Water Resources Modeling in the Mobile River Watershed and Mobile Bay

ABSTRACTThis poster shows detailed results and methodologies on the application of spatial modeling techniques and high performance computing in modeling and simulation of hydrology, hydrodynamics and water quality in water bodies of the Mississippi and Alabama region. Results are presented on the assimilation of MODIS land use datasets into the Hydrological Simulation Program Fortran (HSPF), for hydrologic modeling of the Town Creek watershed and further estimation of nutrient concentrations for selected sub-basins within the watershed. Hydrodynamic modeling approaches (using the parallelized version of the Adaptive Hydraulics system) for the Mobile estuary and surrounding ocean waters are also shown. This research is encompassed within the objectives the NGI project: Spatial Technology and High Performance Computing for Improving Prediction of Surface Water Quality .

BACKGROUNDSurface water quality and hydrodynamic models such as the Hydrological Program Fortran (HSPF), the Adaptive Hydraulic system (ADH), and the environmental Fluid Dynamic Code (EFDC), routinely used by various agencies for water resources modeling, were applied to model hydrology, water quality, and hydrodynamics of water bodies and watersheds in the project area. MODIS Land use datasets and USGS Digital Elevation Models were geo-processed to characterize inland watersheds.

The Hydrologic Simulation Program – FORTRAN (HSPF) model computes the movement of water through a complete hydrologic cycle – rainfall, evapotranspiration, runoff, infiltration, and flow through the ground – and the associated transport of constituents with that flow

ADH is a state-of-the-art ADaptive Hydraulics Modeling system developed by the Coastal and Hydraulics Laboratory, ERDC, USACE, and is capable of handling both saturated and unsaturated groundwater, overland flow, three-dimensional Navier-Stokes flow, and two- or three-dimensional shallow water problems. ADH contains other essential features such as wetting and drying, completely coupled sediment transport, and wind effects. ADH can run in parallel or on a single processor and runs on both Windows systems and UNIX based systems.

The Environmental Fluid Dynamics Computer Code (EFDC) can simulate water and water quality constituent transport in geometrically and dynamically complex water bodies, such as vertically mixed shallow estuaries, lakes, and coastal areas. The EFDC model solves the three-dimensional, vertically hydrostatic, free surface, turbulent averaged equations of motion for a variable density fluid. The model uses a stretched, or sigma, vertical coordinate and Cartesian, or curvilinear, orthogonal horizontal coordinates. Dynamically coupled transport equations for turbulent kinetic energy, turbulent length scale, salinity and temperature are also solved.

Vladimir J. Alarcon, William H. McAnally, John Cartwright, and Rita Jackson

Geosystems Research Institute, Mississippi State University

METHODS

HYDROLOGIC MODELING

Creation of a seamless topographical data of the project area

USGS DEM data (300 m resolution) were downloaded per Hydrological Unit Code covering all the project area.

A topographical mosaic was created using ArcGIS 9.2. Since standard “mosaicking” methods produced areas with

NODATA grid cell values, ArcInfo (GRID) was used to fill those grid cells (con, focalmax, and focalmean commands were used.)

NASA MODIS land use geo-processing Two land use datasets were used in this study : USGS GIRAS

(1986), and NASA MODIS MOD12Q1 (2001-2003). The MODIS data used this research were initially converted to .tiff

format and re-projected to geographical coordinates. Then, ArcGiswas used to re-project the datasets to UTM coordinates and also to the more common GRID dataset format. This new format allowed a re-classification from the 21 IBEP MODIS land use categories to the USGS-GIRAS-HSPF categories

For additional information please contact:Vladimir J. Alarconalarcon@gri.msstate.eduGeosystems Research InstituteMississippi State University

METHODS (continued)HYDROLOGIC MODELINGUsing the topographical and land use datasets, plus the location of

biologically relevant sampling sites, the Upper Tombigbee watershed was delineated and, subsequently, an HSPF model for the watershed was generated.

Two resulting hydrological models (one using MODIS datasets and the other using GIRAS) were calibrated against measured stream flow.

Export coefficients for Total Nitrogen and Total Phosphorus were used to estimate TN and TP concentrations at selected sites within the watershed.

Seamless DEM

RESULTSA comparison of nutrient concentration values for sub-basins 43,

51, and 54 (common sub-basin among the GIRAS and MODIS analyses) showed that average and 3rd-quartile total phosphorus (TP) concentrations do not differ greatly when using either land use dataset. Only maximum concentrations showed to have increased from 6% to 16%. Similarly, only maximum total nitrogen (TN) concentrations were found to have increased when using MODIS land use data (with respect to TN concentrations estimated using GIRAS land use data). Percent increments in TN concentration values are in-between 5% to 15%. When taking into account all sub-basins, average and maximum TP and TN concentration values were not noticeably different.

However, maximum TP and TN concentrations seem to have increased in about 37 % and 34%, respectively, from 1986 to 2003. This increase in maximum nutrient concentrations seems to correlate with the 34% increase in agricultural areas in the Upper Tombigbee watershed, from 1986 to 2003.

HYDRODYNAMIC MODELING Several configurations of structured computational meshes for the

Environmental Fluid Dynamics Code (EFDC) have been generated for comparison with existing ADaptive Hydraulics (ADH) models of water bodies in the project area.

Weeksbay

Mobile Bay and surrounding ocean

ArcGIS

Used to obtain a DEM mosaic covering the project area

ArcInfo

NODATA grid cells are eliminated using zonal

statistics

Mosaic DEM

Seamless DEMHYDROLOGY

HSPFHYDRODYNAMICS

ADH, EFDC

OBJECTIVEHydrological modeling: or purposes of connecting hydrological

processes to biological system response studies in the Upper Tombigbee watershed (Mississippi-Alabama, USA), a hydrological model of the watershed was developed. The model provides stream flow, runoff, and nutrient concentrations to establish relationships between stream nutrients, runoff and discharge, and biotic data.

Hydrodynamic modeling: develop EFDC applications for comparison of EFDC hydrodynamic estimations to output of existing ADH hydrodynamic models.

Study areas

Upper Tombigbee watershed

Mobile bay and Weeksbay

•MODIS LU/LC

•Format: HDF ISIN

coordinates

•FORMAT CONVERSION•MODIS tools: HDF to GeoTiff

•Re-projection: ISIN to Geo Coordinates

•FORMAT CONVERSION

ArcGis: Geotiff to Grid

•RE-PROJECTION•ArcGis: Geo. Coord. to UTM

•RECLASSIFICATION•ArcGis: MODIS LU classes to HSPF LU

classes

•DELINEATED WATERSHED

polygon shape User’s coordinates User-

provided

•TO MODELS•Land use characterization

tables•ASCII

•Land use characterization tables•DBF

GIRAS GIRAS

MODIS MODIS

HYDRODYNAMIC MODELING Coastline and bathymetric datasets from NOAA were used to

generate curvilinear grids for input into the EFDC model. A structured grid generator (UNAMALLA) was used for

generating the structured computational meshes.

•NOAA-NGDC coastline•NOAA-NGDC bathymetry

STRUCTURED GRID GENERATOR UNAMALLA

COMPUTATIONAL MESH

Land use category Average TP Average TN

Row Crops 4.46 16.09

Non Row Crops 1.08 5.19

Forested 0.236 2.86

Urban 1.91 9.97

Pasture 1.5 8.65

Feedlot/Manure Storage 300.7 3110.7

Mixed Agriculture 1.134 16.53

Export Coefficients in Kg/Ha/Year

HYDROLOGIC MODELING From 1986 (GIRAS ) to 2003

(MODIS) agricultural lands increased in almost 34%, forest lands decreased in 16% and range-land almost quadruple in size.

RESULTS

GIRAS MODIS

GIRAS MODIS

Unstructured grid for ADH Structured grid for EFDC

Unstructured grid for ADH Structured grid for EFDC