Rick Hooper

Moving beyond heterogeneity and process complexity: A new vision for watershed hydrology

Field studies in watershed hydrology continue to characterize and catalogue the enormous heterogeneity and complexity of rainfall runoff processes in more and more watersheds, in different hydroclimatic regimes, and at different scales. Nevertheless, the ability to generalize these findings to ungauged regions remains out of reach. In spite of their apparent physical basis and complexity, the current generation of detailed models is process weak. Their representations of the internal states and process dynamics are still at odds with many experimental findings. In order to make continued progress in watershed hydrology and to bring greater coherence to the science, we need to move beyond the status quo of having to explicitly characterize or prescribe landscape heterogeneity in our (highly calibrated) models and in this way reproduce process complexity and instead explore the set of organizing principles that might underlie the heterogeneity and complexity. This commentary addresses a number of related new avenues for research in watershed science, including the use of comparative analysis, classification, optimality principles, and network theory, all with the intent of defining, understanding, and predicting watershed function and enunciating important watershed functional traits.

The role of bedrock topography on subsurface storm flow

We conducted a detailed study of subsurface flow and water table response coupled with digital terrain analysis (DTA) of surface and subsurface features at the hillslope scale in Panola Mountain Research Watershed (PMRW), Georgia. Subsurface storm flow contributions of macropore and matrix flow in different sections along an artificial trench face were highly variable in terms of timing, peak flow, recession characteristics, and total flow volume. The trench flow characteristics showed linkages with the spatial tensiometer response defining water table development upslope. DTA of the ground surface did not capture the observed spatial patterns of trench flow or tensiometric response. However, bedrock surface topographic indices significantly improved the estimation of spatial variation of flow at the trench. Point-scale tensiometric data were also more highly correlated with the bedrock surface-based indices. These relationships were further assessed for temporal changes throughout a rainstorm. Linkages between the bedrock indices and the trench flow and spatial water table responses improved during the wetter periods of the rainstorm, when the hillslope became more hydrologically connected. Our results clearly demonstrate that in developing a conceptual framework for understanding the mechanisms of runoff generation, local bedrock topography may be highly significant at the hillslope scale in some catchments where the bedrock surface acts as a relatively impermeable boundary.

New method developed for studying flow on hillslopes

Hillslope hydrologists have long assumed that the downslope movement of water and solutes can best be described by surface topography since gravitational potential largely dominates hydraulic gradients in steep terrain. Hence with the increased availability of Digital Terrain Maps (DTMs), surface topography is driving many popular hydrological models and is being used to estimate flow pathways in hydrological and geochemical models. This method may suffice at the catchment scale, but at the hillslope scale, flow pathways are not always determined by surface topography. It is at this critical scale (100–10,000 m2) that water flux and the chemical composition of soil water and groundwater can be measured as they move downslope. The complex interactions between water and solutes along hillslope subsurface flow paths have not been well documented. New evidence suggests that for steep hillslopes with thin soils, the fundamental control on hillslope flow paths is the bedrock surface.

Hydrologic processes controlling sulfate mobility in a small forested watershed

The objective of this study was to examine hydrologic control of sulfate mobility in a sulfate-retaining, southeastern United States forested catchment using a mass balance approach. The emphasis of the analysis is on the linkage between inter- and intraannual variations in precipitation and watershed chemical response. Variations in sulfate export were controlled by total annual runoff, discharge pattern, and changes in the concentration-discharge relationship which resulted from the accumulation of sulfur during extended dry periods. Sulfate export was controlled more by runoff than atmospheric deposition of sulfur. Under conditions of similar runoff between years, sulfate export was controlled by both changes in the concentration-discharge relationship and the pattern of discharge. The change in the concentration-discharge relationship appears to be a result of accumulation of sulfate during dry years and subsequent release during wetter years. Hydrologic control of variations in aqueous concentration and sulfate export indicate that the development of temporally robust concentration-discharge models for estimation of mass flux and the assessment of trends in stream-water quality and watershed sulfur retention require ion-term studies.

Predictions in ungauged basins as a catalyst for multidisciplinary hydrology

The face of hydrologic science is changing rapidly, on national as well as on international scales.The increasing complexity of the problems hydrology is asked to investigate in research and practice today often requires solutions that can no longer be obtained by a single hydrologist, but require a multidisciplinary team. One consequence of this trend is the establishment of initiatives that help formulate and implement science programs to engage and energize the scientific community toward achieving major advances. The IAHS Decade on Predictions in Ungauged Basins (PUB) is an initiative of the International Association of Hydrological Sciences (IAHS) [Sivapalan et al., 2003] to advance our ability to make reliable predictions in ungauged basins. Within PUB, the drainage basin (at various scales) is seen as the element that integrates all aspects of the hydrological cycle within a defined area that can be studied, quantified, and acted upon.

Community Modeling in Hydrologic Science: Scoping Workshop on a Community Hydrologic Modeling Platform (CHyMP); Washington, D.C., 26–27 March 2008

As one of two major new initiatives for its next 5-year phase, the Consortium of Universities for the Advancement of Hydrologic Science, Inc. (CUAHSI), is proposing to launch a major effort toward the development of a Community Hydrologic Modeling Platform (CHyMP), which will support a range of research and applications in water cycle science.

Survey provides guidance for consortium's hydrologic measurement facility

The Consortium of Universities for the Advancement of Hydrologic Sciences, Inc. (CUAHSI) began the Hydrologic Measurement Facility (HMF) program in June 2005 to advance hydrologic measurement capability within the research community. To provide guidance for this effort, a recent survey assessed the level of need among the hydrological sciences community for community instruments and facilities.The survey aimed to identify technologies and methodologies that could make major advances in the hydrologic sciences. Between 1 November 2005 and 15 January 2006,363 responses were returned. (45% from hydrologists, 15% soil scientists, 12% geophysicists, 11% biogeochemists, 3% ecologists, 3% geomorphologists, and 11% other disciplines).