My main interest is improving the analysis of hydrologic data, with a focus on the topic of trends streamflow data and surface water quality data. My research on this has resulted in the development of the EGRET software (Exploration and Graphic for RivEr Trends) written in R and available freely on line.
I am a Research Hydrologist Emeritus. The focus of my research is the description and understanding of long-term variability and change in surface-water quality and streamflow. I develop and apply new statistical tools to help characterize these changes to gain the best possible understanding of the nature of the change and its implications from a policy perspective (related to water quality improvement, flood hazard mitigation, water supply planning). This work has resulted in the development of the statistical method (Weighted Regressions on Time, Discharge, and Season - WRTDS) which I have applied to the study of water quality trends in a variety of watersheds including Chesapeake Bay, the Mississippi River, Lake Erie, and Lake Champlain. This technique is a central feature of the EGRET R package. That package is designed to be a “toolbox” for analysis of daily streamflow data and surface water quality data.
My other major recent contribution is the publication of "Statistical Methods in Water Resources" the 2020 edition published as USGS Techniques and Methods (tm4A3). In addition to the pdf and the printed book, the text has on-line resources which include all of the data sets used as examples in the book, all of the R code used in the analysis of those data, and all of the R code used to produce the graphics in the book.
I hold a B.A. in Geology from Earlham College, an M.S. in Geology from the University of Washington, and a Ph.D. in Geography and Environmental Engineering at the Johns Hopkins University. I began my USGS career in 1976 and conducted research on water supply, water quality, pollutant transport, and flood frequency analysis. In 1993-1994 I was Acting Director of the USGS, and from 1994-2008 I was the Chief Hydrologist of the USGS. In 2008 I returned to research and since that time I have focused efforts on describing long-term changes in streamflow and water quality. I retired from the USGS in 2018 but continue to collaborate with colleagues inside and outside the USGS. I am a member of the Water Science and Technology Board of the NASEM and have served on four expert committees of that Board.