Analytic Element Model Database for Neuse River Basin
Michelle Rollins
NCDENR/DWQ, 1617 Mail Service Center, Raleigh, NC 27699-1617 (tel)919-733-5083 (email) Michelle.Rollins@ncmail.net An analytic element model (AEM), GFLOW 2000, has been applied to the Neuse River Basin, which is located in the eastern half of North Carolina, within 2 geologic provinces, the Piedmont and Coastal Plain. The purpose of the models is to show local groundwater flow and nitrate transport, as well as surface runoff pathways throughout the Neuse Basin. Rather than developing a single comprehensive groundwater flow model of the basin, a database of input data files is compiled, from which local models can be assembled. In this manner, the modeling process remains computationally efficient. The database of input files contains strings of linesink, which are used to represent surface water features in the AEM model. Such a linesink file has been created for each 12-digit hydrologic unit in the basin. For the sake of model efficiency and in view of the scale of the hydrologic units, zero order streams are not included. GFLOW 2000 is equipped with a management feature that facilitates the combination of the HUC based linesink input data files into a local groundwater flow model. The linesink data for the area of interest are considered the “nearfield” in the model and the surrounding HUs (linesink files) are treated as “farfield”. Only nearfield data is modified during model calibration and written back to the database files. An HU that was once treated as nearfield may be entered as farfield in a model with an adjacent HU as nearfield. In this manner, model data in the database on disk is gradually updated during the calibration of the various local models. The hydrologic unit management tool of GFLOW 2000 makes it possible to develop a single calibrated linesink database that will allow staff to quickly create site specific models. Staff within the Division of Water Quality will be able to incorporate site specific data from pollution sites or permitted facilities into the models. The models can be used to determine regulatory monitoring requirements and/or spray irrigation rates, and evaluate remediation options. This initial effort provides the Division of Water Quality with a database of linesink strings and limited groundwater information. It also presents a spatial picture of data-rich and data-poor areas, which can be used to guide future groundwater investigations. As further research is conducted in the basin, data will be added to the modeling database.