community i reports are not listed herein. studied but generally are not distributed. -----1940------Boundary of 1940 flood The U.S. Soil Conservation Service, California The Flood Disaster Protection Act of 1973 (U.S. Department of Conservation, and local resource Congress, 1973) requires the purchase of flood insur conservation districts (often soil conservation dis ance after March 2, 1974, or 1 year after the com tricts) provide flood-plain information in their stud munity’s identification as being flood prone, as a ies and reports on watershed work plans for water condition for receiving any form of Federal or Feder shed protection and flood prevention and on water ally related financial assistance for acquisition or shed investigations. These studies were authorized construction purposes in an identified flood-plain in Public Law 83-566, the Watershed Protection and area having special flood hazards that is located Flood Prevention Act of 1954 (U.S. Congress, 1954). within any community currently participating in the Projects authorized under Public Law 83-566 are National Flood Insurance Program. Flood-hazard listed in table 10. The objective of the studies is to insurance would be required when a community formulate plans for improvements to alleviate flood enters the program, and special flood-hazard areas ing and to reduce erosion and sedimentation. The have been identified on flood-hazard boundary reports may include maps that indicate the probable maps. These flood-hazard boundary maps are the limits of flooding, as well as information on flood first maps prepared in the identification process, and depth, flow velocities, and agricultural damage from they show the location of special hazard areas. They floods. Copies of the reports and other unpublished are separate from the Geological Survey’s maps of information may be consulted at district offices flood-prone areas and have been prepared by the or the Soil Conservation Service and cooperating Federal Insurance Administration specifically for agencies. insurance purposes. These maps provide only an approximate delineation of the extent of the 100-year FLOOD-INSURANCE STUDIES flood, and they do not provide information on water- surface elevations usable in estimating depths of The National Flood Insurance Act of 1968 (U.S. flooding. Copies are filed in each eligible community Congress, 1968) was enacted to provide previously and with insuring agencies. unavailable flood-insurance protection to property Communities in the San Francisco Bay region owners in flood-prone areas. Qualification for inclu participating in the National Flood Insurance Pro sion in the flood-insurance program included agree gram are shown in table 10. The coordination of ment by a community to adopt and enforce land-use flood-insurance studies in California has been pro control measures consistent with designated cri j-i vided by the California Department of Water Re V teria. The program is administered by the Federal J sources through the Flood Control Development r-H-; Insurance Administration, U.S. Department of | Branch of the Division of Resources Development. Housing and Urban Development. 38° 17'30" Initially flood-insurance coverage under an emergency program was extended to communities OTHER FLOOD-PLAIN MAPPING that had established eligibility. Subsequent detailed flood-insurance ratemaking studies provide a basis The flood plains of many streams in the San for actuarial insurance rates and coverage under a Francisco Bay region have been mapped by county regular program. The detailed studies, performed for flood control and water conservation districts, muni the Federal Insurance Administration by Federal cipal agencies, and other departments and agencies. Kii.kri-vv.v Jr C\ agencies and other organizations, include develop Some maps show the extent of inundation by major °°.l ment of inundation maps, water-surface profiles for floods, or probable inundation by floods of desig Figure 11.—Flood-hazard map for the Napa area. (Prom Umerinoe, 1970. Area of fig. 24 not ehown designated floods, floodway delineation, and depth- nated recurrence intervals. Other maps have been on original map.) damage curves. The Federal Insurance Administra- prepared in connection with special studies for flood r
LAND-USE planning 23 22 FLOOD-PRONE AREAS /ND FLOOD-LOSS PREVENTION AND REDUCTION MEASURES , , j- nnstream from Dutton Landing. The control and drainage, zoning, planning, and d6' groundelevation at the site is about 15 ft (4.6 m) DISTANCE UPSTREAM FROM DUTTON LANDING, IN KILOMETRES velopment. The map scales and detail are generally ade ab°>OneofIthe graphs in the atlas is a profile of the quate to provide information comparable to that water-surface elevations along the Napa River down from the flood-hazard and flood-plain inundation stream from Dry Creek for the floods of February maps. The maps may be particularly helpful in 1940 and December 1955. This profile (fig. 12) indi studying small local areas in and near cities and the cates an elevation of 16.5 ft (5.03 m) for the flood of adjacent suburban areas. February 27, 1940, at river mile 7^, and presumably Flood-plain maps prepared by county and local also at the fairgrounds. Flood depths at the fair I agencies generally are not published but may be grounds thus would be about 1.5 ft (0.5m). A second available for consultation in the offices of the issuing graph in the atlas is a flood-frequency curve for Napa agency. River (fig. 13) at a gaging station upstream at river INTERPRETATION OF FLOOD-PLAIN MAPS AND mile 13.9 (not shown in fig. 11). The curve indicates a INFORMATION FOR SITE EVALUATION recurrence interval of about 40 years for the 1940 flood. Flood-plain lands within the limits of flooding Planning for the use and management of flood- by the 1940 flood thus are subject to inundation to the plain lands includes consideration of the magnitude levels shown by the flood profile (fig. 12) about once and extent of the flood risk. The several types of flood-plain maps and information reports available in 40 years, on the average. identify flood-prone areas and provide estimates of The 100-year flood generally has been accepted the depth of flooding in some areas. as the base flood for flood-hazard evaluation, flood The accuracy of the delineations of flood-prone insurance, and flood-plain planning. The potential areas depends on the quality and scale of the flood hazard from a flood of this magnitude therefore DISTANCE UPSTREAM FROM DUTTON LANDING, IN MILES maps. The regional maps (scale 1:125,000) of flood- needs to be evaluated. prone areas generally are useful for broad area The extent and depth of inundation from 00- Figure 12.—Profiles of floods on Napa River downstream from mouth of Dry Creek. (From Limerinos, 1970.) appraisal of possible flood hazard. The standard year flood in Napa River may be estimated die quadrangle maps (scale 1:24,000) used for both the increase in water-surface elevation above th- ’-he FLOOD-LOSS PREVENTION AND flood-prone area and flood-hazard maps may provide 1940 flood. The stage difference at the gagin, >n g REDUCTION MEASURES sufficient detail for specific site location and hazard at river mile 13.9 is about 1.5 ft or 0.5 m (19 'd, 6 O a evaluation, especially in nonurban areas. Adequate 57.5 ft or 17.5 m; 100-year flood, 59.0 ft or 18.0 ig. s l» si By W. J. Kockelman appraisal of the vulnerability of a particular build 13). Owing to greater flood-plain width dow< am 5 g « P is The need for preventing and reducing flood loss ing site may require maps of larger scale and greater the stage difference in the vicinity of Third .Meet £ | 4 I has grown with increasing use of, and encroachment detail. The use of flood-hazard maps such as those in and the fairgrounds may be only about two-th is of H 5i.c: 'J 10 31 upon, flood plains. Many methods and devices, both the hydrologic atlases in flood-risk evaluation and in that at the gage, as shown by the 1940 and 1955 flood < 5 planning for urban development and other land use 53 2 5l| structural and nonstructural, are available for the profiles in figure 12. The 100-year flood elevations in D prevention and reduction of flood loss. These is illustrated in a report, “Flood-Hazard Mapping in the city of Napa accordingly would be approximately methods and devices may be used in a variety of Metropolitan Chicago,” by Sheaffer, Ellis, and Spie- 1 ft (0.3 m) higher than the 1940 levels. The corres combinations to provide relief from existing and ker (1970). ponding depth of flooding at the fairgrounds would Figure 13.—Frequency of floods above 39-foot elevation at The flood-hazard maps for the San Francisco be 2.5 ft (0.8 m). potential flood problems. Effective programs for gaging station on Napa River near Napa, California. (From flood-loss prevention1 should be based on an adopted Bay region presented in hydrologic atlases and In a similar manner the flood maps in the Corps Limerinos, 1970.) flood-plain information reports permit some evalu of Engineers flood-plain information reports provide comprehensive plan, although individual methods and devices are often applied without a plan. The ation of flood risk. However, these maps are avail information for flood-risk evaluation in the areas SOURCES OF FLOOD-PLAIN MAPS AND comprehensive planning process is discussed in the able for only a few areas. The following appraisal of covered by the reports. The maps provide data on INFORMATION following section, “Planning for Flood-Loss Reduc flood risk at a site in Napa, Calif., illustrates use of a ground elevations and show the limits of flooding The Geological Survey and other Federal, tion.” Any flood-loss prevention program is most flood-hazard map. from the Intermediate Regional Flood (IRF), equi county, and local agencies have prepared flood-plain effective if based on an adopted comprehensive plan The hydrologic atlas for the lower Napa River valent to the 100-year flood, and from a greater inundation maps and other flood studies for many or flood-plain management program that is being area, by limerinos (1970), provides information standard Project Flood (SPF). Water-surface profiles appropriate for flood-hazard evaluation. Figure 11 areas in the San Francisco Bay region. Information firmly implemented. or ese oods along the major streams are included. on flooding and flood hazards has been presented in shows part of the flood-prone area within the city of fl!)e//SSS?al f°ir flooding at a site from the 100-year Napa. The flood hazard might be evaluated, for pertinent maps and reports. The principal sources of 1 Flood-loss prevention and flood-loss reduction are mutually J J' cfn determined readily from the map, example, for a site such as the fairgrounds, 0.3 mi (0.5 the maps and flood information are indicated in inclusive terms as used in this report. Prevention is usually the ? ePtb of flooding can be estimated from the desired goal; however, it is recognized that under certain circum- km) east of the Napa River at about river mile 7.3, the table 9; the maps and reports available are listed in ground elevations and flood profiles. table 10. j stances reduction may be the more feasible goal. f
FLOOD-PRONE AREAS AND LAND-USE PLANNING FLOOD-LOSS PREVENTION AND REDUCTION MEASURES 25 24 floodwalls, levees, and underground drainage facili- control, such as dams and levees, may encourage Floodproofing.—Floodproofing prevents or re A regional land-use plan can serve as a general development of flood plains in anticipation of addi duces flood loss to existing structures that cannot be framework for subregional, watershed, and com tieS' Construction of flood-control works can be self- tional works being constructed. The public may economically removed from, or that need to be munity land-use plans. An adopted regional land-use defeating As the urban development of flood plains believe that the flood problem has been eliminated, maintained on, the flood plain, such as certain public plan that recommends protecting flood plains from continues, the number of persons and the value of rather than simply abated, by newly constructed utilities, navigation facilities, depots, and ware incompatible development and establishes specific property in areas subject to flooding tend to increase works. Also, such works may not prevent losses from houses. Floodproofing should be considered, how land-use regulations, if implemented, could prevent at rates greater than that at which protection can be great and infrequent floods that exceed the design ever, only where floods are likely to be of short flood loss, protect certain important elements of the provided. Most flood-control works are extensive and flood, often with catastrophic effects. The intelligent duration and have low stages and velocities. natural resource base, including water quality, and costly. For example, to be effective, levees must be of management and regulation of the flood plain is still Floodproofing measures range from structural partially satisfy a need for park and open-space substantial construction, continuous throughout required in conjunction with public works. modifications and installation of special equipment lands. areas with low banks, set back to allow for high- Several Federal programs are available to assist or materials to operational and management safe PROTECTION OF EXISTING DEVELOPMENT water flows, and may need to be supplemented by communities in the construction, repair, or rehabili guards. Many of these measures are discussed and drainage of interior areas. tation of structures and other improvements to pro illustrated in “Introduction to Floodproofing” tect existing development. These Federal programs (Sheaffer and others, 1967) and “Flood-Proofing Coordinating land-use and water-use plans Table 1.—Flood-loss prevention methods and devices include the Snagging and Clearing for Flood Con Regulations” (U.S. Army Corps of Engineers, 1972c). would assure, for instance, that plans for using flood Method or device Purpose Structural modifications and special installation plains for park and recreational purposes would Flood-control works: trol, Flood Control Works, Emergency Bank Pro Protection of existing methods are the most effective as they are not include concurrent establishment of water-quality development. Reservoirs tection, and Small Flood Control Projects programs standards that would accommodate recreational Channel improvements authorized under the Flood Control Acts of 1937, dependent on warning, judgment, decision, and ac Diversions 1941, 1946, and 1948. These programs are discussed tion immediately prior to a flood. uses. Therefore, land- and water-use plans should be Floodwalls and levees prepared together and carefully adjusted to the Flood warning and evacuation in the “Catalog of Federal Domestic Assistance" The feasibility of modifying structures and capability of the resource base to sustain the pro Floodproofing (U.S. Office of Management and Budget, 1974). installing protective equipment or applying special posed land and water uses. Because water-use plans Removal or conversion of Public acquisition Flood warning and evacuation.—Reliable and materials would depend on the materials, age, design are best prepared for a watershed, the mutual adjust existing development. Urban redevelopment features, and the existing and proposed use of the Public-nuisance abatement timely flood warnings would permit temporary evac ment of land-use and water-use plans may be best Nonconforming uses uation of people and some personal properties from structures to be floodproofed. Structural modifica accomplished as part of a comprehensive watershed Conversion of use flood plains to reduce loss of life and property tions include reinforcing basement walls and floor planning program. Public-facility reconstr■: tvn damage. In areas where the time interval between underpinnings to withstand the hydrostatic pres Once land-use and related water-use plans have Discouragement of Public information sures of floodwaters; permanently sealing exterior development. Warning signs the onset of rainfall and flooding is short, such been prepared, adopted, and implemented, many Recordation of hazard ^formation relayed immediately to residents on the openings to basements; using masonry construction; methods and devices are available for preventing or Tax-assessment practice1*; flood plain can result in saving of life and movable erecting low floodwalls; installing water-tight bulk reducing flood loss. These include the protection, Financing policies heads, shutters, and doors; and elevating the lowest Public-facility extension. property. removal, discouragement, and regulation of certain Flood-insurance costs The Joint Federal-State River Forecast Center at floor and access roads to at least 2 ft (0.6 m) above the types of development on flood plains. These methods Regulation of flood-plain Zoning ordinance district Sacramento, Calif., a cooperative program of the 100-year flood. and devices are listed in table 1 and are briefly uses. Special flood-plain regulations National Oceanic and Atmospheric Administration Installing special equipment or applying special described in the following sections. Subdivision ordinances materials may include using special cements for Sanitary ordinances nnd the California Department of Water Resources, Development has occurred and will continue to Building ordinances monitors weather conditions and river stages in the flooring; providing adequate electric fuse protection; occur on flood plains within the San Francisco Bay Pacific Coast area. For the San Francisco Bay anchoring buoyant tanks; sealing of the outside region. Such development, though often convenient, The costs of constructing single-purpose flood- region, the Center issues forecasts of river stages for walls of basements; installing automatic sump advantageous, and profitable to some individuals control structures and improvements may be greater Walnut Creek and the Napa and Russian Rivers pumps, sewer-check valves, seal-tight windows and and economic sectors of a community, sometimes than the benefits from reduced flood-loss risk. How during the flood season. The Center also provides doors, and door and window flood shields; and using wire-reinforced glass. Care must be exercised, how imposes a heavy burden on society. For economic ever, multipurpose structures and improvements, information to the National Weather Service Fore and humanitarian reasons, local, State, and Federal such as low-flow augmentation or recreation, that cast Office at Redwood City for other streams in the ever, to avoid high hydrostatic pressures which governmental agencies may find it necessary to might cause structural damage. provide benefits in addition to flood control may San Francisco Bay region. protect existing developments on flood plains. This prove economically feasible when evaluated within The National Weather Service River District Operational and management safeguards in protection may be provided by flood-control works, t e context of a comprehensive watershed plan. Office at San Francisco International Airport relays clude taking special actions during, or in anticipa flood warning and evacuation, and floodproofing. nvironmental, recreational, and esthetic costs and forecasts and issues flood warnings, when neces tion of, floods such as waterproofing valuable items Flood-control works.—Loss from floods often benefits should be considered even though their sary, to the appropriate county flood-control districts, and merchandise or removing them from areas leads to persistent demands for public-works pro- evaluation might be difficult. State and Federal agencies, and the American Red subject to flood loss; protecting or removing elec grams to provide protection for existing develop Actions and improvements by upstream com Cross. When flash floods are occurring or imminent, trical equipment; discontinuing personal use of areas ments through construction of structures and i:_ lm- munities often impose expenditures on downstream the Forecast Office at Redwood City issues flash- subject to flooding; postponing orders of freight ship provements such as dams, ditches, canals, sluices, 1 communities for public works. Channel improve flood watches and flash-flood warnings to Weather ments; operating emergency pump equipment and holding basins, and detention reservoirs; channel valves; and placing movable bulkheads ments, lor example, may increase flood peaks down- Service offices, various public agencies, and the sewer deepening, straightening, widening, and paving; against doors and windows. Though floodproofing 5n rec*uire public expenditures for down- news media. Flash floods are not a common phenom bypass or diversion channels, dikes, revetments! on-site soil absorption systems for sewage disposal is m oo -control works. Some facilities for flood enon in the San Francisco Bay region. r
FLOOD-PRONE AREAS AND LAND-USE PLANNING 27 26 FLOOD-LOSS PREVENTION AND REDUCTION MEASURES facilities By purchasing easements or development following section, may make some existing uses of advised of flood hazards, would be reluctant to risk sometimes suggested, substituting alternative dis rights flood-plain development can be limited to the flood plains nonconforming. These are uses in property losses and expose their families to the posal systems, such as public sanitary sewer systems certain uses, while the owner receives fair compen or holding tanks, would be more effective. existence at the time of the adoption of a zoning danger and trauma that may accompany floods. As sation for the release of these rights. Easement lines ordinance that do not conform to the use restrictions any program of land-use control will depend on the REMOVAL OR CONVERSION OF EXISTING need not be based on documented flood data because of the ordinance. For example, if residential uses of support of an informed public, using educational DEVELOPMENT the boundaries of the lands to be acquired can be flood plains are prohibited by a zoning ordinance, measures is important. determined by agreement. The use of easements > residences existing on the flood plain at the time of Preparing, announcing, and disseminating Recurrent and frequent damage or hazard to life should include periodic inspection and enforcement adoption of the ordinance would become non- flood-hazard information are effective means for from flooding may be avoided by permanently evac of the land use by the agency holding the easement. conforming. uating the flood plain. This may be accomplished by informing the public. Flood-prone area maps, flood- Easements should be obtained in perpetuity, or for as Zoning ordinances may provide that noncon removing structures or converting them to some use hazard maps, and flood-plain information reports, long as the flood hazard exists. forming uses may be continued but not extended or such as those described in the preceding section, less vulnerable to damage by floods. The feasibility Urban redevelopment.—Flood plains can be of such action depends on the value of the structures, enlarged and, if discontinued for some designated “Delineation of Flood Plains,” are some of the ways redeveloped publicly or privately by purchasing land their adaptability to floodproofing, their effect upon period, ^any future use must conform with the ordi to provide the needed information. that has been determined to be blighted or to have the movement, depth, and storage of floodwaters, nance. The total structural repairs or alterations Warning signs.—Warning signs draw public deteriorated and then clearing and redeveloping the and sufficient citizen interest and concern to support over the lifetime of a nonconforming use may also be . attention to flood hazards, especially the attention of the necessary action by local public officials. Special land. limited to a percentage of the assessed or market potential land purchasers and developers who in attention should be given to removing structures California Commum y eve opmen w value. State enabling legislation may also permit spect sites prior to purchase. Such signs may be most within floodways because of their effect on flood (California Health and Safety Co e, 6c) aut or- eliminating nonconforming uses by providing for effective if they are readily visible to buyers, dev stage and flood velocity. Methods for removal or izes the creation of public redevelopment agencies, the amortization of such uses over a reasonable elopers, and the public, are based upon adequate conversion include public acquisition, urban rede- The law provides for the preparation and adoption of period of time. flood data, and are posted where the 100-year flood velopment, public-nuisance abatement, non- redevelopment plans; acquisition, clearance, dis Conversion of use.—Land uses, improvements, boundaries intersect public rights-of-way. Warning conforming-use provisions in zoning ordinances, posal, reconstruction, and rehabilitation of bhghted and structures that are vulnerable to flood damage signs might take other forms also, such as rubber- conversion of use, and reconstruction of existing areas; and relocation of persons displaced by a can be voluntarily converted to uses less vulnerable stamp impressions on subdivision plats and on public facilities. redevelopment project. Redevelopment su-:. ,icies to loss by floods. Farm feed-storage buildings, for building and zoning permits stating that the sites Public acquisition.—One approach to removing generally are empowered to issue bonds, revive a example, could be converted to sheds for farm equip- are in areas subject to flooding at a given frequency or converting flood-plain development is for a gov- portion of taxes levied on property in the proj r 3.nd • r nt that would not be damaged by floodwaters or or recurrence interval. emmental agency to acquire the developed land. The use Federal grants or loans available ur ■ the disrupt farm operations by being temporarily un- Recordation of hazard.—Recordation provides a flood plains can be acquired through negotiation, Urban Growth and New Community Deve- nt ■vf ’iable; tilled lands might be used for pasture or possible means for alerting land purchasers, local condemnation, tax-delinquency default, dedication, Act of 1970 and the Federal Housing and Cor ty to crops that are less susceptible to flood loss; assessors, and lenders to potential flood hazards. devise, or donation. The governmental agency can Development Act of 1974. These programs hs- ■ nd urban redevelopment areas could be used for This might be done by filing flood-hazards maps with thencontroldevelopmentinthepublicinterest.lt cussed in the “Catalog of Federal Dor Stic parking lots or recreation areas. the appropriate county recorder, together with list may elect to sell or lease part or all of the acquired Assistance” (U.S. Office of Managemeuc and Public-facility reconstruction— Reconstructing ings of the subdivisions or the sections, as identified lands, restricting any development or uses that Budget, 1974). public facilities located on the flood plain, such under the public lands survey system, and requesting would be vulnerable to flood damage. If agricultural Public-nuisance abatement.—Buildings and as roads, bridges, utilities, and community facilities, entry into tract indexes. Abstracts of titles for affec land has been acquired, it might then be leased for structures subject to periodic flood loss often go that are subject to renewal by reason of functional or ted properties and subsequent conveyances then appropriate agricultural uses, thus permitting part unrepaired after a flood, thus initiating a cycle of structural obsolescence may afford opportunity to would contain an entry referencing the hazards. of the acquisition costs to be recovered. deterioration. These buildings and structures can be reduce the risk of flood loss. This might be done by Adopting local subdivision ordinances that require Under the Federal Land and Water Conservation removed or razed by local units of government elevating roads and utilities above flood peaks, flood potential flood boundaries to be shown would auto Fund Act of 1965 and the Federal Housing and applying their public-nuisance abatement powers. proofing, or relocating them in areas not subject to matically result in the filing of pertinent flood- Community Development Act of 1974, grants are For example, Section 203 of the Uniform Building flooding. hazard data with the county recorder along with the available to assist communities in acquiring flood Code, prepared by the International Conference of subdivision plat. plains for park and recreation purposes. These grant Building Officials (1973), which many cities and DISCOURAGEMENT OF DEVELOPMENT Tax-assessment practices.—Real-property as programs are discussed in the “Catalog of Federal counties have adopted provides- sessment is an important factor influencing land-use D°me8tic Assistance" (U.S. Office of Management All Wldings and structures which are structurally unsafe ornot Several methods or devices are available to patterns. In urban and urbanizing areas, the ap and Budget, 1974). prov.ded w.th adequate egress, or which constitute a fire hazard, discourage development on flood plains. They in praisals, assessments, and tax rates on real property Acquiring less-than-fee interest in flood plains or a*e otherw*8e dangerous to human life, or which in relation to clude public-information programs, warning signs, reflect the high demand for land. Owners of flood costs the public less than purchasing the land be- ^8f ng ?8e con8titute a hazard to safety or health, or public recordation of hazard, tax-assessment practices, plains may seek to relieve tax burdens by selling the cause only certain property rights need to be pur- obsolescence °fln*dequate maintenance, dilapidation, financing policies, and public-facility extension less agriculturally productive flood plains for devel chased. Such interest may be in the form of scenic are***un8afe’ building AllT,^ dam*ge’ °* abandonment*** policies. Flood-insurance requirements and costs opment. The public-information, warning, and recor easements for vista protection, conveyance of devel- be ,publif. andThall be abatedTy ZZ 7 may be an additional deterrent. dation programs can alert potential purchasers and opment rights to assure continuance of private parks rena&nitation, demolition, or removal***. Public information.—Public-information pro- | iocai property-tax assessors to those lands subject to and open spaces, and grants of public access and Nonconforming uses.—The adoption and en- grams can help to bring important flood information j flood hazards. A lower assessment and reduced development rights for construction and use of park forcen*ent of zoning ordinances, discussed in a to the attention of the public. Prudent citizens, when demand can result in less economic pressure on the ! owner to convert flood plains to urban use. r
FLOOD-PRONE AREAS AND LAND-USE PLANNING 28 FLOOD-LOSS PREVENTION AND REDUCTION MEASURES 29 REGULATION OF FLOOD-PLAIN USES When constructing public works for flood-loss Zoning ordinance districts.—Zoning ordinances, including on-site sewage disposal.facilities, prevention becomes necessary, the costs of these It is costly to undertake public-works programs adopted and administered by local governmental residential uses, sheltering and confining flood-control works may be assessed in whole or in for the protection of development, difficult to remove agencies, can regulate and restrict the use of land, of animals, and the storing of buoyant, part against those lands that will benefit from the or convert existing development, and probably un water, air, and structures in the public interest. The toxic, flammable, and explosive materials. works. realistic to assume that all future development on the ordinances usually consist of a text setting forth 2. Regulate other uses and structures within the Financing p-olicies.—Almost all building or con flood plain will be discouraged by indirect action. regulations that apply to each zoning district and a flood plain to require floodproofing without struction today involves loans or mortgages by Prohibiting and regulating uses vulnerable to flood map delineating the boundaries of each district to impeding drainage, reducing storage capa private lenders, many of which are insured by the loss under local police powers, however, provides an which the regulations apply. city, increasing flood peaks, or raising flood Federal Housing Administration, Farmers Home efficient and economical method for preventing or Zoning is a widely accepted and effective stages. Administration, or the Veterans Administration. reducing flood loss. For example, the California technique for controlling flood-plain development. 3. Prohibit uses and structures within the flood Compliance by private lenders and Federal agencies Legislature has declared that the primary respon This device can provide direct benefits by restricting way, including filling, dumping, bridge em with policies denying loans or loan insurance for sibility for planning, adopting, and enforcing land- future development of vacant lands in flood plains to bankments, permanent structures, and pri construction on flood plains would discourage flood- use regulations to manage flood plains rests with avert potential damage and by limiting expansion of vate roads that would obstruct the flood plain development. local government (California Water Code, 1971). existing development in flood-hazard areas. way, raise flood stages, increase flood Public-facility extensions.—The availability of Generally, floodways should be restricted to The California Legislature has provided for the velocities, or retard the movement of utilities and other community facilities in flood open-space uses, such as parks, grazing, some types adoption and administration of zoning ordinances floodwaters. plains may attract subdividers, developers, and of agriculture, drive-in theaters, parking lots, and by counties and cities and specifically declared its 4. Prohibit dumping, filling, and erecting any home purchasers. Metropolitan and municipal util outside storage areas, and to selected structures that intention that counties and cities may exercise the structures within the channel that might ities could design and install water-supply and can withstand flood velocities without obstructing maximum degree of control over local zoning matters obstruct floodwaters, and prohibit the sewerage systems that would not have the capacity the movement of floodwaters. The flood plains (California Government Code, 1976a). building of bulkheads, wharves, and piers to serve urban developments proposed on flood should also be limited to open-space uses, but certain The most common general zoning districts except by special permit. plains. Local governing bodies and agencies could uses that are not flood-vulnerable might be pev • tted which contain uses compatible with flood hazards Subdivision ordinances.—Regulating the design adopt and announce policies that they will not if so regulated that reductions in flood water ?• rage are agricultural, open-space, conservancy, and park and improvement of subdivisions is a less frequently authorize, finance, or construct community facilities, capacity and increases in flood stage arr nor. stricts. These districts permit such uses as general used method for controlling flood-plain development. such as roads and schools, to serve areas subject to Isolated filling operations on flood plains r . be ■-»ng, woodlands, wildlife refuges, and public and The California Legislature has provided that every flooding. These actions should be taken well in «*** allowed, but numerous individual fills may, ' mb- are recreation. The general zoning regulations city and county shall by ordinance regulate and advance of developmental pressures; but they can ‘x? supplemented by incorporating flood-plain control subdivisions” (California Government Code, stantial adverse effects on storage capacity n, jod also be used with removal and regulatory methods stage. Therefore, the U.S. Army Corps of E era g.. :xtions into the zoning ordinance text to prohibit 1976b). These ordinances may prohibit subdividing and devices. has stated in one of its flood-plain inforn on agricultural, open-space, conservancy, and lands not suited to the intended uses, subdividing Flood-insurance costs— Flood insurance tradi which would be vulnerable to flood dam- flood plains, and altering flood plains and flood- reports that, “The best rule is to avoid any i) • 1 :of •/'X uses tionally has not been available from private sources the flood plain *** » : For example, the use of flood plains for agri- ways. They may require flood-protection measures because floods lack the essentially random nature (U.S. Army Corps of EngL aers, 1966, p. 26). IVural purposes can be regulated to prohibit farm for building sites and improvement of streets and necessary to a sound insurance program. The Ameri building sites prior to dedication and sale. Devices for prohibiting or regulating flood plain .'-.veilings, the permanent sheltering or restrictive can Insurance Association (1956) has reported that: The approval of subdivisions, acceptance of development include establishing regulatory confinement of animals, and tillage of the flood ways flood insurance covering fixed-location properties in areas subject zones public rights-of-way, and extension of utilities, compatible with the flood hazards involved and without soil conservation practices. to recurrent floods cannot feasibly by written because of the coupled with the developer’s investments in road and virtual certainty of loss, its catastrophic nature, and the reluc incorporating flood-plain regulations in zoning, sub Flood plains which can be zoned for commercial site improvements and the erection of dwellings, tance or inability of the public to pay the premium charge required division, sanitary, and building ordinances. An ex and industrial use because of proximity to existing creates a dilemma for lodal officials. This dilemma to make the insurance self-sustaining. tensive discussion of state enabling legislation, development can be regulated to permit only parking concerns the legality, reasonableness, and economy Flood insurance apparently can be sold at selected legal issues, program administration, and and outside storage and to prohibit the storage of of subsequently applying zoning and other regula feasible rates only with sizable government sub local ordinances relating to flood-plain regulations is buoyant, toxic, flammable, and explosive materials. tions that would prohibit further development on sidies. Unless premiums are related to the risk contained in the U.S. Water Resources Council report Selected parts of flood plains adjacent to proposed lands already subdivided and partially improved. involved, the cost of flood insurance may be con- Regulation of Flood Hazard Areas to Reduce Flood residential development may be placed in a planned sidered a taxation measure. residential district. Regulations can then be imposed This problem could be avoided by prohibiting the sses (1971, 1972). Examples of zoning districts creation of new building sites in areas subject to The National Flood Insurance Program attempts kn-u^eCla^ ^00.^‘P^n» subdivision, sanitary, and so that such flood plains are reserved or dedicated for flooding. to discourage development in flood-hazard areas. building regulations, which can be incorporated into public or private neighborhood parks to serve the This program requires the purchase of flood insur Such prohibition can be accomplished by a exisfing local ordinances, are set forth in Appendices adjoining residential development. ance as a condition for receiving any form of Federal H through L of the “Floodland and Shoreland Special flood-plain regulations.—Regulations in subdivision ordinance that is designed to: 1. Prohibit the creation of building sites on flood financial assistance for construction or acquisition Development Guide” (Southeastern Wisconsin Re- zoning ordinances concerning the use of flood plains in identified flood-hazard areas. This plains subject to the 100-year flood. program is g^onal Planning Commission, 1968). Planning- supplement the basic use and site regulations and discussed in the section “Governmental Organiza * 2. Require the delineation and designation of j- a aspects of these regulatory devices are can be designed to: tion for Flood-Loss Reduction in the San Francisco 1. Prohibit flood-vulnerable uses and structures flood-prone areas on subdivision plats and Reduction.1’’1 “Planning for Fl°od-Ix,ss Bay Region.” within the flood plain and its floodway, certified survey maps. 31 30 FLOOD-PRONE AREAS AND LAND-USE PLANNING PLANNING FOR FLOOD-LOSS REDUCTION Section 17922 of the California Health and Safety Under our democratic form of government, 3. Require dedication or reservation of flood- by State law to prepare and adopt a “comprehensive, Code (1976b) provides for imposing “***substantially long-term general plan for the physical development public participation is essential throughout the plan prone lands for public or private parks or the same requirements as are contained in the most ning process. In fact, most planning efforts funded other community purposes. of the county or city” (California Government Code, recent edition of the ***Uniform Building Code of the by Federal programs are required to provide for sig 4. Require that public and private roads, bridges, 1966). Unless otherwise specified or made clear by International Conference of Building Officials.” nificant public participation. “Public” may refer to and other facilities be designed and con the context, the terms “plan” and “planning,” as elective or appointed political bodies, special-interest structed to withstand flood velocities; pre These ordinances can be used to ensure that the used in this report, refer to comprehensive (or gen interested individuals. Success in imple- vent isolation, utility outages, and disrup structures and their contents are protected from eral) plans and planning. groups, or menting a plan depends on widespread public sup tion of transportation; and not obstruct the flood loss, do not aggravate flood problems, and Land-use plan.—A key component of a compre port which is difficult to achieve if major segments of movement of floodwaters, increase flood provide sound and safe occupancy during floods. The hensive plan providing a link between more general the public are excluded from participating in the velocities, or raise flood stages. opportunity to protect structures from flood loss can goals and policies and the pattern of land develop 5. Require dedication of, or easements along, be increased by a building ordinance that requires: ment. A land-use plan includes objectives, policies, planning process. those drainageways necessary for adequate 1. Foundations, base supports, footings, and and proposals for the type, pattern, and intensity of Decision occur throughout the process, ranging watershed drainage. other anchorages that can withstand flood land use. The land-use plan may be called a land-use from the decision to engage in a planning effort, to velocities and hydrostatic pressures. element, as in the Federal Comprehensive Planning the final approval of a plan and adoption of imple Sanitary ordinances.—Sanitary ordinances are 2. Use of materials that will not be damaged Assistance Program in Section 701 of the Housing menting regulations, programs, and procedures. public laws adopted by local units of government to if submerged. and Community Development Act of 1974 (U.S. Elected public officials have final responsibility for protect the health of the citizens within their juris 3. Elevation of floors and electrical equipment Congress, 1974b) and in the California Planning and most key policy decisions, although persons in non diction. For example, the California Legislature has at least 2 ft (0.6 m) above the level of the Zoning Law (California Government Code, 1976d). elective positions actually make many important provided that cities “***shall take such measures as 100-year flood. In addition, the ground level Functional plan.—A plan for facilities and day-to-day decisions. It is particularly important may be necessary to preserve and protect the public around buildings should be at least 1 ft operations for a specific function of government such that public input precede major policy decisions health, including the regulation of sanitary matters” (0.3 m) above the 100-year flood for at least as transportation, water development, flood control, made by elected officials. The steps in the planning process compose a (California Health and Safety Code, 1970). 15 ft (4.6 m) out from the exterior wails. or flood plain management; it is more specific and rational, systematic approach to informed decision These ordinances can be used to eliminate the 4. Appropriate floodproofing measures, includ usually shorter range than the comprehensive plan. making generally applicable to land-use, functional, health problems resulting from the disruption of ing structural modifications and in ^.illa Area plan.—A plan, expanding upon and con- and area planning as well as comprehensive plan private sewage-disposal systems or contamination tion of special equipment. . ' >tent with the comprehensive plan, for a part of ning. Ideally, the product of the process is an orderly, of private water-supply systems caused by flood 5. Bridge and culvert openings adequate - mss planning jurisdiction, such as a watershed, central logical, and internally consistent plan, or a set of inundation. On-site soil absorption sewage-disposal high-flood discharges and desig . .Cor ■ j.smess district, or other particular area. systems, for example, including septic tanks, absorp plans and programs, to guide public and private maximum passage of debris. THE PLANNING PROCESS decisions. tion fields, and seepage beds and pits, do not function A good example of minimum building sv ds during floods and may become inoperative or clogged Planning is described herein as a six-step Land-use planning is directly relevant to reduc and requirements that could be used to sup t;nt after floodwaters have receded. Such problems v' .cess: (1) Identifying problems and defining goals ing flood losses. The extent of loss from flooding is a can existing building codes is contained in K >d- be avoided by a sanitary ordinance that is designed r?iid objectives; (2) collecting and interpreting data; direct consequence of the use of land. Through a Proofing Regulations” (U.S. Army Corps l . to: :igl- -;p formulating the plan; (4) evaluating impacts; (5) land-use planning and decisionmaking process, neers, 1972c). 1. Require a permit prior to installing any reviewing and adopting the plan; and (6) implement agreement concerning an acceptable level of risk system or constructing or modifying any ing the plan. These steps, as depicted in figure 14, are from flooding can be reached, appropriate uses of building, and require the application for PLANNING FOR FLOOD-LOSS closely interrelated. Plan formulation often indicates flood-prone areas can be determined, and adverse such permit to show the flood-plain boun REDUCTION the need for additional information. Additional in effects of flooding can be mitigated. A land-use plan daries. formation may alter the concept of the objectives and prepared by planners in collaboration with earth By W. E. Spangle and M. L. Blair 2. Prohibit on-site soil absorption sewage- problems, and plan implementation may reveal the scientists, hydrologists, and other specialists thus provides an excellent framework for developing spe disposal systems and private water-supply In general, planning is the process of devising need for additional information or modification of cific programs to reduce flood losses. systems on lands subject to flooding. and carrying out a course of action to reach an the plan. 3. Require the replacement of on-site soil identified objective. As an organized governmental absorption sewage-disposal systems on activity, planning is directed toward improving the flood plains with alternate systems, such quality of decisionmaking and may result in several Public Initiative and response as public sanitary sewerage or flood- kinds of plans serving different purposes. The princi 3 proofed holding tanks. pal kinds of plans discussed in this report include: * Building ordinances.—Building ordinances are y y y * Comprehensive plan.—A plan for the long-term Implement public laws adopted by local units of government to Identify problems Collect and Formulate Evaluate Review and future development of an area considering all major interpret -> adopt plans plans ensure the safety of structures within their juris and define goals plans impacts determinants of growth and change—economic, poli and objectives data diction. Section 17958 of the California Health and tical, social, and physical. When adopted by the Safety Code (1975b) provides that “*** 7 every city or governing body having planning authority, the plan county shall adopt ordinances or regulations im 7 \ 7 \ 7\ becomes the official policy of the agency. A compre Feedback for review and revision posing the same requirements as are contained in the hensive plan is often called a general plan or master regulations adopted pursuant to Section 17922***.” plan. In California, each city and county is required Figure 14.—The planning process. 33 32 FLOOD-PRONE AREAS AND LAND-USE PLANNING PLANNING FOR FLOOD-LOSS REDUCTION Evaluate the impact of alternative land-use concerned with defining appropriate land uses for development, open space, large scale commercial Logical decisions concerning flood-loss reduc patterns on the extent and severity of flooding flood-prone areas. The determination of appropriate and industrial development, and major public tion are likely to result when flooding problems are Evaluate the impact of alternative land-use land uses is a technical-social-political process facilities-including transportation facilities. considered in each step of the land-use planning patterns in terms of potential flood loss. involving personal and corporate aspirations and Ideally the regional plan provides a framework process. The outline below lists, under each step of Review and adopt a plan. Present alternative legal rights, as well as public goals and objectives. A for more detailed county and city land-use planning the planning process, tasks or actions ordinarily plans for review and selection by the appropriate well-conceived and implemented land-use plan can in which both urban and nonurban uses are usually needed for effective land-use planning and decision lead to significant reduction in flood losses with considered in more detail and attention is given to making in flood-prone areas. In many cases, specific legislative body. relatively small public cost, particularly in areas local conditions and problems. A regional plan procedures to be followed are defined by State law. Schedule and hold public hearings. where little or no development of the flood plain has might recommend open-space uses for flood-prone Identify problems and define goals and objec Adopt plan with such modifications as may be occurred. areas; a county or city plan would typically specify tives.—Obtain readily available data for preliminary needed to respond to information provided and More is at stake in deciding land uses in flood- the particular open-space use, such as grazing or identification of flooding problems. opinions expressed at public hearings. prone areas than the potential reduction of flood water-related recreation. Review the data in relation to existing develop Implement the plan.—Prepare and seek adoption losses. The flood plain is an important environ In undeveloped flood-prone areas, nonintensive ment, current land-use plans and policies, projected of regulations and any land-acquisition and capital- mental and ecological resource meriting attention in land uses should be given high priority. Because growth trends, and anticipated changes. improvement programs needed to carry out the plan. flood plains are usually flat and are often overlain Based on community consideration of the Establish guidelines and a procedure for its own right. Flood-prone areas often provide wild with fertile alluvial soils, agricultural uses are fre acceptable level of risk, develop a tentative set of evaluating the effect of development proposals on life habitats, water-recharge areas, fertile soils, quently appropriate. When natural and economic objectives and priorities related to reduction of future flood potential. scenic areas, and lands suitable for recreation and factors favor agricultural uses, more specific deter flood losses. A usual objective is to prevent losses Develop procedures and staff or consultant park uses. Thus, the land-use planner must evaluate minations need to be made concerning the kind of from floods of varying severity up to that of the 100- capability for reviewing hydrologic, soils, and proposed land uses in terms of both the potential year flood. geologic reports, environmental impact assessments, flood risk and the beneficial use of the natural agricultural use. Grazing may have a different impact on flood-loss potential than crop cultivation. Collect and interpret data.—Evaluate adequacy and project proposals. attributes of the flood plain. The impacts of crop cultivation can also vary of available hydrologic and engineering data for Arrange for modification of previous steps as Planning for appropriate flood-plain uses must depending on the kind of crop, the growing season, land-use planning and develop a program for com new or more detailed data become available. also be done in the context of land-use planning for piling needed new data. The generalized model of the planning prc. ess the entire drainage basin. The extent and frequency the structures needed (irrigation structures, storage Arrange with earth scientists and engineers for and list of actions undertaken in each s are of flooding and the resource potential of the flood structures, fencing), the use of pesticides, erosion needed hydrologic studies including maps of flood- necessarily idealized and simplified. Actual -ac- plain may be affected by land-use decisions in up potential, and land-treatment practices. Where crop prone areas, flood profiles, and discharge-frequency tices vary widely depending on the respon i ty, stream areas. In situations where the drainage basin production is permitted on the flood plain, mainte relationships. Map information should relate in authority, and financial position of the p\ . " ig extends beyond a local planning agency’s jurisdic nance of riparian cover adjacent to the streambanks can prevent undue erosion or bank collapse and loss scale and detail to the physical characteristics of the agency; the diversity of the planning area;. of tion, effective planning for flood-prone areas of wildlife habitats. Farm buildings or other flood plain and stream basin and the degree of devel the planning effort; and availability of date or requires interjurisdictional coordination or multi- structures should be located outside the floodway to opment of the area, present and potential. example, planning by regional councils of jurisdictional (regional) planning. avoid obstructing the flow of floodwater. Estimate the probable future demand for land ment (COGs) is likely to emphasize the development If development is proceeding in a stream basin Agricultural use of flood-prone areas reduces considering projections of population growth and of objectives, policies, and criteria for use in or if flood-control works are being considered, plans flood-loss potential below that of urban uses, but distribution, economic activity, social and cultural reviewing projects and plans because the COG’s more specific than local land-use plans are often does not eliminate it. In fact, flood-control works are needs, and transportation requirements. primary source of power derives from Federally needed to focus directly on the flooding problem. often proposed and constructed to protect agricul Use flooding information in combination with mandated review processes. Local planning, on the Such plans, usually called functional plans, consider tural lands from flooding. Such projects should be other data to prepare land-capability maps showing other hand, is more likely to emphasize the develop in depth the land-use/hydrologic relationships in the evaluated for both short- and long-term effects. the relative natural capability of each land unit to ment of objectives, policies, and criteria to serve as a stream basin. Functional plans can provide a bridge Periodic flooding and deposition of sediment is a accommodate each contemplated use. basis for land-use and development regulation— between land-use plans and engineering plans for natural process which forms the rich alluvial soils of Formulate plans.—Consider feasible alternative primarily a local responsibility. flood-control works or specific flood-plain manage flood plains. While the loss of a crop may cause arrangements of land uses, based on land-capability In addition, planning practices are not static. ment regulations. Such functional planning may be immediate economic hardship to the region, the maps, appropriate projections, and economic, social, Planning is in a state of flux, with planners, carried out by a public works department or a flood and political analyses. farmer, or the locality, the replenishment of the soil legislators, and citizens searching for new ways to control district, or by the general planning agency. Prepare and test alternative land-use plans make the The comprehensive plan and planning information by flooding may be a vital long-term benefit. process more effective. The scope of Agriculture is only one of many open-space uses incorporating as much detail as necessary to provide p anning is expanding and its role changing, fresh should provide a framework for the functional which may be appropriate for flood-prone areas. a policy guide for future actions and decisions. approaches are being tried, and new relationships— planning effort whether or not the planning agency Prepare functional water-resources plans for is directly involved. Recreation, especially water-related activities such local, metropolitan-regional, State, and Federal —are stream basins with flooding problems that provide emerging. More than one governmental agency is fre as fishing, boating, and swimming, often has little enough depth and detail to guide the selection of quently involved in planning for a given stream flood-loss potential and may provide valuable public appropriate flood-loss reduction measures. FLOOD.PRONE AREAS-PLANNING FOR APPROPRIATE basin. The plans of the various agencies differ in benefits.Open-space and other low-intensity uses of Evaluate impacts.—Evaluate alternative land- LAND USES scope and specificity, but should be mutually con flood-prone areas may be appropriate to preserve scenic, archeological, and scientific resources or to use plans for environmental, economic, and social In planning for flood-loss reduction, the local sistent. A regional land-use plan ordinarily provides impacts. broad policy guidance for evaluating future urban conserve mineral and timber resources for future use. and regional land-use planner is particularly 34 FLOOD-PRONE AREAS AND LAND-USE PLANNING PLANNING FOR FLOOD-LOSS REDUCTION 35 major reduction in flood-loss potential, flood-contro The use of flooding information in a land The ABAG study focuses on geologic and hydro- Uses such as parking lots, drive-in theaters, or uses works will probably be required. If flood-control capability study is illustrated in the Ohio Depart logic hazards and resources, making excellent use of involving structures with relatively little flood-loss works are constructed, it is important that flood- potential may be appropriate for flood-prone areas. ment of Natural Resources (1974) report “Big Darby many SFBRS products. Natural factors considered plain uses be regulated to prevent an increase in However, the impact of such uses on the natural Creek Corridor Study.” The purpose of the study was in evaluating land capability include earthquakes, damage potential from floods greater than the functions of the flood plain must be carefully to prepare a land-use plan for a stream corridor in flooding, bearing materials, slope stability, erosion/ design flood. Even with flood-control structures evaluated. In particular, the extent of impervious central Ohio “to permit the best use of flood plains sedimentation, and natural resources. Land uses designed for the 100-year flood, it is usually wise surfaces (roofs and paving) must be strictly limited while avoiding flood hazardous construction on considered include agricultural or rural, semirural in ground-water recharge areas if such areas are to planning to restrict occupancy of flood plains to uses them***(and)***to properly evaluate and use the residential, single-family residential, multifamily continue to function. Determining the appropriate which can accept occasional flooding. recreation and natural preservation potential of residential, regional commercial, downtown com uses for specific flood-prone areas thus involves ROLE OF LAND CAPABILITY STUDIES sceni ! I FLOOD-PRONE AREAS AND LAND-USE PLANNING 36 PLANNING FOR FLOOD-LOSS REDUCTION 37 3 Regulations are viewed more favorably by the natural characteristics of the flood plain, the kind courts if they are the product of a consistent, prescribe lot sizes and relationships, requirements ing the physical characteristics of the site or re and level of detail of flood information, and the well-thought-out planning program which for the dedication of lands for public use, limitations quires- that such information be provided by the policies and proposals of the land-use plan. reflects explicit, community-determined on use of hazardous areas, standards for street developer. In either case, the agency staff should Three categories of plan implementation actions improvements, standards for storm drainage, and have sufficient information to set proper data re may be effective in reducing flood losses: goals. Zoning.—A zoning ordinance divides a jurisdic- requirements for other public utilities and facilities. quirements for the developer, and sufficient exper 1. Establishing and administering regulations and establishes for each Subdivision regulations also prescribe procedures tise to review the developer’s reports. on land-use and development through zon tion into districts or zones for review and approval of proposed subdivisions. district requirements governing the use of land and | The administration of land-use and develop ing, subdivision, building and housing In the San Francisco Bay region, the local flood the bulk, height, coverage, and use of structures. Cer ment regulations is a staff function of the reviewing codes, and grading and sanitary ordi control and water conservation district typically re tain zoning classifications and procedures may re agency, and the staff ordinarily makes ministerial nances (most effective in undeveloped views subdivision proposals involving flood-prone duce allowable intensity of development in flood decisions. But, in cases where discretion is allowed, areas); areas and recommends steps to reduce potential plains and (or) require concentrating structures on a the decision to approve or deny a development 2. The execution of programs directly by the flood losses. These may include dedication of ease portion of a site out of the flood plain thus reducing proposal is usually made by the local planning government which has jurisdiction in the ments along water courses for public access, parks, flood-loss potential. Some of the more commonly commission or legislative body. In these cases, the planning area, including actions such as or some other legitimate public purpose; prohibition applied zoning techniques include planned unit de responsibility of the staff is to provide the decision land acquisition for public sites and con of stream channel encroachments; relocation of util velopment (PUD), planned community zoning, making body with all relevant and legally required struction of public facilities; and ities, roads, or other public facilities; protection of information. cluster zoning, agricultural zoning, and flood-plain 3. The review of projects, both public and pri riparian vegetative cover; and elevation of structures PROGRAM DEVELOPMENT AND EXECUTION vate, as required by the National Environ zoning. above the flood level. Recommendations of the flood Planned unit development or planned commun mental Policy Act of 1969 (U.S. Congress, control districts are advisory, but the local legisla Program development and execution involves ity zoning allows development of a large parcel as a 1970), various State environmental laws, tive body has the power, under State law, to attach the systematic use of governmental powers and single unit according to a plan approved by the and the U.S. Office of Management and any of these conditions to the approval of a sub resources to achieve public objectives. Programs legislative body. This technique provides the devel Budget Circular A-95 (1969). division or to deny approval of a subdivision pro describe the direct actions a public agency intends to oper the flexibility to plan for the economic use of a Effective plan implementation depends on the posal for failure to comply with such conditions. undertake including land acquisition, construction active support of residents and organizations within large area within constraints posed by natural fea Wnere there is no flood control district, the responsi- of public facilities, and provision of public services. A a planning jurisdiction. The implementing process is tures and processes. It also gives the public agency : :ty for review and recommendations regarding typical example is a local capital improvement pro intensely political, involving public decisions which the opportunity to review all aspects of the proposal od problems and solutions usually rests with the gram which schedules, over a multiyear period, the have direct impact on the legal rights, economic and and place legally binding conditions on the develop , -v1' or county engineer. capital expenditures proposed for each project or social status, and living and working environment of ment of the property. Flood-prone areas are typically Building and sanitary codes— Building and activity. Constructing a flood-control project, for individuals in a community. Measures to insure left as open space. n : ary codes are regulations adopted by local units example, requires scheduling land acquisition and public participation in decisions concerning imple Cluster zoning specifies the density of permitted government to ensure the safety of structures and construction components in a logical sequence re menting programs and regulations are critical to the development (the number of dwelling units per unit lated to availability or commitment of funds. realization of plan objectives. idents within their jurisdictions. Such regulations of land) and requires that the houses be placed close be effectively used to reduce health hazards and A funding schedule or program is also needed to LAND-USE AND DEVELOPMENT REGULATION enough together to leave a considerable portion of damages from flooding. Typical local ordinance carry out public acquisition of flood-plain lands. the site in open space. Under this device, flood-prone provisions were described in a preceding section Within limits established by Federal and State law, Land-use regulation is largely a prerogative areas may be left in open space with little or no loss of “Flood-Loss Prevention and Reduction Measures.” public agencies may acquire land for public pur granted by the States to local units of government. development potential of a large parcel. Administration of land-use regulations.—Devel poses. Many agencies may acquire land through Although case law and planning legislation differ Agricultural zoning restricts use to specified opment proposals are evaluated for compliance with eminent domain (condemnation at fair market from state to state, general legal principles pertain to agricultural uses. Agricultural zoning applied to appropriate policies, plans, and regulations accord value). Public land may be maintained in open-space all efforts to control land-use and development. flood-prone areas can be effective in reducing losses ing to procedures which are ordinarily specified in uses such as parks, natural preserves, or parking These principles may be summarized as follows: particularly if farm structures are prohibited in the the regulatory ordinances. When ordinances con lots, or, in some cases, sold or leased for appropriate 1. Because the authority to regulate the use of flood plain and appropriate measures are taken to tain detailed restrictions on land use and develop private development or use. private land derives from a local jurisdic prevent encroachment on the stream channel and to ment, administration is straightforward. For ex Land acquisition programs may be critical to tion’s “police power,” regulations, to be reduce erosion. ample, administering flood-plain zoning that pro flood-loss reduction in both developed and unde legal, must promote the “health, safety, Flood-plain zoning restricts the use of officially hibits construction within a flood plain specifically veloped flood-prone areas. In undeveloped flood- morals, and general welfare” of the com- designated flood-prone areas. The zoning is often delineated in the ordinance involves reference to a prone areas, public acquisition of land may be munity. applied to the 100-year flood plain although different map tc determine whether or not a proposed struc effectively used if the land is suitable for a public use 2. Regulation of land use must be reasonable. restrictions may apply to different parts of the flood ture is within the designated flood plain. such as recreation or wildlife conservation, or if While the concept of “reasonableness” has plain depending on flood frequency or loss potential, Regulations which indicate desired results in regulation to reduce flood-loss potential would dis been variously interpreted, it still remains The floodway may be under more severe use limita- more general terms permit greater discretion and criminate against individual land owners. In de the most crucial test of the legality of a regu- tions than the less frequently flooded fringes of the veloped flood-prone areas, public acquisition and ' require greater expertise at the time of review of lation. Prevailing considerations in court flood plain (figs. 5 and 6) development proposals. Planned unit development clearance of land may be appropriate where incen determinations of reasonableness include Subdivision regulations.-The process of divid regulations which call for avoiding natural hazards, tives are lacking, or cannot be reasonably provided. the existence of a rational basis for the ing undeveloped land into buildable parcels is gov for example, can be appropriately administered only for private redevelopment to uses less vulnerable to regulation and equity in its application. erned by subdivision regulations. These typically if the agency staff has detailed information concern- flooding. r 39 38 FLOOD-PRONE AREAS AND LAND-USE PLANNING GOVERNMENTAL ORGANIZATION FOR FLOOD-LOSS REDUCTION short-term uses of man’s environment and the main their responsibilities. This means that local plans Construction of public facilities strongly affects poses and Federally related financing by private tenance and enhancement of long-term productivity, and programs are often framed with an eye to realization of a land-use plan. The timing and loca lending institutions for properties in identified spe and any irreversible and irretrievable commitments Federal and State program funding requirements tion of utility extension, street and highway con as cial flood-hazard areas, unless the community in which would be involved in the pro well as to locally expressed objectives and concerns. struction, and park and school development, for of resources . , which the area is located is participating in the pro posed action should it be implemented. The fact that, until recently, Federal funding has example, all influence the timing and location of gram within one year of its notice of identification as Environmental impact assessment require- been more readily available for flood-control struc urban development. Development of flood-prone being flood prone. ments, similar to those set forth in the Federal legis- tures than for purchase of land or development areas can be discouraged by restricting utility exten The Federal Insurance Administration is lation were adopted by California in the Environ sions, transportation access, and public services rights in flood-prone areas has influenced local de charged with the responsibility to identify all the mental Quality Act of 1970 (California Public Re consistent with an adopted land-use plan. If con cisions concerning flood-loss reduction measures. Nation’s flood-plain areas that have special flood struction of flood-control projects is needed to reduce sources Code, 1976). This act requires an environ Key governmental programs which influence plan hazards. Such an area is defined as being that area of flood losses, programming the actions of several mental impact report (EIR) for all public and private ning for flood-loss reduction and selected govern the flood plain which, on the average, is likely to be governmental agencies—Federal, State, and local- projects which may have significant environmental mental agencies most often directly involved in the flooded once every 100 years (that has a one percent may be involved. impacts, and which involve a discretionary decision planning and decisionmaking process are described chance of flood occurrence in any given year). The by a public agency. Other states have adopted in the following sections. Federal Insurance Administration (written com- PROJECT REVIEW similar requirements since 1970. mun., 1977) has identified 96 communities in the San The requirement for environmental impact as FEDERAL PROGRAMS Francisco Bay region that are eligible for the sale of sessment, whether Federal or State, is, in effect, flood insurance. Flood-hazard areas have been iden Planning agencies are regularly called upon to NATIONAL FLOOD INSURANCE PROGRAM review proposals for projects within or having poten superimposed on the normal review process of the tified in all but two of these communities (see table tial impact on their planning areas. Even in the jurisdiction in which a project is proposed. Projects 10). The eligible communities are all participating in The National Flood Insurance Program was absence of specific procedures or requirements, care subject to environmental impact assessment are still the emergency flood insurance program in which the enacted through passage of the National Flood ful review for consistency with the general plan is a reviewed for conformity with the general plan and limits of coverage are one-half of that of the regular ! Insurance Act of 1968 (U.S. Congress, 1968) and is matter of good planning practices. In recent years, regulations of the appropriate jurisdiction. Local program, and the premiums are subsidized. Upon administered by the Federal Insurance Administra through Federal requirements for the assessment of regulations may require more environmental in I completion of flood-insurance ratemaking studies, environmental impact and the U.S. Office of Man formation than is required by Federal or State law. tion (FIA) in the U.S. Department of Housing and each community will be transferred to the regular agement and Budget A-95 review (1969), such review Urban Development. The program was established program with full insurance coverage available at : promote the public interest by providing appro- has become increasingly formalized. These review GOVERNMENTAL ORGANIZATION FOR : actuarial rates based on the degree of flood risk. in te protection against flood losses through the processes are the major plan-implementing tech FLOOD-LOSS REDUCTION IN THE The specificity of the flood-plain management . . '.ability of flood insurance coverage and the niques of many regional agencies. SAN FRANCISCO BAY REGION requirement of the National Flood Insurance Pro A-95 review.—A-95 review is a procedure de irement of sound flood-plain management regu- gram is directly related to the degree of technical signed to coordinate Federally funded projects with By M. L. Blair and W, E. Spanglf. >ry measures to minimize the exposure of lives data which FIA has made available to a partici State and local planning objectives. Under this pro : property to flood risk. The economic justifica pating community. When a community has submit cedure, notification of application for Federal funds Planning and decisionmaking related to flood tion for the program, which initially requires exten ted an application to participate in the NFIP but has for a wide variety of projects must be submitted to loss reduction in the San Francisco Bay region is sive public subsidies to bring premiums in line with not yet received a Flood Hazard Boundary Map designated State and regional clearinghouse agen- carried out and influenced by a diverse group of what the public can afford, is the reduction of the (FHBM) delineating the special flood hazard area, it cies for review for consistency with State, area-wide, governmental agencies. Typically, efforts to reduce need for and dependence on increasing flood disaster is required to adopt and enforce general flood-plain and local plans and programs. The clearinghouse flood losses are initiated by local government. If relief appropriations through safer construction management measures (Federal Insurance Adminis agency forwards the notification to agencies poten- flood-loss reduction is to be accomplished primarily practices in flood-hazard areas. tration, 1976) which are applicable throughout its tially affected by the project for their review and through regulation, local decisions dominate the The program was amended by the Flood Dis entire jurisdiction. These measures are performance aster Protection Act of 1973 (U.S. Congress, 1973) standards; the development of specific implementa comment. The comments are only advisory, but a effort. However, if major flood-control works are to be } Federal agency must defend in writing any decision constructed, State and Federal agencies are usually under which available limits of flood insurance tion criteria is left to the discretion of the community, to fund a project which has received a negative more directly involved. Because flood-loss reduction coverage were substantially increased. Further, such which has the best knowledge of its own flood review. This assures at least consideration of the often involves a combination of regulatory and coverage became a statutory requirement to secure problem and administrative resources. At all times, review comments of affected public agencies. structural measures, the interplay of government eligibility for Federal financial assistance for acqui however, technical assistance is available from both Environmental impact assessment— The Na- agencies can become very complex, sition or construction purposes within the identified FIA and the coordinating officials designated to tional Environmental Policy Act of 1969 [NEPA] Even when no flood-control works are antici- special flood-hazard areas of the Nation. Federal carry out such responsibilities by each State govern (U.S. Congress, 1970) requires that an environment- pated, flood-loss reduction is influenced by Federal, agencies responsible for the supervision of lending ment. Since some of the following requirements are al impact statement (EIS) be prepared for proposals State, and regional agencies. Federal and State institutions are required to direct such institutions to paraphrased by the FIA, and since the map zones in for legislation and other Federal actions signifi- agencies affect local decisionmaking through re- require flood insurance in connection with real es which each of them apply are omitted for the sake of cantly affecting the quality of the human environ- quirements for funds, criteria for programs shared tate, mobile home, or personal property loans in brevity, the appropriate section of the regulations ment. The statement must include the environmen- responsibility for functions such as transportation identified flood-hazard areas. State-owned proper (Federal Insurance Administration, 1976) is noted i tal impact of the proposed action, any adverse envi- and regulations such as those relating to local ties may be covered by approved self-insurance and should be referred to for the specific regulatory 1 ronmental effects which cannot be avoided should planning or environmental quality plans. language and area of applicability. the proposal be implemented, alternatives to the Local governmental agencies are increasingly Section 202 of the Act prohibits Federal finan When the FHBM is not yet available, the com- proposed action, the relationship between local dependent on Federal and State funds to carry out cial assistance for acquisition or construction pur- r 40 FLOOD-PRONE AREAS AND LAND-USE PLANNING GOVERNMENTAL ORGANIZATION FOR FLOOD-LOSS REDUCTION 41 4 In riverine situations, notify adjacent communities and the haulers is provided, and that where piles or columns are used for used for human habitation (1910.3.e.5). munity must meet the following requirements of Sec State Coordinating Office prior to any alteration or relocation of a elevation, lots are large enough to permit steps, and piling 5. Prohibit the use of fill for structural support (1910.3.e.6). tion 1910.3.a: watercourse and submit copies of such notifications to FIA foundations are stabilized and reinforced (1910.3.C.5). 6. Prohibit the placement of mobile homes, except in existing 5. Require that mobile homes which are not to be located in 1. Require permits for all proposed construction or other devel mobile home parks and mobile home subdivisions (1910.3.e.7). 5. Require that the flood carrying capacity within the altered or mobile home parks or subdivisions meet the foregoing require opment2 (including placement of prefabricated buildings and 7. Prohibit man-made alteration of sand dunes and mangrove relocated portion of any watercourse be maintained (1910.3.b.7). ments (1910.3.C.6). mobile homes) to determine if it lies within a flood-prone area stands which would increase potential flood damage to existing 6 Require that mobile homes meet FIA anchoring standards to 6. In areas subject to shallow flooding, require that all (1910.3.a.l). new structures (1910.3.e.8). 2. Review such development proposals to assure that all neces resist flotation, collapse, or lateral movement (1910.3 b.8). construction and substantial improvements have the lowest floor The implementation of a flood-plain manage 7 Require that an evacuation plan for all mobile home parks (including basement) elevated above the crown of the nearest sary Federal or State permits have been obtained (e.g., Section 404 ment regulatory effort based on the design and high- and subdivisions be filed with appropriate Disaster Preparedness street to the height specified on the FIRM (1910.3.C.7). permits under the Federal Water Pollution Control Act Amend hazard area criteria discussed above as required ments of 1972) (1910.3.a.2). Authorities (1910.3.b,9). 7. Require that non residential structures in areas subject to 3. Review all permit applications to assure that all new con Up to this point, the community has been partici shallow flooding be either floodproofed or meet the foregoing under the National Flood Insurance Program will struction and substantial improvements be: (a) Anchored to pating in the Emergency Flood Insurance Program requirement (1910.3.C.8). have significant effects on land-use planning in 8. Until a regulatory floodway is designated, require that, prior prevent displacement or collapse, (b) Constructed with materials and has received none of the advanced technical many San Francisco Bay region communities. Large and utility equipment which are resistant to flood damage, to such designation, no new construction or other development is areas of the region are subject to either tidal or data (base flood data, floodway, or coastal high- permitted which, when combined with all other existing and (c) Constructed according to methods and practices that minimize riverine flooding—including many highly urbanized flood-damage potential (1910.3.a.3). hazard area delineation) which becomes available anticipated development, will increase the water-surface ele areas. Planners in these areas need detailed, up-to- 4. Review subdivision proposals and other proposed new devel upon conversion to the Regular Program with the vation of the base flood more than one foot at any point within the opment to determine whether such proposals will be reasonably completion of the Flood Insurance Rate Study and its community (1910.3.C.9). date information about the flood-insurance require safe from flooding. If a subdivision proposal or other proposed accompanying Flood Insurance Rate Map (FIRM). The requirements of Section 1910.3.d include ments of the Federal Insurance Administration. new development is in a flood-prone area, any such proposal shall After a community converts to the Regular Program, the requirements of Sections 1910.3.C.1-8, as well as Because the regulations are subject to change, the be reviewed to assure that: (a) Such proposals are consistent with i planner is well advised to contact the Federal Insur the need to minimize flood damage within the flood-prone area, it must meet the requirements of either Section the following: (b) New or replacement utilities are located and constructed in a 1910.3. C, d, or e, depending upon the type of informa 1. Select and adopt a regulatory floodway based on the principle ance Administration for current requirements per manner which will minimize or eliminate flood damage, (c) Ade tion which the study provides. If the study provides that the area chosen for the regulatory flood way must be designed taining to his jurisdiction. quate drainage is provided to reduce exposure to flood hazards to carry the waters of the base flood without increasing the water only base flood data, the community must adhere v (1910.3.a.4). surface elevation of that flood more than one foot at any point FEDERAL DISASTER ASSISTANCE PROGRAM 5. Require new or replacement water systems to be designed to Section 1910.3.c; if it provides a floodway delineate • ■ i (1Sl0.3.d.2). minimize or eliminate infiltration of flood waters into the systems which is typical in riverine situations, as well as 2. Prohibit encroachment, including fill, new construction and Federal disaster assistance supplements the re and discharges from the systems into flood waters (I910.3.a.5). base flood data, Section 1910.3.d must be adhered to; ?>• ruuial improvements, and other development within the sources of State and local governments to alleviate 6. Require new or replacement sanitary sewage systems to be if it provides a coastal high-hazard area define,: . . ed regulatory floodway that would result in any increase in designed to minimize or eliminate infiltration of flood waters into levels in the community during the occurrence of the base the suffering and damage caused by emergencies for coastal areas subject to wave action, Sect) the systems and discharges from the systems into flood waters, discharge (1910.3„d,3). and major disasters, as defined by the Disaster Relief and requirethaton-sitewaste-disposal systemsbe located to avoid 1910.3. e must be adhered to; and in certain cireu vohibit the placement of any mobile homes, except in an Act of 1974 (U.S. Congress, 1974a). This Act, imple impairment of them or contamination from them during flooding stances where communities include both river:. * 1 -jg mobile home park or subdivision, within the adopted mented by the Federal Disaster Assistance Adminis (1910.3.a.6). (floodway) and coastal high-hazard areas, Sec'. > i rory flood way (1910.3.d.4). tration (1975) contains three significant provisions After receiving its FHBM, the community must 1910.3.d and 1910.3.e must be adhered to. he requirements of Section 1910.3.e include in Federal preparedness and disaster assistance continue to enforce the same controls within the area The requirements of Section 1910.3.C include as of Section 1910.3.C.1-9 for the portions of the relating to flood-prone areas. First, financial and defined on the map, as well as the following addi those of Section 1910.3.b, as well as the following . '.‘.‘(-hazard area outside of the coastal high-hazard technical assistance, funded by the Federal govern tional requirements of Section 19l0.3.b: additional requirements: • .** as well as the following additional requirements ment, is offered to the States to develop plans, pro 1. Require that all subdivision proposals and other proposed 1. Require that all new construction and substantial improve which apply within the coastal high-hazard area: grams, and regulations for hazard reduction, disas new developments greater than 50 lots or 5 acres, whichever is the ments of residential structures have the lowest floor (including 1. Obtain the elevation of the lowest habitable floor of all new or lesser, include base flood-elevation data (1910.3.b.3). basement) elevated to or above the base flood level, unless an substantially improved structures, for the determination of appli ter preparedness, and disaster relief. Second, build 2. Obtain, review, and reasonably utilize base flood-elevation exception for the allowance of basements and/or storm cellars is cable flood insurance risk premium rates, and maintain records of ings and mobile homes located within identified data from alternative sources, prior to its being provided by FIA granted to the community by the FIA (1910.3.C.2). all such information (1910.3.e.2) flood-prone areas which are to be replaced, repaired, through its Flood Insurance Rate Study, as criteria for requiring 2. Require that new construction and substantial improve 2. Provide that new construction is located landward of the that all new residential structures and substantial improvements or restored with Federal disaster assistance funds ments of nonresidential structures have the lowest floor (includ reach of mean high tide (1910.3.e.3). to existing structures have their lowest floor (including basement) must conform to the National Flood Insurance Pro ing basement) elevated to or above the base flood level, or flood- 3. Provide that (i) all new construction and substantial im elevated to or above the base flood level, and new nonresidential proofed to or above that level (1910.3.C.3). provements are elevated on adequately anchored piles or columns, gram prior to receipt of that assistance. The major structures and substantial improvements to existing ones have _ Require that, where floodproofing is used for structures in and securely anchored to such piles or columns so that the lowest effect of the program on flood-loss reduction efforts is the lowest floor (including basement) elevated or floodproofed to lieu of elevation, a registered professional engineer or architect portion of the structural members of the lowest floor (excluding to reinforce the provisions of the National Flood or above the base flood level (1910.3.b.4). certify that the floodproofing methods used are adequate to piles or columns) is elevated to or above the base flood level, and 3. Obtain and record the lowest floor level when a permit is Insurance Program that discourage flood-plain de withstand flood depths, pressures, impact and uplift forces, and (ii) that a professional engineer or architect certify that the issued for new construction and substantial improvements for use velopment. Also, Section 314 of Public Law 93-288 other forces associated with the base flood and record such structure is securely anchored to adequately anchored piles or in the determination of applicable flood insurance risk premium (U.S. Congress, 1974a) requires insurance for other certifications or »submit to FIA for approval of local regulations | columns in order to withstand velocity waters andhurricane wave rates (1910.3.b.5). containing detailed floodproofing specifications which meet the wash (1910.3.e.4). hazards on properties assisted under Section 402 or watertight performance standards (1910.3.C.4), 4. Provide that all new construction and substantial improve 419 of the Act, provided that such insurance is 4 For new mobile home parks and subdivisions, expansion to ments have the space below the lowest floor free of obstructions or reasonably available, adequate, and necessary. existing ones, and in those where access, utilities, and pads are be constructed with “breakaway walls” intended to collapse under Third, as a condition of any loan or grant, the State 'The term "development" is defined to mean “any manmade change to improved or substantially improved, require that stands and lots are elevated stress without jeopardizing the structural support, so that the or local government must agree that the natural unimproved real estate including, but not limited to. buildings or other structures, so that the lowest floor of the mobile home will be at or above the impact on the structure by abnormally high tides or wind-driven mining, dredging, filling, grading, paving, excavation or drilling operations." base flood level, that adequate surface drainage and access for water is minimized. Such temporarily enclosed space cannot be hazards in the areas in which the funds of the grants ; t I GOVERNMENTAL ORGANIZATION FOR FLOOD-LOSS REDUCTION 43 42 FLOOD-PRONE AREAS AND LAND-USE PLANNING COMPREHENSIVE PLANNING ASSISTANCE PROGRAM Under these regulations, problems of flooding must or loans are to be used will be evaluated. The State offices, located in Concord, Dixon, Half Moon Bay, : be considered in the development of land-use plans. and local government must also agree that appro Livermore, Morgan Hill, Napa, Santa Rosa, and The Comprehensive Planning Assistance Pro Petaluma serve the 15 resource conservation dis priate action will be taken to mitigate these hazards, COMMUNITY DEVELOPMENT BLOCK GRANT PROGRAM including safe land-use and construction practices. gram, authorized by Section 701 of the Housing and tricts in the San Francisco Bay region (fig. 15). Community Development Act of 1974 (U.S. Con The Community Development Block Grant Pro U.S. ARMY CORPS OF ENGINEERS gress, 1974b), currently provides grants to finance comprehensive planning programs. The purpose of gram, administered by the Department of Housing and Urban Development, was instituted by the As set forth in the Flood Control Act of 1936 (U.S. this assistance is to increase the capacity of States, Housing and Community Development Act of 1974 Congress, 1936), the U.S. Army Corps of Engineers regional governmental bodies, units of general local (U.S. Congress, 1974b). Under this program, Federal has a major responsibility for flood control through government, and other eligible grant recipients to funds are made available to local governments for a out the United States. The Corps studies flood prob plan and manage all the resources available to them wide variety of community activities, many of which lems, recommends solutions, and constructs and in order to achieve the following goals: were previously funded under separate programs. maintains flood-control projects. The Corps under 1. Community betterment, in both rural and Among the activities eligible for grants are the takes major flood-control projects specifically au urban areas, that is responsive to the needs conservation of open space, natural resources, and thorized by Congress and small flood-control proj of the public; scenic areas; provision of recreational opportunities; ects that do not require Congressional authorization. 2. Adequate housing, public facilities, and pub and installation of flood and drainage facilities (U.S. The purpose of major flood-control projects is to lic services that are required to support an Department of Housing and Urban Development, prevent flood losses by construction of channel im improved quality of life; 1976). Funds are also available to meet emergency provements, levees, or dams. Most major projects 3. Conserving and protecting the environment community development needs in Federally declared involving construction of dams are multipurpose, and natural resources for future genera disaster areas. also serving needs for “hydroelectric power, irri tions; and gation, navigation, municipal and industrial water 4. Coordination and management of all func supplies, water-quality control, recreation and en tional planning activities. U.S. SOIL CONSERVATION SERVICE AND RESOURCE CONSERVATION DISTRICTS hancement of fish and wildlife resources” (U.S. Currently, grants usually cover two-thirds of proj? ». * Army Corps of Engineers, 1975d, p. 215). I costs. The Secretary of Housing and Urban Develc Small flood-control projects provide flood- | ment may allocate assistance directly to eligih rhe U.S. Soil Conservation Service (SCS) is control structures at a Federal cost usually less than recipients or through States (U.S. Department e med primarily with watershed management $1 million per project. Both major and small flood- Housing and Urban Development, 1974). and-treatment practices to reduce soil erosion control projects are preceded by thorough hydro- All agencies applying for grants must have r. i sedimentation; it is also involved in flood- logic studies, cost/benefit analyses of alternative adopted land-use element by August 22, 1977 (U 1 '.\ tol projects through Public Law 83-566 (U.S. solutions to flood problems, and detailed project Department of Housing and Urban Development., C . yress, 1954). Under this law, Federal funds are reports. The costs of Corps projects are shared 1975, p. 36862). The element is to identify areas wh ere p virfed for flood-control projects in small water- between the Federal and local governments. States growth should and should not take place giving com ! 8i 'is. The projects are undertaken cooperatively may assume some or all of the local costs. prehensive consideration to environmental factors. with local sponsors and may have water supply, The Water Resources Development Act of 1974 In addition, the regulations require that assisted recreation, or erosion-control functions. The projects (U.S. Congress, 1974c), authorizing Corps projects planning activities be conducted in accord with the are financed partly by State or local funds. Six small for the coming year, requires, for the first time, that National Environmental Policy Act of 1969 (U.S. watershed projects, as identified in table 10, have nonstructural alternatives to reduce flood losses be Congress, 1970) through the inclusion of environ- been authorized by Congress for the San Francisco analyzed in flood-control studies. The local share of mental planning in the comprehensive planning Bay region; one, the Ulatis Creek project, has been the cost of nonstructural alternatives, such as land ! process. Specifically each agency shall (U.S. Depart completed. acquisition and relocation of buildings, is the same ment of Housing and Urban Development, 1975, p. County flood control and water conservation as for structural projects. Three nonstructural proj 36860): districts together with resource conservation dis- ects are authorized by the Act, representing a signifi 1. Identify salient elements of the natural and manmade trices serve as local sponsoring agencies for all cant change in the Corps’ traditional approach. environments, their interrelationships, and major prob authorized small watershed projects in the San Under the Flood Plain Management Services lems and/or opportunities they present for community Francisco Bay region. In California, resource con Program, the Corps prepares flood-plain informa development; servation districts (RCD), like soil conservation dis tion reports at the request of local agencies, under 2. Assess those environmental factors which will: (i) Mini EXPLANATION tricts throughout the United States, are served by takes hydrologic studies for the Federal Insurance mize or prevent undue damage, unwise use, or unwar ranted pre-empting of natural resources and opportun SCS field offices, each headed by a district conserva Nondistrict areas Administration, and provides technical assistance ities; (ii) Recognize and make prudent allowance for tionist. Resource conservation districts may be to government agencies in flood-plain planning and District areas major latent environmental dangers or risks (e.g., floods, formed under provisions set forth in the California management. Corps of Engineers flood-control mud slides, earthquakes, air and water pollution); and Public Resources Code (1970) for “the control of studies, flood-plain information reports, and proj (iii) Foster the human benefits obtainable from use of District boundary ects in the San Francisco Bay region are listed in the natural environment by wise use of the opportun runoff, the prevention or control of soil erosion, the ities available (e.g., use of natural drainage systems for Figure 15.—Resource conservation districts and U.S. Soil Con table 10. development and distribution of water, and the park and recreational areas). improvement of land capabilities.” Eight SCS field servation Service field offices, San Francisco Bay region. r 44 FLOOD-PRONE AREAS AND LAND-USE PLANNING GOVERNMENTAL ORGANIZATION FOR FLOOD-LOSS REDUCTION 45 The districts usually are responsible for drain REGIONAL AND LOCAL PROGRAMS REGIONAL AGENCIES With respect to flooding the plan states as a age flood control, water-supply development, water major policy (Bay Conservation and Development i FLOOD CONTROL DISTRICTS conservation, and several other functions related to Regional agencies influence flood-loss reduction through an extension of their planning, project Commission, 1969, p. 17): Flood-plain regulations in the Bay region are the use of the county’s water resources. They main review, and regulatory powers. These agencies in To prevent damage from flooding, buildings on fill or near the often drafted and administered by county flood tain channels, remove debris and other obstructions shore-line should have adequate flood protection as deter clude the Association of Bay Area Governments, the control districts. All the San Francisco Bay region to waterflow, and provide emergency services in the mined by competent engineers. As a general rule, buildings San Francisco Bay Conservation and Development counties except San Francisco have such districts, event of a flood. The primary functions actually near the shoreline should be at least nine feet above mean sea Commission, and the California Coastal Zone Con level (standard U.S.G.S. datum) or should be protected by but as each district was established by separate performed by the eight districts in the region are servation Commission. dikes of an equivalent height and by any necessary pumping State legislation, the powers and form of organiza shown in table 3. The Association of Bay Area Governments facilities. In the southern half of the South Bay, this height tion are not uniform. For example, the Santa Clara The flood control districts typically draft and should be at least ten feet. Exceptions to the general height Valley Water District is governed by a separately administer regulations responsive to the California (ABAG) is the only regional agency covering the rule may be made for developments specifically designed to elected board, while the other districts are governed Cobey-Alquist Flood Plain Management Act (Cali entire nine-county San Francisco Bay region with tolerate periodic flooding. by the local County Board of Supervisors sitting as fornia Water Code, 1976), which requires prohibition responsibility for comprehensive planning. Estab The California Coastal Zone Conservation Com the district governing board. All the districts are of development within the right-of-way of a proposed lished in 1961 to develop plans and policies pertinent mission (CCZCC) and six subordinate regional com empowered by their establishing legislation to levy flood-control project. In addition, the districts may to region-wide problems, ABAG is a voluntary asso missions have powers comparable to BCDC’s over taxes, acquire property and water rights, enter into administer county, and sometimes city, flood-plain ciation of city and county governments. Implemen California’s coastal areas. In 1972 California voters contracts, issue bonds, establish zones for levying regulations. In most San Francisco Bay region tation of ABAG’s regional plans and policies de adopted, by initiative, legislation creating these com assessments, and exercise the power of eminent counties, permits from the district are required for pends on decisions by State and Federal agencies, missions. The CCZCC, working with the regional other regional agencies, and local units of govern commissions, was charged with preparing a plan for domain in carrying out their functions. encroachment on or obstruction of stream channels. i ! ment. However, ABAG can indirectly influence local managing the California coastal zone. While the decisions through its designation by the Federal plan was being prepared, the commissions control Table 3.—Primary functions of flood control districts in the San Francisco Bay region government as the A-95 Review clearinghouse led development, through a permit process, to ensure Plan, construct. Conserve, Date maintain import, develop Monitor agency for the San Francisco Bay region. In this consistency with the objectives of the establishing Name of estab- flood control water water Project Land use and development regulations district lished facilities supply quality review administered by district capacity, ABAG reviews requests for Federal funds legislation and the emerging plan policies. Coastal 1 sr liable through most Federal programs. A major areas of the San Francisco Bay region are repre Alameda County 1949 x XX Permit for work within easements, rights-of-way owr.; ■ ’ Flood Control by District. Building permit denial in flood-prone or-i.i i fv' iciion is the review of local applications for Com- sented by two regional commissions: Central (San and Water along certain creeks. Two city ordinances regulatin', j.uuuity Development Block Grants. ABAG reviews Mateo County) and North Central (San Francisco, Conservation “designated floodways” for proposed flood-conir- Marin, and Sonoma Counties). The plan was pre District. projects. ised Federal projects for conformity with adopt sented to the Governor and State Legislature in Contra Costa 1951 x Permit for work within stream channels in unincorporoi- ed .egional plans. ABAG also reviews Federally County Flood areas. Subdivision regulations setting minimum dra m iv. : rred environmental impact statements and most December 1975 for adoption and implementation. Control and Water age standards, requiring easements. Permit for grad h Si tc-required environmental impact reports. In the Under the terms of the initiative, the CCZCC and the Conservation soils and engineering geology reports. Prohibition District. C-T: u;- .ai situation in which many projects are com- six regional commissions were to expire on January obstructing water flow, damaging levees, work Jr: county easements. p-^ing for limited funds, a negative finding by 1, 1977, unless legislation was enacted to create suc Marin County x 1953 X Flood-plain zoning applied in Novato area—primary ai.d A. ft A G, although advisory, is likely to be heeded by cessors to them. Flood Control secondary zones. Permit for work in channels in unin and Water In September 1976 the California Coastal Act of corporated and some incorporated areas. Prohibition the funding agency. Conservation on obstructing water flow. The San Francisco Bay Conservation and De 1976 was enacted (California Public Resources Code, District. ! velopment Commission (BCDC) was created by the 1976b), establishing the California Coastal Commis Napa County 1951 x X X Permit for encroachment on channels including 50-foot State legislature to prepare a comprehensive plan for sion and six regional coastal commissions as suc Flood Control strip on either side ofchannel operated and maintained and Water cessors to the commissions created by the 1972 by District. Limited flood-plain zoning applied to right- San Francisco Bay and its shores. The plan was Conservation initiative. Under the terms of the Act, the six regional District. of-way of proposed U.S. Army Corps of Engineers adopted by the State legislature, and BCDC became project on the Napa River. a permanent agency charged with carrying out the commissions will expire 30 days after the last re San Mateo 1959 x X County Flood Permit for construction activities in San Francisquito plan. The adopted plan has legal status and serves as quired local coastal program has been certified, but Creek channel and 15 feet from San Mateo County side. Control District. a guide in the review of projects. BCDC shares no later than January 1, 1981. Santa Clara 1951 x X X The California Coastal Plan is interesting in its Valley Water Permit for construction within “designated floodway” or jurisdiction over land-use decisions with the cities District. withm 50 feet of top of streambank in both unincorpor- and counties which retain normal land-use and emphasis on the beneficial effects of flooding. Ac ated and incorporated areas. Policy for dedication to cording to the plan, these effects include (California District of land in ‘designated floodway.” building permit controls. However, with certain Solano County 1951 x minor exceptions, a permit from BCDC is required Coastal Zone Conservation Commission, 1975, p. Flood Control Permit for construction in channels or altering existing and Water water drainage in unincorporated areas. Subdivision for all projects within its area of jurisdiction (the 83): regulations setting drainage criteria. Limited flood- Conservation plain zoning. water of San Francisco Bay and up to 1,000 ft or the maintenance of salmon and steelhead spawning ground, District. 305 m inland from the Bay shoreline). Thus, in effect, the continued supply of beach sands; Sonoma County 1949 x the removal of vegetation choking the river channel, restoring the Water Agency. Limited flood-plain zoning. Permit for construction in or it holds veto power over any project proposal in near any drainageway. channels capacity to contain minor flood flows; conflict with the San Francisco Bay Plan. ( a ■ fl ' PLANNING FOR FLOOD-LOSS REDUCTION IN THE NAPA VALLEY 47 46 FLOOD-PRONE AREAS AND LAND-USE PLANNING 122°30' 122° 15' the long-term deposition along the floodplain of sediments that provide highly fertile soils; flushing of undesirable salts from the surface layers of soils, and Napa Valley. The case study format necessarily the preservation of valuable plant communities on overflow lands, emphasizes what has been done rather than what such as giant redwood groves. ought to be done. However, in describing the efforts of the agencies involved, the effectiveness of various Recognizing that development in flood-hazard actions within a specific context is made clear. areas not only removes these benefits, but is exposed Because flooding problems are widespread and vari to loss from flooding, the plan contains the following able, and there are many possible responses, a policy statement (p. 84): description of actual responses to a particular prob To avoid the need for new flood control works and interference 38° 45' with natural watershed processes that adversely affect coastal lem can illuminate possibilities and problems which resources such as sand supply and anadromous fisheries, develop may pertain to many different situations. ment in flood-hazard areas shall be regulated as follows: a. Criteria for New Developments in Unprotected Flood-Hazard' description Areas. Only new developments that can sustain periodic flooding and that will not create public burdens by aggravat I ing the flood problem, impeding flood water storage capacity, The Napa River rises just north of Calistoga in : or increasing pressure for new flood control projects shall be northern Napa County and flows south through the allowed in presently unprotected flood-hazard areas (those subject to inundation by a 100-year flood), consistent with the Napa Valley to San Pablo Bay—a distance of 39 mi I existing Federal insurance program. Examples of permis (63 km). Numerous tributaries flow into the river sible uses include agriculture and recreation, with necessary which broadens onto tidal sloughs about 9 mi (14 km) incidental structures. north of San Pablo Bay. North of the city of Napa, b. Restrict Use of Flood-Hazard Areas during Flood-Prone the valley floor is flanked by a series of foothills !hnt Periods. During flood-prone periods, flood-hazard areas shall not be used for log decks or storage of materials that can be reach a maximum elevation of 4,343 ft (1,323 ir J: carried downstream by flood waters unless mitigation (such Mount St. Helena on the county line 7 mi (11 as anchoring devices or berms) is adequate. north of Calistoga. The location of Napa Court c. Review Inland Flood-Hazard Area Projects That Could the San Francisco Bay region is shown in fig* Affect Coastal Zone. It is recommended that the Legislature establish procedures to ensure opportunities for public re The location of the Napa Valley Planning A e > view of proposed inland flood-hazard area projects that shown in figure 16. could adversely affect lives and property in the coastal zone. With the exception of the flat tidal marsh' y,-A. north of San Pablo Bay, the river valley is ent.: PLANNING FOR FLOOD-LOSS REDUCTION within Napa County. The valley, However, ir : IN THE NAPA VALLEY natural feature significant to the entire San F* i •i- By M. L. Blair cisco Bay region because of the economic imports ce of its renowned vineyards, the significance of irs Planning for flood-loss reduction, through struc large nonurban areas to a regional system of open tural or nonstructural measures, usually involves space, and its attractiveness as a locale to accommo i several agencies with differing powers and responsi date a substantial share of projected regional popula bilities. The pattern of relationships among the tion growth. Figure 17 is an aerial view of the Napa agencies is highly variable and often difficult to River as it winds through the city of Napa. trace. Therefore, examining the actual responses of Although only a 1-hour drive from San Fran agencies to a particular flooding problem can be cisco, the valley is bypassed by the Bay area freeway more instructive than attempting to generalize from network and has experienced far less rural-residen very diverse situations. This section describes plan tial development and suburbanization than neigh ning and decisionmaking related to flood-loss reduc boring counties. Napa, Yountville, St. Helena, and tion in the Napa Valley area of the northern San Calistoga, the only incorporated cities in Napa Francisco Bay region. This area was selected for County, are all located in the Napa Valley and have detailed study because it has agricultural, urban, a combined population of approximately 52,400 and urbanizing lands subject to severe flooding; (44,200 in Napa). Another 34,600 people live in the agencies at all jurisdictional levels have been in unincorporated areas of the county, for a total county volved in planning for the flood-prone areas; and population of 87,000 (Napa County Conservation, several different approaches have been tried or Development and Planning Department, 1974a). proposed to reduce flood losses. Wapa County plans and regulations are presently Figure 16.-Napa County and Napa Valley planning area. This study describes the plan formulation and designed to accommodate a population of 115,000 by 48 FLOOD-PRONE AREAS AND LAND-USE PLANNING PLANNING FOR FLOOD-LOSS REDUCTION IN THE NAPA VALLEY 49 ' h 60 35 ui .-.v 25 uj * Ua;/. • , - —--—. u. 7 Z W Q J 10 UJ Q fcj □ Z H c/j 20 UJ > UJ lfl2 cc y UJ > I < 03 o O ccS X D < CO Ha 010 : . ■ the north side of the city (Limerinos, 1970). Second, although of limited capacity and not operated for able ' ■ T 4.—Major floods at the U.S. Geological Survey gaging T:\T-V flood control, several small water-supply reservoirs station Napa River near Napa, California, 1900-196T1 f € >: on the tributaries can retain a portion of the runoff if [From Limerinos, 1970] a storm occurs at a time when the reservoirs are not Elevation above Discharge -/ Date of flood Stage mean sea level (cubic feet fui'. j .merinos reported that: (feet) (feet) per second) At the onset of the storm that caused the December 1955 flood, March 18, 1907 __ 233.8 258.5 223.800 the 'vater level in Lake Hennessey was 14 feet below the spill February 27, 1940 —— 32.8 57.5 22.500 way elevation, and a considerable part of the flood runoff was February 6, 1942 __ 232.8 257.5 222.500 3 ■ stoied in the reservoir. On January 31, the water level was December 31, 1913 __ *31.8 256.5 *21,500 only 1 foot below the spillway elevation, and most of the February 24, 1902...... 228.5 253.2 218,000 ensuing flood runoff spilled. This caused extensive damage January 31, 1963 --- 27.5 52.2 16,900 along Conn Creek and increased the flow of the Napa River December 22, 1955 _ 227.5 252.2 216.800 Figure 17.— Napa River, city of Napa. (Photograph by U.S. Army Corps of Engineers.) through Napa. January 3, 1916 226.8 251.5 216,200 January 21, 1967 26.5 51.2 15,800 the year 2000. Regional and local plans indicate that Third, the construction of levees and other channel February 12, 1925 226.4 251.1 215,700 FLOODING PROBLEMS IN THE NAPA population growth is to be accommodated in or near VALLEY modifications or the presence of debris or channel •No significant floods have occurred since 196/ the existing cities along the Napa River, especially Flooding along the Napa River is a persistent obstructions can affect the extent of damage from a ^Estimated. the city of Napa. problem. The city of Napa has experienced damag given storm. Fourth, runoff characteristics of the The soils, climate, and topography of Napa ing floods 18 times since 1900, or an average of more 220-mi2 (570-km2) drainage basin upstream from the The U.S. Army Corps of Engineers (1965b) Valley are exceptionally well-suited to the cultiva than once every 4 years (fig. 18). According to Oak Knoll Avenue gaging station above Napa also estimated the damage from flooding on the Napa tion of grapes. Some of California’s finest wines are Limerinos (1970), affect the degree and frequency of flooding from a River for three recent floods (table 5). Response to the problem of flooding in the Napa produced in the valley, and the value of land for Flooding of low-lying areas in the city occurs when streamflow given storm. If the storm occurs when the soil is Valley is shared, often without formal coordination, viticulture has in recent years exceeded its value for exceeds 12,000 cfs (cubic feet per second) or at stages above an saturated from the rain of preceding storms, the subdivision development. Although this situation elevation of about 47 feet above mean sea level (gage height, 23 amount of runoff increases. The effect is similar in by a variety of governmental agencies. ABAG, the may be temporary, it is presently (1976) in sharp feet) at the gaging station (at Oak Knoll Avenue) on Napa River areas where the drainage basin has been denuded of Napa County Conservation, Development and Plan near Napa, Calif. ning Department, and the incorporated cities are contrast to the economic situation which contributed The date, elevation, and discharge of the major to the suburbanization of prime agricultural land in involved in general planning for all or part of the floods, in order of magnitude, are shown in table 4. other areas of the Bay region such as the Santa Clara Napa Valley. Detailed water-resources planning The extent of flooding in the valley, caused by :tAlthough shown on Geological Survey maps as Trancas Road, Valley. and often referred to as Trancas Avenue, the official city name is with emphasis on providing flood protection has storms of the same magnitude, may vary for several Trancas Street. been done by the Corps of Engineers, the Soil : i I r PLANNING FOR FLOOD-LOSS REDUCTION IN THE NAPA VALLEY 51 50 FLOOD-PRONE AREAS AND LAND-USE PLANNING 122° 30' Conservation Service, and the Napa County Flood 122°30' Control and Water Conservation District. The plans, ! programs, and functions of these agencies with ! respect to the flood-prone areas in Napa County and ; the nature of hydrologic information used at each jurisdictional level for various purposes are de scribed in the following sections. Table 5.—Estimated loss from three floods on the Napa River ! (Prom U.S. Army Corps of Engineers, 1965b] i Loss, in dollars, at 1963 price levels Type of flood loss 1955 1958 1963 Commercial ______$198,000 $17,000 $237,000 Residential______61,000 23.000 136.000 198.000 Agricultural ...... 187.000 288,000 : 38° Roads and bridges .... 170.000 28.000 80,000 38° 30' 38° 30‘ Public utilities ------24,000 16,000 30' Federal property ___ 1,000 Total------$641,000 $356,000 $667,000 i Area flooded (in acres)----- 9,30011,900 7,200 ' PLANNING FOR NAPA VALLEY- REGIONAL PERSPECTIVE Regional planning for the Napa Valley provides policies and procedures related to urban and open- space uses of the valley lands. ABAG’s “Regional Plan 1970:1990” discusses the relationship between the physical character of the land and the pattern of urban development in the following terms (1970, EXPLANATION p. 4): EXPLANATION It is on the Bay plain area that circles the Bay, and the larger EXPLANATION Hills and mountains valleys of Santa Clara, Napa, Sonoma, Petaluma, Livermore, Prime agricultural lands . . . ■ and Ygnacio that the greatest amount of urban development Flood plains ! Flat land has occurred. These valley lands, separated only by inter vening ridges, are being steadily converted from agricultural Figure 20.—Prime agricultural lands in Napa County. (From Water to urban use to serve the needs of a growing population. Due to Figure 19.—Flood plains in Napa County. (From Napa County Napa County Conservation, Development and Planning De Conservation, Development and Planning Department, 1973.) ! the difficulty of building on steeper slopes, those valley lands partment, 1973.) Figure 21.—Urban areas and areas with slopes less than 15 that remain unurbanized are prime targets for future urban percent in Napa County. (From Napa County Conservation, development. The region will have to choose either to retain PLAN FORMULATION be held in reserve to provide the prime agricultural lands and unique natural settings that i ment category are to Development and Planning Department, 1975.) these lands provide, or to allow them to be transformed by land for urban development beyond 1990, if needed. ABAG’s regional plan (1970) provides a policy According to the plan, major flood plains and below the city. urbanization. i Thus, the regional plan policies recognize and framework for considering the future growth of the drainage channels should be accorded priority for The flatlands of the Napa Valley have excellent address, in general terms, the flooding problem of the Bay region. A major plan policy is that new urban public acquisition to avoid the costs of further flood- agricultural soils (Class II and III according to the Napa Valley and the conflict arising from the high growth should be accommodated in two ways: by the control protection and to provide a means of linking Soil Conservation Service soil capability rating infilling and controlled extension of existing cities potential of the land for both urban and agricultural system) and are prone to flooding; but, because of low the region’s open-space areas. Other open-space uses. The ABAG plan clarifies the potentials and and by the development of entirely new, self- lands, like those with exceptional qualities for the slope and stable soils, they are considered reason conflicts on a regional level and provides a contained communities. The land-use implications specialized agriculture of the Napa Valley, are to be ably well suited for urban development. Figures 19, conceptual framework to guide local land-use plan of this and other ABAG policies adopted by 1970 are preserved by regulation. The plan diagram thus 20, and 21 show the relationship of these character presented graphically on the land-use diagram, ning and decisionmaking. Detailed data were not istics for the Napa Valley. The geographic coinci shows the area north of the city of Napa as needed for formulating the plan. The Geological figure 22, which indicates infilling and extension of permanent open space, primarily on the basis of dence of these features is typical of the Bay region. It Survey regional map of flood-prone areas (Limerinos, existing urban areas in Napa County. agricultural value of the land. The open-space strip is within this general framework of conflicting Lee, and Lugo, 1973), for example, can be used effec Nonurban lands are classed in the ABAG plan along Napa River in the city of Napa provides flood potentials and problems that regional plans attempt as either permanent open space or lands for con tively for planning at this degree of generality. protection and links open-space areas above and to provide policy direction. trolled development. Lands in the controlled develop- I ! ! FLOOD-PRONE AREAS AND LAND-USE PLANNING 52 PLANNING FOR FLOOD-LOSS REDUCTION IN THE NAPA VALLEY 53 122° 30' The plan illustrates how information concern ment rights to an additional 10,954 acres (44.3 km2) ing areas subject to flooding can be combined with of the Napa Valley fall into all «x categories and of Napa River marshlands for an estimated these areas are consequently given high prion* for other data to arrive at a system of priorities for open- $1,664,000 (Association of Bay Area Governments, ! open-space preservation. Table 7 shows the acreages space preservation based on numerous factors. 1972, p. 9). Classifying the 4-million acres (16,200 km2) in in Napa County recommended for open space, The ABAG minimal program indicates that i the Bay region allocated to open space in the categorized according to function. financial responsibility for acquiring development ; Regional Plan was accomplished with existing and rights to the Napa River flood plain belongs to the readily available information. The classification can region. However, ABAG has neither the authority Table 6.-Categories of land serving open-space purposes be refined as more detailed information becomes [From Association of Bay Area Governments, 1972, p. 4]______nor the funds to acquire land or development rights available. Information of a much more detailed Uses ! to land. It may influence decisions through review of Category nature will be needed to implement the open-space grant applications of local governments and special Open space for managed Prime agricultural lands and i preservation program. Identification of specific land districts for State and Federal funds available for the resource production. lands for specialty crops. Lands for grazing. areas (with well-defined boundaries) to be preserved purchase of open space. Lands for mineral production. for open space is required. The plan, however, Through the A-95 review process, ABAG may Lands for water supply. presents a broadly conceived target for preserving also review development projects involving Federal Water areas for fish and ! regionally significant open-space areas. Informa funds for conformity with its open-space plan. The marine life production. ; Open space for preservation Lands, tidelands, marsh, and tion developed and presented at a scale of 1:125,000, agency reviews Federally required environmental of natural and human water areas for fish and such as the regional flood-prone area maps impact statements. There is no requirement for resources. wildlife refuge. : (Limerinos, Lee, and Lugo, 1973), is usually adequate ABAG review of environmental impact reports Notable geological features. Historical and cultural sites for this purpose. mandated for public and private projects by State and places. law. However, most EIRs are voluntarily submitted Areas to provide visual amenity. PLAN IMPLEMENTATION to ABAG for review. Open space for health, Land to protect the quality of To assist in the review function, ABAG’s recent welfare, and well-being. water resources, including ground water. Ay a voluntary association, ABAG has very report “Areas of Critical Environmental Concern” Land for disposal of sev/e.ge, i lbr.Arr powers to implement its plans. Successful (Association of Bay Area Governments, 1975) sets garbage, etc. j forth policies concerning and criteria for identifying Open areas to improve a-^hed in?.;; -c.mentation really depends on the actions of quality. F State, and local governmental agencies. areas of regionally significant environmental con Open space for public safety. Flood control reservoirs, ; :^ .>d A. % s implementing program, therefore, empha- cern which “because of intrinsic qualities demand plains, drainage chan. ;is, si.v measures to encourage other governmental special consideration in the comprehensive plan and areas below dams ning process” (p. 1). The report extends the earlier Unstable soil and fault a ■-.•as. ur ;o act. ABAG proposes the following five Airport flight path zones. acv:.»riS to implement the “Regional Open Space work on the “Regional Open Space Plan—Phase II” (Association of Bay Area Governments, 1972) by EXPLANATION Critical fire zones. PL :a—Phase II” (Association of Bay Area Govern- Open space for outdoor Lands for developed recreation exploring “in much greater detail those land areas recreation. meiii;3, 1972, p. 7). Developed space uses. that merit protection because of intrinsic environ Lands for water-oriented 1. —presenting the two five-year “exemplar” programs as Open space - Controlled recreation. developed; mental characteristics” (unpaged). development Lands for natural environ 2. —reviewing grant applications from jurisdictions within the With respect to stream flooding, the report sets mental experience. region; forth the following regional policy (p. 43): Open space - Permanent I Lands for scenic and 3. —encouraging the preparation of individual open space Protect floodplains of streams that flow through more than recreational travel. elements consistent with the Regional Open Space Plan one jurisdiction from development that will alter floodplain Figure 22.—Association of Bay Area Governments regional plan Open space for shaping Lands to preserve community Phase II; extent or that will be significantly damaged by flooding. for Napa County. (From Association of Bay Area Governments urban growth. identity. 4. —developing a regional Open Space Preservation Information 1970.) Lands to prevent inefficient System (OSPIS); Lands within the 100-year floodplain are subject to urbanization. 5. —participating in a program of coordination and legislative the policy. The following statement is made concern The open-space policies of the ABAG regional advocacy for open space purposes. ing compatible uses: plan are amplified in the “Regional Open Space The two exemplar programs—a minimal preser Within floodplains, uses should be limited to those types of Plan—Phase II” (Association of Bay Area Govern Table 7. Recommended acreage for each open-space category in Napa County. ; vation program and an augmented preservation activities which will be minimally damaged by flooding, such ments, 1972). Six functional categories of open space certain types of agricultural uses, low intensity recrea [From Association of Bay Area Govemments, 1972, p. 6] program—are proposed as alternative 5-year pro as were defined as shown in table 6. Lands designated tional uses and parking. grams. Under the minimal program, 18,954 acres permanent open space and controlled development ______Open-space category Acres The map “Flood-Prone Areas in the San Francisco in the Regional Plan were then assigned to the (76.7 km2) in Napa Valley (presumably prime Total acres serving at least one purpose i Bay Region, California” (Limerinos, Lee, and Lugo, appropriate categories. 399,850 agricultural land) would be preserved by local Managed resource production 1973) is cited as a reference for identifying 100-year 294,931 i zoning, and development rights to 4,154 acres (16.8 Map overlays were prepared showing lands in °f natural and human flood plains. It is emphasized, however, that the resources 177,855 ! km2) of the Napa River flood plain would be acquired each open-space category to allow visual identifica Public 'sat'T and Well-bdn* ..... 270,519 maps are not a part of the plan; they are listed to help tion of lands serving multiple open-space purposes. 31,585 for $7,504,000 (1972 estimates). Under the aug Outdoor recreation ...... mented program, the State would acquire develop- identify locations where the policies might apply. Priority is given to these lands in the open-space Shaping urban growth ...... 188,417 161,813 ! Jm f i FLOOD-PRONE AREAS AND LAND-USE PLANNING 54 The land-use implications of these and other plan PLANNING FOR FLOOD-PRONE AREAS- policies are shown in the plan diagram (fig. 23). NAPA COUNTY take advantage of natural capabilities and mini i The county-wide Conservation and Open Space mize conflict with the natural environment. The Napa River, its environs, problems, and Element, approved by the Board of Supervisors in Goal 4 To work with cities, other governmental units c.t.zens, potentials, dominates planning in Napa County. and the private sector to plan for services, facilities June 1973, contains the same goals and policies for Almost all of the county’s population lives in the and accommodations, including housing, trans land use in flood plains as the adopted Napa Valley river valley, and prospects for substantial develop portation, economic development, parks and rec- Area Plan, with the following additions (Napa ment in other areas of the county are currently reation, open space, and other total County needs. County Conservation, Development and Planning remote because of steep slopes, inaccessibility, and Department, 1973, p. 22): These goals, developed through extensive public distance from major metropolitan centers. A possible Investigate the feasibility of obtaining data to establish a exception to this general observation is the potential participation, are a logical extension of work done on floodway and restrictive zone outside the floodway for all unin for additional recreational development in the Lake the Napa County Open Space and Conservation corporated areas subject to flooding, based on a 100 year storm. Plan and a subarea plan for the Napa Valley. The Identification of flood prone areas will be accomplished by the Berryessa area in northeastern Napa County. I goals guided the preparation of a new land-use Napa County Flood Control and Water Conservation District. Within the last few years, advocates of limited Adopt flood plain zoning in all applicable areas, and investi growth, preservation of environmental quality, and element and provide a framework for future gate the compatibility of zoning areas adjacent to flood plains for conservation have achieved a majority on the revisions or additions to the County General Plan. ] recreational uses. Flood plains along streams which feed Lake County Board of Supervisors. Recent elections in the The Napa County land-use element, adopted in I Berryessa, the Napa River, and the Suisun Marsh are zoned for agricultural uses in the majority. city of Napa, including a 1973 plebiscite favoring a September 1975 by the Board of Supervisors, I Encourage provision for flood insurance. The Napa County limited growth concept, indicate a similar trend. The designates lands for urban growth sufficient to Flood Control and Water Conservation District and the Napa new priorities of the residents of the county were accommodate a population of 115,000 by the year County Board of Supervisors have obtained Federal Government revealed by the response to a survey on growth 2000. The element explicitly recognizes constraints i approval of Napa County for flood insurance and have agreed, in policies. The survey questionnaire was included with | to urban development including potential flooding. return, lo enact local land use and control measures for areas a summary of the county general plan sent to all Flood plains are designated as “limited development having special flooding problems. The controls are to be con sistent v- 1th Federal criteria. registered voters in February 1974. The document areas” to be retained in large parcel sizes pr« ■ ■ arily outlined the impacts associated with three possible for agricultural use (Napa County Consev ■ ion, iblishing flood-plain boundaries can be quite population levels (growth options) for the year 2000 - at this phase of planning. However, apply- Development and Planning Department, 197- :o. 16). : ge- (Napa County Conservation, Development and The Napa Valley Area Plan, a subar: nlan in >: policies, through either regulation or project Planning Department, 1974a): adopted by the Board of Supervisors in 1975, -«• >rth re ordinarily requires data which are both more specific goals and policies covering th. ' se of si and accurate. The Geological Survey flood- (Current population 87,000) flood plains. The goals are (Napa County Cor -irva- pro-- area quadrangle maps of the Napa Valley Low growth __ 115.000 1 (C 'i'S Wharf, Napa, Rutherford, St. Helena, and Medium growth 150.000 tion, Development and Planning Department, High growth .... 200.000 1974b, p. 22-23): Yc- ■ille, scale 1:24,000) showing the areal extent Restrict and regulate urban development in areas of flood of t.100-year flood (fig. 28 and table 10) can be used Over 76 percent of the respondents favored the low- risk. i in framing general plan policies (U.S. Geological growth alternative and associated policies to limit Protect the vegetation and animal habitats of the waterways Survey, 1971). growth. As a result, new general plans are being and flood plains as well as their hydraulic carrying capacity The success of these county planning efforts developed for both the county and the city, reflecting from encroachment of urbah development. depends in large measure on the continued economic Protect existing areas of urban development from flooding. the public consensus on growth limitation. viability of grape cultivation in the Napa Valley. In The related policies are: recent years, public decisions to limit population PLAN FORMULATION Seasonal flooding from streams, deposits of rock and sedi growth, preserve agriculture, and limit flood-plain ment and bank undercutting make some areas difficult to development have been consistent with private land- eve op. Occasional high water levels in the lakes and reser : The Napa County Board of Supervisors recently : use decisions based on land-use economics. voirs flood adjacent areas for short durations. Encourage ; adopted the following new set of land-use planning eve opment and implementation of flood plain manage goals (Napa County Conservation, Development ment programs that protect homes and property, as well as PLAN IMPLEMENTATION and Planning Department, 1975): 8 ream si e vegetation, and control obstruction of natural waterways. i Goal 1 To plan for agriculture and related activities as the M^in watercourse8 and related vegetation as components The county of Napa has the same powers to primary land uses in Napa County and concentrate implement plans—zoning ordinance, subdivision urban uses in the County’s existing cities and tmila ifPen 8paCf18y8.tem’ Develop pedestrian and riding ; urban areas. and wildM6 Wit*1 riparian (stream side) vegetation regulations, building codes, project review, for ex Goal 2 To develop and implement a set of planning policies intervals.lfe Devdop pubHc access at fre£*uent ample— as a city. However, the county s authority which combine to define a population size, rate of extends only to the unincorporated areas. Most of areas as population growth and the geographic distribution Napa County’s unincorporated area is undeveloped of that population in such a manner that the desired “r„rrrse8 and v“°n i quality of life is achieved. except for agriculture, small towns, or other low- : intensity uses. Thus the county is developing and Figure 23.—Napa Valley Area Plan. (From Napa County Con servation, Development and Planning Department, 1974b.) applying policies in essentially nonurban areas. ; 1 FLOOD-PRONE AREAS AND LAND-USE PLANNING PLANNING FOR FLOOD-LOSS REDUCTION IN THE NAPA VALLEY 56 57 by Limerinos (1970, scale 1:24,000) shows the areas flood-plain uses. More needs to be known about the Napa County’s implementation program has six unincorporated areas in Napa County which are not flooded in 1940 and 1955, Provides information effects of different land-management practices on main aspects: flood-plain zoning, establishment of in the Agricultural Preserve District are in the Agri concerning the flood profiles of the 1907, 1940, and the amount of loss sustained from a given flood. agricultural preserves, regulation of watercourse i culture, Watershed, and Recreation (AWR) District 1955 floods, and gives a flood-frequency curve. This However, it is generally accepted that many agri obstruction and riparian cover, watershed protec •: pending completion of the county general plan information is especially useful in applying differ cultural uses are appropriate for flood-prone areas. tion, flood insurance, and project review procedures. revision. Minimum lot size in this district is 40 acres ential restrictions to different areas of the flood plain Unless the cost of losses from flooding in agricul (0.16 km2). The adopted Napa Valley Area Plan Flood-plain zoning.—In 1967, the Board of based on the probability of a flood of a given fre- tural areas is excessive, or erosion and sedimenta Supervisors adopted a very limited flood-plain zon (Napa County Conservation, Development and quency occurring in a given year. tion problems are particularly severe, a single zone ing ordinance to meet the requirements of the Planning Department, 1974b) recommends retention Agricultural preserves.—The county has three that covers the 100-year flood plain and permits only original Cobey-Alquist Flood Plain Management of the minimum parcel size of 40 acres (0.16 km2) in types of agricultural preserves. The Agricultural i agricultural and other open-space uses may be Act (later amended, California Water Code, 1976). the AWR zone, with the possibility of reducing the Preserve District (AP) is intended to apply to fertile sufficient for nonurban areas. It is desirable to The ordinance prevents encroachment in the desig minimum lot size to as small as 5 acres (0.02 km2) valley and foothill areas in which agriculture is and prohibit construction of farm buildings, grading, or nated floodway for which a flood-control project is | under certain conditions. Residential development should continue to be the predominant use. It other farm-related activities within the floodway. proposed or anticipated. The ordinance provides for could be permitted on parcels less than 40 acres (0.16 minimum lot size of 20 acres (0.08 km2), Watercourse obstruction/riparian cover ordi three zoning districts to be applied to flood-prone requires a i km2) after review based on consideration of water areas to regulate uses according to the severity of permits extensive agriculture and processing in nance.—In February 1974 the Napa County Board and sanitation conditions, slope, access, fire haz flood hazard (Napa County Board of Supervisors, addition to grazing and cultivation, and has been of Supervisors adopted Ordinance 447 (Napa County ards, environmental impacts, and growth policies 1967): FP-1 applies to the stream channel and applied primarily to the Napa Valley (Napa County Board of Supervisors, 1974a). The purposes of the and related factors (Napa County Board of Super portions of the flood plain required to carry the Board of Supervisors, 1968). ordinance include reducing flood losses caused by visors, 1974b). floodflow. Permitted structures and uses include The Agricultural Preserve Interim District (API) channel obstructions or water-borne debris, pre In the Napa Valley watershed, five public parks, farming, grazing, utility pipelines, and boat is intended to preserve agricultural uses until an area serving wildlife habitats, and preventing stream- reservoirs, with a combined firm annual yield of ing facilities, and campgrounds from May to Novem is ready for urbanization. It requires a minimum lot bank erosion. A permit is required from the Planning 23,000 acre-ft (28 hm3) of water, provide most of the ber. FP-2 applies to areas flooded by overflow and size of 20 acres (0.08 km2), and it is applied primarily Commi.ision before anyone may deposit or remove county’s water supply. The assurance of both quality backwater relatively free of current. Uses normally in hillside areas (Napa County Board of Super v, sors, any material within a watercourse; excavate within and quantity of this local water supply is critical for permitted in the zoning districts with which the FP-2 1969). a watercourse; construct, alter, or remove any both domestic and agricultural users. Stringent district is combined are allowed as long as the The Agricultural Preserve Extensive District structure within, upon, or across a watercourse; watershed protection measures are easily justified in ground-floor level of structures is above the flood- (AP-E) is intended to apply primarily to grazin > snd plant a: remove any vegetation within a water- this case to protect public health, safety, and welfare. profile level. FP-3 applies to properties in a flood with mostly non-prime soils. It requires a mir am coin. fr; ; >v alter any embankment within a water- Proper watershed management is also important in zone which are protected by flood-control works. All lot size of 100 acres (0.40 km2) and mimimum - ng coi .ri’f Except for the Napa River, the permit require- controlling erosion and sedimentation. uses permitted in the zoning districts with which the district size of 320 acres (1.3 km2). All lands h. P-E men ?plies to the stream channel and a 50-ft (15-m) Flood insurance— On December 10, 1970, the FP-3 district is combined are allowed with no districts are under Williamson Act contracts (Napa wide vrip measured landward from the top of each Napa County Board of Supervisors adopted Resolu additional restrictions. County Board of Supervisors, 1969).4 ban' • i the stream. For the Napa River the require tion 70-155 (Napa County Board of Supervisors, To date (1976) only the FP-1 zoning has been North of the city of Napa, most of the valley has ment applies to a 100-ft (30-m) strip along either side 1970) requesting that flood insurance be made avail applied. The area now covered by this zoning been zoned Agricultural Preserve (AP) since 1968. of the ri ver from the county’s southern boundary to able to property owners in the county. The resolution includes the unincorporated areas along Napa River This zoning establishes agriculture as the primary : St. Helena. The ordinance does not apply in the stated that the county would meet the following land- from Trancas Road south to Edgerly Island. In use of the valley area including the flood plain. The incorporated areas. A map showing streams covered use and control standards established by the Federal general, the district conforms to the proposed right- AP zone was challenged in the courts by the Napa by the ordinance is on file in the Flood Control and Insurance Administration (Federal Insurance Ad of-way for a Corps of Engineers flood-control project. Valley United Farmers, but it was upheld by the Water Conservation District office. ministration, 1971): The ordinance as it is now applied regulates only a uperior Court of the county of Napa, in a decision on This ordinance was intended to alleviate some of (1) Require building permits for all proposed construction or small portion of the county’s flood-prone lands. The other improvements in the community; February 17, 1971, as a proper exercise of police the potential problems associated with agricultural (2) Review all building permit applications for new construc currently zoned districts are designated on a map on powers which benefited not only the public at large, use of the flood plain. It provides the means whereby tion or substantial improvements to determine whether proposed file with the Napa County Flood Control and Water but also those whose land was regulated (Overview the county may prohibit cultivation of farmland building sites will be reasonably safe from flooding. If a proposed Conservation District. Corporation, 1973, p. 20). i immediately adjacent to the banks of the river. building site is in a location that has a flood hazard, any proposed The county has adequate information provided ii ®ecau®e much of the 100-year flood plain along Cultivation to the river’s edge removes riparian new construction or substantial improvement (including prefab by a flood-insurance study and the Geological ricated and mobile homes) must (i) be designed (or modified) and firm aPa 1V-6r 18^^cultural use, betterinforma- cover which may cause increases in bank erosion anchored to prevent flotation, collapse, or lateral movement of the Survey study by Limerinos (1970) to apply flood- rrnn0 ?7rg the impact of flooding on different and collapse, significant increases in river sedimen stucture, (ii) use construction materials and utility equipment that plain zoning to the entire 100-year flood plain of the u * +ifpes *3rming and grazing would be . tation, and loss of wildlife habitats. In addition, the are resistant to flood damage, and (iii) use construction methods Napa River and its major tributaries. The flood- ordinance regulates the deposition of debris in the and practices that will minimize flood damage; e county in determining appropriate ; new insurance study delineates the 100-year flood plain river channel. Debris carried by flood waters is a (3) Review subdivision proposals and other proposed developments to assure that (i) all such proposals are consistent at a scale of 1:12,000 and includes flood profiles major source of damage to agricultural lands. vation Act ofnSwrMv’ a^° ca^ed California Land Conser- with the need to minimize flood damage, (ii) all public utilities and which permit estimation of depth of flooding at Watershed protection.—The extent of flooding facilities, such as sewer, gas, electrical, and water systems are different points in the flood plain. This is important may be affected by man’s use of watershed lands. located, elevated, and constructed to minimize or eliminate flood when considering various flood-loss prevention mea Thus, control of use of the watershed lands can signi damage, and (iii) adequate drainage is provided so as to reduce sures such as floodproofing requirements. The study i ficantly affect potential damage from flooding. Most exposure to flood hazards; and FLOOD-PRONE AREAS AND LAND-USE PLANNING PLANNING FOR FLOOD-LOSS REDUCTION IN THE NAPA VALLEY 59 58 PLAN FORMULATION Authorized by the 1965 Flood Control Act, the project provides (4) Require new or replacement water supply systems and/or 1^0 yeai^floodand reconmiends that the ground floor for channel enlargement and realinement, construction of levees, i sanitary sewage systems to be designed to minimize or eliminate 00 tructure be 1 ft (0.3 m) above that elevation. The The city, like the county, has experienced a floodwalls, and public boat-launching facilities in an 11-mile infiltration of flood waters into the system and discharges from reach downstream from Trancas Road in the city of Napa to of a s advisory; the authority to political changeover as a result of changes in public the systems into flood waters, and require onsite waste disposal recommendations are attitudes towards growth and environmental qual Edgerly Island. systems to be located so as to avoid impairment of them or contam impose requirements rests with the Board of The Federal first cost of the project is estimated at $25,300,000 ination from them during flooding. ity. The 1968 General Plan for the city (Napa City Supervisors. (July 1972). The estimated cost to local interests is $9,680,000. The standards for land-use and control measures Planning Department, 1968) is now considered inadequate to address today’s concerns, and the city The planning process involved in developing the become more stringent as more detailed information THE NAPA COUNTY FLOOD CONTROL AND WATER flood-control project is somewhat unusual. The CONSERVATION DISTRICT council is presently (1976) reviewing a revised is provided to the community by the Federal Insur Corps of Engineers originally proposed to construct ance Administration. general plan (fig. 24, Napa City Planning Depart The Napa County Flood Control and Water ment, 1975). The revised plan stresses the establish a straight-walled channel through the center of the As presently enacted and administered, the city of Napa to carry flood waters. Local authorities Conservation District is a countywide district with ment of a ‘‘residential urban limit line” to confine National Flood Insurance Program provides Napa viewed the Corps project as an opportunity to County with an incentive to prevent inappropriate the County Board of Supervisors acting as the future development to locations close to the presently revitalize the water-front area of the city and create use of flood-prone areas while providing insurance governing board. In addition to responsibilities for developed parts of the city. This is a reduction from an esthetically pleasing and useful linear parkway protection to owners of flood-prone property which is flood control, the District acts as the contracting 55 mi2 (142 km2) to 18 mi2 (47 km2) in the area through the city. They requested that the Corps of already developed. agency for Napa County for water from the State considered appropriate for residential development. Engineers alter its plans to provide a somewhat Water Project, plans for and develops adequate Planning for the flood-prone areas within the Project review.— Information defining the extent wider but less austere channel. The reach of the water supply from all sources within the county, is city of Napa is, and has been, based on the of areas subject to flooding at a given frequency is project through central Napa was redesigned with a very important in the process of reviewing develop involved with assuring adequate water quality, assumption that flood-control works will be con series of steps rather than a straight wall. A land ment proposals for conformity with adopted plans water and sanitation systems of other structed which will eliminate, to a large degree, the supervises scaped linear park with walkways, bike trails, picnic and regulations and for assessing environmental flood nazard within the city. The new plan calls for special districts which are governed by the Bo?.rd of areas, and benches along either side of the channel impact. Any proposal for development within the continuation of a redevelopment project featuring a Supervisors, and provides technical assistance to the became an integral part of the project design. 100-year flood plain, as delineated on the 1:12,000 Board with respect to flood insurance. major government, business, and retail center with The flood-control project became part of a scale maps used in administering the flood insur The District participates in the review / devel in th J 00-year flood plain. The plan diagram shows broader effort to redevelop downtown Napa, upgrade ance program, is reviewed for the county by the Napa a line;-:, park along the river, but the 100-year flood i opment proposals and the development of - • PLANNING FOR FLOOD-LOSS REDUCTION IN THE NAPA VALLEY 60 FLOOD-PRONE AREAS AND LAND-USE PLANNING 61 122° 15' the main coordinating group for the various aspects 122° 20' *a*ief5=T EXPLANATION of the plan. The plan was viewed as a model for inter ’ Medium density 2-9 the prospects for successfully completing the project. 38°20‘ Eld HighdenSily 10-18 NONRESIDENTIAL OFFICE AND COMMERCIAL Professional office Neighborhood, retail, and tourist-oriented commercial INDUSTRIAL OPEN SPACE -----Residential urban limit line vL--==*?-frs** . i local share of Federal flood-control projects. The local share for purchasing the right-of-way required i V for thr. multipurpose project is larger than for the sir.).: i .-purpose flood-control project. Thus, it became imp: vrrunt that the State agree to assume the ad ht.onal costs. Vae Department of Housing and Urban Develop- : mer • under Title I of the Housing Act of 1949, as amended (U.S. Congress, 1949), would provide funds mitte 13 ; for acquiring and clearing the land in central Napa for a redevelopment project to include a county i government complex, a commercial area, and open space along the river. Planning of the various aspects of the project was to be partly financed with a HUD planning grant. The State Division of Highways (now Depart ment of Transportation) was to construct a north- south freeway through Napa which would cross the ■RINCON river twice. Both the county and city of Napa at that LOS- C&R R-jp S\^ I time favored the freeway as an important stimulant 38° 15' a-rs -v*\ to economic and population growth of the county. The Soil Conservation Service, under U.S. Pub 0 14 1 2 MILES lic Law 83-566 (U.S. Congress, 1954), was to con T struct a reservoir on Redwood Creek west of the city 0 5 1 2 3 KILOMETRES of Napa to control flood waters on Napa Creek. Figure 24.— Proposed land-use plan for city of Napa. (Generalized from Napa City Planning Department The project, as originally conceived, required an , 1975.) unusual degree of cooperation among government agencies to coordinate and resolve a number of interrelated problems. The Napa River Technical Figure 25.—U.S. Army Corps of Engineers flood-control project Committee, composed of city and county elected and related projects in the city of Napa. (From U.S. Army Corps representatives and staff members, functioned as of Engineers, 1975c.) t 62 FLOOD-PRONE AREAS AND LAND-USE PLANNING PLANNING FOR FLOOD-LOSS REDUCTION IN THE NAPA VALLEY 63 land use and population projections. However, the Transportation. Changing priorities have in Flood control.—Construction of the Corps of SIGNIFICANCE OF THE NAPA VALLEY EXPERIENCE progress of redevelopment in downtown Napa has fluenced the evolution of the freeway project. At the Engineers flood-control project, authorized by Con : undoubtedly increased potential future flood losses. request of local authorities, the State Department of Flooding problems in the Napa Valley have been gress in 1965, has not yet begun. A major problem The General Design Memorandum indicates a cur Transportation has removed the proposed north- addressed in the plans and actions of numerous has been raising the local share of project funds used ; rent benefit/cost ratio of 1.1'to 1.0 as opposed to a I south freeway through Napa Valley from its plans. agencies with varying degrees of success. Many to acquire land for the right-of-way and to relocate ratio of 1.6 to 1.0 in the 1965 study. As the ratio is With local goals for economic and population growth factors influence the success or failure of any particu roads, bridges, and utilities. The California Re lar action, or group of actions, in reducing flood still favorable, although considerably reduced, I revised downward, the freeway was rejected by local sources Agency originally agreed to provide only losses. Experience in Napa Valley seems to indicate partial reimbursement of the local share of the construction of the project may begin in 1978, if authorities because it was considered to be a possible stimulant to growth. the following factors are particularly important. project cost. The city of Napa was unable to finance environmental and funding problems are finally Redevelopment.—In 1969 the Napa Community Compatibility of flood-loss reduction with gen the remainder. In addition, Federal requirements resolved. f eral community objectives.—A. significant factor in ; The Soil Conservation Service, in cooperation Redevelopment Agency submitted an Urban Re regarding environmental impact statements have reducing flood losses seems to be the compatibility of with the Napa County Flood Control and Water development Plan for the Parkway Plaza Redevelop delayed the start of the construction. flood-loss reduction actions and techniques with Conservation District and the Napa County Re- ment Project (Napa Community Redevelopment The problems over State funding seem to be general community objectives. The fact that the Conservation District, intends to construct a Agency, 1969). The boundaries and land-use plan of resolved. The State has now agreed to provide 75 source flood-prone areas of Napa Valley have other char : flood-control project in the city of Napa to reduce the project are shown in figure 26. More than one- percent of the cost of land acquisition and 90 percent | acteristics important for open space led ABAG to damages from Napa Creek flooding. Under Public half the area is subject to the 100-year flood. In 1970 of the cost of necessary road, bridge, and utility place high priority on preserving the flood-prone funding was received from HUD to acquire and clear relocations. No State funding is presently provided Law 83-566 (U.S. Congress, 1954), the Soil Con areas in open-space uses. Similarly, Napa County’s parcels in the first nine-block section of the project for recreation or fish and wildlife enhancement. servation Service is authorized to construct and goal to limit population growth and maintain agri (fig. 26). This phase of the project has been com The Corps released a draft environmental im maintain multipurpose flood-control projects in cultural uses has led to land-use plans and regula pleted. New buildings housing government offices pact statement in April 1975 (U.S. Army Corps of small watersheds. In 1962 the Congress authorized a tions consistent with reducing flood losses. In the and commercial enterprises have been constructed. Engineers, 1975c). The major concern regarding the project to construct a dam and reservoir on Redwood city of Napa, however, the desire to redevelop flood- New street paving, lighting, brick sidewalks, bench project was voiced by the California Department of Creek west of the city of Napa. Redwood Creek joins prone portions of the downtown area for intensive es, planters, and trees have been added to the area. Fish and Game. The Department objected to the plan Browns Valley Creek just west of the city to form ; and economically valuable uses is inconsistent with to deposit spoils from the river dredging on former Napa Creek which then follows a course throng h the Figure 27 shows part of the area developed in the first reducing flood-loss potential. Even with a completed marshland south of the city which was diked many middle of the city, and joins Napa River ne the pha : :• during and after construction. flood-control project, the redevelopment area would years ago for agricultural use. If the dikes were downtown area of Napa (fig. 25). To prevent!]: vng ■ : 1972, the Urban Redevelopment Plan was be subject to increased losses from floods exceeding removed and the land subjected to tidal action, in downtown Napa requires coordination h , 'on an ^ -;d (Napa Community Redevelopment the 100-year flood. marshes could be restored on the land. The Corps is the creek and river projects. The Soil Cons; . \ on Ac-e' • 1973) to add 11 blocks to the project, and Compatibility of flood-loss reduction efforts with working out a mitigation plan with the Department Service has officially dropped consideratio he fiv. • om HUD are now available to acquire three land-use economics.—Actions to reduce losses will be of Fish and Game involving the provision of public dam project because of rising costs and i ive of blocks. The 11 blocks (fig. 26) are also within more widely accepted if economically viable land marshland elsewhere to compensate for the loss of environmental impact associated with cons; V.g th- •year flood plain. The city of Napa received an uses are permitted. A major reason for the success of potential marshland resulting from the project. the dam and relocating a county highway ll: - gh OP: >:-ce grant from HUD covering 50 percent of Agricultural Preserve Zoning in Napa Valley has The Corps of Engineers recently released a very steep terrain. the - o o of acquiring the first parcel for the linear been the high market value of land for agricultural General Design Memorandum which updates the As an alternative, the SCS is studying the park uses in relation to its value for urban uses. 1965 flood-control study—particularly with respect feasibility of constructing an underground channel The redevelopment area remains subject to fre Compatibility of flood-loss reduction efforts with to the cost/benefit analysis. Changes in the concept to divert excess flow from the stream channel quent flooding, and the potential cost of damages objectives of other agencies.—The chances of re and design of the project, as well as sharp changes in through the downtown area into the river. The Corps ! from a flood on either Napa Creek or Napa River has ducing flood losses are enhanced if actions by a city growth assumptions over the last decade, made such of Engineers may become directly involved with increased because of new construction in the re of county are consistent with programs of other an update necessary. The estimate of future average structural improvements on Napa Creek if the river development area. In addition, under the National agencies with jurisdiction or responsibility in the annual damages from flooding in the 1965 report project is constructed and there is no alternate Flood Insurance Program, the city faces a dilemma. drainage basin. For example, the plans and actions (U.S. Army Corps of Engineers, 1965b) was based on solution to control Napa Creek flooding. Under present regulations the city will be required to of Napa County, with respect to the unincorporated population projections which foresaw almost an enter the program or face the loss of all Federal flood-prone areas, are reinforced by ABAG’s policies Table 8. Population and land-use projections for the Napa eight-fold increase in population from 1960 to 2060 funds. However, even if the city enters the program, and the requirements of the National Flood In (table 8). According to the report, the population basin, 1960-2060 ^orP® Engineers, 1965b. Figures include city of Vallejoand the HUD would be violating its own guidelines if it surance Program and the Disaster Relief Act. In increase would be accompanied by a large shift from part of Solano County between the Napa County line and San Pablo Bay] continued to fund the redevelopment project in the turn, the potential for effective flood-loss reduction agricultural to residential and commercial land uses flood-prone area. The city seems to have little choice through proposed Corps of Engineers and Soil Con (table 8). Changes of lesser magnitude would occur in Land use I i but to push for expeditious construction of flood- servation Service projects is enhanced by the plan Year Population Agricultural Residential and commercial other land uses which account for approximately 40 control structures on both Napa River and Napa ning and regulatory efforts of Napa County. percent of the basin area. Area Percentage of Area Percentage of (acres) basin area (acres) basin area Creek. If the downtown area is protected by flood- These projections are inconsistent with the de 1960 132.000 141,780 control works from the 100-year flood, HUD could, in Intensity of existing development.—It is usually 1980 ---- 260,000 52.0 21,250 7.8 sires of the valley residents as expressed in plans and 127.000 46.5 38,000 13.9 easier and less costly to maintain low flood-loss 2000 390.000 accordance with its guidelines, continue to approve regulations adopted or under consideration. The 113.000 41.4 53.000 19.4 potential in undeveloped areas than to reduce loss 2020 630.000 94,500 the use of Federal funds for the redevelopment future average annual damages from flooding would 2040 34.1 76,000 27.8 potential in already urbanized areas. Napa County, 840.000 74.000 27.1 presumably be lower on the basis of more realistic 2060 .... 1,020,000 92.000 33.7 project. 59.000 21.6 107,000 39.4 •: \ j i i I FLOOD-PRONE AREAS AND LAND-USE PLANNING 64 SUMMARY 65 EXPLANATION 122° 17'30" Availability of hydrologic information.—The specificity of plans and regulations dealing with Residential, medium density flood-prone areas depends on the type, accuracy, and detail of information available to delineate the flood Residential, high density hazard. With more detailed data, particularly precise Residential, high rise mapping of the floodway, the Napa County Flood Control and Water Conservation District could pre Administrative and professional offices pare and seek adoption of flood-plain zoning regula Central business tions covering the entire flood plain with restrictions reflecting varying degrees of flood risk within the Commercial flood plain. Such flood-plain zoning regulations Park could be overlain on, or combined with, the use and site restrictions of the basic or underlying zoning district. NAV'XX Original redevelopment area The Napa Valley case study presents flood-loss Second eleven block redevelopment area reduction efforts in the context of land-use planning : Western I limit of and decisionmaking proceeding from generalized ' flood- Block purchased for linear park regional policies and plans through county planning . prone and regulation to detailed local planning and appli with largely undeveloped flood-prone areas, can cation of both structural and regulatory measures to prevent future increases in flood losses by regulating reduce flood losses. In such a process the information land uses in the flood plain; but, the city of Napa requirements are graduated with the most specific would have to convert existing developed areas to information on flooding needed by cities with de less intensive uses or provide flood-control works to veloped flood plains. significantly reduce flood-loss potential. These mea Although flood-prone areas and responses to sure* are costly and involve coordinating the efforts flooding problems are highly variable, the Napa of varous Federal, State, and local agencies. Valley study provides a reasonably typical view of ■(.•cation of drainage basin with respect to juris- the interplay among agencies, plans, and actions to dir '• ■. cal boundaries.—Effective local efforts to re reduce flood losses within the context of land-use duo: flood losses are easier to carry out if the major planning. Many of the factors affecting success or port'ions of a stream and its drainage area are located failure of flood-loss reduction efforts in the Napa withi.n a single jurisdiction. The Napa River and its Valley can be important in other flood-prone areas. drainage basin, with the exception of a small area of tidal fiats along San Pablo Bay, are within Napa SUMMARY County. Thus the county can integrate drainage basin and flood-plain plans and regulations in a Flood plains historically have provided attrac comprehensive program to reduce flood losses. If the tive and accessible sites for urban development. Use drainage basin covered a multicounty area, the by man has been extensive, and growing urban plans and programs of multiple local jurisdictions pressures are causing still more intensive develop ment. But use of the flood plain has exacted a price in 38° would have to be coordinated to achieve a compre 17' hensive approach to flood-loss reduction. losses from flooding or in costs of suitable protection. 30" Coordination of planning and implementation. Flood-loss reduction traditionally has been ap —When flood-control works are planned to reduce proached through installing structures such as flood-loss potential, related land-use decisions and dams, dikes, levees, channel improvements, and 2000 FEET I public and private facility construction and(or) re seawalls. These have provided only partial reduction of risk from flooding; flood losses have continued to 0 100 200 300 400 location should be appropriately phased to avert 500 600 METRES undue increases in flood-loss potential. Planning rise as a result of continuing encroachment on flood Figure 26.—Parkway Plaza Redevelopment Project in the city of Napa. (From Napa Community Redevelopment Agency, 1969.) related to the Corps of Engineers project in the City plains. of Napa dealt with flood control, urban redevelop In recent years Federal and State policies on ment, highway construction, and relocation in a flood-loss reduction have shifted from reliance on coordinated manner. Not completing the flood- structural works to a balance between structural and control project prior to redevelopment has resulted in nonstructural measures. For example, regulation of an increase (perhaps short term) in flood-loss poten flood-plain development is a requirement for com tial in the city of Napa. munities to qualify for subsidized flood insurance : r 66 FLOOD-PRONE AREAS AND LAND-USE PLANNING SUMMARY 67 and, under certain circumstances, flood-disaster re As the extent of damage from floods is a direct lief. Information on the extent of the flood hazard, consequence of the use of the land, efforts to reduce land use, and development is essential to develop a losses from flooding logically occur within the con sound and effective flood-loss reduction program. text of land-use planning. Land-use planning con Flood-plain information reports, flood maps, siders the future development of an area in terms of . and other information prepared by Federal, State, the economic, political, social, and physical deter and local agencies provide pertinent information on minants of growth and change. The planning pro flooding needed to evaluate flood risk. Flood-prone cess involves identifying problems, defining goals areas in the San Francisco Bay region are delineated and objectives, collecting and interpreting data, on a series of topographic quadrangle maps (scale 1: formulating plans, evaluating impacts, and adopt 24,000) prepared by the Geological Survey. Regional ing and implementing plans. Public participation is maps of flood-prone areas (scale 1:125,000) provide necessary throughout the planning process. an overview of the extent of potential flooding. Many governmental agencies and programs in Many methods and devices are available to re fluence planning for flood-loss reduction. Federal duce flood losses. These include the protection, re programs for flood insurance, disaster assistance, moval, discouragement, and regulation of certain comprehensive planning grants, and community types of development on flood plains. Programs for development grants all have impact on planning for flood-loss reduction are most effective when based on flood-prone areas—primarily a local responsibility. adopted comprehensive plans that are firmly imple A major portion of the cost of flood-control works is mented. Effective flood-loss reduction programs also borne by the Federal Government. State legisla achieve a balance between the use of flood plains and tion defines the powers of local governments to plan, the hydraulic requirements of floods. regulate, acquire land or development rights, or r election of existing development often is otherwise act to reduce flood losses. In addition, no:. r : **ry for economic or humanitarian reasons regional agencies may have specific authority de a ■...•■*; be provided by flood-control works, flood rived from Federal or State legislation to make or vw* . evacuation, and floodproofing. Damage influence decisions related to flood-loss reduction. 8 r. •: - rds from flooding may be avoided through Improved coordination of governmental actions re ! of existing structures or conversion of struc- to reduce flood losses is needed. Flood-loss reduction ti. ess vulnerable uses. Structures within flood- efforts should be integrated into land-use planning w • *y increase flood stage and velocity. Methods for entire drainage basins. There is need also for fo; oval or conversion include public acquisition, coordination in providing data, notably among Fed uri. > redevelopment, public-nuisance abatement, eral agencies such as the Geological Survey, Corps of nor -^onforming-use provisions in zoning ordi Engineers, and Soil Conservation Service, and the nances, conversion of use, and reconstruction of county flood control and water conservation dis existing public facilities. tricts, to assure comprehensive coverage and avail Discouraging development on flood plains may ability of pertinent data. be achieved through public-information programs, Study of the response to flooding problems in the warning signs, recordation of hazard, tax- Napa Valley outlines the complex intergovern assessment practices, financing policies, and public- mental responsibilities involved in developing plans utility extension policies. Flood insurance and programs to reduce flood losses. In addition to requirements and costs may constitute an additional the need for coordinating the actions of numerous ! deterrent. agencies, the Napa Valley experience indicates that The regulation of uses on flood plains provides a factors important in flood-damage reduction include direct means for reducing flood losses through pro compatibility of flood-damage reduction with gen hibition or regulation of uses vulnerable to flood eral community objectives, land-use economics, and damage. In most states the primary responsibility the objectives of other agencies; the intensity of for planning, adopting, and enforcing land-use regu existing development; the availability of hydrologic lations rests with local government. Flood-plain information; and the coordination of planning and development can be controlled through establish implementation. ment of zoning districts and incorporation of flood- The Napa Valley study illustrates a graduated plain regulations in zoning, subdivision, sanitary, approach to flood-damage reduction proceeding and building ordinances. from generalized regional policies and plans through Figure 27.—Part of Parkway Plaza during and after redevelopment. r 68 FLOOD-PRONE AREAS AND LAND-USE PLANNING REFERENCES CITED 69 California Water Code, 1971: West’s Annot. Water Code, sec. county planning and regulation to detailed local Map MF-480, 2 sheets. geles Engineer Diets., 231 p. Sheaffer, J. R., and others, 1967, Introduction to floodproofing: planning and application of both structural and 8401(c). U.S. Congress, 1936, Flood control act of 1936: Public Law 74-738, ____ _1gY5 Cobey-Alquist flood plain management act: West’s Chicago Univ. Center for Urban Studies, Chicago Univ. 49 Stat. 1570, 33 U.S.C. 701. regulatory measures to reduce flood losses. In such a Annot! Water Code, secs. 8400-8415 . Press, III., 61 p. ------1949, Housing act of 1949: Public Law 81-171, title I—Slum process the information requirements are also gradu Crippen, J. R., 1975, Index of flood maps for California prepared Sheaffer, J. R., Ellis, D. W., and Spieker, A. M., 1970, Flood- clearance and urban renewal, 63 Stat. 413, 42 U.S.C. 1441, ated with the most specific delineation of flood-prone by the U.S. Geological Survey through 1974: U.S. Geol. hazard mapping in Metropolitan Chicago: U.S. Geol. Survey 1450-1469. areas needed for urban areas. Survey open-file rept., 29 p. Circ. 601-C, 14 p. ------1954, Watershed protection and flood prevention act of 1954: Although flood-prone areas and responses to Federal Disaster Assistance Administration, 1975, Federal disas Southeastern Wisconsin Regional Planning Commission, 1968, Public Law 83-566, 68 Stat. 666, 16 U.S.C. 1001-1009. ter assistance—Final regulations: Federal Register, v. 40, Floodland and shoreland development guide: Planning flooding problems are highly variable, the Napa ------1960, Flood control act of 1960: Public Law 86-645, title II, no. 103, p. 23251-23269. Guide no. 5, 199 p. sec. 206, 74 Stat. 500, 33 U.S.C. 709a. Valley study provides a typical view of interplay Federal Insurance Administration, 1971, National flood insur- U.S. Army Corps of Engineers, 1956, Report on floods of December ------1965, Flood control act of 1965: Public Law 89-298, title II, among agencies, plans, and actions in attempting to ance program: Code of Federal Regulations, 1975 ed., title 24, 1955 and January 1956 in northern California coastal 79 Stat 1073, 33 U.S.C. 701. reduce flood losses within the context of land-use sec. 1910.3(a). streams: San Francisco [Calif.] Engineer Diet, rept., 137 p. ------1966a, A unified national program for managing flood planning. Factors affecting the flood-loss reduction _____1976, National flood insurance program—Rules and regula ------1965a, Report on floods of December 1964 in northern losses: House Document 465, 89th Congress, 2d sess., 47 p. tions: Federal Register, v. 41, no. 207, p. 46962-46992. California coastal streams: San Francisco [Calif.] Engineer ------1966b, Flood control act of 1966: Public Law 86^-789, title II, efforts in the Napa Valley can be important in other International Conference of Building Officials, 1973, Uniform Dist. rept., 46 p. and appendixes. sec. 206, 80 Stat. 1418, 33 U.S.C. 709a. flood-prone areas. building code: Whittier, Calif., 704 p. ------1965b, Napa River basin, California: Washington, D.C., ------1968, National flood insurance act of 1968: Public Law Kusler, J. A., and Lee, T. M., 1972, Regulations for flood plains: Office of the Chief of Engineers rept., Ill p. 90-448, title XIII of Housing and urban development act of REFERENCES CITED Am. Soc. Planning Officials, Planning Advisory Service rept. ------1966, Flood plain information report on the Des Plaines 1968, 82 Stat. 572, 42 U.S.C. 4001-4127. 277, 68 p. River, Illinois and Wisconsin: Chicago [111.] Engineer Dist. ------1970, National environmental policy act of 1969: Public American Insurance Association, 1956, Studies of floods and Limerinos, J. T., 1970, Floods on Napa River at Napa, California: rept. Law 91-190, 83 Stat 852, 42 U.S.C. 4321-4347. flood damages 1952-1955: New York, N.Y. U.S. Geol. Survey Hydrol. Inv. Atlas HA-348. ------1970, Flood plain information, Coyote Creek, San Fran ------1973, Flood disaster protection act of 1973: Public Law Association of Bay Area Governments, 1970, Regional Plan Limerinos, J. T., Lee, K. W., and Lugo, P. E., 1973, Flood-prone cisco Bay to Anderson Reservoir, Santa Clara County, Cali 93-234, 87 Stat. 975, 42 U.S.C. 4001-4128. 1970:1990, San Francisco Bay region: Berkeley, Calif., 32 p. areas in the San Francisco Bay region, California: U.S. Geol. fornia: San Francisco [Calif.] Engineer Dist. rept., 26 p. ------1974a, Disaster relief act of 1974: Public Law 93-288, ------1972, Regional open space plan—Phase II: Berkeley, Calif., Survey Water-Resources Inv. 37-73, 3 maps, scale 1:125.000. ------1972a, Flood plain information, Guadalupe River, Santa 88 Stat. 143, 42 U.S.C. 5121-5202. 15 p. McGlashan, H. D., and Briggs, R. C., 1939, Floods of December Clara County, California: San Francisco [Calif.] Engineer ------1974b, Housing and community development act of 1974: ------1975, Areas of critical environmental concern: Berkeley, 1937 in northern California: U.S. Geol. Survey Water-Supply Gist. rept., 22 p. Public Law 93-383, 88 Stat. 633, 42 U.S.C. 5301-5317. Calif., 83 p. Paper 843, 497 p. ....——1972b, Flood plain information, Green Valley, Dan Wilson, ------1974c, Water resources development act of 1974: Public Law ------1976, Land capability analysis—A method of applying Napa City Planning Department, 1968, City of Napa gene :y) pi an: ;. rd Suisun Creeks, Cordelia [Solano County], California: 93-251, title I, sec. 73, 88 Stat 16, 33 U.S.C. 701b-ll. earth science information to planning and decisionmaking: Prepared and published by Gordon Hall and Assoc .n . . . San eramento [Calif.] Engineer Dist. rept., 37 p. U.S. Department of Housing and Urban Development, 1974, Berkeley, Calif., 225 p., app. A-D. Francisco, Calif., 82 p. ■ ... 1972c, Flood-proofing regulations: Washington, D.C., Of- Summary of the HUD budget, FY 1975: Washington, D.C., Bay Conservation and Development Commission, 1969, San ------1975, The revised general plan for the city of Napa: ‘So pa, j\a:‘ of the Chief of Engineers rept., 79 p. Office of the Secretary. Francisco Bay plan: Sacramento, Calif., 43 p. Calif., 53 p. - - )73a, Flood plain information, Alamitos Creek, including ------1975, Comprehensive planning assistance program: Fed Bue, C. D., 1967, Flood information for flood-plain planning: Napa Community Redevelopment Agency, 1969, Or'.^K rede .".adalupe Creek, Arroyo Calero, and Santa Teresa Creek, eral Register, v. 40, no. 164, p. 36855-36865. U.S. Geol. Survey Circ. 539, 10 p. velopment plan, Parkway Plaza redevelop men' y oject: r; r^ta Clara County, California: San Francisco [Calif.] ------1976, Community development block grants—Eligible ac California Coastal Zone Conservation Commission, 1975, Cali Napa, Calif., 43 p. Iv-igineer Dist. rept., 22 p. tivities: Federal Register, v. 41, no. 12, p. 2766-2768. U.S. Geological Survey, 1971, Flood-prone areasin the Napa River fornia coastal plan: Sacramento, Calif., 443 p. 1973, Amendments to urban redevelopment plan, Parkway ------1373b, Flood plain information, Alamo and Ulatis Creeks, California Region Framework Study Committee, 1971, Compre Plaza redevelopment project: Napa, Calif. Vacaville [Solano County], California: Sacramento [Calif.] drainage basin, Napa County, California: Cuttings Wharf, Napa, Rutherford, St Helena, and Yountville quadrangles, hensive framework study, California region—Appendix IX, Napa County Board of Supervisors, 1967, Flood plain zoning Engineer Dist. rept., 44 p. Flood control: Pacific Southwest Inter-Agency Comm., U.S. classifications: Ordinance 262. ------1973c, Flood plain information, Fisher Creek, Santa Clara scale 1:24,000. U.S. Office of Emergency Preparedness, 1972, Disaster prepared Water Resources Council, 197 p. 1968, Agricultural preserve district: Ordinance 274. County, California: San Francisco [Calif.] Engineer Dist. ness—Report to Congress: Washington, D.C., U.S. Govt California Government Code, 1966: West’s Annot. Gov. Code, 1969, Agricultural preserve interim district: Ordinance 292. rept., 18 p. Printing Office, 3 v. sec. 65300. 1969, Agricultural preserve extensive district: Ordinance ------1973d, Flood plain information, San Felipe Lake and Pache ------1976a, West’s Annot. Gov. Code, secs. 65800-65912. 309. co Creek, San Benito County, California: San Francisco U.S. Office of Management and Budget, 1969, Circular no. A-95: Washington, D.C., U.S. Govt Printing Office. ------1976b, West's Annot. Gov. Code, sec. 66411. ------1970, Resolution 70-155. [Calif.] Engineer Dist. rept., 17 p. ------1976c, Land conservation act of 1965: West’s Annot. Gov. ------1973e, Flood plain information, Uvas-Camadero Creek, ------1974, Catalog of Federal domestic assistance: Washington, 1974a, Watercourse obstruction and riparian cover: Ordi Code, secs. 51200-51295. nance 447. Pajaro River to Uvas Reservoir, Santa Clara County, Cali D.C., U. S. Govt Printing Office, 744 p. ------1976d, Planning and zoning law: West’s Annot. Gov. fornia: San Francisco [Calif.] Engineer Dist. rept., 19 p. U.S. President 1966, Evaluation of flood hazard in locating Fed 1974b, Agriculture, watershed and recreation zoning: Ordi erally owned or financed buildings, roads, and other facilities, Code, secs. 65000-66180. nance 468. ------1973f, Water Resources development in California: South ------1976e, Subdivision map act of 1974: West’s Annot. Gov. and in disposing of Federal lands and properties: Executive Napa County Conservation, Development and Planning Depart Pacific Division—San Francisco, Sacramento, and Los Code, secs. 66410-66499. Order 11296, Code of Federal Regulations, 1970 ed., title 3, ment, 1973, Napa County conservation and open space ele Angeles Engineer Dists., 244 p. California Health and Safety Code, 1970: West’s Annot. Health p. 181, 33 U.S.C. 701. ment: Napa, Calif., 37 p., 8 maps. ------1975a, Flood plain information, Llagas Creek Unit 1, in and Safety Code, sec. 500. U.S. Water Resources Council, 1968, The Nation’s water re- cluding Edmundson, Church, San Martin, New, Center, Cor------1976a, West’s Annot. Health and Safety Code, sec. 17922. 1974a, Napa County summary general plan: Napa, Calif., sources: Washington, D. C., U.S. Govt. Printing Office, pts. 4 P- ralitos, Tennant, Maple, and Foothill Creeks, Santa Clara ------1976b, West’s Annot. Health and Safety Code, sec. 17958. 1-7. County, California: San Francisco [Calif.] Engineer Dist. ------1976c, Community redevelopment law: West’s Annot. Napa Valley area plan: Napa, Calif., 35 p. _____ 1971, 1972, Regulation of flood hazard areas to reduce Health and Safety Code, secs. 33000-34160. Calif 63 p U8C e*emen*’ ^aPa County general plan: Napa, rept., 31 p. flood losses: Washington, D. C., U.S. Govt. Printing Office, ------1975b, Flood plain information, Rush Creek—Petaluma California Public Resources Code, 1970, Soil conservation and soil v. I, pts. 1-4, 578 p.; and v. II, pts. 5-6, 389 p. Ohio Department of Natural Resources, 1974, Big Darby Creek River to U.S. Highway 101, Marin County, California: San conservation districts: West’s Annot. Pub. Resources Code, White, G. F., 1960, Strategic aspects of urban flood plain occu- corridor study: Columbus, Ohio, 99 p Francisco [Calif.] Engineer Dist. rept., 19 p. sec. 9074. pance: Am. Soc. Civil Engineers Proc., v. 86, HY2, Paper ------1975c, Napa River, draft environmental statement, flood ------1976a, Environmental quality act of 1970: West’s Annot. ?c!reZ?lrP°T^0n’ 19?3’ H°W t0 imPlament open-space plans 2376, p. 89-102. control project, Napa, California: San Francisco [Calif.] Pub. Resources Code, secs. 21000-21176. Ritter R ST'*™ Bay area: Berkeley. Calif., 172 p. —1975, Flood hazard in the United States—A research assess Engineer Dist. rept., 213 p., 17 pis. ------1976b, California coastal act of 1976: West’s Annot. Pub. ’t ,i ^ j upre’ 1972, Maps showing areas of ment: Colorado Univ. Inst. Behavioral Science, Monograph ------1975d, Water resources development in California: South Resources Code, secs. 30000-30900. Bav inan atlon from tsunamis in the San Francisco NSF-RA-E-75-006, 141 p. Bay region, California: U.S. Geol. Survey Misc. Field Studies Pacific Division—San Francisco, Sacramento, and Los An- 70 FLOOD-PRONE AREAS AND LAND-USE PLANNING SOURCES OF FLOOD-PLAIN MAPS AND INFORMATION 71 tive agencies: Washington, D.C., U.S. Govt. Printing Office, Young, L. E., 1962. Floods at Fremont, California: U.S. Geol. 123° 122° 121° Survey Hydrol. Inv. Atlas HA-54. 22 p \ 39° Weber E W., and Sutton, W. G., 1965, Environmental effects »/ of flood-plain regulations: Am. Soc. Civil Engineers Proc., if St //^0Rfi IA1JN / 5^ SELECTED READINGS -poil iSWvP A v. 91, HY4, Paper 4402, p. 59-70; discussion v. 91, HY6, VAt KeTsBWLLE OWER LAKE 4' 9 - I95S . LINCOLNS _ AUBURN p. 249-251. LI & ^ l\ > / Federal Disaster Assistance Administration, 1975, Federal dis White G. F., and Haas, J. E., 1975, Assessment of research on I \ & aster assistance—Final regulations: Federal Register, v. 40, \ fa natural hazards: Mass. Inst. Tech. Press, Cambridge, Mass., N A no. 103, p. 23251-23269. and London, England, 487 p. tz Federal Insurance Administration, 1975, National flood insur S\W W A A 4m ance program—Proposed criteria: Federal Register, v. 40, no. FAIR OAKS _ a^£fOLSOML---- im 954 ST 1941- \ 59, p. 13420-13433. SOURCES OF FLOOD-PLAIN MAPS V-flC Liebman, Ernst, 1973, Legal problems in regulating flood hazard a AND INFORMATION areas: Am. Soc. Civil Engineers Proc., v. 99, HYll, Paper 4iaWI4M- pfe —I 10135, p. 2113-2123. Flood-plain inundation maps have been prepared and other & i Matthai, H. F., Back, William, Orth, R. P., and Brennan, Robert, f* m *4 A A' *Tvr .4, A S '■S 1957, Water resources of the San Francisco Bay area, Cali flood studies made by the Geological Survey and other Federal, —SEBASTOPOL: -SANTA ROSjL- _\sON-ASONOMA. ------Lmt VAEAwLj—iVACAVILLE— —C6URTfj\ND< i ^-FRANKU^.-t EK A # /“• * * > •\1' fornia: U.S. Geol. Survey open-file rept., 55 p. county, local, and private agencies for many areas in the San .mi • m3» U Francisco Bay region. Information on flooding and flood hazards A Perrey, J. I., 1956, Use of zoning principles in flood-plain regula f* 4 4* A' tion: Am. Soc. Civil Engineers Proc., v. 82, HY2, Paper has been presented in pertinent maps and reports. The principal mmh 957, p. 1-10. sources of the maps and flood information are summarized in 4ft Phippen, G. R., 1974, Can a right go wrong?: Water Spectrum, table 9; the maps and reports available are listed in table 10. — f$INT\REYES---peYalLUMAAi.um, LpZ- LODI----- B EtLOTA— U.S. Army Corps of Engineers, Washington, D.C., v. 6, Figure 28 shows the quadrangle maps available in the Bay region. “t. CEil9»39 CE 1907-39 no. 1, p. 31-37. Rantz, S. E., 1971, Mean annual precipitation and precipita Table 9.—Sources of maps and flood information L tion-depth-duration frequency data for the San Francisco \ 38° • 'c Bay region, California: U.S. Geol. Survey open-file rept., 23 p. Types of maps and reports •’•Ap ------1971, Suggested criteria for hydrologic design of storm- f ■?> Flood-prone area Flood- 3L— ^.STOCKT _ MANTECA— drainage facilities in the San Francisco Bay region, Cali maps Flood-' plain Flood- ' 1953 fornia: U.S. Geol. Survey open-file rept., 69 p. hazard information insurance Bo- '. in V/ Regional Quadrangle maps reporta studies ».* ------1974, Mean annual runoff in the San Francisco Bay region, MMSMS f mmvw California, 1931-70: U.S. Geol. Survey Misc. Field Studies u.s. i A Map MF-613. Geological •A* A* Schneider, W. J., and Goddard, J. E., 1974, Extent and develop Survey X (l) X J't — LIVERMORE^: — altamonL -> ment of urban flood plains: U.S. Geol. Survey Circ. 601-J, U.S. Army ■ “’ik-T Corps of 14 p. EXPLANATION 4. Sheaffer, J. R., and others, 1967, Introduction to floodproofing: Engineers (2) lAkA&wM m AN Chicago Univ. Center for Urban Studies, Chicago Univ. U.S. Soil l .-.p sheets showing inundation from Press, 111., 61 p. Conservation ^ - A* Service...... e 100-year flood Spangle, William and Associates, and others, 1973, Application of (3) OARDMA --- CE 19W»+— Federal E 1908 earth-science information in urban land-use planning—State- Insurance B Occasional flooding A of-the-art review and analysis: Available from the Natl. Administration, 4 Tech. Inf. Service, U.S. Dept. Commerce, Springfield, Va., U.S. Depart NTIS PB-238-081/AS, 330 p. ment of • / a AV & ------1976, Earth-science information in land-use planning- Housing /Afp* > A A guidelines forearth scientists and planners: U.S. Geol. Survey and Urban _AN0 NUEVO— ./BEN LOMOND- LiLQS GATOS — HOT SPRINGS- CHECO PASS CE 194(K'I_ CE 1939 m C«»UIMO Circ. 721, 28 p. Development ... x A & • A U.S. Water Resources Council, 1968, The Nation’s water resources: County and V ¥ $ 37° Washington, D.C., U.S. Govt. Printing Office, pts. 1-7. municipal 0 10 20 30 40 50 MILES / " ------1971,1972, Regulation of flood hazard areas to reduce flood agencies...... (4) 1 1 1 J it ( I I I I I I 1 5 losses: Washington, D.C., U.S. Govt. Printing Office, v. I, 'Quadrangle maps available are shown in figure 28 Figure 28.-Topographic map sheets and the flood-prone area maps available in the San Francisco Bay region. r SOURCES OF FLOOD-PLAIN MAPS AND INFORMATION 73 72 FLOOD-PRONE AREAS AND LAND-USE PLANNING available for areas in the San Francisco Bay region Table 10.-Flood-plain maps and information available for areas in the San Francisco Bay region—Continued Table 10.-Flood-plain maps and information A. Flood-prone area maps C. Flood-plain information reports Regional maps: U.S. Army Engineer District, San Francisco, 211 Main Street, San Francisco, CA, 94105. Copies of reports U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA, 94025 generally available from the flood control and water conservation districts and collaborating county agencies. 1. “Flood prone areas in the San Francisco Bay region, California,” by J. T. Limerinos, K. W. Lee, and Flood-plain information for: P. E. Lugo (1973), in three sheets, scale 1:125,000. Map shows areas in the region subject to inunda Rush Creek—Petaluma River to U.S. Highway 101, Marin County (1975). tion by the 100-year flood. Coastal areas subject to a potential hazard from high tides are delineated Alamo and Ulatis Creeks, Vacaville, Solano County (1973). with respect to the 100-year tide. (SFBRS Interpretive Report 4). , Calif- Green Valley, Dan Wilson and Suisun Creeks, Cordelia, Solkno County (1972). 2. “Map showing areas of potential inundation by tsunamis in the San Francisco Bay region Alamitos Creek, including Guadalupe Creek, Arroyo Calero, and Santa Teresa Creek, Santa Clara omia,” by J. R. Ritter and W. R. Dupre (1972), in two sheets, scale 1:125,000. Map shows estimated County (1973). extent of potential inundation from a tsunami wave height of 20 feet at the Golden Gate (recurrence Coyote Creek, San Francisco Bay to Anderson Reservoir, Santa Clara County (1970). interval, about 200 years). Inundation hazard from tsunamis was not included in the delineation of Fisher Creek, Santa Clara County (1973). flood-prone areas shown on the regional map. (SFBRS Basic Data Contribution 52). Guadalupe River, Santa Clara County (1972). Quadrangle maps (fig. 28): Llagas Creek Unit 1, including Edmundson, Church, San Martin, New, Center, Corralitos, Tennant, U.S. Geological Survey. California District, Water Resources Division, 855 Oak Grove Avenue, Menlo Park, Maple, and Foothill Creeks, Santa Clara County (1975). CA, 94025 San Felipe Lake and Pacheco Creek, San Benito County and part of Santa Clara County (1973). 1- Maps, on topographic map sheets, scale 1:24,000, showing areas prone to occasional flooding, Uvas-Carnadero Creek, Pajaro River to Uvas Reservoir, Santa Clara County (1973). prepared in 1969: Calistoga La Costa Valley Palo Alto D. Flood-insurance studies Dublin Livermore San Jose West Communities participating in the National Flood Insurance Program as of October 31, 1975, that have special Niles flood hazard areas identified, and wherein the sale of flood insurance is authorized, include the following: 2. Maps, on topographic map sheets, scale 1:24,000, showing areas prone to flooding from the 100-year County and County and County and flood, prepared 1971-75 (location shown in fig. 28): community community community Aetna Springs Franklin Point Petaluma River Alameda County: Marin County—Continued: Santa Clara County: Allendale Geyserville Pigeon Point Unincorporated area Novato Campbell Altamont Gilroy Point Bonita Alameda Ross Cupertino Antioch North Gilroy Hot Springs Port Chicago Berkeley San Anselmo Gilroy Antioch South Glen Ellen Redwood Point Emeryville San Rafael Los Altos Asti Gualala Richmond Fremont Sausalito Los Altos Hills Benicia Guerneville Rio Vista Hayward Tiburon Los Gatos Bethany Half Moon Bay Rutherford Livermore1 Milpitas Big Basin Hayward San Felipe Newark Napa County: Monte Sereno Birds Landing Healdsburg San Francisco Oakland Unincorporated area Morgan Hill Bolinas Honker Bay North Piedmont Calistoga Mountain View Bouldin Island Hunters Point San Francisco Pleasanton Napa Palo Alto Brentwood Inverness South San Leandro St. Helena San Jose Briones Valley Isleton San Gregorio Union City Yountville Santa Clara Byron Hot Springs Jersey Island San Jose East Saratoga Calaveras Reservoir Jimtown San Leandro Contra Costa County: San Francisco County: Sunnyvale Camp Meeker Kenwood San Mateo Unincorporated area San Francisco City Capell Valley La Honda San Quentin Antioch and County2 Solano County: Castle Rock Ridge Las Trampas Ridge San Rafael Brentwood Benicia Cazadero Laurel Santa Rosa Clayton San Mateo County: Dixon Chiles Valley Liberty Island Santa Teresa Concord Unincorporated area Fairfield Chittenden Los Gatos Hills ; El Cerrito Atherton Rio Vista Clayton Mare Island Saxon Hercules Belmont Suisun City Cloverdale Merritt Sears Point Lafayette Brisbane Vacaville Cordelia Milpitas Sebastopol Martinez Burlingame Vallejo Cotati Mindego Hill Sonoma Pinole Colma Courtland Montara Mountain St. Helena Pittsburg Daly City Sonoma County: Cupertino Morgan Hill Tassajara Pleasant Hill Foster City Unincorporated area Cuttings Wharf Mountain View Three Sisters Richmond Half Moon Bay Cloverdale Davis Mt. George Two Rock San Pablo Hillsborough Cotati Denverton Mt. Madonna Valley Ford Walnut Creek Menlo Park Healdsburg Detert Reservoir Napa Walnut Creek Millbrae Petaluma Diablo Newark Walter Springs Marin County: Pacifica Rohnert Park Dixon Novato Watsonville East Unincorporated area Portola Valley Santa Rosa Dozier Oakland East Winters Belvedere Redwood City Sebastopol Duncans Mills Oakland West Woodside Corte Madera San Bruno Sonoma Elmira Pacheco Peak Woodward Island Fairfax San Carlos Fairfield North Petaluma Yountville Larkspur1 San Mateo Fairfield South Petaluma Point Mill Valley South San Francisco These maps and flood-prone area Woodside 'ParticipatinK in program, but special flood hazard areas not yet delineated. -Determined to have no special flood-hazard areus. Resources Division, U.S. Geological Survey, 855 Oak Grove Avenue, Menlo Park, CaH?94025 ’ W B. Flood-hazard maps U.S. Geological Survey, Denver F’ederal Center, Lakewood, CO, 80225 1. Hydrologic Investigations Atlas HA-54, “Floods at Fremont, California ” hv I F 2. Hydrologic Investigations Atlas HA-348, ‘'Floods on Napa River at Napa! California?’ by J. T. Umerinos ! SOURCES OF FLOOD-PLAIN MAPS AND INFORMATION 75 74 FLOOD-PRONE AREAS AND LAND-USE PLANNING as in the San Francisco Bay region-Continued Table 10.—Flood-plain maps and information available for areas in the San Francisco Bay region—Continued Table 10.—Flood-plain maps and information available for are E. Other flood-control and watershed projects—Continued. E. Other flood-control and watershed Pr°Ject^ q n Francisco, CA, 94105 U.S, Soil Conservation Service. Information pertaining to these and other studies in the region may be obtained U.S. Army Engineer District, San Francisco, Corps of Engineers, 211 Mam Street, a from offices of the Soil Conservation Service (Concord, Dixon, Half Moon Bay, Livermore, Morgan Hill, Napa, Flood control projects: Nature of Santa Rosa, Petaluma) or from offices of cooperating soil conservation districts and county flood control and Status County work water conservation districts. Name Completed 1962. San Lorenzo Alameda Levees and channel Creek. improvements. Not started. Small watershed projects under Public Law 83-566 (U.S. Congress, 1954): Alhambra Creek Contra Costa Channel Project Sponsoring agencies Purpose Year authorized Status improvements, Ulatis Creek .... Complete. diversion. 1961 Under construction Central Sonoma Sonoma County Water Agency. Flood control. 1958 Nearing completion. do Channel enlarge Walnut Creek (1977). Santa Rosa Resource Conservation ment and District. stabilization. Under construction, Lower Llagas Creek Santa Clara Valley Water District. do 1969 Not yet under Corte Madera Marin Channel and Upper Llagas South Santa Clara County Water construction. improvements. in court. Creek. Creek. District. Planning completed. Napa River Napa Channel enlarge Loma Prieta Resource Conservation basin. ment, realinement District. levees. Lower Pine Creek ...... Contra Costa County Flood Control Flood control, 1970 do Alameda Santa Clara Channel Under construction. and Water Conservation District. water storage, improvements. Contra Costa County Resource recreation. Fairfield Solano Channel Planning completed Conservation District, vicinity streams. improvements, 1973. East Bay Regional Park District. diversion. Marsh-Kellogg Contra Costa County Flood Control Flood control. 1959 Nearing completion. Sonoma Creek Sonoma Channel Planning and EIS Creek. and Water Conservation District. basin. improvements. completed 1973. Contra Costa County Resource Warm Springs Dam, do Dam and lake, Planning, land Conservation District, Lake Sonoma. channel acquisition, road oRiver Napa County Flood Control and do 1962 Stalled. improvements. relocation in progress. Water Conservation District. Small flood-control projects: Napa County Resource Conservation Nature of District. Name County work Status San Leandro Alameda Channel Near completion. Creek. improvements. Pinole Creek .. Contra Costa do Completed 1966. Rheem Creek .. do do Completed 1960. Rodeo Creek .. do do Completed 1966. Coyote Creek .. Marin Channel lining. Completed 1965. Green Valley Solano Channel Completed 1962. Creek. enlargement, realinement. Flood control studies: Name County Date authorized Wildcat and Contra Costa ... 1960 San Pablo Creeks. Novato Creek and Marin 1941 tributaries. Pacific coastal San Mateo 1965 streams. South San Francisco San Mateo 1958 streams. Guadalupe River. Santa Clara 1941 Russian River. Sonoma ...... 1958 iHJ.S. GOVERNMENT PRINTING OFFICE: 1977 - 789-025/66 Wl-1 : (t>V<0 i Utl 627.1+ (791+6) W11 Waananen, Arvi 0. Flood-prone areas and land-use planning. DATE ISSUED TO 111 f/A/ilf-r t 7 - ! i I ! : \ n' ■■ i V. i i ; k v * to to 3 3 (9 3 * to a3 o rr o S -n r ‘XU. *'> :S%HS^ O ■ ■ ■ - #tr" O , a ■ ■ ■ ■ u 21 O 2 • ■ • ■ m v: ;:'Tk>r;- : -• ' 1 ' •v. - > 3 • . :n • K. 'V nr' >• ';X.: ... - 3 . • •* - + / *• ff,. «* 9 ■ •• •» . - JfcC- •• ■»£ " V- ? - r; *. -. f • j? ■ . ■ •" ’ • ’ * ; i - A * - R*. 8K* r \\\-&**- ?-■ '**"*•;: ■* *s»W,<4 j*' -=><■ ' •} fir~ £1 . • c. . ■ • ' :fe vassal .. 7%. * - V - r , • &' -ff 4* ■ '•'•••• .. ' ,:■■• •-i-. :.= ■ ate-A*/ •i*' ■ xr--pxj^ m ■m -■■■■’ . : .. , v v :~- y -•• >• :. £ : ■ ■' f*J ■-■'■ . ^ : .-': -sa ■ -• -. •;■-:^.v^2/: -..r I '. ."•'.'..',T ;•■ ! . ...’ - ;! *.l l * f i M' :: ^' v:';- I •. ^ v'. - 'r r ’ i5 •V. ;-.'• W'.-; -•V. --.■ '•.,.. *. V - ■■ ■;■ • ■ ■ . • • i I T- ■ ^X^ xxx ■' -■- # X-~& - - / -:1? . r •• >. ;~v.-^7.; ••-■ •■■'■- ■ -*5^, \. T>g** • ■g