FLOW MODEL DEVELOPMENT USING HYDROSTRATIGRAPHIC INFORMATION FROM DRILLERS’ LOGS

The Hydrostratigraphic Drilling Record Assessment (HyDRA) project is a two year study to develop improved methods for developing aquifer models from drillers’ logs. The Ogallala aquifer has seen significant water level declines in western Kansas. These declines require that effective groundwater management policies be implemented. Groundwater models can provide insight into the impact of aquifer hydrostratigraphy on groundwater management decisions. Development of groundwater models requires subsurface information. Drillers’ logs contain extensive subsurface information. The challenge is converting this highly qualitative information into a digital database. Drillers’ logs from wells in the vicinity of a continuously monitored “index” well in Thomas County, Kansas are used in this project. Water level data collected at the index well since 2007 augment annual water-level measurements obtained in a regional network of wells. Log information from 250 wells in the vicinity of the index well, including descriptions of sediments and lithologies, have been transcribed into a digital database using a recently developed web-based interface that automates much of the associated bookkeeping. The large numbers of disparate terms contained in the logs are then mapped to a relational database of 71 standardized sedimentological/ lithological terms, building on an earlier database. Each of the 71 standardized terms is mapped into one of five hydraulic conductivity categories. The wells are segmented into regular ten-foot intervals and the proportion of each of the five hydraulic conductivity categories is computed within each interval. A 3D data set was created by combining the proportion values with the coordinates of each well and used to interpolate the hydrostratigraphy of the study area. The interpolated hydrostratigraphy is incorporated into a 3D groundwater flow model to simulate the aquifer’s response to irrigation pumping. Here we present the results of an initial 3D groundwater flow model developed using the proposed procedures for employing drillers’ log information. The accuracy of the model will be validated by comparing model-predicted and observed water-level responses.