hec-ras flood modeling little river basin with animation slides

EVALUATING SEA LEVEL RISE AND CLIMATE CHANGE ON FLOODINGCase study: Little River basin, Newburyport, MAPrepared by: River Hydraulics, January 2017

Determine potential flood impacts associated with:

1. sea level rise;2. climate change;3. altering watershed infrastructure.

Problem statement

Opportunity New: HEC-RAS 2-dimensional unsteady flow

“bare earth” LiDAR terrain, free, accuracy in inches

Seamlessly combine LiDAR terrain with surveyed channel bathymetry

HEC-RAS modeling of river and tidal flows throughout a flood event

HEC-RAS automated floodplain delineation on aerial or topo maps

HEC-RAS evaluation of changes associated with culvert and bridge modifications

HEC-Hydrologic Modeling System (HEC-HMS)

Rainfall-runoff modeling for model calibration and determination of flood flow frequencies

Historic precipitation modified to reflect impacts of climate change

Drainage areas, runoff curve numbers, and times of concentration determined using Quantum GIS

The next four slides were produced by River Hydraulics using Quantum Geographical Information System (QGIS)

HEC-RAS model

cell size of 250’ x 250’ selected (large size OK with slope of water surface changes slowly)

Finer mesh with smaller cells along road and railroad embankments

Culverts modeled

One single 2D flow area

Overbank terrain from LiDAR seamlessly merged with previously-surveyed channel bathymetry

Calibration using Mothers Day flood of May 2006 (15” rain over 4 days)

HEC-RAS model parameters

Next Steps

Calibration of HEC-RAS Model

Determine flood boundaries, depths, velocities for various flood frequencies or events using HEC-RAS

• Determine impacts of proposed changes at culverts and bridges to upstream and downstream areas using HEC-RAS