Using grain-size characteristics to model soil water content: Application to dose-rate calculation for luminescence dating Michelle S. Nelson a, * , Tammy M. Rittenour a, b a USU Luminescence Laboratory,1770 N. Research Pkwy, Suite 123, North Logan, UT 84341, USA b Department of Geology, 4505 Old Main Hill, Utah State University, Logan, UT 84322-4505, USA highlights  Using grain size characteristics to generate water retention curves.  Saturation water content was estimated using laboratory and computer modeling.  In situ water content is compared with the model outputs.  Dose-rate variability with new water content estimates is evaluated. article info Article history: Available online 21 February 2015 Keywords: Water content Dose-rate determination Luminescence dating Mean annual water state Soil moisture regime abstract Soil moisture is an important factor for dose-rate determination in luminescence and other dating methods as soil water content impacts sediment bulk density, alters rates of chemical reactions and attenuates effective exposure to nuclear radiation from the surrounding sediments and incoming cosmic rays. Given its importance in dose-rate calculation, methods for measuring and modeling soil water content are discussed, with special focus on semi-arid environments and other situations where modern in situ values are unlikely to be representative of mean soil moisture conditions. We present an alter- native method for calculating sediment water content based on grain-size characteristics using the freely available Rosetta Lite v.1.1 software. Modeled outputs include saturation, residual and other water retention curve (WRC) parameters. WRCs were generated from model outputs using the van Genuchten (1980) equation, and mean annual water state was determined using soil moisture regime maps and classifications. Dose-rate values using modeled outputs and laboratory-measured in situ and saturation water content are compared in a test case using Holocene alluvial sediments from Kanab Creek in southern Utah, USA. Best practices for how to estimate mean annual water state for different soil moisture regimes and past soil moisture content in situations where in situ values are not representative of the burial history are discussed. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Pore-space water content in surficial deposits can range from desiccated to saturated, and can vary between these end members on seasonal, decadal, and/or geologic time-scales. Variations in soil water content are especially dramatic in semi-arid environments that experienced past pluvial climates, such as the southwestern U.S. Water content can vary due to intense short-term precipitation events, seasonal moisture variations, inter-annual to decadal-scale drought and centennial to millennial-scale fluctuations in groundwater levels related to changes in base level and shifts in climatic regime. Moreover, natural and man-made sediment ex- posures are influenced by surface drying effects, reducing soil moisture in the outer decimeter to meter of the sedimenteair interface. Similar drying effects from evapotranspiration can be seen below the land surface, although opposite influences of perched water lenses can also occur at any depth due to imper- meable sediment layers that retard infiltration. Construction of reservoirs and ground water pumping can also alter mean soil moisture at a site. Additionally, chemical weathering of clay min- erals and mineral precipitation in pore spaces (i.e. carbonate) over longer time-scales can also modify the soil water content of a * Corresponding author. E-mail address: michelle.summa@usu.edu (M.S. Nelson). Contents lists available at ScienceDirect Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas http://dx.doi.org/10.1016/j.radmeas.2015.02.016 1350-4487/© 2015 Elsevier Ltd. All rights reserved. Radiation Measurements 81 (2015) 142e149