T262 Geologic Maps, Digital Geologic Maps, and Derivatives from Geologic and Geophysical Maps (Posters)

Wednesday, 12 October 2011
9:00 AM - 6:00 PM
Hall C

SEAMLESS SURFICIAL GEOLOGIC MAP AND DATABASE COMPILATION TO SUPPORT WATERSHED MODELING IN MINNESOTA

Paper number: T262-3
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

We have begun the creation of an internally consistent surficial geologic map of Minnesota using newly formalized stratigraphic nomenclature. This first step has been taken to support hydrologic modeling work by the Minnesota Pollution Control Agency. In these models, water is apportioned to one of three pathways (surface runoff, interflow, and baseflow) by assigning initial values to various parameters related to infiltration. In Minnesota, interflow is the dominant hydrologic component, followed by baseflow. Although soil maps are useful in estimating initial infiltration parameter values, they may not capture the geologic factors that affect interflow, which occurs several meters below the land surface but above the level of the long-term water table. The composition and particle size distribution of the surficial material over this vertical interval is foundational in predicting the partitioning of interflow and baseflow, as well as the timing of interflow.

Surficial geologic mapping at planning scales (generally 1:100,000 or 1:200,000) produced by the Minnesota Geological Survey (MGS) can be made more useful for this purpose. Because they were created at different times by different authors, their shared boundaries sometimes put map units in juxtaposition that have different names, descriptions, and bounding lines. To improve their utility for the purposes of watershed modeling the MGS has revised and joined adjacent maps into a single geographical information system shapefile with continuous map units across the boundaries. A master explanation for the new shapefile contains original and new map units along with an attribute table with map unit characteristics parsed into separate fields. The parsing of descriptive information enables users to create custom maps based on any of the characteristics or combinations of characteristics, and to manipulate the original map units as needed. The MGS has also provided archived data that describes the texture and coarse sand grain lithology of the map units.

The work is supported by the Minnesota Pollution Control Agency and other sponsors.