MODFLOW-NWT model of groundwater flow in the Ozark Plateaus aquifer system

Groundwater in the Ozark Plateaus aquifer system is an important source for municipal, 
industrial, agricultural, and domestic water supply needs across much of southern 
Missouri and northern Arkansas, and smaller areas of southeastern Kansas and 
northeastern Oklahoma. Recent short-term drought conditions have emphasized 
the need to better understand the delicate balance between abundance, sustainability 
and scarcity. A groundwater flow model was developed as the primary tool to assess 
groundwater availability in the aquifer system. The model was developed to benefit 
current and future investigations that involve groundwater-withdrawal scenarios, 
optimization, particle transport, and monitoring network analysis. The model is 
also critical to the ongoing work to quantify groundwater availability in the Ozark 
aquifer system.  
		
The groundwater model simulated 116 years (1900—2016) of hydrologic conditions 
and the response of the groundwater system to changes in stress. Stress applied 
to the groundwater system included changes in recharge and increased groundwater 
withdrawals for water supply. Semi-seasonal stress periods were simulated from the 
later part of 1991 to 2016 to represent higher demand and lower recharge in the spring 
and summer months, and lower demand and higher recharge in the fall and winter 
months. Groundwater pumping increased throughout the simulation period, with a 
maximum rate of about 600 million gallons per day (Mgal/d).  
		
History matching for the Ozark aquifer system model was accomplished by a 
combination of manual changes to parameter values and automated calibration 
methods. Observation data used in the development and evaluation of the model 
included 19,045 hydraulic-head observations from 6,683 wells within the Ozark 
model area that were weighted for use in the parameter estimation software. 
Observation data also included stream leakage estimates summed to calculate 
a net gain or net loss value for each stream.  
		
The majority, but not all, of the recharge component was discharged through 
streams simulated in the model. The total simulated discharge to streams 
fluctuates seasonally between 7,500 and 17,500 Mgal/d with a mean outflow 
of 11,500 Mgal/d. Much of the remaining balance between modeled recharge 
inflows and stream outflows was made up by water moving into or out of 
storage in the aquifer system resulting in changes in modeled groundwater levels.  
		
This USGS data release contains all of the input and output files for the model 
and calibration simulation described in the associated model documentation 
report (https://doi.org/10.3133/sir20185035). This data release also includes 
(1) MODFLOW-NWT (v. 1.1.2) source code, 
(2) PEST++ source code, and 
(3) processing Python scripts and associated instruction files for parameter 
estimation and model calibration using PEST++.

Tags: arkansas, environment, geoscientificinformation, groundwater, groundwater-model, inlandwaters, missouri, modflow-nwt, ozark-plateaus-aquifer, usgs-a2e701f5-118c-4b00-b998-ab497f27d5d9, usgsgroundwatermodel
Organization: Department of the Interior