Utah State University DigitalCommons@USU Reports Utah Water Research Laboratory January 1980 Flood Damage Mitigation in Utah L. Douglas James Dean T. Larson Daniel H. Hoggan Terrence L. Glover Follow this and additional works at: https://digitalcommons.usu.edu/water_rep Part of the Civil and Environmental Engineering Commons, and the Water Resource Management Commons Recommended Citation James, L. Douglas; Larson, Dean T.; Hoggan, Daniel H.; and Glover, Terrence L., "Flood Damage Mitigation in Utah" (1980). Reports. Paper 326. https://digitalcommons.usu.edu/water_rep/326 This Report is brought to you for free and open access by the Utah Water Research Laboratory at DigitalCommons@USU. It has been accepted for inclusion in Reports by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. Flood Damage Mitigation in Utah L. Douglas James Dean T. Larson Daniel H. Hoggan Terrence L. Glover Utah Water Research Laboratory Utah State University Logan, Utah 84322 WA TER RESOURCES PLANNING SERIES January 1980 UWRL/P-80/0 1 COVER During the night of January 20, 1980 (while this report was being typed) heavy rains on frozen ground in northern Utah caused extensive flash flooding in Cache and Box Elder Counties. The damages were con­ centrated in the communities at the base of the Wellsville Mountains and smaller ranges to the north. Mendon was the worst hit community, and the flooding there was compounded by water collecting in an irri­ gation canal which broke in several places causing deep washes. The total damage in the two count ies was about $3 million with 43 percent occurring to roads a~d bridges, 29 percent to land and livestock, and 28 percent to irrigation and other water control systems. Counts of water in up to 200 basements were reported, but no figures on damages to homes were published and indications are that they are a relatively small portion of the total. The pictures on the cover illustrate the kinds of damages caused by a flash flood·in rural Utah. During. the week of February 17, 1980, another .series of heavy rains caused repeat flooding, particularly concentrated in Mendon and Clarkston, that caused a similar amount of damage. FLOOD DAMAGE MITIGATION IN UTAH L. Douglas James Dean T. Larson Daniel H. Hoggan Terrence L. Glover WATER RESOURCES PLANNING SERIES UWRLjP-80/01 Utah Water Research Laboratory Utah State University Logan, Utah 84322 January 1980 ABSTRACT Utah is subjected to flash flooding in mountain canyons, mudflows and shallow water flooding on lowlands at the canyon outlets, storm water flooding after thunderstorms in urban areas, and prolonged periods of inundation in certain lowland areas during snowmelt peri­ ods. In response to these problems, individuals are making private land use and flood proofing decisions, larger communities have storm water collection programs, three federal agencies are involved in structural flood control, and the Federal Emergency Management Agency is manqging a National Flood Insurance Program designed to promote community floodplain management efforts. A framework was developed of the dynamically interactive feedback process through which people at various levels and from various prospectives seek the benefits of floodplain occupancy, experience floods, and respond by changing their occupancy or the flows. That framework then became the background for identifying what state government should do in Utah to correct unsatisfactory aspects of the existing flood hazard and counter measures. The data used in the analysis included magnitudes of major historical snowfall and precipitation events, estimates of 100-year flows for all 105 gaged locations with more than 20 years of record, envelope curves of 100-year flow versus drainage area for Utah basins, descriptions of the major historical floods (by order according to amount of damage 1. Salt Lake City canyons 1952 $6,74,000; 2. Ogden 1979 $1,000,000; 3. Virgin River 1966 $962,000; 4. Sheep Creek (Dag­ gett County) 1965 $802,000), descriptions of the structural flood control projects built or being planned in Utah by the Corps of Engineers, Soil Conservation Service, and Water and Power Resources Service, data with respect to participation in the national flood insurance program of Utah I s 251 communit ies, a survey of the flood hazard in 32 of those communities randomly selected from a stratified sample, and a detailed evaluation of the situations in 7 of them. The study found that the flood hazard in Utah is much more concentrated in smaller basins than is so for other parts of the country and that the major problem lies at the base of the mountains where major damages are regularly being caused by flows at mountain hollows too small for hazard areas to have been mapped through the National Flood Insurance Program. Better methodology needs to be developed and applied for delineating hazard areas from mudflows and shallow water flooding on alluvial fans and other lowlands at the mountain base. Attention needs to be given to the effects of irriga­ t ion canals and bridges on the risk. Designs need to be developed that work with nature in disperSing the flood water and recharging much of it to underground aquifers instead rather than against nature in concentrating the flows in a downstream direction. State actions recommended include 1) providing a continuing forum for interaction among federal agencies and local communItIes, 2) providing technical support for local communities including review of proposed designs for safety, 3) developing structural and flood proofing designs that will be effective in Utah conditions, and 4) interacting with federal agencies on behalf of the local communities. iii ACKNOWLEDGMENTS This project was completed at the Utah Water Research Laboratory with funding provided through its state appropriation (WA33) to study priority problems identified by its Citizen Advisory Council. The authors are also indebted to the support they received from the Utah Division of Water Resources, the Federal Emergency Management Agency, and the 35' Utah communities from which data for the study were col­ lected. iv TABLE OF CONTENTS Chapter Page I THE ROLE OF STATE FLOOD CONTROL PROGRAMS 1 The Flood Control Planning Framework 1 The Floodplain Land Use Context 1 A Focus on Flood Problems in Utah 2 Approaches to Flood Hazard Reduction . 2 Roles of the PrinCipal Flood Control Institutions 2 Role Interaction in the Existing Program 3 Historical Role Development 3 The Federal Influencing Mode 3 State and Local Influencing Modes 5 Guidelines for Formulating a State Program 5 Study Objectives 5 Study Organization 5 II A CONCEPTUAL FRAMEWORK FOR DEFINING A STATE PROGRAM 7 Introduction 7 Components of the Conceptual Framework 7 Initial Conditions 7 The Stimulus 7 Consequences 7 Levels of Impact 8 Dimensions of Impact 8 Loci of Decision Making 9 Alternatives 9 Relevant Information . 10 Guidance for Decision Making 10 Differences Among Decision Loci 11 Limitations in Use of Guidance 11 Differences in Information Used 11 Elements of Perspective . 13 Classification of Conflict Sources 14 Decision Dynamics 14 Overview . 14 Flood Impacts 15 Flood Control Program Impacts 16 Foundations for a Utah Perspective 17 Current State Program. 17 Basis for Long Run Objectives . 18 Perspective for Recognizing Salient Issues 18 Perspective for Flood Program Operation 19 III FLOOD HAZARD IN UTAH 21 Introduction 21 Major Precipitation Events 21 Major Recorded Runoff Events 23 Regional Flood Frequency Studies 24 v -.~. TABLE OF CONTENTS (CONTINUED) Chapter Page Flood Peaks Estimated from Precipitation . 24 Descriptive Information on Historical Floods 25 Hydraulic Analysis . 32 Design Ramifications 33 IV FLOOD CONTROL IN UTAH 35 Introduction. 35 Federal Structural Flood Control Measures 35 U.S. Army Corps of Engineers ... 35 Water and Power Resources Service (Bureau of Reclamation). 36 Soil Conservation Service 36 Program Assessments . .. 36 City and County Structural Flood Control Measures. 40 The National Flood Insurance Program . 40 Program History . 40 Community Requirements and Program Coverage 41 Community Floodplain Management Programs 43 Floodplain Occupancy Choices 52 V SURVEY OF FLOOD PROBLEMS 53 Survey Approach. 53 Sampling Procedure . 53 Information Sought by Community 53 Findings for Counties 56 Box Elder County 56 Cache County . 57 Emery County . 58 Piute County . 59 Uintah County 60 Washington County 61 Findings for Towns and Cities 63 Beaver . 63 Bluff . 63 Bountiful 63 Castle Dale 65 Corinne 66 East Layton 66 Garden City 66 Garland 67 Helper. 67 Hurricane 68 Hyde Park 68 Kamas 69 Kingston 69 Koosharem 69 Midway. 70 Millville 70 Ogden 71 Parowan 73 Pleasant Grove 74 Provo 75 Richmond 76 Sandy 77 Spanish Fork 78 Wales 78 Washington Terrace 79 West Point 79 vi TABLE OF CONTENTS (CONTINUED) Chapter Page Summary of Survey Findings 79 Differences Among Community Types 79 Principal Identified Problems 80 VI ANALYSIS OF FLOOD PROBLEMS 81 Introduction. 81 Classification of Flood Program Problem Types 81 Selection of Communities for Analysis 81 Bountiful . 82 Brigham City 84 Helper 87 Moab 88 Ogden 91 Provo 92 Willard 94 Statement of Problems Identified 96 VII EVALUATION OF PROGRAMS AND RECOMMENDATIONS 97 Introduction. 97 Evaluation of Adequacy of Flood Hazard Information . 97 Evaluation of Effectiveness of Flood Control Activity . 98 Impact Evaluation from a Utah Perspective 99 Recommendations on Potential State Actions 100 Research Recommendations 101 REFERENCES 103 vii LIST OF FIGURES Figure Page 1 Impact dimensions of an implemented action 8 2 Feasibility issues by impact dimension 10 3 Conceptualization of overlapping information sets 12 4 Conflict types associated with various differences in elements of perception 14 5 Location map for record snowpack accumulations (S), precipitation amounts (P), and stream __ al flows (Q) . 22 6 Maximum precipitation recorded in Utah for various durations . 24 7 Normalized Depth-Area-Duration Curve derived by enveloping project cloudburst data (6-hour) 25 8 100-year flows calculated for Utah drainage basins with 20 or more years of record.