Flooding is generally a temporary inundation of water onto normally dry land areas by
overflow of water, an unusual rapid accumulation, mudflows, or runoff of surface waters from
any source. Flooding is the most commonly occurring hazard in Utah despite the state being
one of the driest parts of America. It occurs in Utah in many ways. It can be sudden or slow. It
can affect mountain streams or slot canyons many miles from any rainstorm. It can even occur
far from any river or other water body. Understanding the many forms of flooding in Utah is
helpful to guide mitigation measures. Notably, floods in Utah are not only the most common
but also the most expensive hazard.  Of all the natural disasters occurring in Utah, floods
consistently carry the highest price tag year after year. This underscores the critical importance
of comprehensive flood preparedness and mitigation strategies to safeguard both the state's
residents and its economic interests.

Additionally, Utah's unique geographical features contribute to its vulnerability to flooding. The
state's varied topography, including steep canyons and arid plateaus, can lead to rapid runoff
during intense rainfall. Urban areas, with their impervious surfaces, can exacerbate flooding,
creating challenges for drainage systems. Moreover, the proximity of many communities to rivers
and streams further amplifies flood risks. As climate patterns evolve, understanding and
addressing these localized vulnerabilities will become even more crucial for effective flood risk
management in Utah.

Development changes in Utah, such as urbanization, infrastructure development, and
alterations to natural landscapes can contribute to an increased risk of flooding in the state.
Throughout the state, Kane and Washington county have the highest annualized flooding
frequency, followed by Garfield, Wayne, and Grand county. The expansion of urban areas can
lead to increased impervious surfaces like roads and buildings, reducing natural water
absorption. This can result in higher runoff during storms, increasing the risk of flash floods. The
construction of dams, levees, and other infrastructure can influence local hydrology. While these
structures are often designed to manage water flow, improper planning or maintenance can
lead to increased flood risks.

The implementation of sustainable practices and the establishment of resilient infrastructure
are essential measures to reduce the impact of floods and safeguard Utah communities form
potential consequences arising from extreme weather events. Local authorities and
environmental agencies frequently assume pivotal roles in enforcing regulations aimed at
mitigating flood risks associated with development.

The counties experiencing the most development pressures in the state all participate in the
NFIP, requiring adherence to floodplain management regulations. Despite the pressures from
population growth and increased development being felt in many counties, the overall flood
risk should not be increasing, assuming local floodplain regulations and standards are being
effectively implemented and local mitigation measures to curb stormwater runoff are taking
place. An analysis of development trends in LHMPs (see Section 3.7 Development Trends and
Table 3-3 specifically) did yield some concerns with flooding, notably in Emery, Toole, Weber
counties. The southwestern counties of Beaver, Garfield, Iron, Kane, and Washington also noted
expanding development potentially raising risk with flooding. Grand County noted a top priority
was to create more open space in 100-year and geologic hazard areas. Urbanization
contributing to more runoff was also noted in some of the rapidly growing counties along the
Wasatch Front.

However, significant flood losses often occur outside of mapped flood hazard areas, accounting
for approximately 40% of NFIP flood insurance claims. Rural areas often have outdated flood
hazard mapping or none at all, making floodplain management and risk determination more
challenging. More extensive and improved flood hazard mapping should improve flood risk
determinations to existing and future development over time, though the areas experiencing
the most growth are mapped. Given long-term climate trends including the potential for more
extreme precipitation events that could exceed mapped flood hazard areas, coupled with
increased development and increased runoff associated with urbanization, flood risk may still
increase despite efforts to reduce this risk.