Case Studies

Environmental Homeland Security
Herndon, VA - January 2002

Contributed by: Sorab Panday, Ph.D. Director of Research & Development Don DeMarco, Project Hydrogeologist HydroGeoLogic, Inc.

Simulation and Animation Technology for Addressing Environmental Homeland Security Concerns

ASSERT technology, Advanced simulation to assess the Status and Security of the Environment in Real-Time, was proposed to meet specific Environmental Protection Agency (EPA) water quality objectives, achieve specific U.S. Navy real-time forecasting objectives, and attain national goals to develop forecasting technology to support homeland security.

The plot of the month features results from a rigorous, mass conservative, fully-coupled simulation of surface water and groundwater with chemical transport on the Mobile and connected rivers, estuaries, bays and aquifers in Alabama.

Notable features of the simulation results include:

1. A contaminant release in the surface water and groundwater systems upstream of Mobile Bay.
2. Pollutants are carried downstream in the river and in the subsurface aquifers.
3. A simulated storm causes overland runoff, drastic river fluctuations and flooding.

The pollutants are spread into Mobile Bay and onto the land surface where the river banks overflow.

Environmental problems that require quantification of the entire hydrologic cycle, such as those listed on the left, have received increased attention recently. This awareness has grown as water management practices have evolved in response to population growth and improved technologies.

Problems involving simulation of the complete hydrologic cycle have previously presented significant modeling challenges, primarily because of either model or computational limitations. Earlier models quantified individual hydrologic components using simplified procedures that dangerously compromised details of the flow physics (e.g., unit hydrograph, empirical formulas). Furthermore, models based on complex multidimensional governing equations had not received much attention because of their computational, distributed input and parameter estimation requirements.

Today with the availability of powerful personal computers, efficient computational methods and sophisticated Geographic Information Systems (GIS), remote sensing and advanced visualisation tools such as Tecplot, the hydrologic community is realising the tremendous potential and utility of physically based numerical simulators.

TIntense simulated rainfall causes the Mobile river to flood its banks and spread polluted water across the floodplain. Surface-water and groundwater models such as this are used in support of environmental restoration, water resource assessment and management, human health and ecological risks evaluation, and contaminant hydrogeology.

Recognising the increasing impetus for numerical simulation of complex groundwater-surface water interactions, HydroGeoLogic, Inc. was motivated by the challenge to develop a state-of-the-art, comprehensive, physically-based spatially-distributed model that overcomes both the functional and computational limitations of previous models.

The result of HydroGeoLogic's efforts was the development of MOD-HMS (MODFLOW-Hydrologic Modeling System). MOD-HMS integrates all components of the hydrologic cycle in a single model, that utilises a rigorous, mass conservative modeling approach having fully coupled the surface water flow equations with the 3-D, variably saturated groundwater flow equations. This approach is significantly more robust than previous conjunctive approaches that rely on linkage of separate surface water and groundwater codes. The fully implicit coupling approach used by MOD-HMS provides for a mass conserved solution scheme essential for systems with strong interactions between regimes. MOD-HMS has additional capability for contaminant transport.

MOD-HMS system conceptualisation.

The Mobile Bay project was contracted by the EPA to demonstrate the utility of MOD-HMS as a forecasting tool in support of Homeland Security. ASSERT is a collaborative effort between HydroGeoLogic, Inc., HydroQual and Los Alamos National Laboratories.

Current and future benefits of ASSERT include:

• Evaluation of human-health and ecological risks.
• Improved short- and long-term forecasting of coastal conditions.
• More accurate simulation of environmental quality using a comprehensive, physically based modeling approach.
• Ability to predict the impacts of a wide range of potential environmental security threats.
• Applicability in strategic planning, preparedness assessment, and development of emergency response measures.

Tecplot and advanced visualisation capabilities are critical components of ASSERT technology. Images and animations help conceptualise the problem and results, and there is often the need to display several integrated sets of data simultaneously (for example, contaminant concentrations, surface elevations, rainfall, river fluxes, river depths, hydraulic head contours). Tecplot allows HydroGeoLogic to do this efficiently.

For more information on HydroGeoLogic, Inc. or the capabilities of MOD-HMS, please contact Sorab Panday or Don DeMarco.

Supplemental Information Below

The data for the Mobile Bay animation consists of the following:

• Digital elevation model of the topography - downloaded from EPA GIS sources.
• Bathymetric data defining Mobile Bay contours - downloaded from National Oceanic and Atmospheric Administration data sources.
• Precipitation data - storm event based on historical data provided by our client.
• Solute concentrations - a hypothetical scenario devised to predict the affect of a toxic pollutant discharge into the Mobile River.

Integrated finite-difference discretisation of hydrologic system.

The GIS data was downloaded and processed using HydroGeoLogic's ArcView GIS Interface (AGI). AGI handles spatial data analysis and visualisation of the surface water domain, as well as preparing input files for MOD-HMS. The Tecplot layout consists of ten separate frames containing data. These frames include:

• Six frames showing contoured river concentration data. The data for each river was brought into Tecplot on a quadrilateral based FE-Point grid. HGL wrote a utility to convert the MOD-HMS river output onto a quadrilateral mesh for this purpose. A macro was utilised to re-import new data for all rivers at once when required. Tecplot's flexibility enabled HGL to import each river individually. Contamination contour colors were obtained using a contour color overrides.
• A rectangular based FD-Block mesh for the DEM topography. The continuous color distribution method when used in conjunction with lighting sone effects produced the 3-D effect they were looking for.
• A rectangular based FD-Block mesh for contaminant concentrations excluding rivers. The banded color distribution method provided a nice contrast to the continuous topography contours.
• The time was imported into a separate frame.
• A 2-D plot of river fluxes and precipitation were on a separate frame.
• The flashing arrows and drum of contamination draw attention to the source area. These were achieved using a loop within a macro, whereby colors changes depending on the loop variable.

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