HOW DO HUMAN LAND AND WATER USE, CLIMATE CHANGE, AND HYDRO-ECOLOGICAL SYSTEMS INTERACT?
BALANCING THE NEEDS OF AGRICULTURE AND AQUATIC ORGANISMS IN WISCONSIN
Wisconsin is home to abundant surface and groundwater resources that support both human needs and diverse aquatic ecosystems. However, the relationship between groundwater resources and stream ecology remains poorly quantified at the regional scale, particularly with respect to the relative importance of shifting precipitation patterns and increased groundwater reliance across the state. Given variable data availability at the state-wide scale, we explore the utility of different approaches to quantify hydrological alteration in a management context and explore how quantitative estimates of the effects of groundwater withdrawals on streams can be interpreted in terms of aquatic ecosystem health.
* artwork by Anna Klein, supported through the Flow microgrant*
LARGE WOOD MAY FUNCTION DIFFERENTLY IN SPRING-FED STREAMS
Spring-fed streams throughout volcanic regions of the USA are wider than runoff-fed streams. One hypothesis for this difference is a difference in wood dynamics. Using remote sensing and statistical analysis, we found that a model for stream width in spring-fed streams based solely on length of wood is a better model than one derived from discharge or including both discharge and wood length. This study has implications for river restoration involving large wood.
RAINWATER HARVESTING IN ARIZONA HAS LANDSCAPE-SCALE IMPACT ON HYDROLOGY
Berms are constructed in rangelands in Arizona to detain overland flow, minimizing soil and water loss on the landscape and redistributing plant access to soil moisture. When not maintained, massive gullies can form, resulting in landscape-scale changes in flow paths and water distribution. Working with collaborators at USDA-ARS, I am using remote sensing and process-based modeling to investigate the quantitative impacts of berms on hillslope hydrology.
ROOT-ZONE STORAGE DEFICITS DRIVE CHANGES IN RUNOFF FOLLOWING DROUGHTS
More frequent droughts and increasing temperatures imposed by climate change threaten snowpacks, which sustain mountain water resources globally. Following a recent drought in California, the traditionally used model for snowmelt runoff failed. Here, we present a model that reveals the essential role of root-zone storage dynamics in snowmelt runoff. Through transpiration, montane forests generate water storage deficits in the soils and weathered bedrock that comprise the root zone. These deficits must be replenished by rain and snowmelt before significant runoff generation can occur. Overprediction of 2021 post-drought runoff in California can be primarily attributed to unprecedented root-zone storage deficit magnitudes. Adding a measure of deficit reduced 2021 streamflow prediction error from 100% to 12%.
Read the preprint of this work here.
Hear me talk about this work here.
Image source: NASA Worldview • Graphic by Pai/Bay Area News Group
WHAT MECHANISMS CONTROL HOW WATER MOVES THROUGH HILLSLOPES AND CATCHMENTS UNDER DIFFERENT SCENARIOS?
MODELING INFILTRATION-EXCESS OVERLAND FLOW ON CURVED SURFACES WITH SIMPLE ANALYTICAL SOLUTIONS
A major assumption in many analytical models for overland flow is a rectangular hillslope. We derived an analytical model for overland flow on non-rectangular hillslopes with a hillslope width function described by an exponential function. To test the assumptions of the model, we compared to numerical simulations and laboratory rainfall simulator experiments on machined hillslopes. There was strong agreement, supporting use of the analytical solutions on hillslopes with mild to moderate curvature.
Read the publication here.
WHERE DOES SATURATION OVERLAND FLOW COME FROM?
Water age and flow pathways should be related, but the specifics of these relationships are still unknown. We combine field observations of runoff generation at the Dry Creek catchment in Northern California with StorAge Selection (SAS) age models to explore the relationship between streamwater age and runoff pathways in a saturation overland flow-dominated landscape.
WHAT CONTROLS THE VARIABILITY IN WETTED CHANNEL EXTENT OVER TIME?
Stream networks expand and contract through time. While previous work has detailed mechanisms to describe the extent of wetted channel networks for a given flow level, variability in wetted channel network has not yet been explored in depth. We developed a quantitative conceptual framework to investigate variability in wetted channel extent over time. By applying this framework to a newly compiled database of all sites with wetted channel surveys and flow records, we found that headwater streams may be particularly vulnerable to climate change.
A NEW ARC HYDRO HILLSLOPE TOOL FOR HILLSLOPE ANALYSIS
Hillslopes are a fundamental unit of hydrological analysis. A prerequisite for implementing hillslope-based models to real landscapes is the ability to delineate hillslopes and calculate information about them. Very limited tools are available for this task. To fill the gap, we collaborated with Arc Hydro to develop a hillslope tool that delineates hillslopes, calculates hillslope width functions, and applies analytical solutions to real hillslopes.
HOW RELIABLE ARE CURRENT HYDRAULIC MANAGEMENT PRACTICES?
DOES THE RATIONAL METHOD WORK ON NON-RECTANGULAR AREAS?
The Rational Method, despite or because of its simplicity, is one of the most widely recommended tools for estimating the peak flow of a given return period. The apparent simplicity of the Rational Method masks a number of complicated assumptions. We used analytical and numerical modeling of idealized hillslopes to identify the impacts of hillslope shape on reliability of the Rational Method. We found that the timescale typically used in the Rational Method (the time of concentration) is not always a good estimate for the critical duration, the theoretically appropriate timescale.
Read the publication here.
CAN THE RATIONAL METHOD ACCOUNT FOR TIME-VARYING INFILTRATION BEHAVIOR?
The Rational Method, despite or because of its simplicity, is one of the most widely recommended tools for estimating the peak flow of a given return period. The apparent simplicity of the Rational Method masks a number of complicated assumptions. We used analytical and numerical modeling of idealized hillslopes to identify the impacts of non-constant infiltration behavior on the reliability of the Rational Method. Different assumptions about infiltration behavior can result in large over- or under-estimations of design flows when the Rational Method is applied as traditionally recommended.
Read the publication here.