86Th Legislative Session State Flood Assessment Report to the 86Th Texas Legislature
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State Flood Assessment REPORT TO THE LEGISLATURE 86TH LEGISLATIVE SESSION State Flood Assessment Report to the 86th Texas Legislature Peter M. Lake, Chairman Kathleen Jackson, Member Brooke T. Paup, Member Jeff Walker, Executive Administrator January 2019 www.texasfloodassessment.com www.twdb.texas.gov Table of Contents Executive summary . 2 1 Introduction ������������������������������������������������������������������������������������������������������������������������������� 4 2 Texas floods . 7 2.1 Types of floods ����������������������������������������������������������������������������������������������������������������� 7 2.2 Precipitation influences ����������������������������������������������������������������������������������������������������� 8 2.3 Geography of floods . 9 2.4 Benefits of floods . 11 3 Flood risk ��������������������������������������������������������������������������������������������������������������������������������� 12 3.1 Flood risk to Texans . 12 3.2 Flood risk to the economy ����������������������������������������������������������������������������������������������� 14 3.3 Future risk . 15 3.4 Awareness in Texas ��������������������������������������������������������������������������������������������������������� 15 4 Floodplain management and mapping ������������������������������������������������������������������������������� 16 4.1 What is a floodplain? ����������������������������������������������������������������������������������������������������� 16 4.2 Mapping a floodplain ����������������������������������������������������������������������������������������������������� 16 4.3 Mapping the regulatory floodplain ����������������������������������������������������������������������������������� 18 4.4 Mapping needs in Texas . 20 5 Planning for floods ����������������������������������������������������������������������������������������������������������������� 22 5.1 Current planning efforts in Texas . 22 5.2 Approaches used in other states . 25 5.3 Elements of sound planning . 27 6 Flood mitigation in Texas ������������������������������������������������������������������������������������������������������� 29 6.1 Types of flood mitigation activities . 29 6.2 Cost of mitigation . 31 6.2.1 Anticipated mitigation costs ��������������������������������������������������������������������������������� 32 6.2.2 Available mitigation funding . 32 6.2.3 Mitigation funding shortfall ��������������������������������������������������������������������������������� 33 6.3 Funding sources ������������������������������������������������������������������������������������������������������������ 34 6.3.1 Local funding ���������������������������������������������������������������������������������������������������� 34 6.3.2 State and federal funding . 35 7 Roles and other considerations ��������������������������������������������������������������������������������������������� 37 1 7. Responsibilities for flood mitigation . 37 2 7. Barriers to implementation . 40 3 7. Synergies with water supply ��������������������������������������������������������������������������������������������� 42 8 Preliminary findings and stakeholder priorities . 43 8.1 Preliminary findings . 43 8.2 Limitations and uncertainties in estimating costs . 43 8.3 Stakeholder priorities . 44 8.4 Impact of doing nothing ������������������������������������������������������������������������������������������������� 47 8.5 Benefits of acting now ����������������������������������������������������������������������������������������������������� 47 8.6 Laying a foundation with science and data ����������������������������������������������������������������������� 47 9 Recommendations to the 86th Texas Legislature ��������������������������������������������������������������� 48 9.1 Background ������������������������������������������������������������������������������������������������������������������� 48 9.2 Specific flood recommendations and further background ��������������������������������������������������� 48 References . 51 State Flood Assessment | Texas Water Development Board 1 Executive summary Though Texas has experienced organized according to three key Emergency Management Agency flooding throughout its history, pillars of comprehensive flood (FEMA) to establish insurance losses of life and property in risk management: (1) mapping, rates, these maps currently are recent years—from the 2015 (2) planning, and (3) mitigation. the state’s most utilized tool for Memorial Day Flood in Wimber- assessing flood risk. Based on ley to Hurricane Harvey along Flood risks, impacts, and FEMA data and the State of Texas the Gulf Coast region in 2017— mitigation costs have nev- Hazard Mitigation Plan, roughly 1 highlight the state’s vulnerabilities. er been assessed at the in every 10 Texans is exposed to These disasters, along with six oth- statewide level. Texas has a moderate or high risk of riverine er federally declared flood decla- long and storied history of flood flooding each year; coastal flood- rations since 2015, call attention to events, but until this effort by the ing is projected to become the the need for a clearer understand- Texas Water Development Board costliest weather-related hazard ing of flooding in Texas, from the (TWDB), the state’s risks and to the state; and more than half events themselves to the resources needs have not been evaluated. of recent flood insurance claims needed to mitigate them. For the foundation of this as- occurred outside of areas identi- sessment, we conducted surveys, fied as high-risk flood zones. This report provides an initial workshops, and meetings with assessment of Texas’ flood risks, stakeholders across the state, the Much of Texas is either un- an overview of roles and respon- results of which, both quantita- mapped or uses out-of-date sibilities, an estimate of flood tive and qualitative, are integral maps, leading to wide- mitigation costs, and a synopsis to better preparing for future spread confusion. Mapping of stakeholder views on the future Texas floods. is the first step in identifying and of flood planning. It does not communicating flood risk. FEMA’s seek to fund specific strategies or Flood risks pose a serious flood insurance rate maps show projects related to flood planning, threat to lives and live- the boundary of inundation for mitigation, warning, or recovery. lihoods. Most communities the 1 percent annual chance Preliminary findings summarized in Texas use Flood Insurance flood event—commonly referred in this assessment are derived Rate Maps (FIRMs) to commu- to as the 100-year flood and from stakeholder input and nicate local flood risk. Created often misinterpreted as the line and maintained by the Federal 2 Texas Water Development Board | State Flood Assessment between safe and not safe. How- impacts in upstream or down- assistance for implementation of ever, these maps may not reflect stream communities. Stakeholders flood mitigation activities; (2) im- flood conditions based on the expressed a preference for locally provements to flood risk mapping most current topographic, land led flood planning at a watershed and modeling; and (3) a prefer- use, or rainfall data. Creating scale. This sentiment is consis- ence for collaborative, locally led, flood risk maps using the most tent with stakeholder calls for watershed-based flood planning. recently collected scientific data increased collaboration, coordi- In addition, the TWDB heard and models for all watersheds in nation, and leadership among all a call to expand educational the state could cost up to $604 entities with flood responsibilities. outreach and technical assistance million. Stakeholders prioritized Watershed-based planning seeks opportunities throughout the up-to-date flood risk mapping, to identify multi-benefit solutions state. These priorities emerged including collection and distri- to common flooding problems from myriad suggestions and bution of supporting data and and to bring about efficiency in reflect areas of broad consensus addressing local drainage issues. implementing projects. among stakeholders. Rainfall drives most flood Significant funding is re- Sound science and data events in Texas, but rainfall quired to mitigate flooding are the core elements of data used to inform planning in Texas. Though the responsi- effective planning and flood and design are decades old. bility to prepare for and mitigate mitigation. Through support An updated version of the rainfall flood impacts is primarily local, from the Office of the Governor depth-duration-frequency data most communities do not have and the Texas Legislature, the (Atlas 14, Volume 11) used to the economic resources required TWDB has implemented new model and predict how frequently to accomplish their goals. Stake- initiatives in recent years to a specific flood event might reoc- holders engaged with this assess- better prepare the state for flood cur was published in September ment cited funding to support events. To continue expanding 2018. The data showed that in implementation of mitigation proj- these efforts and to improve areas with significant increases in ects as their greatest need. Antic- data collection, mapping, estimated rainfall, flood risks are ipated statewide flood mitigation and monitoring of conditions likely to be greater than previously costs over the next 10 years are across the state, the agency has thought. However, new analyses estimated to be