Hydraulics/Hydrology Seminar Series
Understanding the role of surface-groundwater interactions in explaining river-floodplain hydrodynamics
Wednesday, April 27, 2016
Majority of the flood inundation maps in the United States are created for 100-year design flow using 1D hydraulic models that do not account for groundwater conditions, floodplain storage and antecedent soil moisture conditions. The problem with the existing flood risk models is the lack of linkage between traditional hydrology, surface water (SW) hydraulics and groundwater (GW) contributions. There are fairly accurate models available for individually modeling each of these physical phenomenon, however, these models do not account for relative impacts between these physical domains. Saturated conditions in sub-surface and floodplain can lead to more severe inundation from low intensity but continuous flood events. The spatial variability of rainfall events also impacts the flood inundation since high intensity events upstream of a reach may change the surface-groundwater dynamics of the region. To understand the effect of sub-surface and floodplain storage, this study combines hydraulic, hydrologic and groundwater modeling approaches for creating flood inundation maps. The application of these modeling procedures depends heavily on the use of open source datasets such as digital elevation models (DEM), soil datasets, stream gauge data and land use data.
The methodology involves creating a large scale surface water model for the Upper Wabash River basin using ICPR (a 2D integrated SW-GW model) and comparing the effect of different rainfall intensity events on the overall floodplain dynamics by obtaining stage-duration and flow-duration relationships for multiple locations within the floodplain. The second step involves coupling this surface water model with a 2D groundwater model and varying the initial water table conditions before the storm events and comparing the floodplain inundation outputs for different rainfall events. The results show both rainfall intensity and existing GW conditions significantly impact the flood depths and floodplain storage.
Siddharth Saksena is a PhD student working with Prof. Venkatesh Merwade. He graduated with a Masters from Purdue University in 2014 and his masters’ research was also focused on developing techniques to improve flood inundation mapping. Siddharth obtained his Bachelors in Civil Engineering from IIT Roorkee, India. He’s the only engineer in a family of doctors as both his parents and his fiancée are in the medical profession.