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Tim Callahan, Professor

Department Chair

Address: SSMB 224C
Phone: 843.953.8278


New Mexico Institute of Mining and Technology
Ph.D. Earth and Environmental Science (with Dissertation in Hydrology), 2001

New Mexico Institute of Mining and Technology, Socorro
M.S. Geochemistry, 1995

University of St. Thomas, St. Paul, Minnesota
B.A. Geology, 1991

Research Interests

Hydrology and Water Resources

Courses Taught

EVSS 639 Wetlands and Watersheds

GEOL 438/438L Hydrogeology and Lab

EVSS 538/538L Introductory Hydrogeology and Lab

GEOL 395/240 Special Topics: Water Resources and Pollution in the Developing World (Abroad Course in India)

GEOL 291/291L Water Resources

GEOL 105 Earth History

HONS 155 Honors Geology I

GEOL 238 Water Resources (no longer taught)

GEOL 101 Dynamic Earth (no longer taught)


Amatya, D., T. Callahan, W. Hansen, C. Trettin, A. Radecki-Pawlik, and P. Meire. 2015. Turkey Creek watershed – A case study of forest hydrology and watershed management on low-gradient Atlantic Coastal Plain, U.S.A. Journal of Water Resource Protection 7: 792-814. DOI: 10.4236/jwarp.2015.710065.

Callahan, T.J., J. Allen, D.M. Amatya, S. Libes, and C. Sawyer (editors). 2014-present. Journal of South Carolina Water Resources. Clemson University Press, Clemson, SC. Available at

Griffin, M.P., T.J. Callahan, and V.M. Vulava. 2014. Influence of soil type and antecedent soil moisture conditions on storm-event flow pathways in lower coastal plain watersheds of the southeastern United States. Water Resources Research 50(10): 8265-8280. DOI: 10.1002/2014WR015941.

Garrett, C.G., V.M. Vulava, T.J. Callahan, and M.L. Jones. 2012. Groundwater-Surface Water Interactions in a Lowland Watershed: Source Contribution to Stream Flow. Hydrological Processes 26: doi: 10.1002/hyp.8257.

Callahan, T.J., V.M. Vulava, M.P. Passarello, and C.G. Garrett. 2011. Estimating groundwater recharge in lowland watersheds. Hydrological Processes 26 doi: 10.1002/hyp.8356.

La Torre-Torres, I.B., D.M. Amatya, G. Sun, and T.J. Callahan. 2011. Seasonal rainfall–runoff relationships in a lowland forested watershed in the southeastern USA. Hydrological Processes 25: DOI: 10.1002/hyp.7955.

Callahan, T.J., C.G. Garrett, and V.M. Vulava. 2010. The role of groundwater recharge in the water budget of lowland watersheds. Proceedings, 2010 South Carolina Water Resources Conference, October 13-14, 2010, Columbia, SC.

Garrett, C.G., V.M. Vulava, T.J. Callahan, M.L. Jones, and C.L. Ginn. 2010. Using water chemistry data to quatify source contribution to stream flow in a coastal plain watershed. Proceedings, 2010 South Carolina Water Resources Conference, October 13-14, 2010, Columbia, SC.

Amatya, D.M., T.J. Callahan, C.C. Trettin, and A. Radecki-Pawlik. 2009. Hydrologic and water quality monitoring on Turkey Creek watershed, Francis Marion National Forest, SC. Proc., ASABE Int’l Annual Meeting, 21-24 June 2009, Reno, NV. Amer. Soc. Agric. Biol. Engin. Pub. No. 09-5999, St. Joseph, MI.

Beltran, B.J., D.M. Amatya, M. Youssef, M. Jones, T.J. Callahan, R.W. Skaggs, and J.E. Nettles. 2009. Impacts of fertilization on water quality of a drained pine plantation: A worst-case scenario. J. Envir. Qual. 39: 293-303, doi:10.2134/jeq2008.0506.

Amatya, D.M., T.J. Callahan, A. Radecki-Pawlik, P. Drewes, C. Trettin, and W.F. Hansen. 2008. Hydrologic and Water Quality Monitoring on Turkey Creek Watershed, Francis Marion National Forest, SC. In: Proc. 2008 South Carolina Water Resources Conference, October 14-15, 2008, North Charleston, SC. 

Sun, G., J. Boggs, D.M. Amatya, C.C. Trettin, Z. Dai, J.M. Vose, I.B. LaTorre Torres, and T.J. Callahan. 2008. Hydrologic Processes of Forested Headwater Across a Physiographic Gradient in the Southeastern United States. In: Proc. 2008 South Carolina Water Resources Conference, October 14-15, 2008, North Charleston, SC.

Vulava, V.M., C.G. Garrett, C.L. Ginn, and T.J. Callahan. 2008. Application of geochemical end-member mixing analysis to delineate water sources in a lowland watershed. In: Proc. 2008 South Carolina Water Resources Conference, October 14-15, 2008, North Charleston, SC. 

Pyzoha, J.E., T.J. Callahan, G. Sun, and C.C. Trettin. 2008. A conceptual hydrologic model for a forested Carolina bay depressional wetland on the Coastal Plain of South Carolina, USA. Hydrol. Process. 22 (14):2689-2998. doi:10.1002/hyp6866. 

Reimus, P.W. and T.J. Callahan. 2007. Matrix Diffusion Rates in Fractured Volcanic Rock at the Nevada Test Site:  Evidence for a Dominant Influence of Effective Fracture Apertures. Water Resour. Res. 43:W07421. doi:10.1029/2006WR005746.

Reimus, P.W., T.J. Callahan, S.D. Ware, M.J. Haga, and D.A. Counce. 2007. Matrix Diffusion Coefficients in Volcanic Rocks at the Nevada Test Site: Influence of Matrix Porosity, Matrix Permeability, and Fracture Coating Minerals. J. Contam. Hydrol. 93:85-95.

Harder, S.V., D.M. Amatya, T.J. Callahan, C.C. Trettin, and J. Hakkila. 2007. Hydrology and Water Budget for a First Order Forested Coastal Plain Watershed, South Carolina. J. Amer. Water Resour. Assoc. 43(3):563-575. doi: 10.1111/j.1752-1688.2007.00035.x. 

Sun, G., T.J. Callahan, J.E. Pyzoha, and C.C. Trettin. 2006. Modeling the Climatic and Geomorphologic Controls on the Hydrology of a Carolina Bay Wetland, South Carolina, USA. Wetlands 26(2):567-580.

Amatya D.M., C.C. Trettin, R.W. Skaggs, M.K. Burke, T.J. Callahan, G. Sun, J.E. Nettles, J.E. Parsons, and M. Miwa. 2005. Five hydrologic studies conducted by or in cooperation with the Center for Forested Wetlands Research, USDA Forest Service. USDA Forest Service Report, Research Paper SRS-40, Asheville, NC.

Dickerson, D. and T.J. Callahan. 2005. Students' Conceptions of Scale Regarding Groundwater. J. Geosci. Educ. 53(4):374-380.

Sun, G., T.J. Callahan, J.E. Pyzoha, C.C. Trettin, and D.M. Amatya. 2004. Modeling the hydrologic processes of a depressional forested wetland in South Carolina, U.S.A. In: Proc. 6th Int’l. Conf. on Hydrosci. and Engin. (ICHE-2004), 30 May-3 June 2004, Brisbane, Australia.

Callahan, T.J., J.D. Cook, M.C. Coleman, D.M. Amatya, and C.C. Trettin. 2004. Measuring and Modeling Storm Water Runoff and Soil Interflow in a Managed Forest, Upper Coastal Plain of the Southeast US. In: Proc. ASAE/CSAE Annual Int’l. Meeting, 1-4 August 2004, Ottawa, Ontario, Canada.

Reimus, P.W., M.J. Haga, A.I. Adams, T.J. Callahan, H.J. Turin, and D.A. Counce. 2003. Testing and parameterizing a conceptual solute transport model in saturated fractured tuff using sorbing and nonsorbing tracers in cross-hole tracer tests. J. Contam. Hydrol. 62-63:613-626. 

Callahan, T.J., P.W.Reimus, P.C. Lichtner, and R.S. Bowman. 2002. Multicomponent effects on the transport of cations undergoing ion exchange in fractured media. In: Bridging the Gap Between Measurement and Modeling in Heterogeneous Media (A. N. Findikakis, ed.). Proc. Int’l. Groundwater Symposium, Lawrence Berkeley National Laboratory, 25-28 March 2002, Berkeley, California, USA. pp. 523-528.

Callahan, T.J., P.W. Reimus, R.S. Bowman, and M.J Haga. 2000. Using multiple experimental methods to determine fracture/matrix interactions and dispersion of nonreactive solutes in saturated volcanic rock. Water Resour. Res. 36(12):3547-3558.