Flow Anisotropy in the Red River Alluvial Aquifer Caddo Parish, Louisiana By: John Hubbard CE 394K

Problem Can ArcView be used effectively to map the potentiometric surface in an anisotropic aquifer? Can flow direction be determined using spatial analyst?

Study Area

Aquifers of Louisiana

Red River Alluvium Covers 2,120 sq. Miles of Louisiana Composed of medium to fine-grained sand and silt. Silt acts as retarding units with-in the alluvium

Wells Data from 69 USGS observation wells were obtained Dates after 1990 were thrown out due to the construction of lock-and-dam. 1980 was selected as an average year with the most data available leaving 38 wells to be mapped

Well Data The high, low elevations of the head in each well were sorted The mean annual head elevation was calculated

Longitude and Latitude Data about each well was obtained from the Louisiana Department of Transportation and Development Longitude and Latitude were sorted in Excel and converted to decimal degrees

Plotting Well Data The Elevation Table and Long/Lat Table were added to ArcView and joined by well number The newly joined elevation table mapped using “Add Event Theme” A decrease in head elevation can be seen from north to south

Spatial Analyst The spatial analyst extension was then loaded and the “surface/interpolate grid” function was used This produces a potentiometric map However, this map shows no reference to the river or the edge of the alluvium

Spatial Analyst 2 The spatial Analyst was run again, however, this time the NHD file 11140202.shp, was placed as a barrier Again, this produces another potentiometric map

More Spatial Analyst The Spatial Analyst was then used to calculate the the aspect of the potentiometric surface to approximate flow direction

Issues and Problems Lack of data No western border River stage was not included Aspect does not account for anisotropy