GIS and Landscape Archaeology along the Anacostia River Geoarchaeological Study of Joint Base Anacostia-Bolling

Outline Background Approach Analysis Field Refinement

Background Joint Base Anacostia-Bolling (JBAB) wanted to evaluate the potential for buried archaeological landscapes throughout JBAB as current survey coverage is incomplete. Many areas have been covered at varying depths. In order to correctly survey these areas to determine if cultural resources exist, a model for new fill depths was needed.

Background Large areas of JBAB can be excluded because they consist entirely of made land: these include virtually all of the Anacostia Annex property as well as a band along the Potomac River shoreline however this area was not well defined.

Approach Marstel-Day created a 3-D terrain model of the Anacostia River shoreline based on maps from 1888 and performed 3D geospatial analyses to determine fill depths of current Anacostia Shoreline. Once completed, Louis-Berger and Geo-Sci Consultants modified the vertical adjustment based on field measurements

Analysis: Georeference and Digitize Maps from 1888 were Georeferenced and contours were digitized. Team used ArcScan to quickly generate a preliminary contour layer. Contours were further refined by hand.

Analysis: Datum Shift After the contours were digitized the team applied a datum shift to the 1888 elevation values to account for changes in how elevation values were calculated between 1888 and current elevation data. Datum shift was to account for changes in how elevation values were recorded in 1888 and today. Value was provided by Louis-Berger based on work completed previously in the region.

Geospatial Analysis Modified Elevation values in 1888 were subtracted from current values determine the minimum dig depths for future cultural surveys completed at JBAB

Model Refinement Maps were originally georeferenced using features believed to be consistent between 1888 and today Railroad Streets This proved to be inaccurate as: Manmade features may have been moved since 1888 The cartographic production accuracy in 1888 may have been poor This initial georeferencing produced an erroneous product

Model Refinement When analysis to determine the change in elevation was conducted, values stated areas with no significant change (areas of dense vegetation and High slope) had value changes of more than 50 feet.

3D Visualization When visualized in 3D the error in georeferencing is obvious Current Elevation Current Elevation and Historical Elevation Overlaid Historical Elevation

Model Refinement The team found that many terrain features were generally the same in both the model from 1888 and the current terrain model These features were used to refine the georeferencing model The new model was deemed sufficient to determine the soil fill depths 1888 Elevation Model Current Elevation Model

Final Analysis output The new raster difference map depicted less severe changes in elevation.

Onsite Model Refinement LB and Geo-Sci Consultants excavated 23 soil cores and 6 trenches to test the modelling Of 29 sample locales, 15 found evidence of historic landscape. Rest were disturbed from modern construction Unexpected benefit: identified two new sites

Onsite Model Refinement Examined variance between calculated and observed depths Found patterned, normal distribution of error Calculated the mean error and then revised the GIS analysis Standard deviation for the refined model is calculated at 1.2 feet

Diego Negron, GISP Paula Bienenfeld, Ph. D. Gregory Katz, RPA Questions? Diego Negron, GISP Paula Bienenfeld, Ph. D. Gregory Katz, RPA