Montana Bureau of Mines and Geology Kevin Chandler Jon Reiten AWRA October 6 th,2011
Funding for this modeling effort came from the RRG project Modeling Aquifer Response to Urban Sprawl, West Billings Area, Montana Sponsored by the Yellowstone Conservation District
Changes in The West Billings Area There was a 23% loss of irrigated lands between 1966 and 1999 (Olson and Reiten,2002). 2000 GWIC Wells in T1S R25E, West Billings Area 1800 1600 Number of Recorded Wells 1400 1200 1000 800 600 400 200 0 1940 1950 1960 1970 1980 1990 2000 2010 2020
Goals for Modeling the West Billings Aquifers Models will be used to represent steady state aquifer conditions in 2000 and in 2009. Transient flow models will be used to model changes in aquifer conditions with changes in land use recharge between 1999 2001 and 2009 2011. Transient flow models will be used to predict possible aquifer conditions resulting from future land use changes.
Modeled Area Billings N Laurel Billings Base Map, Montana NRIS
Terraces in West Billings Billings Terrace 3 Laurel Terrace 2 Terrace 1 From Olson and Reiten, 2002
Model Locations The three aquifer terraces, (Qa1,Qa2,and Qa3 (Gosling and Parshley, 1973; Lopez, 2000)) were split into two model areas. The Northern model includes the area from Big Ditch to BBWC, terrace 3, Qa3. The Southern model includes the area from BBWC to the Yellowstone River, terraces 1 and 2, Qa1 and Qa2.
Northern Model Boundary Grand Ave Central Billings Shilo Dr Neibauer 48th 64th 56th 80th 24th Laurel Airport Rd
Southern Model Boundary Hesper Neibauer 56th Shilo Dr 24th Danford 72nd
Well Used for Stratigraphy Modeling
Northern Model MODFLOW Grid Grand Ave Central Hesper 80th 24th
MODFLOW Grid Cell size 200 ft X 200 ft 43,506 active cells Surface area 20.8 mi² Vertical Magnification 20X
Aquifer Properties The hydraulic conductivity of the terrace gravel aquifer was found to be in the 20 600 ft/day range based on aquifer test results( Olson and Reiten, 2002). The hydraulic conductivity values in layer 2 of the model were varied using coverage polygons and were adjusted in the calibration process to values ranging from 50 to 200 ft/day. Specific yield values were initially set at 0.15 and were varied from 0.001 to 0.10 during calibration to reflect the semi confining silty sand sediment cap which ranges from 0 100 ft thick.
Recharge polygons for the Northern Model
Model calibration Model heads were calibrated using water level measurements collected monthly at 15 wells in the northern model area in 1999 2001 and again in 2008 2010. Surface water flow measurements on the major drains were used to calibrate drain flows from the model. Parameter estimation simulations (PEST) in GMS 7.0 were used during initial steady state model calibration. Hydrograph matching was used in transient model calibration.
Hydrograph Matching for Transient Model Calibration
Calibration to Surface Water Flows
Calibration to Surface Water Flows
June June Jan This is an animation of a 32 month transient simulation with current land use conditions.
June June Jan This is an animation of the head differences between a transient simulation with field irrigation on and a simulation were recharge on fields is reduced to precipitation only. The ditches and canals remain on an provide recharge.
June June Jan This is an animation of the head differences between a transient simulation of current conditions and a simulation with all irrigation turned off including all ditches and canals.
Model Applications Model simulations were run to predict the impact of flood water retention ponds on aquifer conditions as part of the West Billings flood prevention study. Model simulations were used in the site selection for a community water supply well for Yellowstone Boys and Girls Ranch which was needed to replace their contaminated well.
Sharptail Floodwater Retention Pond Changes to Aquifer Heads
Yellowstone Boys and Girls Ranch Feedlot
Questions?
References Olson, J. L., & Reiten, J. C. (2002). Hydrogeology of the West Billings Area: Impacts of Land use Changes on Water Resources. Montana Tech, Montana Bureau of Mines and Geology. Butte Montana: MBMG. Anderson, M. P., & Woessner, W. W. (1992). Applied Groundwater Modeling, Simulation of Flow and Advective Transport. San Diego, California: Academic Press, Inc. Weight, W. D., & Sonderegger, J. L. (2001). Manual Of Applied Field Hydrology. New York: McGraw hill.