Watershed

Oral

398412 - Combined Occurrence of Storm Surge and Rainfall Runoff- Challenges and Options

Wednesday, June 6
8:30 AM - 10:00 AM
Location: Greenway IJ
Co-Authors: Brian Batten, Richmond – Dewberry; Seth Lawler, Fairfax – Dewberry

Major coastal storms originating in the Gulf of Mexico and the Atlantic Ocean often bring significant precipitation inland, creating the possibility for coincident peak stream discharges and elevated coastal flood water levels. Federal and State agencies, including the Federal Emergency Management Agency (FEMA), US Army Corps of Engineers (USACE), and Federal Highway Administration, State Departments of Transportation have come up with guidance to caution water resources and coastal engineers to be aware of this issue in their design. However, in practice, the two hazards have predominately been treated independently, with existing analysis methods that are either too complex or produce counterintuitive results. Events such as Hurricane Floyd (1999) and Hurricane Sandy (2012) have highlighted the need to improve the analysis of coincident surge and rainfall-runoff.
This presentation identifies key physical processes and provides recommended methodologies to estimate frequency flood elevations along tidal reaches of streams. We have selected four approaches which can be applied to tidal stream reaches along the Atlantic and Gulf coasts as well as the Great Lakes.
1. Simulation of observed coastal and inland rain events,
2. Simulation of inland flood elevations of hypothetical rainfall events and coastal storms
3. Joint probability analysis using coastal stages of known exceedance probability - an extension of USACE’s EM 1110-2-1413, and
4. Joint probability analysis based adjusted tide water levels for design storm rainfalls.
Although recommendations focus on approaches most suitable for the eastern part of the contiguous US, the methodologies can be applied elsewhere.

Mathini Paragnana Sreetharan, PdD, PE

Senior Engineer, Associate
Dewberry Fairfax Va

Mathini Sreetharan, Ph.D., P.E., CFM

Dr. Sreetharan has 30 years experience in watershed and floodplain modeling. She is a Senior Engineer at Dewberry and attached to its Fairfax office. She has developed and reviewed flood studies for the Federal Emergency Management Agency’s National flood Insurance Program. Ms. Sreetharan holds a B.S. in Civil Engineering from University of Peradeniya, Sri Lanka and Ph.D. in Civil Engineering from Hertfordshire University in England. She is a Professional Engineer and has been a Certified Floodplain Manager since 2002.

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