Using the Correct Slope in Wave Runup Computations
Lisa Winter, CFM, Coastal Technical Specialist, Michael Baker Jr., Inc.
lwinter@mbakerintl.com, 703-317-6225
The Federal Emergency Management Agency (FEMA) in Region IX has contracted BakerAECOM to
conduct a comprehensive coastal engineering study of the Open Pacific Coast (OPC) of California, which
includes detailed modeling, analyses and mapping of coastal hazards, as part of the California Coastal
Analysis and Mapping Project (CCAMP). The primary coastal flood hazard for much of the California
coastline is wave runup on steep bluffs. FEMA guidance recommends the TAW (Technical Advisory
Committee for Water Retaining Structures) method for computing wave runup on barriers such as steep
dune features, bluffs, and coastal armoring structures.
The TAW method combines wave parameters with key geomorphic parameters, including slope and
barrier toe elevation, to calculate wave runup. Testing of the TAW method on the California coast
revealed that the wave runup and total water level (TWL) results were, in some cases, highly dependent
on the method of slope determination.
The TAW method indicates that the slope be determined iteratively between an elevation at the still water
line minus 1.5 times the wave height at the barrier toe and the runup limit. Because the runup limit is
initially unknown, the first estimate of the average slope is calculated between the points 1.5 times the
wave height at the barrier toe under and above the still water line, ignoring the influence of a berm. On
the Pacific Coast, the selection of the still water line is complicated by static and dynamic wave setup
components which can add significantly to the water surface elevation at the shoreline. Further, the
relation of the water surface elevation to the barrier toe location can impact how much of the foreshore
slope is captured in the average slope computation.
A range of water levels and limits placed on the extent of the foreshore slope were examined in Northern
California to determine an appropriate slope selection to adapt the TAW method to the Pacific coast
environment. An overview of methods, results of sensitivity testing, and a recommended approach will be
presented.
Biography:
Lisa Winter, CFM is a coastal technical specialist with Michael Baker Jr., Inc. involved in the production
and review of coastal engineering analyses and mapping pertaining to FEMA flood insurance studies.
Ms. Winter has over four years of experience working with the National Flood Insurance Program and is
well versed in FEMA’s Coastal Guidelines and Specifications for flood studies on the Atlantic, Gulf, and
Pacific Coasts, particularly in the areas of coastal erosion, overland wave propagations, wave setup,
runup, and overtopping. Previously, Ms. Winter has provided on-site support at FEMA Headquarters
assisting with coastal policy and technical issues as part of FEMA’s Risk MAP program. Ms. Winter
holds a Master of Civil Engineering degree with a coastal engineering focus and a Bachelor of Science
degree in Civil Engineering, both from Johns Hopkins University in Baltimore Maryland.