Bow Basin Flood Mitigation and Watershed Management Project March 31, 2014 Disclaimer AI-EES and Her Majesty the Queen in right of Alberta make no warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information contained in this publication, nor that use thereof infringe on privately owned rights. The views and opinions of the author expressed herein do not necessarily reflect those of AI-EES or Her Majesty the Queen in right of Alberta. The directors, officers, employees, agents and consultants of AI-EES and the Government of Alberta are exempted, excluded and absolved from all liability for damage or injury, howsoever caused, to any person in connection with or arising out of the use by that person for any purpose of this publication or its contents. Further, the list of individuals and the organization they represented, which appears in Appendix A, reflects those who participated in some or all of the working group meetings for this project. Their inclusion on this list does not suggest advocacy for any particular strategy discussed, but rather provides a sense to the reader of the range of perspectives involved in the working group discussions. Bow Basin Flood Mitigation and Watershed Management Project Contents ABBREVIATIONS, ACRONYMS, AND DEFINITIONS ......................................................................... II 1 EXECUTIVE SUMMARY ........................................................................................................... 1 2 INTRODUCTION ....................................................................................................................... 5 3 PROJECT OBJECTIVES AND SCOPE ........................................................................................ 8 4 METHODOLOGY ................................................................................................................... 10 4.1 A Collaborative Approach ............................................................................................. 10 4.2 Project Tools and Technologies ..................................................................................... 10 4.2.1 The Bow River Operational Model (BROM) ..................................................................... 10 4.2.2 Flood Visualization Engine ................................................................................................. 13 4.3 Assessing Potential Flood Mitigation Options: What Are We Mitigating To? ............. 16 5 FLOOD MITIGATION APPROACHES...................................................................................... 17 Relocation ................................................................................................................................. 18 Dry dams ................................................................................................................................... 18 Diversions and channelization .................................................................................................. 21 Wetland storage ........................................................................................................................ 22 Natural river functions .............................................................................................................. 23 Change existing reservoir operations ........................................................................................ 25 Land management ..................................................................................................................... 26 6 FLOOD MITIGATION OPTIONS FOR THE BOW BASIN .......................................................... 27 6.1 Bow River System .......................................................................................................... 27 6.2 Elbow River System ....................................................................................................... 28 6.3 Highwood and Sheep River Systems ............................................................................. 29 6.4 Combinations ................................................................................................................. 31 6.5 Other Options ................................................................................................................. 31 7 MODELLING RESULTS .......................................................................................................... 32 7.1 Bow River System .......................................................................................................... 32 7.2 Elbow River System ....................................................................................................... 55 7.3 Highwood and Sheep River Systems ............................................................................. 73 7.4 Natural Mitigation Options for the Bow Basin .............................................................. 87 8 REACHING MITIGATION TARGETS: MITIGATION COMBINATIONS .................................... 92 8.1 What can be done for 2014? ........................................................................................... 93 8.2 What can be done for 2015? ........................................................................................... 98 8.3 Mitigation Target Scenarios ......................................................................................... 102 8.4 Mitigation Target Scenario 1........................................................................................ 103 8.5 Mitigation Target Scenario 2........................................................................................ 107 8.6 Mitigation Target Scenario 3........................................................................................ 112 9 KEY MESSAGES .................................................................................................................. 116 APPENDIX A: PROJECT PARTICIPANTS .................................................................................. 119 Bow Basin Flood Mitigation and Watershed Management Project i Abbreviations, Acronyms, and Definitions (A)ESRD (Alberta) Environment and Sustainable Resource Development BRBC Bow River Basin Council BRID Bow River Irrigation District BROM Bow River Operational Model CBRH Carseland-Bow River Headworks cdm cubic decametre (1 cdm = 1,000 cubic metres) cms cubic metres per second DUC Ducks Unlimited Canada EID Eastern Irrigation District GIS Geographic Information System(s) GoA Government of Alberta NHN National Hydrography Network SSRB South Saskatchewan River Basin. The South Saskatchewan River Basin includes the sub-basins of the Bow River, Red Deer River, and South Saskatchewan River (including the Oldman and other tributaries) SSRP South Saskatchewan Regional Plan SWCRR South West Calgary Ring Road WRMM Water Resources Management Model Flood fringe* The portion of the flood hazard area outside the floodway. Water in the flood fringe is generally shallower and flows more slowly than in the floodway. New development in the flood fringe may be permitted in some communities and should be flood-proofed. Flood plain The active river valley that can be occupied by streamflow. Typically relatively flat areas of varying width constructed by alluvial processes and over bank deposition from previous flood events. Hydrologically, a flood occurs when streamflow exceeds channel capacity, and water enters the flood plain. Floodway* The portion of the flood hazard area where flows are deepest, fastest and most destructive. The floodway typically includes the main channel of a stream and a portion of the adjacent overbank area. The floodway is required to convey the design flood. New development is discouraged in the floodway and may not be permitted in some communities. * Definitions from Government of Alberta. Bow Basin Flood Mitigation and Watershed Management Project ii 1 Executive Summary Severe flood and drought conditions have occurred in Alberta throughout living memory, history and prehistory. Although droughts have been more common, floods are not rare. The events in June 2013 caused loss of life and devastated homes, businesses, property, infrastructure, and landscapes. Following emergency responses by various authorities and volunteer agencies, the Government of Alberta established the Flood Recovery Task Force to explore and recommend options for responding to future such events. This project was designed to identify, examine and assess the intended and unintended consequences and trade-offs of potential flood mitigation options for the Bow River Basin from a “headwaters to confluence” river system perspective, and to make flood mitigation and resiliency recommendations to the Task Force. The enormous scale, scope, and impact of the 2013 flood were such that many of the mitigation alternatives proposed so far are similarly large and impactful. Most of the options presented in this report have significant costs and carry environmental, social, or economic consequences. No one option is able to meet all needs. The choice of levels of protection in each affected area is a matter of social policy to be decided by elected officials. Once targets are set, the necessary suite of flood mitigation options can be identified and implemented to achieve the target, given the broad range of potential future flood events. Chapter 8 of this report describes three hypothetical target flow rates set by the participants as potential starting