Journal of Hydrologic Engineering

This paper is designed to help readers understand the state of innovation in hydrologic research and relevant lessons from the popular literature of business. We use citations to a paper as a measure of the impact in an area of research. Looking at the citations to all papers for a given year in a journal, they follow a power-law relationship, poorly cited papers being common and highly cited papers being rare. The power law develops because the selection of papers to cite is being biased by the citations of others. Quite remarkably, the slopes of these power laws are the same from journal to journal. Research strands have a life cycle that begins with an important, paradigm-shifting paper. Early papers that also contribute to an emerging research strand are usually well cited. As the number of papers in a strand increases, their impact begins to fall off. Eventually, interest in the strand wanes and researchers drift off to the next opportunity. It is essential for scientists to understand where their research lies in terms of a growth curve and to reposition it as needed. The business literature is clear that success stems from innovation rather than copycat products, with anticipation as a necessary ingredient. Informal indications are that most research scientists are content in their mediocrity. Knowing that a research line is not impacting seems not of a reason to change it. We do not understand the reasons why.

During the last several years, spirited discussions have taken place within the hydrogeologic community regarding the status and future of research in this field of scientific endeavor; some of these exchanges have found their way into the literature and catalyzed special sessions at professional meetings. In this contribution, we draw from and build upon the recent debates, discuss the status of hydrogeologic research and education, present an optimistic view of the future, and offer suggestions that we believe would benefit the development of the field and society at large.

We explore the need for the groundwater research community to take a leadership role in interdisciplinary studies of groundwater resources involving colleagues in the social sciences and humanities. The discussion is founded on recognition that technical research in groundwater hydrology has produced dramatic gains in our understanding of flow and transport in groundwater systems and has resulted in substantial benefit in terms of standard of living, protection of the environment, and remediation of groundwater systems. It is argued, however, that consideration solely of the technical aspects has proved inadequate to address some significant, unmet needs involving the development/management of groundwater resources. These arguments are considered through review of the history of the hydrologic sciences, observations on the interaction of water and humanity from other disciplines, and observations from experience of hydrologic needs in Benin, West Africa. We conclude that interdisciplinary efforts will provide challenging and exciting new areas of research for hydrogeologists and our colleagues from the social sciences and humanities, while simultaneously enhancing sustainability and standards of living.

This paper is a reflection of the development of the field of groundwater hydrology over the past $50\text{years}$ or so. The field of hydrogeology began to grow during the 1960s and expanded rapidly during the 1970s with the recognition of serious environmental problems from hazardous chemicals and the subsequent evolution of stringent environmental regulations. Research opportunities and student interest in solving these environmental problems substantially increased the number and size of graduate programs in hydrogeology fields. Starting in the mid-1990s, a number of factors combined to initiate a change in this trend. Although the environmental and water resources market is stable and quite strong, there is a shortage of students entering the fields of hydrogeology, in spite of a very strong demand. This paper gives a perspective on the causes of this situation.

Reactive transport models contain terms describing microbiological and hydrological processes that control fate and transport of contaminants in porous media. Most models assume that microbial reaction rate is independent of microbial biomass distribution or that biomass is uniformly distributed across media surfaces in a manner that mass transport does not limit reaction rate. Experimental data, as well as some computational models, however, suggest otherwise, indicating a need to experimentally establish how the coupling of microbial biomass and flow distribution influence microbial reaction rates. Nuclear magnetic resonance techniques offer the opportunity to quantify in three dimensions the coupling of microbial biomass and flow velocity distribution in opaque porous media at multiple scales in a noninvasive manner. Experimental data obtained with these techniques can be used to improve the accuracy of boundary conditions used by reactive transport models to predict contaminant fate and transport at the pore and core scales. Further improvements in surface and subsurface magnetic resonance techniques may allow future detection and measurement of microbial biomass distribution in the subsurface at the field scale.

Many of hydrogeology’s most fundamental questions remain unresolved today, a hundred years after the basic governing equations for groundwater flow and transport were formulated. This paper provides a brief overview of the field and outlines the future directions, with a special emphasis on uncertainty quantification.